secondary consolidation behaviour of samarahan … · 2018. 6. 11. · gambut diketahui umum adalah...
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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.
ii
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.
2
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