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COMPARISON OF ULTIMATE BEARING CAPACITY OBTAINED BY
PILE DRIVING ANALYZER AND MAINTAINED LOAD TEST
KAMALENDRAN A/L N. RAJASVARAN
UNIVERSITI TEKNOLOGI MALAYSIA
PSZ 19:16 (Pind.1/97)
UNIVERSITI TEKNOLOGI MALAYSIA
CATATAN: * Potong yang tidak berkenaan. ** Jika tesis ini SULIT atau TERHAD, sila lampirkan surat daripada pihak berkuasa /organisasi berkenaan dengan menyatakan sekali sebab dan tempoh tesis ini perlu dikelaskan sebagai SULIT atau TERHAD.
BORANG PENGESAHAN STATUS TESIS♦
JUDUL: COMPARISON OF ULTIMATE BEARING CAPACITY OBTAINED
BY PILE DRIVING ANALYZER AND MAINTAINED LOAD TEST
SESI PENGAJIAN: 2006/07 Saya KAMALENDRAN A/L N. RAJASVARAN __________________________________________________
(HURUF BESAR) Mengaku membenarkan tesis (PSM/Sarjana/Doktor Falsafah)* ini disimpan di perpustakaan Universiti Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut:-
1. Tesis adalah hakmilik Universiti Teknologi Malaysia. 2. Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk
tujuan pengajian sahaja. 3. Perpustakaan dibenarkan membuat salinan tesis ini sebagai bahan pertukaran antara
institusi pengajian tinggi. 4. **Sila tandakan (√)
SULIT (Mengandungi maklumat berdarjah keselamatan atau kepentingan Malaysia seperti yang termaktub di dalam AKTA RAHSIA RASMI 1972) TERHAD (Mengandungi maklumat TERHAD yang telah ditentukan oleh organisasi/badan dimana penyelidikan dijalankan TIDAK TERHAD
Disahkan oleh _____________________________ _____________________________ (TANDATANGAN PENULIS) (TANDATANGAN PENYELIA) Alamat Tetap: 30, Lebuh Jelutong, Dr. Ramli Nazir Taman Selatan, 41200 Klang, Selangor. Tarikh : 11 May 2007 Tarikh : 11 May 2007
√
COMPARISON OF ULTIMATE BEARING CAPACITY OBTAINED BY
PILE DRIVING ANALYZER AND MAINTAINED LOAD TEST
KAMALENDRAN A/L N. RAJASVARAN
A thesis submitted in fulfillment of the
Requirements for the award of the degree of
Master of Engineer ing (Civil – Geotechnic)
Faculty of Civil Engineer ing
University Technology Malaysia
MAY 2007
ii
“I declare that this project report is the result of my own research
except as cited in references. This report has not been accepted for
any degree and is not concurrently submitted in candidature of any
degree”.
Signature :_______________________________
Name of Candidate: KAMALENDRAN A/L N. RAJASVARAN
Date : 11 May 2007
iii
“I hereby declare that I have read this report and in my opinion
this report is sufficient in terms of scope and quality for the
award of Master of Engineering (Civil-Geotechnics)”.
Signature : ……………………………………….
Name of Supervisor : Dr . Ramli Nazir
Date : 11 May 2007
iv
DEDICATION
To my beloved parents, family and fr iends
I am where I am because of all of you
Please continue to give me your suppor t and encouragement
My humblest thanks and gratitude to all
v
ACKNOWLEDGEMENT
Firstly, my salutations and adoration to God for keeping me in good health
and supplying me with the required knowledge and information to complete this
thesis.
There are no words apt enough to describe the amount of patience and love
shown and showered by my parents whilst I was completing this project. They were
always there when I needed their help and advice. My sincere thanks also to family
members and relatives who have given me the strength and encouragement to carry
on when I had almost given up hope.
My friends were instrumental and played important roles in assisting me to
complete my thesis. They include my course mates, seniors who have graduated,
colleagues and my many other friends. My outmost gratitude to all of them.
I especially would like to express and record my gratitude and thanks towards
Dr. Ramli Nazir, for the huge amount of patience shown by him and for all his
guidance in the preparation of this thesis. Without his patience and assistance, this
thesis would never have been completed.
vi
ABSTRACT
In Malaysia, Maintained Load Test (MLT) is the most common static load
test used for testing of driven reinforced concrete (RC) piles, while Pile Driving
Analyzer (PDA) is currently the most popular dynamic test method. MLT provides
relatively accurate information on ultimate pile capacity and settlement but is costly,
time consuming and difficult to carry out. PDA is much more timesaving, less
expensive and can be carried out with relative ease, but the results are subject to
uncertainties and interpretations of wave stress propagation theories. Results of pile
load tests at a hypermarket development were studied and analysed to create a
comparison between MLT and PDA. From the study, ultimate pile capacities derived
from analysis of PDA were consistently higher than results from MLT. Comparison
of pile settlement results for MLT and PDA was observed to be inconsistent. The
study also recognises that Davisson’s Method is used to obtain ultimate pile capacity
from MLT as it is more conservative compared with other calculation methods. PDA
results were observed to be satisfactory in determining ultimate pile capacity, but a
coefficient of 0.9 or a 10% reduction is suggested to be applied to values derived
from PDA. For future pile testing programs, there is a potential for an increase of
PDA tests to be carried out. However, a limited number of MLT must also be carried
out to determine accuracy of parameters and soil models used in PDA tests.
vii
ABSTRAK
Di Malaysia, Maintained Load Test (MLT) merupakan kaedah ujian
statik yang paling biasa digunakan ke atas cerucuk konkrit bertetulang manakala Pile
Driving Analyzer (PDA) adalah kaedah ujian dinamik yang paling popular. MLT
mampu memberi maklumat yang tepat mengenai keupayaan maksima cerucuk dan
enapan yang dialami, namun ia melibatkan kos dan masa yang banyak, dan sangat
susah dijalankan. PDA lebih senang dijalankan serta melibatkan kos dan masa yang
kurang, namun keputusan ujian dipengaruhi oleh ketidakpastian dan tafsiran
berkaitan teori “wave stress propagation”. Keputusan ujian bebanan untuk satu
projek pasaraya besar telah dikaji dan dianalisa untuk mendapatkan perbandingan di
antara keputusan MLT dengan PDA. Daripada kajian, didapati keupayaan maksima
cerucuk daripada PDA adalah lebih tinggi berbanding dengan MLT untuk semua
cerucuk yang dianalisa. Bagi perbandingan enapan cerucuk pula, didapati bahawa
keputusan daripada MLT dan PDA adalad tidak tetap. Kajian juga menyokong
kaedah Davisson digunakan untuk mendapatkan keupayaan maksima cerucuk kerana
kaedah ini memberikan hasil yang lebih konservatif berbanding kaedah-kaedah lain.
Keputusan keupayaan maksima cerucuk daripada PDA didapati memuaskan, namun
sedikit pengurangan sebanyak 0.9 atau 10% dicadangkan untuk keputusan PDA .
