Optimal length for segmented structure of the metro tunnel obliquely crossing active ground fissure zone

Ground fissure is the most typical geo-hazard in the city of Xi’an. At present, the segmented metro tunnel in Xi’an metro engineering construction are adopted against the active ground fissures and the optimal length of the segmented tunnel structure is the key to the design of the metro tunnel obliquely crossing active ground fissure zone. Considering the Xi’an metro lines passing through active ground fissure zones, the reasonable mode and optimal length of a sectional tunnel with flexible joints are studied in this paper through finite element numerical simulation for the segmented structure of a metro tunnel. The calculation results show that the plastic zone of the tunnel lining is in a small range and mainly distributes in the arch bottom and skewback of the tunnel under the mode of opposite joint, while it is in a large range and relatively complicated in the mode of cantilever, which is comparatively against the reinforced lining. The better of the two modes is opposite joint and the optimal length of the sectional metro tunnel is 15 m. In addition, the main deformation zone of tunnel outside the scope of ground fissures can be segmented according to 10-15 m, the length of the fortified area of tunnel beyond the main deformation zone can be properly increased according to other requirements, such as the tunnel waterproof, adjustment of rail slope, etc. The conclusions can be presented as the reference for structure design of urban metro construction and underground space development under the action of ground fissures.