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है”ह”ह

IS 7317 (1993): Code of practice for uniaxial jacking testfor deformation modulus of rock [CED 48: Rock Mechanics]

IS 7317 : 1993Reaffirmed 2010

( )

Indian Standard

CODE OF PRACTICE FORUNIAXIAL JACKING TEST FOR MODULUS

OF DEFORMATION OF ROCK

( First Revision)

UDC 624.121.54 : 006.76

BIS 1993

B U R E A U O F I N D I A N S T A N D A R D SMANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG

NEW DELHI 110002

December 1993 Price Group 5

ANf~NDMENT ;j6. 1 JULY 1994.~:;

';~'TO

-:IS 7317: 1993 CODE OF PRACTICE FOR UNIAXIAL

JACKING TEST FOR'MODULUS OFDEFORMATION OF WORK

( First Revision)

( Page 5, clause 6.1, line 19 ) - Substitute the word 'elastic' for theexisting word 'delastic".

( Page 7, clause 6.4, line 2 ) - Substi tute the word 'modulus' for theexisting word 'rnudulus'.

( Page 7, clause 6.5, line for the symbol' 5' ) - Substitute the word'plate' for the existing word 'slate'.

( Page 7, clause 6.6, line 2 ) -- Substitute the word 'any' for thee1ti~ng word -and'.

. . ( Page 7, clause 6.6, Formula after line 3 ) - Substitute the followingformula:

Ii - 2p ( ~d 1'" ) [\ I R" + Z' - Z ] ­

pZ ( 1:1')L71/ +Z.- I ]

( Page 7, clause 6.6, Formula after line 3, and at all other places wherecapital 'P' is written. - Substitute small 'po for the existing letter capital'P' at all places in clause 6.6.

( Page 7, clause 6.6, line for the symbol ·0' ) - Add the followingafter the word loading 'in one loading cycle'.

( Page 7, clause 6.6 line for 'he symbol 'E' ) - Substitute 'Ed ==modulus of deformation' for the existing line.

( Page 9, clause 6.6, second para) - Insert the word 'if' after theword' in question'.

( Page 9, clause 6.6, second formula ) - Substitute the following forthe existing formula:

Ii = 2 P( l£j 1'") [ v'X;--+Z"- -fR;.-+ Z" ] +

p~~(IEr1'L[7ii,I\ ZO -fB••\ P J[ Page 9, clause 8.1 (d), last line] - Substitute 'if' for the existing

word 'of'.

(CBD48 )

Printed at Printwell Printers. Aligarh t India

Rock Mechanics Sectional Committee. CED 48

FOREWORD

This Indian Standard ( First Revision) was adopted by the Bureau of Indian Standards, after thedraft finalized by the Rock Mechanics Sectional Committee had been approved by the CivilEngineering Division Council.

In general rock mass is heterogeneous, anisotropic and discontinuous; and its mechanical behaviouris governed by the existence and orientation of discontinuities such as bedding planes. joints.fracture zones. and the degree of weathering etc. These discontinuities may be clean or filled withfine grained material. rough or smooth, and may be continuous or discontinuous. As such, themechanical properties of rock mass differ greatly from the laboratory test results carried out onsmall samples of intact rock. The parameters actually needed in design are the tn-situ properties ofrock mass and not that of intact rock. In designing and constructing engineering structures overor inside the rock mass. the main parameters of importance are its deformability, shear andother strength characteristics. Out of these three parameters, the dispersion in the test results ofshear characteristics and the strength of a particular rock mass has been observed to be small ascompared to the deforrmbility values of the same. The deformation characteristics of in-situ rockis one such property which needs utmost care in its evaluation. It depends largely on the adoptedtechnique of testing. the loaded area. the loading system, and the methodology by which theresults are interpreted.

Modulus of deformation is an essential parameter for the design of tunnels. underground chambers.mines and dam foundations. The deforrnability of the rock mASS will govern the strain conditionsthat develop around an excavation during its initial changes. When designing a structure in or ona rock mass, it is important to know the deformability characteristics of the same for following tworeasons:

a) To assess expected displacements during excavation and relate these to subsequentmonitoring to check stability; and

b) To permit the correct design of any rock support measures that must be able to accomodatethe expected deformation without failure.

