The Construction Methods and Control Mechanisms for Subway Station Undercrossing an Existing Tunnel at Zero Distance

The existing tunnel will inevitably be disturbed when the new subway station is constructed cross under it at zero distance. Three innovative construction schemes were proposed, their effects on deformation control were compared by numerical simulations, and the mechanism of the influence of different tunnel support and excavation methods on the deformation control in them was further explored in order to seek a better scheme in this paper. The results show that the settlement of the existing tunnel in Scheme I (L-type beam + full-face excavation) is the greatest, and that the one in Scheme III (temporary steel column + double-pilot tunnel) is the smallest, but the settlement during excavation changes significantly, along with the large deformation on the side walls of the undercrossing area. Scheme III is not recommended because it is difficult to control and the construction effect is mediocre. Due to the existence of a large free face, the settlement of both sides of the existing tunnel is larger when the L-type beam supports the tunnel, and the bottom of the middle wall bears large compressive stress. The settlement of the existing tunnel excavated by the double-pilot tunneling method is less than that of the full-face tunneling method under the same tunneling support method, and the increase in settlement during the tunneling with the L-type beams is greater than that with the pier columns. In comprehensive consideration, Scheme II (pier column + double-pilot tunnel method) or combined pier column + double-pilot tunnel can control the deformation better.