Mechanical characteristics of rock fracturing based on tension-shearing breaking process

This work aimed to investigate novel rock fragmentation theories and supporting methodologies for deep hard rock. Rock fragmentation models were established by integrating AutoCAD and Particle Flow Code (PFC) software. Preformed boreholes and rock cutting tools were set in the model, and the cutting tools were pulled along the rock free surface to replicate rock fragmentation evolution. The effects of different D/d ratios, borehole depths, pulling velocities and confining pressures on rock fragmentation characteristics were systematically analyzed. The volume of fractured rock blocks is found to be positively proportional to the D/d ratio. The peak rock-breaking load and microcrack count both increase with D/d ratio and borehole depth. The microcracks exhibit a discrete distribution. The peak rock-breaking load reaches a maximum of 57.72 kN at a D/d ratio of 4. The rock-breaking load peaks at 33.99 kN at a borehole depth of 25 mm. Under confining pressure, microcracks develop in sheet-like distribution, and multiple primary and secondary fracture planes are generated under all working conditions. For pulling velocities of 1, 1.5 and 2 m/s, the minimum peak rock-breaking load is observed at a confining pressure of 10 MPa, namely 28.48, 26.62 and 27.39 kN, respectively. For all tested pulling velocities, the number of microcracks reaches its minimum when the confining pressure ranges from 10 to 15 MPa. Confining pressure exerts both promoting and restraining effects on crack propagation. The research findings can provide theoretical references for the optimization of fragmentation methods applied to deep hard rock masses.