LONG TERM CONSOLIDATION STUDY ON THE TROPICAL PEAT

LONG TERM CONSOLIDATION STUDY ON THE TROPICAL PEAT AT

PEKAN, PAHANG, MALAYSIA

MOHD IKHWAN BIN AB KADIR

A thesis submitted in fulfillment of the requirements for the award of the degree of

Bachelor in Civil Engineering

Faculty of Civil Engineering & Earth Resources

Universiti Malaysia Pahang

NOVEMBER 2009

iv

ABSTRACT

Peats are formed by disintegration of plant and organic matters. In Malaysia, the

area covered by peat deposit is about 3 million hectares or 8% of the total area of

Malaysia. Peat has high compressive deformation, very high void ratio and water

content and has low shear strength. It is widely regarded as a problematic soil since it

poses serious problems in construction due to its long-term consolidation settlements

even when subjected to a moderate load. Construction over peat will be subjected to

massive primary and long term secondary and even tertiary settlement. This study will

be conducted to gain a better understanding about the long term consolidation on

tropical peat soil of East Coast of Peninsula Malaysia. The study will focused on the

analysis of consolidation behavior of peat soil based on the time-deformation curve

obtained from Oedometer Test. Based on this test, we can determine the consolidation

time so that we can predict how long the time taken by the soil to settle. In the

determination of consolidation time, the first thing we need to know is the consolidation

coefficient value and this value may be obtained from Oedometer Test. It was expected

that the value of settlement is high since peat is very soft and easily compressed. The

study of the long term consolidation of peat soil is important to predict the amount of

settlement that will occur to the peat soil in a long time period.

v

ABSTRAK

Tanah gambut terhasil daripada penguraian tumbuhan dan bahan-bahan organic.

Di Malaysia, tanah gambut meliputi 3 juta hektar atau 8 % daripada jumlah keseluruhan

keluasan tanah di Malaysia. Tanah gambut mempunyai daya mampat yang tinggi, liang

udara yang banyak, tinggi kandugan air, dan mempunyai kekuatan ricih yang rendah. Ia

dianggap sebagai tanah yang bermasalah kerana menyebabkan masalah serius dalam

industri pembinaan disebabkan oleh ciri mendapan jangka panjang walaupun hanya

dikenakan beban yang rendah. Kerja-kerja pembinaan di atas tanah gambut akan

terdedah kepada mendapan primer dan mendapan sekunder dan mungkin juga

mendapan tertier. Tujuan kajian ini dijalankan adalah untuk meningkatkan kefahaman

dan pengetahuan tentang mendapan jangka panjang terhadap tanah gambut di

semenanjung Malaysia. Kajian ini akan menumpukan kepada analisis ciri mampatan

tanah gambut berdasarkan graf masa-mampatan yang diperoleh daripada eksperimen

Oedometer. Berdasarkan kajian ini, masa mampatan dapat ditentukan dan boleh

digunakan untuk membuat jangkaan masa tanah gambut untuk mendap. Dalam

menentukan masa mendapan, perkara pertama yang perlu dikenalpasti adalah nilai

pemboleh ubah mendapan dan nilai ini boleh didapati daripada eksperimen Oedometer.

Menerusi kajian ini, dijangkakan nilai mendap tanah gambut adalah tinggi kerana ia

adalah tanah yang lembut dan mudah mendap. Kajian ini adalah penting untuk

menjangka jumlah mendapan tanah gambut yang berlaku dalam jangka masa yang

panjang.

