contents top-up course for tcp t3 on gifw and ... existing loose fill slopes (by undertaking in-situ...

Top-up Course for TCP T3 on GIFW and Building Works with Significant

Geotechnical Content

Lecture 4 : Slopes

Presented by: Y C Koo

CONTENTS

• Background• Design Considerations• Construction Supervision• Landscaping• Maintenance

TOPOGRAPHY OF HONG KONG

Land area of about 1100 sq km, 60% of which are natural slopes with 30% > 30°

TOPOGRAPHY OF HONG KONG

Land area of about 1100 sq km, 60% of which are natural slopes with 30% > 30°

TYPICAL GEOLOGICAL SECTION OF HILLSIDE

(Extracted from GEO Publication No. 1/2007)

WHY DO WE HAVE SLOPE WORKS?

• Forming platforms on sloping terrain for development;

• Building infrastructures on or close to steep slopes/ hillsides;

• Upgrading existing slopes, in particular those formed prior to establishment of Geotechnical Control Office (now Geotechnical Engineering Office); and

• Mitigation of risk to existing developments close to natural hillsides.

WHAT CAUSE A SLOPE TO FAIL?

Fei Tsui Road on 13 August 1995

Sau Mau Ping on 18 June 1972

(Photos extracted from CEDD’s website)

• Poorly compacted fill slope• Liquefaction/flowslide of loose

fill caused by surface infiltration and rise in groundwater

Sau Mau Ping on 25 August 1976


• Leakage of drainage pipe

• Masonry wall constructed without adequate geotechnical input


Kwun Lung Lau on 23 July 1994


Shum Wan Road on 13 August 1995• Presence of weak layers, i.e. clay seams• Ingress of water during prolonged rainfall• Water overflow from blocked drainage

Fei Tsui Road on 13 August 1995• Presence of a weak kaolinite-rich layer,

and• Increase in groundwater pressure

following the prolonged heavy rainfall.



Earthquake Sichuan on 12 May 2008

WHAT CAUSE A MAN-MADE SLOPE TO FAIL?

• Inadequate design consideration (e.g. ground water assumptions, geological model, faulty design, etc)

• Surface water (e.g. poor drainage design, inadequate maintenance, etc.)

• Poor construction / Poor workmanship

• Slope deterioration or local weaknesses in slope

• Leakage from water-carrying services

• Changes in surcharge loading (e.g. stockpiling at crest)

SLOPES MANAGEMENT IN HONG KONG

• All designs have to go through the vetting/approval by the Geotechnical Engineering Office (GEO)

• Government projects through project departments• Private projects (under Buildings Ordinance) through the

Buildings Department• Existing government slopes are being upgraded under the

Landslip Preventive Measures (LPM) Programme (now LPMit Programme) instigated by the GEO since the late 1970’s

• Owners of existing private slopes are requested to investigate and repair slopes that they are responsible to maintain through the issue of Dangerous Hillside (DH) Orders and Advisory Letters under the Buildings Ordinance

RELEVANT PUBLICATIONSGeotechnical Manual for SlopesGeoguides

Geoguide 2 – Guide to Site InvestigationGeoguide 3 – Guide to Rock and Soil DescriptionsGeoguide 5 – Guide to Slope MaintenanceGeoguide 7 – Guide to Soil Nail Design and Construction

GeospecsGeospec 3 – Model Specification for Soil Testing

Hong Kong Geological SurveyGeotechnical Area Studies ProgrammeGEO ReportsGEO Technical Circulars / GEO Technical Guidance NotesBD’s Practice Notes for AP, RSE & RGE

(most can be downloaded from CEDD and BD’s websites)

CLASSIFICATION OF SLOPESPNAP 168 (ADV-8): Registration of Slopes and Retaining Walls• Cut Slope and associated retaining wall denoted by “C”, “R” or “CR”:

