COMPARISON OF PREDICTED SETTLEMENT BEHAVIOUR TO THE

FIELD MEASUREMENT OF STONE COLUMN IMPROVED GROUND

SELVEM S/O RAMAN

UNIVERSITI TEKNOLOGI MALAYSIA

COMPARISON OF PREDICTED SETTLEMENT BEHAVIOUR TO THE

FIELD MEASUREMENT OF STONE COLUMN IMPROVED GROUND

SELVEM S/O RAMAN

A Project Report Submitted as a Partial Fulfillment of The

Requirement For The Award of The Degree of Master of

Engineering (Civil-Geotechnics)

Faculty of Civil Engineering

Universiti Teknologi Malaysia

MAY 2006

iv

Dedicated to my mother and late father

v

ACKNOWLEDGEMENT

I would like to extend my greatest thanks to my mother who is the pillar of my

strength and existence. I would like to present this to my late father whom always would

want me to be someone great. I would like to present my effort to the lotus feet of god

for whom has made myself into who I am now. Special thanks and love goes to the one

whom had discovered the softest side in my heart.

Greatest appreciation goes to Ir. Balakrishnan who has contributed directly and

indirectly in my engineering lifefor moulding me into who I am today. Gratitude also

goes to GCU Geotechnics Sdn. Bhd. and for sponsoring me partly for this course. I

would like to thank my supervisor Associate Professor Dr. Aminaton Marto for her

guidance and for the precious time spent to make this project a success. I would also like

to thank all whom have contributed, be it directly or indirectly for this project report.

Thank you so much.

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ABSTRACT

Stone columns form one of the accepted methods of ground improvement at

which large size columns of coarse stones are installed into the ground by means of

special vibrators. It is found that, stone columns increase shear strength of the ground,

thus increasing bearing capacity and stability of the ground as well as to reduce

settlement. The stone column design using Priebe’s method has gained much

widespread use due to its simplicity. However it was found that the settlement

computed using Priebe’s method has always been higher than the field settlement

obtained. A comparison study was carried out between design settlement and field

settlement. Based on the comparison and back analysis it is found that the improvement

ratio of stone column increases with the increase of soil strength. This inherently

implies to that of larger corresponding stone column spacing. Based on the findings,

charts has been made to obtain a settlement reduction factor to be used in calculating

the settlement of the improved ground, resulting in increase in the spacing and reducing

the number of stone columns utilised. The time rate settlement was back calculated

using Asaoka’s method to assess actual coefficient of vertical and horizontal

consolidation. With this, the back calculated spacing together with the coefficient of

consolidation parameters were used to simulate back the field settlement to validify the

findings. Based on the simulation, it was found that the back calculated improvement

ratio and spacing are corresponding well with the actual field settlement. Therefore a

relationship was established for basic soil parameters and the parameters related to

stone column settlement details.

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ABSTRAK

Tiang batu adalah salah satu cara pemulihan tanah yang diterima secara umum di

mana batu-batu dimasukkan ke dalam tanah dengan mengunakan pengetar khas. Tidak

dapat dinafikan bahawa tiang batu menambahkan kekuatan ricih tanah dan secara

langsung menigkatkan keupayaan galas dan kestabilan tanah dan juga mengurangkan

enapan. Rekabentuk tiang batu mengunakan kaedah Priebe telah mendapat kegunaan

meluas kerana ia adalah satu kaedah yang mudah untuk digunapakai.

Walaubagaimanapun Secara amnya enapan yang dikira mengunakan kaedah Priebe

selalunya lebih tinggi daripada enapan sebenar di tapak. Satu perbandingan telah

dilakukan diantara magnitud enapan yang dikira menggunakan kaedah Priebe dan

enapan sebenar di tapak. Melalui perbandingan dan pengiraan balik yang dibuat,

didapati bahawa nisbah pembaikan tiang batu meningkat dengan meningkatnya kekuatan

tanah. Ini secara tidak langsung berkait dengan peningkatan jarak antara tiang batu.

