Thermal effects and infrared detection method for shallow reinforcement corrosion in tunnel linings under natural conditions

With the increase of the service life of the tunnel, the diseases such as water leakage and cracking of the linings have become normal, and the induced reinforcement corrosion gradually emerges. After the reinforcement corrosion to a certain extent, the linings will peel off. Therefore, it is particularly important to discover the corrosion degree and position of reinforcement in time. The heat conduction laws of reinforcement corrosion of the linings under the natural temperature difference are studied through the laboratory tests and numerical simulations, the influence laws of temperature difference inside and outside the linings and the degree of reinforcement corrosion on the inner surface temperature distribution of the linings are analyzed, and the feasibility and applicable conditions of infrared thermography technology for detecting the corrosion of the shallow reinforcement corrosion of the linings are explored. The results show that: (1) The infrared detection is feasible when the temperature difference inside and outside the linings is 1.0℃~11.9℃, and the temperature difference inside and outside the linings can meet the conditions in winter. The minimum temperature difference required by the infrared detection is 3.8℃, 1.8℃ and 1.4℃ when the corrosion rate of reinforcement is 6.51%, 19.02% and 23.16%. (2) The relationship among the corrosion rate of lining reinforcement(ρ), the temperature difference of inner surface of the secondary linings (T₁) and the temperature difference between the inner and outer surfaces of the secondary linings(T₂) is \rho = 1.1 \times 10^5T_2^ - 3.2T_1^3 + 503.7T_2^ - 0.9T_1 . When the temperature difference inside and outside the lining is 3℃~30℃, the detectable corrosion rate of reinforcement is 9.78%~1.18%. (3) Through the heat conduction effect caused by the temperature difference inside and outside the linings, the position and degree of reinforcement corrosion can be comprehensively judged from the temperature distribution on the inner surface of the linings, which provides a new rapid detection method for the corrosion of shallow reinforcement in tunnel linings.