ii

EVALUATION OF INNOVATION LIGHTWEIGHT FILL IN PROBLEMATIC

SOIL

REVENTHERAN A/L GANASAN

A thesis submitted in

fulfilment of the requirement for the award in the

Master by Research

Faculty of Civil and Environmental Engineering

Universiti Tun Hussein Onn Malaysia

MAY 2016

iii

This thesis is dedicated to my loving parents, my younger brother and younger sister

and also to my whole

family for their unconditional love and support.

iv

ACKNOWLEDGEMENT

I would like to express my sincere appreciation to my co-supervisor, Prof. D.C

Wijeyesekera for his enthusiastic guidance and his constant interest throughout this

research. I am truly indebted to him for the tremendous effort he has made in

providing advices, criticisms, encouragement and assistance for the completion of

this thesis. With his generous help, I was able to gain much experience and

knowledge as a researcher throughout the program. I am very proud and honoured to

have him as a friend.

I am also very grateful to have Dr Alvin John Lim Meng Siang as my

supervisor as he always been available in giving suggestion and advice during course

of the research. His absolute support is greatly appreciated. I wish to also express my

gratitude to Prof. Emeritus Dato Dr. Hj. Ismail Hj. Bakar as my co-supervisor who

has always given me his support and motivation to strive for success. Special thanks

also to the support staffs of RECESS, Madam Salina binti Sani, Mr Mudzaffar Syah

bin Kamarudin and Mr Amir Zaki bin Salikin. They have been very kind to provide

guidance to me in the laboratory.

To all my colleagues (Mdm Tuan Noor Hasanah Tuan Ismail and Miss Amira

Ratia) and other researchers I have met, I enjoyed the friendship and the support that

you all have given to me. Many instructive discussions were held including the

difficult and joyful times we have gone through together throughout the years were

deeply appreciated.

Last but not least and most important of all, a heartfelt thanks to my loving

parents for their love, support, patients and encouragement they had given me. Warm

thanks to all my family members and friends as well for placing a trust and believe in

me. It has been an incredible journey; I hope to make them all proud.

v

ABSTRACT

Construction of structures on soft soils gives rise to some difficulties in Malaysia and

other country with soft soils, especially in settlement both in short and long term.

The most critical geotechnical challenges are excessive settlement and differential

settlement leading to hazardous and discomfort in road usage and distress in

buildings. The focus of this research is to minimize the differential and non-uniform

settlement on peat soil with the use of an innovative cellular mat. The behavior and

performance of the lightweight material (in block form) was investigated and in

particular the use as a fill in embankment on soft ground in both physical and

numerical modelling. Peat soil, sponge and innovative cellular mat were used as

physical modelling where else PLAXIS 2D was selected as the numerical modelling

part whereby both of these modelling act as the main research material in this study.

The initial part of this research (physical modelling) had taken place in monitoring in

settlement behaviour thus it will be only done as laboratory testing. The laboratory

model test was conducted in a steel tank of size 100cm (length) x 50cm (width) and

60cm (height). The bottom, back face and the sides of the tank were made of steel.

The front wall of the test tank was fabricated from a 15mm thick perspex glass plate

to observe failure mechanism. The uneven settlement with problem was uniquely

monitored photographically using spot markers. For the numerical method, the

data/input through past literature review and also through the testing done in peat

from Parit Nipah had been applied in both Mohr Coulomb and Soft Soil constitutive

of models thus comparing the occurrence of settlement behaviour including the

presence of new innovative lightweight material. These physical and numerical

modelling were carried out as to simulate the real problem and case study in Parit

Yaani, Batu Pahat, Johor approaching to the bridge connected with embankment.

vi

The mini trial embankment test was built with the innovative cellular mats place

underneath to identify the suitable cover depth thus propose in laying these new

lightweight mats under the embankment surface in the future (real site/field testing).

In the end of the research, the innovative cellular mat have been proven literally in

both physical and numerical modelling in reducing the excessive and differential

settlement up to 50% and 45% respectively compare to the flexible base and rigid

base foundation. This has also improve the stiffness of soils as well as the porous

contain in cellular structure which help in allowing water/moisture to flow through in

or out without condition of floating.

Keywords: Soil settlement, Soft soils, Sponge, Innovative cellular mat, Physical

modelling, Numerical modelling (PLAXIS 2D)

vii

ABSTRAK

Pembinaan struktur di atas tanah lembut didapati menimbulkan beberapa masalah

dan kekangan di Malaysia dan negara-negara lain yang diliputi oleh tanah lembut,

terutama apabila berhadapan dengan enapan berlaku dalam jangka masa pendek atau

panjang. Cabaran yang paling kritikal dihadapi dalam kejuruteraan geoteknik adalah

masalah enapan yang berlebihan dan perbezaan enapan yang membawa kepada

bahaya dan ketidakselesaan terhadap penggunaan jalan raya. Tumpuan kajian ini

adalah untuk mengurangkan perbezaan dan ketidakseragaman enapan pada tanah

gambut melalui penggunaan innovasi selular mat dalam kaedah pemodelan fizikal

dan juga kaedah pemodelan numerik. Penyiasatan telah dilakukan dalam perlakuan

dan prestasi geo-bahan ringan dan khususnya diaplikasi sebagai bahan pengisi

tambak untuk tanah lembut. Tanah gambut dari Parit Nipah Darat, span dan innovasi

selular mat telah digunakan sebagai model fizikal manakala PLAXIS 2D sebagai

model numerik menjadi bahan utama dalam penyelidikan ini. Pemantauan tingkah

laku enapan daripada sebahagian kajian penyelidikan akan diteruskan dalam ujian

makmal. Ujian model (fizikal) makmal telah dijalankan dalam tangki keluli bersaiz

100cm (panjang) x 50cm (lebar) dan 60cm (tinggi). Pada bahagian bawah, belakang

dan sisi tangki diperbuat daripada besi. Dinding di bahagian depan tangki ujian telah

difabrikasi menggunakan perspek dengan ketebalan 15 mm plat kaca untuk melihat

mekanisme kegagalan yang akan berlaku. Data yang diperolehi daripada kajian-

kajian lepas yang dilakukan oleh penyelidik dan kajian semasa tanah gambut di Parit

Nipah terdahulu telah diaplikasikan dalam model numerik. Melalui model numeric

(‘Mohr Coulomb’ dan ‘Soft Soil’) ini, perbandingan akan dilakukan antara setiap

asas berdasarkan kesan daripada penggunaan selular mat berinovasi. Kaedah model

fizikal dan numerik dilakukan mengikut simulasi keadaan sebenar yang berlaku di

jambatan Parit Yaani, Batu Pahat, Johor.

viii

Mini ujian percubaan tambak dibina dengan menutup penuh selular inovatif di bawah

telah mengenalpasti kedalaman sesuai dengan harapan mencadangkan untuk

penghamparan inovasi mat baru di bawah permukaan benteng pada masa akan

datang (tapak sebenar / ujian lapangan). Di akhir kajian ini, innovasi selular mat telah

mengurangkan enapan yang berlebihan dan perbezaan dalam enapan sebanyak 50%

dalam model fizikal dan 45% dalam model numerik berbanding asas-asas lain.

Selular mat ini juga telah meningkatkan kekukuhan tanah di mana rongga-rongga

yang terdapat dalam struktur selular telah membantu mengalir keluar air/kelembapan

dengan sempurna supaya dapat mengelakkan tanah dalam keadaan terapung.

