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GeoSS

GUIDELINES ON GOOD PRACTICES FOR PILE LOAD TEST

USING KENTLEDGE METHOD IN SINGAPORE

Working Group on Pile Load Test

Chairman : Mr Chua Tong Seng - GeoSS

Member : Dr Yet Nai Song - BCA

Mr Heng Kok Hui - ACES

Mr Jerry Lim Kee Chay - HDB

Dr Lim Ken Chai - IES

Dr Veeresh Chepurthy - LTA

Mr Lim Shiyi - MOM

Mr Koo Chung Chong - SCAL

Mr Thomas Molnit - Bauer (M) Singapore

Mr Jimmy Lim - CSC Holdings Limited

Mr Foo Hee Kang - Resource Piling Pte Ltd

Mr Eric Low - Zap Piling Pte Ltd

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GeoSS

1.0 SCOPE AND OBJECTIVE OF THESE GUIDELINES

The scope of these guidelines is l imited to the setup of pile load test using

Kent ledge method for Singapore pract ices.

In Singapore, Kent ledge method of pile load test is commonly used to

determine the geotechnical design values and response of representat ive pi le

to appl ied load, both in term of sett lement or l imit load. The size and height of

Kent ledge can be massive and if not properly designed and erected, it can pose

safety hazard to the workers as well as the publ ic in vicinity. These guidelines

can provide some guidance to the part ies involved in the Kent ledge setup to

ensure that Kent ledge method of pile load test is reliable, safe and acceptable.

2.0 DESIGN OF THE SETUP FOR PILE LOAD TEST STARTS IN DESIGN

OFFICE

Planning of pile load test setup should start f rom the design off ice. The design

of the Kentledge setup should be carr ied out by a Professional Engineer, PE.

The type and amount of Kentledge, setup and its foundation should be proper ly

planned and detai led to ensure that the setup is stable and safe, not only

during erect ion stage, and during pi le load test ing stage but also in the event of

pi le exper iencing unexpected failure in the midst of load test.

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GeoSS

2.1 Type of Kentledge

The type of Kent ledge such as concrete blocks, steel plates or other suitable

dead weights chosen should suit the project and takes into account ground

condit ion, avai labi l i ty of materials, s ite constraint and publ ic safety. Where

possible, Kent ledge type of load test should be set-up at least one t ime the

least width of the Kentledge footprint away f rom public access area or

neighbouring structures/bui ldings.

2.1.1 Load Test Exceeding 3000 Tonnes

I t is general ly not recommended to use concrete blocks as the Kent ledge for

pi le load test exceeding 3000 tonnes because of the signif icant height of the

Kent ledge. In the case of its unexpected col lapse, it can potential ly endanger

the l ives of the workers as well as the public. For large load test exceeding

3000 Tonnes, the project team can consider using steel plates, tension pi les or

ground anchors as the react ion load or adopt ing other alternative method of

test ing l ike bi-direct ional load test.

Large load test exceeding 3000 Tonnes using concrete blocks should only be

carr ied out by competent Special ist Builder (Pi l ing Works) and PE who has the

relevant experience. Careful considerat ions should be made in al l aspects l ike

robustness in design, str ict compliance of design codes, safety of neighbour ing

propert ies, safety of the workers and people carrying out the test, safety of

public passing by the site, and putt ing in place contingency plan if t i l t ing of

Kent ledge occurs during stacking or load test ing.

2.1.2 Weight of Kentledge

The total weight of Kentledge should be greater than maximum test load. This is

to ensure the Kent ledge wi l l remain stable during the test. I t is common to

adopt at least 10% extra weight excluding those of test beams. The stacking of

the full Kentledge should be completed before the start of the test.

Putt ing extra concrete blocks onto the Kent ledge during the loading cycle

should not be al lowed. This is because the full load wi l l be transferred to the

ground in the event of pi le fai lure. As the ground has not been ful ly loaded

earl ier, there is a possibi l i ty of bear ing failure when the full load is suddenly

transferred to the ground. The sudden pressure peak on the ground may also

tr igger unbalanced distr ibut ion of load on the ground. This may potent ial ly lead

to progressive bear ing failure of the ground and eventual toppl ing of concrete

blocks. In any event, any of the four corners of the Kentledge should not be

al lowed to f loat or be upl if ted as this wi l l lead to uneven load distr ibut ion to the

base of the setup.

