Development and Verification of a Vertical Graphene Sensor for Tunnel Leakage Monitoring

To achieve accurate monitoring of water leakage in tunnels, a new vertical graphene sensor is designed and developed. The sensor operates on the principle that the superabsorbent polymer (SAP) swells dramatically upon water absorption. This swelling induces deformation in the vertical graphene (VG) thin film, highly sensitive to such changes. Consequently, water leakage is detected through the resistance alterations in the VG thin film. In this study, the structure, the preparation process, and a simplified theoretical sensing model of the VG thin film are introduced, followed by the structural design, working principle, and calibration experiments of the developed water leakage sensor. Experimental results show that the sensor exhibits ultrahigh sensitivity, with a linearity error of 10.8%, and can detect water leakages as small as 50 μL. To verify the sensor's feasibility, it was deployed in the cross-sea tunnel between the Dayang Station and the Qingdao North Station on Qingdao Metro Line 8, monitoring water leakage of the tunnel surface. Monitoring results indicated that the maximum leakage volume at the leakage location reached 19 mL.