Bimodal Soil-water Characteristic Curve Research Articles

Water characteristic curve of soil with bimodal grain-size distribution

Soil–water characteristic curve (SWCC) is the most fundamental and important soil property in unsaturated soil mechanics. It has been used for analyzing slope stability due to the infiltration of rainfall into slopes and water flow in unsaturated embankments. Generally, SWCC is obtained by laboratory tests. However high cost, long duration and difficulty of the tests impede the application of unsaturated soil mechanics to practical design or analysis. Therefore, several equations have been developed to predict the SWCC using grain-size distribution (GSD) curve. However, most of the equations were limited to soils with unimodal characteristics and the parameters of the equations are not related to the physical properties of the soil. In this paper, an equation to predict SWCC for soils with bimodal characteristics is proposed. The parameters of the proposed equation are related to the physical properties of soil and the variables of SWCC closely. The proposed equation is evaluated with data from the literature and laboratory tests carried out in this study. In addition, the computer codes for the computation of the predicted bimodal SWCC are presented.

Predicting Bimodal Soil–Water Characteristic Curves

Failure of colluvial soil deposits induced by rainfall is a common geohazard in the natural terrain. Many colluvial soils are widely and gap graded with a minimal sand fraction. In order to study the pore water pressures in such gap-graded, unsaturated soil deposits through a seepage analysis and to evaluate the stability of these soil deposits, the soil-water characteristic curves for gap-graded soils must be known. Usually, gap-graded soils exhibit bimodal grain-size and pore-size distributions. This technical note presents a theoretical continuum method for the determination of soil-water characteristic curves for soils with a bimodal or multimodal pore-size distribution. Based on the capillary law, the water content in a multimodal soil is equal to the sum of water stored in each pore series in the soil. Therefore, the bimodal or multimodal soil-water characteristic curves can be obtained by combining the unimodal soil-water characteristic curves for all components of the soil corresponding to the pore series weighted by the respective volumetric percentages. The proposed method is verified using experimental soil-water characteristics data of sand-diatomaceous earth mixtures with dual porosity.

Soil-Water Characteristic Curve Equation with Independent Properties

The soil-water characteristic curve (SWCC) has traditionally been represented using equations whose fitting parameters do not individually correspond to clearly defined soil properties or to features of the curve. As a result, unique sets of parameters are often nonexistent, and sensitivity analyses and statistical assessments of SWCC parameters become difficult. In order to overcome these difficulties, a new class of equations to represent unimodal and bimodal SWCCs is proposed. The chosen fitting parameters are the air-entry value, the residual suction, the residual degree of saturation, and a parameter that controls the sharpness of the curvatures. The physical meaning for the soil parameters is discussed for different soil types. A unique relation between each of the equation parameters and the individual features of SWCCs is assured. The proposed equations are fitted to data corresponding to a variety of soil types and a good fit is observed.

Soil-Water Characteristic Curves and Dual Porosity of Sand–Diatomaceous Earth Mixtures

The soil-water characteristic curves (SWCCs) for sand–pelletized diatomaceous earth mixtures are measured. The measured SWCCs are bimodal due to two distinct pore-size distributions associated with the microscopic (intrapellet) and macroscopic (interpellet) porosity regions of the pelletized diatomaceous earth. The measured data for the bimodal SWCCs are fit with modified forms of the Brooks-Corey, van Genuchten, and Fredlund-Xing SWCC functions, and the microscopic and macroscopic porosity portions of the mixtures are determined from the SWCC fits. Both the total and the microscopic porosity of the mixtures increase with increased percentage by dry weight of diatomaceous earth in the mixtures. However, the macroscopic porosity of the mixtures is essentially independent of the diatomaceous earth content due to the similarity in the particle-size distributions of the sand and the diatomaceous earth. The results suggest that sand–diatomaceous earth mixtures may be useful in applications where an increase in...

Evaluating dual porosity of pelletized diatomaceous earth using bimodal soil-water characteristic curve functions

Evaluating dual porosity of pelletized diatomaceous earth using bimodal soil-water characteristic curve functions