Centrifugal model tests on face stability of slurry shield tunnels under high water pressures

With the development of the national marine strategy and economy in China, more and more cross-sea and cross-river shield tunnels are to be built. The face stability of the shield tunnels is a key problem for the project safety. It will be more difficult to control the face stability under a high water pressure because of the unloading and seepage condition. A device for centrifugal model tests on face stability of shield tunnels is designed. The collapse patterns of the tunnel face and the surrounding soil pressures are investigated through the centrifugal model tests. Some important conclusions are drawn as follows: (1) The collapse of the tunnel face can be divided into four stages. At the first stage, the soil is still in an elastic state and the tunnel face presents a micro deformation. At the second stage, a local collapse happens to the tunnel face and the damaged area is located at the top of the tunnel face. At the third stage, the soil arch is formed, and the limit support pressure is reached. At the last stage, general collapse occurs and the collapse extends to the ground surface. (2) With the decrease of the slurry pressure, the soil pressure first decreases then increases, and a relative stable value is kept at last. The suggested support pressure ratio is 0.98 in this study. (3) The pore water pressure around the tunnel face decreases evidently. The seepage force acting on the soil contributes to the damage of the tunnel face. The conclusions obtained in this study may be useful for the similar projects.