Kata kunci: Pengenapan tanah, Tanah lembut, Span, Inovasi selular mat, Model

fizikal, Model numerik

ix

CONTENTS

TITLE

i

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT iv

ABSTRACT v

CONTENTS ix

LIST OF FIGURES xiv

LIST OF TABLES xxi

LIST OF SYMBOLS AND ABBREVATIONS xxiii

CHAPTER 1 INTRODUCTION 1

1.1 Background of Study 1

1.2 Problem Statement 2

1.3 Aim & Objectives of Study 8

1.3.1 Aim of study 8

1.3.2 Objectives of study 8

1.4 Scope of Study 9

1.5 Significance of Study 9

1.6 Organizational Structure of Thesis 9

CHAPTER 2 LITERATURE REVIEW 11

2.1 Introduction 11

2.2 Concept of Settlement in Soft Yielding Soils and

Methods of Mitigating Settlement 11

2.2.1 Concept of Soil Settlement 11

x

2.2.2 Types of settlements 14

2.2.3 Case Studies of Settlements on Problematic

Ground 14

2.2.3.1 Chronology of events that took place at

The Palace of Fine Arts in Mexico City 15

2.3.3.2 Chronology of events that took place at

The Leaning Tower of Pisa 16

2.2.4 Soil Consolidation Models 19

2.2.5 Field Testing Equipment 21

2.3 Challenging and Problematic Soils 25

2.3.1 Soil Interaction (Soft Soils) 25

2.3.2 Characteristics Properties of Clay Soil 27

2.3.2.1 Properties of soft clay in Batu Pahat 27

2.3.3 Characteristics Properties of Hemic Peat Soil 29

2.3.3.1 Properties of peat soil in Malaysia 29

2.4 Lightweight Fill Material 31

2.4.1 Structure of Cellular Solid 31

2.4.2 Engineering application of cellular structure 34

2.4.3 Cellular Mat Studies on a Foundation 37

2.5 Modelling (Numerical) 42

2.5.1 Geotechnical Software 42

2.5.2 Finite Element Model (PLAXIS 2D) 43

2.5.2.1 Types of Constitutive Modelling in

PLAXIS 2D 44

2.5.2.2 Case Studies of Modelling Involving

PLAXIS 46

2.6 Chapter Summary 52

CHAPTER 3 RESEARCH METHODOLOGY 53

3.1 Introduction 53

3.2 Research and Flowchart Design 53

3.3 The Design of Experiments 55

3.3.1 Materials 58

xi

3.3.1.1 Peat Soil 58

3.3.1.2 Innovative cellular mat 58

3.3.2 Preparation of Materials 60

3.4 Testing 62

3.4.1 Laboratory Testing 62

3.4.1.1 Physical Modelling Testing on Sponge 63

3.4.1.2 Physical Modelling Testing on Hemic

Peat Soil 65

3.4.2 Field Testing 67

3.4.2.1 Trial Embankment Test Using Hollow

Cardboard Boxes Buried in Compacted

to Average Dry Density of 3000 kg/m3

of Red Laterite with Motorcycle

Loading (To determine minimum cover

depth, dmin) 70

3.4.2.2 Trial Embankment Test Using

Innovative Cellular Mats and Red

Laterite with Motorcycle Loading (To

investigate the appropriateness of

the “dmin” cover) 73

3.4.2.3 Testing for Red Laterite Soil

Approaching to Mini Trial

Embankment (To investigate the lateral

deformation of the soil cover) 79

3.4.3 Numerical Modelling Testing 83

3.4.3.1 PLAXIS 2D Modelling Approaching

the Design Scale of Physical Modelling

Laboratory Testing 84

3.4.3.2 Uniformity Modelling of Settlement

and Heaving in PLAXIS 2D with the

Application of Lightweight

Innovative Cellular Mat 88

3.5 Data and Analysis 92

xii

3.6 Safety and Health Precautions 93

3.7 Chapter Summary 93

CHAPTER 4 RESULTS AND ANALYSIS 94

4.1 Introduction 94

4.2 Physical Analysis of Sponge and Hemic Peat Soil

(Refer to 1st Objective) 94

4.2.1 Moisture Content 95

4.2.2 PH Value of Peat Water 95

4.2.3 Analysis of Polypropylene Tubes 96

4.3 Critical Model Study Rigid and Flexible Base on

Yielding Foundations (Simulated using Sponge) 98

4.3.1 Settlement Subjected in Full Sponge 99

4.3.1.1 Analysis and Comparison of

Settlement with Full Sponge 100

4.3.2 Settlement Subjected in Half Sponge and Half

Solid 106

4.3.2.1 Analysis and Comparison of

Settlement with Half Sponge

Foundation 106

4.4 Critical Model Study of Rigid and Flexible Base

Analysis on Yielding Foundation (Simulated using

Hemic Peat Soil) 112

4.4.1 Settlement Subjected in Half Soil and Half

Solid 112

4.4.1.1 Analysis and Comparison of

Settlement with Half Soil Foundation 113

4.5 Numerical Modelling Analysis (Refer to 2rd

Objective) 115

4.5.1 The Numerical Modelling (PLAXIS 2D)

Analysis Approaching to Physical

Modelling (Laboratory Scale) 116

xiii

4.5.2 The Numerical Modelling (PLAXIS 2D)

Analysis with Different in Thickness of

Embankment 131

4.6 Analysis of Mock-Up Trial Embankment using

Prototype Model of Hollow Boxes (Refer to 3rd

Objective) 145

4.7 Analysis of Mini Trial Embankment using Innovative

Cellular Mats (Refer to 4th Objective) 148

4.8 Analysis of Three Different Heights of Red Laterite

Soil Samples Approaching to Mini Trial Embankment

(Soil Behaviour) 155

4.9 Chapter Summary 157

CHAPTER 5 CONCLUSION & RECOMMENDATION 158

5.1 Introduction 158

5.2 Conclusion 158

5.3 Recommendation 161

REFERENCES 163

APPENDIX 171

xiv

LIST OF FIGURES

1.1 Distribution of suitable and unsuitable soils in Malaysia 3

1.2 The site settlement occurs at Parit Yaani, Sri Gading, Johor

(Coordinate of 1.877832, 103.016557)

4

1.3 The marine clay deposited along Parit Yaani’s river covered with

geotextile (2010)

4

1.4 The fill and compaction done on the surface of marine clay soil 5

1.5 Chronological sequence of activity at Parit Yaani Bridge, Batu

Pahat, Johor.

6

1.6 The current situation of site observation (taken on October 22,

2015) with the increment angle of the slant/edge of the

embankment approaching to the Parit Yaani’s bridge

7

2.1 Elastic settlement in shallow flexible and rigid foundation 13

2.2 The diagram in types of settlement 14

2.3 The settlement occur on The Palace of Fine Arts 16

2.4 The soil profile of The Leaning Tower of Pisa 18

2.5 The initial idea used by John Burland and teams which come to

failure

18

2.6 Void ratio – effective stress relationships for different times 19

2.7 Isotaches set for a lacustrine chalk sample 20

2.8 Time resistance for a load step in a oedometer 20

2.9 Schematic arrangement of the hydrostatic profile gauge 21

2.10 Preloading of subsoil 24

2.11 Menard Vacuum Consolidation method used for preloading soft

saturated fine grained soils such as clays, silts or peat.

