Deformation and Failure Analysis of the Urban Cloud Rail Crossing an Active Ground Fissure in Xi'an, China.

Ground fissure is the most common geological catastrophe phenomenon in Xi'an, posing a major security threat to the currently developing urban cloud rail transit system. In this paper, a 3D-FEM calculation model is established to study the influence of the intersection angles between the hidden ground fissure and the cloud rail on the deformation and failure characteristics of the structure. The findings indicate that the pile foundation is under tension in the main deformation area of the hanging wall of the ground fissure, and the negative friction zone (NFZ) appears below the neutral point (buried depth 18 m for intersection angle 30°). The pile foundation is under compression in the footwall, and the pressure it bears is less than the tensile force sustained by the hanging wall pile, and the NFZ is above the middle point. The NFZ of the pile foundation in the hanging wall and footwall increases as the intersection angle decreases. The pile foundation mainly undergoes vertical settlement, and the horizontal displacement is relatively small. The 3D movement of the pile foundation results in settlement and inclination of the superstructure of the cloud rail simply supported beam bridge, such as the pier and track beam. Therefore, the cloud rail bridge should span the ground fissure at a large angle as far as possible, and 3D adjustable support should be adopted to adjust the offset of the track beam caused by the ground fissure. [ABSTRACT FROM AUTHOR]