geoguide2-guide to site investigation
TRANSCRIPT
GEOGUIDE 2
GUIDE TOSITE INVESTIGATION
GEOTECHNICAL ENGINEERING OFFICECivil Engineering DepartmentThe Government of the Hong KongSpecial Administrative Region
GEOGUIDE 2
GUIDE TOSITE INVESTIGATION
GEOTECHNICAL ENGINEERING OFFICECivil Engineering DepartmentThe Government of the Hong KongSpecial Administrative Region
2
© The Government of the Hong Kong Special Administrative Region
First published, September 1987Reprinted, December 1990Reprinted, December 1993Reprinted, September 1996Reprinted, October 2000
Prepared by:
Geotechnical Engineering Office,Civil Engineering Department,Civil Engineering Building,101 Princess Margaret Road,Homantin, Kowloon,Hong Kong.
This publication is available from:
Government Publications Centre,Ground Floor, Low Block,Queensway Government Offices,66 Queensway,Hong Kong.
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An additional bank charge of HK$50 or US$6.50 is required per cheque made in currenciesother than Hong Kong dollars.
Cheques, bank drafts or money orders must be made payable toThe Government of the Hong Kong Special Administrative Region.
FOREWORD
This Geoguide p resen t s a recommended s t andard of good practice for s i t e investigation in Hong Kong, t h e need fo r which was formally recognized a s early as July 1983 by t h e Subcommittee of t h e Building Authority Working Par ty on Geotechnical Regulations. In i t s format and content , t h e Geoguide follows closely t h e British Standard BS 5930 : 1981. Code of Practice fo r Site Investigations, b u t t h e recommendations in t h e British Standard have been adapted t o su i t local conditions and practices. I t should be used in conjunction with t h e companion document, Guide t o Rock and Soil Descriptions (Geoguide 3). These Geoguides expand upon, and largely replace, Chapter 2 of t h e Geotechnical Manual for Slopes.
This Geoguide covers Sections 1 t o 7 of BS 5930, while Section 8 i s dealt with in Geoguide 3. I t has been prepared in such a way t h a t t h e organization and format of t h e British Standard have generally been preserved. Where portions of BS 5930 have been adopted in t h e text without significant amendment, th is is clearly denoted by t h e use of a n i M c typeface.
I t should be noted t h a t th is Geoguide gives guidance on good s i t e investigation practice and, a s such, i t s recommendations a r e not mandatory. I t i s recognized t h a t t h e practitioner will often need t o use al ternat ive methods. There will also b e improvements in s i t e investigation practice dur ing t h e life of t h e document which will supersede some of i t s recommendations.
The Geoguide was prepared in t h e Geotechnical Control Office ( G C O ) u n d e r t h e general direction of M r J.B. Massey. The main cont r ibutors t o t h e document were D r A. Cipullo, M r K.S. Smith and M r D.R. Greenway, with significant contributions dur ing t h e final s t ages of preparat ion from D r P.L.R. Pang and D r R.P. Martin. Mamy o the r members of t h e G C O made valuable suggest ions and contributions.
To e n s u r e t h a t t h e Geoguide would be considered a consensus document of t h e civil engineering profession in Hong Kong, a d r a f t version was circulated widely for comment in early 1987 t o contractors , consulting engineers and Government Departments. Many organizations and individuals made useful and construct ive comments, which have been t aken in to account in finalizing t h e Geoguide, and t h e i r contributions a r e grateful ly acknowledged.
Practitioners a r e encouraged t o comment a t any time t o t h e Geotechnical Control Office on t h e contents of th is Geoguide, s o t h a t improvements can be made t o f u t u r e editions.
E.W. Brand Principal Government Geotechnical Engineer
September 1987
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CONTENTS
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1 T ITLE PAGE
FOREWORD
CONTENTS
PART I : INTRODUCTION
1, SCOPE
2. TERMINOLOGY
PART I 1 : GENERAL CONSIDERATIONS
3, PRIMARY OBJECTIVES OF S ITE INVESTIGATION
4, GENERAL PROCEDURES
4.1 EXTENT AND SEQUENCE OF INVESTIGATION 4.1.1 G e n e r a l 4 . 1 . 2 A d j a c e n t P r o p e r t y
4 . 2 DESK STUDY
4 . 3 S I T E RECONNAISSANCE
4 . 4 DETAILED EXAMINATION AND SPECIAL S T U D I E S
4 . 5 CONSTRUCTION AND PERFORMANCE APPRAISAL
5. EARLIER USES OF THE S ITE
5.1 GENERAL
5.2 TUNNELS
5.3 MINES AND QUARRIES
5 . 4 WASTE T I P S
5 . 5 OTHER EARLIER U S E S
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5.6 A N C I E N T M O N U M E N T S
6, AERIAL PHOTOGRAPHS
6.1 G E N E R A L
6.2 T O P O G R A P H I C M A P S AND A E R I A L P H O T O G R A P H I C IMAGERY 6.2.1 M a p and Plan Scales 6.2.2 A e r i a l Photographic I m a g e r y 6.2.3 O r t h o p h o t o M a p s and Plans
6.3 A E R I A L PHOTOGRAPH I N T E R P R E T A T I O N 6.3.1 Identification and Interpretation of
G r o u n d F e a t u r e s 6.3.2 E x a m p l e s o f A P I i n H o n g K o n g
PART I 1 1 : PLANNING THE GROUND INVESTIGATION
7, INTRODUCTION TO GROUND INVESTIGATION
7.1 O B J E C T I V E S
7.2 PLANNING AND CONTROL
8, TYPES OF GROUND INVESTIGATION
8.1 S I T E S FOR NEW WORKS
8.2 D E F E C T S OR F A I L U R E S O F E X I S T I N G F E A T U R E S OR WORKS
8.3 S A F E T Y O F E X I S T I N G F E A T U R E S AND WORKS 8.3.1 E f f e c t o f N e w W o r k s upon E x i s t i n g
F e a t u r e s and W o r k s 8.3.2 T y p e s of E f f e c t s 8.3.3 P r o c e d u r e
8.4 M A T E R I A L S FOR C O N S T R U C T I O N P U R P O S E S
9, GEOLOGICAL MAPPING FOR GROUND INVESTIGATION
10, EXTENT OF THE GROUND INVESTIGATION
10.1 G E N E R A L
10.2 CHARACTER AND V A R I A B I L I T Y O F T H E GROUND
10.3 N A T U R E O F T H E P R O J E C T 10.3.1 G e n e r a l
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10.3.2 Slope a n d R e t a i n i n g W a l l C o n s t r u c t i o n 10.3.3 Foundations for Structures
10.4 P R E L I M I N A R Y I N V E S T I G A T I O N
10.5 LOCATION
10.6 S P A C I N G
10.7 D E P T H O F E X P L O R A T I O N 10.7.1 G e n e r a l 10.7.2 F o u n d a t i o n s for Structures 10.7.3 E m b a n k m e n t s 10.7.4 C u t Slopes 10.7.5 P a v e m e n t s 10.7.6 P i p e l i n e s 10.7.7 M a r i n e W o r k s 10.7.8 T u n n e l s
11, SELECTION OF GROUND INVESTIGATION METHODS
11.1 G E N E R A L
11.2 S I T E C O N S I D E R A T I O N S
12, EFFECT OF GROUND CONDITIONS ON INVESTIGATION METHODS
12.1 G E N E R A L
12.2 GRANULAR S O I L S CONTAINING B O U L D E R S , C O B B L E S OR GRAVEL
12.3 GRANULAR S O I L S
12.4 I N T E R M E D I A T E S O I L S
12.5 VERY S O F T T O S O F T C O H E S I V E S O I L S
12.6 F I R M T O S T I F F C O H E S I V E S O I L S
12.7 C O H E S I V E S O I L S CONTAINING B O U L D E R S . C O B B L E S OR GRAVEL
12.8 F I L L
12.9 ROCK
12.10 S O I L S D E R I V E D FROM I N S I T U ROCK WEATHERING
12.11 D I S C O N T I N U I T I E S
12.12 C A V I T I E S
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13, AGGRESSIVE GROUND AND GROUNDWATER 65
13.1 G E N E R A L 65
13.2 I N V E S T I G A T I O N O F P O T E N T I A L D E T E R I O R A T I O N O F C O N C R E T E 65
13.3 I N V E S T I G A T I O N O F P O T E N T I A L CORROSION O F S T E E L 65
13.4 I N V E S T I G A T I O N O F F I L L CONTAINING I N D U S T R I A L W A S T E S 66
14, GROUND INVESTIGATIONS OVER WATER
14.1 G E N E R A L
14.2 S T A G E S AND P L A T F O R M S
14.3 F L O A T I N G C R A F T
14.4 WORKING B E T W E E N T I D E L E V E L S
14.5 LOCATING B O R E H O L E P O S I T I O N S
14.6 D E T E R M I N A T I O N O F R E D U C E D L E V E L S
14.7 D R I L L I N G , S A M P L I N G AND T E S T I N G
15. PERSONNEL FOR GROUND INVESTIGATION
15.1 GENERAL
15.2 PLANNING AND D I R E C T I O N
15.3 S U P E R V I S I O N I N T H E F I E L D
15.4 LOGGING AND D E S C R I P T I O N O F GROUND C O N D I T I O N S
15.5 LABORATORY T E S T I N G
15.6 S P E C I A L I S T A D V I C E
15.7 I N T E R P R E T A T I O N
15.8 O P E R A T I V E S
16. REVIEW DURING CONSTRUCTION
16.1 G E N E R A L
16.2 P U R P O S E
16.3 INF ORMATION R E Q U I R E D
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16.3.1 Soil and R o c k 16.3.2 W a t e r
16.4 I N S T R U M E N T A T I O N
PART I V : GROUND INVESTIGATION METHODS
17, INTRODUCTION TO GROUND INVESTIGATION METHODS
18, EXCAVATIONS AND BOREHOLES
18.1 SHALLOW T R I A L P I T S AND S L O P E S U R F A C E S T R I P P I N G
18.2 D E E P T R I A L P I T S AND C A I S S O N S
18.3 HEADINGS OR A D I T S
18.4 HAND A U G E R BORING
18.5 L I G H T C A B L E P E R C U S S I O N BORING
18.6 MECHANICAL A U G E R S
18.7 ROTARY O P E N H O L E D R I L L I N G AND ROTARY CORE D R I L L I N G 18.7.1 G e n e r a l 18.7.2 F l u s h i n g M e d i u m 18.7.3 Inclined D r i l l i n g
18.8 WASH BORING AND OTHER METHODS 18.8.1 W a s h B o r i n g 18.8.2 O t h e r M e t h o d s of B o r i n g
18.9 B A C K F I L L I N G EXCAVATIONS AND B O R E H O L E S
19, SAMPLING THE GROUND
19.1 G E N E R A L
19.2 S A M P L E Q U A L I T Y
19.3 D I S T U R B E D S A M P L E S FROM BORING T O O L S OR EXCAVATING E Q U I P M E N T
19.4 O P E N - T U B E S A M P L E R S 19.4.1 P r i n c i p l e s o f D e s i g n 19.4.2 Sampling Procedure 19.4.3 T h i n - W a l l e d S a m p l e r s 19.4.4 G e n e r a l P u r p o s e 100 mm D i a m e t e r
O p e n - T u b e Sampler
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19.4.5 Split Barrel S tandard Penetration Test Sampler
19.5 THIN-WALLED STATIONARY PISTON SAMPLER
19.6 CONTINUOUS SOIL SAMPLING 19.6.1 General 19.6.2 The Delft Continuous Sampler
19.7 SAND SAMPLERS
19.8 R O T A R Y CORE SAMPLES
19.9 BLOCK SAMPLES
19.10 HANDLING AND LABELLING OF SAMPLES 19.10.1 General 19.10.2 Labelling 19.10.3 Disturbed Samples of Soil and Hand
Specimens of Rock 19.10.4 Samples Taken with a Tube Sampler 19.1.0.5 Rotary Core Extrusion and Preservat ion 19.10.6 Block Samples
20, GROUNDWATER
20.1 GENERAL
20.2 METHODS OF DETERMINING GROUNDWATER PRESSURES 20.2.1 Response Time 20.2.2 Observations in Boreholes and Excavations 20.2.3 Standpipe Piezometers 20.2.4 Hydraulic Piezometers 20.2.5 Electrical Piezometers 20.2.6 Pneumatic Piezometers 20.2.7 Installation of Piezometers 20.2.8 Varying Groundwater P ressures 20.2.9 Soil Suction
20.3 GROUNDWATER SAMPLES
21, TESTS I N BOREHOLES
21.1 GENERAL
21.2 STANDARD PENETRATION TESTS 21.2.1 General Principles 21.2.2 Preparat ion for Testing 21.2.3 Advantages and Limitations 21.2.4 Results and Interpretat ion
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21.3 VANE TESTS 21.3.1 General P r inc ip les 21.3.2 A d v a n t a g e s a n d Limitations
21.4 PERMEABILITY TESTS 21.4.1 General P r inc ip les 21.4.2 P r e p a r a t i o n s f o r t h e T e s t 21.4.3 Variable-head T e s t 21.4.4 Cons tan t -head T e s t 21.4.5 Analys i s of Resu l t s 21.4.6 Formulae f o r Borehole Permeabi l i ty T e s t s 21.4.7 A d v a n t a g e s a n d Limitations
21.5 PACKER (WATER ABSORPTION) TESTS 21.5.1 General P r i n c i p l e s 21.5.2 P a c k e r s 21.5.3 Application a n d Measurement of P r e s s u r e 21.5.4 Measurement of Flow 21.5.5 Execut ion of T e s t 21.5.6 Resu l t s a n d I n t e r p r e t a t i o n
21.6 PLATE TESTS 21.6.1 General 21.6.2 Limitations 21.6.3 P r e p a r a t i o n 21.6.4 Bedding of t h e P la te 21.6.5 Application a n d Measurement of Load 21.6.6 Measurement of Deflection 21.6.7 Execut ion of T e s t 21.6.8 U s e s of t h e T e s t 21.6.9 S u p p l e m e n t a r y T e s t 21.6.10 Horizontal P l a t e T e s t s
21.7 PRESSUREMETER TESTS 21.7.1 T e s t Descr ipt ion 21.7.2 Equipment Cal ibra t ion 21.7.3 Forming t h e T e s t P o c k e t 21.7.4 Resu l t s a n d I n t e r p r e t a t i o n 21.7.5 T e s t s i n Rock
21.8 BOREHOLE DISCONTINUITY SURVEYS 21.8.1 Impress ion P a c k e r S u r v e y 21.8.2 Core O r i e n t a t o r s
22, FREQUENCY OF SAMPLING AND TESTING IN BOREHOLES 129
22.1 GENERAL PRINCIPLES 129
22.2 DETERMINATION OF THE GROUND PROFILE 129
22.3 ROUTINE DETERMINATION OF SOIL AND R O C K PROPERTIES 130
22.4 DOUBLE-HOLE SAMPLING 130
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22.5 SPECIAL TECHNIQUES
23 , PROBING AND PENETRATION TESTING
23.1 GENERAL
23.2 DYNAMIC PROBING
23.3 STATIC PROBING O R CONE PENETRATION TESTING 23.3.1 General Descr ipt ion 23.3.2 Mechanical Cone P e n e t r o m e t e r s 23.3.3 Electrical Cone Pene t romete rs 23.3.4 General Recommendations 23.3.5 Uses a n d Limitations of t h e T e s t 23.3.6 P r e s e n t a t i o n of Resul ts
23.4 STATIC-DYNAMIC PROBING
PART V : FIELD AND LABORATORY TESTS
24 , FIELD TESTS
24.1 GENERAL
24.2 R O C K STRENGTH INDEX TESTS 24.2.1 Point Load S t r e n g t h 24.2.2 Schmidt Hammer Rebound Value
24.3 INFILTRATION TESTS
2 5 , PUMPING TESTS
25.1 GENERAL PRINCIPLES
25.2 GROUNDWATER CONDITIONS
25.3 TEST SITE
25.4 PUMPED WELLS
25.5 OBSERVATION WELLS
25.6 TEST PROCEDURES
25.7 ANALYSIS OF RESULTS
26, DISCONTINUITY SURVEYS
26.1 GENERAL
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26.2 D I S C O N T I N U I T Y R O U G H N E S S S U R V E Y S
27, FIELD DENSITY TESTS
27 .1 GENERAL P R I N C I P L E S
27.2 SAND R E P L A C E M E N T METHOD
27.3 CORE C U T T E R METHOD
27 .4 WEIGHT I N WATER METHOD
27.5 WATER D I S P L A C E M E N T METHOD
2 7 . 6 R U B B E R BALLOON METHOD
2 7 . 7 N U C L E A R M E T H O D S
27.8 WATER R E P L A C E M E N T METHOD FOR ROCK F I L L
28, INSITU STRESS MEASUREMENTS
28.1 G E N E R A L
28.2 S T R E S S M E A S U R E M E N T S I N ROCK
28.3 S T R E S S M E A S U R E M E N T S I N S O I L S
29, BEARING TESTS
29.1 V E R T I C A L LOADING T E S T S 29.1.1 G e n e r a l P r i n c i p l e s 29.1.2 L i m i t a t i o n s o f t h e T e s t 29.1.3 S i t e Preparation 29.1.4 T e s t A r r a n g e m e n t 29.1.5 M e a s u r e m e n t s 29.1.6 T e s t M e t h o d s 29.1.7 A n a l y s i s o f R e s u l t s 29.1.8 Interpretation o f R e s u l t s
29.2 HORIZONTAL AND I N C L I N E D LOADING T E S T S
29.3 P R E S S U R I Z E D CHAMBER T E S T S
29.4 I N S I T U C A L I F O R N I A B E A R I N G RATIO ( C B R ) T E S T S 29.4.1 G e n e r a l 29.4.2 T e s t M e t h o d 29.4.3 L i m i t a t i o n s and U s e o f T e s t
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30. I N S I T U DIRECT SHEAR TESTS
30.1 GENERAL PRINCIPLES
30 .2 SAMPLE PREPARATION
30.3 TEST ARRANGEMENT
30.5 TEST METHODS
30.6 ANALYSIS OF RESULTS
31, LARGE-SCALE F I E L D T R I A L S
31.1 GENERAL
31.2 METHODS OF INSTRUMENTATION
31.3 TRIAL EMBANKMENTS AND EXCAVATIONS
31.4 CONSTRUCTION TRIALS
32. BACK ANALYSIS
32.1 GENERAL
32.2 FAILURES
32.3 OTHER CASES
33. GEOPHYSICAL SURVEYING
33.1 GENERAL
33.2 LAND GEOPHYSICS 33.2.1 Res i s t iv i ty 33.2.2 Gravimetric 33.2.3 Magnet ic 33 .2 .4 Se i smic
33.3 MARINE GEOPHYSICS 33.3.1 General 33 .3 .2 Echo-Sounding 33.3.3 Cont inuous Se i smic Reflection Prof i l ing 33.3.4 S i d e S c a n S o n a r
33.4 BOREHOLE LOGGING
33.5 CORROSION TESTING
30.4 MEASUREMENTS
3 4 , PRINCIPLES OF LABORATORY TESTING
35. SAMPLE STORAGE AND INSPECTION FACIL IT IES
35.1 HANDLING AND LABELLING
35 .2 STORAGE OF SAMPLES
35 .3 INSPECTION FACILITIES
36, VISUAL EXAMINATION
36.1 GENERAL
36 .2 SOIL
36 .3 ROCK
36.4 PHOTOGRAPHIC RECORDS
37, TESTS ON SOIL
37.1 GENERAL
3 7 . 2 SAMPLE QUALITY
37 .3 SAMPLE SIZE
37.4 TEST CONDITIONS
37.5 RELEVANCE OF TEST RESULTS
3 8 , TESTS ON ROCK
PART V I : REPORTS AND INTERPRETATION
39, FIELD REPORTS
40, S ITE INVESTIGATION REPORT
40.1 GENERAL
40.2 DESCRIPTIVE REPORT 40.2.1 Report as Record 40 .2 .2 I n t r o d u c t i o n 40 .2 .3 Descr ip t ion o f S i t e 40.2.4 Geology
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40.2.5 Field Work 40.2.6 Borehole Logs 40.2.7 Incidence and Behaviour of Groundwater 40.2.8 Location of Boreholes 40.2.9 Laboratory Test Results and Sample Descriptions
40.3 ENGINEERING INTERPRETATION 40.3.1 Matters t o be Covered 40.3.2 Data on which Interpretat ion i s Based 40.3.3 Presentation of Borehole Data 40.3.4 Design 40.3.5 Construction Expedients 40.3.6 Sources of Materials 40.3.7 Failures 40.3.8 Calculations 40.3.9 References
REFERENCES
TABLES LIST OF TABLES
TABLES
FIGURES
LIST OF FIGURES
FIGURES
PLATES
LIST OF PLATES
PLATES
APPEND ICES
APPENDIX A : INFORMATION REQUIRED FOR DESK STUDY
APPENDIX B : SOURCES OF INFORMATION
APPENDIX C : NOTES ON SITE RECONNAISSANCE
APPENDIX D : INFORMATION REQUIRED FOR DESIGN AND CONSTRUCTION
APPENDIX E : SAFETY PRECAUTIONS
PART I
INTRODUCTION
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1, SCOPE
This Geoguide deals with t h e investigation of s i tes in Hong Kong for t h e purposes of assessing the i r suitability for civil engineering and building works. and of acquir ing knowledge of s i t e characteris t ics t h a t affect t h e design and construct ion of such works a n d t h e secur i ty of adjacent propert ies . I t is essentially BS 5930 : 1981, Code of Practice for Site Investigations (BSI, 1981a), modified a s considered desirable for use in Hong Kong.
While t h e basic structure and philosophy of BSI (1981a) has been maintained in th is Geoguide, topics of part icular importance in Hong Kong have been supplemented o r rewrit ten in t h e l ight of local conditions and experience. Other sections of BSI (1981a) have been repeated herein without significant amendment, and th i s has been denoted by a n 12al1'c script . Less re levant o r rare ly-used portions of BSI (1981a) have been incorporated only by reference, or have been specifically deleted.
In th i s Geoguide, a s in BSI (1981a). t h e expression "site investigation" has been used in i t s wider sense. I t i s often used elsewhere in a narrow sense t o describe what has been termed herein "ground investigation". The use of soil and rock a s construct ion materials is t rea ted only briefly: f u r t h e r information on th is is given in BSI (1981b).
From Part I1 onwards. this Ceoguide is divided as follows .- Part I/. Part /I deals with those matters of a technical, legal or environmental character that should be taken into account in selecting the site for in determining whether a proposed site is suitable) and in preparing the design of the works.
Part I/I. Part 111 discusses general aspects and planning of ground in vestl'gahon, including the influence of general condihons and ground condihbns on the selection of methods of in vestigation.
Par ts IV and V. Pa r t s IV and V discuss methods of ground investigation, sub-divided a s follows : Par t IV deals with excavation, boring. sampling, probing and tests in boreholes; Pa r t V deals with field tests and laboratory tests on samples.
Part V/. Part V/ deals with the preparation of field reports and borebole logs, the interpretation of the data obtahed from the hvescigafhn and the preparahon of the final site investigation report.
The las t section of BSI (1981a), which deals with t h e description of soils and rocks , is not covered in th is Geoguide. A companion document. Geoguide 3 : Guide t o Rock and Soil Descriptions ( G C O . 1988), has been devoted entirely to th i s topic, and t h e r eader should re fe r t o i t for guidance on t h e description and classification of Hong Kong rocks and soils.
I t may b e noted t h a t t h e r e are some imbalances in t reatment of t h e various topics, with, in some cases. more comprehensive coverage given t o methods t h a t a r e less f requent ly used. Because i t would not be possible t o include full coverage of all available s i t e investigation techniques, methods t h a t a r e well documented elsewhere in t h e l i te ra ture receive abbrevia ted coverage in
this Geoguide.
This Geoguide represents a standard of good practice and therefore takes the form of recommendations. Compliance with it does not confer immunity from relevant statutory and legal requirements. The recommendations given are intended only a s guidance and should not be taken as mandatory. In this respect, it should be realized that improvements to many of the methods will continue to evolve.
2, TERMINOLOGY
A few commonly-used descript ive terms for geological materials and t y p e s of ground investigation a r e often in te rp re ted in different ways and therefore r equ i re definition. In th i s Geoguide, t h e terminology given in t h e following paragraphs has been adopted.
"Rock" re fe r s t o all solid material of natural geological origin t h a t cannot be broken down by hand. "Soil" r e fe r s t o any naturally -formed e a r t h material o r fill t h a t can be broken down by hand and includes rock which has weathered insi tu t o t h e condition of an engineering soil. Fur the r guidance on t h e use of t h e s e terms is given in Geoguide 3 (GCO, 1988).
Excluding any boulders o r cobbles, a "fine-grained soil" or a "fine soil" i s one t h a t contains about 35% or more of f ine material (silt and clay size particles). A "coarse-grained soil" o r a "coarse soil" contains less than 35% of f ine material and more than 65% of coarse material (gravel and sand size particles). Fur the r guidance is given in Geoguide 3.
A "cohesive soil" is one which, usually by v i r tue of its fines content. will form a coherent mass. Conversely a "granular soil" o r a "cohesionless soil" will not form a coherent mass. These simple terms are useful in t h e classification of materials dur ing ground investigation fo r t h e purpose of choosing a suitable method fo r sampling t h e ground. A fine soil i s generally cohesive.
The "matrix" of a composite soil r e fe r s t o t h e fine-grained material enclosing, o r filling t h e spaces between, t h e l a rge r gra ins o r particles in t h e soil.
"Boring" is a method of advancing a cased o r uncased hole (viz a "borehole") in t h e ground and includes a u g e r boring, percussion boring and r o t a r y drilling , in which a dri l l bi t i s rotated into t h e ground for t h e purpose of forming t h e hole. Although t h e term "drillhole" is commonly used in Hong Kong because of t h e popular u s e of t h e ro tary core drilling method in ground investigations, t h e general term "borehole" i s used throughout th i s Geoguide for simplicity, whether t h e hole is bored, augered o r drilled.
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PART I 1
GENERAL CONSIDERATIONS
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3, PRIMARY OBJECTIVES OF SITE INVESTIGATION
Investigatrbn of the site fk an essentrtral prelimnary to the constructlbn of a// u'vil engineering and building works. and the objectrives h making such investrgatrons are as follows :
/a1 Suitability. To assess the general suitabfXty of the site and environs for the proposed works.
/b1 Des~gn. To enable an adequate and economic design to be prepared incfud~ng the design of temporary works.
fc1 Construction. To plan the best method of construction; to foresee and provide aganst d~Yficulties and delays that may arise during construction due to ground and other l o d conditrbns; in appropriate cases, to explore sources of indigenous mater%ds for use in constructrbn /see Sectron 8.4); and to se/ect sites for the dfkpod of waste or surplus materials.
/dl Effect of Changes. To determine the changes that may arise in the ground and environmental conditrons, eeither naturdy or as a result of the works, and the effect of such changes on the works, on aaacent works, and on the environment in general.
/e1 Choice of Site. Where alternatives emkt, to advise on the relative suitabh!ity of dXferent sites, or different parts of the same site.
In additon, site hvestigatrons may be necessary in reportrng upon the safety of existrng features and works /see Sectrbn 8.31, for the design of exte~wons, vertrical or hor~zontal, to emstrng works, and for invesligating cases where failure has occurred /see Sectron 8.21.
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4, GENERAL PROCEDURES
4.1 EXTENT AND SEQUENCE OF INVESTIGATION
4.1. I General
The extent o f the hvestigation depends primarily upon the magnitude and nature of the proposed works and the nature of the site.
A site ~nvestigation wifl norma//y proceed in stages, as fo/laws : desk study; site reconnaissance; detailed examination for design, including ground in vesogation, topographic and hydrographic survey and spec12 studies; follow- up investigatJons during constructJon (Figure 1 ). This may be fohwed by appraisal of performance. Some of the stages may overlap, or be taken out of sequence; for example, the site reconnaissance may well take place before completion o f the desk study.
The costs of a site investigation are low in refatJon to the overall cost of a project and may be further reduced b y intelligent forward planning. Discussion at an e&y stage with a speciaht contractor wifl help to formdate an efficient and economic plan. The technicaf requirements of the investigation shoufa' be the overriding factor in the selection of investigatory methods, rather than the]> cost.
A s far as possibfe, assembly of the desk study hformation shoufd be complete, at least h respect of t h e aspects refated to ground condizbns, before ground in vestJgatJon begins. A preliminary ground in vestigathn may be desirable to determine the extent and nature of the main ground investigation. The extent of the ground investigation is discussed in Chapter 10.
For regional s tudies o r s i t e investigation of projects covering large areas, e.g. road, tunnel o r transmission line routes, techniques such as engineering geological and geomorphological mapping, t e r ra in classification and hazard analysis may b e useful t o delineate critical a reas so t h a t detailed investigations can be concentrated in areas where they are most requi red (Brand e t al. 1982; Griffiths & Marsh. 1984; Hansen. 1982).
4.1.2 Adjacent Proper ty
Because of t h e dense u rban development in Hong Kong, construct ion activities can often affect adjacent property. I t is therefore essential t h a t investigations should cover all fac tors t h a t may affect adjacent proper ty . including fea tures such a s slopes and retaining walls (see Chapter 7 and Section 8.3). Where possible, records of ground levels, groundwater levels and re levant part iculars of adjacent propert ies should be made before, dur ing and a f t e r construct ion. Where damage t o existing s t r u c t u r e s i s a possibility, adequate photographic r ecords should be obtained.
Adjacent buildings, s t r u c t u r e s and buried services, including pipes conveying water, gas o r sewage, should be specifically considered, a s they may b e affected by vibrat ions, ground settlement o r movement, o r changes in groundwater levels dur ing and a f t e r construct ion activities on t h e site. Hospitals and o the r buildings containing sensi t ive ins t ruments o r appara tus should b e given special consideration.
Special permission o r approval must be obtained when t h e s i t e i s above o r near t h e Mass Transi t Railway Corporation's tunnels o r s t ruc tu res . o r is within t h e Mid-levels Scheduled Area (see Appendices A and B; s ee also Chapter 7). The approximate locations of these two fea tu res a r e shown in Figure 2.
4.2 DESK STUDY
A s a f i r s t s t age in a s i te investigation, a desk s t u d y is necessary and AppendixA indicates t h e t y p e s of information t h a t may b e requi red . Much information about a s i te may already b e available in existing records . A summary of t h e important sources of information is given in Appendix B.
A new geological su rvey is cu r ren t ly underway in Hong Kong t o replace t h e existing 1:50 000 scale geological maps and memoir (Allen & Stephens , 1971): new 1:20 000 scale geological maps will become available between 1986 and 1991 (Figure 3). The new geological su rvey u s e s different nomenclature fo r certain major rock divisions and rock types (Addison. 1986; GCO. 1988; S t range & Shaw. 1986); th i s should b e used wherever possible.
An important source of basic geotechnical information is t h e Geotechnical Area Study Programme (GASP) publications available from t h e Government Publications Centre. Systematic t e r ra in evaluation has been under taken at a scale of 1:20 000 covering t h e en t i r e Terri tory (Brand et al. 1982). These publications generally contain Engineering Geology. Terrain Classification, Erosion. Landform and Physical Constraint Maps. Selected a reas of t h e Terri tory have also been evaluated a t t h e 'district ' scale of 1:2 500. b u t these have not been published. The GASP programme and the areas covered by t h e GASP publications a r e shown i n Figure 4, and examples of some of t h e 1:20 000 maps a r e given in Figure 5.
The Geotechnical Information Unit also contains numerous records of boreholes from throughout t h e Terri tory, a s well a s useful r ecords of landslides. rainfall and piezometric data. and laboratory t e s t resul t s on soil and rock samples. Relevant da ta can be easily accessed by geographical location of t h e site. Fur the r details of t h e Geotechnical Information Unit a r e given in Appendix B.
A useful bibliography on t h e geology and geotechnical engineering of Hong Kong is also available (Brand, 1992). Local maps and plans a r e easily obtained (Table 1). and as-buil t records of pr iva te developments a r e retained by t h e Buildings Ordinance Office o r t h e Public Records Office (see AppendixB). Valuable information may often be obtained from aerial photographs. a s discussed in Chapter 6.
4.3 SITE RECONNAISSANCE
A t a n early stage. a thorough visual examination should b e made of t h e site. The extent t o which ground adjacent t o t h e s i te should also be examined is. in general , a matter of judgement ( see Section 4.1.2). In t h e intensely- developed u rban a reas of Hong Kong, i t will usually b e necessary t o inspect existing slopes and retaining walls within and su r round ing t h e s i t e and adjacent propert ies dur ing t h e s i t e reconnaissance s tage . Appendix C gives a summary of t h e procedure fo r s i t e reconnaissance and t h e main points t o be considered b u t should not be regarded as necessarily covering all requirements.
Nearby cut sfopes can reveal soil and rock types and their stablzty characteristics, as can old excavations and quarries. Shilarly, in the vicinity there may be embankments or bu~idings and other structures having a settfement history because of the presence of compress~Ble or unstable soih. Other important evidence that might be obtained from an inspection is the presence of underground excavations, such a s basements and tunnefs. The beha viour of structures simiar to those intended shoufa' also pro vide useful hformatJon, and the absence of such structures may be significant, a s may be also the presence of a vacant site zn the midst of otherwise intensive de vehpment.
Exampfes of earlier uses of the site that may affect new construct~on works are given in Chapter 5.
4.4 DETAILED EXAMINA TION AND SPECIAL STUDIES
For most projects, the design and planning of construction will require a detaded examination of the site and its surround~ngs /see afso Append~k D). Such requirements may necessitate a detailed land survey /see Append~x D.ZI, or an investigation of liabifity to flooding. The hvestigation of ground conditions is dealt with in Parts IZI and IK Other requirements may entail studies of special subjects such a s hydrography /see Appendix D. 3); micrometeorofogy /see Append~k D. 4); sources of mater~als (see Appendix D. 5); disposal of waste materials /see Appendix 0.6); or other en vironmental considerations.
Tbe poss~B~Xty of disused tunnels affecting the site should also be considered (see Section 5.21.
In areas where underground cavities are suspected (Culshaw & Waltham, 1987). it may be necessary to carry out a special study to assess the suitability of the site for development (see Section 7.1 ).
4.5 CONSTRUCTION AND PERFORMANCE APPRAISAL
Construction and performance appraisal are discussed in Chapter 16.
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5, EARLIER USES OF THE SITE
5.1 GENERAL
If a site has been used for other purposes in the past, this can have a significant effect on the present intended use. A careful visual inspechon of a site and the vegetation i t sustains may reveal clues suggesting interference with the natural subsoil conditons at some t h e in the past. Examples are given in Sectlbns 5.2 to 5.6.
Due t o t h e relatively s h o r t history of development in Hong Kong, many instances of previous use of a s i te can be discovered by an inspection of early maps, aerial photographs and o the r historical records (see Appendices A and B).
5.2 TUNNELS
The presence of nearby tunnels may have a profound effect on t h e intended use of t h e si te , and should b e fully considered. In addition t o tunnels in act ive u s e for water supply, sewage conveyance, roads and railways, underground shel ters and disused tunnels (of ave rage dimensions 2 m high and 3 m wide) exist in places throughout t h e Terri tory as a r e su l t of previous wartime activities.
5.3 MINES AND QUARRIES
A relatively minor amount of e i the r opencast o r underground mining has been under taken in Hong Kong, b u t quarry ing fo r rock products has been extensive at some locations, as have borrow a r e a operations. Where th i s has occurred , detailed consideration must be given t o i t s influence on affected sites.
5.4 WASTE TIPS
Waste t ips, used for t h e disposal of domestic refuse , indus t r ia l waste and o the r refuse , may b e found in places throughout t h e Territory. The location of pas t o r p resen t 'controlled tips' opera ted by Government a r e documented, b u t o t h e r t ips may also exist. Harmful indust r ia l wastes may also b e encountered. The u s e of waste t ip s i tes for o the r purposes must consider fully t h e effects of combustible gas, toxic leachate and ground settlement. Furthermore, sites in t h e proximity of waste t i p s may also b e sub jec t t o t h e effects of laterally migrating combustible gas and leachate.
5.5 OTHER EARLIER USES
Much of t h e low-lying land of Hong Kong has been ' extended by successive s tages of reclamation in t h e pas t 80 t o 90 years . Former seawalls and o the r obs t ruct ions may therefore be encountered beneath these areas . The fill materials used have been variable, often containing l a rge boulders and building debris . The fill is often underlain by soft compressible marine sediments.
Natural slopes and boulders, and older c u t and fill slopes and retaining walls, a r e often prone to landslides and o the r forms of instability. I t is of paramount importance t h a t all slope fea tu res on o r adjacent t o t h e s i t e should b e examined for areas of past , c u r r e n t o r potential instability at a n early s t age in t h e s i t e investigation.
5.6 ANCIENT MONUMENTS
A l i s t of gazet ted historical s i tes is maintained by t h e Antiquities and Monuments Office of t h e Government Secretariat , and a permit is r equ i red before commencement of any work within a gazetted historical site. I t is advisable t o consult t h e Antiquities and Monuments Office before enter ing a n y historical s i te , even ungazetted sites. During s i te investigation, a n y discovery of ant iquit ies or supposed antiquit ies should b e repor ted t o t h e Antiquities and Monuments Office (see Appendices A and B).
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6, AERIAL PHOTOGRAPHS
6.1 GENERAL
Aerial photographs can be used in t h e preparat ion and revision of maps a n d plans, and they can as s i s t in t h e identification and general assessment of na tura l and man-made fea tu res , including geology, geomorphology, hydrology a n d vegetation. on o r in relation to a site. They a r e part icular ly useful in t h e assessment of s i t e his tory (i.e. changes in form. materials a n d land use ) a n d can provide valuable information f o r t h e assessment of slope stability (Geological Society, 1982).
Black and white aerial photograph coverage of Hong Kong is extensive. Although partial coverage of t h e Terr i tory is available from 1924, t h e f i r s t complete coverage was obtained in 1963, a s summarised in Table 2. For almost any s i te i n t h e Terr i tory, repeated aerial photograph coverage r ecords t h e land use and development changes t h a t have occurred , as well a s any history of r ecen t instability. The small scale black and white photographs obtained a t flying heights of o v e r 6 000 m a r e more sui table fo r obtaining an overall view of t h e Terr i tory. A small number of t r u e colour. (false) colour inf rared and black and white inf rared photographs a r e also available. Advice on how t o obtain t h e aerial photographs i s given in Appendix 8.1.3.
6.2 TOPOGRAPHIC MAPS AND AERIAL PHOTOGRAPHIC IMAGERY
6.2.1 Map and Plan Scales
Accurate topographic maps and plans can b e produced from aerial photo- g raphs . A part ial catalogue of maps and plans available from t h e Lands Department i s given in Table 1 (see also Appendix B.l.1). Large scale plans (scales 1:500 t o 1:l 000) a r e usually most appropr ia te fo r s i te invest igat ions of small a reas , whereas plans with scales of 1:5 000 t o 1:20 000 a r e more appropr ia te fo r d is t r ic t o r regional s tudies .
6.2.2 Aerial Photographic Imagery
The scale of an image on an aerial photograph i s proportional t o t h e distance between t h e camera a n d t h e subjec t . For an aerial photograph taken vertically, tall objec ts ( tops of hills and buildings) , and objec ts nea r t h e c e n t r e of t h e photograph. c rea te images a t slightly l a rge r scales than low t e r ra in o r similar objec ts nea r t h e e d g e of t h e photograph. Radial distortion about t h e optical axis of t h e camera displaces t h e t r u e vert ical away from c e n t r e of t h e photograph, an effect which becomes more pronounced nea r t h e edges of a photograph. This may c rea te dramatic effects on large-scale photographs with considerable changes in elevation from one portion t o another .
Despite these sources of distortion. fo r s i tes which can b e identified within t h e cent ra l t h i r d of a vert ical aerial photograph and which contain t e r r a in of broadly similar elevation, reasonably accura te scaled images can b e obtained by proportioning t h e distances between objec ts identifiable on a map ( o r plan) and a contact p r i n t of an aerial photograph, and by using th i s proportion rat io a s an enlargement factor . Most aerial photography has been obtained using cameras with la rge format negatives. Prior t o 1963, t h e sizes of t h e contact p r in t s v a r y , b u t a r e usually 162 mm by 175 mm. With few
exceptions, t h e negatives obtained from 1963 t o t h e p resen t a r e 228 mm by 228 mm. The image produced on contact pr in ts is extremely s h a r p , and clear images can be obtained e i the r by viewing t h e contact p r in t s with a magnifying lens o r stereoscope, o r by enlarging all o r p a r t of t h e negative. Enlarged p r in t s can be used even fo r s tudies of small a reas of t h e size of a n individual building site.
6.2.3 Orthophoto Maps and Plans
Orthophoto maps and plans, which consist of rectified ( t r u e t o scale) photographs overpr in ted with contours o r g r ids can be made (overseas only) fo r both vert ical and oblique aerial photography. Rectification of t h e image can be performed optically o r digitally; t h e accuracy is determined by t h e number of control points supplied, t h e degree of rectification desired and t h e scale of t h e original photography.
6.3 AERIAL PHOTOGRAPH INTERPRETATION
6.3.1 Identification and Interpretat ion of Ground Features
Aerial photographs can b e in terpre ted a t a r a n g e of scales and levels of detail t o provide information valuable t o both t h e design of s i te investigations and t o t h e interpretat ion of t h e results . The design of s i te investigations for la rge projects such as rou te corr idors (e.g. roads, railways, pipelines o r transmission lines) can benefit enormously from a preliminary aerial photograph in terpre ta t ion (API) su rvey . This can highlight t h e na tura l and man-induced characteris t ics of t h e te r ra in , noting in part icular hazards and resources t h a t may have a significant effect on t h e feasibility o r design of t h e project. Even when performed fo r smaller s i tes , a n API s t u d y can often provide useful information on t h e distribution and th ickness of natural and fill materials, and may reveal potential problems originating from adjacent land. Sequences of aerial photographs taken a t different da tes can b e compared to determine t h e location, extent and approximate time of filling and reclamation, and t h e sequence of development of a n area.
Aerial photographs, particularly when examined stereoscopically, can often be used t o identify and delineate specific ground fea tures such a s t h e distr ibution of soil types (e.g. colluvial and alluvial deposi ts) , soil th ickness , bedrock type , dep th t o bedrock, f r ac tu re pa t t e rns and spacings, as well a s local relief. API is of part icular value in t h e mapping of "photolineaments". This term re fe r s t o s t r a igh t o r gently-curving fea tures on aerial photographs which a r e usually t h e su r face expression of variations in t h e s t r u c t u r e o r materials of t h e underlying bedrock. Photolineaments a r e usually marked by topographic highs o r lows in t h e t e r ra in b u t sometimes they may be more sub t l e fea tures , which can only b e identified by different vegetation growth. reflecting underlying changes in soil type , soi! th ickness or moisture content . Well-defined l inear depressions usually indicate t h e location of less res is tant bedrock o r of discontinuities in t h e bedrock s t r u c t u r e such as faults , f r ac tu re zones o r major joints. Local linear topographic highs o r lines of boulders o r rock outcrops may indicate t h e presence of a rock uni t t h a t is more re s i s t an t t o weathering.
All t h e f ea tu res mentioned above may be important for t h e interpretat ion of s i te conditions. Early identification by API of major changes in soil and rock t y p e s and fea tu res t h a t a r e likely t o have a significant influence on t h e
local groundwater regime can b e of g r e a t assistance in t h e design of t h e ground investigation and in establishing a geological model for t h e site.
Reviews of API and related mapping techniques a r e contained in Geological Society (1982). Some good examples of t h e use of API techniques a r e provided by Lueder (1959). Van Zuidam & Van Zuidam-Cancelado (1979), Verstappen & Van Zuidam (1968) and Way (1978).
6.3.2 Examples of API in Hong Kong
In Hong Kong, API techniques have been successfully applied t o both specific problems and regional appraisals . Examples of t h e former a r e given in Brimicombe (1982). Bryant (1982) and Koirala e t a1 (1986). Systematic regional API s tudies have been under taken within t h e Geotechnical Area Studies Programme (GASP) t o provide information for planning, resource appraisal and engineering feasibility s tudies (see Section 4.2). The f i r s t of t h e regional GASP repor t s was available in 1987 ( G C O , 1987) and a f u r t h e r eleven repor t s in t h e ser ies were published between 1987 and 1989. All GASP maps a r e available for inspection in t h e Geotechnical Information Unit ( see Appendix B) .
F igure 6 shows an example of a vert ical black and white aerial photo- g raph of p a r t of Hong Kong Island and includes t h e corresponding portion of t h e 1:20 000 scale geological map ( G C O , 19861. Some fea tures of t h e bedrock s t r u c t u r e can be in terpre ted from t h e aerial photograph. For example, t h e location of t h e faul t line shown on t h e geological map can b e clearly seen a s a s t ra ight , deep valley in t h e cent re-eas t p a r t of t h e photograph. Near t h e north eas te rn co rne r of t h e photograph, t h e photolineaments indicated on t h e map can b e seen t o correspond t o less clearly-defined valleys.
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PART I I 1
PLANNING THE GROUND INVESTIGATION
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7, INTRODUCTION TO GROUND INVESTIGATION
7.1 OBJECTIVES
For new works, t h e objectives of ground investigation are t o obtain reliable information t o produce an economic and safe design and t o meet t e n d e r and construction requirements. The investigation should be designed t o verify and expand information previously collected. In Hong Kong, because of in tense u rban development, i t is often necessary t o invest igate t h e effects of new works on t h e safe ty of existing fea tures and works: in part icular , t h e effects on t h e stability of existing slopes and retaining s t r u c t u r e s (see Sections 4.1.2 and 8.3).
The objective of ground investigation related to defects or faihres of existhg features or works (see Section 8.21, or to safety of existing features and works (see Section 8.31, wiiY be directly related to the particular problems ~n vol ved The requirements for i n vestljrathn of materials for constructhn purposes are discussed i n Sectlbn 8.4.
An understanding of the geology of the site i s a fundamentaf require- ment in the planning and interpretation of the ground i n vestigatlbn. I n some cases where the geology is relatively straightforward and the engineering problems are not complex. suffic~ent geofogical hformation may have been provided by the desk study, subject to confirmatibn by t r i d p i t s or boreholes or both. I n other cases, it may be necessary to undertake geolog~cal mapping, which is discussed i n Chapter 9.
O f p rha r y hportance w i l be the establishment of the so17profile or sod and rock prof i / , and the groundwater condit~ons. The profile shouM be obtained by close visual inspection and systematic description of the ground using the methods and term~irology given fir Geoguide 3 ( G C O , 1988), or a suitable alternative system. I n many cases, this. supplemented by limited insitu or laboratory testing, will su f f ie . I n others, it w~Yl be necessary to determine i n detail the engineering properties of the soils and rocks. The extent of the ground hvestigatfon i s discussed i n Chapter 10. Mere appropriate, the geometry and nature of discontinuities shoufd be estabhbed (see Section 12.11).
In many cases. especially in slope design, i t will b e v e r y important t o determine t h e variations in t h e groundwater regime in response t o rainfall.
The investigation should embrace al/ ground i n which temporary or permanent changes may occur as a result of the works. These changes include : changes i n stress and associated strain, changes ~n moisture content and associated volume changes, changes li, groundwater level and flow pattern. and changes in soil properties such as strength and compress1;3ility. Materials placed in the ground may deteriorate. It is therefore necessary to provide informaaon from which an estimate of the corros~~vity of the ground can be made (see Chapter 131.
Special measures may b e requi red to locate disused tunnels o r under- ground cavities, which may collapse, result ing in damage t o s t r u c t u r e s (see Sections 8.3.2. 10.3.3 and 10.7.2). Other hazards may ar ise from earl ier uses of t h e s i te (see Chapter 5 ) .
7.2 PLANNING AND CONTROL
Before commenuhg ground in vestgaton, dl relevant informaton collected frwn the sources discussed in Part I1 should be considered together to obtiui, a prehinary concepton of the ground conditions and the engineering problems that may be involved T h k will assist in plannhg the amount and types of ground hvestigatrbn required
Plannhg of the ground investigation should be flexible so that the work can be varied as necessary h the light of fnsh information. On occasions, especiafly on large or extended sites, a prefimhwy hvestigation may be necessary in order that the main investgatian may be planned to best advantage fsee Sectbns 4.1.1 and 10.4).
The ground investigation should b e largely completed before t h e works are finally designed. I t i s therefore important t h a t sufficient time fo r ground investigation (including dealing with all legal. environmental, contractual and administrative matters , repor t ing and in terpre ta t ion) is allowed in t h e overall programme fo r a n y scheme. For example, in slope design. piezometers should b e installed well in advance t o obtain sufficient groundwater da ta fo r t h e design. Should changes in t h e projec t occur a f t e r completion of t h e main investigation, additional ground investigation may be required. If so, t h e programme should b e ad jus ted to allow fo r t h e additional time requi red .
Somethes, conditons necessitate additondl investigation after the works commence. In tunnelfihg, for example, probing ahead of the face may be required to give warning of hazards or changes in ground conditlbns. The propertes of the ground and also the groundwater levels may vary with the seasons. In plannihg the ~hvestigation, consideraton should be given to predicting the ground conditions at other thes of the year.
The ~hpositon of limitatons on the amount of ground investgation to be undertaken, on the grounds of cost and the, may result h insufficient infomaton beihg obtained to enable the works to be designed, tendered for and constructed adequately, economicdly and on the. Add1'0ond investi- gations carried out at a later stage may prove more costly and result in delays.
A s ground investigations in Hong Kong must often b e under taken in u rban areas (Plate l A ) , i t is often necessary t o obtain road excavation permits. temporary licences or way leaves before commencing t h e ground investigation. For some s i tes i t will be necessary to coordinate t h e works with t h e requirements of t h e t raf f ic police and o the r authori t ies (Plate 1B). Proper identification and maintenance of utilities encountered by t h e works is essential; high voltage power cables. gas distribution lines and o t h e r utilities often p r e s e n t significant safe ty hazards.
Since backfilled pits and boreholes might in te r fe re with subsequen t construct ion, they should b e si ted and backfilled with care. I t is essential t h a t t h e precise location of e v e r y excavation, borehole or probing is properly referenced to t h e 1980 Hong Kong Metric Grid and recorded dur ing t h e execution of t h e fieldwork. I t is also essential t o establish and record t h e ground levels of t h e s e locations. The records should b e such t h a t t h e locations and levels can be readily incorporated in to t h e r e p o r t on t h e invest igat ions (see Sections 10.5 and 40.2.8).
Invest igat ions fo r new works and all o the r building works within t h e
Mid-levels Scheduled Area (Figure 2) must comply with the provisions of the Buildings Ordinance (Government of Hong Kong. 19851, including the submission of the ground investigation plan to the Buildings Ordinance Office for approval and consent to commence the work.
Where the proposed investigation is in the vicinity of the Mass Transit Railway, o r within the limits of the railway 'protection boundary', details and locations of the proposed works, including the depths of any proposed boreholes, should be forwarded to the Mass Transit Railway Corporation for agreement prior to commencement of the work.
Should i t appear during the course of the investigation tha t items of archaeological o r historical significance have been encountered, the Antiquities and Monuments Office should be notified (see Section 5.6).
To obtain the greatest benefit fm a ground investigation, it is essential that there is adequate directrbn and supervisbn of the work by competent personnel who have approprhte knowledge and exper~ence and the authoriy to decide on var~atrons to the ground investigation when required (see Chapter 15).
In planning ground investigations, particular attention should be paid to the safety of personnel. Certain methods present special safety problems, and recommendations a re given in the relevant sections. Other methods involve normal safety precautions appropriate to site o r laboratory work. A list of statutory regulations which may apply to ground investigations is given in Appendix E; this list is not necessarily complete, and if there is doubt over safety precautions, fur ther advice should be obtained.
Appendix A summarises the types of information tha t may be required in planning a ground investigation.
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8, TYPES OF GROUND INVESTIGATION
8.1 SITES FOR NEW WORKS
In vestigat~ons for new works d~Wer from the other types of h vestigatlbn mentioned ILJ Chapter Z in that they are u M y wider li, scope because they are required to y~eld information to assist h selecting the most suitable location for the works, and the des~gn and construction of the works. For example, when slope excavathn has to be carr~ed out, a knowledge of the subsurface materi*als and groundwater cond~*tibns should indkate :
whether removal of t h e material will be difficult.
whether t h e s ides of t h e excavation will b e stable if unsuppor ted o r will r equ i re suppor t ,
whether groundwater conditions will necessitate special measures such a s groundwater dra inage o r o t h e r geotechnical processes.
whether t h e na tu re of t h e ground will change a s a r e s u l t of excavation, e.g. opening of rel ict joints in t h e soil mass,
what form of su r face protection is required.
On the desjyn side, it is necessary to assess such considerations as bearing capacity and setuement of foundations, stability of slopes ~ i , embankments and cuttings, earth pressures on supporthg structures. and the effect of any chemically aggressive ground conditom. For the design of new works, it is important that the range of cond~'tions, including least favourable conditions, should be known. This entays not only a study of the degree of var~kbifity in the soil and rock profiles over the area of the site, but also an appreciation of the possibe hjur~ous effects of groundwater var~ations and weather c0nd~'tibns on the propertis of the various subsurface materials. Where works requ~k excavations into or within rock. iduding weathered rock, the orientatrbn and nature of discontinuities in the rock may be the most hportant factors.
Often, a preliminary design of t h e proposed works is of g rea t ass is tance in t h e identification of parameters t h a t are required t o b e obtained from t h e ground investigation.
Investigations should assess whether t h e proposed works may induce ground movements which could affect adjacent land, services and s t ruc tu res . and whether t h e hydrogeological regime may be adverse ly affected (see Sections 4.1.2 and 8.3) .
8.2 DEFECTS OR FAILURES OF EXISTING FEATURES O R WORKS
The investigation of a site where a falure has occurred is often necessary to estabfish the cause of the faiure and to obtarh the hfonnation required for the design of remedid measures.
Observations and measurements of t h e f ea tu re o r s t r u c t u r e to determine
t h e mode o r mechanism of failure a r e f i r s t needed, and t h e s e will often s u g g e s t t h e origin of t h e trouble, o r at least indicate whether t h e ground conditions were par t ly o r wholly responsible. If th i s is t h e case, a n investigation will b e requi red t o ascertain t h e ground and groundwater conditions relevant t o t h r e e phases of t h e s i te history, i.e. before t h e works were cons t ructed , at t h e time of failure and as they exist a t p resen t (see also Chapter 32). Each problem will need t o b e considered on its merits. Indications of t h e probable cause of a failure will often resu l t in detailed at tent ion being directed t o a part icular aspect o r t o a part icular geological feature.
In the case of slope failure, or where such faihre is considered imminent, 12 is common practice to monitor movements both of the surface and underground The former is conducted b y conventionalsurvey methods and the latter by means of slip indicators or incfinometer measurements. These techniques are fu/y described in BSI 11981b) and in the Geotechnical Manual fo r Slopes (G CO, 1984). It is also usually necessary to monitor groundwater pressures within the various underlying zones (see Chapter 201.
fierefore, an investigation to determine the causes of a failure may be much more detailed in a partzkuhr respect than would n o r d y be the case in an investiga&bn of new works.
8.3 SAFETY OF EXISTING FEATURES AND WORKS
8.3.1 Effect of New Works upon Existing Features and Works
Because of t h e dense u rban development in pa r t s of Hong Kong, i t is often necessary t o invest igate existing fea tures and works in t h e immediate vicinity o r even remote from t h e s i te of t h e proposed new works, t o decide whether t h e existing works a r e likely t o be affected by changes in t h e ground and groundwater conditions b rough t about by t h e new works.
8.3.2 Types of Effects
Existing slopes and s t r u c t u r e s may be affected by changed conditions such as t h e following :
Impeded drainage, which may resu l t in a r i se in t h e groundwater level. This can cause softening of cohesive materials and reduction of s h e a r s t r e n g t h of permeable materials, and give r i se t o increased pore p r e s s u r e s affecting t h e stability of slopes and retaining walls; swelling may resu l t in ground heave.
Excavations o r demolitions in t h e immediate vicinity. which may cause a reduction in s u p p o r t t o t h e slope o r s t r u c t u r e , e i the r by general ground deformation o r b y slope instability.
S t res ses t h a t t h e new s t r u c t u r e may impose on existing slopes o r s t r u c t u r e s , o r on t h e foundation materials below adjacent s t ruc tu res . which can cause slope instability o r d i s t r e s s t o existing s t ruc tu res .
( d ) Vibrations and ground movement result ing from traff ic , v ibra tory compaction, piling o r blasting in t h e immediate vicinity, o r from o the r construct ion activities.
/el Lowering the groundwater level by pumping from wels or dewatering of excavations or tunnels w17l cause an increase in the effective stress in the subsoil affected which can lead to excessive settlement of adjkcent structures. Also, if pumps do not have an adequate filer, the leaching of tihes from the subs017 can easily result in excessive settlement of structures at considerable distance from the pump.
In areas where natura l underground cavities can occur. e.g. k a r s t fea tures in t h e Yuen Long basin, increase in effective s t r e s s o r downward ravelling of soil due t o heavy pumping may lead t o subsidence o r t h e formation of sinkholes (Siu & Wong. 1984).
f f ) Tunnelling operations in the ne~ghbourhood which may cause deformations and subsidence; the effect of tension and compress~un on drainage should not be overlooked.
fg) Alterahon in stream flow of a waterway, wh~ch may cause ~nderc~t t ing of banks or scouring of foundations of wafls, bridges and p~ers, and may be due to works carr~ed out some distance away.
fh) Silahon of the approaches of harbour works or the changing of navigation channel afignments.
8.3.3 Procedure
In the ~hvest~gat~on of the safety of existing features or works, the /list requirement is an apprec~htion of the changes to the ground that are likely to occur. The ground investigahon wifl need to provide knowledge of the subsurface materials, together with the examination and testing of samples to assess the effect that the changed cond12ions are likely to have on these mater~kls. In some cases, it may be necessary to carry out a detailed analysis to estimate the effect of the changed conditins on the safety of the existing features and works.
8.4 MATERIALS FOR CONSTRUCTION PURPOSES
Invest~gations of sites are sometimes requked :
fa) to assess the suitability, and quantities, for construchon work of materials that become available from excavations or dredging, e.g. whether spoil from cuts in road and rayway works win be suitable for li//s in other places,
( b ) t o f ind suitable materials for specific purposes, e.g. t o locate borrow pits o r a reas for ear thworks ( a common problem in Hong Kong where in tense u rban development demands a cons tant search for sui table fill materials); t o
assess the suitability of materials in waste tips that may need to be removed for environmental reasons,
fcl to Jocate suitabJe dXsposaJ s12e.s for waste and dredged rnaterids.
9, GEOLOGICAL MAPPING FOR GROUND I N V E S T I G A T I O N
The object of geological mapping is t o a s sess t h e charac ter , distr ibution and s t r u c t u r e of t h e soils and rocks underlying t h e area. Interpretat ion of t h e geological conditions a t t h e s i te may not be possible without mapping a l a rge r area. An unders tanding of geological f ea tu res is a pre-requisi te t o in terpre t ing t h e geological conditions a t t h e site, and a sui tably t ra ined specialist should normally under take th is task.
A s a base map o r reference, t h e new 1 2 0 000 scale geological maps a r e most useful. These maps will become available between 1986 and 1991 (Figure 3). Two existing 1:50 000 geological maps (which cover t h e en t i r e Terr i tory) a r e also available (Allen & Stephens, 1971). Methods used fo r geological mapping a t t h e regional scale a r e equally sui table fo r s i te specific mapping for ground investigations (Geological Society, 1982; Strange. 1986) and may b e supplemented by interpretat ion of aerial photographs (see Chapter 6) and geophysical investigations (see Chapter 33).
Natural exposures and artificial exposures, such as cut slopes and quarries, beyond the site may provide data on the material and mass characterisbcs of soils and rocks. ~hcludhg, for example, the orientabon, frequency and character of bedding and jbinbhg discontinu~'bes, weathering profiies, and the nature of the junction between superficial and soM formabbns. Such information should be used as a guide only to conditoons likely to be present at the site. Caution is needed in extrapohling data; geologcal deposits may vary laterdy, and very important geo/ogialstructures, such as faults and other majar disconbhuities, may have only a restricted extent.
It may be expedient to hvestigate local conditions at an early stage of the mapphg, ushg mechanically excavated s M o w pits and trenches. The walls of excavations and, where appropr~ate, the f/oor should be mapped at a suitably large scale and sampled before backijlfing takes place.
Slope surface s t r ipping is also commonly used in Hong Kong fo r t h e purpose of geological mapping (see Section 18.1).
Recording of geo/ogcal information should be undertaken at a// stages of the works.
Fur the r information and examples of engineering geological mapping a r e given elsewhere (Burnet t & Styles, 1982; Geological Society, 1972; IAEG, 1981; ICE, 1976; UNESCO, 1976).
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10, EXTENT OF THE GROUND INVESTIGATION
10.1 GENERAL
The extent of the ground investigafion is determined by the character and variability of the ground and groundwater, the type of project, and the amount o f existing information. I t is important that the general character and variabifity of the ground should be estabhhed before deciding on the basic principles of the design of the works.
In Hong Kong. soils derived from insitu rock weathering generally exhibit great variability even within relatively short distances. Granitic and volcanic rocks, which together form the major portion of the solid geology of the Territory, may be weathered to soils typically to depths of 30 m and 10 m respectively. Under certain geological conditions, granitic rocks may be weathered to over 100 m deep. Examples can be found in the Mid-levels area. Ma On Shan and Yuen Long. It i s important to recognize that ground conditions may not always improve with depth; on occasions, hard rock at the ground surface may be underlain by thick zones of weaker material. Similarly. fill materials within reclamations may vary considerably. Hong Kong soils and rocks are further discussed in Geoguide 3 ( G C O . 1988).
