A case study on middle wall stress transformation in shallow buried twin-arch tunnel

LONGSHAN tunnel, with two-way three-lane and large span twin-arch, is located in Wuhu, Anhui province, China. The tunnel is shallow buried in all length and the maximum buried depth is less than 10m. Its geological structure is complicated and over 1/3 of the tunnel is located in fault zone, the classification of the surrounding rock belongs to class V. The on-site monitoring indicates that the stress transformation in the middle wall is obvious in construction, the middle wall stress is determined by excavation and initial support and restrained by other parts. In design, it must be ensured that the middle wall has sufficient strength and stiffness; meanwhile, monitoring and the lateral supporting should be strengthened.