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Sciences in Cold and Arid Regions ›› 2021, Vol. 13 ›› Issue (5): 394-407.doi: 10.3724/SP.J.1226.2021.21033.

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Numerical simulation of electroosmosis in unsaturated compacted clay

KangWei Tang,Feng Zhang(),DeCheng Feng,GuanFu Wang   

  1. School of Transportation Science and Engineering, Harbin Institute of Technology, 73 Huanghe Road, Harbin, Heilongjiang 150090, China
  • Received:2021-05-06 Accepted:2021-09-08 Online:2021-10-31 Published:2021-12-03
  • Contact: Feng Zhang E-mail:zhangf@hit.edu.cn

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Abstract:

The moisture content of a road subgrade in cold regions will increase after freeze-thaw cycles, resulting in subgrade strength and stiffness losses. Electroosmosis is widely used in treating saturated soft soils to decrease the moisture content. The induced moisture migration during electroosmosis in unsaturated soil is much more complex than that of saturated soil because of a series of nonlinear changes in soil properties. This study first uses an exponential function to characterize the relationship between electroosmotic permeability and saturation degree. Then, a one-dimensional model is developed to simulate the electroosmosis-induced moisture migration in unsaturated soil. Simulation results show that electroosmosis reduces the saturation degree of the unsaturated soil, indicating that it can be applied to subgrade dewatering. Key parameters such as soil pore size distribution coefficient, air entry value, and effective voltage significantly affect moisture migration. Electroosmotic properties of unsaturated soils are extremely important to the efficiency of electroosmosis.

Key words: electro-osmosis, unsaturated clay, moisture migration, numerical simulation

Figure 1

One-dimensional model for electroosmosis in unsaturated soil: (a) configuration of electroosmosis; (b) moisture migration through a differential unit"

Table 1

Geotechnical properties and calculation parameters of clay soil"

ParameterValue
Pore size distribution coefficient n2.2
Symmetry parameters of soil-water characteristic curve m1-1/n
Reciprocal of air entry value α0.03
Relative electro-osmotic permeability parameter m20.4
Soil conductivity parameter A0.077858
Soil conductivity parameter B2.051

Table 2

Geotechnical properties and calculation parameters of clay soil"

PropertyValue
Specific gravity2.75
Liquid limit36.98%
Plastic limit25.19%
Plastic index11.79
Maximum dry density1.74 g/cm3
Optimum moisture content17.4%
Initial void ratio0.99
Moisture at saturation50.0%
Residual moisture0.3%
Saturated electroosmotic permeability6ⅹ10-7 m2/(V·s)
Saturated hydraulic permeability5ⅹ10-7 m/s

Figure 2

Custom-made apparatus for one-dimensional electroosmosis test on unsaturated soil (length unit: mm)"

Figure 3

Effective voltage versus time recorded during the electroosmosis experiment"

Figure 4

Comparison of moisture content versus time between the numerical simulation and experiment"

Figure 5

Comparison of the drainage between the model simulation and experiment"

Table 3

Parameter analysis of electroosmosis in unsaturated clay"

ParameterValue
Pore size distribution coefficient n2.2, 5, 10, respectively
Symmetry parameters of soil-water characteristic curve m1-1/n
Reciprocal of air entry value α (k/Pa)0.01, 0.03, 0.05, respectively
Relative electro-osmotic permeability parameter m20.4
Soil conductivity parameter A0.077858
Soil conductivity parameter B2.051
Effective voltage Ue (V)10, 30, 40, respectively

Figure 6

Moisture content change and drainage development versus time for different values of n"

Figure 7

Moisture content change and drainage development versus time for different values of α"

Figure 8

Moisture content change and drainage development versus time for different values of Ue"

Figure 9

Moisture content change and drainage development versus time for different values of m2"

Figure 10

Moisture distribution and average saturation after electroosmosis for different values of m2"

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