Numerical Simulation of the Interaction between Two Parallel Shield Tunnels

The growth in tunnel construction in urban environment makes increasingly complex geological and underground conditions for new tunnels design and construction, which means new tunnels have often to be located very closely to the existing ones. Thus, the prediction of the influence of new shield tunnel construction on the existing tunnel plays a key role in the optimal design and construction of closely parallel shield tunnel to avoid any damage of existing tunnel during and after new tunnel excavation. To investigate the influence of new shield tunnel excavation on the internal forces and deformations in the lining of existing tunnel, this paper presents a series of three-dimensional numerical simulations and parametric analyses performed for two commonly configuration models between two parallel tunnels: horizontal parallel tunnels and inclined parallel tunnels. Special attention was paid to the influence of separating distance and relative position between two parallel tunnels. The results of numerical analysis indicate that the separating distance and relative position between two parallel tunnels have considerable effects on changes in deformations and internal forces in the built tunnel lining. It was found that a new tunnel excavated below and inclined parallel to the existing tunnel would induce higher deformation and bending moment in the lining of the existing tunnel than new tunnel was positioned in horizontal parallel to the existing one. For the two horizontally parallel tunnels, the distance between two tunnels below which the deformation increases substantially is about 3.5 times of tunnel diameter. These insights provide the references for engineers and technicians to make a much more scientific and rational design and construction of close proximity parallel shield tunnel.