Slip-Line Analysis of Passive Limit Support Pressure for Shallow-Buried Shield Tunnel Face

In view of the face stability of a shallow-buried shield tunnel excavation, this paper investigates the problem using an adaptive finite-element limit analysis combined with slip-line theory. First, a series of adaptive finite-element limit analyses are conducted to explore the passive failure mechanisms of the shallow-buried shield tunnel face. Based on the characteristics of the failure mechanisms, a funnel-shaped asymmetric boundary failure mechanism is proposed. Then, a mathematical computational model is established using the slip-line method, which considers the characteristics of the passive failure mechanisms and the stress state of the plastic region in the surrounding soil. The formula for calculating the limit support pressure for the passive failure of the shield tunnel face is derived using the finite-difference method, and the passive failure mechanisms of the face are analyzed. Finally, the calculated results of the model are compared with existing research results and the numerical results in this paper. The results show that the proposed computational model could accurately analyze the face stability of shallow-buried shield tunnels and might have wide applicability in the analysis of the limit support pressure and failure mechanisms of the face in shallow-buried tunnels.