Abstract
In this chapter, an equation to account for the volumetric behavior of unsaturated soils is proposed. This equation is based on the effective stress principle and results in a unifying framework for the volumetric behavior of both saturated and unsaturated soils. The numerical results of the proposed equation are compared with experimental results published by different researchers. These comparisons show that the equation is adequate to account for wetting-drying and net stress loadingunloading paths. This analysis confirms that the effective stress principle can be applied to the volumetric behavior of unsaturated soils.