Modern Mining December 2016

GEOTECHNICAL ENGINEERING

Drape mesh system provides rockfall protection at Rössing

over-mined due to extensive blast damage caused within the sub-drill area. The resultant rock mass comprised a loose package of jointed blocks hanging along the crest of each bench face, which provided a source for rockfall. Temporary measures to mitigate the rockfall risk had been put in place by the mine but a long-term solution to the problemwas required. Geobrugg visited the site with Fairbrother Geotechnical Engineering and discussed the client’s requirements. A drape mesh system was considered the most suitable system as it was the most cost effective and efficient, pro- viding a long term solution to ensure that the trolley line is protected from rockfall and mini- mising the safety risks during installation. The installation process was also a signifi- cant factor owing to the surface area under consideration, as well as the mine’s require- ment to keep the trolley line open for as much of the construction time as possible.

Towards the end of 2015, Fairbrother Geotechnical Engi- neering approached Geobrugg to help themwith a design solution at Rio Tinto’s Rössing uraniummine near Swakop- mund in Namibia. The request was to address the rockfall hazards on the wall above the Trolley 14 access ramp, an area of 110 m high by 270 m long. The solution adopted was a drape mesh system.

T here had been a number of rockfall incidents reported over the years emanating from the western slope of the SJ pit with debris landing on the Trolley 14 access ramp. This ramp is one of the major arteries of the SJ pit and was designated as the main access for the life of mine. The slope above Trolley 14 was designed to be 15 m high benches with a 10 m catch bench; in most cases, however, the crest was

Anchor system for the drape mesh at the crest of the slope.

20  MODERN MINING  December 2016