PREDICTION OF BEARING CAPACITY OF BORED PILE SOCKETTED IN LIMESTONE OF VARYING ROCK QUALITY DESIGNATION

 

 

 

 

 

 

 

 

 

HOSSEIN JAHANMIRINEZHAD 

 

 

 

 

 

 

 

     

UNIVERSITI TEKNOLOGI MALAYSIA

i 

PREDICTION OF BEARING CAPACITY OF BORED PILE SOCKETTED IN

LIMESTONE OF VARYING ROCK QUALITY DESIGNATION

HOSSEIN JAHANMIRINEZHAD

A dissertation submitted in partial fulfillment of the

requirements for the award of the degree of

Master of Engineering (Civil – Geotechnics)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

July 2011

iii  

This thesis is dedicated to my beloved wife, family and friends

iv  

ACKNOWLEDGEMENT

I would like to take this opportunity to express my deep and sincere gratitude

to my supervisor, Assoc. Prof. Mohd For Mohd Amin, a dedicate lecturer in Faculty

of Civil Engineering for his encouragement and expert advice, regarding the

planning, processing in order to complete this dissertation. The ideas and concepts

have had a remarkable influence on my entire project in this field. And also I must

appreciate from Dr. Nurly Gofar for her effectual helps in editing this project.

During this work I have collaborated with many persons for whom I have

great regard, and I wish to extend my warmest thanks to all those who have helped

me with my work in the Faculty of Civil Engineering in Universiti Teknologi

Malaysia, especially Assoc. Prof. Ir. Azman Kassim.

I owe my loving thanks to my parents and my wife who always, pray for my

success in everyday life. Without their encouragement and understanding it would

have been impossible for me to finish this work.

Thank you very much

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ABSTRACT

Reliable design of cast in-situ micropiles depends greatly on data pertaining

to the properties of the rock mass, which include Rock Quality Designation (RQD)

and modulus of deformation. However, this data are difficult and costly to acquire

for it requires direct measurement on the rock mass. Consequently, the design of

micropiles is often based on semi-empirical method. This study is aimed at

establishing relevant correlations between properties of rock mass and selected

parameters for the design of micropile socketed in limestone. Data used for the

correlations are properties of limestone in Pandan Indah, Kuala Lumpur. For natural

material like rocks, anisotropy and discontinuity may lead to variations of its

properties. Consequently, it often requires a large number of field data to ensure

reliability of correlations. It also noted that the use RQD, to describe the

discontinuous nature of limestone, is not that reliable. Despite of these constraints,

this study has shown the existence of some forms of correlations between design

parameters of piles and characteristics of the rock mass. Correlation exists between

mobilised skin frictions (FS) and RQD. Rock with lower RQD tends to induce a

higher FS. A good correlation exists between RQD and in-situ deformation modulus

(Em) obtained from Pressuremeter test. This implies that RQD value can be used for

estimating Em of in-situ limestone. Further verification shows that for rock with

RQD < 25 %, the value of Em drops as much as 99 % (compared to intact modulus

(Ei)). Similar behavior is observed on the effect of RQD on the dynamic modulus

and Poisson’s ratio. With regard to the material properties of limestone, it is found

that its Uniaxial Compression Strength (UCS) is about 26 times its Point-load index

strength (IS), and Tensile strength (TS) is less than one-tenth of the UCS. More field

data is essential to improve the reliability of the established correlations.

