Abstract
Rockfall is a frequent hazard in mountainous areas, but risks can be mitigated by the construction of protection structures and slope modification. In this study, two rock slopes along a highway in western Colorado were monitored monthly using Terrestrial Laser Scanning (TLS) before, during, and after mitigation activities were performed to observe the influence of construction and weather variables on rockfall activity. Between September 2020 and February 2021, the slopes were mechanically scaled and reinforced using rock bolts, wire mesh, and polyurethane resin injection. We used a state-of-the-art TLS monitoring workflow to process the acquired point clouds, including semi-automated algorithms for alignment, change detection, clustering, and rockfall-volume calculation. Our initial hypotheses were that the slope-construction activities would have an immediate effect on the rockfall rate post-construction and would exhibit a decreased correlation with weather-related triggering factors, such as precipitation and freeze-thaw cycles. However, our observations did not confirm this, and instead an increase in post-construction rockfall was recorded, with strong correlation to weather-related triggering factors. While this does not suggest that the overall mitigation efforts were ineffective in reducing rockfall hazard and risk of large blocks, we did not find evidence that mitigation efforts influenced the rockfall hazard associated with the release of small- to medium-sized blocks (<1 m3). These results can be used to develop improved and tailored mitigation methods for rock slopes in the future.
Highlights
Rockfall is a common hazard in mountainous areas
In the period where construction took place, we assumed that all volume loss corresponded to scaling; note that this was reasonable given that rockfall rates are typically low during this season in Colorado [8]
This study used Terrestrial Laser Scanning (TLS) to record rockfall occurring on two slopes in western Colorado before, during, and after slope construction was performed, with mechanical scaling and polyurethane resin (PUR) injection being the major activities
Summary
Rockfall is a common hazard in mountainous areas. Because rockfall events often develop in a brittle fashion and without adequate warning [1], forecasting of individual failures is difficult, so the risk is often reduced in practice by the construction of permanent protection structures and/or excavation of the slope. Measuring the change in rockfall probability in response to various external factors, such as human activity or construction, seasonal weather patterns and storms, or long-term climate change, is an active area of research [3,4,5,6,7,8]. The effects of constructing retention fences or berms can be evaluated using numerical runout simulations, which inform the placement and size of structures to optimally reduce rockfall hazard [9,10]. Remote sensing is widely used in open-pit mining to assess slope stability and anticipate large failures, which minimizes production delays and improves the safety of workers [11,12]
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