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2.1.3 Kentledge Blocks Arrangement

Kent ledge blocks arrangement should be designed by PE. The pattern of the

blocks arrangement should take into account stacking sequence and designed

to enhance stabi l i ty of the individual block as wel l as the whole of the

Kent ledge setup.

2.1.4 Kentledge Height to Width Aspect Ratio.

The height to width rat io of the Kentledge setup should not be more than 1.5 for

stabi l i ty. For area with neighbour ing structures/bui ld ings, the rat io should be

reduced to not more than 1 by increasing the width of Kentledge.

2.2 Design of Foundation

The foundation for the setup should be designed to support the full weight of

the Kent ledge.

2.2.1 Check Geotechnical Bearing Capacity of Kentledge Base

The design check should be based on representat ive soi l invest igat ion results

at the location of the Kent ledge setup. There must be adequate site

invest igat ion to establ ish the possible var iat ion of sub-soi l layers below the

foundation of the Kentledge. Soi l parameters should be selected f rom

appropr iate test data or previous experience in s imi lar soils. The factor of

safety for al lowable bear ing capacity for foundation support ing the Kentledge

can be computed based on convent ional Terzaghi ’s bear ing capacity equat ion

or other methods using sound engineer ing principles. This geotechnical factor

of safety should generally be in the order of 2.5 to 3, with upper value to be

adopted for large load test or load test near neighbouring structures/build ings.

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GeoSS

2.2.2 Effect of Kentledge Setup on Neighbouring Slopes and Structures

For Kentledge setup on top of a slope, or on top of an exist ing earth retaining

structures, the potential reduced bearing capacity of the ground need to be

analysed. The effect of the massive Kentledge bearing on ground needs to be

assessed. This is to ascertain that the stabi l i ty of neighbouring slopes and

structural integrity of exist ing earth retaining structures and bui ld ings are not

affected. Excavation works next to the Kent ledge should be prevented unless

adequately designed. Proper drainage should be provided to avoid excessive

rain water seepage into the ground support ing the Kent ledge base dur ing wet

weather condit ion.

2.2.3 Differential and Consolidation Settlement of Kentledge Base

Care should to be taken to ensure that there wi l l be no signif icant sett lement of

the Kent ledge base. Adverse condit ion may ar ise where there is a varying soi l

prof i le with sof t ground, c lose to a slope, canal or excavation. This could leads

to dif ferential sett lement. As a good guide, the calculated dif ferential sett lement

for Kentledge base should be within 1 in 150.

Where the ground below the base of the Kentledge wi l l l ikely to exper ience

consol idat ion sett lement, the rate of consol idat ion sett lement should be

examined. This is to ensure that it wi l l not cause instabil i ty of the Kent ledge

setup dur ing load test ing, or in the event of sudden pressure peak on the

ground result ing f rom a sudden pi le fai lure. I t is cautioned that a large

computed total sett lement under the maximum test load could be indicat ive of

inadequate geotechnical safety factor and designer should take all necessary

measures to reduce the magnitude of the total sett lement.

2.2.4 Ground Improvement

I f the bearing capacity check indicated insuff icient factor of safety or when

sett lement wi l l be excessive, surface or soi l improvement may be necessary.

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2.2.5 Deep Foundation

I f shallow foundation is insuf f icient to achieve adequate factor of safety or when

sett lement wil l be excessive, deep foundation wi l l be required. The design of

deep foundation such as steel H-piles or steel circular pipes should follow

conventional pil ing design based on SS CP4: 2003.

2.2.6 Other Systems

Other systems l ike react ion anchors or piles can be used. The design of such

systems should comply with their respect ive Codes.

2.3 Design of Structural Members

Design of structural members i.e. transfer beam, main beam, secondary beam,

steel box, steel mat, steel pi les should comply with BS5950-1:2000. Where re-

used structural steel is used, the PE should consider any imperfect ions and

condit ions of such materials in his design.

