LABORATORY EVALUATION OF HORIZONTAL COEFFICIENT OF CONSOLIDATION. ch OF FIBROUS PEAT SOIL

WONG LEONG SING

UNIVERSITI TEKNOLOGI MALAYSIA

LABORATORY EVALUATION OF HORIZONTAL COEFFICIENT OF CONSOLIDATION, ch OF FIBROUS PEAT SOIL

WONG LEONG SING

A project report submitted in partial fulfill ment of the requirements for the award of the degree of Master of Engineering (Civil-Geotechnics)

Faculty of Civil Engineering Universiti Teknologi Malaysia

NOVEMBER 2005

iii

To my beloved mother and father

iv

ACKNOWLEDGEMENT

First of all, I would like to thank my supervisor, Dr. Nurly Gofar for guiding me in the writing of this project report. Her opinion and advice were indeed helpful in the making of this project report a success. I would also like to express my sincere gratitude to Yulindasari Sutejo, a UTM research student for providing secondary data and assistance in my laboratory work. Without her help, the data for the project would not be available for analysis in this project report. Acknowledgement is not complete without thanking the technicians in UTM Geotechnical Laboratory for assisting either directly or indirectly in my laboratory work. Their assistance enabled me to complete this project report on time.

v

ABSTRACT

Encountered extensively in wetlands, fibrous peat is considered as problematic soil because it exhibits unusual compression behaviour. When a mass of fibrous peat soil with both vertical and horizontal drainage boundaries is subjected to a consolidation pressure, rate of excess pore water dissipation from the soil in the horizontal direction is higher than that in the vertical direction. The rates of excess pore water dissipation from the soil in the vertical and horizontal directions are measured by vertical and horizontal coefficient of consolidation (cv and ch) respectively. This project report presents laboratory findings on the consolidation behaviour of fibrous peat from Bahru village, Pontian, Johor with respect to one-dimensional vertical and radial consolidation. Results from hydraulic consolidation tests indicate that the ch/cv ratio of the soil is greater than 1 when the soil is subjected to consolidation pressure of 50 kPa, 100 kPa, and 200 kPa. This implies that the utilization of horizontal drain maybe suitable for soil improvement to accelerate the settlement of fibrous peat soil.

vi

ABSTRAK

Ditemui secara meluas di kawasan paya, tanah gambut berfiber merupakan tanah bermasalah kerana ia mempunyai sifat pengukuhan yang luar biasa. Apabila sesuatu jisim tanah gambut berfiber yang terdedah kepada sistem saliran air secara menegak dan mendatar dikenakan tekanan, kadar lesapan air terlebih secara mendatar adalah lebih tinggi berbanding dengan kadar lesapan air terlebih secara menegak daripada tanah tersebut. Kadar lesapan air terlebih secara menegak dan mendatar daripada tanah tersebut ditentukan oleh kadar pengukuhan tanah secara menegak dan mendatar (cv dan ch) masing-masing. Laporan projek ini membincangkan hasil kajian di dalam makmal tentang sifat pengukuhan tanah secara menegak dan mendatar bagi sampel-sampel tanah gambut berfiber yang didapati dari kampung Bahru, Pontian, Johor. Hasil ujian pengukuhan hidraulik menunjukkan bahawa nisbah ch/cv untuk tanah tersebut adalah lebih daripada 1 apabila tanah itu dikenakan tekanan 50 kPa, 100 kPa, dan 200 kPa. Ini menandakan bahawa penggunaan sistem saliran air secara mendatar mungkin sesuai bagi mempercepatkan proses pemendapan tanah gambut berfiber.