Deformation modulus of rock mass may be determined by bore hole jack test. uniaxial jacking test,pressure chamber test and radial jacking test etc. In case of uniaxial jacking tests, the loading of ajointed rock mass has to be arranged in the direction conforming to design requirement.Alternatively. it may be determined in two perpendicular directions and the value in requireddirection computed according to normal-practice.

The results of bore hole jack tests may be used only as an index of rock mass deforrnability andthere is strong dependence on jack-rock interaction and moreover the corrections are uncertain.Flat jack tests are severely limited by access problems, and onlv shallow rock in a disturbed statecan be used to measure deformability adjacent to exposed surface and the results do not provide thedeformability of the rock mass. Radial jacking tests and pressure chamber tests are better as theycause deformation of much larger volume of rock mas, around the drift/tunnel and hence are mostrepresentative. But these tests are difficult to conduct and are very expensive.

The main disadvantage of all the above methods except in the bore hole jack tests, is that theresults are influenced by blast damage and stress relief and therefore controlled excavation methodsare required. The bore hole jack tests have the :vivantale that large number of locations can betested rapidly and hence the test is sometimes used without recognition of its limitations. On theother hand Uniaxial Jacking tests are easy to conduct. relatively cheaper. and are much simpler.This test determines how in-situ rock reacts to controlled loading and unloading cycles and providedata on deformation m ldu1i, erect> and rebound. The modulus of deformation of rock mass islower than the elastic modulus of intact rock material as determined in the laboratory.

This standard was first published in 1974. This revision provides a general discussion of theUniaxial jacking test procedures. The revised code uodates the information and explains in moredetail tho procedures utilised to accornolish the test. This also gives recommended interpretation ofthe m 1dulu. of deformation for use in technical analysis.

In the formulation of this standard. due weightage bas been given to international coordinationamon~ tne standards and practices in different countries in addition to relating it to the practicesin the field in this country.

In reporting the result of a test or analysis. made in accordance with this standard. if the final value,observed or calculated, is to be rounded off, it shall be done in accordance with IS 2 : 1960 'Rulesfor rounding off numerical values (revised )'. The number of significant places retained in therounned off value should be the same as that of the specified value in this standard.

IS 7317 : 1993

Indian Standard

CODE OF PRACTICE FORUNIAXIAL JACKING TEST FOR MODULUS

OF DEFORMATION' OF ROCK

( First Revision)

a) Rock quality designation ( RQD );

b) Point load strength index of the rockmaterial;

c) Number of joint sets, their dip and strike;d) Spacing and condition of joints:

e) Ground water condition: dry/damp/wetldripping/flowing;

f) Rock mass rating (RMR) and rockmass quality ( Q );

g) Modulus of elasticity of rock material;

h) Special features that is, presence of shearor fault zones etc;

j) Method adopted for excavation of the driftthat is by controlled blasting, handchiselled or by any other means; and

k) Description of damages due to blasting.

2.4 Testing in drifts, tunnels or any other under­ground openings is preferred for convenience.In the absence of such facility, the test may belocated close to the sides of open excavations forfoundation or abutments.

2.5 After selecting the test site, the geologist shallprepare a three dimensional map showing themicro geology of the in-situ rock mass fallingunder the inlluence of test. The following infor­mation pertaining to the test location maypreferably be collected and jointly recorded by ateam of geologists and engineers:

1 SCOPE

1.1 This standard covers the method for thedetermination of modulus of deformation of rockmass by uniaxial loading technique in whichpressures are exerted on two parallel flat rockfaces on the two opposite sides of a sectionof a drift, gallery or tunnel by means ofhydraulic jacks. The applied stress and theresulting displacements are used for the determi­nation of the modulus of deformation by thehelp of the appropriate elastic theory. Themodulus of deformation is not a constantparameter, its value depends upon the stress levelalso. The choice of the design value for thein-situ modolus of deformation or elastic modulusthus becomes a matter of engineering judgement.

1.2 The creep characteristics of the rock massmay be computed from the graphs of displacementversus time.

1.3 The effects of anisotropy may be determinedby applying the load in any desired direction.However, in jointed rocks, the test shall beconducted in the direction conforming to designrequirement.

:2 SELECTION OF TEST SITE

2.1 Prior to selecting a test site location, allavailable surface and sub-surface geological dataof the exploratory drift shall be complied andanalysed hy the geologist. A three dimensionalportrayal of these data shall also be prepared in 3 PREPARATION OF TEST SITEplotted form.

