Customer: Environment Waikato
Contract type: Construct Only
Location: Te Aroha, Waikato, New Zealand
Construction Period: 14 months
Tui Mine is an abandoned mine on the western slopes of Mount Te Aroha and is considered to be the most contaminated site in the country. In the 1960s, the mine extracted copper, lead, and zinc sulphides. When the mine was abandoned in 1973, waste, rock ore dumps, and mine tailings were left behind. The mine tailings are stored behind a dam that is unstable and leaching various minerals, including heavy metals, into neighbouring waterways, adversely affecting the stream ecology. McConnell Dowell helped to restore the site so it could be used for public recreation in the future.
The challenge was to rehabilitate and stabilise the old mine and improve the stability of the tailings dam in extremely difficult ground conditions and in very confined spaces. It was an isolated site with difficult access to the lime injection points. Access was gained through regenerating bush that had open stopes through to ground level
The McConnell Dowell team in conjunction with our subcontractor, Hiway Stabilisers, neutralised the ground water with lime and stabilised the access tunnel, which allowed us to block off the entrances.
The project was tendered on innovative ideas and these continued as the project advanced and included: a specially designed rail mounted conveyor to minimize hand shovelling of blasted rock; use of self-compacting concrete to rock contact in the plug; a purpose build pump port with knife gate built into the plug formwork; a purpose built lime slurry mixing and pumping system; and the modification of of winch and abseiling equipment that would function in a confined mine and ore chute. Special trolleys were built that ran on top of pre-constructed 315 OD PE pipe that allowed 3.5 t of bagged concrete to be transported into the Level 4 portal for pipe ballast.
Key to Success
A key success factor has been our flexible project management and close collaboration with the client and consultant. Early site visits allowed us to get a good overview of site conditions and provide information to the designers to help finalise the design. The flexibility of our team allowed us to deal with any unforeseen elements, which necessitated ongoing modifications to the scope of works and variations to the contract. The contract was completed ahead of time and to budget.