Untuk program pengujian cerucuk yang bakal dilakukan pada masa hadapan,
terdapat potensi untuk menambahkan bilangan ujian PDA yang dilakukan. Namun,
MLT perlu juga dijalankan pada kadar yang minima untuk mendapatkan kepastian
mengenai parameter and model tanah yang digunakan dalam ujian PDA.
viii
TABLE OF CONTENTS
CHAPTER
TITLE PAGE
DECLARATION ii
DEDICATION iv
ACKNOWLEDGEMENTS v
ABSTRACT vi
ABSTRAK vii
TABLE OF CONTENTS viii
LIST OF TABLES xi
LIST OF FIGURES xii
LIST OF SYMBOLS xiv
LIST OF APPENDICES xvi
1
INTRODUCTION
1
1.1 Background 1
1.2 Problem Statement 3
1.3 Objectives 3
1.4 Scope and Limitations 4
2 LITERATURE REVIEW 5
2.1 Driven Reinforced Concrete (RC) Piles 5
2.2 Maintained Load Test (MLT) 9
2.2.1 Background 9
2.2.2 Equipment and Test Procedure 10
2.2.3 Measurement of Settlement 12
ix
2.3 Pile Driving Analyzer (PDA)
2.3.1 Background
2.3.2 Wave Equation Analysis
2.4 Advantages and Disadvantages of MLT and PDA
13
13
15
20
3 METHODOLOGY 21
3.1 Background
3.2 Data Collection
3.3 Data Analysis and Results
3.4 Summary
21
23
23
24
4 DATA ANALYSIS AND RESULTS 25
4.1 Background of Case Study
4.2 Soil Condition
4.3 Analysis of MLT
4.4 Analysis of PDA
4.5 Comparison of Analysis on MLT and PDA
25
28
29
35
36
5 DISCUSSIONS 39
5.1 Quantitative Evaluation of Results
5.2 Consistency and Pattern of Results
5.2.1 Ultimate Pile Capacity
5.2.2 Pile Settlement
5.3 Reasons and Factors Affecting the Results
5.3.1 Ultimate Pile Capacity
5.3.2 Pile Settlement
5.4 Usage of Coefficient
5.5 Importance of Study and Further Discussions
39
39
41
42
42
42
44
45
46
6 CONCLUSIONS AND RECOMMENDATIONS 49
5.1 Conclusions
5.2 Recommendations
49
50
x
REFERENCES
51
Appendices A - B 53 - 60
xi
LIST OF TABLES
TABLE NO.
TITLE PAGE
2.1
2.2
4.1
4.2
4.3
4.4
4.5
4.6
5.1
Advantages and Disadvantages of RC Piles
Comparison of MLT and PDA in terms of respective
advantages and disadvantages
Details of analyzed piles
Classification of cohesive soils (Bowles, 2006)
Methods of obtaining pile capacity in static load test
Time lapse of pile tests after pile driving
Ultimate pile capacities obtained through MLT and
PDA
Pile settlement based on MLT and PDA
Estimation of coefficient for PDA test results
8
20
27
29
31
37
38
38
40
xii
LIST OF FIGURES
FIGURE NO.
TITLE PAGE
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
3.1
4.1
Driving of RC piles
Set up for pile driving
Typical kentledge arrangement for MLT
Typical arrangement for a Maintained Load Test
(MLT)
Set up for measurement of settlement
Testing of pile using PDA
Wave equation theory set-up and parameters
Strain gauges and accelerometers are fixed to RC
piles during PDA testing
Flow Chart for the study
Typical load settlement graphs for pile load tests
(Tomlinson, 1994)
6
7
11
11
12
14
16
17
22
30
xiii
4.2
4.3
Derivation of ultimate capacity using Brinch
Hansen’s Method
Comparison of ultimate pile capacity by Fellenius
(1980)
33
34
xiv
LIST OF SYMBOLS
A
B
β
c
D
E
F
fcu
i
P
R
R
-
-
-
-
-
-
-
-
-
-
-
-
Cross section Area of the pile
Diameter of pile
Ratio of impedance before and after section
considered
Wave speed
Embedment depth of pile
Modulus of Elasticity of the pile material
Compression force
Compressive strength of concrete at 28 days age
Incident (velocity)
Test load
Soil resistance
Reflected velocity
xv
se
snet
st
v
z
-
-
-
-
-
Elastic settlement of the pile
Net settlement
Total settlement
Velocity
Impedance
xvi
LIST OF APPENDICES
APPENDIX
TITLE PAGE
A
B
Analysis on MLT Results
Pictures on Case Study During
Construction
53
58
CHAPTER 1
INTRODUCTION
1.1 Background
The magnitude of activities involving piling in a country normally
corresponds with the development of that particular country. In Malaysia, piling
activities are currently active all around the country due to the numerous
development projects that are ongoing, funded by both the Government and the
private sector. Types of piles used for these development projects can broadly be
divided into displacement and replacement piles. Driven reinforced concrete (RC)
pile is type of displacement pile that transmits loads from structures into the soil
stratum through shaft friction and end bearing capacity of the pile.
Construction of foundations using RC piles is popular and widespread in
Malaysia, especially for buildings that are of limited height. Construction of driven
RC piles foundation is commonly chosen by developers as it is relatively time saving
with a flexible construction schedule, the RC piles are normally readily available and
construction methodology is straightforward and not complicated.
2
However, if driving is not carried out properly, it will result in piles that have
not adequately set. Set criteria for driven RC piles are pre-determined by calculation
before pile-driving activity begins. If the set criterion for a certain pile is not
achieved, excessive settlement of the particular pile may be encountered and this will
eventually affect the stability and integrity of the supported structure or building.
Given the many uncertainties inherent in the design and construction of piles,
it is difficult to predict with accuracy the performance of a pile. In order to mitigate
and prevent such occurrences, and comprehensive pile-testing program must be
incorporated in every project. Loading tests can be carried out on preliminary piles to
confirm the pile design or on working piles as a proof loading tests. Although pile
load tests add to the cost of foundation, the saving can be substantial in the event that
improvement of to the foundation design can be materialized. Pile tests can generally
be divided into two main categories, which are static and dynamic tests. An example
of static testing is the Maintained Load Test (MLT) while Pile Driving Analyzer
(PDA) is a type of dynamic test.
MLT has been traditionally used to test piles in static condition. Most projects
require a certain number of driven RC piles to be selected and tested by the MLT
method. The MLT test method is well known to be cumbersome due to the test set
and testing process. It is a very costly test method and the long duration required for
testing makes it undesirable. Unfortunately, the MLT is one of the most direct
methods of testing driven RC piles and if procedures are strictly followed, the results
are extremely reliable and the settlement of driven RC piles can be accurately
determined.
Testing using PDA has gained popularity in recent years due to it being
relatively cost-efficient, timesaving and easy to perform. Due to its cost which is
much less compared to MLT, PDA can be performed on more driven RC piles thus
providing a bigger sample of tested piles.
3
However, accuracy of data from PDA testing can sometimes be in doubt due
to the uncertainties in the energy transmitted to the pile during testing and wave
stress propagation theories.
As both of the methods have their own advantages and disadvantages, a
combination of data obtained from MLT and PDA testing is proposed to provide a
clear picture of the driven RC pile bearing capacity and expected settlement.
1.2 Problem Statement
At present, not many comparisons have been made between PDA and MLT
testing for driven RC piles, specifically for cohesive soil in Malaysia. Accurate and
detailed studies showing attempted calibration between PDA and MLT in order to
gauge the effectiveness of PDA is not normally carried out. By comparing the results
of ultimate pile capacity using both PDA and MLT, it is envisaged that eventually,
the number of MLT can be reduced and substituted by conducting more PDA tests
instead. Thus, by comparing the results from PDA and MLT, the Engineer will gain
the confidence and reliability of using numerous PDA with limited MLT tests.
1.3 Objectives
The main objectives of this research are:
a) To determine the most appropriate calculation method for obtaining pile
capacity from MLT.
b) To determine the ultimate capacity of driven RC piles in cohesive soil
utilizing data from MLT and PDA respectively.
4
c) To compare results and data obtained from MLT and PDA. The
correlation is to be used for future testing programs for cohesive soil
whereby the number of MLT can be reduced and replaced with more
PDA tests
1.4 Scope and Limitations
For the purposes of this research, only driven RC piles in cohesive soil will be
considered. This limitation is necessitated by the available data, which involves
driving of RC piles in mainly cohesive soil.
