Experimental study on differential rockburst characteristics of granite with single and parallel double structural planes

The effect of structural planes on rockburst is a core issue in deep rock mechanics, yet the differential failure mechanisms induced by parallel double structural planes remain poorly understood. This study performs biaxial compression tests on granite specimens with a circular hole, combined with synchronized video monitoring and acoustic emission detection, to systematically compare rockburst characteristics under three conditions: intact rock, a single 45° structural plane, and parallel double 45° structural planes. Specimens with a single 45° structural plane exhibit progressive rockburst failure characterized by early damage initiation and slow evolution. The single structural plane imposes strong geometric constraints and significantly restrains the radial expansion of rockburst pits. In contrast, specimens with double structural planes present sudden rockburst failure with late initiation and rapid development. Stress superposition at crack tips and cooperative crack propagation attenuate the boundary constraint effect and promote the deep radial expansion of rockburst pits. AE analysis reveals that tensile cracks dominate the failure process of intact specimens. The shear crack proportion rises sharply to 33.6% in double-structural-plane specimens, indicating that shear crack coalescence drives the radial expansion of rockburst pits. These findings enrich the mechanism of structure-type rockbursts and support risk assessment for deep fractured tunnels.