Abstract:

A new Metro tunnel is planned to pass underneath an existing Metro station. In the paper, the Metro structures are simulated by means of finite element software. Two cases, i.e., Case 1 “double rectangular tunnels passing closely underneath existing Metro station” and Case 2 “double horseshoeshaped tunnels passing underneath adjoining existing Metro station”, are studied. Conclusions drawn are as follows: 1) The new tunnel should be located as far away from the central columns of the existing Metro station as possible, so as to avoid stress concentration; 2) As the distance between the elevations of the tracks of the two Metro lines increases, the settlement and the maximum and minimum principal stresses of the floor of the existing Metro station induced by the excavation of the tunnels below reduce gradually. When the clear distance between the two Metro lines is 3 m, the settlement of the floor of the existing Metro station induced by the excavation of the tunnels below is only 0.9 m, which is 14.5% of that in Case 1; and the maximum and minimum principal stresses induced are 75% of those in Case 1; 3) Monitoring shall be strengthened during construction, and if necessary, support replacement shall be made to facilitate secondary lining construction.

Key words: Metro station, tunneling closely underneath existing Metro station, tunneling underneath adjoining existing Metro station, numerical simulation, Metro tunnel