SECONDARY CONSOLIDATION BEHAVIOUR OF SAMARAHAN PEAT SOIL

Aishah Nur Dyana Binli .Iohari

Bachelor of Engineering with Honours (Civil Engineering)

2017

SECONDARY CONSOLIDATION BEHAVIOUR OF SAMARAHAN

PEAT SOIL

AISHAH NUR DYANA BINTI JOHARI

This project is submitted in partial fulfilment of the

requirement for the degree of

Bachelor of Engineering with Honours

(Civil Engineering)

Faculty of Engineering

Universiti Malaysia Sarawak

2017

Dedicating this to my family, and my friends

for their infinity support, patience, and inspiration

i

ACKNOWLEDGEMENT

In the name of Allah S.W.T, most gracious and most merciful, may Allah the Almighty

keep us His blessings and tenders. Alhamdulillah, all praises to Allah this study is

completed on time without any uncomfortable occurrences.

Through this acknowledgement, I express my sincere gratitude to all those involved in

my study. Firstly, I would like to express my appreciation to my Final Year Project

supervisor, Dr. Fauzan Sahdi for his valuable guidance, patience, support and

inspiration throughout the study.

My special thanks to Encik Haji Affandi, Encik Mohammad Zaidi Serah, Mr. Amuda

Akeem and Mohd. Nazri Zaidan, for providing valuable assistance during this study.

Highest appreciation goes to my wonderful family, especially my parents, Mr. Johari

bin Ali and Mdm. Faziawati Abdullah for all the encouragement and support whenever

I needed them. A special thanks to Azmeera binti Shaibi for lending her laptop

throughout the semester and not to forget Muhammad Atif bin Norzan Shah, Farahiyah

‘Aqilah binti Yaman, Nur Aliaa binti Mohamad and all others who helped me in every

way in completing this study. Thank you.

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ABSTRACT

Peat is generally known as having the characteristics of problematic soil that are

high in moisture content, high in void ratios, has a great degree of porosity, very

high initial permeability that is 100 to 1000 times greater compared to soft clay and

silt deposits. Peat in the engineering field is known as the highest secondary

compression index to compression index ratio. Due to these circumstances,

constructions on peat are usually avoided as the structures built on peat may

experience catastrophic failure.

Hence, this study attempts to determine the secondary consolidation behavior of

Sarawak peat using a one-dimensional oedometer consolidation test on disturbed

and undisturbed samples obtained from Kampung Mang and Kampung Meranek,

Samarahan. In settlement expectations, the higher the fiber content, the greater the

compression index.

The relationship of coefficient of consolidation 𝑐𝑣 of Kampung Mang and Meranek

peat soil decreases as the stress increases. Other than that, the values of compression

index 𝐶𝑐 and secondary compression index 𝐶𝛼 are found to vary with pressure and

time, respectively.

iii

ABSTRAK

Gambut diketahui umum adalah sejenis tanah yang mempunyai ciri-ciri bermasalah

tinggi dengan kandungan kelembapan, tinggi dalam nisbah lompang, mempunyai

tahap keliangan yang tinggi, kebolehtelapan awal sangat tinggi iaitu 100 sehingga

1000 kali lebih besar berbanding dengan tanah liat dan kelodak deposit lembut.

Gambut dalam bidang kejuruteraan juga dikenali sebagai indeks mampatan

sekunder yang paling tinggi kepada mampatan nisbah indeks. Oleh kerana keadaan

ini, pembinaan di tanah gambut biasanya dielakkan kerana struktur yang dibina di

atas tanah gambut mungkin mengalami risiko kegagalan.

Oleh itu, kajian ini bertujuan untuk melihat tingkahlaku penyatuan sekunder gambut

Sarawak menggunakan ujian pengukuhan oedometer satu dimensi ke atas sampel

terganggu dan tidak terganggu yang diambil dari Kampung Mang dan Kampung

Meranek, Samarahan. Dalam jangkaan penyelesaian, lebih tinggi kandungan serat,

lebih besar indeks mampatan.