>3m high cut slope including any associated retaining wall

>3m high retaining wall

• Fill Slope and associated retaining wall denoted by “F” or “FR”:

>5m high fill slope including any associated retaining wall

• Fill Slope and associated retaining wall denoted by “F” or “FR”:

<5m high fill slope including any associated retaining wall posing a direct risk to life with C-T-L category 1 and 2

• Disturbed Terrain denoted by “DT”:

natural slope containing repairs to landslip scars or a series of composite cut and fill slopes where the ground surface has been disturbed (e.g. terraced ground for cultivation)

SOURCE OF INFORMATION• Civil Engineering and Development Department’s Website

(http://www.cedd.gov.hk/eng/index.htm)

• CEDD’s Hong Kong Slope Safety Website (http://hkss.cedd.gov.hk/hkss/index.htm)

• Lands Department’s Slope Maintenance Responsibility Information System(http://www.slope.landsd.gov.hk/smris/index.html)

• Buildings Department’s Website (http://www.bd.gov.hk/english/index_e.html)

• CEDD’s Geotechnical Information Unit

• BD’s Building Information Centre

• Building Records Access and Viewing On-line (BRAVA) (http://bravo.bd.gov.hk)

• Utility Companies / Water Supplies Department / Drainage Services Department

• Records kept by Private Owners

FORMATION OF SLOPES

Rock Cut Slope

Natural SlopeFill Slope Soil Cut Slope

1. Geological Profile / Degree of Weathering of Rock

2. Topography / Slope Profile

3. Groundwater Level and Response to Rainfall

4. Adverse Geological Features (e.g. Clay / Kaolin Seam, Soil Pipe)

5. Surcharge / Effects from Adjoining Foundations

6. Stabilization Measures

KEY SLOPE DESIGN CONSIDERATIONS SITE INVESTIGATION• Desk study (site history, aerial photograph

interpretation, existing ground investigation data, previous geotechnical assessment, previous landslide records, etc.)

• Site reconnaissance (walk over) inspection• Topographical survey• Ground investigation

a) Drillholesb) Trial pitsc) In situ testsd) Laboratory testse) Groundwater monitoring

DESK STUDY

Topographical maps and plans

Aerial photos, geological maps and memoirs, past SI records, past landslide records

Past studies

Meteorological, Hydrogeological information

Past records of construction activities

Utility services and tunnels

Lease and engineering conditions

TYPICAL GROUND INVESTIGATION FOR SLOPE DESIGN

• Drillholes sunk to sufficient depths, ideally from slope crest and terminated beyond slope toe

• Piezometers (sometimes with Halcrow buckets or automatic loggers) installed inside drillhole for monitoring of groundwater for at least a wet season

• Retrieve undisturbed samples for laboratory testing• Continuous sampling in selected drillholes for identifying adverse

geological features• Trial pits for shallow ground investigation, especially useful for

investigating existing loose fill slopes (by undertaking in-situ density tests and compaction tests)

• Existing hard surface covering should be stripped for confirmation / identification of underlying materials

• Where possible, inspection scaffolding be erected on existing rock slope surface for rock joint mapping

A TYPICAL GROUND INVESTIGATION PLAN

• How many holes/ pits are enough?

• What field tests to be carried out?

• What samples to be taken?

• What lab tests to be carried out and how to specify?

• How many piezometers? At what depth?

Ground Investigation• Boreholes• Trial pits• In situ tests (SPT, in situ

density, rock joint survey…)• Laboratory tests (PSD, LL/PL,

density, water content, triaxialcompression, chemical, uniaxial compression, rock joint friction,…)

• Groundwater monitoring

Geotechnical Interpretation• Geological profile• Groundwater conditions• Characterization of soils/rocks• Densities• Strength parameters (c’, φ’, cu,

UCS, joint friction)• Deformation parameters (E, υ)• Permeability (k, kv/kh))• Aggressivity (resistivity, pH,

concentration of soluble sulphate and choride ion)

Direct measurement/Interpretation

GEOTECHNICAL INTERPRETATION

A TYPICAL SITE FORMATION PLAN SITE FORMATION

• Forming the site to the required profile for sitting the proposed development

• May consist of a combination ofa) Reprofiling -

Cutting/Fillingb) Stabilisation measure

e.g. soil nailsc) Retaining wallsd) Surface drainagee) Subsoil drainage

SLOPE STABILITY ANALYSIS

• Soil slopes usually based on limit equilibrium analysis.

