SINKHOLE HAZARD ASSESSMENT USING BOTDR, TDR, AND GPR TECHNIQUES

Sinkholes are closed depressions on land surface and serve as direct links between the surface and the underlying aquifers. Soil void can form abruptly and then expands progressively until a sinkhole develops. The goal of this research is to develop a cost-effective and efficient method to monitor the soil void formation and propagation, which would potentially prevent and greatly reduce damages caused by future sinkhole collapses. Recent monitoring methods include Ground Penetrating Radar (GPR), inclinometers, Interferometric Synthetic Aperture Radar (InSAR), real-time water pressure monitoring in karst opening, the Brillouin Optical Time Domain Reflectometry (BOTDR), and Time Domain Reflectometry (TDR). The unique features of the BOTDR and TDR techniques such as distributed measurement, long distance range, high resolution, and remote monitoring make them more effective to monitor soil voids and sinkhole development. An experimental study of monitoring the process of sinkhole collapse using BOTDR technology demonstrates that in-situ measurements of 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. GPR and In-situ monitoring of soil strain using TDR technique were applied in several karst areas in China. These two methods are more cost effective. GPR can also be used to detect near surface soil voids in a more effective and timely manner.