load resistance behaviour and installation assessment of driven

LOAD RESISTANCE BEHAVIOUR AND INSTALLATION ASSESSMENT OF DRIVEN SPUN PILE

VIGNESHWARAN KARUNANIDEE

UNIVERSITI TEKNOLOGI MALAYSIA

LOAD RESISTANCE BEHAVIOUR AND INSTALLATION ASSESSMENT

OF DRIVEN SPUN PILE

VIGNESHWARAN KARUNANIDEE

A Project Report Submitted as a Partial Fulfilment of The

Requirement For The Award of The Degree of Master of

Engineering (Civil-Geotechnics)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

APRIL 2010

iii

Dedicated to the late Mr.Subramaniam, beloved brother who shared my every

moment of joy and sorrow

iv

ACKNOWLEDGEMENT

I would like to extend my utmost gratitude to my parents, whose sacrifice and

love have made me who I am today. I’m grateful to have been given a chance to

acquire proper education by them despite difficulties. Many thanks to my siblings

and dear friends, who tirelessly supported and gave encouragement through-out this

period. Ultimately, this is a special dedication to my late brother, who always

believed in me and prayed for my success, thus moulded the person I have become.

May his soul rest in peace!

I express my sincerest thanks to Ir.Narayanan Ramasamy who taught me well

and contributed so much, for me to become a person who am I now. Deepest thanks

also to Geopave Consultants Sdn Bhd for lending their support and sponsoring this

study. Not forgetting my entire working colleague for extending their help in various

forms.

My deepest appreciation to Professor Dr. Khairul Anuar Kassim for his

advices, guidance, valuable comments and all the precious time spent in the

preparation of this project paper. I would also like to thank my fellow postgraduate

course mates for their help, who constantly shared their ideas in this study. Finally,

thanks to all who have contributed directly or indirectly in completing project paper.

Thank you so much.

v

ABSTRACT

Three (3) numbers of fully instrumented with global strain gauges and

extensometer test Spun piles, namely PILE-A, PILE-B and PILE-C were installed

using 25Ton hydraulic hammer along the coastal area which represent various

subsoil conditions based on soil investigations. The static load test on instrumented

piles provide more information on pile behaviour when loaded such as shaft

resistance at different layer and end bearing, elastic shortening, toe movement,

development of shaft and base resistance during pile displacement. This

information leads to a correlation between SPT-N value and ultimate shaft and end

bearing resistance. Therefore an attempt was made on this study to analyze the load

test results of these instrumented spun piles to develop the correlation for subsoil at

coastal area. It is assessed that the ultimate shaft friction values in the upper soft

clays generally range from about 12 kPa to 20 kPa. Ultimate Shaft friction values

for lower lying materials below soft clays with SPT N values from about 4 to 50

(blows/300mm) range of 2N kPa and a limiting shaft friction value of about 150

kPa. The ultimate end bearing values correlate to about 80N to 120 N kPa. Spun

piles need to be closely observed during installation using hydraulic impact

hammer to avoid any damages on pile and at pile joints. All the piles are fully

monitored during installation using PDA analyzer and the results assessed to verify

the installation technique. The assessment shows that all 3 piles were successfully

installed without integrity problems. A theoretical drivability study also carried out

using GRLWEAP software to provide drivability assessment and compared with

actual drivability of the piles. Results from GRLWEAP is very much similar to data

occurred during pile installation and confirms the drivability of spun piles at this

coastal area without integrity problem. The GRLWEAP software offers variety of

model and analysis option which lead to proper selection of equipments at site.

vi

ABSTRAK

Tiga cerucuk spun yang diinstrumentasi dengan alat-alat ukur gobal

strain gauge dan Extensometer, iaitu PILE-A, PILE-B dan PILE-C didorong dengan

menggunakan tukul hidrolik 25tan di sepanjang kawasan pesisir yang terdiri

daripada pelbagai jenis lapisan tanah berdasarkan penyelidikan tanah. Ujian beban

statik pada cerucuk spun yang diinstrumentasi memberi maklumat lebih lanjut

mengenai perilaku cerucuk ketika dimuat dengan beban iaitu seperti geseran di

antara pelbagai lapisan tanah dengan cerucuk dan komponen rintangan hujung,

pemendekkan elastik, pergerakan hujung cerucuk, pembangunan rintangan dengan

permukaan cerucuk dan hujung cerucuk terhadap pergerakan cerucuk. Maklumat

ini membolehkan kepada korelasi antara nilai SPT-N dengan daya rintangan antara

permukaan cerucuk dan rintangan hujung cerucuk. Oleh kerana itu satu percubaan

dilakukan pada kajian ini untuk menganalisis hasil uji beban dari cerucuk spun

yang diinstrumentasi untuk mengembangkan korelasi di anatara lapisan tanah bagi

kawasan pesisir. Hasil daripada ujian ini menunjukkan bahawa nilai geseran

permukaan cerucuk dengan tanah liat lembut marin (soft marine clay) adalah

daripada 12 kPa hingga 20 kPa. Nilai geseran maksimum anatara permukaan

cerucuk dengan tanah di bawah tanah liat lembut marin dengan nilai N SPT

daripada 4 hingga 50 (blows/300mm) adalah 2N kPa dan nilai geseran maksimum

permukaan cerucuk dihadkan kepada 150 kPa. Nilai rintangan hujung cerucuk

dianggarkan sekitar 80N hingga 120N kPa. Pemanduan Cerucuk spun ke dalam

tanah mengunakan tukul hidrolik 25tan perlu dilakukan dengan cermat bagi

mengelakkan kerosakan pada cerucuk dan sendi cerucuk. Ketiga-tiga cerucuk spun

dipandukan ke dalam tanah dengan mengunakan tukul hidrolik 25tan dan

diperhatikan dengan PDA Analyzer bagi mengesahkan teknik panduan ini.

Penilaian ini menunjukkan bahawa ketiga-tiga cerucuk ini berjaya dipandukan

tanpa sebarang masalah integriti. Sebuah kajian secara teori dilakukan terhadap

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teknik panduan ini dengan menggunakan perisian GRLWEAP untuk mengesahkan

teknik pemanduan ini dan juga dibandingkan dengan keputusan diperolehi oleh

PDA Analyzer di tapak. Keputusan analisis daripada GRLWEAP sangat mirip

dengan keputusan PDA dan ini mengesahkan teknik memandu cerucuk di kawasan

pesisir tanpa masalah integriti. Perisian GRLWEAP menawarkan pelbagai pilihan

model dan analisis yang mendorong pemilihan peralatan yang sesuai di tapak

pembinaan.

viii

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

ABSTRAK vi

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 2

1.3 Objectives 3

1.4 Scope 3

1.5 Importance of the Study 4

ix

2 LITERATURE REVIEW 5

2.1 Driven Piles 5

2.2 Geotechnical Design of Driven Piles 6

2.2.1 Behaviour of Axially Loaded Piles 7

2.2.2 Geotechnical Capacity of Driven Piles 8

2.2.3 Semi Empirical Method 9

2.2.4 Simplified soil mechanics Method 11

2.2.5 Fine Grain Soils 11

2.2.6 Coarse Grain Soil 13

2.3 Analysis of pile driving 14

2.3.1 Introduction to Dynamic Method 15

2.3.2 Wave Equation Model 16

2.3.3 Wave Equation Analysis 17

2.3.4 Wave Equation Analysis Software 18

2.3.5 Wave Equation Applications 19

2.3.6 Interpretation of Wave Equation Results 20

2.3.7 Wave Equation Limitation 21

2.4 Pile Instrumentation 22

2.4.1 Interpretation of Strain gauge Measurement 24

2.5 Load Deformation Analysis 26

3 METHODOLOGY 30

3.1 Introduction 30

3.2 Data Collection 31

3.3 Data Analysis and Results 32

3.4 Summary 33

4 DATA ANALYSIS AND RESULTS 34

4.1 Analysis of data 34

x

4.2.1 Load transfer behaviour of spun pile 36

4.2.2 Ultimate shaft friction and SPT-N value 36

4.2.3 Generation of load transfer curve for

shaft and base 37

4.2.3.1Shaft friction 38

4.2.3.2 End bearing 40

4.3.1 Pile driving stresses and pile integrity

using continuous PDA monitoring 42

4.3.2 Pile drivability assessment by GRLWEAP

Software 44

5 CONCLUSION AND RECOMMANDATIONS 46

5.1 Conclusion 46

5.2 Recommendations 47

REFERENCES 48

APPENDICES A – H 50 - 108

xi

LIST OF TABLES TABLE NO TITLE PAGE

4.1 Spun pile properties 34 4.2 Sub-soil profile summary at BH-MLT A 35 4.3 Sub-soil profile summary at BH-MLT B 35 4.4 Sub-soil profile summary at BH-MLT C 35 4.5 Shaft friction for pile PILE-A 38 4.6 Shaft friction for pile PILE-B 39 4.7 Shaft friction for pile PILE-C 39 4.8 Base friction for test piles PILE-A, PILE-B

