methods for estimating ocr and consolidation...

i

Methods for Estimating OCR and Consolidation

Properties of Soil from the Results of Piezocone

Tests

September 2017

Department of Science and Advanced Technology

Graduate School of Science and Engineering

Saga University

CHANMEE NACHANOK

ii

Methods for Estimating OCR and Consolidation

Properties of Soil from the Results of Piezocone

Tests

A dissertation submitted in partial fulfillment of the requirement for the degree of Doctor of

Philosophy in Geotechnical Engineering

By

CHANMEE NACHANOK

Examination Committee: Prof. Jinchun Chai (Supervisor)

Prof. Katsushi Ijima

Prof. Takenori Hino

Associate Prof. Daisuke Suetsugu

Prof. Dennes T. Bergado (External Examiner)

Asian Institute of Technology, Thailand

Nationality: Thai

Previous Degrees: Bachelor of Civil Engineering

Sirindhorn International Institute of

Technology (SIIT), Pathum thani, Thailand

Master in Civil Engineering

Asian Institute of Technology

(AIT), Pathum thani, Thailand

Scholarship Donor: MEXT (Ministry of Education, Culture, Sports,

Science, and Technology)

Department of Science and Advanced Technology

Graduate School of Science and Engineering

Saga University, Japan

iii

ACKNOWLEDGEMENT

The author wishes to express his deepest and sincerest gratitude to his supervisor

Professor Jinchun Chai for his affectionate and unfailing guidance, motivation, energetic

encouragement, helpful criticism and suggestions at every stage for this PhD study. His wide

knowledge and logical way of thinking have been a great value for the author. Without Prof.

Chai’s help, this dissertation work could not be complete. The author is also grateful to his

former supervisors, Professor Dennes T. Bergado, who appreciated intentions in the studies

and supported in applying this scholarship.

The author is also very grateful to all the examination committee members, Prof.

Katsushi Ijima, Prof. Takenori Hino, and Associate Prof. Daisuke Suetsugu for their valuable

suggestions and comments on the dissertation. Sincere thanks and appreciation are due to

external examiner, Prof. Dennes T. Bergado for his advice and suggestions. Special thanks to

Mr. Akinori Saito for his help and assistance on laboratory testing.

The author would like to acknowledge with appreciation to the scholarship grant

provided by MEXT (Ministry of Education, Culture, Sports, Science, and Technology) which

made it possible to pursue his doctoral studies at Saga University, Saga, Japan.

Sincere thanks are due to his seniors, Dr. Apichat Suddeepong, Dr. Sailesh Shrestha, Dr.

Xu Fang, and Dr. Suman Manandhar, to colleagues, Mr. Nattasit Srinurak, PhD student, Mr.

Nutthachai Prongmanee, PhD student, Mr. Zhou Yang, PhD student, Mr. Peerapat Khaimook,

PhD student, and Mr. Lu Yi Tian, PhD student, for kindly helping the author in various ways

during the course of the study. A word of thanks goes to all his friends and Thai community

who help the author get through three years of study and made the author feels like home.

Last but not least, the author expresses a lot of gratefulness to his mother, and Ms.

Piyachat Kongkrijak for their endless inspirations supports and all necessary helps during the

course of this study. Finally, the author dedicated this work to his late father, for

encouragement to the author for pursuing his degree.

iv

Affectionately dedicated

To

my beloved mother and father

v

ABSTRACT

This study focused on using the results of piezocone sounding (uCPT) and dissipation

tests to estimate overconsolidation ratio (OCR) and consolidation properties (ch and kh) of

soil. Currently, several existing methods for estimating OCR from uCPT results are ranging

from empirical to theoretical approaches. Therefore, the methods for estimating OCR from

uCPT results have been investigated. M oreover, the ex isting m ethods for estim ating

consolidation properties (ch and kh) of soil from uCPT results a r e in v e s t ig a t e d u s in g

laboratory model test results and the field cases.

The applicability of three (3) existing methods for estimating OCR from uCPT has been

investigated with twelve (12) field cases around the world. All of existing methods have

empirical parameters, and if the empirical parameters can be determined properly, reasonable

values of OCR can be estimated. However for underconsolidated deposits, some of existing

methods performed poorly. Therefore, a new method for estimating the value of OCR based

on Modified Cam Clay theory has been proposed and modifications of existing method to be

applicable for underconsolidated sites have been carried out. Finally, the proposed method

and the modified existing methods have been evaluated using field data and it is shown that

the proposed method can yield better results.

Totally fifteen (15) laboratory model tests on piezocone penetration (uCPT) and

dissipation were conducted using five types of soil and over consolidation ratio (OCR) of 1,

2, 4, and 8. Five types of soil, namely, remolded Ariake clay, Ariake clay mixed with a sand

with sand/clay ratios (by dry weight) of 50:50 (Mixed soil 1), 60:40 (Mixed soil 2), 70:30

(Mixed soil 3), and 20:80 (Mixed soil 4), respectively were used in the laboratory model

tests. The laboratory model ground was prepared in a cylindrical container (chamber) made

of PVC and has an inner diameter of 0.485 m and a height of 1.0 m. The soils were

thoroughly mixed with a water content of about 1.2 times their liquid limits (LL), and

carefully poured into the chamber layer by layer until the thickness of the model ground was

0.8 m. Piezometers were placed at pre-determined locations in the model to measure the pore

water pressure during pre-consolidation process. An air pressure was applied to pre-

consolidate the model ground. Once the degree of pre-consolidation was more than 95%, the

air pressure was adjusted to achieve the desired value of OCR. After the pre-consolidation,

the thickness of the model ground was about 0.6 m. In case of OCR > 1.0, unloading would

induce negative pore pressure in the model ground. In this kind of case, the piezocone

vi

penetration and dissipation was conducted after the negative excess pore pressure dissipated.

Two mini piezocones (u2) have cone tip angle of 60° with diameters of 30 mm 20 mm were

used in the laboratory test. The filter for pore pressure measurement is on the shoulder of the

cones. The penetration rate adopted was 25 mm/min (0.4 mm/s).

Based on dissipation test results, all measured dissipation curves are non-standard type

where u2 increased initially and then dissipated with time. Therefore, Chai et al. (2012a)’s

method is used for estimating the coefficient of consolidation (ch) from uCPT laboratory

model test results. As a result, the method performed reasonably well for all soil types. (For

Mixed soils; results are lying between ratios of ch/cv of 0.2 to 1.0, and for Ariake clay; results

are line between ratios of ch/cv of 1.0 to 2.0). Therefore, it is recommended that the method

can be used in engineering practice of estimating ch from the results of piezocone dissipation

test. However, when applying the existing method (Chai et al. 2011) for estimating

permeability (kh) to the model test results indicates that the method performed poorly for

overconsolidated soils. It can be seen that under the condition of a given maximum

consolidation pressure the measured values of kv slightly increased with OCR, while the

estimated values of kh decreased with OCR significantly for all the soil types.

Thus, Chai et al. (2011)’s method has been modified to be applicable for overconsolidated

soils. Since in the method, kh is a function of0'v

u

(∆u is the measured excess pore water

pressure and σv0 is the initial effective vertical stresses), the basic idea of the modified

method is to include the effect of OCR on0'v

u

. Then the modified method for

estimating kh corresponding to yield vertical effective stress (σvmax) and vertical effective

stress (σv0) for OCR >1.0 has been established. In case of estimating the value kh

corresponding to yielding vertical effective stress, the proposed method needs two

parameters, namely, OCR and a model parameter, α. While if the value of kh corresponding to

the initial vertical effective stress is required, two more parameters, i.e. swelling index (Cs)

and the initial void ratio (e0) are needed. It is suggested that Cs and e0 have to be estimated

based on local data-base about soil properties; and OCR can be estimated using the results of

uCPT. As for α value, it is related to soil types. It is recommended to classify the soil type

using Robertson’s (1990) method. Finally, the modified method was evaluated to two (2) sites

in Japan and one (1) site in China. By comparing the estimated values of kh from the results of

uCPT and the measured values of kv, it shows that the modified method resulted in much

better estimation of values of kh.

vii

TABLE OF CONTENTS

Chapter Title Page

TITLE

ACKNOWLEDGMENT

ABSTRACT

TABLE OF CONTENTS

LIST OF TABLES

LIST OF FIGURES

LIST OF NOTATIONS

i

iii

v

vii

xi

xii

xvii

CHAPTER 1 INTRODUCTION

1.1 Background 1

1.2 Objectives and Scopes 2

1.3 Organization of the dissertation 3

CHAPTER 2 LITERATURE REVIEW

2.1 Introduction 5

2.2 Measurements from Piezocone Test 5

2.3 Methods for estimating overconsolidation ratio (OCR) 10

2.3.1 Undrained shear strength (su) approach (Method 1) 11

2.3.2 Normalized tip resistance (Qt) approach (Method 2)

2.3.3 Approach based on cavity expansion and critical state soil

mechanics theories (Method 3)

2.3.4 Limitation of methods

12

13

14

2.4 Methods for Estimating Coefficient of Consolidation (ch) 15

2.4.1 Methods for standard dissipation curves 15

2.4.2 Methods for non-standard dissipation curves

2.4.3 Discussions

16

16

2.5 Methods for estimating permeability (kh) 17

2.5.1 Existing methods to estimate permeability 17

2.5.2 Discussions 21

2.6 Summary and discussions 22

viii

CHAPTER 3 METHOD FOR ESTIMATING OCR

3.1 Introduction 23

3.2 Field case histories 23

3.2.1 Sites in Japan (Group 1)

3.2.1.1 Saga site

3.2.1.2 Yokohama site

24

24

30

3.2.2 Sites in China, Korea and Egypt (Group 2)

3.2.2.1 Lianyungang site, China

3.2.2.2 Two sites in Busan, Korea

3.2.2.3 Port Said site, Egypt

31

31

32

33

3.2.3 Sites in Finland and Sweden (Group 3)

3.2.3.1 Perniö site, Finland

3.2.3.2 Five sites in Sweden

34

34

35

3.3 Evaluating the applicability of the existing methods

3.3.1 Group 1

3.3.2 Group 2

3.3.3 Group 3

3.3.4 Discussions

38

38

41

44

46

3.4 Proposed method 47

3.5 Modification of the existing methods for underconsolidated

deposits

48

3.5.1 Undrained shear strength (su) approach (Method 1)


48

49

3.5.3 Cavity expansion and critical state soil mechanics

theories’ approach (Method 3)

3.5.4 Parameters needed in each method

49

50

3.6 Applying the proposed method and the modified methods to the

field cases

3.6.1 Proposed method to the sites in Group 1

3.6.2 Proposed method and the modified Methods 1, 2 and 3 to

the sites in Group 2


50

50

51

54


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CHAPTER 4 EVALUATING THE METHODS FOR ESTIMATING

CONSOLIDATION PROPERTIES

4.1 Introduction 57

4.2 Laboratory model tests

4.2.1 Laboratory scale piezocones

4.2.2 Penetration system

4.2.3 Model chamber

4.2.4 Set-up and test procedure

4.2.5 Limitations of the laboratory model test

4.2.6 Soil samples and case tested

4.2.7 Results of the dissipation tests

57

57

59

59

61

64

64

66

4.3 Comparison of measured and estimated coefficient of

consolidation from laboratory piezocone test results

72

4.4 Comparison of measured and estimated permeability from

laboratory piezocone test results

76


CHAPTER 5 MODIFIED METHOD FOR ESTIMATING PERMEABILITY

5.1 Introduction 82

5.2 Laboratory model test results 82

5.3 Void ratio (e) and permeability (k) relationship of soil 85

5.4 Modified method

5.4.1 Basic considerations

5.4.2 Obtaining kh0

86

86

87

5.5 Comparing with laboratory model test results 91

5.6 Methods for determining the parameters 96

5.7

5.8

5.9

Procedure for using the modified method

Application to field cases

5.8.1 Case 1: Saga, Japan

5.8.2 Case 2: Yokohama, Japan

5.8.2 Case 3: Shanghai, China

Conclusions

96

98

98

100

102

105

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CHAPTER 6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

6.1 Summary

6.1.1 Methods for estimating OCR

6.1.2 Methods for estimating ch

6.1.3 Methods for estimating kh

106

106

107

108

6.2 Conclusions

6.2.1 Proposed method for estimating OCR

6.2.2 Evaluating the existing methods for ch and kh

6.2.3 Modified method for estimating kh

109

110

110

111

6.3 Recommendations for Further Research 112

REFERENCES 113

xi

LIST OF TABLES

Table No. Caption of The Tables Page

2.1 Summary of the parameter Nkt 11

2.2 Summary of the parameter k 12

2.3 Summary of parameters needed in each method 14

3.1 Summary of parameters needed in each method (including the proposed

method)

50

4.1 Physical properties of the soils tested 65

4.2 Conditions of model tests conducted 66

4.3 Conditions and results of model tests conducted (ch) 72

4.4

4.5

4.6

Comparison of ch and cv values from CRS test on Ariake clay samples

Conditions and results of model tests conducted (kh)

Comparison of kh and kv values from CRS test on Ariake clay samples

73

76

80

xii

LIST OF FIGURES

Figure No. Caption of The Figures Page

1.1 Flow chart of this dissertation 4

2.1 Location of pore pressure elements 5

2.2 Piezocone penetration test results at a location in Saga, Japan 6

2.3 Total and effective stress area of cone 7

2.4 Standard dissipation curve 9

2.5 Non-standard dissipation curve 10

2.6 Basic concept of Elsworth and Lee’s (2005) method 18

2.7 Relationship between measured non-dimensional hydraulic conductivity

KD and BqQt from piezocone test (data from Elsworth and Lee 2007)

19

2.8 Bi-linear relationship between measured non-dimensional hydraulic

conductivity KD and BqQt from piezocone test (data from Chai et al.

2011)

20

2.9 Half-spherical flow 21

3.1 Location of all uCPT investigated sites 24

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

Soil strata, piezocone sounding results and measured values of OCR at a

location H15-308 of Saga site















25

25

26

26

27

27

28

28

xiii

3.10

3.11

3.12

3.13

3.14

3.15

3.16

3.17





Soil strata, piezocone sounding results and measured values of OCR of

Yokohama site


Lianyungang site


DIS-5 site, Busan


D2 site, Busan


Port Said site, Egypt


Perniö site, Finland

29

29

30

31

32

33

34

35

3.18 Variation of uCPT qt and OCR with depth at Gammelgården site,

Sweden

36

3.19 Variation of uCPT qt and OCR with depth at Hjoggböle site, Sweden 36

3.20 Variation of uCPT qt and OCR with depth at Sunderbyn site, Sweden 37

3.21 Variation of uCPT qt and OCR with depth at Umeå bangård site,

Sweden

37

3.22 Variation of uCPT qt and OCR with depth at Västerslätt site, Sweden 38

3.23 Comparison of the measured and the predicted values of OCR using the

Method 1 for the sites of Group 1

39



40



41



42



43

xiv



44



45



46


proposed method of Group 1

52


proposed method for the sites of Group 2

52

3.33

3.34

Comparison of the measured and the predicted values of OCR using

modified Method 1 for the sites of Group 2

Comparison of the measured and the predicted values of OCR using


53

53

3.35 Comparison of the measured and the predicted values of OCR using


54



55

4.1 Schematic diagram of laboratory model test 58

4.2 Laboratory scale piezocones (Hossain 2014) 59

4.3 Opening locations of piezometer (a) outside of chamber; (b) inside of

chamber

60

4.4 A rubber sleeve (a) A rubber sleeve installed above the piston; (b)

Function of the rubber sleeve

60

4.5 Drainage layer in chamber 62

4.6 Typical settlement curve of pre-consolidation of the model ground 63

4.7 Typical pore water pressure curves at P4, P5 and P6 during pre-

consolidation of the model ground for the Mixed soil 2 with OCR = 8.0

63

4.8 Grain size distributions of soils 65

4.9 Non-standard dissipation curves of Ariake clay of OCR = 1.0, 4.0 and

8.0 (Hossain 2014)

67

4.10 Non-standard dissipation curves of Mixed soil 1 of OCR = 1.0, 2.0, 4.0

and 8.0

68

xv

4.11 Non-standard dissipation curves of Mixed soil 2 of OCR = 1.0, 2.0, 4.0

and 8.0 (Hossain 2014)

69

4.12

4.13

Non-standard dissipation curves of Mixed soil 3 of OCR = 1.0, 2.0, 4.0

and 8.0

Non-standard dissipation curves of Mixed soil 4 of OCR = 1.0, 2.0, and

8.0

70

71

4.14 Comparison of measured cv with estimated ch of Ariake clay 73

4.15 Comparison of measured cv with estimated ch of Mixed soil 1 74

4.16 Comparison of measured cv with estimated ch of Mixed soil 2 74

4.17

4.18

Comparison of measured cv with estimated ch of Mixed soil 3

Comparison of measured cv with estimated ch of Mixed soil 4

75

75

4.19 Comparison of measured kv with estimated kh of Ariake clay 78

4.20 Comparison of measured kv with estimated kh of Mixed soil 1 78

4.21 Comparison of measured kv with estimated kh of Mixed soil 2 79

4.22

4.23

Comparison of measured kv with estimated kh of Mixed soil 3

Comparison of measured kv with estimated kh of Mixed soil 4

79

80

5.1 Relationship between 0'v

u

and OCR of Ariake clay 83


u

and OCR of Mixed soil 1 83


u

and OCR of Mixed soil 2 84

5.4

5.5

Relationship between 0'v

u

and OCR of Mixed soil 3

Relationship between 0'v

u


84

85

5.6 Permeability of clays obeying the linear variation of logarithmic of

permeability with void ratio (after Hamidon 1994)

86

5.7 Values of model parameter (α) of Ariake clay 88

5.8 Values of model parameter (α) of Mixed soil 1 89

5.9 Values of model parameter (α) of Mixed soil 2 89

5.10

5.11

Values of model parameter (α) of Mixed soil 3

Values of model parameter (α) of Mixed soil 4

90

90

5.12

Comparison of measured kv with estimated kh using both Chai et al.

