Geology Reference
In-Depth Information
needed, and in some circumstances it will be necessary to close
roads or evacuate areas temporarily, especially where blasting is to
be used. The use of a risk register, as piloted for tunnels (Brown,
1999), with clear identi
cation of particular risks and responsible
parties, helps to ensure that all hazards and consequences are
adequately dealt with during construction. Decision analysis
is now widely applied at an early stage to assess whether to
mitigate slope hazards (e.g. by rockfall catch nets) or to remedi-
ate/resolve the problem by excavation and/or support approaches.
If construction of intrusive engineering measures to stabilise
hazards might be unduly risky, then passive protection can be
adopted instead. A hybrid solution is often the most pragmatic
approach for extensive, dif
cult slopes where some sections might
be stabilised by anchors and buttresses, with other sections
protected by nets and barriers (Carter
et al
., 2002; Pine &
Roberds, 2005).
Some of the options for improving the stability of slopes are illustrated
(2011). These can be split into
passive
options that either deal with
the possible failure by controlling surface deterioration at source, or
installing preventative reinforcement to increase local factors of safety,
or adding walls or buttresses to restrain detached debris before it
causes injury or damage, and
active
measures that enhance overall
Factors of Safety of larger sections of slope by major engineering
works, including cut backs or buttresses or heavy tie-back cable
anchors.
Many risks can be mitigated cost-effectively through surface treatment
to stabilise or remove relatively small blocks of rock. Surface drainage
is important, using adequately sized concrete channels with a fall
across the slope and channels down the face that may be stepped to
reduce velocity of
flow. Further guidance is given in GCO (1984a) and
in Ho
et al
. (2003).
There is a temptation to use hard slope treatments such as shotcrete
to constrain loose blocks at the slope surface but such measures, if not
properly designed, can restrict drainage from the slope, hide the geo-
logical situation from future investigators and can themselves cause a
hazard as the shotcrete deteriorates, allowing large slabs of shotcrete to
detach. Furthermore, shotcrete is increasingly an unacceptable solu-
tion for aesthetic reasons and there is a push towards landscaping high
visual slopes where safety is not compromised (GEO, 2000b).