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TABLE OF CONTENTS

CHAPTER

TITLE

PAGE

1 INTRODUCTION 1

1.1

1.2

1.3

1.4

Background

Aims of project

Objectives of study

Scope of project

1

3

3

3

2 LITERATURE REVIEW

5

2.1

2.2

2.3

Introduction

Fibrous peat soil

Structural arrangement of fibrous peat soil

5

6

6

2.3.1

2.3.2

Permeabili ty of fibrous peat soil

Consolidation behaviour of fibrous

peat soil

9

14

2.4 Consolidation theory

2.4.1 One-dimensional consolidation 21

2.4.1.1 Determination of vertical

coefficient of consolidation,

cv

26

2.4.2

2.4.3

Secondary compression

Horizontal consolidation

30

41

2.4.3.1

2.4.3.2

Radial drainage to centre

Radial drainage to periphery

41

45

viii

2.5

2.6

Measurement of horizontal coefficient of

consolidation, ch of fibrous peat soil

Field evidence of fibrous peat soil

improvement

48

49

3

METHODOLOGY 53

3.1

3.2

3.3

Introduction

Preliminary tests

Hydraulic consolidation tests

53

54

56

3.3.1

3.3.2

3.3.3

Cell assembly and connections for

hydraulic consolidation tests

Test procedures of hydraulic

consolidation tests

Graphical analysis of Rowe cell

consolidation test

56

63

69

3.4 Hydraulic permeabili ty tests

3.4.1

3.4.2

Cell assembly and connections for

hydraulic permeabili ty test

Test procedures for hydraulic

permeabili ty tests

71

75

4 RESULT S AND DISCUSSION

79

4.1

4.2

Soil identification

Standard consolidation tests

79

80

4.2.1

4.2.2

Determination of range of

consolidation pressures

Evaluation of long term compression

of the soil

80

80

4.3 Hydraulic consolidation tests 81

ix

4.3.1

4.3.2

4.3.3

Vertical consolidation test

Radial consolidation test

Results comparison between

hydraulic consolidation tests with

radial and two-way vertical drainages

82

88

92

4.4 Permeabili ty tests 97

4.4.1

4.4.2

4.4.3

Initial permeabili ty

Hydraulic permeabili ty

Results comparison between constant

head and hydraulic permeabili ty tests

98

101

101

5 CONCLUSIONS AND RECOMM ENDATION

103

5.1

5.2

Conclusions

Recommendation

103

104

REFERENCES 105

Appendices A - D

107-121

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LIST OF TABLES

TABLE NO. TITLE

PAGE

2.1 Values of natural water content, wo, initial vertical coefficient of permeabili ty, kvo, and c./cc for peat deposits (Source: Mesri et al., 1997)

13

2.2 Change in tp and ts with pressure for Portage peat (average values for all tests) (Source: Dhowian and Edil, 1980)

18

2.3 Theoretical time factors for one-dimensional consolidation (Source: Leonards, 1962)

25

2.4 Determination of ch, the horizontal coefficient of consolidation (Source: Hausmann, 1990)

49

3.1 Rowe cell consolidation tests – Data for curve fitting (Source: Head, 1986)

71

4.1 Basic properties of the peat soil

79

4.2 Soil compression parameters of hydraulic consolidation tests on the fibrous peat soil samples under 50 kPa consolidation pressure analyzed by different methods

93

4.3 Soil compression parameters of hydraulic consolidation tests on the fibrous peat soil samples under 100 kPa consolidation pressure analyzed by different methods

94

4.4 Soil compression parameters of hydraulic consolidation tests on the fibrous peat soil samples under 200 kPa consolidation pressure analyzed by different methods

95

4.5 Range of ch/cv ratio based on Taylor’s method

96

4.6 Range of coefficient of secondary compression, cα ratio evaluated using Casagrande’s method

96

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4.7 Degree of consolidation (%) at which the secondary compression of the fibrous peat soil begins

97

4.8 Results summary of constant-head and hydraulic permeabili ty tests of the fibrous peat soil

102

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LIST OF FIGURES

FIGURE NO. TITLE PAGE 2.1

(a) Schematic diagram of deposition of fibrous peat deposit (b) Schematic diagram of multi-phase system of fibrous peat (Source: Kogure et al., 1993)

