Abstract:With the advancement of urban underground space development, the design of the foundation pit for newly-built tunnels should fully reserve the conditions for the long-term shield tunneling at the lower level. Focusing on the Shanghai Waiqingsong Highway Tunnel Project, and for the parallel development of new tunnels and long-term rail transit, the research is carried out on the design of foundation pits under the circumstances of temporary traffic restrictions during the construction period. A calculation model is established using the finite element software MIDAS GTS/NX to obtain the internal force distribution mode of the retaining structure composed of short underground diaphragm walls and long construction piles. And combined with the field monitoring data, the force rationality of this theory is verified. The result shows that the internal force distribution of the retaining structure composed of short underground diaphragm walls and long construction piles basically conforms to the stiffness distribution theory. The most of the bending moment internal forces are borne by the short underground diaphragm wall, and the overall stability of the foundation pit is controlled by the long construction pit method. A trestle system is used of the first concrete strut as a trestle beam. In the case where the space for pile foundation layout is limited, the lattice columns of the pit can be embedded within the central wall of the tunnel, the force-bearing capacity of the trestle system can meet the internal force deformation requirements of the foundation pit and the traffic needs of social vehicles during construction, which can provide a useful reference for similar deep foundation pit projects in this area.
