Coupling of a water permeability function with a bounding surface hydromecahnical model for unsaturated soils

The unsaturated permeability function is an important soil property function used in the numerical modeling of saturated–unsaturated soil systems. The permeability function is generally predicted by integrating along the soil-water characteristic curve (SWCC) starting at saturated soil conditions. The integration is based on a particular integral formula. The Fredlund–Xing–Huang permeability function is a flexible integration technique used for calculating the unsaturated permeability function. The original permeability theory published by Fredlund, Xing, and Huang in 1994 specified that the air-entry value (AEV), ψaev, be used as the lower limit of the integration when calculating the permeability function. However, as there was no analytical procedure available for the calculation of the AEV on the SWCC, it became common practice to start the integration procedure from a value near zero. The assumption was made that the error associated with starting the integration from an arbitrary low value was minimal. While this might be the case in some situations, the error can be quite substantial in other situations. This paper undertakes a study of the effect of the lower limit of integration on the calculation of the permeability function. Comparisons are made between starting the integration from various values below the AEV and starting the integration from the calculated AEV, ψaev. A mathematical algorithm is also proposed for the calculation of the AEV for integration purposes. The results show that the relative coefficient of permeability can be significantly underestimated when the lower limit of integration is smaller than the AEV. The recommendation is that the AEV always be used as the lower limit of integration in the Fredlund–Xing–Huang permeability equation.

Download Full-text

A Bounding Surface Plasticity Model for Unsaturated Soils Accounting for the Void Ratio Dependency of the Water Retention Curve

Poromechanics VI ◽

10.1061/9780784480779.132 ◽

2017 ◽

Cited By ~ 1

Author(s):

H. Moghaddasi ◽

G. Alipour Esgandani ◽

A. Khoshghalb ◽

B. Shahbodagh-Khan ◽

N. Khalili

Keyword(s):

Unsaturated Soils ◽

Water Retention ◽

Void Ratio ◽

Water Retention Curve ◽

Plasticity Model ◽

Bounding Surface ◽

Retention Curve ◽

Bounding Surface Plasticity ◽

Surface Plasticity

Download Full-text

A new constitutive model of unsaturated soils using bounding surface plasticity (BSP) and a non-associative flow rule

Innovative Infrastructure Solutions ◽

10.1007/s41062-016-0005-z ◽

2016 ◽

Vol 1 (1) ◽

Cited By ~ 7

Author(s):

Ba Tien Lai ◽

Henry Wong ◽

Antonin Fabbri ◽

Denis Branque

Keyword(s):

Constitutive Model ◽

Unsaturated Soils ◽

Flow Rule ◽

Bounding Surface ◽

Bounding Surface Plasticity ◽

Surface Plasticity

Download Full-text

A General Air-phase Permeability Function for Airflow through Unsaturated Soils

Slopes and Retaining Structures Under Seismic and Static Conditions ◽

10.1061/40787(166)29 ◽

2005 ◽

Cited By ~ 2

Author(s):

a-Te ◽

Limin Zhang ◽

Delwyn G. Fredlund

Keyword(s):

Unsaturated Soils ◽

Phase Permeability ◽

Permeability Function

Download Full-text

A Bounding Surface Viscoplastic Constitutive Model for Unsaturated Soils

Poromechanics VI ◽

10.1061/9780784480779.130 ◽

2017 ◽

Cited By ~ 1

Author(s):

Thi Ngoc Mac ◽

Babak Shahbodagh ◽

Nasser Khalili

Keyword(s):

Constitutive Model ◽

Unsaturated Soils ◽

Bounding Surface

Download Full-text

Predicting the permeability function for unsaturated soils using the soil-water characteristic curve

Canadian Geotechnical Journal ◽

10.1139/t94-062 ◽

1994 ◽

Vol 31 (4) ◽

pp. 533-546 ◽

Cited By ~ 445

Author(s):

D.G. Fredlund ◽

Anqing Xing ◽

Shangyan Huang

Keyword(s):

Water Content ◽

Soil Water ◽

Unsaturated Soil ◽

Unsaturated Soils ◽

Characteristic Curve ◽

Degree Of Saturation ◽

Residual Water ◽

Soil Water Characteristic Curve ◽

Coefficient Of Permeability ◽

Permeability Function

The coefficient of permeability for an unsaturated soil is primarily determined by the pore-size distribution of the soil and can be predicted from the soil-water characteristic curve. A general equation, which describes the soil-water characteristic curve over the entire suction range (i.e., from 0 to 106 kPa), was proposed by the first two authors in another paper. This equation is used to predict the coefficient of permeability for unsaturated soils. By using this equation, an evaluation of the residual water content is no longer required in the prediction of the coefficient of permeability. The proposed permeability function is an integration form of the suction versus water content relationship. The proposed equation has been best fit with example data from the literature where both the soil-water characteristic curve and the coefficient of permeability were measured. The fit between the data and the theory was excellent. It was found that the integration can be done from zero water content to the saturated water content. Therefore, it is possible to use the normalized water content (volumetric or gravimetric) or the degree of saturation data versus suction in the prediction of the permeability function. Key words : coefficient of permeability, soil-water characteristic curve, unsaturated soil, water content, soil suction.

Download Full-text