3.1 The size of the drift or gallery in which testsare to be carried out shall be kept as small asrequired for testing. so as to reduce the numberof packing plates or the size of the interveningtruss placed across the tunnel. The size of theexploratory drift shall be such that the distancebetween the loaded area and a restraining tunnelsurface shall be at least equal to the radius of theloaded area so that any restraint would noteffect the calculated moduli significantly, asshown in Fig. 1.

2.2 After detailed exploration, sufficient geologicalmapping, and reviewing all available informationin the exploratory drifts, the zone of the influenceof the structure (dam. tunnel, under-groundopenings, etc), may be divided into differentIythological units and then sub-divided furtherinto various structural zones. In each of thesesimilar zones, a minimum of about four tests maybe carried out. If large variations are found inthe obtained results, additional confirmatory testsshould be carried out to be able to choose designvalues for each zone. The minimum size of the opening convenient for

the test being about 1'25 III wide and about 2·2 m2.3 The test site shall be selected such that the high. The excavation of the drift shall be madegeology at the test location is representative of in such a manner as to cause minimum distur­the geology of the area loaded by the structure banee of rock to be tested. Blasting shall not beto be built. allowed during final preparation of the test site'.

IS 7317 : 1993

SITE CONOI lION B (IDEALIZED)

SITE CONDITION A (IDEALIZED)

4.2' For some typical test set ups Fig. 2, 3 and 4may be referred.

4.2.1 Figure 2 A/Fig. 2 B depicts the arrangementfor vertical/horizontal test set up in small driftsand galleries where the deformations aremeasured with respect to the bearing plates.

4.2.2 Figure 3 shows a similar test set up in awider tunnel. However, for inclined tests, suitablesupporting structures may be designed.

4.2.3 Figure 4 indicates an inclined test set up ina small drift where the deformations are measuredinside the rock mass along the centre line of theloaded area.

4.3.2 The loading apparatus shall be such that itis capable of applying simultaneous uniformpressures to two test areas on the opposite rockfaces prepared. A calibrated hydraulic jack ofcapacity commensurate with the required stressor a minimum of 200T and capable of maintain­ing the desired pressure to within 2 percent of aselected value throughout the duration of the testshall be used for load application. The hydraulicpump system with necessary fittings, valves, gaugesand hoses shall also have sufficient pressurecapacity and volume for applying the desiredloads. Generally it shall be preferred to use apump with plungers of two sizes, the larger onefor the lower pressure range and the smaller onefor the higher pressure range. Cast iron packingplates of 75 mm thickness or material of equiva­lent rigidity. shall be placed in between thehydraulic jack and the steel plates in contact withthe rock faces. Two of the packing plates shouldbe of special design and should be provided withfour equally spaced holes through which micro­meter dial gauges are attached to measureindependently the displacement or deformation ofrock at the top and the bottom. The final gap, ifany, between the plates should be closed bymoving the plunger forward by operating the

4.3 Set Up for Narrow Drifts and Galleriel

4.3.1 The minimum size of the steel hearing plateshall be 25 mm thick and 600 mm diameter. Thesize of the plate to be used at a given test siteshall however not be less than 3 to 4 times theaverage spacing of joint or crack pattern subjectto the limitations of the testing capacity available.Two such circular or square rigid steel platesshall be placed in contact with the rock surfacewith an intervening layer of I : I cement mortaror plaster of paris. The maximum thickness ofthe intervening layer shall be about 5 mm. Thetest location shall be saturated with water tosimulate seepage at site. The mortar shall beallowed to cure sufficiently to obtain adequatestrength prior to commencement of test. Thespace between the steel plate and the mortarlayer and between the steel plate and the packingplate should be filled with teflon sheet of sufficientthickness in order to have a uniform transfer ofload.

'·5 Rmin.--,2R

--I-

FIG. 1 DISTANCE BETWEEN THP LOADEDARBA AND THB RESTRAINING SURFACE

3.2 After site selection, the area selected fortesting shall he carefully prepared as quickly RS

possible, preferably within 15 days of the test siteselection. In case of rocks being susceptible toloosening and weathering, tests should be con­ducted within thirty days of excavation of driftto obtain properties of fresh rock mass.

3.2.1 All loose rock material shall be removedby using chipping hammers and drills. The finaltrimming of rock to provide two parallel, con­centric and smooth rock faces, about 5 em largerthan the test plate shall be done by means ofchisel and hammer. The areas shall be finallyground smooth. There shall be an understandingbetween the field engineers and test engineers onthe importance of careful treatment of rockduring all excavation phases.

