SOFT GROUND IMPROVEMENT BY PREFABRICATED VERTICAL DRAIN

(PVD)

NOR AISAH BINTI KHALID

A project reportsubmitted in fulfilment of the

requirements for the award of the degree of

Master of Enineering (Civil-Geotechnics)

School of Engineering

Faculty of Civil Engineering

Universiti Teknologi Malaysia

DISEMBER 2018

iii

DEDICATION

This thesis is dedicated to my father, who taught me that the best kind of

knowledge to have is that which is learned for its own sake. It is also dedicated to my

mother, who taught me that even the largest task can be accomplished if it is done

one step at a time.

iv

ACKNOWLEDGEMENT

The completion of this thesis, I’m very gratefull to ALMIGHTY “ALLAH S.W.T”.

Without his grace and blessing this study would not have been possible. Firstly, I

would like to thank the department of civil engineering for giving me the opportunity

to produce this thesis by providing facilities such as equipment machine to enable me

to make a sample and done the testing. I also like to thank to my supervisor,

Associate Prof. Ir. Dr. Azman Bin Kassim who have provided guidance and detailed

explanation to me from start until the thesis was completed. Besides, I want to thank

my examiner, Muhammad Azril Hezmi and Dr Norzurairahetty Mohd Yunus. I

would like to state the highest gratitude towards my parents had a lot of support and

encouragement morally and financially in producing this paper. Thanks are also

owed to whosoever had contributed to this work either directly or indirectly. Your

support to successful accomplishment of this project will never forget from my

memory. My most gracious appreciation to my friends. Who were hardworking in

produced this thesis and are willing to exchange ideas in helping me prepare this

special work.

v

ABSTRACT

Soft soil improvement in the project requires the consideration of the

preloading programme. This method long track record of success and may be

a unexpected time delay. Then one of the solutions is to use surcharge that fill

must extend horizontally at certain depth beyond the perimeter of the planned

construction. Surcharge must remain in place for months or years, thus

delaying construction. Since this project needs to be completed within 2 years

and the time given to increase the soil strength is 6 months only. Based on

that reason, Prefabricated Vertical Drain (PVD) was added to expedite this

process. It decreases the overall time required for completion of primary

consolidation and also decreases the amount of surcharge load required to

achieve the same desired amount of consolidation over a given period of

time.At BH 9 and BH10, without surcharge the untreated ground would

required about 2.5 year time to eliminate most of settlement. To achieve

99.3% and 99.2 % degree of consolidation the estimated time required is

about 1.5 year. PVD was adopted to expedite the consolidation settlement.

The consolidation degree 99.3 % were required to ensure that anticipated

consolidation settlement of 895mm and 901mm due to permanent fill alone

and compensation settlement permanent fill are completely eliminated and no

excess pore water pressure left in the soil for BH9 and 860.56mm and

868.066mm for BH10. With the introduction of PVD and surcharge fill of

1m, the required degree of consolidation, Ureq of 99.3% (borehole 9) and

99.2% (borehole 10) was expected to be expedited within a designed rest

perod of 6 months. However the evaluation against settlement monitoring

results indicated that the corresponding achieved degree of consolidation over

6 months time was about or more than 90% but less than 99.3%

vi

ABSTRAK

Penambahbaikan tanah lembut dalam projek memerlukan pertimbangan

program preloading. Kaedah ini mencatat rekod kejayaan yang panjang dan mungkin

merupakan kelewatan masa yang tidak dijangka. Kemudian salah satu daripada

penyelesaiannya adalah dengan menggunakan Surcharge yang mengisi mesti

horizontal consolidation pada kedalaman tertentu di luar perimeter pembinaan yang

dirancang. Surcharge harus tetap di tempat selama berbulan atau tahun, sekali gus

melambatkan pembinaan. Oleh kerana projek ini perlu disiapkan dalam masa 2 tahun

dan masa yang diberikan untuk meningkatkan kekuatan tanah adalah hanya 6 bulan.

