Stabilisation time analysis method for deep tunnels considering rheological effects and lining influence

In tunnel design, the stand-up time of the surrounding rock and the stabilization time of the rock-structure after support are crucial parameters. These parameters affect excavation methods, excavation cycles, rock reinforcement strategies, and the timing of support installation. Currently, evaluations are largely empirical, based on surrounding rock classification, making it challenging to ascertain the long-term stability of the rock-structure. Utilizing creep damage model theory, we derived the viscoelastic-plastic response of surrounding rock under creep. A method for calculating tunnel support time under various geological conditions was proposed, combining longitudinal deformation curves. The stabilization time of surrounding rock-primary support under different conditions was derived from tunnel support characteristic curves. Key findings include: ① The stand-up time of unsupported surrounding rock decreases with increased tunnel depth, increases with higher GSI (Geological Strength Index), and extends with greater maximum allowable displacement. ② The stabilization time for supported surrounding rock-structure increases as support distance decreases, support time decreases, support stiffness increases, and reserved deformation increases. The sensitivity order of support parameters impacting stabilization time is primary lining support time > safe distance from second lining to face > primary lining stiffness. ③ Analysis of the Leye Tunnel DK504 + 050 section confirmed this method reliability, providing reliable initial data for future section predictions. This study enhances tunnel engineering theory and ensures tunnel construction safety and cost-effectiveness.