(2011) and the modified method of Ariake clay

91

xvi

5.13


(2011) and the modified method of Mixed soil 1

92

5.14



93

5.15

5.16

5.17

5.18

5.19





Example of variation of measured kv/kv0 and estimated kh/kh0 ratios with

OCR (a) Ariake clay; (b) Mixed soil 1.

CPT soil behavior type chart (Modification from Robertson 1990)

Piezocone penetration test results at Saga site

94

95

95

97

98

5.20

5.21

Soil strata, measured values of OCR and permeability at Saga site


(2011) and the modified method at Saga site

99

99

5.22 Piezocone penetration test results at Yokohama site 101

5.23 Soil strata, measured values of OCR and permeability at Yokohama site 101

5.24


(2011) and the modified method at Yokohama site

102

5.25 Piezocone penetration test results at Shanghai site 103

5.26 Soil strata and measured values permeability at Shanghai site 103

5.27


(2011) and the modified method at Shanghai site

104

xvii

LIST OF NOTATIONS

A Sleeve friction area

AN Effective area of cone

AT Total cross-sectional area of cone

an Neat area ratio

Bq Pore pressure ratio

bn Constant for calculating sleeve friction

ch Coefficient of consolidation of soil in horizontal direction

cv Coefficient of consolidation of soil in vertical direction

Cc Compression index

Ck Constant in the modified method, and Ck =0.5e0

Cs Swelling index

CRS Constant rate of strain consolidation test

d1 Diameter at the face of the cone

d2 Diameter at the shoulder of the cone

d3 Diameter at the shaft of the cone

Eu Young’s modulus

e0 Void ratio

Fc Measured axial force

fs Sleeve friction

Fr Friction ratio

Fs Measure axial force over the sleeve

ft Total sleeve friction

G Shear modulus and/ or “Gmax”

hs Height of sleeve

IP Plasticity index

Ir Rigidity index, and Ir = G/su

k Constant in Method 2 equation

kh Permeability of soil in horizontal direction corresponding to σv0

kh0 Permeability of soil in horizontal direction corresponding to σvmax

kv Permeability of soil in vertical direction corresponding to σv0

kv0 Permeability of soil in vertical direction corresponding to σvmax

KD Dimensionless of soil permeability

xviii

K0 Coefficient of earth pressure at-rest

LL Liquid limit

M The slope of critical state line, and M =6 sin '

3 sin '

m Constant in Method 1 equation

mCPTu Constant in Saye et al. (2013)’s method

Nkt Cone bearing factor OCR Overconsolidation ratio

OCRm Measured value of OCR

OCRp Predicted value of OCR

pOCR Average value of the predicted OCR

Pc Maximum consolidation pressure

PL Plastic limit

p Mean effective stress

qc Cone resistance

Q Rate of spherical flow

q Deviator stress

qt Corrected tip resistance

QNC Constant in Saye et al. (2013)’s method

Qt Normalized cone resistance

R Radius of the cone

R2 Coefficient of determination

S Constant in Method 1 equation, and S = 1

2sin ′

su Undrained shear strength

T* Modified time factor

t Time measured corresponding the given degree of consolidation

t2 Thickness of the sleeve at shoulder location of the cone

t3 Thickness of the sleeve at shaft location of the cone

t50 Time for 50% degree of consolidation

t50c Corrected time for 50% degree of consolidation

tumax Time for the measured excess pore water pressure to reach its maximum value

T50 time factor at 50% consolidation predicted by the theory of uncoupled

consolidation analysis

xix

u Pore water pressure

u1 Pore water pressure measured on the face of cone

u2 Total pore water pressure measured at cone shoulder

u3 Total pore water pressure measured at cone shaft

us Static pore water pressure or hydrostatic pressure

umax Maximum pore water pressure measured and/ or “umax”

u50 Pore water pressure at 50% degree of consolidation

U Rate of cone penetration on basic concept of Elsworth & Lee’s method

Model parameter

Internal friction angle of soil

e The change of void ratio

u Pore water pressure measured at cone shoulder (-) hydrostatic pressure (= u2 –

us)

umax Maximum of pore pressure minus initial of pore pressure measured (= umax –

ui)

0'v NC

u

The ratio of 0'v

u

corresponding to normally consolidated state

0'v OC

u

The ratio of 0'v

u

corresponding to overconsolidated state

Δv Rate of volume penetration

w Unit weight of water

ρs Specific gravity

p Maximum past consolidation stress

v0 Total vertical (overburden) stress

v0 Effective vertical (overburden) stress

vmax Maximum vertical (overburden) consolidation stress

η The ratio of q/p

κ The slopes of unloading-reloading curves in an e- ln(p) plot

λ The slopes of virgin loading curves in an e- ln(p) plot

Constant in Method 3 and the proposed method, and = 1 – κ/λ

1

CHAPTER ONE

INTRODUCTION

1.1 Background

In geotechnical engineering, piezocone penetration test (uCPT) is widely used as an

economic and efficient site investigation technique (e.g., Campanella and Robertson 1988;

Lunne et al. 1997; Liu et al. 2008). Cone penetration tests have been used for site

investigation since 1932 when P. Barentsen, a Dutch engineer, used the cone to measure tip

resistances with a depth of 4 m from the ground surface (Broms and Flodin 1988). The main

advantages of uCPT are its simplicity, repeatability, and speedity. uCPT provides near

continuous measurements of tip resistance (qt), sleeve friction (fs), and pore water pressure

(u) at the shoulder (standard) of the cone. The cone can be hold at a pre-determined depth to

measure the pore pressure dissipation process, which is called piezocone dissipation test.

From the results of the piezocone penetration and dissipation tests, the soil profile and other

engineering properties, such as undrained shear strength (su) of clayey deposits (e.g.,

Campanela and Robertson et al. 1988; Arulrajah et al. 2005), permeability of soil in

horizontal direction (kh) (e.g., Robertson et al. 1992; Lunne et al. 1997; Sully et al. 1999;

Elsworth and Lee 2005; 2007; Chai et al. 2011), coefficient of consolidation (ch) of soils in

the horizontal direction (e.g., Teh and Houlsby 1991; Arulrajah et al. 2007; Sully et al. 1999;

Chai et al. 2012a) and Overconsolidation ratio (OCR) (Robertson 1990, Mayne and Kemper

1988; Wroth 1984) can be estimated. Overconsolidation ratio (OCR) can be determined from laboratory oedometer test using

undisturbed soil sample. However, to retrieve undisturbed soil sample is costly, and test

results can be influenced by several factors such as sample disturbance, interpretation method

employed for determination the maximum past consolidation pressure (σp), etc. To minimize

these problems, numerous researches have been carried out and existing methods for

estimating OCR from uCPT results are ranging from empirical to theoretical approaches

(Mayne 1991; Trevor and Mayne 2004; Lunne et al. 1997), which required some empirical

parameters.

2

To evaluate the coefficient of consolidation (ch) of the soil from the piezocone

dissipation test results, generally the theoretical results of radial consolidation are used

(Baligh and Levadoux, 1986; Teh and Houlsby, 1991; Robertson et al., 1992; Sully et al,

1999; Chai et al, 2004; Robertson 2010). Most methods for evaluating the coefficient of

consolidation in horizontal direction (ch) from piezocone dissipation test results are based on

the assumption that during dissipation process, the measured pore water pressure reduces

monotonically which is called “standard” dissipation curve. Among these existing methods

for estimating ch from piezocone dissipation test, the most widely used is the one proposed by

Teh and Houlsby (1991). However, in heavily overconsolidated clay deposits or dense sand

deposits, when the dissipation starts, there is an increase of measured pore water pressure

initially, and then dissipated with time to hydrostatic value (Lunne et al. 1986; Battaglio et al.

1986; Sully et al. 1999; Burns and Mayne 1998) which is called “non-standard” dissipation

curve. The most widely accepted method for “non-standard” dissipation curve is proposed by

Chai et al. (2012a).

Elsworth and Lee (2005; 2007) proposed a method based on basic assumption is that

during the piezocone penetration, a “dynamic steady” spherical flow of pore-water will form

around the tip of the cone and the diameter of the spherical cavity is assumed to be the same

as the diameter of the cone. Then applying Darcy’s law to an assumed spherical flow during

the penetration of the cone, the permeability (kh) in horizontal direction of soil can be

estimated. However, this method is applicable only for sands and it is not applicable for

clayey soil deposits. Chai et al. (2011) modified Elsworth and Lee’s method and extend the

range to be applicable for almost all soil types in normally or lightly overconsolidated states

(OCR < 2.0). While, there are many clayey soil deposits, with OCR ≥ 2.0 and even for 1.0 <

OCR ≤ 2.0, what is the effect of OCR on estimated value of kh is still not clear.

1.2 Objectives and Scopes

For soil investigations, borehole works are very costly and it is very difficult to obtain

high quality undisturbed samples. These problems can be minimized if the design parameters

can be estimated from the results of in-situ tests, such as uCPT tests. This study is focused on

estimating OCR and consolidation properties of soil, e.g. coefficient of consolidation (ch) and

permeability (kh) in the horizontal direction from piezocone test results. The main objectives

of this study as the followings:

3

To establish a reliable method for estimating OCR from uCPT results.

To establish reliable methods for determining the coefficient of consolidation (ch) and

permeability (kh) in the horizontal direction from laboratory model test results of

piezocone tests. The estimated ch and kh values from laboratory model test are

compared with that the values from laboratory oedometer test results.

To compare and confirm the predictions with the laboratory model test results and

field cases.

1.3 Organization of the dissertation

This dissertation is divided into six chapters. Fig 1.1 shows the flow chart of this

dissertation. First chapter, Introduction, gives background, objectives and the scope of the

research.

Chapter 2 presents a literature review regarding to various existing methods that have

been used to determine the overconsolidation ratio (OCR), coefficient of consolidation (ch)

and permeability (kh) in horizontal direction from piezocone test results, as well as their short

comes.

Chapter 3 presents the proposed method for predicting the overconsolidation ratio (OCR) and its validation. Furthermore for two existing methods, modifications have been made so

that they can be applied to underconsolidated deposits.

Chapter 4 describes the laboratory set-up of piezocone penetration and dissipation test,

the soils used for laboratory model tests, cases tested and the test results. The comparison of

the results from the laboratory model test and the estimated consolidation properties by the

existing methods are also presented in this chapter.

Chapter 5 presents a proposed method for estimating permeability (kh) from piezocone

test results for overconsolidated soils. The comparison of laboratory measured and estimated

results with the proposed method are also presents in this chapter also. Moreover, validations

of the proposed method by using 3 field cases are discussed.

Finally, the conclusions drawn from this study and recommendations for future works

are given in Chapter 6.

4

Fig. 1.1 Flow chart of this dissertation

METHODS FOR ESTIMATING OCR AND CONSOLIDATION

PROPERTIES OF SOIL FROM THE RESULTS OF PIEZOCONE

TESTS

CHAPTER ONE

Introduction

CHAPTER TWO

Literature Review

CHAPTER THREE

Method for Estimating OCR

CHAPTER FOUR

Evaluating the Methods for Estimating Consolidation

Properties

CHAPTER FIVE

Modified Method for Estimating Permeability

CHAPTER SIX

Summary, Conclusions and Recommendations

5

CHAPTER TWO

LITERATURE REVIEW

2.1 Introduction

In this chapter, the widely exisiting methods for estimating the value of OCR, coefficient

of consolidation (ch) and permeability (kh) from uCPT and piezocone dissipation test results

are reviewed, and their short comes are discussed.

Fig. 2.1 Location of pore pressure elements

2.2 Measurements from Piezocone Test

The standard cone penetration provides nearly continuous measurements of tip resistance

(qt), sleeve friction (fs) and pore water pressure (u2) at the shoulder of the cone (standard

cone) or face, or shaft of the cone (Fig. 2.1). As an example of piezocone penetration test

results at a location in Saga, Japan are shown in Fig.2.2.

6

Fig. 2.2 Piezocone penetration test results at a location in Saga, Japan

(1) Tip resistance (qt)

The measured axial force (Fc) divided by the cross-sectional area (AT) gives the

measured tip resistance, qc = Fc/AT. While, this stress must be corrected for pore water

pressures acting on the slot behind the shoulder of the cone (Fig. 2.3). Therefore, the true

total tip resistance from the soil is calculated by the following equation (Baligh et al. 1981;

Campanella et al. 1982):

21 .

t c nq q a u (2.1)

0

2

4

6

8

10

12

14

16

0 500 1000 1500 2000

qt (kN/m2)

0

2

4

6

8

10

12

14

16

0 100 200 300 400 500 600

u2 (kN/m2)

Hydrostatic pressure

fs (kN/m2)

Depth

(m

)

0

2

4

6

8

10

12

14

16

0 25 50 75

7

where qt = corrected total tip resistance, u2 = measured pore pressure at the shoulder of the

cone, an = net area ratio = AN/AT = 0.60 to 0.90, where AT is total cross-sectional area of the

cone and AN is the effective area of the cone (Fig. 2.3).

Fig. 2.3 Total and effective stress area of cone

(2) Measured pore water pressure (u)

The pore water pressures (u) can be measured at different positions on the piezocone.

The filter element for measuring u can be at the face (u1), the shoulder (u2), or shaft (u3) of

the cone (Fig. 2.1). The most widely used cone is u2 type and it is called standard cone.

2

24

NA d

2

14

TA d

Filter element

8

(3) Sleeve friction (fs)

The measured axial force over the sleeve (Fs) is divided by the sleeve area (A) to obtain

the sleeve friction, fs = Fs/A. However, this too requires a correction two pore water pressure

readings are needed (u2 and u3), taken at both the top and bottom ends of the sleeve (Fig. 2.3).

Hence total sleeve friction (ft) can be described by the following equation (Jamiolkowski et

al. 1985):

2t s nf f b u

(2.2)

32 2 3 3 1

2

/n s

ub d t d t d h

u

(2.3)

where d1, d2, d3 are the diameter at different location of the cone; t2, t3 are the thickness of the

sleeve at different location of the cone (Fig. 2.3); hs is the height of sleeve. For most

practically used cone, the value of bn is small and bn = 0.014 is suggested for the Swedish

CPTu standard (e.g., Lunne et al. 1997).

(4) Normalized tip resistance (Qt), sleeve friction (Fr) and pore pressure ratio (Bq)

The result from CPT data can be presented in terms of normalized cone resistance (Qt),

friction ratio (Fr), and the pore pressure ratio (Bq) (Wroth 1984). The expressions for Qt, Fr ,

and Bq are as follows:

0

0

-

'

t vt

v

qQ

(2.4)

0

-

sr

t v

fF

q (2.5)

0

-q

t v

uB

q

(2.6)

where v0 and v0 are respectively the total and effective overburden pressure, v0 = v0 – us,

and us is the equilibrium hydrostatic pore water pressure. u = u2 – us, u2 is the pore water

pressure measured at shoulder of the cone.

9

(5) Dissipation curves

When the peizocone penetrates into the ground and halted at the predetermined depth,

the penetration induced excess pore pressure will subsequently dissipate. The recorded pore

pressure variation during dissipation process is called “dissipation curve”. Generally, there

are two types of dissipation curve. First type shows monotonic decreasing of measured pore

water pressure (u2) with elapsed time and it is called “standard” curve as shown in Fig. 2.4.

Normally, this type of the curves occurs in normally consolidated clay deposits or loose sand

deposits (Burns and Mayne 1998).

