Abstract: A new three-dimensional curved solid failure model by combining semi-circular platform and partial sphere was proposed to calculate limit support force of shield tunnel excavation face. At present, wedge-shaped models were generally used to calculate the supporting force of excavation face by using limit equilibrium method, in which the lateral friction force of sliding face was estimated as a known quantity. However, it is difficult to estimate the lateral friction force accurately because the lateral friction force of sliding surface is affected by many factors. In this paper, the symmetry of the curved solid model was used to solve the support force of the excavation face, and the calculation accuracy was improved by avoiding the estimation of the lateral friction force of the sliding surface. Furthermore, the force acting on the semi-circular platform model above the tunnel vault was analyzed given consideration to the variation of the lateral pressure coefficient caused by the principal stress deflection, and the analytical solution of the vertical stress in the soil was derived considering soil arching effect when the sliding surface is a spatial curved surface. Then the rationality of the proposed model was verified through examples analysis. Examples analysis show that the proposed model is simple, effective and practical. It can be widely used in the stability analysis for shield tunnel excavation face.

Key words: shield tunnel, soil arching effect, excavation face stability, supporting pressure, curved solid