Kaimai Tunnel project: Tunnel boring machine

After extensive investigations at the planning stage of the project, it was decided to purchase a hardrock full-face tunnel-boring machine to excavate the tunnel in a single pass. A complex contract was arranged for both the supply of the machine and the supply and servicing of cutters for the duration of the project. Back-up equipment was designed and built in New Zealand by the Ministry of Works and Development. The machine was not successful in boring the blocky andesite prevailing at the western end of the tunnel The softer ignimbrites prevailing in the eastern half of the tunnel presented few problems to the machine and it bored approximately 5 km of tunnel from the eastern end. Operations from the eastern end of the tunnel were severely hampered in the early stages by major breakdowns. Assessment of the machine's performance revealed that, although not as spectacular as was envisaged, it met expectations and justified the use of this tunnelling method at Kaimai.