Civil Engineering Reference
In-Depth Information
Figure 12.18
High scaler
suspended on rope and
belt while removing loose
rock on steep rock slope
(Thompson River Canyon,
British Columbia,
Canada) (TRB, 1996).
because the scalers are not able to direct the crane
operator to move quickly in the event of a rock
fall from the face above them.
An important component of a scaling opera-
tion in wet climates is the removal of trees and
vegetation growing on the face, and to a dis-
tance of several meters behind the crest of the
slope. Tree roots growing in fractures on the rock
face can force open the fractures and eventually
cause rock falls. Also, movement of the trees by
the wind produces leverage by the roots on loose
blocks. The general loosening of the rock on the
face by tree roots also permits increased infiltra-
tion of water which, in temperate climates, will
freeze and expand and cause further opening of
the cracks. As shown in Table 12.1, approxim-
ately 0.6% of the rock falls on the California
highway system can be attributed to root growth.
removal is in progress, and until the slope has
been made safe and the road has been cleared of
debris. Where there are pipelines or cables bur-
ied at the toe of the slope, it may be necessary
to protect them, as well as pavement surfaces
or rail track, from the impact of falling rock.
Adequate protection can usually be provided by
placing a cover of sand and gravel to a depth of
about 1.5-2 m. For particularly sensitive struc-
tures, additional protection can be provided by
rubber blast mats.
12.6 Protection measures against rock falls
An effective method of minimizing the hazard
of rock falls is to let the falls occur and control
the distance and direction in which they travel.
Methods of rock fall control and protection of
facilities at the toe of the slope include catch-
ment ditches and barriers, wire mesh fences, mesh
hung on the face of the slope and rock sheds.
A common feature of all these protection struc-
tures is their energy-absorbing characteristics in
which the rock fall is either stopped over some dis-
tance, or is deflected away from the facility that is
being protected. As described in this section, it is
12.5.4 Rock removal operations
Where rock removal operations are carried out
above active highways or railroads, or in urban
areas, particular care must be taken to prevent
injury or damage from falling rock. This will usu-
ally require that all traffic be stopped while rock