Another type is that when dissipation test started, u2 first increasing from an initial value

to a maximum and then decreasing to a hydrostatic value, which is referred as “non-standard”

curve as shown in Fig. 2.5, this type of dissipation often occurs in overconsolidated clay

deposit or dense sand deposit.

Fig. 2.4 Standard dissipation curve

10

Fig. 2.5 Non-standard dissipation curve

2.3 Methods for estimating overconsolidation ratio (OCR)

In geotechnical engineering, generally a parameter called overconsolidation ratio (OCR)

is used to indicate the stress history of a soil deposit, which can be determined by conducting

laboratory oedometer consolidation test using undisturbed soil sample. However, retrieving

undisturbed soil sample is costly, and test results can be influenced by several factors such as

sample disturbance, interpretation method employed for determination of the maximum past

consolidation pressure (σp), etc. Therefore, many empirical methods for determining the

value of OCR have been proposed using the results of piezocone sounding (Mayne 1991;

Trevor and Mayne 2004; Lunne et al. 1997).

11


Piezocone sounding results are widely used for estimating undrained shear strength (su)

of clayey soils through empirical correlations (Baligh et al. 1980). The equation is as follows:

0t v

u

kt

qs

N

(2.7)

where qt is corrected tip resistance and Nkt is a cone bearing factor. Table 2.1 lists some

proposed values (ranges) of Nkt.

Table 2.1 Summary of the parameter Nkt

Reference Nkt Location/Comment

Aas et al. (1986) 8-16 For clays (3% < Ip < 50%) Nkt increases with Ip

Rad and Lunne (1988) 8-29 Nkt varies with OCR

Powell and Quarterman (1988) 10-20

Karlsrud (1996) 6-15 Nkt decreases with Bq

Rashwan et al. (2005) 11 Ariake clay, Japan

Hong et al. (2010) 7-20 Busan clay, Korea 25% < Ip < 40%

Almeida et al. (2010) 4-16 High plasticity, soft clay, 42% < Ip < 400%

Larsson (2015) 16.3 Swedish clay, Sweden

Ladd and Foott (1974) developed a method to express the normalized behaviour of soils,

which is named as SHANSEP method (stress history and normalized soil engineering

properties). SHANSEP testing was developed at MIT and was a widely used method for

evaluating the undrained shear strength of soil from the relationship between su/σv0 and OCR

which can be expressed by following empirical equation:

0'

u

v

msS OCR

(2.8)

where S and m are constants. Ladd and DeGroot (2003) indicated that for most soils, m is

approximately 0.8 and 0.22 for S. For organic soils, not including peats, they recommend a S

value of 0.25. Using simple shear (DSS) test results under normal consolidation condition,

Wroth (1984) proposed an equation estimating S as follows:

12

1

sin '2

S (2.9)

where is internal effective friction angle of a soil. By combining Eqs. (2.7) - (2.8), an

expression for OCR can be derived as follow (e.g. Mayne 1986):

1/

0

0

1

'

m

t v

vkt

qOCR

N S

(2.10)


Another empirical method that was extensively used for evaluating OCR from uCPT

results using normalized tip resistance (Qt) in Eq. (2.4). The relationship between OCR and

Qt can be expressed as (Mayne and Kemper 1988):

0

0't v

v

qOCR k

(2.11)

where k is a constant. Table 2.2 summarizes some proposed values of k.

Table 2.2 Summary of the parameter k

Reference k Location/Comment

Lefebvre and Poulin (1979) 0.25-0.4 Norway & UK sites

Mayne and Holtz (1988) 0.4 World Data

Larsson and Mulabdic

(1991)

0.29 Scandinavian Soils

Mayne (1991) 0.33 Cavity Expansion & Critical State Soil

Mechanics Analysis

Leroueil et al. (1995) 0.28 Eastern Canada Clays

Chen and Mayne (1996) 0.305 205 Clay sites

Lunne et al. (1997) 0.2-0.5

Mayne (2001) 0.65(Ip)-0.23 Ip is plasticity index.

Mesri (2001) 0.25-0.32 su/p=constant interpretation

Abdelrahman et al. (2005) 0.2-0.5 Port Said Site, Egypt

Pant (2007) 0.14 Louisiana Soils - 7 Sites

13

Based on SHANSEP approach, Saye et al. (2013) proposed a two-parameter method to

estimate the value of OCR from Qt as follows:

1/ CPTum

t

NC

QOCR

Q

(2.12)

where QNC and mCPTu are two empirical constants. It was suggested that QNC can be

estimated from plasticity index (Ip) and mCPTu from liquid limit (LL) as follows:

For 9, 23.18 2.36P NC PI Q I (2.13)

For 65 9, 3.98 0.031P NC PI Q I (2.14)

For 14, 0.021 0.48P CPTu PI m I (2.15)

For 14, 0.80P CPTuI m (2.16)

For LL 32, 5.9 LL 25 45.6NCQ (2.17)

For 100 LL 32, 3.69 0.019 LL 25NCQ (2.18)

For LL 35, 0.013 LL 25 0.65CPTum (2.19)

For LL 35, 0.80CPTum (2.20)

Since Eq. (2.11) only needs one empirical parameter but Eq. (2.12) needs two empirical

parameters (QNC and mCPTu), it is considered that Eq. (2.11) is more practical and it is used in

this study.

2.3.3 Approach based on cavity expansion and critical state soil mechanics theories

(Method 3)

Mayne (1991) proposed a method for estimating OCR by combining the theories of

cavity expansion and critical state soil mechanics. OCR can be computed by the following

equation:

14

1/

2

0

12

1.95 1 't

v

q uOCR

M

(2.21)

where M is the slope of critical state line in p-q plot (p is mean effective stress and q is

deviator stress), M =6 sin '

3 sin '

), and = 1 – κ/λ (λ and κ are slopes of virgin loading and

unloading-reloading curves in void ratio, e versus ln(p) plot). The range of κ/λ is 1/5 to 1/10,

and therefore, = 0.8 to 0.9.

Trevor and Mayne (2004) collected some field data and modified Eq. (2.21) with a

correction factor as follows:

1/

2

0

12(0.029 0.409 )

1.95 1 't

v

q uOCR M

M

(2.22)

2.3.4 Limitation of the methods

Soil parameters and/or empirical parameters needed in each method are summarized in

Table 2.3.

Table 2.3 Summary of parameters needed in each method

Method Soil properties Empirical

parameters

1 - Nkt, S, m

2 - k

3

As indicated in Table 2.3, except Method 3, all the existing methods need some empirical

parameters. There are disadvantage and advantage of involving some empirical parameters.

The disadvantage is that the value of some empirical parameters need to be back fitted using

measured values or determined based on local experience; and the advantage is the properties

of local soils can be indirectly considered into the empirical parameter. There is a need to

15

identify which method can result in consistently more reliable values of OCR using field

measured uCPT sounding results and laboratory directly measured values of OCR.

2.4 Methods for estimating coefficient of consolidation (ch)

2.4.1 Methods for standard dissipation curves

The methods of estimating the value of ch from the standard dissipation curves have been

proposed by Torstensson (1977), Baligh and Levadoux (1986), and Teh and Houlsby (1991).

Torstensson (1977) suggested that the pore pressures in the soil caused by steady cone

penetration can be estimated by the solutions corresponding to cylindrical or spherical cavity

expansion theories. Torstenson proposed to estimate the coefficient of consolidation at 50%

of consolidation by the following expression:

250

50

h

Tc R

t (2. 23)

where T50 = time factor at 50% consolidation predicted by the theory of uncoupled

consolidation analysis (finite different method) as a function of /u u

E s and the type of cavity

(cylindrical or spherical); Eu = Young’s modulus and su = undrained shear strength of the clay

respectively; t50 = measured time to achieve 50% consolidation; and R = radius of the cone.

Baligh and Levadoux’s (1986) solution was developed based on linear consolidation

analysis and initial pore pressure distributions calculated by the strain path method for

undrained penetration with soil properties of Boston blue clay. At a given degree of

consolidation, the predicted horizontal coefficient of consolidation is obtained as:

2

h

T Rc

t

(2. 24)

where T* = time factor (at 50% degree of consolidation, T* = 5.6), t = measured time

corresponding to the given degree of consolidation.

The most widely used method is the one proposed by Teh and Houlsby (1991). Based on

the results of the initial pore pressure distribution proposed that ch can be calculated as well

as dissipation process depend on the value of rigidity index of soil (Ir = G/Su).

16

* 2

50

r

h

T R Ic

t (2.25)

where T* = modified time factor corresponding to 50% degree of consolidation. For pore

pressure filter located at the shoulder of the cone, T* = 0.245, where G is the shear modulus,

and su is undrained shear strength.

2.4.2 Method for non-standard dissipation curves

As for the non-standard dissipation curve, only few methods are available. Chai et al.

(2012a) conducted uncoupled dissipation analysis with different initial u distributions using

finite different method, and proposed an empirical equation for correcting t50. The correction

equation is as follows;

50

50 0.67 0.3

max

50

1 18.5200

c

u r

tt

t I

t

(2.26)

where t50c is the corrected time for 50% dissipations of the measured maximum excess pore

water pressure, tumax is the time for measured excess pore pressure to reach its maximum

value. Then substitute t50c into Eq. (2.25) in the place of t50 to calculate the value of ch.

2.4.3 Discussions

For a standard piezocone with a shoulder filter element (u2), the dissipation tests show

two types of dissipation curves. One is monotonically decreasing pore water pressure, which

is often observed in normally consolidated deposit and designated as the “standard”

dissipation curve. However, in overconsolidated cohesive soils, a dissipation curve shows an

initial increase in pore water pressure and then decrease to hydrosatic pressure, which is

called “non-standard” dissipation curve. The most widely used method for estimating the

coefficient of consolidation in horizontal direction (ch) for standard dissipation curve is

proposed by Teh and Houlsby (1991). As for non-standard dissipation curve, Chai et al.

(2012a) proposed an empirical equation for correcting t50 as t50c which substitute the t50c value

in the place of t50 into the equation proposed by Teh and Houlsby (1991).

17

2.5 Methods for estimating permeability (kh)

There are several methods for estimating kh values from piezocone sounding records.

Most of the proposed methods are empirical, and some of them only provide a likely range of

kh value (Robertson et al. 1992). Elsworth and Lee (2005; 2007) proposed a semi-theoretical

equation for estimating kh value, but the method is only applicable to sandy soils. Chai et al.

(2011) modified Elsworth and Lee’s (2007) method, and the modified method is applicable to

most soil types.

2.5.1 Existing methods to estimate permeability

(a) Elsworth and Lee’s method

Elsworth (1991) proposed analogy exists between cone penetration and the behavior of a

point normal dislocation moving within a saturated porous elastic medium and leaving a

remnant void. The penetrometer displaces a volume, and with the advancing of the cone

which represented by a point normal dislocation of equivalent volume. The point dislocation

within a saturated porous elastic medium couples displacements with the generation of

undrained pore pressure within the surrounding area and also allows forming a steady flow

around the void, where rate of the flow is controlled by permeability.

Elsworth and Lee (2005) proposed a method based on the dislocation model (Elsworth

1991) with finite radius penetrometer approach. The basic assumption is that during the

piezocone penetration, a “dynamic steady” spherical flow of pore-water will form around the

tip of the cone and the diameter of the spherical cavity is assumed to be the same as the

diameter of the cone. The rate of spherical flow of pore water through the periphery of the

cavity (Q) is assumed to be equal to the rate of volume penetration ( v) of the cone (the

continuity assumption).

Applying Darcy’s law to the assumed spherical flow, and assuming that zero excess pore

water pressure exists at an infinite distance from the cone, an explicit equation has been

derived to calculate the soil permeability. The basic concept of this method is illustrated in

Fig. 2.6. The equation proposed by Elsworth & Lee (2005) for estimating the value of kh is:

0

0

4 '

4 '

D w h vh D

v w

K U R kk or K

R U

(2.27)

18

where kh is the permeability of soil in horizontal direction, u2 is the absolute pore water

pressure measured by the piezocone, us is the initial hydrostatic pore water pressure, γw is the

unit weight of water, and KD is a dimensionless soil permeability index, which can also be

expressed as:

1

D

q t

KB Q

(2.28)

Elsworth and Lee (2005) described that Eq. (2.27) can only be used for the case of

partially drained conditions in the soil ahead of and surrounding the cone penetrometer. This

means that the value of k of the soil must be low enough for excess pore water pressure to be

generated, and at the same time it must also be high enough to allow formation of “dynamic

steady” pore water flow around the cone.

Elsworth and Lee (2007) collected some of the available data from field piezocone

soundings and measured soil permeability values (k) for the same soils, and suggested that Eq.

(2.27) should be used only for BqQt < 1.2, that is, for soils with k > 10-5 m/s, which

corresponds to fine sand.

Fig. 2.6 Basic concept of Elsworth and Lee’s (2005) method

19

Fig. 2.7 Relationship between measured non-dimensional hydraulic conductivity KD and BqQt

from piezocone test (data from Elsworth and Lee 2007)

As a consequence, Elsworth and Lee (2007) modified the KD – (BqQt) relation and

suggested a new equation (Fig. 2.7):

1.6

0.62D

q t

KB Q

(2.29)

(b) Chai et al. (2011)’s method

Chai et al. (2011) modified Elsworth and Lee’s (2007) method and proposed semi-

theoretical equations for calculating kh values from uCPT sounding results. The bi-linear KD -

(BqQt) relationship proposed is as follows (Fig. 2.8):

For BqQt ≤ 0.45 1

D

q t

KB Q

(2.30)

20

and for BqQt > 0.45 4.91

0.044

( )D

q t

KB Q

(2.31)

Fig. 2.8 Bi-linear relationship between measured non-dimensional hydraulic conductivity KD

and BqQt from piezocone test (data from Chai et al. 2011)

Further, as shown in Fig. 2.9, during the piezocone penetration, water cannot flow into

the cone (in the direction shown by the arrow A). Therefore it is more appropriate to assume

that the surface area for water flow is only a half sphere, in that case Eq. (2.27) can be

modified as:

0

2 '

D wh

v

K U Rk

(2.32)

Chai et al. (2011)’s method extended the range to be applicable for almost all soil types

in normally or lightly overconsolidated state.

21

Fig. 2.9 Half-spherical flow

2.5.2 Discussions

Elsworth and Lee (2005; 2007) proposed a method for estimating permeability (kh) of

soil in horizontal direction from piezocone sounding results by applying the Darcy’s law to

an assumed spherical flow during the penetration of the cone. This method is only applicable

for sand deposits. Chai et al. (2011) modified Elsworth and Lee (2005; 2007)’s method and it

is applicable for almost all soil types in normally or lightly overconsolidated states. However,

in heavy overconsolidated state, the estimated value of kh from uCPT results is still not clear.

2R

22

2.6 Summary and discussions

Piezocone sounding (uCPT) and dissipation tests are efficient and economic site

investigation methods. Currently, there are several existing methods for estimating

overconsolidation ratio (OCR) from the results of uCPT. Most of them are based on empirical

approach which requires some empirical parameters. There is a need to identify which

method can result in most consistent and reliable value of OCR when compare with the

directly measured values.

Piezocone dissipation tests show two types of dissipation curves. The methods for

estimating the coefficient of consolidation in horizontal direction (ch) from dissipation test are

reviewed and the methods for estimating the values of permeability (kh) from uCPT results

are also reviewed. The applicability of existing methods for estimating kh is range from the

soils in normally to lightly overconsolidated states. However, in natural soil deposits, there

are many soils in heavy overconsolidated state, which is still not clear. To investigate

regarding this matter, a series of laboratory model tests of uCPT and dissipation process were

conducted with different soil samples and OCR values. Consequently, the applicability of

existing methods for estimating ch and kh from laboratory model test results of uCPT and

dissipation process is need to be evaluated.

23

CHAPTER THREE

METHODS FOR ESTIMATING OCR

3.1 Introduction

Three (3) existing methods for estimating OCR from piezocone penetration test (uCPT)

results were reviewed in Chapter 2. In this chapter, twelve (12) field case histories have been

collected from literatures, and then the applicability of the existing methods are evaluated and

discussed. The values of OCR estimated from uCPT results using different method are

compared with measured data from laboratory oedometer tests. Then new method based on

modified Cam Clay theory (Roscoe and Burland 1968) is proposed. Moreover, existing

methods are modified to be used for underconsolidated deposits.

3.2 Field case histories

In order to evaluate the applicability of the existing methods, data from 12 sites from

different countries around the world as indicated in Fig. 3.1 have been collected. For ease to

present the results, these sites have been divided into 3 Groups. Group 1 contains of 2 sites in

Japan, Saga site and Yokohama site. Group 2 has 1 site at Lianyungang, China, 2 sites at

Busan, Korea and 1 site at Port Said, Egypt. Group 3 contains of 5 sites in Sweden and 1 site

in Finland.

