Civil Engineering Reference
In-Depth Information
12.6.4 Rock catch fences and attenuators
Wire-rope nets.
Nets with energy absorption
capacity ranging from 40 to 2000 kJ have been
developed as proprietary systems by a number of
manufacturers (Geobrugg Corporation and Isofer
Industries). The components of these nets are a
series of steel I-beam posts on about 6 m cen-
ters, anchored to the foundation with grouted
bolts, and guy cables anchored on the slope.
Additional flexibility is provided by incorporat-
ing friction brakes on the cable supporting the
nets and the guy cables. Friction brakes are loops
of wire in a steel pipe that are activated during
high energy events to help dissipate the impact
forces (Figure 12.24). It has also been found
that nets are effective in containing debris flows
because the water rapidly drains from the debris
material and its mobility is diminished (California
Polytechnical State University, 1996).
The mesh is a two-layer system comprising a
50 mm chain link mesh, and either woven steel
wire-rope mesh or interlocking steel rings. The
During the 1980s, various fences and nets suitable
for installation on steep rock faces, in ditches and
on talus run-out zones were developed and thor-
oughly tested (Smith and Duffy, 1990; Barrett
and White, 1991; Duffy and Haller, 1993). Nets
are also being used in open pit mines for rock fall
control (Brawner and Kalejta, 2002). A design
suitable for a particular site depends on the topo-
graphy, anticipated impact loads, bounce height
and local availability of materials. A common
feature of all these designs is their ability to
withstand impact energy from rock falls due to
their construction without any rigid components.
When a rock impacts a net, there is deformation
of the mesh which then engages energy absorbing
components over an extended time of collision.
This deformation significantly increases the capa-
city of these components to stop rolling rock
and allows the use of light, low cost elements in
construction.
W 8
48
steel post
×
16 mm (min.) wire rope
with braking element
Wire rope
anchor
Grout
Friction brake
3m
Drill hole
100 mm dia.
Ring net
Chain link
mesh
0.06 m (max.)
0.75 m (min.)
0.75 m
Concrete
Figure 12.24
Geobrugg rock fall fence (TRB, 1996).