4 TEST SET UP

4.1 The test set up depends upon various condi­tions of testing, that is, whether the test iscarried out in a small drift or in a wider tunnelor in an open trench; whether the test is carriedout in a vertical or horizontal or inclineddirection; and whether the resulting deformationsare measured with respect to the bearing plate.or outside the loaded area or inside the rockmass along the centre line of the loaded surface.

2

pump. A small initial load, about O'S kg/cm 2

should be applied and allowed to remain for aminimum period of 24 h to allow for the settingof cement mortar or 6 h for setting of plaster ofparis before starting the test. Before applying theinitial load it should be ensured that all thepacking plates are concentric with the plunger ofthe jack, and in turn concentric with the plates.

4.3.3 The dial gauges capable of reading up to0'002 mm with a minimum travel of 10 mmshould be set up to give deformations of the fourcorners of each bearing plate. By moving thebrass screws, the gauges should be adjusted toshow initial reading nearly three fourths of theentire range of travel of the gauge.

Deformations of the two plates should bemeasured independently as the type and conditionof the rock may be different at the two facesbecause of loosening or stress rei ief in the rockmass in the roof or sides of the drift.

ROCK MASS2·5cm THICK STEELPLATE 60cm OIA

IS 7317: 1993

4.4 Set Up for Wider Tunnel Locations

4.4.1 The set up is shown in Fig. 3 and it issuitable for horizontal loading for locations inwider tunnels. In this case also the deflections ofeach face are measured separately with respectto independent datums located at a distance ofabout J to .. times the size of the plate, along theaxis of the tunnel. The deflection is recorded bythe help of four dial gauges at one face.

4.5 Set Up for Drifts where the Deformations areMeasured Inside the Rock Mass

4.5.1 The typical set up has been shown in Fig. 4.In this case, 600-1 000 mm diameter flat jacksshall be used in place of bearing plates at thetwo ends. In the set up, the deformations shallbe measured at the centre of the loaded areaboth at the surface and at different depths usingmultiple point extensometers located in centralNX-76 mm diameter bore hole and with referenceto a datum fixed at a depth of 6 times platediameters.

PLATES WITH LEGS Ai120

0FOR FIXING DIAL GAUGeS

HYDRAULICJACK

WOODENPACKING

2m(APPROX)

2m(APPROX)---------- -.

ROCK MASS

FlO. 2A SET Up OF EQUIPMENT FOR UNIAXIAL JACKING TeST IN VERTICALDIRECTION IN NARROW DRIFTS OR GAl.lARIES

3

IS 7317 : 1993

'Scm THICK C I PLATESWITH PLANE FACE

FACE DRESSED PARAllE LAND COAlED WITH 5mmCEMENT MORlAR

ANGLE fRON FRAME FORSUPPORT ING HVD JAC KHYDRAULlC PUMP ANDPACKING PLATES ANDPROVIDED WrTH STEEL ATBASE FOR EASY SLIDINGINTO POSlTlON ---.....:-----+~--",

3·0m

1·0m

STRAIN GAUGE

HYDRAULICJACK

CYLINDER STRAINGAUGE

lTO PUMP

SEC x-xFIG. 28 SET Up FOR UNIAXIAL JACKING EQUIPMENT FOR NARROW

DRIFTS AND GALLARJES

5.S Rock deformation shall be recorded atsufficient intervals and a minimum of six readingsduring the first hour of each load increment ordecrement is recommended.

S.6 The maximum load at which the test is to beconducted shall correspond to 1'2 to l"S time theanticipated maximum stress liable to be developedbecause of the proposed structure. Care shall betaken to check that the rock mass is not stressedbeyond its strength. The test shall be conductedin a total number of five cycles. Each cycle shallconsist of 20 percent of maximum test stress. Ineach cycle of loading, the load increments may beat least one fifth to one tenth of the test loadinvolved in each cycle; the unloading, may bedone in three steps. The test being a cyclic

5.4 The test shall be started after allowingsufficient time for setting of cement mortar

5.1 After all components of the test set areinstalled, they shall be checked jointly by thefield and test engineers. A final check of allmechanical, hydraulic and electronic components( if any) shall be made after the mortar pads areplaced and again before the first load incrementis applied.