If not specified, the piezocones used had an apex angle of 60° with a tip area of 1000

mm2, and the filter for pore water pressure measurement was at the shoulder of the cone (u2).

The penetration rate was 20 mm/s.

24

Fig. 3.1 Location of all uCPT investigated sites

3.2.1 Sites in Japan (Group 1)

3.2.1.1 Saga site

Along the coast of Ariake Sea (a semi-enclosed inland bay), Kyushu, Japan, deposited

clayey soil layers, called Ariake clay with a thickness of 10 to 30 m. In this area, a highway

project is currently under construction. uCPT tests were conducted for the site investigation

along the route of the project adjacent to boreholes (Ariake Sea Coastal Road Development

Office (ASCRDO), Saga Prefecture, 2008). uCPT test results at ten (10) locations, which

have detailed information on groundwater level and laboratory measured values of OCR were

chosen to apply the method for evaluating OCR. Figs. 3.2 to 3.11 show the soil strata,

piezocone sounding results and measured values of OCR at ten (10) locations of Saga site.

25

Fig. 3.2 Soil strata, piezocone sounding results and measured values of OCR at a location

H15-308 of Saga site



0 1000 2000

qt (kN/m2)

0 300 600

Dep

th (

m)

u2 (kN/m2)

0

2

4

6

8

10

12

14

16

Silty Clay

Clay

Silty Clay

Sandy Silt

Sand

Hydrostatic Pressure

0 1 2 3

OCR

0 5000 10000

qt (kN/m2)

0 100 200 300 400

Dep

th (

m)

u2 (kN/m2) OCR


0

2

4

6

8

10

12

14

16

18

Silty Clay

Clay

Silty Clay

Silty Sand

Sand

0 1 2 3

26





0 1000 2000 3000 4000

qt (kN/m2)

0 200 400 600 800 1000

Dep

th (

m)

u2 (kN/m2)


0

2

4

6

8

10

12

14

16

18

Silty Clay

Clay

Silty Clay

Sand

Clayey Silt

0 1 2 3 4

OCR

0 1000 2000 3000

qt (kN/m2)

0 100 200 300 400 500

Dep

th (

m)

u2 (kN/m2) OCR


0

2

4

6

8

10

12

14

16

18

Silty Clay

Clay

Sand

0 1 2 3 4

27





0 1000 2000 3000

qt (kN/m2)

0 200 400 600 800 1000

Dep

th (

m)

u2 (kN/m2)


0

2

4

6

8

10

12

14

16

18

20

22

24

SandSilty Clay

Clay

Sand

0 1 2 3 4

OCR

0 1000 2000 3000 4000

Dep

th (

m)

qt (kN/m2)

0 200 400 600 800

u2 (kN/m2)


0

2

4

6

8

10

12

14

16

18

20

Sand

Clay

Silty Sand

Clay

Sand

0 1 2 3 4

OCR

28





0 200 400 600 800 1000

Dep

th (

m)

qt (kN/m2) u2 (kN/m

2)


0 1000 2000 3000 40000

2

4

6

8

10

12

14

16

18

20

22

24

26

28

Embankment

Clay

Silty Sand

0 1 2 3

OCR

0 1000 2000 3000 0 400 800 1200

Dep

th (

m)

qt (kN/m2) u2 (kn/m

2)


0

2

4

6

8

10

12

14

16

18

20

Sand

Clay

Sand

OCR0 1 2 3

29





0 1000 2000 3000

qt (kN/m2)

0 100 200 300 400 500

Dep

th (

m)

u2 (kN/m2)


0

2

4

6

8

10

12

14

Sand

Clay

Sand

0 1 2 3

OCR

0 1000 2000 3000

qt (kN/m2) u2 (kN/m

2)

0 100 200 300 400

Dep

th (

m)


0

2

4

6

8

10

12

14

Sand

Clay

Sand

0 1 2 3

OCR

30

3.2.1.2 Yokohama site

The Japanese Geotechnical Society (JGS) organized an activity of simultaneously

conducting piezocone penetration test (uCPT) by several companies at a site in Yokohama,

Japan in 2007 (Suemasa et al. 2009). The data used in this study is from one of the

organizations (organization C). From the ground surface, the soil deposit consists of a 4 m

thick sandy clay, underlain by a fine sand layer to a depth of about 10 m and followed by a

sandy clay layer about 10 m thick. The soil strata, the results of uCPT and measured values of

OCR are given in Fig. 3.12.

Fig. 3.12 Soil strata, piezocone sounding results and measured values of OCR of Yokohama

site

0 6000 12000 18000

qt (kN/m2) u2 (kN/m

2)

Depth

(m

)D

epth

(m

)

Dep

th (

m)

OCR0 250 500 750 1000


0

2

4

6

8

10

12

14

16

18

20

22

Sandy clay

Fine sand

Sandy clay

0 1 2 3 4 5

31

3.2.2 Sites in China, Korea and Egypt (Group 2)

3.2.2.1 Lianyungang site, China

Liu et al. (2008) reported the results of a site investigation in Lianyungang, China. The

soil strata, the results of uCPT and measured values of OCR are given in Fig. 3.13. From the

ground surface, the typical soil strata consist of a 2 m thick of weathered clayey crust,

followed by a marine clay layer about 10 m thick and underlain by a silty clay layer. The

groundwater level was around 1 m depth from the ground surface.

Fig. 3.13 Soil strata, piezocone sounding results and measured values of OCR of

Lianyungang site

0

2

4

6

8

10

12

Weathered Clayey Crust

Marine Clay

Dep

th (

m)

0 250 500 750 1000

qt (kN/m2) u2 (kN/m

2) OCR

0 100 200 300 400


0 1 2 3 4 5

32

3.2.2.2 Two sites in Busan, Korea

Singh and Chung (2015) reported the results of two site investigations (D2 and DIS-5) in

the floodplain, central-west of the Nakdong deltaic plain near Busan. The typical soil profile

consists of a silty sand of 4 m thick from the ground surface, followed by a thick, soft and

compressible silty clay layer up to 32 m depth and underlain by sandy gravel and sand layers.

The groundwater level was around 0.5 m at D2 site and 1.0 m at DIS-5 site from the ground

surface. The soil strata, the results of uCPT and measured OCR at DIS-5 and D2 sites are

given in Fig. 3.14 and 3.15, respectively. At these sites a larger cone with a tip area of 1500

mm2 was used.

Fig. 3.14 Soil strata, piezocone sounding results and measured values of OCR of DIS-5

site, Busan

0

5

10

15

20

25

30

Silty Sand

Silty Clay

Dep

th (

m)

0 400 800 1200

qt (kN/m2) u2 (kN/m

2) OCR

0 200 400 600 800


0 1 2

33

Fig. 3.15 Soil strata, piezocone sounding results and measured values of OCR of D2 site,

Busan

3.2.2.3 Port Said site, Egypt

Salem and El-Sherbiny (2013) reported the results of a site investigation of a thick

deposit of underconsolidated clay deposit located in eastside of Port Said, Egypt. The soil

strata, the results of uCPT and measured values of OCR are given in Fig. 3.16. The

stratigraphy consists of a silty fine sand dredged from nearby canal with a thickness of 5 m,

followed by dredged very soft to soft silty clay with a thickness of 5 m. Below it is a medium

dense silty fine sand with a thickness of 2.5 m, followed by alternating thin layers of silty

clay, silt, and silty fine sand with a thickness of 3.5 m, and underlain by a very soft to

medium stiff silty clay layer of about 30 m thick. The groundwater level was at a depth of 6.7

m from the ground surface.

0

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

32

Silty Sand

Silty Clay

Dep

th (

m)

0 400 800 1200

qt (kN/m2) u2 (kN/m

2) OCR

0 200 400 600 800 1000


0 1 2 3

34

Fig. 3.16 Soil strata, piezocone sounding results and measured values of OCR of Port

Said site, Egypt

3.2.3 Sites in Finland and Sweden (Group 3)

3.2.3.1 Perniö site, Finland

Lehtonen et al. (2015) reported a full-scale embankment failure test at one section of

non-operational railway track near the town of Perniö, Finland. Extensive soil investigations

including uCPT were performed to characterize the foundation conditions at the site. The soil

strata at the site consists of an old fill made of sand and gravel with a thickness about 1.5 m,

followed by 1 m thick of weathered clay crust layer, underlain by 3.5-4.5 m thick of soft clay

layer and another 1.5 m thick of sandy silt layer. The ground water level was around 1.3 m

from the ground surface. The soil strata, uCPT results and measured values of OCR are

shown in Fig. 3.17.

0

5

10

15

20

25

30

35

40

Silty Fine Sand

Very Soft to Medium Stiff Silty Clay

Dep

th (

m)

Soft Silty Clay

Medium Dense Fine Sand

Silty Clay/ Silt/ Silty Fine Sand

0 500 1000 1500

qt (kN/m2) u2 (kN/m

2) OCR

0 250 500 750 1000


0 0.5 1 1.5

35

Fig. 3.17 Soil strata, piezocone sounding results and measured values of OCR of Perniö

site, Finland

3.2.3.2 Five sites in Sweden

Westerberg et al. (2015) reported the results of site investigations including uCPT at five

sites along the north-eastern coast of Sweden (Gammelgården, Hjoggböle, Sunderbyn, Umeå

bangård and Västerslätt sites). Although detailed soil properties are not reported, at the sites

soil were classified as organic clays and organic silts. The properties of the soils at each site

varied but their geological histories are similar. The measured values of qt and OCR at five

sites are shown in Figs. 3.18 to 3.22.

0

2

4

6

8

Sand and Gravel filled

Weathered Clay Crust

Soft Clay

Silty Clay

qt (MN/m2) OCR

Dep

th (

m)

0 0.5 1 0 1 2 3

36

Fig. 3.18 Variation of uCPT qt and OCR with depth at Gammelgården site, Sweden

Fig. 3.19 Variation of uCPT qt and OCR with depth at Hjoggböle site, Sweden

0

2

4

6

8

10

12

0 200 400 600 800 0 1 2 3

Dep

th (

m)

qt (kN/m2) OCR

0

2

4

6

8

10

12

0 200 400 600 800 0 2 4 6 8

Dep

th (

m)

qt (kN/m2) OCR

37

Fig. 3.20 Variation of uCPT qt and OCR with depth at Sunderbyn site, Sweden

Fig. 3.21 Variation of uCPT qt and OCR with depth at Umeå bangård site, Sweden

0

2

4

6

8

10

12

0 200 400 600 800 0 1 2 3

Dep

th (

m)

qt (kN/m2) OCR

0

2

4

6

8

10

12

0 200 400 600 800 0 1 2 3 4 5

Dep

th (

m)

qt (kN/m2) OCR

38

Fig. 3.22 Variation of uCPT qt and OCR with depth at Västerslätt site, Sweden

3.3 Evaluating the applicability of the existing methods

In this section, from twelve (12) case histories mentioned in the previous section, the

values of OCR estimated from uCPT results using different methods are compared with the

measured data from laboratory oedometer tests.

3.3.1 Group 1

Undrained shear strength (su) approach (Method 1)

Chai et al. (2013) reported the results of consolidated undrained triaxial compression tests

on undisturbed Ariake clay samples and from the results of effective stress path, the internal

friction angle of Ariake clay was around = 39°- 40° (assuming cohesion c = 0). Using =

40° for both Saga and Yokohama sites, a value of S in Eq. (2.8) can be evaluated as 0.32 (Eq.

(2.9)), and m = 0.9 was assumed (for Arake clay, κ/λ ≈ 0.1; then m ≈ = 0.9). For Ariake

0

2

4

6

8

10

12

0 200 400 600 800 0 1 2 3 4 5

Dep

th (

m)

qt (kN/m2) OCR

39

clay deposit Nkt in Eq. (2.10) has been reported as 11 (Rashwan et al. 2005), the same value

also applied for Yokohama site. Comparisons of the predicted and the measured values of

OCR for both Saga and Yokohama sites are given in Fig. 3.23. Among the results, there are 3

points at Saga site, where the evaluated values of OCR by Method 1 are less than 1.

Coefficient of determination (R2) is used to quantitatively evaluate the scatter of the

predicted values from 1:1 line in Fig. 3.23.

ipp

imp

OCROCR

OCROCR

R2

2

2 1 (3.1)

where OCRp is predicted value of OCR, OCRm is the measured value of OCR, and pOCR is

the average value of the predicted OCR. For the data in Fig. 3.23, the value of R2 is only

0.039. The reasons for the lower value of R2 are: (1) scatter of the data points and (2) the most

data are concentrated in OCR range of 1 to 2, which tends to result in smaller value of R2.

Fig. 3.23 Comparison of the measured and the predicted values of OCR using the


0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

OC

R P

red

icte

d

OCR Measured

Saga

Yokohama

1:1

R2 = 0.039

40

Normalized tip resistance (Qt) approach (Method 2)

For Saga and Yokohama case, value of k in Eq. (2.11) was back evaluated as 0.30. Fig.

3.24 shows the comparison of measured and predicted values of OCR using the Method 2. In

this case, there are 4 points where the predicted values of OCR are less than 1 at Saga site.

The value of R2 is only 0.050 for this method.



Cavity expansion and critical state soil mechanics theories’ approach (Method 3)

For the data collected in this study, it has been found that the original method proposed

by Mayne (1991) has better performance than the modified one by Trevor and Mayne (2004).

Therefore for Method 3, OCR values were evaluated by Eq. (2.21). The value of = 40°,

and = 0.9 was applied. Fig. 3.25 shows the comparison of the values of OCR. Using the

0

1

2

3

4

5

6

0 1 2 3 4 5 6

OC

R P

red

icte

d

OCR Measured

Saga

Yokohama

1:1R2 = 0.050

41

Method 3, there are 8 data points at Saga site, where the predicted values of OCR are less

than 1. The value of R2 is only 0.038 which is the lowest value among all the methods.

From the above comparisons, all the methods have scattering results; however, the

Method 2 shows the best performance with highest R2 value for Group 1.

3.3.2 Group 2

In this Group, at Lianyungang and Port Said sites, the deposits were in an

underconsolidated state (Liu et al. 2008 and Salem and El-Sherbiny 2013).




The friction angle for the soils at Lianyungang site was = 24° which was calculated

from the reported M value (Liu et al. 2011), hence the value of S in Eq. (2.8) can be evaluated

0

1

2

3

4

5

6

7

0 1 2 3 4 5 6 7

OC

R P

red

icte

d

OCR Measured

Saga

Yokohama

1:1

R2 = 0.038

42

with a value of 0.2. Liu et al. (2008) reported the value of m in Eq. (2.8) of 0.97, and Nkt of

15.

For Busan sites, Singh and Chung (2015) reported the value of S in Eq. (2.8) to be 0.24

and constants m was 0.63. Chung et al. (2002) reported the value of = 29°. Chung et al.

(2012) reported Nkt = 11.25.

Hamza et al. (2002) reported the value of Nkt for East Nile Delta Clay in a range of 16-

30, and higher the plasticity index (Ip), the higher the value of Nkt. The value of Nkt = 20 was

evaluated using reported Ip = 60. Further = 25° was evaluated from Ip (Hamza and Shahien

2009). So the value of S = 0.21 (Eq. (2.8)) was adopted, and m = 0.9 was assumed.

Comparison of predicted values of OCR by Method 1 and the measured data for

Lianyungang, Busan and Port Said sites is given in Fig. 3.26. The value of R2 is 0.391.

Fig. 3.26 Comparison of the measured and the predicted values of OCR using the Method 1

for the sites of Group 2

0

1

2

3

4

5

0 1 2 3 4 5

OC

R P

red

icte

d

OCR Measured

Lianyungang

Busan

Port Said

1:1

R2 = 0.391

43


For Lianyungang site, value of k in Eq. (2.11) was back evaluated as 0.29. Whereas k

was 0.4 for Busan sites reported by Singh and Chung (2015). As for Port Said site, k was 0.3

(Salem and El-Sherbiny 2013). Fig. 3.27 shows the comparison of measured and predicted

values of OCR using Method 2 with the value of R2 of 0.504.



Cavity expansion and critical state soil mechanics theories’ approach (Method 3)

In Eq. (2.21), applying = 0.97 for Lianyungang site and = 0.63 for Busan sites

(adopting = m). Hamza et al. (2003) found the typically value of κ/λ ≈ 0.1 then the value of

= 0.9 was applied for Port Said site. Fig. 3.28 shows the comparison of measured and

predicted values of OCR using Method 3. The value of R2 is 0.163 which is the lowest value

among all the methods.

0

1

2

3

4

0 1 2 3 4

OC

R P

red

icte

d

OCR Measured

Lianyungang

Busan

Port Said

1:1

R2 = 0.504

44



From the above comparisons, the Method 2 shows the best performance with highest R 2

value for Group 2. While the Method 3 shows under predict results for Busan sites.

