A Closed-Form Equation for Effective Stress of Unsaturated Saline Clay Considering Capillary and Osmosis Effects

Abstract

The interaction mechanism between matric suction and osmotic suction was clarified through the analysis of certain physicochemical effects on unsaturated saline clay. The Young–Laplace equation for unsaturated saline clay was then derived by considering the contribution of the chemical potential to the Gibbs free energy at the air–solution interface. An effective stress equation for unsaturated saline clay considering the capillary and osmotic effects was obtained by utilizing a soil skeleton stress equilibrium analysis method. The definition and calculation formula for the osmotic efficiency parameter was determined by analyzing the chemical osmotic effect. Finally, the volume deformation and shear strength of unsaturated saline silty clay were tested under different salt content and matric suction conditions, and the validity of the effective stress equation was verified through tests on expansive clay saturated with salt solution. The results indicated that the effective stress–based generalized effective stress equation for unsaturated saline clay, taking into account the effect of the salt solution on the pore liquid pressure, usw, was related to osmotic suction and the osmotic efficiency parameter. The osmotic efficiency parameter is the ratio of change in the surface tension at the air–solution interface to the change in the corresponding osmotic suction, which reflects the strength of the chemomechanical coupling in the micropore space and its smooth transition to the macroscopic scale. In addition, the validation demonstrated that the proposed effective stress equation was able to uniformly describe the mechanical phenomena of unsaturated saline clay. Our findings provide a convenient way to simulate the mechanical behavior of unsaturated clay in saline environments.