The increased costs of underground mining have continually challenged engineers to identify opportunities for alternatives to common approaches to underground development. Considerations to the design of horizontal and vertical development at the Dugald River mine targeted inclined raise boring to reduce horizontal development, not only to reduce cost, but to allow development activities to focus on other areas of the mine.
The mine plan consists of 50 raise bored ventilation shafts, of which 17 have been mined to date with diameters ranging from 3.1 m to 5 m and lengths from 30 m to 200 m. The expected performance and stability of these shafts has been determined using methodologies proposed by McCracken and Stacey (1989) and further refined by Peck, Coombes and Lee (2011). Actual raise performances have been collated and compared to a database of raise bore performances across Australia as presented by Coombes, Lee and Peck (2011), and form a database of raise bore performance specific to Dugald River.
Opportunities to further optimise the mine plan and reduce costs have seen the introduction of large diameter-inclined raise bored ventilation shafts to minimise the required lateral development to connect the ventilation circuits. Large diameter inclined shafts ranging between 3.1 m and 4.5 m in diameter have been successfully mined with dips down to 70°, reducing the cost of lateral development by more than $1 million over the next two years.
Both technical and operational challenges were overcome in
the mining of large diameter-inclined raise bores, including modification
- existing methodologies of assessing shaft wall stability for inclined
raises. These included variations of the McCracken and Stacey method and the
utilisation of the modified stability number (N’) previously developed for
stope performance (Potvin, 1988).
- both the collar and toe development profiles, including the general set-up
of the raise bore drill rig to reduce the operational risks associated with
Due to their success, inclined raises have been designed for subsequent stages of the life-of-mine ventilation system at Dugald River. This has resulted in significant capital cost savings for the mine.
Carswell, J F, Reitsema, G and Lee, M, 2017. Vertical and
inclined raise bore performance at Dugald River mine, in Proceedings 13th AusIMM
Underground Operators’ Conference 2017, pp 313–320 (The Australasian Institute
of Mining and Metallurgy: Melbourne).