3.3.3 Group 3

Since the pore pressure measurement (u2) from uCPT was not reported at Sweden sites,

Method 3 is not used for the sites in Group 3.


For Finland site, Lehtonen et al. (2015) reported a friction angle () of 25° for the soft

clay. Using = 25°, a value of S in Eq. (2.8) can be evaluated as 0.21, and m = 0.85 was

0

1

2

3

4

0 1 2 3 4

OC

R P

red

icte

d

OCR Measured

Lianyungang

Busan

Port Said

1:1

R2 = 0.163

45

assumed. The value of Nkt was evaluated as 15 from the values of reported undrained shear

strength from field vane shear tests.

For Sweden sites, Larsson et al. (2010) reported = 30° for clayey soils and m = 0.85 in

Eq. (2.8). The value of Nkt was 16.3 (Larsson 2015). Comparison of the predicted and the

measured values of OCR for the sites of Group 3 is given in Fig. 3.29. The value of R2 of this

method is 0.391.




For Finland site, value of k in Eq. (2.11) was back evaluated as 0.30. As for Sweden

sites, Larsson and Mulabdic (1991) reported k = 0.29. Fig. 3.30 shows the comparison of the

measured and predicted values of OCR using the Method 2. The value of R2 is 0.634.

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

OC

R P

red

icte

d

OCR Measured

Finland

Sweden

1:1

R2 = 0.391

46



From the above comparisons, both Method 1 and 2 shows over predict results for

Sweden sites. However, the Method 2 performs better with higher R2 value for Group 3.

3.3.4 Discussions

From above comparison, it can be seen that relatively, the Method 3 performed poorly.

As for Methods 1 and 2, they include empirical parameters, and if the empirical parameters

can be back-fitted using local case histories, reasonable values of OCR can be resulted. To

further increase the accuracy of the estimated value of OCR from the results of uCPT, a new

method for estimating the value of OCR based on Modified Cam Clay theory (Roscoe and

Burland 1968) will be discussed in detail in the next section. Another point is that

fundamentally, all the methods cannot be used for underconsolidated sites, like the sites in

Lianyungang, China and Port Said in Egypt. For the methods to be applicable to the

underconsolidated sites, some modification is needed and the modified methods will be

present in the next section.

0

1

2

3

4

5

6

7

8

9

10

11

0 1 2 3 4 5 6 7 8 9 10 11

OC

R P

red

icte

d

OCR Measured

Finland

Sweden

1:1

R2 = 0.634

47

3.4 Proposed method

The widely used equation for estimating undrained shear strength (su) of clayey soils

from uCPT results is as follow (Baligh et al. 1980):

0t v

u

kt

qs

N

(2.7 bis)

where q t is corrected cone resistance, N kt is a cone bearing factor, and v0 is the total

overburden pressure. And in most clayey deposits, the values of N k t are av a ilab le in th e

geotechnical literature.

On the other hand, Modified Cam Clay (MCC) model (Roscoe and Burland 1968) is one

of the most widely used models for soft clay soils. Under triaxial compression condition,

MCC predicts undrained shear strength (su) of a soil sample as:

2 2

1 2

'

2u

p Ms M OCR

M

(3.2)

where M is the slope of critical state line in p-q plot (p is mean effective stress and q is

deviator stress), M=6 sin '

3 sin '

), = 1 – κ/λ (λ and κ are slopes of virgin loading and unloading-

reloading curves in void ratio, e versus ln(p) plot.), p = σv0(1+2K0)/3, η=q/p, and q= (1-

K0)σv0. K0 is coefficient of earth pressure at-rest which is the function of OCR, and can be

expressed by Mayne and Kulhawy’s (1982) equation as:

sin '

0(1 sin ')K OCR

(3.3)

where is internal friction angle of soil.

By combining Eqs. (2.7) and (3.2), an expression for OCR can be derived as followed:

1/1/1 2

0

2 2

2

'

t v

kt

q MOCR

N Mp M

(3.4)

Since η is a function of OCR also, to predict OCR from Eq. (3.4), an iteration process

needs to be used. Starting by assuming OCR = 1 and inputting it to the right side of the

equation, and a new value of OCR will be resulted in the left side. Then, by using the newly

obtained value of OCR into the right side, and repeat the procedure until the difference of

48

OCR value inputted in the right side and the resulting value of OCR (estimated value) on the

left side is less than 0.05.

In Eq. (3.4), p is calculated using effective overburden pressure and the coefficient of

earth pressure at-rest (K0). For a underconsolidated deposit (OCR < 1.0), the actual mean

effective stress should be OCR p). Then Eq. (3.4) will be modified as:

1/1/1 2

0

2 2

2

' OCR

t v

kt

q MOCR

N Mp M

(3.5)

3.5 Modification of the existing methods for underconsolidated deposits

Designate the effective overburden pressure as the vertical stress calculated by effective

unit weight of soil strata. For a newly reclaimed deposit, the vertical effective stress in the

deposit which is also the maximum vertical effective stress the soil experienced at that time,

can be less that the effective overburden pressure. This kind of condition is called

underconsolidated state which the value of OCR will be less than 1.0. There are two sites

collected from this study belong to this type. To apply the existing methods for estimating

OCR from uCPT results to underconsolidated deposits, some modifications are needed.


The equation for estimating OCR with undrained shear strength (su) approach is as

follow:

1/

0

0

1

'

m

t v

vkt

qOCR

N S

(2.10 bis)

where S and m are constants. Where σv0 is calculated under the condition that the self weight

induced consolidation was finished.

To use this method for an underconsolidated case, σv0 should be replaced by OCRσv0

and the value of m should be 1.0, and Eq. (2.10) will become as:

49

0

0

1

'

t v

kt v

qOCR

N OCR S

(3.6)


The method for evaluating OCR from uCPT results using normalized tip resistance (Qt)

in Eq. (2.4). The relationship between OCR and Qt can be expressed as (Mayne and Kemper

1988):

0

0't v

v

qOCR k

(2.11 bis)

To use this method for an underconsolidated case, σv0 should be replaced by OCRσv0

and Eq. (2.11) will become as:

0

0't v

v

qOCR k

OCR

(3.7)

3.5.3 Cavity expansion and critical state soil mechanics theories’ approach (Method 3)

Mayne (1991) proposed a method for estimating OCR by combining the theories of

cavity expansion and critical state soil mechanics. OCR can be computed by the following

equation:

1/

2

0

12

1.95 1 't

v

q uOCR

M

(2.21 bis)

In Eqs. (2.21), vertical effective stress (σv0) is calculated as effective overburden

pressure. In the case of OCR < 1.0, the actual vertical effective stress should be: OCRσv0

and the equations will be modified as follows:

1/

2

0

12

1.95 1 '

t

v

q uOCR

M OCR

(3.8)

50

In Eqs. (3.6), (3.7) and (3.8), OCR is in both sides, and iteration process is required to

determine the value of OCR.

3.5.4 Parameters needed in each method

Soil parameters and/or empirical parameters needed in each method are summarized in

Table 3.1.

Table 3.1 Summary of parameters needed in each method (including the proposed method)

Method Soil properties Empirical

parameters

1 - Nkt, S, m

2 - k

3

Proposed Nkt,

3.6 Applying the proposed method and the modified methods to the field cases


Using = 40°, Nkt =11 and applying = 0.9, the predicted OCR values are compared

with the measurements in Fig. 3.31. There are 5 data at Saga site the predicted values of OCR

by the proposed method are less than 1. The value of R2 of the proposed method is only

0.065.

From the above comparisons with other existing methods, although the data are scattered

(low R2 values for all methods), generally the data points are around 1:1 line. Comparatively,

the proposed method resulted in less scatters.

51

3.6.2 Proposed method and the modified Methods 1, 2 and 3 to the sites in Group 2

Proposed method

Applying all parameters, the predicted OCR values by the proposed method are

compared with the measurements in Fig. 3.32. The value of R2 of the proposed method is

0.640.

Modified undrained shear strength (su) approach (Method 1)

By applying S = 0.2, m = 0.97, Nkt = 15 for Lianyungang site, S = 0.24, m = 0.63, Nkt =

11.25 for Busan sites, and S = 0.21, m = 0.9, Nkt = 20 for Port Said site, respectively. The

predicted OCR values by modified Method 1 (for underconsolidated deposits) are compared

with the measurements in Fig. 3.33. The value of R2 is 0.396.

Modified normalize tip resistance (Qt) approach (Method 2)

For Lianyungang site, value of k was back evaluated as 0.29, whereas k was 0.4 for

Busan sites. As for Port Said site, k was 0.3. Fig. 3.34 shows the comparison of measured and

predicted values of OCR using modified Method 2 with the value of R2 of 0.509.

Modified cavity expansion and critical state soil mechanics theories approach (Method 3)

By applying = 0.97, = 24° for Lianyungang site, = 0.63, ’=29° for Busan sites,

and = 0.9, = 25° for Port Said site, respectively. Fig. 3.35 shows the comparison of

measured and predicted values of OCR using modified Method 3. The value of R2 is 0.184.

From the comparison between Method 1 and modified Method 1 (comparing between

Fig. 3.26 and 3.33), it can be seen that for the modified equation (Eq. (3.6) yielded a higher

value of R2 with a small different. As for Method 2 and modified Method 2 (comparing

between Fig. 3.28 and 3.34), the modified equation (Eq. (3.7)) resulted in better prediction

with higher R2 value. As for Method 3 and modified Method 3 (comparing between Fig. 3.28

and 3.35), the modified equation (Eq. (3.8)) resulted in better prediction with higher R2 value.

52


proposed method of Group 1



0

1

2

3

4

5

0 1 2 3 4 5

OC

R P

red

icte

d

OCR Measured

Saga

Yokohama

1:1

0

1

2

3

4

0 1 2 3 4

OC

R P

red

icte

d

OCR Measured

Lianyungang

Busan

Port Said

1:1

R2 = 0.065

R2 = 0.640

53

Fig. 3.33 Comparison of the measured and the predicted values of OCR using modified




0

1

2

3

4

5

0 1 2 3 4 5

OC

R P

red

icte

d

OCR Measured

Lianyungang

Busan

Port Said

1:1

0

1

2

3

4

0 1 2 3 4

OC

R P

red

icte

d

OCR Measured

Lianyungang

Busan

Port Said

1:1

R2 = 0.396

R2 = 0.509

54



From the comparisons of the data in the Group 2, it shows that the proposed method (Fig.

3.32) resulted in better prediction with highest R2 value (R2 = 0.640).


The value of = 0.85 was applied for all sites in Group 3. The predicted OCR values by

the proposed method are compared with the measured data in Fig. 3.36. For the proposed

method, the value of R2 is 0.702.

When comparing with the results in Figs. 3.29, 3.30, and 3.36, it indicates that for the 6

sites in Group 3, the proposed method resulted in best predictions of the value of OCR.

0

1

2

3

4

0 1 2 3 4

OC

R P

red

icte

d

OCR Measured

Lianyungang

Busan

Port Said

1:1

R2 = 0.184

55




In this chapter, a new method has been proposed. Also, modifications have been made

for existing methods for them to be applied to underconsolidated deposits. Then all methods

were applied to 12 case histories collected from 6 different countries. The estimated values of

OCR have been compared with measured data, and usefulness of each method has been

discussed.

As indicated in Table 3.1, except Method 3 (cavity expansion theory), all the Methods

need some empirical parameters. There are disadvantage and advantage of involving some

empirical parameters. The disadvantage is that the value of some empirical parameters need

to be back fitted using measured values or determined based on local experience; and

advantage is the properties of local soils can be indirectly considered. As a result, Method 3

has a poor performance for the 6 sites in Groups 1 and 2. In Method 3 and the proposed

method, the friction parameter, M, for Cam Clay theory is needed. Since Cam Clay theory

0

1

2

3

4

5

6

7

8

0 1 2 3 4 5 6 7 8

OC

R P

red

icte

d

OCR Measured

Finland

Sweden

1:1

R2 = 0.702

56

assumes that the shear strength of clayey soil is purely frictional (cohesion, c = 0), the value

of M should be evaluated using the effective stress path of triaxial test results adopting c = 0

condition.

By applying the methods to 12 case histories, it has been shown that if the parameters

(soil properties and empirical parameters) can be determined properly, all the methods can

result in a reasonable prediction. By comparing the predicted and measured values of OCR,

the proposed method had a better performance and resulted in less scattered data.

57

CHAPTER FOUR

EVALUATING THE METHODS FOR ESTIMATING

CONSOLIDATION PROPERTIES

4.1 Introduction

The piezocone penetration test (uCPT) provides continuous measurements of tip

resistance (qt), sleeve friction (fs) and pore water pressure (u2) at the shoulder of the cone. In a

laboratory set-up the uCPT induced excess pore water pressure around the cone can also be

measured (kim et al. 2007). Laboratory tests have an advantage that the soil samples for

model piezocone test and for oedometer tests can be almost exactly the same.

To evaluate the existing methods for estimating ch and kh from uCPT results, a laboratory

model tests on piezocone penetration and dissipation test are conducted. In this chapter, the

laboratory set-up of piezocone penetration and dissipation test, the soils used for laboratory

model tests, cases tested and the piezocone test results as well as the directly measured values

of ch and kh from oedometer test results are described. Then the comparison of directly

measured and estimated value of ch and kh are also presented. Finally, the discussion and

conclusion will be presented at the end of this chapter.

4.2 Laboratory model tests

The device used for the laboratory model tests is shown in Fig. 4.1. The main parts of

this device are: laboratory scale piezocones, penetration system and model chamber.

4.2.1 Laboratory scale piezocones

The piezocones used in these laboratory experiments has a tip angle of 60° with a

diameter of 20 mm (this study) and 30 mm (Hossain 2014). The pore water pressure filter is

located at the shoulder of the cones (standard type). Fig. 4.2 shows the two types of

piezocones used.

58

Fig. 4.1 Schematic diagram of laboratory model test

59

Fig. 4.2 Laboratory scale piezocones (Hossain 2014)

4.2.2 Penetration system

The penetration system consists of a reaction frame, a motor and a speed control unit

which are shown in Fig. 4.1. The penetration rate adopted in this study was 25 mm/min (0.4

mm/s). A servo motor is used to control the penetration rate. Since the penetration depth is

relatively small and to reach a steady rate in a short time period, a rate of 50% of the

maximum rate of the motor was adopted.

4.2.3 Model chamber

The cylindrical chamber is made of PVC and has an inner diameter of 0.485 m with a

height of 1.0 m (Fig. 4.1) and openings for piezometer (Fig. 4.3). A piston system driven by

air pressure was used to apply consolidation pressure to the soil sample. The sealing between

the piston and the container was achieved using a rubber O-ring placed in a slot around the

piston as well as a rubber sleeve installed above the piston (Fig. 4.4).

(a) 20 mm diameter

piezocone (b) 30 mm diameter

piezocone

Filter

element

Filter

element

60

(a) (b)

Fig. 4.3 Opening locations of piezometer (a) outside of chamber; (b) inside of chamber

(a) (b)

Fig. 4.4 A rubber sleeve (a) A rubber sleeve installed above the piston; (b) Function of

the rubber sleeve

Piston

Piezometer

opening

Piezometer

opening

Piezometer

61

4.2.4 Set-up and test procedure

(1) Set up the model. Firstly, silicon grease was smeared on the inner surface of the

cylindrical chamber to reduce possible friction between the chamber and soils (white color

silicon grease around the inner surface of chamber as shown in the Fig 4.3). Then three layers

of non-woven geotextile (about 138 g/m2) were placed at the bottom of the cylindrical

chamber to act as a drainage layer, and then six 0.1 m wide geotextile strips were lined

vertically along the inner periphery of the chamber to facilitate drainage by outward radial

flow of the pore water (in Fig. 4.5). The soils were thoroughly mixed at a water content of

about 1.2 times their liquid limits and left in the laboratory for one day before put into the

model. Then the soil was carefully poured into the chamber layer by layer until the thickness

of the model ground was 0.8 m. Piezometers were placed at pre-determined locations in the

model to measure the pore water pressure during pre-consolidation process. Finally, three

layers of the non-woven geotextile were placed on the top of the model ground to act as a

drainage layer and the piston system was setup.

(2) Pre-consolidation. The air pressure was applied to pre-consolidate the model ground.

Once the degree of pre-consolidation was more than 95% (checked from the measured

settlement curve as shown in Fig. 4.6), the air pressure was adjusted to achieve the desired

value of OCR. For example, firstly the model ground was pre-consolidated with a pressure of

96 kPa (applied air pressure was 100 kPa, but considering the effect of the shaft installed on

the top of the piston, the effective consolidation pressure was about 96 kPa) and then the

consolidation pressure was adjusted to be 12 kPa (air pressure of 12.5 kPa), to result in the

value of OCR = 8.0. After the pre-consolidation, the thickness of the model ground was about

0.6 m. In case of OCR > 1, unloading induced negative pore pressure in the model ground. In

this kind of case, the piezocone penetration was conducted after the negative excess pore

pressure dissipated which generally took a few days (in Fig. 4.7).