Daripada perbandingan dan pegiraan balik, sebuah carta telah di sediakan untuk

mendapatkan faktor pengurangan enapan dimana carta itu boleh digunakan dalam

pengiraan enapan yang secara tak langsung dapat menambahkan jarak antara tiang batu

dan seterusnya mengurangkan bilangan tiang batu yang diperlukan untuk mencapai

enapan yang sama. Kadar enapan juga dikira balik mengunakan kaedah Asaoka untuk

mendapatkan pekali pengukuhan tegak dan ufuk. Dengan mengunakan data pengiraan

balik ini, enapan sebenar di kira balik untuk mengetahui samaada data-data pengiraan

balik itu benar ataupun tidak. Daripada pengiraan balik, telah didapati bahawa, jarak

antara tiang batu dan nisbah pembaikan tiang batu berhubung rapat. Maka satu

hubungan telah dicapai untuk parameter asal tanah dan parameter enapan tiang batu.

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TABLE OF CONTENT

CHAPTER TITLE PAGE

DECLARATION 1 ii

DECLARATION 2 iii

DEDICATION iv

ACKNOWLEDGMENT v

ABSTRACT vi

ABSTRAK vii

TABLE OF CONTENT viii

LIST OF TABLES xi

LIST OF FIGURES xii

LIST OF SYMBOLS xiv

LIST OF APPENDICES xvi

1 INTRODUCTION 1

1.1 Introduction 1

1.2 Background of Study 3

1.3 Objectives of Study 4

1.4 Scope of Study 4

2 DESIGN OF STONE COLUMNS 6

2.1 Introduction 6

2.2 Available Design Methods 8

2.3 Priebe’s Method 9

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CHAPTER TITLE PAGE

2.4 Consolidation Rate of Stone Column Improved

Ground 16

2 2.5 Findings by others 19

3 STONE COLUMN CONSTRUCTION 20

3.1 Introduction 20

3.2 Vibro Replacement Method (Wet Method) 21

3.3 Vibro-Displacement Method (Dry Method) 22

3.4 Case Borehole Method or Rammed Columns 25

4 RESEARCH METHODOLOGY 27

4.1 Introduction 27

4.2 Phase I : Literature and State of the Practice Review 27

4.3 Phase II : Data Collection 28

4.4 Phase III : Analysis of Data 29

5 SITE FOR CASE STUDY 30

5.1 Introduction 30

5.2 Subsoil Condition 32

6 ANALYSIS AND DESIGN OF STONE COLUMN

GROUND IMPROVEMENT 33

6.1 Introduction 33

6.2 Stone Column Design 34

6.2.1 Input 34

6.2.2 Analysis 43

6.2.3 Output 45

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CHAPTER TITLE PAGE

6.3 Construction Method Implemented for Reference

Project 45

6.3.1 Stone Column Material 45

6.3.2 Sand for Working Platform and Drainage 46

6.3.3 Installation Method (Wet Top-Feed

Method) 47

6.3.4 Construction Tolerances 48

6.4 Instrumentation 48

7 ANALYSIS AND RESULTS 50

7.1 Introduction 50

7.2 Analysis Design Details 50

7.3 Results of Analysis 51

7.4 Discussion 57

8 CONCLUSION 61

8.1 Conclusion 61

8.2 Recommendation for Further Studies 62

REFERENCES 64

Appendices A-F 67 - 162

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LIST OF TABLES

TABLE

NO.

TITLE PAGE

5.1 Location details of stone column improvement work 32

6.1 Estimation of constrained modulus for clays 37

7.1 values to be adopted in the design 51

7.2 Values of , cv and ch adopted in the design 51

7.3 Back analysis summary of Pribe’s Method 53

7.4 Back analysis summary of Han and Ye’s method through

Asaoka’s method 53

7.5 Summary of relationship of stone column fundamental

properties and subsoil properties 57

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xii

LIST OF FIGURES

FIGURE

NO.

