lecture 3- engineering of slope - g&p geotechnics sdn bhd · g&p geotechnics sdn bhd ( )...

G&P Geotechnics Sdn Bhd (G&P Geotechnics Sdn Bhd (www.gnpgroup.com.mywww.gnpgroup.com.my))G&P Geotechnics Sdn Bhd (G&P Geotechnics Sdn Bhd (www.gnpgroup.com.mywww.gnpgroup.com.my))

By Ir. Dr. Gue See Sew & Ir. Dr. Wong Shiao Yunhttp://www.gnpgeo.com.my

ENGINEERING OF SLOPEENGINEERING OF SLOPEPlanning, Design, Construction & Planning, Design, Construction &

Maintenance ConsiderationsMaintenance Considerations

Cover courtesy of JURUTERA Sept 2008 ed.

G&P Geotechnics Sdn Bhd (G&P Geotechnics Sdn Bhd (www.gnpgroup.com.mywww.gnpgroup.com.my))

CONTENTS

•• IntroductionIntroduction• Policies & Legislation•• Planning of HillPlanning of Hill--Site DevelopmentSite Development•• Analyses & Design of SlopesAnalyses & Design of Slopes•• Design of Slope Strengthening WorksDesign of Slope Strengthening Works•• Construction Control & Site SupervisionConstruction Control & Site Supervision•• Maintenance of SlopesMaintenance of Slopes•• ConclusionConclusion


INTRODUCTIONINTRODUCTION


Soil Nailed Slope Failure


Policies and LegislationPolicies and Legislation


IKRAM

IEM

Urban & Rural

Planning

Department

(JPBD)

Ministry of

Housing & Local

Government

(MHLG)

MPAJ(Local Authority)

JMG

DOE

Governmental

& Private

Agencies

Source of Hillsite Development Guidelines


Simplified Slope Classification

Insitu terrain 25°°°° - 35°°°°Class III

Insitu terrain < 15°°°°Class I

Insitu terrain 15°°°° - 25°°°°Class II

Insitu terrain > 35°°°°Class IV

Gradient of Natural TerrainClassifications


Policies and Legislation

• These guidelines & regulations:– are conflicting & unclear– are too complicated for implementation– are subjected to various interpretations

• IEM has formulated policies and procedures for landslide risk mitigation on hillsite developments


THE INSTITUTION OF ENGINEERS, MALAYSIA

POSITION PAPER FOR MITIGATING THE RISK

OF LANDSLIDE ON HILL-SITE

DEVELOPEMENT

IEM


Legend:HT = Total height of slopeHL = Localised heightαααα G = Global angle of slopeααααL = Localised angle of slope

ααααG

ααααL1

HL1

HL2

ααααL2

Ground Profile

IEM


Current Status

• JKR – Guidelines for Slope Design, 2010

• DBKL – Guidelines for Planning of Hilly & Sloping Areas, 2010

• Negeri Selangor – Guidelines for HillsiteDevelopment


PLANNING STAGEPLANNING STAGE

Photo courtesy of http://freephotooftheday.clientk.com


Planning StagePlanning Stage• Desk Study (e.g. geological map, aerial photos)• Site Reconnaissance

Geological Input

Terrain Mapping

Geological Mapping

Erosion &

Instability Evaluation

Surface Hydrogeological

Assessment, Natural Water Course

Terrain

Classification(JMG)

Rock Type JointsWeathering

grades

Geohazard & Geological

Constraints


SI Planning


Planning of Development LayoutPlanning of Development Layout• Geotechnical input in early stage • Maximise environmental preservation by

clustering development


Planning of Development LayoutPlanning of Development Layout• Allow higher density development within

minimum plinth area• Leave green on hill slope

Photo courtesy of www.lushhomemedia.com


Photo courtesy of http://freephotooftheday.clientk.com

ANALYSIS & DESIGN ANALYSIS & DESIGN

OF SLOPESOF SLOPES

Photo courtesy of http://temp2.fotop.net


Analysis & Design of SlopesAnalysis & Design of Slopes

• ACT 133 & UBBL

• Natural slopes adjacent to development shall be assessed on its existing slope safety.

