Field methods of measuring discontinuities for rock slope stability analysis on Price Mountian, VA

The stability of man-made rock slopes is greatly influenced by the orientation of the discontinuities in the rock mass. To determine kinematic and kinetic stability of rock slopes, discontinuity orientations must be measured safely and precisely with cost effectiveness and time efficiency. Several methods exist for taking field measurements of discontinuity orientations. The objective of this study was to compare the traditional method of hand measuring discontinuity orientations using a Brunton compass against hand measurements from a smartphone with inclinometer application software and the remote sensing techniques terrestrial digital photogrammetry and ground based LiDAR. The field site was a rock outcrop along Stroubles Creek Road on Price Mountain, Virginia. The Price Mountain structure is a doubly plunging anticline window in the Pulaski Thrust Sheet. The rock outcrop consists of the Upper Price Formation, a Mississippian sandstone with interlayered coal seams. The site features bedding planes that dip steeply into the slope face, yielding toppling failures. In addition, several distinct sets of joints exist creating both planar and wedge failures. In this study rock slope stability analyses considered a hypothetical excavation in the Upper Price Formation for the purpose of open pit coal mining. In order to compare the methods, three surveys were performed at this site. The first was a window mapping method in which discontinuity orientation measurements are made using both a Brunton compass and a smartphone with an inclinometer application. The second survey utilized was a terrestrial digital photogrammetry survey, which produced unusable results due to lighting problems, and was subsequently abandoned. Finally, a ground based LiDAR survey was conducted. Stereographic analysis of the discontinuities was used to evaluate discontinuity sets, the average orientation of these sets, and the kinematic stability of possible planar, wedge, and toppling failures. The average orientations of the sets along with field observations were then used in probabilistic factor of safety analyses using Monte Carlo simulations to quantify the probability of planar, wedge, and toppling failure for each survey method. Results were then compared to assess the relative accuracy of the methods, as well as their relative time efficiency, cost effectiveness, and safety. These results show that while remote sensing techniques can be conducted faster and more safely than hand measurements, they must be calibrated with field observation in order to ensure the best results. Remote sensing techniques, while very practical and effective, cannot completely replace traditional geologic field observations and experience