TITLE PAGE

2.1 Application ranges for vibro techniques 7

2.2 Unit cell concept 8

2.3 Design chart for vibro replacement 11

2.4 Consideration of column compressibility 12

2.5 Determination of depth factor 15

2.6 Determination of depth limit value for depth factor 16

2.7 Typical embankment found on stone columns 18

3.1 Vibro replacement method (wet method) 22

3.2 Vibro replacement method (dry top-feed method) 23

3.3 Vibro replacement method (dry bottom-feed method) 24

3.4 Case borehole method (rammed columns) 26

4.1 Analysis procedure 29

5.1 Project location 31

6.1 Tip resistance and friction ratio CPT soil classification chart 36

6.2 Relative density relationship for moderately compressible,

uncemented, unaged quartz sands 39

6.3 Influence of compressibility on ucemented, unaged,

predominantly quartz sands 40

6.4 Expanded soil behaviour type classification chart with

equivalent overburden normalized friction angle and relative

density trends 41

6.5 Proposed correlation between cone bearing and peak friction

angle for quartz sands 42

6.6 Converting the multi layered subsoil into single layer 44

6.7 Typical instrumentation scheme at stone column improved

ground 49

7.1 Relationship between normalized improvement ratio and

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undrained shear strength 54

7.2 Relationship between normalized spacing and undrained shear

strength 54

7.3 Relationship between normalized settlement reduction factor

and undrained shear strength 55

7.4 Relationship between normalized improvement ratio and

friction angle 55

7.5 Relationship between normalized spacing and friction angle 56

7.6 Relationship between normalized settlement reduction factor

and friction angle 56

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LIST OF SYMBOLS

A Grid area

Ac Stone Column Area

c Cohesion

ch Coefficient of horizontal consolidation

cv Coefficient of vertical consolidation

d Depth of subsoil layer from ground

Dc Constrained modulus of stone column material

Ds Constrained modulus of subsoil

fd Depth factor

H Thickness of subsoil

KaC Coefficient of active earth pr essure of column material

mv Coefficient of volume change

n Settlement improvement ratio

Nk Cone factor

Pc Pressure within stone column along the depth

Ps Pressure within soil in tributary area

qc Cone friction

R Settlement reduction factor

Su Undrained shear strength

Ur Degree of consolidation (radial only)

Urv Degree of consolidation (both radial and vertical)

Uv Degree of consolidation (vertical only)

Coefficient of constrained modulus

ig Settlement of improved ground

og Settlement of unimproved ground

c Friction angle of stone column material

s Friction angle of subsoil

xv

s Bulk density of subsoil

s Poisson’s ratio of stone column material

vo Insitu overburden stress

xvi

LIST OF APPENDICES

APPENDIX TITLE PAGE

A Analysis Summary 67

B Analysis for CH254890 to CH255095 77

C Analysis for CH261950 to CH263125 95

D Analysis for CH272100 to CH272350 113

E Analysis for CH297250 to CH 288250 130

F Analysis for CH299400 to CH299625 146

CHAPTER 1

INTRODUCTION

1.1 Introduction

In quest of knowledge and demand, there is ever increasing awareness of new

technologies created or found by man. The field of geotechnical engineering is not

new to this phenomenon. Over the last century, the field of geotechnical engineering

has achieved many milestones with brilliant ideas and advancements. The ground

improvement techniques is one of the area which has attained lots of interest and

improvements due to an interesting fact that ‘anything can be constructed anywhere

if only proper foundation is laid’.

Many methods for ground modification and improvement are available

around the world now, including dewatering, compaction, preloading with and

without vertical drains, grouting, deep mixing, deep densification and soil

reinforcement are among those. Many of these techniques, such as dewatering,

compaction, preloading and grouting, have been used for many years. However,

there have been rapid advances in the areas of deep densification (vibro-compaction,

deep dynamic compaction, compaction piles, and explosive densification), jet and

compaction grouting, deep mixing, and vibro-replacement and vibro-displacement in

2

recent years. These methods have become practical and economical alternatives for

many ground improvement applications.