vi  

ABSTRAK

Kebolehgantungan rekabentuk cerucuk mikro tuang di-situ amat bergantung pada data mengenai sifat-sifat massa batuan di tapak, dan data ini merangkumi nilai RQD dan modulus perubahanbentuk. Walaubagaimanapun data ini sukar dan mahal untuk diperolehi kerana ia memerlukan pengukuran secara terus ke atas batuan di tapak. Oleh yang demikian rekabentuk cerujuk mikro selalunya berasaskan kepada kaedah separa empirikal. Kajian ini bertujuan untuk mewujudkan beberapa korelasi di antara sifat-sifat massa batuan di tapak dan beberapa parameter penting bagi rekabentuk cerucuk mikro dalam batukapur. Data yang digunakan bagi mewujudkan pertalian ini adalah sifat-sifat batukapur di Pandan Indah, Kuala Lumpur. Bagi bahan semulajadi seperti batuan, ciri anisotropi dan ketakselarasan boleh menyebabkan wujudnya variasi dalam sifat sampel. Oleh yang demikian bagi batuan, ianya memerlukan bilangan data di tapak yang lebih banyak bagi memastikan ketepatan korelasi yang diwujudkan. Pemerhatian juga menunjukkan penggunaan nilai RQD bagi menggambarkan ketidakselaran jasad batuan adalah kurang sempurna. Di samping kekangan yang dihadapi, kajian ini telah berjaya membuktikan wujudnya beberapa bentuk pertalian di antara parameter rekabentuk cerucuk dan sifat-sifat massa batuan di tapak. Wujud pertalian di antara geseran kulit yang digerakkan (FS) dan RQD. Batuan yang mempunyai nilai RQD yang lebih rendah akan mengaruhkan nilai FS yang lebih tinggi. Pertalian yang baik wujud di antara RQD dan modulus perubahanbentuk (Em) di tapak, yang diperolehi dari ujian Pressuremeter. Ini membuktikan bahawa nilai RQD boleh digunakan bagi menganggarkan nilai Em bagi batukapor di lapangan. Penelitian lanjut menunjukkan bagi batuan dengan nilai RQD < 25 %, nilai Em nya menurun hampir 99 % (dibandingkan dengan modulus tak terusik Ei). Ciri-ciri yang hampir sama dilihat dari segi kesan RQD ke atas modulus dinamik dan nisbah Poisson. Dari segi sifat bahan batukapur, didapati nilai UCS nya adalah 26 kali lebih besar dari IS, dan nilai TS pula kurang dari 1/10 nilai UCS. Bilangan data di tapak memainkan peranan yang penting dalam memastikan ketepatan pertalian yang telah diwujudkan.

vii  

TABLE OF CONTENTS

CHAPTER TITLE PAGE

TITLE i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES xi

LIST OF FIGURE xiii

LIST OF APPENDICES xvi

LIST OF SYMBOLS xvii

1 INTRODUCTION 1

1.1 Background 1

1.2 Problem of statement 2

1.3 Objectives of study 3

1.4 Methodology 4

1.5 Scope of study 4

2 LITERATURE REVIEW 5

2.1 Introduction 5

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CHAPTER TITLE PAGE

2.2 Mass and material properties of rock 6

2.2.1 Intact and discontinuous rock 7

2.2.2 Measuring the discontinuous nature of rock mass 8

2.3 Empirical correlations for rock mass properties 17

2.3.1 Rock mass modulus 18

2.3.2 Rock mass bearing pressure 19

2.4 Foundation problems in limestone 22

2.4.1 Kuala Lumpur Limestone 22

2.4.2 Foundation problems in limestone 25

2.5 Bored pile design 26

2.5.1 Classification of bored piles 26

2.5.2 Geotechnical capacity of bored piles 27

2.5.3 Design approach of bored pile in rock 28

2.5.4 Load transfer mechanism 34

2.5.5 Other considerations in bored pile design 36

2.6 Field tests related to bored pile design 38

2.6.1 Pressuremeter test 39

2.6.2 Instrumented trial shaft 44

3 RESEARCH METHODOLOGY 46

3.1 Introduction 46

3.2 Study area and rock type 47

3.3 Data used in the study 49

3.3.1 Laboratory data 49

3.3.2 Field data 54

3.3.2.1 Static axial load test 56

3.3.2.2 Pressuremeter Test 57

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CHAPTER TITLE PAGE

3.3.2.3 PS suspension logging 60

3.4 Approach in establishing the correlations 63

3.5 Other correlations for rock properties 63

4 ANALYSIS OF DATA & DISCUSSION 66

4.1 Introduction 66

4.2 Laboratory data 67

4.2.1 Correlation between index and direct strength 67

4.2.2 Correlation between tensile and compressive strength 69

4.2.3 RQD based on primary wave velocities 70

4.3 Field data 71

4.3.1 Pressuremeter test 71

4.3.2 Suspension PS logging 74

4.3.3 Static axial load test 75

4.4 Proposed correlations for field data 77

4.4.1 Relationship between data from PMT & PS logging 77

4.4.2 RQD versus ultimate skin friction 78

4.4.3 RQD versus static modulus 82

4.4.4 Dynamic modulus and RQD 84

4.5 Intact UCS and RQD 85 5 CONCLUSIONS & RECOMMENDATIONS 88

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CHAPTER TITLE PAGE

5.1 Introduction 88

5.2 Conclusions 89

5.3 Recommendations 90

REFERENCES 91

APPENDICES A-D 94-177

xi  

LIST OF TABLES

TABLE NO. TITLE PAGE

2.1 Rock Quality Designation RQD (Barton et al., 1974) 11

2.2

Modulus reduction factor (KE) based on RQD (Biewniaski, 1984)

