A Novel Approach on Monitoring Fully Grouted Rock Bolt Instrumented with Distributed Fiber-Optic Sensor for Groundwater Characterization: Laboratory Feasibility Experiments

Abstract

This study introduces a new method to detect high-saturation zones using active heating-based distributed fiber-optic sensing (AH-DFOS) with a fully grouted rock bolt (FGRB). Using Rayleigh-based phase-noise compensated optical frequency-domain reflectometry (PNC-OFDR), temperature changes were measured in a fibre-instrumented cement grout specimen with simulated high-saturation zones. Results show AH-DFOS can effectively identify water zones and closely spaced fractures, especially with a separate sensing cable. A thermal halo effect was observed, and wider saturation zones showed slower temperature change. This method has significant practical implications for groundwater characterisation in geotechnical applications, including slope stability assessment, tunnelling, foundation monitoring, and dam reinforcement, where rock bolts are commonly employed as stabilizing structures.