Tunnel face ground loss under cutterhead vibration in sandy ground with different degrees of saturation: Insights from DEM simulations

Tunnel face ground loss (TFGL) emerging in shield tunnelling can trigger ground movement and impose threats to surrounding structures. However, the impact of cutterhead vibration on TFGL in sandy soils with varying degrees of saturation has been largely unexplored. To fill this gap, an innovative numerical model based on computational fluid dynamics-discrete element method (CFD-DEM) and adhesive rolling resistance linear contact algorithm is established for the simulation of TFGL. Meanwhile, algorithms are proposed to account for the effects of cutterhead vibration and support pressure. Results from the validated model reveal that the TFGL can be exacerbated by seepage and opening enlargement, but mitigated by apparent cohesion. The cutterhead vibration can merely exacerbate the relatively small TFGL, which implies the unjamming effect of the particle at the opening. The balanced support pressure (BSP) required for TFGL prevention rises remarkably with the increases in opening ratio, vibration amplitude, and frequency. The maximum BSP in unsaturated sandy ground reaches up to 0.18 γD , which is significantly less than that of 1.62 γD observed in saturated sandy ground. The tangential and radial intervals with the largest TFGL are located within the ranges of 82.5°–97.5°, and 0.3 D ≤ r loss ≤0.45 D , respectively. The increase in support pressure can alter the time-dependent development of TFGL from linear to stepwise, leading to convergence. The support pressure required for convergence is increased by cutterhead vibration and seepage, but decreased by apparent cohesion. Lastly, the prospects of the numerical study on TFGL under cutterhead vibration are also discussed.