Study of the cutter-rock interaction mechanism during TBM tunnelling in mudstone: insight from DEM simulations of rotatory cutting tests

The rock breaking mechanism plays a significant role in TBM (tunnel boring machine) performance prediction, which has not yet been understood satisfactorily. In this work, a series of rotary cutting simulations via a particle-based DEM (discrete element method) for mudstone were conducted to explore the rock breaking mechanism and cutter-rock interaction during TBM tunnelling. Different cutting scenarios were considered. The rock breaking events were inferred from the breakage of bonds between particles constituting the mudstone. The spatial distribution of microcracks was obtained in the form of bond breaks between particles. The cracking features of mudstone are different from those reported for hard rocks. The characteristics of the contact stress distribution were also analysed and fitted by a combined Hertz-Weibull model. The distribution ranges of bond breaks and cutter-rock contact stress are both positively related to the penetration depth but not largely dependent on the cutting radius. However, the side force has a negative relationship with the cutting radius, and this dependency is more significant with increasing penetration depth. The bond-break distribution is skewed to the outer side of the cutter due to different cutting trajectories and centrifugal effects. Moreover, the bonds tend to break towards the existing cutting groove due to the release of radial confinement. The variation in cutting forces interrelates with the bond breakage events, which reduces the local stiffness and strength of the rock. The existence of the former cutting groove yields eases rock breakage and associated smaller cutting forces.