• In-line with judgement by Justice James Foong in the Highland Tower case.


IMPORTANTIMPORTANT Slope Stability FactorsSlope Stability Factors

• Soil Properties

• Slope Geometry• Groundwater table• Slope Maintenance



• Soil Properties

Steep Rockface Gentle Beach



• Slope Geometry

• Steep Slopes Has Higher Risk of Failing

Steep Slope Gentle Slope



• Groundwater table

• High Groundwater Increases Risk of Failure

Low Groundwater Table

High Groundwater Table


• Rainwater = Runoff + Infiltration

Erosion Rise in Water Level

• Design for 10-yr ARI or representative groundwater level.

• Slopes of High Risk-to-Life �– check sensitivity of water level.

Groundwater TableGroundwater Table


SLOPE STABILITY ANALYSISSLOPE STABILITY ANALYSIS


Methods of Stability AnalysisMethods of Stability AnalysisAnalyse as SOIL = Grade IV to VI

Methods :- (Should check both)

(A) Circular Slip Failure (e.g. Simplified Bishop)

- for deep layer without structural features.

(B) Non-Circular or Wedge Slip Failure

(e.g. Janbu , Morgenstern & Price)

- failures often at relict joints or boundaries between weathering zone.


External LoadingExternal Loading

• Loadings from :-– Traffic– Building Foundations– Retaining Wall– Spoil heaps


FACTOR OF SAFETYFACTOR OF SAFETY

• Considers TWO Main Factors :– Risk-to-Life – Economic Risk

• Three Level of Risks :-– Negligible , Low , High


HighStorage of Dangerous Goods

HighOccupied Buildings (residential, etc)

LowPublic waiting areas (bus stops, petrol stations, railway platforms)

LowRoads with high traffic

LowDensely used playgrounds, car parks.

NegligibleStorage Compound

NegligibleRoads of low traffic

NegligibleOpen-air recreation, Country Parks

RiskRisk--toto--LifeLife


Economic RiskEconomic Risk

HighExcessive structural damages

HighEssential services (extended period)

LowRoads of Statagic importance

LowEssential services (temporary loss = power, water, gas mains etc.)

LowRural Roads + Primary Distributor Roads

NegligibleOpen air car parks

NegligibleRoads of low traffic & not sole access

NegligibleOpen-air recreation, Country Parks


Cut & Fill Soil SlopesCut & Fill Soil Slopes• Mainly follows Geotechnical Manual for Slopes of

Hong Kong– Vertical height of slopes: 5m - 6m (≤ 7.5m)

– Berm width ≥ 1.5m

• Topsoil to be properly removed.

• No buried water-carrying services to be embedded on the crest of fill slopes – To prevent saturation of fill slopes due to pipe leakage.


Bukit Bukit AntarabangsaAntarabangsa Failure 2008Failure 2008

PIPE FAILURE


Bukit Bukit AntarabangsaAntarabangsa Failure 2008Failure 2008


Fill SlopesFill Slopes• Encourage robust system

Rock Toe


Surface DrainageSurface Drainage• Cast-in-situ RC berm drains instead of

precast drain.


Fill Slopes Over ValleysFill Slopes Over Valleys• To have catchment study• To have adequate surface and subsurface

drainage


DESIGN OF SLOPE DESIGN OF SLOPE

STRENGTHENING WORKSSTRENGTHENING WORKS

Cover courtesy of www.archdaily.com


DESIGN OF SOIL NAILED SLOPEDESIGN OF SOIL NAILED SLOPE


Required Space

SLOPE CHASING


DESIGN CONCEPT

• Common design reference– BS8006 : Code of practice for Strengthened/

reinforcement soils and other fills (1995)– Federal Highway Administration (FHWA) :