Investigations include a range of "methods '; e. g. excavations, borehok, probing, see Chapters I7 to 23. The factors determining the selection of a particular method are diicussed in Chapters If, I2 and I7 to 23. In genera4 the recommendations in Sections 10.2 to 10.7 appfy irrespective of the method adopted, and the term "exploration point" is used to describe a position where the ground is to be exdored b y any partkular method
Each combination of project and site is Me& to be unique, and the foflowing generalpohts should therefore be considered as guidance in planning the ground investigation and not as a set of rules to be applied rigidly in every case.
10.2 CHARACTER AND VARIABILITY OF THE GROUND
The greater the natural variabifity of the ground, the greater wi'l be the extent of the ground jhvestigation requii-ed to obtain an ihdicatlbn of the character of the ground The depth of exp/orahon is generafly determined by the nature of the works projected, but it may be necessary to exp/ore to greater depths at a lihited number of poihts to establish the overall geological conditions. The technical development of the project should be kept under continuous review, since decisions on the design will influence the extent of the jir vestigation.
It ii jhportant to realize that the detailed geology of a site can be no more than inferred from aerial photography, surface outcrops and subsurface information at the positions of the explorathn points. The possibility remains that significant undetected variations or discontinuities can exist, includihg lateral or vertical varjahons within a given layer. The uncertainties can be reduced but, except by complete excavation. can never be whofly eliminated b y a more ihtensive inveshgation. The use of angled boreholes can in certain cases greatly assist interpreting vari~hons between vertical boreholes (see also Section 10. l. 81. In some circumstances, additonal information between investigation points can be obtained b y geophysical methods (see Chapter 331.
10.3 N A T U R E OF THE PROJECT
3 . General
The investigation should yield sufficient data on which to base an adequate and econom~'cal design of the project. It should in aadit~on be sufficient to cover possible methods of construction and, where appropriate, to indicate sources of constructhn materials. The lateral and vertical extent of the invesbgathn should cover aLf ground that may be s~gnificantfy affected by the new works or their constructzbn. Two typical examples are the zone of stressedgruund beneath the bottom of a group of pii'es; and an adJ;lcent slope, the stabZty of which may be reduced by the works.
10.3.2 Slope and Retaining Wall Construction
Due t o t h e extensive construct ion of slopes and retaining walls in Hong Kong, detailed guidance on t h e na tu re and content of s i t e investigation for these f ea tu res is given in Tables 3 and 4. Fur the r discussion of t h e design and construct ion of slopes and retaining walls is given in t h e Geotechnical Manual for Slopes ( G C O . 1984) and in Geoguide 1 : Guide t o Retaining Wall Design (GEO, 1993).
10.3.3 Foundations fo r S t ruc tu res
Most s t r u c t u r e s in Hong Kong a r e founded on piles. Hand-dug caissons. driven piles, machine-bored piles and ba r re t t e s a r e commonly used. A general approach t o planning a ground investigation suitable for pile design purposes is given in ICE (1978). The investigation should make a full appraisal of t h e s i te and t h e ground conditions should be invest igated a t dep ths well below t h e proposed pile toe level t o allow for variations in t h e pile design. Knowledge of t h e groundwater conditions i s also required. Fur the r advice on ground investigation fo r foundations is given in Section 10.7.2. BSI (1986) and Weltman & Head (1983).
In areas where major s t ruc tu ra l defects in rock may occur (e.g. k a r s t fea tures in t h e Yuen Long basin, o r major shea r o r faul t zones) , more intensive investigation and g rea te r exploration dep ths than normally recommended may be requi red . Consideration may need t o be given t o locating underground cavities within t h e zone of influence of t h e loaded area, a n d t o identifying o the r possible significant fea tures such as steeply-dipping rockhead, f r ac tu res and al ternat ing soil and rock layers.
Recommendations on t h e dep th of exploration fo r foundations for s t r u c t u r e s , including shallow foundations, a r e given in Section 10.7.2.
10.4 PRELIMINARY INVESTIGATION
Before deciding on a full investigation programme, i t may b e advisable t o excavate t r ial pits o r t o s t r i p t h e su r face cover from slopes fo r a preliminary assessment of ground conditions. These should be carefully examined, logged and sampled (see Section 18.1).
For la rge projec ts requi r ing s taged ground investigations, i t will often be useful dur ing t h e f i r s t s t age t o c a r r y o u t a geophysical s u r v e y in addition t o
some widely-spaced boreholes t o identify those a reas which requ i re more detailed investigation.
1 0 . 5 LOCATION
The points of exploration, (e.9. boreholes, soundings, pits) should be located so that a general geological view of the whole site can be obtained, together with adequate detays of the engineering properhes of the soils and rocks and of groundwater conditlbns. More de tded informahon shouM be obtained at positbns of important structures and earthworks, at points of special engineering difficulty or importance, and where ground conditions are compficated, e.9. suspected buried va/lys, old s/ipped areas and underground cavities. Rigid, preconceived patterns of pits, boreholes or soundkgs shouM be avoided. In some cases, it wig not be possible to locate subsurface features until much of the ground investigation data has been obtained In such cases, the programme of in vestigations shou/d be modfled accordingly.
The locations of boreholes and o the r exploration points should only b e planned a f t e r t h e desk s t u d y , s i te reconnaissance and geological mapping a r e completed. I t i s often useful t o locate boreholes at t h e intended positions of la rge deep foundations. For slopes, boreholes should generally b e located along anticipated critical slope sections, a s well a s uphill and downhill for area and regional stability s tudies.
For tunnels and incfined shafts, boreholes should be offset so as not to interfere with subsequent construction. For other structures, the need to offset boreboles and trial excavahbns from criticapoints should be considered In most cases, boreholes should be carefufly backfilled, concreted or grouted up. Tr~kl excavations shouM be located outside proposed foundation areas.
I t is essentid that accurate locations and ground levels for all exploration points should be estabfished, I necessary b y survey (see Section l.2).
10.6 SPACING
Although no hard and fast rules can be laid down, a relatively close spacing between points of &orahon, e.g. I0 to 30 m, wi/ often be appropriate for structures. For structures small in plan area, explorahon should be made at a minimum of t h e points if possible. Where a structure consists of a number of adjacent units, one exp/oration poht per unit may suffice. Certain engineerhg works, such as dams, tunnels and major excavations, are particularly sensih've to geological conditons, and the spacing and locahon of exploration points shouM be more closely related to the detailed geology of the area than I> usual for other works.
In t h e case of a proposed c u t slope extending from soil into rock, t h e level of bedrock along t h e face of t h e cutt ing is important. Consideration should b e given t o obtaining t h e subsurface profile by additional drilling and geophysical means. In t h e case of reclamation, v e r y closely spaced boreholes may b e requi red t o locate and delineate buried obstruct ions such a s remnants of an old seawall.
10.7 DEPTH OF EXPLORATION
10.7.1 General
The dep th of exploration is governed by t h e dep th t o which t h e new project will affect t h e ground and groundwater o r b e affected by them. Normally, exploration should be taken below all deposits t h a t may be unsuitable for foundation purposes, e.g. fill and weak compressible soils, including any weak materials overlain by a s t r o n g e r layer. The exploration should be taken th rough compressible soils likely t o cont r ibute significantly t o t h e settlement of t h e proposed works, generally t o a depth where s t r e s s increases cease t o b e significant, o r deeper.
In Hong Kong, i t is common practice to drill into rock fo r a dep th of a t least 5 m t o establish whether corestone, boulder o r bedrock has been encountered. However, t h e final depth of drilling will depend on t h e need t o prove bedrock. In some cases, i t will be necessary t o drill deeper than 5 m t o establish conclusively t h e presence of bedrock, for example, i n investigations fo r end bearing piles (see Section 10.7.2). In o the r instances, i t may not be necessary t o terminate drilling in rock (see Section 10.7.4).
More specifica//y. the recommendations given ~n Sections I'D. Z 2 to I'D. Z 8 may be considered for certain types of work. I t is not always necessary that every exploration should be taken to depths recommended in SectJons IO.l.2 to 10.Z8. In many instances, it wi// be adequate IF one or more boreholes are taken to those depths in the early stages of the field work to estabfish the general subsurface profile, and then the remainder sunk to some lesser depths to exp/ore more thoroughly the zone near the surface which the initial exphrahon had shown to be most relevant to the problem in hand
10.7.2 Foundations for S t ruc tu res
In the case of foundations for structures, the depth of exphratron should be at least one and a half times the width of the loaded area. Commonsense will indicate exceptions to this guidefine; for example, 12 would not usually be necessary to continue drilfing for long distances in strong rock. For foundations near the surface, the loaded area is considered as either :
(a/ the area of an individual footing, or
(bl the plan area of the structure, where the spacing of foundahbn footings is less than about three tJhes the breadth, or where the floor loading is significant, or
(cl the area of a foundation raft.
In each case, the depth should be measured below the base of the footing or raft.
Where piled foundations are considered to be a possibi/ity, the length of pile usually cannot be decided unt17 an advanced stage of the project. No exp/icit rules can be given for the depth of exploration, but the fohwing offer some guidance :
(a) Fill and weak compressible soils seldom contr ibute t o t h e sha f t res is tance of a pile and may add down d r a g t o t h e
load on it. The whole pile load. possibly with t h e addition of down drag . will have t o be borne by t h e s t ronger materials lying below t h e weak materials, e i the r in end bearing o r th rough sha f t resis tance.
The length of driven piles is often determined initially by t h e driving resistance, and subsequent ly checked by load t e s t s . Hence, in such cases, t h e length of t h e pile is not accurately known until t h e piling cont rac t begins, b u t i t may b e possible t o gain a n early indication from s tandard penetration t e s t (SPT) blow counts.
In t h e case of end bearing piles in s t rong rock, boreholes should be of sufficient depth t o establish conclusively t h e presence of bedrock. The rock should then b e f u r t h e r explored, usually by means of ro ta ry drilling, t o such a dep th t h a t t h e engineer directing t h e investigation (see Section 15.2) is satisfied t h a t t h e r e is no possibility of weaker materials occurring lower down t h a t could affect t h e performance of t h e piles. This will usually r equ i re penetrat ing a t leas t 5 m, o r two and a half times t h e diameter of t h e pile, whichever is l a rge r , below t h e proposed founding level of t h e pile. For boreholes car r ied o u t dur ing construction t o prove sat isfactory pile founding levels, t h e dep th of penetration may have t o be increased where la rge corestones o r boulders a r e suspected o r have been identified nearby.
In weathered rocks, i t may not always be feasible t o locate underlying f resh rock. Foundations in th is case must often b e founded in t h e weathered rock, and proving t h e s t r e n g t h and continuity of t h e material below t h e intended founding level and t h e location, na tu re and orientation of discontinuities may then suffice.
Pile-supported ra f t s on clay may be used solely t o reduce settlement. In these cases, t h e depth of exploration is governed by t h e need t o examine all subsurface materials t h a t could contr ibute significantly t o t h e settlement. Similarly, for pile groups on clay, i t will be necessary t o e n s u r e t h a t t h e dep th of exploration i s sufficient t o prove t h e adequacy of t h e founding material below t h e toe of t h e piles.
Based on the informat~bn of the probable subsurface profile obtained from the desk study, the genera/ guidance given in fal to (el above,and an assessment of the types of pile likely to be considered, the engineer directing the hvestigathn shouh' determine the depth of exploraation and be ready during the course of the field work to modify this depth as appears to be necessary. In any event, exp/oration should at some pofnts be taken below the depth to which it is cons~'dered Mely that the longest piles wil penetrate.
I t should be noted t h a t if any s t r u c t u r e i s likely t o be affected by subs idence due t o collapse of underground cavities (e.g. k a r s t fea tures in t h e Yuen Long basin) o r any o the r causes, g rea te r exploration dep ths than those recommended in th i s Section may be requi red .
10. Z 3 Embankments
For embankments on alluvial and marhe soils, the depth of the exploraation should be sufficient to check possible shear failure through the foundation materials and to assess t%re likely amount of any settlement due to compress~Ble materids. In the case of water-retaining embankments, investigation should explore all materials through which piping could be initiated or significant seepage occur.
10.7.4 C u t Slopes
The dep th of exploration for c u t slopes should b e sufficient t o permit full assessment of t h e stability of t h e slope. This may necessitate proving t h e full dep th of any relatively weak o r impermeable materials such as decomposed dykes (Au. 1986). In general, exploration for slopes should extend a minimum of 5 m below t h e toe of t h e slope o r 5 m in to bedrock, whichever i s shallower. However, one o r more exploration points should in all cases extend below t h e toe of t h e slope o r excavation, i rrespective of bedrock level. Groundwater conditions, including t h e possibility of perched o r multiple water tables, should also be determined.
10.7.5 Pavements
For pavements, t h e dep th of exploration should be sufficient t o determine t h e s t r e n g t h and drainage conditions of possible sub-grades . Exploration t o a dep th of 2 t o 3 m below t h e proposed formation level will probably b e sufficient in most cases.
For shallow s d p~pefines, it wil frequently be suffiient to take the depth of exploration to 1 m below the invert le veL For deeper p~pelines the depth of explora&o should be sufficient to enable any likely difficultres in excavating trenches and supporting the p~;Oelines to be discovered; a depth a t least I to 2 m below the invert level may be advisable. Large pipelines, especially those in ground of low bear~hg capacity, require specid consideration.
10.7.7 Marine Works
For marine works, the effects described in Sections 10.7.2 and 10.7.3 may apply and, in additbn, consia'erafion shouh' be given to the effects of fi'dal variations.
In many cases of reclamation, i t may be sufficient t o terminate drilling short ly below t h e base of any sof t deposi ts t h a t a r e present .
10.7.8 Tunnels
For tunnels, it is important to take the exploration to a generous depth below the proposed hvert level because changes in design may result in the lowering of the level of the tunne4 and because the zone of lnfluence of the
tunnel may be extended by the nature of the ground at a greater depth.
Long horizontal boreholes parallel to the proposed tunnel alignment are extremely useful, particularly where the location of the proposed tunnel i s overlain by thick layers of deeply weathered rock (McFeat-Smith, 1987).
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11, SELECTION OF GROUND INVESTIGATION METHODS
11.1 GENERAL
Although the character of the ground and the technic& requirements are the most important aspects in the selection of methods of ground investigation, sefectrbn may also be ifluenced by the character of the site, the avdab~xty of equipment and personneL and the cost of the methods.
The specialist na tu re of ground investigation work should a t all times b e considered. In most cases i t will be necessary t o employ a cont rac tor who is experienced in t h e type of investigation work which is being proposed, and who has p roper equipment and experienced personnel t o c a r r y o u t t h e works.
11.2 SITE CONSIDERATIONS
The topography, nature of the ground surface, surface water, the existence of buifd~hgs or other structures and land 'owner~h~>' may cause problems of access to the locations for borehofes, or interfere with g e o p h y s ~ ~ ~ f methods. For example, on very steeply sloping open sites, it may be necessary to construct an access road or lower the equ~pment down the sfope or haul it up. Where the working pos12ion is on steeply sloping ground. it will be necessary to form a hor~zontaf work~ng area by excavation or the use of staging (Plate 2A). On sites that are obstructed by buildings and other structures, it may be necessary to demofish wa//s to gain access. Alternatively, it may be possible to lift the equ12ment over obstructions ushg a crane or to use special equ~>ment that can be dismantled and man-handled through the bu17ding and used in a confined space. Gaining access to sites covered by water presents special problems fsee Chapter 14). I f the ground surface is soft, it can be traversed o d y by very light equ~kment. Where th~k would not be effective, access roads for heavier equipment will be required Alternatively, the use of heficopters or hovercraft may be appropriate.
For ground investigation within o r requi r ing access th rough privately- owned land, including propert ies of t h e utilities companies and armed forces, permission should f i r s t be obtained from t h e owners. For Government land, approval should b e sough t from t h e re levant District Lands Office. For sites u n d e r t h e control of Government, approval must b e obtained from t h e re levant Department concerned. Such s i tes include reservoi rs , service reservoi rs , roads. highways, country parks , Urban Council parks , etc . Permission t o e n t e r a s i t e for purposes of ground investigation may place f u r t h e r restr ict ions on . the methods used. For example, i t may be necessary t o control o r eliminate t h e r e t u r n of flushing media from boreholes t h a t affect adjacent slopes, fish ponds. cultivated fields, o r highways (see Section 18.7.1). Also, t h e presence of foundations and services often res t r i c t t h e use of inclined drilling th rough existing retaining walls into adjacent propert ies .
Access for drilling r i g s should b e assessed in t h e field with t h e assistance of plans, maps and aerial photographs. Timber scaffolding is often used in Hong Kong t o provide access over rugged t e r ra in and t o cons t ruc t drilling platforms in ve ry s t eep t e r ra in (Plate 28). As such scaffolding can account fo r a la rge portion of t h e total cos t of t h e investigation, ca re should b e taken t o locate boreholes fo r ease of access where possible.
Most methods of boring and field tes t ing requ i re a supply of water. On
a s i te where water is not available, i t will be necessary t o a r range for a temporary supply t o b e provided. In t h e u rban area, water can often b e obtained from fire hydran t s upon application t o t h e Water Supplies Department for t h e h i re of a metered adaptor . In r u r a l a reas water may be obtainable from wells, r ive r s o r streams. On s i tes where t h e provision of water p resen t s a major problem, i t may be necessary t o t r anspor t t h e water in bowsers, o r t o use al ternat ive methods of investigation; for example, with ro tary drilling an a i r foam flush could b e used instead of water f lush (see Section 18.7). Where water is used a s t h e flushing medium, adequate measures should be provided t o prevent silt and o the r debr is in t h e flushing r e t u r n from enter ing t h e permanent drainage system, the reby causing siltation and o the r problems. Such measures may include set t l ing basins and sand/s i l t t r aps .
Other s i te considerations which may r e s t r i c t t h e methods used a r e as follows :
(a) Trees on Government land are protected, and should be preserved as f a r a s possible in gaining s i te access o r in choosing investigation points. Permission t o lop o r c u t down a n y t r e e s will not b e granted unless good cause is shown.
( b ) 'Fung shui ' aspects of some s i tes a r e of g r e a t social and religious significance, and local advice should b e sought in planning t h e investigation.
(c) Buried utilities and services a r e v e r y common and must be accounted for , a s must subways and o t h e r tunnels (e.g. Mass Transi t Railway tunnels) t h a t may pass beneath t h e site.
( d l Seismic s u r v e y s employing explosives may be res t r ic ted o r prohibited in built-up areas.
(e) Noise restr ict ions may prohibit t h e use of certain methods of investigation.
( f ) The difficulty in s torage of spoil may r e s t r i c t t h e use of t r ial pi ts on some sites.
Fur the r advice on planning a ground investigation and relevant sources of information can be found in Appendices A and B (see also Sections 4.1.2 and 7.2).
12, EFFECT OF GROUND CONDITIONS ON INVESTIGATION METHODS
12.1 GENERAL
This chap te r considers t h e fac tors involved in t h e choice of t h e most sui table procedures fo r boring, drill ing, sampling, probing and field t e s t s , as determined by t h e cha rac te r of t h e ground. Specific r e fe rence i s made t o t h e ground conditions commonly encountered in Hong Kong; these a r e f u r t h e r described elsewhere (Brand & Phillipson, 1984; Endicott. 1984; G C O , 1988; Phillipson & Brand. 1985). The following sect ions should be r ead in conjunction with Table 8, which summarises typical sampling procedures f o r different t y p e s of materials ( see Section 19.1). F requen t reference i s made to classes of sample quality, which a r e defined in Table 9 (see Section 19.2).
The determination of the groundwater cond12ions I> a most important part of a ground investigation. I t f~volves the installation of p~ezometers and borehole or field testing (see Chapters 20, 21 and 25), and is not, in genera/, a major consideration in the choice of a procedure for dri / / ig and sampling. Ceophys~kd methods are often a useful means of interpolating between boreholes in a variety of ground cond~Zions (see Chapter 33).
12.2 GRANULAR SOILS CONTAINING BOULDERS. COBBLES O R GRAVEL
Some types of colluvium a n d alluvium may fall into th is ca tegory , a s may some fill a n d soils derived from insi tu rock weathering. al though t h e la t te r two t y p e s a r e considered more fully in Sections 12.8 and 12.10.
Within t h e limits of cos t , t h e bes t method for invest igat ing th i s t y p e of ground i s by means of a d r y excavation (see Sections 18.1 and 18.2). The excavation permits t h e s t r u c t u r e of t h e ground t o b e inspected, samples t o be obtained. a n d field t e s t s t o b e used t o measure insi tu dens i ty , s t r e n g t h and deformation character is t ics ( see Chapters 27. 29 and 30).
If i t i s necessary t o invest igate t h e ground below t h e groundwater table. dewatering may b e requi red t o obtain a d r y excavation. The possible effects on adjacent ground of a n y dewatering should f i r s t be assessed. however, and i t may b e necessary in some cases t o adop t al ternat ive methods of investigation below t h e groundwater table.
Rotary water f lush drilling may be employed (see Section 18.7). using a t r ip le- tube core-barre l with r e t r ac to r shoe fo r matrix material a n d a diamond drill b i t f o r boulders . I t may also be possible t o use a U l O O sampler ( see Section 19.4.4) in matrix material t o obtain class 3 o r 4 samples. The use of a i r foam a s a f lushing medium may enhance co re recovery and sample quality.
During boring, t h e r e may be difficulty in advancing t h e boreholes and. consequently, in obtaining samples of adequate quality. Boring may be under t aken with t h e l ight cable percussion method using t h e shell ( see Section 18.5). and employing t h e chisel when rock fragments too l a rge t o e n t e r t h e shel l a r e encountered. The sides of t h e borehole must be suppor ted with casing. Disturbed samples taken from t h e shell a r e usually only class 5 (grading incomplete) because t h e fine fraction may have been washed o u t and t h e coa r se f ragments may have been broken up by use of t h e chisel.
Borehole tests can be used to obtain an indicatlbn of the properties of the ground. The standard penetrahon test (see Sect~on 21.21 will give some indication of relative density. Occasional high values that are unrepresentative of the true relative density will be obtained when the penetrometer encounters coarse graveL In ground contahfhg cobbles or boulders, the standard penetratlbn test gives an increasing proportion of unrealisticaly high results. The borehole permeabifity test fsee Section 21.41, may give a reasonable indication of permeability, and the results can also be used to give a guide to the proportion of tihe particles in the soiL A more rehble assessment of permeability wifl be obtained from a pump~hg test, (see Chapter 25). The cone penetration test fsee Sechon 23.31, has limitations where there is a s~gn~flcant content of boulders or cobbles. It is also limiited because of the inabimy of the cone to penetrate dense gravel. The "static-dynamic" test (see Section 23.41, is useful for this purpose, although its results win also be affected where cobbles or boulders are encountered The pressuremeter is useful in coarse granular so~7s when held w12hin a slotted casing (see Section 21.71.
12.3 GRANULAR SOILS
These soils include sands, silty sands and sandy silts, and are fairly common in alluvial or marine deposits. Boreholes in these materials may be sunk by the light cable percussion method using the shell, or by rotary drilling. Disturbed samples taken with the shell are likely to be deficient in fines, and therefore of class 5 only. Samples suitable for a particle size distribution test , class 4 , may be obtained using the split barrel standard penetration test sampler. Larger class 4 samples can sometimes be obtained using UlOO sampling equipment with a core-catcher.
The action of forcing a sampler into granular soils tends to cause a change in volume, even if the area raho is s d (see Sectrbn 19.4.1/21), and hence the density of the s a m e may not be representative of the layer. In some cases, a piston samp/er wi7.J be effective (see Section 19.51,' this should produce class 2 sampLes or, where the so~7 is loose or very dense, class 3 samples. However, in both cases the moisture content of the samples may be unrepresentative of the insitu ground With clean sand, normal samp/ng equipment may fail to recover a sample, and it wi/ then be necessary to use the compressed a> sand s-er /see Sechbn 19.7),' sample classes w17l be similar to those obtained with a piston sampler.
In shallow investigations above the water table, excavations or hand augering (see Sechbn 18.41, may be used.
A guide to the relative density of granular so17s is obtained by the standard penetration test. However, the results can eas17y be invWated by loosening of the so17 below the water table. Where it IS important that the relative density should not be underestimated, for example when a driven p17e prokct is being inveshgated, the relative density should be assessed by the cone penetration test.
Approxhate values of the strength and compressibility parameters can be estimated on an empirical basis from the results of the standardpenetration test or, preferably, from the results of the cone penetratlbn test. Pressuremeter tests are also usefuL A more direct determination requires the use of plate tests carried out in a dry excavation (see Sechon 21.6 and Chapter 291.
Permeabifity may be assessed from borehole permeabifity tests (see Section 2I.31, or by pumping tests (see Chapter 251.
12.4 INTERMEDIATE SOILS
These include clayey sands , clayey si l ts and si l ts , and may be encountered in alluvial and marine deposits. The selection of methods of ground investigation will depend on whether t h e material behaves a s a granular soil o r a cohesive soil.
12.5 VERY SOFT TO SOFT COHESIVE SOILS
These include sandy clays, silty clays o r clays. They a r e commonly encountered in marine and alluvial deposits. The normally consolidated and lightly overconsolidated marine clays may be sensitive, while t h e alluvial silty clays a r e generally insensitive.
Rotary drilling o r t h e l ight cable percussion method may b e used t o advance holes in sof t cohesive soil. Considerable ca re is requi red with ro ta ry drilling t o avoid change of water content and d is turbance by t h e drilling fluid. Class 1 samples can be obtained by using a piston sampler. Class 2 o r 3 samples can sometimes be obtained with an open- tube sampler. Continuous samples, usually class 3, can be obtained with a Delft sampler (see Section 19.6). Disturbed samples from t h e clay c u t t e r of t h e l ight cable percussion method a r e generally class 4. Where t h e borehole contains water , i t may be necessary t o use t h e shell, in which case class 4 samples can b e obtained provided t h a t lumps of intact soil can be recovered.
The insitu vane t e s t is by f a r t h e most sat isfactory means of measuring t h e undrained shea r s t r e n g t h of sof t clays, b u t t h e penetration vane test appara tus is much t o b e prefer red t o equipment which is used in boreholes (see Section 21.3). Vane t e s t s a r e particularly effective if combined with s ta t ic cone penetration t e s t s ( see Section 23.3). For laboratory t e s t purposes (part icularly oedometer t e s t s ) la rge diameter samples (g rea te r than 150 mm) should be obtained wherever possible. The compressibility values obtained from Rowe cell t e s t s on large diameter samples (see Chapter 37 and Table 12) may b e used in conjunction with insi tu cons tant head permeability measurements t o give a reasonable estimate of r a t e of consolidation settlement.
12.6 FIRM TO STIFF COHESIVE SOILS
These materials may b e encountered as layers within marine o r alluvial deposits.
Rotary drilling can be used, b u t considerable ca re i s requi red t o avoid change of water content and d is turbance by t h e drilling fluid. The re t rac table t r ip le- tube core-barrel can b e used in ro ta ry drilling t o obtain class 2 and sometimes class 1 samples. The 100 mm open-tube sampler can be used t o obtain class 2 t o 3 samples. Alternatively. t h e l ight cable percussion method with clay c u t t e r can be used, which will r e su l t in class 5 samples.
12.7 COHESIVE SOILS CONTAINING BOULDERS, COBBLES O R GRAVEL
Most colluvium and some types of alluvium fall in to th is category, a s may some fill and soils derived from insitu rock weathering, although t h e l a t t e r two types a r e considered more fully in Sections 12.8 and 12.10.
W M n the fim12s of cost, the best method of investigating cohesive soils containing boulders, cobbles or gravel is by a dry excavation. The excavathn wiiY enable the structure of the ground to be inspected, samp/es to be obtained, and field tests for the determination of the insitu density, strength and undrained deformation character~str'cs to be carr~ed out.
When using borehole methods of investigation, th i s type of ground p resen t s difficulties in both advancing t h e hole and recovering samples of adequate quality. Rotary drilling is often employed, using tr iple-tube core- ba r re l s equipped with a r e t r ac to r shoe for t h e matrix materials and diamond- impregnated drill bits for rock fragments and boulders. Class 1 samples can be obtained by employing a i r foam flush with t h e la rge diameter t r ip le- tube core- barrel. Class 1 t o 2 samples may be obtained with re t rac table t r ip le- tube core-barre ls and water flush. The use of U l O O samplers can yield class 2 o r 3 samples of t h e matrix material, while t h e spl i t ba r re l s t andard penetration test sampler can b e used t o obtain class 3 t o 4 samples. The s t andard penetration t e s t is sometimes used t o obtain a rough indication of s t r e n g t h , b u t i t may give misleading resul t s if boulders and cobbles a r e present .
F17l can conskt of replaced natural ground, or waste materkls of various origins. The uniformity of fi/l w i l depend on the degree of control which has been imposed, on the quality of the incoming material and on the method of placing and compaction. In older filL there may have been little or no control of the filfing operation, and the major problem in planning the ground investigation wi/ be to assess the variation in character and quality across the site. Often, the variation wifl be random.
Conventronal methods of boring, sampling and hsitu testing, as appropriate to the character of the ground, can give informatron on the thickness and properties of the fil/ at the particular locations of the boreholes or ins12u tests. It I> essentid to ensure that the borehofe is always fufly cased through fil/ to avoid contamination of the natural ground from falling materiaL Pits and trenches are particularly useful for investrgating the nature and var~kbi/iy of fil/ (see Chapter 181.
In combustible AHs, temperature measurements may be necessary. It should be noted that on waste tips, burning materials below ground may give rise to toxic or flammable fumes from the borehole. TIP fies may also create voids, which may coflapse under the weight of an investiqation rig. Lagoons w12hin waste tips may be areas of very soft ground.
12.9 R O C K
Rotary diamond bi t core drilling with water f lush is normally used in rock. Soils derived from insi tu rock weathering a r e f u r t h e r considered in Section 12.10. Double-tube o r t r ip le- tube core-barrels may b e employed, with t r ip le- tube core-barrels giving b e t t e r core recovery and causing less
dis turbance , especially in highly f rac tured o r jointed rock. The use of l a rge r - sized equipment producing cores of about 100 mm diameter o r more will also help t o improve core recovery.
Soft in f l l ing of rock discontinuities can sometimes be lost due to erosion by the flush water, and air or air foam flush driyfing may be deskable. I n genera/ rotary core dr17fing with a d~hmond dri7l bit will produce samp/es which may allow an assessment of the character and engineering properhes of the intact rock materia1 Such sampies may a/so give some indicat~on of the frequency and dip angle of the discontinuities but not their dip direction, unless special techniques are used The use of borehole periscopes, impression packers, cameras, and television cameras may be usefuZ i n thh connection /see Section 21.81. I n many cases, rotary core sampZes give no indication of the character of any infZfing of the discontinuities.
I n a ground investigatlbn using light cable percussion borihg or rotary core drilfing, an indicatlbn of the properties of the rock mass can be obtained from tests ih borehoZes. For certaih of such tests, howevec it wifl be necessary to take into account the probable effects of disturbance of the ground by the drilling process. The standard penetration test /see Section 21.21, can give a rough indication of the variation of strength and cornpress~'bAity i n weak rock. The permeabifity test (see Section 21.41, or the packer or Lugeon test (see Section 21.51, may give a measure of the mass permeabi7ityY which i n turn can give an lhdication of the presence of open jbints and other water-bearihg discontli7uities. Where appficable, the plate test (see Section 21.51, and diyatometers such as the pressuremeter (see Section 21. I), can be used to investigate deformation properties and possibly also the strength.
The best method for determining the properties o f a rock mass, including the orientahon of dikcontinuities, i s visual ihspection, and field tests carried out i n excavations, caissons or headings (see Chapter 181.
12.10 SOILS DERIVED FROM INSITU R O C K WEATHERING
Weathered rock t h a t can be rega rded and t rea ted essentially a s soil from an engineering viewpoint occurs extensively throughout Hong Kong. These materials a r e derived primarily from t h e chemical decomposition of t h e parent bedrock, and the i r charac ter depends on t h e pa ren t rock type. Soils derived from grani te a r e typically silty o r clayey sands. while those derived from tuff and o the r volcanic rocks a r e often sandy o r clayey silts. These soils v e r y often contain corestones of less decomposed rock within a more decomposed matrix, and i t is not uncommon to encounter grani te corestones a s la rge a s 3 m o r more. The dep th over which decomposed material changes to f r e sh rock is extremely variable and is related t o t h e rock type , joint pa t t e rn , t h e spacing of t h e joints, faulting. alteration, and t h e position of t h e water table (GCO. 1988).
Where these soils occur a t shallow depth , pits a r e probably t h e most effective means of investigation; class 1 block samples of t h e matrix material can usually b e obtained for laboratory tes t ing and t h e exposure can be fully described and logged.
Rotary drilling can be used t o advance boreholes in these materials provided considerable ca re is taken t o limit d is turbance by t h e drilling fluid. Retractable t r ip le- tube core-barre ls can generally be used t o obtain class 2 and
sometimes class 1 samples. Class 1 samples can be obtained using a large diameter t r ip le- tube core-barre l with a i r foam flush. Open-tube samplers generally provide class 2 t o class 4 samples. The spl i t ba r re l s t andard penetrat ion t e s t sampler can b e used t o obtain small class 3 or 4 samples.
Borehole tests can be used t o obtain a n indication of t h e propert ies of t h e ground. The s t andard penetrat ion test will give some indication of densi ty and degree of weathering, although t h e presence of corestones may give unrealistically high results . The s t andard penetration test can generally provide useful information fo r t h e initial assessment of likely pile founding depths . The borehole permeability test may give a reasonable indication of permeability. The pressuremeter may b e useful fo r measuring ground stiffness.
In most rocks, the mass properties depend largely on the geometry and nature of the discontinuities. This can requ~ie the engineering properties to be measured in the plane of the discontinu~'tres along specific orientathns determined by the anti'c~pated directions of the stresses to be applied The controf by discontinuities over the strength and deformtlbn characteristi'cs of a ground mass is less obvious in so17s derived from ihsitu weathering than in moderately weathered to fresh rock, but may be equa//y imgortant.
There are no satisfactory drilng or bor~ng techniques available for ensuring that the core recovered can be orientated over the full depth penetrated, but borehole discontinuity surveys can be conducted f e e Seelion ZI.81. In sofi!s, the discntzhuitis are often des t~yed by the dr~Zing and therefore overlooked Where d~kcontinuities are inp port ant to the eng~heering problems in volved, i M u exposures of discontinuitJes are necessary to obtah data on the2- or~entatrbn and nature. After iMal ~hvestigations using interpretation of aerial photographs, surface outcrop logging and the drilfing of vertical and inclined or~entated holes, it may be necessary to form full surface auposures, large dimeter boreholes, trenches, pits or adits to allow visual inspection around and within the undisturbed ground mass, and measurement of the relevant discontinuity data (see Chapter 261. In some projcts, suitable exposures may be provided in exca vatibns necessitated by the permanent works. The extractrbn or insitu preparation of orientated test smples can be carried out in these exca vations, together with orientated large scale tests. The orlentation of the excavations controls thek intersection with the discontinuities and, consequently, the discontinuity data that can be obtained Generally, three orthogonal exposures are required to define fully the spatial distribution of the d~kcontinuiti'es. The extent of the excavations is governed by the spauhg between discontinuities and the size of the works.
12.12 CAVITIES
Ground containing natura l o r man-made cavities can be found i n Hong Kong (e.g. caverns in kars t , disused tunnels and old mineshafts) and t h e cavities may be vacant o r infiIIed (Culshaw & Waltham. 1987). Difficulties may b e experienced in advancing a borehole through such ground. A var ie ty of drilling techniques may need to be t r ied , and precautions should b e taken t o p reven t dropping of t h e drill s t r ing , a n d to maintain verticality of t h e hole. Care may also b e requi red to avoid g round subsidence dur ing investigation (see Section 8.3.2). Close supervision is essential fo r such investigations.
13, AGGRESSIVE GROUND AND GROUNDWATER
13.1 GENERAL
In some areas , soil, rock and groundwater may contain certain cons t i tuents in amounts suff icient t o cause damage t o Portland cement concrete o r steel, While insi tu weathered rocks and the i r associated soils in Hong Kong are generally not aggress ive , th i s should be confirmed by ground investigation and laboratory tes t ing whenever t h e use of ground anchors , reinforced fill s t r u c t u r e s o r o the r susceptible s t r u c t u r e s a r e contemplated. Investigations fo r aggress ive ground and groundwater should be considered fo r all s i tes where t r anspor ted soils a r e encountered, and fo r all marine sites.
The principal const i tuents causing damage t o concrete are sulphates, which are most common in clay soils and acidic waters . Total su lphate contents of more than 0.2% by weight in soil and 300 parts pe r million in groundwater a r e potentially aggress ive (BRE. 1981).
Corrosion of metal i s caused b y electrolytic o r o the r chemical o r biological actions. In indust r ia l areas, corrosive action may ar ise from individual waste products t h a t have been dumped on t h e site. In r i v e r and marine works, t h e possible corrosive action of water, sea water and o the r saline waters , and t r a d e eff luents may also requ i re investigation. In a marine environment, t h e most seve re corrosion is found in t h e 'splash zone' (i.e. t h e zone t h a t is only wetted occasionally). The saline concentration in groundwater near t h e sea may approach t h a t of seawater. particularly in t h e case of reclaimed land. In es tuar ine situations, t h e r e may b e a n a d v e r s e condition because of alternation of water of different salinities.
13.2 INVESTIGATION OF POTENTIAL DETERIORATION OF C O N C R E T E
Laboratory tests t o a s sess t h e aggress iveness of t h e ground and groundwater agains t Portland cement concrete include determination of pH value and sulphate content (BSI. 1975b). Reference should be made t o BRE (1981) regarding t h e determination of water-soluble su lphate concentrations. The pH value may be al tered if t h e r e is a delay between sampling and test ing. s o field determinations should be made if possible.
Water sampled from boreholes may be al tered by t h e flushing water used in drilling. o r b y o the r flushing media employed. Therefore su lphate and acidity tests carr ied o u t on samples from boreholes may not b e representa t ive unless special precautions a r e taken (see Section 20.3).
13.3 INVESTIGATION OF POTENTIAL CORROSION OF STEEL
The likelihood of corrosion of s tee l can be assessed from tests of resist ivi ty, redox potential. pH, chloride ion content , total su lphate content , su lphate ion content , and total sulphide content. Details of t h e s e t e s t s , and re levant limits for a relatively non-aggressive environment for steel, are given in t h e Model Specification for Reinforced Fill S t ruc tu res (Brian-Boys et al. 1986). Chemical tests should be done on undis turbed specimens which have been placed in clean airsealed containers immediately a f t e r sampling. If bacteriological at tack is expected, undis turbed specimens should be placed in sterilized containers and tes ted in accordance with BSI (1973) (see also
Section 13.2 and Table 12).
13.4 INVESTIGATION OF FILL CONTAINING INDUSTRIAL WASTES
Industrid waste products can contain a wide range of chemicals, depending on the industrial processes from which the waste products are derived. Some chemicafs are h~ghly aggressive to concrete or steel ~ i r underground structures, and some can be highly obnoxious or even poisonous. The fast two characteristics can present major construction problems, e.g. the disturbance or disposal of contaminated ground, or the disposd of contaminated groundwater. L ocal enquiries may give some indication of the orig~ns of the waste materials, and the pH value and sulphate content for the fil/ and the groundwater will genera//y give some indication of the magnitude of the contminatlbn. It may then be necessary to carry out a detarjed chemical study of the ground conditions.
Further guidance i s given by Naylor et a1 (1978).
14, GROUND I N V E S T I G A T I O N S OVER WATER
14.1 GENERAL
Sinking boreholes below water presents special d~yficult~es in comparison with working on dry land. A reasonably stable working platform may be provided, such as a staging, barge or sh& and the borehole sunk through a conductor pipe spanning between the working platform and the water bottom. rncreasing use is being made of a var~ety of penetration testing techniques (Blacker & Seaman, 1985). In some cases, it may be feasible to lower specidy designed boring, driflng orpenetration testing equipment to the water bottom to be operated by remote control or a diver. With remote controL operation is restricted to a s~hgle continuous process. Penetration depths vary from less than 5 m for some devices, to 20 m or more for others. Geophysical techniques are also used to augment the informaoon obtained from boreholes, or a s a prefiminary investigation before putting down borehofes (see Chapter 33).
A s in land investigations t h e choice of suitable equipment for marine investigations depends primarily on t h e expected ground conditions and t h e purpose of t h e investigation. Additional factors t h a t must be considered in marine investigations include t h e water depth , heave of t h e c r a f t caused by wave action, tidal fluctuations, and water c u r r e n t s (Blacker & Seaman. 1985). Also, t h e requi red working a rea for a drilling vessel must include a safe margin fo r anchor lines beyond t h e dimensions of t h e c r a f t itself. A typical sp read of anchors would be u p t o 50 m on e i the r s ide of t h e craft.
The scope of the work, including the methods of drilling, samphhg and insitu testhg, requires careful considera&on depending on the parthuhr difficulties of the site. When working over water it is essenttkl that due consideration is given to safety requirements, navigational warnings, and the regulations of Government Departments and other authorities.
To avoid in ter ference with marine traff ic , t h e Marine Department must be notified of investigations so t h a t a Notice t o Mariners can b e issued. Special consideration must be given t o s i tes where t h e investigation o r associated c r a f t could p resen t a hazard. For example, c r a f t working close t o t h e runway of Kai Tak Airport must not pose a hazard t o aircraft ; permission fo r any such work must f i r s t b e obtained from t h e Civil Aviation Department. Similarly. permission must b e obtained from t h e Mass Transi t Railway Corporation, t h e Cross Harbour Tunnel Co. Ltd, t h e Water Supplies Department, o r t h e various public utility companies if work is t o be car r ied o u t near submerged tunnels , pipelines o r major utilities (see Appendices A and B).
Ground invesfiyafions conducted from above water are often more expensive and time consum~hg than comparable hvest~gathns conducted on dry land, and there may be a temptation to economize by reduchg the scope of the ~hvestigatlbn. The extent of the requirement for ground investigabons shouM be realisticafly assessed, shce econom~es in th~k direction can turn out to be false.
Tropical cyclones may lead t o disruption of investigations, especially in t h e summer months. I t i s a usual insurance requirement t h a t vessels proceed t o a typhoon shel ter when t h e s t rong wind warning signal number 3 o r above has been issued (o r is forecast) by t h e Royal Observatory.
14.2 STAGES AND PLATFORMS
Mere stable working platforms are available or can be provided, such as oil dr17ling platforms and jetties or purpose-bu17t scaffold stages and drilfing towers, 12 is generdy possible to use conventional dry-land ground investigation drilfing equipment and conventional methods of sampling and insitu testing. When working from existing structures, it may be necessary to construct a cantilevered platform over the water on which to mount the drilling rig. m e n drjyfing close to the shore in relatively shallow water, it may be more convenient to construct a scaffold staging from land to the borehole location. Alternative&, it may be more economical to construct a scaffold or other tower a t the borehole locathn, in which case some means of transporting the drilfing equ~bment to the tower wifl need to be provided. Some towers are constructed such that they can be moved from one borehole location to another without having to be dismantled.
Jack-up platforms, and special craft fitted with spud legs, can be floated into positlbn and then jkcked out of the water to stand on their legs. They can combine manoeuvrability w12h fu/fi/ent of the requirement for a fked w o r m platform.
Jack-up and other fixed platforms effectively overcome the problem of heave and allow a high standard of drilling, testing and sampling to be achieved. Jack-up platforms currently available in Hong Kong are capable of operation in water depths not exceeding about 12 m (Plate 3A).
The design of dl staging, towers and platforms should take into account the nature of the seabed, fluctuating water levels due to tides, waves and swefl conditions. It is essential that such constructibns should be sufficjently strong for the boring operations to resist waves, tidal flow and other currents and floatihg debris.
14.3 FL UA TINC CRAFT
The type of floating craft suitable as a drjYfing v e d depends on a number of factors such a s whether the water is sheltered or open, the anchor holding properties of the seabed, whether accommodation for the personnel is required on board, the like& weather conditlbns, the depth of water and the strength of currents. In inland water, a small anchored barge may suffice, but in less sheltered waters a barge should be of substanthl size, and anchors wi/ require to be correspondi&y heavy. In offshore conditions, a ah12 is often employed, and it may then be possible to accommodate the personnel on board, with a saving in auxifiary su&y vessels.
An auxifiary vessel will be required to handle the moorings if a barge is used for the work, but in certah cases a sh@ may be able to lay and pick up its own moorings. Generdy, four or s~k poht moorings will be required, and anchors should have the best hold~hg capacity feas~Ble. In water deeper than 80 m, conventional moorings become difficult, and the use of vessels maintained in position by computer-controlled thrusting devices should be considered.
Special techniques are required to deal with fluctuating water levels due to tides, waves and swell conditions (Plate 3 B ) , particularly with rotary drilling where a constant pressure between the drill bit and the bottom of the borehole is required (Smyth & Mcsweeney, 1985). When the heave is
anticipated t o exceed about 300 mm, i t is necessary t o employ a heave compensator system if high quality samples a r e t o be obtained. Heave compensator systems allow t h e drill s t r ing and sampling equipment t o b e isolated from t h e vert ical movements of t h e c r a f t (Blacker & Seaman, 1985).
Pontoons and barges should be anchored a t t h e co rne r s using anchor lines a t leas t five times t h e dep th of water. In exposed waters , motorized mooring winches a r e necessary.
14.4 WORKING BETWEEN TIDE LEVELS
Sinking boreholes between high and low t ide levels may b e achieved using scaffold stagings. platforms (see Section 14.2) o r flat-bottomed pontoons, o r by moving drilling r i g s t o t h e location dur ing periods permitted by t h e tides.
When i t is intended t o conduct drilling operat ions from flat-bottomed c r a f t res t ing on t h e seabed a t low t ide, t h e profile and condition of t h e seabed should be assessed in advance.
14.5 LOCATING BOREHOLE POSITIONS
Close t o shore, borehole positions and o the r investigation points can be se t -out b y radiation from known shore stat ions with distances measured by Electronic Distance Measuring (EDM) equipment. Fur the r offshore. o r when visibility is bad, electronic position fixing techniques can be used.
Set t ing-out by radiation usually involves t h e initial placement of a marker buoy within 5 rn of t h e specified position. The marker buoy should b e f i t ted with a line of suff icient length t o allow for tidal variations and wave heaving. An auxiliary float on a 5 m line can also be tied t o t h e marker buoy t o indicate t h e direction of t h e cu r ren t . This will help in manoeuvering t h e drilling c r a f t into position. Once t h e drilling c r a f t has been anchored over t h e s inker of t h e marker buoy, f u r t h e r measurements from t h e known shore stat ions can b e taken. The position of t h e drilling c ra f t can b e adjus ted by means of anchor winches until t h e borehole is positioned within 1 m of t h e requi red position. All borehole positions should be related t o t h e 1980 Hong Kong Metric Grid, o r if a s i te gr id is used, t h e s i te gr id should b e related t o t h e 1980 Hong Kong Metric Grid such t h a t s t andard co-ordinates can be obtained.
14.6 DETERMINATION OF REDUCED LEVELS
Reduced levels are generafly transferred to a drilfing vessel from shore by setting up a tide gauge close to the shore. Tbe gauge is read at frequent intervals throughout the tia'al cycles at the same time as readings of water depth are taken on the dr~jrfing vessel. Corrections may be necessary to allow for tidal variations when the distance between the tide gauge and the vessel is s&ni&ant.
Reading of t h e t ide gauge can be facilitated by noting both t h e c r e s t and t r o u g h levels of at least six consecutive waves. An average of t h e mean c r e s t level and mean t rough level can be adopted as t h e t ide level at t h a t instant . The t ide gauge should be referenced t o Hong Kong's Chart Datum
(which is 0.146 m below Principal Datum), so that the reading can be used to obtain the reduced levels of the seabed and subsurface geological boundaries.
14.7 D R I L L I N G , S A M P L I N G AND T E S T I N G
Marine investigations commonly encounter interbedded marine and allu- vial deposits underlain by weathered bedrock. Each stratigraphic horizon may contain distinctly di f ferent materials and may require di f ferent investigatory techniques (Beggs. 1983; see also Chapter 12).
For marine investigations, the rofary open hole method of advancing a hole is preferred to the rotary wash boring method (see Section 18.7.1). Drilling mud should be used as a flushing medium and to stabilize the hole when casing is not required. Cable tool boring techniques may be used to advantage in some situations, for example the identification of suitable marine borrow areas. Rotary drilling with a retractable triple-tube core-barrel (see Section 19.8) is often employed in soils derived from insitu rock weathering, as for land-based investigations.
I f a fixed platform is not used during sampling, particular care must be taken to prevent sample disturbance due to heave. Continuous sampling o f sof t soils can be undertaken with a Delft or Swedish foil sampler, but these are particularly sensitive to heave and should only be attempted from a fixed platform. With the Delft samplers, care should be taken to prevent necking of the nylon jacket due to unbalanced fluid pressures, and ripping o f the jacket due to shells in marine deposits.
A range of field tests in boreholes is useful in marine investigations, including standard penetration tests. vane shear tests and permeability tests. Static cone penetration testing and geophysical testing are also o f value. In the case of vane shear tests , i t is preferable to provide a stable support for the equipment on top o f a sof t marine mud seabed (Fung e t al, 1984).
A special category of marine investigations involving only shallow-depth seabed materials is often required for pipeline foundations, pollution monitoring and similar projects. Disturbed, shallow-depth seabed samples may be obtained for these purposes with a grab sampler, gravity corer or vibrocorer. The grab sampler is the simplest of these devices, but i t can only obtain samples from the uppermost 0.5 m of the seabed. The gravity corer normally consists of an open barrel 3 m in length that is allowed to fall and penetrate the seabed under its own weight. The vibrocorer is driven b y a motorized vibrator and can penetrate 3 to 6 m depending on the nature of the seabed materials. The samples recovered using these methods are generally o f poor quality but nevertheless should be suitable for classification testing. The principal advantage of these methods is the speed with which samples may be recovered over a considerable area (Blacker & Seaman. 1985).
15, PERSONNEL FOR GROUND INVESTIGATION
15.1 GENERAL
In view of t h e importance of ground investigation as a fundamental component of t h e p roper design and efficient and economical construction of all civil engineering and building works, i t i s recommended t h a t personnel involved in t h e investigation should be familiar with t h e purpose of t h e work, and should have appropriate specialized knowledge and experience.
15.2 PLANNING AND DIRECTION
The person planning and direct ing t h e ground investigation should be a suitably qualified and experienced engineer o r engineering geologist. This person should have a universi ty degree in civil engineering o r geology, o r an equivalent professional qualification, and a t least four years post-qualification engineering experience, some of which should be local experience on projec ts of a similar na tu re t o t h e one being contemplated. If t h e ground conditions a t t h e s i te a r e anticipated t o be complex and t h e safety and economy of t h e project a r e significantly influenced by t h e ground conditions, t h e person planning and directing t h e ground investigation should possess, in addition. specialized qualifications o r experience in geotechnical engineering, and specialized knowledge in s i te investigation pract ice in Hong Kong.
The person planning and directing t h e ground investigation should be thoroughly familiar with t h e project requirements and capable of liaising effectively with t h e project des igner o r client throughout all phases of t h e investigation (Figure 1). This person should determine t h e content and extent of t h e investigation, direct t h e investigation in t h e field and laboratory, and assess t h e resul t s in relation t o t h e projec t requirements. Pa r t of these duties may be delegated t o geotechnical specialists o r sui tably t ra ined and experienced subordinates.
15.3 SUPERVISION IN THE FIELD
Ground investigation works should generally be car r ied o u t u n d e r t h e supervision of a suitably qualified and experienced engineer o r geologist. assis ted b y trained and experienced technical personnel. The supervis ing engineer o r geologist should have a universi ty degree in civil engineering o r geology, o r an equivalent professional qualification, and at least four years post-qualification engineering experience, some of which should have been in ground investigations. Technical personnel should possess a certificate in civil engineering from a polytechnic and at least one year of specialized training and experience in ground investigations, including training in t h e p roper logging and description of ground conditions.
The supervis ing engineer o r geologist should be full time or p a r t time on site, depending on such fac tors as t h e :
(a) size of t h e investigation.
( b ) na tu re of t h e project.
( c ) complexity of t h e anticipated ground conditions,
( d ) complexity of t h e sampling and field tes t ing schedule.
( e ) reliability of t h e contractor 's personnel under taking t h e ground invest igat ion works.
Increasing size a n d complexity of t h e pro jec t , as well a s increasing complexity of g round conditions and investigation techniques , o r decreasing reliability of t h e contractor 's personnel, should all lead t o heavier time commitments f o r t h e supervis ing engineer o r geologist. The supervisor will normally b e requi red full-time on s i t e whenever i t i s planned t o c a r r y o u t works which a r e critically dependent on a high s t andard of workmanship for the i r success o r safety. Only when minor ground investigation works a r e under taken fo r confirmatory purposes, a n d where the works involve simple investigation techniques , should full delegation of t h e supervision of t h e works to technical personnel be contemplated.
Technical personnel will normally b e requi red full-time on site. Several technical staff may b e r equ i red on s i t e if a number of drilling r igs a r e operat ing simultaneously, if severa l field t e s t s or ins t rument installations a r e being under taken simultaneously, o r if t h e works a r e widely sca t te red .
The supervis ing engineer o r geologist should be aware of t h e t y p e 'of information requi red from t h e investigation, and should always maintain close liaison with t h e engineer o r engineering geologist direct ing t h e ground investigation ( see Section 15.2). o r with t h e pro jec t des igner , t o e n s u r e t h a t t h e project requirements a r e satisfied. In most cases , i t i s worthwhile fo r t h e pro jec t des igner t o spend some time on s i te dur ing t h e ground investigation works in o r d e r to apprec ia te fully t h e actual ground conditions. Wherever possible, t h e supervis ing engineer o r geologist should be independent of t h e cont rac tor under taking t h e ground investigation works. If t h i s i s not t h e case, t h e engineer o r engineering geologist planning and direct ing t h e ground investigation should t ake s t e p s t o e n s u r e t h a t t h e r e is an adequate level of s i te supervision a n d t h a t reliable information i s obtained from t h e works.
15.4 LOGGING AND DESCRIPTION OF G R O U N D CONDITIONS
The supervis ing technical personnel ( see Section 15.3) should be responsible for recording t h e information obtained from boreholes o r o t h e r invest igat ions a s i t ar ises . This information should include a measured record of the subsur face profile with rock and soil descript ions, a n d a record of t h e drilling and sampling techniques used. In complex ground conditions. o r when t h e information i s particularly important, t h e supervis ing engineer o r geologist should r ecord th is information a s i t a r i ses . In some cases, i t may b e necessary t o obtain specialist advice on t h e logging and description of g round conditions (see Section 15.6).
Detailed descript ions of t h e ground conditions encountered and of all rock and soil samples obtained should b e made in accordance with Geoguide 3 (GCO, 1988), o r a sui table al ternat ive system. All personnel under taking logging and descript ion of ground conditions should be thoroughly familiar with t h e system t o be used and sui tably experienced in i t s application.
15.5 LABORATORY TESTING
The testing of soil and rock samples should be carried out in a laboratory approved by the directing engineer o r engineering geologist referred to in Section 15.2. The laboratory testing should be done under the control. of a suitably qualified and experienced supervisor, and all laboratory technicians should be skilled and experienced in the type of tes t they a re conducting. The laboratory testing schedule should be finalised only af ter selected samples have been examined by the person directing the investigation o r by the supervising engineer o r geologist. The latter should supervise the more complex tests.
15.6 SPECIALIST ADVICE
Depending on the complexity of the ground conditions and the nature of the project, specialist advice on particular aspects of the ground investigation may be needed. For example, the advice of an experienced engineering geologist may be required on such aspects as :
(a) full detailed geological descriptions of soils and rocks,
(b) differentiating fill from insitu materials, o r boulders/ corestones from bedrock.
(c) identifying and classifying colluvial deposits.
(d) rock mass classifications,
(e) geological and groundwater models of ground conditions a t the site.
Similarly, the advice of an experienced instrumentation specialist will be invaluable for the planning, calibration. installation. commissioning and data interpretation of the more complex geotechnical instruments.
15.7 INTERPRETATION
The interpretation of the ground investigation should be directed by the engineer o r engineering geologist referred to in Section 15.2. incorporating any specialist advice obtained (see Section 15.6).
15.8 OPERATIVES
The driller in charge of an individual drilling rig should be skilled and experienced in the practice of ground investigation by means of boreholes and simple sampling and testing techniques. Operators of other equipment used in ground investigations should have appropriate skills and experience. Any timbering. shoring o r other support required in excavations or caissons should be installed only by suitably skilled workmen. All operatives should be familiar with and observant of safety precautions (see Appendix E).
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7 5
16, REVIEW DURING CONSTRUCTION
16.1 GENERAL
There I> an hherent difficulty in forecasting ground conditions from ground in veshgations carried out before the works are started since, however ~htensive the inveshgation and whatever methods are used, only a sma// proportion of the ground is examined.
fie primary purpose of the review during construction is to determine to what extent, if any, ~h the light of the conditlbns newly revealed, conclusions drawn from the ground investigation are required to be revised.
In some cases, additional information is found which may necessitate amendment of the design or the construction procedures. In certain cases, it may therefore be appropriate to initiate a site procedure in the early stages of the contract, so that correct and agreed records are kept during the duratlbn of the contract by both the engineer and the contractor. Tbe purposes of these records are :
fa) to assist in checking the adequacy of the design,
fbl to assist in checking the safety of the works during constructlbn and to assess the adequacy of temporary works,
(cl to check the findings of the ground investigathn and to provide a feed-back so that these findings may be reassessed,
fdl to check h i t i a l assumptlbns about ground conditlbns, including groundwater, related to construction methods,
fel to provide agreed information about ground condihbns in the event of dispute,
f f l to assist in checking the suitabifity of proposed instrument installations,
fg) to assist in decid'ng the best use to be made of excavated materials,
/hl to assist in the reassessment of the initial choice of construction plant and equ~;Oment.
16.3 INFORMA TION REWIRED
16.3.1 Soil and Rock
Accurate descriptions of all material encountered below ground level should be made in accordance with Geoguide 3 (GCO, 19881, or a suitable alternative system. The subsurface profile revealed on site should be recorded
and compared with that anticipated from the ground investigaton. The descriptions should be made by an engineer or geologist /see Section 15.41. It may be advantageous to arrange for the site to be inspected by the organization that carried out the site investigations, partrkuMy if ground conditions appear to differ s~gnif iant ly from those described in the ground in vestigation.
16.3.2 Water
It is most important to record accurately a/l informatrbn about the groundwater obtained during construction, for comparison with informton recorded during the investigation. The informaton should cover the flow and static conditons in a// excavations, seepage from slopes, seasonal variatons, tidal variations in excavatons or tunnels near the sea or estuaries, suspect or known artesian conditrons, the effect of weather conditions on groundwater, and any unforeseen seepage under or from water-retah~hg structures. The effect of groundwater lowering should also be recorded in observatfon holes to determine the extent of the cone of depress~on.
Groundwater rises due to the damming effects of new construction or temporary works should likewise be recorded.
16.4 INSTRUMENTATION
On many types of structures, such as earth dams, embankments on soft ground, some large buiMngs with underground construction, exca vations and tunnels, it is prudent to consider regukr observatons by means of instrumentation ~h order to check that construction works can proceed s&y (Bureau of Reclamation, 1987; DiBiagio & Myrvoll, 1982). Such observations may include measurement of pore pressure, seepage, earth pressure, settlement and lateral movements (see also Sectons 8.Z 28.3 and 31.21. The instrumentation may be usefully conthued after construction h order to observe the performace of the project. This is part'cularly necessary i n the case of earth dams for maintaining a safe structure under varying conditons, and ~h other cases for gaining valuable data for future design.
For projects involving slopes, i t is common practice in Hong Kong to monitor groundwater levels and pore pressures, and their response to rainfall. Methods of measuring pore water pressures are given in Chapter 20. In many situations, i t will also be essential to monitor movements and the condition of nearby buildings and structures.
PART IV
GROUND 1 NVESTI GATION METHODS
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17, INTRODUCTION TO GROUND INVESTIGATION METHODS
There is a considerable variety of methods of ground investigation, and normally a combination of methods is employed to cover the technical requirements and the range of ground conditions tha t a re encountered. The factors involved in the selection of methods a re discussed in Chapters 7 to 16. Particular attention should be paid to the safety of existing features. s t ructures and services in the course of ground investigation. Advice on planning and control is given in Section 7.2 (see also Appendix A). The selection of methods may be influenced by the character of the site (see Section 11.2), and particular ground conditions often dictate which specific investigation technique should be used (see Chapter 12). Attention should also be given to the safety of personnel (see Appendix El.
Insitu tests that are carried out in boreholes as part of a borehoe investigation are described ih Chapter 21. Other insitu tests, for which a borehofe either I> unnecessary or I> o d y an inwWdentd part of the test procedure, are descriaed ih Chapters 24 to 33. Laboratory tests on soil and rock are discussed in Chapters 31 to 38. The collecOon and recordihg of data I> discussed in Chapters 39 and 40.
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18, EXCAVATIONS AND BOREHOLES
18.1 SHALLOW TRIAL PITS AND SLOPE SURFACE STRIPPING
Shallow trial pits are usually dug by hand using a pick and shovel, and commonly extend to a depth of about 3 m. It is essential that the pit sides are guarded against sudden collapse in order to protect personnel working in the pit. For this purpose, timber shoring is usually provided when excavation is deeper than 1.2 m. The spacing of the shoring should be sufficiently wide to allow inspection of the pit'sides. Shallow trial pits may also be dug by machine; a hydraulic back-hoe excavator is the most commonly used.