and PILE-C 41

4.9 Summary of continuous PDA monitoring results 43 4.10 Comparison of GRLWEAP and continuous PDA

Monitoring results 44

xii

LIST OF FIGURES FIGURE NO TITLE PAGE

2.1 Typical distribution of a load along the length

of an axially loaded pile 6

2.2 Model of axially loaded pile 8 2.3 Critical embedment ratio and bearing capacity

factor for various soil friction angle

(after Meyerhof, 1976) 10

2.4 The α value recommended by API RP2A (1986) 12 2.5 Chart for estimating the bearing capacity factor Nq 14 2.6 Typical Wave Equation Model 17 2.7 Typical Bearing Graph 19 2.8 Constant capacity analysis 21 2.9 Typical wave equation drivability study vs depth 22 2.10 Approximate spun pile instrumentation method

diagram 23

2.11 Numerical model of an axially loaded pile 27 2.12 Load transfer curves for shaft and tip resistance 29 3.1 Flow chart of the study 31 4.1 Correlation of ultimate shaft friction and SPT-N value 40

xiii

4.2 Correlation between ultimate end bearing and SPT-N Value 42

xiv

LIST OF SYMBOLS

fsu - Ultimate shaft resistance

fbu - Ultimate base resistance

Ks - Ultimate shaft resistance factor

Kb - Ultimate base resistance factor

N - SPT value

L - Length in soil

D - Diamater of pile

Qd - Applied load

Qb - Tip load

Qs - Shaft load

f - Unit load transfer in skin friction

q - Unit load transfer in end bearing

Ab - Cross section area of base

As - Side surface area of pile

Qt - Ultimate point resistance

α - Adhesion factor

su - Undrained shear strength (kPa)

Kse - Effective stress shaft resistance factor (can assumed as Ko)

σv ’ - Vertical effective stress (kPa)

Ф’ - Effective angle of friction (degree) of fined grained soils

Nc - Bearing capacity factor

K - Coefficient of lateral earth

σ’ - Effective stress pressure at the point of interest

Ф - Friction angle between soil and pile wall

qb - End bearing

σ’v - Effective vertical stress

xv

Nq - Bearing capacity factor

W - Ram weight

H - Ram drop height

R - Pile capacity

s - Pile penetration per blow

Rd - Dynamic soil resistance

Js - Smith damping value

Vp - Pile element velocity

Rs - Static soil resistance

P - Pile load along shaft

ε - Strain

Ec - Concrete secant modulus

Ac - Cross section area of pile section

Mt - Tangent modulus of composite pile material

β - Shaft resistance factor for coarse grained soils.

σ - Stress (load divided by cross section area)

dσ - Change of stress

dε - Change of strain

Ap - Cross-sectional area of the shaft at the plane of strain gauges

Ecomp - Composite modulus of concrete & steel at the strain gauge plane

Es - Secant modulus of composite material

E - Young’s modulus

υ - Poisson’s ratio

A - Slope of tangent modulus

B - y-intercept of tangent modulus line

D - Diameter of the pile,

xvi

LIST OF APPENDICES

APPENDIX. TITLE PAGE

A Subsoil Profile 50

B Analysis for Instrumented Spun Pile PILE-A 54

C Analysis for Instrumented Spun Pile PILE-B 63

D Analysis for Instrumented Spun Pile PILE-C 72

E PDA continuous Monitoring Results 81

F GRLWEAP Results – 25 Ton Hammer 91

G Comparison of PDA and GRLWEAP Results 95

H GRLWEAP Results – 10 Ton Hammer 105

CHAPTER 1

INTRODUCTION

1.1 Background

Foundation is an essential and important part of any structure that transmits

the structural loads safely to the underlying soils or rock. Foundations can be

classified into shallow foundations and deep foundations. Unlike structural materials

such as steel or concrete that can be manufactured to specifications, the subsoil

condition and geology varies from location to location and foundations are to be

designed to suit specific site conditions. Where competent soils to sustain the

structural loads are not available at a shallow depth, deep foundations such as driven

piles and bored piles are commonly used. In Malaysia, to support high loading

structures such as tall rise buildings and bridges, deep foundations are commonly

used. Considering the economy and ease of pile installation, deep foundation

comprising of driven piles are common when the method is assessed feasible at a

particular project site.

In Malaysia, pre-cast pre-stressed spun concrete piles are manufactured

locally and are commonly used to support bridges and heavy coastal structures such

as jetties and ports. They have been installed in deep marine deposits in the coastal

areas. Spun piles are basically driven into soil by two methods; with hydraulic

2

impact hammer for high loading capacity achievement, and by jacked-in method to

minimize the noise and vibration to surrounding environment in urban areas.

Geotechnical capacity of Spun piles are normally designed based on the

standard penetration test results (soil investigation) in Malaysia and pile capacity

verified by pile tests such as high strain Pile Dynamic Test (PDA) and Static Loads

(maintain load) Test. In order to get more accurate and detailed verification, fully

instrumented pile with multi level strain gauge and extensometer can be subjected to

static load test to establish site specific correlation of the shaft and end bearing

parameters against the field test results such as Standard Penetration Tests (SPT).

Spun piles installation need to be closely observed while using hydraulic

impact hammers to avoid any damage. During driving, the piles can be monitored

continuously for driving stresses and pile integrity using a Pile Driving Analyser.

Proper pile installation and quality control is an important element in every driven

piling project. The piles must be driven to the required capacity without integrity

problems. Some drivability studies need to be carried out prior to installation using

existing data to refine the driving methods and equipments to be used.

Since the usage of large diameter spun piles driven with hydraulic impact

hammer is being commonly used, and in many occasions, installation difficulties

related with pile breakage due to improper choice of driving equipment and

installation methods have been experienced, an attempt has been made to assess the

installation of Driven Piles and also study its load resistance behaviour in this

project.

1.2 Problem Statement

There are many methods are studied to verify the load and settlement of piles.

But for the driven spun pile, the most appropriate method to verify the capacity and

pile integrity is static load test and pile driving analyser method. However, it is

3

difficult to verify the shaft friction contributed by each different soil layers and load

transfer behaviour of pile.

Since the large diameter spun piles driven with hydraulic impact hammer is

being commonly used, and in many occasions, installation difficulties related with

pile breakage due to improper choice of driving equipment and installation methods

have been experienced. During construction Stage, verification of suitability of the

pile driving equipment, hammer performance, driving stresses induced in piles, pile

integrity; verification of the capacity at end of driving and with time and pile

settlement need to be observed.

1.3 Objectives

The aim of conducting this study is to analyze spun pile installation by driven

method and load resistance behaviour of driven spun pile. In order to achieve the

purpose of study, three objectives had been identified:

1) To develop a correlation in between ultimate shaft and base resistance and

SPT-N value using load transfer behaviour of spun pile based on

instrumented test pile.

2) To assess the drivability of large diameter spun piles at coastal area using

available continuous PDA monitoring results.

