ICEFALL HAZARDS ALONG U.S. TRANSPORTATION CORRIDORS - ARE ROCKFALL CATCHMENT DITCHES SUFFICIENT?

摘要

Ice accumulation can unknowingly wreak havoc on surface rock excavations and lead to an increase in the frequency of rock and icefall events along highways subject to significant precipitation and cold temperatures. Although icefall may logically be treated as a variation of a classic rockfall problem, there are some significant differences between rockfall and icefall hazard evaluation. These differences are primarily related to the transient nature of ice accumulation thickness and distribution. Ice slabs can fall from high above, or can slide or topple depending upon underlying slope geometry. High-energy icefall impacts can also generate shatter, which can result in the release of ice projectiles. Based on a preliminary poll of DOT's in various northern tier states subject to ice development, icefall hazards are not routinely considered as part of the rock slope design process. Ditches designed to accommodate rockfall capture may not be sufficient to mitigate icefall events, and in such cases, other treatments and engineering controls may be warranted. Engineered netting systems can maintain rockfall events; however, ice can accrete to the outside of the netting and present itself as an icefall hazard. Ice build-up mitigation techniques can consist of drainage elements, periodic cold-weather maintenance efforts, or topographic enhancements. In cases where source zone treatment is not permissible, engineered barriers may be incorporated for mitigating the risk of icefall impact to the traveling public. This paper will cite project examples and describe some of the challenges associated with icefall evaluation, prediction of ice distribution, ditch effectiveness, the importance of long-term monitoring and maintenance programs, and mitigation strategies for dealing with the under-represented problem of icefall.