Manual for Design & Construction Monitoring of Soil Nail Walls (1998)

– Department of Transport (DoT) : Design Manual for Roads and Bridges, Vol. 4, Section 1, Part 4, HA68/94 (1994)


FREE LENGTH FIXED LENGTH


DESIGN CONCEPT- FRICTION

• Ultimate Unit Friction– fsu=4~6 NSPT

• Ultimate Friction for Each Nail– fsuAsL

As = Surface Area of NailL = Length of Nail


DESIGN CONCEPT- FRICTION

• Ultimate Unit Friction– fsu=4~6 NSPT

• Ultimate Friction for Each Nail– fsuCL

C = Circumference of NailL = Length of Nail


DESIGN CONCEPT- STEEL

• BS8110 (Ultimate) : TN = 0.87 × fy × As

• FHWA (Allowable) : TN = 0.55 × fy × As

• Steel Elements/Connection : BS5950• Reinforced Concrete : BS8110


MODE OF FAILURES

• Three Modes of External Stability

SLIDING TOPPLING BEARING CAPACITY


Failure Mode –

Nails Pull Out of Resistant Zone

b) Pullout Failure

Failure Mode –

Face Failure and “Active” Zone Sliding Off Front of Nails

a) Face Failure


MINIMUM FOS: 1.40

Failure Mode –

Tensile Failure of Tendon

c) Nail Tendon Failure


Soil NailsSoil Nails

Grid Beam System

(allow landscaping

around the soil nail)

Typical soil nail slope

configuration with

shotcrete/Gunite facings

(for slope steeper than 1V:1H)


Soil Nails

Commonly used

Steeply cut slopes of 25m - 30m (4V:1H gradient) Fully Shotcrete Soil Nail Slope


Individual Nail Head System


Grid Beam System


Soil Nails• Proper design of the soil

nail facing is important

when gradient ≥ 60°

Example of facing failure

CORRECTMain reinforcement at back of steel plate

INCORRECTMain reinforcement in front of steel plate

Main reinforcement

Steel plate

Main reinforcement

Steel plate

Shotcrete facing

Shotcrete facing

Soil face

Soil face


DESIGN OF ROCK DESIGN OF ROCK STRENGTHENINGSTRENGTHENING


INTRODUCTION


INTRODUCTION

• Used to stabilize weak rock mass.

• Acts in the same manner as soil nail.


TYPES OF FAILURES - SLIDING

MULTIPLE BLOCKS/MULTIPLE PLANE SLIDING

SINGLE BLOCK/SINGLE PLANE SLIDING

SINGLE BLOCK/STEPPED PLANE SLIDING


SLIDING FAILURE

Planar Failure


TYPES OF FAILURES - WEDGE

SINGLE WEDGE

/MULTIPLE INTERSECTING PLANES

SINGLE WEDGE

/TWO INTERSECTING PLANES


WEDGE FAILURE


TYPES OF FAILURES - TOPPLING

Toppling failure in hard rock which can form columnar structure separated by steeply dipping discontinuities


TOPPLING FAILURE


STEREOGRAPHIC PLOT ANALYSIS

Wedge Failure Zone

Toppling Failure Zone


STRENGTHENING OPTIONS

• Shotcreting– To prevent loose rocks from falling

• Scaling– To chisel off small loose rocks

• Rock Bolt– To stabilize large rock mass


NETTING


SCALING


SHOTCRETING


ROCK BOLT


CONSTRUCTION CONSTRUCTION CONTROL & SITE CONTROL & SITE

SUPERVISIONSUPERVISION


• Site Supervision & Coordination:

• Site personnel with sufficient knowledge & experience

• Close coordination & communication with design engineers

• Maintain detailed site records

CONSTRUCTION CONTROL


SUSTAINABLE HILLSITE DEVELOPMENTSUSTAINABLE HILLSITE DEVELOPMENT

• Creation of Standard Operating Procedures (SOP)

