Study on the influence of TBM disc cutter on the penetration of extremely hard rock in Zijing Tunnel

The reasonable setting of TBM disc cutter penetration depth is crucial for its rock-breaking efficiency in extremely hard rock geology. In the construction section of the Dujiangyan to Mount Siguniang Zijing Tunnel project, which encountered extremely hard diorite rock (with uniaxial compressive strength exceeding 230 MPa), to reveal the influence of penetration depth on disc cutter cutting of extremely hard diorite rock, the following steps were taken: Firstly, using a self-developed small-scale disc cutter linear rock-breaking test platform, experiments were conducted for four penetration depths: 1.5, 2.0, 2.5, and 3.0 mm, under fixed cutter spacing and with/without confinement conditions. Secondly, employing a high-precision crystalline rock material modeling method based on three-dimensional particle clusters, a full-scale numerical model of disc cutter linear cutting of diorite rock was established. Seven penetration depths ranging from 1.0 to 10.0 mm were tested under a fixed cutter spacing of 80 mm. Results indicate that under lateral confinement, diorite failure shifts from slip and extrusion to crushing, while under no confinement, it primarily spalls laterally with increased rock debris and ejection distance as penetration increases. Disc cutter normal force rises with penetration, with a critical 4mm point after which load increases slowly but penetration significantly, marking an efficient rock breaking stage. Specific energy efficiency peaks at 3mm penetration in tests and 4mm in simulations, attributed to test bench limitations. Combined results suggest an optimal penetration of 4mm.