SETTLEMENT OF EMBANKMENT ON SOFT SOIL TREATED WITH CONVENTIONAL PRELOADING - SURCHARGE

Azahar Bujang

Master of Engineering (Civil) 2012

Pusar Khidmal MaJdumalAUUt lit\.

lJNJVERS MALAYSJA S AW '

•

Dedicated to my beloved parents, sisters, brothers, nieces, nephews andfriends, and also especially to

my soul mate.

iii

ACKNOWLEDGEMENT

First of all, a million thank you to my supervisors for the support, patient and

encouragement throughout this study. Their guidance and advises has made this

study a successful. Not forgetting a million thank you to Dr. Norazzlina M. Sa'don

for a valuable lesson in short period of times.

Besides, I would like to dedicate my gratitude to all Faculty of Civil

Engineering's Lecturers and laboratory technician for all the cooperation during my

studies here.

I would like to express my gratitude and love to my loving family especially

my parents, Bujang Bin Suhaili and Jalipah Bt Suni for their encouragements,

supports and endurance during the period of my studies. Not forgetting to all my

family members for their supports. Finally, I would like to give my love and thank

you to my soul mate, Richard R. for the supports and always stand by me.

All the names mentioned above and in generally have made this research a

successful one and contributed a very memorable experience for me.

iv

I ABSTRACT

(structures that are built on soft soil are subjected to the excessive amount of

settlements and the settlement is attributed to consolidation process. In this study, the

structure that been analysed is the road way embankment. In the loads from the

structures, the settlement will occur in a period of time. The prediction of the

settlements for embankment is very important in order to prevent the constructed

road way settles in shorter period of time. The settlements that occur in the shorter

period of time can consider as a failure. The most common method to accelerate the

process of consolidation in Sarawak is conventional preloading with surcharg~ In

this project, Chainage 250 at the connecting road to a bridge in Pantu, Sri Aman was

used for the analYSis) Magnitude and time required to achieve 90% of the

consolidation process were calculated manually using the Terzaghi's one

dimensional method and Asaoka's method. By Terzaghi's method, Equation 2.25

predicted the final settlement is 2.153m and as from Equation 2.23; the predicted of

final settlement is 2.067m. The time to achieve 90% of consolidation is 1387 days.

According to Asaoka's method, the final settlement is 2.362m, while for the time

required to achieve 90% of consolidation is 137 days.

v

ABSTRACT

Kerja-kerja pembinaan di atas tanah lembut akan menyebabkan berlakunya

enapan tanah pada kadar yang berlebihan. Selain itu, enapan tanah ini juga telah

disumbangkan oleh proses pengukuhan. Di dalam kertas kerja ini, kerja benteng

untuk jalan raya telah dipilih untuk dibuat penyelidikan. Daripada bebanan yang

didapati daripada jalanraya, ia boleh menyebabkan berlakunya enapan tanah secara

mendadak. Penentuan kadar enapan untuk jalanraya adalah penting supaya enapan

tanah dapat dikawal sepenuhnya. Apabila jalanraya yang telah siap dibina dan

enapan tanah berlaku dalam masa yang singkat, ia akan dikira sebagai kegagalan

dalam pembinaan struktur jalan. Oleh itu, untuk mengenalpasti dan memahami

konteks dalam kes-kes enapan tanah, satu cara yang selalu dipraktikkan di Sarawak

iaitu menggunakan prapembebanan surcaj. Di dalam projek ini, Chainage 250 di

jalan yang menghubungkan jambatan di Pantu, Sri Arnan telah dipilih untuk

digunakan dalam analisis. Nilai enapan dan masa yang diperlukan untuk pengukuhan

tanah telah ditentukan secara kiraan manual iaitu menggunakan teori Terzaghi 1­

dimensi dan kaedah Asaoka. Dengan menggunakan kaedah Terzaghi, ramalan untuk

enapan terakhir menggunakan Equation 2.25 dan 2.23 adalah 2.153m dan 2.067m.

Tempoh masa yang diperlukan untuk mencapai 90% konsolidasi ialah 1387 hari.

