A novel approach for modelling soil water characteristic curves with hysteresis

Soil-water characteristic curves can be defined as the relationship between the degree of saturation and suction of an unsaturated soil. Geomaterials, such as clays, sands, and geotextiles, usually exhibit hysteresis between drying and wetting curves. In addition, each drying and wetting curve is nonlinear in shape, which may be approximated by sigmoid curves. In geotechnical engineering, it is common to adopt analytical expressions for these curves that must be calibrated iteratively by trying different values for the constitutive parameters. In this paper, a novel approach for modelling the nonlinear saturation-suction response with hysteresis is presented, where a simple differential equation is introduced to describe the shapes of the curves. The great advantage of this new technique is the ease with which the parameters can be determined. In addition, the implementation of the resulting equations into fully hydro-mechanical models for numerical analyses is straightforward. Some features of the behaviour predicted with the new representation are studied and validations against real laboratory curves for soils are presented. The technique is simple, yet versatile due to the rational basis used in the deduction of the equations, which allows for future extensions to soils displaying more complex unsaturated behaviour. (C) 2009 Elsevier Ltd. All rights reserved.