Dual-Tube Configuration of FBG Sensors For Monitoring Internal Strains and Deformation of Soil Slope Through Laboratory Model Tests

The occurrence of rainfall results in a rise in pore-water pressure and a reduction of the soil’s shear resistance, thereby triggering slope failures that could pose hazardous risks to human life and infrastructure loss. To mitigate and minimise such catastrophic events, the employment of advanced instruments such as fibre Bragg grating (FBG) has captured attention in geo-structures monitoring. This is primarily attributed to their characteristics such as high capacity for multiplexing and compact size. This study developed soil strain sensors using FBG technology to monitor the soil behaviour of rainfall-induced soil slopes by evaluating the overall deformation from the internal strain monitored in both vertical and horizontal directions. The FBG sensors were multiplexed and protected by a dual-layer tube. The packaged FBG sensors are constructed with measured strain and temperature sensitivity to evaluate the responses of the packaged FBG towards both mechanical and thermal properties. The interaction between the soil slope and the packaged FBG was also evaluated in the pull-out test. The feasibility of the developed FBG monitoring system for real-time monitoring of strains has been presented through experimental and numerical analysis conducted on a non-homogenous residual soil slope subjected to 6.67 × 10^–6 m/s rainfall intensity. The data show that direct installation of FBG sensors is extremely sensitive to soil movement, measuring soil strain at microstrain levels in both horizontal and vertical orientations. These findings from both analyses reveal that strain distribution data are associated with the direction of the force applied.