Newmont Waihi Gold contracted BPC to construct two steel lined vertical shafts from the mine surface to the mine gallery a further 90 metres below.

The completed shafts while identical in dimension performed two different functions, the first providing a conduit for ventilation and the second providing Emergency Access /egress.

Each completed shaft was 2.50 metres in diameter and lined with a 20mm steel casing.

A significant challenge overcome by the project team was ignimbrite, andesite and quartz material encountered on the shaft alignments with compressive strengths of 330 MPa.

A considerable amount of specialised tooling was developed in-house to overcome the variable drilling material encountered. namely chisels and rotary drilling heads.  Also utilised during the project were a 600t capacity Oscillator and the R625 rotary drill rig.

The work scope included:

• Placing of a permanent 50m sheet pile retaining wall.
• Design and construction of a temporary steel working platform for the R625 Rotary Drill Rig.
• Construction of a 30m x 8m x 300mm reinforced concrete slab.
• 4 x 900 dia UC Torque Reaction piles incorporated into slab for the Oscillator housing.
• Drilling of two shafts at 2.5m dia x 90m to 0.5% vertical tolerance.
• Steel lining both shafts with 20mm casing.

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