THREE-DIMENSIONAL STRENGTH REDUCTION NUMERICAL SIMULATION OF THE FACE STABILITY OF SHIELD TUNNEL UNDER SEEPAGE CONDITION

The three-dimensional numerical simulation combined with strength reduction was used to study the face stability of shield tunnel under seepage condition. According to the non-convergence condition in numerical simulation, the safety factors in active and passive deformation modes were obtained. The relationship between the safety factor and the support pressure ratio were obtained by summarizing the numerical results. Safety factor shows a maximum value, which correspond s the optimal support pressure. The optimal support pressure without seepage equals to the lateral earth pressure at rest, and the optimal support pressure under seepage condition is higher than the lateral earth pressure at rest. The limit support pressures of tunnel face under active and passive failure condition with seepage are higher than those without seepage.