Construction World September 2016

GEOTECHNICAL

ECONOMICAL SOLUTION to rockfall protection When we think about

8-12 m in height and 4 to 8 metre in depth, depending on the size of the machinery that will be used. These benches help prevent rocks falling all the way down the entire face of the wall. Sometimes additional rockfall mitigation measures are required. More and more companies are looking for solutions that have less impact on the environment and are more cost-effective. Geobrugg’s range of products provide rockfall mitigation solutions that are not only aesthetically more pleasing, but are easier to install and more cost-effective. Situation at Rio Tinto Towards the end of 2015, Fairbrother Geotechnical Engineering approached Geobrugg to help them with a design solution at Rio Tinto’s Rossing Uranium Mine near Swakopmund in Namibia. Extensive blast damage within the sub-drill area have left the rockmass on the particular access ramp to comprise of loose rocks and jointed blocks that hung precariously along the crest of the bench face. This situation is a potential source for rockfall. The low catch capacity in certain parts of the slope posed a risk to equipment and possible injury to people. This would lead to increase in production cost. Although temporary measures to mitigate the risk had been put in place by the mine, they required a long-term solution to adequately minimise danger posed by the rockfall hazard. Solution provided Considering the geological condition at the mine, a draping system was recommended. This option would not only proof cost effective, but would be an efficient solution to ensure that the trolley line is protected from rockfall. The draping system comprising 15 000 m 2 of Geobrugg’s QUAROX PLUS® mesh was installed by Fairbrother’s trained specialists. The wall in question was approxi-

mining, the picture of a worker with hard hat, overhaul and gumboots

comes to mind. He is usually working

underground in a tunnel hundreds of metres below the earth’s surface.

>

South Africa have some of the deepest mines in the world, so you can imagine the amount of roads/tunnels criss-crossing the

earth below our feet. To protect people and equipment, the tunnels are lined with mesh. In some mines, Geobrugg’s high tensile steel mesh (breaking load of 1 770 N/mm 2 ) had been used for ground support in the tunnels. The majority of the tunnels in the gold and platinum mines, have for years and continue to do so today, been safeguarded with mild steel (breaking load of 500 N/mm 2 ) and lacing as the preferred method for roof support. South Africa’s other commodities like iron ore and copper are mined on the surface. And even though the environmental challenges for surface or open pit mines are different, they still require safety measures to protect their most valuable assets – the workers and the equipment. Even though the roads inside an open pit mine are not numbered P, R or N, and probably don’t appear on Google Maps, they can’t be neglected as they ensure that the operations of the mine run smoothly. A typical open pit mine has pit walls that are excavated at an angle and the walls are stepped/benched. The benches vary between

QUAROX® PLUS draping system is a cost- effective mitigation solution.

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mately 110 m high and 270 m long and easily accessible via a haul road. Enough room for installation of anchors to pin down the draping system, was present. The secondary mesh on the QUAROX PLUS® rolled cable nets are factory pre-installed. The Geobrugg® Supercoating finish on the cable nets gives it three times longer lifespan than hot dip galvanized cable nets. The slope draping solution used at Rio Tinto’s mine is a combination of DELTAX® mesh (secondary) and QUAROX® rolled cable nets (3,9 m x 30 m per roll). The superior qualities of QUAROX® rolled cable nets compared to conventional cable nets, allowed for easier and more efficient installa- tion. No extra work is required before

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View of the QUAROX® PLUS nets with pit underneath.

GBE barrier during installation showing mesh panels pre-installed at factory.

CONSTRUCTION WORLD SEPTEMBER 2016