Mechanical Responses of Underlying Tunnels Subjected to Surface Surcharge in Soft Ground

Abstract

A case history of surcharge-induced large deformations and noticeable leakages occurring on existing underlying twin tunnels in soft ground is presented in this paper. The field conditions are well-documented in terms of the processes of the surcharge and discharge as well as the structural mechanical responses of the tunnels. The longitudinal distribution curve and evolution of the tunnel vertical displacement are investigated in association with the surcharge and discharge activities. Structural damages and transverse deformations, including water leakages, cracks, unfilled corners, dislocations, and horizontal convergences, are also explicitly examined and analyzed. To derive insight into the relationship between the tunnel deformations and the surcharge, the ground settlements at different elevations due to the surcharge are calculated using a simplified method without considering the effect of the existing tunnel. Further, a modified two-stage method is adopted to estimate the longitudinal tunnel settlements, bending moments, and shear forces, in which the tunnel and underlying ground are modeled as a Timoshenko beam and Winkler foundation, respectively. Finally, for the upcoming preparation for the tunnel operation and planned road construction, practical suggestions for strengthening the tunnel and future construction activities are proposed.