Modelling of shear creep behaviour in unsaturated rough rock joints using the grain-based stress corrosion model

Using the parametrically designed battery pack in Grasshopper, a Voronoi grain-based discrete element model was established in the three-dimensional distinct element code, incorporating progressively increasing grain equivalent diameters. A grain-based stress corrosion model, enhanced with an improved stress corrosion theory, was further proposed to simulate both the direct shear characteristics and shear creep behaviour of unsaturated sandstone under varying normal stresses. The mesoscopic parameters, including the contact properties between grains and the stress corrosion parameters, were then calibrated. This ensured that the model could accurately reproduce the mechanical properties of sandstone observed in laboratory tests. The modelling results indicated that tensile cracks were the dominant cracks generated during the shear process under various saturations and normal stresses, along with a few shear cracks. A significant negative correlation was observed between the joint roughness coefficient (JRC) and the ratio of long-term to peak shear strength. Additionally, increased normal stress or decreased saturation were both found to accelerate the time-dependent failure process, leading to a shorter time-to-failure under constant shear loading. We summarize that the proposed model effectively characterizes the direct shear and creep behaviour of unsaturated sandstone at varying roughnesses and normal stresses.