Abergeldie won category 4 (projects worth $A20-75 million) at the Civil Contractors Federation’s New South Wales Earth Awards and is now a finalist for the national award.

CCF’s annual Earth Awards are awarded to highlight excellence in construction technique, environmental management and project management.

The ventilation shafts were bored at 4.81m and 5.91m diameter to provide fully-lined shafts of 4m and 5m diameter to a depth of 260m.

The shafts were drilled using an innovative construction method called blind boring, an alternative to traditional methods such as raise boring and drill and blast.

Blind boring involves stabilising the shaft by filling it with water and removing the cuttings through a process called reverse circulation.

Blind boring allows drilling in difficult ground conditions or through strata with high-pressure aquifers.

Safety is greatly improved, as there is no need to enter the shaft during construction and soil is deposited on the surface rather than having to be removed through the mine.

BHP Billiton’s requirement for fully hydrostatic ventilation shafts with a 50-year life span was met through the design and installation of a composite steel and concrete shaft lining.

The installation of the liner was technically complex, involving the fitting of a “stem” of liners weighing more than 2000 tonnes.

As the Dendrobium mine is located in a Sydney water catchment area, Abergeldie implemented a strict project environmental management plan to control risks such as access track erosion and the release of sediment-laden material from the work site.