Influence of three-bench three-step excavation method on longitudinal deformation profiles in three-centered arch tunnels

Abstract

Longitudinal deformation profiles, one of the three curves in the convergence-confinement method, is widely used to analyse tunnel deformation and optimize tunnel supports. Due to the complex geological and excavation method, accurate wall deformation of the whole excavation process can hardly be obtained by in suit monitoring or analytical calculation. In this paper, a 3D numerical model with homogeneous rock layer, considering three-bench three-step excavation, is established to analyse the wall deformation of the face during the whole excavation process. Deformation increases sharply at the face when the rock mass is removed. The pre-deformation is then highlighted in different construction steps, which is quite different from the full-face excavation. Compared with the full-face excavation method, the pre-deformation of the upper bench and the mid bench are almost the same, while the pre-deformation of the low bench is larger. Finally, a new fitting formula is proposed for the normalized radial displacements occurring ahead of and behind the excavation of the tunnel for the three-step excavation method. The new formula can predict the longitudinal deformation of tunnel well and provide theoretical guidance for supporting.