An FEM-based analysis of the chemo-hydro-mechanical coupling behavior of saturated active clays

Interaction between soil matrix (minerals) and water plays a crucial role in controlling the hydraulic and mechanical behaviors of active clays. However, it has not been characterized to a satisfactory extent during analyzing these behaviors of soils. To address this gap, a chemo-hydro-mechanical (CHM) coupling theoretical model based on the chemo-mechanical coupling theory for multiphase porous media is developed, which can quantitatively characterize the complex physico-chemical interactions between the charged clay skeleton and pore fluid. A generalized flow equation explicitly accounting for the effects of chemo-osmosis is derived. To simulate the constitutive behavior of soils, the concept of generalized effective stresses is introduced and incorporated into the modified Cam-Clay (MCC) model. A fully coupled CHM finite element procedure is developed using the adaptive relaxed Picard iteration method, in combination with an implicit closest point projection method (CPPM) for the integration of the constitutive model. The validity and reliability of the proposed model and procedure are verified by simulating boundary value problems for saturated clay under chemo-mechanical loading conditions. The results show that the proposed model effectively unifies seepage, osmotic flow, osmotic deformation (consolidation and swelling), and osmotic-induced deformation mechanisms in saturated active clays. The proposed finite element procedure is capable of capturing the CHM coupling behavior of soils, and can be utilized as a helpful tool for characterizing the CHM behavior of clays in engineering practice.