Face stability analysis of shallow shield tunneling in layered ground under seepage flow

This paper presents a limit equilibrium model for the shield face stability with special emphasis on the effects of ground heterogeneity and seepage flow. The model considers a new wedge mechanism whose inclination is capable of changing across soil layers to account for the spatial variation of soil mechanical properties. The limit equilibrium of the mechanism is established by using the method of slices, which considers horizontal arching without the need for arbitrary assumptions on soil stress distribution. The deterioration effects of groundwater flow are included by evaluating seepage force in the limit equilibrium based on an analytical hydraulic head field. To assess the proposed model, three-dimensional coupled pore fluid flow and stress finite element simulations are conducted. The above two methods are compared under different combinations of ground profiles, soil parameters, and hydrogeological conditions. These comparative analyses show the suitability of the limit equilibrium model. The influences of how horizontal arching is considered on the computed necessary face pressures under complex geological and hydrogeological conditions are explored.