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

2005 ◽  
Author(s):  
a-Te ◽  
Limin Zhang ◽  
Delwyn G. Fredlund
Keyword(s):  
Unsaturated Soils ◽  
Phase Permeability ◽  
Permeability Function

A Flexible Wall Permeameter for the Determination of the Water Permeability Function in Unsaturated Soils

2011 ◽  
Vol 34 (5) ◽  
pp. 103595
Author(s):  
L. D. Suits ◽  
T. C. Sheahan ◽  
M. P. H. Moncada ◽  
T. M. P. de Campos ◽  
G. Steger
Keyword(s):  
Water Permeability ◽  
Unsaturated Soils ◽  
Permeability Function ◽  
Flexible Wall

scholarly journals Examination of the estimation of relative permeability for unsaturated soils

2015 ◽  
Vol 52 (12) ◽  
pp. 2077-2087 ◽  
Author(s):  
Feixia Zhang ◽  
D.G. Fredlund
Keyword(s):  
Lower Limit ◽  
Unsaturated Soils ◽  
Integral Formula ◽  
Characteristic Curve ◽  
Soil Conditions ◽  
Mathematical Algorithm ◽  
Soil Systems ◽  
Permeability Function ◽  
Unsaturated Permeability ◽  
Flexible Integration

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.

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

1994 ◽  
Vol 31 (4) ◽  
pp. 533-546 ◽  
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.

Permeability function for unsaturated soils with different initial densities

2014 ◽  
Vol 51 (12) ◽  
pp. 1456-1467 ◽  
Author(s):  
Guoqing Cai ◽  
Annan Zhou ◽  
Daichao Sheng
Keyword(s):  
Unsaturated Soils ◽  
Initial Density ◽  
Degree Of Saturation ◽  
Water Retention Curve ◽  
Additional Parameter ◽  
Soil Water Retention Curve ◽  
Soil Water Retention ◽  
Density Dependent ◽  
Initial Void Ratio ◽  
Permeability Function

This study proposes an approach to simulate the effects of initial density on the relative coefficient of permeability for unsaturated soils. The density-dependent permeability function is derived based on (i) an incremental relationship between the degree of saturation and the initial void ratio with various suctions and (ii) the relationship between the permeability function and the soil-water retention curve (SWRC). Only one additional parameter is required in the proposed function, which can be calibrated using a conventional SWRC test. A number of test results in the literature are employed to validate the proposed density-dependent permeability function, and the model predictions indicate good agreement with the experimental data in the literature.

Use of instantaneous profile and statistical methods to determine permeability functions of unsaturated soils

2009 ◽  
Vol 46 (7) ◽  
pp. 869-874 ◽  
Author(s):  
Henry Krisdani ◽  
Harianto Rahardjo ◽  
Eng-Choon Leong
Keyword(s):  
Statistical Method ◽  
Unsaturated Soils ◽  
Pore Water Pressure ◽  
Direct Method ◽  
Water Pressure ◽  
Residual Soils ◽  
Profile Method ◽  
Permeability Function ◽  
Direct And Indirect Methods

This paper presents the determination of permeability functions by direct and indirect methods. The direct method used in this study was the instantaneous profile method, while the indirect method used was the statistical method. The instantaneous profile method was adopted to calculate permeability functions of residual soils used in laboratory slope models. Pore-water pressure measured using tensiometers along the slope models and independently measured soil-water characteristic curves (SWCCs) were used for the instantaneous profile calculation. To obtain a continuous permeability function, the instantaneous profile results were then fitted using the statistical method.

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