Fracture behaviour of transversely isotropic rocks under pure mode III fracture: Experiment and numerical simulation

The fracture behaviour in transversely isotropic rocks is significantly affected by stratification planes. In this paper, experimental tests were carried out using edge-notched disc bending (ENDB) specimens with different stratification plane inclination angles to investigate the fracture characteristics of transversely isotropic rocks under pure mode III loading. The influence of stratification plane inclination fracture toughness and fracture pattern were also analysed. An effective numerical model for ENDB specimens was established to simulate and analyse the microscale fracture process under pure mode III loading in PFC3D, and flat-joint contact (FJC) and smooth-joint contact (SJC) were used to simulate the rock matrix and stratification, respectively. The simulation results showed that the fracture plane development trend of specimens with different inclinations is different. For the specimens with stratification plane inclinations of 0 degrees, 15 degrees, 75 degrees and 90 degrees, the cracks at both ends of the prefabricated notch develop symmetrically. However, for specimens with inclinations of 30 degrees and 60 degrees, the propagation behaviour along the stratification plane occurs prior to cutting the stratification planes. In addition, higher stratification plane strength and wider spacing lead to higher peak loads. The fracture trajectory extends along the stratification plane more obviously with the decrease in the stratification plane strength, and the development degree of the fracture trajectory along the stratification plane decreases with the decrease in the stratification plane spacing.