Deformation and failure analysis of metro shield tunnel induced by active ground fissure in Xi'an, China

Abstract

Ground fissure is an important urban geohazard in Xi'an, China, which poses a security threat to Xi'an metro construction. In this paper, a 3D numerical model was performed to analyze the mechanical behavior of shield tunnel of Xi'an metro (line 8) crossing an active ground fissure. The results indicate that the lining structure near the ground fissure is in a tension–compression state. The deformations of tunnel and surrounding soil do not match owing to their different stiffness, and then the bottom of the tunnel in the hanging wall and the top of the tunnel in the footwall separate from the soil, resulting in the reduction of support from surrounding soil. The tunnel at the ground fissure is subjected to large shear force, and the structure presents segment dislocation and lining cracks around bolts when the ground fissure dislocation reaches 20 cm. The deformation and failure of shield tunnel orthogonally intersecting with ground fissure is in a shear failure mode. It is suggested that structural reinforcing measures such as special segments and bolts are needed within the influence area of the ground fissure.