Stability analysis of shield tunnel face under complex ground conditions

Abstract

Current underground space development features ever-increasing scales. More and more planned tunnel lines have alignments that are characterized by varying passing depths. Both conditions make it more frequent that the shield tunnel face is exposed to heterogeneous ground consisting of distinct soil layers and hydraulic loads, which makes it remarkably challenging to maintain a stable shield face. This work presents a limit equilibrium model to analyze the face stability of shield tunnel under complex ground conditions. The model is consistent with the existing method of slices for uniform soil profile in that the effect of horizontal arching is considered without the need of an a priori assumption on the distribution of horizontal stresses, but extends it to the stratified ground by allowing the variation of failure mechanism across soil layers. Three-dimensional coupled pore fluid flow and stress finite element analyses are performed to study the tunnel face stability in heterogeneous ground consisting of horizontal layers and subjected to hydraulic loads. The results show that the multilayer wedge model can compute limit support pressures that are reasonably close to finite element solutions. Lastly, the finite element method and the multilayer wedge model are employed to analyze the stability of tunnel face in aquifer-aquitard alternate layers with confined water.