Use of Brillouin optical time domain reflectometry to monitor soil-cave and sinkhole formation

With the economic development in China, sinkholes have become one of the main geological hazards during highway, railway and oil-pipe construction in the karst regions of southwestern China. This paper introduces an experimental study of monitoring the process of sinkhole collapse using Brillouin optical time domain reflectometry technology. In a series of tests of an experimental model, sinkholes are induced by pumping simulated karst water. Real time strains of optical fibers buried in sediments and soil damages are measured. One segment of soil along with buried optical fibers was excavated to verify the final positions of optical fibers and their relation to soil deformation. Results of the experimental study demonstrate that positions of peak strain in optical fibers correspond well to areas of maximum disturbance and soil void formation. Changes of optical fiber strains in different soil layers are good indicators of vertical disturbance in soil. Time series of optical fiber strain analysis exhibit the progress of horizontal disturbance in soil.