Influence of healing time, technological void and temperature on the shear behavior of the GMZ bentonite healing interface

Abstract

Bentonite is an engineering barrier in the deep geological repository (DGR), and its mechanical properties are negatively impacted by the presence of technological voids. Based on direct shear test and mercury intrusion porosimetry (MIP) technique, the effects of healing time, technological void and temperature on the healing interface shear behavior of Gaomiaozi (GMZ) bentonite were studied. The results indicate that the shear strength of healing interface is directly related to the dry density of the interface, which is influenced by healing time, technological void and temperature. Within the healing time range studied, as healing time increased, bentonite continued to swell, leading to a rise in the dry density of the interface and an enhancement in shear strength. During this process, constrained by the limited swelling space, the intra-aggregate porosity decreases at first and then increases until stabilizing, while the inter-aggregate porosity is on the contrary, which reduces the distance between particles, thereby increasing the cohesion and friction angle of the interface. When the initial void of the interface increases, the shear strength at the interface significantly decreases, with corresponding reductions in cohesion and friction angle. As the temperature increases, the shear strength increases, notably in cohesion, while the friction angle shows no clear pattern of change. This is primarily attributed to the rearrangement of bentonite particles, the reformation of interlayer physical and chemical bonds, and the reduced viscosity of pore fluids. The findings of this study provide important insights into the mechanical stability of engineered barriers in the DGR.