CHAPTER 2
LITERATURE REVIEW
In this chapter, four main sub-topics will be presented. These include
literature review on driven reinforced concrete piles, maintained load test, pile
driving analyzer and the comparison between maintained load test and pile driving
analyzer in terms of their advantages and disadvantages. Information for this chapter
is based on published literature on topics related to this thesis with the relevant
publications listed in the references.
2.1 Driven Reinforced Concrete (RC) Piles
Reinforced concrete (RC) piles are pre-cast members that are driven into the
ground. RC piles are normally produced in a centralized casting yard by independent
pile manufacturers, many of whom posses their own concrete batching plants.
Usually, these manufacturers produce a variety of piles according to different types,
sizes and lengths. In order to be used for a particular construction project, the piles
must meet the requirements of the project Technical Specifications. Client or
Contractors will choose piles from these manufactures taking into account
considerations such as supply, pricing, delivery time and distance from project site,
quality and availability of required sizes/lengths.
6
RC piles usually are manufactured with a square or octagonal cross section,
although RC piles in other shapes can also be produced. Sizes of RC piles in the
market normally range between 250mm to 450mm in diameter and are manufactured
in lengths of 12m to 30m. They are able to carry working axial loads of 450 kN to
3500 kN (Coduto, 2001). However, RC piles of different lengths, cross sections and
capacities from those listed above are also produced depending on the needs and
requirements of construction projects. RC piles are normally driven into the ground
using machinery such as pile drivers equipped with drop hammers, as shown in
Figure 2.1.
Figure 2.1 Driving of RC piles
7
Pre-cast driven RC piles are either made using ordinary reinforcement or may
be pre-stressed. Pre-cast piles made using ordinary reinforcement are designed to
resist bending stresses during loading/unloading and transport to the project site from
the casting yard. They are also designed to resist bending moments from lateral loads
and to provide sufficient resistance to vertical loads and tension forces developed
during driving of the piles. During pile driving, the head of RC piles can be severely
damaged if not adequately protected. Therefore, sufficient cushioning and damping
must be provided in the drop hammer and driving set-up. This normally involves
usage of hammer cushions and pile cushions. A typical set-up of drop hammer and
pile driving is as shown in Figure 2.2.
Figure 2.2 Set up for pile driving
8
Even though driven RC piles are the most popular type of displacement piles
used in the country, there are a few drawbacks that are associated with its use. Some
of the advantages and disadvantages of these piles are listed in Table 2.1.
Table 2.1: Advantages and Disadvantages of RC Piles
Advantages Disadvantages
Material of preformed section can be inspected before driving
Pile section may be damaged during driving
Driven cast-in-place concrete piles are adaptable to variable driving lengths
Founding soil cannot be inspected to confirm the ground conditions as interpreted from the ground investigation data
Installation is generally unaffected by groundwater condition
Ground displacement may cause movement of, or damage to, adjacent piles, structures, slopes or utility installations
Soil disposal is not necessary Piles cannot be easily driven in sites with restricted headroom
Driving records may be correlated with in situ tests or borehole data
Excess pore water pressure may develop during riving resulting in false set of the piles, or negative skin friction on piles upon dissipation of excess pore water pressure
Displacement piles tend to compact granular soils thereby improving bearing capacity and stiffness
Underground obstructions cannot be coped with easily
Cause less ground disturbance
Heavy piling plant may require extensive site preparation to construct a suitable piling platform in sites with poor ground conditions.
9
2.2 Maintained Load Test (MLT)
There are a few methods to carry out static load test on RC piles. These
include MLT, Constant Rate of Penetration (CRP) test and Osterberg load test,
among others. As previously mentioned in Chapter 1, MLT has been traditionally
used to test piles in static condition and is the preferred method of statically testing
piles.
2.2.1 Background
In the design process, geotechnical engineers normally estimate pile capacity
from soil strength estimates obtained from site soil investigations to obtain a
preliminary design length for bidding purposes. Numerous correlations and empirical
correction factors for soil strength were developed for Standard Penetration Test
(SPT), Cone Penetration Test (CPT), or other soil sampling tools.
However, there is generally considerable scatter in strength prediction results
and local experience does not transfer to differing conditions or differing sampling
methods. Numerous prediction events have demonstrated that such predictions are
generally highly inaccurate, particularly in sandy soil conditions where strength is
determined by SPT N-values (Long, 2002). Thus, because of large inherent risk due
to poor prediction accuracy, most code requires a safety factor of around 3 for piles
installed using only a static analysis. In general practice, driven piles are almost
never installed to a depth from a static analysis alone, but the final installation is
governed by blow count determined by dynamic methods or confirmed by a static
load test such as the MLT.
The objectives of pile testing with MLT include the determination of the load
bearing capacity of the driven piles, the settlement and residual settlement of the pile
under load and determination of the stiffness of the soil/pile system in regards to the
10
design load.
The ultimate load of a driven RC pile may range from a few tonnes to more
than a thousand tonnes. As such, the provision of a reaction or load to jack against
requires careful consideration. Normally, a reaction of around 20% more than twice
the working load is provided for testing purposes. The centre of gravity of the
reaction mass must be as near as possible to the pile axis. Particular attention to the
set up and geometry of the pile-reaction arrangement must be emphasised to
minimize interaction between pile-reaction and to avoid any movement of reference
beams.
2.2.2 Equipment and Test Procedure
The most common method of providing the reaction to the pile under test is
by utilising kentledge. Kentledges are specially cast concrete blocks that normally
weight between 2.5 to 5 tonnes each. The load can be symmetrically distributed and
placed with ease over the testing frame, as the blocks are usually equal in weight and
size. Load is applied to the test pile by means of a hydraulic jack.
A normal MLT will consist of 2 loading cycles. During the first cycle, the
pile will be gradually loaded until its proposed working load in step loads. Each step
load is usually about one-fourth of the proposed working load. The step loads are
maintained for a certain period of time (normally 1 hour) until the proposed working
load is achieved whereby the load will be maintained for a longer period (around 8
hours). The process is repeated in reverse and loads are decreased in steps until there
is no load applied to the pile. For the second cycle, the pile is gradually loaded in
steps until 2 times the proposed working load. Once the maximum required load is
achieved, it is held for a period of about 24 hours and then the loads are decreased in
steps.
11
Figure 2.3 Typical kentledge arrangement for MLT
Figure 2.4 Typical arrangement for a Maintained Load Test (MLT)
12
2.2.3 Measurement of Settlement
Dial gauges are used to measure the settlement of the pile under test. These
dial gauges are attached to the reference beams, which are positioned on either side
of the pile. For any load, Q the net pile settlement can be calculated using the
following equation:
snet = st - se (1)
where, snet = net settlement
se = elastic settlement of the pile
st = total settlement
The values of Q can be plotted against the corresponding net settlement in a
graph. The ultimate load bearing capacity of the pile can then be determined from the
plotted graph.
Figure 2.5 Set-up for measurement of settlement
13
2.3 Pile Driving Analyzer (PDA)
2.3.1 Background
Dynamic testing was pioneered by Dr. G.G. Goble and his colleagues at Case
Western Reserve University in Cleveland Ohio and is now a routine pile capacity
evaluation method. Dynamic testing requires measuring pile force and velocity
during hammer impact and subjecting this data to a signal matching analysis to
determine the soil behavior. Extensive correlations between static and dynamic
testing have verified the method’s reliability
PDA is one of the most widely used dynamic test equipment in the market. It
was developed by Pile Dynamics Inc., USA. PDA is used at site to perform the first
stage of interpretation of stresses in real-time. The hardware of the PDA consists of
strain and accelerometer gauges connected to it. It can be regarded as a computer
loaded with software to capture the strains and accelerations measured near the pile
top, which then computes a closed-form solution of the pile-soil-hammer system in
real-time.
