Africa to build first incline sand tunnel

2 August 2011

Work started last month on Africa’s first inclined sand tunnel according to contractor Redpath South Africa. International diamond producer, Gem Diamonds awarded a ZAR 67M contract to mining giant Redpath for the development of the sand tunnel at the re-commissioned Ghaghoo Diamond Mine in Botswana. Redpath bagged the contract over its competitors because it opted for cost-saving conveyor belts over dumper trucks for much removal.

Redpath mine manager Olaf Iversen said that project involves constructing the tunnel to 112m vertically below the surface at an inclination of eight degrees. The site, which is located approximately 200km north of Gaborone, falls within in the Central Kalahari Game Reserve.

“The first phase of the project is due to begin in July 2011 with the establishment of a box cut 25m deep and 171m long into the Kalahari sand, which will provide safe and secure access to the underground mine.” he explained. “The box cut and portal support is expected to be completed in November 2011, by which time we will begin excavation work for the concrete-lined segmented sand tunnel, 403m in pure sand and 121m in transition from sand to basalt, which acts as a cylindrical shield to protect workers and equipment located underground.”

Iversen said that labourers will work within the 50t shield in order to move the tunnel forward segment-by-segment, by loading the sand onto the conveyor belt before it is fed out of the mine. “The width of each segment for this particular project is 0.61m, and we are aiming to move forward six segments or 3.6m per day.”

A Gem Diamonds technical representative said, “During the tender process, Gem Diamonds provided each contractor with a specific design for the segmented tunnel; however, the process of clearing the excavated sand was left open. Redpath South Africa was the only contractor that recommended the cost-effective use of conveyor belts for the removal of the sand, as opposed to articulated dump trucks. Although the initial set-up costs of the conveyor belts are high, the long-term running costs are significantly-lower than using trucks, which will ultimately improve the overall efficiency of the project.”

The sand tunnel is due for completion at the end of June 2012; however, Iversen admits that Redpath South Africa faces numerous challenges in the upcoming months, including managing the transition from sand to basalt where water could possibly be intersected. The entire scope of the project will have to be undertaken using diesel-powered generators in a region with no electricity.