Manakala untuk kaedah Asaoka, nilai enapan terakhir ialah 2.362m dah tempoh

untuk mencapai 90% konsolidasi ialah 137 hari.

vi

1

Pusat Kbidmat laklumat Akademik sm M LA 1.4 AJUNAK

TABLE OF CONTENTS

CHAPTER TITLE

DECLARATION

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

ABSTRAK

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF SYMBOLS

LIST OF APPENDICES

INTRODUCTION

1.1 BACKGROUND

1.2 PROBLEM STATEMENT

1.3 AIM & OBJECTIVES OF STUDY

1.4 SCOPE OF THE STUDY

1.5 PROJECT FRAMEWORK

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PAGE

ii

iii

iv

v

vi

vii

xi

xii

xiv

xv

1

3

4

5

6

2 LITERATURE REVIEW

2.1 GENERAL

2.2 PHASE RELATIONS

2.3 PRELOADING TECHNIQUES

2.2.1 Theory of Consolidation

2.2.2 Theory ofone-dimensional consolidation

2.2.3 General theory of three dimensional consolidation

2.3 FIELD MONITORING

2.3.1 Settlement Monitoring

2.3.2 Prediction of Final Settlement Based on

Field Observation

2.4 CASE STUDIES

2.4.1 Vacuum preloading consolidation of reclaimed land

2.4.2 Recent developments of ground improvement with

PVD on soft Bangkok clay

2.5 SUMMARY

8

9

12

14

17

24

26

27

30

33

33

36

37

3 METHODOLOGY

3.1 INTRODUCTION 38

3.2 DATA ACQUISITION 39

3.3 CALCULATION OF SETTLEMENT BASED ON

TERZAGHI THEORY 40

3.4 ANALYSIS OF SETTLEMENT BASED ON ASAOKA'S

viii

41METHOD

423.5 CASE STUDIES

3.5.1 Ground Improvement with Prefabricated

Vertical Drain (PVD) 42

3.5.2 Ground Improvement with Vacuum Preloading 47

4 ANALYSIS AND RESULTS

4.1 INTRODUCTION 53

4.2 SUMMARY OF SITE INVESTIGATION REPORT 54

4.2.1 Soil Profile 54

4.2.2 Properties of clay 55

4.2.3 Final Settlement Results 58

4.2.3.1 Terzaghi's method 58

4.2.3.2 Asaoka's method 58

4.2.3 .3 Field Monitoring 59

4.2.3.4 Comparison of Asaoka's method and

Terzaghi's method with the Field Monitoring 59

4.2.3.5 Compilation of the study results with case

Studies 61

ix

5 CONCLUSION AND RECOMMENDATION,

5.1 CONCLUSION 62

5.2 RECOMMENDATIONS 64

REFERENCES 67

APPENDICES 70

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4.3

LIST OF TABLES

TABLE NO TITLE PAGE

2.1 Time factor for degree of consolidation

(Taylor, 1948) 24

2.2 Properties of the soils (Shang et al 1998) 34

3.1 Summarized Settlement Rate

(Bergado and Patawari 2000) 44

3.2 Boreholes Location and Site Layout of

East Pier, Xingang Port (Shang et al 1998) 45

3.3 Summarized vacuwn method characteristics

(Shang et at 1998) 50

3.4 Criteria of soil improvement (Shang et at 1998) 51

4.1 Summary of the Subsoil Condition 55

4.2 Properties of clay 56

Results comparison 60

4.

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LIST OF FIGURES

FIGURE NO TITLE PAGE

2.1 Phase Relation of Soils (Das, 2000) 10

2.2 Principles of Consolidation (Das, 2008) 17

2.3 Consolidation Process: Stress vs Time Plot 19

2.4 Consolidation curves according to Terzaghi theory

(Taylor, 1948) 23

2.5 Typical arrangement of instrumentation

monitoring program (after Rixner et aI., 1986) 30

2.6 Time vs Settlement Curve (Tan and Gue, 2000) 32

2.7 Graphical presentation of Asaoka's method

(Asaoka, 1978) 32

2.8 Site layout of the East Pier, Xingang Port,

Tianjin, China (Shang et al 1998) 34

2.9 Soil profile determined for borehole logs

(Shang et al 1998) 34

3.1 Flow Chart of the study 39

3.2 Generalized Soil Profile and Properties

(Bergado and Patawaran 2000) 43

3.3 Time - Settlement Plot using Different Methods

at Section 2bll, SBCH Project

(Bergado and Patawaran 2000) 44

3.4 The location of the boreholes with Divisions and Subdivisions (Shang et al 1998) 46

3.5 Contour map showing settlement due to surface

xii

LIST OF SYMBOLS

Final ~ett1emelltSf

Sc Primary con~olicl,\tion ~enlement

Ss Secondary compre~~ion.

