Abstract: The authors investigate the rock-breaking efficiency of the disc cutter in tunnel boring machines and the damage modes of the crushed rock slices under different surrounding rock pressures. Based on the principles of servo and linear parallel bonding theory, the discrete element software PFC2D is employed to establish a two-dimensional simulation model of the rock-breaking process, calibrated with parameters specific to granite. Six surrounding rock pressure conditions of 1, 5, 10, 15, 20, and 30 MPa are set and the cutter penetrating the rock by 5 mm is simulated. The propagation of microcracks in the rock, the specific energy consumption of the cutter during the breaking process, the evolution of tensile shear cracks, and the failure modes of the broken rock pieces are analyzed. The results reveal the following: (1) As surrounding rock pressure increases, the internal rock cracks transition from along-crystalline to through-crystalline cracks, with the proportion of shear cracks rising from 9.4% to 21.3% at 1 and 30 MPa, respectively. (2) At a surrounding rock pressure of 10 MPa, the cracks within the two disc cutters become interconnected, leading to the generation of larger rock fragments compared to the other five pressure conditions. Consequently, the specific energy consumption is reduced, indicating a more effective rock-breaking performance. (3) Following a 5 mm penetration of the disc cutter into the rock, the radial propagation of cracks is constrained as the surrounding rock pressure increases.

Key words: tunnel boring machine, surrounding rock pressure, crack development, failure mechanism, specific energy, disc cutter