Shallow trial pits permit the insitu condition of the ground to be examined in detail both laterally and vertically, and allow mass properties to be assessed. They also provide access for taking good quality (block) samples and for carrying out insitu tests. rial pits are particularly useful for investigating and sampling soils derived from insitu rock weathering and colluvium, both of which often exhibit a high degree of variability. Pits may also be used to investigate the dimensions and construction details of old retaining walls, and to ascertain the exact position of buried utilities and services.
The field record of a shallow trial pit should include a plan giving the location and orientation of the pit, and a dimensioned section showing the sides and floor. Ground conditions should be fully described in accordance with Geoguide 3 (GCO, 1988) or a suitable alternative system, and samples taken should be fully documented. Two examples of trial pit logs are given in Figures 7 and 8. Logs should always be supplemented with colour photographs of each face and of the base of the pit. The positions and results of any field testing should also be recorded, such as insitu density tests or Schmidt hammer, hand penetrometer and hand shear vane index tests.
Material excavated from trial pits should be stockpiled in such a manner that it does not fall back into the pit or cause instability of the pit excavation, e.g. by surcharging the adjacent ground. Wooden hoardings anchored by steel bars driven into the ground are often used on steep slopes to retain spoil from falling back into the pit. The spoil should be placed and covered so as not to be washed downhill during rainstorms or allowed to enter surface drainage systems.
It is advisable to backfill pits as soon as possible after logging, sampling and testing have been completed, since open pits can be a hazard. Recommendations on backfilling are given in Section 18.9. Pits that must be left open temporarily should be covered and sealed so that rain water cannot enter; they should also be securely fenced off if readily accessible by the public.
Trial pits can be extended readily into trenches or slope surface stripping. The latter is used extensively in Hong Kong to investigate both natural and man-made.slopes, and generally consists of a 0.5 m wide strip, extending from the crest to the toe of the slope, in which the ground has been laid bare of vegetation, chunam plaster or other coverings. Bamboo scaffolding or access ladders are provided for inspection, logging and reinstatement.
An example of a log sheet for slope surface stripping is given in Figure 9. Colour photographs of salient geological features revealed by the stripping should always be obtained. Fill is sometimes used to smooth the surface of a cu t slope before application of the chunam plaster; if this is encountered in slope stripping the depth of excavation should be increased if possible to reveal the t rue nature of ground beneath.
18.2 DEEP TRIAL PITS AND CAISSONS
Deep trial pits, shafts and caissons a re normally constructed by hand excavation using various methods for supporting the sides. Temporary o r permanent liners a re necessary for the protection of personnel working in these excavations, but it is also necessary to consider the need to expose the ground for inspection and logging; considerable judgement and experience is often required to establish suitable procedures for such excavations.
Hand-dug caissons 1 m in diameter and larger a re commonly used in Hong Kong for foundation construction to depths of 30 m o r more. Typically, cast-insitu concrete liners a r e used in soil, while the caisson is left unlined in rock. These caissons may be particularly useful for the investigation of rock a t or near the founding level of large foundations (Irfan & Powell. 1985). An example of a caisson log is given in Figure 10. I t is recommended tha t the guidance notes on the technical and safety aspects of hand-dug caissons issued by the Hong Kong Institution of Engineers (HKIE, 1981) should be followed.
Workhg in deep shafts w17f be dangerous unless the appropr~ate safety precau&ons are str12tly foffowed Attention should be given to the poss13le occurrence of ~nj'urious or combustl3fe gases or of oxygen deflcienc~es. Correct methods of ~nspectlon shoufd be foffowed and appropriate precautlbns shoufd be taken (see Section 7.2 and Appendix E) . Oxygen-consumhg engines that emit fox12 exhaust fumes, such as petrol-driven pump motors, shoufd not be empfoyed in shafts.
18.3 HEADINGS OR ADITS
Headings a re driven from the bottom of shafts o r laterally into sloping ground, and can be used for the insitu examination of the ground o r existing foundation structures. and for carrying out special sampling o r insitu testing. Further considerations are given in BSI (1981a).
18.4 HAND AUGER BORING
The hand auger bor~hg method uses fight hand-operated equl-t. The auger and driff rods are usudfy fifted out of the borehofe w~?hout the aid of a tr~bod, and no borehofe casing is used Borehofes up to 200 m d~.ameter may be made ~n suitable ground conditions to a depth of about 5 m. The method can be used ~n self-supporak-g ground without hard obstructions or gravel -sized to boulder-sized partl'cfes. Hand auger borehofes can be used for groundwater observatlons and to obtain disturbed sampfes and s d open-tube sampfes.
18.5 LIGHT CABLE PERCUSSION BORING
Light cable percussion boring is an adaptation of common well-boring methods, employing a clay cutter for dry cohesive soils, a shell (or bailer) for granular soils, and a chisel for breaking up rock and other hard layers. The drill tools are worked on a wire rope using the clutch of the winch for percussive action. The shell can only be used when there is sufficient water in the borehole to cover the lower part of the shell.
Light cable percussion boring cannot be used for boring into or proving rock, and it is severely restricted in bouldery ground where the frequent use of a heavy chisel is required. The widespread occurrence in Hong Kong of bouldery colluvium and corestone-bearing soils derived from insitu rock weathering has therefore curtailed the use of light cable percussion boring, as has the widespread need to core into and prove rock. However, the method can be used to investigate the finer-grained marine sediments and alluvium found in the flat coastal areas.
18.6 MECHANICAL AUGERS
Mechanical augers, comprising a continuous-flight auger and a hollow stem, are suitable for augering soft cohesive soils and may be suitable for firm cohesive soils. They are of limited use in soils with boulders or corestones and are therefore seldom used in Hong Kong. Further considerations are given in BSI (1981a).
18.7 ROTARY OPEN HOLE DRILLING AND ROTARY CORE DRILLING
18.7.1 General
Rotary drilling, in which the drill bit or casing shoe is rotated on the bottom of the borehole, is the most common method of subsurface exploration used in Hong Kong (Chan & Lau, 1986) . The drilling fluid, which is pumped down to the bit through hollow drill rods, lubricates the bit and flushes the drill debris up the borehole. The drilling fluid is commonly water, but drilling mud or air foam are often used with advantage (see Section 18.7.2).
There are two basic types of rotary drilling : open hole (or full hole) drilling, in which the drill bit cuts all the material within the diameter of the borehole; and core drilling, in which an annular bit fixed to the outer rotating tube of a core-barrel cuts a core that is returned within the inner stationary tube of the core-barrel and brought to the surface for examination and testing. Drill casing is normally used to support unstable ground or to seal off open fissures which cause a loss of drilling fluid. Alternatively, drilling mud or cement grout can be used to seal open fissures.
In ground investigations, rotary core drilling has the important advantage over rotary open hole drilling of providing a core sample while the hole is being advanced, and it is recommended for most situations. In rotary open hole drilling, drill cuttings brought to the surface in the flushing medium can only provide an indication of the ground conditions being encountered. However, rotary open hole drilling is useful for rapid advancement of a borehole required for field testing or instrument instal- lation, and samples may be obtained between drill runs even when the open hole technique is used.
Water used a s a flushing medium in ro ta ry drilling may have a deleterious ef fec t on both t h e stability of t h e surrounding ground and on t h e samples obtained, and i t s u s e must be carefully considered (see Section 18.7.2). A c r u d e adaptation of t h e ro ta ry open hole method, often termed ro tary wash boring, may be particularly detrimental in th is regard . This method involves advancing t h e hole by casing alone, with t h e inside of t h e casing cleaned o u t by su rg ing and flushing. Water p ressures sufficient t o f lush t h e casing a r e often high and may lead t o increased pore p ressures (or reduced pore suct ions) in t h e su r round ing ground. When drilling on a slope o r behind an old masonry retaining wall, fo r example, th i s may be detrimental t o stability and may actually t r i g g e r rapid collapse. Also, in soils containing gravel-sized fragments, i t is impossible t o f lush out. all t h e coarse fragments, i r respect ive of t h e water p r e s s u r e employed, and they will accumulate in t h e base of t h e hole. These fragments will affect t h e representa t iveness of f u r t h e r sampling and tes t ing done in t h e borehole. In sof t o r loose ground, t h e flushing water may not only c a r r y t h e cut t ings up th rough t h e casing, b u t also u p around t h e outside of t h e casing, t h u s crea t ing a large zone of d is turbed material which can extend fo r some distance below t h e bottom of t h e hole. A s a result , samples obtained from ro ta ry wash boring may be d is turbed, a t least over a portion of the i r length. In marine investigations, t h e s t andard ro ta ry open hole method should therefore be used in preference t o ro tary wash boring (see Section 14.7).
Rotary drilling r igs a r e available in a wide r a n g e of weights and power r a t ings in Hong Kong. Rigs a r e normally sk id mounted, with a typical configuration as shown in Figure 11. They a r e commonly available with a power ra t ing in t h e r a n g e of 10 t o 50 horsepower and capable of s table drill s t r i n g rotation u p t o 1 500 o r 2 000 rpm. Drilling r i g s should be mounted on a stable platform such t h a t a force of 12 t o 15 kN can b e applied to t h e drill bi t without movement of t h e rig. In choosing a r ig , consideration must b e given t o t h e expected depth and diameter of t h e hole t o be drilled, t h e possible casing requirements, and s i t e access. Rigs should generally have a minimum ram s t roke length of 600 mm, and b e able t o opera te with a minimum of vibration. The sizes of commonly-used core-barrels , casings and drill rods a r e shown in Table 5.
Smaller scale ro ta ry drilling r i g s a r e also available and can sometimes b e used t o g r e a t advantage in special situations. Hand-portable ro ta ry core drills may often be useful for coring through existing concre te o r masonry retaining walls; horizontal boreholes often enable t h e wall th ickness and backfill materials t o b e determined.
DrMng is in part an art, and its success is dependent upon good practice and the ski1 of the operator, partkularly when coring weathered, weak. partMly cemented and fractured rocks, where considerable expertise is necessary to obtain fu// recovery of core of saakfactory qua/ity. This is greatly inhenced by the choice of core-barrel and cutt~hg bit type (see Section 19.81 and by the method of extruding, handfing andpreservaoon of the core fsee Section 19.10.51.
18.7.2 Flushing Medium
Careful selection of a f lushing medium which is compatible with t h e equipment employed and sui table fo r t h e ground t o be drilled is v e r y important. Water is t h e simplest f lushing medium. Other f luids used a s f lushing media are drilling muds (which consist of water with clay o r
bentonite), water with an additive such a s sodium chloride, a i r foams and polymer mixtures. The main advantage of these o the r flushing media i s t h a t drill cu t t ings may be removed a t a lower flushing velocity and with less dis turbance t o t h e ground. The use of drilling mud can also minimise t h e need for casing of t h e hole, as i t helps t o stabilise t h e sides and bottom of t h e hole in caving soils. Another advantage of drilling mud is t h a t i t can reduce soil d is turbance a n d hence improve sample quality. However, drilling mud is not recommended if permeability t e s t s are t o be car r ied o u t in t h e borehole, o r if piezometers a r e t o be installed. Fur the r guidance on t h e u s e of drilling mud i s given by Clayton et a1 (1982).
The use of a i r foam as a flushing medium has enabled increased core recovery and quality t o be achieved in colluvium and soils derived from insi tu rock weathering (Phillipson & Chipp, 1981; 1982). This technique involves t h e injection of foaming concentra te and water in to t h e a i r s tream produced b y a low volume, high p ressure air compressor, a s shown diagrammatically in Figure 12. A polymer stabi l iser is added when drilling below t h e water table. The foam is forced down t h e drill rods in t h e conventional manner. and a slow-moving column of foam with t h e consistency of aerosol shaving cream car r i e s t h e suspended cut t ings t o t h e surface. Compared with water, t h e air foam has a g rea te r ability t o maintain t h e cut t ings in suspension, and t h e low uphole velocity and low volume of water utilized s e r v e t o reduce d is turbance of t h e core and surrounding ground. The air foam also res i s t s percolation in to open f i ssures , and it stabilises t h e borehole walls. The polymer stabi l iser , however, has t h e disadvantage of coating t h e walls of t h e hole such t h a t insi tu permeability tes t ing may not b e representat ive.
When investigating potentially unstable slopes. o r when drilling in to failed slopes t o obtain samples from t h e slip zone, t h e u s e of water as t h e f lushing medium may not be advisable (see Section 18.7.1). A i r foam flushing, o r in some instances, air flushing should b e considered t o reduce t h e r i sk of slope movement in such cases.
18.7.3 Inclined Drilling
Inclined boreholes can often be used to g r e a t advantage in ground investigations (McFeat-Smith, 1987: McFeat-Smith et al. 1986). While they a r e generally more costly than similar vert ical holes, t h e y often allow additional geological da ta t o b e obtained.
Inclined holes may be found t o deviate in both dip and direction from t h e intended orientation (Craig & Gray. 1985). This is particularly common in t h e vert ical plane due t o t h e weight of t h e drill rods . Some of t h e fac tors which contr ibute t o deviation a r e :
(a) worn and undersized drill rods, rods much smaller t h a n t h e borehole, and overly flexible rods ,
( b ) drilling r i g rotation and vibration, which t ends t o produce spiraling in t h e hole, and
(c) difficult ground conditions, such as bouldery soils o r soils containing corestones.
In situations where deviation is detrimental, i t can b e minimised by t h e use of securely-anchored drilling r i g s a n d platforms, a v e r y stiff drill s t r ing
and core-barre ls a t least 3 m long coupled t o drill rods of t h e same diameter as t h e core-barre l o r to r o d s f i t ted with centralizers. Directional control may also be achieved by careful adjustments t o rotational speeds, t h r u s t pressures . and t h e location of central izers placed on t h e drill rods. In some difficult ground conditions, such as colluvium containing v e r y ha rd boulders within a loose soil matrix, i t may b e v e r y difficult t o control t h e deviation of inclined holes.
Several ins t ruments a r e available fo r measuring borehole orientation o r deviation, such as t h e Eastman-Whipstock single-shot o r multi-shot photo- graphic s u r v e y tools, t h e Pajari mechanical single-shot surveying ins t rument and t h e ABEM Fotobor multi-shot photographic probe. The function of t h e Eastman and Pajari tools i s t o record t h e orientation of a gimballed magnetic sphere , by photographic and mechanical means respectively. This precludes t h e use of t h e s e ins t ruments within steel casings o r at tached to steel rods , o r in areas where o the r magnetic d is turbances may b e anticipated. The ABEM Fotobor r ecords cumulative deflection measurements photographically within t h e borehole and i t can b e used within steel casings. Multi-shot tools such a s t h e ABEM Fotobor, o r t h e multi-shot version of t h e Eastman-Whipstock tool. a r e useful f o r under taking complete borehole su rveys , b u t may b e cumbersome fo r taking repeated deviation checks dur ing drilling, in which case single-shot tools may be preferable.
18.8 WASH BORING AND OTHER METHODS
18.8.1 Wash Boring
Wash boring utilizes t h e percussive action of a chisel bit to break u p material t h a t is f lushed to t h e su r face by water pumped down t h e hollow drill rods. In ground which is liable t o collapse, casing may b e dr iven down t o s u p p o r t t h e sides of t h e borehole, o r drilling mud may be used. The fragments of soil b r o u g h t t o t h e su r face b y t h e wash water a r e not representa t ive of t h e cha rac te r and consistency of t h e materials being penetrated, and t h e flushing water may d i s tu rb t h e surrounding ground in t h e same manner a s t h e ro ta ry wash boring method discussed in Section 18.7. For these reasons, wash boring is seldom used in Hong Kong.
18.8.2 Other Methods of Boring
There are many other methods of borhg, which have been developed generafly to obtain maximum penetration speed, e.g. rotary percussive drilfing for blast holes and grouthg. When such boreholes are sunk for purposes other than ground iff vestigation, hinited informaobn about ground conditons may be obtained, provided that the boreholes are drfled under controlled conditons, with measurement of rate ofpenetration, observaoon of drilling character13tics. and sampHng of the drfling flushings fXorner & Sherrel' 19771.
One such ro ta ry percussive method is t h e Overburden Drilling Eccentric method, o r ODEX (Plate 4A), which is based on t h e principle of under - reaming. During drilling in soil, an eccentr ic reamer bit swings o u t and drills a hole l a r g e r than t h e ou te r diameter of t h e casing, which is inser ted at t h e same time as t h e hole i s being advanced. The percussive action may be provided by e i ther a top hammer o r a down-the-hole hammer. When t h e desired dep th has been reached, t h e drill rods a r e ro ta ted in a r e v e r s e direction t o allow t h e reamer to be folded in and t h e bit t o b e re t rac ted
t h rough t h e casing, which remains in t h e hole. Drilling may t h e n b e f u r t h e r extended into rock by replacing t h e ODEX bit with a normal rock drill bit. This method is not commonly used in ground investigations a s no in tac t samples a r e obtained, b u t it has been used in Hong Kong t o install long horizontal drains in colluvium (Craig 81 Gray. 1985) and for drilling th rough bouldery fill t o prove t h e bedrock profile. I t may also be a useful technique fo r t h e location of cavities in k a r s t te r ra in (Horner & Sherrel l , 1977).
18.9 BA CXFLLING EXCA VA TIONS AND BOREHOLES
Poorly-compacted backfill wdl cause settlement at the ground surface and can act as a path for groundwater. The latter effect can cause very ser~bus incon venince if the backr'ied exca vatrons or 6oreholes are on the s2e of future deep exca vathns, tunnels or water-retaining structures. It could a/so lead to the future po//ution of an aquifer. For boreholes in dry ground, it possible to use compacted so17 as a backfill although the procedure is often unsuccessfu~ in preventing the flow of water. The best procedure is to refill the borehole with a cement-based grout introduced at the lowest point by means of a tremie p$e. Cement alone wi/l not necessarily seal a borehole, on account of shrinkage, and it is often preferable to use a cement-bentonite grout, e.g. mix proportios about four to one, with no more water added than is necessary to permit the grout to flow or to be pumped. The add~~tron of an expandhg agent may be necessary. It is possible to compact the backfi7l of excavations by means of the excavator bucket or other mechanical means. In some cases, weak concrete may be used, e.g. to fill a small hole on a steeply sloping face.
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89
19, SAMPLING THE GROUND
19.1 GENERAL
The main purposes of sampling a r e t o establ ish t h e subsur face geological profile in detail, a n d t o supply both d is turbed and undis turbed materials fo r laboratory test ing. The selection of a sampling technique depends on t h e quality of t h e sample t h a t i s requi red and t h e cha rac te r of t h e ground. part icular ly with r e g a r d t o t h e extent t o which d is turbance occurs before, du r ing o r a f t e r sampling. The principal causes of soil d is turbance a r e listed in Table 6 (Clayton e t al, 1982) a n d a r e f u r t h e r discussed by Clayton (1984).
I t should be borne in mind t h a t t h e overall behaviour of t h e ground i s often dictated by planes o r zones of weakness which may be p resen t (e.g. discontinuities). Therefore, i t i s possible to obtain a good sample of material t h a t may not be representa t ive of t h e mass. Because of this . and t h e f r e q u e n t need t o modify t h e sampling technique t o su i t t h e ground conditions, ve ry close supervision of sampling i s warranted (see Chapter 15). In choosing a sampling method, i t should be made clear whether mass propert ies o r in tac t material propert ies a r e t o be determined (see Section 12.11). The distinction between mass and material propert ies i s discussed f u r t h e r in Geoguide 3 ( G C O . 1988).
There are four main techniques for obtdining samples (Hvorslev, 19481.'
fa) taking disturbed samples from the dr~i'l tools or from excavating equipment in the course of boring or excavation (see Sectlbn 19.31,
fb1 drive samphg, in which a tube or spLit tube sampler having a sharp cutting edge a t its lower end IS forced into the ground either by a static thrust or by dynamic impact (see Sections 19.4 to 19.7),
fc1 rotary samp/ing, lh which a tube with a cutter a t its lower end ~k rotated ihto the ground, thereby produc~~g a core s@e (see Sectlbn 19.81,
fd) takjhg block samp/es spec~ally cut by hand from a tr~hl pit. shaft or heading (see Section 19.91.
Sampfes obta~hed by techniques (b1, fc1 and fdl wifl often be suffic~entJy intact to enable the ground structure wl'thin the s a m e to be examined. The quamy of such samp/es can vary considerably, depending on the technique and the ground cond~'t~ons, and most wi7f exh~Bit some degree of d~kturbance. A method for class~yfying the guafity of the sampfe given in Sechun 19.2. Sections 1.9.3 to 19.9 describe the various sampfing techniques and give an indication of the sampfe quak2ie.s that can be expected Intact samples obta~hed by te~hnlque~ (b), fc1 and /dl are u s u d y taken in a vertical direction, but specially orientated samples may be required to investigate particular features.
The mass of sample requi red fo r various purposes i s determined by t h e cha rac te r of the ground and t h e t e s t s t h a t a r e t o b e under taken. Guidance on t h e mass of soil sample requi red fo r different laboratory tests i s given in Table 7.
A summary of the typical sampling procedures for materials commonly encountered in Hong Kong i s given in Table 8, which should be read in conjunction with Sections 19.3 to 19.9.
19.2 SAMPLE UUALITY
The sampfing procedure shouh' be selected on the bas13 of the quality of the sample that is requ~i-ed, and is assessed largely by the suitabfity of the sample for appropriate laboratory tests. A classificatian for soil samples developed in CermanyfIdeI et a4 19691 provides a useful basis for c/assfying samples h terms of quality /Table 91.
In some cases, whatever sampling methods are used, it wi// only be possible to obtain samples with some degree of disturbance, Le. class 2 at best. The results of any strength or compressibility tests carried out on such samples should be treated with caution. Samples of classes 3, 4 and 5 are conmonly regarded as 'disturbed samples:
A further consideration in the selection of procedures for taking chss 1 sampies 13 the size of the sample. Thk is determined largely by the geological structure of the ground, which, for soi4 is often referred to as 'the fabric' @owe, 19721. Where the ground contains d13continuities of random orientation, the s a m e dzee ter , or width, sbould be as large as possible in relation to the spau'ng of d~kcontinuitibs. Alternatively, where the ground contains strongly orientated discontinuities, e.g. in johted rock, I? may be necessary to take samples which have been specidly orientated. For h e so& that are homogeneous and ikotropli?, samples as sm& as 35 mm in d i e t e r may be used. However, for general use, samples 100 nun in d ~ k t e r are preferred since the results of laboratory tests may then be more representative of the mass propertlis of the ground. In special cases, samples 150 mm and 250 mm ~h diameter are used (Rowe, 19721.
BSI N975b; 197501 give precise details of the mass of so17 sample required for each type of test. Where the approximate number of tests is known, it is a simple matter to estimate the total amount of soil that has to be obtained. If the programme of laboratory tests is uncertan, TabAe 7 gives some guidance on the amount of soil that should be obtahed for each series of tests. Where materials for mineral aggregates, sands and flters are behg considered, detads of the size of sample requked are given in BSl f1975al.
19.3 DISTURBED SAMPLES FROM BORINC TOOLS OR EXCA VATM EQUIPMENT
The quality of the sample depends on the technique used for sinking the borehole or excavation and on whether the ground is dry or wet. When disturbed samples are taken from below water in a borehole or excavation, there is a danger that the samples obtahed may not be truly representative of the ground. This I> particukify the case with granular soils conta'n~hg fines, which tend to be washed out of the tool. This can be partly overcome by plachg the whole contents of the too/ h t o a tank and allow~hg the fines to settle before decanting the water.
The following classes of samp/e can generally be tupected from the various methods of boring and sampling :
fa) Class 3. Disturbed samples from dry excavabons and from dry boreboles sunk either by a clay cutter ushg cable percussion equ~pment or by an auger.
b Class 4. Disturbed samples obtaned in cohesive soLJ from excavabbns, or from boreholes sunk either by a clay cutter using cable percusshn equ~pment, or by an auger, in condiClbns where water is present.
fc) Class 5. Disturbed samples in granufar soil from wet excavabons or from any borehole sunk by a shell ushg cable percuss~bn equ~pment or from any borehole sunk by a method in which the dr5'l debris is flushed out of the borehole, e.g. rotary open hole dr~yling, wash boring.
Care should be taken to ensure that the sample is representative of the zone or layer from which it I> removed, and has not been contaminated by other mater~as.
19.4 OPEN- TUBE SMPLERS
19.4.1 Princ~pfes of Design
11) General. Open-tube samplers consht essentialy of a tube that is open a t one end and fitted at the other end with means for attachment to the drill rods. A non-return valve permis the escape of ai or water as the sample enters the tube, and assists iff retaking the samp/e when the tool I> withdrawn from the ground Figure 13 shows the basic detays of a sampfer suitable for general use having a single s a m e tube and simple cutbhg shoe. The use of sockets and core-catcher 12 discussed h Secbon 19.4.4. An alternative sampler incorporates a detachable inner finer.
The fundamental requirement of a sampling toof I> that it should muse a s little remoulding and d~kturbance as possibe on behg forced into the ground The degree of d~kturbance 13 controlled by three features of the design : the cutting shoe, the inside wall friction and the non-return valve.
12) The cutbh.q shoe. The cutting shoe should n o r d y be of a des~gn similar to that shown in F~gure 13 and 12 should embody the fohwing features
fa) Inside clearance. The hternaf diameter of the cutmg shoe, D,, shoufd be slightly less than that of the sample tube, D,, to give inside clearance, typically about 1% of the d ~ d t e r . This allows for s/ight elasb'c expansion of the sample as it enters the tube, reduces fr~'cbonal drag from the ins^-de wa/l of the tube and he& to retain the sample. A large ins~~de clearance should be a voided s~nce it would permit the sampfe to expand. thereby increasing the disturbance.
fb) Outside clearance. The outside d~;tmeter of the cutting shoe, D,, should be slightly greater than the outshfe diameter of the tube, Dr. to give outside clearance and fac~Xtate the withdrawal of the sampler from the ground The outside clearance should not be much greater than
the inside clearance.
fc) Area rath. The area raho represents the volume of so17 displaced by the sampfer in proportion to the volume of the sample (Figure 13). It should be kept a s s d as possible consistent with the strength requirements of the sampfe tube. The area ratro is about 30% for the general purpose IOU mm dikmeter sampler, and about 10% for a thin-walled samp/er. Scnne special samplers have a large outside diameter Dr. relative to the internal diameter D,, e.g. in order to accommodate a loose inner liner. The sampling disturbance is reduced by using a cutting shoe that has a long outside taper, and ik consi'derably less than that which wouM be expected from the calculated area ratio.
3 Wal/ friction. This can be reduced by a suitable inside clearance. and by a clean, smth finikh to the i'nsi.de of the tube.
(4) Non -return valve. The non -return valve should have a large orifice to allow a? and water to escape quickly and easily when driving the sampler, and to assist in retention of the sampfe when removing the sampler from the borehole.
Typi'cal designs of open-tube samplers whi'cb are used for various purpqses are descrfbed in Sections 19.4.3 to 19.4.5.
19.4.2 Sampling Procedure
Before a sample is taken, the bottom of the borehole or surface of the excavaoon or heading should be cleared of loose or dikturbed materi-al a s far a s possible. Some or a// of any such loose or dikturbed materm that is left will n o r d y pass into the 'overdrve' space.
Below the water table, certain types of laminated soils occurring below the bottom of the borehole or excavatjon may be dikturbed if the natural water pressure in the lamha&ons exceeds the pressure imposed by the water within the borehoe or excavatbn. To prevent this effect, it is necessary to keep the level of the borehole water above the groundwater level appropriate to the location of the s d e .
The samp/r can be driven into the ground by dynarm2 means, using a drop weight or sMng hannner, or by a continuous stat12 thrust, using a hydraulic jack orpulley block and tackfe. There is litt/e published evidence to indicate whether dynamic or static driving produces less sample disturbance, and for most ground condioons it is probable that there ik no significant difference. The driving effort for each sample may be recorded as an indicazYon of the consistency of the ground.
The distance that the t d ik driven shoufd be checked and recorded as, if driven too far, the soil will be compressed in the sampler. A sampling head with an 'overdrve' space (Figure 131 will allow the sample tube to be campletely filled without rikk of damaging the sampie. After dri'vihg, the sampler ik stead17y withdrawn. The length of s@e that is recovered should be recorded, compared ~9th the diktance that the too/ was driven, and any dikcrepancy i'nvestigated For example, if the lengCh of the s u e is less than
the d~ktance driven, the sample may have exper~enced some compression or, alternative&, the sample tool h a y have permitted the samp/e to s/l;o out 8s the tool was being withdrawn. ,",
19.4.3 Thin -Walled Samplers
Thin-wded samp/ers are used for soils that are partl'cularly sens~iYve to sampling disturbance, and consist of a th~n-waled steel tube whose lower end is shaped to form a cutting edge with a s d ins~ile clearance. The area rat20 is about 10%. These samp/rs are suitable only for h e so i s up to a fim consistency, and free from large particles. They generally give class 1 samples in all fine cohesive so ik ~nc lud~hg sensitive clays, provided that the soil has not been disturbed by sinkng the borebole. SSamps between 75 mrn and 100 mrn in diameter are normally obtaneo'; sampfes up to 250 nun in d~klmter are often obtained for spec~klpurposes. It should be noted that d~kturbance at the base of a borebole in weak soil will occur below a certain depth because of stress relief: Piston samples penetrating we// below the base of the borehole are therefore preferable (see Sect2on 19.5). A typ~cal thin -wa/ed sampler illustrated in Figure 14.
19.4.4 General Purpose 100 mm Diameter Open-Tube Sampler
The 100 mm diameter open-tube sampler, often termed the U l O O sampler (Plate 48). i s a fairly robust sampler that can be used for many Hong Kong soils, but the driving action during sampling i s likely to introduce some disturbance. The highest sample quality that can be obtained is class 2 a t best (Whyte, 1984).
The details of the sampler is illustrated in Figure 13 and mis ts of a sample barreL about 450 mm in length, with a screw-on cutding shoe and drive head The area rat20 13 about 30%. Sample barrels can be coupled together w~2h screw sockets to form a longer sampler. Two standard b a r d , foming a sampler about 1.0 m in length, are often used for sampflng soft clays (Scrota & Jenn~ngs, 1958), although the increased length of the sample tube may lead to some disturbance. In soils of low cohesion, such as silt and silty h e sand, the s&e may fall out when the tool 13 withdrawn from the g m d Sample recovery can be ~mproved by insert2ng a core-catcher between the cutting edge and the sample barrel. When u s ~ h g a core-catcher, the sample qua/2y is unlikely to be better than c h s 3.
Smaller samplers of about 50 mm or 75 mm dJ.hk?ter can be used if use of the 100 mm samp/er I> precluded by the borehole s~ze. The smaller samplers are of s1b1172r design, except that the cut t~hg edge may not be detachable.
19.4.5 Sp/it Barrel Standard Penetratrbn Test Sampler
The split b a r d sampler is used in the standard p e k a t i o n test and is described JR Test I9 of BSI N975b). It takes samples 35 nun nunh d ~ h e t e r and has an area rat2O of about 100%. It ~k used to recover small samples, partl'cularly under condit2ons wh~ch prevent the use of the general purpose 100 mm sampler, and gives class 3 or class 4 samples (see SectJbn 21.2 and Figure 25).
19.5 TW-WALLED STATIONARY PISTON SAMPL ER
The thin-walled stafionary p~kton sampler (Plate 4C ) consists of a thin - walled sample tube conta'n~ng a close-fitthg sliding p~kton, wh12h is slightly coned a t its lower face. The sample tube ~k fitted to the drive head, wh~bh 13 connected to hollow dr17l rods. The piston is Dked to separate rods wh~bh pass through a slid~hg ~Jb in tff the drive head and up inside the hollow rods. Clamping devices, operated a t ground surface, enable the p~kton and sample tube to be locked together or the piston to be held statrbnary whlye the sample tube is driven down. F~gure 15 shows the bas12 deta7s of a statibnary piston sampler. The sample dimter is normally 75 nun or 100 mm, but samplers up to 250 mm d~heteer are used for spe& so17 condithns.
Ini&ialy, the piston is locked to the lower end of the sample tube to prevent water or slurry from entering the sampler. In soft clay, w~yh the piston in this pos~.tJbfl, the sampler can be pushed below the bottom of the borehole. When the sample depth is reached, the p~kton is held stabbnary and the sample tube is driven down by a static thrust until the drive head encounters the upper face of the piston. An automatic clanp in the drive head prevents the piston from dropping down and extruding the sample while the sampler is withdrawn.
The samp/er is normally used ih low strength fine so17.s and gives class 1 samples in silt and clay, including sensitive clay. Its ability to take samples below the disturbed zone and to hold them d ~ r ~ n g recovery gl'ves an advantage over the thin -waled sampler descr~i5ed in Sectbn 19.4.3. Although normally used J> soft clays, spec~kl p~kton samplers have been designed for use in stryf c/aus (Rowe, 1972).
19.6 CONTNUOUS SOIL SAMPLING
19.6. 1 General
Continuous soil sampling can produce samples up to 30 m in length ~h soils such as recent fine alluvial deposits. This ~k of partlbular value for ~'denttfying the so17 '/abr~b' &'owe, 1972) and gives results supark to those which can be obtained by consecutive drive sampling. The Swedish system /Xjeffman et al, 1950) takes samples 68 mm in diameter us~hg steel fo~7s to eliminate l'ns~kk fdction between the sample and the tube w d The Delft system, wbicb uses fighter equ~bment and offers two sizes of sample, 1%
descrl'bed more fully in Sectrbn 19.6.2.
19.6.2 The Delft Continuous Sampler
The D&t continuous sampler. developed by the Laborator~bm vmr Grondmechanica of Delft, Holland, is available in two s h to take cont~nuous samples 29 mm and 66 nun in diameter /Delft Soil Mechanics Laboratory, 1977). The 66 mm sampler is pushed into the ground w ~ l h a conventronal Dutch deep sounding mach~he hhav~ng a thrust of 200 kN The sampler is advanced by pushing on the steel outer tubes. and the sample is fed automathally ~h to a nylon stockinette sleeve wh~kh has been treated to make it ~inperv~ous. The sample witb~h the sleeve fed into a thin-waLJed plastic inner tube filled to the appropriate level with a bentonite-barytes supporttng flu~Y of s~in~i'ar dens12y to the surround~ng ground The upper end of the nylon sleeve I> fked to the top cap of the sample, wh~bh is connected through a tens~on cable to a
ftuedpoint at the ground sudace. Extens~on tubes I m in length are added as the sampler is pushed into the ground. Tbe sampler normah'y has a maximum penetration of 18 m, but i'n suitable ground with a modified magazine and increased thrust, samples up to 30 m i'n length can be obta'ned The 29 mm sampler is of s1k7ar design and requires less thrust to effect penetration. Class 2 to class 3 samples can be obtained with these samp/ers.
The samples are cut into I m lengths and placed ~ ' n purpose-made cases, samples taken with a 66 mm sampler being reta'ned in the plastic tubes. The 66 mm samples are suitable for a range of laboratory tests. The 29 mm samples are used for visual ex&natron and the determinatron of bulk density and index propertres. After specimens have been removed for testr'ng, the samples are split and are then descr~'bed and photographed in a semi-dried state when the soil fabric can be more readily identrued For 29 mm samples, only one half of the split materikl is used for testr'ng, thus preserving a continuous record of the ground
19.7 SAND SAMPLERS
The recovery of tube samples of sand from below the water table presents special problems because the sample tends to fa / / out of the samp/e tube. A compressed air sampler (Elkhop, 19481 enables the sample to be removed from the ground into an air chamber and then lifted to the surface without contact with the water in the borehole. The sampler is general/y constructed to take s-es 60 mm in d ~ h t e r . If the sampler I> driven by dynam~c means, the change in volume of the sand caused by the dri-w'ng gives a sample quality not better than class 3. However, if static thrust is used, generally &ass 2 and sometrines class I samples can be recovered An alternative design (&rota B Jennings, I9581 introduces a bubble of a> at the base of the sampler before it is withdrawn fm the ground
19.8 ROTARY CORE SAMPLES
Samples are obta'ned by the rotary core dri'/ig procedures described in Sectrbn 18. I. The q u m y of sample may vary considerably depending on the character of the ground and the type of coring equ~pment used (BS/, I974al.
Core-barrel s izes commonly used in Hong Kong a r e given in Table 5, together with t h e core sizes produced. Single-tube core-barrels a r e seldom used, as t h e core-barrel ro ta tes direct ly agains t t h e core and core recovery is usually unsat isfactory. Double-tube and t r ip le- tube ba r re l s a r e used. with applicability and limitations a s follows :
(a) Double-tube core-barrels , with a n i n n e r t u b e mounted on bear ings which does not ro ta te agains t t h e core, can normally b e used in f r e s h to moderately decomposed rocks. However. these barre ls do not protec t t h e core from t h e drilling fluid unless t h e equipment is modified. In addition, t h e core is often removed b y hanging t h e ba r re l in a near vert ical position and tapping on t h e s ides of t h e barrel . In highly f r ac tu red rocks th i s can resu l t in a jumble of rock fragments in t h e core box and may make logging and measurement of f r a c t u r e s t a t e indices difficult. The use of a core ex t ruder is recommended in such situations. An example of a
double-tube core-barrel is shown in Figure 16 (see also Plate 4D) .
( b ) Triple-tube core-barrels, containing detachable liners within the inner barrel that protect the core from drilling fluid and damage during extrusion, are suitable for use in fresh to moderately decomposed rock and some of the stronger highly decomposed materials. They are particularly useful in coring highly fractured and jointed rock as the split liners facilitate the retention of core with the joint system relatively undisturbed. An example of a non-retractable triple-tube core-barrel (with split liners) is shown in Figure 17 (see also Plate 4E).
When coring soils derived from insitu rock weathering. triple-tube core-barrels fitted with a retractable shoe a re normally used (Table 5). The cutting shoe and connected inner barrel projects ahead of the bit when drilling in soft material and retracts when the drilling pressure increases in harder materials. This greatly reduces the possibility of drilling fluid coming into contact with the core a t o r jus t above the point of cutting. These cutting shoes can be added to the same triple-tube core- barrel used for coring fresh to moderately decomposed rock. Alternatively, and fa r more commonly in Hong Kong, a Mazier core-barrel (Figure 18 and Plate 4F) is used. However, i t should be noted that the Mazier has a tungsten carbide tipped cutting shoe and is therefore not suitable for coring fresh to moderately decomposed rock. When rock o r corestones a re encountered, a core-barrel with a diamond-impregnated drill bit has to be used to advance the hole (e.g. the double-tube Craelius T2-101 barrel as shown in Figure 16). The Mazier core-barrel has an inner plastic liner which protects the sample during transportation to the laboratory. The 74 mm diameter core obtained with the Mazier is compatible with the commonly -used laboratory triaxial testing apparatus.
High quality (class 1) core samples of soils derived from insitu rock weathering and colluvium can be obtained using the large diameter triple-tube core-barrels i n conjunction with air foam as the flushing medium (see Section 18.7.2). Samples of class 1 to class 2 can also be obtained using the Mazier sampler in conjunction with air foam o r water as the flushing medium.
Another type of triple-tube barrel is the wireline core-barrel. This non- retractable barrel incorporates a line mechanism for withdrawing the inner barrel up through the drill rods without withdrawing the outer barrel o r rods from the hole. This core-barrel may be used in fresh to moderately decomposed rock, and in very deep vertical o r inclined holes to achieve more rapid drilling progress.
Further discussions of core-barrels, drilling techniques and their suitability to materials found in Hong Kong can be found in Brand & Phillipson (1984). Brenner & Phillipson (1979) and Forth & Platt-Higgins (1981 1.
19.9 BLOCK SAMPLES
Block samples are c u t by hand from material exposed in trial pi ts a n d excavations. They are normally taken in fill, soils derived from insitu rock weathering and colluvium in o r d e r to obtain samples with t h e leas t possible disturbance. The procedure is also used t o obtain specially orientated samples, e.g. t o measure t h e s h e a r s t r e n g t h on specific discontinuities. The location a n d orientation of a block sample should always b e recorded before t h e sample is separa ted from t h e ground. Block samples should b e taken and handled a s described in Section 19.10.6. More detailed recommendations fo r block sampling are given in USER (1974).
19.10 XANDLINC AND LABELLING OF S2MfLE.S
19.10. 1 General
Samples may have cost a considerable sum of money to obtain and should be treated with great care. The usefulness of the results of the laboratory tests depends on the qu&y of the samples at the tibe they are tested It is therefore hportant to e s t a b m a satikfactory procedure for handling and labef ig the samples, and also for their storage and transport so that they do not deteriorate, and can readily be identi3ed and drawn from the sample store when required.
The s&es should be protected from excessive heat and temperature variatrbn, which may lead to deter~oration in the seahng of the sample containers and subsequent damage to the samples. The temperature of the sample store will be Muenced by the c h a t e , but I? 13 recommended that the samples should be stored at the lowest temperature practikable wwithn the range Z•‹C to IS•‹C The d d y temperature variatrbn within the store should not exceed ZO•‹C.
19.10.2 Labelling
All samples should be labefled fmmed12tely after being taken from a borehole or excavation. If they are to be preserved at their natural moisture content, they wil at the same time have to be sealed in an aiitight container or coated in wax. The label should show a// necessary information about the sample, and an addiobnal copy should be kept separately from the sample; thh latter ~k n 0 r . y recorded on the da@y field report. The label should be marked with indelible J M and be sufficienlry robust to withstand the effect of its environment and of the transport of the sample. The sample itself should carry more than one label or other means of identincatrbn so that the sample can sti7l be identi i ld if one label ~k damaged.
The sample label should give t h e following information, where re levant :
(a) name of contract.
( b ) name o r reference numbers of t h e site.
(c) reference number, location and angle of hole.
(d ) reference number of sample,
(e) date of sampling.
( f ) brief description of the sample.
( g ) depth of top and bottom of the sample below ground level, and
(h) location and orientation of the sample where appropriate (e .g. a sample from a trial pit).
l9.lO.3 Disturbed Samples of So17 and Hand Spec~hens of Rock
Where samples are required for testhg, or where it is desirable to keep them in good conditon over long periods, they should be treated as described below.
Immediately after being taken from a borehole or exca vaton, the sample should be placed in a non-corrodible and durable contaher of at least 0.5 kg capacity. wh~eh the sample should /il/ witb the minimum of air space. The contaher should have an airtight cover or seal so that the natural moisture content of the sample can 62, maintained uno7 tested in the laboratory. For rock samples, an alternative procedure is to coat the sample lh a layer of paraffin wax. A microcrystalline wax is preferred because it is less Mely to shrink or crack. Large disturbed s-es that are requked for certah laboratory tests may be packed in robust containers or p h t k sacks.
Tbe sample containers should be numbered and the tear-off slip or a label as described in Secton l9.lO.Z should be placed ~h the contaner hmediately under the cover. An ia'enbkal label should also be securely Iixed to the outskie of the contaher under a waterproof seal /war or plastksI. The containers should be carefully crated to prevent damage during transit. During the intervals wMe the samples are on site or in transit to the sample store, they should be protected from excessive heat.
For hand samples of rock, the reference number shauld be recorded by panting d~iectry on the surface of the samp/e or by attaching a label Samples should then be wrapped in several thkkness of paper and packed in a wooden box. It is advisable to include in the wrapping a label of the type described in Section l9.lO.Z.
19.1 0.4 Samples Taken with a Tube Sampler
The following recommendatons are appflcable to a17 samples taken witb tube samplers, except those taken with thick-walled samplers (see Section 19.4.51. The precautons for handfling and protectlbn of s d e s are to be regarded a s a minimum requ~iement for samples taken by the usual methods. In special cases, 12 may be necessary to take more elaborate precaubons. For samples that are retained in a tube or liner, procedure fa1 should be foflowed,. for other samples, procedure fbl should be foflowed.
fa) Immediately after the sample has been taken from the borehole or excavation, the ends of the sample shouId be removed to a depth of about 25 mm and any obv~ously d~kturbed sod ih the top of the s-er should also be removed. Several layers of molten wax, preferably
microcrystalline wax, should then be app/ed to each end to give a plug about 25 mm in th~kkness. The molten wax should be as cool a s possible. It is essenhal that the sides of the tube be clean and free from adhering soil. I f the sample is very porous, a layer of waxed paper or alumhum foil should be placed over the end of the sample before app/yig the wax.
Any remaning space between the end of the tube or h e r and the wax should be tightly packed with a material that IS less compressible than the sample and not capable of extracting water from it. and a close- fitthg lid or screw-cap should then be placed on each end of the tube or liner. The lids should IT necessary, be hem in positon with adhesive tape.
(6) Sampls that are not retahed IR a tube should be wholly covered with several layers of &ten paraffin wax, preferam m~'crocryst//ine wax, hnmed~ktely after be~hg removed from the samp/ng tooL and then should be t&bt& packed with suitable mater%al h t o a metal or plastic conta'ner. The lid of the container should be held h position with adhesive tape. If the sample is very porous, it may be necessary to cover it with waxea' paper or alummi/m foil before applying the &ten wax.
A label bearing the number of the sample should be placed inside the container just under the lid. The label should be placed a t the top of the s.wr.de. In addWon, the number of the sample should be panted on the outside of the contaner, and the top or bottom of the sample should be lhdl'cated. The liners or contaners should be packed in a way that wiyl minlinize damage by vibration and shock dur~hg trans12.
For soft marine soil samples, the tube or liner should be held vertically. keeping the sample in the same direction as i t left the ground, and extreme care should be taken during all stages of handling and transportation.
19.10.5 Rotary Core Extrusion and Preservation
After recovery of the core-bard to the surface, every effort should be made in subsequent handling to ensure that, as far as poss~'ble, the quality of the core is mahtahed in its natural state unM it I> finally stored
Except h relatively strong and massive rocks, core is dmst inevitably disturbed IT it is removed from the barrel held in a vertr'cal posii3on and then placed into the core box. The barrel should be held in a hor~kontal pos~~oon, and the core extruded into a tray in such a manner that it is continuously supported Ran-water guttering or other convenient/y avdable r~qgid split tube can be used for this purpose. When 12 is required to preserve the core such that it does not dry out, a conven~ent metbod is to extrude it from the core-bard into skving formed of thh-gauge polyethylene, agan supporhhg the core with rigid split tube. Where selected lengths of core are to be preserved a t their natural mkture content for laboratory tesahg, any dr17ling mud contaminatjbn and softened material should first be removed; the sample should then be wrapped z h foi4 coated with successive layers of waxed cheese cloth and labelled as descried 121 Section 19.10.2
In the extrus~on process, the core should preferably be extruded iff the same direcbbn a s it entered the barrel. Extruders should be of the p~kton type, preferably mechanically activated, since water-pressure type extruders can lead to water contact with the core, and to damage by impulsive stressing of the core. It should be noted that in weak, weathered or fractured rocks, extrusion can lead to core d~kturbance, however carefully it is done. The use of a low-friction transparent plastjc finer in the inne/ tube of a modified conventional double-tube sw~'vef core-barrel overcomes the majority of the problems encountered in core extrusion, and fau7itates preservaoon of the core in the conditrbn in which it is recovered. The general practice is to tape the outside of the sleeved core every 200 mm, and lengthwise along the overlap in the plastic sheet, and then, with the aid of plastic guttering for extra support, the core can be boxed without too much disturbance to the fabr~k. However, the presence of abrasive and frmtured m k s may preclude the use of such h e r s .
The difficulz2es of extrus~on and preservat~on can be overcome by the use of tr~plee-tube core-barrels with low-friction h e r s (see Section 19.8). Split hher tubes are an ideal method of examiining the recovered core w~xhout further damage after the dr~yling process. On the other hand, seamless metal m e r s and plastik h e r s are partkularly useful where core is to be removed from site for logging or where confined, undisturbed samples are required for sample preservation and subsequent laboratory testhg.
It is usual to preserve a/l core obta'ned from the borebole for the period of the main works contract to wh~kh the core dr17ling relates. This is con venientfy achieved with wooden or plastic core boxes, u s u d y between I m and 1.5 m ~ ' n length and divided long12ud~hally to hold a number of rows of core. The box shoufd be of such depth and the compartments of such ~ ~ 7 t h that there is mini& movement of the cores when the box J> closed fCeological Society, 1970). The box should be fitted with a h~k-ged /id and strong fastener, and should be designed so a s not to be too heavy for two persons to lift when the box ~k full of core.
In remowng the core from the barrel and plac~hg 12 in the bau, great care should be taken to ensure that the core is not turned end for end, but lies i'n its correct natural sequence. Depths below ground surface should be indicated by an indelible marker on sma// spacers of core d~.ameter size that are inserted in the core box between cores from successive runs. Were there is fayure to recover core, or where specimens of recovered core are removed from the box for other purposes, t h ~ k should be indicated by spacing-blocks of appropriate length. Both the /id and the box should be marked to show the site location, borehole number and range of depth of the core with~h the box,
addi~on to the number of the box in refatJon to the total sequence of boxes for that borehole. Core box mark~hg should be done so as to facilitate subsequent photography which, ~Yrequired, should be carried out a s soon a s 13 practicable after recovery of the core, and before descr~;O~on, sampling and testJhg.
19.10.6 Block Samples
Sample cutting should be carried out as quickly as possible to prevent excessive moisture loss, and the sample should be protected from rain and direct sunlight. The sample should be trimmed to size in plan while still connected at i t s base (Plate 5A). The sides should be protected with aluminium foil or grease-proof paper. and then coated with a succession of
layers of microcrystalline wax, reinforced with layers of porous fabr ic (e.g. muslin), if requi red . A close-fitting box with t h e top and bottom lids removed should then b e slid down over t h e sample (Plate 5B). The top of t h e sample should b e trimmed flat, marked with location and orientation, coated as described above, and t h e top lid at tached t o t h e box. ensur ing a close fit. The sample may then b e c u t d o n g i t s base, and t u r n e d over slowly and carefully fo r trimming and coating of t h e bottom pr ior t o attachment of t h e bottom lid. A s t rong , rigid, close-fitting box is required t o minimize sample d is turbance dur ing t r a n s p o r t and t o p reven t discontinuities from opening.
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103
20, GROUNDWATER
20.1 G E N E R A L
The determination of groundwater pressures is of the utmost importance since they have a profound influence on the behaviour of the ground during and after the constructfbn of engineering works. There is always the possibfXty that various zones, particululy those separated b y relatively impermeable layers, wwil have different groundwater pressures, some of wh~cb may be artesian. The locatfon of highly permeable zones in the ground and the measurement of water pressure in each is particdarly linportant where deep excavation or tunnelling is requ~ked, since special measures may be necessary to deal with the groundwater. For accurate measurement of groundwater pressures, it is generally necessary to install piezometers. The groundwater pressure may vary with tfme owing to rainfa//, ti& or other causes, and it may be necessary to take measurements over an extended period of t h e 1j7 order that such variatfons may be investfgated When designing drainage works, it IS nerdy desirable to determine the contours of the water table or piezometric surface to ascertah the direction of the natural drainage, the seasonal variation and the influence of other hydrological factors.
The monitoring of groundwater levels and pore p ressures , and t h e i r response t o rainfall, is car r ied out routinely in Hong Kong, a s th i s information i s vital t o t h e design and construction of slopes, excavations in hillsides, and s i te formation works. The choice of piezometer t y p e depends on t h e predicted water p ressu res , access for reading, service life and response time requi red . Open-hydraulic (Casagrande) piezometers a r e often used in soils derived from insitu rock weathering and colluvium, which a r e generally relatively permeable. Other piezometer t y p e s may be used for specific projects; t h e available types a r e described in Sections 20.2.3 t o 20.2.6, and t h e i r advantages and disadvantages are summarized in Table 10.
Slope failures in Hong Kong a r e normally t r igge red by rainstorms. The response of t h e groundwater regime t o rainfall var ies widely from s i te to site. ranging from virtually no response t o a large immediate response. The measurement of t r ans ien t response is therefore v e r y important ( see Section 20.2.8). In o r d e r t o provide design data, groundwater monitoring should extend over at least one wet season; t h i s wet season should ideally contain a storm t h a t has a r e t u r n period of g rea te r than t en years. For s i te formation works which involve subs tant ia l modifications t o t h e hydrogeological characteris t ics of t h e site. t h e period of monitoring may need t o b e extended t o beyond t h e end of t h e s i t e formation works. Ground conditions in Hong Kong may produce perched o r multiple water tables which must also b e considered when installing and monitoring piezometers (Anderson et al, 1983).
I t may also b e necessary t o measure negative pore water pressures , o r soil suction (see Section 20.2.9). In many cases, existing groundwater da ta in t h e vicinity of t h e s i te will be available in t h e Geotechnical Information Unit (see Section 4.2). and may be useful in planning a n appropr ia te groundwater monitoring scheme.
An additional consideration in u rban areas is t h e contribution of leakage from water-bearing services t o t h e overall groundwater regime. This contribution can b e significant at some sites. Hydrochemical analysis of groundwater may aid t h e identification of t h e leak, e.g. t h e presence of fluoride a t t r ibutable t o leakage from f r e s h water mains. Advice on chemical
analysis of groundwater and related interpretat ion techniques such as tr i l inear plotting of cation and anion contents a r e given in ICE (1976).
Borehole permeability tests are described lh Section 21.4, packer, or Lugeon, tests are described in Secoon 21.5 and large-scde pumping tests are d e d b e d fh Chapter 25.
20.2 METHODS OF DETERMINING GROUNDWATER PRESSURES
20.2. I Response Time
Al l the methods descr12ed in Section 20.2 require some flow of water into or out of the measuring device before the recorded pressure can reach equifibrjkm with the actual groundwater pressure. For an excavation or a borehole, a large v o h e of water may flow before the water level reaches equifibr~um with the groundwater pressure. On the other hand, some types of piezometer requke only a very small change in volume of water in order that the groundwater pressure may be read Tbe rate a t which water flows through the soil depends on the permeabifity. The &he required for a measuring device to indicate the true groundwater pressure is known as the response time and depends on the quantity of water required to operate the device f 'volume factor% the 'shape factor' of the piezometer (Brand & Premchitt. 19801, the permeabiiWy of the porous element, and the permeability of the ground The selection of a suitable method for measuring the groundwater pressure will largely be determined by the response time (Penman, 1986).
20.2.2 Observations in Boreholes and Excavations
The c r u d e s t method of determining t h e groundwater level i s by observation in an open borehole o r excavation. This method may involve a long response time unless t h e ground is v e r y permeable, and observations should b e made at regular time intervals until i t i s established t h a t t h e water level has reached equilibrium. The readings will be misleading if rain o r su r face water is allowed t o e n t e r t h e open hole. Readings taken in a borehole shor t ly a f t e r completion of drilling should be t rea ted with caution, a s i t i s unlikely t h a t equilibrium will have been re-established.
The reliability of water level observations in boreholes o r excavations can be somewhat improved by t h e installation of a s tandpipe, a s shown in Figure 19. A s tandpipe (not t o be confused with t h e s tandpipe piezometer described in Section 20.2.3) consists of a n open-ended tube of ha rd plastic of approximately 19 mm internal diameter which has been perforated e i ther over i t s en t i r e length o r j u s t t h e lowest 1 t o 2 m. The perforated section, with openings over a t least 5% of i t s su r face area , should b e wrapped in a suitable f i l ter fabric. The space between t h e t u b e and t h e wall of t h e borehole o r excavation is normally backfilled with medium t o coarse sand and f ine gravel t o act a s a filter. The top 0.5 m around t h e s tandpipe should be sealed to p reven t t h e ingress of surface water. While readings taken in a s tandpipe a r e more controlled than in an open borehole, s tandpipe response time i s still slow, and if zones of different permeabilities have been penetrated, flow between zones may occur. Standpipe readings may therefore not be representa t ive of actual groundwater levels. These drawbacks can largely b e overcome by t h e installation of open-hydraulic o r o the r piezometers.
20.2.3 Standpipe Piezometers
The standpipe piezometer, perhaps be t t e r termed t h e open-hydraulic piezometer, consists of a t u b e with a porous f i l ter element on t h e end t h a t can be sealed into t h e ground a t t h e appropr ia te level (Figure 19). Two types of fil ter elements, viz t h e high a i r e n t r y filter and t h e low a i r e n t r y f i l ter , a r e generally used. Depending on t h e size and uniformity of t h e pores, t h e f i l ter can sustain a p ressu re difference between a i r and water on i t s su r face due t o t h e effect of surface tension. The maximum p r e s s u r e difference t h a t can be sustained is known as t h e a i r e n t r y value of t h e filter. The smaller t h e size of t h e pores. t h e h igher will be t h e filter 's a i r e n t r y value, b u t t h e lower will b e t h e filter's permeability. and th i s can give r i se t o a long response time. A high air e n t r y f i l te r can be used t o measure matric soil suction, a s a i r can be kept o u t of t h e measuring fluid system, which is then allowed t o come in to equilibrium with t h e su r round ing negative pore water p r e s s u r e (see Section 20.2.9). The f i l ter cannot, however, p reven t t h e e n t r y of a i r by diffusion, hence t h e need t o f lush air bubbles o u t of t h e measuring system from time t o time. A low air e n t r y f i l ter has la rge pores and therefore does not impede t h e passage of air. Low a i r e n t r y f i l ters a r e therefore not suitable for measuring pore water p ressu res in unsatura ted ground.
The Casagrande-type device is t h e most f requent ly installed s tandpipe piezometer (Plate 6A). I t has a cylindrical (low a i r e n t r y ) porous element protected by a perforated rigid sheath about 35 mm in diameter and 300 mm long. This element is connected t o a 19 mm o r 25 mm internal diameter pipe. The response time of th i s t y p e of piezometer is comparatively slow, b u t it generally does not become a significant factor until t h e soil permeability is less than about m/sec (Hvorslev. 1951). A t t h i s permeability, t h e response time should not be more than a few hours when t h e piezometer is installed within a 150 mm diameter by 400 mm long sand pocket.
Open-hydraulic piezometers a r e normally installed in boreholes. Access t o t h e top of t h e piezometer is generally requi red in o r d e r t o measure t h e water level with a dipmeter ( see Section 20.2.8) o r similar device, al though t h e water level can be read remotely using a n air-bubbling system (see Section 20.2.8). The piezometer top should be well protected, b u t i t must remain vented t o t h e atmosphere.
If t h e pore p r e s s u r e temporarily d rops below atmospheric, t h e open- hydraulic piezometer will cease functioning, b u t being self de-airing, i t will resume sat isfactory operation without maintenance. The piezometer t u b e should generally not be smaller than 12 mm internal diameter o r t h e self de- airing function may be impaired (Vaug han. 1974).
The main advantages of an open-hydraulic piezometer are i t s simplicity and reliability. Also, water can b e pumped down t h e pipe t o f lush o u t blockages. Moreover, i t can b e used t o determine t h e permeability of t h e ground in which t h e t ip is embedded (see Section 21.4). I t s main disadvantage is slow response time in soils of low permeability.
20.2.4 Hydraulic Piezometers
In hydraulic piezometers, also termed closed-hydraulic piezometers, t h e groundwater p ressu re is detected in a small piezometer t ip with porous walls and conducted th rough small diameter plastic tubes t o a remote point, where t h e p r e s s u r e is measured, usually with a mercury manometer, Bourdon gauge o r
p r e s s u r e t ransducer . A i r i n t h e t u b e s will cause er roneous readings , and because of th is t h e tubes must b e kep t full of water and routinely de-aired.
Various t y p e s of hydraulic piezometers are available, t h e most common being t h e twin- tube t y p e s shown in Figure 20. In these piezometers, t h e t ip i s connected t o t h e measuring point by two tubes. s o t h a t water can b e circulated t o f lush o u t any air bubbles. This should be done in such a way t h a t t h e p ressure in t h e t ip is lef t approximately at working pressure .
In o r d e r t o avoid cavitation, t h e measuring point and connecting t u b e s should not b e more than 7 m above t h e piezometric level being measured (Penman, 1978). Hydraulic piezometers a r e not self de-airing and regu la r maintenance i s requi red fo r sat isfactory performance. The hydraulic leads facilitate remote reading, and t h e measuring point can b e separa ted laterally from t h e piezometer t ip b y fairly long distances.
A closed-hydraulic piezometer has a s m d response tihe and can be used for measuring rapid changes ~h pore water pressure due to rahfall infiltraOon, pressure changes due to tidal variathn or to changes of stress induced by superhposed loads or excavathns. It can a130 be used for ihsitu measurements of permeab~jrity. In zones of high permeability, care should be taken to see that the /im&hg permeability of the porous tip is considered
20.2 5 Electrical P~ezometers
Electrical p~ezometers have a pressure transducer located h e to the porous element. Very rapid response t~ines can be achievedprovided the tip is de-aied mere long term stability is required. or the s~gnal I> to be transmitted over a long distance, the transducer I> u s u d y of the vf..rathg wire type. The mah disadvantage of the electrcal piezometer 13 that it requires calibrathn, wh12h cannot be checked easily after insta//athn. It should be noted that some transducers have temperature-sens12ive elements, so that check cahbrattons should be carried out at groundwater temperature. Moreover. it is not always easy to check that the instrument I> behaving reliably. De-aihhg is not possible after installatrbn, and mislead~ng results can be obtahed. parb'cularly ~h unsaturated so17s or so17s contahing gas, e.g. methane in organ2 soils. The electrical p~ezometer cannot be used for ihsitu permeabiZty measurements /Penman, 1960).
Electrical piezometers have not been widely used in Hong Kong.