11

2.3 Major rock classification system (Bieniawski, 1989) 13

2.4 Strength of intact rock material (Singh and Goel, 1999) 14

2.5 Rock Quality Designation RQD (Singh and Goel, 1999) 15

2.6 Spacing of discontinuities (Singh and Goel, 1999) 15

2.7 Condition of discontinuities (Singh and Goel, 1999) 15

2.8

Grouping of rating of RMR of rock mass (Singh and Goel, 1999)

16

2.9

Design parameters and eng. properties of rock mass (Singh and Goel, 1999)

17

2.10

Net allowable bearing pressure qa based on RMR (Mehrotra, 1992)

17

2.11

Net Safe Bearing Pressure for various rock types (Singh and Goel, 1999)

21

2.12 Value of Nj for equation (2.5) (Singh and Goel, 1999) 22

2.13 Summary of Rock Socket Friction Design Values 31

2.14 Typical Friction Angle for Intact Rock (Wyllie, 1991) 37

3.1 List of laboratory tests and number of tests conducted 50

3.2

Statistical values of selected rock properties obtained from lab tests

50

3.3 Number of PMT test, depth and RQD 60

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TABLE NO. TITLE PAGE

4.1 RQD based on direct and indirect method 70

4.2

Data obtained from Pressuremeter Test on rock of different RQD

73

4.3

Deformation, tangent and secant modulus at different RQD

74

4.4

In-situ modulus of limestone measured using PS Logging

75

4.5 Data from static axial load test on cast in-situ micropiles 76

4.6

Measured ultimate skin friction (FS) at different RQD, and FS calculated using Tomlinson (2001) and Neoh (1998)

79

4.7

Reduction of deformation modulus due to discontinuity (RQD)

84

4.8

Distribution of intact UCS of limestone based on RQD grouping

87

xiii  

LIST OF FIGURES

FIGURE NO. TITLE PAGE

     

2.1 Illustration of rock mass (Edelbro, 2003) 6

2.2 Rock mass and intact rock (Brady and Brown, 1985) 7

2.3.a Rock mass exhibits discontinuities and often weathered 8 2.3.b

Intact rock samples in lab test are free from large scale discontinuities

8

2.4 Joints in granite rock 9

2.5 Joints intersecting in various directions 9

2.6 Cores obtained from drilling/coring in jointed rock 10

2.7

Effect of number of intersecting joints on rock mass quality (expressed in term of RQD)

11

2.8

Effect of joint number and orientation on rock strength (Hudson, 1989)

12

2.9

Safe Bearing Pressure based on laboratory UCS, RQD and fracture spacing (Waltham, 2002)

19

2.10

Allowable bearing pressure for a jointed rock mass (Peck et al., 1974)

20

2.11 Kuala Lumpur Karst Area (Price, 1998) 23

2.12

Typical section of Karst Formation (Tarbuck and Lutgens, 2005)

24

2.13 A view of Karst formation in Malaysia 24

2.14 Schematic of bored pile 30

2.15

Rock Socket Reduction Factor with respect to Unconfined Compressive Strength (Tomlinson, 2001)

32

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FIGURE NO. TITLE PAGE

2.16

Rock Socket Correction Factor with respect to Rock Mass Discontinuity (Tomlinson, 2001)

32

2.17

Relations between Socket Roughnesses, Socket Reduction Factor and Normalised Rock Strength (Kulhawy and Phoon, 1993)

34

2.18

Distribution of Socket Resistance with respect to Socket Length and Modulus Ratio (Pells and Tuner, 1979)

35

2.19

Idealised representation of major components of bond (Littlejohn and Bruce, 1977)

36

2.20 Current state of pressuremeter testing (Clarke, 1995) 40

2.21 The Elastometer 100 (Clarke, 1995) 41

2.22

(a) Probe in borehole, and (b) curve obtained from PMT (Bullock, 2004)

42

2.23 Sample graph for Tangent Modulus and Secant Modulus 43

2.24 Instrumented pile shaft (Hanifah and Lee, 2006) 45

2.25

Mobilised shaft friction versus pile movement under increasing axial load (Panji Bersatu Sdn. Bhd., 2010a)