(3) Penetration test. The rate of the cone penetration adopted was 25 mm/min (0.4 mm/s),

which is the 50% of maximum rate of the system. During the penetration process, the pore

water pressures at the shoulder of the cone were recorded. When the shoulder of the cone

reached 0.3 m from the surface of the model ground, the penetration was stopped, and then

the dissipation tests were conducted (not analyzed in this study).

62

Before a penetration test, the filter element was saturated by the following three steps:

(a) the filter element was boiled in water for one hour to remove possible air bubbles

entrapped in it;

(b) the boiled filter element was put in a vacuum chamber and applying a vacuum pressure

of about 80 kPa for twenty four hours and kept in water;

(c) the filter element was assembled under water.

When the penetration reached the predetermined depth, the cone was hold and the

dissipation process was monitored.

(4) Oedometer consolidation test. After uCPT, soil samples were taken to determine the

value of permeability by using multi-stage-load (MSL) oedometer tests, and for some cases

constrain rate of strain (CRS) consolidation tests.

Fig. 4.5 Drainage layer in chamber

Geotextile strip

Geotextile at the

bottom of the

chamber

63

Fig. 4.6 Typical settlement curve of pre-consolidation of the model ground

Fig. 4.7 Typical pore water pressure curves at P4, P5 and P6 during pre-consolidation of

the model ground for the Mixed soil 1 with OCR = 8.0

-250

-200

-150

-100

-50

0

0.001 0.01 0.1 1 10 100 1000

Set

tlem

ent

(mm

)

Time (hour)

-20

0

20

40

60

80

100

0 100 200 300 400 500 600

Exce

ss p

ore

pre

ssure

(kP

a)

Time (hour)

Piezometer 4

Piezometer 5

Piezometer 6

Unloading

Unloading

64

4.2.5 Limitations of the laboratory model test

(1) Lower penetration rate. The adopted cone penetration rate of 0.4 mm/s is much lower

than that used in the field of 20 mm/s. Although under a rate of 0.4 mm/s, the model ground

still deform in a very close to an undrained condition (Kim et al. 2008), the behavior of clays

is strain rate dependent and the lower rate will have an effect on the cone penetration induced

excess pore water pressure.

(2) Boundary effect. For any model test, there is a scale and boundary effect. For the

model test setup of this study, considering a disc soil slice with a diameter of 485 mm,

penetrating a cone with a diameter of 30 mm into the center of the disc, the volume of the

cone penetrated will be about 0.38% of the volume of the disc soil slice. And for a cone with

a diameter of 20 mm, the volume will be about 0.17% of the slice. Due to the constrain effect

of the wall of the model, there was almost no horizontal radial displacement at the boundary.

While heaving of the model ground was monitored. Chai et al. (2014) reported that the radial

boundary constrain effect increased measurement pore pressure of piezometer located near

the boundary. The larger the diameter of the cone, the larger the effect will be. As for the

pore pressure measured at the shoulder of the cone, for the conditions adopted, the effect was

less significant when compared with that near the boundary.

As for drainage boundary, it is also different from the field condition. In the field and in

the horizontal radial direction, at infinite distance, it is drained. While in the laboratory, the

six geotextile strips provided certain drainage but at other locations are undrained.

4.2.6 Soil samples and cases tested

Five types of soil, namely, remolded Ariake clay, Ariake clay mixed with a sand with

sand/clay ratios (by dry weight) of 50:50 (Mixed soil 1), 60:40 (Mixed soil 2), 70:30 (Mixed

soil 3), and 20:80 (Mixed soil 4), respectively were used in the laboratory model tests. The

grain size distributions of the soils are shown in Fig. 4.8. Some physical properties of these

soils are listed in Table 4.1 and the cases tested are summarized in Table 4.2. The results of

using the remolded Ariake clay and the Mixed soil 2 are from Hossain (2014). After uCPT,

soil samples were taken to measure the value of coefficient of consolidation (cv), and

permeability (kv) in the vertical direction by using oedometer tests. For the Ariake clay

65

samples, constant rate of strain (CRS) consolidation tests with the vertical or horizontal radial

drainage were also conducted to check the anisotropy of the coefficient of consolidation and

the permeability of the soils.

Fig. 4.8 Grain size distributions of soils

Table 4.1 Physical properties of the soils tested

Soil properties Liquid limit

(LL)

(%)

Plastic limit

(PL)

(%)

Specific

gravity

(ρs)

Void

ratio

(e0)

Compression

index

(Cc)

Swelling

index

(Cs)

Ariake clay 114.00 60.60

2.62-

2.65

2.36 0.80 0.16

Mixed soil 1

(50:50)* 56.71 24.13 1.02 0.35 0.07

Mixed soil 2

(60:40)* 44.24 21.28 0.89 0.28 0.06

Mixed soil 3

(70:30)* 39.85 21.29 0.81 0.23 0.05

Mixed soil 4

(20:80)* 70.28 30.46 1.48 0.50 0.10

* sand/clay ratios (by dry weight)

66

Table 4.2 Conditions of model tests conducted

Soil Case σvmax*

(kPa)

σv0*

(kPa)

OCR Cone

diameter

(mm)

Remark

Ariake

clay

1 96 96 1 30

2 96 48 2 30 Hossain

3 96 24 4 30 (2014)

4 96 12 8 30

Mixed

soil 1

1 96 96 1 20

2 96 48 2 20 This

3 96 24 4 20 study

4 96 12 8 20

Mixed

soil 2

1 96 96 1 20

2 96 48 2 20 Hossain

3 96 24 4 20 (2014)

4 96 12 8 20

Mixed

soil 3

1 96 96 1 20

2 96 48 2 20 This

3 96 24 4 20 study

4 96 12 8 20

Mixed

soil 4

1 96 96 1 20 This

2 96 48 2 20 study

3 96 12 8 20

*σ vmax is the maximum vertical consolidation stress, and σv0 is the initial vertical effective

stress in the model ground before piezocone penetration.

4.2.7 Results of the dissipation tests

The piezocone can be held at a predetermined depth to measure the pore pressure

dissipation process. For the laboratory model tests, the dissipation curves for u2 measured at

67

the shoulder of the cone of Ariake clay, Mixed soil 1, Mixed soil 2, Mixed soil 3, and Mixed

soil 4 are shown in Figs. 4.9, 4.10, 4.11, 4.12 and 4.13, respectively.

(a)

(b)

(c)

Fig. 4.9 Non-standard dissipation curves of Ariake clay of OCR = 1.0, 4.0 and 8.0

(Hossain 2014)

OCR = 1.0

v0 = 96 kPa

OCR = 4.0

v0 = 24 kPa

OCR = 8.0

v0 = 12 kPa

68

(a) (b)

(c) (d)

Fig. 4.10 Non-standard dissipation curves of Mixed soil 1 of OCR = 1.0, 2.0, 4.0 and 8.0

OCR = 1.0

v0 = 96 kPa

OCR = 2.0

v0 = 48 kPa

OCR = 4.0

v0 = 24 kPa

OCR = 8.0

v0 = 12 kPa

69

(a) (b)

(c) (d)


(Hossain 2014)

OCR = 1.0

v0 = 96 kPa

OCR = 2.0

v0 = 48 kPa

OCR = 4.0

v0 = 24 kPa

OCR = 8.0

v0 = 12 kPa

70

(a) (b)

(c) (d)


OCR = 1.0

v0 = 96 kPa

OCR = 2.0

v0 = 48 kPa

OCR = 4.0

v0 = 24 kPa

OCR = 8.0

v0 = 12 kPa

71

(a)

(b)

(c)

Fig. 4.13 Non-standard dissipation curves of Mixed soil 4 of OCR = 1.0, 2.0 and 8.0

As shown in Fig 4.9 to 4.13, all measured dissipation curves are non-standard type


method is used for estimating the coefficient of consolidation (ch) from uCPT results.

OCR = 1.0

v0 = 96 kPa

OCR = 2.0

v0 = 24 kPa

OCR = 8.0

v0 = 12 kPa

72

4.3 Comparison of measured and estimated coefficient of consolidation from laboratory

piezocone test results

Using Chai et al. (2012a)’s method, the estimated values of ch are listed in Table 4.3 and

compared with the measured values of cv (from oedometer test) in Figs. 4.14 to 4.18. The

values of Ir were estimated referring reported values in the literature (Chai et al. 2015).

Table 4.3 Conditions and results of model tests conducted (ch)

Soil

properties

Case Cone

diameter

(mm)

tumax

(min)

umax

(kPa)

t50

(min)

t50c

(min)

Ir Measured

cv

(m2/min)

Estimated

ch

(m2/min)

Ariake

clay

1 30 0.35 128.92 83.65 60.48 100 5.40×10-6 9.10×10-6

2 30 0.75 93.70 79.59 47.94 100 5.70×10-6 1.15×10-5

3 30 1.40 73.48 107.76 59.26 100 9.00×10-6 9.30×10-6

4 30 0.65 52.18 83.34 52.68 100 9.90×10-6 1.05×10-5

Mixed

soil 1

1 20 0.25 97.25 62.36 44.76 120 2.46×10-5 5.91×10-6

2 20 0.35 87.67 62.72 42.07 120 3.00×10-5 5.72×10-6

3 20 1.10 76.50 68.70 34.44 120 3.66×10-5 7.58×10-6

4 20 0.45 61.58 71.33 46.53 120 3.57×10-5 5.66×10-6

Mixed

soil 2

1 20 0.45 110.08 62.37 40.19 120 2.46×10-5 6.81×10-6

2 20 0.30 93.35 57.43 39.76 120 2.04×10-5 6.87×10-6

3 20 1.50 68.86 63.48 28.56 120 3.00×10-5 9.68×10-6

4 20 0.70 69.96 47.44 24.44 120 2.70×10-5 1.10×10-5

Mixed

soil 3

1 20 0.30 88.00 49.33 32.46 120 5.40×10-5 8.12×10-6

2 20 0.2 77.00 41.82 28.99 120 4.02×10-5 9.11×10-6

3 20 0.35 67.33 39.18 23.43 120 2.88×10-5 1.12×10-5

4 20 0.25 60.92 39.42 25.69 120 2.28×10-5 1.03×10-5

Mixed

Soil 4

1 20 0.40 103.83 89.12 63.06 110 9.60×10-6 4.07×10-6

2 20 0.40 73.75 106.69 72.93 110 1.02×10-5 3.52×10-6

3 20 0.95 65.42 103.48 62.06 110 1.70×10-5 4.14×10-6

For the mixed soils, the sand contents were more than 50% and for initially well mixed

sands, there is no significant stress induced anisotropy (Chai et al.2015). As a result, the

73

values are lying between ratios of ch/cv of 0.2 to 1.0 (in Figs. 4.15 to 4.17). As for the Mixed

soil 4, the values are also lying between the ratios of ch/cv of 0.2 to 1.0 (Fig. 4.18). The reason

behind this is that due to the boundary effect mentioned in previous section, the measured

excess pore pressure dissipated slower; hence the t50c is higher which caused the lower

estimated ch values. As for the remolded Ariake clay (Fig. 4.14), ch/cv ratios from the results

of the CRS tests are listed in Table 4.4 with an average value of 1.27. This value is less than

the value of about 1.5 reported by Chai et al. (2012b), which is an average value for vertical

effective stress up to 1000 kPa. While the maximum consolidation stress in this study was

only up to 96 kPa. The larger the consolidation stress, the larger the stress induced

anisotropy.

Table 4.4 Comparison of ch and cv values from CRS test on Ariake clay samples

Test

cases

Type of

soil

σv0

kPa OCR cv (m

2/min) ch (m2/min) ch/cv

1

Ariake

clay

96 1 4.93×10-5 6.25×10-5 1.27

2 48 2 5.07×10-5 6.94×10-5 1.37

3 24 4 3.13×10-5 4.09×10-5 1.31

4 12 8 1.28×10-4 1.46×10-4 1.14

Average 1.27

Fig. 4.14 Comparison of measured cv with estimated ch of Ariake clay

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03

c vM

easu

red

(m

2/m

in)

ch Estimated (m2/min)

Ariake clay

ch=cv

ch=2cv

74

Fig. 4.15 Comparison of measured cv with estimated ch of Mixed soil 1


1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03

c vM

easu

red

(m

2/m

in)


Mixed soil 1

ch=cv

ch=cv/5

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03

c vM

easu

red

(m

2/m

in)


Mixed soil 2

ch=cv

ch=cv/5

75



1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03

c vM

easu

red

(m

2/m

in)


Mixed soil 3

ch=cv

ch=cv/5

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03

c vM

easu

red

(m

2/m

in)


Mixed soil 4

ch=cv

ch=cv/5

76

4.4 Comparison of measured and estimated permeability from laboratory piezocone test

results

The estimated values of kh using laboratory model test results by Chai et al. (2011)’s

method are compared with the measured values of kv from oedometer test in Figs. 4.19 to

4.22 and listed in Table 4.5.

Table 4.5 Conditions and results of model tests conducted (kh)

Soil

properties

Case σvmax*

(kPa)

σv0*

(kPa)

OCR Cone

diameter

(mm)

∆u

(kPa)

Measured

Permeability

kv (m/s)

Estimated

Permeability

kh (m/s)

Ariake

clay

1 96 96 1 30 123.16 8.00×10-10 3.18×10-9

2 96 48 2 30 89.24 9.32×10-10 1.34×10-9

3 96 24 4 30 69.13 1.08×10-9 3.17×10-10

4 96 12 8 30 47.39 1.30×10-9 1.32×10-10

Mixed

soil 1

1 96 96 1 20 97.33 2.01×10-9 6.73×10-9

2 96 48 2 20 81.08 2.45×10-9 1.43×10-9

3 96 24 4 20 63.83 2.87×10-9 3.07×10-10

4 96 12 8 20 45.17 3.27×10-9 1.12×10-10

Mixed

soil 2

1 96 96 1 20 99.55 2.05×10-9 6.03×10-9

2 96 48 2 20 85.29 2.33×10-9 1.11×10-9

3 96 24 4 20 60.82 2.94×10-9 3.89×10-10

4 96 12 8 20 54.89 3.10×10-9 4.29×10-11

Mixed

soil 3

1 96 96 1 20 85.25 3.11×10-9 1.29×10-8

2 96 48 2 20 68.54 3.39 ×10-9 3.26×10-9

3 96 24 4 20 59.33 3.89×10-9 4.40×10-10

4 96 12 8 20 53.83 4.47×10-9 4.72×10-11

Mixed

Soil 4

1 96 96 1 20 101.50 9.10×10-10 5.48×10-9

2 96 48 2 20 72.084 9.86×10-10 2.54×10-9

3 96 12 8 20 42.917 1.50×10-9 1.43×10-10

*σ vmax is the maximum vertical consolidation stress, and σv0 is the initial vertical effective

stress in the model ground before piezocone penetration.

77

From Figs. 4.19 to 4.23, it can be seen that under the condition of a given maximum


estimated values of kh decreased with OCR significantly for all the soil types. This indicates

that further research is needed to include the effect of OCR in the methods for estimating the

value of kh from the results of uCPT.

For the remolded Ariake clay, kh/kv ≈ 1.27 from the CRS tests was obtained (Table 4.6).

For the cases of OCR = 1.0, generally the estimated values of kh are larger than the measured

values (i.e. kh/kv > 1.27). For the mixed soils, it was planned to measure both kh and kv by

CRS tests also but the horizontal drainage CRS tests for the mixed soils were not successful.

This is because horizontal drainage CRS test has a porous drainage tube inserted into the

center of the specimen, the friction between the mixed soil (50% or more than 50% sand) and

the drainage tube was significant. Then MSL consolidation tests were conducted using

specimens of reconstituted Mixed soil 1 cut both in the vertical and horizontal directions. For

example, under a consolidation pressure of 100 kPa, the kh/kv = 1.02 (kh = 2.09×10-9 m/s and

kv = 2.05×10-9 m/s) was obtained. Chai et al. (2014) also reported that for a sand/clay mixture

with sand content more than 50%, the stress induced anisotropy can be ignore. Therefore, for

mixed soil with sand content of equal of more than 50%, the stress induced anisotropy is

small and can be ignored.

