Constitutive model for soaking-induced volume change of unsaturated compacted expansive soil

Abstract

Several researchers have proposed models extending the independent stress state variables approach to describe the nonlinear nature of the normal consolidation line (NCL) for unsaturated soils. However, there are few models that can describe both the nonlinear nature of the NCL and the non-monotonic variation of collapse potential for unsaturated compacted expansive soils (USCES). In this paper, a constitutive relationship is proposed for the USCES that can be used for interpreting and modeling both the nonlinear NCL and non-monotonic collapse potential by taking account of the influence of macro and microstructure in the term specific volume, υ. In this model, effective degree of saturation, Se is used as one of the state variables, and υ is assumed to linearly decrease with increasing net vertical stress, or mean net stress, when Se is at constant condition. A series of oedometer tests were conducted by soaking the USCES specimens to validate the proposed model. The results of the study suggest that there is a good comparison between the measured data and the prediction curves of NCL during compression using the proposed model. In addition, the model provides excellent predictions of the soaking-induced non-monotonic collapse potential.