Slope Monitoring With Fiber-optic Sensing Can Provide Early Landslide Warning

OptaSense and the British Geological Survey (BGS) have been using an OptaSense fiber-optic Distributed Rayleigh Sensing (DRS) system to monitor strain changes on a slope that forms part of the BGS National Landslide Laboratory in North Yorkshire, UK. The slope is instrumented with a wide variety of geotechnical measurement equipment and the collaboration between OptaSense and the BGS provides a unique opportunity to both study the slope in more detail and validate the OptaSense system for slope stability monitoring. The OptaSense system allows the BGS to observe changes in the slope to a level of detail never possible before. Very small strain changes can be seen by the equivalent of over 1,000 sensors covering the slope allowing ground movements to be studied in much greater detail. Coupled with the ability to monitor over several months, this enables greater understanding of landslide events.  Storms over the winter caused several small landslides that were clearly visible on the OptaSense system, which showed the precise regions and timings of the activity with a sub-microstrain level of detail, revealing interesting features such as ripples following ground movements in the regions of highest activity. The output of the OptaSense system has now been compared to several traditional instruments and the output on the fiber correlates well with resistivity measurements made on an Electrical Resistivity Tomography (ERT) array, moisture content sensors, thermometers and ground movement measured by surveys of GPS marker posts and LiDAR scans. The results of this study of the slope and validation of the OptaSense system were presented at the 2021 American Rock Mechanics Association (ARMA) Geomechanics Symposium.