The first of six water control doors designed to counter water ingress has been completed for the De Beers Venetia Underground Project (VUP).

The huge water control door has a steel frame 8 m high, 8 m wide, and 1 m thick and is designed to hold back a 100 m head of water. Its construction has been undertaken by underground mining contractor Murray & Roberts Cementation, who says its scope of work includes a further three doors, with construction of the second door already started.

The new underground mine, a large-scale caving operation, is being developed directly beneath the current openpit and at times of heavy rainfall, the pit will act as a giant funnel, potentially allowing large volumes of water to penetrate the underground workings. The water control doors are designed to seal off the ‘dry’ side of the mine, where the water pumps and other critical infrastructure are located, from the ‘wet’ side, where mining operations on the kimberlite pipe take place. The water control doors will be activated in the event of water inflows into the mine exceeding the capacity of the underground pumping system, which will have the ability to pump 4 500 m3/h out of the mine.

Murray & Robert Cementation contracts manager for the construction of underground works at the VUP Jacques Labuschagne says the construction of the water control doors is not a run-of-the-mill assignment for the company.

“This is not a ‘first’ for Murray & Robert Cementation but certainly the sheer size of these doors is unusual,” he says. “Our task was to construct the water door in the roughly 9-m-high by 9-m-wide excavation, and one of the immediate challenges was the considerable undulations of rock surface due to the blasting required to create the excavation. One of the main consequences of this was that the 40 mm steel rock anchors – each of which varied in length – required to anchor the door into the host rock increased from 120 to 234 in number, which was necessary to ensure the integrity of the structure.”

The steel sections making up the door were prefabricated on surface by a specialist steel company and transported down the decline in sections. These sections, which weighed up to 8 t each, were then lifted into place by the Murray & Roberts Cementation team. The completed structure comprises about 60 t of steel. In addition, approximately 80 m3 of concrete had to be poured to seal the area around the door to create a watertight interface between the door and the host rock.

The water control doors are just one part of Murray & Robert Cementation’s contract for construction of the VUP’s infrastructure. The work includes the construction of pumps stations, water walls, automated ventilation doors and truck loadout ramps.

The De Beers VUP is said to be one of the biggest and most complex mine developments underway in the world and will see a vast underground mine – based on the cave mining method – replacing the openpit operations which have sustained the Venetia mine since it was opened in 1992. The VUP is designed to extend the mine’s life until at least 2046 and aims to produce around 4.5-million carats a year. The vertical shaft and the decline of the VUP were both completed by Murray & Roberts Cementation.