Deformation behaviors of existing tunnels caused by shield tunneling undercrossing with oblique angle

The impact of twin shields tunneling undercrossing with an oblique angle on the existing tunnels is complicated and still lacks of understanding. This paper investigated the deformation behaviors of the existing tunnels with new twin tunnels construction undercrossing obliquely based on numerical simulation on a case history in Changsha, China. The accuracy of numerical analysis was verified in comparison with the field measurement. The variation of the ground settlement trough and the earth pressure acting on the existing tunnel during the shield tunneling was analyzed. Then, the transversal deformation, internal forces and torsion behavior of the existing tunnels induced by the new tunnels excavation were obtained. Additionally, a parametric study was conducted to investigate the impact of the intersection angle between the new and existing tunnels on the deformation behaviors of the existing tunnel. The results show that due to oblique intersection, the transversal deformation and internal forces of the existing tunnel show obvious asymmetrical characteristic, and an unrecoverable local torsional deformation of the existing tunnel on both side of new tunnel can be observed after shield tunneling. The parametrical analysis indicates that the intersection angle significantly influences on the maximum settlement of the existing tunnel bottom, which is up to 27.53% larger in parallel case than that in perpendicular case, and decreases rapidly as the interaction angle varies from 30° to 60°. Nevertheless, the maximum settlement of the existing tunnel crown is unaffected by the intersection angle.