Hubungan koefisien penggabungan 𝑐𝑣 tanah gambut Kampung Mang dan Meranek

berkurangan apabila tekanan meningkat. Selain itu, nilai indeks pemampatan 𝐶𝑐 dan

indeks pemampatan sekunder 𝐶𝛼 didapati berbeza dengan tekanan dan masa.

iv

TABLE OF CONTENTS

Acknowledgement Page

Abstract i

Abstrak ii

Table of Contents iv

List of Tables vi

List of Figures vii

List of Equations ix

List of Annotations xi

Chapter 1 INTRODUCTION

1.1 Background 1

1.2 Problem Statement 3

1.3 Objectives 5

1.4 Thesis Outline 6

Chapter 2 LITERATURE REVIEW

2.1 Overview 7

2.2 Introduction of Peat 7

2.3 Peat Distribution in Malaysia 9

2.4 Permeability of Peats 12

2.5 Compressibility of Peats 14

2.5.1 Primary Compression 15

2.5.2 Secondary Compression 17

2.5.3 Experiment on Middleton Peat

using Oedometer Tests

21

2.6 Summary 24

Chapter 3 METHODOLOGY

3.1 Overview 25

3.2 Basic Properties Testing of Peat Soil 25

3.2.1 Field Testing – Von Post Testing 26

3.2.2 Moisture Content Test 28

3.2.3 Organic Content Test

(Loss on Ignition)

