guidelines on good practices for pile load test using kentledge

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
Revision 1: 1st Sept em ber 2011
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
GeoSS
1.0
SCOPE AND OBJECTI VE OF THESE GUI DELI NES
The scope of these guidelines is lim ited to the setup of pile load test using
Kent ledge method f or Singapor e pract ices.
In Singapore, Kent ledge method of pile load test is commonly used to
determine the geotechnical design values and response of r epresentative pile
to applied load, both in t erm of settlement or lim it load. The size and height of
Kent ledge can be m assive and if not properly designed and erected, it can pose
saf ety hazard to t he workers as well as t he public in vicinit y. These guidelines
can pr ovide some guidance to the part ies involved in the Kent ledge setup to
ensure that Kent ledg e method of pile load test is reliable, saf e and acceptable.
2.0
DESIGN OF THE SETUP FO R PILE LO AD TEST STARTS I N DESIGN
OFFICE
Planning of pile load test setup should st art f rom the design off ice. The design
of the Kentledge set up should be carr ied out by a Prof essional Engineer, PE.
The type and amount of Kentledge, setup and its f oundation should be proper ly
planned and detailed to ensur e that the setup is st able and saf e, not only
during erection stage, and during pile load testing stage but also in the event of
pile exper iencing unexpected f ailur e in t he 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 suit able
dead weights chosen should suit the project and takes int o account ground
condition, availabilit y of materials, site constraint and public saf ety. W here
possible, Kent ledge type of load test should be set-up at least one t ime the
least width of the Kentledge f ootprint away f rom public access area or
neighbouring structures/buildings.
2.1.1 Load Test Exceeding 3000 Tonnes
It is generally not recommended to use concr ete blocks as the Kent ledge f or
pile load test exceeding 3000 tonnes because of the signif icant height of the
Kent ledge. In the case of its unexpected collapse, it can potentially endanger
the lives of the wor kers as well as the public. For large load test exceeding
3000 Tonnes, the pr oject team can consider using steel plates, tension piles or
ground anchors as the react ion load or adopt ing other alt ernative method of
testing like bi-direct ional load test.
Large load test exceeding 3000 Tonnes using concrete blocks should only be
carried out by competent Specialist Builder (Piling W orks) and PE who has the
relevant experience. Caref ul considerat ions should be made in all aspects like
robustness in design, strict compliance of design codes, saf ety of neighbour ing
propert ies, saf ety of the workers and people carr ying out t he test, saf ety of
public passing by the site, and putting in place contingency plan if tilting of
Kent ledge occurs during stacking or load testing.
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 will remain stable during the test. It is common to
adopt at least 10% extra weight excluding those of test beam s. The stacking of
the f ull Kentledge should be complet ed bef ore the start of the test.
Putting extra concr ete blocks onto the Kent ledge during the loading cycle
should not be allowed. This is because the f ull load will be transf erred to the
ground in the event of pile f ailure. As the ground has not been f ully loaded
earlier, there is a possibilit y of bear ing f ailure when the f ull load is suddenly
transf erred to the ground. The sudden pressure peak on the ground may also
trigger unbalanced distribution of load on the ground. This may potent ially lead
to progressive bear ing f ailure of the ground and eventual toppling of concr ete
blocks. In any event, any of the f our corners of the Kentledge should not be
allowed to f loat or be uplif ted as this will lead to uneven load distribution to the
base of the setup.
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GeoSS
2.1.3 Kentledge Bl ocks Arrangement
Kent ledge blocks arrangement should be designed by PE. The pattern of the
blocks arrangement should t ake int o account stacking sequence and designed
to enhance stabilit y of the individual block as well as the whole of the
Kent ledge setup.
2.1.4 Kentledge Height t o Width Aspect Rat io.
The height to widt h ratio of the Kentledge setup should not be more than 1.5 f or
stabilit y. For area with neighbour ing st ructures/buildings, the ratio should be
reduced to not more than 1 by increasing the width of Kentledge.
2.2
Design of Foundati on
The f oundation f or the setup should be designed to support the f ull weight of
the Kent ledge.
2.2.1 Check Geotechnical Bearing Capacit y of Kentledge Base
The design check should be based on r epresentative soil investigation results
at the location of the Kent ledge setup. There must be adequate site
investigation to est ablish the possible var iat ion of sub-soil layers below the
f oundation of the Kentledge. Soil parameters should be selected f rom
appropr iate test dat a or previous experience in similar soils. The f actor of
saf ety f or allowable bear ing capacit y f or f oundation supporting the Kentledge
can be computed based on convent ional Terzaghi’s bear ing capacit y equat ion
or other methods using sound engineer ing principles. This geotechnical f actor
of saf ety should generally be in t he or der of 2.5 to 3, with upper value to be
adopted f or large load test or load test near neighbouring structures/buildings.
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GeoSS
2.2.2 Effect of Kentledge Setup on Neighbouring Slopes and Str uctures
For Kentledge setup on top of a slope, or on top of an exist ing earth retaining
structures, the potential reduced bearing capacit y of the ground need to be
analysed. The eff ect of the massive Kentledge bearing on ground needs to be
assessed. This is t o ascertain that the stabilit y of neighbouring slopes and
structural integrit y of existing earth retaining structures and buildings are not
aff ected. Excavation works next to t he Kent ledge should be prevented unless
adequately designed. Proper drainage should be provided t o avoid excessive
rain water seepage into the ground supporting the Kent ledge base dur ing wet
weather condit ion.
