Abstract：Most urban subway tunnel use parallel form as the tunnel design and construction scheme. And the construction methods are divided into shield method or subsurface excavation method according to different factors such as the geological conditions. Because the urban underground space has become more and more crowded, the study on the influence degree of the existing tunnel due to underlying twin-parallel tunnels excavation is particularly important. In this paper, the simplified analytical method is proposed baesd on the two-stage method to obtained the longitudinal deformation of existing tunnel due to underlying twin-parallel tunnels excavation. In first stage, the impact of twin underlying tunneling on the existing tunnel is taken as the superposition of two separate modified Gauss-distributed loading induced by each twin tunnels. In second stage, the existing tunnel is simplified as Timoshenko beam on Winkler foundation. Then the problem was analytically solved accordingly by using Galerkin method. The proposed prediction method is verified with the practical tunnel engineering. Finally, the parametric studies including different tunnel location, formation loss rate and relative bending stiffness and mechanics parameters of soils are presented to investigate the influence rules on longitudinal deformation of metro tunnels.