• Commercial computer programmes readily available.

• Numerical analysis using finite element/finite difference method may be necessary for assessing ground movement associated with the works.

• Apart from the stability requirements, fill slopes require adequate compaction and drainage provisions to prevent liquefaction failure.

• Rock slopes usually analysed by joint surveys and results presented as detailed mapping and on stereoplot. Typical failures by assuming either plane, wedge or toppling failure modes. Require detailed site inspection for confirmation of treatment works required.

LIMIT EQUILIBRIUM ANALYSIS OF SOIL SLOPES• Mostly based on method of slices (see Table 5.5

of Geotechnical Manual for Slopes)• Methods differ by statics equation and

assumptions in inter-slice forces• Janbu Rigorous method or Morgenstern & Price

method are commonly used • Factor of Safety: Ratio of the average available

shear strength of soil along the critical slip surface to that required for maintaining stability

• Recommended Factor of Safety against Failure for New Cut Slopes for a Ten-year Return Period Rainfall

(Extracted from PNAP APP-109)

TYPICAL SLOPE STABILITY ANALYSIS TYPICAL SLOPE DEFORMATION ANALYSIS

SOIL NAILS IN SLOPE FORMATION OR UPGRADING / IMPROVEMENT WORKS

SOIL NAILS DESIGN PRINCIPLE

Allowable Pullout Resistance TSG provided by soil-grout bond:TSG = (c’PL + 2Dσv’μL)/FSG

P = perimeter of soil nailc’ = effective cohesion of soilL = bond length of soil nail in passive zoneD = diameter of soil nailσv’ = effective vertical stressμ = coefficient of apparent cohesion (= tanφ’)FSG = Factor of safety against pull-out failure at soil-grout interface

(Extracted from Geoguide 7)

Allowable Tensile Capacity TT of soil nail:TT = fy A’/FT

fy = characteristic yield strength of soil-nail reinforcementA’ = effective cross-sectional area of soil nail reinforcementFT = Factor of safety against tensile failure of soil-nail

reinforcement

DETAILS OF SOIL NAILSComponents:• Soil nail reinforcement• Cement grout • Centralizer• Coupler• Nail head• Copper wire for TDR• Heat-shrinkable sleeve• Corrugated plastic

sheathing (for Class 1)

FILL SLOPES

Failure modes:• Shearing failure along a sliding surface• Surface washout• Liquefaction of loose soil with collapse of soil structure

(Extracted from GEO Report No. 96)

Triggers and Contributory Factors of Fill Slope Failure

FILL SLOPES

Debris Mobility for Different Mechanism and Scale of Fill Slope Failures in Hong Kong


FILL SLOPES


Liquefaction ModelBehaviour of Soil Element on Failure Surface

(Extracted from HKIE’s study report on “Soil Nails in Loose Fill Slopes ”

FILL SLOPESImprovement by recompaction

Issues:• Steep temporary cuts• Destruction of vegetation

Design recommendations• Recompaction to a vertical

depth of not less than 3m• Provision of drainage blanket

(Extracted from CEDD Standard Drawings)

FILL SLOPESImprovement by soil nailing

Slope at Sau Mau Ping (extracted from Housing Department’s website)

Applicability• Relative degree of compaction of fill not

less than 75%• No significant sign of distress, history of

movement, heavy seepage, nor weak zone• Not located in an old valley where

groundwater level may be high due to subsurface water flow or leakage from water-carrying services (Extracted from HKIE’s study report on “Soil Nails

in Loose Fill Slopes ”

Design recommendations• Potential failure assuming minimum

steady state undrained shear strength to be checked.

