The Face Stability Analysis of Shield Tunnels Subjected to Seepage Based on the Variational Principle

The stability of tunnel face remains a great challenge for tunnel engineers, especially when excavation is in a complex stratum under the water table. This paper aims to investigate the stability of soil in the front of a shield tunnel face induced by the presence of insufficient cabin pressure under the water table, on the basis of a variational principle and an upper bound theorem. The analytical expression of the rupture surface for the tunnel face is obtained, and the shapes of the rupture surface are plotted. Comparisons are made to check the present approach against the solution provided by numerical simulation techniques in order to show that the proposed method is valid. The parameter analysis indicates that the groundwater seepage has a significant effect on the range of the rupture surface for the shield tunnel face.