Dynamic collapse characteristics of the tunnel face induced by the shutdown of earth pressure balance shields(EPB):A 3D material point method study

The collapse of the tunnel face is a prevalent geological disaster in tunnelling.This study employs a three-dimensional(3D)material point method(MPM)to simulate the dynamic collapse process and post-failure mechanisms of the tunnel face.The specific focus is on the scenario where the auxiliary air pressure balanced shield with a partially filled chamber is shut down.To assess the suitability of the 3D MPM,numerical solutions are compared with the results from small-scale experimental tests.Subsequently,a series of large-scale numerical simulations is conducted to explore the dynamic collapse characteristics of the tunnel face induced by the shutdown of the EPB shield under various support air pressures and cutter head conditions.The temporal evolution of the accumulated soil masses in the soil chamber and ground responses under different support air pressures,cutter head types and opening ratios are discussed.In particular,the associated surface subsidence due to the tunnel face collapse is determined and compared with empirical solutions.Numerical results confirm the applicability of the 3D MPM for simulating the large-scale tunnel face collapse scenarios,spanning from small to large deformation analysis.