A hyperbolic model for volume change behavior of collapsible soils

Finite element computer programs are frequently used to analyze and design embankments and similar earth structures. In most of the available computer programs, lack of a proper constitutive relationship to deal with volume change when an increase in the degree of saturation occurs, namely collapse phenomena, is a major handicap. In this paper, volume change results obtained from isotropic compression tests conducted on unsaturated compacted soil specimens are presented. Dependence of the bulk modulus of the soil on water content is investigated. Next, a hyperbolic formulation for volume change behavior of unsaturated soils taking into account variation of soil water content is presented. This hyperbolic model relates mean applied stress, volume change, and water content and represents a three-dimensional surface, the so-called "state surface". Suitability of the proposed model to predict collapse phenomena is verified by examining the model prediction against available experimental data.Key words: hyperbolic, unsaturated soil, collapse, volume change, suction pressure, bulk modulus.