Pneuma02 systems comprise two aii-Med tubes connecfihg the measurhg point to a valve located close to the porous element. When the air pressure h the input line equah the water pressure in the porous element, the valve operates, thereby holding constant the pressure eithor ih the return line or in the supply h e . The operation of the valve requkes a s d volume change in the porous element, and in impermeable clays this can lead to difficulbes. Also, dirt enter~hg the lines can prevent valve operation. The pneumatic piezmneter is cheap and easy to instd and has a rapid response. It cannot be used for insitu permeabZty measurements /Marsfand. 19731. Pneumatri: piezometers have the same lim12atrons as electrical p~kzometers ih that they cannot be checked and the porous tips cannot be de-aied after instaffation.
The use of pneumatic piezometers in Hong Kong is described by Handfelt et al (1987).
20.2.7 Installation of Piezometers
The success of pore water pressure measurement depends upon the care taken during instdation and seahhg of the p~ezometer or standp~pe. The porous element should be fully saturated and filled with de-aired water before installaation.
In soft ground, the porous element can often be pushed or driven ihto position. It is, howe ver. necessary to a void clogg~hg the porous element if 12 is pushed thmugh soft clays. This can be ach~eved by us~ng a drive- p~ezometer wh~'ch has a removable sleeve that covers the element during driving Parry, 19717 In day. a pushed or driven piezometer shears and remoulds the chy, destroys the fabric in the clay adjacent to the porous element, and can lead to erroneous measurements of insitu permeab12ty. It should also be noted that the actfbn of push~hg or driving may set up high excess pore-pressures, wh~kh in so i s of low permeability may take a long the to diss~pate. In harder ground, the instrument J> installed in a borehole with the porous element surrounded by weLl-graded sand. Above the sand, the borehole should be sealed off: preferably with grout.
The typical method of installation of a piezometer in a borehole is illustrated in Figure 21. The tip should be placed within a sand pocket in the specific zone for which pore pressures a re to be measured, referred to a s the response zone. The length of the response zone should be a t least four hole diameters, preferably not less than 400 mm. Washed sand with particle sizes in the range 0.2 mm to 1.2 mm is recommended for the response zone in most soils derived from ins i tu rock weathering. For coarse transported soils (e.g. alluvial and marine sands and gravels), filters should be specifically designed to match the surrounding material (GCO. 1984).
Bentonite should be used to provide a seal above the sand pocket, and if the piezometer has not been installed near the base of the borehole. a bentonite seal should also be placed beneath the sand pocket. The length of bentonite seals is typically 0.5 m, although longer seals may be preferable. especially on the upper side of the piezometer. Bentonite balls approximately 25 mm in diameter, formed from powdered bentonite and water. may be used to form the seals. An alternative is to use compressed bentonite pellets. in which case sufficient time should be allowed for the swelling action of the pellets to occur before grout is placed on top of the seal.
The remaining sections of the borehole, both above the upper seal and beneath the lower seal (if applicable), should be filled with a cement- bentonite grout of the same o r lower permeability than the surrounding soil. A tremie pipe should be used to place the grout. The volume of grout used should be compared with the volume of the hole to be grouted.
The compositfon of the grout m ~ k will depend on a variety of factors, such as the availability of materials, the r e q u ~ b d permeability, the type and make of bentonite, the condition of the borehole and the groundwater levels. The grout should be easily pumped, of the required permeab~jrity, and flex~3le. The constituents should not segregate while the grout is sMl liquid. A typical mix might be four parts of bentonite mired thomughly with e ~ g h t to twelve parts of water, to which is added one part of ord~hary Portland cement.
Special mixes and chemical additivs may be necessary if the grout is to be used in sea water or very acid water.
Poor sealing of the piezometer will permit the migration of water from one level to another, and may render the readings meaningless. The installation of more than one piezometer in a single borehole is not generally recommended. If two piezometers a re placed in a single hole, great care must be taken to achieve proper seals.
A well-drained, lockable surface box should be provided for every piezometer installation (Figure 21).
After installation, a response tes t should be conducted on each piezometer where possible. t o check the adequacy of the installation. The response tes t may be of the falling head type, with the results presented on falling head permeability tes t result sheets. Unexpected results in a response tes t may indicate tha t the piezometer is defective. Similar response tests carried out a t intervals during the life of the piezometer a re also recommended to ensure tha t readings remain valid. In soft cohesive soils, care should be exercised to ensure that the head used in response tes ts does not cause hydraulic fracture in the soil.
20.2.8 Varying Groundwater Pressures
In additrbn to varying response to ra'nfalI, water pressures may show seasonal variation, response to tr'dal changes or may be affected b y abstractibn from ne~ghbouring wells or b y other causes. Where i t is finportant to take account of these effects, adequate periods of observation should be adopted
Groundwater levels in open-hydraulic piezometers o r standpipes a re commonly measured with battery-operated electrical dipmeters (McNicholl & Cho, 1985). This technique relies on the conductivity of the groundwater to complete a circuit. In some instances the dipmeter may fail to function until the conductivity of the water has been increased, for example by the addition of a few crystals of common salt (sodium chloride).
Groundwater levels o r pressures should be recorded and plotted systematically. A typical record sheet is shown in Figure 22, where the readings have been plotted on a time base for ease of interpretation, together with corresponding rainfall data.
The observation of peak groundwater response i n open-hydraulic piezometers o r standpipes can be measured using a string of piezometer 'buckets' (Figure 23 and Plate 6 8 ) . The buckets a re filled progressively a s water rises in the piezometer and will retain their water even if the piezometric pressure subsequently falls. By using a series of closely-spaced piezometer buckets, the peak transient response during o r af ter a rainstorm can be recorded a t a convenient time later on. The buckets a re tied to a weighted nylon string a t selected depth intervals above the normal base water level and can be pulled to the surface for readings. They might typically be placed a t 0.5 m intervals within the range of 2 m both above and below the critical groundwater level assumed in the design. A typical data sheet is shown in Figure 24. Care should be taken when handling the string to ensure tha t it does not drop into the borehole (thus rendering the piezometer use- less), o r tha t i t does not tangle and reduce the spacing between the buckets.
Another method for recording transient water levels in open-hydraulic piezometers or standpipes is the automatic bubbling recorder, o r 'bubbler' system. In this system, a small diameter air line is installed down to the piezometer tip with a small air flow sufficient to produce several bubbles per minute. The air pressure required to release bubbles can be equated to the water pressure produced by the height of water in the standpipe.
An electronic pressure transducer and "Scanivalve" have been used for automatic recording of a number of piezometers (Pope e t al. 1982). Functioning of the system may be controlled by a microprocessor, allowing variation in the number of piezometers read. the dwell time on each piezometer, and the interval time between readings.
20.2.9 Soil Suction
Measurement of matric soil suction. o r negative pore water pressure, in the range 0 to -80 kPa can be undertaken in the field with tensiometers. A high air en t ry pressure ceramic tip allows equilibrium to be achieved between soil moisture and a confined reservoir of water within the tensiometer. A vacuum gauge is located a t the top of the tensiometer. A t suctions greater than -80 kPa, water inside the tensiometer cavitates and is lost through the ceramic tip. An example of a tensiometer is shown in Plate 6C.
The pressure exerted by the column of water within the tensiometer must also be considered; for example. if the tip were located 1.5 m vertically beneath the gauge, the maximum soil suction tha t could be measured would be reduced t o -65 kPa. When suction measurements a re required a t greater depths, a caisson may be excavated and tensiometers installed through the sides of the caisson (Sweeney, 1982). The reliability of a tensiometer depends on a good contact between the soil and the ceramic tip, and a good seal between the tensiometer tube and the soil.
For measurement of soil suctions beyond the range of tensiometers. psychrometers may be used (Richards. 1971). although their accuracy is doubtful. The measurement of soil suction in Hong Kong slopes has been reviewed by Anderson (1984).
20.3 CROCINDWA ATER SAMPLES
Care should be taken to ensure that samples are representative of the water-bearing zone from whkh they have been taken and that they have not been contanuhated or d ~ l ~ t e d by surface water or water used for boring. Water samples should be taken as soon as possible after the water-bear~hg zone has been met in the borehole. If other water-bear~hg tones occur a t higher levels, these shouM be sealed off by the borehole cashg. A s far as is possible, all the water in the borehole should be removed by pumping or baling, and the s a m e taken fm water which collects by seepage. About one litre should be coL4ected in a clean glass or hert plastic bottle, rinshg the bottle three Limes with the water being sampled before filling. More stringent requirements may apply ih certain cases, e.g. use of sterilized containers /see Chapter 131. Even when precauttons are taken, water samples from boreholes may be unrepresentative. Better resuks can be obtahed IT samples can be taken from a standpipe p~ezometer sealed withh the relevant zone. Water samp/es may deterforate rapl-dly and should therefore be tested as soon as poss~Ble after sampling.
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111
21, TESTS I N BOREHOLES
21.1 GENERAL
This chap te r describes various tests t h a t may b e conducted a s supplementary t o a ground investigation carr ied o u t by boreholes. The tests described a r e generally under taken as an integral p a r t of t h e drilling operation. Additional field t e s t s a r e described in Chapters 24 t o 33, and include some t e s t s which can also b e conducted in boreholes. The division of t h e s u b j e c t matter has been somewhat a rb i t r a ry ; therefore, where coverage of a part icular t e s t is not given in th i s chapter , i t should b e sough t in later chapters .
21.2 STANDARD PENETRATION TESTS
21.2.1 General Principles
The s t andard penetrat ion t e s t is a f requent ly used dynamic penetration t e s t and is described in Test 19 of BSI (1975b). A small d is turbed soil sample (quality class 3) is normally obtained when t h e spl i t ba r re l sampler i s used (Figure 25 and Plate 7A). The test resu l t s have been related empirically t o soil parameters and foundation conditions, especially in s a n d s and gravels.
Minor variations from t h e specified equipment and procedures can seriously affect t h e resul t s of t h e test (De Mello. 1971; Ireland et al. 1970; Nixon, 1982; Skempton. 1986). I t is important t h a t t h e t e s t is carr ied o u t precisely as described in Test 19 of BSI (1975b). except t h a t t h e following modifications should be incorporated :
(a) An automatic release t r i p hammer (Plate 78) should b e used t o d r ive t h e sampler.
( b ) The weight of t h e hammer in t h e d r ive assembly should be 63.5 kg.
(c) The diameter of t h e borehole should b e between 60 mm and 200 mm.
( d ) Drill rods with a s t i f fness equal t o o r g r e a t e r t h a n t y p e BW rods should be used to reduce ene rgy dissipation.
These modifications br ing t h e t e s t procedures into conformity with t h e proposed international s tandardizat ion of t h e test (ISSMFE, 1977).
21.22 Preparaobn for Testing
It is necessary to clean out the bottom of the borehole. When the test is carried out below the groundwater level. certain types of soil may be loosened below the base of the borehole by the acaon of the boring tools and by pressure d~Yferences between the groundwater and water ih the borehole. This effect can be paro'cularfy severe in sands. The effect can be reduced by keeping the borehole topped up with water and by very careful operaoon of the boring tools but often these exped~ents will not be completely successfuL
The drill casing should not be advanced ahead of t h e borehole where a
standard penetration test is to be performed.
21.2.3 Advantages and Limitations
The great merit of the test, and the main reason for its widespread use, is that it is simple and inexpensive. The soil strength parameters which can be inferred are very approminate, but give a useful guide in ground conditlbns where it may not be possible to obtain borehole sampZes of adequate quality, e. g, gra vels, sands, silts, chy containing sand or gra vel and weak rock. In conditlbns where the quality of the 'undisturbed' samp/e is suspect, e.g. very sJty or very sandy clays, or hard clays, it is often advantageous to alternate the samp/ng with standard penetration tests, thereby obtahing a check on the strength. I f the samples are found to be unacceptably disturbed, it may be necessary to use a different method for measuring strength, e.g, the plate test described in Sections 21.6 and 29. I.
When the test is carried out in granular sods below groundwater level, the so17 may become loosened, even when the test is carried out in strict accordance with BSI (19756) and the borehole has been properly prepared. In certain circumstances, it can be u s e m to contihue driving the sampler beyond the distance specified, adding further dry1 rods as necessary. Although this is not a standard penetration test, and should not be regarded as such, it may, a t least, give an indication as to whether the deposit is really as loose as the standard test may indicate. When there is good reason to believe that unrealstically low vahes are being recorded, considerafion should be glSven to the use of some other test which can be performed independently of a borehole, e, g. the cone penetration test described in Section 23.3.
When the test is carried out in soils derived from insitu rock weathering in Hong Kong, it is commonly extended to high blow counts, sometimes in excess of 200. However, it is recommended that the test should be discontinued when the blow count reaches 100 or if the hammer bounces and insignificant penetration is achieved, as is frequently the case when corestones are encountered. If the test is curtailed due to hard driving, the number of blows used to achieve the actual penetration should be measured and recorded (e.g. Blow/Penetration = 100/80 mm), and this may be used to estimate the blow counts for 300 mm penetration.
In the construction of bored pdes, the test is sometlines carried out in boreholes consl'derably larger in diameter than those used for ground in vestiga tion work. The result of the standard penetration test is dependent upon the dimeter of the borehole, and these tests should not be regarded a s standard penetration tests. They may, however, pro vide useful informa tlbn to a plying contractor, parb'cularly if he has considerable experience in their use.
21.2.4 Results and Interpretation
The resulting N value is defined as the number of blows required to drive the standard split spoon sampler a distance of 300 mm. The sampler is initially driven 150 mm to penetrate through any disturbed material at the bottom of the borehole before the test is carried out. The number of blows required for each 75 mm advance in the initial seating drive should be recorded; the test may then proceed, with recording of the number of blows required for each 7 5 mm incremental advance of the test drive.
When t h e test i s used in soils derived from insitu rock weathering, i t should be noted t h a t t h e empirical relationships developed for t r anspor ted soils between N value and foundation design parameters. relative densi ty and s h e a r s t r e n g t h may not be valid. Corestones, for example, can b e responsible for misleadingly high values t h a t a r e unrepresenta t ive of t h e mass. In view of this , t h e test should only be used to give a rough indication of relative s t r e n g t h in these soils, o r t o develop site-specific correlations.
21.3 VANE TESTS
21.3.1 Genera: Principles
A cruciform vane on t h e end of a solid rod is forced in to t h e soil and t h e n ro ta ted (Figure 26). The to rque requi red to ro ta te t h e vane can b e related to t h e s h e a r s t r e n g t h of t h e soil. The method of ca r ry ing o u t t h e t e s t i s described in Test 18 of BSI (1975b). Vanes can take t h e form of borehole vanes o r penetration vanes, t h e l a t t e r being much more reliable. The test can be extended t o measure t h e remoulded s t r e n g t h of t h e soil. This is done by tu rn ing t h e vane through t en complete rotations. A pause of not more than one minute is permitted to elapse and t h e vane test is t h e n repeated in t h e normal way. The degree of d is turbance caused by rotat ing t h e vane differs from t h a t obtained by remoulding a sample of clay in t h e laboratory, and t h e numerical value of t h e sensi t ivi ty of t h e clay determined b y these procedures is not s t r ic t ly comparable with t h e resul t s obtained from laboratory triaxial tests.
The test is normally res t r ic ted t o fair ly uniform, cohesive, fully- sa tu ra ted soils, and is used mainly fo r clay having an undrained s h e a r s t r e n g t h of up to about 75 kPa. The resu l t s are questionable in s t r o n g e r clays, or if t h e soil t e n d s to dilate on shear ing o r is f issured.
In Hong Kong, t h e vane test i s invaluable in t h e marine sediments (Fung et al. 1984; Handfelt et al. 1987). However. some s t r a t a a r e sandy o r contain shells, in which case vane s h e a r resul t s should b e in terpre ted with caution. Marine muds are generally v e r y soft, and it is often necessary t o provide a separa te s u p p o r t frame on top of t h e seabed t o c a r r y o u t t h e vane test (see Section 14.7).
It should be noted that the undraned shear strength determined by an insitu vane test is. i n genera/, not equal to the average value calculated at faM i n the field e.g. h the fa7ure of an embankment on soft clay. The discrepancy between /ied and vane shear strengths generuy increases as the day becomes more plastk (8jerrum, 19731.
21.3.2 Advantages and Limitations
The mah advantage 13 that the test itself causes /ittle d~kturbance of the ground. Th13 I> partz'culzly apparent ~ i ) sensitive clays, where the vane test tends to give higher shear strengths than those derived from laboratory tests on samples obtahed with the genera/ purpose sampler described in Section 19.4.4. I n these condihns, the vane test results are g e d l y considered to be much more reliable. If the test 13 carried out in so2 that is not uniform and contains even thin layers of laminatrbns of sand or dense s17t, the torque may be misleadingly high. The presence of rootlets i n organic so17s, and also of coarse parOWes, may lead to erroneous results.
With t h e penetration vane t e s t appara tus (vane borer) described in Test 18 of BSI (1975b3. t h e vane and a protect ive casing (Plate 8) a r e forced into t h e ground by jacking. A t t h e requi red depth , t h e vane is advanced a s h o r t distance ahead of t h e protective casing. t h e test is conducted, and t h e casing and vane a r e then subsequent ly advanced to the next required depth. However, with th is t y p e of test i t is not always possible t o penetrate t o t h e desired layer without t h e assistance of pre-boring.
Small hand-operated vane t e s t ins t ruments a r e available for use in t h e sides o r bottom of an excavation. These devices can also be used on samples, with t e s t s done e i the r in t h e field o r in t h e laboratory. The resu l t s t h u s obtained a r e generally adequate for t h e purpose of classifying t h e consistency of cohesive soils ( G C O , 1988). Comparative hand vane t e s t s car r ied o u t in both t h e field and laboratory may provide a n indication of possible d is turbance dur ing handling and transportat ion of t h e sample.
21.4 PERMEABILITY TESTS
The determination of insitu permeability by tests fh boreholes i n volves the application of an hydraulic pressure i n the borehole different from that ~ i , the ground, and the measurement o f the flow due to this difference, The pressure i n the borehole may be increased by introducing water into it, whfcb i s commonly. c d e d a falfing-head or inflow test, or it may be decreased by pumping water out of it i n a rising-head or outflow test. The pressure may be held constant durfng a test fa constant-head test) o r it may be Mowed to equahe to i ts origfhal value fa variable-head test). The techn~*ue i s strictly applicable only to the measurement of permeability o f soi/s below groundwater level, although an approximate assessment may be made above t h ~ s level (Schmid, 19661. However, t h ~ s approxhate value wfYl r e f i c t the fnfi7traatrbn capacity o f the subsurface materia/ rather than i ts permeabfPty fsee dm Section 24.3). A great varfety of tests are included under this heading, varying from the very crude, where simple problems can be solved by shp le means, to the sophisticated when the nature o f the problem demands more refined data.
21.4.2 Preparatfons for the Test
I n the s~inplest form o f test, preparation consists of cleaning out the bottom o f the borehole. The test is then conducted by measuring the rate of flow o f water out o f the borehole into the soil, or vice versa, through the open end of the casing. The borehole may be extended beyond the bottom of the casing, thus increasing the surface through which water can flow. If necessary, the uncased part o f the borehole is supported by a suf'table AYter material Water leak~ng through the casing joints has at trines been found to cause m~sleading results and the problem has been overcome by the use of f ibre rhgs.
Misleading resul t s can also a r i se if any r e t u r n flow occurs u p t h e outside of t h e casing.
For more accurate measurements, a perforated tube or a suf'tab1e piezometer tip i s instded, which is then surrounded by a granular /iltr to prevent erosion o f the ground, and the casing withdrawn. It i s essential that
the filter material used has a permeabii'ity much greater than that of the soil being tested. Recommendatrons for sealing the borehole above the granular filter are gi'ven ih Sectron 20.27. In order to avoid errors in flow measurement due to compression and solution of trapped air in the leads, ceramic piezometer tips should be saturated with de-aked water before ins ta l la th
Permeability tests can be carried out at various depths in the borehole as drilling progresses. Figure 27 shows a suitable test arrangement.
Before a permeabi/ity test is conducted, it IS essentral to determhe the level of the natural groundwater table by one of the methods described in Chapter 20.
Measurements of water level taken soon after cessation of drilling usually do not represent equilibrium values, and a series of measurements may be necessary. If a piezometer is finally installed in the borehole. the piezometric data obtained from monitoring may provide a check on the measurements taken at the time of the test.
The period required for constant-head tests is decreased and the inter- pretation simplfied if short lengths of borehole are used for the test. Pore pressures should be in equilibrium before the test is performed, and with clays of low permeability it can take several months for the pore pressures set up by the drilling of the borehole to equa/lie. For soih derived from ihsii'u rock weathenhg and co//uvium, equalizatton typicdy occurs very much faster.
21.4.3 Variable-head Test
The fist operatlbn is either to fi// the piezometer tube with water (falling-head tesN or to force the water level down by a fbot-pump or bikycle pump (rising-head test). The head in the borehole IS then dowed to equalize with that in the ground, the actual head being measured at ihtervals of trine from the commencement of the test. The depth of the borehole should be checked to determihe whether any sediinent has come out of suspension or whether the bottom of the borebole has heaved during the test period
21.4.4 Constant-head Test
A constant-head test is normally conducted as an i f l o w test ih whikh arrangements are made for water to flow into the ground under a sensi'bly constant head. It ik e s senW to use clean water. It wf l not be possible to achieve a constant head IT the groundwater level IS not constant or the head lost by frictrtrb in the pipes is sigdficant. Where a high flow rate is antrcipated and where the ihstallatrbn comprises a piezometer tip surrounded by a iWter materied, two standpipes should be installed, one to supply the water and the other to measure the head in the Mter materihl surrounding the piezometer tip. The rate of flow of water IS adjusted unt2 a constant head is achieved and, in the s i rnes t form of test, flow IS allowed to contrhue unM a steady rate of flow IS achieved. In some ground, this may take a long period of time, and, in such cases the method suggested by Gibson N963) may be used, in whikh the actual rate of flow is measured and recorded at intervah from the commencement of the test.
21.4.5 Analysis of Results
There are numerous pubL&bed fomulae for calculating permeability from these tests, many of them part/y empiricaL Those given by Hvorsfev (19511, which are reproduced h outhne in Section 21.4.6. are much used and cover a large number of conditons. They are based on the assumption that the effect of so17 compressib~jrity 1s negligible. The method given in Gibson N963) for the constant-head test is afso indicated This gives a more accurate result with compressiible soils.
I t must be emphasized t h a t t h e formulae given in Section 21.4.6 a r e s t eady-s ta t e equations sui table for calculation of permeability when t h e test is car r ied o u t below t h e water table. In Hong Kong, it is often necessary t o measure permeability above t h e water table. In th is case, t h e s teady-s ta te equations can only be used if t h e time over which t h e test is conducted becomes v e r y long. Under t h e s e circumstances, permeability should be assessed using t h e constant-head test in terpre ted according t o Method 2 in Section 21.4.6(2), with H, measured from t h e c e n t r e of t h e response zone in t h e test.
21.4.6 Formufae for Borehole PermeabhYty Tests
(II Method 1 (after Hvorsfev, 19511.
For constant-head test,
and for vanable-head test,
A . . . . . fceneral approach) I31 k = F(t2 - t') loge z- where k I> the permeability of soil,
q I> the rate of flow
F is the />take factor (Figures 28 and 291,
H, is the constant head,
HI is the variable head measured at t h e t, after commencement of test,
Hz is the variable head measured at tihe 1; after commencement of test,
A is the cross-sectionaf area of borehole casing or standpipe as appropriate,
T I> the bask time factor (Figure 331.
It shouh' be noted the above formulae assume that the natural ground- water level remains constant throughout the test. For the cam where the natural groundwater varies, see Hvordev f19511.
(21 Method Z. (Constant-head Test, after Gibson, 19631.
where k 13 the permeabzity of so~z
C IS the coeffic~knt of consolidahon or swelling,
q, IS the steady state of flow /read off the q, I/Jt graph at f/[t = 01,
F is the intake factor (Figures 28 and 29A
He is the constant head
r 13 the radius of a sphere equal in surface area to that of the cylindrical tip,
n is the slope of the q, 1/Jt graph.
The followfi?g points regarding this method should be noted :
fa1 Heads are referred to natural groundwater level before the test.
fbl The method makes dowance for the compressibility of the soil and also permits the coefficient of consoldahon or swe//ing to be calculated
fc1 The //,w q, has, in theory, a linear relationsh& with 1 . In prachke, it may take same hours for the plot to came on a straight h e . The line can then be extrapolated to give q, and n, where the test would otherwise take too long.
21.4.7 Advantages and Limliations
For most types of ground, M d permeabiTty tests y~e ld more &able data than those carried out in the laboratory, because a larger volume of mater~kl i3 tested. and because the ground is tested hsitu, thereby avoiding the d~kturbance associated with sampflng. The appropriate choke of dr17ling method and careful drilling technique are necessary to avoid d~kturbing the ground to be tested. In granular soils, the ground may be loosened below the bottom of the borehole; in layered deposits of varying permeability, a s k h of remoulded mixed mater%al may be formed on the walls of the borehole, thus blocking the more permeable layers. h johted rock, the johts may be blocked by the dr i lhg debris.
In v e r y sof t marine clays, i t is v e r y difficult t o c a r r y o u t a successful permeability t e s t because of t h e low permeability of t h e soil, i t s compressibility, and t h e possibility of hydraulic f r ac tu re aris ing from t h e relatively la rge head requi red for a falling-head o r constant-head tes t .
Constant-head tests are likely to give more accurate results than var12ble-head tests, but, on the other hand, variable-head tests are simper to perform. The water pressure used in the test should be less than that whkh wifl disrupt the ground by hydrauhk fracturing. It has been shown that ser~bus errors may be introduced if excessive water pressures are used IBjerrum et a/, 19721. In general. it is recommended that the total increase in water pressure should not exceed one half the effective overburden pressure. With soh's of high permeabifity, greater than about m/s, flow rates are fikely to be large and head losses at entry or exit and in the borehole may be high. In this case, fieldpump~ng tests, where the pressure distribuabn can be measured by piezometers on radial fines away from the borehole, will probably yield more accurate results; these are described ]in Chapter 25. When the test is carried out within a borehole using the dr i l casing, the lower limit of permeabifity that can be measured reliably is determined by the watertightness of the casing jbints and by the success achieved in seaihg the casing into the ground In so2 the refiable lower hi t I> about lo-* m/s. In lower permeab17ity soils and unweathered rock, it is a d v k b l e to carry out the test using a standpipe or piezometer which is seaM within the test length using grout. In ground of low permeabifity, the flow rate may be very small. and measurements may be subject to error owing to changes in temperature of the measurihg apparatus.
The permeability of a compressible soil is influenced by t h e effective stress at which i t is measured, and t h e r e may be significant differences between t h e r e su l t s of inflow tes ts . in which effective stress is reduced, and t h e resul t s of outflow tes t s , in which i t is increased. The test t o b e used should model t h e field conditions a s closely a s possible, e.g. where t h e conditions indicate increasing effective s t r e s s , such a s in embankment construct ion, a rising-head t e s t should be used; fo r t h e case of decreasing effective s t r e s s , such a s when assess ing t h e quanti ty of inflow into an excavation, a falling-head t e s t would b e appropriate. The permeability of soil a round t h e borehole may also be influenced by changes in i t s stress history owing t o installation of t h e borehole and any previous permeability t e s t s performed on it.
The compressiibity is influenced in a sidlar way, and this may affect the results achieved The accuracy with which the coefficient of permeabifity may be deduced from variable-head tests decreases with the coefficient of consofida&bn of the soil being tested In princ~ple, the coefficient of conso/iration or s w e h q may be deduced from the results o f both constant- head and variable-head tests. In praca'ce, results of only limited accuracy can be obtained, owing to dXficulties in interpretation and the extent to which the stress history of the soil adJbcent to the borehole is modified b y the installarion of the borehole.
Execution of the borehole permeability test requires much experthe, and s d faults in technique lead to errors of up to one hundred tlines the actual value. Even with considerable care, an individual test result is often accurate to one s~gn~ficant figure only. Accuracy will usua//y be improved by ana/ysing the results of a ser~es of tests. However, in many types of ground, particularly stratified soil or jointed rock. there may be a very wide variatlbn in permeability, and the permeability of the mass of ground may be determined
by a relatively thh layer of hzgh permeability or a ma/br joint. Very considerable care is needed in ~nterprethg the test data. In cases where a reliable result 13 required, the programme of borehole permeability tests is generally followed by a full-scale pumping test (see Chapter 251.
21.5 PACKER (WATER ABSORPTION) TESTS
21.5.1 General Principles
The packer or Lugeon test gives a measure of the acceptance by hsitu rock of water under pressure. The test was originally introduced by Lugeon (19331 to provide an acceptable standard for testhg the permeabi/ity of dam foundatbns. In essence, it comprises the measurement of the volume of water that can escape from an uncased sectrbn of borehole in a given time under a given pressure. Flow is confined between known depths by means of packers, hence the more general name of the test. The flow 13 confined between two packers h the double packer test, or between the packer and the bottom of the borehole in the single packer test. The test is used to assess the amount of grout that the rock will accept, to check the effectiveness of grouting, to obtain a measure of the amount of fracturing of the rock (Snow, 19681, or to give an approxhate value of the permeability of the rock mass adjacent to the borehole.
The results of the test are usua/y expressed in terms of Lugeon units. A rock is said to have a permeabifity of I Lugeon i/; under a head above groundwater level of I00 m, a I m length of borebole accepts I /ire of water per mhute. Lugeon did not specify the dXmeter of the borehole, which 13 usually assumed to be 76 mm fN size), but the test I> not very sensitive to change in borehole dimeter unless the length of borehole under test is small
When t h e packer test is carr ied o u t at shallow depths. a s is f requent ly t h e case in Hong Kong, t h e applied water p r e s s u r e must b e limited t o a value t h a t will not cause hydraulic f rac tur ing of t h e ground (see Section 21.5.3). This often leads to t h e test being conducted a t p r e s s u r e s of 50 t o 500 kPa. and extrapolation is t h e n necessary t o obtain t h e Lugeon value equivalent t o a 100 m water head (approximately 1 MPa pressure) .
If t h e rock discontinuity spacing is sufficiently close fo r t h e test section t o b e representa t ive of t h e rock mass, a mass permeability can be calculated a s described in Section 21.5.6. A simple ru le t h a t is sometimes used t o conver t Lugeon values in to mass permeability is t o take one Lugeon as equal t o a permeability of 10- m/s.
A s t h e packer test is used t o assess t h e potential for water t o penet ra te rock discontinuities, clean water should be used a s t h e drilling fluid when forming t h e borehole, r a t h e r t h a n drilling mud. If drilling mud has been used. t h e hole should be thoroughly f lushed o u t prior t o packer test ing; appropr ia te explanatory notes should also b e given with t h e test data. In si tuat ions where only salt water i s available t o conduct t h e t e s t , t h i s should also b e clearly indicated on t h e t e s t resul ts .
21.5.2 Packers
Several types of packer are in use, such as the mecban~kal tailp~be, the manual mechan~kal-expanding packer and the hydraulic self -expanding packer.
but b y far the most commonly used is the pneumatk packer.
This comprkes a rubber canvas duct tube which can be iMated aganst the sides of the borehole by means of pressurized gas (Figure 31). Bottled nitrogen or oxygen IS fed down the borehole through a small diameter nylon tube. The inflafion pressure has to be sufficient to expand the packer against the head of water in the borehole, but not sufficient to cause heaving of the ground surface or fracturing of the rock. A useful rule of thumb 1% that the pressure, in kPa, should lie between 12 times and 17 times the depth, in metres, of the borehole. The difference between the diameter of the uninflated packer and the d i e t e r of the borehole should be such that the packer can be easily inserted. A t the same t h e , the inflated diameter of the packer should be sufficient to provide an efficknt seaL A double packer is two packers connected by a length of p&e of the same length as the test section. The test water is introduced between the packers.
21.5.3 Application and Measurement of Pressure
Water pressure is applied by a flush pump as used for diamond bit core dr17ling. The maximum water pressure which should be applied should not be suffic~ent to cause uplift of the ground or to break the seal of the packers li, deep holes in weak rock. The standard head of 100 m above groundwater level may not be attainable in these conditons.
The applied pressure should not exceed overburden pressure a t the test depth, and it may be necessary to keep the pressure well below the overburden pressure, as under some circumstances vertical cracks can develop in weak rocks at pressures much lower than this value. Excessive pressure may be detectable by careful analysis of the t e s t data, e .g. an abrupt change of slope in a graph plot of applied water pressure versus flow rate may indicate possible hydraulic fracture during the test.
The pressure to be deterdned for use in the calculation of permeabi/ity is that causing flow into the rock itselL This is somethes measured directly, but it is more usual to measure it at ground level by means of a Bourdon gauge, .with the read~hgs adjusted in accordance with the following expression :
where h is the pressure head causing flow into the rock fml,
P IS the Bourdon gauge reading converted to head fml,
H I> the he~ght of Bourdon gauge above the mid-point of test secthn fm/.
H, is the he~ght of natural groundwater level above the mid- point of test section fml,
H, is the friction head loss in the pipes fml.
The pressure gauge should be positioned so that it wifl give a true reading without interference from local pressure var~k&ons induced by flow through the pipe work. The natural groundwater level should be measured before the test begins. This is not always easy, especjally when the rocks are of low permeability, and water has been used for flushing purposes during
d i g If necessary, separate observation wells should be instafled, and the groundwater levels should be measured over a period to establish the general groundwater level. Friction head loss in the pipes is best estabfished by means of a calZbrathn test, with the p&e work laid out on the ground
Calibration must be carried out for each tes t arrangement (pump, packer. valves and by-pass, pressure gauge and flowmeter) with various lengths of drill rods and varying flow rates. All pressure gauges and flow meters used in the tes t should be calibrated regularly.
21.5.4 Measurement of Flow
The rate of flow of water may be measured either by a flowmeter or by direct measurement of flow out of a tank of known dimensions by means of a d~pstikk or depth gauge. Where a flowmeter is used, it should be hs tded upstream of the pressure gauge, we// away from bends or fittihgs in the pipework. and in accordance with the manufacturer's instructions. The accuracy of the meter should be checked before the test begins, and periodically afterwards, by measuring the time taken to fill a container of known volume a t different rates of flow. Where the flow out of a tank is to be measured, the use of one large tank can lead to haccuracfes where the p h area is large and the fall in level correspondingly smaL A better arrangement is to use a number of s d containers.
Flowmeters a re prone to inaccuracies. especially a t low flow rates, and calibrations should therefore be carefully checked on site. Industrial water meters commonly available in Hong Kong are not sufficiently accurate for use in the packer test. For very low flows. a rotameter board with a series of graduated tubes can provide an accurate measurement of flow rate, as can an orifice plate meter.
21.5.5 Execution of Test
The test may be carried out either a s a single or as a double packer test. The single packer test is gener- to be preferred because any leakage past the packer can be detected, whereas leakage past the lower packer ~h the double packer test cannot. However, the single packer test n o r d y has to be done period~kally dur~hg the dr17fing of the hole, which makes it more cosuy. An important point I> to ensure that the packer is properly seated ~h the borehole. Where a complete core has been recovered from the borehole, or where appropr~ate logg~hg or television inspecIron has been carried out, a careful examinathn may reveal suitable places to seat the packer. Where the seating proves unsatistactory, the length of the test section should be altered or test sections overhpped, so as to seat the packer a t a different depth in the borehole.
While the number of packer tes ts carried out in a borehole depends on the requirements of the project, i t is usual to tes t the whole length of the borehole that is in rock. However, the upper limit of testing may be constrained by the highest level a t which a packer can be sealed satisfactorily. Typically, overlapping tests a re used, each having a tes t section length of 3 to 6 m. In any case, the tes t section length should not be less than ten borehole diameters so as to minimise end effects.
I t is customary to run a staged tes t a t each location, using different
pressures . A f ive-stage t e s t is desirable, with t h e maximum pressure applied in t h r e e equal increments and then reduced with decrements of t h e same amount (Figure 32). The data obtained from these measurements a r e particularly useful in assist ing in t h e interpretat ion of t h e behaviour of t h e rock u n d e r test.
The water level in t h e borehole above t h e packer should be observed dur ing each t e s t , as a r is ing level may indicate t h a t leakage is occurring around t h e upper packer.
21.5.6 Results and In terpre ta t ion
The varying values of p ressu re and flow recorded dur ing t h e t e s t may b e plotted a s shown in Figure 33. The in te rp re ted Lugeon value. L, i s given by t h e formula :
where 100 is t h e s t andard head of water (m).
1 is t h e length of test section (m).
q is t h e flow rate (l i t res/minute) ,
h is t h e p r e s s u r e head causing flow into t h e rock (m) (see Section 21.5.3).
q / h i s t h e slope of g r a p h a s shown in Figure 33.
Where a test has been conducted at p ressure heads considerably less t h a n t h e s t andard 100 m head, t h e Lugeon value may be somewhat over- estimated by t h e above formula, due t o possible differences in ene rgy loss between laminar flow (a t low head) and tu rbu len t flow ( a t high head). Fur the r considerations on test interpretat ion a r e given by Houlsby (1976).
21.6 PLATE TESTS
21.6.1 General
The plate test is one particufar applcation of the vertical l0ad1~g test, and the general procedures for the test are described in Secoon 29.1. Only the specific problems which anke from carrying out the test in the bottom of a borehole are d~kcussed in thh SecLton. Wherever pracLti7ab1ee the test should be conducted in a borehole whhh is of sufficient d~~ameter for a technician to enter, clean out the bottom, and bed the plate evenly on undisturbed ground Careful attention should be directed towards safety for operators working below ground (see Section 18.2 and Appendix El. Mere, for reasons of economy, the test 13 conducted in a small dimeter borehole, the cleaning of the bottom and the bedding of the plate has to be done from the surface, so that 12 ~k very difficult to be certain that the plate is not resting on disturbed materLal. This would of course, l m 2 the value of the resufts.
The techniques used for tests in large and sma// dXmter boreholes differ in some respects and, where differences occur, the methods are described separately in Chapter 29. The diameter of the plate used sboufd so
far a s practicable, be equal to that of the borehole, provided that care is taken to elimfnate cohesion or fricbon on the side of the plate. Except in strong materials, the plate should have a skirt as shown in Figure 43 (see Sectkm 29.1'. 41. Where the diameter of the plate is significantly less than that of the borehole, the results of the test become difficult to interpret. A t a hole-diameter to plate-diameter ratio greater than about 3:Z the parameters being measured are t h e pertaining to a load a t a free surface and not a t depth under confined conditons, which are usuafly the conditons of interest.
The general limf'tafions of the verthal load test are discussed in Section 29.1.2 and they ap&y similarly to the borehole test. Additiondfy, in the bottom of a borehole it is more difficult to ach~eve a satisfactory bedding of the load!hg plate on the test surface, and hence values obtained for the deformation parameters may be of hitea' significance.
Where. necessary, casing should be used to support the sides of the borehole and to sea/ off water seepages from materials that are above the test elevation. When the test is to be carried out below the prevailing water table, dewatering by pumping or baling from within the borehofe may cause seepages which disturb the ground and have an adverse effect on its deformathn characteristics. It wouM then be necessary to resort to external dewatering (see Section 29.1.21. If the test is undertaken only for measuring the strength parameters, disturbance due to groundwater seepage may be a less significant factor and the borehole may be emptied, Lf th~s is possible, wwhe the plate is being installed. The water shouM be allowed to return to its normal rest level before the test is commenced. Alternatively, the plate can be instded under water, altbough it may not then be poss~Ele to set the plate sufficienuy accurately for the deformation characteristics to be measured.
21.6.4 Bedding of the Plate
(11 Large Diameter Borehok. Subject to safety requirements (see A p p e n d i x E), a technician shouh' be lowered to the bottom of the borehole to remove a// loose soil manually, after which the plate is bedded a s described in Section 29.1.3.
(21 S d Diameter Boreholes. The cleaning lj. carried out by means of a suitable auger or hinged bucket operated at the end of a drifl rod assembly. A layer of neat cement mortar is then placed at the bottom of the boreme by means of a tremie or bottom opening bucket, and the plate lowered down the hole and lightly pressed on to the surface of the mortar. Plaster and resins can also be used for bedding.
21.6.5 Applicaoon and Measurement of Load
The plate is usuafly loaded through a column formed by a steel tube, with the load applied to the cofumn by means of an hydraulic jack operating against the resistance of kentledge, tension p17es or ground anchors, as described in Section 29. I. 4.
21.6. 6 Measurement of Deflection
The movement of the plate under load is generafly transmitted to did gauges at the surface by means of a settlement measurement rod that is located within the steel tube by which the load is applied The rod is restrained from lateral movement by rod guides fied within the tube. Methods of supporting the did gauges are given in Section 29.1.4.
21.6.7 Execution of Test
The method of carrying out the test is given in Section 29.1.6.
21-6.8 Uses of the Test
fII Large Diameter Boreholes The main use of the test is to determine the strength and deformation character~ktks of the ground It is sometimes used to establish the working load of plies ( Sweeney & Ho. 1982).
(2) S d Diameter Boreholes. The deformoon characteristks obtaned are of very dubious value owing to doubts about the elim~nafio~ of ground disturbance and errors resulting from unsatisfactory bedding of the plate. The main use of the test is for measuring the strength characteristks of those cohesive soils in which undisturbed samples cannot be obtained, e.g. some gravefly clays and very weak rocks. The plate diameter shouh' be large in relation to the structure of the ground.
21.6.9 Supplementary Test
Although not stricuy a plate test, a test is sometimes made by Lqsitu methods to determine the coefficient of fricthn between the ground and concrete as an ah' to the assessment of shaft fricaon for pile design. A t the bottom of a borehole is placed either a layer of compressible material or a suitably-designed co/apsib/e container. The shaft above t h ~ s level 1% then fifled with concrete while the casing is withdrawn. When the concrete has sufficiently matured, the load is applied, and the deflecthn measured in a manner s~hilar to that described in Section 21.6.6. fiere the shaft fr ichn of only part of the ground prome is required, as in a rock socket, the concrete is first brought up to the level of the top of the ground layer concerned. and the shaft is conhnued in smaller dimeter.
21.6.10 Horizontal Plate Tests
The plate t e s t may also be conducted horizontally within a large diameter borehole or caisson (Whiteside. 1986). In this case, either two tests can be conducted simultaneously on opposite s ides of the caisson, or the caisson wall opposite the t e s t can simply be used to provide the necessary reaction force. Casing or lining of the caisson must of course be kept well away from the test location. Guidance on interpretation of test results is given in Section 29.2.
21.7 PRESSUREMETER TESTS
21.1.1 Test Descr-ption
In a pressuremeter test, a probe is inserted k t o a pocket below the bottom of a borehole or directly into the appropriate size of borebole and avpanded laterdy by compressed a? or gas. The appfied pressures and resulthg deformations are measured and enable the strength and deformation characteristics of the ground to be investigated
The earlest instrument, and that in most general use, is the M h r d pressuremeter /&nard 1965). With this instrument, the lateral load is appled by a probe consisting of a water-filled central measuring cell flanked by two guard cells, either gas-Meed or water-/lied, depending on the type of ~ffstrument.
Readings are taken at the ground surface on pressure and volume gauges whkh are connected to the central cefl by means of a back-pressured annular pfastik tube. The pressure tube and probe must be calibrated on site. The function of the guard cefls is to ensure a condition of plane strain in the ground in contact with the central ceh! The probes are manufactured in four sizes up to 75 mm d~.meter, and can be operated at considerable depths. The Mknardpressuremeter can be used in soil or weak rock, but is not suitable for stronger rock, since the instrument I> fimited by its sensitivity to the tube calibration. I t can be used in granular soils where special means are used to insert it.
Another pressuremeter that has been developed has a 150 mm dimeter gas-expanded probe in which the deformation is measured directly by potentimeters located 1j7 the centre of the probe OfcXinlay & Anderson, 1979. It can be used to determine the deformation characteristics of the more deformable weathered rocks.
A wireline-operated push-in pressuremeter exists and has been in use in an offshore environment (Fyffe et al, 1986). Self-boring pressuremeters , which can b e inser ted in to some soil types with minimal d is turbance , have also been developed (Baguelin e t al, 1978; Windle & Wroth, 1977). Pressuremeter tes t ing in rock is described in Section 21.7.5.
21.7.2 Equipment Calibration
The probe and tubing of t h e pressuremeter r equ i re calibration on si te , a s follows :
(a) Pressure calibration. This is t o account for p r e s s u r e losses which occur because of s t i f fness of t h e r u b b e r membrane and slotted s tee l sheath of t h e probe.
( b ) Volume calibration. This is t o account for volume losses which occur because of expansion of t h e connecting tubes.
P ressure and volume calibrations should be car r ied o u t a t t h e beginning and end of a tes t ing programme, o r whenever lengths of connecting t u b e s a r e changed, new shea ths o r membranes are installed, a n y water line subjec ted t o vacuum o r p ressu re has been suddenly released, o r any o the r factor affecting
t h e calibration has changed. In addition, t h e hydrostat ic p ressu re due t o fluid in t h e t e s t equipment below t h e p r e s s u r e gauge should be determined prior t o each t e s t .
21.7.3 Forming t h e Test Pocket
The formation of a suitable test pocket is a crucial s t e p in pressuremeter tes t ing , a s t h e test data a r e obtained by radial expansion of t h e probe of only a few millimetres and even a th in d is turbed zone around t h e pocket will affect t h e resul t s . The test pocket must therefore be formed with minimal d is turbance of t h e sidewalls, and with t h e p roper diameter for t h e ins t rument t o b e used. The water f lush ro tary open hole drilling technique with open-ended casing ( ro ta ry wash boring, see Section 18.7.1) should not be used t o form t h e t e s t pocket. Briaud & Gambin (1984) have outlined pro- cedures for preparat ion of an acceptable t e s t pocket of t h e requi red diameter, a s well as methods of placing t h e probe and conducting t h e test.
21.7.4 Results and Interpretat ion
The t e s t is normally conducted by increasing t h e p r e s s u r e in equal increments and taking volumetric readings a t time intervals a f t e r application of each p ressure increment. Values of t h e soil deformation modulus are then in te rp re ted from these data. Winter (1982) has discussed t h e presentation and interpretat ion of resul t s for both g ranu la r and cohesive soils. A discussion of t h e application of t h e pressuremeter t o foundation design in Hong Kong is given by Chiang & Ho (1980).
21.7.5 Tests in Rock
In strong rocks, i t is necessary to use instruments of high sensifi'vity in wh12h the deformation of the rocks is measured over smell strain ranges by electronic transducers located within the probe. There are two types of instrument available : a flexibfe type, 73 mm in diameter, operated hydrau/icaly b y OH to a pressure of about I 4 MPa /Rocha et a/, 1966k and a rigid type, consisting of a steel cylinder spkt vertically into two halves and called the Goodman jack /Goodman et al, 19681. The rigid type I> afso operated hydraulically by oil but with a considerably higher pressure than the flexible type, and is therefore part12uMy suitable for rocks in the h e r modulus range.
The Goodman jack i s capable of exerting p ressures in excess of 60 MPa within a normal N X size borehole. A method of estimating t h e insitu modulus of deformation from t e s t s with th i s device is presented by Heuze (1984).
21.8 BOREHOLE DISCONTINUITY SURVEYS
21.8.1 Impression Packer Survey
An impression packer s u r v e y provides a n assessment of t h e orientation and a p e r t u r e of discontinuities in a borehole in rock by means of an inflatable r u b b e r membrane which p resses a n impressionable thermoplastic film agains t t h e borehole wall (Figure 34 and Plate 9 ) . The impression packer can be used t o provide da ta for t h e design of rock slopes, excavations o r tunnels (Brand et
al, 1983; Gamon, 1984a; S t a r r & Finn, 1979), and i t can be used in conjunction with t h e packer (water absorption) t e s t t o define t h e location, orientation and opening of discontinuities where high water losses have occurred.
The impression packer device is commonly available in s izes t o f i t N and H size boreholes. A borehole length of about 1.5 m can be su rveyed with each tes t , a f t e r which t h e device must b e withdrawn from t h e hole and t h e thermoplastic film changed. Tests can b e conducted a s drilling progresses , b u t more commonly a ser ies of overlapping t e s t s a r e r u n a f t e r drilling has been completed in o r d e r t o obtain a full s u r v e y of t h e borehole. Use of t h e device is usually res t r ic ted t o vert ical o r slightly inclined boreholes.
Care must b e taken when lowering t h e device into t h e borehole s o t h a t t h e thermoplastic film is not scuffed o r damaged. The packer may be inflated b y e i the r a i r p ressu re o r water p r e s s u r e applied th rough a cent ra l perforated tube . Two metal leaves, cu rved t o match t h e borehole wall, t he reby force t h e impressionable thermoplastic film agains t t h e borehole wall, causing a permanent impression t o be regis tered on t h e film. The device must b e fully deflated before removal, o r t h e film may be damaged.
The device may be orientated in t h e borehole in two ways, depending on t h e accuracy requi red :
(a) By positioning t h e two metal leaves in a known direction a t t h e surface , and subsequent ly marking th i s direction on each dri l l rod a s t h e device is lowered into t h e borehole. This method, sui table only in shallow holes and when drill rods a r e utilized, is usually only accura te t o about i5" in orientation a t best .
( b ) By t h e use of a n orientation ins t rument at tached t o t h e bottom end of t h e device. The orientation of a floating compass i s set within a fixative solution a t t h e time t h e packer is inflated, providing a record of orientation t h a t can la ter b e t r ans fe r red onto t h e thermoplastic film. Somewhat be t t e r accuracy may b e achievable with th i s technique.
I t i s recommended t h a t t e s t sections should b e overlapped to t h e extent t h a t a t leas t one discontinuity common t o adjacent sections is recorded. This will provide data for checking t h e north direction between successive impressions. Data from such s u r v e y s should also b e checked agains t re levant da ta from surface exposures whenever possible.
An example of an impression packer s u r v e y is given in Figure 35.
21.8.2 Core Orientators
Several devices a r e available fo r determining t h e orientation of drill core, of which t h e Craelius core orientator has been widely used (Hoek & Bray, 1981). This mechanical device is usually installed in a fixed orientation in a core-barre l , and i t initially p ro t rudes ahead of t h e ba r re l in o r d e r t o sense and record t h e contour of t h e rock surface. The core orientator t h e n proceeds up t h e core-barre l and core drilling commences. Upon re t r ieval of t h e core sample, t h e uppermost core segment can again b e matched agains t t h e core orientator and its relative orientation can b e determined. The remainder
of t h e core r u n may then b e oriented with r e spec t t o t h e uppermost core segment.
The Craelius core orientator can opera te in s teeply inclined o r horizontal boreholes a s well as vert ical holes, b u t it does not provide information on t h e a p e r t u r e o r infilling of discontinuities, nor does it provide a permanent record of discontinuities. In addition, t h e orientation of t h e core must be determined relative t o t h e uppermost core segment, and th is may prove difficult where core recovery is poor o r where t h e core contains sub-horizontal joints (Gamon. 1984a).
22, FREQUENCY OF SAMPLING AND TESTING I N BOREHOLES
22.1 GENERAL PRINCIPLES
The frequency of +mpfing and tesbhg in a borehole depends on the information that is &ready avdable about the ground condibbns and the techmkd objectives of the investigation. fn genera/, the field work w17l cover three aspects, each of which may require a different sampfing and tesbhg programme and may also requke phashg of operatrbns. These aspects are a s foflows :
(a) the determination of the character and geological s t ructure of the ground,
(b) the determination of the properties of the various zones o r materials whose locations have been determined in (a). using routine techniques for sampling and testing.
(c) the use of special techniques of sampling and testing in ground for which routine techniques may give unsatisfactory results.
22.2 DETERMINATION OF THE G R O U N D PROFILE
In areas where suitable information about the ground profile is available from previous investigations, it may be possible t o reduce the need for this aspect. Otherwise, it is necessary to determine as fa r as possible the location, character and s t ructure of each zone in the soil o r rock mass. Some zones may be quite thin, and continuous sampling of the entire borehole may be required in order to obtain the necessary information.
In soils derived from insitu rock weathering, colluvium and some fill materials. the ground profile can be defined by taking samples using a triple- tube core-barrel. Samples should be taken continuously o r a t close intervals supplemented by standard penetration tests. Continuous rotary coring should be undertaken in fresh to moderately decomposed rock. Where a run with the rotary core-barrel results in poor core recovery, it may be useful to t r y to recover a small drive sample using the split barrel SPT sampler. However. this does not obviate the need to adjust the rotary coring equipment and techniques in order to obtain the best core recovery possible.
In fie cohesive soi4 and some s~7ty sand consecutive drive samples can be obtahed using the 100 mm diameter sampler, or similar. In soft clay or sand the barrels of the sampler can be coupled together to form a sampler 1 m in length and, if necessary, the core-catcher can be used to help retah the samp/s. In soft days, it I> generdly g& practice to obtah a t least one complete profile for the site ushg the conC1;7uous &ton sampfing technique. Specid sampfing equ~bment is avayable for taklhg long continuous samples A soft clay, lmse sik and loose s a y sand /see Secbbn 19.6).
In coarse granular sofi such as gravel it J> advisable to take disturbed samples from the drill tools /see Section 19.31, together witb split barrel standard penetration test samples /see Section 19.4.5) at about 1 m fhtervds.
Some of the so17 samples obtained by drive sampfing or rotary cor~hg, if
not required for 'undisturbed' tests, should be spkt along their longitudinal axis and carefufly examined and described in their fresh condition. This exercise should be repeated later when soil is in a semi-dried state and the fabric may be more readily identified Where h~ghly variable ground conditions are expected, it may be advantageous to s1h.4 one or more boreholes first, either by rotary core samp/ng or by cable tool boring with conthuous tube sampling. The cores or tube samples can then be examined to give guidance for samp/ing at selected depths in other boreholes which are sunk subsequently close to the initial borehfes (see Sechon 22.4).
22.3 ROUTINE DETERMINATION OF SOIL AND ROCK PROPERTIES
Once t h e zones o r materials whose propert ies a r e likely t o b e re levant t o t h e technical objectives of t h e investigation have been identified, these proper t ies may be assessed using routine o r special techniques ( t h e l a t t e r a r e discussed in Section 22.5). The programme of sampling and tes t ing should be varied t o s u i t t h e part icular requirements of t h e investigation and t h e equipment t h a t is in use.
The following programme is an example of a reasonable sampling and tes t ing f requency where a borehole is being sunk th rough colluvium o r weathered rock in to f r e sh rock by means of ro tary coring :
(a) Colluvium and soils derived from insitu rock weathering. A t t h e top of each zone o r layer in t h e ground, and the rea f t e r a t 1.5 t o 3 m intervals . a n 'undisturbed' sample, i.e. class 1 o r class 2 sample (see Section 19.2), followed by a s t andard penetration t e s t should b e taken. A d is turbed sample should be recovered from t h e SPT sampler whenever possible.
( b ) Moderately decomposed t o f r e s h rock. Continuous ro tary core sampling should be undertaken.
22.4 DOUBLE-HOLE SAMPLING
In th is method. a borehole is f i r s t sunk t o ascertain t h e ground profile. A second borehole is then sunk adjacent t o t h e f irs t , b u t a t a sufficient distance away from i t t o avoid t h e d is turbed zone, and samples a r e taken at predetermined levels. This method may be used where high variability in ground conditions i s expected, e.g. in variable sedimentary deposits, o r fo r t h e location and sampling of t h e s h e a r zone material in a failed slope.
22.5 SPECIAL TECHNIQUES
Special techniques of sampling and test ing include t h e following :
(a) Sampling techniques. These include t h e use of sand samplers, piston samplers and continuous soil samplers.
( b ) Testing techniques. These include vane t e s t s , cone penetration tests, plate t e s t s , pressuremeter tests, packer tests and discontinuity surveys .
Some of the equipment used in these techniques IS fragile, and easily damaged ~Yused ~ i r unsuitable ground It shouldpreferab/y be used on/y where it is known that ground cond'bns are suitable.
Using a special sampfing technique, the frequency of sampling lir sand and in soft sensitive clay will in general be determined by s~inilar consider- ations to those given in Section 223. However, if the material requiring the use of a special sampling technique is of l~inited thickness, it may be adviable to take samples a t s d e r than usual depth intervals so as to obtain a sufficient quantity of that materiaL
In the borehole vane test, only the small volume of clay that is rotated by the vane IS tested, and individual results often show a considerable scatter. For this reason, vane tests should be carried out as frequently as possible. The vertical interval will be determined by the depth at which the test is carried out below the bottom of the borehole; this interval is usuafly 500 mm. Chser spacing can be obta~ned using the penetration vane apparatus.
The cone penetration, pressuremeter and packer tests , a s well as discontinuity surveys, are generally taken continuously, or such that complete coverage of the borehole is provided.
Where a ser~es of plate tests is required at increasing depths, the minimum spacing is determined by the depth to which the so17 has been stressed by the test. A vertical interval of about four times the borehole dimeter is usuafly adequate.
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23, PROBING AND PENETRATION TESTING
23.1 GENERAL
Probing from the surface probably represents the oldest method of inves&gating the depth to a hard layer where the overlying material I> weak and not unduly thick. The simplest probe is a sharpened steel rod wh12h I> pushed or driven into the soil unt2 it meets resistance. The method I> st~i'l of use where other means of site investiga&on have d'sclosed relatively t h ~ n layers of very soft soils overlying much harder sods. In such cases, the th~kkness of the soft layer may be determined over a wide area very quickly and economicdly. The method has many binitations, and a vatiety of more sophisthated apparatus has been developed, both in an attempt to overcome these drawbacks and to extend the use beyond that of detecting a hard layer, e.g. to give some measure of the affowable bearing capacity of the s017s present. Two distinct types of probe have been developed : one where the probe is driven into the sod by means of some form of hammer blow the other where the probe is forced into the so11 by a s t a t k load.
23.2 DYNAMIC PROBING
The appara tus for dynamic probing comprises a sectional rod f i t ted at t h e end with a cone whose base i s of g rea te r diameter t h a n t h e rod. I t i s dr iven in to t h e ground by a constant mass falling th rough a fixed distance. A device commonly used in Hong Kong is t h e GCO Probe (Figure 36 and Plate 10A). which is essentially a l a rge r and heavier version of t h e Mackintosh Boring and Prospecting Tool. Probe resu l t s are v e r y useful fo r assess ing t h e dep th and degree of compaction of buried fill, making comparative qualitative assessments of ground characteris t ics , and in supplementing t h e information obtained from t r ia l pits and boreholes. Probing has also been carr ied o u t in t h e base of hand-dug caissons (Evans e t al, 1982). Probe resu l t s are normally repor ted a s t h e number of blows pe r 100 mm penetration, as shown in Figure 37.
A s additional r o d s a r e added fo r probing a t depth , t h e driving ene rgy provided t o t h e t ip is at tenuated by t h e additional mass of t h e rods. Correction of t h e probe values is sometimes made t o allow fo r t h i s effect. The correction is negligible at t h e shallow dep ths a t which many probings terminate, and i t is unnecessary to apply a correction if only qualitative comparisons between probe resul t s at similar dep th a r e being undertaken.
The fac t t h a t t h e rod and couplers are somewhat smaller in diameter than t h e base of t h e cone prevents , t o some extent , sha f t friction from influencing t h e resul t s ; however, at dep th in cer ta in soils, t h i s fac tor should also b e considered.
The primary use of dynamic probing is t o interpolate da ta between t r ia l pi ts o r boreholes rapidly and cheaply. Therefore, probing should f i r s t b e car r ied o u t adjacent t o a t r ia l pi t o r borehole where ground conditions are known, and then extended t o o the r areas of t h e site. A s with o the r t y p e s of penetrometers, probing may 'sometimes b e unsuccessful in soils containing corestones, cobbles or boulders. In fill o r completely decomposed rock, t h e maximum depth t o which a GCO probe can be dr iven is about 15 m. In o r d e r t o minimise damage t o t h e equipment, probing should terminate when t h e blow count reaches 100, o r when t h e hammer bounces and insignificant penetration
i s achieved.
23.3 STATIC PROBING OR CONE PENETRATION TESTING
23.3.1 General Description
Several t y p e s of s ta t ic probing equipment have been developed and a r e in u s e th roughou t t h e world (De Ruiter, 1982; Sanglerat. 1972). The basic principles of all systems a r e similar, in t h a t a rod is pushed in to t h e ground and t h e res is tance on t h e t ip (cone resistance) i s measured by a mechanical, electrical o r hydraulic system. The res is tance on a segment of t h e rod sha f t (friction sleeve resistance) may also b e measured. Static probing, o r cone penetrat ion test ing, i s also known by a number of o t h e r descript ive terms. depending on t h e manufacturer o r opera to r of t h e part icular device being used.
There is no British Standard for cone penetration tes t ing , b u t suitable recommendations a r e given b y t h e ISSMFE (1977) and t h e ASTM (1985k). Both of t h e s e t e s t s t a n d a r d s recognize a number of traditional t y p e s of penetro- meters, a n d i t is imperative t h a t t h e actual t y p e of ins t rument used is fully documented, as t h e in terpre ta t ion of t h e resul t s depends on t h e equipment used. Two common t y p e s of penetrometers, mechanical and electrical, a r e described f u r t h e r in Sections 23.3.2 and 23.3.3 respectively.
The reaction requi red to achieve penetration of t h e cone may be obtained by screw anchors, t h e weight of t h e th rus t ing machine, kentledge. o r a combination of these. When cone penetration tes t ing is done in shallow water , t h e th rus t ing machine may b e secured t o a jack-up platform (see Section 14.7).
