Transient rock breaking characteristics by successive impact of shield disc cutters under confining pressure conditions

In intricate geological conditions characterized by moderate karst formations, that include soft rock layers above and harder rock beneath, shield tunneling poses significant risks, including cutterhead damage, tunnel segment deformation, and potential ground collapse. Therefore, it is imperative to gain a profound understanding of the dynamic mechanical responses that rock bodies exhibit during tunnel construction. This study adopted the developed shield disc cutter model, combined with actual geological parameter conditions of shield tunnel projects, to apply different impact pressures to three groups of rock bodies using the cutter model. The major objective is to investigate the dynamic mechanical behavior of the rock under up to 20 successive impacts by shield disc cutters. The experimental findings unveil that at identical impact pressures, as the number of impacts increased, there was a gradual escalation in the peak amplitude of the wave reflected from the rock, accompanied by a simultaneous reduction in the peak amplitude of the transmitted wave. This phenomenon indicates the accumulation of internal damage within the rock form successive impacts, resulting in a diminished capacity of the rock to withstand external impact loads. Furthermore, the dynamic modulus of the rock displayed an initial increase followed by a subsequent decrease in response to successive impact disturbances, with a critical point emerging at approximately 15 successive impacts. Moreover, key parameters such as peak stress, peak strain, and loading rate exhibited notable dependencies on impact rate, effectively characterized by a proposed statistical regression formula under typical confining pressure conditions. This underscores this study for understanding the rock-breaking mechanism of shield disc cutters.