Mechanism and Remediation of Substructure Heave in Operating High-Speed Railway Tunnels: Insights from a Case Study

Substructure heave in high-speed railway tunnels poses a challenge to operational safety and maintenance. This study investigates an operating tunnel to clarify the heave mechanisms and evaluate effective remediation strategies. In-situ stress measurements, lithological analysis, and laboratory tests indicated the presence of swelling behavior in gypsum-bearing marly limestone beneath the invert. A humidity-based swelling constitutive model was established, and inverse analysis was used to quantify the swelling ratio of the surrounding rock. Numerical simulations were conducted to examine deformation characteristics and anchor pipe responses under different excavation segment lengths. Field monitoring recorded a maximum invert uplift of 103.7 mm, mainly associated with limestone swelling and further influenced by groundwater infiltration and horizontal tectonic stress. A segmented remediation approach was implemented, including full invert reconstruction using reinforced concrete and foot-locking anchor pipes in severely affected sections, and localized mortar thinning in moderately affected ones. Simulation results indicated that a 3 m excavation segment was effective in controlling deformation. Subsequent monitoring suggested that the implemented measures performed as intended, while residual uplift highlighted the need for continued long-term observation. The findings contribute to the improved understanding of substructure heave mechanisms in expansive rock and provide practical guidance for similar high-speed railway tunnels.