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Rockfall Protection Rockfall NettingGalt Geotechnics determined
that a passiveRockfall Protection system was required at Hills 3
to5 on the East-West Road at Cape Preston.The original design for
rock batters called for slopesat 1v:1h, with 3m wide benches each
6m verticallydown the slope. Difficulties during construction
meantthat the design batters were not achieved. Typically,batter
slopes of 1.2v:1h and 1.3v:1h, with nobenches, were excavated to a
maximum verticalheight of 14m. The highly weathered and medium
toclosely jointed exposed rock (200mm to 500mmdiameter) on the
batters meant that there was a riskof falling rocks impacting on
the roadway below.
Galt Geotechnics recommended that either aMaccaferri flexible
rockfall fence with a minimum
energy dissipation of 500KJ or an approved draperynetting system
be used to control potential rockfalls.Due to the fact that the
batters were easily accessibleand space constraints existed at the
toe, theMaccaferri woven Rockfall netting drapery wasconsidered to
be the most appropriate for the siteconditions.Specialised Geo , a
specialist contractor, wasawarded the Rockfall protection system
installationcontract. Specialised Geo is an Australian drilling
andcivil construction company specialising in difficult
andhazardous constructions throughout Australia.
Geofabrics , the Maccaferri agents and distributors inWA,
supplied the woven mesh Rockfall netting andtechnical assistance to
Specialised Geo.On batters over 5m in height, 5400m of
hexagonallywoven Galmac+PVC coated mesh was installed inonly seven
days using a crew of five workers (a drilloperator and four mesh
installers).
Unlike a single twist (chain link) type mesh thats primary
purpose is security fencing, Maccaferri typedouble twisted
(sometimes referred to as triple twist) hexagonally woven mesh was
specifically developedto contain rocks. The double twist ensures
thatunraveling cannot occur should one or more meshwires be damaged
during installation or in-service.Independent testing has shown
that Maccaferri meshretains 88% of its strength when one mesh wire
is cutwhereas single twist (chain link) type mesh retainsonly 26%
of its tensile strength during punch tests.
Project: East-West Road, Cape PrestonDate: June 2010Client: MCC
Mining
Engineer: Galt GeotechnicsContractor: Georgiou (Rockfall Netting
Installer: Specialised Geo)Location: Cape Preston, Karratha,
Western Australia
The Batter Prior To Netting Placement
The 2mx50m Rolls About To Be Installed
Maccaferri Rockfall netting drapery systems have beenused
extensively throughout Australia to make mine sitessafe. In Western
Australia, West Angeles, Alcoa, PerthHills Quarry and now Cape
Preston, to name but a few,have utilized these highly engineered
and provensystems.
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Typical Top Anchor Detail Typical Bottom Anchor Detail
One Of The Batters Protected with Woven Mesh Drapery Netting
Anchor Detail At Top Of Slope
The anchors at the top of the slope comprised of 20mm Gewi-bar
(DSI) with 150mm square plate and domed
nut fully grouted to 2m depth at 2.5m centres. Due to the
presence of loose material at the crest, a length ofcable was used
to connect the (setback) anchor to the drapery.The woven mesh was
connected to 8mm cable with a minimum 0.5m overlap at the top of
the slope andsecured in two rows using high tensile stainless steel
clips also supplied by Geofabrics.The anchors at the toe of the
slope comprised of 20mm Gewi-bar (DSI) with 150mm square plate and
domednut fully grouted to 2m depth at 5m centres. All drilled holes
were 50mm and anchors were fully groutedwith a mix design
conforming to AS2350 and AS3583.
Typical Woven Mesh Drapery System Detail
