Study on rock mass stability of large scale complex underground tunnels in the urban underground

The paper focuses on the rock mass stability of large complex tunnels in urban area. The study is based on an adjacent tunnel project involving seven parallel and intersect tunnels in China. The third longitudinal expressway and the metro line 5 share HongYanCun Bridge to cross the Jialing River. Due to the limitation of the elevation of the GongYanCun bridge, the four-tunnel of the third longitudinal expressway (the main tunnel of left line, the main tunnel of right line, A ramp and B ramp) are located above the subway station tunnel of the metro line 5. And the two three-lane large scale tunnels are located on the left and right spandrel of the station main tunnel; the minimum distance is about 1.3m. The seven tunnels are intersected, adjacent and parallel in a long distance. Using 3D numerical simulation method, the stability influence during the construction process has been studied. The study mainly includes: the variation characteristics of rock mass stress, displacement and plastic zone, the deformation rule of the supporting structure. The study results can be applied to modify and optimize design and construction; it will also be a valuable reference for the similar projects.