45

3.1 Flowchart of this project 47

3.2 Location of project area 48

3.3 Ultrasonic velocity test 51

3.4 Schmidt Hammer test 51

3.5 Point-load index test 52

3.6 Indirect tensile strength test 52

3.7 Uniaxial compression test 53

3.8 Instrumented core sample 53

3.9 Drilling for trial shaft test 54

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FIGURE NO. TITLE PAGE

3.10 Grouted in-situ trial shaft 55

3.11 Static axial load test 55

3.12 Monitoring of PMT 56

3.13 Rotary Drill Rig 57

3.14 OYO Elasmeter-2 with HQ Sonde probe 58

3.15 A section of PMT Sonde Prob 59

3.16 Procedure of pressuremeter test 59

3.17 Schematic showing suspension logging system 61

3.18 Suspension PS Logger (Model-3660) 61

4.1

Correlation between UCS and Is for limestone bedrock in Pandan Indah

68

4.2

Comparison between Brazilian (Tensile) (TS) and UCS strengths of intact rock samples

69

4.3 Typical PMT curve 72

4.4

Mobilised skin friction versus pile settlement in rock of different RQD

76

4.5 Graph of dynamic Young’s modulus versus deformation modulus 77

4.6 Mobilised ultimate skin friction versus RQD 80 4.7

Static deformation modulus of limestone (from PMT) versus RQD 82

4.8 Dynamic modulus (from PS Logging) versus RQD 85

4.9

Intact core for UCS test and jointed core obtained from drilling

86

xvi  

LIST OF APPENDICES

APPENDIX TITLE PAGE

Appendix A Laboratory test data - material or intact properties  94

Appendix B Static axial load/trial shaft test data - mass properties  102

Appendix C

Pressuremeter test and Suspension PS Logging data - mass properties  113

Appendix D Seismic refraction survey data - mass properties 169

xvii  

LIST OF SYMBOLS

α - Rock socket reduction factor with respect to quc

Ab - Pile base area

AS - Pile shaft area

B - Footing width in cm & Pile diameter

β - Reduction factor with respect to the rock mass effect

c - Cohesion

D - Diameter of socket & Depth of pile base below rock surface

δ - Opening of joint in cm

E - Young’s Modulus

Ei - Elastic Modulus of intact rock

Eid - Deformation modulus of intact rock material

EP - Pile Modulus

Er&Em - In-situ Rock Modulus (Mass Rock Modulus)

Erd - Deformation modulus of in-situ rock mass

Es - Secant Modulus

Et - Tangent Modulus

fb - Unit base resistance for the bearing layer of soil

Fb - Partial Factor of Safety for Base Resistance

Fg - Global Factor of Safety for Total Resistance

fS - Unit shaft resistance for each layer of embedded soil

FS - Partial Factor of Safety for Shaft Resistance

FOS - Factor of Safety

FS - Mobilised Skin Friction

G - Modulus of rigidity (Shear Modulus)

g - Acceleration due to gravity, 9.8m/sec2

xviii 

γ - Effective density of rock mass

h - Depth of socket in rock

i - Number of soil layers

IS - Point-load index strength

- Poisson’s ratio

MRF - Mass Reduction Factor

Nc & Nφ & Nγ  - Bearing capacity factors

Nd - Depth factor

Nj - Empirical coefficient depending on the spacing of discontinuities

qa - Allowable safe bearing pressure

Qag - Allowable geotechnical capacity

Qbu - Ultimate base capacity

qC - Average uniaxial crushing strength of intact rock material

Qsu - Ultimate shaft capacity

quc - Unconfined compressive strength (UCS) of intact rock

ρ - Density of limestone, g/cm3

R2 - Coefficient of Determination

RMR - Rock Mass Rating

RQD - Rock Quality Designation

S - Spacing of joint in cm

SBP - Safe Bearing Pressure

t - Ton

TS - Tensile strength

UCS - Uniaxial compressive strength

VF - Field compression (primary) wave velocity, m/s

VL - Laboratory compression (primary) wave velocity, m/s

VP - Compression (Primary) wave velocity, m/s

VS - Shear (Secondary) wave velocity, m/s

Ψ - Socket roughness

1

CHAPTER 1

INTRODUCTION

1.1 Background

Most problems in rock engineering and construction involve either the

strength of the in-situ rock mass or the compressibility of the rock mass. For

purposes of design it is necessary to represent, in equations of engineering mechanics

the corresponding numerical values representing an appropriate in-situ property.

Strength values and modulus values determined from laboratory testing of intact rock

cores are recognized as not being directly applicable to the in-situ rock mass because

of the scale effect.

Presence of joints in rock mass has rendered it to be discontinuous in nature.