23.3.2 Mechanical Cone Penetrometers
Two common mechanical cones, t h e Dutch mantle cone and t h e Dutch friction sleeve cone, a r e shown in Figure 38 (see also Plate 10B). These cones were developed mostly at t h e Delft Soil Mechanics Laboratory in t h e 1930's. With e i the r type , t h e cone is pushed in to t h e ground by a ser ies of hollow push rods. With t h e mantle cone, t h e force on t h e cone is then measured as t h e cone is pushed downward by means of inne r rods inside t h e push rods. This force i s generally measured at t h e ground su r face by a hydraulic load cell. With t h e friction sleeve cone, t h e same initial measurement is made, and t h e n a second measurement is taken while t h e cone and friction sleeve a r e toge the r pushed downward a f u r t h e r increment. The friction is calculated by deducting t h e former reading from t h e lat ter . This procedure is normally repeated a t r egu la r dep th in tervals of 0.2 o r 0.25 m.
An al ternat ive quick continuous method of penetrat ion is sometimes used with t h e mantle cone. In th i s method, t h e cone and push r o d s a r e pushed in to t h e ground with t h e cone permanently extended a n d connected t o t h e load cell. Accuracy is reduced in th i s operation, however, a n d t h e f r ee movement of t h e cone should b e checked at f r e q u e n t intervals .
For accurate work, the weight of the inner rods should be taken into account in calcufai2ons. In very soft soils when sound~ngs are carried to a significant depth, the weight of the Inner rods may exceed the force on the cone or cone plus jacket; in these c~kcumstances, it is lhpossible to obtai~ readings. Thzk effect can be reduced b y the use of alumzhium inner rods. The
inner rods should be free to slide ins]-de the push rods, and the cone, and fr~ktron jacket where used, should be checked for free sliding both at the start and at the end of each penetratron test. All push rods and inner rods should be straight, clean and we//-oiled in terdy . The accuracy of the load and pressure gauges should be checked period~'cally by calibratron.
23.3.3 Electrical Cone Penetrometers
A number of types of electr~'cally-operated cone are in use, and these generafly lhcorporate vibratrng wire or impedance strain gauges for measuring the force on the cone and fr~ktron jacket. In use, the cone ~k advanced at a uniform rate of penetratron by pressure on the top of the push rods, and signals frm the load-measur~hg devl'ces are carried to the surface by cable threaded through the push rods. Forces on the cone, and frictron jacket, can either be dlkplayed on a readout at the surface or recorded autmatrkally on a chart recorder, punched tape or magnetr'c tape. Exclusive recording on punched tape or magnetrk tape which does not allow direct access to the data during or immediately after sounding 13 not recommended Provision should be made for calibration of the force-measurlhg system at regular intervals, preferably on site. An inchnometer built into the cone is avdable with some equ~;Oment.
The cones are generafly parallel-sided, and the friction jkcket, where fitted, ~k immediate& behind the point, as shown Figure 39a (see also Plate 10B). However, parallel-sledded electrical cones do not give exactly the same results as those obtained witb the mechanical cone penetrometer, altbough the dfyference is usudy of little hportance. Electr~kal cones with a profile modified to give better agreement witb the mechanical cone are also avadable /Figure 39b and cl.
One particular type of electrical cone penetrometer is the "Brecone", which has a combined 5 kN and 50 kN force measurement range (Rigden et al, 1982). I t has the advantage of being able to measure cone resistances in clays containing dense sand layers without suffering damage to the more sensitive load cell.
The recently developed "piezocone", which incorporates a pore pressure transducer within an electrical cone, has also found application in some Hong Kong marine investigations (Blacker & Seaman, 1985: Fung et al, 1984: Koutsoftas et al, 1987)
23.3.4 General Recommendations
The following general recommendations apply to cone penetration testing. whether undertaken with mechanical o r electrical cone penetrometers :
fal The cone cross-sectronal area should be 1 000 mm? and the cone apex angle should be 605
fbl The fricclbn sleeve, JT present, should have a surface area of 15 000 mm 3.
fcl The rate of penetration should be 20 r 5 mm/s.
/dl Force measurements should be accurate to wfthin ?5% of the maximum force reached in the test.
23.3.5 Uses and Limitations of t h e Test
The cone penetrometer test is relatively quick to carry out, and inexpensive in cornparson with boring, s@ng and laboratory testing. It has traditonaily been used to predict driving resistance, skin fricoon, and the end bearing capacity of driven p17es in granular soils. In recent years, the cone penetrometer test has also been used to give an indication of the contJfluous soil profile by interpretation of the r a t 0 of friction sleeve and cone resistances. In addition, there is substantial pubfished informtion relaohg cone resistance value with other soil parameters.
The cone penetrometer test is also the preferred substitute for the standardpenetration test in soil conditons where results of the latter test are suspect, and where hard driving is not antbpated. The test is aIso commonly used as a rapid and economical means of interpolating between borehok. Although it may be possible to estimate the type of so17 through which the cone is passing a s described above, it is preferable to carry out the test in conjunction with some other means of determ~h'ng the nature of the soil present.
Cone penetration is limited by both t h e safe load t h a t can b e car r ied by t h e cone, and t h e t h r u s t available fo r pushing i t into t h e ground. I t is also limited by t h e compressive s t r e n g t h of t h e inner rods ; some machines are capable of c rush ing t h e inner rods before t h e r a t ed capacity of t h e machine is reached. Because of limited cone capacity, penetration normally has t o b e terminated where dense sand o r gravel, highly t o moderately decomposed rock, o r cobbles are encountered. For th i s reason, cone penetration tes t ing in Hong Kong has been limited t o t h e Recent alluvial and marine sediments.
23.3.6 Presentation of Results
Results are normally presented graphicfly with cone resistance /and local skin friction where a fricton jacket cone is used) plotted against depth. The friction ratio, defined a s ffricton resistance/cone resistance) x 100, may also be plotted agru'nst depth. This ratio is used to assist in interpreting the soil type penetrated. Suitable scales for plotting the results are given in ISSMFE UP??).
23.4 STATIC-DYNAMIC PROBING
The s t andard penetration test is r a t h e r insensi t ive in loose materials and i s not t r u l y re levant t o cohesive soils. On t h e o the r hand, t h e cone penetrometer is of limited u s e when dense o r stiff layers a r e encountered. The static-dynamic test combines t h e two methods (Sherwood & Child, 1974); t h i s technique i s f u r t h e r discussed in BSI (1981a).
PART V FIELD AND LABORATORY TESTS
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24, FIELD TESTS
24.1 GENERAL
Field tests are generally des~rable where it is considered that the mass characteristics of the ground would differ appreciably from the material characteristics determined by laboratory testrhg. These differences generdy arise from several factors, the most important of which are the extent to which the laboratory samples are representative of the mass, and the qua/ity of the sample that can be obtained for laboratory testing. Factors affecting sample quality are dealt with in Chapter 12 and attention is drawn to factors affecting the representative nature of a laboratory s.wn.de. These factors are partly related to the insitu cond12ions of stress, pore pressure and degree of saturation, and can be altered from an unknown insitu state by the sampling processes. Consequently, their influence cannot be accounted for in laboratory testhg.
The material tested insitu by a field test is analogous to a laboratory sampJe, and can be considered a s a 'field same'. The insitu conditrbns of a field sample may be affected by the process of gaining access to the test position fe.g. digging a trial p i0 but, generafly, the effect is very much less than for a laboratory sarn.de.
More obvious, however. are the controfled effects of the nature, orientation, persistence and spacing of dicontinuities fGeolog~kal Society, 19721, the nature of any infilfing, and the size of sample required for it to be representative. To ensure that they are representative, the selection and preparation of samples in the field is subject to the same requirements a s for laboratory s a d e s . Considerable attent~on should be given in the field to these aspects, because, generdy, fewer field tests can be carried out than laboratory tests.
The size of sample tested in a fild test w17l depend on the nature of the ground and type of test, and may vary from a fraction of a metre, such a s in the insitu triawial state of stress measurements, to several metres for fied tri;?/s, to one or two kilometres in the pumping test.
Field tests may therefore be necessary where the preparation of representative laboratory samples is complicated by one or more of the following conditions :
fal The spacing of the discontrnuitres in the mass being considered is such that a .sa.w.de representing the mass, including the discontinuitl'es, wouM be too large for laboratory test equipment. The discontinu~'tres are assumed to govern the geomechanical response of the mass relative to the scale of the engineering structure concerned
fbl There is difficulty in obtaining samples of adequate quality owing to the lack of cohesion or ~ireversible changes in mechanical propertres, resulting from changes in pore pressure, degree of saturation and stress environments during sampLing and from physical disturbance resulting from the samp/ing procedure.
(cl There is difficulty in determining the ~hs i tu conditions such as those of pore pressure, degree of saturation, and stress environments for reproduction in the laboratory testing.
/dl Sample disturbance due to delays and transportation from remote sites is excess~'ve.
The locations and levels of all field tests should be fully recorded dur ing t h e execution of t h e work. The records should be such t h a t t h e locations and levels can be readily incorporated into t h e r epor t on t h e investigation (see Sections 10.5 and 40.2.8).
Some field t e s t s a r e relatively inexpensive and a r e under taken on a routine basis (e.g. field densi ty t e s t s described in Chapter 27, t h e various borehole and penetration t e s t s previously described in Chapters 21 and 23, and t h e index t e s t s described in Section 24.2). Other field t e s t s a r e expensive and must be designed specifically t o account for both t h e na tu re of t h e works and t h e cha rac te r of t h e ground mass. These la t te r t e s t s should not be under taken before a comprehensive unders tanding of t h e geology and na tu re of t h e ground has been obtained.
24.2 R O C K STRENGTH INDEX TESTS
24.2.1 Point Load S t reng th
The point load s t r e n g t h index t e s t measures t h e s t r e n g t h of rock material by means of a concentrated load applied t o specimens of rock core o r i r regular lumps of rock (Figure 40). The t e s t gives an indi rec t measure of t h e tensile s t r e n g t h of t h e rock, which has been correlated with t h e uniaxial compressive s t r e n g t h (Bieniawski, 1975; Broch & Franklin. 1972; Norbury, 1984). The t e s t resul t s a r e a useful aid t o rock description and classification ( G C O , 1988). The point load s t r e n g t h s of some Hong Kong rocks a r e discussed by Gamon (1984133, Irfan & Powell (1985) and Lumb (1983).
A s t andard t e s t procedure has been recommended by t h e ISRM (1985). Specimens of rock core can be tes ted in e i ther an axial o r diametral mode, as can i r regular lumps of rock, provided specified shape cr i te r ia a r e met. The t e s t r e su l t s a r e dependent on t h e size of t h e specimen tes ted , and a 50 mm s tandard reference diameter has been selected for t h e repor t ing of results .
The t e s t is intended t o measure primarily t h e in tac t s t r e n g t h of t h e rock material, and specimens for tes t ing should therefore b e selected t o meet t h e necessary shape cr i te r ia without incorporating discontinuities. Similarly, t h e failure surface from each t e s t should be examined, and i f t h e failure passes along a discontinuity, t h e t e s t r e su l t should be discarded.
The main advantages of t h e point load t e s t a r e t h a t a la rge number of t e s t s can b e completed rapidly, with minimal sample preparation. The t e s t equipment is easily portable, and by tes t ing samples of t h e same material in various orientations, indications of s t r e n g t h anisotropy and tensile (spl i t t ing) s t r e n g t h of discontinuities can be obtained.
Point load tests can be car r ied o u t in t h e field o r in t h e laboratory. In e i ther case, t h e visual examination and logging of samples described in Section 36.3 should be under taken prior t o test ing. a s t h e t e s t is destruct ive.
24.2.2 Schmidt Hammer Rebound Value
The Schmidt impact hammer can be used t o measure t h e ha rdness of rock. This device, originally developed t o measure t h e ha rdness of concrete, measures t h e rebound of a spring-loaded piston from a metal anvil res t ing on t h e su r face to be tested. The height of t h e piston rebound i s taken a s an empirical measure of rock hardness , a n d th is value has been correlated with rock and weathered rock propert ies (Hencher & Martin, 1982; Hucka. 1965; Irfan & Powell, 1985).
The Schmidt hammer i s a portable, hand-operated device a n d i s available in two models, i.e. t h e L t y p e (impact ene rgy of 0.735 N-m) and t h e N t y p e (impact e n e r g y of 2.207 N-m). The N Schmidt hammer i s more robus t , and generally t o be prefer red fo r field tes t ing of rock exposures. Brown (1981) recommends a s t andard t e s t method for t h e t y p e L hammer, b u t t h e recommendations a r e equally applicable to t y p e N hammers.
Although t h e Schmidt hammer i s quick a n d easy t o use, g r e a t c a r e should b e taken when tes t ing weak rocks , o r any rock su r face which i s rough , c racked o r f i ssured . In s u c h cases. i t i s recommended t h a t a number of seat ing blows a r e taken initially, t o e n s u r e a good contact between t h e rock su r face and t h e hammer head. Poole & Farmer (1980) concluded t h a t reliable values could be obtained by ignoring artificially low readings and selecting peak rebound values from a minimum of five consecutive impacts at a point. The Schmidt hammer i s relatively insensi t ive on v e r y weak rocks which yield rebound values below 10, and i t cannot b e used on rock core unless t h e core i s held in a heavy vice o r a s teel cradle.
The Schmidt hammer t e s t provides a rapid quanti tat ive assessment of rock ha rdness and i s sui table fo r use in trial pi ts o r caisson excavations. o r on su r face exposures. Use of t h e t e s t r e su l t s i s discussed f u r t h e r in Geoguide 3 ( G C O . 1988).
24.3 INFILTRATION TESTS
The limiting infiltration r a t e fo r water enter ing t h e soil can be determined with a double r ing infiltration t e s t (F igure 41). The t e s t i s commonly car r ied o u t a t t he bottom of a t r ial p i t o r caisson. Water i s fed from graduated bottles t o t h e exposed soil su r face in t h e inne r r ing , and t o t h e annu la r space between t h e r ings. The amount of water flowing o u t of t h e bottle i s measured with time. The flow u n d e r s t eady-s t a t e conditions i s used t o determine t h e limiting infiltration r a t e (Figure 42). Because of t h e percolating water from t h e o u t e r r ing ( t h e 'buffer zone'), water within t h e i n n e r r ing i s constrained t o infi l t rate vertically in to t h e ground, resul t ing in a flow with approximately uni t hydraulic gradient . Therefore, t h e limiting infiltration r a t e is roughly equal t o t h e ' sa tura ted ' field permeability of t h e soil. In pract ice, complete sa tura t ion of t h e ground may not occur d u e t o en t rapped a i r in t h e soil voids, in which case t h e t e s t r e s u l t will only give a lower bound value f o r t h e sa tu ra t ed permeability (Schmid, 1966). The t e s t can b e performed a t success ive dep ths t o give a complete permeability profile.
I t i s also possible t o perform simpler s ingle r ing infiltration t e s t s and c r u d e soakaway t e s t s (i.e. timing a known water head loss in a s teel t ube , hole o r t r ial pit of s t andard dimensions). However, i t must be appreciated t h a t no buf fe r zone i s provided in s u c h t e s t s t o encourage vert ical infiltration. The r e su l t s may be useful in a comparative sense b u t should not be r ega rded a s an
142
indication of the true permeability of the soil.
25.1 GENER :AL PRINCIP
25, PUMPING TESTS
LES
In principle, a pumping test involves pumphg at a steady known flow from a well and observing the drawdown effect on groundwater levels at some distance away from the pumped welL In response to pumping, phreatic and piezometric leveh around the pumping we// will fall, creating a 'cone of depression'. The permeability of the ground is obtained by a study of the shape of the cone of depression, which is indicated by the water levels in the surrounding observation wells. The shape of the cone of depression depends on the pumping rate, the duration of pumping, the nature of the ground, the existence, or otherwije. of intermediate or other boundaries, the shape of the groundwater table, and the nature of recharge.
From the data obtained from the test, the coefficients of permeabifity, transmissivity and storage can be determined for a greater mass of ground than by the use of the borehole tests described in Chapter 21. The results can be used in the evaluation of dewatering requirements and groundwater resources, as we// as in the design of positive groundwater cut-offs. It shouh' be noted that a given coefficient of transmissivity can result from many different distributions of permeabifity wfth depth. I f the test is intended for the evaluation of permeability in the design of dams and other similar projects where seepage is an important consideratrun, the use of down-the-hole vel0c1'ty pmfifing a t constant outflow can provide a permeabifity prome of the ground.
Pumping tests can be expensive, requiring adequately screened and developed pumping and observation wens, suitable pump~hg and support equipment, andpersonneL Care should be taken therefore to design a suitable test programme. Before attempting to carry out a pumping test, refiab/e data should be obtained on the ground prohi/e, if necessary by means of boreholes sunk especidy for the purpose. The geolog~kal units encountered may then be grouped into hydrolog~'cal units on the basis of permeabifity ( Leach & Herbert, 1982).
The naturaf groundwater conditrons should be determined by careful monitoring over a sufficient period before the pumping test. Ideafly, the conditlbns should be stable during the test; Lf they are not, the fluctuat~bns have to be recorded.
Fluctuations can be caused by rainwater infiltration, tides, groundwater extraction from wells, and nearby construction activities. This i s particularly important in highly permeable ground subject to rapid recharge.
The interpretation of the data from a pumphg test can be .compficaated and is much affected by the inferred ground conditrbns and by the influence of any boundaries. Where necessary, expert advice should be sought.
In Hong Kong. pumping tests have been used occasionally to determine hydrogeological parameters (as described above) but are more often carried out for the purpose of estimating the yield of water wells. They are also conducted occasionally to provide data for the design of major dewatering schemes associated with the construction of deep basements. The possible effects on adjacent ground and structures, e .g. settlements and inducement of negative skin-friction on piles, should be carefully considered before conducting a pumping test ( see Section 8.3.2(e)). Pumping test proposals for
private developments must be submitted to the Buildings Ordinance Office for approval and consent prior to the commencement of works (see Appendix A.8).
25.2 CROUNDWA T ' CONDITIONS
There are two main types of groundwater conditons, confined and unconfined. and these shouh' be recognized for analybbal and design purposes.
fa) Confined. I f the ground under investr'gation is fufly saturated and the water is confined under pressure between two impermeable layers, then confined conditions are said to exist.
fbl Unconfined. If the original phreatib level is everywhere below the upper surface of the aquifer, then unconfined conditions are said to auist.
Intermediate between the above two groundwater conditbns is a third called the semi-confined condition. In this case, fully saturated ground is overlain by material of signficant but lower permeabi/ity, and s~gnificant leakage takes place across the boundary in response to pumping. Andysis of data from semi-confined conditions is possible, but the condition 15 less commonly encountered than the other two types.
The three types of groundwater conditions may be recognized by the t e s t response (BSI , 1981a).
25.3 TEST SITE
Although the choice of test site may be dictated by practibd con- siderations, such as access and avai/abjXty of existing borebolees. the site should be representative of the area of interest. The hydrological conditions should not change appreciably over the site. It IS essental that discharged water is not able to return to the ground under test.
25.4 PUMPED WELLS
Pumped wels shouh' be of sufficient dlhA9ter to permit the inserton of a rising main and pump of a suitable type and capacity, together with a standpl;oe and velocity meter, if required. They should be provided witb an adequate well screen, and fifter pack where necessary, to prevent the with- drawal of fine part'des from the surrounding soil. The minimum borehole d~ameter whkb will achieve this purpose is often 300 mm. It is desirable that they penetrate the full depth of the water-bearing zone being tested. Where the ground is composed of two or more independent horiions, each should be tested separately. Where fufly penetrathg cond12ions do not exht, the data have to be corrected before analysis. In a// cases, the screen intake area shoula' be such as to ensure that the maximum velocity of water enter~hg the well is not greater than about 30 mm/s to ensure that hydraufic well looses are of an acceptable /eve/.
I6 during the test, changes in the shape of the cone of depression that are due to extraneous causes are a significant fraction of those due to pumping, then the resulthg estimate of permeabi/ity may become unacceptable.
Such influences can be corrected by monitoring Mdton, l962/, both before and d u r k testing. Where possible, and within the limitations set by the permeability, the pumping rate should be chosen so that resulting changes in water leveh are much greater than those due to extraneous causes, thus minimizing the effects of the latter on the results.
Suctlbn pumps can be used where the groundwater does not have to be depressed by more than about 5 m below the htake chamber of the pump, and drawdown can be increased by setting the pump in a pit. For greater depths, submersible pumps are preferable. The more permeable the ground, the greater the pump capacity required to produce measurable drawdowns in the observation we&.
It is essenh.d that the dlicharge is kept constant for the durahon of the test and that a// the water level observahons are related to a hhe-scale referred to the onset of pumphg.
It particu/ar/y important to mahtmh a constant pumping rate when vertical flow velou'ties in the pumping well are being measured for the purpose of determining the relative permeab~jrihes of spec~zc horiions in the ground under test. The pumping rate may be cohtroM by a gate valve in the discharge fine or by varying the speed of the pump, or both. The rate of flow from the pump may be measured by a flow or or12ce meter, or by a notch tank with automahk recordng.
It is important that pumping wefls should be adequate& developed. Development of a well is the process by which particles surrounding the screen are rearranged, with coarsening grade and better uniformity towards the screen; it can be achieved in a number of ways (Johnson, 1982). Maximum development is ind~kated when the ratio of pumping rate to fall in water level in the pumping we/l reaches a maximum. Fine partices from the ground are removed during development, resulting in a stab& porous and permeable medium surrounding the welL
Successful well development resul t s in reduced hydraulic head losses a s t h e water e n t e r s t h e pumping well but , i n any case, these losses (well losses) should b e accounted for in t h e analyses of t e s t resul ts .
In Hong Kong, pumping tests a r e sometimes carr ied o u t in la rge diameter hand-dug caissons. This has several disadvantages, a s t h e caisson may only par t ly penet ra te t h e aqui fer being tes ted , and t h e well s to rage is large. Also. high well losses a r e often incur red , and for th i s reason observation wells should always be used in conjunction with pumping tests in caissons.
25.5 OBSERVATION WELLS
Observation wells should have an in ternal diameter la rge enough t o permit insertion of a dipmeter o r o the r water-level measuring device, b u t if t h e diameter . is too large th is may cause a time lag in drawdown. Standpipes with an internal diameter of 19 mm a r e often used. Observation wells should penet ra te t h e same ground a s t h e pumping well and should permit e n t r y of water from t h e full dep th of ground being tested. If the re i s any r i sk t h a t f ine soil particles may clog t h e observation wells, t hey should be su r rounded by a sui tably graded f i l ter material.
Although the permeab~jrity of the ground may be estimated from the
pumping wel/ drawdown data alone, more reliable values are obtained using data from one or more observa&on web. The recommended mh~inum number of observation weh's required to yield reasonably representative results is four, arranged in two rows at right angles to each other. Their distances from the pumping we// should approx~inate to a geometr~kal series. It may be necessary to add more wefls if the initlal ones yield anomalous data. I f linear boundary conditions are associated with the site /e.g. river, canal or an impermeable subsurface bedrock scarp, fault or dyke), the two rows of observation wells are best arranged p a r a m and normal to the boundary.
The mh~inum distance between observafion wells and the pumphg well should be ten times the pumping we// radius, and at least one of the observation wells in each row shouh' be at a radid distance greater than twice the thickness of the ground being tested. However, unless the pumping rate is very hgh, and the duration of pumping long, partrkularly in low permeability ground under unconfined conditions, falls in water levels may be s W at such distances. Prehininary calculations using assumed permeabifities esthated from borehole data wifl help to indicate the fikely response in observation weUs to pumping. Hence the appropriate distance of the observation wells from the pumping we// and the th ing o f observations can be assessed.
In additon to the observation wefls described above, it is desirable to have an additional standpipe inside the pumping well in order to obtan a rehkble record of the drawdown of the well itself
Depths to water levels shou/d be measured to within 25 mm. This usua//y means that measurement devices have to be checked at regular ~ n t e r v i agahst, for example, a graduated steel tape.
The water levels can be monitored with either an electrical dipmeter or an automatic well level recording system.
25.6 TEST PROCEDURES
Once the character of fluctuatJons and other extraneous influences has been established, the test programme designed and the wels developed, pumping of the ground at a constant rate should commence. Water levels in a// we& are then measured with respect to time since commencement of the pumping. Typically the frequency of measurement might be at 1 m ~ n h t e r v a h for the first 15 min and at regular logarihmic intervals thereafter. Some- times, shorter intervals may be required initially. Therefore each wefl may have to be monitored b y independent observers for the first 100 min, and then b y one or more observers thereafter. In distant observation we& where head changes are smdd automatic recorders can be used, although these generdy require observation wells of 100 mm d~ameter or greater.
The measurements should be plotted during the course of pumping to evaluate the quality of the data, the nature of the response, and the required duration of pumping. Johnson (1982) and Kruseman & DeRidder (1980) have discussed the time requirements for both steady and non-steady state pumping tests carried out on confined, semi-confined and unconfined aquifers.
In all cases, water levels shou/d continue to be monitored wit15 respect to time from cessation of pumping unM recovery of levels to the original values is complete. A s in the drawdown phase, recovery data shouM be taken at 1 m h intervals for 15 mi' following cessa&on of pumping and thereafter at
regular intervals on a logarithmic scale.
25.7 ANALYSIS OF RESULTS
There a r e two forms of analysis of pumping test data :
(a) Steady state . If pumping continues long enough, water levels cease t o fall, and t h e hydraulic condition of t h e ground is said t o be in a s teady s t a t e with r e spec t to time.
( b ) Non-steady s ta te . Before equilibrium is reached, water levels fall at a changing r a t e with respect to time and t h e hydraulic condition of t h e ground is said t o be in a non-steady state.
The simpler form of analysis is t h e s teady s t a t e type , b u t t h e necessary duration of pumping can b e significantly longer t h a n t h a t necessary fo r non- s teady s t a t e analysis. The analysis technique is also dependent on aquifer response, i.e. whether confined o r unconfined conditions are present . A summary of some of t h e available analysis techniques is given in BSI (1981a). and t h e s e a r e f u r t h e r discussed by Johnson (1982) and Kruseman & DeRidder (1980).
A number of simplifying assumptions regarding ground conditions are required in whatever method of analysis is used, and i t is therefore common t h a t t h e actual drawdown da ta collected in t h e field may lead t o ambiguities in t h e analysis. This may.be caused by inhomogeneity and anisotropy in t h e aquifer , o r t h e presence of unknown b a r r i e r s to groundwater flow. In some cases , high flow velocities around t h e well may invalidate t h e use of Darcy's law, upon which most methods of analysis are based.
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26, DISCONTINUITY SURVEYS
26.1 GENERAL
Discontinuities such a s joints usually control t h e mechanical behaviour of a rock mass. Where surface exposures o r outcrops of t h e rocks exist, a joint s u r v e y may be car r ied o u t t o a s sess t h e r i sk of joint-controlled instability, e.g. in c u t slopes and excavations.
The methods and equipment used t o c a r r y out a joint s u r v e y a r e described in ISRM (1978). and techniques for analysing t h e r e su l t s a r e given by Hoek & Bray (1981). Fur the r guidance on joint su rveys and description can b e found in Geoguide 3 ( G C O . 1988).
During analysis, ca re must be taken t h a t rare b u t critical joints a r e not overlooked by t h e usual statistical methods of da ta sor t ing (Beattie & Lam, 1977: Brand e t al, 1983). An experienced supervis ing engineer o r geologist ( see Section 15.3) should visi t t h e s i te t o examine in detail t h e na tu re of those discontinuities t h a t have been identified a s critical. The slope o r exposure should be examined again dur ing construction for t h e presence of unfavourable joint sets not identified in t h e su rvey . The need t o c a r r y o u t a joint su rvey fo r c u t slopes formed in soils derived from insitu rock weathering should also b e considered; unfavourably orientated relict joints may cause slope failures.
26.2 DISCONTINUITY ROUGHNESS SURVEYS
I t i s often not possible t o account fully fo r discontinuity roughness in an insi tu o r laboratory s h e a r tes t , due t o limitations on t h e length of t h e joint plane which can be tes ted in s t andard equipment, and on t h e selection of representa t ive sampling points. Therefore, discontinuity roughness s u r v e y s a r e often under taken t o supplement such t e s t s .
Procedures fo r under taking and in terpre t ing field roughness s u r v e y s a r e described in detail by t h e ISRM (1978). The most commonly-used method is t o employ a s e t of thin circular plates of various diameters. These are taken in to t h e field and a series of discontinuity dip directions and dip angles a r e measured in t u r n for each plate when placed on t h e discontinuity surface. The accuracy of these measurements is improved by taking a la rge number (e.g. 50 o r more) readings for each plate and by ensur ing t h a t t h e discontinuity su r face i s relatively la rge and reasonably representa t ive of a part icular joint set. The resu l t s a r e often presented as contoured polar diagrams on an equal-area s tereographic projection. The smallest base plate will give t h e la rges t sca t t e r of readings and t h e la rges t roughness angles (and vice versa) . A graphical plot of maximum roughness angles v e r s u s plate diameter i s often used t o a s sess t h e sensi t ivi ty of t h e relationship between roughness angle and length of potential shea r displacement along t h e discontinuity plane.
The main engineering use of a field roughness s u r v e y is for t h e assess- ment of design values of discontinuity s h e a r s t r e n g t h (Hoek & Bray, 1981). This is achieved b y combining t h e s u r v e y resul t s with da ta from di rec t s h e a r t e s t s o r assumed basic friction angles. Methods fo r in terpre t ing t h e contribution of roughness t o discontinuity s h e a r s t r e n g t h in Hong Kong grani te a r e discussed by Hencher & Richards (1982); t h e application of a roughness s u r v e y a t an engineering s i t e in North Point. Hong Kong i s described by Richards & Cowland (1982).
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27, FIELD DENSITY TESTS
27.1 G E N E R A L PRINCIPLES
Field test ing of soil bulk densi ty is a common and useful procedure. When coupled with moisture content determinations, t h e test resul t s can be used t o obtain t h e d r y densi ty of t h e soil. A major use of such test ing is for t h e control of compaction of embankments, where i t forms t h e 'field' portion of a relat ive compaction t e s t ( the o the r portion of t h e t e s t being carr ied o u t in t h e laboratory). Field density tes t ing may also be used in evaluation of insitu materials and old fills, where i t provides a direct determination of densi ty t h a t is independent of t h e sampling d is turbance normally p resen t in laboratory tes ts .
In essence, most of t h e available methods of field densi ty test ing depend on t h e removal of a representa t ive sample of soil, followed by determinations of t h e mass of t h e sample and t h e volume i t occupied prior t o removal. However, t h e nuclear methods discussed in Section 27.7 a r e a n exception t o th is general rule. Mass determinations a r e relatively straightforward b u t accura te measurements of sample volume a r e more difficult and may lead to significant variations in t e s t resul t s , depending on t h e technique used, which is in t u r n dependent on t h e na tu re of t h e soil being tested.
All t h e t e s t methods described below requ i re physical access t o t h e soil insitu. Therefore, they a r e normally res t r ic ted t o soil within 2 t o 3 m of t h e surface, al though t h e y can also be used equally well within caissons o r shafts . Use of t h e nuclear probe technique is a n exception t o th i s dep th limitation.
The methods described generally measure bulk density, and representa t ive moisture contents a r e requi red if t h e d r y densi ty is t o be calculated. Ideally, t h e weight of t h e moisture content sample should be determined on site, t hen t h e sample should be t r anspor ted t o the laboratory for oven d ry ing in accordance with BSI (1975b3, Test 1A. Otherwise, t h e en t i r e sample has t o b e p rese rved in an a i r t ight container until i t can be weighed. Alternatively, a rapid determination of moisture content can be made using a microwave oven. t h e 'Speedy' moisture t e s t e r , o r one of t h e rapid methods described in BSI (1975b3, Test I. However, all such rapid determinations should b e thoroughly correlated with t h e s t andard oven-drying technique fo r t h e part icular soil t y p e being tested. In any case, moisture content samples should b e a s representa t ive and a s la rge a s practical, o r severa l determinations should be made in o r d e r t o obtain a reliable mean value.
With t h e exception of t h e water replacement method for rock fill (see Section 27.81, t h e methods outlined below a r e described f u r t h e r in Test 15 of BSI ( l975b) o r t h e ASTM s t a n d a r d s quoted.
27.2 SAND REPLA CEMENT METHOD
BSI (197561 describes three variathns on the sand replacement method. The first, employing a small pouring cyhder, is used for f i e and medium grained soi/s, as defined in BSI N975b/. The second, using a large pouring cyhder, is suitable for fine, medium and coarse grahed soils, The third, the scoop method, may be used for fine, medium and coarse graned soils, but it is less precise than the first two and yields less rehkble results; its use should be restricted to occasions where no pouring cylinder is available.
These methods are unsuited to soils containing a high proporfion of very coarse gravel or larger particles because the apparatus 12 not large enough to cope with a hole of suffiient size to obtain a representative sample; also the sand win tend to run into the interstices of the material, thus leading to inaccurate results. The method cannot be used in so17s where the volume of the hole cannot be maintained constant. It also loses accuracy in soils where it is difficult to excavate a smooth hole because the sand cannot easily occupy the full volume.
The test should not be carried out when compactim plant is operating nearby, or when ground vibrations are present.
The calibration of the sand i s sensitive to humidity and should be checked daily. The sand should be oven-dried and stored for about a week for the moisture content to reach equilibrium with atmospheric humidity. After each test , the sand should be dried and sieved to remove arty extraneous material before further use.
27.3 CORE CUTTER METXOD
The core cutter method is described in BS/ 09756). The method depends upon being able to drive a cylndrical cutter into the soil without significant change of density and to retain the sample inside it so that the known internal volume of the cylinder is completely W e d It is therefore restricted to fine so17s that are sufficiently cohesive for the sample not to fa// out, and to completely decomposed rock free of large fragments. The method is g e n e r w less accurate than the sand replacement method because driving the sampler tends to alter the density of the soil.
27.4 WEIGHT IN WA TER METXOD
The weight in water method is d e d b e d in BSI N975b). It is applcable to any so17 where representative samples occur in discrete lumps that wi7l not disintegrate during handlng and submersion in water. In practice the method is restricted mainly to cohesive soils.
27.5 WA TER DISP LA CEMENT METHOD
The water displacement method is described in EST 09756). It is an alternative to the weight in water method and has the same lm12afions.
27.6 RUBBER BALL DON METHOD
A descr~bfibn of the rubber ba//oon, or densometer, method can be found in ASTM f1985b). In essence it is a water replacement test with a rubber membrane retain~ng the water. It is an alternative to the sand replacement method with the limitation that it is not suitable for very soft so17 which win deform under slght pressure, or in which the volume of the hole cannot be maintained constant. The ASTM standard does not describe the apparatus in precise terms and hence the method couM be used for coarser soils than the sand replacement method if a sufficiently large apparatus were constructed
The densometer allows a simpler and more rapid determination of density
t han t h e sand replacement method, b u t t h e appara tus is somewhat cumbersome and may be prone t o leakage ( G C O . 1984).
27.7 NUCLEAR METHODS
Nuclear methods of densi ty measurement at shallow dep th a r e described in ASTM (1985e). They do not measure densi ty directly, and calibration curves have t o be confirmed for each soil type , which involves measuring t h e densi t ies of representa t ive samples of t h e soils concerned b y one of t h e d i rec t methods discussed in Sections 27.2 t o 27.6. However, once th i s has been done, and provided t h e r e a r e no significant changes in soil, t h e method is v e r y much fas t e r t h a n t h e o thers . I t is therefore most sui ted t o situations where t h e r e is a continuous need for many densi ty determinations over a period of time, and where t h e soils do not v a r y t o any significant extent. I t should be noted t h a t t h e densi ty determined by nuclear methods is not necessarily t h e average densi ty within t h e volume involved in t h e measurement.
The measurement of moisture content at shallow dep th by t h e nuclear technique is described in ASTM (1985h). In many modern nuclear instruments. measurements of both densi ty and moisture content a r e made simultaneously. A s t h e moisture content determination is indirect , i t is essential t h a t nuclear determinations (which often overestimate moisture content of local soils obtained by t h e oven-drying method) a r e correlated with conventional oven- d ry ing moisture determinations for t h e part icular soil being investigated.
Nuclear measurements of densi ty and moisture content can b e made at dep th by employing a nuclear probe within a borehole (Brown, 1981; Meigh & Skipp, 1960). This technique may be particularly useful when undis turbed samples cannot be obtained readily, such a s in some fine g ranu la r soils. A s only indi rec t measurements a r e obtained, t h e limitations mentioned above fo r shallow nuclear techniques apply equally well t o t h e nuclear probe.
All nuclear techniques utilize radioactive materials, and appropr ia te safe ty precautions must be followed. The use and handling of nuclear ins t ruments should be fully in accordance with t h e manufacturer 's recommendations and applicable regulations (see Appendix E).
ZI. 8 MA TER REPLA CEMENT METHOD FOR ROC' FILL
The methods quoted in Secthns ZZZ to ZI.7 can rarely be used in materids conta'ning a substanM fracthn larger than coarse grave4 and the water replacement method, which is described below, has been dewked for such soils. AAlthough it is not covered by any standard specificatJon, some experience in its use has been gahed In principe, it cons~kts of excavating a hole large enough to obtain a representative sample, fining the hole with f l ~ i b l e po/yetbylene or simIi'ar sheeting and then determz'nhg the volume of water required to fi// the hole. A 'density rzhg' is used as a template for the size o f hole and aho as a datum from which to measure water levels. Th~k IS made up from structural steel plate, and for rack /i// may be Z m in d~kmeter, ZOD m in height and provided with a mark on the insI.de.
The procedure I> to place the ring on a levelled surface, packing sand under it where it I> not in contact with the soi4 and weighhg it down with sandbags. Polyethylene sheeting is placed over the rig, pressed into it and smoothed out as far as poss13le so as to fine completely the cyfindrkal cavity
so formed A measured supply of water is then run into it and the volume required to fill it up to the mark on the density ring I> noted
The polyetbyJ.ene sheeting is then removed, the hole excavated, and the spo17loadedlinto s k ~ p s for subsequent weighing and grading, 2requ1ied Care is needed in the excavaaon to ensure that the density ring is not disturbed and, to this end, the edge of the excavation should be kept a t least 150 mm away from the inner edge of the ring. The sides of the hole should be trimmed to minimize projecting stones.
Polyethylene sheeting is then placed over the ring and hole and partidly secured with sandbags. Water I> then run in from a measured source and, at the same time, the po/yethylene lining is fed into the hole, helping it into crevices and minimking folds. This continues until the water level is again up to the mark on the inside of the density ring. The difference in the two volumes is then a measure of the volume of the hole. It is customary to aflow the water to remain in the hole for a period of t h e to see whether there is any fafl of water level which would indYcate leaks in the polyethylene lining.
The accuracy of the results of this test can be enhanced by attention to the following detahs :
(a) The hole should be made as large as possible,
b The sides of the hole should be made as smooth as possible.
(c) A s th~in a gauge of pohetbylene as possh5le should be used, consistent with it not fracturing tw easiy. Two sheets of 0.1 mm polyethylene laid together have been found to be sathfactory. It is not quite so flexible a s one sheet of the same thickness, but is less prone to punctures.
Accounts of the practhaf use of this method can be found ekewhere (Frost, 1973; Stephenson, 1973),
155
28, INSITU STRESS MEASUREMENTS
28,l GENERAL
The stresses existing in a ground mass before changes caused by the apflication of loads or the formation of a cavity within the mass are referred to as the 1nih.2 insitu state of stress. These stresses are the resultant of gra vitathnal stress and residual stresses related to the geological history of the mass.
Data on the initlk/ insitu state of stress lir rock and so17 masses before the execution of works are increas~ngly important in design, more particularly when using lin12e element analysis. The mpst favourable or~entation, shape, execution sequence and support of large and complex underground cavitks and the predicthn of the fiial state of stress existhg around the completed works are dependent on knowing the initial insitu state of stress. Measurements of insitu stress have shown that in many areas the horizontal stresses exceed the vertical stress, which in turn often exceeds that calculated assuming that only gravity is acting on the ground mass.
Measurement of insitu stress in so17s may be made, although the equ~pment used generdy provides an estimate of horizontal stress only. In order that both total and effective stresses can be estimated, it is usual to measure the pore water pressure in addiion to the total stress.
The interpretation of insitu stress measurements requires specialist experience.
28.2 STRESS MEASUREMENTS IN ROCK
The methods available are generally based on induced stress changes, achieved in some cases by over-coring or slotting an instrumented test area.
Over-coring is used for measurement within the rock mass, whereas slotting is used for surface stress measurements. Measurements taken have to be a d h t e d to take account of the redistributlbn of stresses as a result of formation of the borehole or slot, and, in the case of underground works, when the measurement is made in the zone of influence of the main access, such as an adit. The accuracy of most methods of measurement of ~hsitu stress in rock fimits their use to locatrbns where the rock cover is at least 75 m. Stress measurements may also be determined from the measurement of disp/acements of the walls of a tunnei or of an expiratory adit, close to the working face.
With the exceptJon of the static equifibrium method /Morgan & Panek, 1963), the a vailable techniques generally require that the material in which the measurements are made behaves in a near elast~k, homogeneous and isotropic manner, and that it is not excessively fractured or prone to sweliXng as a result of the effects of drilfing water. For the over-cor~hg methods, the elastic behav~our is assumed to be reversible, the elastk constants behg obtained from laboratory tests.
Stress measurements may be made us~ng electrical strain gauges, photo- elastic discs, sofid inclusions and systems for measur~ng the diametral change of a borehole. Some equ~pment is des~gned to measure stress change with
t i , or stress change due to an advanwhg excavation, whereas other equipment ik designed to obtain an instantaneous measurement of stress. The technique selected has to be chosen in relatrbn to the rock materia and mass q u a y . Strain gauges cannot be reliably to highly porous or wet rock.
Special methods for measuring and interpreting the uniaxial, biaxial or triaxial state of s tress in a rock mass are described in BSI (1981a).
The report on the results of insitu stress measurement should include information on the followihg :
fa) Location of test and direction and depth of the boreholes, method of dr2ling and dimters of cores.
b Depth below ground level of the point of measurement.
fc) Gdogikal descri)tion of the rock materia and rock mass.
fd) Type and sizes of straih gauges, and strain readings to the nearest 10 micro-strah.
/el Temperature and humidity at the test location, and temperature of the flush water if amcable.
f f ) The modulus of elastikity, 6 and Poisson's ratio, ?L of the rock sampled fm each stress measurement area, as determined from statik laboratory testing of core {preserved at insitu moikture content) over the appropriate stress path.
(g) The six components of stress fox, rr,, &, r,,, T,,, L/ at each point to the nearest 100 kPa.
fh) The three prinwpal stresses and thmi directions fto the nearest degree), dated to both a borehole or adit awik system and a global w k system.
02 Cohur photographs of the cores or test location.
(17 Date of measurement and date at which the excavation passes the poiht of measurement.
28.3 STRESS MEASUREMENTS IN SOILS
The analysis of the response of soil masses to applied loads requires reliable data on their strength and deformatrbn characteriktiks, and, as these are stress dependent, a knowledge of the insitu state of stress assists in thek evaluatrbn by laboratory testhg.
Diiect insitu measurements of the ihi'tikl state of stress in smi's is difficult because the dikturbance created by gaining access to the ground mass ik generally non-reversible, and several tiines that produced by a stress- relieving technique. The accuracy of most instruments that have been developed suffers because of the dikturbance created h the ground on ihsertion.
It is usual to masure only horizontal stress, and to make assumptions concerning the level of verb'cal stress based on the overburden depth. On& total stress may be measured; therefore, to determine the effecti've stress conditbns, the pore water pressure at the test level has to be measured or assumed. Methods of detennh~ng pore water pressure in the M d are dlkcussed in Secbon 20.2
In soft clays, hydraulic pressure cells have been carefully jacked into the ground, o r installed in a pre-bored hole (Kenney. 1967). The "Camkometer", a self boring pressuremeter, reduces disturbance to a minimum by fully supporting the ground it penetrates (Windle & Wroth, 1977). The total horizontal insitu s t ress may then be obtained by measuring the contact pressure. Facilities to measure pore pressure a re available in the same instrument. Hydraulic fracturing has also been used to estimate minimum horizontal stresses in soft clay (Bjerrum & Anderson. 1972).
In large excavations, pressure cells a re sometimes used to measure the contact pressure between the soil and a retaining structure. The type and position of a cell should be chosen with great care, because t h e introduction of the cell into the soil causes a redistribution of the s t resses around it, and
- the e r rors depend on the geometry of the instrument. Details of the types of cells available and the problems tha t may be encountered when using them are given by Brown (1981) and Hanna (1985). Some of the factors that affect the accuracy of contact pressure cells a re discussed by Pang (1986).
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29, BEARING TESTS
29.1 VERTTCAL L OAD/NC TESTS
29.1. 1 General Princfples
Insitu verthal loading tests hvolve measuring the applied load and penetration of a plate being pushed into a sod or rock mass. The test can be carried out in shallow pits or trenches, or at depth h the bottom of a borehole, pit or adit (see Secaon 21.61. In soils, the test is carded out to de temne tbe shear strength and deformation characteristr'cs of the materfkl beneath the loaded plate. The ultimate load is often not attanable h rocks, where the test I> more frequently used to determine the defomaation characteristics.
The test is usually carrfed out either under a series of rnahtaned loads or at a constant rate of penetrabon. In the former, the ground is allowed to consohdate under such a load before a further ~ncrement is applieed,. this wil/ yield the drained deformahon characteristics and also strength characteristics if the test is continued to fa7ure. In the latter, the rate of penetration is generally such that little or no drainage occurs, and the test gives the corresponding undrahed deformafion and strength character~ktt'cs.
It should be emphasized that the results of a single loadfhg test apply only to the ground whf'ch is s~gnificmtly stressed by the plate; thk IS typically a depth of about one and a half tiines the df.ameter or width of the plate. The depth of ground stressed by a structural foundation wi;% in general, be much greater than that stressed by the loading test. For this reason, the r e s u b of load~hg tests carried out at a shgle elevah-on do not n o d l y give a direct indfbath? of the &owable bear~ng capacity and settlement characteristics of the full-scale structural foundathn. In order to determhe the variathn of ground propertres with depth, it wf7l g e n e d y be necessary to carry out a series of plate tests at different depths. These should be carrid out such that each test subjects the ground to the same effecive stress level it would receive at working load
Where tests are carrfed out h rock, blastrirg for rock excavaaon may seriously affect the rock to be tested This effect can be minlinied by u s h g s d charges, and by l inhhhg the excavafion by hand methods.
29.1.2 Limiattons o f the Test
The man lim'tathn of the test lies fh the possibfZity of ground disturbance during the excavaoon needed to g a h access to the test position.
Excavafion causes an unavoidable change in the groundstresses and may result in h-eversible changes to the properties whf'cb the test is intended to study. In spite of this effect, the moduli determined from plate tests are more &able and often many t . 2 . ~ ~ higher than those obtained from standard laboratory tests. In a project whkh ihvolves a large excavation, e.g. a bu17di'ng with a deep and extensfive basement, the excavation may cause dfkturbance to the ground beneath, with a consequent effect on the defomathn characteristics. In such a case, it wf7l be necessary to allow for thh unavoidable disturbance when interpretihg the results of Joadhg tests.
When camying out the test below the prevailing groundwater table, the seepage forces assou'ated with dewatering may affect the properties to be measured This effect is most severe for tests carried out at signiifiint depths below the water table in sods and weak rocks. It may therefore be necessary to lower the water table by a system of wells set outside and below the test positibn.
29.1.3 Site Preparathn
It is necessary to ensure that any material loosened or softened by the excavauon 13 removed and that the plate will lie in direct planar contact with the sample surface. It 1s essentia/ that th13 surface is undisturbed. planar and free from any crumbs or fine loose debrk Where access is possible the surface is best prepared by hand; elsewhere, special tools are required to trim and prepare the surface from a remote point. A s the sample preparation involves stress d e f and exposure to different temperature and humidity conditibns, the delay between setting up and testihg should be minimzed and the tihe lag should be reported with the results.
l.ne even transference of load onto the test surface can best be achieved by setting the plate on a suitable bedd~ng material, which usually consists of cement mortar or plaster of paris. Where the test is being performed to measure the deformation character~istics of a relabbvely stiW materia4 considerable care is required in setting the plate, and a series of bedd~hg layers may be needed /Ward e t a/, 1968). Changes in water content of the ground being tested shouh' be kept to a min~imm.
29.1.4 Test Arrangement
The test I> subject to scale effects. Several plate sizes and shapes are used, the most ccnnmon being uicu/ar plates ranging from 300 mm to 1 000 mm in d i m t e r . The choice depends on the problem be~hg studied In rocks, plates larger than 1 000 mm d'kmeter may be used. depending on the johting frequency, The test arrangement used by the U.K. Bu17ding Research Establishment 13 shown in Figure 43 and 13 fully described elsewhere /Marsland. 1971; 1972; Ward et a/, 1968).
The need sometrines ar~kes to measure displacements in the ground below the plate /Marsland B Eason, 1973; Moore, 1974). The plate has to be rigid and the d~iectibn of the resultant appfled load has to be vertical and without eccentr~WYy. The loading may be applied directly by kentledge or j'acking agahst a reaction system provided by means of kentledge, tension piles or ground anchors. Where kentledge 13 used. it should be supported on a properly designed frame or gantry such that there is no poss131Xty of the load ti7ting or ca'lapsihg. The foundations of this frame or gantry should be sufficiently far away from the sample not to affect 12s behaviour to any significant extent. Where tension piles or ground anchors are used. they should be sited sufhently far away from the sample so as to have no s~gn~Zcant influence on its behaviour. The normal practice 13 to maintain a m~nimum distance of three t iks the plate diameter from the centre of the plate to the centre of the pile, The amount of kentledge or jacking resistance that needs to be provided I> governed by the purpose for which the tests are carried out and also, to some Went, by econom~'c considerations. In genera/, the nearer the soil or rock under the plate approaches the point of shear failure, the more hWrthwh~7e are the data derived from the tests. The test is sometines
conducted ih a sihilar fashion to the constant rate of penetration fCRPI test for piles (ICE, 19781.
The penetratibn or deflectibn of the plate should generally be measured at the centre and the edge of the plate. In order to minihize the effect of poor bedding and sample dikturbance. the dikplacement of the material at some depth beneath the prepared test surface can be determined by inserting reference datum rods anchored at various depths W;zlace e t al, 19691. Such measurements are intended to provide more realistik data on the mass behavihur of the ground; they are usualy taken through a central hole in the loaded plate.
The dikphcement of the plate is related to a fied datum. This often consists of a reference beam supported by two foundations positioned outside the zones of ifluence of either the loaded area or the reaction area. The deflecction-measurihg equipment has to be set up li, such a way that any t i l tng of the plate wi2 not cause errors in the measurements. Dial gauges are dften used and the rods transm'ttihg the displacements of the plate should ihcorporate a b d joint or other sim1ar device to elimhate the effects o f bendihg. The reference beam and measuring devices should be protected fm the d i k c t rays of the sun and from wind by means of tarpaulins or other forms of shelter; errors of measurement can eas17y arise fnxn these causes.
A comparable arrangement for performing the test in an adit is given in BSI (1981a).
29.1.5 Measurements
/fl Ap~lied Forces. The load on the plate 13 best measured by means of a load eel4 which should be capable of readihg to an accuracy of 1% of the maximum load I t ik advisable to have the cell calibrated over the anticipated range of loadihg before and after the test programme.
(21 Displacements. Dikplacements ih the direcrbn of load appkatron may be measured by didgauges or electri'cal transducers and the readings can be taken continuously if requiked DikplaCements should be measured to an accuracy of 0.1 mm.
(31 Le. fiecords of tihe for the various stages of setting-up and testing are required parti'cu/ary where cycl~c loadihg and creep tests are being carried out.
(41 Tem~erature. The measurement of temperature will be required ih the event that correctibns to the settlement or load readings are considered necessary.
29.1.6 Test Methods
(11 General. The test 13 most frequently used to measure the ultihate bearing capacity. In cases where setdements and elastic deformaation character13tiks of the ground need to be detemined as in rock foundations. care should be exeruked to work at stresses that are relevant. The observatrbn of defomation, parti'cululy at low stress lev& requiies the utmost care in sample preparation and settrig-up irmeaningful results are to be achieved The errors that can be introduced by sample dikturbance and
inaccuracies of measurement can often be similar ii, size or greater than the data sought.
The effect of sample dikturbance can be reduced, to some extent, by carrying out prefiminary cycks of loadhg and unloading. The maximum load ii, these cycles should not exceed the intended load. The rate of loading should be suffic~ently rapid to prevent any s~gnificant consofidation or creep. After two or three cycles, the stress/sett/ement graph will generdy tend to become repeatable, and the test can then be extended to the main tes thg programme. The data from the preliminary load-cycles give an indicatlbn of the effect of the sampfing disturbance. The undrained deformation modu4 as measured after prefiminary load-cycfing, generally give a more refiable 1ndicar2bn of the true properties of the undisturbed ground
(21 Maintained Load The load is u s u d y app/ied IR equal ihcrements, with each increment being maintained untY a// movement of the plate has ceased. or an acceptably low rate of increase has been reached The increments are continued up to some multipe of the proposed working load, to failure or to the full avdable load When the test is carried out to ihves&yate the deformation characteristlics of the ground, 12 13 preferable to carry out preliminary load c y c h g . Cycles of unloading and reloading may a/so be carried out at various stages in the main test to gain some indicatlbn of the relative amounts of reversible e. 'elastic Y and irreversible deformt2on that have occurred If the rate of unloading and reloading is sufficient/y rapid, the s h e of the load/deformatron curve may be used to determine the undrained deformaobn modulus, or an approximaation to it. However, ~n relatively permeable ground this may not apply.
3 Constant Rate of Penetration. Constant rate of penetratlbn tests are more suitable for soils. Such tests are descr18ed b y Marsland (19711 for plates ranging from 38 mm to 868 mm diameter. using a penetration rate of Z.5 mm/mn. Where the maximum bearing capacity is not clearly defined, the value of the bearing pressure at a settlement of 15 per cent of the plate diameter is used I f the undrained deformation modulus IS required, the plate diameter should be greater than 750 mm. but it is preferable to carry out a separate test wi2h the load apphed increment&y at a rapid rate.
4 Creep. The measurement of creep under sustained loads 12 some- tlhes carried out in connecfion with the design of foundatlbns which are highly stressed or where the structures concerned are particuMy sensitive to settlement /Meigh e t a4 19731. If the structure ik to be subjected to fluctuating loads, the test programme will probabb include cycfic loading.
29.1.7 Analysis of Results
The assumpOons made for the analysis are that the material is homo- geneous, elastk, isotropic and that the classic equation for the penetration of a rigid c~rcular plate on a semi-infinite plane surface appfies :
where E I> the elasth modulus,
q is the pressure app/ied to the plate,
S I> the average setuement of the plate,
B is the di-meter of the plate,
V is Poisson 3 ratio.
This equation can be used when the test is carried out either at the ground surface or in a pit whose p h dihensions are at least five trines those of the plate /Ireland e t a/. 19701. If the test ~k carried out at the end of a borehole, the expressbn becomes :
where Id is a depth correctibn factor (Burland, 19691. when the test is carried out in an adit, other modificatrbns to this equation will be required depending on the extent and planarity of the tested surface (Carter & Booker, 1984). Finite element ana/ysk can sometihes be appfied to problems where rigorous solutions are not available, although the problem of cboos~hg representative soil parameters to put into the analysis still remans. An equatrbn for cdculatihg the modulus at any depth beneath the centre line of the loaded plate is given elsewhere (Benson et al. 1970; Wallace e t al, 1970). For johted rock, Poisson's ratio can be assumed to be between 0.10 and 0.25 for pracb'cal purposes.
For cohesive so& an estihate of the undrahed shear strength, C,, can be obtained from the plate test carried out ih a borehole by using the following equation .'
9" - YH . . . . . . . NO1 C" = N,
where q, ik the ultihate bearing capacity of the soil under the plate. When this is not dearly defined the bearhg pressure at a penetration of 15% of the diemeter is used,
Y is the bulk density of the soiX
X is the height of soil above test ]eve/.
N, is the bearing capacity factor. For a rigid ciicuhr plate at the base of a deep shaft of the same diameter as the plate, N, ~k assumed to have a value of 9.25. However, IT the plate has a significantly smaller dieameter than the shaft, or IT the depth is less than four tihes the plate diameter. the value of N, may be smaller and approaches 6.15 for a circular surface load Some dlowance should be made for side shear on the plate where this is appropriate.
29.1.8 Interpretation of Resufts
The correct hterpretatibn of the behaviour of the mass of ground under investigation requires a careful examination of the results, not only of the loading tests, but also of other data concerning the ground ( Sweene y & Ho, 1982). Dependihg on the objectives of the investigation, such data m g b t
include the geological structure, the nature and d'ktribufion of disconthu~'tl'es. and the variability of the ground
Several deformation moduli can be obtained from these tests, depending on the method used and the application (Brown. 1981). The results obtained will r e f / c t the effects of the width and frequency of the discontinu~'~es and wi'l give an indicatlbn of the mass behaviour under loading. The stress level at which these parameters should be examined w17l depend on the working stress levels. In the case of tests on rock in adits, it may be necessary to consider the insitu stresses in the test samp/e.
The moduli to be used for design purposes should be those which d a t e to the ground at the t h e of construction and after it has been affected b y the construction procedures,. for example, a deep excavatlbn might affect the deformation moduli of a so~Y, and blasting may affect the properfies of a rock. Sometlhes, the effect of a construcfion procedure may be suf/li&ntly severe to justify the examinatlbn of alternative methods of construction.
O n completron of the test, full identifia&on of the material beneath the loaded area should be carried out b y samphhg and testing in the laboratory. Results obtained from these tests wf l in many cases ass&t in extrapolating the test results to other areas on the site.
29.2 HORIZONTAL AND INCLINED LOAD/NC TESTS
Basically, horfzontal and i n c h e d loading tests are the same as vertkal loading tests, and are carried out and andysed li, a comparable way /see Section 21.6.101. Loading tests at a preferred orientatlbn are carried out to invesaqate particular characteristl'cs of the ground They are frequently carr~ed out in rock for hvestljrations concerning tunnels and underground excavations (Brown. 1981; Carter & Booker, 1984). A s~hp le lateral loading test, carried out between the opposite sides of a trial pit or caisson using an hydraulic jack, forms a very convenient means of measurhg the insitu modulus and shear strength of soils. Interpretatlbn of the elastk modulus of soil from lateral loading tests shouh' follow the advice given b y Carter & Booker (1984). Care should be taken to support the we~ght of the jack and other loading equ~pment so as to prevent the applicafion of shearhg forces to the test area.
29.3 PRESSURIZED CHAMBER TESTS
The test is carried out in an underground excavation or length of tunnel and consists of charging the chamber with water under various pressures and measuring the deformathn moduli of the surrounding ground The test I> generally carried out for projects h v o l v h g tunnels carrying water under pressure.
The test site should preferably form part of the actual excavation, or be of the same size and para//e/ to the axis in representative ground The length of a test sectlon should be at least five bhes the excavated diameter, unless allowance can be made for the end effects. The method of excavation used should be capable of producing a formed surface of s~hilar quality to the actual excavaoon. In order to ascertai, whether the modulus determhed is drained, partlblly drained or undrained, it is necessary to know the draffage conditlbns wh'ch applied during the test.
29.4 INSITU CALIFORNIA BEARINC RATIO fCBR) TESTS
29.4.1 General
The CBR method of flexible pavement design is ementidy an empirical method in which design curves are used to estimate a pavement thickness appropr~ate to the CBR of the so11 There is no unique CBR of a soil and ih any CBR test the value obtained depends very much on the manner in which the test is conducted The design curves are usually based on one carefully specified method o f measur~hg the CBR, and this is usuafly a laboratory method. The parameter requ~ied for the des~gn of flexible pavements is the C&? attahed by the soil at formation level after al/ necessary compactkm has been carried out, the pavement has been laid and sufficient time has elapsed for equilibr~um mo~sture content to become established. Before embark~hg on insitu CBR tests, it is therefore necessary to consider carefufly how relevant they wi'l be to the proposed design method, and whether the condition of equi/irium moisture content I> Mely to pertah.
29.4.2 Test Method
The test is carrled out by the method described in Test 16 of BSI f1975b) excluding the compactrun, and subject only to those alteratJons necessary to enable it to be carrfed out in the field The load is generally applied through a screw jack using the weight of a vebkle as j;lcking resistance, and deflectrons are measured by dial gauges carried on a bridge with ~hdependent foundatrons resting on the ground we// clear of the test area. A circular area of about 300 mm diameter is t r i m e d flat, spec~al care being taken with the central area on whkh the plunger w12 bear. A thin layer of fine sand may be used to seat the plate but the use of sand to seat the plunger itself should be avoided. If it is rinpossLble to trim the soil suffiaently to obtah good seatrhg of the plunger, a thin layer of plaster of paris may be used, care being taken to remove any plaster extend~hg beyond the area of the plunger. Further deta& of the ihsitu test are given elsewhere (Road Research Laboratory, 195.2,).
29.4.3 Llinitatrons and Use of Test
The test is unsuitable for any soil contah~hg partr'cles of longest dimens~on greater than 20 mm because the seating of the plunger on a large stone may lead to an unrepresentative result. The test 13 of dubk~us value with sands because it tends to give results much lower than the laboratory tests on whkh the design charts are based. T h h because of the confining effect of the mould h the laboratory tests. The test is most suited to clay sois, subject always to the soil under test being at equZbrium mohture content. The moisture content at a depth of I to 2 m below ground surface. where the soil is normally unaffected by seasonal mokture content changes, often gives a good indication of the equfZbrium moisture content, provided that there is no s~gnificant change of soil type. An alternative is to carry out the test directly beneath an existrhg pavement having identr'cd subsoh' conditions to those of the proposed constructron; t h ~ k method has been used with some success for the deslgn of mifield pavements.