• Formation of a centralisedinstitution/agency for hillside development



• Simply it is more effective

• Far more difficult to overthrow while policies can easily be changed due to change of political parties



• Important to ensure sustainable hillsitedevelopment even after the issue is no longer ‘hot’

• Promises can easily be broken while institutions often last and are more difficult to overthrow


Applies For

Temporary &

Permanent Works

Contractor to be

Penalised for Non-

compliance

BOQ item For Temporary Slope

Protection Works

Legal Provision: Earthworks

Specification

Via

Contractual

Measures

CONSTRUCTION CONTROL


SPECIFICATION & BOQSPECIFICATION & BOQ


12.0 TEMPORAR Y WORKS12.1 The Contractor shall allow in the tender for the cost of providing the necessary design, statutory submission, construction, testing and monitoring of all temporary works, including the subsequent removal of all recov erable temporary structures, f or thesatisfactory completion of the earthworks. He shall be responsible f or the overall adequacy and safety of all temporary works. All temporary works shall comply with requirements of BS 5975.12.2 Temporary works means all planning and works carried out by the Contractor to construct the permanent works designed by the Consultant complying with all specifications, drawings and workscope. This includes but not limited to necessary field and laboratory tests, temporary tracks, excav ation, f illing, proper cover and protection to exposed slopes, sequence and timing of works, necessary temporary drainage, pumping of water, emergency contingency measures, saf ety of site, rectif ication and strengthening measures, methodology and method statement of all works, and etc.12.3 The scope of temporary construction shall include but not limited to:(a) Lif e safety measures such as hoardings, barricades, nettings, signboards, etc.(b) Ground improv ement and/or ground water cut off systems using jet grout piling, etc.(c) Ground water recharging systems, surf ace and groundwater drainage system using surface or subsoil drains, sumps, etc.(d) All other measures necessary for the saf e perf ormance of the temporary works, such as maintaining, adding, upgrading, strengthening, adapting, modifying, re-positioning, taking down and re-fixing f rom time to time, etc.12.4 Temporary works shall be the sole responsibilities of the Contractor. S.O.’s approv al or consent of Contractor’s method statement on all temporary works shall not relieve the Contractor’s sole responsibilities to ensure all temporary works comply to good engineering practice, and Contractor’s own time and cost to rectify any defects, non-compliance to good engineering practice or possible long term instability/failure and serviceability problems of the temporary works or caused by temporary works.12.5 The Contractor shall employ a Professional Engineer to design and supervise the construction of the temporary works. A certif ied copy of the design calculations and construction drawings for the temporary works shall be made av ailable to the S.O. f or the purpose of record.12.6 The Contractor shall make all necessary statutory submissions in connection with his temporary works, and secure f rom the local Authority the required clearances and the statutory permit to commence work. He shall comply with the requirements of the local Regulations governing his design and construction of the temporary works, including any statutory requirements that may be imposed from time to time during the tenure of the contract.12.7 All temporary works especially but not limited to temporary accesses and temporary earthworks (temporary cut or temporary f ill) shall not cause f ailure and shall not induce instability or serv iceability problems in the long term. All temporary cut and f ill by Contractor that will be left behind after completion of permanent works shall hav e the same Factor of Safety on stability and Serv iceability conditions as permanent works. These temporary works by Contractor shall also comply with all requirements, specifications, drawings and workscope applicable for similar ty pe of permanent works (e.g. slope angle, compaction of fill, surface drainage, retaining structures, strengthening measures if necessary, etc).12.8 Temporary works by the Contractor that in the opinion of the S.O. will cause instability or serv iceability problems (either short term or long term) in any way, the S.O. will order remedial works to be provided immediately at the Contractor’s own expense with not additional perf ormance time. Such instruction will not relieve the Contractor of his sole responsibility f or the temporary works. The remedial works carry out shall comply to all requirements, specif ications, drawings and workscope of similar ty pe of permanent works (e.g. cut, f ill, retaining walls, strengthening works, etc).

