Effect of leaching on geotechnical properties of Busan marine clay and stabilized dredged clay
- Abstract
- In coastal area of Busan, marine clay deposit usually contains soluble salt in soil skeleton pores and dredged clay taken from navigation channels or construction sites also has a lot of salt in clayey soil. The amount of soil salinity depends on the concentration of salt in the seawater and changes with geological environment over long periods. Natural marine clay deposited in seawater condition tends to have high void ratio and high strength, low compressibility due to flocculated structure. In Busan marine clay consisted of the upper and lower clay deposits, the soil salinity of lower clay layer is significantly lower than that of upper clay layer, which results in higher settlement in this clay. Moreover, salt has some negative effect on strength development and compressibility for stabilized dredged clay as dredged clay is mixed with cement.
A leaching process can change the natural marine clay and salt-rich dredged clay into leached clay and non-salt dredged clay, respectively. This process causes the change in geotechnical properties not only in natural marine clay but also in stabilized dredged clay. Moreover, few researches have been carried out on the leaching effect on the geotechnical properties of Busan marine clay, neither in undisturbed state nor in stabilized dredged clay. Therefore, the objective of this study is to evaluate how leaching affects the geotechnical properties of Busan leached marine clay and non-salt dredged clay in comparison with unleached marine clay and salt-rich dredged clay, respectively.
In this study, soil salinity is checked using the CPC-401 salinity meter with the soil-extract method. The in-situ salinity of unleached marine clay and salt-rich dredged clay is about 16-18 g/l and 28-30 g/l, respectively. The leaching process is a time-consuming procedure to obtain unleached clay and non-salt dredged clay. For natural marine clay, leaching process to obtain a leached specimen required permeating distilled water from the top to the bottom of the specimen. In order to get leached undisturbed specimens from unleached undisturbed specimens after leaching, the constant rate of strain (CRS) equipment is modified to perform the leaching process in the cell chamber. Leached specimen is assumed to reach the soil salinity of 3 g/l obtained after about 25 days. For salt-rich dredged clay, the leaching process is soil-washing using fresh water several times until the soil salinity reaches 0g/l. The non-salt dredged clay is obtained after 6 times of soil-washing, then dried in natural condition to have same initial water content of salt-rich dredged clay.
In this investigation, the effect of leaching on geotechnical properties of both Busan marine clay and stabilized dredged clay were experimentally evaluated. The experimental method of investigation consists of determining the physical properties, unconfined compressive strength, stress-strain and compressibility characteristics of both the unleached and leached specimens. The behavior characteristics of the leached and unleached marine clay specimens were evaluated using several series of constant rate of strain (CRS) tests with various strain rates. While the non-salt and salt-rich dredged clays are mixed with cement to form non-salt rich stabilized dredged material and salt-rich stabilized dredged material, which are composite geomaterials, noted as CGM-N and CGM-S, respectively. The microstructures, strength and compressibility characteristics of CGM-N and CGM-S were assessed using scanning electronic microscope (SEM), unconfined compression test, and oedometer test at 7 and 28 days of curing time.
The experimental results reveal that the compressibility of leached clay increases as its salinity decreases. However, the void ratio, Atterberg limits, and preconsolidation pressure in the leached samples are lower than those of in unleached clay after leaching and CRS test. The increased compressibility and decreased preconsolidation pressure may be induced from a weakening of the interparticle bonds in the leached soil skeleton. The CRS test results with various strain rates reveal that higher strain rates correspond with higher levels of effective stress and higher apparent preconsolidation pressure in both leached and unleached clays.
Also, experimental results exhibit that salt concentration of clayey soil affect not only to change microstructure of CGM but also to reduce the significantly the strength and yield stress of mixture. However, the compressibility of CGM-S is larger than that of CGM-N. The yield stress has linear relationship with unconfined compressive strength for all CGM mixtures with the magnitude of 0.33, regardless of non-salt or salt-rich dredged clay.
Keywords: leaching, salinity, Busan marine clay, stabilized dredged clay, strain rate, compressibility characteristics, and strength.