Coefticient of con~0licl1tion

Coetlicient of compre~c;,ion

o Overburden pres~ure of soil o

u Degree of con~0licl1tion

Bulk Density

\Vet Density Y t

Coefticient of con~0licl1tioll for vertical drainage

Coetlicient of vohulle change= ~£ uv

Unit weight of water'".

e Void ratio

Time interval

Thickne~~ of the con~olidatuuz clay laver - . .. Height of drainage path

i une factor

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APPENDIX A

APPENDIXB

APPENDIXC

APPENDIXD

APPENDIXE

APPENDIXF

LIST OF APPENDICES

SITE INVESTIGATION REPORT

CONSTRUCTION DRAWINGS

SETTLEMENT READINGS

ROAD EMBANKMENT CONSTRUCT10N METHOD

OF STATEMENT

CALCULAnONS

CALCULATIONS

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xv

treatment (Shang et at 1998) 47

3.6 Comparison of Maximum Surface Settlement

between Embankment 2 and Previous

Embankment TS3 at SBIA Site

(Bergado and Patawaran 2000) 49

3.7 Typical layout of the vacuum preloading method

(Shang et al 1998) 52

3.8 Contour map showing settlement due to vacuum

preloading (Shang et al 1998) 52

4.1 Soil profile 54

xiii

CHAPTER 1

INTRODUCTION

1.1 Background

Nowadays, the development all over the world especially within the urban area rapidly

develops. The development included high-rise building, highway to be built on problematic

soil such as soft clay. Soft clay is a type of soils that have low shear strength and high

compressibility. With those main characteristics, the load induced by the construction may

results in bearing capacity failure and excessive settlement. Soft clay settles from

compression which consists of elastic settlement and consolidation. The large proportion of

the settlement on soft clay is attributed to consolidation process. This process may continue

for a long time depending on the ability of the soil to dissipate excess pore water pressure due

to the construction load. There are several important factors that influence settlement which

are listed as follows:

- Water table

Soil permeability

Soil drain

- Load to be placed on the soil

1

The most common type in treating the soft soil is embankment. An embankment

refers to a volume of earthen material which involved placing and compaction for raising the

grade of a roadway above the level of the existing surrounding ground surface. Embankment

materials consist of soil, aggregate and rock or crushed paving material. In general, there are

two types of embankment. The types are single stage embankment and multi stage

embankment. In single stage embankment, the load is applied in single stage and will cause

the shear failure in soft soil; while in multi stage embankment, the load is applied in multi­

stage where it will increase the strength in soft soil .

In the embankment works especially in multi stage embankment, the monitoring of

the settJement is a must. The main reason for the monitoring is to verify the field observing of

settJement achieve the required. It indicates that a certain percentage of settlement has taken

place and therefore the residual settlement will be negligible or will not cause interruption to

the service of the construction. In the verification stage, a several methods have been

developed to predict the final settlement based on the field observation. The methods are

Asaoka's method, hyperbolic method and viscosity method. By predicting the final

settlement, the degree ofconsolidation could be calculated at any time. The method chosen in

this study was Asaoka's method since it provides a good prediction of final settlement. As for

the comparison of final settlements, two case studies were adapted. For the first case study,

the method chosen was preloading using prefabricated vertical drains (PVD). This study was

conducted in Bangkok, Thailand. The second case study was on the performances of vacuum

preioading which located in Tianjing, China.

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1.2 PROBLEM STATEMENT

Structures that are built on soft clay are subjected to the extreme settlement. The extreme

settlement is a result from the consolidation process that can be continued for a quite some

times. The consolidation process might be shortened. The periods that effected are depending

on the ability of the soil to dissipate excess pore water pressure due to the construction load.

