Excavation-induced fault instability: Possible causes and implications for seismicity

摘要

Fault rupture and associated seismicity have been reported frequently in underground excavation. The mechanism that drives the human-induced geohazards still eludes explanation, and uncovering this mechanism relies heavily on our understanding of the failure characteristics of fractured rock. We carried out the triaxial compression testing and discrete element modelling on intact and fractured granite samples to consider the controllable change of the angle beta between the maximum principal stress orientation and pre-existing fracture orientation and to interpret the complicated mechanism of fault rupture adjacent to rock excavation. Our results show that the reduction of the angle beta leads to the failure pattern of fractured samples changing from the tensile failure of rock matrix to the shear failure along pre-existing fractures. This transition results in relatively small b value, as small magnitude AE events decrease in the rock matrix and large magnitude AE events concentrate along pre-existing fractures. The change of b value in the pre-peak stage is independent to the angle beta, implying the challenge in rock failure prediction. Our study also indicates that fault rupture adjacent to rock excavation is due to the changes of magnitude and orientation of principal stresses, and the associated seismicity is likely dependent on the portions of rock matrix and fractures involved in the failure process.