ABSTRACT
In recent years, micromechanical models for effective stress in unsaturated soil have also been developed. For example, Lu & Likos (2006) built up a model by considering the van der Waals attraction, electrical double layer repulsion, chemical cementation and capillary forces. Li (2003)
1 INTRODUCTION
The concept of effective stress for soil mechanics was first introduced by Terzaghi (1936). It can be simply interpreted as the stress that is directly responsible for the soil skeleton’s deformation. Later on, this concept was further extended to unsaturated soil by Biship (1959) as
− ( )wu−u (1) where σ ij
′ is the effective stress, ua is the pore air pressure, δ ij is the Kroenecker’s delta, χ is the effective stress parameter, and uw is the pore water pressure. Equation (1) triggered a long-time debate on the validation of effective stress principle in unsaturated soil. Critical and comprehensive reviews on it can be found in the work of Khalili et al. (2004) and that of Nuth & Laloui (2007).