When comparing the absolute values of the estimated kh from the results of uCPT and the

laboratory measured kv, there is a question of applicability of Eq. (2.30), which was proposed

based on the results field uCPT. Assuming that two different penetration rates, U1 and U2

should result in the same kh, from Eqs (2.30) and (2.32), it requires:

4.91

1 1

2 2

U u

U u

(Δu1 and

Δu2 are corresponding measured excess pore water pressure with penetration rate of U1 and

U2, respectively). But there is no theoretical basis for this. Therefore, it is not guaranteed that

the empirical equation proposed using the filed measured data can be correctly applied to a

laboratory condition. Further the response of natural undisturbed soil deposit during a

piezocone penetration process will be different from that of a remolded and reconstituted

model soil deposit. Therefore, the comparison is more emphasized on the tendency rather

than the absolute values, and to use it for investigating the relative effect of OCR is rational.

78

Fig. 4.19 Comparison of measured kv with estimated kh of Ariake clay

Fig. 4.20 Comparison of measured kv with estimated kh of Mixed soil 1

1.0E-10

1.0E-09

1.0E-08

1.0E-10 1.0E-09 1.0E-08

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Ariake Clay

Chai et al. (2011)

kh=kv

kh=1.5kv

OCR 1

2

48

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-10 1.0E-09 1.0E-08 1.0E-07

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Mixed soil 1

Chai et al. (2011)

kh=kv

OCR 1

24

8

79



1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Mixed soil 2

Chai et al. (2011)

kh=kv

OCR 1

248

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Mixed soil 3

Chai et al. (2011)

kh=kv

OCR 1

248

80


Table 4.6 Comparison of kh and kv values from CRS test on Ariake clay samples

Test

cases

Type of

soil

σv0

kPa OCR kv (m/s) kh (m/s) kh/kv

1

Ariake

clay

96 1 5.26×10-10 5.89×10-10 1.12

2 48 2 5.34×10-10 6.71×10-10 1.26

3 24 4 5.72×10-10 8.93×10-10 1.56

4 12 8 1.58×10-9 1.77×10-9 1.12

Average 1.27


Fifteen (15) laboratory model tests on piezocone penetration and dissipation were

conducted with different soils and OCR values. All of the dissipation curves are non-standard

type. Therefore, Chai et al. (2012a)’s method was used for estimating the coefficient of

consolidation (ch) in horizontal direction of soil from the dissipation test curves. The

comparison between estimated (ch) and measured (cv) values shows that, for the mixed soils

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-10 1.0E-09 1.0E-08 1.0E-07

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Mixed soil 4

Chai et al. (2011)

kh=kv

OCR 1

8

kh=1.5kv

2

81

(sand: clay ratio of 50:50, 60:40, 70:30, and 20:80), the values are lying between ratios of

ch/cv of 0.2 to 1.0. The reasons behind this is that due to the boundary effect mentioned in

previous section, the measured excess pore pressure dissipated slower, hence the t50c is higher

which caused the lower estimated ch values. As for the remolded Ariake clay, ch/cv ratios are

between 1.0 and 2.0 generally agree with the ch/cv ratios from CRS test results. It is concluded

that Chai et al. (2012a)’s method can result in acceptable ch values from piezocone

dissipation test results.

Chai et al. (2011)’s method for estimating the permeability (kh) in horizontal direction of

soil was evaluated by the comparison between estimated (kh) and measured (kv) values. It

shows that under the condition of a given maximum consolidation pressure the measured

values of kv slightly increased with OCR, while the estimated values of kh decreased with

OCR significantly for all the soil types. Therefore, the existing method for estimating kh from

piezocone sounding results performed poorly for overconsolidated soils. A new method has

been developed in this study and the details will be presented in the next chapter.

82

CHAPTER FIVE

MODIFIED METHOD FOR ESTIMATING PERMEABILITY

5.1 Introduction

In chapter 4, Chai et al. (2011)’s method was evaluated by the comparison between the

estimated (kh) and laboratory measured (kv) values. As a result, the method performs poorly

for overconsolidated soils. Hence, a new method has been developed for estimating kh from

the piezocone sounding results in overconsolidated deposits. The details of the modified

method are presented in this chapter. Moreover, the evaluation of the proposed method using

three (3) field cases will be presented as well.

5.2 Laboratory model test results

Since in existing methods (Elsworth and Lee 2005; 2007 and Chai et al. 2011), kh has a

relationship with KD which is a function of0'v

u


pressure and σv0 is the initial effective vertical stresses).

From fifteen (15) cases of laboratory model uCPT results (details see chapter 4), the

relationship between 0'v

u

and OCR are plotted in Figs. 5.1 to 5.5. It can be seen that the

value of 0'v

u

increased with OCR. As mentioned earlier, KD reversely related to (i.e.

with increase of0'v

u

, KD decrease). Consequently, from Eq. (2.32), the value of

estimated kh is decreased with OCR significantly for all the soil types. However, for a given

soil and given maximum consolidation pressure, kh will increase with OCR. Therefore, there

is a need to develop a method to consider the effect of OCR on estimating the value of kh.

83

Fig. 5.1 Relationship between 0'v

u

and OCR of Ariake clay


u


0

1

2

3

4

5

0 2 4 6 8 10OCR

Ariake Clay

0

1

2

3

4

0 2 4 6 8 10OCR

Mixed soil 1

84


u



u


0

1

2

3

4

5

0 2 4 6 8 10OCR

Mixed soil 2

0

1

2

3

4

5

0 2 4 6 8 10OCR

Mixed soil 3

85


u


5.3 Void ratio (e) and permeability (k) relationship of soil

One of the major factors affecting permeability (k) of soil is void ratio (e). For a given

soil, the larger the void ratio is, the higher the value of permeability (Fig.5.6) as follows

(Taylor 1948):

0 10 k

e

C

h hk k

(5.1)

where kh0 is in situ permeability at void ratio e0, Ck is a constant (Ck =0.5e0 (Tavenas et al.

1983)), and ∆e is the change of void ratio.

0

1

2

3

4

0 2 4 6 8 10

OCR

Mixed soil 4

86

Fig. 5.6 Permeability of clays obeying the linear variation of logarithmic of permeability with

void ratio (after Hamidon 1994)

5.4 Modified method

5.4.1 Basic considerations

Since in existing methods, kh is a function of0'v

u

, the basic idea is to include the

effect of OCR on0'v

u

. The following steps are proposed to do so.

(1) Based on the results of the laboratory test, estimate the value of 0'v NC

u

corresponding to OCR = 1.0 from the measured value of 0'v OC

u

of OCR > 1.0, and then

87

obtain the value of kh corresponding to yield vertical effective stress (σvmax) by Chai et al.’s

(2011) method and designate it as kh0.

(2) In case of the value of kh corresponding to initial vertical effective stress (σ v0) is

required, it can be evaluated approximately by using Taylor’s (1948) equation. Taylor’s

equation was proposed for clay soils. While, according to our test results, it can be

successfully applied to clayey sand for OCR up to 8. Assume that kh for OCR > 1.0 can be

calculated by Eq. (5.1). For ∆e, it can be calculated as:

logse C OCR (5.2)

where Cs is swelling index. In Eq. (5.1), if the laboratory measured value of permeability is

available, it should be used to calibrate the value of Ck. If it is not available, Ck = 0.5e0

suggested by Tavenas et al. (1983). Substituting Eq. (5.2) into Eq. (5.1), then kh can be

represented as:

0

2

0

sC

e

h hk k OCR (5.3)

5.4.2 Obtaining kh0

Figs. 5.7 to 5.11 show the relationships of OCR-0 0' 'v vOC NC

u u

. It can be seen

that 0 0' 'v vOC NC

u u

increased with OCR in a non-linear form. By observing the

shape of the curves, it is proposed that;

0 0' 'v vOC NC

u u OCR

(5.4)

where α is a model parameter. From the results of the laboratory tests, for the Ariake clay, α

= 0.52, for the Mixed soil 1 (Ariake clay mixed with a sand with sand/clay ratios (by dry

weight) of 50:50), α = 0.60, for the Mixed soil 2 (sand/clay ratios of 60:40), α = 0.66, for the

Mixed soil 3 (sand/clay ratios of 70:30), α = 0.75 and for the Mixed soil 4 (sand/clay ratios of

20:80), α = 0.56.

88

Fig. 5.7 Values of model parameter (α) of Ariake clay

As indicated by Eq. [9], that under a given σvmax condition, for OCR = 1.0, (σv)NC = σvmax,

and for OCR > 1.0, (σv)OC = σvmax/OCR. So if α = 1.0, 0 0' 'v vOC NC

u u

. For α < 1.0,

0 0' 'v vOC NC

u u

. Therefore, a soil that has more clay content, the smaller the value

of α, the smaller of the ratio of 0 0' 'v vOC NC

u u

.

y = 0.9844x0.5208

R² = 0.9949

0

1

2

3

4

0 2 4 6 8 10

OCR

Ariake Clay

α = 0.52

89

Fig. 5.8 Values of model parameter (α) of Mixed soil 1


y = 1.0183x0.6041

R² = 0.9966

0

1

2

3

4

0 2 4 6 8 10OCR

Mixed soil 1

y = 0.9878x0.6646

R² = 0.9909

0

1

2

3

4

5

0 2 4 6 8 10OCR

Mixed soil 2

α = 0.60

α = 0.66

90



y = 0.9496x0.7512

R² = 0.9932

0

1

2

3

4

5

0 2 4 6 8 10OCR

Mixed soil 3

y = 0.958x0.5641

R² = 0.9911

0

1

2

3

4

0 2 4 6 8 10

OCR

Mixed soil 4

α = 0.75

α = 0.56

91

Then, the value of 0'v NC

u

which is a function of BqQt is used to calculate KD in Eqs.

[4] or [5] for OCR > 1.0 and designated as (KD)NC. Therefore, the value of kh0 corresponding

to yielding vertical effective stress (σvmax) can be calculated as:

0

02 '

D wNCh

v

K Uak

OCR

(5.5)

by substituting Eq. (5.5) into Eq. (5.3), kh (OCR > 1.0) corresponding to initial vertical

effective stress (σv0) can be calculated as:

0

21

02 '

s

D wNCh C

e

v

K Uak

OCR

(5.6)

5.5 Comparing with laboratory model test results

Applying the existing (Eq. (2.32)) and modified methods (Eq. (5.6)) to the laboratory test

results, the estimated values of kh are compared with the laboratory measured kv in Figs. 5.12

to 5.16.

Fig. 5.12 Comparison of measured kv with estimated kh using both Chai et al. (2011) and the

modified method of Ariake clay

1.0E-10

1.0E-09

1.0E-08

1.0E-10 1.0E-09 1.0E-08

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Ariake Clay

Chai et al. (2011)

Modified Method

kh=kv

kh=1.5kv

OCR 1

2

48

2

48

92


modified method of Mixed soil 1

It can be seen that when applying the modified method to all the cases, the ratios between

kh/kv were closer to the kh/kv = 1.5 line. Comparing with kh/kv = 1.5 line is because normally

permeability in the horizontal direction is higher than that in the vertical direction and for

Ariake clay kh/kv ≈ 1.5 (Chai et al. 2012b). Moreover, the estimated kh/kh0 (kh0 corresponding

to σvmax and kh corresponding to σv0) ratios by the modified method for the Ariake clay and

the Mixed soil 1 are shown in Fig. 5.17. The corresponding laboratory measured ratios kv/kv0

are also included for comparison. It can be seen that both the measured and estimated ratios

increased with OCR.

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-10 1.0E-09 1.0E-08 1.0E-07

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Mixed soil 1

Chai et al. (2011)

Modified Method

kh=kv

OCR 1

24

8

2

48

93



As shown in Figs. 5.12 to 5.16, generally the estimated values of kh are larger than 1.5kv.

The exact reasons remain unclear, but there are two possible reasons considered. One is that

the penetration rate adopted in the laboratory test was much lower than that in the field.

Although the penetration rate is included into Eq. (5.6), due to viscosity nature, the response

of clayey soils is strain rate dependent, and the lower penetration rate may have an effect on

the estimated value of kh. Another possible reason is that the method of Chai et al. (2011) is

an empirical one, and it may not result the exact value of kh for all normally consolidated

clayey soils even.

From Figs. 5.12 to 5.16, it can be seen that generally the estimated values of kh are larger

than 1.5kv, i.e. the estimated values of kh are larger than the values from laboratory oedometer

1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Mixed soil 2

Chai et al. (2011)

Modified Method

kh=kv

OCR 1

2

48

2

84

94

test. As discussed earlier, the model tests had their limitations and Eqs. (2.30) and (2.32) were

proposed using the field data and their applicability to the model test is not theoretically

guaranteed. Therefore, for the comparison in Figs. 5.12 to 5.16, it is more emphasized on the

tendency rather than absolute values. The effectiveness of the modified method will further

validated by applying it to field cases in the next Section in this Chapter.



1.0E-11

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-11 1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Mixed soil 3

Chai et al. (2011)

Modified Method

kh=kv

OCR 1

248

2 4

8

95



(a) (b)

Fig. 5.17 Example of variation of measured kv/kv0 and estimated kh/kh0 ratios with OCR (a)

Ariake clay; (b) Mixed soil 1.

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-10 1.0E-09 1.0E-08 1.0E-07

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Mixed soil 4

Chai et al. (2011)

Modified Method

kh=kv

OCR 1

8 8

kh=1.5kv

2

2

1

1.5

0 2 4 6 8 10

k/k

0ra

tio

OCR

Ariake Clay

kv/kv0

kh/kh0

1

1.5

2

0 2 4 6 8 10

k/k

0ra

tio

OCR

Mixed soil 1

kv/kv0

kh/kh0

96

5.6 Methods for determining the parameters

In case of estimating the value kh corresponding to yielding vertical effective stress, the

proposed method needs two parameters, namely, OCR and a model parameter, α. While if the

value of kh corresponding to the initial vertical effective stress is required, two more

parameters, i.e. swelling index (Cs) and the initial void ratio (e0) are needed. It is suggested

that OCR and α need to be determined using the results of uCPT. As for the values of e0 and

Cs, they need to be estimated based on existing local data-base.

(1) OCR

There are several methods in the literature for estimating the value of OCR from uCPT

results (Mayne and Kemper 1988; Mayne 1991; Ladd and DeGroot 2003). And a new

method has been proposed from this study in chapter 3 (Chanmee et al. 2017). If a locally

validated method is available, it should be used. If not, the proposed method from this study

for estimating OCR from uCPT results is suggested:

1/1/1 2

0

2 2

2

'

t v

kt

q MOCR

N Mp M

(3.4 bis)

The proposed method needs three (3) parameters (internal friction angle (ϕ), cone bearing

fac to r (Nkt), and = 1 – κ/λ (λ and κ are slopes of virgin loading and unloading-reloading

curves in void ratio, e versus ln(p) plot)) or the method proposed by Mayne and Kemper

(1988) can be used:

tOCR k Q (2.11 bis)

where k is an empirical parameter. If there is no locally validated value, k = 0.3 is suggested

for clayey soils.

(2) α

The value of α is related to soil types. It is suggested to use Robertson’s (1990) Bq – Qt

chart (Fig. 5.18) to clarify soil type using the results of uCPT. From the results of this study,

only α values of soil types 3, 4, and 5 are recommended as 0.55, 0.65 and 0.75 respectively.

5.7 Procedure for using the modified method

The steps for evaluating the value of kh from the results of uCPT are as follow:

97

(1) Calculate Bq and Qt from the results of uCPT.

(2) Calculate OCR by Eq. (3.4) or (2.11). If OCR = 1.0, go to step (5).

(3) Use Bq – Qt chart (Fig. 5.18) to classify the soil and determine the value of α (Fig.

5.18).

(4) Calculate 0'v NC

u

from the measured 0'v OC

u

from Eq. (5.4).

(5) Calculate KD by Eq. (2.30) or (2.31).

(6) Calculate the value of kh0 corresponding yielding vertical effective stress (σ vmax) by

Eq. (5.5).

(7) Estimate the values of initial void ratio (e0) and swelling index (Cs) based on local

data-base. If the values of e0 and Cs cannot be estimated, stop here.

(8) Calculate kh corresponding initial vertical effective stress (σv0) by Eq. (5.6).

Zone of Soil behavior type

1. Sensitive, fine grained

2. Organic soils-peats

3. Clays-clay to silty clay

4. Silt mixtures clayey silt to silty clay

5. Sand mixtures; silty sand to sand silty

6. Sands; clean sands to silty sands

7. Gravelly sand to sand

Fig. 5.18 CPT soil behavior type chart (Modification from Robertson 1990)

1

10

100

1000

-0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4

Qt

Bq

21

3

4

5

6

7

α = 0.55

α = 0.65

α = 0.75

98

5.8. Application to field cases

To validate the applicability of the modified method, two field cases in Japan (at Saga and

Yokohama sites), and 1 case in Shanghai, China were analyzed.