29

3.2.4 Fiber Content Test 30

3.2.5 Specific Gravity Test 32

3.3 Oedometer Test 34

Chapter 4 RESULT AND DISCUSSION

4.1 Overview 41

4.2 Site Investigation 41

4.3 One-Dimensional Oedometer Test on 44

v

Disturbed and Undisturbed Samples

4.3.1 Effects of Vertical Stresses on

Primary Consolidation

46

4.3.2 Secondary Compression Index and

Compression Index Ratio, 𝐶𝛼/𝐶𝑐

48

4.4 Summary 50

Chapter 5 CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions 52

5.2 Recommendations 53

REFERENCES 54

APPENDIX A 57

APPENDIX B 60

APPENDIX C 64

APPENDIX D 68

APPENDIX E 72

vi

LIST OF TABLES

Table

Page

2.1 Common sizes of fibrous peat particles 9

2.2 Summary of peat distribution in Sarawak 10

2.3 Consolidation parameters for peat specimen by Johari (2016) 21

3.1 Von Post Scale: Degree of humification 25

3.2 Suggested initial pressure for oedometer test 35

4.1 Summarized basic properties of Kg. Meranek and Kg. Mang

peat soil

42

4.2 Values of 𝑐𝑣 44

4.3 Values of 𝐶𝑐 46

4.4 Values of 𝐶𝛼 and 𝐶𝑐 values for Kg. Mang 47

4.5 Values of 𝐶𝛼 and 𝐶𝑐 values for Kg. Meranek 48

vii

LIST OF FIGURES

Figure

Page

1.1 Distribution of peat in state of Sarawak 2

1.2 Values of natural water content and compression index for

peats

3

1.3 Settlement of pipeline in Sibu Town 4

1.4 Settlement under a lamp post in Sibu Town 5

2.1 Network of fibrous elements and perforated hollow particles

of James Bay peat

8

2.2 Major peatlands in Peninsular Malaysia 10

2.3 Major peatlands in Sarawak 11

2.4 Major peatlands in Sabah 11

2.5 Cross-section of a peat dome close to Marudi 12

2.6 Data on coefficient of permeability of fibrous peats 13

2.7 Relationship between Ck and eo for fibrous peat as compared

to silt and clay

14

2.8 Graph of settlement during consolidation 16

2.9 Three plots of settlement data from soil consolidation 16

2.10 Typical EOP e versus log curves of Middleton and James Bay

peat

17

2.11 Start of secondary compression 17

2.12 Relationship between Cα and Cc 18

2.13 Values of Cα/Cc vs consolidation pressure σ 18

viii

2.14 Illustration of symbols used in consolidation analysis for peat 20

2.15 Permeability of Middleton peat 21

2.16 εv vs log σv′ of Middleton peat 22

2.17 Values of Ck for peat 22

2.18 EOP e vs. log σv′ of undisturbed samples of Middleton peat 23

3.1 Flow chart of peat soil testing 25

3.2 Placement of samples in a muffle furnace for organic content

test

29

3.3 Pycnometers containing kerosene and peat samples in a

dessicator

32

3.4 Consolidation apparatus: Oedometer (fixed ring type) 34

3.5 Oedometer apparatus sets 35

4.1 Location of Kg. Meranek from Universiti Malaysia Sarawak 40

4.2 Location of Kg. Mang from Universiti Malaysia Sarawak 41

4.3 Collection of samples 41

4.4 Samples for organic content test, before and after drying 43

4.5 Graph of void ratio vs log stress for Kg. Mang peat soil 45

4.6 Graph of void ratio vs log stress for Kg. Meranek peat soil 46

4.7 Graph of 𝐶𝛼 vs 𝐶𝑐 for Kg. Mang 48

4.8

Graph of 𝐶𝛼 vs 𝐶𝑐 for Kg. Mang 49

ix

LIST OF EQUATIONS

Equation Page

3.1 Moisture content of sample, W 28

3.2 Loss of ignition, N 30

3.3 Organic content, H% 31

3.4 Initial mass of dry soils as-received mass, Msa 31

3.5 Initial mass of dry soils oven-dried mass, Mso 31

3.6 Fiber content, FC 33

3.7 Mass of soil, g1 33

3.8 Mass of water in full bottle, g2 33

3.9 Mass of water used, g3 33

3.10 Volume of soil particles, Vs 33

3.11 Particle density, ρs 33

3.12 Specific gravity, Gs 33

3.13 Initial moisture content, wo 37

3.14 Initial bulk density, ρb 37

3.15 Initial dry density, ρd 38

3.16 Initial void ratio, e 38

3.17 Height of solid particles, Hs 38

3.18 Height of specimen, H 38

3.19 Void ratio, e 38

3.20 Coefficient of volume compressibility, mv 39

x

3.21 Coefficient of consolidation, 𝑐𝑣 39

3.22 Compression index, 𝐶𝑐 39

3.23 Coefficient of secondary compression index, 𝐶𝛼 40

xi

LIST OF ANNOTATIONS

Symbol Meaning Symbol Meaning

Cc Compression index σ Consolidation pressure

Ck Permeability change index σv′ Effective vertical stress

Cr Recompression index σz′ Stress

Csα Secondary rebound index t Time

Ci Initial compression index tp Duration of primary

consolidation

Cα Secondary compression index εv Vertical strain

eo Initial void ratio IL Incremental Loading

e Void ratio EOP End of Primary

kvo Coefficient of permeability in

vertical direction at eo

CRS Constant Rate of Strain

kho Coefficient of permeability in

horizontal direction at eo

ASTM American Standard for

Testing Materials

kv Coefficient of permeability in

vertical direction

kg Kampung

kh Coefficient of permeability in

horizontal direction

1

CHAPTER 1

INTRODUCTION

1.1 Background

In general, peat deposits are organic soils with problematic characteristics such

as high compressibility, very high void ratio and low shear strength (Ahamad, 2005).

Peat deposits are formed by incomplete decomposition of plant and organic matters

under damp and anaerobic conditions (Sa'don, Karim, Jaol, & Lili, 2015). As stated by

MacFarlene (1969), the in-situ rate of biochemical degradation of peat deposits are

mostly very slow due to the high rate of acidity of pore water, waterlogged anaerobic

conditions and relatively low ground temperature. It is estimated that about eight to

eleven percent of global peat deposits are located in tropical or subtropical areas (Moore

and Bellamy, 1974; Shier, 1984). This includes the 100% of peat lands in Indonesia,

Malaysia, Brazil, Uganda, Zambia, Venezuela and Zaire.

Malaysia has about 3 million hectares of peat lands which equals to

approximately 8% of the total area of the country (Hassan et. al., 2013). According to

Sa’don (2015), in Sarawak alone, peat lands cover approximately 1.7 million hectare of

the state. Figure 1.1 shows the distribution of peat in Sarawak.

