High-sensitivity water leakage detection and localization in tunnels using novel ultra-weak fiber Bragg grating sensing technology

Abstract

Water leakage poses a serious threat to tunnel integrity and safety, making early detection critical. However, traditional techniques struggle with high-sensitivity leak monitoring. This paper presents a novel super absorbent polymer (SAP)-coated ultra-weak fiber Bragg grating (UWFBG) strain sensing cable for enhanced water leakage detection and localization in tunnels. The cable’s response and resulting morphological/strain changes upon leakage contact are characterized. When water interacts with the SAP-coated region, the polymer rapidly absorbs it and expands, producing a significant localized strain reduction. The cable demonstrates the repeatability for leakage sensing, addressing existing challenges. Tunnel model tests establish it can discriminate single-point, multi-point and linear leakages. Analysis of strain variations under different leakage rates, down to 1.5 mL/min, confirms strong performance for early warning. Installation along tunnel joints also enables leakage detection. In summary, the distributed SAP-UWFBG cable sensing system offers high sensitivity, real-time leakage monitoring capabilities critical for ensuring tunnel structural integrity and safety through its fast response to even minor leakage events.