Abstract: During the process of rock fragmentation assisted by free surfaces using cutters of tunnel boring machine (TBM), once the disc cutters complete breaking the rock near the vertical free surface, the vertical free surface transforms into an inclined one. To investigate the impact of the inclined free surface on rock fragmentation by disc cutters, three-dimensional models were created using peridynamics. A series of numerical studies was conducted, considering variations in the inclination degree of the free surface and the distance between the cutter and the free surface. The simulation results indicate two rock fragmentation modes: internal crack extension and internal crushed zone expansion. With the distance between the cutter and the free surface fixed at 40 mm, the rock fragmentation mode transitions from internal crack extension to internal crushed zone expansion as the tangent cot θ of the inclination angle θ of the free surface increases. The peak normal force of the disc cutter and rock fragmentation energy consumption increase as the cotangent of the free surface angle increases. The rock fragmentation efficiency of the internal crushed zone expansion mode is lower than that of the internal crack extension mode. Furthermore, within the increase of distance range from the cutter to the free surface, the peak normal force of the disc cutter, rock fragmentation energy consumption, and rock fragmentation volume increase gradually, leading to an improvement in rock fragmentation efficiency.

Key words: peridynamics, three-dimensional rock fragmentation by TBM disc cutters, free surface, degree of inclination, distance from cutter to free surface