Since the relationship between the settlement and time is not a linear, large percentage of

settlement may usually take place at the earlier time. With the indication of the field

observation., it will not cause disruption to the service of the construction. Asaoka's method is

used in order to predict the settlement and the degree of consolidation can be calculated at

anytime.

During the subsoil investigation, some of the design parameters were not being

carried out as usual since the process of embankment is not a major scope in this project.

Therefore, due to the incomplete and inadequate data, some of the design values based on the

soil parameters used in this study were mostly taken from previous published works.

Based on the field observation of this project, the first part of the analysis is the

prediction of the time-settlement behaviour of an embankment using the conventional

preloading which is surcharge. The results were then compared with the predictions made

using Asaoka's method. The comparisons were included as follows:

- Final settlement

Coefficient of rate ofconsolidation

Time required to achieve 90% consolidation

3

For the second part, the results from the first part were compared with the results obtained

tom the case studies. The case studies consist of two in different methods of improving the

soft soils. The methods were:

- Preloading with PVD

- Vacuum preloading

1.3 AIM & OBJECTIVES OF STUDY

a. To predict the final settlement of an embankment that treated with the conventional

methods based on

i) Terzaghi 1-D consolidation analysis

This method is to analyse and predict the final settlement based with the soil

parameters of the sample

ii) Asaoka's method based on field observation data.

This method is to predict the final settlement by graphical approached based

on the monitoring results on site.

b. To compare the following results obtained:

i) Magnitude of final settlement between Terzaghi 1-D consolidation and

Asaoka's method

ii) The time required to achieve 90% consolidation between the method

mentioned in (a) and data obtained from the settlement plate readings.

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I PUSlt Khidmat MakJumat Akademik ffNl\'F.RSm MALAYSIA SA RAWAf<

c. The results from (a) and (b) was then compared with the results from published case

studies as follows:

i) Preloading with PVD

ii) Vacuum Preloading

1.4 SCOPE OF THE STUDY

The present study is based on site investigation (SI) and settlement monitoring data from

the Proposed Bridge near Pantu, Sri Aman Division, Sarawak. The SI data collected consists

of 8 boreholes along the road alignment and a number of settlement plates. These data are

used to determine the soil profile. The monitoring data is collected based on 8 numbers of

settlement plate and 10 numbers of settlement gauges. However, only 1 bore log was used

since it is theroad construction section and the settlement plate was placed at CHO+250 (refer

to Appendix A).

The scope of the analysis and discussion are limited to the objectives of the study.

Other design criteria such as the bearing capacity, degree of consolidation, and the pressure

appned and undrained shear strength were not being discussed in details. Calculation and

lD8lysis of this study were carried out by applying manual calculation and Microsoft Excel.

The Microsoft Excel is used to produce the settlement vs time plot and graphical plot by

Asaoka's Method. The detennination of the soil parameters from laboratory works are not

carried out throughout the study because the main objective of this study is to detennine the

settlement behaviour and time. Apart from the objectives, the laboratory works were not done

during the construction period of the proposed bridge project. After the settlement and time

5

of consolidation are detennined, then a comparison between theoretical and actual are

performed and presented. The SI report and the settlement reading for 12 months with seven

days interval for every monitoring reading are taken into consideration.

1.5 PROJECT FRAMEWORK

Chapter 1 presents the Introduction, Problem Statement, Objectives of the study,

Scope of the study and Project Framework. Introduction provides an overview about this

study. Problem Statement explains the problem that occurs in present situation, pertaining to

the thesis topic. The Objectives of the study listed the main aims and objectives of this study.

Scope of the study elaborates on how the calculations and analysis were done. It also

mentioned the location of the settlement plate was located and the numbers of bore log that

were done during the site investigation stage.

