Research on the Influence of Newly Built Subway on Existing Structure in Collapsible Loess Area

Research purposes: In order to study the influence of tunnel construction on existing tunnels in collapsible loess area, the ground loss caused by tunnel construction is simulated by geotechnical centrifuge test and by controlling the vault settlement of new shield tunnel. Considering the distance between new tunnels and existing tunnels, the maximum vertical displacement of inverted arch and the variation rule of surrounding rock pressure of existing subway tunnels are studied under multiple working conditions. Research conclusions:(1) The maximum vertical displacement of inverted arch of existing tunnels increases linearly with the increase of stratum loss rate and the decrease of net distance of tunnels. Based on this, the control criteria for vault settlement of newly built tunnels in the course of single-line shield tunneling are proposed: net distance of 0.5D, 0.4D, 0.3D and 0.2D is 25 mm, 19 mm, 14.5 mm and 12.6 mm, respectively. (2) Surrounding rock pressure at inverted arch of existing tunnels decreases more obviously than that at arch waist and vault, and the pressure at the upper part of newly built shield tunnel tends to increase. Arch effect is formed in the upper part of newly built tunnel within a certain height range. (3) The research results are analyzed and compared with the measured data of inverted arch of existing subway structure, and the optimal fitting formula can provide prediction curves for similar projects in collapsible loess area. © 2019, Editorial Department of Journal of Railway Engineering Society. All right reserved.