OceanaGold’s Waihi gold mine is a narrow vein underground mine located on the North Island of New Zealand.
As part of the mine extension project from the Correnso to the Martha orebody, a new ventilation shaft was required to be raise bored through some challenging ground.
As part of the Martha extension project, Waihi required an upgraded ventilation system to ensure sufficient air quality for the Martha underground.
Part of this upgrade required raise boring a 4.5 metre diameter return air rise, 120 metre long, from level 800 to level 920.
The top 40 metres of the shaft was expected to be in poor ground due to the presence of narrow quartz veins. Additional reinforcement was required to assist with the stability of the shaft through this section.
Minova supplied 540 joinable glass fibre reinforced polymer (GFRP) bolts for the reinforcement of the ventilation shaft.
Design of the GFRP pattern involved evenly spacing 23 holes around the circumference of the ventilation raise, offset 0.5 metres from the proposed shaft wall.
An additional four holes were positioned in the centre of the shaft to provide face support to the raise bore. Twenty GFRPs were required for each hole and were grouted once installed.
During excavation of the ventilation raise, there were no issues encountered within the expected poor ground which had been reinforced with GFRP bolts.
No overbreak was observed through this section of the shaft either.