A Novel Method for Determining the Crack Closure Stress of Brittle Rocks Subjected to Compression

Excerpt

The mechanical properties of rocks are important in rock mechanics. The rock damage process begins with the closure of original microcracks, continues with the generation, propagation, and coalescence of new microcracks, and finally ends with the formation of a macroscopic failure surface (Morgan et al. 2013). There are four crucial stress thresholds in the progressive failure process of rock under compression, namely, the crack closure stress (CC), crack initiation stress (CI), crack damage stress (CD) and peak strength (PS) thresholds. According to the stress thresholds, the failure process of rock is divided into five stages, i.e., the crack closure stage, elastic deformation stage, crack stable growth stage, crack unstable growth stage and post-peak stage (Brace et al. 1966; Bieniawski 1967a, b, c; Martin 1993; Cai et al. 2004; Diederichs et al. 2004; Amann et al. 2011; Nicksiar and Martin 2013; Ündül et al. 2015; Wang and Cai 2018). The CC characterizes the density of pre-existing microcracks in rock. The CI represents the initiation of new cracks and the termination of the elastic deformation stage. The CD is the critical point where the contribution of the lateral dilation component to the volumetric strain exceeds that of the axial compression component; it corresponds to the long-term strength of rock. The peak strength is the most common and direct index for evaluating rock strength and has been widely used for various rock strength criteria. …