Study on Failure Mechanism of Rock-Like Specimen with Closed Non-Persistent Fractures Under Confining Pressure

The closed non-persistent fractures commonly developed in rock mass seriously affect the stableness of surrounding rock disturbed by excavation. Considering the fracture inclination and confining pressure, based on laboratory experiments of rock-like specimens, the implication of closed non-persistent fractures on the mechanical behavior and failure mode of the specimen is analyzed. The results suggest that the peak strength of specimens with closed non-persistent fractures change approximately parabolically, first descending and then ascending with increasing inclination, and the lowest value is obtained when the inclination is 60°. With increasing confining pressure, the degree of peak strength anisotropy decreases gradually, the softening modulus decreases, the residual strength increases, and the failure characteristic of the specimen change from brittle to ductile. Hoek–Brown (H–B) strength criterion can depict the strength feature of the specimen with a closed non-persistent fracture more accurately than Mohr–Coulomb (M–C). In the condition of confining pressure, planar shear failure occurs along the fracture with an inclination of 60°, but prefabricated fractures with inclinations of 0°, 30° and 90° have no noticeable effect on the specimen failure mode. There are prominent distinctions in the strength characteristics and failure mode between specimens with open and closed non-persistent fractures, and the implication of open fractures on the failure form of specimens is more greater than that of closed fractures.