Investigation of deformation of existing tunnel due to above excavation unloading considering tunnel lateral response.

The safety of underlying metro tunnels is significantly compromised when the excavation of the overlying foundation pit is not properly conducted. Currently, research on the longitudinal deformation of tunnels induced by upper excavation typically relies on the Pasternak model, which assumes the tunnel behaves as a slender beam with a circular cross-section. However, due to the complexity in characterizing convergence deformation under lateral loading conditions, few studies have systematically explored its influence on the tunnel deformation. In this study, a theoretical model considering the lateral response of the tunnel was developed. Then, analytical evaluations of engineering cases were performed to validate the model's accuracy. The results indicate that the proposed model provides a more accurate prediction of tunnel deformation due to overlying excavation compared to the Pasternak and Winkler foundation model. Additionally, the maximum vertical displacement of the tunnel increased with the widening of the foundation pit. It was also found that the maximum vertical displacement of the tunnel decreased almost linearly with an increase in the burial depth of the tunnel. In comparison to these two factors, the distance between the tunnel axis and the foundation pit had less influence on the tunnel deformation induced by excavation. The conclusions provide a theoretical reference for engineering calculations and practical applications.