S.] Test shall be conducted continually on a 24hours a day basis utilising load ranges andincrements compatible with the particular designconsiderstions.

5 TEST PROCEDURE provided between the steel plates and pressedrock faces. The initial load applied shall be

!.1 As far as possible, preference shall be given reduced to bare minimum to hold the steel platesto the testing technique shown in Fig. 4. However, in position, say about O'S kg/cm 2

•

if it is not possible to deploy this test set up, thenthe set up shown in Fig. 2 or 3 may be used.

loading test, the load shall be brought down tothe initial load applied to hold the plates inposition, each time before reloading for anothercycle. Deflection given by dial gauges and thecorresponding loan (or stress) shall be noted.The dial gauge readings should be continued tillit is less than one division over a period of thirtyminutes. Besides, the duration of each pressureincrement may be determined by the creepcharacteristics of the rock mass. Plot of deform­ation versus time shall be prepared by conductingseparate test. This plot is useful for studying thecreep characteristics of the rock. In uniaxialjacking test the duration of load increment foreach cycle shall be fixed up to one hour in generaland may be increased up to five hours dependingupon the rock mass condition. However,experience of the test party and critical exarnin­ation of observations during the first pressureincrement can be used to modify time require­ments for successive increments. The resultsshall be plotted in the stress deformation diagramwhich forms the basis of interpretation foranalysing the behaviour of the rock mass underimposed load and for determining the values ofthe deformation and elastic moduli, and themagnitude of irreversible deformations.

5.7 After the test is completed, the installationprocedure is reversed and the entire set up isretrieved for subsequent use. The concrete padsshall be removed so as not to create a safetyhazard by having them fallen by the action ofgravity at some later date.

IS 7317 : 19935.8 The data observed during the test may beplotted to give deformation versus stress, time anddepth below the surface curves (see Fig. 5, 6and 7) to calculate moduli of deformation/elasticity at various stress levels. creep factors andthe variat ion of moduli with respect to depth.

5.9 The creep test as shown in Fig. 6 is essentialfor weak/soft rocks.

6 INTERPRETATION OF THE TEST DATA

6.1 Because rock mass is not truely an elasticmaterial, there is considerable latitude availablein selecting the type of modulus to be computedfor the design purpose. A II moduli are computedfrom Baussinesq formula for a homogeneouselastic half space; the only difference is the por­tion of the curve used by the designer to obtainthe deformation and stress changes. In the cyclicloading tests. it is usually found that large de­formation occur in the first loading cycle whilethe recovery of the strain on removal of the loadis comparatively very small indicating a per­manent set in the rock mass by closing of cracksand JOInts. The deformations in the 2nd, 3rd,4th and 5th cycles of loading are used for calcul­ating the deformation moduli at different stresslevels. Similarly, the recovery in the 2nd, 3rd,4th and 5th cycles of unloading are used forcalculating the delastic moduli at the correspond­ing stress levels. For reporting the averagedeformation modulus and the elastic modulus,the values corresponding to the last cycle may beconsidered.

CALIBRATEDDIAL GAUGE"-,--­

(1 QIV • ·002 mm)

CONCRETE PEOEST~L

FOR HYDRAULIC PUMP

FIG. 3 SET Up FOR UNIAXIAL JACKING EQUIPMENT rOR WIDER TUNNEL LOCATIONS

5

fRANSDUCERLEAD WIRE

FLAT JACKAPPR~X$>1m CIA

CONCRETEPAD »:

fXMPBX MEASURING ANCHORS(S OR MORE PER HOLE)

MP8X SENSOR HEAD

_ RUBBER SLEEVEovER LEADWIQES

NOTE TIMBfR PLATFORM FORSUPPORT DURING ERECTIONNOT SHOWN

PARli Cl E BOARD PAD

APREPARED 0\ AME 'fER15 TO 2 TIMESFlAT JACK DIAMETER

DATA ACQUISITIONSVSlEM ---

NX 76mm 01ACORE DRill HOLEAPPROX 6 FLATJACKOlAMETERS DEEP

IS 7317 : 1993

FIG. 4 SET Up FOR UNIAXIAL JACKING EQUIPMENT IN DRIFTS WHERBDEFORMATIONS ARE MEASURED IN~IJ)B THE ROCK MASS

'·00-60·40·2o

18

14

72

E~ '0 t----t----~---+_--~_f__+__+_-#_---_4IA

......0'

oX

'8 ~---+----+-----+---~.""""f.4----l...----t

56

~ 3 2 t----+---+-----t.....,...+--f--++-+--f-;---~VlenLIJa.....V) 2'

