DEM Analysis on Rock‐Breaking Impact Effect of Shield Disc Cutter in Typical Soft and Hard Composite Strata

During shield tunneling in composite strata, the disc cutter's abnormal damage rate rises sharply under interface impact, due to strata inhomogeneity. This study investigates the dynamic response and the cause of the peak impact force of disc cutters at soft‐hard rock interfaces using the discrete element method. Simulations of linear cutting processes under varying interfacial bonding strengths were conducted to compare the dynamic response characteristics of the disc cutter in soft rock, hard rock, and interfacial zones. Through the failure characteristics of the composite rock and the law of crack propagation, the influence of the rock damage evolution on cutter loading states was analyzed, thereby elucidating the origins of force variations experienced by disc cutters at interfacial zones. The results show that lithological differences disrupt the continuity of the dense rock core at the interface. The weakened interfacial bonding strength redirects crack propagation, delaying failure initiation in the soft rock near the interface. The stress attenuation across the interfacial transition zone reduces damage accumulation in the hard rock, enhancing rock‐breaking resistance of the hard rock against the cutter during interface crossing. When the disc cutter transitions into the hard rock stratum, the normal force reaches a peak magnitude. At the interface, the normal force increases by 34% compared to the homogeneous hard rock zone. The research clarifies the mechanism of disc cutter impact at the interface, providing a reference for alleviating abnormal damage induced by interfacial effects.