Investigation on the Failure Characteristics and Fracture Classification of Shale Under Brazilian Test Conditions

The failure characteristics and the various induced fractures of shale are investigated in this paper. Brazilian tests were conducted for different inclination angles of the weak planes of shale (θ  = 0, 15, 30, 45, 60, 75, 90°). Different loading rates were applied (V  = 0.005 kN/s, 0.02 kN/s, 0.1 kN/s, and 0.5 kN/s). The results show that there is an increase in the Brazilian split strength (BSS) with the increase in the inclination angle from 0° to 90°, with possibly a local dip for 45°. When θ  = 45°, both the split modulus (Es) and the absorbed energy (U) had the minimum values, whereas the fracture maximum deviation distance (L′max) had the maximum value. The geometrical trajectory of the fracture in shale samples can be classified into three types, namely the through fracture, the non-through fracture, and the multiple fracture. The BSS, Es, and U of shale gradually increased with the increase in loading rate. Additionally, the fracture is more close to the center. This is because, as the loading rate increases, the time for the propagation and evolution of internal damage of shale decreases.