Abstract:

Shield departure and reception is one of the most important issues when shield crosses working shaft. In the paper, complex 3D calculation model is established, with shield crossing Meizizhou circular ventilation shaft as background，and numerical simulation is conducted by using solid elements and soil spring releasing excavation load. Firstly, the grade of the plain concrete that the shield will cut is analyzed. Conclusion is drawn that C15 concrete, which can not only decrease the difficulty of shield crossing, but also can guarantee the safety and stability of the retaining structures, should be adopted. Secondly, the deformation and internal forces of the retaining structures, including the diaphragm wall, the inner wall and the ring beam, are analyzed. Conclusion is drawn as follows: Compared to those before shield crossing, the maximum deformation and internal force of the diaphragm wall after shield crossing increase by 45% and 228% respectively, the maximum circumferential moment and the maximum vertical positive moment of the inner wall increase by 200% and 54% respectively, and the maximum circumferential moment of the top beam increases by 1 160%. Therefore, during the design of the works, the reinforcement for the zones of the diaphragm wall, inner wall and top beam with large stress shall be strengthened so as to ensure the successful crossing of the shield.

Key words: Weisanlu rivercrossing tunnel in Nanjing, shield departure and shield reception, ventilation shaft, retaining structure, stability