Longitudinal responses of shield tunnel subjected to surcharge considering dislocation

Surcharge due to improper soil dumping and irregular backfilling often causes excessive deformation along the adjacent shallow tunnel in soft-soil areas. Tunnel structures are usually modelled with beam elements where the bending of the concrete segments is considered while the shearing dislocation between segmental rings is usually ignored. In this work, a Timoshenko beam was used to consider such dislocation of a shield tunnel under surcharge and a Pasternak foundation was used to account for the tunnel-soil shear effect. A numerical method was then developed to assess the effect of surcharge loading on the longitudinal responses of the underlying tunnel based on a two-stage method. The proposed solutions were verified using a case history from Shanghai and a three-dimensional numerical simulation from the literature. Results of a further parametric study showed that the deformation induced by surcharge loadings would be underestimated without the shearing-induced dislocation of tunnel segments, which could overpredict the serviceability of the underlying tunnel in surcharge accidents.

Automated summary

Improper soil dumping and irregular backfilling can lead to excessive deformation of shallow tunnels in soft-soil areas due to surcharge. This study developed a numerical method, using Timoshenko beams and Pasternak foundation, to assess the effect of surcharge loading on tunnel responses. Results showed that neglecting the shearing-induced dislocation of tunnel segments could underestimate the deformation induced by surcharge loadings and lead to overprediction of the serviceability of the tunnel in surcharge accidents.