7

2.2

Photomicrographs of fibrous peat (Source: Terzaghi et al., 1996)

8

2.3

Micrographs of Middleton fibrous peat; (a) horizontal plane, (b) vertical plane (Source: Fox and Edil, 1996)

9

2.4

Permeabili ty of Middleton peat in vertical and horizontal directions (Source: Mesri et al., 1997)

11

2.5

Coefficient of permeabili ty versus void ratio for vertical and horizontal specimens of Portage peat (Source: Dhowian and Edil, 1980)

12

2.6

Vertical strain, normalized effluent outflow, and excess pore pressure versus logarithm of time for a Portage peat specimen under the first stress increment (back pressure = 560 kPa) (Source: Dhowian and Edil, 1980)

15

2.7

Consolidation data for a Portage peat specimen (back pressure = 560 kPa) (Source: Dhowian and Edil, 1980)

17

2.8

Log time-compression curve of fibrous peat soil for one-dimensional consolidation

19

2.9

One-dimensional consolidation (a) Terzaghi’s model (b) Stress-time curve (Source: Whitlow, 2001)

22

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2.10

Average degree of consolidation due to vertical drainage (= percent vertical consolidation) as a function of time factor, Tv (Source: Hausmann, 1990)

24

2.11

Theoretical time factor, Tv (logarithmic scale) related to average degree of consolidation, Uv (%) due to vertical drainage (Source: Head, 1982)

24

2.12

Square-root of theoretical time factor, Tv 0.5

related to average degree of consolidation, Uv (%) due to vertical drainage (Source: Head, 1982)

25

2.13

Theoretical relationships between time factor and degree of consolidation for vertical drainage for two methods of measurement (Source: Head, 1986)

26

2.14

Typical vertical consolidation test results (Source: Smith and Smith, 1998)

28

2.15

The square-root of time method (Source: Smith and Smith, 1998)

29

2.16

Types of time-compression curve of soil 31

2.17

Relationship between the degree of consolidation of theoretical time-pore water pressure dissipation curve, Ub and the average degree of consolidation, Uave from theoretical time factor-compression curve (Source: Robinson, 2003)

34

2.18

(a) Time-compression curves, and (b) time-degree of consolidation from the measured pore water pressure dissipation curves for peat (Source: Robinson, 2003)

35

2.19

(a)-(f) Degree of consolidation from the pore water pressure dissipation curves (Ub)-compression plots for peat at different load increment ratios (LIR) (Source: Robinson, 2003)

36

2.20

(a) Time-total settlement curves for peat under a load increment ratio (LIR) of 0.33, and (b) Time-settlement curve after removing the secondary compression (Source: Robinson, 2003)

38

xiv

2.21

Theoretical log Uv - log Tv plot (Source: Sridharan and Prakash, 1998)

39

2.22

7\SLFDO�ORJ�/�- log t plot of brown Mexico City clay (Sridharan and Prakash, 1998)

40

2.23

Average degree of consolidation for radial flow versus time factor for free strain and equal strain boundary conditions; radial inflow tests with the drain spacing ratio = 5 (Source: Trautwein, 1980)

43

2.24

Different drain patterns: equivalent cylinder (Source: Holtz et al., 1991)

45

2.25

Theoretical curve relating square-root time factor to degree of consolidation for drainage radially outwards to periphery with ‘equal strain’ loading (Source: Head, 1986)

46

2.26

Theoretical time-factor relationship with degree of consolidation for drainage radially outwards with ‘ free strain’ loading (Source: McKinlay, 1961)

47

2.27

Soil profile at the Dalarovagen site (Source: Larsson, 1986)

50

2.28

Measured settlement, excess pore pressures and load at Dalarovagen site (Source: Carlsten, 1988)