3) To compare the PDA results with GRLWEAP software output and

confirms the drivability of large diameter spun piles at this coastal area.

1.4 Scope

In this project paper special attention is provided to the fully instrumented

large diameter driven spun pile by hydraulic drop hammer method at coastal area

4

(marine Clay) and underlain by residual soils. The spun piles are vertically tested

with both static load test and high strain dynamic test.

The data for this paper is obtained from real time projects conducted in

construction industry. In this case, the piles are fully instrumented and continuously

monitored using Pile Driving Analyser during installation.

1.5 Importance of Study

Pile instrumentation with strain gauges and extensometer should be installed

at appropriate depth will provide developed shaft friction capacity and end bearing

capacity at different type of layer and load transfer behaviour of pile during loading

and settlement. This valuable data will lead to optimization in pile length and safe

foundation as well as huge cost saving in the project. Spun pile drivability analysis

using existing continuous PDA results available and soil investigation results enable

evaluation of driving methods, pile stresses to be controlled to avoid integrity

problem, and equipment type and ability of spun pile to be driven at require depth.

CHAPTER 2

LITERATURE REVIEW

2.1 Driven Piles

A driven pile is a deep foundation which is a part of structure used to transfer

the loading of structure to bearing ground located at some depth below ground level.

Driven piles are normally manufactured at factory and installed at site using pile

driver. Generally driven piles are of timber, concrete and steel. The concrete piles are

in shape of square, octagonal and rounds in cross section. These concrete piles are

reinforced with steel bar and pre-stressed during manufacturing. Driven piles, also

known as displacement piles, is advantageous because the soil displaced by driving

the piles compresses the surrounding soil, causing greater friction against the sides of

the piles, thus increasing their load-bearing capacity.

The driven piles can installed at site by two methods, by hydraulic impact

hammer and injection method. Injection method preferably replace hammer impact

method at site where development at adjacent site already taken place to avoid noise

and vibration due hammering.

6

2.2 Geotechnical design of Driven Piles

Piles are generally used for two purposes; 1) to increase the load carrying

capacity, 2) to reduce the post settlement of foundation. The applied load will be

transferred through soft soil stratum to stiff soil stratum which called end resistance

of pile and also distributing the loads by friction along pile shafts which called shaft

resistance. The figure 2.1 shows typical load distribution of a pile along to its full

length. The transfer of load as shown in figure is extremely difficult to predict and

difficult to quantify by analytical method.

Figure 2.1: Typical distribution of a load along the length of an axially loaded pile.

Driven piles are controlled by geotechnical capacity (load carrying capacity)

since its only can driven into certain depth into hard stratum. Generally driven pile

designed based on the pile driving formula or the static formula. The static formula

has been identified as more reliable and well known in designing driven piles. The

limit equilibrium method used in this formula to compute pile static resistance at tip

of pile and along the shaft of pile. Shaft friction has a direct application in granular

soil and less applicable in cohesive soil. However shaft friction has been traditionally

used in cohesive soil with considering minimal contribution to the total resistance.

7

The soil parameter normally derived from field test and laboratory test to be used in

the static formula.

2.2.1 Behaviour of Axially loaded Piles

The pile stiffness for axial loading can be represented by load versus

settlement curve at the top of pile. There are few analytical methods are based on the

theory of elasticity which more possible in solving the behaviour of group of piles

spaced closely under axially loading. This method have solution proposed by

D’Appolonia and Romualdi (1963), Thurman and D’Appolonia (1965), Poulos and

Davis (1968), Poulos and Mattes (1969), Mattes and Poulos (1969) and Poulos and

Davis (1980).

The Second method for obtaining the response of pile under axial load is soil

represent with set of nonlinear mechanism which known as t-z method. This method

was developed by Seed and Reese (1957) and further studies carry out by Coyle and

Reese (1966), Coyle and Sulaiman (1967) and Kraft et al (1981). Figure 2.2 shows a

model of T-Z method where the applied load Q is in equilibrium state by a tip load of

Qb with shaft load Qs. In figure 2.2c the pile is replaced with elastic spring and soil

replaced with set of nonlinear mechanism along the pile and at the tip. From the

hypothetical set of mechanism, the t of the curves representing the load transferred

and the z shows the shaft displacement. It is understood no load will be mobilized

from pile to soil if no relative movement in between them. The movement is depends

on the applied load, position of pile, stress – strain characteristics of pile material and

load transfer curves. The load transfer curve is can only derived with based on full

scale loading test with range satisfied. The non-linear curves shown in figure 2.2d

are predicted by Coyle and Reese (1966) and Coyle and Sulaiman (1967) after few

numbers of successful field test.

8

Figure 2.2: Model of axially loaded pile

2.2.2 Geotechnical Capacity of Driven Piles

The geotechnical capacity of pile defines as ultimate soil resistance against

load applied to resist the pile from displace further into ground without increment of

load. The static equations are well established to compute the geotechnical capacity

with few procedures. The very basic equation for compute the ultimate bearing

capacity of piles is as follows:

Qd = Qs + Qb = fAs + qAb, (2.1)

Where

Qs = total skin friction resistance, kN

Qb = total end bearing, kN

f = unit load transfer in skin friction (normally varies with depth), kPa

q = unit load transfer in end bearing (normally varies with depth), kPa

Ab = cross section area of base (m2)

As = side surface area of the pile (m2)

9

There is no general agreement in methods of obtaining f and q. There are

several methods been adopted depends on the site and literature studies carried on.

There are two major types of methods a) semi empirical method and b) simplified

soil mechanic method.

2.2.3 Semi Empirical Method

Semi-empirical correlations have been extensively developed relating both

shaft resistance and base resistance of driven piles to N-values from Standard

Penetration Tests (SPT N-values). The mobilized resistance on the SPT is differing

from on site to other sites results. So semi empirical method used to generalize the

different results into common equation to be used in deriving the geotechnical

capacity of pile within the study area. In the correlations established, the SPT N-

values generally refer to uncorrected values before pile installation. The commonly

used modified Meyerhof Equation correlations for driven piles are as follows:

fsu = Ks x SPT N-value (kPa) (2.2)

fbu = Kb x SPT N-value (kPa) (2.3)

Where:

Ks = ultimate shaft resistance factor

Kb = ultimate base resistance factor

SPT N-value = Standard Penetration Tests blow counts (blows/300mm)

For the shaft resistance, Ks = 2 but limited to 200 kPa is proposed by

Meyerhof after many studies and field tests carried out on driven piles. At the local

practices and studies show the Ks of 2 to 2.5 extensively used based on soil types.

10

Based on field observations, Meyerhof (1976) also suggested that the ultimate

point resistance, Qt, in a homogeneous granular soil (L = Lb) can be obtained from

standard penetration numbers as

Qt = 40NL/D ≤ 400N; limited to 10,000kPa (2.4)

where N is an average standard penetration number (about 10D above and 4D below

the pile point)

Figure 2.3: Critical embedment ratio and bearing capacity factors for various soil

friction angle (after Meyerhof, 1976)

11

2.2.4 Simplified soil mechanics Method

Generally the simplified soil mechanics methods for bored pile design can be

classified into fine grained soils (e.g. clays, silts) and coarse grained soils (e.g. sands

and gravels).

2.2.4.1 Fine Grained Soils

The ultimate shaft resistance (fsu) of piles in cohesive soils can be estimated

based on the semi-empirical undrained method as follows:

fsu = α x su (2.5)

Where

α = coefficient that is a function of su , (adhesion factor)

su = undrained shear strength at depth (kPa)

Based on API method the adhesion factor can be obtain from figure 2.4

where the α value is correlated from the undrained shear strength. Whitaker & Cooke

(1966) proposed that α value will be lies in the between of 0.3 to 0.6 for stiff over-

consolidated clays, while Tomlinson (1994) and Reese & O’Neill (1988) report a

values in the range of 0.4 to 0.9. The α values for residual soils of Malaysia is in

range of 0.8 to 1.0 for soft clay and 0.4 is used for stiff clays is. The value of α to be

used shall be verified by preliminary pile load test.