24

2.12 An example of typical field setup used in data acquisition system 25

2.13 Structure of human’s skin (cell) 32

xv

2.14 Minor burns on top layer of skin 32

2.15 An aluminium honeycomb 33

2.16 Open-cell polyurethane foam 33

2.17 Closed-cell polyethylene foam 33

2.18 Polymer cellular foam structure- low density open cell spray foam

insulation has been installed to fill and seal stud cavities of this

prefabricated wall panel and shipped to the site for final

installation

35

2.19 Left: Standard honeycomb sandwich design. Right: Advanced

features of the composite core structure manufactured with

selective laser melting (SLM)

35

2.20 Wood cellular structure used in built pyramid 36

2.21 Cork cellular made up as brick in construction 37

2.22 Design and construction of expanded polystyrene fill as a

lightweight soil replacement

38

2.23 A typical tyre bale with dimensions 39

2.24 An example of embedded pile row using PLAXIS 2D 44

2.25 3-D modelling created with PLAXIS 3-D TUNNEL 49

2.26 Simulation of ring footing in the numerical analysis 50

2.27 Geometry Model of Raft Foundation without Skirt 50

2.28 Geometry Model of Raft Foundation with two sides vertical Skirt

and one side vertical skirt

51

2.29 Global geometry of the axisymmetric model 51

2.30 Mesh deformation after analysis 51

2.31 Slope geometry and parameters 52

3.1 The flowchart for the overall project 54

3.2 The peat soil which taken from the site 58

3.3 The arrangement of cellular mat in octagonal shape in side view 59

3.4 The arrangement of cellular mat in hexagonal shape in plan view 59

3.5 The real moulded from hot chamber of innovative cellular mat 59

3.6 The parameters and geometries contained in both octagonal and

hexagonal cell.

60

3.7 The physical modelling test 62

xvi

3.8 The three different sticks attached in between sponge layers 63

3.9 The small modelling box made from plywood placed on the

surface of the sponge

64

3.10 The mats(1 – layer) which will be made from cardboard at the

thickness of 5mm placed on the sponge

64

3.11 The constant position of DSLR camera in the experiment 65

3.12 The small modelling box made from plywood placed on the top

and middle surface of half soil and half solid

66

3.13 The innovative cellular mats (3 – layers) arranged on the surface

of the half soil and half solid.

67

3.14 The road construction (laterite over soft soil) 68

3.15 Three A4 boxes (void) with different thickness (50mm, 100mm

and 150mm) were initially used as cellular prototype

70

3.16 The laterite soil hauled and transported in the formwork/mould

with the height of 0.65m from road pavement.

71

3.17 The motorcycle will be used as moving load across the mini trial

embankment

72

3.18 The conditions of the prototype of innovative cellular mats were

still kept in intact after the initial test was carried out

72

3.19 Three innovative cellular mats with different thicknesses (50mm,

100mm and 150mm respectively) with the surfaces covered by

fabrics

73

3.20 The innovative cellular mats was placed inside the

formwork/mould with the dimension of 2.0m (L) x 0.8m (W) x

0.4m (H) at the RECESS

74

3.21 The laterite soil was taken from RECESS area and then place into

the formwork into three level where each level was compacted

using the plate compacter to ensure the constant density (mass of

laterite soil per volume of formwork) in each every time/run the

testing conducted

74

3.22 The formwork was removed to get a mini embankment before

proceed for the testing

76

xvii

3.23 15 rod steels in dexion structure was pointed respectively on the

surface of the mini embankment to determine the initial reading

before the moving load being imposed

76

3.24 The platform was set at the two edges of mini embankment

respectively and the motorcycle (moving load) was imposed

through the mini embankment

77

3.25 After the first run of the moving loading, the 15 rod steels in

dexion structure was pointed respectively on the surface of the

mini embankment to measure the first deformation value using

electronic vernier calliper before commencing for the next second

and third run of motorcycle loading testing

77

3.26 The geotechnical core cutter was used in three different points

along mini embankment to determine the possible constant

density for each per run time the test being conducted

78

3.27 The mini embankment was demolished to investigate the physical

damage on three innovative cellular mats with different thickness.

The conditions of the innovative cellular mats were still kept in

intact after the three runs of motorcycle loading was carried out

78

3.28 Three moulds of PVC pipe (100mm dia.) were placed between

the dexion frame structures. The preparation occurred in RECESS

1

79

3.29 The laterite soil was pour in three different PVC pipes (different

heights) then compacted every three layers using rod hammer.

80

3.30 Three samples of the laterite soils (compacted) placed in the

dexion frame structures

81

3.31 The steel rods and metal plate were placed on the surface of

laterite soils respectively.

81

3.32 Initial loadings of 1 kg were placed respectively attached to steel

rods and metal plates.

82

3.33 At the static loading of 40 kg, the 350mm height of laterite soil

start to bulging and buckling

82

xviii

3.34 The 300mm(middle) height of laterite sample begin to buckling

meanwhile the 350mm(right) height of laterite sample starting to

collapse.

83

3.35 Modelling done in PLAXIS 2D in axisymmetric model (MC and

SSC model)

85

3.36 The mesh generated in flexible foundation course 86

3.37 The mesh generated in rigid foundation course 86

3.38 The mesh generated for both full design of 1 and 4 layers of mat

foundation course

87

3.39 The mesh generated for both space/width design of 1 and 4 layers

of mat foundation course

87

3.40 Initial condition for water weight applied in model 88

3.41 Embankment modelling done in PLAXIS 2D in axis-symmetry 89

3.42 The mesh generated in flexible foundation embankment course 90

3.43 The mesh generated in rigid foundation embankment course 90

3.44 The mesh generated for both full design of 1 and 4 layers of mat

foundation embankment course

91

3.45 The mesh generated for both space/width design of 1 and 4 layers

of mat foundation embankment course

91

3.46 Initial condition for water weight applied in model 92

4.1 The acidity level value of peat water, 3.40 (Left) whereas the pH

value of normal water, 7.69 (Right).

96

4.2 Figure 4.8: Compression test using Universal Testing Machine,

(a: Single tube unsoaked, b: Single tube soaked in peat water, c:

Single tube soaked in tap water, d: Double/twin tube soaked in tap

water & e: Double/twin tube soaked in peat water)

97

4.3 The placement of three equal sizes of sponges in the physical

modelling box with the full dimension of 100cm (length) x 50cm

(width) x 40cm (height).

99

4.4 The schematic diagrams of three equal sizes of sticks (different

colours) placed between sponges in the physical modelling box

99

4.5 The graphical results obtained from flexible full sponge 102

4.6 The graphical results obtained from rigid full sponge 103

xix

4.7 The graphical results obtained from mats 1-layer full sponge 104

4.8 The graphical results obtained from mats 4-layers full sponge 105

4.9 The placement of combined half sponge and half solid 106

4.10 The graphical result obtained from flexible half sponge 108

4.11 The graphical result obtained from rigid half sponge. 109

4.12 The graphical result obtained from mat’s 1-layer. 110

4.13 The graphical result obtained from mat’s 4-layers. 111

4.14 The combination setup of half peat soil and half solid 113

4.15 Definition on the vertical movement of foundation 115

4.16 Selected curve points in connectivity of PLAXIS 2D 125

4.17 Example of total displacement movement occurred in

embankment thickness of 2m [(a): Flexible foundation, (b): Rigid

concrete foundation, (c): Mat 1-layer full foundation, (d): Mat 1-

layer s/w foundation, (e): Mats 4-layers full foundation & (f):

Mats 4-layers s/w foundation] occurred in MC model

132

&

133

4.18 Example of total displacement movement occurred in

embankment thickness of 2m [(a): Flexible foundation, (b): Rigid

concrete foundation, (c): Mat 1-layer full foundation, (d): Mat 1-

layer s/w foundation, (e): Mats 4-layers full foundation & (f):

Mats 4-layers s/w foundation] occurred in SSC model

134

&

135

4.19 Selected curve points in connectivity of PLAXIS 2D 136

4.20 Uniformity graphical depict the settlement pattern/behaviour

(Point A) over heave pattern/behaviour (Point B) against the

embankment thickness over the constant peat thickness

144

4.21 The mock-up mini trial embankment applied for three hollow

boxes (as mats prototype with different thicknesses) for four

rounds/turns

146

4.22 The settlement analysis occur within three different thicknesses of

innovative cellular mats

150

4.23 The detail settlement analysis occur in the real mini trial

embankment

151

4.24 The condition of mini trial embankment before and after the test

conducted

153

xx

4.25 The observation done for both before and after the testing in

every soil thicknesses

156

5.1 The field settlement design/mode (propose) shown in

embankment area jointed with concrete bridge located at Parit

Yaani, Batu Pahat, Johor.

