Face Stability Analysis for a Shield Tunnel in Anisotropic Sands

Shield tunnels are widely used in urban underground construction. The stability of the tunnel face has become a crucial issue in shield tunneling. In this paper, the anisotropy of friction angles is taken into account in the upper theorem of limit analysis of the tunnel face. A formula of the anisotropic friction angles is established and applied in the limit analysis of the tunnel face, and the anisotropic parameters can be determined by the simple triaxial compression tests. The results are compared with existing works to validate the reasonability of the proposed method. Two types of constant friction angles are adopted to compare the anisotropic effects on the support pressures distributed uniformly on the tunnel face and the failure mechanism. The results show that the anisotropy of friction angles will lead to an increase in the support pressures and obviously influence the shape and range of the failure pattern. The anisotropy of friction angles should be considered in the stability analysis of the tunnel face.