Numerical Simulation of the Shear Behavior of Rock Joints Filled with Unsaturated Soil

Weak infilled discontinuities commonly exist in rock masses, in which the infill degree of saturation largely influences the overall joint shear behavior and ground stability. However, so far, research on the shear of infilled joints at unsaturated conditions is rare, especially those performed in numerical simulation. To the authors' knowledge, no attempts have been made to investigate the shear-induced variations in unsaturated soil parameters, which are vital for proposing the infilled-joint constitutive models. For the first time, a series of constant water content direct shear tests on the unsaturated infilled-joint soil were conducted using the numerical software Fast Lagrangian Analysis of Continua (FLAC)/Two-Phase Flow. Intrinsic soil-water retention and permeability models were updated in the FISH subroutine to consider porosity. Results highlight the disadvantage of the built-in models in FLAC. Initial infill saturation and other factors, including physical shear rate, joint roughness, infill thickness, and normal stress, all showed effects on the joint shear strength consistent with literature reports. Shear-induced variations in the mean values of Bishop effective stress and permeability of the infill layer were emphasized.