Abstract: Large deformation of soft rock tunnels is an engineering and technical challenge that must be addressed to realize the ambition of becoming a leading nation in tunnel construction. However, the intricate relationship between rock deformation constraint/release, rock pressure and lining bearing capacity remains ambiguous, posing theoretical obstacles in selecting appropriate support types and determination of design parameters. To tackle this challenge, this study adopts theoretical analysis method to model and analyze the mechanism of large deformation of soft rock tunnels, attempting to establish a theoretical relationship among these factors. Firstly, theoretical formulations are presented to elucidate the relationship between rock pressure/lining bearing capacity and lining thickness, revealing the theoretical reason why, when the lining thickness is less than a certain critical value, increasing its thickness induces a greater rate of increase in surrounding rock pressure than in the bearing capacity of the lining. Secondly, the generalized Kelvin model is employed to characterize the time-dependent deformation of surrounding rock, and the deformation process of yielding lining is simplified into the deformation release stage and deformation control stage. A tunnel mechanical model describing the interaction between surrounding rock and yielding lining is established, and analytical solutions for tunnel/lining displacement and lining pressure at different deformation stages are provided. The above analytical solutions for yielding lining supported tunnels can further be degenerated to those under the strong support action. Moreover, the reliability and feasibility of the theoretical model established in this study are well verified by comparing with results in previous reference and by applying it in a practical project. Finally, based on the proposed analytical solutions, a comprehensive parametric investigation is conducted, including the deformation capacity of surrounding rock, thickness of strong support, tunnel yielding displacement, and yielding resistance. The results indicate that under some large deformation conditions, if strong support is used, the required lining thickness is excessively large, necessitating the adoption of yielding lining. There exist reasonable ranges for both the yielding displacement and yielding resistance of yielding lining, which should be determined considering the mechanical properties of surrounding rock and lining. The concise tunnel theoretical model provided in this study can play an important theoretical support for the rapid design in the preliminary stage of related projects.

Key words: soft rock tunnel, time-dependent deformation, strong support, yielding lining, supporting effect