DEFORMATION IN mm

FlO. 5 DEfORMATION Versus STRFSS ApPLlBD6

IS 7317 : 1993

o

...zw~LIJU«..JQ..(/) ...o~u·;:0:enO«....IL&J~

OAYl DAY 2 DAY) DAY4 DAYS DAYS DAY7 DAY8 DAY9 DAY10 DAY110AY12

TIME (DAYS)

I Ir: MPQ ~MPQ

l.f~ MPo

OMPc oMP.

le MP o~ ~

li.2'8 MPa I.~~

~"l,oMPa ~N

J OMP I

E 0-75e

L&JU

~ex~ 0·50

~

zot:04:~ 0.25aou..l.Uo~

uoa:

FIG. 6 ROCK DnFORMATIO~ AT SURFACE Versus TIME-UNIAXTAL JACKING TEST

6.2 The deformation of a rock is partly elastic( reversible) and partly plastic ( irreversible) andincludes mainly deformation of rock, displacementon account of closure of joints existing in the rockmass and displacement by sliding along the fissures.The sum tota I of these is called the deformationof the rock mass. which is thus complicated andincludes elastic, plastic and time dependentbehaviour.

6.3 The pu rpose of the uniaxial jacking test is todetermine the extent to which the rock mass shalldeform under externally applied loads. Care isthus needed in the interpretation of the results ofthe tests so that the settlement of the structure iscorrectly estimated. Computations for the deter­mination of modulus of deformation shouldinclude all deformations due to applied loadswhether elastic or plastic and the creep effect andexclude any deformation on account of blastdamage, surface preparation or any other loosen­ing effect which is assumed equal to deformationin the first cycle resulting in consolidation ofdisturbed zone of rock mass.

6.4 The effect of creep shall be taken care ofwhile computing the deformation mudulus.

6.S The evaluation of deformation modulus isbased on Boussinesq solution for a point load oninfinite homogeneous, isotropic and linearlyelastic material.

m = 0"96 for circular plate, and 0·95 forsquare plate;

v = Poisson's ratio of the rock from thelaboratory tests on representativerock cores. If its value has not beendetermined in the lab, it may takento fall between 0·20 and 0·30. Itsvalue for different rock types shall beassumed as 0·20 for excellent rockssuch as granite, etc, 0·25 for gneiss,quartzites, etc, and 0·30 for micaschist, slates, etc;

S = deformation of the test slate in oneloading cycle in em;

P = total load on the test plate in kg; andA =:I area of test plate in em".

Similarly clastic modulus ( Ee ) shall be calculat­ed for ea~h cycle from the above equation bytaking ()equal to recoverable deformation of thatcycle.

6.6 For the test set up described in 4.~t the dis­placement at and point beneath the centre of acircular loaded area is expressed as follows:

2P ( 1 - v2) [_._.- ]

cS = ---e--" viR'J +- z- - Z -

p Z ( I + v ) 1- Z -=- - 1 J'E L y'Ra + z»

The modulus of deformation correspondingto test set up described in 4.3 And 4.4, for eachcycle shall be calculated from the foJIowingformula:

( 1 - v' ) PEd = m --8- X -\/j-=-

where

Ed = modulus of deformation in kg/ern";

where8 = displacement in the direction of loading,

Z = Distance from loaded surface to thepoint where displacement is measured,

p =a stress at loaded surface,

R = radius of loaded area,v = Poisson's ratio of the rock, and

E = modulus of elasticity.

7

IS 7317 : 1991

ROCk OISPlACEME NT (m mJ

I.L..o ',0J:to- '.3a.UJ

o '·6

o 0 02., 0·203 0·305 0·406 0·5.08 0·6

-l.----1~T"--...ENSOR HEAO"

r:"~

!J

{,

//~/11J

J

IIVDEEPEST EXTENSOMETER ANCHOR

6·'

0·3

0·6

O·g

1'2

1·5

5·5

5·8

'·95·2

<n"'" 1·8cr~ 2·'2:~ 2,4

~ 2·7o:I: 3·0

ANCHOR DEPTHS

Sensor Head OOm

Anchor One 0'5 m

Anchor Two 1'1 m

Anchor Three "8 m

Anchor Four 2'4 III

Anchor Five 3'2 m

Anehor S~X 4'3 m

Anchor Seven 6'0 m

0- Depth where rock deformation was measured when load were applied at surface ( 0- Depth)

