Numerical analysis of cut-and-cover excavation part of a cross-river tunnel

The riverside parts of cross-river tunnels, including embedded section and open section, are usually constructed by the excavation method. Limited by the inadequate supply of urban land, the construction field and surrounding environment of such excavation are becoming more and more complex when the cross-river tunnel is built in the center of city. Puxi riverside section of Shanghai Dapu Road double-line tunnel project is located in the present Rihui River where the geological conditions and adjacent underground structures are complex. To ensure the safe construction process of the cut-and-cover tunnel structure, the refilled soil in river channel is improved after the mud layer in the riverbed is removed, and then the open excavation is carriedout in the refilled soil layer. A numerical method, in which hardening-soil model is adopted, is used to analyze the behaviors of the cut-and-cover excavation and to discuss the ground settlement and displacement of adjacent structures. Comparison shows that the predicted value of the retaining structure displacement, ground settlement and motion of adjoining construction are approximately consistent with the measurements. It is also demonstrated that the proposed construction method for such a excavation in refilled river is efficient.