Distinct element analysis of unstable shear failure of rock discontinuities in underground mining conditions

• Unstable shear failure analyses can be done using UDEC and CY joint model.
• Stable and unstable failures can be distinguished in numerical simulations.
• Models show failure processes of regions on a discontinuity during excavation.
• Failure stability correlates to stress field and loading stiffness.
• Various factors impact loading stiffness and stability of a discontinuity.

The work presented in this paper focuses on improving the understanding of shear failure stability associated with underground mining by considering the relative stiffnesses of wall rocks and the failing discontinuity in addition to important shear strength and stress drop parameters. The study uses the Universal Distinct Element Code (UDEC) with the optional constitutive law, the continuously yielding joint model. The mine-scale numerical model consists of an advancing tabular excavation below a large horizontal discontinuity. Using this model, extensive simulations were performed to study the failure stabilities at selected points along the discontinuity as a function of mining geometry and the material properties of the discontinuity and its wall rocks. The results show that the failure stability is governed by the relative stiffnesses of the failing discontinuity and the loading stiffness of the wall rocks. The proneness and intensity of unstable failures is found to increase with increased normal stress and decreased loading stiffness. The findings also indicate that the loading stiffness is reduced with increased mining, decreased distance to discontinuity, and decreased elastic modulus of the rock resulting in an increased probability of unstable failures along the discontinuity.