Abstract: The overall excavation efficiency of tunnel boring machines (TBMs) in highly intact and extremely hard rock formations is low. To address this issue, a case study is conducted at the Beishan underground laboratory project, and a composite rock fragmentation technology integrating TBM excavation and blasting techniques is proposed. This technology prefabricates fractures in the rock mass ahead of the tunnel face through blasting. The induced prefracturing reduces the integrity and overall strength of the rock mass, after which the TBM performs subsequent excavation. First, numerical analyses are conducted to examine the effects of borehole charge length, borehole spacing, and borehole arrangement on blasting performance using single-hole, five-hole, and eleven-hole numerical models. On this basis, key blasting parameters, including charge length, borehole spacing, and charge structure, are optimized. Lateral tunnel wall blasting tests are then performed to determine feasible parameters for tunnel face presplitting blasting and combined TBM disc cutter rock fragmentation tests. Each borehole is charged with a single 200 g explosive cartridge using a three-stage decked charging mode; empty holes are arranged, and a simultaneous detonation scheme is adopted to avoid excessive rock mass damage while achieving a satisfactory presplitting effect. Finally, tunnel face presplitting blasting and TBM disc cutter combined rock fragmentation tests verify the rationality of the selected blasting parameters and the feasibility of the proposed composite technology. The results show that the average TBM tunneling speed increases by 65.9% in charged sections, 29.9% in uncharged sections, and 42.3% over the entire blasting cycle. A tunnel face borehole drilling system integrating reserved cutterhead holes and three cutterhead-mounted advance drilling rigs is proposed and is tested and applied at the Beishan underground laboratory.

Key words: TBM tunnel, highly intact and extremely hard rock, aided disc cutter rock fragmentation technology, presplitting blasting, numerical simulation, tunneling test, tunneling efficiency