Abstract: The stability study of shallow-buried soil tunnel has always been a key problem in tunnel engineering. The existence of pore water pressure can contribute to the collapse of shallow-buried soil tunnels that has serious influence over the safety of life and property. In this paper, the three-dimensional collapse mechanism of a shallow-buried earth tunnel with a circular top arc is constructed. Based on the nonlinear Mohr-Coulomb failure criterion and the limit analysis upper bound method, the collapse range of the shallow-buried earth tunnel is derived considering the pore water pressure. The formula for solving the optimal upper limit of support force is established. Moreover, the proposed method is compared with existing research for rationality verification of the method. The effects of different parameters on the collapse range, gravity and support force of the collapsed soil are analyzed. The results show that the pore water pressure has significant impact on the collapse range of the shallow buried soil tunnel as well as the gravity and support force of the collapsed soil. The effects of pore water pressure on the collapse range and weight of the collapsed soil are complex, while the support force increases with the increase of the pore water pressure coefficient. Moreover, the collapse range, gravity and support force of shallow soil tunnel are influenced with varying degrees by different parameters. This method can provide theoretical support for the design optimisation of shallow-buried soil tunnel.

Key words: shallow buried soil tunnel, nonlinear failure criterion, pore pressure, three-dimensional collapse mechanism, upper limit theorem