Evaluating In-Situ Block Volume Distribution for Prediction of a Rockfall Volume Distribution in Glenwood Canyon, Colorado

ABSTRACT: Rockfalls are a significant and costly geological hazard in areas characterized by steep topography and fractured rock masses. They frequently occur along cut slopes in rock, where the network of discontinuities forms blocks of varying sizes and shapes that are largely controlled by the orientation, spacing, and persistence of the joint sets. Previous research suggests that in-situ fracture networks may serve as the primary control on rockfall volume distributions, such that in-situ block size at a given site can be assumed to be a first-order representation of the rockfall volume distribution. This study aims to evaluate to what extent in-situ block volume distributions can be used to accurately predict actual rockfall block volumes. To answer this question, scanline mapping was performed to allow for fracture network characterization at a field site in Glenwood Canyon, Colorado that is actively monitored for rockfall occurrences. Dip, dip direction, spacing, aperture, persistence, joint roughness, and joint alteration were recorded. Theoretical in-situ block size distributions were calculated using a Monte Carlo simulation based on the scanline measurements. Results are compared to the distribution of rockfall volumes detected via LiDAR change detection. It is demonstrated that unlike the rockfall volume distribution, the in-situ block size distribution does not follow a clear power law distribution, and practical implications are addressed.