162

xxi

LIST OF TABLES

2.1 Some other causes in soil settlements 12

2.2 Categories of settlement 12

2.3 The elastic parameters of various soils 14

2.4 Chronology of events that took place at the Palace of Fine Arts,

Mexico

15

2.5 Chronology of events that took place at The Leaning Tower of

Pisa

17

2.6 The description and types of model 19

2.7 Critical analysis of vacuum preloading 23

2.8 Geotechnical properties of soft soils in Malaysia 26

2.9 Physical properties of Batu Pahat soft clay 28

2.10 The physical properties of peat soil in Malaysia 30

2.11 Physical and chemical properties of organic soil 30

2.12 Properties of lightweight materials applied in construction field 40

2.13 Types and descriptions of soil model 44

2.14 Case Studies of PLAXIS Modelling 46

3.1 The completed preparations and testing in this whole Research 55

3.2 Geometric equations 60

3.3 Physical properties of typical hemic peat soil in Johore, Malaysia 61

3.4 Underground utilities apparatus all depths are from the surface

level to the crown of the apparatus

69

4.1 Moisture content of disturbed hemic peat soil 95

4.2 The data taken from compression test for average of every three

samples of polypropylene tubes respective condition/state (after

one month)

97

4.3 The differences in settlement design in foundations (full sponge) 100

4.4 The differences in settlement design in foundations (half sponge) 107

xxii

4.5 The differences in settlement design in foundations (half peat

soil)

114

4.6 The input parameters and properties from past literature review

for PLAXIS 2-D

116

4.7 The input properties of polypropylene for PLAXIS 2-D 117

4.8 The total displacement and mesh deformation occurred in each

foundation for the case of Mohr-Coulomb soil model

117

4.9 The total displacement and mesh deformation occurred in each

foundation for the case of Soft Soil Creep soil model

121

4.10 The settlement rate occurred at every connectivity points in

Mohr-Coulomb of soil model

126

4.11 The settlement rate occurred for every connectivity points in Soft

Soil Creep of soil model

128

4.12 Comparison analysis between numerical and physical modelling 131

4.13 The settlement and heaving occurred in every connectivity points

in Mohr-Coulomb soil model

136

4.14 The settlement and heaving occurred in every connectivity points

in Soft Soil Creep soil model

140

4.15 The uniformity ratio between embankment/peat and

settlement/heaving

144

4.16 The geotechnical properties of laterite soil for the mock-up mini

trial embankment

147

4.17 The settlement data for three turns using moving loading in mini

trial embankment

148

4.18 The properties of laterite soil using core cutter testing equipment

for the real mini trial embankment

152

4.19 The condition of the innovative cellular mat after three runs

(moving loading) in real mini trial embankment

154

4.20 The properties of moulded cylindrical laterite soil approaching to

mini trial embankment

157

xxiii

LIST OF SYMBOLS AND ABBREVATIONS

B x L Breadth x Length

Q Uniform loading

Df Depth between foundation to soil surface

H Height between hard boundary (rock layer) to foundation

Z Depth below foundation area

Es Modulus of elasticity

St Total settlement

▲ Total strain/deformation

dt/d𝜀 Time resistance

H Hydrostatic head probe

BS British Standard

BSCS British Soil Classification System

USCS Unified Soil Classification System

D10 Effective size

D30 Diameter of the particle size at 30% finer

D60 Diameter of the particle size at 60% finer

RECESS Research Centre of Soft Soil

RECESS 2 Research Centre of Soft Soil (Computational, Mathematical &

Software Modelling)

UTHM University of Tun Hussein Onn Malaysia

W Natural water content

LL Liquid limit

PL Plastic Limit

PI Plasticity Index

Gs Specific gravity

xxiv

Cc Compression Index,

TRRL Transport and Road Research Laboratory

LR Laboratory Research

𝛾unsat Soil unit weight above phreatic level

𝛾sat Soil unit weight below phreatic level

kx Horizontal permeability

ky Vertical permeability

Eref Young’s modulus

ʋ Poisson’s ratio

cref Cohesion

𝜑 Friction angle

Ψ Dilatancy angle

s/w Spacing per width

DSLR Digital single-lens reflex camera

EPS Expanded polystyrene

SD Standard Duty

HD Heavy Duty

EHD Extra High Duty

UHD Ultra High Duty

EA Stiffness Area of material

EI Stiffness Inertia of material

d Height of material

w Weight of material

Mp Plastic moment of material

ρ Density

ρd Dry Density

E Void Ratio

n Porosity

1

CHAPTER 1

INTRODUCTION

1.1 Background of Study

In modern Civil Engineering, emerging problems are solved using modelling both

physical and numerical. Modelling is defined as a process of solving physical

problems by appropriate simplification of reality. The skill in modelling is to spot the

appropriate level of simplification, distinguish important features from those that are

unimportant in a particular application and use engineering judgment. The

advancements in computational techniques and material science are incorporated into

a numerical modelling based on the analysis of physical phenomena and constitutive

laws applied majorly in roadway/highway engineering. There are particularly three

main generic classification of modelling which are:

Interpretation: The use of the model to help in interprets field or laboratory

data. For example, the development of a model to help back-analyse a suite of

monitoring information.

Design: In this application, a model is develops to help compare the relative

performance of various design alternatives, with less emphasis on the final

predicted performance.

Prediction: Finally, the model will provide a final quantifiable prediction of

actual field behaviour.

2

In soft yielding foundation the self-weight of the structure cause excessively

undesirable settlement. This constraint intuitionally involved any of the construction

of structures on soft soils to be further undergoing settlement neither in short or long

term. Constructions of structures (highway embankment etc.) on soft soils have given

rise to major time dependent and varying differential settlement issues in Malaysia

and elsewhere. These lead to traffic hazards (discomfort in road usage and distress in

buildings).

The settlement occurs as large as 0.5m recorded (Burland et. al, 2009)

maximum have been occurred in the leaning tower of Pisa and was recorded. Soft

soils experience with low strength and rapid settlement for some foundations in

unavoidable circumstances which lead to the ground failure. An example of soft soils

is soft organic clays which have the characteristics of very low shear strength and

lacks compressibility. An extreme example is organic peats.

Peat soil, sponge and innovative cellular mat used in Final Year Project

(FYP) study sounds promising and academically challenging (Ganasan et. al, 2015).

The innovative cellular mat act as a lightweight fills material to exert little pressure

to soft soil and also to reduce the self-weight of embankment. The prediction in

settlement behaviour from this part of research will be done in both laboratory and

field testing. The uneven settlement with problem which was uniquely monitored

photographically using spot markers from the physical model testing will be analysed

further using the numerical modelling.

