Assessment of discontinuity-controlled rock slope instability for debris slide initiation: a GIS-based kinematical analysis in the Great Smoky Mountains National Park, TN, USA

Unfavorable orientations of geological discontinuities and their geometrical relationship with the topographic slopes play a crucial role in controlling slope instability. This study developed a GIS-based kinematic model based on the mutual relationship between topographic slope and geological discontinuities to delineate rockfall zones and understand their spatial association with debris slide head scars in the Anakeesta rock formation of the Great Smoky Mountains National Park, Tennessee, USA. We mapped the exposed debris slide head scars from aerial photographs, satellite imagery, and field surveys and orientations of geological discontinuities were measured from the field along with other geotechnical parameters. Findings revealed the presence of four distinct sets of discontinuities, resulting in 11 possible slope failure mechanisms that could predict 57% of the existing debris slide. Wedge failure was the most prominent mode of slope failure, with wedge forming between the bedding plane and a joint set predicted for 27% of all failures in the debris slide head scars. The final rock kinematical susceptibility model was developed using the cumulative prediction capacity of individual discontinuity-driven kinematical rockfall failures through a weighted sum analysis. The model classified 77.9% of the area as safe, 14.7% to be moderately, and 7.4% as highly prone to kinematical rockfall failure. The susceptibility model was validated using the receiver operating characteristic curve on test data, which yielded an area under the curve (AUC) value of 65%, indicating a discriminatory power of the model separating the debris slide and non-debris slide scars. Finally, the spatial association between the kinematical susceptibility model and existing debris slide was statistically confirmed through a spatial Kolmogorov–Smirnov test of complete spatial randomness, signifying the role of kinematic rockfalls in generating the debris slide scars in the study area.