Berdasarkan sebab itu, Prefabricated Vertical Drain (PVD) telah ditambah untuk

mempercepat proses ini. Ia mengurangkan masa keseluruhan yang diperlukan untuk

menyelesaikan penyatuan utama dan juga mengurangkan jumlah beban Surcharge

yang diperlukan untuk mencapai jumlah pemampatan yang diinginkan yang sama

sepanjang tempoh tertentu. Pada BH 9 dan BH10, tanpa surcharge tanah yang tidak

dirawat memerlukan sekurang-kurangnya 2.5 tahun untuk menghapuskan

kebanyakan penyelesaian. Untuk mencapai tahap penyatuan 99.3% dan 99.2%,

anggaran masa yang diperlukan ialah 1.5 tahun. PVD telah digunakan untuk

mempercepat penyelesaian penyatuan. Penyatuan 99.3% diperlukan untuk

memastikan bahawa penyelesaian konsolidasi yang dijangkakan dari 895mm dan

901mm disebabkan oleh pemanggilan tetap dan penyelesaian pemendapan kekal

sepenuhnya dihapuskan dan tiada tekanan air liang berlebihan yang tersisa di dalam

tanah untuk BH9 dan 860.56mm dan 868.066mm untuk BH10 . Dengan pengenalan

PVD dan Surcharge mengisi 1m, tahap penyatuan yang diperlukan, Ureq 99.3%

(BH9) dan 99.2% (BH10) dijangka dipercepatkan dalam perod istirehat yang

dirancang selama 6 bulan. Walau bagaimanapun penilaian terhadap keputusan

pemantauan penyelesaian menunjukkan bahawa tahap penyatuan yang sama yang

dicapai dalam tempoh 6 bulan adalah kira-kira atau lebih daripada 90% tetapi kurang

daripada 99.3%.

vii

TABLE OF CONTENTS

TITLE PAGE

DECLARATION ii

DEDICATION iii

ACKNOWLEDGEMENT ivv

ABSTRACT v

ABSTRAK vi

TABLE OF CONTENTS vii

LIST OF TABLES ixx

LIST OF FIGURES x

LIST OF ABBREVIATIONS xi

LIST OF SYMBOLS Error! Bookmark not defined.

LIST OF APPENDICES xxiv

CHAPTER 1 INTRODUCTION 1

1.1 Problem Background 4

1.2 Problem Statement 5

1.3 Objective of study 5

1.4 Scope of study 5

CHAPTER 2 LITERATURE REVIEW 7

2.1 Ground Improvement 6

2.1.1 Physical Stabilization 7

2.1.2 Chemical Stabilization 9

2.2 Surcharge Preloding 11

2.3 Drain properties 17

2.4 Properties of filter 19

2.5 Prefabricated Vertical Drain (PVD) Design 20

viii

CHAPTER 3 RESEARCH METHODOLOGY2Error! Bookmark not defined.

