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Guidelines ofr Pile Load Testing
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Revis ion 1 : 1s t
Sept em ber 2011
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
Revis ion 1 : 1s t
Sept em ber 2011 1
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.
Revis ion 1 : 1s t
Sept em ber 2011 2
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.
Revis ion 1 : 1s t
Sept em ber 2011 3
GeoSS
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.
Revis ion 1 : 1s t
Sept em ber 2011 4
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.
Revis ion 1 : 1s t
Sept em ber 2011 5
GeoSS
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.
Revis ion 1 : 1s t
Sept em ber 2011
GeoSS
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
Revis ion 1 : 1s t
Sept em ber 2011 7
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.
Revis ion 1 : 1s t
Sept em ber 2011 8
GeoSS
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