12.7 All temporary works especially but not limited to temporary accesses and temporary earthworks (temporary cut or temporary fill) shall not cause failure and shall not induce instability or serviceability problems in the long term. All temporary cut and fill by Contractor that will be left behind after completion of permanent works shall have the same Factor of Safety on stability and Serviceability conditions as permanent works. These temporary works by Contractor shall also comply with all requirements, specifications, drawings and workscope applicable for similar type of permanent works (e.g. slope angle, compaction of fill, surface drainage, retaining structures, strengthening measures if necessary, etc).

Temporary Works


Borrow Pit24.3 The Contractor shall be responsible for locating borrow pits. Designated

borrow pits shown on the Drawings only indicate to the Contractor potential areas for borrow. Whether the Contractor obtains materials from the designated or his own borrow pit, it shall be his responsibility to ascertain the suitability of the pit with respect to the quantity and quality of the materials, which shall be subject to the approval of the S.O. The Contractor shall pay all necessary fees, taxes or royalties to the appropriate authorities and observe all relevant regulations. The Contractor shall keep the borrow pits free from ponding water and the excavation neat and tidy and shall carry out necessary erosion and environmental protection measures following the agreed method statement or as instructed by the S.O.

24.4 The contractor shall submit method statement on cutting or filling andturfing at the borrow pit or dump site for approval of the S.O.. After cutting or dumping, all the slopes shall be formed to a stable gradient and close turfed or protected by other approved surface protection method. Provision of drainage, siltation pond and preventive measures of pollution shall also be included in the method statement.

Borrow Pit


33.5 Turfing shall be carried out within seven (7) days after formation of the final slope profile as shown in the Drawings and/or where directed by the Engineer. Otherwise, the Engineer reserves the right to engage external party to carry out the work and deduct the additional cost incurred accordingly from the contract. The type of turf shall be as indicated in the Drawings or other alternative type as approved by the Engineer and shall be free of lallang and essentially free of weeds.

Penalty33.21 The Contractor who fails to implement the Works as per above Sub-

sections 2.2.8.1, 2.2.8.2 and 2.2.8.3 shall bear the time and cost of turfing/hydroseeding works carried out by others under the direction of the S.O.

Turfing


BOQ

Requirements on

Temporary Worksincluded in BOQ


BOQ

Requirements

on Borrow Pitincluded in

BOQ


BOQ

Requirements

on Turfingincluded in

BOQ


METHOD STATEMENTMETHOD STATEMENT


CUT SLOPESCUT SLOPES


CUT SLOPES & EARTH EXCAVATION


Important to turf & construct berm drain every berm



FILL SLOPESFILL SLOPES


FILLING OF PLATFORM & SLOPES


• Closed turfing within 7 days

• Encouraged Horizontal groves

Surface Protection of SlopesSurface Protection of Slopes


SLOPE SLOPE

MAINTENANCE MAINTENANCE

MANUALMANUAL


MaintenanceOur experience:

Formation of rills and gullies which caused erosion and localized landslips


Maintenance

• Referred to the guidelines from Hong Kong GEO– Routine Maintenance Inspections by laymen – Engineer’s Inspections

• Maintenance scheme has more emphasis recently


Poorly Maintained DrainsPoorly Maintained Drains


Well Maintained DrainsWell Maintained Drains


Poorly Maintained DrainsPoorly Maintained Drains



Close Turfing

Proper Drainage System


Poorly Maintained SlopesPoorly Maintained Slopes

G&P Geotechnics Sdn Bhd (G&P Geotechnics Sdn Bhd (www.gnpgroup.com.mywww.gnpgroup.com.my))Well Maintained Slope – PRSS Bangi

Well Maintained SlopesWell Maintained Slopes

lecture 3- engineering of slope - g&p geotechnics sdn bhd · g&p geotechnics sdn bhd ( )...

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