Distinct element modelling of mining-induced instability of a heterogeneous fault

Deep underground mining/excavation in rock masses can induce unstable slip of a fault, triggering a common catastrophic geological hazard, fault-slip burst. Although several studies investigated the induced dynamic movement of a fault, the role of roughness heterogeneity in controlling fault instability remains poorly understood. Here, we simulated the stable/unstable slip of faults with heterogeneous roughness at both laboratory and field scales using the Universal Distinct Element Code (UDEC) incorporating the continuously yielding joint model. The heterogeneity of fault roughness was realized in UDEC by assigning stochastic-generated contact properties statistically following the classic Weibull function. We found that both the failure pattern and energy partition of the heterogeneous fault undergoing unstable slip were heavily constrained by the mechanical and geometric heterogeneity of the surface asperities. Aseismic faults can be seismic when heterogeneities in shear stiffness and initial friction angle were accounted for, and the higher degree of heterogeneity, the higher the released seismic energy and thus the induced moment magnitude. Therefore, rational assessment of the risk of fault-slip burst in rock-engineering practice should consider the modulation of the fault roughness heterogeneity on the stable-unstable transition of fault slip.