Numerical study on instability of rock structural planes induced by stress disturbances

Abstract

The activities in deep underground engineering may induce variations in the stress state of the rock, increasing the risk of engineering disasters. The decrease in normal stress σ_n and the increase in shear stress τ_s are considered as important causes for activation of rock structural planes to induce rockburst, earthquake and other disasters. In this study, numerical simulations are performed to reveal the influences of different stress paths on the dynamic slip mechanism of rock structural planes. The results show that the rock structural plane loaded to the near-critical failure state enters a slow slip state as the stress varies, and the frictional strength decreases with the exponentially increasing shear displacement d_s, eventually resulting in dynamic slip. The displacement-driven mode overestimates the friction parameters µ by up to 14.5% compared with the stress-driven mode. The slow slip continuously weakens the ability of the structural plane to tolerate stress variation. The continuity and discontinuity of stress variation on structural plane affect the strengthening mode of µ. The stepwise stress path causes the stress on the structural plane to change dramatically, and may either cause the structural plane return to a slow-slip state or activate the structural plane to dynamic slip. Compared with the variation stress in σ_n, the variation stress in τ_s is more sensitive to triggering dynamic slip. The d_s before dynamic slip is an important reference for evaluating the extent to tolerate stress variation. With increasing d_s from 0.68 mm to 1.26 mm, the τ_s required to trigger dynamic slip decreases from 1.67 MPa to 1.49 MPa, suggesting that the ability of structural planes to tolerate stress variation is reduced.