Abstract： The face stability mechanism for slurry shield under the layered ground condition is of great significance. During the process of the shield tunnelling, the original structure and the strength of the soil around the face will be changed due to the slurry gradual infiltration into the excavation face. Thus, in order to connect and quantify the relationship between the mechanical property and the microscopic structure, the triaxial experimental tests coupled with the numerical simulation method for evaluating the tunnellinginduced ground movement were introduced, Then, based on the actual geometry of the failure mechanism in clay, a modified wedge model with its corresponding analytical solution for the critical face support pressure was presented. For the layered ground condition, it is recommended that the slurry support pressure should be controlled to a relatively low level due to the softening characteristic of clay soil, and it is the pressure produced by the shield cutter bits and transferred to the excavation face contributes to face stabilization. The geometry of the failure mechanism in this ground condition resembles the case in sand: it exhibits a chimneylike failure mechanism, can be better described by the wedge stability models, and the maximum displacement of the ground just occurs on top of the tunnel face.