vi

TABLE OF CONTENTS

CHAPTER TITLE PAGE

DECLARATION i

DEDICATION ii

ACKNOWLEDGEMENT iii

ABSTRACT iv

ABSTRAK v

TABLE OF CONTENTS vi

LIST OF TABLES x

LIST OF FIGURES xi

LIST OF SYMBOLS xiii

LIST OF FORMULA xv

1 INTRODUCTION

1.1 Background of Study 1

1.2 Problem Statement 3

1.3 Objective of Study 4

1.4 Scope and Limitation of Study 4

1.5 Expected Result 5

1.6 Thesis Organization / Framework 5

vii

2 LITERATURE REVIEW

2.1 Introduction 7

2.2 Background 9

2.3 Peat Soil 11

2.3.1 Types of Peat 11

2.3.2 Classification of Peat 12

2.3.3 Physical and Chemical Properties 15

2.3.4 Shear Strength 19

2.4 Compressibility 20

2.4.1 Primary Consolidation 21

2.4.2 Secondary Consolidation 23

2.4.3 Coefficient of Consolidation 25

2.4.4 Logarithm-of-Time Method 26

2.4.5 Square Root Time Method 27

2.5 Methodology / Experimental 28

2.6 Sampling of Peat 31

2.7 Summary of Literature Review 31

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3 METHODOLOGY

3.1 Introduction 34

3.2 Sampling 37

3.2.1 Location of Sampling 37

3.2.2 Sampling Steps 37

3.3 Determination of Engineering Properties 38

3.3.1 Determination of Water Content 39

3.3.2 Determination of Liquid Limit 40

3.3.3 Determination of Specific Gravity 41

3.3.4 Determination of Fiber Content 43

3.3.5 Determination of Organic Content 43

3.4 Consolidation Test 44

3.4.1 Preparation of Sample 44

3.4.2 Consolidation Data 47

3.4.2.1 Project 48

3.4.2.2 Specimen 49

3.4.2.3 Water Content 49

3.4.2.4 Read Table 50

3.4.2.5 Consolidation Table 51

3.4.2.6 Calibration 52

3.4.3 Starting a Test 53

3.4.4 Data Analysis 54

3.4.4.1 Void Ratio-Time Curve 54

3.4.4.2 The e log p’ Curve 55

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4 RESULTS AND DISCUSSIONS

4.1 Introduction 57

4.2 Soil Classification 58

4.3 Index Properties 59

4.3.1 Water Content 60

4.3.2 Liquid Limit 60

4.3.3 Specific Gravity 60

4.3.4 Initial Void Ratio 60

4.4 Consolidation Parameters 61

4.4.1 Coefficient of consolidation 63

4.4.2 Compression Index 64

4.4.3 Secondary compression index 65

4.4.4 Coefficient of permeability 66

4.4.5 Coefficient of volume compressibility 67

5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions 68

5.2 Recommendations 70

REFERENCES 71-73

APPENDICES 74-84

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LIST OF TABLES

NO TITLE PAGE

2.1 Classification of peat based on organic and fiber content 13

2.2 Classification of peat based on degree of decomposition 14

2.3 Physical properties of peat based on location 17

4.1 Laboratory result of organic and fiber content for sample 1, 2 and 3 58

4.2 Comparison result of study with previous researchers 59

4.3 Summary of Index properties by present study and previous researchers 59

4.4 Consolidation parameters sample 1 61



C1 Test sheet for natural water content for sample 1 76



C4 Specific gravity for sample 1 78


xi


C7 Organic content for sample 1 79



C10 Fiber content for sample 1, 2 and 3 80

xii

LIST OF FIGURES

NO TITLE PAGE

2.1 Extent of Peat in Peninsular Malaysia 10

2.2: Extent of Peat in East Malaysia 10

2.3 Cassagrande’s Log Time Curve 20

2.4 Variation of average degree of consolidation with time factor, Tv 25

2.5 Logarithm-of-time method for determining coefficient of consolidation 27

2.6 Square-root-of-time method 28

2.7 Fully automated consolidation machine 29

3.1 Flow chart of study 36

3.2 Location of sample taken 37

3.3 Sampling work 38

3.4 Liquid Limit graph 41

3.5 Fully automated consolidation machine 44

3.6 Part of consolidation cell 45

3.7 Steps of installation of consolidation cell 46

xiii

3.8 Property Sheet 47

3.9 Project window 48

3.10 Specimen window 49

3.11 Water Content window 50

3.12 Read Table window 50

3.13 Consolidation Table window 51

3.14 Example how to do a calibration 52

3.15 Positioning the consolidation cell 53

3.16 Void ratio-time curve for load of 12.5 kPa 54

3.17 The e-log p’ Curve 55

4.1 Coefficient of consolidation versus consolidation pressure 63

4.2 Compression index versus consolidation pressure 64