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Figure 1.1: Distribution of peat in state of Sarawak (Source: Sarawak, D, 2017)

According to Ramli (2009), amorphous peat and fibrous peat are two categories

of peat found in Malaysia. The organic grains of amorphous peat are smaller compared

to fibrous peat (Ng & Eischens, 1983). Process of consolidation can be divided into

three stages; initial compression, primary consolidation and secondary consolidation. In

this study, the three important parameters to be acknowledged are coefficient of

consolidation, cv, consolidation index Cc and finally secondary compression index, Cα.

According to Mesri & Godlewski (1997), secondary consolidation is significant in peat

deposits because of three main reasons. Firstly, peat exists at high natural water content,

void ratios and exhibit high values of compression index, Cc . Secondly, peat deposits

display the highest values of secondary compression index and compression index ratio,

Cα/Cc among other geotechnical materials and finally, primary consolidation period of

peat can be completed in a short time in typical field situations.

According to Kadir (2009), excavating and replacing from peat with good

quality soil has been practiced by the engineers for construction of peat lands. However,

this leads to high initial costs or uneconomic design. Brawner (1958) suggested other

solutions for construction such as avoiding peat lands, displacing or precompression.

Precompression or preloading is known as an alternative that is technically,

environmentally beneficial and economical resolution (Brawner, 1958).

It is important to understand the characteristics of peat and its behavior under

compression because any construction over peat soils are exposed to great primary and

long term secondary settlement.

3

1.2 Problem Statement

Peat lands are challenging for construction of roads, housing developments,

industrial parks due to its subsurface conditions. Construction on peat lands may have

high initial costs and/or continued maintenance operation (Colley, 1950). Peat lands in

Malaysia are usually avoided to prevent any unwanted serviceability consequences on

the building in years later. However, due to modern development and increment in

demand of land development, constructions of residential and commercial buildings on

peat are unavoidable (Hassan, 2013).

According to Jarrett (1983), long term consolidation settlement and also

instability may occur even with only a moderate increase in load. In natural condition of

peat soils, it can be concluded that peat soils are unsuitable for supporting foundation or

overburden stress. Compared to soft clay and silt deposits, fibrous peat deposits have

very high initial permeability which is usually 1,000 times higher (Mesri & Aljouni,

2007). Peat deposits are known to have high in-situ void ratios and exist at high natural

water contents therefore, peat deposits produces high values of compression index,

Cc =∆e

∆logσv′ where e is the void ratio and σv

′ is the effective vertical stress. Figure 1.2

shows the values of natural water content and compression index for peats (Mesri &

Aljouni, 2007).

Figure 1.2: Values of Natural Water Content and Compression Index for Peats as

Compared to those of Soft Clay and Silt Deposits (Mesri & Rokshar, 1974)

4

Upon loading or compression, the permeability of fibrous peats decreases dramatically.

The natural condition of peat soils contribute toward cases of buildings and

infrastructures settlement which is very common on areas covered with peat soils

(Hassan, 2013).

According to a research, long term settlements of road embankment and also

pavement deformations are common in Sibu, Sarawak and according to Vincent (2010),

this have resulted in unsafe road quality and high road operation and maintenance costs.

Some other common cases in Sibu area are settlement of residential buildings;

reinforced concrete drains and also pipelines disruption (Hassan, 2013). Figure 1.3 and

Figure 1.4 show the settlement that occurred near the Salim-Airport Road By-Pass in

Sibu, Sarawak.

Figure 1.3: Settlement of pipeline; gaps between the pipeline and ground surface in

Sibu Town, Sarawak (Razali, 2013)

PIPELINE

GROUND

5

Figure 1.4: Settlement under a lamp post in Sibu Town, Sarawak (Razali, 2013)

1.3 Objectives

This study mainly focuses on the secondary consolidation behavior of peat from

Kampung Meranek and Kampung Mang, Kota Samarahan.

The objectives of this study are:

i) To determine the basic properties of peat from Kampung Mang and

Kampung Meranek.

ii) To conduct a consolidation test on Kampung Mang and Kampung Meranek peat

soil and establish the relationship of coefficient of consolidation, Cv vs effective

stress, σ′

iii) To establish the relationship of secondary consolidation index and compression

index ratio, Cα/Cc of Sarawak peat.