51

2.29

Swelli ng and settlement versus logarithmic of time at Dalarovagen site (Source: Carlsten, 1988)

52

3.1

Flowchart summarizing the methodology of the project

54

3.2

Two-way vertical drainage and loading condition for hydraulic consolidation test in Rowe cell with ‘equal strain’ loading (Source: Head, 1986)

56

3.3

Cutting rings containing soil sample are fitted on top of the Rowe cell body

57

3.4

A porous disc is used to slowly and steadily push the soil sample vertically downward into the Rowe cell body

57

3.5

Schematic diagram of fill ing of distill ed water into the diaphragm (Source: Head, 1986)

58

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3.6

Realistic view of filli ng of distill ed water into the diaphragm

58

3.7

Diaphragm inserted into Rowe cell body (Source: Head, 1986)

59

3.8

Diaphragm is correctly seated (Source: Head, 1986)

60

3.9

Radial drainage to periphery, and loading condition for hydraulic consolidation test in Rowe cell with ‘equal strain’ loading (Source: Head, 1986)

61

3.10

Fitting porous plastic liner in Rowe cell: (a) initial fitting and marking, (b) locating line of cut, (c) final fitting (Source: Head, 1986)

62

3.11

Peripheral drain fitted into the Rowe cell body

63

3.12

Arrangement of Rowe cell for consolidation test with two-way vertical drainage (Source: Head, 1986)

64

3.13

Arrangement of Rowe cell for consolidation test with radial drainage to periphery; pore pressure measurement from centre of base of sample (Source: Head, 1986)

68

3.14

Downward vertical flow condition for hydraulic permeabili ty test in Rowe cell (Source: Head, 1986)

72

3.15

Arrangement of Rowe cell for permeabili ty test with vertical flow (downwards) (Source: Head, 1986)

73

3.16

Horizontally outward flow condition for permeabili ty test in Rowe cell (Source: Head, 1986)

73

3.17

Arrangement of Rowe cell for permeabili ty test with horizontal drainage to periphery (Source: Head, 1986)

74

3.18

Arrangement for hydraulic vertical permeabili ty test using one back pressure system for downward flow (Source: Head, 1986)

76

xvi

4.1

Oedometer log time-compression curves of a sample of the fibrous peat soil

81

4.2

Graphical plots of hydraulic vertical consolidation test of the fibrous peat soil samples analyzed by Casagrande’s method based on settlement

84

4.3

Graphical plots of hydraulic vertical consolidation test of the fibrous peat soil samples analyzed by Casagrande’s method based on dissipation of excess pore water pressure at the centre of sample base

84

4.4

Graphical plots of hydraulic vertical consolidation test of the fibrous peat soil samples analyzed by Taylor’s method

85

4.5

Degree of vertical consolidation with two-way vertical drainage due to dissipation of excess pore water pressure (Ub) – compression plots of the fibrous peat soil samples at different consolidation pressures (Robinson’s method)

85

4.6

Graphical plots for the analysis on the beginning of secondary compression due to vertical consolidation with two-way vertical drainage of the fibrous peat soil samples using Robinson’s method (a) Log time-total compression curves for vertical consolidation on the fibrous peat at different consolidation pressures (b) Log time-primary consolidation curves after removing the secondary compression

86

4.7

Graphical plots for the determination of coefficient of secondary compression, cα due to vertical consolidation with two-way vertical drainage of the fibrous peat soil samples analyzed from Robinson’s method

87

4.8

Graphical plots of hydraulic vertical consolidation test of the fibrous peat soil samples analyzed by Sridharan and Prakash’s method

87

4.9

Graphical plots of hydraulic radial consolidation test of the fibrous peat soil samples analyzed by Casagrande’s method based on settlement

89

xvii

4.10

Graphical plots of hydraulic radial consolidation test of the fibrous peat soil samples analyzed by Casagrande’s method based on dissipation of excess pore water pressure at the centre of sample base