To obtain a reliable ultimate capacity from dynamic pile testing, some very
basic guidelines must be followed. The hammer input must produce a minimum set
per blow so that the soil is loaded sufficiently to mobilize the full soil strength. In
cases where the set per blow is very small (e.g. large “blow count”), the dynamic pile
test will activate only a portion of the full soil strength and thus will under predict the
true ultimate capacity, so the result is conservative. The pile capacity of driven piles
often changes with time after installation (usually increases due to “setup”, although
in some cases reduction due to “relaxation” are found). To measure these time
dependent capacity effects, the driven pile should be tested by re-strike after an
appropriate waiting time. Re-strike tests are recommended standard practice for
capacity evaluation by dynamic pile testing (Likins, 2004).
14
Dynamic testing provides other benefits for driven RC piles. Dynamic pile
testing provides valuable additional information on driving stresses, which if too
large can result in pile damage. Pile integrity can be evaluated dynamically for both
location and extent of damage, if any. Proper hammer performance is extremely
important for driven piles because engineers rely on the blow count (or set per blow)
as a driving criteria for pile acceptance, thus implicitly assuming that the hammer is
performing properly.
Figure 2.6 Testing of piles using PDA
By periodical monitoring throughout larger projects it can be assured that the
hammer is performing properly and consistently during the entire project so that the
same initial driving criteria can be used for all piles with confidence. Periodical
testing can check site variability and investigate the cause of piles that are too short
or too long or that have unusual blow count records to determine if the cause is the
hammer or the pile or the soil. According to Likins (2004), guidelines for checking
site variability and periodic hammer verifications are mentioned in certain codes
such as Pile Driving Contractors Code (PDCA).
15
The generally used procedure is to use a drop weight for the impact so that
the drop height and number of blows applied is controlled. A relatively thin plywood
cushion (typically 50 to 100 mm) is placed at the pile top to distribute the loads.
Usually an initial small impact is applied to check the instrumentation and alignment.
Blows with increasing drop height are then applied until either the stresses reach the
strength limits of the pile, or until the set per blow exceeds about 3 mm which
activates the full capacity, or until the result indicates a capacity sufficiently in
excess of the requirements for the project, whichever comes first.
As mentioned by Likins (2004), the recommended drop weight is at least 1%
of the required ultimate capacity to be proved for shafts installed in clay soils or into
rock sockets. For piles with larger expected end bearing contributions, the
recommended percentage increases to at least 2% of the load to be tested.
2.3.2 Wave Equation Analysis
Blows from a drop hammer will create a stress wave on the pile top. This
stress wave travels from the pile top through the pile to the toe. Gauges mounted on
the pile just below the pile top measure the strains and accelerations as the wave
travels down. The pile material and soil surrounding the pile dampen, transmit and
reflect the wave as it travels down the pile. At the pile toe (tip), the stress wave is
reflected back to the top of the pile. As the wave makes it way to the top, the gauges
measure the strains and accelerations due to the returning wave.
16
Figure 2.7 Wave equation theory set-up and parameters
17
As the stiffness of the pile is known, the force can be calculated from the
strain measurements. The accelerations can be integrated over time to yield the
velocity of the waves. The force and velocity measurements are the principal data
used in the PDA to compute the unknown soil resistance. By examining the force and
velocity trace, a diagnosis of the characteristics of the pile-soil-hammer system can
be made and abnormalities in pile driving can be detected. In most PDA applications,
the hammer is not instrumented and only the pile-soil system is considered and
analysed.
Figure 2.8 Strain gauges and accelerometers are fixed to RC piles
during PDA testing
18
Current PDA testing method is based on a one-dimensional wave propagation
theory. For a stress wave travelling down a pile due to a hammer impact on the pile
top, the compression force and velocity are related by the following equation:
F = Zv (2)
Z = EA/c (3)
where, F = compression force
Z = impedance
v = velocity
E = Young’s Modulus
A = cross-section area
c = wave speed
For a given material, E, A and c are constants. As the wave travels down the
pile, any change in the pile impedance such as changes in cross-section area, splices
or defects will cause the wave to be reflected. The governing equations for the force
and velocity transmitted and reflected at points of impedance change are given by:
Ft = 2Fi / (1+β) (4)
Fr = Fi / (1-β) / (1+β) (5)
vt = vi2β / (1+β) (6)
vr = vi(β-1) / (1+β) (7)
where, i = incident
t = transmitted
r = reflected
β = ratio of impedance before and after section considered
19
In addition to changes in the pile impedance, the soil resistance along the pile
will also affect the wave propagation. Part of the incident wave will be reflected due
to the soil resistance. The governing equations for the force and velocity transmitted
and reflected due to soil resistance are as follows:
Ft = -R/2 (8)
Fr = R/2 (9)
vt = vr = -R / (2Z) (10)
where, R = soil resistance
The force or velocity trace at the pile top due to a hammer blow therefore can
be analytically computed by applying the equations to a discrete finite element model
of the pile-soil-hammer system and solving it in the time domain. The wave input
can be either the measured force or velocity. By suitably adjusting the soil model, the
computed force or velocity trace can be made to match the actual measured value.
Once this is achieved, the soil model is said to be represent the actual soil
condition. The resulting soil model then provides the required information on the soil
resistance and its distribution along the pile length. The pile model usually is a
known input, except where it is required to determine unknown defects in the piles.
20
2.4 Advantages and Disadvantages of MLT and PDA
Table 2.2: Comparison of MLT and PDA in terms of respective advantages and
disadvantages
Test Type Reaction
System
Maximum
Test Load
Advantages Disadvantages
Maintained Load Test
(MLT)
Kentledge Normally around. 3000 kN
(300 tonnes).
Higher test loads are possible.
Suits all soil conditions and pile types. Manual and automated systems available. Piles can
be instrumented. Tension and lateral
testing possible. Very high test loads
achievable.
Kentledge tests are relatively
expensive. Setting up and
dismantling the test equipment
involves operatives
working at height. Long duration. Kentledge and
frame are required
Pile Driving
Analyzer (PDA)
Piling hammer
or separate
drop weight
3000 kN (generally, but can be greater).
Hammer weight
should be in the range 1
to 2% of load
Fast and relatively inexpensive.
Suitable for both driven and bored piles. Correlation with static tests on
bored piles generally good.
May require calibration with
static test. Results may be
unrepresentative in soils that
exhibit relaxation. Correlation of dynamic and
static results on piles in cohesive soils and chalk must consider time-related
effects and the length of pile
tested.
CHAPTER 3
METHODOLOGY
3.1 Background
The study was conducted based on data from a single project site.
Description on the project will be presented in Chapter 4. The data were grouped in
static and dynamic test results. Analysis of the different data was carried out
separately.
High strain dynamic test and CAPWAP analysis results from the each of the
data were reviewed in terms of shaft distribution and pile load-settlement. Similarly
the same procedures were employed to MLT results. The output of the PDA results
and CAPWAP analysis, and MLT analysis were compared to obtain a relationship.
The results were compared based on ultimate pile bearing capacity and settlement.
Discussions on the obtained results are presented and conclusions made based on the
results. Finally, recommendations are provided.
22
The methodology of the study is as presented in Figure 3.1 below.
