1. Research Center of Coastal and Urban Geotechnical Engineering, Zhejiang University, Hangzhou 310058, China 2. Engineering Research Center of Urban Underground Development of Zhejiang Province, Zhejiang University, Hangzhou 310058, China
A series of experiments were conducted by triaxial permeameter to analysis the permeability anisotropy of soft soil. The effects of electrolyte type, ionic molar concentration and consolidation pressure on permeability anisotropy and the corresponding microscopic mechanisms were investigated, with remolded kaolin as the research object. Results showed that under one-dimensional consolidation, kaolin particles, most having flat structure, tended to orientate perpendicularly to the direction of the major principal stress and the pore area of remolded kaolin in vertical profile was much larger than that in horizontal profile. As a result, permeability anisotropy ratio (ratio of horizontal to vertical permeability coefficients) was greater than one. Permeability anisotropy ratio decreased with the increase of consolidation pressure, of which the main reason was that the amount of large pores, which had higher compressibility, in vertical profile was larger than that in horizontal profile. Malaysia kaolin has flocculated structure if prepared in ultrapure water, while has dispersed structure in saline solution. The measured permeability anisotropy ratio in ultrapure water was larger than that in saline solution, which was the consequence of more large pores in vertical profile than that in horizontal profile in ultrapure water. The vertical and horizontal profiles had similar amounts of large pores in saline solution. Test results also revealed that the electrolyte type and ionic molar concentration had little effect on the permeability anisotropy ratio of Malaysia kaolin.
Tab.2Differences between inflow and outflow in S1HP1 and S3HP1 tests and horizontal permeability coefficients
Fig.1Radial strain curve of S1HP1 in process of consolidation and seepage
土样
离子 种类
cB/ (mol?L?1)
p/kPa
${k_{\rm h}}$/ (10?7 cm?s?1)
${k_{\rm v}}$/ (10?7 cm?s?1)
${r_k}$
S1
超纯水
?
100
21.19
15.28
1.39
200
16.12
12.24
1.32
300
12.38
10.27
1.21
S2
钠离子
0.10
100
12.87
10.75
1.20
200
9.90
8.46
1.17
300
7.16
6.72
1.07
S3
钾离子
0.10
100
14.86
12.31
1.21
200
10.57
9.17
1.15
300
8.56
7.73
1.11
S4
钙离子
0.10
100
10.77
9.39
1.15
200
8.41
7.44
1.13
300
5.95
5.55
1.07
S5
钠离子
0.01
100
13.66
11.56
1.18
S6
钾离子
0.01
100
14.07
11.71
1.20
S7
钙离子
0.01
100
11.89
9.80
1.21
Tab.3Experimental data of permeability anisotropy ratios of remolded kaolin prepared with different solutions under various pressures
Fig.2Sketch of particles arrangement of remolded kaolin
Fig.3Permeability anisotropy ratios of remolded kaolin prepared with different solutions under various pressures
Fig.4Portable pH meter
Fig.5Relationship between pore ratio and vertical permeability coefficient of kaolin under different microstructures
Fig.6Sketch of microstructures of remolded kaolin prepared with 0.10 mol/L KCl solution and ultrapure water
Fig.7Relationship between permeability anisotropy ratio of remolded kaolin and consolidation pressure at different solutions
Fig.8SEM binary images of remolded kaolin prepared with ultrapure water and 0.10 mol/L KCl solution under consolidation pressure of 100 kPa
Fig.9SEM binary images of remolded kaolin prepared with ultrapure water and 0.10 mol/L KCl solution under consolidation pressure of 300 kPa
S/像素
竖向孔隙数量
水平向孔隙数量
100 kPa
300 kPa
100 kPa
300 kPa
0~50
951
381
872
349
50~200
149
64
175
40
200~500
31
9
24
2
500~1 000
9
0
1
0
1 000~2 000
4
0
0
0
>2 000
1
0
0
0
合计
1 145
454
1 072
391
$\bar S$/像素
47.1
34.02
35.75
28.26
Tab.4Pore distribution of remolded kaolin prepared with ultrapure water under consolidation pressure of 100 kPa and 300 kPa
Fig.10Curves between permeability anisotropy ratio and logarithm of ion concentration of remolded kaolin prepared with different solutions
溶液类型
0.01 mol/L
0.10 mol/L
ωL
ωP
ωL
ωP
超纯水
65.35
40.04
65.35
40.04
氯化钠
63.99
42.61
59.67
40.25
氯化钾
63.36
42.36
59.22
40.33
氯化钙
63.12
41.03
58.89
40.18
Tab.5Liquid and plastic limits of remolded kaolin prepared with different solutions
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