Stability Analysis of Shield Excavation Surface with Curved Body Model

Currently, the limit equilibrium method of wedge shape is generally adopted for the stability of the excavation surface in shield tunnel construction. In this method, the sliding surface is approximated by a plane, and the lateral friction force of the sliding surface is estimated and assumed to be a known quantity to derive the equilibrium equation and calculate the support force of the excavation surface. However, it is difficult to accurately estimate the lateral friction force of the sliding surface because of many factors that affect such friction, for example, soil arching. In this paper, a sliding block model of curved surface body composed of a semicircular platform and a partial sphere is proposed for the stability of the excavation surface in shield tunnel construction. By using the symmetry of the surface body model, there is no need for estimating the friction force of the sliding surface during the stability analysis of the excavation surface, and the calculation accuracy of the limit support pressure is improved. Furthermore, the force analysis of the semi-circular platform surface model above the tunnel vault is carried out. Considering the variation of the lateral pressure coefficient caused by the deflection of the principal stress under the soil arch effect, the analytical solution of the vertical stress in the soil is derived when the sliding crack surface is curved. Finally, we present a sensitivity analysis of various parameters affecting the support force of the excavation face through the study of examples. The influencing factors and changing rules related to the support force of the excavation face are also discussed.