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Monitoring
of rockfall
All rock slopes are subject to weathering, caused mainly by
rain seeping into the rock and changes in temperature. With
time fragments of rock may detach from the slope and fall.
In some situations these fragments can be large and potentially
life threatening and it is therefore important that rock faces
are inspected on a regular basis.
Most rockfall occurs following heavy rainfall and after periods
of frost and thaw. Therefore inspections should take place
at least annually, and typically are done after the end of
winter. Checks on the condition of rock faces can be carried
out visually using binoculars, from high-lift machines or by
remote access methods (such as ropes). Photographic records
are essential, together with careful records of debris collected
annually at the bottom of identified sections of slopes. This
will help to identify any changes to particular sections of
the rockface and highlight potential future dangers.
 Differential
weathering of limestone and shales resulting in overhangs and
rockfall. |
 Rockfall
in a limestone quarry.
Signs that are noted during annual monitoring include:
• Widening or movement across cracks and joints
• Erosion of weathered and other weak materials
• Evidence of recent rockfall
• Vegetation growth on the face (the roots may force cracks
open)
• Seepage of water from the face
Any support measures present on the face, such as netting,
bolting, anchoring or sprayed coating, should also be inspected
at least annually to ensure that adequate anchorage remains
and that corrosion has not been significant. (Most netting
has a 40 to 60 year life when appropriately treated).
On the basis of evidence from the inspection, an assessment
is made as to whether any additional support measures are required,
or whether the controlled removal of loose rocks (known as
face scaling) will be needed.
Clearly, whenever a rock face remains after the closure of
a quarry, sufficient space must be left at its base to allow
for monitoring, and any rockfall protection that may be appropriate. |
