Construction World December 2016

Specialist Contractors or Suppliers B REHABILITATION OF EMMARENTIA DAM SPILLWAY

altering outlet structures, repairing the box culvert outlet, widening the control section and constructing a gabion wall on the eastern side of the outlet.  Maccaferri Africa not only supplied the gabions and Castoro ® mattresses, but due to the labour intensive solution and the importance of the construction, offered on site in order to ensure installation was carried out according to best practice, which also proved to allow faster installation. Site inspection during the course of the construction ensured the highest quality of the gabions and mattresses. The project was started in April 2015 and was completed in April 2016. The value of the Maccaferri products was approximately R800 000, with the full value of the contract for the spillway being around R5-million.

In 2009 Johannesburg Roads Authority (JRA) identified several issues at Emmarentia Dam (located on the Westdene Spruit, a tributary of the Jukskei River) from the stability of the dam wall to the return channel. On the return channel they discovered erosion of the banks and undermining of existing gabion and concrete walls. In April 2015 the rehabilitation project was awarded to Endecon Ubuntu for the civil engineering, and King Civil and Lettam Building and Civil were appointed to carry out the work. Maccaferri Africa was appointed as the sole supplier of Gabions and Castoro ® Mattresses for the return channel rehabilitation. The 103 year-old landmark was in need of maintenance following the recent floods, which had damaged the aging infrastructure. While significant improvements to Emmarentia

Dam were undertaken in 1988, a recent comprehensive investigation conducted by JRA showed that preventive maintenance and flood-retention protection was required to safeguard the dam’s integrity and ensure the safety of residential properties downstream. Furthermore it was discovered that continued erosion could expose the banks and possibly undermine existing

Project information • Company entering: Maccaferri Africa • Client: Johannesburg Road agency

• Start date: April 2015 • End date: January 2016 • Main contractor: King Civil Engineering Contractors • Consulting engineer: Endecon Ubuntu • Subcontractor: Lettam Building & Civils

municipal roads located next to the return channel. Improving Emmarentia dam’s flood-prevention facility, to protect properties located downstream of the dam from flooding, included excavating and repairing the pipework and surrounding soil at the stormwater structures located along the dam. The project scope also included ROCKFALL PROTECTION FOR WESTERN HIGH WALL SJ Pit at Rössing Uranium

44

Project information • Company entering: Fairbrother Geotechnical Engineering • Client: Rössing Uranium • Start date: September 2015 • End date: June 2016 • Main contractor: Fairbrother Geotechnical Engineering • Project manager: Rössing Uranium • Project value: NAD8,5-million

Towards the end of 2015, Fairbrother Geotechnical Engineering approached Geobrugg to help them with a design solution at Rio Tinto’s Rössing Uranium Mine near Swakopmund in Namibia. The Rössing Uranium Ltd (RUL) operates as a large low-grade open cast uranium mine and is a subsidiary to the Rio Tinto Group of companies. The mine is located some 65 km NE of the town of Swakopmund in Namibia. The request was to address the rock fall hazards on the wall above the Trolley 14 access ramp, an area of 110 m high by 270 m long. The slope above Trolley 14 was designed to be 15 m high benches with a 10 m catch bench, however in most cases the crest was 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 precariously along the crest of each bench face, which provided a source for rockfall. The crest area had low capacity on the slope resulting in the rocks landing on

provided for a long term solution to ensure that the trolley line is protected from rockfall and minimised the safety risks during installation. The installation

process was also a significant factor owing to the surface area under consideration as well as the mines requirement to keep the trolley line open for as much of the construction time as possible. This project was a first, as the Quarox Plus drape system had not been used in the African Mining operations. Another important point for this project is that the drape mesh installation’s CO 2 footprint far exceeds the conventional shotcrete solutions offer added benefits to this project. The installation of the draping system was managed by Fairbrother Geotechnical Engineering using their own employees and

the access ramp and posing a threat of both equipment damage and injury risks. Temporary measures to mitigate the risk had been put in place by the mine, but a long term solution to adequately minimise danger posed by the rockfall hazard was 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,

supplemented by seven rope access technicians (RATs) provided by ASC. The proximity of a haul road at the top of the slope allowed for the provision of track mounted crawler rigs to install the anchor system for the drape mesh at the crest of the slope. The project was successfully completed in March of 2016.

Construction WORLD

DECEMBER • 2016