I&u CBR tests have sometimes been carr~ed out lh conj#nc&on with imi tu density and moisture content tests and then /inked with laboratory compacthn tests. A careful study of all the resulohg data may allow a
reasonable design parameter to be chosen for suitable soils. Attempts have somet/mes been made to use the test as a means of controlfing the compaction of fi// or natural formatlbns, but they have not usually been successful and the procedure cannot be recommended.
30, INSITU DIRECT SHEAR TESTS
30.1 GENERAL PRINCIPLES
In th i s tes t , a sample of soil o r rock is prepared and subjec ted t o d i rec t shear ing insitu. The applied s t r e s ses and boundary conditions a r e similar t o those in t h e laboratory direct shea r test. The t e s t is generally designed t o measure t h e peak s h e a r s t r e n g t h of t h e intact material, o r of a discontinuity (including a rel ict joint in soil), a s a function of t h e normal stress act ing on t h e shea r plane. More t h a n one t e s t i s generally requi red t o obtain representa t ive design parameters.
The measurement of residual shear strength can present ma&- practical problems in arranging for a sufl'iiently large length of travel of the shear box. but a usefulindication of residual strength may be obtained by conthuing the test to the limits of travel of the apparatus. In certain applications, the test may be designed to establish the strength of the hterface between concrete and rock or soil
Insi tu shea r t e s t s on soil may b e carr ied o u t e i ther within boreholes (Bauer & Demartinecourt. 1982; Handy & Fox. 1967) o r near t h e ground su r face (Brand et al, 1983b). Equipment for test ing close t o t h e ground surface in t r ial pits may b e adopted t o enable test ing t o b e car r ied out within deep excavations, la rge diameter sha f t s o r caissons. Insi tu s h e a r t e s t s on specific discontinuities in rock may also be conducted using similar equipment; t h e resul t s may b e used t o confirm t h e s t r e n g t h of discontinuities derived from laboratory t e s t s and field roughness s u r v e y s (see Section 26.2).
30.2 SAMPLE PREPARA TIQN
Samples are generally prepared a t the bottom of pits or trenches in soA Adits are more common for rock testing. The excavathns permit access to the material at the zone of interest, and in many cases provide a suitable means of setting-up the reaction for the applied forces.
The orientation of t h e sample and t h e forces applied t o i t a r e generally governed by t h e direction of t h e forces which will become effective dur ing and on completion of t h e works, b u t modified t o take account of t h e orientation of significant discontinuities. In many cases, however, t o facilitate t h e se t t ing-up of t h e test, t h e sample is prepared with t h e shea r plane horizontal. The normal and shear ing s t r e s s e s a r e generally imposed a s forces applied normally and along t h e s h e a r plane. However, an inclined s h e a r force passing th rough t h e cen t re of t h e shea r plane may be prefer red a s th i s t e n d s t o produce a more uniform distribution of stress on t h e s h e a r su r face (Brown, 1981).
A s a rough guide, the sample dimension shoula' be a t least ten t h e s that of the largest partice; in rock, the sample s ~ z e should reflect the roughness of the rock discontinuity being tested For stronger rocks, the s a m e can be rendered with suitably strong cement and reinforced concrete to ensure adequate load distribut~on. The equipment shouM be of robust construcbon. Samples between 300 mm and 1 500 mm square have been used for testing soil and weak rocks. Larger samples may be requked in ground containing boulders or in coarse fi// material.
Great care has to be exercised in preserving the environmental
conditions when fording the excavation. Excavaton techniques whkh would affect the dikconthuites in the sample test area shouh' be avoided, e.g. t h e which give r ~ k e to crumbling, fracturing or excessive dynam~k shock loading. Hand sawing, cuttihg and dfeamond dr17ling should be used to prepare and trim the sample. Adequate protection from the elements should be provided F~hal exposure and trimming of the sample to fit the loading frame and the testing itself should all be completed with m~himum delay to a void possible significant changes ih the moikture and stress conditbns of the sample. If tests are carried out below the water table, precautons should be taken to avoid the effects of water pressure and seepage fsee Section 29.1.21.
m e r e it I> htended to test one d~kcontinuity only, care has to be taken to avoid d~kturbance to the surface of the discontinuity, and to prepare the sample so that the forces are a p p W correctly in the plane of the discontinuity. The spat'al orientathn of the discontinuity should be defined by dip d2-ectbn and dip measurements.
Where draned condhlbns are required, suitable draihage layers can be inserted around the s d e and on the loaded upper surface.
With the borehole shear device, there is no sample preparation as such. but care i s required during the formation of the borehole s o as to limit disturbance of the surrounding soil (Bauer & Demartinecourt, 1985).
30.3 TEST ARRANGEMENT
The equipment for app/ying the norma/ load can consist of weights, kentledge, hydraulic rams, flat jacks acting agahst the excavaton m o X or an anchor system. The reacton system should ensure the unl'form transfer of the normal loads to the test sample and minimum resistance to the shear displacement, e.g. by the use of low-friction devices such as ball seathgs or &ers s( Brown, 1981 ). A porous phton or other suitable medium can be used to d~ktribute the load where drahed cond~'tbns are required The alignment of the force needs to be maintahed during the test.
The shearing force apphkation system should ensure that the load I> applied un~Yormly over the p h e of shearing, and that the load and geometrical centroids are matched to eliminate movement. &%ere an i h c h e d shear force is required, the resultant of the.sbear force shouMpass through the centre of the base of the shearing plane (Brown. 198 1 1. I f a constant norma/ load lk required for this type of test, suitable reducton has to be made to the applied normal load durihg testing to compensate for the increase in vertkal component with increashg shear force. The shear force application can be developed by sim17ar means to the normal loading. In both cases, care has to be taken to ensure that the ground reactbn does not extend to the san?.de. The reacton system can frequently be provided by the excavation sidewalls. In certah cases, it may be necessary to provide the shear force by traction on a system anchored by pi& or cables. Suffic~ent travel in the shear force application system should be provided so that the complete test can be run without interruptrbn.
30.4 MEASUREMENTS
Prov~k~on should be made for the following :
fa) The appled forces shouM be capable of being measured with an accuracy of 92% of the mminum forces reached in the test.
fb) Shear. no& and lateral displacements should be measured Suflicibnt travel should be provided to run the cmplete test without the need to reset the gauges. The anchorage datum of each gauge needs to be rigid and set up at a paint sufliuenffy remote that 12 is not affmted by the forces appfied during testing.
fc) Steps should be taken to guard agahst tbe effects of changes in temperature. Alternatively, temperatures should be measured and any sensitive equipment shouid be calih-ated.
30.5 TEST METHODS
The s t resses applied in the testing programme should be within the range of the relevant working stresses a t the site, including those applied by the final structure. if appropriate. Where drained tes t conditions a re required. a consolidation stage is necessary to allow the pore water pressures to dissipate under each increment of normal load. The rate of consolidation should be monitored. as this is useful for determining the ra te of shearing (Brown, 1981). For drained tests, the ra te of shearing has t o be sufficiently slow to ensure tha t induced pore pressure changes a re a very small proportion of the shear stress. A t best, the appropriate shear ra te can only be estimated prior to the test , and experience gained in similar soil o r rock conditions and with similar tes t configurations is beneficial.
On completion of the test , full identification of the material sheared should be carried out by visual examination. sampling and laboratory testing. Photographs of the shear surface form a useful record of the tes t conditions and may assist in the interpretation of results.
30.6 ANALYSIS OF RESULTS
Graphs of consolidation behaviour (if applicable) and shear force (or s t ress) plotted against both normal and shear displacements a r e prepared in the analysis. The peak shear s t ress and corresponding shear and normal displacements may then be obtained and related to the applied normal stress. When failure occurs i n a plane dipping a t an angle to the applied shearing force, this should be accounted for in the analysis (Bishop I Little. 1967).
For tests on discontinuities in rock, the results from individual tests should not be extrapolated to the rock mass without confirmation tha t the surface tested is representative of the overall roughness of the discontinuity (see Section 26.2).
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171
31, LARGE-SCALE FIELD TRIALS
31.1 GENERAL
Large-scale field trikls are carried out in such a manner that the ground I> tested on a scale and under conditions comparable with those prevailing in the project under ~hvest~gatrbn. However, such trials are likely to be costly in terms of instrumentation, the requirements for purpose-made equipment and technical support. The methods and types of instrumentatrbn available for monitoring tkld tests are given in b r ~ e f outline in the fohwing sectrbns, together with some of the more common large-scale fied trials used to obtain geotechn~cal data for design and construction.
Large -scale fiild trials involve the princzples of site in vestigatlbn embodied in this document, and wou/d usuafly include the use of ground investigation techniques ah-eady described. Large-scale field trials are not standard tests, and should be designed to suit the ~hdiv~'dual requirements of the proposed works and the particular ground on wh~kb or within which they are to be performed. On large pro/;ects, field tr~als can provide the necessary desfgn parameters, a s we// as valuable constructhn data on excavatron, handling and placing, resu/ting in considerable savings and enhanced safety. Such methods and trials can be usefully extended into the construction stage, and also to the monitoring of the interrelated response of the ground and structure after completion under the working conditions.
31.2 METHODS OF INSTRUMENTATION
Several techniques can be used in ground investigation t o monitor displacements and s t r a ins associated with known o r suspected ground move- ments result ing from slope failures, foundation displacement, subsidence and ground response in large-scale field t r ia ls (BGS. 1973; Brown. 1981; BSI, 1981b; G C O , 1984; Hanna, 1985). A review of instruments commonly used in Hong Kong is given by Coleman (1984). Handfelt et a1 (1987) have described t h e performance of t h e instrumentation used in an offshore t e s t fill (see also Foott et al, 1987).
Ground movements are generdy associated with stress redistribuaion and pore pressure changes which are character~ktrc of the particuhr ground. Total stress can be monitared using total pressure c e h /see Chapter 281, while normal and shear stresses can be measured by special transducers (Arthur & Roscoe, 1961). The techniques for the measurement of pore pressure response are covered in Sectrons 2O.Z. 3 to 20.2.6.
Ground movements are generafly measured in terms of the displacement of po~hts which can be positioned on the surface of the ground or with~ff the ground mass. The absolute movement of a point has to be referred to a stable datum, and sufficient measurements should be taken to define movement in three d~hensions if this is required. Some of the c o m y - u s e d techniques pennit the movement or relative displacement of points to be referenced to arbitrary hor~zontal and vertical planes. Tb~k relative movement can be used to obtain strain.
Surface observations of ground movements can b e made by an accura te s u r v e y (Cole & Burland, 1972). An accuracy of 20.5 mm can b e achieved in levelling (Froome & Bradsell. 1966) and t ( 5 mm + 5 ppm) fo r distance
measurement using electro-optical instruments (Mayes, 1985). Care has to be taken to position datum points away from the effects of movements due to load and water changes.
Vertical movements can be observed by means of settlement gauges with an accuracy o f 0 . 1 mm fEjerrum et a/, 19651; more detaih are given by Dunnicfiff (19711. Mulopoint displacement measurements can also be employed fEurland et a4 19721. The use of vertical tubes gives an accuracy of about t 3 mm fpenman, 19691. A fu/ / profile-measuring technique which uses a torpedo traversing a flexible tube i s described by Penman & M12chell (19701. Telescopic tubes, ~hcfinometers and tensioned wires anchored in boreholes at stable points can also be used for measuring strains or displacements.
Lateral movements can be measured by offsets and triangulation. Rods, telescopic tubes and tensioned wkes can also be employed Where a torpedo i s used, access from both ends of the tubing i s preferable.
Photogrammetric techniques can be used to survey inaccessible sites such as steep slopes and ravines (Borchers. 1968). The accuracy of measurements taken by a photogrammetric method is about ~1/10000 of the camera to object distance under normal working conditions (Cheffins & Chisholm, 1980).
31.3 TRTAL EMBANKMENTS AND E K A VAT/ONS
The construchon of trial embankments may serve three purposes. &>st, the quality and compaction characteristics of avdable borrow materials can be determined at the field scale and compared with laboratory test results; second, the characteristics and performance o f placing and compachhg equ~pment can be investigated, third, the strength and settlement characteristics of the ground on which the embankment is placed can be exdned . F d u r e of a trLd embankment will usualy not be of mdybr consequence, and therefore a tr ial bank may be constructed so as to hduce fa ihre defiberately, either i n the embankment alone or i n the embankment and the foundations. However, any lhstalled instrumentation may be destroyed Such fa7ures sometimes occur i n an unexpected manner, and the engineer shouM take precautions to ensure that no in jury to persons or unexpected damage i s caused. Tbe value of such a fa ihre is that back analysis {see Chapter 321, can be used to check strength parameters. Bishop & Green (1973) have described the development and use of tr ial embankments.
Compaction tria/s can hclude experiments with variable borrow materials, layer thicknesses, amounts of watering and amounts of work performed in compacthn, Measurements should be made of insitu density and water content; the results should be compared with those from laboratory compaction tests, to obtain a specificathn standard, and with ins12u borrow p i t densities, so that the degree of bulking or volume reductkn can be estimated for given quantitres fESL 198161. Trials o f equipment can also be undertaken. Care should be taken not to vary too many factors at the same time, otherwke the effects of variathn of an hdividua/ factor cannot be esthated
Trial excavathns yieM informathn on the material excavated and the performance of excavating equipment,' they also permit more detailed examination of the ground than is possible from borehole samples. Exca va&ons can be cons2ructed such that falures are caused defiberateh; hence they can sometlines be used to test the short-term stability o f excavated shpes. However, fa7ures i n deep excavations are correspondingly more dangerous than
failures of filk and increased vigilance is needed
I f the maximum information is to be gained, adequate instrumentation of trial embankments or excavations is essentid together with continuous observation (see Secthn 31.21. The scale of trid embankments or excavatJons needs careful consideration. Clearly, the more closely the size of the trial approaches that of the prototype, the more directly app/icab/e w17l be the results obtaned from the trial.
31.4 CONSTRUCTION TRIALS
In many projects, considerable value can be derived from trials carried out before the commencement of the permanent works. Such trids permit the evaluation of the procedures to be adopted and the effectiveness of the various aupedients. A s with all large scale testing, a prior knodedge of the characteristics of the ground 13 essenth/. The resufts of the trial will often permit an assessment of the properties of the ground and hence enable a correlation to be made with other results obtained from routhe ground investigation methods.
A wide range of construction methods is c o d y tested in trials, e,g. pile tests, ground anchor tests, compaction tests for earthworks, ekperihentaf shafts and adits for tunnels, grouting, tr~al blasts for explosives and dewatering.
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175
32, BACK ANALYSIS
32.1 GENERAL
Natural or man-made condihbns on a site sometimes create phenomena which may be used to assess parameters that are otherwise difficult to assess or which may be used as a check on laboratory measurements. Examples of such phenomena are slope failures and settlement of structures. It may then be possiMe, starting from the observed phenomena, to perform a back ana/yss, for example, in the case of a slope failure, to arrive at shear strength parameters which fit the observed facts. Back ana/ysis of settlements is also possible, but care is required in assessing actual loadings and the hhes for which they have acted
All applications of back analysis should b e accompanied by r igorous geological and geotechnical investigations, which should include a thorough review of t h e history of t h e problem and examination of relevant climatic and groundwater records. Back analysis should only b e used if i t i s applicable t o t h e problem in hand and t h e ground conditions encountered. All parameters t h a t can have a significant effect on t h e analysis should b e carefully considered. Since i t is v e r y r a r e fo r a unique analytical solution t o be obtained, sensitivity s tudies a r e normally car r ied o u t t o a s sess t h e effect of parameters t h a t cannot be obtained by d i rec t means. The pitfalls of back analysis a r e discussed f u r t h e r by ~ e r 6 u e i l & Tavenas (1981).
32.2 FAILURES
In Hong Kong, numerous landslides a r e caused by in tense rainfall eve ry year , and back analysis i s sometimes carr ied o u t t o der ive s h e a r s t r e n g t h parameters a s p a r t of t h e design procedure for slope remedial or preventive works. However, a note of caution is necessary regarding t h e interpretat ion and use of t h e results . Although t h e failure itself can be s tudied in g rea t detail a f t e r t h e event , i t i s extremely r a r e t o have accura te information on t h e specific ground conditions a t t h e time of failure, particularly with r ega rd t o pore water p ressu res (Hencher e t al. 1984). For th i s reason, back analysis may b e j u s t a s useful in permitting a rational, qualitative assessment of t h e failure mechanism as in deriving information specifically on s h e a r s t r e n g t h parameters fo r use in design (Hencher & Martin, 1984).
32.3 OTHER CASES
Although back analysis i s carr ied out typically when slope fai lures o r significant ground movements have occurred , i t can b e useful in o the r cases where conventional predict ive methods may not lead t o realistic design solutions. An example of th i s application in Hong Kong is in t h e design of preventive works fo r existing s teep slopes formed in soils derived from insitu rock weathering. In such cases, conventional slope stability analysis will often yield factors of safe ty less than unity even when a slope has stood safely without s igns of d i s t r e s s fo r many years. Shear s t r e n g t h parameters obtained from back analysis of hypothetical failure surfaces th rough t h e existing slope often allow a more realistic form of stability improvement t o be made than would be possible from conventional analysis. However. i t is v e r y important t o check t h a t t h e assumptions made in t h e back analysis a r e valid; fo r example, t h e failure surfaces selected should be realistic and t h e proposed works should
not r e s u l t in a n y subs tant ia l change t o t h e form of o r loadings on t h e slope. Similarly, in t h e prediction of settlements in variable ground, o r in ground from which i t i s impossible t o r e t r i eve representa t ive samples, back analysis of settlement da ta from a n adjacent s i t e in similar materials may b e t h e only sat isfactory means of producing sensible predictions.
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33, GEOPHYSICAL SURVEYING
33.1 GENERAL
Geophysics a speciafized method of ground investzgation. Where a geophyskal investigation is required, the engineer directing the ground investigation (see Section 15.21 would nordly entrust it to an organ~zatrbn speciafizing in this work. This organliatzon wdl usua/ly adv13e on the detays of the method to be used and will interpret the results once they have been obtained into a form that can be used directly by the dziectzhg engineer. There 13 advantage in mahtaining a close hison between the directing engineer and the geophysicist since difficult ground conditions may give rise to problems of interpretation and hence a need for further zhvestigatzon. Engineering appfications of geophysics have sometzines been disappointing, and it is important that the type of hformatzon supp/ied by the investzgation is suitable for the project (Griffiths & King, 1983; Ridley Thomas, 19821. The htention of the following sections is to fist the various geopbysicd methods whkh are currently a vazhble, to give some indicatzon of the problems they may help to solve and to indicate the fimz'tation of each method. The appficabifity of the various geophysica2 methods is summarized lh Table 1 1.
Adequate borehole control is essential for the interpretation of geophysicaf observathns, which are best included in a ground investzgation employing more con ventzonal methods.
The aim of most geophysical methods of ground investigatzbn is to locate some form of subsurface anomaly where the materials on either side have markedly dzyferent physical properties. These anomdies may take, for example, the form of a boundary between two rock types, a fault, underground services, or a cavity. In the initial stages it win almost &ays be necessary to check the true nature of these anomales by physical means, nordly by boreholes. Once a correlatzon between the geophysical test results and the underground phenomena has been established, the geophys~'cal investigation may then yield useful results rap~Idly and economically. It foLhws that, where there 13 no distinct change in physical propertkc across the anomaly, the geophysical investigatzon may not detect a boundary. Geophysid methods can also be used to deduce soil and rock parameters; when this is done. the results obtained shouki always be confirmed by directly measured parameters.
Geophysical survey techniques are based on determining variatzons in a physical property, such as electrical conductivity fresktivity1, variations in density fgra vimetrlk1, magnetic susceptz'bifity fmagneticl or velm2y of sonic waves fsezkmic1. Anomafies such as near surface disturbance (often known as Woz3e9 are common in the urban environment and may Mt the usefulness of geophys~ks in these areas. Moreover, a geophysical anomaly does not always match an engineer~hg or geological boundary, and often there is a transitzon zone at a boundary. Thzk may lead to a margin of uncertaznty, for example, in detemuning the depth of sound rock that has a weathered boundary or overlying boulders.
Good results in geophysical techniques are obtained when the geo/ogcal conditions are relativey szhple, with large clear-cut contrasts in the relevant physical properties between the formatzons. However, less favourable ground condithns may st271 warrant consideratrun of geophysics, partzcularly a t an ear@ stage in an investigatzon, because of the relatively low cost and h~gh speed of the methods, e.g. to assist in ehhhatrirg alternative explanations of .
the geology. It may a t t im be necessary to use two or more methods on a trial and error basis to ascertain which yie& the most reliable results.
Geophysical surveying is genera& used in a ground inveshgation to make a prefiminary and rapid assessment of the ground conditions. In favourable condZions, a geophysical technique may jhdicate varjatlbns and anomalies which can be correlated witb geological or man-made features. The results of geophysical survey can then be used to ~hterpolate the ground condihons between boreholes, and to indicate locations where further boreholes are needed so that the significance of a geophys~kal anomaly can be investigated
33.2 LAND GEOPHYSICS
33.2 1 Resistivity
This technique is used for in vestigating the simper geological problems. A current is usuafly passed into the ground through two metal electrodes, and the potential difference is measured between two similar electrodes fBS/, 1965). With suitable deployment of the electrodes, the system may be used to provide information on the variation of geo-electrical properties witb depth (depth probes), lateral changes in res~stivity (constant separation tra versing) or local anomdous areas lequipotenhhl survey). e.g. karst features, disused tunnels or shafts. The unsuspected presence of electrical conductors, e.g. pzpes or cables, under the site wili of course, render the results unrelkble. The interpretation of the results obtained by this method does not always provide a definl'te solution, particuMy as the number of subsurface layers increases, because it involves a curve matching technique which requh-es the assumption of idealised conditions.
33.2.2 Gra v~inetric
In ground investigation, the gravity survey is nerdy fimited to locating large cavitles or faults. Precision levelfing and positionlirg of the . instrument a t each station is essentiaL With the more accurate instruments now available, it is possible that the gravity survey method wi// become a useful tool in Iocatlirg hidden shafts and smaller cavities.
33.2 3 Magnetic
Local changes in the earth's magnetic field are assoc~hted with changes in rock types. In suitable circumstances, the technique may locate boundaries fe.g. faults or dykes) between rocks which display magnetic contrasts. However, its main use in the civd eng~neering field is the location of buried metafliferous man-made objects, such a s cables or pipelines. It can sometimes be used for locating OM mine shafts and areas of fij% In using this method to detect the locatlbn of faults or dykes, it is, of course, essenhhl to ehinhate the poss1E17ity that the anomaly detected is in truth buried metal.
33.24 Seismic
The seism~c technique, either refection or refraction, may be used to locate subsurface boundaries which separate materials havlhg dXferent values
of sonic wave velocities. In carryhg out geophysical surveys on land, the refraction method is the one most frequently used. It involves producing seismic waves, either from a snm7 explosive charge or from a mechanical source fe.g. a hammer), and measuring accurately the time taken for them to travel from the point of origin to vibration detectors fgeophones) at varying distances away.
The greatest use of th& technique is in the determ~naation of bedrock level (McFeat-Smith et al. 1986). Therefore, 12 IS commonly used iff the estimation of quanti'ties of soft mated& avadable from a borrow area site. One limitaation of seismic refraction, however, IS that when the velocity of transmiss~on in the upper layer is greater than that below fe.g. if very compact gravel overhks a clay), then the intervening boundary cannot be detected and false layers may appear to be present. Another use of this technique I> to provide wave velocity data for the assessment of h s i t u dynamk modulus values of rock masses fMeigh, 1977). O n l y rarely will the dynamic and static modulus values be the same. Environmental consideratibns sometlines limit the applicatibn of this test. For example, exp/sives cannot be used in urban areas, and where the site lies near to the source of vibrations, such as a busy road, the lnduced vibration may not be detectable.
By travershg a seismic refraction survey configuration, the resulting variation of velocity along the traverse can be used to indicate areas of different rock types or fracture zones. This information is useful in dec~'ding the type of equ~bment to be used for rock excavation.
Direct seismic measurements can also be taken between two boreholes. or from surface to borehole or borehole to surface. These techniques may be useful for assessing the properties of the intervening rock mass, and in detecting geological features such as cavities. Cross hole surveys, i.e. between boreholes. may provide the best geophysical means for detecting cavities at depth (McCann et al. 1987). but results can only be confirmed by subsequent drilling.
33.3 MARINE GEOPHYSICS
33.3.1 General
lu'ih suitable md~fications of equipment, the land survey techn~bues, such as s e k m ~ c refraction, magnetik and gravimetric techniques, may be extended to the marine environment. Of greater use, however, are the techniques that have been developed specifically for offshore work; these are described ~n the fofloowing three sections. It is necessary to a p d y tidal corrections to the data obtahed, reduchg them to an appropriate datum level for proper interpretation. I t is also important to establish preche survey control 17 the capacity for detailed structural identZcafibn I> to be explo12ed fully. Where appropriate, electronic naviqation systems should be employed.
In Hong Kong, the presence of sewage-rich seabed layers and certain naturally gassy marine mud deposits results in 'masked zones', which can severely limit the effectiveness of a geophysical survey.
33.3.2 Echo -Soundhg
A continuous water depth proflye dong the track of a survey vessel is
obtmhed b y using an instrument that measures the the taken for a short pulse of a high frequency sound wave to travel from a transducer attached to the survey vessel down to the seabed and back again. Such profies are combined to produce a bathymetric chart. However, additronal control may be required to ascertain whether the sounding is reproducing reflectrons from soft surface sediinents or higher density maten2 underneath, and dual frequency sounders may be useful for th~i.
33.3.3 Continuous Seismic Reflechon Profiling
The use of continuous s e ~ k m i refiecoon profizng should always be ~ 0 f l s ~ ' d e ~ e d as a complementary aid to exploratory boreholes in major offshore investigations. An extension of the echo-sounding principle is used to provide informaobn on sub-seabed acoustic reflectors which usually correspond to changes ~h materid types. The instrumentation required, especially the types of acoustk source, depends on the local ground cond~'trons and its choke should therefore be left to a geophysickt who has suitable exper~ence. A s a guide. the higher frequency sources such as pingers' and 'high resoluthn boomers' are generally suitable for resolving near surface layering, whereas 'standard boomers' and 'sparkers' are more suited for coarser and t h ~ i k e r layers. Typically, h g h redut ion boomers have a resolution of about 0.5 m and a depth penetrahon of about 80 m.
The results may give a vkual representaoon of geologfid features. but quantitative data on depths to interfaces can only be determined if vel0c1.oe.s of transm~ision are known.
There are two mah Mtat lons to the technique. Firstly. 12 cannot u s u d y delineate the boundary between two different materikls that have s1in17ar geophysical characteristhx; secondly, in water depths of less than about 2 m, near-seabed ref/ctors may be obscured b y multlkle reflectlbns originathg from the seabed. O t h e r problems are described in Table 11.
33.3.4 Side Scan Sonar
This is an underwater acoustk technique analogous to oblique aer12 photography, enabling dz>conthu~'oes and profiles offset fm the line of traverse to be recorded for subsequent bathymetric charthg by echo-sounding or other techniques. It is based on the reflctlbn of high frequency p u b of sound b y the seabed. The results provide a quantitative guide to the posioon and shape of seabed features and a qualitative gukfe to the type of seabed material. The system is partkularly useful in searches for rock outcrops, pipelines, trenches and seabed obstruct~ons, such as wrecks.
W12h suitable instrumentaoon, certain geophyskd techniques may be adapted to provide logs of boreholes that are anahgous to convenfional geologial logs. These borehole logs may be used for geologial correltrbn purposes across a site. ~dd~%ionally, analysh of the data can assist ih the assessment of insitu values of parameters such as dynamic moduli and density. The normal techniques cons~kt of sehmic /structural data), eleceical fstratigrphical data), gamma gamma fdensity datal, natural gamma fstrahgraphical datal and cal~;Oer fborehole diameter datal; all these techniques
are d~kcussed by Brown (1 981 ). Experience in the use of these methods I> at present relatively lim'ted and the data obtruned should always be correlated agahst the examinathn and testhg of borebole samples and against the results of other insitu tests.
33.5 CURRUSIDN TESTING
Electrical res~ktrkity may be used to assess the corrosivity of sods towards ferrous materials. Con venobnal traverses with fixed hterva/s between electrodes enable rapid coverage of the ground and the locaoon of areas of low res~ktivjty. The spacing between electrodes should be appropr~kte to the depth of bur12 of the ferrous materfa. The conventibnal 'expansion' technique using "depth probes" (see Secfion 33.211 may also be used to determine the var~athn in so17 resistivity with depth. Generdy, the likelihood of severe corros~bn decreases as the resistivity rises (see Chapter 13 and Table 12) .
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34, PRINCIPLES OF LABORATORY TESTING
The ams of laboratory testing of samples of soil and rock may be summarized as follows :
fa/ to identify and classify the sampfes with a vfew to making use of past experfence w~2h mater~kls of similar geofoqical age, origin and condition, and
fb/ to obtain soil and rock parameters relevant to the technical objectives of the investigation.
A thorough discussion of laboratory test ing is beyond t h e scope of th is Geoguide. However, some basic aspects a r e briefly reviewed i n Chapters 35 t o 38 a s laboratory test ing is considered t o be a pa r t of t h e ground investigation, and t h e overall s i t e investigation would normally not be complete without i t . Fur the r guidance on laboratory test ing of rocks and soils is given i n Brown (1981) and BSI (1975b3 respectively. The Geotechnical Manual for Slopes ( G C O . 1984) discusses t h e test ing of Hong Kong rocks and soils in particular. Guidance on t h e description and classification of Hong Kong rocks and soils is given i n Geoguide 3 (GCO, 1988).
A general unders tanding of t h e ground conditions a t a s i t e i s essential before embarking on a programme of soil and rock test ing. I t is also necessary t o consider carefully how t h e data obtained from t h e tests a r e t o be used, and whether t h e information can ass is t in t h e solution of t h e engineering problems concerned. As general guidance. t h e t e s t method t o be used should have d i rec t relevance t o t h e engineering problem at hand and should simulate t h e field conditions a s closely as possible.
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35, SAMPLE STORAGE AND INSPECTION FACILITIES
35.1 HANDLING AND LABELLING
The general procedures for handling and labelling of samples in the field are given in Sec&bn 19.10. Samples should be treated with equal care on arrival at the core store or at the laboratory.
35.2 STORA CE OF SAMPLES
A n orderly procedure shou/d be established so that each sampfe is registered on arrival and is then stored away in such a manner that it can be located readily when required for examinalbn or testing. Disturbed samples should be stored on shelves, and, where jars are used, they should be placed in purpose-made carrirs. General purpose 100 mm diameter samples shou/d be stored on their sides in purpose-made racks, while thin-walled or piston samples containing soft clays shouM be stored ver&bally with the same orientation as in the field prior to sampling. The sample storage area should be of sufficient size to cater for the number of samples being hand/ed. without overcrowding (see also Secoon 19.10.1).
35.3 INSPECTMh' FACILITIES
An important feature is a sufficient area for the temporary stacking of the samples, and an adequate amount of bench space for the actual inspection. The fohwing equipment should be provided :
(a) an extruder for removing general purpose 100 mm diameter samples from the sampler tubes,
fbl an adequate number of trays to enable disturbed samples of granular soils to be &;Oped out for inspection, and some means of returning them quickly to the]> containers afterwards,
fcl spatulas and knives for splitthg general purpose 100 mm diameter samples,
fd ) dilute hydrocMoric acid for the ia'en&Zcation of soils and rocks,
fel a water supply and appropriate sieves for washing the fines out of samples of soils to facilitate descr~ption of the coarser particles, and for cleaning rock cores and block samples,
f f J a balance suitable for check~hg that the weight of bulk samples I> adequate for testing,
fg) a sufficient number of dustbins, or other means of disposal, to contain samples not required after inspec&on,
fhl means o f resealing samples required for further use,
fi) washing facifities for the person inspecting the samples, so that notes can be kept as tidy as possible,
lj) hand lens, geological hammer, penknife, metre scale and protractor for logging cores,
fk) simple stereo-microscope with magnification to x30, where necessary,
f/l adequate photographic facilihes (see Section 36.4).
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36, VISUAL EXAMINATION
36.1 G E N E R A L
The exam~hraOon and demp t i on of samples of so17 and rock i s one of the most linportant aspects of ground investigation. The results of a ground investigatlbn may need to be used long after the disposal o f the samples, i n which case the descriptions are, i n many cases; the only remaining evidence of what was discovered.
Detailed guidance for t h e description of soils and rocks is given in Geoguide 3 ( G C O , 1988).
36.2 SOIL
All disturbed soil samples, both jar and bulk, shouh' be examined individually and described by means of a permanent record made either on site or short& after the samples arrive i n the laboratory. It i s customary during sample descript~on to examine the ends of undisturbed samples or to examine the jar sample obtained from the cutting shoe where it has been used, or both. However, all undisturbed samples shou/d be re-examined each time a specimen is taken for testing as colour changes or drying o f the s a m e may have taken place. m e n it i s known that no further soil testing i s likely to be required, the remaining undisturbed samples shou/d be extruded and split down the midde fo r examinatlbn, description and photographing.
36.3 R O C K
A complete rock descriptlbn should cover both the rock material and rock mass characteristics. The latter cannot be determined from individual samples, but may be deduced to some extent from many sampfe descriptions and other data. Where the mater~hl characteristics are not obvious, thin sections are a valuable aid to f i rs t assessments made with a hand lens.
In t h e examination and description of la rge rock samples and rock cores, part icular attention should be paid to t h e location and na tu re of discontinuities. The reduced level of shea r zones and o the r major discon- tinuities should be deduced a n d recorded. Other details such a s orientation. roughness and infilling should also be noted. If t h e discontinuities contain infilling material, both th i s and t h e adjacent materials should be described. Where possible, an undis turbed sample of both t h e infill and i t s surroundin,g material should be extracted for test ing purposes. For projects where t h e na tu re of discontinuities i s particularly important, a separa te detailed discontinuity log should be prepared (Figure 35).
36.4 PHOTOGRAPHIC RECORDS
Photographic records, particulary if they are in colour, are a most valuable supplementary record, althaugh they cannot reflace visual descripoon comp/ete/y. Where the purpose of the photographs i s to provide a continuous record, the same scale should be used throughout. The photographs shou/d be free from distortlbn norma/ to the surface and should contain a clear scale.
A s t andard colour c h a r t should be included in all colour photographs. When photographing rock core, t h e b e s t effect can often be obtained by wetting t h e surface of t h e core f irs t . Soil samples should be photographed a t natural moisture content wherever possible, particularly if test ing is t o be under taken on t h e samples. In some instances, allowing a soil sample to d r y o u t partially may make differences in composition o r s t r u c t u r e clearer (see Section 22.2).
189
37, TESTS ON SOIL
37.1 G E N E R A L
Laboratory tests on soil are undertaken on a routine basis to determine classification, strength, deformation, permeability, compaction and pavement design parameters. Dispersion, collapse potential, chemical and corrosivity tests may also be carried out. Table 12 lists the range of laboratory tests on soil and groundwater, together with references and remarks on their use. Some of these tests are reviewed in more detail in the Geotechnical Manual for Slopes ( G C O . 1984). It is important to ensure that tests are carried out on samples that are truly representative of the materials at the site. For this purpose, a full and accurate description of all samples tested should always be recorded. When laboratory tests are not likely to be representative of the mass behaviour of the ground at the site, the laboratory tests should be supplemented or replaced by appropriate field tests.
fn many cases, a field test wifl give more reafistic resufts than a laboratory test because of reduced problems of sampfe disturbance. However. there is a large body of practr'cal experience behind some of the common laboratory tests, and when the data derived from them are used w11h skdL reliable predictions can be obtahed. The general consideratlbns set out in the following four sections should be borne in mind.
37.2 SAMPLE QUALITY
Quah2y classes are defined in Secbon 19.2 It is essenttkl that the sample used is of sufficiently h~gh quality for the test in questlbn. HaffdHng of samples ~ i , the field is described li, SectJon 19.10. When samples arrive in the laboratory, dl necessary steps should be taken to ensure that they are preserved and stored at their natural moisture content and suffer the minimum amount o f shock and disturbance. Very often tests are carried out on 'undisturbed' samples whlich are far from undisturbed. In addition, the samp/ing process itself will have released the ii71'21kl state of stress in the samp/e.
In preparing the laboratory test specimen, there is further disturbance and unavoidable change in the stress conditons, and hence the test is not generdy carried out under the same stress C O ~ ~ J - ~ O ~ S as those which exist in the natural ground (see Section 37.41.
37.3 SAMPLE SIZE
For disturbed sampfes, the amount of so17 required for any partjcular test I> given in Table 7. A s the behaviour of the ground I> greaffy affected by discontinuioes, 'undisturbed' samples should ideafly be sufficiently large to include a representative pattern of these discontinuities. ThLs can often be achieved by the use of large 'undisturbed' samples.
37.4 TEST CONDITIONS
Where the test can be carried out under severaf d~yferent sets of conditons, e.g. in the determinoon of soil strength, the parb'cular test
selected should be the one in which the cond~'&ons correspond most closely to t h e that win exist in the field at the particular t h e which is being considred ~h the des~gn.
37.5 RELEVANCE OF TEST RES'UL TS
Some laboratory tests are suitabl.. on& for partkul 'r types of sod In cases, where a test has been carried out and it is found later that the test was not relevant to the actual sample used, the result shouh' be discarded.
38, TESTS ON ROCK
The behaviour of rock masses is often controlled by the nature of the discontinuities present and their orientation to the stresses created by the works or during their construction. In most cases, the scale of disconthuitlis is such that tests on laboratory specimens may yield results whch cannot be appfied directly to the behaviour of the rock mass. In considering laboratory tests on rock, a clear distinction needs to be made between tests which relate to the behav~bur of the ruck mass as affected by the proposed constructhn and tests which are relevant only to the rock materid.
Laboratory t e s t s on rock material a r e under taken t o determine classi- fication. s t r e n g t h and deformation parameters. Tests t o determine t h e basic s h e a r s t r e n g t h of specific discontinuities may also be undertaken. Table 13 l is ts t h e r ange of common laboratory t e s t s on rock, together with references and remarks on the i r use. Some of these t e s t s a r e reviewed in t h e Geotechnical Manual for Slopes (GCO, 1984) and BSI (1981a). The significance of t h e size and quality of t h e sample, t h e t e s t conditions and t h e relevance of t h e resul t s , a s discussed in Chapter 37 for soils, also apply in general t o tests on rock.
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PART V I
REPORTS AND INTERPRETATION
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39, FIELD REPORTS
The essential requirement of a field r epor t i s t h a t i t should contain all t h e da ta necessary for t h e subsequen t interpretat ion and u s e of t h e borehole o r field test . Field r epor t forms should b e easy t o fill in and well laid o u t so as t o encourage t h e opera tor o r field supervisor t o record all necessary data. Such forms can in many cases be based u p m t h e i l lustrat ive logs contained in th is Geoguide, b u t these need not b e regarded a s s t andard a s o the r forms may also be satisfactory. Examples of o the r field r epor t forms can be found in BSI (1981a).
The existing ground level, t h e location of a n y boreholes, and t h e location and level of any points of sampling o r tes t ing , should always be recorded. Where possible, t h e locations should take t h e form of reference coordinates based on t h e Hong Kong Metric Grid and levels should b e referenced t o t h e Hong Kong Principal Datum.
Daily r epor t s form t h e basis of good field r epor t s on ro tary drilling. I t is not uncommon fo r dri l lers t o keep the i r r ecords on odd sc raps of paper while drilling i s in progress and t o make up the i r daily r epor t forms from these notes at t h e end of t h e day. This practice should b e s t rongly discouraged and t h e dri l ler should b e provided with a s t andard notebook which can, if necessary, be checked against t h e daily r epor t a t a l a t e r date.
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197
40, SITE INVESTIGATION REPORT
Interpretation is a contrhuous process which shouM begin in the prehhinary stages of data coflectron and should proceed as information fm the ground invesligation becomes available. By using this information J? 13 often possible to detect and resolve a n o d e s as fied and laboratory work progresses. Engineering problems should be considered as the data becomes available so that the engineer in charge of the ~nvestigation can decide what additional exploration and testing needs to be carried out or conversefy, where appropriate, what reductions in his original programme are possible.
When an engineer~hg interpretatrun and recommendations are requ~ied the report is best prepared in two distinct and separate parts, one a descriptive report covering theprocedures employed and the data obtained, and the other the analysis, conclusions and recommendations. A general account of the style and format of a report is given ekewhere (Palmer, 19571.
40.2 DESCRIPTIVE REPDRT
40.2.1 Report as Record
In preparing a report, it should always be remembered that a few months after it is written, when all the samples have been destroyed or rendered unrepresentative, the report w1jr1 be the o d y record of what was found Generdy, the results will be presented in an appropriate format ln a formal report, which shouh' be bound and issued in a number of copies. This f o r d report wi// contain a description of the site and the procedures used, together with tables and d~kgrams giving the results. In additrbn, there w~jrl be the field and laboratory report forms and data sheets, whkb provide a detaiM record of the data that were obtahed These forms are sametlines not included in the f o r d report, but shoufd in any case be preserved for a suffic~ently long periad so that they can be made a va~Yable for reference when necessary at a later date.
A copy of all descriptive reports should normally be lodged in the data bank of the Geotechnical Information Unit (see Appendix B).
40.2.2 Introduction
The report should have an introductron stating for whom the work was done, the nature of the in vestigatron and its genera/ /ocatron, the purpose for which the investigatrbn was made and the period of trine over which the work was carfled out.
40.2.3 Description of Site
The report should contain an unambiguous description of the geogra- phical location of the site, s o that the area covered by the investigation can be located readily at a later date. This should include street names together with Hong Kong Metric Grid references and a location map at an appropriate scale. The description should also include general statements on site
conditions at the time of investigation.
40.2.4 Geology
A n account should be given of the geology of the site, and the sources from which the information was obtahed should be stated (see Section 4.21. The amount of the data included wil depend upon the nature of the work being planned and also upon the amount of data available. The soil and rock types identified and described in the report should be linked with the known geology of the site, see Geoguide 3 ( G C O , 1988).
40.2.5 Field Work
A n account should be given of the methods of investigation and testing used. It should include a description of a// equipment used. e.g. types of dr17iing rigs and took. A note should be made of any d2Yficu/tls exper~enced. e. g. problems in recovering samples. Tbe dates when the exploratory work was done should also be recorded. together with a note about the weather conditions where appropr~ate. The report shouh' contan a drawing indicating the positions of all pits, borehoks, field tests, etc. I t should contain sufficient topographkal ~nformathn so that these positlbns can be located at a later date.
4#,2.6 Borehole Logs
1 Genera/. The final borehole logs should be based on the visual examination and descriptrbn o f the samples, the laboratory test results where appropriate, the drifler's da7y report forms and what I> known of the geology of the site. Being an interpretation of ground data which may at times be confiicting. the logs should be finaiised only when the appropriate field and laboratory work has been conpleted. It IS important that dl relevant data collected b y the driller, once checked and amended where necessary, shouM be recorded.
The method of presentation of the data IS a subject on whkh there can be no hard and fast rules. In prhcip/e, the borehole logs shouh' give a picture in diagrams and words of the ground profi/e at the particular point where the borehole was formed. The extent to which minor variations in soil and rock types should be recorded. together with any disconthuities and anomaiies, will depend on the various purposes for which the information wifl be used.
Most organizations carrying out site investigation have standard forms for borehole logs. It IS se/dom practicable in these to make aflowance for all data which may possibly need to be recorded. It is therefore hportant that an adequate space for remarks is available to allow a record to be made of items that are not specifically covered. An expedient which makes a standard form rather more flexible is to leave one or more columns without headings so that they can be used according to the data to be recorded.
A l l borehole logs are a compromise between what it is desirable to record and what can be accommodated. lu%rat is actually presented will need to be considered i n d ' u a f l y for each inves&gatzon. Where the data are copious, it may be preferable to record part of them elsewhere ~h the report,
with a cross-reference on the logs. The subsechons whkh follow indicate the data which a well-prepared borehole log may contain.
f2l General Data Common to Al l Logs. The foflowing should be recorded on all logs :
/a) title of inveshgation,
/bl job number or report number.
fcl location detailed by grid references,
/a') date of exploration,
/el borehole number and sheet number. e.g. sheet 2 of 2
/// method of forming borehole, e.g. cable percussion or rotary,
fgl make and model of plant used,
( h ) ground level related to the Hong Kong Principal Datum,
fil d~ameter of borehole,
fJ'I dimeter of casing and depth to which the casing was taken,
fkl a depth scale such that the depth of sampfing, tests and change IR ground conditions can be readily determined,
/I, depth of termination of borehole,
fml depths of observatlbn wells or piezometers, where these have been ~hstalled, together with details of the installation, preferably in the form of a diagram,
fnl groundwater levels measured subsequent to the com- pletion of piezometers, unless recorded separately.
(3) Le.qend and Symbols. The ground profiles shouh' be illustrated by means of a legend using the symbols ii'lustrated on figures in this document, andmore fuflypresentedinGeoguide 3 (GCO, 1988) . The legendis most commonly placed near the centre of the sheet, which enables reduced levels, depths, thicknesses and sampling data to be arranged conveniently on either side. An alternative is to have it a s the extreme right hand column, which enabfes the logs of adJhcent and nearby boreholes to be readily compared wit3out fold~hg or cutting the sheets.
Apart from the symbols referred to above, no recommendahons are given for the many other symbols required for the preparation of borehole logs. Many different types are in use, and provided an adequate key is given with every set of borehole logs, there shouh' be no difficulty in interpreting them. The symbols may be given on a separate sheet or on each sheet Both methods have advantages and corresponding disadvantages. The first saves space on the actual logs, thus enabling a greater depth to be logged on each sheet or a larger 'remarks' space to be provided. It does have the
disadvantage that the reader may need constantly to refer back to the key.
f4l Light Cable Percuss~on Boring. For light cable percussion bor~hg, in addition to the items referred to in Sections 40.2.6f21 and 40.2.6f3, the foflowinq information should be recorded in the log :
fa/ A descr~bfion of each zone or materid type together with its thickness.
fbl The depth and level of each change of zone or material type.
fcl The depth of the top and bottom of each tube sample, or bulk sample and its type (see Chapter 191; the depth of each small disturbed sample.
/dl The deith at the top and bottom of each borehole test, and the nature of the test.
( e ) For standard penetration tests, it should always be noted if the sampler has not been driven the full 450 rnrn required for the test (see Section 21.2.3).
ffl The date when each section was bored.
fgl A record of water leveh, including rate of rise of water /eve/, depth of water in the borehole a t the start and f i n i s h of a shift, and the depth of casing when each observation was made.
fhl A record of any water added to facilitate boring.
5 Rotary Dr17fing. For rotary drilling, in additon to the items referred to in Sectlbns 40.2.6f21 and 40.2.6f31, the following information should be recorded in the log :
fa) A description of a// ground cond1Zi0n.s encountered
fbl The depth and level of each change in ground conditions.
fcl The depth of the start and finish of each core run.
fdl The core recovery for each run, usuafly expressed as percentage total core recovery( G C 0 . 1988 ) .
fel For rock, the fracture state, expressed in terms of one or more of the foflowing : rock quality designation /ROD), solid core recovery or fracture index (GCO, 1988).
f f l The date when each section of the core was drilled
fgl An indication of the drifling water recovery for each core run, with a note on any change in colour.
fhl A record of the depth of water in the hole a t the start and finish of a shift and the depth of the casing, where
used, at the t h e the observafions were made.
0 A record of tests carried out, such a s permeability and packer tests.
fj, The or~entation of the boreholes.
(8) Summary or Condensed Log. Where an investigation contains a large number of deep boreholes, the full logs can add up to a substantial weight of paper, and to include all of these in each copy of the report may be unnecessary. An alternative i s to include only summarized or condensed logs in the report itself, provided these are sufficiently comprehensive and significant details are not omitted.
An example of a borehole log is given in Figure 44 .
40.2.7 Incidence and Behaviour of Groundwater
/n order to obtain a clear understanding of the incidence and behavbur of groundwater, it is essential that al/ data collected on the groundwater shouh' be included and that, where no groundwater was encountered, this too should be recorded. &%ere the informaatlbn derived from boreholes is not too voluminous, it is best included in the logs. When this is not possible, the data should be given elsewhere in the report and cross-referenced in the boreme logs. m e r e the pos12ion of the borehole casing at the time o f an observation is relevant, 12s positlbn should be stated All other data, including those from separate observation wells or piezometers, should be given separately. Where drMng with water or air flush has been used, this should be recorded and 12s effect on groundwater levels should be assessed.
The report should contan a plan showing the prec~se location and top level of each borehole (see Chapter 39).
40.2.9 Laboratory Test Results and Sa&e Descr~pfions
Where test procedures are covered b y recognized standards, the reporting o f the results shouM be in accordance with those standards, where they are not so covered, relevant data should be given. For example, i n a triaial compression test the actual numerical result on each specimen should be given and not only the hterpreted parameters, Where an extensive programme of testing has been undertaken, a summary should be provided in addition to the detailed results. The precise test carried out should a/so be stated without ambiguity. Where the test is reasonably standard, for instance "consoLidaated drained t r ~ k i a l compression test on 100 mm diameter samples'; the name alone wAl suffice, but where the test is not standard, a full d e s ~ r ~ p t ~ ~ n should be given.
The visual descriptions of a// samples tested should appear in the report. The precise method of recording them wifl depend upon circumstances. I t may be convenient to show them on the same sheets as the results o f the laboratory tests, or a separate table may be preferable.
In a n y even t , t h e descript ions should all appea r in one place. A t times, t h e resul t s of t h e laboratory t e s t s . and in part icular t h e identification t e s t s , will indicate a soil different from t h a t indicated by t h e visual description. The original description should not be discarded on t h a t account b u t should be preserved a s a record of t h e obse rve r ' s opinion. If soil descript ions have been modified in t h e l ight of laboratory t e s t data, th is should be indicated clearly in t h e r epor t , see Geoguide 3 ( G C O , 1988). The laboratory r e p o r t forms and da ta shee t s should be filed fo r possible f u t u r e reference (see Section 40.2.1).
40.3 ENGINEERING ZNTERPRETA TION
40.3,J Matters to be Covered
Methods of analysing ground data and apply~hg them to the solution of engineering problems are not covered ~n this Geoguide. Guidance on analysis and application of ground data may be found in various Britsh Standards (e.g. BSI. 1965; 1973; 1974b; 1975a; 1977; 1981b; 1986) and localguidance documents (e.g. Geotechnical Manual fo r Slopes and Geoguide 1 ) . Sections 40.3.2 to 40.3.9 deal w12h the form of the report, and fist the most common topics on which advice and recommendations are required. Tbese sectJons also contain some guidance on what shou/d be included. The topics are listed briefly under the general headings : design, construction expedients, sources of mater~als, and f i e . It is Mely that ~ i z many cases the d e n t commiss~oning the investigation wz7l indicate those aspects of the project on which he requires advice and recommendations; the topics fisted below are intended as a guide where t h z s may not have been done.
40.3.2 Data on which Interpretation is Based
fie data on which the analysis and recommendations are based shouh' be clearly indicated. The information generafly comes under two separate head'ngs :
(a/ Information related to the project (which is usually suppfied b y the des~gnerl. For example, for buiMings and other structures this should include full details on the /Oadlhg (including dead and five loadsl, column spacing (where appropriate/, depth and extent of basements and details of neighbouring structures. For earthworks, the he~ght of embankments, the materials to be used and the depths of cut slopes are relevant to the interpretatJon.
fb1 Ground parameters (which are usuafly selected from the descriptive report by the engineer who performs the analyszk and prepares the recommendatJbns). There is no universally accepted method of selecting these parameters, but the following approach may he& to arrive at refible values :
fil compare both laboratory and insitu test results with ground descriptJons,
fiil cross-check, wherepossible, laboratory and insitu results in the same ground,
hi2 colect individually acceptable results for each ground unit, and decide repre- sentative values appropriate to the number of results,
fivl where possible, compare the representative values with pubfished data for similar geological formathns or ground units.
40,3,3 Presentatrbn of Borehole Data
For the purpose of analys~s, it I> frequently necessary to make simp/iying assumptions about the ground profile at the site. These are best conveyed in a report by a series of cross sections i//ustrating the ground profile, simpfified as requ~ked, and showing the groundwater levels. The sections should preferably be plotted to a natural scale. I f it is necessary to exaggerate the vertical scale, the mult~;Olying factor should be hinited to a void conveying a misleading impression. Mere the ground information is either very var~kble or too sparse to enable cross sechons to be prepared, indJ'v~'d~ia/ borehole logs plotted diagrammatically are an acceptable alternative. I f it is particularly important to prepare cross sections, sparse and variable informat~on can sometimes be supplemented by means of hformation from soundings and geophysical in v e s t i g a t h on areas between borehok. It can be helpful to indicate relevant soil parameters on cross sechons, for example, results of standard penetration tests, triaxial tests and representative parameters from consoMation tests.
In certain engineering problems, i t may be useful t o cons t ruc t contours of t h e bedrock and groundwater surfaces from borehole data. In marine investigations, contours of t h e seabed. and contours and isopachs of t h e various s t ra t igraphic units below t h e seabed, may b e cons t ructed .
40.3.4 Design
The following list, which is by no means exhaustive, fffdicates the topics on which advice and recommendations are often requ~ked, and also what should be included in the report.
( a ) Slope stability: geological model; s h e a r s t r e n g t h parameters; water p ressu res for t h e design condition; assessment of r isk t o life and economic r i sk ; recommended slope angle. Comment should be made on surface dra inage and protection measures, and on a n y subsurface drainage requi red . For rock slopes, a n assessment of potential failures due t o unfavourably orientated discontinuities should be made. Possible methods of stabilizing local a reas of instability and surface protection measures should be recommended. Advice on monitoring of potentially unstable slopes should also b e given ( G C O . 1984).
( b ) Retaining walls: e a r t h and water p ressu res ; passive and frictional resistance; foundation bearing capacity, see Geoguide 1 (GEO, 1993).
(c) Embankments: stabifity o f embankment foundahons; assessment of amount and rate of settlement and the possibifity o f hastening 12 by such means as vertical drains; recommendations for side shpes (see fa) abovel,. choice of construction materiXs and methods.
fdl Drainage.' possible drainage methods during construction for works above and below ground; general permanent land drainage schemes for extensive areas.
(e) Basements: earth and water pressures on basement walls and floor; comment on the possibility of flotation. An estimate of the rise of the basement floor during construction should be made. where appropriate.
If) P~i/es.' types of piles suited to the ground prome and environment; estimated safe working loads, or data from which they can be assessed; estimated settlements o f structures.
fg) Ground anchors: bearing ground layer and eshhated safe loads, or data from wh12 they may be calculated, e.g. suitabifity tests (Brian-Boys & Howells, 1984).
/hl Pavement des~gn: design Cafiforn~k Bearing Ratios; type and thickness of pavement; possibifity o f using soil stabfization for forming pavement bases or sub-bases; recommendations, where appropriate, for sub -grade drainage.
f i) Tunnels and underground works. methods and sequence o f excavation; whether exca vahun is likely to be stable without support,. suggested methods o f f i n g i n unstable excavahons; possible use of rock bolting; possibi/ity o f encountering groundwater, and recommendatrons for deafing with it.. specia1 features for pressure tunnels.
fj) Safety of neighbourhg structures: fikely amount of movement caused by adbcent excavations and groundwater lowering, compressed air working, grouhng and ground freezing or other geotechnical processes. The possibifity o f movement due to increased loading on adjacent ground may also need to be considered
fkl Monitoring o f movements: need for measuring the amount of movement taking place i n structures and slopes, together w12h recommendahons on the method to be used (see Sectian 16.4); recommendahons for taking photographs before the commencement of works (see Section 4.1.21.
1 Chem~eal attack: protechon of buried steel or concrete against attack from aggressive soils and groundwater.
40,3.5 Construction Expedients
comments and recommendabons are often required on the points listed below. Safety aspects should be included where appropriate.
/al Open excavations; method and sequence of excavabbn; what support is needed; how to avoid 'boiling' and bottom heave; esbhated upward movement of floor of excavation; relative merits of sheet pihng and diaphragm or contiguous bored p17e wa//s where appropriate.
/bl Underground excavations; method and sequence of excavation and the need for temporay roof and side support.
/cl Groundwater: Me ly flow, head and quantity and how to deal with 12.
/d/ Driven piles, bored piles and ground anchors: methods of driving or construction suited to the ground profile, environment and neighbouring buildings.
/el Grouting: types of grouts Me ly to be successful in the ground and recommended method o f injecbon.
ftl Mechanical improvement of so17 below ground /eve/. suitabifity of techniques for the consolidation of loose soils.
40.3.6 Sources of Materjals
The foflow~hg are suggested :
fa) F i f l possibility of using excavated mater~hl for filfing with an assessment of the proportions of usable materiak methods and standards of compaction; possible off-site sources of filk bulking factor.
(b) Filter materials, concrete aggregates, road base and surfacing materials: possible sources and the suitability of the materials from these sources.
Where site ~hves&gabon has been undertaken ~h an attempt to ~'denbyy the cause of faii'ures the undermenboned points may be relevant.
fal Foundations: nature and d'hensions of the foundabbns; idenbficathn of the cause of faihre and, where appropriate, an estimate of the amount of settlement which has already occurred, together with an assessment of how much more is likely to occur and its probable effect on the structure; cause of excessive vibrations of machhe foundabbns; recommendations for remedial measures.
fbl
fcl
fdl
fe)
Landsfides: cc/assificatJbn of the type of movement and locatfun of the fa~jrure planes; recommndathns for immediate stabifizing expedients and long term measures.
Embankments: identification of whether the seat of faihre f i e within the embankment itself or the under/yig foundatJun, the probable cause and suggested method of repair and strengthening.
Retaining waLls; cause of failure or excessive defectJon; forecast of future behaviour of wall and recommendations where appropriate for strengthening it.
Pavements; determfnation of whether the f a k - e is within the pavement itself or the sub-grade and recommendations for repairs or strengthening or both.
Where cdculations have been made, they shouM be included as an append~k, or a clear indication of the methods used shouM be given.
40.3.9 References
Al l pubfished works referred to h the report shouM be fisted.
REFERENCES
Addison, R . (1986). Geology of Sha Tin. 1:20 000 Sheet 7. Hong Kong Geological Survey Memoir No. 1, Geotechnical Control Office. Hong Kong. 85 p.
Akroyd. T.N.W. (1969). Laboratorv Testing in Soil Engineering. Soil Mechanics Ltd. London, 249 p.
Allen. P.M. & Stephens. E.A. (1971). Report on t h e Geological Survey of Hong Kong, 1967-1969. Hong Kong Government Press , 116 p, plus 2 maps.
American Public Health Association (1985). S tandard Methods for t h e Examination of Water and Wastewater. (Sixteenth edition). Pa r t 427- Sulfide. American Public Health Association. Washington D.C.. p p 470- 478.
Anderson. M.G. (1984). Prediction of Soil Suction for Slopes in Hong Kong. G C O Publication No. 1/84. Geotechnical Control Office. Hons Kons,
Anderson, M.G., McNicholl, D.P. & Shen, J.M. (1983). On t h e effect of topography in controlling soil water conditions. with specific r ega rd t o c u t slope piezometric levels. Honq Kong Engineer, vol. 11. No. 11. p p 35-41.
Ar thur , J.R.F. P Roscoe. K.H. (1961). An e a r t h p r e s s u r e cell for t h e measurement of normal and s h e a r s t resses . Civil Engineering and Public Works Review, vol. 56, pp 765-776.
ASTM (1985a). Standard test method fo r penetration test and spl i t -barre l sampling of soil. Test Designation D1586-67. 1985 Annual Book of ASTM Standards. American Society fo r Testing and Materials. Philadelphia, vol. 04.08, pp 298-303.
ASTM (1985b3. Standard test method fo r densi ty and uni t weight of soil in- place by t h e r u b b e r balloon method. Test Designation D2167-84. 1985 Annual Book of ASTM Standards , American Society fo r Testing and Materials. Philadelphia, vol. 04.08, pp 342-347.
ASTM ( 1 9 8 5 ~ ) . S tandard t e s t method for triaxial compressive s t r e n g t h of undrained rock core specimens without pore p ressure measurements. Test Designation D2664-80. 1985 Annual Book of ASTM Standards, American Society fo r Testing and Materials, Philadelphia, vol. 04.08. pp 429-434.
ASTM (1985d). S tandard t e s t method fo r laboratory determination of pulse velocities and ultrasonic elastic cons tants of rock. Test Designation D2845-83. 1985 Annual Book of ASTM Standards. American Societv fo r Testing and Materials. Philadelphia. vol. 04.08. pp 445-452.
ASTM (1985e). S tandard test methods for densi ty of soil and soil aggrega te in place by nuclear method (shallow depth) . Test Designation D2922-81). 1985 Annual Book of ASTM Standards. American Societv for Testing and Materials. Philadelphia. vol. 04.08. pp 463-472.
ASTM (1985f). S tandard t e s t method for direct tensile s t r e n g t h of intact rock core specimens. Test Designation D2936-84. 1985 Annual Book of ASTM Standards , American Society for Testing and Materials, Philadelphia, vol. 04.08, pp 473-477.
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TABLES
[BLANK PAGE]
227
L I S T OF TABLES
Table No.
Page No.