- Issued Date
- 2011
- Awarded Date
- 2011. 2
- Type
- Dissertation
- Publisher
- Pukyong National University
- Affiliation
- Ocean Engineering-Pukyong National University
- Department
- 대학원 해양공학과
- Advisor
- Professor Yun-Tae Kim
- Table Of Contents
- CHAPTER 1: INTRODUCTION
1.1 Overview and scientific background 1
1.1.1 Overview 1
1.1.2 Scientific background 4
1.1.2.1 Geotechnical properties of Busan clay 4
1.1.2.2 Field leaching in Busan clay 6
1.1.2.3 Dredged clay in Busan and stabilizing technique 12
1.1.2.4 Soluble salt 13
1.2 Scope and objectives 16
1.3 Organization 17
CHAPTER 2: LITERATURE REVIEW
2.1 Introduction 19
2.2 Soil structure 20
2.1.1 Early concepts 20
2.2.2 Microfabric observation methods 24
2.3 Laboratory leaching test 26
2.3.1 The salt leaching theory 26
2.3.1.1 Before leaching 27
2.3.1.2 After leaching 28
2.3.2 Leaching apparatuses 29
2.3.2.1 Rowe hydraulic cell 31
2.3.2.2 Modified oedometer equipment 32
2.3.3 Some important factors of leaching test 35
2.3.3.1 Target salinity value 36
2.3.3.2 Duration of leaching 36
2.3.3.3 Sequence of leaching test 38
2.4 Effect of leaching on geotechnical properties of marine clay 39
2.5 Consolidation by constant rate of strain (CRS) test 43
2.6 Strain rate effect on the compressibility of soft clay 46
2.7 Effect of leaching on stabilized dredged clay 50
2.8 Summary 52
CHAPTER 3: EXPERIMENTAL METHOD
3.1 Introduction 53
3.2 Definition of salinity 54
3.2.1 Water salinity 55
3.2.2 Soil salinity 55
3.3 Laboratory method for measuring salinity 56
3.3.1 CPC-401 salinity meter 56
3.3.2 Soil-extract method 57
3.3.3 Calibration step 58
3.3.4 Measuring procedure 58
3.4 Salinity measurement value 60
3.4.1 Natural marine clay 60
3.4.2 Salt-rich dredged clay 64
3.5 Laboratory leaching test 65
3.5.1 Natural marine clay 65
3.5.1.1 Diagram of leaching test 65
3.5.1.2 Modified constant rate of strain (CRS) equipment 67
3.5.2 Salt-rich dredged clay 71
3.5.2.1 Diagram of leaching test 71
3.5.2.2 Scanning electronic microscope (SEM) test 73
3.5.2.3 Unconfined compression test 73
3.5.2.4 Oedometer test 74
3.6 Summary 76
CHAPTER 4: EFFECT OF LEACHING ON GEOTECHNICAL PROPERTIES OF MARINE CLAY AND ITS RATE DEPENDENCY
4.1 Introduction 78
4.2 Materials for testing 79
4.3 Leaching procedure and CRS testing 81
4.4 Effect of leaching on physical properties 83
4.4.1 Effect of leaching on void ratio 83
4.4.2 Effect of leaching on Atterberg limits 85
4.5 Effect of leaching on compressibility characteristics and its strain rate dependency 87
4.5.1 Effect of leaching on e-log???Sv curves 87
4.5.2 Effect of leaching on stress-strain curves 91
4.5.3 Effect of leaching and strain rate on preconsolidation pressure 93
4.5.4 Effect of leaching on compression index and swelling index 98
4.5.5 Effect of leaching on hydraulic conductivity 100
4.6 Summary 103
CHAPTER 5: EFFECT OF LEACHING ON STABILIZED DREDGED CLAY
5.1 Introduction 104
5.2 Materials and leaching process 105
5.3 Experimental program 106
5.4 Effect of leaching on physical properties 108
5.4.1 Specific gravity 108
5.4.2 Unit weight 108
5.4.3 Post curing water content 110
5.4.4 Post curing initial void ratio 110
5.5 Effect of leaching on stress-strain behavior 113
5.6 Effect of leaching on unconfined compressive strength 113
5.7 Effect of leaching on compressibility characteristics 115
5.7.1 Stress-strain curves and void ratio-vertical pressure curves 115
5.7.2 Compression index and swelling index 117
5.7.3 Yield stress 119
5.8 Summary 121
CHAPTER 6: CONCLUDING REMARKS
6.1 General conclusions 122
6.1.1 Leaching process on Busan marine clay and dredged clay 122
6.1.2 Effect of leaching on physical properties 123
6.1.3 Effect of leaching on mechanical characteristics 123
6.1.3.1 Compressibility and its rate dependency of marine clay 123
6.1.3.2 Strength and compressibility of stabilized dredged clay 124
6.2 Recommendations 125
REFERENCES 126
- Degree
- Doctor
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