Multi-scale analysis of the influence of red-bed lithological interface on tunnel deformation and instability

Abstract

Red-bed is a stratigraphic combination widely distributed all over the world. However, with the construction of engineering projects, red-bed-related disasters have become increasingly prominent. This study focuses on tunnel deformation in the red-bed sandstone-mudstone interface section of the Leye Tunnel on the Chongqing-Kunming High-Speed Railway. By utilizing on-site data collection, laboratory testing, and numerical simulation methods, we developed a systematic research approach for red-bed tunnel deformation encompassing macroscopic mechanical characteristics, mesoscopic contact characteristics, and microscopic damage characteristics. This method clarifies the multi-scale degradation-disaster preparation characteristics of the red-bed lithological interface and their impact on tunnel deformation and instability. The study results indicate that the lithologic interface is a fundamental factor controlling deformations in red-bed tunnels and is also crucial in determining the deformation and failure modes of the lining structures. Sandstone, with its strong mechanical properties and occlusal mineral contacts, resulting in cracks in the initial support. In contrast, mudstone has weaker mechanical properties, with mineral particles encapsulated by clay minerals, which manifests as deformation of the steel arch in the lining structure. Notably, when the mudstone-to-sandstone ratio on the palm face is 1:1, the tunnel displacement field area is significantly larger than that of homogeneous stratum sections on both sides. However, surrounding rock deformation is controlled by the stronger sandstone. Therefore, it is necessary to pay attention to the engineering geological problems caused by the red-bed, to guarantee the efficient implementation of the major national strategies.