Figure 3.1 Flow Chart for the study
Data from PDA and pile dr iving records
Data from MLT and pile dr iving records
Dr iven RC Piles
Pile Load - Settlement Pile Load - Settlement
Shaft Distr ibution Shaft Distr ibution
Ultimate Pile Bear ing Capacity
Compar ison and Discussions
Conclusions & Recommendations
Stage 1 – Data Collection
Stage 2 – Data Analysis & Results
Stage 3 - Summary
23
3.2 Data Collection
The first stage of this study included identification of an appropriate
construction project. The data required was from driven RC piles that were tested
both by MLT and PDA. The results were made sure to be complete for comparison
purposes.
There were many data obtained but data that contained only a particular test
method, either MLT or PDA alone were rejected during this stage of study
3.3 Data Analysis and Results
The second stage of this study was to analysis the data that was obtained from
the construction site. Based on the raw data, pile load vs. settlement data were
tabulated and subsequently plotted.
The PDA data were also analyzed based on shaft distribution. The shaft
distribution was obtained from results of CAPWAP analysis. These results were
tabulated for easier presentation. The percentage of shaft distribution through the
length of the pile in regards to the total capacity obtained was observed.
In the MLT tests, certain pile capacities were obtained. The same also
applies to PDA tests whereby capacities of piles were also obtained. Both the
capacities were compared available methods and plotted to get a comparison for all
of the analyzed piles.
24
3.4 Summary
The third and final stage of the study was to draw a conclusion based on the
results of the analysis. It is understood that from previous studies there has been
good correlations and comparisons between dynamic test and static load test results.
The result that was derived from the analysis were carefully studied based on
the objectives. The closeness and the deviation between the results obtained were
checked.
Reasons and factors that influence test results were identified and presented.
Recommendations were included to for use during future pile load testing programs
and for further research works on similar subjects.
CHAPTER 4
DATA ANALYSIS AND RESULTS
Raw data in various forms and sources were organized and compiled, as
previously mentioned in Chapter 3. Subsequently, analysis was carried out on all of these
data in order to obtain results and findings. Analyzed data was only from the case study.
In the following chapter, the results are presented in paragraph and tabular formats.
4.1 Background of Case Study
The area of interest (case study) that was researched was a hypermarket
development project in Bandar Kinrara, Puchong, Selangor Darul Ehsan. The
hypermarket development project covers an area of approximately 7.98 acres. The
hypermarket project development area is mostly of cut formation and its elevation is
higher than the surroundings.
Construction of this hypermarket was necessitated due to the amount of people
residing in nearby areas and the purchasing power of local residents, especially residents
of the affluent Bandar Kinrara.
Recognizing this potential, the managing company of the hypermarket chain
decided to construct a two and half storey building, and not just a typical single storey
building to house the hypermarket and other tenants. In addition, the managing company
was also determined to provide numerous facilities and amenities such as the power cart
system that is not normally found in most hypermarkets.
Due to this, loading from the structural and architectural components as well as
mechanical and electrical (M&E) equipment was significant. Type and capacity of piles,
pile groups and the piling layout was designed taking into consideration the huge loading
requirements of the project. At locations with heavy loading such as the water tank area,
pile groups of up to 6P-350 (6 numbers of 350mm x 350mm RC piles) were required.
Dimension of the pile cap for the 6P-350 pile group was 2850mm x 1800mm x 1800mm
(height).
Piling was carried out using driven RC piles and all of these piles were driven
until set. A set criterion was pre-determined before commencement of piling activity by
means of calculation using Hiley’s Formula. The set criteria used was a maximum of
25mm settlement for 10 blows by the hammer (25mm/10 blows) and this set criteria was
the same for all pile sizes. Sizes of piles used for the project were 250mm x 250mm,
300mm x 300mm and 350mm x 350mm. There were approximately 998 piling points for
the whole development. Piling was carried out using 7-tonne hydraulic hammers with
drop heights of 300mm, 400mm and 600mm for the different pile sizes. A total of five
numbers of driven RC piles were analyzed for the purposes of this study. Details of the
analyzed piles are given in Table 4.1.
Table 4.1: Details of analyzed piles
Gr idline/Pil
e ReferencePile Size (mm)
Height of Drop
Hammer (mm)
Pile Penetration
(m)
14/B 300 x 300 400 18.2
12/C 350 x 350 600 17.4
1/H 350 x 350 600 18.6
8/P 300 x 300 400 14.7
17/H 250 x 250 300 16.8
Note: Gridlines set by project Architect. Gridlines used as convention to identify piles
During piling, all of the 998 piles points that were driven into the ground were
identified to have fulfilled the set criteria, as shown in the relevant piling records. Upon
completion of the piling activity, a testing program was specified by the Engineer to
identify the capacities, condition and integrity of the driven piles and also to determine
the magnitude of further settlement of the driven piles under working and test loads.
The testing program for the driven piles consisted of both static and dynamic test
methods. MLT was chosen for the static load test and dynamic testing was carried out
using PDA. For the data analysis, the number of piles studied and analyzed was limited to
five. All in all, testing by MLT was carried out on six piles and PDA was carried out on
thirty piles. Only five piles were studied due to the restrictions of available data to be
analyzed, as tests on most other piles were carried out by either static or dynamic means
only, and not by both methods.
4.2 Soil Condition
For the soil investigation (SI) program, a total of twelve boreholes were carried
out. These boreholes were evenly spaced out and distances between boreholes were
limited to less than 50 meters to maximize data and knowledge of the sub-soil condition.
Sub-surface exploration was carried out using a multi-speed wash boring rig. Standard
Penetration Test (SPT) was carried out at 1.5m intervals until the termination of the
borehole. Termination was determined by either achieving seven consecutive SPT - N
values of 50 or by coring through 2m of rock.
Disturbed soil samples were extruded from the split-spoon sampler. Undisturbed
samples were obtained by jacking thin-walled tubes into soft cohesive layers and mazier
sampler used for stiffer soil layers (SPT – N values more than 15). Measurement of
groundwater table was carried out in the borehole using standpipes.
Data from the boreholes were analyzed and a soil profile for the development was
subsequently created from the results of the analysis. As shown in Table 4.1 above, the
penetration depths of the driven piles are between 14m to 19m from the ground level.
Analysis results from the soil profile show that the soil layers corresponding to the pile
penetration depths mainly consist of cohesive soils. There are only traces of cohesionless
soil such as sandy soils and gravel in a limited number of boreholes. Majority content of
soil layers corresponding to pile penetration depths were observed to be silt and clay.
According to Bowles (1996), cohesive soils can be classified according to the
SPT – N values. This classification is as shown in Table 4.2 below. Generally, the SPT –
N values for soil layers corresponding to pile penetration depths were observed to range
between 11 and 50. Based on the system of classification by Bowles (2006), the soil
strata for the analyzed pile locations in the case study is mainly made up of stiff, very
stiff and hard cohesive soils.
Table 4.2: Classification of cohesive soils (Bowles, 2006)
SPT – N values (range) Consistency
0-2 Very soft
3-5 Soft
6-9 Medium
10-16 Stiff
17-30 Very stiff
>30 Hard
4.3 Analysis of MLT
Data obtained from the MLT tests included loads imposed upon by the kentledge
system and the settlement of the tested pile due to the corresponding loads. Applied loads
were measured in units of tons and later converted to kilo Newton (kN) to be used for
calculation purposes. Settlement was measured in millimeter (mm). Data from MLT tests
on the five analyzed piles were plotted on load vs. settlement graphs.
Tomlinson (1994) had plotted many load vs. settlement graphs for different soil
conditions, including cohesive soils, and varying types of piles. Figure 4.1 illustrates
some of these graphs.
Figure 4.1 Typical load settlement graphs for pile load tests
(Tomlinson, 1994)
From the case study, a separate graph was plotted for each of the analyzed pile.