4.3 Secondary compression index versus consolidation pressure 65

4.4 Coefficient of permeability versus consolidation pressure 66

4.5 Coefficient of volume compressibility versus consolidation pressure 67

A1 Sampling work 74

B1 Consolidation cell 75

B2 Consolidation cell part 75

B3 Consolidation machine 75

B4 Apparatus layout for consolidation test 75

E1 Graph void ratio-pressure for sample 1 83

xiv

LIST OF SYMBOLS

ASTM = American Standard Method

Cc = Compression Index

Cv = Coefficient of Consolidation

Cα = Secondary Compression

D = Diameter of Sample

D0 = Initial reading; Deformation

D100 = Deformation correspond to U = 100%

e = Void Ratio

e0 = Initial Void Ratio

Gs = Specific Gravity

Ha = Hectare

k = Coefficient of Permeability

mv = Coefficient of Volume Compressibility

p’ = Consolidation Pressure

Sc = Consolidation Settlement

Ss = Secondary Compression

xv

T = Time

T50, T90 = Theoretical Time Factors

Tv = Vertical Theoretical Time Factor

σ = Effective Stress

xvi

LIST OF FORMULA

NO ITEMS PAGE

2.1 Shear Strength 19

2.2 Primary consolidation (normally consolidated clay) 21

2.3 Primary consolidation (Over consolidated clay) 22

2.4 Primary consolidation (Over consolidated clay) 22

2.5 Secondary compression index 24

2.6 Secondary consolidation 24

3.1 Water content 39

3.2 Specific gravity 42

3.3 Ignition loss 43

3.4 Organic content 43

3.5 Compression index 56

4.1 Coefficient of consolidation 63

4.2 Compression index 64

xvii

4.3 Secondary compression index 65

4.4 Coefficient of permeability 66

4.5 Coefficient of volume compressibility 67

CHAPTER 1

INTRODUCTION

1.1 Background of Study

Peat is form by disintegration of plant and organic matters. It was identified as a

one of a major group of soil found in Malaysia. According to Huat (2004), there are 3

million hectares or 8% area in Malaysia covered with peat.

In Peninsular Malaysia, they are found in the coastal areas of the east and west

coast, especially in the coastal areas of west Johore, Kuantan and Pekan district, the

Rompin-Endau area, northwest Selangor and the Trans-Perak areas in the Perak Tengah

and Hilir Perak district. In Sarawak, peat occurs mainly between the lower stretches of

the main river course (basin peat) and in poorly drained interior valleys (valley peats).

They are found in the administrative division of Kuching, Samarahan, Sri Aman, Sibu,

Sarikei, Bintulu, Miri, and Limbang. In Sabah, the organic soils are found on the coastal

areas of the Klias peninsula, Krah swamps in Kota Belud, Sugut and Labuk estruaries

and Kinabatangan floodplains.

2

Generally, peat is grouped into two categories; amorphous peat and fibrous peat.

Amorphous peat is the peat with less than 20% of fiber content. It contain mostly

particles of colloidal size (less than 2 microns), and the pore water is absorbed around

the particle surface.

Fibrous peat is defined as a peat that contains more than 20% of fiber content.

Both of amorphous and fibrous peat has own characteristics. However, in term of

prediction of settlement and dissipation of pore pressure, they are show very close

similarity.

In general, the process of consolidation can be divided into three stages. Each

stage will display their respective characteristic. Those three stages are:

I. Immediate/initial deformation.

II. Primary Consolidation

III. Secondary Compression.

The primary consolidation of fibrous peat is much larger than that of other soils

due to high initial water content, while the secondary compression occurs due to not

only compression of solid particles, but also the plastic yielding (buckling, bending, and

squeezing) of the particles (Samson and La Rochelle, 1972). Secondary compression is

more significant part of compression of peat and plays important role in determining

total settlement because it is occur during the design life of a structure after rapid

primary consolidation. The consolidation process will take a long time because the

composition of the soil is not homogenous and have high fibrous content.