Selected Maps, Plans and Aerial Photographs Available from the Lands Department
Aerial Photographs Available from the Lands Department (two sheets)
Guidance on Site Investigation for Slopes and Retaining Walls in Hong Kong
Content of Site Investigation for Slopes Retaining Walls in Hong Kong
Sizes of Commonly-used Core-barrels, Casing and Drill Rods Used in Hong Kong
Principal Causes of Soil Disturbance
Mass of Soil Required for Various Laboratory Tests
Expected Sample Quality from Different Sampling Procedures for Hong Kong Materials
Soil Sample Quality Classification
Evaluation of Piezometer Types
Field Geophysical Techniques Used in Ground Investigations
Tests on Soils and Groundwater (four sheets)
Tests on Rock
1
2
3
4
5
6
7
8
9
10
11
12
13
- -
[BLANK PAGE]
229
Table 1 - Selected M a ~ s . Plans and Aerial Photographs Available from the Lands kpartment
I Legend :
Coverage
Full
NT & Islands
Urban
Urban & NT
Urban & NT Townships
Urban, Shatin, Tsuen Wan & Tsing Yi
Kowloon Hong Kong
Full
Full
Full
Full
Full
Map Sheet 7 & 11
Full *
-
See Figure 3 for See Table 2 for
Number of
Sheets Size (mml
Series No.
HPlC
-
HM2OC
HM50CL HM50CP
HMlOOCL
HMZOOCL
HGM2O
full programme further details
of the new geological survey
Price Per COPY 1987 HK$
Table 2 - Aerial Photographs Available from the Lands Department (sheet 1 of 2, large scale photographs)
*
Year
1924
1945
19L9
1956
1959
1961
1963
1964
1967
1968 - 1971
1972
1973
1974
1975
1976
1977
1978 t 0
present
p~
Approximate I Coverage 1%) 4 Remarks
Approx. I: 1L 000
30 I Medium to low resolut ion. s ing le f rames w i t h incidental stereo overlap.
Medium t o good resolution. Almost a l l areas except east -west s t r i p f rom Tuen Mun to Sai Kung.
Good resolut ion. Excel lent coverage of
30 1 north-west New Terri tories. Good coverage of lowland areas.
I Good resolut ion ; some stereo overlap.
lo 1 Good resolution ; sma l l rel ief exaggeration.
Excellent resolut ion. f u l l stereo coverage. Coverage of a l l areas except Mai Po to Sha Tau Kok.
40 I Coverage o f t runk roads .
20 1 Coverage o f ma in Urban Area only.
20 1 Coverage of Urban Areas.
30 I Coverage of trunk roads.
I Urban Areas only
90 Most of Territory.
30 1 Coverage of nor th -west and west New Territories .
30 1 Coverage of north - west and west New Territories.
b0 I Coverage of Urban Areas and New Towns.
I Detailed coverage of north-west and north New Territories plus New Towns.
60 Annual coverage of Urban Areas inc luding New Towns and lowland areas.
Table 2 - Aerial Photographs Available from the Lands Department (sheet 2 of 2, high altitude photographs)
Approximate Coverage (%) Year
1954
196L
1973
1974 - 1976
1977
1978
1979
1980
1981
1982
1983
198L
1985
1986
1987
Remarks
HKI I K
Good resolution
Excellent resolution. Mosaic of aerial photographs available. East to west fl ight lines. L to 5km apart .
Good resolution. East to west f l ight lines 3 to Skm apar t .
Good resolution. Annual coverage. East to west fl ight l ines. 1 to Lkm apart.
Obliques only
Obliques only of Urban Area. Coverage of Lantau, west New Territories and Sha Tin.
Complete coverage.
Complete coverage.
Southern hal f of Territory only
Complete coverage.
Urban Area and Lantau only
Complete coverage
Complete coverage.
Almost complete coverage.
Coverage of Urban Area. Clearwater Bay and Sai Kung Peninsula.
Complete coverage.
Complete coverage
Complete coverage.
Table 3 - Guidance on Site Investigation for Slopes and Retaining Walls in Hong Kong
S. I. Class Boundaries for
Soi l
Rock
Legend : I H Height of feature 0 Angle of feature oc Angle of natural hi l ls ide
(Table L )
Different Features
Other Features
F i l l Slope
S.I. Class
Retaining Wal l
Cut slope Retaining wall . . . .
Notes : ( 1 ) This Table is intended to provide general guidance only. I t should be read in conjunction w i th Table 4 . Each situation must be assessed on i t s own merits to decide on the appropriate scope of the S . I . . More or less intensive S.I. than that recommended may be required, depending on the part icular si te conditions.
1 2 ) Irrespective of the above S.I. c lass boundaries, the leas t str ingent 5.1. class for different r isk categories should be Class 1 for 'High' r i s k . Class 2 tor 'Low' r isk and Class 3 for 'Negligible' r i s k . The r isk categories are those given in the Geotechnical Manual for Slopes IGCO, 198LI and should be assessed wi th reference to both the present use and the development potential of the s i te.
Table 4 - Content of Site Investigation for Slopes and Retaining Walls in Hong Kong
Angle of Natural Hillside in the Vicini
Detailed topographical and geological survey o f the s i te and i t s surroundings. Stabilit: analysis of features wi th in the site, using strength and groundwater parameters obtained f rom the investigation
Topographical and geological survey of the s i te and i t s surroundings. Stability analysis of features within the site. For f i l l slopes steeper than 1 on 3, remoulded strength tests on f i l l should be carr ied out.
Assessment of surrounding topography and geology fo r mdication of s tabi l i ty . Visual examination of geologica 1 materials .
A 61 C1 D E l F1 GI 82 C2 E2 F2 G2
E3 G3 As for 0 ' t o 20'. Survey of boulders and hydrological features affecting the site. Extend investigation Locally outside Limits of s i te t o permit s tabi l i ty analysis of features above and below the s i te.
AS fo r 0' t o 20'. Survey of boulders and hydrological features affecting the s i t e .
B1 D 82 C2 G2
E 3 G3 As for 0'to 20'. w i t h survey o f topography and geology, including survey of boulders and hydrological features af fect ing the s i te .
4. Examination of terrestrial photographs. aer ia l photos and geological maps
3. Survey o f 1. boulders and hydrological features 2. topographical, geological and
sur face drainage features
:. Mapping o f 1 . geological s t ructures 2 . sur face features
1. Ground inves t i ga t~on , such a s t r i a l p i ts , boreholes, cor ing , probing and piezometer installations. as appropriate
E. Sampling
of the Site, oc
Greater than 40"
As for 20' t o 40'. Extend investigation more widely outside Limits of s i t e t o permit s tab i l i t y analysis of features above and below the s l t e .
As f o r 20' t o 40'. Extend investigation outside l im i t s of s i t e t o permit s tab i l i t y analysis o f features above and below t h e s i t e .
A B1 C1 D 82 C2 E2 F2 G2
E3 G3 As for 20'to 40'. Area outsidc the s i t e boundary should also be examined for potentia instabi l i ty .
1 . q u a l i t y c lass I o r 2 2 . q u a l i t y c lass 3 3 . q u a l i t y c lass G
F. Fie ld measurements o f 1 , permeabi l i ty 2 . pore pressures
G. Laboratory tes ts I . in tac t strength tes ts f o r soils and
rock j o in t s , remoulded s t reng th tes ts for f i l l
2 . dens i ty t e s t s for f i l l mater ia ls 3 . c lassi f icat ionl index tes ts
Notes : (1 1 Th i s tab le i s intended t o provide general guidance o n l y . It should be read in conjunction w i t h Table 3 .
( 2 ) Insta l lat ion of instruments f o r long te rm monitoring o f ground displacements and pore pressures should be considered during the s i te investigation s t a g e .
Table 5 - Sizes of Commonly-used Core-barrels, Casings and Drill Rods Used in Hong Kong
Core - barrels Casings Drill Rods
Double - tube
Nominal Diameter
;i;n
Triple -tube
Nominal Diameter
Design
NMLC
Mazier * 7 L 1 0 1 **
3C-MLC 7 6 11 1
Legend :
* With retractor shoe ** With or without retractor shoe
Flush - jointed
OD Outer diameter I D Inner diameter
Flush - coupled
Design 43% Coupling I
Notes : ( 1 ) This l i s t i s not exhaustive and should not imply the exclusion of other recognised core barre ls and casing I r o d s systems.
( 2 ) For addit ional information, reference can be made to BS LO19 : Part 1 (BSI 197La) on ro ta ry core dr i l l ing equipment and Figure 29 of BS 5930 ( BSI ,1981a 1 .
( 3 I A l l dimensions are rn mi l l imetres.
23 5
Table 6 - Principal Causes of Soil Disturbance
Before Sampling During Sampling After Sampling
Stress relief
Remoulding
Stress relief
Swelling
Compaction
Displacement
Base heave
Piping
Caving
Stress relief
Migration of water within the sample
Loss of moisture
Overheating
Vibration
Chemical changes
Disturbance during extrusion
Displacement
Shattering
Stones at the cutting shoe
Mixing or segregation
Failure to recover
Note : Table adapted from Clayton et a l (1982).
Table 7 - Mass of Soil Required for Various Laboratory Tests
Mass of Sample Required Purpose of Sample Soil Type
Soil indentification. including Atterberg l imits; sieve analysis; moisture content and sulphate content tests
Clay, si l t , sand
Fine and medium gravel
Coarse gravel
Compaction tests All
Clay, silt, sand Comprehensive examination of construction materials, including soil stabilization
Fine and medium gravel
Coarse gravel
Note : Table taken from BS 59: 0 ( BSI, 1981a
Table 8 - Expected Sample Quality from Different Sampling Procedures for Hong Kong Materials
Typical Composition of Materials
Composition of soils varies depending on the nature of parent rock material. Soi ls derived from granitic rock are usually s i l ty and clayey sands soi ls derived from volcanic rock are usually sandy and clayey s i l ts .
Fresh or variably decomposed rock fragments (boulders. cobbles and gravels) within a matr ix of varying proportions of sand, silt and clay
The fol lowing materials can be found : [a) Granular soils (sands,
silty sands or sandy s i l t s )
(b) Very sof t to soft cohesive soils (sandy clays, s i l ty clays or c lays)
tc) F i rm to very st i f f cohesive soi ls
[ d l Cohesive and granular soils containing boulders. cobbles or gravel
Variable material. which can include compacted or uncompacted soil, rock fragments and building debris mixtures
Al l rock types found in Hong Kong, including boulders in colluvium
Sampling procedure
Hock sample fr'om dry excavation Large diameter triple-tube core-barrel 1102mm diameter cores) w i th retractor shoe, air-foam f lush Iriple-tube core-barrel (3 74mm diameter cores) with retractor shoe UlOO sampler SPT spl i t barrel sampler w i t h or without liner 3ulk samples and jar samples from dry open excavation Light percussion shell and chisel for boulders
The sampling procedures for soils derived from insitu rock weathering P P P ~ Y .
Piston sampler or compressed air sand sampler UlOO sampler (w i th core-catcher) SPT spl i t barrel sampler Light percussion shel l
Piston sampler Thin-walled sampler UIOO sampler Delft continuous sampler Light percussion clay cutter ( d r y boreholes) or shell (wet boreholes)
Triple-tube core-barrel w i th retractor shoe UlOO sampler Light percussion clay cutter
The sampling procedures for soi ls derived from insitu rock weathering apply.
See sampling procedures for relevant soi l type and composition under 'Alluvial and Marine Deposits' above.
guide.
Material Type
Soils derived from insitu rock weathering
Colluvium
Alluvial and marine deposits
F i l l
I
I Rock
Notes : ( I )
Diamond core dri l l ing with double or triple-tube core-barrel. The latter generally causes less disturbance and gives better core recovery, especially in highly fractured or jointed rocks.
( 2 ) The quality c lasses are defined in Table 9. ( 3 ) The expected qual i ty c lasses g iven should only be taken as a guide. as
sample qual i ty i s highly dependent on workmanship and on the compactness tor consistency) and grading of the soi l .
The typical composition of materials should only be taken as a general
- xpectec Quality Class
Table 9 - Soil Sample Qual i ty Classi f icat ion
Class 1
Class 2
Class 3
Class L
Class 5
Sample Quality Soil Properties that
Can Be Reliably Determined
Classification, moisture content, density, strength, deformation and consolidation characteristics
Classif ication, moisture content, density
Classification, moisture content
Classif ication
None (approximate sequence of materials only 1
Notes : I1 1 Large diameter class 1 and class 2 samples are often sufficient to allow the ' f ab r i c ' of the soil to be examined. Sometimes th is moy also be done using class 3 and class L samples.
(21 Remoulded properties can be obtained using class 1 to class L samples.
( 3 I Table taken from BS 5930 ( BSI ,1981a 1.
Table 10 - Evaluation of Piezorneter Types
U - m Piezometer Pressure Responsc $ 1 Type I Range I Time
Open- hydraulic (Casagronde)
[High oir to ony Moderote a entry positive
pressure) pressure
Closed- hydraulic [Low air entry pressure)
Pneumatic positive pressure CC
Atmospheric '' Of z,"idpipe Slow
Any positive pressure
pressure
Moderate
Electric vibrating wire type
Rapid
Rapid Any positive pressure
Below -1 Variable
De-airing Capability
Self de-airing
tan be de-aired
Remote Reading
Capability
Not normally. but possible with bubbler system
Can be de-alred
Cann-ot be de-o,red;only partipt!y self de-alrlng
As above
As
Can be de-owed
Not relevant
Yes
Long-term Reliability
Very good
Yes
Yes some head loss over long
Yes, but special cable requlred
Yes, but with core because of transmission losses
Yes
Short distances only
Depends on pressure measuring system 1) Mercury manometer -
very good 2 ) Bourdon gauge - poor
in humid atmosphere 3) Pressure transducer -
moderate but easily reploced
As above
Moderate to poor, but very little long term experience available
Signal quality degenerates w ~ t h time; instrument life about ten years, but reliability of instrument that cannot be checked is always suspect
Poor
Good
Instrument life one to two years; little long term experience available
Recommendations
First choice for measurement within positive pressure rangc unless rapid response or remot' reading required; response peaks can be detected by us1 of Halcrow buckets system.
Other
Fairly insitu permeability cheap ;
~ ~ , " ~ m ~ ~ n be made
if required'
Advantages
Cheop, simple to reod 8 maintain; insitu permeability measurement possible.
Fairly cheap; insitu permeability mwsurements ,n low permeability soil are
Fairly cheap; no gouge house required.
-
-
Cheop. simple to read and maintain.
-
Disadvantages
Vandal damage often irreparable,
Gauqe house usually required; regular de-airing necessary; uncovered tubing liable to rodent attack or damage if left exposed.
Useful when remote reading. for artesian pressures.
AS very regular de-airing required when measuring suctions.
No method of checking jf pore water Or 'Ore 'Ir pressure is measured.
As above; expensive;
~Z';~/;;'J$# be checked.
As above.
Vandal damage Often
irreparable; de-airing required.
Not accurate between 0 and -1 atmosphere.
Useful for meosuring small suctions.
Only suitable when tip almos' always below groundwater leve and no large suctlons occur.
Not generally recommended.
Not recommended.
First choice for meosuring pore suction.
Research stage at the momer
Table 1 1 - Field Geophysical Techniques Used in Ground Investigations
Technique Application Remarks
-- -
Seismic refraction
--
Mapping of subsurface mater~a l interfaces (including groundwater table). Determination of compression wave velocities. Location of geological features (e.g. f au l t s and caverns ).
- - -
A hammer impulse may be used for shallow Investlgatlons, but explosive charges are needed for deep investigations (>30mJ. Excessive background 'noise' may preclude surveys a t some sites. May be unreliable unless velocities increase with depth and bedrock surface is regular. Variable weathering patterns often complicate interpretation. Data are indirect and represent averages.
Seismic direct methods
Gravimetric I Location of geological features. I Normally used only to locate cavit ies, e.g. in kars t terrain.
Electrical resist ivi ty
Magnetic
Determination of mater ia l propert ies of the ground (sonic wave velocit ies, dynamic moduli and rock- mass qual i ty ). Location of geological features.
Seismic reflection
Uphole, downhole and crosshole surveys are carried out. Data are indirect and represent averages, and may be affected by other mass characterist ics.
Mapping of subsurface material interfaces (including saltwater boundaries). Estimation of soi l resistivity (hence corrosivi ty). Location of geological features. and underground cavities, e.g. disused tunnels.
Location of buried metalliferous man-made objects (e.g. cables and pipelines) and geological features.
Mapping of the seabed and material interfaces below the seabed.
Variable weathering patterns often complicate interpretation. Water table location often l imits the depth for pract ical study as conductivity r ises sharply i n saturated mater ia ls & makes differentiation between horizons impossible.
Large scale surveys are generally carried out from an aircraft .
Long continuous traces can be obtained. Background 'noise', so l id waste on the seabed, gas bubbles trapped within sediments, and variable weathering patterns often complicate interpretation. Does not provide sound velocities. Computation of depths to interfaces requires velocity da ta obtained by other means, e.g. borehole correlation. laboratory tests (Table 13).
Side scan sonar - I
Magnetic ---I Mapping of the seabed (surface only). Location of rock outcrops, gravel deposits, pipelines, wrecks, etc.
Location of metalliferous man-made objects on or below the seabed (including sunken vessels).
The technique does not give accurate distances or depths to an object, and i s generally used as a search tool only.
Sunken objects on the seabed can render the location of specific objects d i f f icu l t .
Echo sounding Bathymetric mapping to determine water depths. Suspended sediments created by dredging the seabed can render the dredged levels obtained by th is method unreliable. The trace obtained by the echo sounder should be checked against depths obtained by conventional methods, e.g. by the use of a gravity corer.
Table 12 - Tests on Soils and Groundwater (sheet 1 of 4 )
Name of Test
Moisture content
Liquid and p las t~c l lm~ ls (Atterberg l imits)
Lineor shrinkage
Speclftc gravity
Particle size d is t r lbut~on :
lo1 Sieving
Laboratory vane shear
Recommended References
BS 1377 IBSI . 1975 b l Test l ( A l , Geotechnlcal Manual for Slopes (GCO. 198LI. Seclion 3.2.2
BSI 11975b) Test 21AI or 2181 and Test 3; Geotechnical Manual for Slopes Section 3 2 . 3
BSI 11975bl Test 5
BSi l1975b) Test 6 ; Geotechnical Manual for Slopes. Section 3.2.L; Lambe 11951 1 Chapter 2
la1 BSI 11975 b l Test 7 I A ) ; Geotechnical Manual for Slopes, Section L.6; B r ~ a n - Boys e t a l 119861 Clause 5.1
I b l BSI I1975 b l Test 7lC) or 71D); Geotechnical Manual for Slopes. Section 3.2.5
Wilson 11963)
Remarks
Frequently used i n the determination of soil properties. e.g, dry density. degree of saturation. Soils containing halloysitic clays. gypsum or calci te con lose water of c rys ta l l~so t~on when heated. and should be dried o l various temperatures ta assess the effect on determination of moisture content.
Used to classify f ine-grained soils and as an aid in classifying the fine fraction of mixed soils Soils containing halloysitic clays must be tested o t natural moisture content.
Used to detect the presence of expansive clay minerals. Limited application i n Hong Kong.
Frequently used in the determination of other properties. e.g. void ratio, particle size dts t r~but ion by sedimentation
Wide application i n Hong Kong in the classification of s o ~ l s .
l a ) Sieving gives the groding of so11 coarser than silt. Care is required with soils derived from insitu rock weothermg, to ovold crushing of soil grains during disaggregation. The standard method of dry slevlng IBSI, 1975 b Test 7 I B l I i s not recommended for general use In Hong Kong. As a variat ion to the standard method of wet sieving 1851. 1975b Test 71AI). i t will be appropriate to exclude the use of dispersont when determining part icle size distr ibut ion for certaln appllcatlons. e.g. for designing f i l ters. and in selecting fill for reinforced fill structures.
I b l The proportion of the soil passing the finest sleve 163 p m l represents the combined silt and cloy fraction. The relative proportions of silt and clay can only be determined by sedimentation.
A useful test for c lass~fy lng sl l ts and clays in term of consistency See also Geoguide 3 (GCO. 19881.
Table 12 - Tests on Soils and Groundwater ( s h e e t 2 of 4 )
Category of Test
L 0 * : u C 2
e 0
'D C 0
In - .- 0 V)
C 0
In - m 0 I-
X L > .- In e L 0 0
'D C 0 - 0 0 .- E, r 0
--
Name of Test
Organic matter content
Sulphate content : 'a) Totol sulphate content of
so11
Ib) Sulphote ion content of groundwater and oqueous sod extracts
Total sulphide content of groundwater and aqueous soil extracts
pH value
Chloride Ion content
Carbonale content
Resistivity
Redox potential
Bocter~ological tests
Recommended References
851 11975bl Test 8
la1 BSI 11975 b l Test 9
I b l BSI 11975 b l Test 10
American Public Health Association 119851 Part 427
BSI ( 1975 b l Test 11 IA1
Department of Transport 119761 Clause 2722
Road Research Laboratory (19521
Brion- Boys et a1 119861 Clause 5.L
Brian - Boys et a l (1986 1 Clouse 5.5
BSI 119731
Remarks - - - -
Detects the presence of organic molter. which can :
l i t interfere with the hydration of Portland cement In soil -cement pastes.
i i i ) influence shear strength. bearing copocity and compressibility.
l i i i ) influence the magnitude of the correction foctar require when using nuclear methods to estimate the insitu ma~sture content of sails IASTM. 1985hl.
l iv l promote microbiological corrosion of buried steel.
These tests assess the aggressiveness of soil and groundwater to burled concrete ond steel. Local experience indicates that sulphate content of Hong Kong soils is generally low. Therefore Test 9 of 8.51 11975 b l IS normally adequate.
Assesses the aggressiveness of soil and groundwater to buried steel
Assesses the aggressiveness of sol1 and groundwoter to buried concrete and steel.
Assesses : lil the aggressiveness of soil to buried concrete and steel ;
l i i ) the suitability of tone aggregate for use in concrete.
The reference describes the method using the Collins calcimeter
Assesses the potentiol far electrochemical corroston of buried steel. The quoted reference gives a test method for compacted f i l l . as opposed to f ield measurement using the four electrode method (see Section 33.2 11. Corrosion of steel in soils is discussed in BSBOOL IBS1.1986) and King 119771.
Assesses the likelihood of sulphote reductng bacteria' being present, which promote microbiological corrosion of buried steel. The quoted reference gives a test method for compocted f i l l . 0s opposed to field measurement. which is described i n CPt021 iBS1.19731.
Undisturbed specimens should be stored ~n olr-sealed, sterilized containers.
Table 12 - Tests on Soils and Groundwater (sheet 3 of 4 )
- ategory )f Test
Name of Test
Trioxlol compression tests
la1 Quick undrained
( b l Consolidated drained
l c l Consolidated undrained wi th measurement of pore water pressure
Direct shear test
Consolidotion
lo1 One-dimensional consolidotlon ( oedometer test I
I b l Tr iaxial consolidation
I c l Rowe ce l l
Modulus of deformation
Recommended References
la1 BSI 11975 b l Test 21
( b l Bishop 8 Henkel 119761
I c l Geatechnlcal Manual for Slopes, Sections 3.7 and 3.8 ; Heod 119861
Akroyd 119691; ASTM 11985 il Geotechnical Manual for Slopes Sections 3.7 and 3.9 ; Heod I1986 1
la1 BSI 11975 b l Test 17
I b l Bishop 8 Henkel (19761
I c l Rowe B Barden 119661; Head 119861
Heod 11986 1
Remarks
The qulck undralned test gwes undrolned shear strength In terms of to ta l stresses, and has appl~cat lon t o sho r t - t e rm s tab~l ! ty and bea r~ng capaclty analyses E f f e c t ~ v e stress onalysls 15 relevant t o most sol ls and engmeertng appllmtlons ln Hong Kong . consequently the consolldated dramed test or consalldated undrolned test w ~ t h measurement of pore water pressure should generally be used Tests should be c a r r ~ e d out In the stress range appropriate to the analysls
For saturated cloys w ~ t h undra~ned shear strength less than about 75 kPo, the l ns~ tu penetratlon vane test 1 see S e c t ~ o n 21 3 1 , used In conjunction wlth the cone penetratlon test I see Sectlon 23 3 I. will normally be the best method for measuring undromed shear strength A number o f other t rmx la l tests are possrble. e g fol lure by mcreasmg pore pressure. decreasing KT3 etc T r l a x ~ a l tests can also be used t o f m d KO
A usefu l and practical al ternotwe to the consolldoted drotned t r ~ a x ~ o l test for sheor strength measurements on fill co l luv~um and 5011s derlved from weather~ng of rock ~ n s l t u The test speclmen can be orlented to measure shear strength on o pre-determmed plane The m o p l lml to t~on of the test IS t he speclmen thickness whlch governs the maxlmum portlcle srze that c o n be tested Common speclmen slzes ore 60 mm and 100 mm square by 2Omm thlck The less common 60mm dlometer by 20mm thlck and 300mm square by 160mm thlck dlrect sheor boxes hove olso been used In Hong Kong
These tests yleld soi l parameters from whlch the amount and time scale of settlements con be calculated The simple oedometer test 15 the one in general use . Although reosonoble assessment of settlement can be made from the results of the test, estimotes of the time scale hove been found t o be extremely inaccurate for some so i ls . This i s particularly true for cloy s o ~ l s containing layers and partings of slit and sand, where the horizontal permeability 1s much greater than the uertlcal . In these cases, more rel iable data moy be obtoined from tests In tho Rowe ce l l , which i s ovolloble In slzes up t o 250 mm diameter and where a larger and potent ial ly more representative sample of soil can be tested (see Section 12.51. Another olternotrve 1s to obtain values of permeobility. k from rnsltu permeob~l l ty tests, and combme them wi th coefficients of volume decrease, m, obtained from the simple oedometer test
Values of the modulus of deformatlon of sol[ can b e obto~ned f rom the s t ress-s t ra ln curves from tr loxlal compression tests, where the test specimens hove been consolldated under effective stresses wrrespondlng t o those In the field However, values obtolned In thls way frequent ly do not correlate wel l w l t h I n s ~ t u observot~ons I t IS now generally considered tha t the p la te test ( see Sectton 21 6). the pressuremeter I see Sectlon 21 7 ) and back onalysls of exlstmg structures y ~ e l d more rellable results
Table 12 - Tests on Soils and Groundwater (sheet 4 of 4 )
Nome of Test
Permeability :
la1 Constant head permeability test
I b l Falling head permeability test
I c l Triaxial permeability test
Id ) Rowe cell
Dry density 1 moisture content relationship
California bearing ratio ICBRl
Double oedometer test
Double hydrometer test ldispersion lest l Exchangeable sodium percentage test
Emerson crumb test lturbidity test 1 Pinhole test
Recommended References
fa ) Akroyd 119691
f b l Akroyd 119691
f c l Bishop 8 Henkel 119761; Head 119861
Id1 Head 119861; Rowe Borden 11966)
851 11975b1 Tests 12. 13 and 14
Akroyd f19691. 051 (1975 b l Test 16
Hilf 119751; Holtz f19f.81
Decker 8 Dunnigan 11977 1
Flanagan 8 Holmgren 119771
Standards Association of Australia 11980 1 Sherord et a l 119761
Remarks
The constant head test is suited only to soils of permeability roughly within the range l ~ - ~ r n l s to 10-*mls. For soils of lower permeability the fall ing head test is opplfcoble. For various reasons, principally sample size and ground varlobllity, laboratory permeability tests often yield results of limited value, and insitu tests should generally yleld more representative data l see Section 21.L). The Rowe cell allows the direct measurement of permeability by a constant head, with a bock pressure and confining pressures more closely consistent with the field state, and by both vertical and radial flow.
Indicates the degree of compaction that can be achieved at different molsture contents and with different compactive effort. Test 12 is commonly used in Hong Kong. It is carr ied out in conjunction with determinotions of insitu dry density I ASTM. 1985b; ASTM. 1985e; ASTM. 1985h; 851. 1975b Test 15; see also Chapter 271.
This is an empirical test used i n the design of flexible pavements. The test con also be curried out lnsitu l see Section 29.6 I, but the results may be substantially different from the laboratory test due to the difference in the confining condition. especially for sands.
Assesses the potential for soils to collapse on wetting
Used to identify disperswe soils. in order to assess the potential for dispersive piping and internal eroslon to occur in slopes and earth structures. The different tests M y not give consistent indications of dispersion. consequently i t i s advisable to use more than one test method.
Table 13 - Tests on Rock
Name of Test
Water content, porosity. density, absorption. swelling. and slake durability
Sonic wave velocity (sound velocity 1
Thin sect ion
Point load
Unioxml compresslve strength and deformability
Tr iaxial ComDression
- -
D~rect and indirect tensde strength
D~rect shear
Recommended References
Brown 119811 pp 79 - 9L
ASTM 11985d1; Brown 119811 pp 105 - 110
Brown 119811 pp 73 - 77: Oearman 8 lr fan 119781
Gamon 11984b); l r tan 8 Powell 119851; ISRM 119851; Lumb 119831
ASTM 1198591; ASTM 11985il; Brown 1198i i pp 113 - 116. Cbpullo 8 lr fan 1198L I. Gamon 8 Szeto 119841. Haas 119831. Howkes 8 Mellor 119701
- --
ASTM 11985~ I ; Brawn 119811 pp 123 - 127; Franklin 8 Haek 11970 1; Hosk 8 Franklin 119681
ASTM 11985 f 1 ; Brown 11981 I pp 119 - 121 ; Hawkes 8 Meltor 11970 1
Brown 11981 1. pp 135 - 137; Franklin 119851; Geotechnical Manual for Slope IGCO. 19841 Section 3.10; Gyenge 8 Herget 119771; Hencher 8 Richards 119821; Hoek 8 Broy 119811; R~chards 8 Cowland 119821; Ross-Brown 8 Watton 119751
Remarks
Used for classification and choracterisat~on of rocks
Used to measure ve loc~ l~es of compresston and shear waves for the determlnatmn of elostac constants of ~sotroplc and sl~ghtly omsotrop~c rocks The test results ore used I" conjunct#on wdh geophys~cal survey data (Table Ill, and to assess dynamlc properties of rock Tests are usually carrled out on small specimens
usmg u l t rosonr frequencies
Used for petrographic descr ipt~on of texture. fabric and state of alteration in rock material.
Used to meosure the p o ~ n t load strength index and strength anlsotropy The results are used as an ~ndex test for strength classification of rock material, and to predict i t s uniaxial compressive strength. see Geogulde 3 (GCO. 1988).
The test can be carried out on pleces of drll l core or ~r regu lar lumps of rock . I t can also be carr ied out In the f ie ld (see Section 24 2 1 I
Used for direct determination of uniaxial compresslve strength. and for determination of stat ic Young's Modulus of Elast ic i ty and Pmsson's ra t io .
The results can be used in conpnctlon w ~ t h ~ntormation on the nature and spacing of d i scon t~nu~ t~es to assess allowable bearing stress and settlement in rock foundation deslgn. stability of underground excavations and to design rock support measures. They may olso be used for classification of rock materlal IDeere 8 Miller. 19661. Unioxial compressive strength can be used to classify rock moterml for descr~pf ive purposes. see Geogulde 3 I GCO. 1988).
- - -- -
Used for determmat~on of trmxlal compresswe strength, stotlc Young's Modulus of E las t l c~ t y and Po~sson's rot lo Test results are used to assess the stablllty of underground excovatlons and to deslgn support measures
Used ~n stabt l~ ty assessment of underground excavat~ons Specimens for dlrect tests are dlfflcult to prepare, and md~rect tests such as the 'Brazl l Test' a re more commonly performed
Used to determine the shear strength character6stics of rock discontinuities. The Robertson Shear Box and the Golder Associates Shear Box are routmely used. Both are sufficiently portable far f ie ld use, but specimen preparation time i s a disadvantage. The results are used in rock slope stability analysis, and for local stabi l i ty calculations in tunnels.
FIGURES
[BLANK PAGE]
247
LIST OF FIGURES
Figure No.
Page No.
S tages of a Site Invest igat ion
Locations of t h e Mid-levels Scheduled Area a n d Mass T rans i t Railway
Programme of t h e New Geological S u r v e y
The Geotechnical Area S tudies Programme
Examples of Maps Available in t h e Geotechnical Area Studies Programme
Comparison of Geological Map a n d Aerial Photograph fo r Ident i fying Major S t r u c t u r a l a n d Lithological Fea tures
Trial Pit Log (Example 1)
Trial Pit Log (Example 2)
Example of a Log Shee t fo r Slope Sur face S t r ipp ing
Example of a Caisson Log
Typical Configuration of a Rotary Drilling Rig
Typical Arrangement of Air Foam Mixing a n d Flushing System
General Pu rpose Open-tube Sampler
Thin-walled Sampler
Thin-walled Stat ionary Piston Sampler
Example of a Double-tube Core-bar re l (Craelius T2-101)
Example of a Non-retractable Triple- tube Core-barrel (Triefus HMLC)
Example of a Retractable Triple- tube Core-barrel (Mazier)
Typical S tandpipe and Open-hydraul ic Piezometers
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Figure No.
Page No.
Typical Twin-tube Closed-hydraulic Piezometer Tips
Typical Installation Details of a Piezometer in a Borehole
Example of Piezometer Record
Piezometer Buckets (British Pa tent No. 1538487)
Example of Piezometer Bucket Data
Split Barrel Sampler fo r S tanda rd Penetrat ion Test
Vane Shear Devices
Typical Arrangement fo r Field Permeability Test
In t ake Factors , F, in Borehole Permeability Tests
Relationship between Dimensionless In take Factor a n d Length to Diameter Ratio of Piezometer
Example of Results from Falling-head Permeability Test
Typical Arrangement fo r Packer (Water Absorption) Test
Example of Packer (Water Absorption) Test Data
Example of Packer (Water Absorption) Test Calculations
Impression Packer Device
Impression Packer Survey and Discontinuity Log
G C O Probe
G C O Probe Record
Mechanical Cone Penetrometers
Electrical Cone Penetrometers
Point Load Tes ter and Example Data
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
Figure No.
4 1 Typical Arrangement for Double-ring Constant-head Field Infiltration Test
4 2 Example of Results from Field Infiltration Test
4 3 Typical Arrangement for Plate Load Test
4 4 Example of a Borehole Log (two sheets )
Page No.
- - - - -
[BLANK PAGE]
Site lnvestigation Stage
Desk Study
Preliminary
Main
Construct ion
Post - construction
I
Investigation j Design and Construction Activities I I Progress
Recognition of need for project + I INITIAL PROJECT CONCEPTION J
I I Desk study, to obtain basic knowledge of ground conditions +
Recognition of major problems +
Site reconnaissance and preliminary
field investigations
t Design of main
ground investigation
t Ground lnvestigation +
l nformation recovered during investigation
I . Report on Mam
Ground l nvest igat ion
I
Basic project concept designs
Confirmation or amendment of design concept
4 prelimindry l ~ e t a i l e d
Design
Modifications to detailed design
Finalise Design of Project
CONSTRUCTION 1 t I
I
Recording actual + ground conditions 4 Modifications to design
I I + Further inv&tigation 4 Modifications to design
i ! I I COMPLETION OF CONSTRUCTION I
Monitoring behaviour in operation Maintenance works
Legend :
) Exchange of information
Note : Figure adopted from IAEG (1981 ) .
F igure 1 - Stages o f a Site Invest igat ion
NEW TERRITORIES
HONG KONG
(r/J@ Mid-levels Scheduled Area ---- Mass Transit Railway
Figure 2 - Locations of the Mid-levels Scheduled Area and Mass Transit Railway
Geological Memoir Nos. 1 : 2 0 0 0 0 Map Sheet Nos.
Map Coverage Date 1 : 20 0 0 0 Sheet Nos. Available
I Legend :
* Minor p a r t o n l y . pub l ished i n Memoir No. 2
I Note : 1 : 2 0 0 0 0 Map Sheet No. I wi l l no t be i nc luded in t h e new geological survey.
Figure 3 - Programme of the New Geological Survey
I Boundaries of the GASP Areas
Geotechnical Area Studies Programme (GASP) Reports and Maps
( 1 : 20 000 scale mapping]
I - Hong Kong and Kowloon
I I - Central New Territories
I11 - West New Territories
I V - North West New Territories
V - North New Territories
V I - North Lontou
VII - Clear Water Bay
VIII - North East New Territories
I X - East New Territories
X - Islands
X 1 - South Lantau
XI1 - Territory of Hong Kong
Date Available
Note : Reprints o f all maps are held in the Geotechnical Information Unit.
Figure 4 - The Geotechnical Area Studies Programme
Geotechnical Land Use Map Engineering Geology Map
0 200 400 600 800 1 OM)m
Scale :- 1 : 20 000
Legend :
Class I - Low Geotechnical Limitations 1-1 Colluvium lunditterentiated
mi Class I1 - Moderate Geotechnical Limitations E d Hong Kang Granite
F d Class I11 - High Geotechnicol v{ Dominantly broclastic Rocks with Limitations some Lavas
Class I V - Extreme Geotechnicat m] Quartz Monzonite Limitations
VTA General instability
--- Geological boundary I solid I
- -- - - - - Geological boundary 1 superficial I
--- Photogeologicol lineament
. . - - Catchment boundary
5% Str ike and dip of beds
Note : Examples taken from GASP Report I - Hong Kong and Kowloon.
Figure 5 - Examples of Maps Available in the Geotechnical Areas Studies Programme
Logged by : A.N. Chan Method of Excavation : Hand ( timber shoring Date Excavated : 1.1.1983 Checked by : A.N. Lau fu l l height)
Slope No. : 11SW - B ICR685
Location : Garden Road
Date : 5.1.83 Co-ordinates : E 3 4 4 4 4 . 4 4 N 15555.55 Date Backfil led : 20.1.1983
Trial Pit No.
Sheet 1 of 1 I TP - 6
--
egend Description . . .. a Loose. dry, l ight brown,gravelly si l ty SAND (F i l l )
Loose, dry. l ight brown.grovelly si l ty SAND with many roots ( F i l l )
Loose t o medium dense, dry, reddish brown, slightly SAND,with pieces of glass
Sott,moist,dark brown.orgnnic, slightly gravelly. SILTICLAY (Old Top Soi l
Soft, moist.reddish brown, gravelly, SILTICLAY (Colluvium-matrix I . Slakes easi ly. Hand penetrometer strength = 40 kPa
"
- Contractor : A.N. Company I
3 " rn
-LT lnsitu density I Undisturded I test sample, hori.
Angular t o sub-angular cobbles of moderately strong, dry. dark greenish grey. inequigranular. moderately decomposed coarse ash TUFF ( CoIIuvium - rock f ragrnent )
Moisture Undisturbed content test I sample, vert.
A Water sample El Block sample Seepage C-I Photograph . Small disturbed + Bench mark sample
Works Order No. : 2 11 193 Engineer : A. N. Lau L Partners
Figure 7 - Trial Pit Log (Example 1)
I Trial Pit NO. : TRN 6 Face C Sheet 3 of 4
: Nil Date Backfilled : 2 / 4 \ 8 2 Co-ordinates : E 4238112 N 19234.75
Type of Excavation : Hand-dug Contractor : A.N. Company Study Area : Area A
Location : King's Park Date Excavated : 171 3 182 Ground Level : 87.1 mPD
Figure 8 - Trial P i t Log (Example 2)
~ c k e d i a Locatior
Ap Ls Contrac
A.N. I Date St
12. - listance
from Datum
( m l 14
Ptoiect : Slope Datum (toe) Datum (crest Strip NO. : I Works Co-ordinates : Co-ordinates : s4 I : E 33 320.12 E 33331.23 Slope No. : Slope a ei Chau N 11 302.43 N 11 302.11 Ch. 4+95 to1
ted : 83 - Slope Angle -
30'
I
Date Completed : Date Reinstated : Logged by : Checked by : 19.12.83 2 6 . 1 2 . 8 3 A.N. Chan A. N. Lau
[educed Level
[mPD)
18.0-
14.6-
12.4 -
11.3-
10.0-
6.0 -
Description and Sample Data
disc on ti^
Legend Dip Directio~ I k- I I
Drainage channel (300 x 250mm ) I I Natural slope covered with small trees and grass with colluvium below. Boulder of strong to very strong, dry. dark greenish grey, slightly decomposed f i ne ash TUFF, 600 mm i n diameter.
Too of chunamed cut slooe ~
Loose. dry, l ight yellowish brown, si l ty SAND - with some sub- rounded boulders of highly te moderately decomposed f ine ash TUFF I Colluvium 1 . The boulders are up to 3OOmm -'t) '-.:' in diameter and their proportion decreases - . - . in an upward direction on the slope. -:.---- Extremely weak, dry. l ight yellowish brown,- highly decomposed f ine ash TUFF (very dense, slightly gravelly sandy SILTICLAY 1. -
Moderately strong, dry, dark yellowish brown, moderately decomposed fine ash TUFF with very closely-spaced, persistent lover 15 rn I rough and planar, tight and dry joints dipping 10' - 20'. Very weak highly decomposed material exists adjacent to
isome joints. I
Very strong, dry. dark greenish grey, 23C/71, sl ightly decomposed fine ash TUFF. 215167. Joints are medium-spaced, persistent, 23015 6, rough and planar, t ight and dry, with 302115,
yellowish brown surface staining. 235172
~ a s e of the slope 1 1 !J
Remarks :
Legend :
Small disturbed sample Large disturbed sample Block sample lnsitu density test Moisture content test Water sample Seepage Photograph
Sketch Plan : >-\ 4
Nature 0 Infil l ing -
Grade Is!
Surface staining
Sketch Section : Nalural slope .."., inage channel
b ~ h u n a r n e d slope
k ~ o c k slope
Figure 9 - Example of a Log Sheet for Slope Surface Stripping
qoject : New Territories Trunk Road Caisson No: 1 of Bridge 18 .ocation: North Tai Po to Lam Kam Road Diameter : 1 . 2 5 rn
rtethod of Excavation : Hand- dug Co-ordinates: E m N 34 902 0 . 0 l o 2 9 . 5 m Ground Level: 4 9 . 0 3 rnPD
Weathered Mass Zone
:ompletely weathered lranodiorite
18.0
Highly weathered lranodiorite
24.5
Moderately weathered lranodiorite
28.4 Slightly
weathered jranodiorite
29 .5 -
Legend :
D v IV
ma
31.03
Ground water level 26.53 V
24 .53
22.83
20.63
3 0 I Base of Caisson 1 19.53
Material grades
Completely decomposed - Joint
Discontinuities
The joints are medium-spoced, rough md planar and dry. Some joints :ontain quartz veins. 2-3 mm thick. i sub-vertical fault of less than 00 mm thick containing so f t :ohesive soi l i s present.
The joints are closely to medium- spaced, rough and planar and dry . Some joints contain quartz veins, 1 - 3 mm th ick.
The joints ore closely t o medium- ;paced, rough and planar, very narrow ~ n d dry. and contain extremely weak iighly decomposed rock. F I = 4 . The joints ore dominantly vertical or rub-vertical , medium-spaced, rough ~ n d plonar. extremely narrow and dry with brown-stains. Occasional joints :ontain extremely weak highly decomposed .ock, 2-5mm thick. Some horizontal oints are widely-spaced. F I = 3 .
The joints a n medium to widely-spaced .ough and planar, t ight and dry with wown-stains.OccasionaL joints contain rxtnmely weak highly decomposed rock, 2 - 5 mm thick. F I = 2 .
(1) Mixtures of Grades I V and V materials
q-m Mineralized quartz vein present are shown
Highly decomposed using overlapping F I Fracture index symbols.
Moderately decomposed ,, Schmidt hammer test ( 2 ) Discontinuity data onor I Slightly decomposed at 0.9m c l c are given separately. or Fresh
-- f -- Fault AD Air dr i l l test I Contractor : A. N. Company
iheet 2 of 2
- inish
- I Tests
T
H
- 1 A1
2 1 d by :
A.N. Chan
late : 2 9 - 6 - 84
. . Date Star ted : 4 - 6 - 8 4 Date Finished: 2 6 - 6 - 8 4
Figure 10 - Example of a C a i s s o n Log
Bolt and clevis Double sheave
Water swivel
Wire drum hoist
Cathead hoist Pressure hose Swivel drill head
Diamond casing shoe '-'m~mf- Drill rod coupling
Drill rod Rock
Core- barrel
Reamer Diamond bit
I Note : Figure adopted from Acker Drill Co. Inc. data.
Figure 1 1 - Typical Configuration of a Rotary Drilling Rig
Valves :
A Air supply control B Foam pump speed control C Drilling supply fluid control D By - pass control
Air Air from
pressure
Rotary swivel
Water and foam additive
Suction hose
200 litre drum-
Figure 12 - Typical Arrangement of Air Foam Mixing and Flushing System
- Sinker bar
02, - D: Area ratio 1%) = ( 1001
D2C
Inside clearance 1 % 1 = Ds - Dc (1001 D c
Outside clearance 1 % 1 = Dw - - D~ (1001
Sliding hammer
Drive head
Vents to ball valve assembly
1' Sampler head with overdrive space
Sample tube 100mm diameter by 500mm Length
Cutting shoe (see detail 1
Sample tube
Cutting shoe
(a) Ul00 Sampling (b ) Detail of Cutting Shoe and Arrangement Definition of Sampler Proportions
Notes : ( 1 ) The open-tube sampler may also be attached to dri l l rods and driven or pushed into the ground by the drilling r ig or SPT hammer.
( 2 ) Two sample tubes may be coupled together to provide a Longer sample or additional overdrive space.
( 3 ) The vents in the sampler head should have a minimum collective cross sectional area of 600 mmz to allow tree exit of air and water above the sample.
( 4 ) A core-catcher device (not shown) may also be included with the cutting shoe.
( 5 ) Samplers smaller in diameter than the U 100 are available which are of similar design.
Figure 13 - General Purpose Open-tube Sampler
- Non - return valve with parts having a minimum cross sectional area of 600mm2 to allow free exit of water and air above sample
- Screws attaching sample tube to drive head
- Thin -walled sampler tube, samples commonly 75 to 100mrn diameter by I m long
Figure 14 - Thin-walled Sampler
Coupler to hollow drill rods
- Piston rod screw clamp, left hand thread
- Spring-loaded cone clamps
- Exit ports
- Piston rod
- Thin-walled sample tube, samples commonly 75 or 100mm diameter by Irn long
Piston with rubber sealing ring and vacuum release screw
Figure 15 - Thin-walled Stat ionary Piston Sampler
Dri l l rod coupling
Water f lush duct
B e a r ~ n g housing
Inner tube, cores commonly 61 to 79 mm diameter by I m long
Ex tens~on tube
Core l ~ f t e r case
Figure 16 - Example of a Double-tube Core-barrel (Craelius T2-101)
Water f lush duct
Split inner tubes, cores commonly 52 to 102 mm diameter
- Dril l rod connection
- Plug to blow out valve
. Bearing housing
Blow out valve
Reaming shel l
Core l i f ter Adaptor Dril l b i t
Figure 17 - Example of a Non-retractable Triple-tube Core-barrel (Triefus H M L C )
Drill rod coupling
Retractor spring
Drill bit
Flush water
(a) Coring Soft Material ( Inner tube extended )
( b ) Coring Harder Material (Inner tube retracted 1
Liner, core 7Lmm diameter by I m long
Inner barrel cutting shoe, 72mm internal diameter ( max. protrusion 50 mm
Figure 18 - Example of a Retractable Triple-tube Core-barrel (Mazier)
Ventilated plastic cap --1
Protectwe drained metal surface box (lockable )
19mm 1.0. plastic pipe . ,.
Gravel or sand ,
Perforated plastic 'Io 11 1 pipe fi lter w r a p p , i d A , fabric
Cement - bentonite
Tamped bentonite pellets or bentonite balls
-PVC pipe. 19mm I .D. lower part perforated
Low air entry porous plastic f ilter-or similar, 300mm x 35 mm 0.13.
(a ) Standpipe (b) Open- hydraulic Piezometer (C ) Casagrande - type Open- hydraulic Piezometer
I ~ o t t o scale
Figure 19 - Typical Standpipe and Open-hydraulic Piezometers
Twin plastic tubes
Rubber
!
Filter 75 mm x 50 mm O.D.
(a) Piezometer Tip for Use in Borehole
Twin nylon- polythene tubes. approx. 3 mm I.D.
5 mm O.D.
Rubber gasket
Fine - pored high air entry pressure stone, 100 mm long by 37 to 50 mm diameter
Rubber gasket
(b) Piezometer Tip for Use in Embankment
Note : Figures based on BS 5930 ~BS1.198la) and Penman (1986) .
Figure 20 - Typical Twin-tube Closed-hydraulic Piezometer Tips .
Ground level in urban area Ground level
2 1 n rural area
500 sq.
Drain conduit laid to
daylight face
T
iron
with vent hole
Bottom of hole v
Notes : (1) Scale is diagrammatic.
( 2 ) All dimensions are in millimetres.
Figure 21 - Typical Installation Details of a Piezometer in a Borehole
Location : Royal Observatory Co-ordinates :
Ground level. 1L9.3mPD Top of standpipes P I & P 2 I L ~ . S ~ P [
150 - 0
1L8
Installed
ILL
132l I I I I I I
April May June JULY August
Raingauge : R 0 1 Distance from site : 0.1 km
Project : Slope Remedial Works Piezorneters : P1 & P2
1
-
- Legend : - Observed piezometric response
pierorneter tip level
Figure 22 - Example of Piezometer Record
Rigid plug. 250 by LO approx.
Non -sl ip bowline knots
Auxiliary draingge
Nylon fishing line
Halcrow bucket. British patent No. 1 5 3 8 ~ 8 7 (See detail )
6 number lead weights (min. total weight 1009 1
Figure 8 knot
(a) Assembled Bucket String
Intake hole
Plastic float for easy visual observation of water level in bucket
FRONT VIEW SIDE VIEW
0 10 20mm - Scale
(b) Bucket Detail
Notes: (1 ) Scale is diagrammatic. ( 2 ) Assembled bucket string must fit into a 19 mm internal
diameter standpipe without sticking.
Figure 23 - Piezometer Buckets (British Patent No. 1538487)
Piezometer Buckets Record
Piezometer No. : P 1
Location : Royal Observatory
Number : 5
Depth : 2.5 rn - 5.5rn Buckets :
Spacing : 0.75 rn Date Installed : 2 14 183
Design (Critical) Water Level :
145.5 mPD
Tip Level :
143.lrnPD
Depth of Critical Water Level below Top of Standpipe :
4.0 m
Ground Level :
149.3 rnPD
Date
12.5.83
20.6.83
11.7.83
2 .8 .83
14.8.83
30.8.83
Legend
Level of Top of Standpipe : 149.5 rnPD
Depth of Tip below Top of Standpipe : 6.4rn
Measured G.W. L. Depth* l m l
Dry
5.9
6.2
5.5
4.6
3.8
:
Depth measured from top of
standpipe
Figure 24 - Example of Piezometer Bucket Data
Buckets Found
Depth* (m)
G. W. L. Depth*
lnd~cated by Buckets
(m)
> 5.5
4.8 - 5.5
> 5.5
3.3 - 4.0
4.0 - 4.8
<2.5
to
J
Comments /Weather
Sunny 'I.
Fine
Sunny
Cloudy
Cloudy
After storm I fine today Exceeds cri t ical depth
J
Contain
1 2 3 4 5
d
d
2.50
Recorded by
HYC
WPF
HYC
HYC
CKC
HYC
3.25 4.00
Water
J
J
J
d
J
J
Bucket No. :
4.75 5.50
1 2 3 4 5
Connection to BW or larger dr i l l rods
Notes: (1 IF igurebasedon B S 1 3 7 7 ( B S l . l 9 7 5 b ] . ( 2 ) A slightly enlarged inner diameter of the split barrel is permitted, provided
removable (iners are always used which have an inside diameter of 35mm. ( 3 ) A ball valve in the base of the coupling as shown in ASTM l1985a 1 is also
permitted. (4 ) All dimensions are in millimetres.
Figure 25 - Split Barrel Sampler for Standard Penetration Test
Torque measuring
-
Sleeve (packed with grease)-
Extension rods
( a 1 Borehole Vane Test
( b ) Penetration Vane Test
k D 4 SECTION
VIEW FROM BOTTOM
(c ) Details of Vane
Note : Figure based on BS 1377 (051, 1975b).
Figure 26 - Vane Shear Devices
Hollow dri l l rods or GI pipe with watertight couplings (or standpipe piezometer 1
The water level inside the casing to be maintained a t the same level as the
Borehole casing
Bentonite seal (Attapulgite may be used i n saline water)
Graded filter material
Base of standpipe perforated
wrapped in fi lter fabric
% I - 100- 150 diameter borehole
Notes : ( I ) Scale is diagrammatic.
(21 All dimensions are in mill imetres .
Figure 27 - Typical Arrangement for Field Permeability Test
(a) Soil Flush with Bottom at lmpervious Boundary
(b l Soil Flush with Bottom (c) Well Point or Hole in Uniform Soil Extended at
lmpervious Boundary
F = 2 n ~ F = 2 0 l o g , [ ( ~ ~ ~ l + J h LID)^)^ 1+(8IT)(LIDl
( d l w e l l Point or Hole (el Soil i n Casinq with ( f ) Soil in Casing with Extended i n Uniform Bottom at impervious Bottom i n uniform Soil Boundary Soil
~ o t e s : ( 1 ) Expressions come from Hvorslev (1951 I; figure based on BS 5930 [BSI. 198la)
( 2 ) Values are primari ly for tests carried out through the open ends of bore- holes. Case Id ) may be used for tests carried out using piezometer tips, but more accurate results wi l l be obtained by using Figure 29 especially for values of L 1 0 > 2 .
13 ) Cases (e) and (1) assume the permeability of the soil in the casing to be the same as that below it. Where this is not so. see Hvorslev (1951)
(4) Cases [a) and l b ) tend to measure the mean permeability of the soil; I c ) and (d l the ver t ica l permeability; [ e l and ( f ) the horizontal permeability. Where the horizontal permeability is much greater than the vertical permeability. a l l tests w i l l tend to measure the former .
F i g u r e 28 - I n t a k e Fac to rs (F), in Borehole Permeabi l i ty Tests
For cyl indr ical piezometers
L is the length D is the diameter
I 1 I I I
0 2 4 6 8 10 Length 1 Diameter Ratio of Piezometer (LID)
Notes : ( 1 1 Graph comes from Brand & Premchitt I1980 1 . ( 2 ) Where a piezometer tip is surrounded by a granular filter material.
i t is the dimensions of this filter which should be used to derive valiles of F.
(31 Where L is large compared with D . the test will tend to measure the horizontal permeability of the soil .
[ L ) Where the horizontal permeability of the soil i s much greater than the vertical . the test will measure the former. whatever the relation between L and D .
(5) The intake factor may also be calculated from the expression I Brand & Premchitt . 1980 :
F = 2.L7rL log, i1.2 LID +J( 1 + 11.2 LID 12)1
Figure 29 - Relationship between Dimensionless Intake Factor and Length to Diameter Ratio of Piezometers
Falling - head Permeability Test
FIELD DATA : Borehole D~~~ BH1 18.12.86
Drillhole D7 Observer A-N. Chan
Use only CLEAN water for test . Has water been added during boring ? W I N O
Internal diameter of casing . 127 m m -
I- Depth of casing = l.07n above G.L.
Depth of water at t ime of lest = 11.66 m below G.L.
Depth of casing E 10.67 m below G.L.
Depth of hole = 12.9 m below G.L.
Diameter of hole
D : 160 mm
0.1 I
0 2 4 6 B 10 12 14 16 18 20 22 Time Imin)
CALCULATIONS : A K = , q
where : A . * : 0.01539 m2 L
F = 2.s7(based on case (d l in Figure 28 T z 12min x 60 z 720sec
Figure 30 - Example of Results from Fall ing-head Permeability Tes t
By-pass valve
Surge bottle r Water
supply control valve
lnf lating pressure I valve Drill rod
Air line taped to dri l l rods Uncased borehole
lnf lated single pneumatic packer in testing position
Discontinuities
O n :: Bottom of borehole
v
( a 1 Single Packer Test Arrangement
I: Control perforated r o d 7
Airline connecting top % and bottom packers-
/ /'
X- Top packer
5 Bottom packer
( b 1 Arrangement of Double Packer
F i g u r e 31 - Typ ica l Ar rangement for Packer (Water Absorp t ion) Tes t
Field Data f r o m Water Absorption Test Borehole No. T 3 Test No. 4
-- -- -
Gauge p r e s s u r e 1 2 4 kPa
Date of tes t 24 . 11.75
Packer t y p e ( de le te a s necessary ) St~gtel Doub le
Packer pressure 276 kPa
Tested by A . N . Chon
Tested Sec t ion f rom 19.81 m t o 22.86 m
Depth o f Hole at Time of Test 33.86 m
De ta i l s of Casing at Time of Test - Gauge Height above Ground Level 1.32 m
I SECOND PERIOD Gauge p ressu re 248 k P a
Depth t o Cen t re o f Test Section ( measured down l ~ n e of borehole) 21 34m
D e p t h t o Groundwater Level ( measured down l ine of borehole ) 21.34m
T i m e m i n u t e s )
F lowmete r
.8y3skdt r e a d i n g ( 1 )
Water take ( 1 )
0
218.6
T i me ( m i n u t e s ) - read ing ( 1 )
Water take ( 1 )
T i me ( m i n u t e s )
F lowmeter - reading 1 1
Water take ( 1 )
Figure 32 - Example of Packer (Water Absorption) Test Data
5
229.3
THIRD PERIOD Gauge p r e s s u r e 3 7 2 k ~ a
0
281.8
FOURTH PERIOD Gauge p r e s s u r e 2 4 8 kPa
0
255.9
10
239.9
2.14
5
296.4
Average FI ow
( I l m i n 1
T i me ( m i n u t e s )
Flowmeter
Q+F+='+ r e a d i n g ( I 1
10.8 10.7
5
276.6
15
250.7
10.6
10
3 1 1 .2
2 . 9 6 14 .6
0
54.5
Average
Flow ( I l m i n 1
10
297.5
4.17
3.10 Water take ( I
15
326.3
14.8
21.0 20.7
5
69.9
Average F l o w
( I l m i n 1
15.1
15
318.5
20.9
FIFTH PERIOD Gauge p r e s s u r e 124 kPa
Average
FI o w
l l m i n )
10
85.4
15.7 15.4
15
101.1
15.5
T ime ( m i n u t e s )
Flowmeter reading - ( 1 1
Average F low
( I / m i n )
0
377.3
10
400.0
2.28 Water take I 1
5
388.6
15
411.5
11.3 11.4 11.5
Water Absorption Test Borehole No. T3 Test No. 4
Legend of Test Section
3.05m
( 1 Vertical Depth
to ground- water from
S. L. 21.3Lrn ( 2 1 Height o t Pressure
Gauge above 3. . 1.32m (31
Date of Test 24.11.75
Packer Type (delete as necessary) Smgkl Double Pneumatic,-
Packer Pressure 276 kPa
Flow I Gauge Pressure
Test Section from 19.81 rn to 2 2 . 8 6 rn
Depth of Hole at Time of Test 33.84 rn
Diameter of Hole in Test Area 102 rnrn
Drillhole Inclination from Horizontal 90'
Casing Deta~ls GRANITE GRADE I 1
Fr ic t ion Headloss 1 Total Head
Rock Type - 1 in Basic in Extra
Pipe Rods or h
Work I pipes 1 (2.3.6-7-8 1 1
where I = length of test section in metres 1 A . N . I A.N. Chan I
From graph : q/h = 3 4 / 5 4
100 ~ = - q = 2.06 lugeon units I h
Note : If groundwater level unknown or below test section use depth to centre of test section.
Figure 33 - Example of Packer (Water Absorption) Test Calculations
Tested by Calculated by
Top body, connection to drill rod or cable
Blee hole
Foam rubber pad i- Brass or
4/- Pins to guide leaves
Brass or stainless steel leaf with foam rubber pad on outer surface
Impressionable thermoplastic film
L
Central perforated metal tube, approx. length 1.8m
Inflatable rubber membrane
Retraction rings or springs
Bottom body
Nose cap or orientation instrument
stainless steel leaves
Impressionable thermoplastic film
Drillhole wall
/ -Inflatable rubber
Central perforated membrane metal tube
( a 1 Deflated Position
( b ) InfIated Position
Notes : ( 1 ) Scale is diagrammatic. ( 2 ) The rubber membrane may be inflated either by water pumped down
through hollow dri l l rods or by compressed air ( a i r line connected to top body). The latter arrangement must be used when the device is suspended from a cable.
( 3 ) Figure adopted from Triefus data sheet (Tr iefus Industries (Aus t ra l ia ) Pty L td ) .
Figure 34 - Impression Packer Device
Impression Packer Survey - Discontinuity Log
Project : Stage 2 Studies I Sheet I of 3
Location : Slope no. llSW-C(C207, Mt. Davis Road I Logged by : A.N. ~ h a n l Checked by : A.N. Lau
Drillhole No. : SBHI
Orientation : Co-ordinates : E 830 610 N 814 942
Vertical Ground Level : +127.65 mPD
Nature and orientation of discontinuties
Extremely weak, dry, l ight brownish red, inequigranular, completely decomposed coarse ash TUFF (Dense. sandy clayey SILT1
Stronq to very strong, dry, dark g reen~sh grey mott led with black. inequigranular, sl ight ly decomposed coarse ash TUFF
Joint
Joint
Type Dip direction. Aperture D.Fault zone D ~ D 1.Wide 12200mml
Nature of Infilling Consistency of lnfillinq Uneveness O.Clran Soil strength Rock strength (small-scale roughness)
1.Fault -
in 2.Mod.wide160-200mml 1.Surlace staining l.yery soft 2. Join1
degICeS 3.Mod.narror(20-6Omm~ 2.Decomposedl 2.Soft
>.Cleavage &.Narrow 16-20mml disintcgraled rock 3.Firm L.Schistosity 5.VWY n a r r o w l l - 6 m m l 3.Granular r o i l *Stiff i. Shear plane 6.Ext. na r rowb0-2mm) 4,Cohcsivc ro i l 5.Very s t i f f 8 . Fissure 7.Tight I z r r o l 5.Buartz or hard
1. Tension crack 6.Calcilr I. Foliation 7. Manganese
I . Bedding 8.Kaolin 9.Othrr-specify
6,Extrcmely weak
7.Very weak &Weak 9.Moderaldy weak
1O.Moderatcly strong 1l.Slrong
12,Yery strong I3,Extrrmely strong
1.Rough stepped 2.Smooth sleppcd
3.Slickcnslided stepped &.Rough undulltinp 5.Smooth undulating 6.Slickenslided undulating
7.Rough planar 8.Smooth planar 9,Slickenslidcd planar
Figure 35 - Impression Packer S u r v e y a n d Discontinuity Log
Guide rod, 20 @
10 kg sliding hammer with handles.