89

4.11

Graphical plots of hydraulic radial consolidation test of the fibrous peat soil samples analyzed by Taylor’s method

90

4.12

Degree of radial consolidation with periphery drainage due to dissipation of excess pore water pressure (Ub) – compression plots of the fibrous peat soil samples at different consolidation pressures (Robinson’s method)

90

4.13

Graphical plots for the analysis on the beginning of secondary compression due to radial consolidation with radial drainage to periphery of the fibrous peat soil samples using Robinson’s method (a) Log time-total compression curves for radial consolidation on the fibrous peat at different consolidation pressures (b) Log time-primary consolidation curves after removing the secondary compression

91

4.14

Graphical plots for the determination of coefficient of secondary compression, cα due to radial consolidation with radial drainage to periphery of the fibrous peat soil samples analyzed from Robinson’s method

92

4.15

Graph of coefficient of permeabili ty at standard temperature of 20°C, ko (20°C) versus initial void ratio, eo of the fibrous peat soil samples

99

xviii

LIST OF SYMBOLS

A - Area of sample

AC - Ash content

B - Pore pressure parameter

cc - Compression index

ch - Horizontal coefficient of consolidation

cr - Recompression index

cv - Vertical coefficient of consolidation

cα, cα1 - Coefficient of secondary compression

cα2 - Coefficient of tertiary compression

D - Diameter of sample

e - Void ratio

eo - Initial void ratio

FC - Fiber content

Gs - Specific gravity

H, Ho - Initial thickness of consolidating soil layer

h - Head loss due to the height of water in the burette

i - Hydraulic gradient

kh - Horizontal coefficient of permeabili ty

kho - Initial horizontal coefficient of permeabili ty

kv - Vertical coefficient of permeabili ty

xix

kvo - Initial vertical coefficient of permeabili ty

L - Longest drainage path in consolidating soil layer; equal to half of H with top and bottom drainage, and equal to H with top drainage only

m - Secondary compression factor

mv - Coefficient of volume compressibili ty

OC - Organic content

p - Consolidation pressure

po - Initial pressure

p1 - Inlet pressure

p2 - Outlet pressure

Q - Cumulative flow

q - Rate of flow

r - Radius of sample

Tr - Radial theoretical time factor

Tv - Vertical theoretical time factor

t - Time

ts - Time to reach end of secondary compression

tp - Time to reach end of primary consolidation

Ur - Average degree of consolidation due to radial drainage

Uv - Average degree of consolidation due to vertical drainage

u - Excess pore water pressure at any point and any time

uo - Initial excess pore water pressure

w - Natural moisture content

û+s - Change in height of soil layer due to secondary compression from time, t1 to time, t2

xx

û+t - Change in height of soil layer due to tertiary compression from time, t3 to time, t4

ûS - Pressure difference

0i - Instantaneous strain

0p - Primary strain

0s - Secondary strain

0t - Tertiary strain

�w - Unit weight of water

1v - Effective vertical stress

δ - Total compression

δp - Primary consolidation settlement

δs - Secondary compression

xxi

LIST OF APPENDICES

APPENDIX TITLE PAGE A

Soil sampling

107

B Apparatus for constant-head permeabili ty test

109

C Apparatus for hydraulic consolidation tests

111

D Steps for various methods used to evaluate vertical and horizontal coefficient of consolidation (cv and ch) and coefficient of secondary compression (c.) of the fibrous peat soil

113

CHAPTER 1

INTRODUCTION 1.1 Background

When a load is applied to a saturated soft soil, it is initially carried by the

pore water within a soil mass. The resulting pore water pressure, in excess of the

hydrostatic water pressure is termed excess pore water pressure. As water dissipates

from the soil pores, the applied load is gradually shifted from water to soil particles.

The load transfer is accompanied by a volume change. This process is generally

known as consolidation.

