SLOPE INSTABILITY ANALYSIS AND DETECTION OF VOLUMETRIC CHANGE USING A SMALL UNMANNED AERIAL VEHICLE (SUAV)

Monitoring of unstable slopes involves assessment of the extent of damage, rate and volume of displacement, surface topography, and detection of fractures that could be responsible for rock slope failures. Small Unmanned Aerial Vehicle (sUAV) systems are a popular method to collect very high resolution imagery, and recent studies have applied the technology in landslide mapping and monitoring. This study demonstrated the application of sUAV technology for slope instability assessment between two time periods. The objective of the study was to assess the potential change in slope morphology due to slope failure events through a time series analysis of different images obtained from a sUAV. The study was performed in Erwin, Tennessee, along an unsafe road cut in a metamorphosed dolomitic bedrock that has a continuous history of rock failure. The sUAV images were obtained during fall 2016 and fall and winter 2018 using a DJI Phantom 3 Professional. The images were processed using Agisoft Photoscan software to build a 3D dense point cloud of the area. Subsequently, high resolution digital elevation models (DEMs) and orthomosaics were generated using the point cloud data to determine the failure surface change and calculate volumetric differences. Further, the orthomosaics aided in identifying changes in the failure zone via visual interpretation and for extracting the information about geological discontinuities. Slope angle and aspect maps were generated from the high resolution DEMs to perform a GIS-based kinematic analysis for slope instability. Using ArcMap and ArcGIS Pro, the DEMs were also used to measure the volumetric change of slope failure extent over time. The result identified rock displacement and volume change in the rock slope exposure, which was validated by in-situ observations. Kinematic analysis further revealed the presence of planar rock block failure, and possibility of further failure along the exposed and weathered discontinuity surfaces. This research substantiates the importance of high resolution sUAV imagery for analyzing slope instability in areas which are unsafe for conventional field mapping.