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Sunday, October 17, 2010 |
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The Letseng Diamond Mine – an award winning success
:: News
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Source: Shaun Butler
Stefanutti Stocks Civils recently completed the process plant at the Letseng Diamond Mine in the remote Maluti Mountains of Lesotho, located 3 100m above sea level.
The footprint of the bulk rock excavation was set at 30m wide to the toes of the embankment and 95m long, incorporating five stepped terraces with heights varying from three to ten metres. The proposed location of the plant was set on the existing 17 degree sloping ground surface to facilitate a gravity fed process plant. The levels from the top of rock terraces were required to facilitate the surface bed to be laid in falls.
The scope of work encompassed:
• Primary crusher foundation walls and suspended slab;
• two cone crusher foundation walls and suspended slabs;
• the main building and crane
column foundations;
• bins, screens and platform foundations;
• thickener foundations;
• clear water foundations constructed as circular wall footings;
• access stairs to the pathways on either side of the buildings;
• surface beds including up
stand kerbs;
• retaining walls to support
terraced backfilling;
• gunniting of sloping rock faces on
the inside of the plant;
• dish drains;
• MCC building;
• stockpile tunnel and plant
feed conveyor;
• tailings conveyor; and
• clarified & potable water pump station.
The complexity of the contract was not in the construction but rather the conditions that are prevalent in Lesotho.
The road to site, in addition to being incredibly steep (with gradients of up to 15% at an altitude of 3 100m asl) also
contained a number of acute hairpin bends. This meant that we had to take into consideration the length and type of vehicles that could take the turns and make the climb. During the winter, the roads were covered in ice and snow, and it was a common occurrence that graders had to be sent to recover vehicles.
The temperatures in the Lesotho mountains range between plus 20 and minus 20 degrees Celsius, with an average temperature of six degrees. The project won a Fulton Award for the cold weather concreting, which presented many challenges to the design engineers and the construction management on site. “The prevailing temperatures meant that we were casting concrete in sub-zero conditions,” says Shaun Butler, contracts director. “In order to cast the concrete, a special mix design was required and concrete had to be heated and specially cured through the application of thermal blankets”.
The altitude took its toll on our senior staff, some of whom suffered from altitude sickness and respiratory problems. “This meant an influx of our younger Stefanutti Stocks colleagues,” says Shaun. “The average age of the supervisory staff on site was 27 years old - and the successful completion of this project under trying conditions, is a great achievement for the ‘young’ team!”
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