Further analysis was carried out on the graphs to obtain the ultimate pile capacity for
each of the five analyzed piles. Calculations for the settlement of the tested piles were not
required as pile settlement under loading and residual settlement is readily available from
the MLT test reports. However, a review of the test reports was carried out and the
settlement values stated in these reports were checked. Based on the review results, the
settlement values were accurately reported. This conclusion was made after comparing
the settlement values to the actual field records attached together with the reports, which
was verified by the Engineer’s representative.
According to Fellenius (1980), there are various methods of interpretation
proposed by many authors to obtain ultimate pile capacity from load-deformation curves
in a static load test. Some of these methods are listed in Table 4.3, based on explanations
by Murugan (2006).
Table 4.3: Methods of obtaining pile capacity in static load test
Author(s) and Year Explanation on Method
Davisson (1972) Obtain the load corresponding to the movement,
which exceeds the elastic compression of the pile by
a value of 4mm plus a factor equal to the diameter of
the pile divided by 120. This method was developed
in conjunction with the wave equation analysis.
Fuller and Hoy (1970) Proposed a simple definition that the failure load is
equal to the test load for where the load movement
curve is sloping 0.14mm/kN. This method penalizes
long piles because the larger elastic movements
occurring for a long pile, as opposed to the short pile,
causes the slope 0.14mm/kN to occur sooner.
It can be summarized that the load vs. settlement graphs is the basis for all of the
various methods of determining ultimate pile capacity. Each author used the basic form
of the graph and devised their own method of calculation. An example of this is the
Brinch Hansen’ Method, which is also based on the load vs. settlement graph. The plot
for this method is shown in Figure 4.2.
Figure 4.2 Derivation of ultimate capacity using Brinch Hansen’s Method
Figure 4.3 Comparison of ultimate pile capacity by Fellenius (1980)
According to Coduto (2001), the Davisson’s method is one of the most popular
methods used for analysis of static load tests. The Davisson’s method produces
conservative results, especially if slow MLT is carried out. It also takes into account the
elastic compression of a pile that has no side friction.
Derivation of ultimate pile capacity using Davisson’s method can be given as the
following, Coduto (2001):
4mm + B/120 + PD/AE (1)
and
E = 4700 √fcu (2)
Where, B = diameter of pile
P = test load
D = embedment depth of pile
A = cross section area of pile
E = modulus of pile material
fcu = compressive strength of concrete at 28 days age
The Davisson’s method was selected for the analysis of ultimate pile capacity for
the case study as it produces the most conservative results. Calculation using the
Davisson’s method is also straightforward and is not complicated. This was an important
factor to consider as five graphs were plotted; one graph for each of the analyzed piles in
the case study.
4.4 Analysis of PDA
During dynamic pile testing, PDA provided peak pile forces, which was
converted to pile stresses, under each strike of hammer impact. Analysis of these pile
force measurements indicated that there were no significant damage to the piles during
testing.
Case Pile Wave Analysis Program (CAPWAP) software was used for the analysis
of data from PDA field tests. Through CAPWAP, the pile mobilized capacity, skin
friction, end bearing and settlement data at working and test loads were obtained.
According to Murugan (2006), pile capacity obtained from the CAPWAP analysis
on the PDA test results is considered to be fully mobilized if the net set of 3mm is
achieved at the time of testing. Based on this criteria, it was analyzed that all of the five
piles in the case study had achieved the mobilized capacity and the required test load at
the time of testing.
During the analysis using CAPWAP, adjustments and reasonable judgments had
to be made for certain parameters involved in the calculations. These parameters include
the soil resistance distribution, quake and damping factors. Consistent adjustments of the
soil models used had to be made in order to achieve the best fit with the prevailing
ground conditions for each of the five analyzed piles.
4.5 Compar ison of Analysis on MLT and PDA
According to Das (2004), the time lapse of testing after end of driving for piles is
stated as EOD. For the case study, the EOD for both MLT and PDA for all five analyzed
piles are presented in Table 4.4.
The time lapse (waiting period) between pile driving and testing enables soil set-
up around the driven piles. The longer the time interval, it is expected that the shaft
friction contribution would be larger towards the pile capacity (Murugan, 2006). From
the analysis, the above was confirmed as shaft friction contribution in piles 17/H, 8/P and
12/C were significant, mostly due to the wider time interval between pile driving and
testing. For pile 1/H, the shaft contribution was analyzed as only 42% and the time
interval between driving and testing was only 6 days.
Table 4.4: Time lapse of pile tests after pile driving
MLT PDA
Time Lap se Time Lapse Shaft Fr icti
on (k
N) % of Pi
le Capaci
14 /B 5 da ys17 da ys 10 99
12 /C 6 da ys19 da ys 16 38
1 /H 12 da ys6 da ys 11 58
8 /P 17 da ys19 da ys 12 46
17 /H 25 da ys27 da ys 17 66
After completion of the analysis on MLT and PDA tests data, it was observed th
at there is a variation between results for settlement and ultimate pile capacity derived fo
rm these two different testing methods. While the results for ultimate pile capacity w
as consistent, the results for settlement was not consisten
t
Analysis results for ultimate pile capacities are presented in Table 4.5 below. It is
observed that for all analyzed piles, the ultimate pile capacity derived from the PDA
testing method is higher compared to capacity derived through MLT testing. The
consistency of results based on the analysis can be deemed satisfactory.
Table 4.5: Ultimate pile capacities obtained through MLT and PDA
Pile Capacity (kN)
(kN)
ML T PDA
1850 2011
260 0 277 6
255 0 277 6
1800 2070
/
H
1690 2011 However, analysis results from the static and dynamic tests for p
ile settlement does not indicate consistency. In fact, it was observed there is no clear patt
ern of results in terms of settlement measured by MLT and PDA. For piles 12/C, 1/
H and 8/P pile settlement from PDA showed higher values compared to values derive
d through MLT. For piles 14/B and 17/H, pile settlement from MLT was higher compared
to settlement derived through PDA. Settlement results of the five piles obtained throug
h both methods are listed
Table 4.6: Pile settlement based on MLT and PDA
on MLT and PDA
ettl emen
m)
PDA 1 4/B20 0 1
13 12/C2 80
5 13 1/H2 80
9 22 8/P2 00
0
.
70 17 17/H140 9.66 7 Discussions and interpretation of results obtai
om the analysis are presen
CHAPTER 5
DISCUSSIONS
In Chapter 4, results obtained from the analysis of data were presented in
paragraph and tabular formats. In this chapter, the results are discussed and commented
upon in terms of:
1) Quantitative values (higher, lower, etc.)
2) Explanation and interpretation of the results
3) Reasons and factors affecting the results
5.1 Quantitative Evaluation of Results
Results of the analysis carried out for pile ultimate capacity using both MLT and
PDA was presented in Table 4.5. Subsequently, results of pile settlement calculated
based on MLT and PDA methods were presented in Table 4.6.
The difference in ultimate pile capacities obtained from these two methods is
shown in Table 5.1.
Table 5.1: Difference between pile ultimate capacity through MLT and PDA
Pile Capacity (kN)
(kN)
14/B 1850 2011 161
12/C 2600 2776 176
1/H 2550 2776 176
8/P 1800 2070 270
17/H 1690 2011 321
Mean = 221
Generally, analysis of available data showed that ultimate pile capacity derived
from PDA testing is higher when compared to the ultimate pile capacity derived from
MLT using the Davisson’s method. The highest difference calculated was 321 kN for pile
17/H. Dimension of this pile is 250mm x 250mm and its design working load is 700 kN.
