The Vertical and Horizontal Displacements of Cross-river Twin-tunnels Surroundings Induced by Tunneling

Twin-tunnels are widely constructed in large cities because of their many advantages. The first tunnel (named tunnel_1) constructed before a period time than the second tunnel (named tunnel_2) which is to reduce the disturbance between twin-tunnels. In this paper, a three-dimensional scale model of twin-tunnels is established utilizing the discrete element method (DEM) with PFC3D, this model aims to investigate the difference of the vertical displacements and the horizontal displacements of the surroundings in construction process. The numerical results indicate that the peak vertical and horizontal displacements of the surroundings around tunnel_2 are larger than those around tunnel_1. The vertical and horizontal displacements of particles decrease with the distance from the out edge of the twin-tunnels shield lining increases. The existence and evolution of soil arching during tunneling process exert great influence on the stress state and deformation of twin-tunnels surroundings. The peak horizontal displacements are larger in the lateral points of twin-tunnels, while the peak vertical displacements are larger in the vault and bottom points, the tunnel excavation leads the particles around the twin-tunnels move to new location to achieve new equilibrium state. The peak vertical and horizontal displacements occur in own tunnel excavation process, whereas the adjacent tunnel construction affects the displacements as well. The excavation and existence of tunnel_1 have magnified effect on the vertical and horizontal displacements of tunnel_2.