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when mine water discharge is a concern.
Sometimes bats will inhabit the inner mine
workings and a special gate can be added to
allow them to pass through. The gate thus
provides a potential habitat for the endangered
species that are on the federal Species
at Risk Act list.
SRC started using stainless steel caps in
2009, although this method has been used
in northern Saskatchewan since 2005. They
are built off site and transported to mine
openings by ice road where the segments
are assembled and installed.
While this has proven more cost effective
than concrete for remote applications,
it has its drawbacks. Other than their unnatural
aesthetics, stainless steel caps don’t
work for openings where the local bedrock’s
stability is questionable.
Boulder closures
For relatively narrow openings where anchoring
rocks are too unstable or a steel cap
is at risk of being damaged by falling rock,
a boulder closure method is an option. This
requires locally sourced boulders of adequate
size and the equipment to move
them. But its beauty is in its simplicity.
Because of the specific conditions required,
the boulder closure method is
rarely used at the Satellite Sites. At one of
the sites, the closure was constructed by
placing large boulders side-by-side over
the opening. This was then covered with
smaller boulders and waste rock. Local
soil was added as a final layer, and timber
and branches were spread to promote
natural revegetation.
The boulders selected were uncracked
and angular to provide an interlocking
fit, minimizing the closure’s erosion
and degradation from repeated freezing
and thawing.
Backfills
For horizontal openings like adits and portals,
which appear almost like small caves,
the simplest solution is often the best.
When local waste rock from the mine is
present, the materials can be pushed and
compacted back into the mine opening.
SRC found this option was occasionally
superior to a concrete bulkhead as it blends
with the terrain, requires minimal maintenance
and reinforces the stability of the
mine entrance. It also reduces the risk of
exposure to naturally occurring radioactive
material associated with the waste rock
and inner mine workings.
Special design considerations are needed
when water discharges are present, but the
coarse nature of the backfill material allows
a certain amount of groundwater to percolate
through.
For vertical openings where information
on the mine workings is limited and
obstructions may be present, this method
is avoided.
Polyurethane foam
Polyurethane foam is a quick and easy
method for addressing immediate public
safety concerns. It is a relatively inexpensive
closure to install, easy to ship in boxes
and is built by mixing two compounds on
site and pouring it in the opening. A vent
pipe is installed to allow venting from the
mine workings, and soil is used to cover
and protect the foam from forest fires and
ultraviolet radiation.
thinkbigmagazine.ca | Quarter 4 2019 | Think BIG 43
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