1.2 Problem Statement

Soft soil areas are rapidly being used for infrastructure construction and other

related development due to the limited availability of ‘suitable’ ground for

infrastructure construction. Figure 1.1 shows the area covered by suitable and

unsuitable soils in Malaysia. These challenges arise towards engineer facing in all

sorts of problem to design and construct foundation of building, road and highway

embankment. It is because structures construct on peat soil are often affected by

stability due to high compressibility, low shear strength and high permeability. They

are subjected to massive primary and long-term consolidation settlement even when

subjected to a moderate load.

3

The most critical geotechnical challenges are excessive settlement and

differential settlement leading to hazardous and discomfort in road usage. Many

conventional methods (pile, vertical drain, soil replacement, soil stabilisation etc.)

have been used to reduce these problems. However due to self-weight from the

conventional methods used could not maintain the soil structure allowing them

become as secondary subject towards excessive in soil settlement.

Figure 1.1: Distribution of suitable and unsuitable soils in Malaysia (assess from

http://image.slidesharecdn.com/malaysiaaspbangkok2015-150923134133-lva1-

app6892/95/malaysia-8-638.jpg?cb=1443015770, on April 6, 2016)

The site settlement was observed at the bridge located near Parit Yaani as

shown in Figure 1.2. Apparently this bridge was constructed on the marine clay

(problematic soil) thus allowing the real time of the settlements happen. At the end of

the slope of the bridge having a large amount of settlement which was approximately

0.5m gave uneasy to the vehicles to pass over the bridge at the certain speed (very

slow) to avoid any damages occur.

4

Figure 1.2: The site settlement occurs at Parit Yaani, Sri Gading, Johor (Coordinate

of 1.877832, 103.016557)

The bridge construction at Parit Yaani was commenced on June 1st, 2010.

Initially the construction area was covered with palm oil field with smaller size of

old bridge. Then the Public Work Department of Batu Pahat took in charge for

releasing the funding in demolishing the old bridge and rebuilding new bridge

consist of full reinforced concrete on the marine clay soil. During the whole period of

construction, the marine clay soil deposited along the river was covered with

geotextile (Figure 1.3) in order to prevent from the preliminary structures built

collapse in the river.

Figure 1.3: The marine clay deposited along Parit Yaani’s river covered with

geotextile (2010)

Vertical crack occur on

bridge similar as in the

modelling.

5

According to the engineer in-charge for highway department from Public

Work Department (JKR) of Batu Pahat, before the piling works began, the sand and

laterite soil was fill and compacted (Figure 1.4) on the surface of the marine clay.

The fill work was took place about three months to get an appropriate smooth surface

layer.

Figure 1.4: The fill and compaction done on the surface of marine clay soil

The technician from Public Work Department of Batu Pahat stated that the

condition of soil surrounding in Batu Pahat have high intolerance level of acidity

which may cause effect to the reinforced concrete structure. Thus most of cement

used in Batu Pahat province were mixed readily with the chemical substances due to

fulfil the needs in become at least partially compatible with the soft soil structure in

this area. In other word the cement used was not pure ordinary Portland applied in

Batu Pahat area. After the full installation of bridge using Industrial Building System

(IBS) based for the superstructure work, the pavement was lay on the rigid form

along the bridge. At the both end of the bridge having with the occurrence of the

slanting embankment, three layers of soil treatment consist of geotextile and geogrid

were placed on the surface of road base before covered with binding and wearing

layer (pavement) as the finishes. The construction of the bridge was completed on

July 2nd

, 2013 and the defect liability was started upon the completion of bridge work

for almost one and half to two years. During this liability period, the edge/slant

which supported by the reinforced concrete bridge had undergone settlement

movement from horizontal then proceed to the vertical direction for the total of four

times. This bridge has been used for non-stop during the day by light vehicles and

during night time fully exceled by heavy transportations (trucks and buses).

6

For these numbers of settlements occurrence, the soil treatment using three

layers were induced approximately once every five months starting from November

2013, April 2014, September 2014 and recently ended on February 2015 (Figure

1.5).

November 2013

April 2014

September 2014

February 2015

Figure 1.5: Chronological sequence of activity at Parit Yaani Bridge, Batu Pahat,

Johor.

7

The current situation of the angle of the slant/edge of the embankment approaching

to the Parit Yaani’s bridge has been increased has shown in Figure 1.6. The defect

liability period has been ended however this bridge is still monitored for time being

by the Public Work Department due to the curiosity intrigued in them of how to

overcome the problem for the settlement occur in the horizontal movement. The

engineer and the technician from Public Work Department of Batu Pahat proposed in

using sheet pile and placed at the end of the bridge, despite this idea as an proposal

the issue raised was the cost for the material and the installation of permanent sheet

pile are expensive than the soil treatment and reconstruction works.

Figure 1.6: The current situation of site observation (taken on October 22, 2015) with

the increment angle of the slant/edge of the embankment approaching to the Parit

Yaani’s bridge

Recently some of the constructions developers have been tried in solving

these extensive problems by using lightweight material such as expanded polystyrene

EPS, tyre shred etc. These material were capable in reduce the pressure exert in soil.

The most popular lightweight material used was EPS as it has extreme low density.

Nevertheless this lightweight material also has a weakness regard in buoyancy failure

(closed porous) which not allow water or moisture to pass through it. Thus the soil

experienced in over saturated which lead into excessive settlement from the applied

load. Other than that, this EPS is weak in the chemical (take times) which at the end

it will crumple and become the source of food for the insects such as termites, ants

and others.

8

Another application used was lightweight concrete pile which generally has

low density and low strength compared with normal concrete pile. According to

(Suleimen et.al, 2010) the use of the lightweight concrete for piling is very rare due

to high porosity and poor in strength. Hence in this research, an innovative cellular

mat will be used as a new lightweight product with open porous for overcome the

soft soil settlement problem.

1.3 Aim & Objectives of Study

1.3.1 Aim of study

The aim of this research is to investigate the efficacy of the application of a

porous lightweight product that will minimize the differential and non-uniform

settlement on soft yielding soils.

1.3.2 Objectives of study

To achieve the above aim, following objectives in this research are:

i. To investigate through physical modelling the settlement behavior of

continuous and discontinuous stiff mat structures on sponge and on yielding

soils (peat).

ii. To evaluate the results of numerical modelling (PLAXIS 2D) for the cases of

embankment design for the application of with and without the innovative

cellular mat.

iii. To assess the depth of influence of traffic loading by carrying out simulated

embankment prototypes.

iv. To develop appraise propose design methodology guideline for the

performance of a cellular mat in laboratory and field scale with appropriate

instrumentation.

9

1.4 Scope of Study

In this research, the engineering characteristics of peat soil and lightweight

material were determined through critical comprehensive review of past literature

and focused in laboratory testing. The mini trial embankment (physical modelling)

was demonstrated to find out critically performance of the cellular mat from the

strength (difference in thickness/height) viewpoint.

Only PLAXIS 2D tool of modelling was adopted where this numerical

method had look at the specific case of an embankment with the laboratory

information from samples of peat collected from Parit Nipah were both compared

with published data and was used in this research. The capability and potential of

innovative cellular mat was further analysed through field performance.

1.5 Significance of Study

This study offers investigation into conceptual product development of new

lightweight material to reduce the soil settlement. This study will also lead to a

simple and cost effective in construction technology to overcome the soft soil

settlement where this new innovation of lightweight material is capable in:

Easy installation with the embankment

Reduce and redistribute the pressure exerted from loading to the soil

1.6 Organizational Structure of Thesis

This thesis comprises total of five chapters, then followed by the list of

references and appendices. In the first chapter will be basically emphasize the

introduction to the background of study, problem statement (a case study was done

with collaboration of Public Work Department (JKR), Batu Pahat, Johor which

majorly investigate the approach bridge built on the soft yielding soils located at

Parit Yaani, Batu Pahat, Johor.), the aim and objectives, scope of study followed by

the significant obtained from this research study.

