Kaimai Railway Tunnel

Engineering Work (eg road, bridge, sawmill, dam)


The Kaimai Tunnel is 8.9 kilometres long and was excavated between 1969 and 1976. It is New Zealand's longest railway tunnel and was the first project in New Zealand to use a ‘full face hard rock’ Tunnel Boring Machine (TBM).

The Ministry of Works began construction work in January 1969. Although the geology along the tunnel alignment varied considerably there was sufficient massive unbroken rock to justify the purchasing of a TBM. Manual excavation through the loose alluvial material commenced on the west side with the intention of using the TBM once the andesite was reached. Excavation of this section proved very difficult with the TBM's steel sets constantly sinking and at one stage a disastrous fall occurred, trapping 12 men and causing the deaths of four.

Once through to the andesite the machine commenced boring. However the andesite was very broken and large pieces would come loose and rotate around the cutting face causing much damage. This meant progress was slow and expensive.

It was finally decided to remove the TBM and transfer it to the eastern portal where it would be working in ignimbrite. This rock was softer and had fewer joints. The rate of progress in this heading varied considerably but averaged about 25 metres per week.

In the meantime, slow manual progress continued in the western section. Geothermal heating of the rock also became a problem and refrigeration plants had to be installed in both sections.

In the end, the TBM completed about half the tunnel's excavation. It was considered to have been marginally successful, but more than anything it provided valuable experience for other projects involving large scale machine tunneling.

'Kaimai tunnel disaster memorial,'  Ministry for Culture and Heritage, updated 3 February 2015 (www.nzhistory.net.nz).

B D Hergan. "Kaimai Tunnel: a geological section through an ancient volcano." In Geotechnics on the Volcanic Edge: Tauranga, March 2003, New Zealand Geotechnical Society Symposium (Wellington: IPENZ, 2003), 65-70. See attachment below.


Hegan, Kaimai Tunnel, 2003 (5MB).pdf
The Kaimai Railway Tunnel (650 KB).pdf


Kaimai Range. The west portal is between Gordon and Turangamoana and the east portal is north of Whakamarama.

Bay of Plenty, Waikato

Access Info
There is no access to the tunnel other than by rail.

Nature of Engineering
Rail Transportation


Kaimai Railway Tunnel, Tauranga County, Bay of Plenty, 1981. Whites Aviation Ltd: Photographs. Ref: WA-75607-F. Alexander Turnbull Library, Wellington, New Zealand. http://natlib.govt.nz/records/22303252

(Click image to enlarge )

Lat: -37.699085 Long: 175.846202