Study on optical fiber sensing system for safety monitoring of underground utility tunnel

In response to the absence of effective monitoring methods for the safety of underground utility tunnels, a monitoring system for underground utility tunnel pipelines based on interferometric distributed optical fiber vibration sensing (iDOFVS) technology is proposed. This system has been successfully applied for online safety monitoring of over 69 km-long underground utility tunnel pipeline in the Guangdong-Macao In-Depth Cooperation Zone in Hengqin. The system utilizes MZ-Sagnac iDOFVS, replacing traditional point sensors with single-mode optical fibers. A passive trigger unit is installed at the manhole cover to detect vibration signals along the tunnel and disturbances caused by manhole cover openings. Abnormal events are identified through data processing and subsequently reported to the operation and maintenance management section. Since its implementation in December 2019, the system has detected nearly a hundred unreported construction incidents, one cable theft, and one cable joint discharge accident, offering an innovative solution to ensure the safe operation of urban underground infrastructure.