Once a rock mass excavation has been constructed and the facility has been put into operation, the status quo is going to change. Changing stresses, the effects of annual climatic changes, freeze-thaw cycles, ice jacking, weathering and erosion all lead to a condition in which the long-term stability of the excavation may be questioned. If the rock excavation is a drill and blast cut alongside a highway or railway, for example, blocks of rock isolated by natural or excavation-induced discontinuities may become detached from the main mass of rock and fall or slide under gravity. If a falling rock block reaches the travelled portion of a highway, or the tracks of a railway, then a rockfall hazard exists. The safety of the travelling public, the infrastructure itself and the vehicles using the facility are compromised.

The Ministry of Transportation, Ontario has commissioned the development of the “Rockfall Hazard Rating System – Ontario (RHRON)” based on the Oregon DOT’s “Rockfall Hazard Rating System (RHRS) with modifications to suit the engineering geology of Ontario. Having been involved in critical reviews and concept development and various stages of the project, I am familiar with the process of generating RHRON ratings for rock slopes, and designing mitigating solutions to reduce the hazard.

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