5.8.1 Case 1: Saga, Japan

In Saga plain along the coast of Ariake Sea (a semi-enclosed inland bay), Kyushu, Japan,

deposited clayey soils, called Ariake clay with a thickness between 10 to 30 m. For a

highway construction, several boreholes together with uCPT adjacent to the boreholes were

carried out in Saga plain. The results of laboratory oedometer tests using undisturbed soil

samples and the results of the corresponding uCPT at one of the sites are analyzed here. The

results of uCPT are shown in Fig. 5.19 (ASCRDO 2008). The piezocone used in this site had

a diameter of 35.7 mm (cross-section area of 1000 mm2), an apex angle of 60°, and the filter

element for pore water pressure measurement at the shoulder of the cone (standard type). The

rate of penetration adopted was 20 mm/sec. The soil profile, groundwater level, and the

laboratory measured values of permeability (kv) and the values of OCR from the results of the

oedometer test are shown in Fig. 5.20.

Fig. 5.19 Piezocone penetration test results at Saga site

99

Fig. 5.20 Soil strata, measured values of OCR and permeability at Saga site


modified method at Saga site

0

5

10

15

20

kv Permeability (m/s)'v0 and P'c (kN/m2)

Dep

th (

m)

Sandy Clay

Silty Clay

OCR

0 50 100 150 200

P'c'v0

10-9 10-8 10-70 2 4

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-03

1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04 1.0E-03

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Chai et al. (2011)

Modified Method

kh=1.5kv

100

The estimated values of kh from the piezocone sounding results using both Chai et al.’s

(2011) and the modified methods are compared with measured values of (kv) in Fig. 5.21. For

using the modified method, the values of e0, Cs and α adopted were 2.5, 0.08 and 0.55

respectively.

Generally, the results from the modified method are closer to kh/kv =1.5 line. However, it is

noted that there are three points for which the values of kh are more than 10 times the

corresponding values of kv. These three points were located in a sandy clay layer. The kh from

uCPT may include the effect of thin sand layers or sand seems in the deposit, but laboratory

oedometer test might fail to reflect the effect because usually a relative uniform clay soil

sample would be selected for laboratory oedometer test.

5.8.2 Case 2: Yokohama, Japan

The Japanese Geotechnical Society (JGS) organized an activity of simultaneously

conducting uCPT by several companies at a site in Yokohama, Japan, in 2007 (Suemasa et al.

2009). The data used in this study are from one of the organizations (organization C). From

the ground surface, the soil deposit consists of a 4 m thick sandy clay, underlain by a fine

sand layer to a depth of about 10 m and followed by a sandy clay layer about 10 m thick. The

piezocone used in this site had the same specifications as the one used in Saga site. The

results of uCPT (JGS 2009) are shown in Fig. 5.22. The soil profile, groundwater level, and

the laboratory measured values of OCR and kv are shown in Fig. 5.23.

After applying both Chai et al.’s (2011) and the modified methods to the case, the results

are compared in Fig. 5.24. In the modified method, the values of e0, Cs and α adopted were

1.55, 0.057, and 0.55, respectively (JGS 2009). It shows that the results from the modified

method are closer to kh/kv = 1.0 line. At Yokohama site, the kh/kv ratio is not known. Also, it

can be seen that there are two points for which the values of kh are more than 100 times the

corresponding value of kv. Again these two points were located in a sandy clay and fine sand

layer. It is considered that the interpreted kh value may reflect the effect of the thin sandy

layers but the laboratory oedometer tests failed to do that.

101

Fig. 5.22 Piezocone penetration test results at Yokohama site

Fig. 5.23 Soil strata, measured values of OCR and permeability at Yokohama site

0

5

10

15

20

0 1200 2400 3600

Tip resistance (kPa) Pore water pressure (kPa) Sleeve friction (kPa)

Dep

th (

m)

Hydrostaticpressure

0 250 500 750 0 50 100 150 200

0

2

4

6

8

10

12

14

16

18

20

22

kv Permeability (m/s)'v0 and P'c (kN/m2)

Dep

th (

m)

Sandy Clay

Sandy Clay

Fine Sand

OCR

0 100 200 300

P'c'v0

10-9 10-8 10-70 2 4

102


modified method at Yokohama site

5.8.3 Case 3: Shanghai, China

Shanghai is located on the alluvial plain of the Yangtze River Delta, China. A case of

uCPT together with values of kv from oedometer tests in Shanghai has been reported by Xu et

al. (2009) and Shen et al. (2015). At the site, from the ground surface, the soil deposit

consists of a 5 m thick gray mucky clay, underlain by a gray mucky silty clay layer to a depth

of about 15 m and followed by a gray silty clay layer about 15 m thick. The piezocone used

in this site had a cross-section area of 1500 mm2, an apex angle of 60°, and the filter element

for pore water pressure measurement is located at the shoulder of the cone (2 mm behind the

conical tip). The rate of penetration adopted was 20 mm/s and the results of uCPT are shown

in Fig. 5.25 (Shen et al. 2010). The soil profile, groundwater level, and laboratory measured

values of kv are shown in Fig. 5.26.

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-05

1.0E-04

1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06 1.0E-05 1.0E-04

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Chai et al. (2011)

Modified Method

kh=kv

103

Fig. 5.25 Piezocone penetration test results at Shanghai site

Fig. 5.26 Soil strata and measured values permeability at Shanghai site

0

5

10

15

20

25

30

35

0 1000 2000

Tip resistance (kPa) Pore water pressure (kPa)

Dep

th (

m)

Hydrostaticpressure

0 250 500 750 1000 1250

0

5

10

15

20

25

30

35

kv Permeability (m/s)'v0 (kN/m2

)

Dep

th (

m)

Gray Mucky Clay

Gray Silty Clay

Gray Mucky Silty Clay

Dark green Silty Clay

0 100 200 300

'v0

10-10 10-9 10-8 10-7

104

For the Shanghai site, OCR values were not reported. The values of OCR were estimated

from the results of uCPT by Eq. (2.11) with k = 0.3. The range of the estimated OCR values

for this site was around 1.0 to 1.9 which agrees with range of 1.0 to 2.0 reported by Li et al.

(2012) and Ye and Ye (2016) for the clayey deposit in Shanghai, China. After applying both

Chai et al.’s (2011) and the modified methods to the case, the results from the modified

method are closer to kh/kv = 1.0 line (for Shanghai site, the kh/kv ratio is not known) as shown

in Fig. 5.27. The values of e0 and Cs from Xu et al. (2009) are 1.2 and 0.035 (Cs ≈ 0.1Cc),

respectively, and the value of α adopted was 0.55.


modified method at Shanghai site

1.0E-10

1.0E-09

1.0E-08

1.0E-07

1.0E-06

1.0E-10 1.0E-09 1.0E-08 1.0E-07 1.0E-06

kv

Mea

sure

d (

m/s

)

kh Estimated (m/s)

Chai et al. (2011)

Modified Method

kh=kv

105

5.9. Conclusions

Most existing methods for estimating the field permeability in the horizontal direction (kh)

from the results of piezocone sounding (uCPT) results related kh to 0'v

u

ratio (∆u is

measured excess pore pressure and σv0 is initial vertical effective stress at a depth

considered), but do not consider the effect of overconsolidation ratio (OCR) on0'v

u

.

Therefore, they are not applicable for a overconsonsolidated deposit. Based on the results of

laboratory model tests of piezocone penetration (uCPT) conducted in this study, a modified

method has been proposed.

In case of estimating the value kh corresponding to yielding vertical effective stress, the

proposed method needs two parameters, namely, OCR and a model parameter, α. While if the

value of kh corresponding to the initial vertical effective stress is required, two more

parameters, i.e. swelling index (Cs) and the initial void ratio (e0) are needed. It is suggested

that Cs and e0 have to be estimated based on local data-base about soil properties; and OCR

and α can be estimated using the results of uCPT.

The modified method has been applied to three (3) field cases. The measured values of

permeability in vertical direction (kv) from oedometer test were available at all the sites. By

comparing the estimated values of kh from the results of uCPT and the measured values of kv,

it shows that the modified method resulted in much better estimation of the values of kh.

106

CHAPTER SIX

SUMMARY, CONCLUSIONS AND RECOMMENDATIONS

6.1 Summary

Since there are many equations mentioned in this study, the summary of all existing

methods, proposed method and modified method are rehearsed in this section.

6.1.1 Methods for estimating OCR

Existing methods

(1) Undrained shear strength (su) approach (Method 1)

1/

0

0

1

'

m

t v

vkt

qOCR

N S

(2.10 bis)

For underconsolidated deposits

0

0

1

'

t v

kt v

qOCR

N OCR S

(3.6 bis)

where S and m are constants, v0 is effective vertical stress, qt is corrected tip resistance and

Nkt is a cone bearing factor.

(2) Normalized tip resistance (Qt) approach (Method 2)

0

0't v

v

qOCR k

(2.11 bis)

where k is a constant and v0 is total vertical stress.


0

0't v

v

qOCR k

OCR

(3.7 bis)

107

(3) Approach based on cavity expansion and critical state soil mechanics theories (Method 3)

1/

2

0

12

1.95 1 't

v

q uOCR

M

(2.21 bis)


1/

2

0

12

1.95 1 '

t

v

q uOCR

M OCR

(3.8 bis)

where M is the slope of critical state line in p - q plot (p is mean effective stress and q is

deviator stress), M=6 sin '

3 sin '

), u2 = measured pore pressure at the shoulder of the cone, and

= 1 – κ/λ (λ and κ are slopes of virgin loading and unloading-reloading curves in void ratio, e

versus ln(p) plot).

Proposed method

1/1/1 2

0

2 2

2

'

t v

kt

q MOCR

N Mp M

(3.4 bis)


1/1/1 2

0

2 2

2

' OCR

t v

kt

q MOCR

N Mp M

(3.5 bis)

where p = σv0(1+2K0)/3, η=q/p, q= (1-K0)σv0. K0, and sin '

0(1 sin ')K OCR

.

6.1.2 Methods for estimating ch

Existing methods

Standard dissipation curves

108

* 2

50

r

h

T R Ic

t (2.25 bis)

where T* = modified time factor corresponding to 50% degree of consolidation. For pore

pressure filter located at the shoulder of the cone, T* = 0.245, R is radius of the cone, and Ir is

rigidity index (Ir = G/Su) where G is the shear modulus, and su is undrained shear strength.

Non-standard dissipation curves

50

50 0.67 0.3

max

50

1 18.5200

c

u r

tt

t I

t

(2.26 bis)

where t50c is the corrected time for 50% dissipations of the measured maximum excess pore

water pressure, tumax is the time for measured excess pore pressure to reach its maximum

value.

6.1.3 Methods for estimating kh

Existing methods

Chai et al. (2011)’s method

For BqQt ≤ 0.45 1

D

q t

KB Q

(2.30bis)

and for BqQt > 0.45 4.91

0.044

( )D

q t

KB Q

(2.31bis)

02 '

D wh

v

K U Rk

(2.32 bis)

where kh is the permeability of soil in horizontal direction, u2 is the absolute pore water

pressure measured by the piezocone, us is the initial hydrostatic pore water pressure, γw is the

109

unit weight of water, KD is a dimensionless soil permeability index, Qt is the normalized cone

resistance, and Bq is the pore pressure ratio.

Modified method

0 0' 'v vOC NC

u u OCR

(5.4 bis)

where 0'v NC

u

is the ratio of 0'v

u

corresponding to normally consolidated state,

0'v OC

u

is the ratio of 0'v

u

corresponding to overconsolidated state, and α is a

model parameter.

The value of kh0 corresponding to yielding vertical effective stress (σ vmax) can be

calculated as:

0

02 '

D wNCh

v

K Uak

OCR

(5.5 bis)

The value of kh (OCR > 1.0) corresponding to initial vertical effective stress (σv0) can be

calculated as:

0

21

02 '

s

D wNCh C

e

v

K Uak

OCR

(5.6 bis)

where Ck is a constant (Ck =0.5e0), ∆e is the change of void ratio and Cs is swelling index.

6.2 Conclusions

This study focused on using the results of piezocone sounding (uCPT) and dissipation

tests to estimate overconsolidation ratio (OCR) and consolidation properties (ch and kh) of

soil. Currently, several existing methods for estimating OCR from uCPT results are ranging

from empirical to theoretical approaches. To further increase the accuracy of the estimated

value of OCR from the results of uCPT, a new method for estimating the value of OCR based

on Modified Cam Clay theory has been proposed and evaluated using twelve (12) field cases

around the world. Based on the laboratory model test and analysis results, the existing

110

m ethods for estim ating perm eab ility (kh) from uCPT results a re no t applicab le to

overconsolidated soils. Then a modified method for estimating (kh) from uCPT has been

proposed and validated.

6.2.1 Proposed method for estimating OCR

The applicability of three (3) existing methods for estimating OCR from uCPT has been

investigated with twelve (12) field cases around the world. All of existing methods have

empirical parameters, and if the empirical parameters can be determined properly, reasonable

values of OCR can be estimated. However for underconsolidated deposits, some of existing

methods performed poorly. Therefore, a new method for estimating the value of OCR based

on Modified Cam Clay theory has been proposed and some modifications of existing method

to be applicable for underconsolidated sites have been carried out. Finally, the proposed

method and the modified existing methods have been evaluated using field data and it is

shown that the proposed method can yield better results.

6.2.2 Evaluating the existing methods for ch and kh

(1) Laboratory model tests.

The laboratory model ground was prepared in a cylindrical container (chamber) made of

PVC and has an inner diameter of 0.485 m and a height of 1.0 m. The soils were thoroughly

mixed with a water content of about 1.2 times their liquid limits (LL), and carefully poured

into the chamber layer by layer until the thickness of the model ground was 0.8 m.

Piezometers were placed at pre-determined locations in the model to measure the pore water

pressure during pre-consolidation process. An air pressure was applied to pre-consolidate the

model ground. Once the degree of pre-consolidation was more than 95%, the air pressure was

adjusted to achieve the desired value of OCR. After the pre-consolidation, the thickness of

the model ground was about 0.6 m. In case of OCR > 1.0, unloading would induce negative

pore pressure in the model ground. In this kind of case, the piezocone penetration and

dissipation was conducted after the negative excess pore pressure dissipated. Two mini

piezocones (u2) have cone tip angle of 60˚ with diameters of 30 mm 20 mm were used in the

laboratory test. The filter for pore pressure measurement is on the shoulder of the cones. The

penetration rate adopted was 25 mm/min (0.4 mm/s).

111

Five types of soil, namely, remolded Ariake clay, Ariake clay mixed with a sand with

sand/clay ratios (by dry weight) of 50:50 (Mixed soil 1), 60:40 (Mixed soil 2), 70:30 (Mixed

soil 3), and 20:80 (Mixed soil 4), respectively were used in the laboratory model tests. The

values of OCR adopted were 1, 2, 4, and 8. Totally fifteen (15) cases were conducted.

(2) Existing method for ch.

From dissipation test results, all measured dissipation curves are non-standard type


method is used for estimating the coefficient of consolidation (ch) from uCPT laboratory

model test results. As a result, the method performed reasonably well for all soil types. (For

Mixed soils; results are lying between ratios of ch/cv of 0.2 to 1.0, and for Ariake clay; results

are line between ratios of ch/cv of 1.0 to 2.0). Therefore it is recommended that the method can

be used in engineering practice of estimating ch from the results of piezocone dissipation test.

(3) Existing method for kh.

Chai et al. (2011) proposed a method for estimating k h from the results of uCPT.

Applying the method to the model test results indicates that, the method performed poorly for

overconsolidated soils. It can be seen that under the condition of a given maximum


estimated values of kh decreased with OCR significantly for all the soil types.

6.2.3 Modified method for estimating kh

Chai et al. (2011)’s method has been modified to be applicable for overconsolidated soils.

Since in the method, kh is a function of0'v

u


pressure and σv0 is the initial effective vertical stresses), the basic idea of the modified

method is to include the effect of OCR on0'v

u

. In case of estimating the value kh

corresponding to yielding vertical effective stress, the proposed method needs two

112

parameters, namely, OCR and a model parameter, α. While if the value of kh corresponding to

the initial vertical effective stress is required, two more parameters, i.e. swelling index (Cs)

and the initial void ratio (e0) are needed. It is suggested that Cs and e0 have to be estimated

based on local data-base about soil properties; as for OCR and α can be estimated using the

results of uCPT.

The modified method was evaluated to two (2) sites in Japan and one (1) site in China. By

comparing the estimated values of kh from the results of uCPT and the measured values of kv,

it shows that the modified method resulted in much better estimation of values of kh.

6.3 Recommendations for Further Research

To increase the applicability range of the modified method, laboratory model tests

conducted by using different soil types are needed. Moreover, numerical analysis is a

powerful tool and capable for uCPT simulations. Therefore, the uCPT simulation is also

alternative approach for this study.

113

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