An experimental investigation on stress-induced cracking mechanisms of a volcanic rock

In underground excavations, different failure features can be induced by complex geological stresses. Therefore, many researchers have investigated rock behaviour and failure mechanisms under high-stress conditions. This study investigated the different failure characteristics to determine the stress-induced cracking mechanisms. Accordingly, a series of tests were performed on a volcanic rock (rhyodacite) under one- to three-dimensional stress states. The results indicated that the samples exhibited different failure characteristics/modes under different stress states. Under 1-D and 2-D compression, the rock exhibited unstable brittle failure induced by tensile cracking (Mode I fracture). Under axisymmetric triaxial stress (σ1 > σ2 = σ3 > 0), the rock exhibited stable failure, and as σ3 increased, the failure mode transitioned from Mode I fracture to Mode II fracture to distributed cataclastic failure. In contrast, under a three-dimensional differential stress state (σ1 > σ2 > σ3 > 0), the risk of unstable failure increased with increasing σ2, and the rock exhibited localized shear failure (Mode II fracture). Based on the acoustic emission (AE)-based cracking classification method, further studies were also conducted on the failure mechanism. Finally, based on the energy release and cracking propagation, the mechanism of the σ2 effect on unstable failure was assessed. •Three stress-induced cracking mechanisms were revealed.•Tensile cracks were preferentially induced during the failure evolution.•The unstable failure can be induced by a higher (σ2-σ3).