A simplified method for estimating the longitudinal and circumferential behaviors of the shield-driven tunnel adjacent to a braced excavation

The construction of soil excavations will inevitably have an adverse effect on the adjacent tunnels. However, the structural responses of existing shield-driven tunnels adjacent to a braced excavation and their serviceability are still not fully understood. This paper presents a simplified method for evaluating the longitudinal and circumferential behaviors of the shield-driven tunnel adjacent to a braced excavation. To capture both shear and bending deformation of segmental linings, an appropriate model was adopted to study the longitudinal tunnel deformation features based on the Timoshenko beam theory. A continuous ring structure under a plane strain condition was used to determine the circumferential behavior of segmental lining. Case history was used to verify the developed simplified method. Systematic parametric studies were performed to develop a better understanding of the governing factors of the tunnel behaviors, including excavation-tunnel relative position and the retaining wall deflection. Furthermore, the serviceability limit state of shield tunnels was quantified using the defined three factors of safety, which enables a quick assessment of the excavation-induced tunnel damage potential. The contours of factor of safety can also be employed to determine the envelope of the excavation influence zones.