Ruakuri cave

The project

Avalon excavated hundreds of tonnes of rock to create a 30m tunnel connecting two areas of show cave. We also constructed 250m of suspended walkway above the cave’s underground river. A limestone passage floor had to be lowered to achieve levels for wheelchair access.

Ruakuri cave abounds with sensitive glow-worms and beautiful but delicate stalactites and calcite formations. Work had to be carried out under very strict resource consents with vibration and air quality monitoring. Because of our reputation for handling protected environments, Avalon was consulted for a blasting proposal.

A compressor on the surface powered our drilling plant via a 70m vertical borehole. Avalon crew had to access the site by "tubing" down the stream-way in wet suits before changing into dry gear for the long and muddy shift underground.

Very lightly charged holes with frequent intermediate relief holes and a "Nonel" detonation system were planned to minimise airblast. The blast was successfully fired late one night. The seismograph recorded a maximum 16mm/s vibration; 4mm/s below the resource consent's allowable limit. Air quality remained acceptable and no formations were damaged.