Face Stability Analysis of Slurry Shield Tunnels in Rock-Soil Interface Mixed Ground

When shield tunneling in rock-soil interface (RSI) mixed ground, maintaining the stability of the tunnel face is very challenging. This study aims at the investigation of the face stability of slurry shield tunnels in RSI mixed ground. A new apparatus was developed to simulate pressurized slurry supporting the tunnel face in centrifuge tests. The progressive failure of the tunnel face was triggered with slow decrease of slurry pressure. With two equivalent model tunnels of circular shape and semicircular shape, the variations of soil (water) pressure and the displacement field in front of the tunnel can be obtained simultaneously. The face failure was found to be a local collapse in the upper soil layer. The limit support pressure was picked out at the sudden change of the measured soil or water pressures. Then the classical wedge-prism model was introduced and modified to calculate the limit support pressure for slurry shield tunnels in RSI mixed ground considering the partial collapse. Numerical analysis was applied to verify the theoretical analysis and sensitivity analysis was performed to estimate the influence of different parameters on the theoretical solutions.