Abstract: It is difficult to monitor the underground tunnel lining in an all-weather manner due to its concealment. An intelligent monitoring method of tunnel lining based on self-sensing FRP (fiber reinforced plastic) bar embedded with optical fiber is proposed in this paper. The optical fiber sensor is embedded in the fiber reinforced plastic to form self-sensing FRP bar, which is installed in the tunnel lining, to monitor the stress state of the tunnel lining in a real-time and all-weather manner. The monitoring results can show the circumferential stress of the tunnel lining and predict the risk of crack generation. The intelligent monitoring method is used to monitor Chentang tunnel in Guangzhou-to-Shantou high-speed railway. The main factors affecting the safety of lining structure during the period from lining construction to operation are surrounding rock pressure, temperature difference stress caused by hydration heat and stress caused by concrete drying shrinkage. The temperature difference stress caused by hydration heat can lead to a large tensile stress on the inner side of the lining. Therefore, reasonable construction measures need to adopt to avoid cracking caused by temperature effect. The proposed intelligent monitoring method is capable of monitoring the tunnel lining stress-strain state in real time, for a long period of time and in all weather. This self-sensing system will continuously and timely reflect the risk of tunnel lining cracking during the tunnel operation, providing a technical guarantee for the operational safety of high-speed railroad trains.

Key words: intelligent monitoring of lining, stress state at full stage, lining cracks, fiber bragg grating, self-sensing FRP bar