Theoretical framework for large-strain shear resistance of Kaolin clays under chemo-mechanical loadings

The normal stress, strain rate, and pore fluid chemistry significantly influence the large-strain shear response of clays and received great attention for engineering practice. The effect of inundation pressure, consolidation pressure, pH of aqueous solutions, and di-electric on the shear response of kaolin was experimentally investigated. The strain-softening behaviour was observed under normally consolidated (NC) conditions as observed in the past studies on different clays. However, this anomalous shear response with volumetric contraction is not understood. Thus, for the first time, the strain-softening behaviour of NC clays was addressed from an effective stress approach using physico-chemical analysis of kaolin. In this study, the drained shear strength response of NC kaolin was investigated under physico-chemical influence using ring shear tests. A theoretical framework was developed by including micromechanism of clay fabric evolution during shear and explicit expressions for electro-chemical forces. The proposed framework was used to estimate the shear resistance from the modified effective stress approach to interpret the experimental results. The proposed framework provides useful expressions for predicting the shear strength behaviour of kaolin clays, which were validated with experimental data from the present study and literature studies. The new conceptual framework satisfactorily explained the peak and residual shear strength variations under different chemo-mechanical loading for NC conditions. The proposed model adequately predicted the effective stress paths, peak, and residual envelopes in ring shear stress conditions for NC kaolin soils.