Analysis on Overlying Pipe Deformation Induced by Tunnel Excavation Considering Detachment Effect

Considering the engineering characteristics of shallow buried tunnels in loess area and probable large deformation of soil, the overlying pipe was divided into pipe-soil detached area and pipe-soil deformation coordination area during excavation process, and a calculation model considering pipe-soil detachment interaction was proposed. On the basis of considering the influence of pipe buried depth on subgrade reaction modulus, the modified semi-infinite Pasternak elastic foundation beam model was used to consider soil continuity. After applying free-soil displacement load to pipe by two-stage method, the mechanical models and governing differential equations of both the detached area and coordination area were established, and the theoretical solution was given. Then, through comparison with the existing model test data, the proposed method in this paper was verified to be accurate, and the solution of pipe deformation without considering detachment was conservative. Finally, the main influencing factors of pipe deformation were compared and analyzed. Results show that, the maximum deformation of pipe increases with the increase of soil loss, and decreases with the increase of pipe-tunnel spacing, pipe stiffness and soil strength, but the magnitude of decreases are slowed down with the increase of each parameter. The range of detached area increases with increase of pipe stiffness, soil elastic modulus and pipe-tunnel spacing, while the maximum deformation difference which represents the degree of pipe-soil detachment increases with the increase of pipe stiffness, but contradicts with soil elastic modulus and pipe-tunnel spacing.