12

Figure 2.4: The α value recommended by API RP2A (1986)

Effective stress method also can be used in obtain the capacity of pile which

will consider the effective stress of pile. This method is representative for the pile

capacity calculation because considering the effect of effective stress change on the

Kse values to be used. This method is more appropriate to be used at site which

consist high water table. The value of ultimate shaft resistance may be estimated

from the following expression:

fsu = Kse x σv ’ x tan Φ’ (2.6)

Where

Kse = Effective Stress Shaft Resistance Factor (can be assumed as Ko)

σv ’ = Vertical Effective Stress (kPa)

Φ’ = Effective Angle of Friction (degree) of fined grained soils.

Although the theoretical ultimate base resistance for bored pile in fine grained

soil can be related to undrained shear strength as follows;

fbu = Nc x su (2.7)

Where

Nc = bearing capacity factor

13

For depth relevant for piles, the appropriate value of Nc value is 9 (Skempton

1951) although due allowance should be made where thi tip of pile penetrates a stiff

layer by only small amount. A linear interpolation should be made between N=6 for

the case of the pile tip just reaching the bearing stratum, up to N=9 for the pile tip

penetrate the bearing stratum by 3 diameter or more.

2.2.4.2 Coarse Grained Soils

Experiment results for driven piles in sands below considerable scatter for

value of skin friction and end bearing. The following recommendation for computing

unit value of skin friction and end bearing for piles in sand are consistent with state

of practice, but still subjected to pile load test verification. The API recommendation

for side resistance for driven piles in cohesionless soils is as follows:

f = Kσ’ tan Φ (2.8)

K = coefficient of lateral earth

σ’ = effective stress pressure at the point of interest

Φ = friction angle between soil and pile wall

And K value of 0.8 was recommended for open ended pile and 1.0 is recommended

for close ended pipe piles.

For the end bearing, the qb may be expressed in terms of the effective vertical

stress σ’v and bearing capacity factors Nq as

qb = σ’v . Nq (2.9)

14

Values of Nq quoted in the literature vary considerably, but those derived by

Berezantzev et al. (1961) are used most widely for design of deep circular

foundation. Figure 2.5 shows the variation of Nq with friction angle.

Figure 2.5: Chart for estimating the bearing capacity factor Nq

2.3 Analysis of Pile Driving

From very beginning, there many attempts been made to find conventional

method for determining the load cab carry by a pile. Dynamic data obtained during

pile driving were used to predicting the capacity. The only data we will obtain during

pile driving is numbers of blows (pile set). Concepts equating the energy delivered

by the hammer to the work done by the piles as it penetrates the soil were used to

obtain pile capacity expression which called pile formulas (dynamic method).

Another method to modelling the pile driving is wave-equation method. This method

is very interesting because of its ability not only in predict load capacity, but also

very useful yield stresses in the piles during driving. The wave-equation method is a

semitheoretical method which reliability in predicting bearing capacity and driving

stresses depends on the accuracy of the pile parameters and soil properties.

15

2.3.1 Introduction to Dynamic Methods

The earliest attempts at developing dynamic methods were based on

empirical correlations between hammer weight, blow count, and other factors with

the static capacity. These are collectively known as the pile driving formulas. Since

the mid 1800’s, over 450 dynamic formulas for pile driving control have formulated.

In their simple form, these formulas relate hammer energy to the work of soil

resistance, or simply:

W. h = R. S (2.10)

Where

W = ram weight

H = ram drop height

R = pile capacity

s = pile penetration per blow.

Pile driving formulas are attractive, and they continue to be widely used in

practice. Unfortunately, the accuracy of these methods is less than impressive.

Although the principle of conservation of energy is certainly valid, pile driving

formulas suffer because it is very difficult to accurately account for all of the energy

losses in a real pile driving situation. The sources of these uncertainties include the

following (Coduto D.P 1994):

1) The pile, hammer, and soil types used to generate the formula may not be

the same as those at site where it is being used.

2) The hammers do not always operate at their rated efficiencies.

3) The energy absorption properties of cushions can vary significantly.

4) The formulas do not account for flexibility of the pile.

5) There is no simple relationship between the static and dynamic strength of

soils.

16

A technically superior representation of the pile installation process can be

found in the wave equation analysis, which is a numerical solution of the pile driving

process. The development of one dimensional wave equation analysis was one of the

most remarkable engineering accomplishments of the 20th century (George Goble,

2004).

2.3.2 Wave Equation Model

The first computer solution of the wave equation was developed by Smith

(1960). In the wave equation, the pile hammer, helmet, and pile cushion are modelled

by a series of rigid mass elements connected by weightless springs. The springs are

assigned stiffness equal to EA/L for each element. E is the elastic modulus of the

material, A is the cross sectional area, and L is the length of the mass element.

Hammer and pile cushions are represented by additional springs whose stiffness are

calculated from area, modulus of elasticity, and thickness of cushion materials. In

addition, coefficient of restitution (COR) is usually specified to model energy losses

in cushion materials. The COR is equal to one for a perfectly elastic collision which

preserves all energy and is equal to zero for a perfectly plastic condition which loses

all deformation energy. In this way, the computer model accounts for the mass and

flexibility of the hammer-helmet-pile system.

The soil resistance along the embedded portion of the pile and at the pile toe

is represented by both static and dynamic components. Therefore, both static and a

dynamic soil resistance force acts on every embedded pile segment. The static soil

resistance forces are modelled by elasto-plastic springs and the dynamic soil

resistance by linear viscous dashpots. The displacement at which soil changes from

elastic to plastic behaviour is referred to as the soil ‘quake’. In the smith damping

model, the dynamic soil resistance is proportional to the pile element velocity (Vp)

and the static soil resistance (Rs). This can be presented in equation form as:

17

Rd = Js . Vp. Rs (2.11)

where Js is the Smith damping factor. The Smith wave equation model of the ram,

hammer cushion, helmet, pile cushion, pile and soil is given in Figure-2.6.

Figure 2.6: Typical Wave Equation Model.

2.3.3 Wave Equation Analysis

The wave equation analysis is performed over extremely small, incremental

time steps. First, a soil model and pile capacity is assumed. Then, the analysis is set

in motion by selecting hammer efficiency. This efficiency is used to compute the

impact velocity of the hammer mass elements for an input hammer stroke. For each

time step, the computer calculates the acceleration, velocity, and displacement of

each element including the displacement of the pile toe element. Element forces and

notions are calculated during this time step by placing all masses in dynamic

equilibrium such that force equals mass time acceleration. This process is continued

18

for incremental time steps until the toe segment starts to rebound. Then, the

permanent penetration of the pile is calculated by subtracting the average value of the

shaft and toe quake from the maximum toe displacement. The pile penetration can be

plotted versus the pile capacity for one point on a wave equation bearing graph. A

typical wave equation bearing graph including driving stress levels is shown in

Figure-2.7.

2.3.4 Wave Equation Analysis Software

The first publicly available wave equation software was the TTI program

developed at Texas A&M University. In 1976, researchers at the Case Institute of

Technology developed the WEAP (Wave Equation Analysis of Piles) program. It has

been in the public domain. The WEAP program has since formed the basis for other

more advanced proprietary programs.

The WEAP program computes the following:

1) The blow count (number of blows/ unit length of permanent set) of a pile

under one or more assumed ultimate resistance values and other dynamic

soil resistance parameters, given a hammer and driving system.

2) The axial stresses in a pile corresponding to the computed blow count

3) The energy transferred to the pile.

19

Figure 2.7: Typical Bearing Graph.

Based on these results, the following can be indirectly derived:

1) The pile’s bearing capacity at the time of driving or re-striking, given its

penetration resistance (blow count)

2) The stresses during pile driving.

3) The expected blows count if the actual static bearing capacity of the pile

is known in advance (i.e. from a static soil analysis).