3.1 Case Study 2Error! Bookmark not defined.

3.2 Soil investigation 24

3.3 Subsoil condition 27

3.4 Geotechnical Design

3.4.1 Primary consolidation Settlement Analysis 33

3.4.2 Horizontal Consolidation Settlement Analysis 36

3.5 Ground improvement work 38

3.6 Instrumentation 41

3.7 Prefabricated Vertical Drain Installation 44

CHAPTER 4 RESULT AND DISCUSSION

4.1 Primary Consolidation Settlemnt without

PVD (BH9) 48

4.2 Horizontal Consolidation Settlement analysis

with PVD and time-rate of settlemnt 56

4.3 Consolidation settlement anlysis without

PVD (BH10) 60

4.4 Horizontal Consolidation Settlment analysis

with PVD and time-rate of settlement (BH10) 67

CHAPTER 5 CONCLUSION AND RECOMMENDATIONS 73

5.1 Conclusion 7Error! Bookmark not defined.

5.2 Recommendation 74

REFERENCES 75

ix

LIST OF TABLES

TABLE NO. TITLE PAGE

Table 3.1 Description of borehole 8 34

Table 3.3 Description of borehole 9 36

Table 3.4 Design parameter for consolidation settlement analysis 42

Table 3.5 The radial drainage properties adopted into the

horizontal consolidation analysis with PVD 46

Table 3.6 Ground improvement 48

Table 3.7 Method for ground improvement. 49

Table4.1 Final settlement = 892.464m 65

Table 4.2 Settlement curve with surcharge 66

Table 4.4 : With preloading alone or withoud Prefabricated

vertical loading (PVD), the analysis result of

primary consolidation settlement are summarized 68

Table 4.5 The specific time that achieved required uh is then

the optimal time for such drain spacing 70

Table 4.6 The following table is the estimated required resting

time with various spacing of Preafabricated

vertical drain (PVD) 71

Table 4.7 The computation of time-rate of settlement by

integrating prealoading and PVD 72

Table 4.9 Value of settlement without surcharge versus time 78

Table 4.10 Value of settlement Versus Time for Surcharge 79

Table 4.11 The specific time that achieved required uh is then the

optimal time for such drain spacing 84

Table 4.12 The following table is the estimated required resting time

with various spacing of Preafabricated vertical drain (PVD) 84

Table 4.14 : The computation of time-rate of settlement by integrating

prealoading and PVD 85

x

LIST OF FIGURES

FIGURE NO. TITLE PAGE

Figure 2.1 Principle precompression 11

Figure 2.2 Plot of U against ∆σ(ρ)/∆σ(f) for values of

∆σ’(p)/σ’o 12

Figure 2.3 Soil close to be midplane will continue to settle1Error! Bookmark not defined.