Depending on the packing of the soil mass and the drainage boundary

condition, the dissipation of excess pore water would naturally take either vertical or

horizontal flow path. The packing of the soil mass is usually governed by the soil

fabric, the shape of soil particles, and other material content. The term fabric

describes the geometrical arrangement of soil particles with respect to each other.

Generally, the greater the range of particle sizes, the smaller the total volume of void

spaces there will be.

Fibrous peat soil has many void spaces existing between the solid grains. Due

to the irregular shape of individual particles, fibrous peat soil deposits are porous and

the soil is considered a permeable material. Flow of water is occurring not only

through the inner voids within organic particles but also the outer voids between

organic particles and soil particles in the soil mass. Hence, for saturated fibrous peat

soil , the actual path taken by pore water as it flows through void spaces is tortuous

2

and erratic because of the random arrangement of the soil particles and organic

coarse particles. In this case, velocity of pore water varies considerably with the flow

direction.

The discussion in the preceding paragraph shows that the dissipation of

excess pore water pressure would follow a flow path which is dependent on the

packing of soil mass and the velocity of flow varies considerably with flow direction.

Despite of this fact, conventional consolidation theory developed by Terzaghi (1925)

considers that consolidation process takes place in vertical direction only. Up to

recently, analysis of consolidation is very often based on this theory where horizontal

consolidation of soil is ignored.

The importance of horizontal consolidation emerges with the development of

soil stabil ization method especially the use of preloading system with vertical drains.

Vertical drains are used to provide horizontal drainage system in compressible soil

layer so that water would flow radially from the soil into the vertical drains. With the

use of surcharge and vertical drains, the consolidation process is accelerated by

shortening the length of the drainage path for the pore water escaping from the soil

layer. In this case, horizontal drainage flow plays an important role in the

consolidation process. Thus, an economic design of vertical drains depends on a

rational assessment of the horizontal coefficient of consolidation, ch (Berry and

Wilkinson, 1969).

Horizontal drainage becomes even more important in view of the fact that for

most transported soils, horizontal coeff icient of consolidation, ch is normally greater

than vertical coefficient of consolidation, cv. Thus, the knowledge of horizontal

coefficient of consolidation, ch is very important in the selection of suitable soil

stabili zation method for soft organic soils and peat.

3

1.2 Aim of project The project focuses on the study of horizontal coefficient of consolidation, ch

of fibrous peat soil and to compare the results with it’s vertical coefficient of

consolidation, cv through laboratory investigation. This is important to emphasize the

applicabil ity of knowledge of horizontal coefficient of consolidation, ch on the

development of soil improvement method for construction on fibrous peat soil.

1.3 Objectives of study In order to achieve the aim of the project, the study consists of the following

objectives:

1. To study the compressibil ity characteristics of fibrous peat soil based on the

consolidation curves obtained from hydraulic consolidation tests for vertical and

horizontal drainage

2. To study the effect of secondary compression on the determination of vertical

and horizontal coefficient of consolidation (cv and ch) of fibrous peat soil

3. To compare the vertical and horizontal coeff icient of consolidation (cv and ch) of

fibrous peat soil under a range of consolidation pressures

4. To compare the vertical and horizontal coeff icient of permeability, (kh and kv) of

fibrous peat soil under a consolidation pressure

5. To outline the use of knowledge of horizontal coefficient of consolidation, ch on

the development of soil improvement method for construction on fibrous peat

soil

1.4 Scope of project

The project is concentrated on the laboratory measurement of consolidation

parameters for fibrous peat soil found in Bahru village, Pontian, Johor with the

primary focus on the comparison of vertical and horizontal coeff icient of

4

consolidation (cv and ch) measured by Rowe consolidometer in laboratory using

‘ identical’ sample. Since creep deformation is significant in fibrous peat soil ,

laboratory investigation is also carried out to analyze the long term compression

behaviour of the soil.