10

Chapter two describes the critical literature review of the settlement behavior

under short or long term of taken period. This chapter begins with the discussion in

concept of soil settlement, case studies in problematic ground, field testing used for

settlement, properties of peat soil, structure of cellular solid and the properties of

geotechnical software (PLAXIS 2D). Through this discussion had included the

findings and testing made in the past by the expertise in geotechnical engineering.

Moving on the chapter three describing the methodology of research which

reviews overall work phases done according to the flowchart and Gantt chart. This

chapter will peculiarly describe how the research need to be carried out in a correct

manner based on the given standard procedure and application with respect to this

research.

In chapter four, the minimum values of settlement (cover depth) was obtained

throughout mock-up test using trial embankment (physical modelling) done in

Research Centre of Soft Soil (RECESS), UTHM. The testing was carried out with

the acquisition of monitoring the settlement behavior using appropriate size of

innovative cellular mat as a lightweight material. At the partial end of physical

modelling, this data was analyzed and computed into graphical form. In numerical

modelling, PLAXIS 2D was applied using the data from past literature of review and

also through the testing done for peat from Parit Nipah thus comparing the predicted

and actual settlement scenarios with the occurrence of cellular mats.

Chapter five had presented the conclusion and recommendation of the

findings through the achievement of the aim and objectives in this study.

CHAPTER 2

LITERATURE REVIEW

2.1 Introduction

This chapter gives the reader with a critical review of published literature on the

following aspects related to the research.

Concept of settlement in soft yielding soils and methods of mitigating

settlement

Challenging and problematic soils

Lightweight fill material

Modelling (Physical and Numerical)

Soil settlements occur principally due to undesirable geotechnical properties

with foundation soil and changes in external loading and/or water table. There are

challenging ground condition (e.g. uneven and non-homogenous, high moisture

content peat beds) in Malaysia where such non-uniform settlement is a hazardous

problem.

2.2 Concept of Settlement in Soft Yielding Soils and Methods of Mitigating

Settlement

2.2.1 Concept of Soil Settlement

When a load is applied or the pore water pressure is decreased in compressible

foundation layer, it increases the vertical effective stress. This stress causes a time

12

dependent vertical strain of the soil resulting the ground to move downward. This

downward movement of the ground is called settlement. According to Terzaghi

(1925) in (Das, 2006), the main problem encountered in soil mechanics was the soil

settlement which is directly caused by consolidation of soft soils. Table 2.1 outlines

the soil settlement scenarios that occur due to other causes.

Table 2.1: Some other causes in soil settlements

Causes in

settlements Description of the way in settlements occur References

Changes in

temperature Severe shrinkage (furnaces) in clay soils occurs due to drying out. Wray, 1995

Vegetation Draining effect of the roots from trees. Atkinson,

2007

Lowering in

groundwater

Water table in the surrounding ground is lowered when water is

pumped from an excavation- change in hydrostatic conditions- soil

above the reduced water table may shrink and has an increase in

effective stress- soil beneath water table may consolidate.

Atkinson,

2007

Moisture

content

Soft clays expand due to changes in volume (increase or decrease

of water content)

Foster et. al,

2013

Loss of lateral

support

Deep excavation alongside existing foundations- bearing capacity

of soil directly beneath a footing is dependent on the lateral support

provided by the surrounding soil

Khan, 2012

Effects of

mining

subsidence

Coal mining – Coal is continuously mined across a wide surface as

workings advance, the space left is partly filled with waste material

and the pit props removed. Then the unsupported roof slowly

subside with the overburden, up to the ground surface thus undergo

settlement

Foster et. al,

2013

Seepage and

scouring

Movement of water carries in fine particles: Seepage- removal of

soil particles by surface water or stream to scouring

Ouyang et.

al, 2015

The four phases of soil settlement that usually occur is outlined in Table 2.2.

Table 2.2: Categories of settlement (Das, 2006)

Categories

of

settlement

Explanations

Elastic

settlement

Known as immediate settlement, occur due to elastic deformation of dry soil with moist

and saturated soils without any change in the moisture content. Generally based on

equations derived from the theory of elasticity shown in Figure 2.1.

Primary

settlement

Occur in change of the saturated cohesive soil’s volume with the presence of expulsion

of the water that occupies the void spaces. The results can be identified from the

standard 1-Dimensional consolidation test. Types of primary consolidation:

Normally consolidated clays:- Present effective overburden pressure =

maximum pressure the soil has been subjected to in the past

Over-consolidated clays (𝜎′o + Δ𝜎′av < 𝜎′c):- Present effective overburden

pressure < maximum pressure the soil has been subjected to in the past.

Over-consolidated clays (𝜎′o < 𝜎′c < 𝜎′o + Δ𝜎′av):- Over-consolidated clays are

mostly subjected to marine clays - sedimentation increases the surcharge on the

soil but subsequent erosion removes much of the load.

Secondary

settlement

Occurs at constant effective stress, related to the long-term of settlement in saturated

cohesive soils which compute the result in plastic adjustment of soil fabrics. Important

when come to the case of all organic and highly compressible inorganic soils.

Tertiary

settlement

Results of material creep under the effective stress and depend on rheological properties

of soil as well as time dependent in a long period.

13

The soil structure interaction also plays a significant role in the distribution of

settlement. Figure 2.1 compares a schematically the elastic settlement profile for

flexible and rigid foundation. As seen in figure the interaction from the rigid

foundation is to redistribute the stresses in such a way to provide a uniform rigid

foundation settlement. Leshchinsky and Marcozzi (1990) mentioned that the effect of

stiffness of a shallow foundation on its ultimate load bearing capacity has been

observed from the behavior of small-scale flexible and rigid foundation models

resting on dense sand. The results indicate that reducing the foundation’s stiffness at

soil interface may significantly increase its load-bearing capacity but also associated

with increased settlement. It is suggested that the apparent increase in bearing

capacity is due to differences in the contact pressure distributions combined with the

phenomenon of progressive failure.

Apparently for thick and rigid footings, the pressure distribution under the

footings is normally assumed to be linear. If uniform and symmetrical loadings are

exerted on the footings, the bearing pressure is uniformly distributed. Bowles (1987)

explores further the variation due to interaction of the type of foundation with the

soft soil. The rigid foundation is similar to the application of lintels (resist

compressive, bending and shear stresses) which usually are smaller members

spanning and carrying only the loads immediately above window and door openings

(Christine Beall, 1993). Thus the properties of lintels is similar to the proposed new

lightweight material which is expected reduce settlement occurs and help in

improving the soil structure interaction in soft yielding soils.

Figure 2.1: Elastic settlement in shallow flexible and rigid foundation (Das, 2011)

14

The determination of this elastic settlement needs value of modulus of elasticity and

poisson’s ratio. Nominal value of these different soils is given in Table 2.3.

Table 2.3: The elastic parameters of various soils (Abd Aziz, 2009)

Type of soil Modulus of Elasticity, Es (MN/m2) Poisson’s ratio, μs

Loose sand 10.5 – 24.0 0.20 – 0.40

Medium dense sand 17.25 – 27.60 0.25 – 0.40

Dense sand 34.50 – 55.20 0.30 – 0.45

Silty sand 10.35 – 17.25 0.20 – 0.40

Sand and gravel 69.00 – 172.50 0.15 – 0.35

Soft clay 4.1 – 20.7

0.20 – 0.50 Medium clay 20.7 – 41.4

Stiff clay 41.4 – 96.6

2.2.2 Types of settlements

According to Lambe and Whitman (2008), settlements can be occurring in three

different ways such as:

(i) Uniform settlement – The structure settled constant and uniformly

(ii) Tilt settlement – The structure experience in differential of settlement

(iii) Non-uniform settlement – The structure settled due to elongation

These three types of settlement can be seen according to the related places which

sketched in Figure 2.2.

