Multiscale fracture characteristics and failure mechanism quantification method of cracked rock under true triaxial compression

The failure mechanism of rock masses is an important issue concerning the safe construction of underground engineering. Here, we conduct a series of true triaxial experiments on sandstone to investigate the fracture characteristics and failure mechanism of cracked rock. The multiscale fracture characteristics of the fracture surface are summarized, and the mechanisms of different types of fractures are identified. A novel method for quantifying the rock failure mechanism is proposed. The applicability of the Mohr-Coulomb criterion is also discussed. The experimental results reveal that the fracture mechanism can be qualitatively defined by the multiscale fracture characteristics. Four types of fractures with different mechanisms are classified. The correlation between the fractal dimension and the fracture mechanism is established by fractal theory. Based on the fractal dimension, the rock failure parameter delta is defined to quantify the rock failure mechanism, and the influence of sigma(3), sigma(2), and pre-existing flaws on the rock failure mechanism is studied. The proportion of tension fractures in the failure of rock has a positive correlation with sigma(3) and a negative correlation with sigma(2). The presence of pre-existing flaws has a significant promoting effect on the development of fractures. However, this promoting effect presents no obvious bias on the initiation of tension or shear fractures.