Abstract: Leakage has a serious impact on the safe operation of tunnels. In recent years, the distributed optical fiber sensing (DOFS)-based leakage monitoring technology has become one of the hot topics in the field of development and utilization of underground space. In view of the deficiency of the common tunnel leakage monitoring technology, a new temperature-sensitive optical sensing cable for tunnel leakage is developed based on the principle of wet-bulb thermometer, and a DTS-based tunnel leakage distributed sensing method is proposed. The feasibility and the influencing factors of the distributed sensing method for tunnel leakage were investigated and verified through lab model tests. The results show that the developed temperature-sensitive optic sensing cable can be used to accurately identify leakage events. The sensing cable has good repeatability by the experiments of several dry-wet cycles. The influence of the leakage speed, ambient wind speed and leakage duration on the identification of leakage events is insignificant. The threshold criteria for leakage event identification is proposed, i.e. when the relative temperature drop between different sampling points of the sensing cable reaches or is greater than 0.5 ℃ , and the temperature drop rate within 2 hours reaches or is greater than 0.4 ℃ /h, it can be judged as leakage. 

Key words: tunnel, leakage, DTS, distributed sensing, temperature sensitive