Failure mechanism of tunnel face and soil arch effects in auxiliary air balanced shield using three-dimensional material point method

The collapse of tunnel face poses a serious threat to the safety of tunnel construction, and a comprehensive understanding of the entire evolutionary failure mechanism is the key premise for disaster prevention and treatment measures. By using the three-dimensional material point method (MPM), the large deformation behaviours of the collapse of tunnel face in the auxiliary air pressure balanced shield are investigated. The effectiveness of the MPM in analyzing the failure problems of tunnel face is validated by comparing the results of the limit support force, ground settlement and stress distribution with those of the experimental tests. Subsequently, a series of field-scale numerical simulations are conducted to explore the dynamic characteristics of collapse of tunnel face, response of ground deformation, and evolution of soil arch under various burial depths, support air pressures and cutter head types. The results demonstrate that the development rate and final mass of the collapse of tunnel face 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 the ground deformation induced by the collapse of tunnel face, and the collapse of ground surface grows rapidly when the soil arch reaches the ground surface and vanishes. The MPM can effectively capture the entire dynamic process of the collapse of tunnel face in the auxiliary air pressure balanced shield, therefore providing valuable insights for preventing the collapse of tunnel face and predicting the post-failure behaviors in similar projects.