Replacing the peat with good quality soil is still commonly practiced by the

engineer when the construction has to take place on peat deposit. However, this method

of solution leads to uneconomic design. Other alternative construction and stabilization

methods such as surface reinforcement, preloading, chemical stabilization, sand or stone

column, pre-fabricated vertical drains, and the use of piles also commonly used.

3

Construction over peat will subjected to massive primary and long term

secondary settlement. Therefore, it is essential to understand the characteristics of peat

and to interpret the compressibility parameters of peat deposit. Based on that parameter,

the prediction of time period of settlement can be made.

1.2 Problem Statement

Peat is known as a one of the most problematic soil in the world. It can pose

serious problem in the construction industry due to its consolidation settlement. It can be

a nightmare for the engineer to design the structure over peat deposit. The characteristics

of peat which is low in shear strength and easily compressed make it considered as

unsuitable for the structure to be built on it. In settlement analysis, it is often that the

long term compressibility parameters of peat is underestimated or neglected. This

situation can lead to problem regarding on the structure stability in the future. The

knowledge on the shear strength and compression behavior is essential as it enables

designers to understand the response of the soil to load and to suggest proper

engineering solutions to overcome the problem.

4

1.3 Objective of Study

Based on the importance of compressibility characteristics of peat in the

evaluation of its response to loading, the following objectives were set for the study:

Main Objective:

1) To determine the long term consolidation parameters of tropical peat.

Specific Objective:

1) To determine engineering properties of Pekan peat.

2) To determine the consolidation parameters using fully automated consolidation test.

1.4 Scope and limitation of Study

The test was conducted using fully automated consolidation machine. The peat

sample that used in this research study is tropical peat obtained from area of Pekan,

Pahang. This experimental research limits its scope on the compressibility characteristics

of peat based on time-compression curve obtained from consolidation test. The

engineering properties of peat samples such as moisture content, liquid limit, organic

content, fiber content, specific gravity, bulk density and dry density will be determined

before conducting the consolidation test. The consolidation parameters like coefficient

of consolidation (Cv), compression index (Cc), coefficient of volume compressibility

(mv), and secondary compression index (Cα) also was determined for settlement

analysis.

5

1.5 Expected Result

Through this research, it was expected that the properties of peat at the study

location can be identified. The engineering properties such as moisture content, liquid

limit, organic content, fiber content, and specific gravity will be determined through the

result of laboratory testing. The consolidation parameters which are important in

predicting the settlement also expected to be determined through the consolidation test.

1.6 Thesis Organization / Framework

This thesis is consisted of five chapters. Chapter 1 presents general information

regarding background, problem statement, objectives, scope of study, expected result,

thesis organization/framework and gant chart/schedule of the project. Chapter 2 is

literature review that provides the background of the study on different topics related to

the research. This chapter outlines information on the general characteristics of peat, the

definitions that relate to the research topic, the theory of consolidation, the

compressibility of peat, the materials, and the methodology/experiments in general.

Chapter 3 described about the overall experimental program including laboratory

tests in detail. The research methodology includes sampling of peat and laboratory soil

tests performed to classify the soil and to determine the engineering properties of peat.

This chapter also discusses the detail set up and procedures of consolidation test using

fully automated consolidation machine.

Result and Analysis was discussed in chapter 4. Analysis of the test data for

determining the compressibility parameters are presented and discussed in detail in this

chapter. The applications of consolidation parameters from consolidation test for

settlement analysis time-compression curve also discussed in this chapter.

6

Chapter 5 is Conclusion and Recommendation. It was presented the summary

and conclusions of major findings of this research and recommendation for future work

on the topic related to the present study.

