Progress of brittle microfracturing in crystalline rocks under cyclic loading conditions

Abstract

The stress at onset of yielding for the walls of deep underground excavations in hard rock is significantly less than the laboratory strength of intact rock samples. The wall stability is rather controlled by the microfracturing strength of the rock (i.e. crack propagation (CD) and initiation (CI) thresholds). Factors such as loading and unloading effect of excavation, glaciation, stress rotation in front of a tunnel face, etc. can contribute to the progressive damage of the rock, influencing the CI and CD thresholds and therefore contributing to the damage intensity around underground openings. The effect of stress rotation and stress fatigue on crack damage thresholds is systematically investigated in this paper through state-of-the-art laboratory testing and monitoring techniques in combination with advanced grain-based numerical modelling.