• Soil nails to be bonded to competent subsurface stratum

• Nail spacing not more than 2m horizontal and 1.5m vertical.

• Grillage beams tying nail heads together to be provided.

ROCK SLOPE Rock Slope Formation - Kornhill

ROCK SLOPERock Joint Mapping



ROCK SLOPE Failure Mode

(Extracted from Hoek & Bray – Rock Slope Engineering)

ROCK SLOPEStereoplot

N

E

S

W

POLE LEGENDPOLES

CONTOUR LEGENDSCHMIDT POLECONCENTRATIONS% of total per 1.0 % area

Minimum Contour = 4Contour Interval = 4Max.Concentration = 26.4

EQUAL AREALOWER HEMISPHERE

106 Poles Plotted106 Data Entries

Siu Sai Wan Estate 11SE-D/C191

Findings from Stage 2 Study (BVHKL)

ROCK SLOPEStereoplot

1

2 3

12

23 13

99

99

N

E

S

W

MAJOR PLANES ORIENTATIONS# DIP/DIR. 1 83/308 2 43/079 3 05/084 12 33/035 23 00/090 13 04/035 99 75/055

EQUAL AREALOWER HEMISPHERE

106 Poles Plotted106 Data Entries

Siu Sai Wan Estate 11SE-D/C191

Findings from Stage 2 Study (BVHKL)

Toppling

DaylightEnvelope

Slopeface(75, 055)

Frictioncone(25 deg)

ROCK SLOPE STABILIZATION WORKS• Rock dowels (untensioned steel reinforcement bars similar to soil nails but

without the nail heads, designed to take shear loads from small overhangs)

• Rock bolts and rock anchors – tensioned steel elements installed to unstable blocks or slope face (not recommended as permanent measure as regular check on residual loads are required)

• Scaling – removal of loose blocks on the slope surface

• Buttress walls – used to support large overhang rock blocks or large wedge or highly jointed rock mass

• Dentition – infilling of concrete/shotcrete to minor imperfections on the rock slope surface

• Wire mesh – PVC coated mesh to fix securely on slope surface to prevent from minor rock falls

• Shotcrete – either reinforced or plain for protection on highly fractured rock surface, but getting increasingly unpopular for their dull appearance

• Raking drains – installed at locations of where high seepage are evident

ROCK SLOPE STABILIZATION WORKS

Typical Details of Concrete ButtressTypical Details of Rock Dowel

Typical Details of Dentition



Buttress wall

ROCK SLOPE STABILIZATION WORKSDentition


Rock Dowels

Fall of loose blocks protected by wire mesh

NATURAL TERRAINNatural Terrain Hazard Mitigation

a) Open hillside landslide

b) Channelised debris flow

c) Rock fall/ Boulder fall

Checkdam

Boulder Fence

SLOPE SUPERVISION REQUIREMENTS IN HONG KONG

• Superseded 2005 edition and became effective from 31 Dec 2010.

• Incorporated amendments to cover minor works.

• Other minor refinements, such as basic values for assessment of the scale of works.

Code of Practice for Site Supervision 2009(a) Quality SupervisionEnsuring that the building works or street works are carried out in

general accordance with the provisions of the Buildings Ordinance and Regulations and with the plans approved and any order made or condition imposed.

Supervision Tasks:

(i) Checking that the works are carried out in general accordance with provisions of the Buildings Ordinance and regulations;

(ii) Checking that the works are carried out in accordance with the plans approved by the Building Authority and any order made or conditions imposed; and

(iii) Checking that the design assumptions agree with the actual site conditions.

(b) Site Safety Supervision

Controlling hazards from works so as to minimize the risk to:

(i) The workers on site;

(ii) All persons around the sites; and

(iii) Adjoining buildings, structures and land.

