Failure mechanism and mechanical analysis in horizontal bedded surrounding rock with high in-situ stress

This study focuses on the Xuanzhenguan Tunnel, a representative engineering associated with the Lanzhou-Chongqing Railway in China. The tunnel has a total length of 7,447 m, with a maximum burial depth of approximately 265 m. The surrounding rock consists of medium-thick, horizontally bedded argillaceous siltstone with high integrity, and no groundwater was encountered during excavation. However, the construction process revealed severe deformation and structural failure. To analyze the damage characteristics of the tunnel and the influencing factors, field investigations, three-dimensional in-situ stress measurements, and laboratory rock mechanics tests were conducted. A geomechanical model, referred to as the horizontal compression-buckling failure, has been proposed to describe the behavior of horizontally bedded rock formations under high in-situ stress. Utilizing the principles from plate mechanics theory, a rectangular thin-plate mechanical model was developed, and the buckling equation under biaxial loading was derived to ascertain the critical load. For the deformed section between DK626 + 840 and DK626 + 850, the critical load was 12.3 MPa. Parametric analyses demonstrated the effects of load ratio, aspect ratio, plate thickness, span, and rock mechanical properties on the critical load. These findings offer practical recommendations for the design and construction of similar tunnel projects and hold considerable significance for engineering applications.