2.3.5 Wave Equation Applications

A bearing graph provides the wave equation analyst with two types of

information:

1) It establishes a relationship between ultimate capacity and driving

resistance. From the user’s input data on the shaft and toe bearing

20

resistances, the analysis estimates the permanent set (mm/blow) under

one hammer blow.

2) The user usually develops a bearing graph (Figure-2.7) or an inspector’s

chart (Figure-2.8) for different pile lengths and uses these graphs in the

field, with the observed driving resistance, to determine when the pile has

been driven sufficiently for the required bearing capacity.

3) Driveability study to evaluate the ability of the pile to be driven to a

required depth and capacity. (Figure-2.9).

2.3.6 Interpretation of Wave Equation Results

Following is the methods to interpret the wave equation results obtain from

the analysis:

Check the pile stresses to see whether a safe pile installation is possible

1) If blow count is excessive (greater than 240 blows/foot or 800 blow/m),

reanalyse with more powerful hammer

2) If blow count is acceptable but compressive stresses are unacceptably

high, reanalyse with either a decreased stroke or an increased cushion

thickness.

3) If blow count is low but tension stresses are too high for concrete piles,

either increases the cushion thickness or decrease the stroke or use a

hammer with a heavier ram, and then reanalyse.

4) If both the blow count and compressive stresses are excessive, increase

cross sectional area if applicable, and reanalyse.

21

2.3.7 Wave Equation Limitation

A wave equation analysis requires input assumptions that can significantly

affect the program results. Potential error sources include assumptions on hammer

performance, hammer and pile cushion properties, the soil resistance distribution, as

well as the soil quake and damping characteristics. Insight into these assumptions can

be obtained through dynamic measurements.

Dynamic measurements of force, velocity and energy at the pile head can

readily be compared to the wave equation computed values in the first pile segment.

Adjustment to the wave equation input parameters can be made depending upon the

agreement between the measured and computed values. This approach is the simplest

use of the data available from dynamic measurement and is an easy way to calibrate

the wave equation thereby reducing the potential error sources.

Figure 2.8: Constant Capacity Analyses

22

Figure 2.9: Typical Wave Equation Drivability Study versus Depth

2.4 Pile Instrumentation

Pile load test is being carried out traditionally to assess the displacement of

pile when subjected to loading. For this test basically equipments required are

calibrated hydraulic jack or load cell, dial gauges or LVDT’s (Linear Variable

Differential Transformers) and direct levelling using a surveyor’s precise level and

rod referenced to a fixed datum (benchmark) to measure the displacement at pile

head.

Instrumentation is major part in pile testing to develop the load transfer curve

of pile. In the current engineering practise, understanding of the load transfer and

bearing behaviour of piles mainly through analysis of instrumentation full-scale load

tests. For driven piles, the application of instrumentation is more challenging and

difficult due to significant difference in method of pile installation. To overcome this

problem, approximate instrumentation method used by installing either an

instrumented reinforcement cage or an instrumented pipe into hollow core of spun

23

pile and in filled with grout. Figure 2.10 shows typical section of approximate spun

pile instrumentation scheme.

Figure 2.10: Approximate spun pile instrumentation method diagram

Generally load test will be carried out to measure the displacement of the pile

head when applied with working load. Displacement is very important data during

load test and by conventional test method only the pile head displacement can be

measured will be applied in developing the load settlement curve which will not be

so accurate.

Another method to predict the exact load transfer curve along the pile, fully

instrumentation is used along the pile depth up to toe of pile to assess incremental

strain measurement along full length if pile to determine the distribution of load

transfer from pile to the soil. These provide information on pile tip movements or

deflections along the pile. Instrumentation consists of equipment such as

Extensometer (strain rods) and the electric strain gauges (or vibrating wire strain

gauges).

Extensometers used to measure shortening or displacement over specified

lengths of pile shaft. These may be single mechanical rods anchored at a designated

level to measure the shortening from the top. Vibrating wire (VW) strain gauges

24

designed to measure strain in reinforced concrete or mass concrete, whereby this

vibrating wire strain gauge is typically tied to a reinforcing cage. Readings are

obtained with a VW readout or data logger. Advantages of strain gauge is it provides

good conformance and minimizes inclusion effects, has built-in temperature sensor

and intrinsically reliable VW signal transmission

2.4.1 Interpretation of Strain gauge Measurement

Using the test data for pile with fully instrumented, the load distribution can

be computed from the measured changes in strain gauges readings and pile

properties. The load transferred at mid-point of each anchored interval can be

computed as follows:

P = ε x Ec x Ac

(2.12)

Where

ε= average change in strain gauges readings

Ec= concrete secant modulus in pile section

Ac= cross section area of pile section

It is very difficult to predict the modulus of concrete where it is not constant

over the length and the modulus computed from pile head actually is combination of

steel and concrete. The stress-strain curve can with sufficient accuracy be assumed to

follow a second-degree line: y=ax2 + bx + c, where y is stress and x is strain

(Fellenius, 1989).

The tangent modulus method also can adopt for measuring the load transfer

of pile by measure the secant modulus of pile from tangent modulus line (Fellenius,

2001). Every measured strain value can be converted to stress via its corresponding

strain- dependent secant modulus.

25

The equation for tangent modulus is as follows:

BAddM t +== εεσ (2.13)

This can integrate to:

εεσ BA+⎟

⎠⎞

⎜⎝⎛= 2

2 (2.14)

However

σ - Es x ε (2.15)

Therefore

Es = 0.5 Aε+B (2.16)

where

Mt = tangent modulus of composite pile material

Es = secant modulus of composite pile material

σ = stress (load divided by cross section area)

dσ = changes of stress from one load increment to the next

A = slope of the tangent modulus line

ε = measured strain

dε = change of strain from one load increment to the next

B = Y-intercept of the tangent modulus line

The stress strain relation is non linear in contrast, the tangent modulus of

composite material is a straight line. This line can be used to establish the expression

for the secant modulus. Every measured strain value can therefore be converted to

stress and load via its corresponding strain-dependant secant modulus.

26

2.5 Load Deformation Analysis

Two analytical methods are used in computation of the load settlement curve

of an axially loaded pile. The first method is known as theory of elasticity which

been discussed by D’Appolonia and Romualdi (1963), Thurman and D’Appolonia

(1965), Poulos and Davis (1968), Poulos and Mattes (1969), Mattes and Poulos

(1969) and Poulos and DFavis (1980) on methods derived from this theory. These

methods use Mindlin’s (1963) equations for stress and deformations at any point in

the interior of semi-infinite, elastic and isotropic solids resulting from a force applied

at another point of the solids. The displacement of pile is calculated by applying the

influences of load transfer in the shaft friction and tip resistance. This method takes

the stress distribution within the soil into consideration, so this method applicable in

solving the behaviour of group piles. (Poulos, 1968, Poulos and Davis, 1980). This

method also is oversimplified by allowing the elasticity based methods to work under

condition where soil stratified into different layer, strength and compressibility.

The second method used in computing the load-settlement is load transfer

method (t-z method). This method was first developed by Seed and Reese (1957) and

subsequently further studies on this carried by Coyle and Reese (1966), Coyle and

Sulaiman (1967) and Kraft et al. (1981). It is assuming Winkler concept where the

load transfer at a certain pile section and the pile tip resistance are independent of the

displacement elsewhere. This method can also differentiate the stress resist by

different layers and can deal with any complex composition of soil layers with any

nonlinear relationship of displacement versus shear force (Coyle and Reese, 1966

and Coyle and Sulaiman, 1967).

Figure 2.11 shows typical mechanics of loaded pile where axial load applied

at pile head and undergoes displacement. Based on the figure the strain in the

elements due to axial load P is calculated by neglecting the second order term dP:

EAP

dxdz

−= (2.17)

27

dxdzEAP p−= (2.18)

where

P = axial force in the pile

E = Young Modulus of the pile material

Ap = cross section area of the pile

Figure 2.11: Numerical model of an axially loaded pile.

