Study on the mechanical behaviors and fracture characteristics of secondary tunnel lining in layered strata

A critical issue encountered during the construction and operation phases of layered rock tunnels is the cracking of the secondary lining caused by asymmetric loading. To address this concern, we conducted an analysis of the asymmetric deformation characteristics and support mechanical behavior in common layered rock tunnels in China. We proposed indicators for asymmetric deformation and support force specific to layered rock tunnels. We investigated the internal force and fracture distribution characteristics of the secondary lining through similarity model tests and discrete element numerical analysis. Subsequently, we proposed an optimal support design method. The results reveal that: (1) Layered rock tunnels exhibit distinct asymmetric deformation characteristics, resulting in uneven pressure on the support. This asymmetric pressure eventually transfers to the secondary lining, leading to rupture. (2) With an increase in the lateral pressure coefficient, the deformation pattern of the surrounding rock evolves from a funnel shape to a butterfly shape. Supporting stress gradually concentrates in the direction of tectonic stress, and the fracture mode of the secondary lining transforms from perpendicular lamination compression damage to extrusion damage in the direction of tectonic stress. (3) A reduction in layered spacing weakens the bearing capacity of the surrounding rock and diminishes the safety factor of the secondary lining. The secondary lining experiences damage, progressing from spandrel cracking to shedding a large area from the vault to the haunch. As the layer angle increases from 0° to 90°, the unsafe position of the secondary lining shifts from the vault to the haunch. (4) Reduced layered strength leads to more pronounced asymmetric deformation of the surrounding rock, concentrating secondary lining fractures within a specific range perpendicular to the layering plane. Structural instability arises due to damage on the side parallel to the layering plane. (5) Increasing the length of anchor rods in the direction perpendicular to the layering effectively enhances the self-supporting capacity of the surrounding rock and reduces structural stress on the initial support and secondary lining. The use of long and short anchor supports significantly improves the safety coefficient of the secondary lining, ensuring its stability. © 2025 Elsevier Ltd