Theoretical analysis of the overburden stratum load on metro tunnel induced by active ground fissure

Ground fissures are the most common urban geohazard in Xi’an, China. The activities of ground fissures often trigger stratum dislocation, which do harm to the built metro tunnels. Thus, tunnel structures must be designed to reasonably withstand the stratum load during ground fissure activity. In this study, a simplified solution was proposed to calculate the stratum load and the vertical stress of metro tunnel under the action of active ground fissure. The stress characteristics of metro tunnel subject to ground fissure dislocation were analyzed and its progression was divided into three stages, the initial elastic stage, the local void area stage, and the maximum void area stage. The vertical stress of the tunnel at each stage was calculated according to the corresponding mechanical characteristics. Compared with results from numerical simulations, the calculation method developed in this study, which accounts for the stratum holding effect and slip plane, is reliable and reasonable. Additionally, according to the variability of stress magnitude and the impacted range, the tunnel is roughly divided into four stress zones, namely, stability and influence zones in the footwall, and deformation and micro deformation zones in the hanging wall of the ground fissure. This theoretical analysis provides a reference for stratum load calculations and engineering design of metro tunnels crossing active ground fissures.