The total load transfer through an element dx is expressed by using the modulus µ in

the load transfer curve Figure 2.12a.

dP= -µ.z.l.dx (2.19)

or lzdxdP ..µ−= (2.20)

28

where

l = circumstance of a cylindrical pile or the perimeter encompassing an H-pile

µ = modulus in the load transfer curve in Figure 2.12a

Equation 2.17 is differentiated with respect to x and equated with equation

2.20 to obtain:

lzEAdxd ..µ−= (2.21)

Pile tip resistance is the product of a secant modulus υ and the pile-tip

movement ztip (See Figure 2.12b)

Ptip = υ. ztip (2.22)

Equation 2.21 is the basic differential equation that must be solved. Boundary

condition at the tip and the top of the pile must be established. The boundary

condition at tip of the pile is given by equation 2.22. At top of the pile, the boundary

condition may be either a force or a displacement.

29

Figure 2.12: Load-transfer curves for shaft and tip resistance

CHAPTER 3

METHODOLOGY

3.1 Introduction

The study was conducted on available data from various sources. Foremost,

data collected are from fully instrumented driven spun pile and pile subjected to high

strain dynamic testing (PDA). The site selected is at coastal line (marine stretch)

which consists of soft marine clay up to 20-30m depth.

The methodology of the whole studies is summarized in a flowchart and

shown in Figure 3.1.

31

Figure 3.1 Flow Chart of the Study

3.2 Data Collection

The first stage of this study is including identification of sites that used

instrumented driven spun pile as foundation for the structure at Marine clay formation.

Based on the geological map, the marine soft clays fall under Quaternary formation

which consists of Marine and continental deposits with clays, silts, sands, peat with

minor gravel. This quaternary formation generally falls at coastal area of peninsular

Malaysia. The piles selected were pre-cast pre stressed spun concrete piles driven closed

ended with a standard X-pointed shoe. During driving, the piles were monitored

Spun Piles

WEAP Analysis based on soil parameter and driving equipments

Load transfer curve for shaft and base

Conclusion & Suggestion

Stage 1 – Data Collection

Stage 2 – Data Analysis & Results

Stage 3 - Summary

Instrumented driven spun pile results

Continuous PDA monitoring results and SI results

Driving assessment based on continuous PDA monitoring results data

32

continuously for driving stresses and pile integrity using a Pile Driving Analyser. Subsequently, static load test was performed on the preliminary test piles that were

instrumented with Global Stain gauges within the annulus of the closed ended piles and

the following are obtained:

a) load versus settlement behaviour

b) obtain shaft friction in various soil layers and end bearing

For the drivability assessment of spun pile, the required data are soil

investigation results (SPT N-Values), continuous PDA monitoring results, driving

equipment details and lab test results on SI data. For the load transfer behaviour

analysis, the driven spun piles with fully instrumented with strain gauges and subjected

to static load test are isolated. The information required from instrumented spun piles is

strain gauge and rod extensometers readings and SI data. The piles are tested to failure

which will provide the most useful information in terms of ultimate shaft friction of

different soil strata, ultimate end bearing and load-transfer characteristics that can

utilized in the assessment of design working piles. All the results and data are completed

for analysis purpose.

3.3 Data Analysis and Results

The second stage of this study is analysis of the data that obtained from the sites.

Two types of analysis are proceeded to achieve the study’s objectives. For the first

objective of the study, the readings from instrumented test pile such as tell-tale

extensometer readings and strain gauge readings analysed. The load distribution is

calculated from the measured changes in global strain gauge readings and pile

properties. The ultimate average load resistance at shaft and base from instrumentation

readings analysis for different soil profile plotted against SPT N value (SI data).

33

For the assessment of drivability of spun piles, continuous PDA monitoring

results during driving is analysed and the stresses developed are checked. At same time

the theoretical drivability studies carried out by GRLWEAP software by using soil

parameters (SI data) and driving equipments data obtained from site. This software is

produced the theoretical stresses and driving requirement for the proposed site. Data

obtained during pile driving, the continuous pile driving analyzer results also compared

with GRLWEAP results to verify the stresses developed during installation.

3.4 Summary

The third and final stage of the study is draw a conclusion based on the results of

the analysis. The result that was derived from the analysis carefully studied based on the

objectives of the research. The correlation of ultimate shaft resistance to SPT N-values

and load transfer behaviour for shaft and base of the spun piles in soft Marine clay

formation produced. The drivability of spun pile on specific formation fully analysed

and comparison provided for theoretical assessment against actual driving data.

Recommendations also included to improve the quality of the tests and results and to

refine the tests for more useful findings in the future.

The closeness and the deviation between the results obtain checked. There are

some deviations between the results and the causes are identified. Suggestion also

included to improve the quality of the tests and to refine the tests for better comparison

in the future.

CHAPTER 4

DATA ANALYIS, RESULTS AND DISCUSSION

4.1 Analysis of data

Three (3) numbers of preliminary test piles were carried out in the marine

stretch of the proposed bridge, namely PILE-A, PILE-B and PILE-C. The piles were

pre-cast pre-stressed spun concrete piles driven closed ended with a standard X-

pointed shoe. During driving, the piles were monitored continuously for driving

stresses and pile integrity using a Pile Driving Analyzer. Subsequently, static load

test was performed on the preliminary test piles that were instrumented with Global

Stain gauges within the annulus of the closed ended piles. Following Table 4.1

describes the properties of spun pile used:

Table 4.1: Spun pile properties

Pile Diameter 1000 mm nominal

Wall Thickness 140 mm

Concrete Grade 80N/mm2

Effective Pre-stress 7 N/mm2

Pile penetration length below sea bed level

PILE-A – 43m

PILE-B – 57.5 m

PILE-C – 33.8 m

35

Subsoil profiles at the test pile location PILE-A, PILE-B and PILE-C are

shown in Appendix A. Boreholes were carried out close to PILE-A, PILE-B and

PILE-C locations namely, BH-MLTA, BH-MLT-B and BH-MLT C. Based on the

boreholes carried out adjacent to the test pile locations, the sub-soil conditions can be

summarized as follows:

Table 4.2: Subsoil profile summary at BH-MLT A

Depth below sea-bed (m) Soil Description SPT N values

(blows/300mm) 0 to 3m Very soft CLAYS 0

3 to 27m Silty CLAYS 4 to 20 27 to 46.5m Silty SANDS 20 to 50 46.5 to 57m Silty SANDS >50

Table 4.3: Subsoil profile summary at BH-MLT B


(blows/300mm) 0 to 27m Very soft CLAYS <4

27 to 52.5m Silty CLAYS 20 to 50 52.5 to 66 m Silty SANDS >50

Table 4.4: Subsoil profile summary at BH-MLT C


(blows/300mm) 0 to 12m Very soft CLAYS <4

12 to 24m CLAYS 6 to 15 24 to 35m SANDS 25 to 30 35 to 41m CLAY 10 to 15 41 to 47 SANDS 50 47 to 53 CLAY 10 to 20 53 to 63 SANDS > 50

36

4.2.1 Load transfer behaviour of spun pile

The instrumentation scheme adopted for the instrumented test piles – PILE-

A, PILE-B and PILE-C is shown in appendix B, C and D respectively. The

instrumentation comprises of global strain gauges and extensometers that can be

interpreted to obtain load distribution with depth, shaft friction, end bearing and load

transfer curves (shaft friction versus mid-shaft movement and end bearing versus pile

toe movement).

4.2.2 Ultimate Shaft Friction and SPT-N value

In local practise, it is common to investigate the site by boreholes and

standard penetration test carried out to determine the resistance of soil. The number

of blows count N value is used in correlate the shaft resistance of pile and the end

bearing. The nearest boreholes used in correlate the shaft friction and end bearing

resistance of these piles. The shaft friction is divided into the section as per the

arrangement of the instruments to ease the correlation.