105

REFERENCES

1. Berry P.L., and Wilkinson, W.B. The Radial Consolidation of Clay Soils.

Geotechnique. 1969. 19(2): 253-284.

2. Dhowian, A.W., and Edil, T.B. Consolidation Behavior of Peats. Geotechnical

Testing Journal. 1980. 3(3): 105-114.

3. Kogure, K., Yamaguchi, H., and Shogaki, T. Physical and Pore Properties of

Fibrous Peat Deposit. Singapore: 11th Southeast Asian Geotechnical Conference.

1993.

4. Terzaghi, K., Peck, R.B., and Mesri, G. Soil Mechanics in Engineering Practice.

3rd Edition. New York: John Wiley & Sons. 1996.

5. Fox, P.J., and Edil , T.B. Effects of Stress and Temperature on Secondary

Compression of Peat. Canadian Geotechnical Journal. 1996. 33(3): 405-415.

6. Mesri, G., Stark, T.D., Aljouni, M.A., and Chen, C.S. Secondary Compression of

Peat with or without surcharging. Journal of Geotechnical and

Geoenvironmental Engineering. 1997. 123(5): 411-421.

7. Collesell i, F., Cortellazzo, G., and Cola, S., “Laboratory Testing of Italian Peat

Soils,” Geotechnics of High Water Content Materials, ASTM STP 1374, Edil ,

T.B., and Fox, P.J. (Eds.), American Society for Testing and Materials, West

Conshohocken, PA, 2000.

8. Edil , T.B. Recent Advances in Geotechnical Characterization and Construction

over Peats and Organic Soils. Putrajaya (Malaysia): 2nd International

Conferences in Soft Soil Engineering and Technology. 2003.

9. Lan, l.T. A Model for One-dimensional Compression of Peat. Ph.D. thesis.

University of Wisconsin, Madison, U.S.A; 1992.

10. Colley, B.E. Construction of Highways over Peat and Muck Areas. Am.

Highways. 1950. 29(1): 3-6.

11. Bardet, J.P. Experimental Soil Mechanics. New Jersey: Prentice-Hall. 1997.

12. Whitlow, R. Basic Soil Mechanics. 4th edition. Essex: Pearson Education Ltd.

2001.

13. Robinson, R. G. A study on the Beginning of Secondary Compression of Soils.

Journal of Testing and Evaluation. 2003. 31(5): 1-10.

14. Hausmann, M.R. Engineering Principles of Ground Modification. New York:

McGraw-Hill . 1990.

106

15. Head, K.H. Manual of Soil Laboratory Testing, Volume 2: Permeability, Shear

Strength and Compressibility Tests. London: Pentech Press Limited. 1982.

16. Head, K.H. Manual of Soil Laboratory Testing, Volume 3: Effective Stress Tests.

London: Pentech Press Limited. 1986.

17. Smith, G.N. and Smith I.G.N. Element of Soil Mechanics. 7th edition. Cambridge:

Blackwell Science Ltd. 1998.

18. Sridharan, A., and Prakash, K. Secondary Compression Factor. Geotechnical

Engineering. 1998. 131(2): 96-103.

19. Holtz, R.D., Jamiolkowski, M.B., Lancellotta, R., and Pedroni, R. Prefabricated

Vertical Drains: Design and Performance. Oxford: Butterworth-Heinemann Ltd.

1991.

20. Head, K.H. Manual of Soil Laboratory Testing, Volume 1: Soil Classification and

Compaction Tests. London: Pentech Press Limited. 1980.

21. Hartlen, J., and Wolski, W. (Eds.). Embankments on Organic Soils. Armsterdam:

Elsevier Science B.V. 1996.

22. Gofar, N., and Sutejo, Y. Engineering Properties of Fibrous Peat. Senai

(Malaysia): Seminar Penyelidikan Kejuruteraan Awam (SEPKA), Universiti

Teknologi Malaysia (UTM). 2005.