Determination of unsaturated permeability function for clayey silt

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.

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New approach to improve soil-water characteristic curve to reduce variation in estimation of unsaturated permeability function

Canadian Geotechnical Journal ◽

10.1139/cgj-2015-0199 ◽

2016 ◽

Vol 53 (4) ◽

pp. 717-725 ◽

Cited By ~ 9

Author(s):

Arezoo Rahimi ◽

Harianto Rahardjo

Keyword(s):

Soil Water ◽

Distribution Curve ◽

Characteristic Curve ◽

New Approach ◽

Soil Water Characteristic Curve ◽

Permeability Function ◽

Wide Range ◽

Unsaturated Permeability ◽

Complete Measurement ◽

Data Points

The unsaturated permeability function is often estimated from the soil-water characteristic curve (SWCC) of a soil. A complete SWCC measurement can improve the estimation of the unsaturated permeability function. In most laboratories, the SWCC can be measured up to a suction of 100 kPa using a Tempe cell. However, complete measurement of the SWCC is an expensive and time-consuming task. Therefore, this paper presents a new approach to estimate SWCC data points beyond 100 kPa suction to complement the SWCC measured up to a suction of 100 kPa. The new SWCC is then used to estimate the unsaturated permeability function. The proposed approach uses knowledge of the grain-size distribution curve and measured SWCC data at 100 kPa suction to estimate the SWCC data points beyond 100 kPa suction. To verify the proposed procedure, SWCC tests were conducted over a wide range of suctions for coarse kaolin and a triaxial permeameter system was used to directly measure unsaturated permeability of the coarse kaolin. The proposed procedure is found to reduce the variation between unsaturated permeability functions estimated by various estimation models.

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Prediction and modeling of permeability function and its application to the evaluation of breakthrough suction of a two-layer capillary barrier

Canadian Geotechnical Journal ◽

10.1139/cgj-2016-0339 ◽

2017 ◽

Vol 54 (6) ◽

pp. 778-788 ◽

Cited By ~ 9

Author(s):

W.M. Yan ◽

C.F. Chiu ◽

Ka-Veng Yuen

Keyword(s):

Joint Probability ◽

Water Retention Curve ◽

Capillary Barrier ◽

Empirical Formulas ◽

Deterministic Method ◽

Retention Curve ◽

Permeability Function ◽

Unsaturated Permeability ◽

Silty Loam ◽

Joint Probability Density

Different empirical formulas have been proposed to describe the water retention curve (WRC) and relative permeability (kr) of soils. This paper presents a Bayesian framework that evaluates not only the most probable empirical fitting constants, but also their joint probability density function. A dataset containing two soil classes — sand and silty loam — compiled from the UNSODA database is used for illustration. First, model constants of the van Genuchten’s WRC formula are calibrated and subsequently used to predict kr of the studied soils using two existing formulas based on Mualem’s and Burdine’s models. The best estimated kr in both formulas is found to skew towards the lower side of the measurement. Then, a new three-parameter empirical formula is proposed to describe kr with suction while the model constants are calibrated from the permeability data. Using the proposed framework, the statistical distribution of kr and subsequently the unsaturated permeability (kunsat), as a function of suction, can be obtained. The results are then applied to a hypothetical two-layer capillary barrier composed of soils of the compiled dataset to determine the breakthrough suction (ψBT) of the barrier. The proposed Bayesian approach gives a probabilistic distribution of ψBT instead of a single value in the traditional deterministic method.

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Laboratory testing of seepage in concrete

E3S Web of Conferences ◽

10.1051/e3sconf/202019503030 ◽

2020 ◽

Vol 195 ◽

pp. 03030

Author(s):

Miklós Pap ◽

András Mahler ◽

Salem Georges Nehme

Keyword(s):

Water Retention ◽

Water Retention Curve ◽

Underground Structures ◽

Pore System ◽

Retention Curve ◽

Soil Function ◽

Concrete Mixtures ◽

Permeability Function ◽

Flow Through

Due to the construction of underground structures and hazardous waste storages, understanding and modelling of water flow through concrete has become a major topic for life-span analyses. The water retention curve (WRC) is an essential unsaturated soil function, which can be determined not only for soil samples, but also for other porous media. This paper deals with the determination of drying water retention curve for six different concrete mixtures that provide a substantial characteristic for the investigation and modelling of seepage through the pores of concrete. According to the complex pore system of the concrete, the bimodal function of van Genuchten (1980) and Fredlund and Xing (1994) models were used for curve fitting. The fitted curves were used to estimate the permeability function using Fredlund et. al (1994) model.

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