Abstract: To address the construction challenges of tunnel boring machine (TBM) for intact hard rock small-radius curved spiral tunnels, a case study is conducted on the spiral ramp project of the Beishan Underground Laboratory. Numerical simulations, laboratory tests, factory tests, and on-site tests are employed to conduct research, innovation, and practice focusing on efficient rock breaking and mucking, small-radius turning, and high-precision control of spiral turning. The following results are achieved: (1) For heavy-duty 20-inch disc cutters, the load-bearing capacity and maximum allowable wear are increased by 19% and 23% respectively. The conical cutterhead realizes optimal rock breaking with proper free surface distance. The front-mounted disc cutters with a spacing of 60 mm is 13 mm smaller than that of conventional cutterheads. Combined with the micro-blasting artificial fracture-assisted rock breaking technology, these multiple measures significantly improve the rock breaking efficiency in intact hard rock. (2) By innovating the main structure of the TBM and optimizing the design of its rear auxiliary system, a customized mobile survey station guidance system is developed to achieve precise guidance and direction adjustment of the TBM in small-radius curved spiral tunnels. (3) Nearly 20 measures are implemented, including multi-point drive, customized conveyor belt, reduced belt strength, increased belt width, reduced belt speed, double belt storage bins, two-section lap joint, and adaptive adjustment. These measures ensure the smooth and efficient mucking of the spiral continuous belt conveyor in small-radius turns. Relying on the aforementioned key technologies, the Beishan No. 1 TBM successfully completed all construction, and traversed seven compound curves with negative gradients. The project demonstrates excellent borehole quality and alignment control accuracy, while maintaining minimal disturbance to the surrounding rock.

Key words: tunnel boring machine, spiral tunnel, numerical simulation, conical cutterhead, artificial fractures, auxiliary rock breaking, spiral continuous belt conveyors, double belt storage bin