Abstract:

[Objective] This study focuses on the issue of cracking in the support structures of high-temperature water diversion tunnels during the operation period caused by excessive tensile stress. An active thermal control strategy involving the application of thermal insulation coatings with specific thicknesses before water flow in the tunnel is proposed and systematically quantified. This study evaluates the regulatory effect of this strategy on the temperature and stress fields throughout the life cycle of the tunnel (from construction to operation) and its role in improving crack resistance safety. [Methods] Based on a three-dimensional thermo-mechanical coupled finite element method, a typical high-temperature water diversion tunnel was used as the engineering background. The temperature evolution and stress response of the structure under different thermal insulation coating thicknesses were precisely simulated. [Results] The thermal insulation coating significantly improved the temperature gradient of the secondary lining. As the coating thickness increased, the temperature difference between the inner and outer sides notably decreased. The application of thermal insulation coating before water flow in the tunnel effectively suppressed the temperature difference between the inner and outer sides of the secondary lining and the resulting tensile stresses. The coating thickness was positively correlated with the reduction in tensile stress, leading to a corresponding decrease in the area of zones that did not meet crack resistance safety criteria. In particular, when the coating thickness was 2 mm, the peak tensile stresses at all key locations of the secondary lining were below the ultimate tensile strength of the material. Except for localized high-stress zones, the crack resistance safety factor in the majority of the zones remained stable above 1.6, significantly outperforming the no-coating or thin-coating schemes. [Conclusion] Pre-applying a thermal insulation coating of appropriate thickness (such as 2 mm) before water flow in the tunnel is a highly efficient and innovative thermal control and cracking prevention strategy. This source-intervention approach significantly reduces the tensile stresses induced by temperature loads, fundamentally enhancing the structural safety and durability of high-temperature tunnels during long-term operation. The research findings provide direct quantitative design guidance and key technical support for similar engineering projects.

Key words: high-temperature water diversion tunnel, finite element simulation, temperature field, stress field, crack resistance safety degree