Extension rod, 136 (tobeadded - as required 1 f
L5' chamfer
20 9
I
45' chamfer
Coupler
Coupler, see detail
Point
Point . &- see .eta,[
Notes : ( 1 ) A l l dimensions are in millimetres . ( 2 1 The hammer should be provided w i th a 2 2 mm diameter central hole. The
hammer should be drilled out as necessary so that i ts weight (including handles) is 10.0 f 0.1 kg.
( 3 ) The point should be sufficiently sharp that x + 1.5 mm . ( 4 I Only straight extension rods should be uti l ised j rods deviating Smm or more
from a straight Line at any point should not be used.
Figure 36 - GCO Probe
GCO Probe Record
Site : Fill Slope along Slip Road No.1. Shatin I Probe NO. : P 3
Logged by : A . N . Chan E 836600 N 825 100
Job : FilL Slope Investigation
Contractor : A.N. company
Blows 1100mm
F i g u r e 37 - GCO Probe Record
Date : 16/3/83 Level 50.77 mPD
Co-ordinates
lnner rod. 35 9 w lnner rod.
Mantle -
Cone angle 60'-
( a ) Collapsed (b) Extended
Dutch Mantle Cone
Friction sleeve
Mantle
Cone angle 60"
( c ) Collapsed (d) Extended '3)
Dutch Friction Sleeve Cone
Notes : ( 1 All dimensions are in millimetres. ( 2 ) Details shown follow the ISSMFE (1977). 131 The friction sleeve cone extends in two increments to reach the position shown in (d) . The mantle is first extended .-.
35 mm, then the mantle and friction sleeve together are extended another 35 mm.
Figure 38 - Mechanical Cone Penetrometers
/+ Cable
- Adjustment r ing
- Strain gauges
- Friction sleeve
- Strain gauges
- Load cell
Electric cable
( a ) Electrical (b) Constricted- type ( c ) Constricted-type Friction Cane Electrical Cone Electrical
Friction Cone
Notes : ( 1 1 (a ) af ter BS5930 (BSI , l 9 8 l a ) . l b ) 8, ( c ) after Delft Soil Mechanics Laboratory 11977).
( 2 ) Scale is diagrammatic. ( 3 ) Al l cones shown are 35.6mm drameter with 60' cone angle.
Figure 39 - Electrical Cone Penetrometers
Adjustable crosshead
Conical platen (see detail)
Quick release valve Conical Platen Detai l
Schematic Diagram of Point Load Tester
Point Load Test New Territories Trunk Road
Project : Contracl 529 180
Location : North Tai Po to Lam Kam Road - NO. or eptt
I m) - '10
- 11 M
Rock Type Moisturc and Conditio~
Description
-
Very strong ,dry greenish grey to grey, inequigranular, slightly decomposed, medium to coarse -grained GRANODlORlTE ,with reddish brown stains from original joint surfaces around the edges.
L isture Condition
A loi
d - air ary 5 - saturated n - nalural moisture
21 Test Type and Direction d - diametral n - axial L - irregular lump /I - parallel to planes of weakness 1- perpendicular lo planes of weakness r - random or unknown orientation
- Test Type and
irtctior
Borehole No. s 4 Test Machine : ELE PLT 3 la te Tested : 7 1 8 183
Ram Area : - rested by : KYC
#ample Width, W
(mm) - - -
83
Diametral f
Gauge Platen pressure Failurc
eparation. at Load,
Failure
quivalen )iameter:
De
(mml - 8 3
83
91.37
Axial 0.3W < D < W D~~ E L W D I ~
Irregular Lump iJQ
0.3W < D < W
- orrectior Factor,
F
- 1.26
1.26
1.31
Figure 40 - Point Load Tester and Example Data
Test pit or caisson
I I 10 litre bottles A .f I with calibrated
t
graduations frame with
Constant head Stiff nylon of water for tubing supplyins
water
Outer steel ring, Test surface, hand 600mm diameter excavated and level
Inner steel ring, 300mm diameter
F igure 41 - Typical Arrangement for Double-ring Constant-head Field Inf i l t rat ion Test
Settlement measurement Reference
Main loading frame
gf column Loading I Line of tension piles
Loading column
\I L Measuring column
Centralising fins
Skirt Loading plate
Bedding material
I Details of Loading Plate
Note : Figure adopted from Brown (1981 1 and BS5930 1 BSI, 1981a I .
Figure 43 - Typical Arrangement for Plate Load Test
Pro jec t :
Loca tmn
C o n t l ( l ~ t 0 r
Remarks :
Co-ordinates : E 12197.74 N 19259 5 5 Sheet N o : Of
Lom T I P I Ground Leve l : 9 1 6 mPD I Logged by : A N Chon I Checked by : AN. Lou
A. N Cornpony Orlentatmn ' V e r t i c a l
- e p t h of
2s,ng %re1
Imm - 1LOl
8.2 - 11011
Field Tests. Samples ond
Instrumentottan 1%)
nspectlon pot 0 50
excovoted t o 1 5 m d e p t h
From s ~ t e format ion drowmg no A130791 or lg tno l ground leve l before cans t ruc tmn of f l l l P la t farm and playground wa r apprax 8 8 m P D
~ o t e of wo rks 2 2 / 2 / 8 6 t o 2 L 1 2 1 8 6 + Descrtptlon o f M o t e r m l s I Grodr
:ancrete s l ob , lOOmm t h l c k .
.o(rse. p~nk f sh grey. ongular COBBLES of - nedwm to coorse-gro~ned slightly jecomposed granite wi th much coarse grovel. -
F i l l 1
.oose. reddish brawn. s l l t y l clayey. sondY - ;RAVEL w ~ t h ~ccos iono l ongular cobbles 2nd some roo t l e t s
: F i l l 1
Medlum dense yellowish brown silty SAND ~ t h OCCOSIO~OI sub-ongulor grovel ond cobbles o f moderotely t o h lgh ly decomposed coarse-grotned g ron l t e
I Calluvlum 1
Extremely weok. i l gh t redd lsh brown. completely decomposed c o a r s ~ - g r a i n e d GRANITE I Medum dense to dense, Sandy SILT 1 CLAY 1 1
Moderately weok. yellowish brown \ C ~ n e ~ u ~ ~ r a h l o r , moderotely decomposed coarse to medium-grolned GRANITE w i t h sub- ho r~zon to l , closely-spaced, smooth ond ~ L a n a r , t l gh t . b lock-s ta ined jotnts 1 Strong. pmklsh grey. inequigronulor, slightly decomposed coarse t o m e d u m - g ro~ned GRANITE ' 4 1 t h generally wldely-spoCed lOltlt5 Smooth and planar. t g h t , b lock-s to lned j m t dlppmg a t 7 0 ' ot 9 1 - 9 3 m . Sub-horrzontal, smooth ond planar. t l g h t . brown-stained jolnts a t 9.6, 10.2 and 10 5 m I see Sheet 2 I
. Smol l d ts turbed eomple I t Large disturbed somole
I Plant used Longyeor L 3 L . .
Type of bo r l ng l d r i l l l n g : Ro tmy d r l i ~ n g
I U76.100 Undasturbed dr , v e sample. of 76 mm ~l,,~h,,,~ medium - water or 100 mm d o I b low coun t , depth1 I
Figure 44 - Example of a Borehole Log (sheet 1 of 2)
M o r n m p l w c n l n g water Level I SPT inner sample
Stondord penetratton tes t N value I I b low count I p e n e t r a t ~ o n 1
$ P e r m e a b # l t y l es t
8 20 - 11 5 0 m 101 mm 11 50 - 1 2 t o m 89mm 12 10 - 18 1 0 m 76mm
C w m g tubes
0 0 0 - 8 2 0 m PW 8 20 - 1 2 I O m NW
2112
18 1
12 1
7 6
a t
3H depth
:arlng
Na ls r
2 3 1 2
13 2
12 1
3 5
2112
13 2
12 1
7 8
2212
- - -
2212
8 2
8 2
3 0
2312
8 2
8 2
2 9
Barehole No A 11 P r q c c t Project A Job No L T l D L l 1 1
Co-ordonotes E 42L97 7L N 19259 55 - - Sheet NO 2 0 1 2
L o c o t ~ o n Lom Tin I Ground Level 91 6 mPD
Contractor A N Cornpony Or~en lo tm- Verl8col
Date of works 2 2 1 2 1 8 6 to 24 1 2 1 8 6
Sample
Field Tests. Samples ond
n s t r u m e n t a t ~ o n
e g e r
- i + + + i + - X X
< ' X ,
X X . . L X . . X X
< . X - + +
, + + +
* + - + . +
+ + , + + +
6 + 4
* + + + , +
+ + , + + + , + + +
* + + +
+ + + + , + -
Sl~ght ly decomposed GRANITE I see Sheet 1 - for deta115 1 .. II
Weak yellowish brown. mequ~granu lar , highly \- decomposed coarse-grained GRANITE from - 1 0 7 - l l O m - NII recovery f rom 11 0 - 11 5 m
Small disturbed sample No 10 conto lns dense. - !iZlP pcnklsh brown sandy SILT wi th some rel lct graolte tex ture IHlghly to completely - decomposed GRANITE 71 - Strong l lght pmklsh grey ~nequtgronu lar sl lght ly decomposed medlum to coarse-gramed - n GRANITE with s u b - h o r ~ z o n t o l c lose ly -spaced
- rough and pionor t lgh l b rown-s to lned ]o,nts -3 Moderately to hbghly decomposed rock recovered os angular gravel o t 12 5 - 12 a m - n
Very strong hght p m k l s h grey ~nequ~gronu lar . - f resh. medwm to c a o r s e - g r a ~ n e d GRANITE - wtth generally widely-spoced p n t s Smooth ond plonor tight b r o w n - s t a ~ n e d p n t s dbppmg o t 40' o t 13 3 m and 1L 8 m
-
Closely-spoced. smooth and p lanar , t ~ g h t , b r o w n - s t o m e d p n t 5 dlpplng a t 10" a t 15 0 - 15 5 m
Sub-vertical medium-spaced. smooth and unduldt8ng d o r k green joints wbth 1 - 2mm t h ~ c k chlorite lnf l l l a t 17 1 - 17 6 m S u b - h o r ~ z o n t a l , smooth and plonar t lght. wh l te -s tamed p n t coated wl lh k a o l m of 18 Om
Jlezometer A l l b
Borehale complete a t 18 l m depth t
P l o d used Longyeor L 3 L
Type of borlng I dr l lhng
Rotary drlllkng
F l u s h ~ n g medium Water
D~ometer of b o r n g I drl l l lng
0 00 - 8 2Om l4Omm 8 20 - 11 5 0 m 101 mm
11 50 - 12 1 0 m 8 9 m m 12 10 - 18 1 0 m 7 6 m m
Casing tubes
0 0 0 - 8 2 O m PW 8 20 - 12 t o m NW
Remarks I Legend
Small disturbed somple
+ Lorge d ls tu tbed somple
U76 100 Undisturbed drlve samples of 76mm or 100 mm d m I blow count depth I
1 M o l t e r sample
a SPT ltner somple
Standard penetrat ion test N va lue I blow count I penetrot lon I
$ Permeabl l l ty test
Plezometer A t l b mstol led o t 17 3 m depth below ground surfoce w l l h sand filter from 18 l m to 12 l m . benton l te sea l f r o m 1 2 l r n to 8 Zm, plezometer A110 lns to l led o t 7 5 5 m depth below ground surfoce w l l h sand filter f rom 8 2 m to 69rn. bentonlte s e a l l r o m 6 9 m t o 4 5 m and cement -benton~ lc grout f rom L 5 m to ground sur foce
F i g u r e 44 - Example of a Borehole Log ( s h e e t 2 of 2)
PLATES
[BLANK PAGE]
Plate No.
299
LIST OF PLATES
Drilling in Urban Areas of Hong Kong
Drilling in S teep ly Sloping Ground
Ground Inves t iga t ions o v e r Water
Drilling a n d Sampling Equipment ( t h r e e s h e e t s )
Block Sampling
Groundwater P r e s s u r e Measuring Equipment
S t a n d a r d Pene t ra t ion Tes t Equipment
Pene t ra t ion Vane Tes t Appa ra tu s (Geonor A/S)
Impression Packe r S u r v e y Equipment
P rob ing a n d Pene t ra t ion Tes t Equipment
Page No.
1 2 3 4 5 6 7 8 9 10
A : Drilling in a Densely -developed Urban Area
B : Drilling. in the Middle of a Busy Road
Plate 1 - Dri l l ing i n U r b a n Areas of Hong Kong
A : Working Plat form for Dr i l l i ng on a Slope
B : Timber Scaffolding for Access
Plate 2 - Dr i l l i ng in Steeply Sloping Ground
A : Jack - up Plat form
B : Power Swivel Dril l ing System Mounted on a Barge
Plate 3 - Ground Investigations over Water
I A : The ODEX D r i l l B i t B : The U100 Sampler
--
Plate 4 - Dril l ing a n d Sampl ing Equipment ( s h e e t 1 of 3 )
s
C : T h i n -wa l l ed S t a t i o n a r y P i s t o n D : Components o f a D o u b l e - t u b e Core- Sampler ba r re l (C rae l i us T2 - 101 I
P l a t e 4 - Dril l ing a n d Sampl ing E q u i p m e n t (sheet 2 o f 3 )
E : Components Of a Non-retractable Triple- tube Core - barrel ITriefus HMLC)
F : Components of a Retractable Triple - tube Core - barrel 1 Mazier )
Plate 4 - Drilling and Sampling Equipment ( shee t 3 of 3 )
A : Trimmed Block Sample
B : Protection of Block Sample
Plate 5 - Block Sampling
A : Casagrande B : S t r i n g of Piezome-ter C : Tensiometer Je t f i l l ) Piezometer Tip B u c k e t s 1 B r i t i s h
Patent No. 1538L871
Plate 6 - Groundwater P r e s s u r e Measur ing Equipment
A : Torque Measuring Device
B : Vane Body
P l a t e 8 - P e n e t r a t i o n V a n e T e s t A p p a r a t u s ( G e o n o r A / S )
APPENDICES
- - - - - [BLANK PAGE]
APPENDIX A
INFORMATION REQUIRED FOR DESK STUDY
[BLANK PAGE]
3 1 7
CONTENTS
TITLE PAGE
CONTENTS
A . l GENERAL
A . 2 MAPS, PLANS AND CHARTS
A . 3 GROUND CONDITIONS
A.4 METEOROLOGICAL AND HYDROLOGICAL INFORMATION
A.5 PAST RECORDS
A.6 SERVICES AND UTILITIES
A.7 LEASE AND ENGINEERING CONDITIONS
A.8 PLANNING A GROUND INVESTIGATION
A.9 REFERENCES
P a g e No.
3 1 5
3 1 7
3 1 9
3 1 9
3 1 9
3 1 9
3 2 0
3 2 0
3 2 0
3 2 2
3 2 4
--
[BLANK PAGE]
A.l GENERAL
A desk s t u d y involves t h e collection and review of information required for t h e planning of t h e projec t and of t h e s i te investigation.
Sources of information a r e given in Appendix B.
A.2 MAPS. PLANS AND CHARTS
Topographic maps and plans a r e useful for s tudying t h e general f ea tu res of t h e s i te , and for identifying ground fea tures of engineering significance, e.g. slopes, retaining s t r u c t u r e s , s treams, tunnels , burial g rounds and obstruct ions such a s transmission lines and towers. They a r e also useful fo r t h e assessment of t h e effect of t h e proposed works on adjacent propert ies and s t ruc tu res . and for the identification of works areas , s torage a reas and access, including temporary access fo r construction purposes.
For works t o be car r ied o u t in a marine environment (e.g. seawalls and piers). Admiralty c h a r t s and t ide tables should also be refer red to.
In some cases, old maps may be useful, e.g. t o check t h e location and extent of a n old seawall o r a buried stream course. Archaeological maps may also b e requi red t o establish t h e boundaries of a n archaeological site.
A.3 G R O U N D CONDITIONS
The following information should b e refer red t o for a preliminary s tudy of t h e ground conditions :
(a)
( b )
(c)
Aerial photographs. These a r e particularly useful for s tudying t h e s i te history, pas t instability of t h e ground. erosion, surface hydrology, vegetation, photolineaments and o ther surface geological fea tures , and for identifying t h e presence of colluvium, alluvium, fill and boulders (see Chapter 6) .
Geological maps and memoirs. These provide detailed information on t h e geology of t h e distr ict . and a r e useful a s a basis for evaluating t h e likely influence of t h e local geology on t h e proposed works and in t h e selection of t h e ground investigation methods.
Pas t s i t e investigation records. These should b e s tudied and useful information extracted. Availability of good s i te investigation records in t h e vicinity of t h e s i t e will great ly a s s i s t t h e planning of t h e ground investigation, and may reduce t h e scope and extent of t h e investigation requi red .
A.4 METEOROLOGICAL AND HYDROLOGICAL INFORMATION
Local rainfall records should b e collected where t h e proposed works requi re slope and dra inage design. Hydrological information. where available, i s useful in dra inage studies. including t h e assessment of flooding r i sk and t h e influence of t h e proposed works on t h e local and downstream dra inage regimes.
In t h e design of temperature-sensi t ive s t ruc tu res , o r where t h e per- formance of t h e construction materials can be affected by temperature, da ta on ambient tempera tures (including a i r and ground temperatures) and solar radiation should be re fe r red to.
A.5 PAST RECORDS
Pas t construct ion records. for both t h e s i te and for adjacent properties. should b e obtained where appropriate, t o provide information on t h e following :
(a) Site formation works such a s construction of slopes, retaining s t r u c t u r e s and basements.
(b) Foundation works such a s piling.
(c) Details of preventive o r remedial works and of any continuing monitoring of, for example. ground anchor installations. horizontal drain installations, building settlements, and slope and retaining wall movements.
( d ) Tunnels and disused tunnels , including details of linings and ground suppor t .
Records of pas t failure. flooding and settlement of ground and s t r u c t u r e s should also be noted and s tudied where necessary.
A.6 SERVICES AND UTILITIES
Details and locations of existing services and utilities, including stormwater dra ins , sewers, f r e s h and sa l t water mains, f i re f ighting mains. electrical cables, gas mains and telephone ducts . should be re fe r red t o for t h e following purposes :
(a) Assessment of t h e effect of t h e proposed works (including ground investigation works) on t h e existing services and utilities, e.g. t h e ef fec t of dewatering settlement on a n old water main o r gas main.
( b ) Provision of services and utilities for t h e project , e.g. provision of cooling water for t h e air-conditioning system.
(c) Provision of temporary electricity and water supplies for t h e ground investigation.
A.7 LEASE AND ENGINEERING CONDITIONS
Except where a n investigation is being planned for a s i te t h a t has not been allocated t o t h e projec t (e.g. an investigation t h a t is fo r t h e purpose of selecting s i tes o r establishing t h e suitability of a s i te) . t h e r e should be available a s e t of lease conditions o r engineering conditions. depending on whether t h e proposed project is t o b e under taken privately o r by Government. I t is essential t h a t these conditions a r e s tudied thoroughly dur ing t h e desk s tudy o r a s soon a s they become available.
Engineering conditions a r e issued by t h e appropriate District Lands Office of t h e Lands Department, and lease conditions a r e normally issued b y t h e Registrar GeneraVLand Officer. These conditions govern t h e use of t h e site. They also s e t down the requirements and restr ict ions on development, and define t h e responsibilit ies of t h e related part ies and authorities. The following items a r e normally covered :
(a) Requirements. These normally include :
( i) formation and landscaping. (ii) layout of t h e site. (iii) access, (iv) possession af t h e site.
( b ) Restrictions. Examples of common items covered a r e :
non- building areas . height of s t ruc tu res . removal of t r ees , dumping on Government land and public roads. drainage rese rves . pile driving. blasting. use of water supply , establishment of rock crushing plants.
(c) Responsibilities. The conditions normally cover responsi- bilities for :
(i) maintaining both t h e stability of t h e land and i t s su r face condition. within, and where appropr ia te , adjacent to t h e si te .
(ii) in ter ference with o r damage t o roads. services, drains, channels, etc .
(iii) water supply. ( iv) connections t o sewers and stormwater
dra ins , ( v ) drainage.
The following local s t a tu tes may be mentioned in t h e lease conditions :
The Buildings Ordinance and i t s subs id iary Regulations (Government of Hong Kong, 1985). governing t h e safe ty and t h e design and construct ion s t a n d a r d s of buildings t o b e erected, and t h e planning and administrative procedures t o b e followed. This Ordinance also governs s i t e investigation work within t h e Mid-levels Scheduled Area.
The Fire Services Ordinance (Government of Hong Kong, 1981a). governing t h e provision of f i re services. installations and equipment. and t h e provision of access fo r f i re services. appliances and personnel.
The Waterworks Ordinance (Government of Hong Kong. 1974). governing t h e supply of f r e sh water a n d sa l t water.
and t h e s t andards of plumbing, installations and equipment.
( d ) The Dangerous Goods Ordinance (Government of Hong Kong. 1983). governing t h e storage, t ransportat ion and use of dangerous goods.
In some cases, special clauses may also be p resen t in t h e lease conditions. For example, a geotechnical clause may be used t o indicate t h a t a s i te is considered t o b e geotechnically difficult t o develop, hence forewarning a developer t h a t a high degree of skilled geotechnical engineering inpu t will be required.
A.8 PLANNING A G R O U N D INVESTIGATION
In planning a ground investigation, t h e effect of t h e proposed works on t h e ground. on adjacent propert ies and s t r u c t u r e s and on existing services and utilities, should be thoroughly examined. For example, t h e ef fec t of flushing water from drilling on existing slopes and retaining walls should be considered.
Requirements and restr ict ions imposed by local s ta tu tes should b e studied and observed in t h e planning and execution of t h e investigation. For example. t h e Summary Offences Ordinance (Government of Hong Kong. 1981b) r e s t r i c t s t h e use of powered mechanical equipment between 7 p.m. and 7 a.m.. and on any public holiday, including Sundays. This Ordinance also controls t h e general level of noise a t night, i.e. from 11 p.m. t o 6 am. , even if powered mechanical equipment i s not being used. S ta tu tes governing safety, health and welfare of workmen a r e given in Appendix E.
Land matters should be dealt with well in advance of t h e requi red date of commencement of investigations. For th i s purpose, t h e appropr ia te District Lands Office of t h e Lands Department, and, where appropriate, t h e relevant District Office. should b e consulted, s o a s t o a r range for unhindered access for t ranspor t ing equipment t o site, and to enable work to be car r ied o u t on site. The land matters should include :
( a ) confirmation of land ownership and lot boundaries.
( b ) permission t o e n t e r in to and t o t r anspor t equipment th rough adjacent land,
(c) permission t o c a r r y o u t ground investigation work outside t h e s i te boundaries,
( d ) allocation of any necessary works areas and s torage areas.
I t is important t h a t t h e exact locations of s i te boundaries of private and Government land. and of allocated works areas and s torage areas , should b e ascertained from t h e appropr ia te District Lands Office. The appropr ia te District Survey Office of t h e same Department may also have t o b e consulted for information on delineation of t h e ground, especially in t h e New Territories where land demarcation has not been carr ied o u t t o a high s t andard in t h e past.
The District Lands Office should also b e consulted on matters relating t o 'fung shui ' and burial grounds .
Where t r ees need t o b e felled o r removed. prior permission should be obtained from t h e appropriate District Lands Office. who will consult t h e Agriculture & Fisheries Department, Urban Services Department o r Regional Services Department, a s appropriate. Whenever possible, permission should be sought twelve months in advance, so t h a t t h e root system of any t r e e suitable for t ransplant ing may be prepared fo r t h e move.
The approval of t h e Buildings Ordinance Office, must b e obtained for s i te investigation work t h a t falls within t h e Mid-levels Scheduled Area. Plans showing t h e boundary of t h e Mid-levels Scheduled Area may be viewed in t h e Buildings Ordinance Office and t h e Geotechnical Engineering ,Office. Pumping test proposals for pr iva te developments must also be submitted t o t h e Buildings Ordinance Office fo r approval.
Information on t h e as-buil t alignment of t h e Mass Transi t Railway and i t s "protection boundary" may be obtained from t h e Mass Transi t Railway Corporation, whose advice must b e sough t where t h e proposed ground investigation work falls within t h e protection boundary.
If i t i s necessary t o excavate public roads, road excavation permits must be obtained from t h e Utilities Section of t h e Highways Department. Where the proposed ground investigation work may d i s rup t t h e use of public footpaths, s t r e e t s o r roads , including high speed roads. t h e Highways Department should be consulted.
In cases where i t is necessary t o d ischarge eff luents into public dra ins o r sewers, permission m u s t f i r s t b e obtained from t h e Drainage Services Department. The Environmental Protection Department must also b e consulted where toxic eff luents a r e involved.
If it is intended t o use explosives. for example in a seismic s u r v e y , t h e prior permission of t h e Commissioner of Mines a t t h e Civil Engineering Department must be obtained.
In t h e case of marine investigations, t h e Marine Department must be notified of t h e details of t h e proposals. so t h a t notices t o mariners can be issued. Special restr ict ions may b e imposed by Director of Marine where works i s t o be car r ied o u t in close proximity t o fairways, channels, typhoon shel ter ent rances , terminals and piers. There may be circumstances where contractors vessels will need t o provide mooring arrangements outside typhoon shel ters for the i r vessels dur ing t h e passage of typhoons. Where investigations a r e proposed close t o t h e runway of Kai Tak Airport. permission must f i r s t be obtained from t h e Civil Aviation Department. Similarly, permission must b e obtained from t h e Mass Transi t Railway Corporation, t h e Cross Harbour Tunnel Co. Ltd, t h e Water Supplies Department, o r t h e various public utility companies. if investigations a r e proposed near submerged tunnels , pipelines o r utilities.
Where t h e proposed ground investigation works fall within a gazetted historical s i te , permission must be obtained from t h e Antiquities & Monuments Office of t h e Government Secretariat before commencement of any work. The Antiquities & Monuments Office should also be consulted before any historical s i te is en te red , even if i t is not gazetted.
A.9 REFERENCES
Government of Hong Kong (1974). Waterworks Ordinance ( and Waterworks Regulations). Laws of Honq Kong. Chapter 102. revised edition 1974. Hong Kong Government Pr in ter . 45 p. (Amended from time t o time).
Government of Hong Kong (1981a). Fire Services Ordinance (and Fire Services Regulation). Laws of Hong Kong. Chapter 95. revised edition 1981. Hong Kong Government Printer . 45 p. (Amended from time t o time).
Government of Hong Kong (1981b). Summary Offences Ordinance (and Subsidiary Legislation). Laws of Honq Konq. Chapter 228. revised edition 1981. Hong Kong Government Pr in ter . 26 p. (Amended from time t o time).
Government of Hong Kong (1983). Danqerous Goods Ordinance (and Dangerous Goods Requlations). Laws of Hong Konq. Chaoter 295, revised edition 1983. Hong Kong Government Pr in ter . 278 p. (Amended from time t o time).
Government of Hong Kong (1985). Buildinqs Ordinance (and Building Regulations). Laws of Honq Konq. Chapter 123. revised edition 1985. Hong Kong Government Pr in ter . 387 p. (Amended from time t o time).
APPENDIX B
SOURCES OF INFORMATION
- - - -
[BLANK PAGE]
327
CONTENTS
T ITLE PAGE
CONTENTS
B.1 MAPS. PLANS AND AERIAL PHOTOGRAPHS 8 . 1 . Maps and Plans Produced by t h e Survey & Mapping
Office B.1.2 Other Maps 8 .1 .3 Aerial Photographs
B.2
B.3 GEOLOGICAL MAPS AND MEMOIRS
ADMIRALTY CHARTS, TIDE TABLES AND NOTICE O N SHIPPING MOVEMENTS
B.4 METEOROLOGICAL AND SEISMOLOGICAL INFORMATION
B.5 HYDROLOGICAL INFORMATION
B.6 PAST RECORDS B.6.1 Records from Previous Investigations B.6.2 Design and Construction Records 8 .6 .3 Other Public Records
B.7 SERVICES AND UTILITIES
B.8 LOCAL LIBRARIES 8.8.1 The Geotechnical Information Unit of t h e
Civil Engineering Library 8.8.2 Other Libraries
B.9 ADDRESSES OF LOCAL ORGANIZATIONS
8.10 REFERENCES
Page No.
325
327
329 329
329 329
329
330
330
330
331 331 331 331
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B.1 MAPS. P L A N S AND AERIAL P H O T O G R A P H S
B.l.l Maps and Plans Produced b y t he Survey & Mapping Office
The Survey & Mapping Office o f t he Lands Department provides basic large-scale plans, derived medium-scale plans, approved town plans. and topographic maps o f Hong Kong. A list o f t he currently available plans and maps, and their coverage, is given i n Table 1.
Services o f f ered b y the Survey & Mapping Office include t he supply o f negative or photographic copies o f available maps and plans, as well as producing enlargements and reductions. These services are available from the Office's Map & Plan Sales outlets. together with map catalogues, and leaflets on t he services o f f ered and on copyright. Orders for enlargements and other nonstandard items should be placed well in advance, t o allow time for production and delivery.
8.1.2 Other Maps
Other map sources include the following :
( a ) Early maps o f Hong Kong are held for re ference b y t he Survey & Mapping Office and t he Public Records Office.
( b ) The Antiquities & Monuments Off ice o f the Culture Division, Municipal Services Branch holds a series o f large-scale archaeological maps covering the whole o f Hong Kong. which include historical buildings and boundaries o f archaeological sites. The maps are not available t o members o f the public, bu t they can be examined b y authorized personnel in connection with Government projects.
( c ) The Hong Kong Archaeological Society holds selected maps.
B.1.3 Aerial Photographs
Aerial photographs may be purchased from the Survey & Mapping Office's Map & Plan Sales outlets. Services include the supply o f vertical and oblique aerial photographs as contact, whole or partial-frame enlargement prints. Indexes and contact prints of aerial photographs may be inspected only at t he Map and Plan Sales (Hong Kongf outlet. Once the reference numbers o f t he required photographs have been obtained, orders may be placed at either t he Hong Kong or Kowloon outlets.
The availability o f black and white vertical aerial photography is summarised in Table 2. Aerial photography exists for some parts o f t he Territory back t o 1924 and full coverage i s available from 1963 onwards.
8.2 G E O L O G I C A L MAPS AND M E M O I R S
A new geological survey o f Hong Kong i s being carried out b y t he Geotechnical Engineering Office o f t he Civil Engineering Department. The survey began i n 1982 and. when completed in 1991. will comprise a series o f
fifteen maps and six memoirs, providing detailed descript ive and 1:20 000 scale map coverage of t h e en t i r e land and sea a rea of t h e Terri tory. The coverage. relationship and phasing of t h e maps and memoirs a r e shown in Figure 3. The new publication ser ies will replace t h e c u r r e n t reference geological document, namely t h e 1:50 000 scale maps and memoir by Allen & Stephens (1971). Both the new and existing maps and memoirs can be obtained from t h e Government Publications Centre, o r from t h e Map & Plan Sales outlets of t h e Survey & Mapping Office.
The Planning Division of t h e Geotechnical Engineering Office is the reposi tory for geological records . These include t h e field observations embodied in t h e geological maps and memoirs, manuscript geological maps a t 1:10 000 scale. and offshore data. Requests for information should be directed t o the Chief Geotechnical Engineer of t h e Planning Division. The Geotechnical Engineering Office also holds a collection of representa t ive rock t y p e s and thin sections. These a r e available for inspection by arrangement. The superficial deposits, weathering, s t r a t ig raphy , tectonic history, s t r u c t u r e and metamorphism of Hong Kong have been reviewed by Bennett (1984a. 1984b, 1 9 8 4 ~ ) . A summary of t h e na tu re and occurrence of Hong Kong rocks and superficial deposi ts is given in Appendix A of Geoguide 3 ( G C O , 1988).
B.3 ADMIRALTY CHARTS, TIDE TABLES AND NOTICES O N SHIPPING MOVEMENTS
Admiralty c h a r t s may be obtained from t h e accredited agen t in Hong Kony. namely George Falconer Ltd (see Section B.9). Tide tables a r e readily available in Hong Kong a t t h e Government Publications Centre and selected bookshops.
The Marine Department i ssues notices t o mariners regularly concerning ship movements and harbour obstruct ions.
B.4 METEOROLOGICAL AND SEISMOLOGICAL INFORMATION
The Royal Observatory collects and publishes meteorological information in Hong Kong. Daily weather r epor t s and forecasts a r e issued together with individual tropical cyclone, thunders torm, landslip and flood warnings. Rainfall records a r e published monthly and annually. and a l is t of publications on meteorological s tat is t ics is available from t h e Observatory.
The Royal Observatory also maintains a well-equipped seismological unit. from which local information may be obtained.
B.5 HYDROLOGICAL INFORMATION
The Water Supplies Department has a comprehensive system of stream gauging in t h e main catchment areas, and th is information is published in annual r epor t s on rainfall and runoff.
B.6 PAST RECORDS
B.6.1 Records from Previous Invest igat ions
The Geotechnical Information Unit of t h e Geotechnical Engineering Office
holds reports o f previous site investigations, which o f ten include borehole logs and results from laboratory testing o f soils and rocks. Reports are referenced b y means o f a simple map grid system.
The Geotechnical Information Unit also contains a large amount o f other information o f direct relevance t o site investigation, and this is described in Section B.8.1.
B.6.2 Design and Construction Records
Several Government Departments possess information that is o f value t o t he planning and execution o f site investigation in Hong Kong. bu t this i s o f t en not readily accessible. However, arrangements can usually be made for specific information t o be made available t o bona f ide users.
Each Government Department retains i t s own files on projects that are carried out under i t s control. Copies o f design reports and record drawings o f completed projects are also kept . A brief summary o f information possessed b y some o f t he Government Departments is given below.
The Architectural Services Department maintains records o f Government buildings.
The Buildings Ordinance Office o f the Buildings Department retains records o f private developments for about seven years following their completion, a f t er which time the files are transferred t o t he Public Records Office. Permission t o view a particular set o f records may be obtained from the Buildings Ordinance Office, who will require t o know the address o f t he property and the lot number.
The Civil Engineering Office o f the Civil Engineering Department maintains records o f all known waste t ips in Hong Kong. The Geotechnical Engineering Office o f t he same Department holds records o f all known disused tunnels and quarries, and maintains records o f all known retaining walls and man-made slopes, and some natural slopes.
The Highways Department holds records o f t he majority o f public roads and road tunnels.
The Mines and Quarries Division o f t he Civil Engineering Department maintains records o f all known disused mines.
The Water Supplies Department holds records o f water tunnels, catch- waters, reservoirs and ancillary structures.
B.6.3 Other Public Records
The Public Records Office o f Hong Kong is t he central repository for the permanent archives o f the Hong Kong Government. The majority o f i t s holdings date from 1945. b u t i t does have some much earlier material. I t maintains catalogued collections o f maps and photographs dating from 1860. together with almost complete collections o f the Hong Kong Government Gazette. Blue Books, Sessional Papers. Annual Departmental Reports. Ordinances and Regulations, and Hong Kong Hansard. The Sessional Papers are o f particular interest because, from 1889, they include t he Annual Reports o f t h e Director o f Public Works,
which give information on failures and remedial works. Also of great value is the comprehensive newspaper collection held by the Public Records Office.
The Government Secretariat Library contains information that could be useful from an historical point of view. This includes Sessional Papers, Administrative Reports, Statistical Abstracts and Legislative Council Minutes. The Photographic Library and Reference Library of the Information Services Department holds sets of old photographs, microfilm of newspaper cuttings and other useful material.
A. list of gazetted historical sites is maintained by the Antiquities & Monuments Office of the Government Secretariat.
B.7 SERVICES AND UTILITIES
Information on gas, electricity, telephone, and similar services, including both the locations and details of existing facilities and the provision of further services, should be sought from the private companies supplying these services. The addresses of the major utility companies are listed in Section B.9.
Information on the location of water supply mains (including private cooling water mains), public drains and sewers may be sought from the relevant Government Department. The Water Supplies Department holds records of public water mains, and applications for water supply should be directed to the Department's Consumer Services Division. The Drainage Services Department maintains as-built records of public drains and sewers.
B.8 LOCAL LIBRARIES
B.8.1 The Geotechnical Information Unit of the Civil Engineering Library
The Geotechnical Information Unit forms part of the Civil Engineering Library, which is operated by the Geotechnical Engineering Office of the Civil Engineering Department. In addition to records from previous site investigations, the Geotechnical Information Unit contains records of landslides, rainfall and piezometric data, Geotechnical Area Studies Programme maps, a catalogue and records of existing cut, fill and natural slopes and retaining walls, and factual reports and drawings prepared by Government Departments and Consulting Engineers for a wide range of large and small building and civil engineering projects. Notable examples of the latter are the various Landslide Studies Reports and the Mid-levels Study Report, which were commissioned by the Government. It also contains a large collection of published and unpublished documents specific to Hong Kong (including references on site investigation), together with geotechnical and geological textbooks and journals. '
Almost 1500 items are known to have been published specifically on aspects of the geology and geotechnical engineering of Hong Kong. These are listed in the Bibliography on the Geology and Geotechnical Engineering of Hong Kong to May 1994 (Brand, 1994) produced by the Geotechnical Engineering Office. A full copy of every 'short' publication listed is kept in the Geotechnical Information Unit, together with copies
of the title and contents pages of the 'long' publications. These copies are contained in bound volumes by year of publication and then in alphabetical order by authors' surnames. Full copies of some of the 'long' publications are also available in the Geotechnical Information Unit, but these are shelved separately. Copies of new publications are added to the collection as they become available.
All the information in the Geotechnical Information Unit may be consulted by bona fide users. Photocopying facilities are available.
B.8.2 Other Libraries
The City Hall Public Library and the Kowloon Central Library each houses a reference section which contains a number of published documents on the geology and geotechnical engineering of Hong Kong, together with some unpublished reports. They also house Hong Kong Collections of considerable interest. No direct access is permitted to the shelved items, and items required for examination must first be located in the card catalogue syskems. Photocopying facilities are available for public use.
The University of Hong Kong, the Chinese University of Hong Kong and the Hong Kong Polytechnic University each has a large library which contains a collection of general geological and geotechnical information. All three, however, can only be accessed by special permission, although this is usually not difficult for bona fide visitors to obtain. The University of Hong Kong maintains an outstanding Hong Kong Collection, which contains considerable unpublished information, as well as a large number of master and doctoral degree theses on geological and geotechnical topics. Photocopying facilities are available in the library.
B.9 ADDRESSES OF LOCAL ORGANIZATIONS
Agriculture & Fisheries Antiquities & Monument Offices, Department, 136 Nathan Road, 3rd,6th.8th8llth-14th Floors, Tsirn Sha Tsui, Kowloon. Canton Road Government Offices, (Tel.: 2721 2326) 393 Canton Road, Kowloon. (Tel.: 2733 2211)
Architectural Services British Forces Hong Kong, Department, HMS Tamar, 35th Floor, Hong Kong. Queensway Government offices, (Tel.: 2588 3111) 66 Queensway, Hong Kong. (Tel.: 2867 3628)
Buildings Department, 12th-18th Floors, Pioneer Centre, 750 Nathan Road, Kowloon (Tel.: 2626 1616)
China Light & Power Co. Ltd., 147 Argyle Street, Kowloon. (Tel.: 2678 8111)
Chinese university of Hong Kong Library,
12% Milestone, Tai Po Road, Sha Tin, New Territories. (Tel.: 2609 7301)
City University of Hong Kong, Run Run Shaw Library, Tat Chee Avenue, Kowloon. (Tel.: 2788 8311)
Civil Engineering Office, 15th Floor, Civil Engineering Building, 101 Princess Margaret Road, Homantin, Kowloon. (Tel.: 2762 5111)
Drainage Services Department, 43rd Floor, Revenue Tower, 5 Gloucester Road, Wan Chai, Hong Kong. (Tel.: 2877 06601
George Falconer (Nautical) Ltd., 178-180 Queen's Road Central, Hong Kong Jewellery Building, Hong Kong. (Tel.: 2854 2882)
Geotechnical Information Unit, Civil Engineering Library, LG1,Civil Engineering Building, 101 Princess Margaret Road, Homantin, Kowloon. (Tel. : 2762 5148)
Highways Department, 5th Floor, Homantin Government Offices, 88 Chung Hau Street, Homantin, Kowloon. (Tel.: 2762 3333)
Hong Kong and China Gas Co. Ltd., 363 Java Road, Quarry Bay, Hong Kong. (Tel.: 2880 6988)
City Hall Public Library, City Hall, Connaught Road Central, Hong Kong. (Tel.: 2921 2555)
Civil Aviation Department, 46th Floor, Queensway Government Offices, 66 Queensway, Hong Kong. (Tel.: 2867 4332)
Cross Harbour Tunnel Co. Ltd. Administration Building, Hunghom, Kowloon. (Tel.: 2333 4141)
Electrical and Mechanical Services Department, 98 Caroline Hill Road, Hong Kong. (Tel.: 2808 3620
2808 3817)
Geotechnical Engineering Office, 15th Floor, Civil Engineering Building, 101 Princess Margaret Road, Homantin, Kowloon. (Tel.: 2762 5111)
Government Publications Centre, Ground Floor, Lower Block, Queensway Government Offices, 66 Queensway, Hong Kong. (Tel.: 2537 1910)
Hong Kong Archaeological Society, C/O Museum of History, lock 58, Kowloon Park, Kowloon. (Tel. : 2367 1124)
Hong Kong Electric Co. ~ t d . 9th Floor, The ~lectric Centre, City Garden, Hong Kong. (Tel.: 2843 3111)
Hong Kong Polytechnic university Hong Kong Telecom. Library, P.O. Box 9896,
Yuk Choi Road, Hong Kong Telecom Centre, Hunghom, Kowloon. 979 King's Road, (Tel.: 2766 6863) Quarry Bay, Hong Kong.
(Tel.: 2888 2888)
Hong Kong University of Science & Kowloon Central Library, Technology Library, Clear Water Bay, .
Kowloon. (Tel.: 2358 6747)
5 Pui Ching Road, Homantin, Kowloon. (Tel.: 2926 4055)
ow loon-Canton Railway Corporation, KCRC House, 9 Lok King Street, Fo Tan Station, Shatin, New Territories. (Tel.: 2688 1333)
Map Publications Centre (Hong Kong) ,
14th Floor, Murray Building, Garden Road, Hong Kong. (Tel.: 2848 2480)
Marine Department, Harbour Building, 38 Pier Road, Hong Kong. (Tel. : 2852 3001)
Mines and Quarries Division, Civil ~ngineering Department, 7th Floor, Civil Engineering Building, 101 Princess Margaret Road, Homantin, Kowloon. (Tel.: 2762 5331)
Public Records Office, Tuen Mun Government Storage Centre, 1 San Yick Lane, Tuen Mun, New Territories. (Tel.: 2460 3736)
Regional Services Department, Regional Council Building, 1-3 Pai Tau Street, Shatin, New Territories. (Tel.: 2601 8500)
Survey & ~apping office, Lands Department, 14th-15th,21st Floor, Murray Building, Garden Road, Hong Kong. (Tel.: 2848 2278)
Lands Department, Mezzanine Floor, 1st-4th.14th-15th Floors, Murray Building, Garden Road, Hong Kong. (Tel.: 2848 2198)
Map publications Centre (Kowloon). 382 Nathan Road, Kowloon. (Tel.: 2780 0981)
Mass Transit Railway Corporation, Chevalier Commercial Centre, 8 Wang Hoi Road, Kowloon Bay, Kowloon. (Tel.: 2993 2111)
Post Office, General Post Office, 2 Connaught Place, Central, Hong Kong. (Tel.: 2921 2332)
Rediffusion(Hong Kong)Ltd., Flat C, 1st Floor, Hang Fook Building. 17-23 Shang Hai Street, Kowloon. (Tel.: 2730 0272)
Royal Observatory, 134A Nathan Road, Tsim Sha Tsui, Kowloon. (Tel.: 2926 8200)
Town Reading Centre, 6th Floor, West Wing, Central Government Offices. Hong Kong. (Tel.: 2810 3693)
University of Hong Kong Library, Urban Services Department, Pokfulam Road, 42nd-45th Floors, Hong Kong. Queensway Government Offices, (Tel.: 2859 2203) 66 Queensway,
Hong Kong . (Tel.: 2867 5596)
Water Supplies Department, Immigration Tower, 7 Gloucester Road, Wanchai, Hong Kong. (Tel.: 2829 4500)
B.10 REFERENCES
Allen, P.M. & Stephens, E.A. (1971). Report on the Geological Survey of Hong Kong, 1967-1969. Hong Kong Government Press, 116 p, plus 2 maps .
Bennett, J.D. (1984a). Review of Superficial Deposits and Weathering in Hong Kong. GCO Publication No. 4/84, Geotechnical Control Office, Hong Kong, 51 p.
Bennett, J.D. (1984b). Review of Hong Kong Stratigraphy. GCO Publication No. 5/84, Geotechnical Control Office, Hong Kong, 86 p.
Bennett, J.D. (1984~). Review of Tectonic History, Structure and Metamorphism of Hong Kong. GCO Publication No. 6/84, Geotechnical Control Office, Hong Kong, 63 p.
Brand, E.W. (1994) . Bibliography on the Geology and Geotechnical Engineering of Hong Kong to May 1994 (GEO Report No. 39). Geotechnical Engineering Office, Hong Kong, 202 p.
GCO (1988). Guide to Rock and Soil Descriptions (Geoguide 3). Geotech- nical Control Office, Hong Kong, 189 p.
APPENDIX C
NOTES ON S ITE RECONNAISSANCE
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T ITLE PAGE
CONTENTS
C . l GENERAL
C.2 PREPARATORY WORK
C.3 GENERAL PROCEDURE
C.4 INFORMATION ON GROUND CONDITIONS
C.5 S I T E INSPECTION PRIOR TO COMMENCEMENT O F GROUND INVESTIGATIONS
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C . l GENERAL
The purpose of the site reconnaissance is to confirm and supplement the information collected during the desk study (see Section 4.2). The site reconnaissance may include both site inspection and local enquiries concerning existing and proposed features on and adjacent to the site.
Although site reconnaissance is normally carried out after completion of a thorough desk study (see Section 4.2 and Appendix A), an early site visit/reconnaissance preceding the desk s tudy may sometimes be very useful.
C.2 PREPARATORY WORK
Prior t o undertaking the site reconnaissance, the following preparations should be made :
(a) Permission to gain access to the si te should have been obtained from both the owner and occupier.
(b) The site plan, topographic and geological maps and the necessary equipment should be available; for example, notebook, pencil, large clip board, camera. measuring tape, geological compass (compass and clinometer), geological hammer, penknife and hand lens ( ~ 1 0 ) . For large sites, a range finder and binoculars may also be useful. Any equipment necessary to ensure the safety of field personnel should also be included.
C.3 GENERAL PROCEDURE
Where appropriate, the following procedure may be adopted :
The whole area should be traversed, preferably on foot. and photographs should be taken of selected features of the site and its surroundings.
The proposed location of work shown on plans should be set-out.
Differences and omissions on plans and maps (e.g. site boundaries, buildings. roads, etc) should be recorded.
An inspection should be made of the details of all existing structures, and. where appropriate, records should be made.
Potential obstructions (e.g. transmission lines. telephone lines, historical features. large trees, gas and water pipes. electricity cables and sewers) should be recorded.
Access, including the effects of construction traffic and heavy construction loads on existing roads, bridges and services, should be checked.
Water levels, direction and ra te of flow in nullahs and streams, and also flood levels and tidal and other fluctuations, should be noted where relevant.
Features of the adjacent property should be recorded. and the likelihood of these being affected by proposed works should be assessed.
Old structures, and any other features, should be inspected and relevant records should be made.
Local inhabitants should be interviewed about the past uses of the site, structural damage t o buildings on o r near the site, flooding and land instability. Such information should be treated with due caution, but should be recorded and evaluated.
C.4 INFORMATION O N GROUND CONDITIONS
Data on and relating to ground conditions should be gathered and recorded, as follows :
(a) Surface features, both on site and nearby should be studied and recorded, preferably in conjunction with geological maps and aerial photographs. The following should be noted :
(i) Slope angles. types of slope (convex o r concave) and sudden changes in slope.
(ii) Comparison of topography with previous map records o r aerial photographs t o check for the presence of erosion, cu t slopes, fill o r buried stream courses.
(iii) Surface features which may indicate geological faults. shear zones, previous slope instability o r kars t formation.
(iv) Positions and extent of tension cracks o r other features which may indicate impending slope instability.
(b) An inspection should be made of soil and rock outcrops and cu t slope exposures, both on site and nearby. Relevant details should be recorded.
(c) Where relevant, groundwater levels. positions of wells and springs, the occurrence of seepage, and any evidence of seepage erosion, including soil pipes and sinkholes. should be assessed and recorded.
(dl The surface drainage pattern and any evidence of active soil erosion from surface water (e.g. gullies) should be noted.
(e) The na tu re and distr ibution of vegetation on t h e site should b e s tudied and noted; th i s information may provide an indication of soil and groundwater conditions.
( f ) The condition of embankments, buildings and o the r s t r u c t u r e s (e.g. tunnel portals and ventilation sha f t s ) in t h e vicinity should b e s tudied and recorded.
( g ) On extensive o r more complex projects , a site reconnaissance s u r v e y should b e car r ied out , followed b y t h e production of engineering geological maps and /o r plans and an evaluation of t h e t e r ra in based on t h e underlying soils, vegetation cover. and o t h e r f ea tu res (see Chapter 9 ) . This type of mapping should be car r ied o u t with t h e assistance of a n engineering geologist.
C.5 SITE INSPECTION PRIOR TO COMMENCEMENT OF G R O U N D INVESTIGATIONS
A supplementary s i t e visi t will often b e necessary j u s t prior to commencement of t h e actual ground investigations. Where appropriate, t h i s should include t h e following activities :
(a) The locations and conditions of access to t h e working s i tes should b e inspected and recorded.
(b) Obstructions, such a s power cables, telephone lines. boundary fences and t renches , should b e located and recorded.
(c) Areas for sample s to rage should b e identified.
(d ) Where applicable, sui table points of water supply and electricity supp ly should b e located and recorded.
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APPENDIX D
INFORMATION REQUIRED FOR DESIGN AND CONSTRUCTION
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CONTENTS
TITLE PAGE
CONTENTS
D . l GENERAL
D.2 DETAILED LAND SURVEY AND ENGINEERING ASSESSMENT
D.3 HYDROGRAPHIC AND HYDRAULIC DATA
D.4 INFLUENCES OF WEATHER
D.5 MATERIAL SOURCES
D.6 DISPOSAL OF WASTE AND S U R P L U S MATERIALS
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D.l GENERAL
In addition t o t h e determination of ground conditions at t h e site, which are considered elsewhere in th i s Geoguide. o t h e r information t h a t may be requ i red fo r design and construct ion i s briefly summarised in t h e following sections.
The items l is ted in th i s Appendix a r e by no means exhaustive, and re levant guidance documents on t h e information requirements fo r design and construct ion should b e consulted fo r additional advice. Time const ra in ts may limit t h e extent of detailed s t u d y t h a t can b e given t o t h e project , in which case allowance should be made in t h e design, e.g. by adopting conservative assumptions for design parameters.
D.2 DETAILED LAND SURVEY AND ENGINEERING ASSESSMENT
A detailed s u r v e y of t h e s i t e and i t s boundaries, showing means of access, utilities a n d services, easements and dra inage networks, will be necessary. Survey coordinates should b e referenced t o t h e 1980 Hong Kong Metric Grid and levels t o t h e Hong Kong Principal Datum. Exact locations of s i t e boundaries should b e ascertained from t h e appropr ia te District Lands Office (see Appendix A.8). The following may also be requi red :
Part iculars of existing s t r u c t u r e s o r obstruct ions, and whether t h e y have t o be demolished o r maintained.
Part iculars of adjacent o r nearby s t r u c t u r e s t h a t may b e affected by works on t h e si te , including building heights. floor levels, t y p e s of foundations, s t ruc tu ra l condition, and o the r per t inent information.
Part iculars of adjacent slopes and retaining walls t h a t may affect t h e site, including assessment of stability a n d details of a n y necessary s u p p o r t o r remedial works. This assessment should include boulders t h a t may pose a hazard t o t h e s i t e or t h e work.
Locations and dep ths of any underground obs t ruct ions o r fea tures , such as tunnels o r cavities, where known, with suppor t ing details.
Locations of s u r v e y markers and bench marks nea r t h e si te , with accompanying details; documentation of s i t e markers and bench marks.
D.3 HYDROGRAPHIC AND HYDRAULIC DATA
The design of s t r u c t u r e s in, adjoining o r near t h e sea , nullahs or streams may requ i re information on t h e following :
(a) Marine s u r v e y data, t o supplement t h e Admiralty c h a r t s and o the r available data.
( b ) Detailed information about nullah o r stream flows, size and na tu re of catchment areas. t idal limits, flood levels
and their relation to the Hong Kong Chart Datum.
(c) Observations on tide levels (referred to Chart Datum) and the rate of tidal fluctuations, velocity and direction of currents, and wave data.
(dl Information on scour and siltation, movement of foreshore material by drift; stability conditions of beaches, breakwaters and training works.
(el Locations and details of existing nullahs, streams and marine structures, wrecks and other obstructions above and below the water line; the effect of obstructions and floating debris on permanent and temporary works, including clearances of obstructions.
(f) Observations on the condition of existing structures, such a s attack by marine growth and borers, corrosion of metal work, disintegration of concrete and attrition by floating debris o r bed movements.
(g) Data on water quality.
D.4 INFLUENCES OF WEATHER
Information on the following may be necessary :
(a) Predictions of surface water flows and groundwater levels resulting from rainfall events with re turn periods of 10. 50 and 200 years, o r from more extreme rainfall events.
(b) Groundwater responses to major rainstorms, including ~ ro jec t ions o r assessments of response to a one-in-ten . - year rainfall event.
(c) Local wind speeds and wave heights generated during tropical cyclones.
(d) Range of temperature, seasonal and diurnal.
D.5 MATERIAL SOURCES
Sources of materials for construction may need to be located and proven, including :
(a) fill and filter materials for earthworks and reclamation,
(b) road base and surfacing materials.
(c) concrete aggregates.
(dl stone for building, pitching, o r riprap,
(e) water.
351
( f ) topsoil fo r landscaping.
D.6 DISPOSAL OF WASTE AND SURPLUS MATERIALS
sites fo r disposal of wastes o r s u r p l u s materials may need t o b e located. and methods of disposal resolved, fo r such materials as :
(a) excavated soil and rock.
( b ) d redged materials.
(c) building debr is and construct ion wastes,
(d l liquid wastes.
Access t o controlled t i p s and public dumping a r e a s must be determined. as well as t r a n s p o r t requirements and environmental controls.
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APPENDIX E
SAFETY PRECAUTIONS
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TITLE PAGE
CONTENTS
E . l GENERAL
E . 2 SAFETY REGULATIONS
E.3 SERVICES AND UTILITIES
E.4 WORK DISRUPTING ROADS. STREETS OR FOOTPATHS
E.5 REFERENCES
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E.l GENERAL
The prime factors required to ensure safe working conditions a re supervision by a competent person and the engagement of a suitably experienced contractor who possesses adequate resources for the project in hand.
Emergency procedures should be decided a t the commencement of a job. A first aid kit should be readily accessible. and should include items suited to the working conditions. Efficient communications with outside services (police. f ire and hospital) should be established. Safety helmets, gloves, safety footwear, goggles and masks should always be worn when required.
Reference should always be made to relevant Ordinances and Safety Regulations, and to the British Standards and Codes of Practice for advice on the manufacture and use of equipment.
E.2 SAFETY REGULATIONS
A comprehensive set of regulations exists i n Hong Kong governing the safety, health and welfare of personnel employed in construction works. For construction sites generally. the principal statutory requirements a re given in the Factories and Industrial Undertaking Ordinance and its subsidiary Regulations (Government of Hong Kong, 1985). and the Construction Sites (Safety) Regulations (Government of Hong Kong. 1983a). These statutes cover general as well as specific areas of construction works, including :
(a) Excavations, caissons and shafts, dealt with under Part VI of the Construction Sites (Safety) Regulations.
(b) Construction sites situated on o r adjacent to water, dealt with under Regulation 52A in Part VII of the Construction Sites (Safety) Regulations.
(c) Use of lifting appliances and lifting gears, dealt with under Parts 11, I11 and V of the Construction Sites (Safety) Regulations.
(d) Working in the vicinity of cables, dealt with under Regulation 47 in Part VII of the Construction Sites (Safety) Regulations.
The use of explosives and compressed gas (for example, in seismic surveys) is dealt with under the Dangerous Goods Ordinance and its subsidiary Regulations (Government of Hong Kong. 1983b).
The use of equipment incorporating radioactive sources is dealt with under the Radiation Ordinance and its subsidiary Regulations (Government of Hong Kong, 1982). Such equipment should always be used fully in accordance with the manufacturers' recommendations.
Reference should also be made to the following publications :
(a) A Guide to the Construction Sites (Safety) Regulations (Labour Department. 1985). which briefly sets out the provisions of the Construction Sites (Safety) Regulations
and explains t h e law in simple language. This is designed s o tha t , besides serving a s a handy reference, i t also se rves as a check-list of mat ters requi r ing attention.
( b ) Reference Manual f o r Construction Sites Inspection Report (Labour Department, 1986). which contains most of t h e requirements t h a t are necessary t o maintain a favourable working environment fo r t h e workforce and t o comply with t h e provisions of t h e Construction Sites (Safety) Regulations.
(c) BS 5573 : Code of Practice for Safety Precautions in t h e Construction of Large Diameter Boreholes for Piling and Other Purposes (BSI, 1978). This describes t h e safe ty precautions t h a t should b e taken, t h e specific safe ty requirements fo r t h e equipment t o b e used, and t h e gas hazards which might b e encountered in deep and large- diameter boreholes.
(d l Guidance Notes on Hand-dug Caissons (HKIE. 19811, which deals with t h e safe ty and technical aspects of hand-dug caissons.
E.3 SERVICES AND UTILITIES
In u rban areas, significant hazards may be encountered from underground services such a s electricity and gas. Part icular at tent ion should be paid t o t h e hazards result ing from damage t o high voltage power cables, gas pipelines and associated installations. Before any t r ia l pits, probes or boreholes are commenced in a reas where t h e r e may b e underground services, hand-excavated inspection pi ts should b e used t o establish t h e presence or otherwise of all such services. Hand-operated power tools may b e necessary in inspection pits t o a s s i s t excavation th rough ha rd materials. b u t should be used with extreme care.
E.4 WORKS DISRUPTING ROADS, STREETS O R FOOTPATHS
For works on o r adjacent t o public roads and pavements, t h e requi re- ments of t h e Road Traffic (Traffic Control) Regulations (Government of Hong Kong, 1 9 8 3 ~ ) must b e complied with. Reference should also be made t o t h e Code of Practice fo r t h e Lighting. Signing & Guarding of Road Works (Highways Office. 1984).
E.5 REFERENCES
BSI (1978). Code of Practice for Safetv Precautions in t h e Construction of Large Diameter Boreholes fo r Piling and Other P u r ~ o s e s (BS 5573:1978). British S tandards Inst i tut ion, London, 8 p.
Government of Hong Kong (1982). Radiation Ordinance (and Radiation Regulations). Laws of Hona Kona. Chapter 303. revised edition 1982. Hong Kong Government Pr in ter , 47 p. (Amended from time t o time).
Government of Hong Kong (1983a). Construction Sites (Safety) Regulations. Laws of Honn Kong. C h a ~ t e r 59. revised edition 1983. Hong Kong Government Printer. 58 p. (Amended from time to time).
Government of Hong Kong (1983b). Dangerous Goods Ordinance (and Dangerous Goods Requlations). Laws of Honq Kong. Chapter 295, revised edition 1983. Hong Kong Government Printer. 278 p. (Amended from time to time).
Government of Hong Kong (1983~). Road Traffic (Traffic Control) Requlations. Laws of Honq Konq. C h a ~ t e r 374, revised edition 1983. Hong Kong Government Printer. 134 p. (Amended from time to time).
Government of Hong Kong (1985). Factories and Industrial Undertakings Ordinance (and Subsidiary Legislation). Laws of Hons Kong. Chapter 59, revised edition 1985. Hong Kong Government Printer. 270 p. (Amended from time to time).
Highways Office (1984). Code of Practice for the Liqhtinn. Signing & Guardins of Road Works. Hong Kong Government Printer. 41 p.
HKIE (1981). Guidance Notes on Hand-dug Caissons. Hong Kong Institution of Engineers. 15 p.
Labour Department (1985). A Guide to the Construction Sites (Safety) Regulations. Hong Kong Government Printer, 48 p.
Labour Department (1986). Reference Manual for Construction Sites Ins~ec t ion Re~ot-t. Hong Kong Government Printer. 24 p.