Supervision Tasks:

(i) Monitoring that the site operations and working methods meet safety standards set out in the Building Ordinance and codes of practice and that unsafe practices are not being followed;

(ii) Checking that general and minor safety aspects of the building works or street works are properly carried out;

(iii) Checking that work carried out on site complies with the approved, accepted or submitted method statements and precautionary and protective measures.

Code of Practice for Site Supervision 2009

SUPERVISION OF SOIL NAILING WORKS

General• Statutory requirements : PNAP 284 (APP-135)• Code of Practice for Site Supervision 2009 : Quality

Supervision for Soil Nailing Works• Geoguide 7 – Guide to Soil Nail Design and

Construction

(i) Quality supervision of soil nailing works should be provided by the RGE and his TCP T5 and T3, as well as by the AS of the RSC (Site Formation) and his TCP T4 and T1.


(ii) For all soil nailing works, at least one TCP T3 of the RGE and one TCP T1 of the RSC are required to be resident full-time on site during every stage of works for each soil nail. The RSC is required to notify the RGE’s TCP T3 before the commencement of any stage of the works. The RSC is also required to prepare detailed inspection, measurement and test records for each soil nail as per the approved plan requirements.


(iii) Key records on supervision of soil nailing works (Appendix IX) should also be prepared and certified by the RGE’s TCP T3 who carries out the inspection, measurement or check. A full set of all certified records should be kept on site for inspection by BD staff.

Proforma from Appendix IX of the Code of Practice for Site Supervision 2009


SUPERVISION OF SOIL NAILING WORKSDuties of RGE’s TCP T3 on Quality Supervision for Soil Nailing Works• Prepare and certify the Key records on Supervision of Soil Nailing Works

(pro forma from Appendix IX of the Code of Practice)• Report to RGE’s TCP T5 concerning any anomalies during construction• Check setting out positions• Supervise drilling of soil nail holes• Check assembly of soil nail reinforcement• Supervise insertion of soil nail reinforcement• Supervise grout and preparation of grout• Supervise grouting of soil nail hole• Supervise construction of soil nail heads• Supervise all pull-out tests


(Extracted from Code of Practice for Site Supervision 2009)

Setting-out• Check whether any existing utilities, channels, trees, foundations, other structures

or proposed works would be affected.


Drilling• Drilling by percussive drilling rigs, sometimes hand held rotary coring machine at

space restricted site.• Ensure diameter of drill bit compatible with the designed diameter of the soil nail

hole• Instruct the contractor to remove any smaller drill bits off site immediately.• Check control measures against dust, water, noise, etc.• Check location, orientation and inclination – setting up of the drilling rod be

checked correctly. Generally alignment should not exceed 2 degrees.• Check for flushing medium and hole collapse in particular for drilling under water.

Temporary casing and dewatering measures may be necessary.• Drilling records for each nail to be prepared.• Check diameter and depth of the hole upon completion of drilling.



Soil nail assembly and insertion• Check threaded portions of steel bars are adequate for fixing the nut, couplers and

bearing plates.• Check centralizers, grout pipes, conducting wire (for NDT) are fixed securely onto

steel bar.• Check heat-shrinkable sleeves, corrugated plastic sheathing, washer and nut,

bearing plate.• If high groundwater exists, wait until water level drops or alternatively dewatering

measures have to be in place.• Final check on the galvanizing quality of all steel components.• Check diameter and length of steel bars before installation.• Ensure no obstruction during installation of steel bars.


SUPERVISION OF SOIL NAILING WORKSGrouting

• Grout usually comprises ordinary Portland cement and water, withadmixtures. Water cement ratio usually 0.38 to 0.42.

