Homer Tunnel, State Highway 94
Engineering Work (eg road, bridge, sawmill, dam)
In 1935 five men with shovels and wheelbarrows began to pierce this 1240m tunnel into the Cleddau Valley and the magnificent country beyond.
Shovels, picks and wheelbarrows were the bulldozers of the day; isolation and deprivation the constant companions of the men employed on the work. With an average rainfall of 250 inches (6350mm), heavy snowfall and avalanche danger, conditions were severe for both tunnellers and road gangs. Accommodation was in canvas tents that seldom saw the sun for six months of the year. Pay was on a contract basis which meant that, with the continuous rainfall, wages were often reduced to a mere pittance, sometimes as little as £1 6s ($2.60) per month.
The tunnel section is 24ft x 18ft, the length 4118ft and on a down gradient of 1 in 10 from the eastern portal; the western portal being inaccessible until the tunnel was pierced.
The rock could be described as of a granite type and therefore quite stable. Although full-face tunnelling could have been used on a more level grade, a 14ft x 9ft heading was put through to ease the problems of seepage water discharge, and of ventilation, then enlarged in one operation to the required size by a system of ring drilling.
The Upper Hollyford and Cleddau Valleys are typical of nature’s glacial handiwork, with a floor approximately 800m wide, walls almost vertical for 800m, and then lying back approximately 30º, vast areas of snowfields, up to 2500m elevation with an annual snow precipitation of approximately 5000mm. As a source for avalanches, this could be equal to anything in the world.
Two types of avalanches, the wet and the dry, occur. The wet avalanche occurs when snowfields become unstable and slide off the mountains. The wet type provides plenty of noise and take an appreciable time to cascade down the mountain. It is regular and can be predicted.
Dry avalanches have a different cause. They occur when it is snowing on the tops, are noiseless, until suddenly a terrific air blast occurs, and a snow cloud of the atomic bomb type emerges. The blast from this is powerful enough to shear off 50cm diameter beech trees without uprooting them, throw 40kg 10cm water pipe 200m and blow over a 4-tonne tractor. Ordinary temporary structures are as straw and in one case a 100m mass of reinforced concrete avalanche protection, the basic design of which was based on continental design for avalanche areas, was demolished.
In one specific dry avalanche, it was estimated that 250,000 tonnes of snow and ice, glissaded off the snowfield, and fell, as a blanket 450m. When it landed, the entrapped compressed air burst out releasing energy calculated at 450MW.
So the road took its toll. In July 1936 a tunneller was killed and several men injured when an avalanche struck the tunnel entrance. A reinforced shelter built out from the tunnel mouth proved to be no certain protection, for the following year, the engineer in charge and tunnel superintendent, both at work near the tunnel entrance, were killed by avalanche blast.
Nevertheless work continued and ‘hole-through’ was achieved in February 1940. World War II held up the work and in 1945 the massive reinforced concrete approach was destroyed by another avalanche. The damage is still evident.
In 1953 a private contract was let for the tunnel completion and in the summer of 1954 the first private car drove through. Now there are over a quarter of a million vehicles each year.
Design and roadworks: Public Works Department
Tunnel construction: P.W.D. and Downer & Co Ltd
IPENZ “Engineering to 1990” project
This item of New Zealand’s engineering heritage was recognised as part of the IPENZ “Engineering to 1990” project which the Institution organised to help celebrate the country’s sesquicentenary in 1990. A plaque was unveiled to mark the significance of this tunnel as part of the development of the nation.
State Highway 94, Te Anua to Milford Sound
Nature of Engineering
Natural Hazard Protection, Infrastructure (incl. Road, water, ports)
(Click image to enlarge)
(Click image to enlarge)
Lat: -44.764416 Long: 167.983661