Published in Australian Longwall Magazine
The Springvale coal mine, which is 50%-owned by Centennial Coal, needed a safe solution for ground and water control problems common in the area. The upper 63m of strata consisted of typical occurrences such as weak, weathered sandstone with aquifers below the weathered zone.
Ardent Underground’s method for stabilising the weak rock was to keep the shaft completely filled with drilling fluid during the entire drilling and lining process. Typically, all the excavated rock cuttings are brought to the surface through the centre of a 500mm diameter drill pipe using reverse fluid circulation, eliminating handling and disposal of the cuttings underground.
“The blind boring method of shaft construction is particularly appropriate for mines such as Springvale that have limited capacity to store waste rock in development headings,” Ardent Underground technical director John Zeni said.
The top section of Springvale’s unstable ground was drilled at 4.7m diameter, and then lined with steel casing. This provided temporary support while the shaft boring continued at 4.25m diameter down to the coal seam.
The permanent shaft lining consisted of a unique composite of steel and concrete which is the first of its type to be installed in Australia. The impermeable outer shell for the shaft lining was delivered to the construction site where steel reinforced concrete was formed and poured into each of the 120 individual three-metre long casing sections.
The liner sections were assembled into a continuous pressure bearing, watertight cylinder as they were lowered into the completed shaft. The shaft is expected to remain completely dry and maintenance-free beyond the estimated 30-year life of the Springvale mine.
The finished shaft is 3.5m in diameter and 357m deep.
Ardent Underground’s methods do not require any personnel to enter the shaft or the mine during any part of the construction process, resulting in the safest known method of shaft construction available.