• Water should be clean and uncontaminated.• Soil nails should be grouted within the same day of insertion.• Mixers for grout shall be a high-speed colloidal type.• Grouting commences from the lowest point and that grout is pumped

into the hole under a continuous and steady rate to prevent entrapping air. A head of typically 1m shall be maintained above the mouth of drillhole until initial set of grout.

• Excessive grout leak should be monitored to verify validity of assumed geological model, also to determine actions to be undertaken, such as staged grouting, sleeving over grout leak by using casing.

• Grouting records to be prepared.

SUPERVISION OF SOIL NAILING WORKSGrout Tests• Flow cone test to test grout’s fluidity. Normally 2 tests are undertaken per batch of

mix. Grout having an efflux time of <15 seconds should be rejected.• Bleed tests are also carried out following mixing of grout. Tests are done to test

the absorption characteristics of grout. Criteria for bleed tests are:- bleeded water at 3 hours should be <0.5% by volume- maximum bleeded water should be <1%- water should be re-absorbed within 24 hours

• Compressive cube strengths of grout to the designed 28-day strength

Soil Nail Record – Drilling and Grouting



Construction of soil nail head• Check threads of reinforcement bar thoroughly cleaned and treated with hot-dip

galvanized coating or protected with zinc-rich paint.• Check concrete thoroughly compacted.

SUPERVISION OF SOIL NAILING WORKSPull-out TestGeneral• To verify pull out capacity of soil nails, i.e. design assumptions• Undertaken prior to installation of permanent soil nails• Tested nails will be abandoned and not to be used as permanent nails• Designer to review test results and to revise length of soil nails accordingly


SUPERVISION OF SOIL NAILING WORKSPull-out TestEquipment and Set-up• Ensure all apparatus used have been calibrated• Accuracy of pressure gauges and dial gauges be confirmed to required specifications,

usually having tolerances <2kN and <0.05mm respectively• Bearing plate/concrete pad should be firmly cast on soil surface• Jacking cylinder is positioned parallel to test bar and perpendicular to bearing

plate/concrete pad to ensure the soil nail is stressed in the right direction


SUPERVISION OF SOIL NAILING WORKSPull-out TestProcedures• Normal test load should not in any case

exceed 90% of ultimate tensile strength as sudden failure would be dangerous to testing crew.

• All personnel should not be standing facing the direction of the bar during stressing of the soil nail bar.

• Check test loads at each loading/unloading cycle, the time that each load is held constant, deformations measured from the dial gauges. 3 loading/unloading cycles are required to bring the soil nail to the required testing load.

• Record results accordingly.

SUPERVISION OF SOIL NAILING WORKSPull-out Test Result


Non-destructive Testing• Encourage high construction standards and promote self-imposed improvements.• Use as a construction audit tool. Build up overall picture of the integrity of the

installed soil nails.• Time Domain Reflectometry tests are usually undertaken. For detail procedures see

GEO Report No. 133 “Non-destructive Tests for Determining the Lengths of Installed Soil Nails” and “Guidelines on Test Procedure & Sample Test Results using Time Domain Reflectometry (TDR) to Determine the Length of Installed Soil Nails”.


(Extracted from GEO’s “Guidelines on Test Procedure using Time Domain Reflectometry (TDR) to Determine the Length of Installed Soil Nails”)

Determining Length of Soil Nails by Time Domain Reflectometry

SUPERVISION OF SOIL NAILING WORKSRESULTS OF NON-DESTRUCTIVE TESTING –TIME DOMAIN REFLECTOMETRY (TDR)

RESULTS OF NON-DESTRUCTIVE TESTING –TIME DOMAIN REFLECTOMETRY (TDR)


FILLING WORK ON SLOPE

• PNAP 55 (APP-15) : Site Formation Temporary or Permanent Filling Work

• PNAP 83 (APP-28) : Requirements for Qualified Supervision • Disastrous consequence of flowslides of loosely placed earth fill

resulting from inadequate compaction• RGE’s TCP T3 be full-

time on site• Carry out day-to-day

check on compliance with working procedures and specifications


• Soil filling cannot be adequately compacted during inclement weather, rock fill works are better than soil fill works under wet conditions.