Therefore, the variation of ultimate pile capacity amounts to approximately 46% of the
design working load for that particular pile. The mean difference for all five analyzed
piles between the two testing methods was calculated to be 221 kN or approximately 22.5
tonnes.
In terms of pile settlement, the difference observed from both testing methods is
as shown in Table 5.2.
Table 5.2: Difference in pile settlement based on MLT and PDA
ed on MLT and PD A
MLT PDA 14 /B200
71 13 -3. 71 12 /C28
.25 13 1 .75 1 /H28
.49 22 7 .51 8 /P20
.70 1 7 6. 30 17/H1
9.66 7 -2.66 Note: “+” sign denotes settlement calculated by PDA is high
ile “-“ denotes that settlement calculated by PDA is lo
w
e
r than by MLT From Table 5.2, it is shown that for the majority of analyzed p
les, settlement derived by PDA is higher than the settlement values derived from MLT.
The difference in values of pile settlement calculated by PDA compared to MLT rang
es from between 1.75mm to 7.51mm. However, for two of the analyzed piles, results of
pile settlement from PDA were lower than the results from MLT. Overall, settlement of
piles obtained from both methods were within the tolerances allowed by the Project
Specifications, which is a maximum settlement of 25mm when tested at the Test Load
(twice
Working Load).5.2 Consistency and Pat
tern of Results5.2.1 Ultimate P
ile Capacity In terms of consistency, the results for comparison of ultimat
e pile capacity derived from both MLT and PDA methods were satisfactory. It was obser
ved that in all cases of analysis, the values obtained through PDA were higher than v
alues from MLT. There was a variation in the percentage of difference between resul
ts from PDA and MLT for each analyzed pile, when compared to
t
As an example, the test load for pile 14/B is 1962 kN (200 tonnes) therefore the
percentage of difference is 8% whereas for pile 17/H the test load is 1373 kN (140
tonnes) and the percentage of difference is 23%. However, the variation in difference is
not an important factor in analyzing the piles and therefore it was not considered in the
analysis and presentation of results. In summary, results for analysis of ultimate pile
capacity were observed to be consistent and were satisfactory, without any significant
deviations.
5.2.2 Pile Settlement
Unlike the analysis for ultimate pile capacity, results of pile settlement obtained
from both PDA and MLT were not consistent and did not display a clear pattern. Due to
this, it was not possible to produce a coefficient or correlation for predicting settlement
based on results of the analysis. When only PDA is used in a testing program, the
accuracy of pile settlement obtained is perpetually in doubt. Therefore, MLT must also
be carried out in any testing program in order for calibration and checking to be carried
out on values of pile settlement from PDA.
5.3 Reasons and Factors Affecting the Results
5.3.1 Ultimate Pile Capacity
Analysis of PDA tests carried out on five samples of piles had yielded higher
values of ultimate pile capacity when compared with analysis results from MLT. As
MLT is acknowledged to be one of the most reliable and accurate pile load testing
methods, identification of factors affecting the results of this study is concentrated on
analysis carried out for PDA. Two main factors that may have brought about this set of
results are the parameters and soil model used in the CAPWAP analysis.
In CAPWAP analysis, the software will iteratively modify the soil model until a
“best-fit” match is obtained. Then, a test engineer will use his knowledge and judgment
to manually fine-tune the soil model parameters until he is satisfied that an acceptable
and reasonable result is obtained (Sam, 2006). Therefore, the accuracy of test results are
subjective and depend to a large extend on the competency of the personnel conducting
the testing at site and carrying out the software analysis in the office.
Besides this, the method of conducting PDA tests itself may influence the results
of the analysis. In most cases, in order to obtain a proper soil model and parameters, a
particular pile under test is struck several times by the hydraulic drop hammer. This
process will be repeated until the tester is satisfied with the results. Sometimes, even
before the tester fine tunes the soil model parameters, the operator of the crane will strike
the pile under test a few times in order to achieve the required drop height. The dynamic
force repeatedly being transmitted to the pile prior and during testing will affect the
accuracy and results of PDA analysis.
According to Fleming et al. (1994), capacity of a driven pile increases with time
following installation, especially in cohesive soils such as clay and silt. This is due to set-
up, attributed to dissipation of excess pore water pressure generated during installation.
Excess pore water pressure generated during pile driving will influence the values of pile
capacity during testing. The excess pore water pressure will dissipate over time, which
will result in greater pile capacity (Das, 2004). . For nearly all analyzed piles, there was a
larger time interval between piling and testing by PDA, when compared to testing by
MLT. Higher ultimate pile capacity values from PDA may to some extend be attributed
to this factor.
When piles are driven into soft clay, a zone surrounding the clay becomes
remolded or compressed. This results in a reduction of undrained shear strength. With
time, the loss of undrained shear strength is partially or fully regained (Das, 2004). In
addition to this, thixotropic effect (hardening of disturbed cohesive soil layers) and
consolidation will increase pile capacity with advancement of time. These factors are
important in analyzing the higher results obtained through pile testing by PDA method.
However, it must also be noted that the Davisson’s method was used for the
analysis of MLT results. As previously mentioned in Chapter 4, the ultimate pile
capacities derived from the Davisson’s method is more conservative and less than
ultimate pile capacity values derived from other methods. Davisson’s method was
selected for this study as it provides a higher degree of safety as it assumes lower
capacities of piles compared with other methods. In this connection, the lower values of
ultimate pile capacity obtained through analysis of MLT are significantly affected by the
application of Davisson’s method. Most probably, if another method was applied, the
difference between ultimate pile capacity from PDA and MLT would not be as high. It is
also possible that for some of the analyzed piles, the values obtained from MLT might
even be higher compared to values from PDA, if other calculation methods were used.
Further studies should be carried out to examine this hypothesis.
5.3.2 Pile Settlement
For pile settlement, the results of analysis were inconsistent. The inconsistency
may be due to testing of piles being carried out without sufficient time interval between
driving and testing. According to Bowles (1996), piles in cohesive soils should be tested
after sufficient lapse for excess pore water pressures to dissipate.
Derivation of pile settlement under controlled loading through MLT is accepted
to be accurate. This condition is true if the test set-up, especially the monitoring frame
(reference beam) is properly installed and is kept free from disturbances. Dial gauges
must also be calibrated prior to use and protected from vibration, movement or shock.
For all of the analyzed piles, the above conditions were practiced during testing, as
verified by the Engineer’s Representative. Therefore, it is safe to deduce that the
settlement results obtained from MLT are accurate.
In view of the above, the inconsistency of results and the difference of pile
settlement values are brought about by the PDA analysis. As previously mentioned in
Section 5.3.1, soil model parameters, competency of tester and disturbance to pile by
application of dynamic force will also result in discrepancies in pile settlement values.
5.4 Usage of Coefficient
A comparison of results of ultimate pile capacity by PDA and MLT methods can
be categorized as shown in Table 5.1. The column for Coefficient / Reduction Factor is
derived by dividing the values from MLT with the ultimate pile capacity values obtained
from PDA.
Table 5.1: Estimation of coefficient for PDA test results
Pile Capacity (kN)
MLT P DA DA DA
1 4/B1 850 2 011 0
12/C 2600 2776
1/H 2550 2776
8/P1 800 2 070 0.87
7/H1690 201
0.84 Mean = 0.90 From Table 5.1, an average coefficient or reduc
n factor of 0.9 is obtained. Therefore, test results for ultimate pile capacity de
rived from PDA tests, may be multiplied by the value of 0.9 or a reduction of 10% applie
d, if piling and testing are carried out in similar conditions to the case study.