Figure 2.4 Plot of midplane degree of consolidation against Tv 14

Figure 2.5 (a) and (b) : Sand drains 15

Figure 2.6 Conceptual illustration of band-shaped PVD and

equivalent diameter of drain well

( Indraratna et al.,2005a ) 17

Figure 2.7 Assessment of equivalent diameter of band-sshaped

vertical drains (indraratna et al., 2005a) 18

Figure 2.8 A typical cross-section of band shaped drain

(Holtz et al., 1991) 18

Figure 3.1 Proposed site is in Lahad Datu, Sabah, Malaysia 23

Figure 3.2 Location of borehole 8 24

Figure 3.3 Location of Borehole 9 25

Figure 3.4 Location of borehole 10 26

Figure 3.5 Soil Profile 40

Figure 3.6 Sketch of ground improvement at BH 9 50

Figure 3.7 Sketch of ground improvement at BH 10 50

Figure 3.8 Synthetic core 52

Figure 3.9 Geotextile filter jacket 52

Figure 3.10 Anchor Plate and Wick Drain. 53

Figure 3.11 Mandrel together with Anchor Plate 54

Figure 3.12 Prefabricated Vertical Drain Installation 55

xi

Figure 3.13 Illustration of construction sequence 58

Figure 4.4 Settlement Curve without Surcharge 64

Figure 4.2 Settlement Curve for Surcharge (895.021mm) 67

Figure 4.3 Settlement Curve for Surcharge ( 901.442mm) 67

Figure 4.4 Graph for settlement curve with and without PVD 73

Figure 4.5 Degree of consolidation curve for with and without PVD 73

Figure 4.6 Settlement Curve without Surcharge ( 860.56mm) 79

Figure 4.7 Settlement curve for surcharge (868.066mm) 80

Figure 4.8 Settlement curve for surcharge 81

Figure 4.9 With preloading alone or withoud Prefabricated

vertical loading (PVD), the analysis result of

primary consolidation settlement are summarized. 82

Figure 4.10 : Degree of consolidation with and without PVD 87

xii

LIST OF ABBREVIATIONS

Cc - Compression Index

Ch - Horizontal coefficient of consolidation

CR - Compression ratio

Cr - Recompression Index

Cv - Vertical coefficient of consolidation

De - Diameter of equivalent cylinder of soil

dm - Diameter of mandrel

ds - Diameter of smear zone

dw - Equivalent well diameter

eo - Initial void ratio

F - Factor considering three compenet

F(n) - Drain spacing factor

F(r) - Well resstance factor

F (s) - Smear effect factor

H - Thickness of compressible layer

Hd - length of drainage path

Ho - initial thickness of compressible soil layer

Kh - Hotrizontal permeability coefficient

Ks - Reduced permeability coefficient in the smear zone

Kv - Vertical permeability coefficient

Ldrain - Length of vertical drain

N - Spacing ratio

OCR - Over consolidation ratio

P’c - Preconsolidation pressure

P’o - Initial effective stress

Qw - Discharge capacity of drain

S - Drain or well spacing

S - Smear ratio

Sc - Primary consolidation settlement

Sn - Settlement at specific time

Sp - Final primary settlement

St - Magnitude of settlement at specific time

Sult - Ultimate primary settlement

F - Time or duration

Th - Horizontal time factor

Tv - Vertical time factor

xiii

Uav - Average or overall degree of consolidation

Uh - Degree of horizontal consolidation

Ureq - Required cegree of consolidation

Uv - Degree of vertical consolidation

Uw - Pore water pressure

σt - Total vertical stress

γbulk - Bulk density

Pcp - Primary consolidation settlement due to permanent

embankment load

Pc(p+f)- - Primary consolidation settlement due to surcharge preloading

xiv

LIST OF APPENDICES

APPENDIX TITLE PAGE

Appendix A Drawing that contain location of Borehole 76

Appendix B Detail borehole including type and depth of

soil and SPT-N value 77

Appendix C Drawing Detail of Chainage 78

1

CHAPTER 1

INTRODUCTION

1.1 Problem Background

Ground Improvement Technology may be utilized as a treatment for the

unacceptable subsurface conditions specially in soft clay. Soft ground improvement

is for soft soil that have low bearing capacity and high compressibility of these

deposits affect the long term stability of major infrastructure such highway

embankment. Therefore it is imperative to stabilize these soil before commencing

construction to prevent unacceptable settlement. One of oldest and simplest methods

is removal and replacement simply to remove and replace the soil. Soils that will

have to be replaced include contaminated soils or organic soils this method is usually

practical only above the groundwater table.

In the past, various method was use for the ground improvement. Its

categorizes into two which is by chemical stabilization and mechanical stabilization.

For the Chemical Stabilization. The method include the Lime Stabilization, Cement

Stabilization and Fly Ash Stabilization. For the Mechanical Stabilization, its include

vibroflotation, Dynamic Compaction, Blasting, Precompression and Sand Drain.

Well known that compressibility and shear strength of soil can be greatly improved if

water content in soil can be significantly reduced. One common method improving

soft soil is to be reduce the water content of soil through consolidation. For

consolidation to occur it must be an increases the effective stress. This can be

achieve by increase the total stress or reduce pore water pressure. Some recent

development of soft soil consolidation and soft soil improvement are review. Over

the year preloading have been use to more conventional the original compacted sand

drain.

2

According to soil classification system, soil improvement through

consolidation or preloading belong to the category of ground improvement

without admixture in cohesive soil. Preloading is best suited for soft, fine-

grained soils that will experience excessive settlement under a structure’s

load. Fill soil utilized for preloading is typically delivered to the area with

dump trucks. Dozers are then used to push the soil into a mound. The

mound’s height depends on the pressure required to achieved desired

improvement. In very soft sites, piezometers and inclinometers may be

required to avoid the abrupt placement of fill.

