| 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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