FIG. 7 ROCK DEFORMATION Versus DEPTH-UNIAXIAL JACKING TESTWITH BOR.EHOLE EXTf;NSOMfTF.RS

8

At the loaded surface, where value of "Z' is zero,the above equation may be rewritten as:

Ed = 2.P.R ( I - v'Z lIS

But in the test set up in question, the load shallbe applied through a circular flat jack with a holein the centre and therefore considering R, asinner radius and R. as outer radius of the flatjack the displacement expression becomes as:

S = ~ ( IJ::;;._~ rV R2~ + z: -

]PZ2 (I + v )

vi Rl~ + Z" + Ed

[VRI·

I

! Z' VRl+z,']By putting the values of Ri, R 2• and Z. the dis­placement at a particular point' I' or '2' may beexpressed as:

81 ~; P. ( r: )/Ed or S2 -= P. ( K2 )/Ed

Therefore. the modulus of deformation of therock mass in the zone between depth 21 and Z2may be determined from the following equation:

Ed = P. ( Ki - K2 )/( S1 - <'5 2 )

6. 7 Besides. creep factor shall also be calculatedfor each cycle by the following expression( see Fig. 6):

Creep Factor ( %)~ cr~ep of.' he eye,le x 100deformation during

load increase

7 REPORTING OF THE RESlJLTS

7.1 In addition to the information in 2.5, thereport of the test should also include thefollowing:

a) Whether the test was conducted in a driftor on a rock surface in open;

b) Location of the test site indicating threedimensional coordinates, drift number,chainage, etc;

c) Extent of rock/loose burden above the testsite;

d) Whether the test was conducted on floor,or on roof or on side walls;

e) Period elapsed between excavation of thesite and testing;

f) Direction of testing, that is, whether vertical.horizontal or inclined;

g) Orientation of the rock mass stratificationand the direction of loading during testing;

h) A complete geological description of therock mass with RMRand Q.

j) In-situ stresses in the rock mass;k) Name of the testing agency;

m) A description of the uniaxial apparatusincluding the photos of the installed equip­ment, specifications, accuracy, sensitivity of

9

IS 7317 : J993

all the pressure and deformationinstruments;

n) Tabulation of the observed data;p) Plots of stress Versus deformation, time

Versus deformation and depth Versusdeformation;

q) Deformation and elastic moduli at differentstresses levels;

r) Creep factors at different stress levels;8) Any other relevant information; andt) A plot between EdlEr and RMR will help

in selecting design deformation modulus.

8 APPLICATION OF MODULUS OFDEFORMATION

8.1 The designer should be careful in applicationof in-situ moduli of rock mass on the followingpoints:

a) Modulus of deformation (Ed) for staticanalysis of foundation of dams, etc,corresponding to various stress levels inthe rock foundation;

b) Dynamic modulus for dynamic analysis ofdams, etc, which may be taken equal toelastic modulus (Ee) corresponding tothe maximum stress level of the test. Thisis recommended because dynamic deforma­tion will be simulated more realistically byEe)han by Ed;

c) Elastic modulus ( Ee ) for design of con­crete lining in pressure tunnels and pen­stocks, etc, because internal water pressureleads to reduction of deviatoric stresseswithin the rock mass;

d) In practice, the in-situ rock mass lies underconfining pressure due to depth, but thedeformation modulus is measured withalmost no confining pressure. Besides, indrifts the tests are performed in elasto­plastic zone near the surface of the rockmass. Th us. in poor rock masses theincrease in modulus of deformation withconfining pressure and depth below groundsurface becomes important and pronounced.However, it leads to a conservative designof borehole extensorneters are not used; and

e) In river valley projects, rock mass getssaturated in some areas after chargingwater conductor system/after filling ofreservoir. The modulus of deformation andelastic modulus are reduced drasticallyspecially in poor rocks with water sensitiveminerals. Thus these moduli should bemultiplied by suitable correction factorsfor saturation where tests are not done onsaturated rock masses.

NOTES1 The settlement of foundations of high dam! speciallyin narrow valleys should be analysed by the 3 DFinite Element Method ( Two dimensional analysis isfound to give very conservative and unrealisticresults ).2 If the behaviour of the rock mass is plastic, non­linear analysis should be performed.

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