However, depending how preloading is applied, this method can be

subdivided into preloading using fill, preloading using fill, preloading using

vacuum pressure and combination between combined fill and vacuum

preloading method. Because of the min risk of damage to utilities from lateral

ground movement and significant reduction in the price of flexible, the

combination between combined fill and vacuum preloading method has been

choosen. Since most compressible low-lying soils have very low permeability

and are often thick, a length time period is usually needed to achieved the

desired primary degree of consolidation. One drawback of this surcharge

technique is that not suitable to be applied for a sufficiently long period

which may at time become impractical due to stringent construction schedule

and deadlines. From that reason combination of preloading and surcharge h

When surcharge pressure is applied which is to increase the effective stress is

depends on the dissipitation of pore water. Their installation can significantly

reduce the preloading period Once sufficient consolidation has occurred, the

fill can be removed and construction process takes place. The surcharging

method places soil fill on-site to pre-consolidate existing soil prior to

construction. Combination preloading and surcharge is one of the most

successful technique for improving shear strength of low-lying area because

it load the ground surface to induce a greater part of ultimate settlement t. In

order to control the development of excess pore pressure a surcharge is

usually raised as a multi-stage exercise with rest period between the loading

stage. In this instances, the height of surcharge can be excessive for an

economic perspective and stability consolidation. Since soft soils have low

3

permeability, the desired consolidation takes very long time to occur, even

with very high surcharge load. Therefore with tight construction schedules,

combination of preloading and surcharge may not be a feasible solution.

Hence, sand or vertical drains may be used to accelerate consolidation

process by reducing the drainage paths length.

Therefore Prefabricated Vertical Drain (PVD) become part of these

core technologies. Prefabricated Vertical Drain (PVD) have been used

successfully in many soil improvement and highway embankment in the

world. Design and construction method for soft soil improvement .

Prefabricated Vertical Drain (PVD) have also been used for some other

relatively new method such as dynamic consolidation for clay. In both case

the main purpose of using Prefabricated Vertical Drain (PVD) is apply

drainage part that the time taken for the consolidation of soft soil or

dissipitation of excess pore-water pressure can be substantially reduced.

Prefabricated Vertical Drain (PVD) can be install quicker with min

environmental implication and quarrying requirements. Prefabricated Vertical

Drain (PVD) also known as wick drains consist of channeled synthetics core

wrapped in geotextile fabric. They are flexible, durable, inexpensive and have

an advantage over sand drains is that they don't need drilling. as been applied

to shorten the time period.

4

1.2 Problem Statement

At sites where an inadequately performing subsurface material may

negatively impact the stability, function or construction system. Ground

Improvement Technology serves to improve or stabilize the subsurface material’s

performance or to improve the load conditions applied to the unsatisfactory

subsurface material. Soft soil improvement in the project requires the consideration

of the preloading programme. This method long track record of success and may be a

unexpected time delay. Then one of the solutions is to use surcharge that fill must

extend horizontally at certain depth beyond the perimeter of the planned

construction. Surcharge must remain in place for months or years, thus delaying

construction. Since this project needs to be completed within 2 years and the time

given to increase the soil strength is 6 months only. Based on that reason,

Prefabricated Vertical Drain (PVD) was added to expedite this process. It decreases

the overall time required for completion of primary consolidation and also decreases

the amount of surcharge load required to achieve the same desired amount of

consolidation over a given period of time. More than that it increases the rate of

strength gain due to consolidation of soft soils when short-term stability is of

concern.

1.2.1 Research Objectives

The objectives of the research are :

1. Interprete borelog from the site investigation about the soil conditions for

design purposes.

2. Calculate settlement due to preloading.

3. Calculate settlement due to preloading surcharge and prefabricated vertical

drain (PVD)

5

1.3 SCOPE OF STUDY

This study is based on soil investigation work from Lahad Datu,

Sabah, Malaysia. The sample collected consist three (3) number of borehole

that can be interprete about the type of soil and the depth of soft clay. These

data are listed to determine soil profile. The scope of analysis and discussion

are limited to the objective of study which is the settlement value correlation

with the time from variation condition of ground improvement either by

preloading, combination preloading surcharge and preloading surcharge

combined with Prefabricated Vertical Drain (PVD). Instrumentation

Prefabricated Vertical Drain (PVD) was selected in the field is desirable as it

provided insight to the consolidation distribution development with depth.

Calculation and analysis for the design criteria were carrying out by applying

manual calculation and misrosoft excel that will come out with the graph

settlement vs time and degree of consolidation vs time.

79

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and speeding up consolidation”. Proc. 8th ECSMFE, pp1201-1206

80

Chu, J. and Raju, V.R. (2013 Prefabricated vertical drains. In Ground Improvement,

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Holtz, R.D., Jamiolkowski, M., Lancellotta, R. and Pedroni, R. (1991).

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