In Chapter 2, it is a discussion of the literature review. At the beginning part of the

chapter, a discussion has been done regarding the theories of three phases of soils that

produced some equations that will detennine the final settlement, and the time required to

achieve the 90% of consolidation. In the middle of the chapter, discussions were made to the

theories that were introduced by Karl Terzaghi, Akira Asaoka and Maurice A. Biot. The

theories were one dimensional theory of consolidation, Asaoka's method and a general theory

oftbree dimensional consolidations respectively. Later in this chapter, another discussion has

been made which are the field monitoring review and also the case studies that involves 2

other methods, which are preloading with PVD and vacuum preloading.

6

I Chapter 3 is the chapter that represents the research methodology of this study. It

explained and elaborated the steps that were used in order to determine and achieve the

objectives ofthe study. In introduction, it's explained better the steps that were taken and also

shown the flow chart of this study. It's also shown briefly the methods that were adapted to

determine the final settlement. Finally, in this chapter it is discussed the information and

methods used in the case studies.

Chapter 4 is the chapter that presented the results that have been determined from the

calculations and also from the graphical methods. It is also shown the comparison and

analysis based on the theoretical data, predicted data and monitoring data.

The fmal chapter in this study is Chapter 5. It consists of the conclusions and

recommendations for future works. The conclusions are the discussion that is summarized

from the previous chapters. The most important thing for the conclusion is either the

objectives ofthe study have been achieved or not. And for the recommendations, matters that

have been discussed were on how to make this study more accurate and efficient in

discussing the preloading with conventional surcharge.

7

,

CHAPTER 2

LITERA TURE REVIEW

I GENERAL

Chapter 2 represented the literature review for this study. It's explained the theories

involved in determining the settlement induced by the conventional surcharging and also

consolidation process during the preloading period. The first part of this chapter explained

details the meaning of the soils parameters such as the void ratio, e; the degree of

tIIUration, S and the submerged unit weight, y'. The second part of Chapter 2 elaborated on

preloading techniques which involved the surcharge, m. The third part of the chapter

deacribed how the equations for final settlement and the time required to achieve 90% of

CODIOlidation were produced from the justifications of theory of consolidation by Terzaghi,

1943. The generalised of three-dimensional consolidation was also explains in details in the

third part of this chapter. Later on this chapter, the guidance for Asaoka's method was stated

. sequence to determine the actual settlement based on monitored data from the selected case

.audy based on the existing project by using the conventional preloading method. Lastly, the

discussion were made regarding the different method of ground improvement beside

COIWentional preloading, which were preloading with prefabricated vertical drains (PVD) and

8

PHASE RELATIONS

Generally, soils contain 3 main components which are air, water and soil grains.

components also called as the three phases since either in geotechnical problem or

~ tests, these 3 components are the most important components to be determined.

BOil grains also known as the solid phase is always present in soils and mostly it consists

particles resulting from weathering of the rock. While for the air and water, which also

_ ....... as the gas and liquid phases are occupying the pores or voids between the soils

liquid phase does not completely fill the voids, then the remaining space is occupied by

ps phase. It is usually air but can also include other gases such as methane and carbon

·de from organic materials, (Coduto, 1999).

The identification of the relative proportions of solids, water and air in particular soils

VfIlY important because their proportions have a significant effect on its behaviour. In order

understand the relationship between the phases in soil, quantitative methods were

developed by geotechnical engineering. The phase relationships in term of mass-volume and

'.iIIa-volume for a soil mass are shown in Figure 2.1.

9

--------------

I

-

a) Soils

V air a 1::-=-_=-_=_=_=_-=-_-=-_-=-_-=_-=_-=_--=i_

V ---------_-_-_-_-_-_-_-_ V V -:-:-:-: water-:-:-:-: M

w -:------- --....---------:.----­ W

"t

M s

b) Phase Diagram

Figure 2.1 Phase Relation of Soils (Das, 2000)

As shown in Figure 2.1, it is assumed that Fig. 2.1 (a) is a soil mass which include the

tine phases. And for Fig. 2.1 (b) shown the three phases is separated that known as the Phase

Diqram. It also shown the volumes (left) and masses (right). The water content, w in the

. is defined as the total amount ofwater that present in the soils.

M W = ~ x 100(%) 2.1

Ms

orpnic soils and some marine clay, the value of w may be greater than 100% since the

__Ie value for most soils is below 100%.

The void ratio, e and porosity, n are expressed in the equations below;

10