The shaft friction of the pile is determined as follows:

fsu = Ka x Na (kPa)

Where:

Ka = ultimate shaft resistance factor (1.7-3)

Na = SPT-N value along pile shaft

The end bearing resistance is determined as follows:

Fbu = Kb x Nb (kPa)

Where:

Kb = Ultimate end bearing resistance factor (250 – 400 for driven piles)

Nb = SPT-N Value at end of pile

37

4.2.3 Generation of Load Transfer Curve for Shaft and Base

Friction value of each layer is derived based on instruments reading during

maintain load test. Load distribution curves along the shaft & based derived based on

the changes in strain gauge and estimated pile properties. Load transferred at each

segment calculated as follows:

1) Assuming the strains in steel is same as strains in concrete; load at strain level

is computed as follows:

Pave = εApEc

Where

Pave = load at mid-point for each segment

ε = average change in global strain gauge reading

Ap = Cross section area of pile

Ec = Concrete Modulus in pile section

Concrete modulus, Ec is non-linear and was back-calculated by measuring

the segmental strains for pile section and the pile top forces. Fellenius (2001)

method using tangent modulus estimated is approached to back calculate the

concrete modulus.

2) Average shaft resistance at each segments calculated using load distributions

computed at the strain gauge levels:

fsm = (P top of segment – P bottom of segment) / (pile cross sectional area)

3) The load transfer curve for shaft and base is generated as per following

method:

a) Pile was divided into segments between the strain gauge levels. For each

segment, the mid-segment movement of the pile shaft was linearly

interpolated between the movement of the bottom of segment and the top

of segment that are obtained using extensometers.

38

b) The same process was repeated for the subsequent head load and head

settlement and the corresponding strain gauge and extensometer readings

along the pile length. Therefore for each pile, the load transfer curve for

shaft was generated for each pile segment and one load transfer curve for

the base.

Appendix B, C and D shows the load transfer characteristic of shaft and base of these

three piles.

4.2.3.1 Shaft Friction

The load distribution with depth for PILE-A, PILE-B and PILE-C is given in

appendix B, C and D respectively. Following are the summary of interpreted ultimate

shaft friction values based on the test pile results:

Table 4.5: Shaft friction for pile PILE-A

Depth Instrument Level Soil Type Average SPT N

value blows/300mm (SPT N range)

Ultimate shaft

friction (kPa)

0 to 7.4 Seabed to level B soft CLAY 4 (0 to 6)

20

7.4 to 21.3 Level B to level C silty CLAY 7 ( 4 to 9)

55

21.3 to 31.8

Level C to level D sandy CLAY

14 (7 to 29)

48

31.8 to 38.2

Level D to level E silty SAND 37 (21 – 50)

58

38.2 to 42.5

Level E to level F silty SAND 47 (40 to 50)

160

39

Table 4.6: Shaft friction for pile PILE-B



Ultimate shaft friction (kPa)

0 to 7.5 Seabed to level B soft CLAY

0

21

7.5 to 21 Level B to level C soft CLAY

0

2

21 to 30.5 Level C to level D silty CLAY

3 (1 to 8)

45

30.5 to 39 Level D to level E silty SAND

27 (20 – 50)

62

39 to 49 Level E to level F silty SAND

24 (15 to 30)

22

39 to 55.5 Level F to level G silty SAND

36 (20 to 50)

22

Table 4.7: Shaft friction for pile PILE-C



Ultimate shaft friction (kPa)

0 to 5 Seabed to level B soft CLAY 0

12

5 to 13.5 Level B to level C Soft CLAY

0

27

13.5 to 28.5

Level C to level E CLAY/SAND 20 (6 to 30)

49

28.5 to 32.2

Level E to level F SAND 35 (25 – 50)

312

Based on the results obtained from instrumented test pile following is the discussion

on the results:

1) The ultimate shaft friction values in the upper soft clays generally range from

about 12 kPa to 20 kPa.

2) Shaft friction values for lower lying materials (predominantly Silty SANDS /

SANDS and with some mixed layers of silty CLAY and with SPT N values

40

ranging from about 4 to 50 blows/300mm ) are plotted against average SPT N

values in Figure 4.1. It is assessed that in these materials the ultimate shaft

friction values range from 1N to 3N with an average of 2N kPa where N is

the uncorrected SPT N value and a limiting shaft friction value of about 150

kPa

3) Few readings show unpractical values and discarded during the analysis of

the instrumentations.

Figure 4.1: Correlation of Ultimate shaft friction and SPT-N value

4.2.3.2 End Bearing

The piles are displaced during the maintain load test and it is assessed that the

load was fully mobilised in the piles. It is assessed that the load at final level of

segment is sustained by end bearing. The load sustained by end bearing is divided

41

into cross section of base of pile to compute the end bearing resistance. The

interpreted end bearing values for all three piles are summarized as follows:

Table 4.8: Base friction for test piles PILE-A, PILE-B and PILE-C

Based on the results of instrumented test pile, the following is assessed:

1) The ultimate end bearing values correlate to about 80N to 120 N kPa where N

is the uncorrected SPT N value. This range is low in comparison to the

recommendations in literature for driven piles in silty SANDS/SANDS (300

to 400N). When overburden correction is applied on the SPT N values, the

ultimate end bearing values correlate to about 140 to 270 N (applying Liao

and Whitman 1986 method) and 170 to 350 N (applying Skempton 1986

method) where N is the corrected SPT N value for overburden. The ultimate

end bearing correlation with SPT-N value is shown in figure 4.2.

Test Pile No. Average SPT N value for depth of

3 x pile diameter below toe of pile

Ultimate end bearing

(kPa)

PILE-A 35 2740

PILE-B 50 6142

PILE-C 30 2418

42

Figure 4.2: Correlation between Ultimate End Bearing and SPT-N Values

4.3.1 Pile driving stresses and pile integrity using continuous PDA monitoring

All three piles were continuously monitored during installation to control the

stresses developed in the piles. The PDA results obtained are shown in appendix E.

The pile driving stresses and the pile integrity obtained by continuous monitoring

using pile driving analyzer (PDA) during driving of the preliminary test piles

summarized as follows in table 4.9:

43

Table 4.9: Summary of continuous PDA monitoring results

From the PDA results, the following is the discussion of the results:

1) Based on AASHTO (1994), the recommended compression stress limit

during driving is 0.85fc – fpe = 61 MPa (where fc = concrete compressive

strength = 80 MPa and fpe = effective pre-stress = 7 MPa). The maximum

driving compression stress generated in the pile (23 to 36 MPa) are well

within the limits recommended.

2) Based on AASHTO (1994), the recommended tension stress limit during

driving is 0.25 (fc’)1/2 + fpe = 9.2MPa for normal environments (criteria 1),

and tension stress limit of fpe = 7MPa for severe corrosive environments

(criteria 2). The maximum driving tension stress generated is less than criteria

1 but slightly exceeds criteria 2 at certain depths.

3) The integrity of the piles is satisfactory and the piles had no apparent damage.

Pile No.

Depth at which pile was monitored (m)

Drop Height (mm)

Energy Transferred (max) (ton.m)

Compression Stress (MPa)

Tension Stress (MPa)

Pile Integrity

PILE-A 11 to 43 100 - 600

12.28 4 to 23 0.4 – 6.2 Good

PILE-B 26.5 to 47 100 - 600

13.42 6 – 30 0.8 – 8.5 Good

PILE-B Restrike

47 to 57 200 - 1000

15.57 15 - 26 1.8 – 7.1 Good

PILE-C 8.5 to 33.5 100 - 800

13.79 5 - 33 0.9 – 9.1 Good

44

4.3.2 Pile drivability assessment by GRLWEAP software

There is need of pre assessment required on the drivability of spun piles to

avoid construction problem during driving of piles. GRLWEAP software was used to

obtain the theoretical stresses of these piles and compared with actual PDA results

obtained at site during driving. The stresses obtain from GRLWEAP software and

PDA test are compared and summarized as followed in table 4.10 below:

Table 4.10: Comparison of GRLWEAP and continuous PDA monitoring results

Further analysis carried in GRLWEAP using 10 Ton hammer to study the

drivability of piles using same soil properties and pile properties. Following is the

discussions arise from the GRLWEAP analysis results:

1) All the stresses developed in GRLWEAP are similar to the stresses developed

during pile driving. The actual compressive stresses and capacity picked up

by PDA is showing lesser than assessed by GRLWEAP software except for

capacity of Pile-C. The GRLWEAP software also determines the set criteria

required to achieve the designed load and length required.

