Abstract: When the earth pressure balanced shield is tunneling in the stratum with a high water table (for example, a tunnel constructed below the river by the shield), the hydraulic head difference between the ground and the shield’s chamber can produce seepage force acting on the tunnel face. The seepage force can lead to the failure of the tunneling face, in order to investigate the failure of the tunneling face considering the seepage flow. A device for the centrifugal model tests is developed, including: rigid model container, tunnel model, loading system, water table control system and water storage tank. The size of the rigid model container is 1 000 mm in length, 450 mm in width and 1 000 mm in height. Due to the symmetry, the tunnel model is made from a D-shape steel tube. The diameter of the tunnel model D is 100 mm the tunnel face is a D-shape aluminium plate with the drainage holes. The drainage holes allow the seepage water to flow into the tunnel. Loading system consists of a hydraulic actuator, a cylindrical loading rod, a linear variable differential transformer (LVDT) and control software. The loading system is used to fulfill the tunnel face retreating. The water table control system consist a flow pump, some hoses, a metal pipe with some holes and a solenoid valve. The water table control system allows keeping an invariant water table and steady seepage during the tests. Water storage tank is used to store seepage water. A series of the model tests with different water tables are conducted. The depth between the crown of the tunnel model and the water table are 1D, 2D and 3D. The depth of the overburden is 1D. The silty sands are used in the tests. The sands are collected from the beach on Qiantang River. A pressure cell is placed between the tunnel face and the loading rod. It is used to measure the support pressure. The armature of LVDT is connected to the loading rod. The LVDT is used to measure the horizontal displacement of the tunnel face. The results show that the effective support pressure decreased when the face plate is retreating. The effective support pressure increased slowly after reaching the minimal value. In the limit state, effective support pressure increased linearly with the hydraulic head .

Key words: shield tunneling, face stability, steady state seepage, centrifuge, effective support