• Temporary protection of earthwork is required, such as covering by tarpauline cover

• Source of filling materials to be approved, usually CDG and CDV are considered suitable materials

• QC tests on materials: PSD, plastic index, etc

• Benching into the slopes is required prior to receiving new fill materials

Details of Benching for Placement of Fill on Existing Ground


(Extracted from CEDD Standard Drawings)

FILLING WORK ON SLOPE• Thickness of each filling layer is commonly

250mm to 300mm, depending on the output power from the vibratory roller.

• In-situ field dry densities of compacted fill shall not be less than 95% of the maximum dry density (Geospec 3: Model Specification for Soil Testing).

• All testing records must be kept on site• Monthly assessment report on the filling work

be included to the monthly T5 Report .

Relative compaction Rc = ρd/ρmax x 100%

whereρd is the in situ dry density and ρmax is the maximum dry density

Determination of Dry Density/ Moisture Content Relationship

FILLING WORK ON SLOPEDetermination of In situ Bulk and Dry Density


DRAINAGE PROVISION ON SLOPES

• Reference: Geotechnical Manual for Slopes, GEO• Majority of slope failures are associated with drainage problems due

to intense rainfall during extreme weather

• Efficient and adequate drainage provisions on slope are therefore absolutely essential

DRAINAGE PROVISION ON SLOPES• Drainages are provided as surface and/or sub surface measures• Surface provisions are by means of surface channels• Sub surface provisions are by means of horizontal or raking drains,

counterfort drains, filter drainage blankets, weepholes (behind retaining walls or hard surfaces)

MONITORING GROUND MOVEMENT

MONITORINGGroundwater Level

LANDSCAPING ON SLOPE

• Reference:

LANDSCAPING ON SLOPE

• Green solution is preferred even on rock slopes.• Shotcrete should be kept to a bare minimum.

GREENING OF STEEP SLOPES

A few proprietary methods available in the markets, with varied degree of success

Creat Toyo-Mulching GeofibreG&E Soil Panel System

NFY Soil Panel System

MAINTENANCE OF SLOPE• PNAP 189 (APP-79) - Geoguide 5: Guide

to Slope Maintenance

• Typically an Engineer Inspection to be undertaken once every 5 years (for slopes having C-T-L of 1 and 2, or more frequent where poor conditions warrant such inspection)

• Routine Maintenance to be carried out annually, preferably before to the on set of the wet season

• Design and construction of slopes should bear this in mind

• Construction to cater for future access considerations to undertake Engineer Inspection and Maintenance of Slopes in future

SAFE ACCESS TO SLOPE MAINTENANCE SAFE ACCESS TO SLOPE MAINTENANCE

BURIED WATER-CARRYING SERVICESPNAP 183 (APP-79) – Keep Buried Services out of SlopeRecommendations:1.Buried services not be placed nearer to slope crest than a distance equal to the height of the slope.2.Re-route existing services to fulfill (1) if opportunities arise.3.In case impractical to site the buried services outside the crest area, then

- Slope design to take into account possible water leakage;

- Lay service above ground service;- House service within ducting system;- Provide stop valves for water mains.

4.In fill slopes, sewers and drains to be provided with flexible jointing to accommodate differential settlement.

DETECTION OF LEAKY BURIED SERVICE• Leak Noise Correlator Survey• Ground Microphone Survey• CCTV Survey• Man Entry Survey

CLOSING REMARKS

• Slope engineering is not purely analysis and design. Field observation and construction quality control are equally important.

• Slope stability is affected by various factors. Their assumptions requires dedicated on-site verifications during construction.

• Hence, adequate and close supervision of slope works is absolutely essential.

The End

contents top-up course for tcp t3 on gifw and ... existing loose fill slopes (by undertaking in-situ...

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