Figure 2.2: The diagram in types of settlement (Lambe and Whitman, 2008)

2.2.3 Case Studies of Settlements on Problematic Ground

These case of studies had been taken from 2 different places in order to identify the

problem occurs on structure towards the soil.

15

2.2.3.1 Chronology of events that took place at The Palace of Fine Arts in

Mexico City

The Palace of Fine Arts (The Palacio de Bellas Artes) was built comprising a

structural steel frame supported on a raft (or mat) foundation 1.8 to 3 m thick. The

building is approximately rectangular with overall dimensions of 81.4 m by 118.9 m

while the height was measured 44 m high from surface. Table 2.4 shows the

chronology event where the settlement and the remedies taken at the Palace of Fine

Arts, Mexico City.

Table 2.4: Chronology of events that took place at the Palace of Fine Arts, Mexico

City (Modified from http://elearning.shu.edu.cn/tlx/pdf/54_94.pdf access on October

7, 2014)

Year Description of event Conceptual Remarks

1904-

1934 The city built in and completed late due to unwanted problem.

Took long period to

complete during war

state

1907

A survey was taken on top the raft before the steel frame had

been constructed showed a noticeable dish-shaped profile with

a maximum settlement in the middle of 38 mm.

Initial settlement occur

in the middle during

construction

1908 The steel frame had been completed the partly built structure

had settled 1.68 m

The settlement kept

increased due to the

add selfweight

1910

A diagonal crack appeared across the raft. At this time the

settlement was peaking at 43 mm per month (about 1.4 mm per

day) and the north-west corner was settling faster, possibly as a

result of more loading at this end.

Short term settlement

occur (43 mm per

month) forming a

diagonal crack

1911-

1912

Stabilisation measures were carried out consisting of encircling

the structure with a row of steel sheet piling about 3 m away

from the structure to resist the horizontal pressures. The grout

was used at ratio of 1:2 cement with sand mixture and about

20,000 bags of cement and 4000 m3 of sand were injected. The

rate of settlement was reduced to 11 mm per month but it was

still continuing.

Stabilisation method

using cement grout

injected to the soil

beneath

1950

According to (Thornley et al,. 1955), the palace was settling at

a rate of 38 mm per year. The structure had settled 3 m below

the ground level. This settlement happen in contact with

contributed of groundwater abstraction pumping. It was found

that the Palace itself was settling at a rate of nearly 125 mm per

year and that most of the settlement was occurring within the

clay to 33 m below ground level. Pile foundations taken to the

first sand stratum had been used successfully to support

adjacent part of buildings. Several old Spanish buildings had to

be removed to prepare the site where these were found to have

been supported on pile foundations but the piles were removed

and the voids filled with concrete.

Pile foundation and

concrete (fill void) was

implemented to reduce

the settlement as

possible

1960-

onwards

The weight of skyscrapers being built around the Palace had

pushed the subsurface water and soil around sufficiently to

raise the building.

Reducing groundwater

table

16

Figure 2.3 shows soil profile beneath the foundation of The Palace of Fine Arts.

Figure 2.3: The settlement occur on The Palace of Fine Arts

(http://elearning.shu.edu.cn/tlx/pdf/54_94.pdf access on October 7, 2014)

2.2.3.2 Chronology of events that took place at The Leaning Tower of Pisa

The present of the leaning Tower of Pisa currently stands at a height of 55.86 m on

the low (south) side and 56.7 m on the high (north) side. The weight of the tower is

estimated to be 16,000 tons. The tower currently leans at an angle of 3.97° but leaned

at an angle of 5.5° prior to the stabilization efforts in the late 20th to early 21st

centuries. The table 2.5 shows the prior of chronology happened where the

settlement and the remedies taken at the Leaning Tower of Pisa.

17

Table 2.5: Chronology of events that took place at The Leaning Tower of Pisa

(Burland et al., 2009)

Year Description of event Conceptual Remarks

1173

AD

The tilt of the tower was first noticed during the initial phase of

construction. Engineers tried to overcome the problem by

making the columns and arches of the third story slightly taller

on the sinking side.

Undrained condition

1372

Upon the completion of the tower, the builders made a final

attempt to compensate for the lean by angling the eighth (top)

story bell chamber.

Increased self-weight

without proper planning

causing tilt of tower

1911 Measurements revealed that the top of the tower was actually

moving at a rate of around 0.05 inch a year.

Movement/tilt observed

every year (no method

was comply to mitigate

the initial problem)

1935

The first modern attempt at stabilization of the tower occurred

in 1935 sealed the base of the tower by drilling a network of

holes into the foundation and then filling them with a cement

grout mixture. Unfortunately this method caused a slightly

increasing the lean.

Stabilizing foundation

using cement grout mixer

1975

The 800 year old mystery was finally solved by John Burland,

an English geotechnical engineer who discovered that the

primary cause of the tilt was a fluctuating water table (Figure

2.4) which would perch higher on the tower’s north side thus

causing the tower’s characteristic slant to the south.

Fluctuating water table

1990 The Tower of Pisa had tilt more than 5°. Increased in tilt

1991

An international team of geotechnical engineers, structural

engineers, and historians were gathered in an attempt to save the

famous landmark.

Discussion among

engineers for preservation

work

1992

The preservation team (led by John Burland) finally took action

when the first story was braced with steel tendons, to relieve the

strain on the vulnerable masonry.

Structural work using

steel tendons to relieve

strain of foundation

1993 600 tons of lead ingots were stacked around the base of the

north side of the tower to counterweight the lean.

Additional weight used to

reduce lean

1995

The team opted for 10 underground steel anchors to invisibly

yank the tower northwards. This was only served to bring the

tower closer to collapse than ever before. The anchors were to

be installed 40 meters deep from tensioned cables connected to

the tower’s base. On the night of 7 September 1995, the tower

lurched southwards by more than the previous year as shown

in Figure 2.5. The team was summoned for an emergency

meeting and the anchor plan was immediately abandoned and

another 300 tons of lead ingots were added in a desperate

attempt to prevent the loss of the tower.

Anchorage plan was

abandoned due to the

tower lurched southwards

which may cause the

collapse of tower

1999-

2001

Soil extraction was a viable solution that would be acceptable to

all concerned parties as it had the advantage of not touching the

tower itself thereby placating the art historians. The process

involved the installation of helical drills surrounded by hollow

steel casings to remove soil from below the high north side of

the tower. This would create a condition of controlled,

localized, subsidence and allow gravity to coax the structure

back upright. Approximately 77 tons of soil had been removed

and the tower had been straightened by 44 cm, returning to its

inclination. While more soil could have been removed, the soil

extraction program reduced the stress on the vulnerable first

story enough to be safe yet also maintained the distinctive lean

of the landmark. The team estimated that it would take

approximately 200 years for the tower to return to its pre-

stabilization inclination and the tower was reopened to the

public in December 2001.

Soil extraction which

additional soils were

removed to reduce the

extensive differential

settlement of the leaning

tower.

18

2003-

2009

Prof. Burland introduced a new drainage system beneath the

Pisa’s north side upon discovering that the root cause of the lean

was a perched water table upon the upper silt layer below the

north side of the tower which fluctuated during the rainy season,

sometimes coming within 12 inches of the surface. The new

drainage system addressed this condition and is hoped to

permanently alleviate additional movement. The inclination

continues to be monitored daily and revealed that the tower did

not move at all between 2003 and 2009.

