Discontinuity characterization for slope stability assessment using combined aerial photogrammetry, and geophysics approach

An expeditious and precise slope stability assessment approach is required to mitigate the personnel and economic losses due slope failure disaster. This study successfully determines various discontinuity properties such as degree of fracturing, discontinuities orientation and persistence using combine unmanned aerial vehicle (UAV) and 2D electrical resistivity tomography (2D ERT) to evaluate the stability of the slope. The discontinuity orientations govern the various modes of failure such as planar, wedge, and flexure toppling. Whereas the degree of fracturing of the rock mass evaluates the quality of the rock mass using Rock Quality Designation (RQD) index. In addition, the persistence is defined as the extent to which the discontinuity on exposed surface rock intruded inside the rock mass. The 3D point cloud from UAV images allows to obtain the discontinuity orientations to analyse the potential failure at the site. The upper portion of the slope has no risk of planar and wedge failure, whereas 20% of the discontinuities are favourable for flexure toppling. In contrast, at the lower section of the slope 1.04%, 4.86% and 20% discontinuities are prone to planar, wedge and flexure failure respectively. At the same time the RQD index obtained via UAV survey reveals that the respectively area covered by very poor, poor, fair, good, and excellent rock were 7 m2, 3904 m2, 38,775 m2, 42,943 m2, 1546 m2. The ERT survey enable to estimate the area covered by poor, fair, good and excellent rock were 4 m2, 1650 m2, 2592 m2, 27,729 m2, and 55,200 m2, respectively. Both the UAV and 2D ERT survey shows the poor-quality rock in the north-east of the slope that reveals that the discontinuities are extended inside the rock mas. This study, therefore, conclude that the combined 2D ERT and UAV approach is efficient and expeditious approach for comprehensive slope stability assessment.