2.2.3 Differential and Consolidation Settlem ent of Kentledge Base
Care should to be taken to ensure that there will be no signif icant settlement of
the Kent ledge base. Adverse condit ion may ar ise where t here is a var ying soil
prof ile with sof t ground, close to a slope, canal or excavation. This could leads
to diff erential settlement. As a good guide, the calculated diff erential settlement
f or Kentledge base should be wit hin 1 in 150.
W here the ground below the base of the Kentledge will likely to exper ience
consolidat ion sett lement, the rat e of consolidation settlement should be
examined. This is t o ensure that it will not cause inst abilit y of the Kent ledge
setup dur ing load t esting, or in the event of sudden pressure peak on the
ground resulting f rom a sudden pile f ailure. It is cautioned that a large
computed total settlement under t he maximum test load could be indicat ive of
inadequate geotechnical saf ety f actor and designer should take all necessar y
measures to reduce the magnitude of the total settlement.
2.2.4 Ground Improvement
If the bearing capacit y check indicated insuff icient f actor of saf ety or when
settlement will be excessive, surf ace or soil improvement may be necessar y.
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GeoSS
2.2.5 Deep Foundation
If shallow f oundation is insuf f icient to achieve adequate f actor of saf ety or when
settlement will be excessive, deep f oundation will be requir ed. The design of
deep f oundation such as steel H-piles or steel circular pipes should f ollow
conventional piling design based on SS CP4: 2003.
2.2.6 Other Systems
Other systems like r eaction anchors or piles can be used. The design of such
systems should comply with their respect ive Codes.
2.3
Design of Struct ural Members
Design of structural members i.e. transf er beam, main beam, secondar y beam,
steel box, steel mat, steel piles should comply with BS5950-1:2000. W here reused structural steel is used, the PE should consider any imperf ections and
conditions of such materials in his design.
2.3.1 Bending Moment Capacit y
The structural members should be checked f or ultimate moment capacit y.
2.3.2 Shear Capacit y
The structural members should be checked f or ultimate shear capacit y.
2.3.3 Torsional Buckling
The structural members shall be checked f or lateral torsional buckling.
2.3.4 Beam Web Bearing and Web Buckling
The structural members should be checked f or web bear ing and web buckling
2.3.5 Beam Deflection
The def lection of the beam under f ull load should be check to ensure it will not
compromise the over all stabilit y of the set-up.
2.4
Draw ing of Pile Load Test Set up
It is important that all the design consider ation and output be clearly shown in
the drawing to ensur e compliance and easy of site super vision.
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GeoSS
f or
illustration
only
The spacing of beams derived f rom the design calculation sh
should
ould be proper ly
indicated in the drawings.. The size and g
grade of steel should be shown f or all
beams. Concrete block size and stacking details are impor tant and should be
shown in drawing.
3.0
IMPLEMENTATION DURING CONSTRUCTION STAG E
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GeoSS
3.1
Site Super vision by Competent Staff
The pile load test should be super vised by a competent staff i.e. PE. The PE
who designed the Kentledge setup and Qualif ied Site Super visor, QSS should
inspect the setup during erect ion, and load testing to detect if there is any
abnormally and inst abilit y of the setup. Load test should only be allowed to
start af ter inspect ion by PE and he cert if ied that there is no saf ety or stabilit y
concern.
3.2
Construction to foll ow Design Draw ing
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 cells and dial gauges should have valid calibr ation certif icates.
3.3
Instrumentation and Monitoring
Instrumentation should be installed to monitor the stabilit y of the Kentledge
setup, f rom the stacking of Kentledge to load test ing stage. The f our bases of
the Kent ledge should be monitored using leveling. The base readings should be
taken f or the instruments and top of test pile bef ore stacking of concrete
blocks. The rate of settlement and rate of diff erential settlement rate should be
checked at regular interval. The main st eel beam should also be monitored to
ensure that there is not tilting or uplif ting. W here possible, data collect ion
should be carr ied out remote f rom the kentledge base. In t he event that the
instrumentation readings indicate instabilit y or trend of instabilit y, the sit e staff
must report to the PE so that appropr iat e actions could be taken immediately.
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GeoSS
3.4
Safet y of Workers
The saf ety of wor kers is paramount. Project team to note dut ies and
responsibilities stipulated under the W orkplace Saf ety and Health Act and its
subsidiar y legislations which include W SH (Construct ion) Regulation 2007 and
W SH (Risk Management) Regulation 2006.
Some good pile load testing practices, f or instance, testing 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 pile load test should address the
installat ion, test ing, dismant ling and t he zone of possible collapse of the
Kent ledge.
Saf e work procedures f or installation, testing and dismant ling of Kentledge
should be implemented. Br ief ings should be carried out to all personnel
involved in the wor ks and key areas of the saf e work procedures should be
eff ectively communicated to the workers.
During the erection and dismant ling of the Kentledge, workers will be exposed
to W ork-At-Height risks. Fall Protect ion Plan should be developed, implemented
and ef f ectively com municated to the wor kers.
Project team should also ref er to SS 515:2005 on pile load t est bef ore the start
of the test.
REFERENCES
BS 5950-1:2000 Structural Use of Steel W orks in Building
SS CP4:2003 Code of Practice f or Foundation
SS 515:2005 Code of Practice f or Supervision of Structural W orks
W orkplace Saf ety and Health Act
W orkplace Saf ety and Health (Construct ion) Regulation 2007
W orkplace Saf ety and Health (Risk Management) Regulation 2006
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