2.3.1 Bending Moment Capacity

The structural members should be checked for ult imate moment capacity.

2.3.2 Shear Capacity

The structural members should be checked for ult imate shear capacity.

2.3.3 Torsional Buckling

The structural members shall be checked for lateral torsional buckling.

2.3.4 Beam Web Bearing and Web Buckling

The structural members should be checked for web bear ing and web buckl ing

2.3.5 Beam Deflection

The def lect ion of the beam under ful l load should be check to ensure it wi l l not

compromise the overal l stabi l i ty of the set-up.

2.4 Drawing of Pile Load Test Set up

I t is important that al l the design considerat ion and output be clearly shown in

the drawing to ensure compliance and easy of site supervis ion.

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The spacing of beams derived f rom the design calculat ion sh

indicated in the drawings. The size and g

beams. Concrete block size and stacking details are

shown in drawing.

3.0 IMPLEMENTATION DURING

derived f rom the design calculat ion should

. The size and grade of steel should be

Concrete block size and stacking details are important and should

IMPLEMENTATION DURING CONSTRUCTION STAGE

for i l lustrat ion

only

6

ould be proper ly

be shown for al l

and should be

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GeoSS

3.1 Site Supervision by Competent Staff

The pi le load test should be supervised by a competent staff i .e. PE. The PE

who designed the Kentledge setup and Qual if ied Site Supervisor, QSS should

inspect the setup during erect ion, and load test ing to detect if there is any

abnormally and instabi l i ty of the setup. Load test should only be al lowed to

start af ter inspect ion by PE and he cert if ied that there is no safety or stabi l i ty

concern.

3.2 Construction to follow Design Drawing

On site, Kentledge base should be prepared according to design calculat ion.

The dimension of the Kent ledge base should be constructed according to the

drawing. Beam sizes and steel grade area should be as specif ied in the

drawing. Load cel ls and dial gauges should have val id cal ibrat ion cert if icates.

3.3 Instrumentation and Monitoring

Instrumentat ion should be instal led to monitor the stabil i ty of the Kentledge

setup, f rom the stacking of Kentledge to load test ing stage. The four bases of

the Kent ledge should be monitored using level ing. The base readings should be

taken for the instruments and top of test pi le before stacking of concrete

blocks. The rate of sett lement and rate of dif ferential sett lement rate should be

checked at regular interval. The main steel beam should also be monitored to

ensure that there is not t i l t ing or upli f t ing. Where possible, data col lect ion

should be carr ied out remote f rom the kentledge base. In the event that the

instrumentat ion readings indicate instabil i ty or trend of instabil i ty, the site staff

must report to the PE so that appropr iate act ions could be taken immediately.

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3.4 Safety of Workers

The safety of workers is paramount. Project team to note dut ies and

responsibi l i t ies st ipulated under the Workplace Safety and Health Act and its

subsidiary legis lat ions which include WSH (Construct ion) Regulat ion 2007 and

WSH (Risk Management) Regulat ion 2006.

Some good pi le load test ing pract ices, for instance, test ing by remote control

where workers do not need to go under the massive Kentledge setup to

increase the test load and to take load test readings can be considered.

Risk assessments on the execution of the pi le load test should address the

instal lat ion, test ing, dismant l ing and the zone of possible col lapse of the

Kent ledge.

Safe work procedures for installat ion, test ing and dismant l ing of Kentledge

should be implemented. Br ief ings should be carr ied out to all personnel

involved in the works and key areas of the safe work procedures should be

effect ively communicated to the workers.

During the erect ion and dismant l ing of the Kentledge, workers wi l l be exposed

to Work-At-Height r isks. Fal l Protect ion Plan should be developed, implemented

and ef fect ively communicated to the workers.

Project team should also refer to SS 515:2005 on pi le load test before the start

of the test.

REFERENCES

BS 5950-1:2000 Structural Use of Steel Works in Building

SS CP4:2003 Code of Pract ice for Foundation

SS 515:2005 Code of Pract ice for Supervis ion of Structural Works

Workplace Safety and Health Act

Workplace Safety and Health (Construct ion) Regulat ion 2007

Workplace Safety and Health (Risk Management) Regulat ion 2006

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