Rockfalls are one of the most common types of slope failures that affect cut slopes along roadways in mountainous regions. The Rockfall Hazard Rating System (RHRS), started in Oregon and adopted by various U.S. states, is used to rate cut slopes with respect to their likelihood of releasing rockfalls. Existing rating systems use semi-quantitative approaches to rate geological and non-geological factors. The main geologic factors are favorability/unfavorability of orientation of discontinuities with respect to the orientation of slope faces and likelihood of differential weathering leading to undercutting of strong rock units. Digital surface models (DSMs) derived from light detection and ranging (LiDAR) and photogrammetry have been used to remotely characterize rock mass. This research introduces an expanded application of DSMs to quantify geologic factors that contribute to the likelihood of rockfall events. The method is hence referred to as the Quantitative Geologic Rockfall Rating System (QG-RRS). Four DSM-based parameters, A, B, C, and D, have been identified to evaluate geologic factors. These parameters quantify the likelihood of discontinuity orientation-controlled failures (parameter A), the degree of undercutting (parameter B), rockfall activity based on rockfall release surfaces (parameter C), and rockfall volume from rockfall voids (parameter D). This rating system, although not inclusive of other non-geological factors, appears to provide reproducible quantitative estimation of geologic factors that control rockfall generation.

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