Strain burst vulnerability criterion based on energy-release rate

Violent rock failures such as strain burst are significant issues during excavations in rock mass under the influence of high stress and temperature. Triggering mechanism of strain burst is associated with the intrinsic rock properties, e.g. fracture toughness. Understanding the fracturing behaviours of rocks is, therefore, significant for assessing the stability of underground rock engineering structures. In this paper, quasi-static mode I fracture toughness tests were conducted with cracked chevron notched semicircular bend (CCNSCB) granite specimens to investigate the relationship between the strain burst mechanism and its fracturing behaviour using servo-controlled MTS testing machine. The tests were performed at various strain rates, and specimens were subjected to different temperatures. Energy characteristics in quasi-static fracture of granite samples were quantitatively studied, and a new strain burst vulnerability criterion based on energy-release rate for brittle rocks was proposed. The results revealed that the quasi-static fracture toughness and energy-release rate are highly dependent on strain rate and temperature. In the view of energy principle, under the same strain rate, more energy was dissipated and released with an increase in the temperature. When the strain rate was high, strengthening effect became more remarkable, and the strength of granite increased under all temperatures compared to quasi-static conditions. The strain burst propensity index was proposed based on the energyrelease rate. The effects of strain rate and temperature on strain burst vulnerability were further discussed.