However, there are numerous limitations to the application of the coefficient due to
the huge number of variables involved in load tests and due t
o
differing site conditions.5.5 Impor tance of S
t
u
dy and Fur ther Discussions According to Likins (2004), after correlating stati
and dynamic tests, the Pile Driving Contractors Association (PDCA) code allows substit
ution of three dynamic tests for one static test, in determining the quantity of further test
ing. Thus, with at least one successful correlation, the PDCA suggests that 5% static te
sting can be translated into testing 15% of the piles dynamically, for the same suggested g
lobal safety factor of 1.65. It is probably implicitly assumed that the large number of test
s allows site variability to be properly assessed and hammer performance to be evalu
ated periodically thro
u
g
The PDA is a very useful tool in evaluating the ability of pile driving equipment
to install piles to the desired depth without damage. It can be used to show the variability
of likely pile capacity across the site by using the PDA on several test piles installed
across the site. It can be calibrated to be more site specific by calculating input factors
from static compressive load tests, such as the MLT.
Once the output data correlates with the load test results, confidence can be
gained in other PDA predictions. It can be used to change the length of piles when test
results indicate a savings can be made. This is usually of value on large projects when a
small reduction in pile length can result in big savings because of the large number of
piles driven.
The PDA is perceived as less costly than a traditional static load test such as the
MLT. A value analysis should be performed on the net savings when longer or more piles
are used. The value in PDA testing is in the ability to test a large number of piles instead
of just a few, as in the case of MLT. The variability in load capacity across a site can be
evaluated with the goal of lowering the safety factor used for the project.
An important point to consider in pile load test program is that piles are normally
designed to be in pile groups. Regardless of how individual pile capacity is analysed,
piles are usually in groups. Therefore, a significant amount of research must be carried
out to analyse ultimate pile capacities and settlement in pile groups when tested using
both MLT and PDA.
This study has successfully analysed driven RC piles in cohesive soils and
presented the results, also providing interpretation and discussions on these results. It can
be summarized that the number of tests involving PDA in a testing program should be
increased to obtain a bigger sampling proportion. From the study, a coefficient or
reduction factor was calculated. A similar coefficient or factor should be applied to PDA
results for future projects due to the numerous variables that are involved in PDA tests.
The magnitude of the coefficient or reduction factor will depend on many contributing
points such as type of soil, site condition, parameters that are used, among other
considerations. MLT should be carried out in order to calibrate the PDA tests. However,
the number of MLT should be limited due to its many constraints.
CHAPTER 6
CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions
In this study, an attempt was undertaken to compare the ultimate bearing capacity
results derived from MLT and PDA tests. The comparison was carried out based on data
obtained for the piling and load test programs carried out for a hypermarket development
in Puchong, Selangor Darul Ehsan. Findings of the study were presented in Chapter 4 and
discussions on the findings were made in Chapter 5.
In summary, the following conclusions can be made based of results of the study:
1) In terms of ultimate pile bearing capacity, results from the analysis were observed
to be consistent and there was a clear pattern in terms of the method of testing that
provided higher values. It was observed that ultimate pile bearing capacity
obtained from PDA were higher than results derived from MLT, for all analyzed
piles;
2) For pile settlement, there was no clear pattern or consistency in results derived
from both testing methods. In some cases, it was observed that settlement shown
in PDA results were higher, while in other cases settlement results in MLT were
higher;
3) A coefficient of 0.9 or 10% reduction was obtained from the study to be applied to
results from PDA tests. However, there are numerous limitations to the
application of the coefficient due to the huge number of variables involved in load
tests and due to differing site conditions;
4) Even though the number of MLT tests may be reduced and substituted with more
PDA tests, a limited number of MLT must still be carried out in order to gauge
the accuracy and consistency of PDA test results. MLT also provides more
conservative results, which can be used for design purposes if testing is carried
out on test piles and not working piles.
5.2 Recommendations
From this study, a few recommendations can be made, as listed below:
1) Increase the number of PDA tests in a pile load-testing program in order to
achieve a greater sampling ratio for driven piles. It is more practical to increase
the number of PDA instead of MLT due to considerations involving cost, time
and effort;
2) A coefficient or a reduction in terms of percentage is recommended to be applied
to results of ultimate pile bearing capacity obtained from PDA;
3) Further research must be carried out to analyze ultimate pile capacities and
settlement in pile groups when tested using both MLT and PDA;
4) Further research is suggested to test the applicability of the coefficient derived
from this study in other areas/locations, with mainly cohesive soil and using only
driven RC piles.
51
REFERENCES
Aarsleff Piling, et al. (2006). Handbook on Pile Load Testing. Kent, England.
Federation of Piling Specialist.
Atkinson, J. (1993). An Introduction to the Mechanics of Soils and Foundations:
Through Critical State Soil Mechanics. Berkshire, England. McGraw – Hill.
pp. 74-86.
Bowles, J.E. (1996). Foundation Analysis and Design – 5th Edition. Illinois,
USA. McGraw – Hill.
Craig, R.F. (2001). Soil Mechanics – 6th Edition. London, UK. Spon Press.
Cudoto, D.P. (2001). Foundation Design: Principles and Practices – 2nd Edition.
New Jersey, USA. Prentice Hall.
Das, B.M. (2004). Principles of Foundation Engineering – 5th Edition.
California, USA. Brooks/Cole-Thomson Learning.
England, M. (1992). Pile Settlement Behaviour: An Accurate Model. Proceedings
of the Fourth International Conference on the Application of Stress Wave
Theory to Piles. The Hague, Netherlands. pp. 91
52
Fleming, W.K., Weltman, A.J., Randolph, M.F., Elson W.V. (1994). Piling
Engineering – 2nd Edition. Glasgow. UK. Blackie Academic & Professional.
Geotechnical Engineering Office (2006). Foundation Design and Construction.
Kowloon, Hong Kong. Civil Engineering and Development Department,
Government of Hong Kong. pp. 264-292
Gravare, C.J., Hermansson, I., Svensson, T. (1992). Dynamic Testing on Piles in
Cohesive Soil. Proceedings of the Fourth International Conference on the
Application of Stress Wave Theory to Piles. The Hague, Netherlands. pp.
409-411.
Sam, M.T. (2006). Understanding Dynamic Pile Testing and Driveability.
Petaling Jaya, Malaysia. Monthly Bulletin of the Institution of Engineers,
Malaysia. pp. 8-15.
Wakiya, Y., Hashimoto, O., Fukuwaka, M., Oki, T., Shinomiya, H., Ozeki, F.
(1992). Ability of Dynamic Testing and Evaluation of Bearing Capacity
Recovery from Excess Pore Pressure Measured in the Field. Proceedings of
the Fourth International Conference on the Application of Stress Wave
Theory to Piles. The Hague, Netherlands. pp. 665-670.
53
APPENDIX A
Pile 14/B
0
50
100
150
200
250
0 5 10 15 20
Settlement (mm)
Lo
ad
(T
on
s)
54
Pile 1/H
0
50
100
150
200
250
300
0 5 10 15 20
Settlement (mm)
Lo
ad
(T
on
s)
55
Pile 8/P
0
50
100
150
200
250
0 2 4 6 8 10 12
Settlement (mm)
Lo
ad
(T
on
s)
56
Pile 12/C
0
50
100
150
200
250
300
0 2 4 6 8 10 12
Settlement (mm)
Lo
ad
(T
on
s)
57
Pile 17/H
0
20
40
60
80
100
120
140
160
0 2 4 6 8 10 12
Settlement (mm)
Lo
ad
(T
on
s)
58
APPENDIX B
Pictures on Case Study Dur ing Construction
Driving of RC piles using 7 tonne hydraulic hammer
59
Piling being carried out according to gridlines
Jointing of RC piles by welding
60
Kentledge arrangement that was used for MLT
Instrumentation used for the MLT