In his SME MineXchange presentation on Tuesday, Timothy O’Brien of Gall Zeidler Consultants, displayed how using an engineered tunnel approach in the construction and repair of mine access tunnels could result in extended life of mine and an effective risk management process.

During his talk, ‘An Engineered Tunnelling Approach for Mine Access Tunnels’, in Phoenix, Arizona, he revealed details about an ambitious project recently carried out at Rio Tinto’s Bingham Canyon copper mine, in Utah, USA.

With the C-6 tunnel at the mine – used to transport crushed ore from the open pit – suffering from decay, Gall Zeidler Consultants was drafted in to not only inspect the tunnel, but also carry out rehabilitation work on the ground support system to restore access to the tunnel. It chose a system made up of yielding steel sets for this project, knowing that this could cope with the varying condition of the 4.57 km-long tunnel that was built in 1959 originally as a rail tunnel.

The biggest challenge for the consultants was this support system needed to be constructed without interrupting the conveyor system working underneath, which sees 70,000 t of crushed rock conveyed daily.

The engineers came up with a solution that was elevated above the conveyor, allowing crushed material to keep running through the tunnel, according to O’Brien.

The consultants also developed a two-year ground control management plan, including a monitoring and instrumentation program and trigger action response plan to monitor tunnel structural integrity in response to future mining activities.