2) The tensile stress developed in the GRLWEAP is too low if compare to the

tensile stress measured by PDA at site during pile driving.

PILE-A PILE-B PILE-C

PDA GRL-

WEAP

PDA GRL-

WEAP

PDA GRL-

WEAP

Max. Compression

Stresses (MPa)

23 30 30 30 33 34

Max. Tension Stresses

(MPa)

6.2 1.1 8.5 1.5 9.1 0.9

Max. Ultimate Bearing

capacity (ton)

507 530 555 571 501 475

45

3) The further study carried out using 10 Ton hammer shows that the piles can

be driven with limited stresses in pile. However the piles can’t penetrate

certain soil layer due to the insufficient of hammer energy. This lead to the

lower working capacity of piles. Driving large diameter piles using 10 Ton

hammer will consume more time and will delay the construction progress.

All the GRLWEAP analysis results for 25Ton hammer, comparisons of PDA and

GRLWEAP and GRLWEAP results for 10 Ton hammer are appended in appendix F,

G and H respectively

CHAPTER 5

CONCLUSION AND RECOMMANDATIONS

5.1 Conclusion

The results obtained from the analysis and assessment carried out and

discussion in chapter 4, the following can be concluded:

1) The correlation between ultimate shaft and base resistance and SPT-N value

is obtained based on the analysis instrumented test pile results in this study.

The following correlation can be used as design guideline for future driven

spun pile (closed ended) at this coastal area:

a. For the Soft Marine Clay with SPT-N value equal or lesser than 4

blows/300mm, ultimate shaft friction is

fsu = 12 to 20 kPa

b. For lower lying materials below soft clays with SPT-N value more

than 50 blows/300mm, ultimate shaft friction is

fsu = 2 x SPT ‘N’ (kPa), limited to 150 kPa

c. For the lower lying material below Soft Marine Clay, the ultimate end

bearing values correlate to about

fbu = (80 to120) x SPT ‘N’ (kPa), limited to 6000 kPa

47

2) The large diameter spun piles are can be driven to set by driven method with

hydraulic hammer into deeper level without any integrity problem to the spun

piles.

3) The GRLWEAP analysis confirms the stresses developed in piles and shows

that large diameter spun pile can be driven using hydraulic hammer.

4) All the future large diameter spun pile at this coastal area can be design and

driven using GRLWEAP software as guideline.

5) The drivability of spun piles using different type of equipments also can be

tested in the GRLWEAP in advanced to avoid construction problem.

5.2 Recommendations

Although this study provide better understanding in load resistance behaviour

of spun piles in Coastal area, further study can be carried out to resolve few issues:

1) Further study on behaviour of different type of piles at coastal area and

correlation need to be develop and confirm the correlation from current study.

2) The tension stresses obtained at site during PDA test is significantly higher

than GRLWEAP result. Further studies can be carried out to resolve this

issue.

3) The correlation of base resistance is based on 3 piles only. More test piles

need to be carried out to obtain the reasonable correlation value for end

bearing.

4) The installation of instruments needs to be closely observed to avoid any

instruments failure after pile installation.

REFERENCES

Australian Standard (1995). AS 2150-1995. Piling-Design and Installation. Standards

Association of Australia. NSW.

Bengt H. Fellenius (22 & 23 April 1998). Recent Advance in The Design of piles for

Axial Loads, Dragloads, Downdrag, and Settlement. ASCE and Port of NY&NJ

Seminar.

Bengt H. Fellenius (14-16 February 2002). Determining the True Distributions of Load

in Instrumented Piles. ASCE International Deep Foundation Congress.

Geotechnical Special Publication No. 116. Orlando, Florida.

Faisal Hj.Ali, Lee Sieng Kai (2007), A new instrumentation method for driven

prestressed spun concrete piles, EJGE

Fellinius B.G. (1980). The analysis of results from routine pile loading tests. Ground

Engineering, London, Vol. 13, No. 6.Fellinius B.G. (1989). Tangent modulus of

piles determined from strain data. The American Society of Civil Engineers,

ASCE, Geotechnical Engineering Division, the 1989 Foundation Congress, F. H.

Kulhawy, Editor, Vol. 1.

Fellinius B.G. (2001). From Strain Measurements to Load in an instrumented

Pile.Geotechnical News Magazine, Vol 19, No.1.

49

Goble, G.G., Rausche, F., And Likins, G (1980). The Analysis of Pile Driving – A State

of the Art. Proc. Of the 1st International Conference on Application of

Stresswave Theory to Piles. Balkema, Stockholm Sweden.

Hannigan,P.J, Goble, G.G, Thendean, G., Likins, G.E and Rausche,F.(1998), Design and

construction of driven pile foundation, Volume 1 & 2, FHWA H1-97-013,

Washington D.C

Lymon C.Reese, William M. Isenhower, Shin-Tower Wang (2006) Shallow and Deep

Foundation, USA, John Wiley & Sons.

Patrick J Hannigan (1990) Dynamic Pile Monitoring and Analysis of Pile Foundation

Installations, Deep Foundations Institute.

Pile Dynamics, Inc (2000). Capwap for Window – Manual 2000. Ohio, USA. Page 2-1

to 2-2.

Poulos H.G. and Davis E.H. (1980). Pile Foundation Analysis and Design. Wiley &

Sons, New York. (reprinted by Krieger Publishing, Malabar, Florida, 1990).

Randolph M.F. and Wroth C.P. (1978). Analysis of deformation of vertically loaded

piles. Journal of the Geotechnical Engineering Division, ASCE, Vol. 104 (GT12).

Seed H. B., and Reese L. C. (1957). The Action of Soft Clay Along Friction Piles

Transactions. American Society of Civil Engineers, New York, NY, Vol 122.

U.S. Department Of Transportation, Federal Highway Administration (FHWA) (1996).

Design and Construction of Driven Pile Foundations. Publication No. FHWA-

HI-96-003. Two volumes.

W.G.K Fleming et al (1992), Piling Engineering, Halsted press, John Wiley & Sons.

APPENDIX A

SUBSOIL PROFILE

51

PILE-A

52

PILE-B

53

PILE-C

54

APPENDIX B

ANALYSIS OF INSTRUMENTED SPUN PILE

PILE-A

55

INSTRUMENTATION SCHEME

PILE-A

56

PILE – A

57

PILE-A

60

LOAD TRANSFER CURVES – PILE-A

63

APPENDIX C


PILE-B

64

INSTRUMENTATION SCHEME

PILE-B

65

PILE-A

66

PILE-B

69

LOAD TRANSFER CURVES – PILE-B

72

APPENDIX D


PILE-C

73

PILE-C

74

PILE-C

75

PILE-C

78

LOAD TRANSFER CURVES – PILE-C

81

APPENDIX E

PDA CONTINUOUS MONITORING RESULTS

82

PILE-A

83

PILE-A

84

PILE-A

85

PILE-B

86

PILE-B

87

PILE-B

88

PILE-C

89

PILE-C

90

PILE-C

91

APPENDIX F

GRLWEAP RESULTS – 25 Ton Hammer

92

PILE-A

93

PILE-B

94

PILE-C

95

APPENDIX G

COMPARISON OF PDA AND GRLWEAP RESULTS

96

PILE-A

97

PILE-A

98

PILE-A

99

PILE-B

100

PILE-B

101

PILE-B

102

PILE-C

103

PILE-C

104

PILE-C

105

APPENDIX H

GRLWEAP RESULTS – 10 Ton Hammer

106

PILE-A

107

PILE-B

108

PILE-C

load resistance behaviour and installation assessment of driven

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