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

Abstract

Weak infilled discontinuities commonly exist in rock masses, in which the infill degree of saturation largely influences the overalljoint shear behavior and ground stability. However, so far, research on the shear of infilled joints at unsaturated conditions is rare, especiallythose performed in numerical simulation. To the authors'knowledge, no attempts have been made to investigate the shear-induced variationsin unsaturated soil parameters, which are vital for proposing the infilled-joint constitutive models. For thefirst time, a series of constant watercontent direct shear tests on the unsaturated infilledjoint soil were conducted using the numerical software Fast Lagrangian Analysis ofContinua (FLAC)/Two-Phase Flow. Intrinsic soil-water retention and permeability models were updated in the FISH subroutine to considerporosity. Results highlight the disadvantage of the built-in models in FLAC. Initial infill saturation and other factors, including physical shearrate, 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 Abstract: Weak infilled discontinuities commonly exist in rock masses, where the infill degree of saturation largely influences the overall joint shear behaviour and ground stability. However so far, researches on the shear of infilled joints at unsaturated conditions are rare, especially those carried out in numerical simulation. Also to the authors' knowledge, no attempts have been made to investigate the shear-induced variations in unsaturated soil parameters that 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 FLAC/Two-Phase Flow. Intrinsic soil-water retention and permeability models were updated in 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 emphasised.

Cylindrical Caved Space Stability Analysis for Extension Prediction of Mining-Induced Surface Subsidence

“…Equation ( 12) enables the prediction for orientation (θ) and depth (z) where slip failure along the inclined discontinuities will take place, and it shows the occurrence of slip failure heavily depends on the property (c ′ and μ ′ ) of discontinuities. This means the slip failure along discontinuities and associated extension of surface subsidence may suddenly occur due to the dramatic decrease of discontinuities' cohesion, such as when the infill in discontinuities is saturated because of heavy precipitation or underground water [37]. Additionally, laboratory tests have demonstrated the strength of discontinuities will reduce after the slip failure [38].…”

Effects of Gouge Fill on Elastic Wave Propagation in Equivalent Continuum Jointed Rock Mass

“…Natural rock joints are filled with gouge material ranging from fluids (e.g., water or oil) to viscoelastic particulate soils (e.g., sand, silt, and clay). The effects of gouge fill on wave propagation in jointed rock masses have been examined extensively in analytical and experimental studies [5][6][7][8][9][10][11][12]. Prior research noted that the presence of gouge fill greatly influences the mechanical behavior and seismic response of the jointed rock mass for single and multiple joints.…”