Loading...
Quantifying causes and variability of rockfall activity: comparison of rock slopes monitored using terrestrial remote sensing
Phillips, Cameron
Phillips, Cameron
Citations
Altmetric:
Advisor
Editor
Date
Date Issued
2024
Date Submitted
Collections
Research Projects
Organizational Units
Journal Issue
Embargo Expires
Abstract
Rockfall is a major geohazard in mountainous areas where infrastructure is developed adjacent to steep, rocky terrain. Multiple major roadways, including Interstate-70, were constructed through the Rocky Mountains of Colorado by blasting and excavating rock to create space for the road, resulting in unstable road cuts. Inventories of rockfall created using remote sensing or observational methods are frequently used to characterize rockfall hazard by analyzing the volume distribution of past rockfalls. The relationship between rockfall magnitude and frequency can be represented by a negatively scaled power law with two fit parameters: an activity constant (A) and scaling exponent (B). Spatially normalizing the power law by rockfall source zone area allows for comparison of rockfall activity between different slopes through the normalized activity constant (Ast), which can be used to prioritize rockfall scaling and mitigation.
This research seeks to determine the slope, rockmass, climate, and database variables that influence the rockfall power law. The impact of total monitoring time on uncertainty of the power law was assessed using bootstrapped 95% confidence intervals on the fit parameters. Site-specific effects were found; slopes that experience more uniform rockfall frequency and volume over time have lower parameter uncertainty over the observed volume range, while the parameters for inventories that contain large events relative to the rest of the volume distribution are more uncertain. Sufficient monitoring time to adequately characterize a rock slope for hazard analysis ultimately depends on the rockfall rate, the range of observed volumes, and the maximum geologically feasible event size. Uncertainty of the power law parameters tends to be lower for larger inventories.
Analysis-of-variance and regression were used to identify the variables that influence Ast and overall rockfall activity for a database of 44 rockfall inventories. Monitoring method was found to have a large, confounding effect on the results, so only the 34 terrestrial remote sensing inventories were considered for further analysis. Rockmass condition, lithology, whether a slope is natural or cut, freezing intensity, and winter precipitation displayed possible influence on the forecast frequency of different rockfall volumes using the power law.
The power laws for seven Colorado cut slopes were compared with slope features, rockmass characteristics, and climate at each site. Variations in lithology and general rockmass structure are the best predictors of rockfall activity for Colorado cut slopes. Sedimentary slopes experience more rockfall activity than crystalline slopes, which is attributed to differential erosion of sedimentary layers causing frequent rockfalls. Local climate (including precipitation, snowmelt, and freeze-thaw) mostly affects seasonal trends in rockfall frequency and not long-term rockfall activity differences.
Associated Publications
Rights
Copyright of the original work is retained by the author.