Study on response characteristics of in-service shield tunnel considering joint influence under foundation pit excavation

This study investigates the structural response of in-service tunnels during excavation to provide an accurate evaluation of their service status. Existing theoretical analytical models typically simplify tunnels as continuous long beams, overlooking the reduction in stiffness at segment joints; this fails to reflect real-world conditions. To address this, a discontinuous beam-Pasternak model is established which accounts for joint stiffness weakening, and a theoretical solution for the tunnel's structural response under excavation unloading is derived using the finite difference method. The model's rationality and accuracy are validated through comparison against two sets of measurement data and calculation results from existing models. The results show that the displacement curve calculated by the proposed model shows discontinuity in the abrupt change at joints, which is advanced. In certain cases, the parameters of the proposed model can be aligned with those of existing models by using specific values. The influence of the critical parameters of the proposed model on the structural response of the in-service joined tunnel is further analyzed. The findings of this study may offer a practical method for swiftly assessing the structural response characteristics of in-service tunnels during excavation unloading.