While most of these technologies were originally developed for uses other

than seismic risk mitigation, many of the recent advances in the areas of deep

densification, jet and compaction grouting, and deep mixing methods have been

spurred on by the need for practical and cost effective means for mitigating seismic

risks. Many of these methods have also been applied to increase the liquefaction

resistance of loose, saturated, cohesionless soils.

Ground improvement techniques basically utilize the effects of increasing

adhesion between soil particles, densification and reinforcement to attain on or more

of the following:

(1) increased strength to improve stability,

(2) reduced deformation due to distortion or compressibility of the soil mass,

(3) reduced susceptibility to liquefaction, and

(4) reduced natural variability of soils.

Of many techniques of ground improvements, stone column has gained lots

of popularity since it has been properly documented in the middle of the last century.

As in most new ground improvement techniques that were developed in foreign

countries, experience has preceded the development of theory and comprehensive

guidelines. Potential applications of stone column include the following :

(1) stabilizing foundation soils,

(2) supporting structures,

(3) landslide stabilization, and

(4) reducing liquefaction potential of clean sands.

The high potential for beneficial use of stone columns is mainly as a ground

improvement technique to strengthen weak and soft soil. This includes the area of

highway, railway and also airfield applications prompted a comprehensive

investigation to determine how and why the system works so well, and to develop

3

appropriate design and construction guidelines. This has resulted in many empirical

design concepts to be published for the purpose of designing the stone column.

1.2 Background of Study

Vibro replacement or stone column has been adapted and utilized as one of

the effective ground improvement method since early 1980’s. This can be referred

back to the ground improvement carried out at certain parts of North South

Expressway, Keretapi Tanah Melayu (KTM) double tracking between Seremban and

Rawang and many more locations throughout the country.

The stone column technology is not new as far as Malaysia is concern, simply

because of the history and the number of contractors engaged in this business. The

major players who were also pioneers in stone column construction in Malaysia are

Keller (M) Sdn. Bhd. and Bauer (M) Sdn. Bhd. There are many other local stone

column contractors now in the market besides these two foreign companies.

Even though the design of stone column is broadly based on empirical

methods, there are a lot of studies being carried out to date to improvise the design

and detailing of the stone columns to match the following details:

(1) local subsoil condition and

(2) local construction methodology.

Most of the cases, there are instrumentations carried out at those areas

improved by stone column but those data have never been utilized fully for the

purpose of improvising the design methodologies adopted. Thus it is appalling that

we, Malaysians have to rely heavily on the foreign research and approach to solve

our own problems.

4

Therefore, an attempt is being made to understand the major principle behind

the stone column ground improvement which is to reduce the total settlement, in

local geotechnical context.

The design works has been carried out based on certain subsoil parameters

derived from the soil investigation carried out at site. This design has been carried

out based on one of the empirical methods available. While the method is predicted

to provide relatively good assessment of the details needed, there is much to be done

to improvise the design approach by comparing the results with the field

instrumentation results. By doing so, it is assumed, at this stage that there could be

some improvement in the context of the detailing such as spacing and number of

stone columns.

1.3 Objectives of Study

The main objectives of the study are as follows:

(1) to predict the settlement behaviour of stone column improved ground

using Priebe’s Method (Priebe H. J., 1995),

(2) to compare the predicted settlement with the field settlement.

(3) to suggest improvisation in the design method adopted based on results

obtained in the comparison study.

1.4 Scope of Study

This study is confined to the following scopes:

(1) This study is to focus on the writer’s own design work carried out using

Priebe’s Method (Priebe H. J., 1995) only.

5

(2) The construction of stone column was carried out based on top feed vibro

replacement method (wet method).

(3) The data collected for the areas or locations of stone column ground

improvement in Malaysia only.

(4) The minimum number of data set is limited to 5 numbers.

(5) The study focuses only on the settlement behaviour of the stone columns.

64

REFERENCES

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Technological Institute, Singapore.

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65

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