Study of the tunnel face failure mechanism and soil arching effect in auxiliary air balanced shield using the three-dimensional Material Point Method

The tunnel face collapse poses a serious threat to the safety of tunnel construction, and a comprehensive understanding of the entire evolutionary failure mechanism is a key premise for disaster prevention and treatment measures. This study employs the three-dimensional Material Point Method (MPM) to investigate the large deformation behaviours of the tunnel face collapse in the auxiliary air pressure balanced shield. The proposed method is validated by comparing results with small-scale experimental tests. Subsequently, a series of field-scale numerical simulations is conducted to explore the dynamic characteristics of the tunnel face collapse, ground deformation response, and soil arch evolution under various burial depths, support air pressures and cutter head types. The results demonstrate that the development rate and final mass of the tunnel face collapse are reduced by the support of air pressure and cutter head, and a faster early collapse rate is observed in a deeper burial depth. The soil arch emerges with ground deformation induced by the tunnel face collapse. The support of air pressure and cutter head, along with a deeper burial depth, is beneficial for the maintenance of soil arch. Due to the stabilizing effect of soil arch, the ground surface settlement shows low sensitivity to the tunnel face collapse until the soil arch vanishes once reaching the ground surface. The MPM method can effectively capture the entire dynamic process of the tunnel face collapse in the auxiliary air pressure balanced shield, therefore providing valuable insights for preventing tunnel face collapse and predicting post-failure behaviors in similar projects.