Abstract: To address the equipment challenges in the excavation of non-blasting, short-distance, non-circular cross-section hard rock tunnels—poor adaptability of TBMs due to their long bodies and low cost-effectiveness and poor economic efficiency of cantilever roadheaders—and to meet the requirements of efficient, safe, and flexible excavation for such tunnels, the authors conduct the research and development as well as performance verification of a cantilever TBM for hard rock tunnels. Based on extrusion rock breaking and the advantages of stable rock breaking by TBM disc cutters and swing rock breaking by cantilever roadheaders, an innovative concept of "suspended rock breaking" is proposed. Subsequently, a variety of hard rock cutterheads suitable for the cantilever TBM are designed; additionally, based on the structural characteristics of the cutterhead, a novel type of combined construction method of suspended rock breaking + expansion cracking assistance is developed. Meanwhile, with the conical hard rock cutteread as the research object, physical model tests under multiple operating modes are carried out to monitor the parameters of the rock breaking process in real time, and the roughness index of the rock slag generated from the tests is analyzed to verify the adaptability of the equipment and the construction method. The results show that: (1) The cantilever TBM can adapt to the turning of small-radius tunnels and operations in non-circular cross-sections such as rectangular and horseshoe shapes, with no blasting vibration during construction. (2) By utilizing the structural property of rocks that "they are resistant to compression but not to shear", the cantilever TBM achieves considerably higher excavation efficiency in hard rock formations than traditional cantilever roadheaders.

Key words: cantilever TBM, novel cutterhead, suspension rock cutting, hard rock tunnel, rock slag, roughness index