Drainage system was

accumulated to prevent

water table fluctuate

during the rainy season

Figure 2.4: The soil profile of The Leaning Tower of Pisa (Burland et al., 2009)

Figure 2.5: The initial idea used by John Burland and teams which come to failure.

(http://madridengineering.com/case-study-the-leaning-tower-of-pisa/ access on

October 7, 2014)

19

2.2.4 Soil Consolidation Models

There are four common types of models used for consolidation testing as explained

in Table 2.6. These models are useful in determine the types, parameter and

characteristics of soils.

Table 2.6: The description and types of model (Olsson, 2010)

Types of

model Descriptions of model

Taylor’s

model

One of the first theories (Figure 2.6) where secondary consolidation was at least partly

involved in the primary consolidation was presented by Taylor & Merchant (1940) and a

first model that looked at the change in the void ratio with a change in effective stress

and time was outlined by Taylor (1942).

Isotache’s

model

Suklje (1957) presented a more generalised theory, where the rate of strain depends on

the mean values of void ratio and the effective stress. This relationship was presented

using a set of isotaches (Figure 2.7). This was the first model to suggest that the

behaviour of clay is governed by a unique relationship between effective stress, void

ratio and rate of strain. In this model, creep occurs during both the primary and

secondary consolidation phases. This model also accounted for that the time-dependent

strains are influenced by the layer thickness, hydraulic conductivity and drainage

conditions.

Bjerrum’s

model

Bjerrum (1967) presented a unique relationship between void ratio, overburden pressure

and time. Any given value of the overburden pressure and void ratio these corresponds

to an equivalent time of constant loading and a certain rate of delayed consolidation. The

model is intended to explain the apparent pre-consolidation stress and over consolidation

ratio of virgin clays resulting from ageing. The volume change occurred could be

divided into two components instant and delayed compression. "Instant" compression

occurs simultaneously due to increase in effective stress and causes a reduction in the

void ratio until an equilibrium value is reached at which the structure effectively

supports the overburden pressure. "Delayed" compression represents the reduction in

volume at unchanged effective stresses.

Time

resistance

concept

Janbu (1969) presented the time resistance concept (Figure 2.8) and stated that it was a

powerful and instructive tool for clarifying the stress- and time dependent behaviour of

soils under compression, swelling or recompression.

Figure 2.6: Void ratio – effective stress relationships for different times, Taylor

(1942) in Olsson, 2010

20

Figure 2.7: Isotaches set for a lacustrine chalk sample from Suklje (1957) in Olsson,

2010

The Figure 2.8 shows the results from a single load step in an oedometer test.

The sample is drained at the top and pore pressure is measured at the impermeable

bottom. If time were to be considered as an action and strain as a response to this

action, Janbu defines time resistance as:

R = dt/d𝜀 (2.1)

Figure 2.8: Time resistance for a load step in a oedometer (Svanö et al., 1991)

21

2.2.5 Field Testing Equipment

In this section various kind of tools and machineries are used in order to collecting

the specific data of settlements such as:

(i) Hydrostatic profile gauge - The hydrostatic profile gauge (shown in

Figure 2.9) consisted of a control unit, a readout unit and a length of triple

tubing connected to a settlement probe which can be pushed (with

aluminium rods) or pulled (with a draw-cord) through the access tube.

Two of three small tubes are filled with water and are constantly back-

pressurized in order to overcome surface tension effects, and to prevent

the formation of bubbles. Measurements of elevation are taken at regular

intervals in an access tube which is laid in a sand-filled trench. The

hydrostatic head at the probe 'H' is measured with the aid of a differential

pressure transducer. These readings are related to a reference pin outside

the tube and in this manner a complete profile of the tube can be

established. By comparing profiles taken at different times, the vertical

displacement of the tube can be determined to an accuracy of ± 1.0 cm,

which is excellent for this application. (Zvanut, 2003)

Figure 2.9: Schematic arrangement of the hydrostatic profile gauge (Zvanut,

2003)

22

(ii) Pre-loading technique in ground improvement - The purpose of

preloading is to increase the shear strength of the soil, to reduce the soil

compressibility and to reduce the permeability of the soil prior to

construction and placement of the final construction load and prevent

large and/or differential settlements and potential damages to the

structures.

Conventional Preloading: The simplest solution of preloading is a preload

using an embankment. According to Bhattacharya and Basack (2011),

when the load is placed on the soft soil, it is initially carried by the pore

water. When the soil is not very permeable, which is normally the cases,

the water pressure will decrease gradually because the pore water is only

able to flow away very slowly in vertical direction. In order not to create

any stability problems, the load must mostly be placed in two or more

stages. The principle is shown in Figure 2.10. If the temporary load

exceeds the final construction load, the excess refers to as surcharge load.

The temporary surcharge can be removed when the settlements exceeds

the predicted final settlement. This should preferably not happen before

the remaining excess pore pressure is below the stress increase caused by

the temporary surcharge. By increasing the time of temporary over-

loading, or the size of the overload, secondary settlement can be reduced

or even eliminated. This is because by using a surcharge higher than the

work load, the soil will always be in an over-consolidated state and the

secondary compression for over-consolidated soil is much smaller than

that of normally consolidated soil. This will benefit greatly the subsequent

geotechnical design.

Vacuum Preloading (Figure 2.11): Bhattacharya and Basack (2011) again

also mentioned that there is a different type of loading used for preloading

when the conventional preloading is not feasible because of soft soil

being too weak to take even a small height of embankment. In such cases,

vacuum preloading can be applied. Kjellman first introduced vacuum

preloading in1952 to accelerate consolidation where atmospheric pressure

replaces surcharge load. Arrangement for consolidation of soil through

23

vacuum preloading consists of a set of vertical drains, a sand layer

(drainage path) over it that is sealed from atmosphere by an impervious

layer/membrane. Horizontal drains are placed in the drainage path and

finally connected to a vacuum pump. Further to this, extra arrangement

may be arranged to make it airtight. The vacuum pump creates negative

pressure in the drainage path. Negative pore water pressure is generated

with the application of negative pressure, which results in increase in

effective stress in the soil which ultimately leads to an accelerated

consolidation. Table 2.7 shows the critical analysis of vacuum preloading.

Table 2.7: Critical analysis of vacuum preloading (Bhattacharya and

Basack, 2011)

Advantages Disadvantages

No extra filling is required

Shorter construction time

No heavy machinery is

required

No chance of penetration of

chemical admixture in

ground and hence

environment friendly

Causing isotropic

consolidation eliminates the

risk of failure under

additional permanent

construction load.

There is no risk of slope

instability beyond

boundaries

Rate and magnitude of

loading can be controlled

and thereby settlement can

be controlled

Keeping the drainage system effective

under the membrane that expels water

and air becomes more difficult

throughout the whole pumping

duration

Maintaining a leak proof system is also

a very difficult task

Maintaining an effective level of

vacuum is not also an easy task

Difficulties in anchoring the system at

the periphery

Lateral seepages are reduced towards

the vacuum area

24

Figure 2.10: Preloading of subsoil (Bhattacharya and Basack, 2011)

Figure 2.11: Menard Vacuum Consolidation method used for preloading soft

saturated fine grained soils such as clays, silts or peat.

(http://www.vibromenard.co.uk/techniques/vacuum-consolidation access on

October 25, 2014)

(iii) Data acquisition system – Monitoring and retrieve the data of settlement

automatically by data logger (shown in Figure 2.12). It is a best method to

determine the vertical settlement and pore water pressure occur from

ground level.

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