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