7

CHAPTER 2

2.0 LITERATURE REVIEW

2.1 Introduction

Peat is known as a most problematic soil since it poses serious problem in

construction industry due to its long term consolidation settlement. The major problem

associated with such construction is the prediction of settlement because the

conventional analysis usually under predicts the secondary compression or creep which

continued for a long time. The behaviors of peat which is easily compressed make it

unsuitable for the structure to be built on it. The low strength often causes stability

problem and consequently the applied load is limited or the load has to be placed in

stages. Large deformation may occur during and after construction period both vertically

and horizontally, and the deformation may continue for a long time due to creep.

Therefore, a good prediction of settlement is very important to get a good engineering

design and solve this problem.

Recently, the utilization of peat-land in Malaysia is quite low although

construction on marginal land such as peat has become increasingly necessary for

economic reasons. Engineers are reluctant to construct on peat because of difficulty to

8

access the site and other problems related to unique characteristics of peat. Therefore,

not much research has been focused on the behavior of peat and the development of soil

improvement method for construction on peat soil area.

Replacing the peat with good quality soil is still a common practice when

construction has to take place on peat deposit even though most probably this effort will

lead to uneconomic design. Approaches have been developed to address the problems

associated with construction over peat deposits (Lea and Brawer, 1963; Berry, 1983;

Hansbo, 1991). Alternative construction and stabilization methods such as surface

reinforcement, preloading, chemical stabilization, sand or stone column, pre-fabricated

vertical drains, and the use of piles were discussed in literatures (Noto, 1991; Hartlen

and Wolsky, 1996; Huat, 2004, and others). The selection of the most appropriate

method should be based on the examination of the index and engineering characteristics

of the soil. The knowledge on the shear strength and compression behavior is essential

as it enables designers to understand the response of the soil to load and to suggest

proper engineering solutions to overcome the problem.

The characterization of the peat soil has a significant effect for the consolidation

behaviour as well as the strength of peat soil. Bearing Capacity of peat soil was very low

and was apparently influenced by the water table and the present of subsurface woody

debris (Islam et al., 2008 and Andriesse, 1988). Hence, in its natural state, peat is

considered as unsuitable for supporting any structure.

9

2.2 Background

In Malaysia, the area covered by peat deposit is about 3 million hectares or 8%

of the total area of Malaysia. On the west coast of Malaysian Peninsular, the deposits are

formed in depressions consisting predominantly of marine clay deposits or a mixture of

marine and river deposits especially in areas along river courses (R. Hashim et al.,

2008).

Peat soils occur both in the highland and lowlands, however, the highland

organic soils are not extensive. The lowlands peat occurs almost entirely in low-lying,

poorly drained depressions or basins in the coastal areas.

In Peninsular Malaysia, they are found in the coastal areas of the east and west

coast, especially in the coastal areas of west Johore, Kuantan and Pekan district, the

Rompin-Endau area, northwest Selangor and the Trans-Perak areas in the Perak Tengah

and Hilir Perak district. In Sarawak, peat occurs mainly between the lower stretches of

the main river course (basin peat) and in poorly drained interior valleys (valley peats).

They are found in the administrative division of Kuching, Samarahan, Sri Aman, Sibu,

Sarikei, Bintulu, Miri, and Limbang. In Sabah, the organicsoils are found on the coastal

areas of the Klias peninsula, Krah swamps in Kota Belud, Sugut and Labuk estruaries

and Kinabatangan floodplains (www.mardi.my).

In tropical region such as Sarawak, Malaysian Peninsular and Sumatera, the peat

form a doomed deposit consists of two layers: the top layer consist of fibrous peat

containing long and slender roots and rootlets, while the bottom is a dense woody peat

derived from the decomposition of the vegetation (Cameron, 1989).

10

Extent of Peat in Malaysia

Figure 2.1 and 2.2 shows the extent of peat in peninsular Malaysia and east Malaysia.

Figure 2.1: Extent of Peat in Peninsular Malaysia

Figure 2.2: Extent of Peat in East Malaysia

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LONG TERM CONSOLIDATION STUDY ON THE TROPICAL PEAT