6

1.4 Thesis Outline

The key purpose of this research is to analyse the secondary consolidation

behavior of Sarawak peat in Kampung Mang and Meranek. This thesis is divided into

five chapters to represent the works in this research.

Chapter 1 introduces the general background of peat and complications it

caused. Scope of the study and the objectives are included in this chapter.

Chapter 2 is the literature review that describes any data and information related

to peat study including engineering properties of fibrous peats, time and stress-

compressibility interrelationship and secondary compression of peat with or without

surcharging.

Chapter 3 discusses the methodology of how this research will be done. The

analysis of the data needs to be done in order to find out the secondary consolidation

behavior of peat.

Chapter 4 gives the outcomes and discussions of the analysis on the secondary

consolidation behavior of Samarahan peat.

Chapter 5 reviews all the assembled conclusion of the study where the

consolidation behavior of Kampung Mang and Kampung Meranek peat are discussed

and compressed. The suggestions for future review are given as well.

7

CHAPTER 2

LITERATURE REVIEW

2.1 Overview

In this chapter, the consolidation behavior, particularly secondary consolidation,

is reviewed. Aside from that, peat distribution in Malaysia, focusing more on Sarawak is

explained and discussed in this chapter as well. This chapter summarizes some of

previous studies related to peat consolidation.

2.2 Introduction of Peat

As indicated by Huat (2004), meaning of peat varies between soil science and

engineering. As suggested by soil researchers, any dirt with natural substance more

noteworthy than 35% is characterized as peat soil. From the perspective of geotechnical

designers, any dirt that has natural substance more significant than 20% is known as

natural soil and peat is characterized as those having a natural substance of 75%.

Concerning the moisture content of peat, the range is between 100 - 1300% on a dry

weight premise. The high water substance is brought on by buoyancy and a high pore

volume that outcomes in low mass thickness and low bearing limit.

Peat deposits are generally known as a problematic soil with high

compressibility, very high void ratios and low stability (Ahamad, 2005). The

characteristics of peat such as highly permeable and compressible causes it to be

unsuitable to build structures on it and this has caused serious problems in the

construction industry (Kadir, 2009). Since peat is low in shear strength, stability failure

occurs frequently and therefore the applied load is limited or placed accordingly in

stages. Primary consolidation in peats can be completed within weeks or months in

normal ground conditions. According to Mesri & Godlewski, (1997) and Kadir (2009),

8

secondary compression is significant in peat deposits since they have high void ratios,

great values of compression index, Cc and possess high value of secondary compression

index to compression index ratio, Cα/Cc compared to clay and silt deposits therefore

huge deformations may occur for a long time.

Malaysia lands consist of 3 million hectares of peat lands which equals to 8% of

the total area of the country (Hassan et al., 2013). The biochemical composition of the

parent material of peat affects its engineering properties (Mesri and Aljouni, 2007) and

natural water content of peat is the most advantageous index property for any

applications in engineering (Lea & Brawner, 1963; MacFarlane 1969; Yamaguchi,

Othira, & Kogure, 1985b). Due to high acidity of pore water, saturated anaerobic

conditions, and fairly low ground temperatures in majority of peat deposits, the in-situ

rate of biochemical degradation is extremely time-consuming (Mesri and Ajlouni,

2007). Both amorphous peat and fibrous peat are two categories of peat. According to

Ng and Eischens (1983) and Edil and Wang (2000), the organic grains of fibrous peat

are larger than amorphous peat, also amorphous peat fabric occur at lower void ratios

and exhibits lower permeability anisotropy, lower compressibility, lower friction angle

and greater coefficient of earth pressure at rest. However, in terms of consolidation,

both peats have similar behavior (Ramli, 2009).

Fibrous peat particles consist of 33.33% to 66.67% of water content (Ohira

1977). According to Mesri and Ajlouni (2007), the hollowed particles are highly

permeable, extremely compressible and highly malleable. Scanned electron

microphotograph (SEM) of James Pay, Canada peat is shown in Figure 2.1. The

physical characteristics of fibrous peat particles are large and comprises of thin leaves,

fragments of long stems, rootlets, cell walls and also fibers. Table 2.1 shows the

common sizes of fibrous peat particles.

(a) Vertical section

(b) Horizontal section