Expressed in terms of Rock Quality Designation (RQD), this discontinuous to nature

makes a rock mass to behave differently than intact rock samples used in laboratory

tests. Some forms of reduction on the properties must be applied as intact rock is

usually stronger than a discontinuous rock. In bored pile design, the mass properties

of the rock mass are the essential input parameters. The socket skin friction for

instance, is estimated using the rock mass properties (e.g. in-situ modulus and RQD)

and the related pile and rock socket dimensions. Surface roughness and strength of

2

the socket wall (main contributor to the skin friction) are difficult to quantify as they

depend on rock strength, RQD and method of drilling. It is due to the intricate

interactions between the pile and the surrounding rock mass that the design of a

bored pile is semi-empirical and relies greatly on established correlations. Despite

these interacting factors, certain components which dictate the pile behaviour can be

quantified through laboratory and field tests. The measured properties can be

established in the form of correlations and used for predicting conditions of rock

mass and consequently, to assess whether the design of bored pile in this rock is

acceptable.

Hence it is thought that if the corresponding values for the in-situ rock mass

are known (e.g. safe bearing pressure and in-situ modulus) then, correlation between

intact and mass properties could be recognized. Some correlations exist between

mobilised skin friction and RQD of the surrounding rock. It is also found that joints

(i.e. RQD) dictate the in-situ modulus of limestone, and consequently, correlation

exists between RQD, intact and in-situ modulus (Barton et al., 1974; Waltham, 2002;

Singh and Goel, 1999). However, these in-situ properties must be measured in the

field using relevant methods such as Pressuremeter tests which have been carried out

at the project site. Without any related and viable number of field data, it may be

difficult to ascertain useful correlations, even though the laboratory data is abundant.

1.2 Problem Statement

Reliable design of a bored pile relies greatly on data pertaining to properties

of rock mass surrounding the pile socket. However, these properties such as skin

friction, in-situ modulus are difficult and costly to acquire for it requires direct

measurement on the in-situ rock. When such data is lacking, the design is often

based on semi-empirical method. Unfortunately, this method may lead to some level

of uncertainty on whether a pile is over- or under-design. It is thought that there are

3

means to verify the reliability of the design approach. For instance, if characteristics

of the pile and properties of the in-situ rock can be correlated to certain level of

reliability, then this correlation can be used to verify suitability of the design. In

addition, correlation between intact and mass properties of a rock can be used to

predict the characteristics of its in-situ mass, and this information is vital for proper

design of bored pile.

1.3 Objectives of Study

This study is aimed at establishing some correlations between properties of

intact rock and in-situ rock, with specific focus on design of bored pile in limestone.

In achieving the aim, following objectives are set forth:

1) To identify and to establish relationships between selected intact (material)

properties and discontinuous (mass) properties of limestone, with focus on

laboratory properties like compressive strengths and compression (primary)

wave velocity.

2) To verify current approach in designing micro piles in limestone and criterion

used in validating the geotechnical capacity of the pile (e.g. mobilised skin

friction) and the condition of rock (e.g. RQD).

3) To identify and to establish correlations between designs criterion of pile and

mass properties of in-situ rock, with focus on mobilised skin friction and

RQD.

4) To establish correlations between selected rock mass properties (in-situ

modulus of deformation and Poisson’s ratio) and its discontinuous state

(RQD), particularly those correlations relevant to design of micro pile in rock.

4

1.4 Methodology

To achieve the desired goals, the following steps are adopted. Compilation of

related notes and reports on bored pile design, rock mass and rock material properties

that are important for design approach. Appropriate material properties of limestone

through various laboratory tests and characterisation of intact rock samples was

collected. Field data (provided by Unit Geoteknik Jalan, Jabatan Kerja Raya

Malaysia, and other parties and contractors involved in the site investigation work

and field tests) which include site investigation report, static axial compression load

tests and Pressuremeter test was compiled too. And finally analysis of data to

establish suitable correlations for verifying reliability of existing practice on micro

pile design, and for predicting in-situ conditions of limestone rock mass was done.

1.5 Scope of Study

This study was carried out on Limestone bedrock in Pandan Indah, Kuala

Lumpur. Data used was related rock properties obtained from laboratory tests and

field tests in that site. Field data provided by Unit Geoteknik Jalan, Jabatan Kerja

Raya Malaysia, and other parties and contractors involved in the site investigation

work and field tests obtained from laboratory tests. These field performance tests

were included trial shafts and in-situ assessment (Pressuremeter test) on limestone

bedrock. Weakening effects in expressing the discontinuous nature of limestone is

due to presence of joints only, effect of weathering and cavities were not considered.

The correlations established are used as guides for checking the performance and

reliability of micro pile socketed in limestone. Others correlations were proposed to

relate typical material and mass properties of limestone.