Unloading-induced failure of brittle rock and implications for excavation-induced strain burst

Abstract

Understanding the unloading-induced failure characteristics of brittle rock is essential for predicting excavation-induced strain burst. We conduct both the laboratory experiments and discrete element simulations to investigate the deformation, failure pattern, and strain energy evolution of the Bukit Timah granite. The laboratory tests with radial unloading show that the radial strain mainly contributes to the change of volumetric strain in the unloading process. The numerical tests with the flat-jointed contact model reproduce the Hoke-Brown failure envelope of the rock, and simulate the unloading-induced rock failure under different combinations of initial confining pressure and unloading rate. The evolutions of strain energy release and failure pattern show that higher unloading rate likely induces violent failure, in terms of greater lateral expansion and more ejected fragments. The micromechanical analyses on the particle velocity and tensile contact force reveal that the non-uniform rock deformation concentrates at lateral surfaces and results in strain burst with fragment ejection. The Hoek-Brown failure criterion well predicts the confining pressure at failure when the rock is laterally unloaded at lower unloading rate, but likely overestimates the stress level at higher unloading rate.