Factors Influencing Post-Construction Responses of Underlying Tunnel below Excavation Base in Gravelly Clay

This paper investigates the response mechanism behind an existing tunnel subjected to a long and deep collinear excavation in Shenzhen granite residual strata. The maximum excavation depth was 18.0 m and the minimum residual soil depth above the tunnel crown was only 6.3 m, causing appreciable tunnel heave and transverse deformation. Two-dimensional parametric numerical study is adopted to examine the impacts of influential factors (excavation dimensions, ground permeability coefficient, and exposure time of the excavation base) on the tunnel responses. The hardening soil model with small strain (HS-Small) is used to model the soil stress–strain behavior. It is found that the long-term deformation of the tunnel after excavation and unloading cannot be ignored. The soil will continue to consolidate and deform, and the tunnel will continue to heave with soil due to the dissipation of the negative excess pore water pressure. The long-term deformation of the tunnel after excavation and unloading is significantly affected by the excavation geometry. With the increase in excavation width B , the final tunnel heave after excavation and unloading increases first and then tends to be stable. Furthermore, the relative position of the tunnel and the excavation base is also one of the major contributors to the long-term deformation of the tunnel. The growth of tunnel deformation Δ f and the exposure time T are exponentially negatively correlated with L y . The change in the permeability coefficient k has no effect on the final stable tunnel heave and the growth of tunnel deformation Δ f , which is exponentially negatively correlated with the exposure time T.