Hard-rock Otira digging for B.skm

Press, 2 November 1989, Page 15

Hard-rock Otira digging for B.skm

In 1908, Robert Speight (later to become curator of Canterbury Museum and professor of geology at Canterbury College) delivered a lecture to the Canterbury Philosophical Institute on what geological phenomena were likely to be encountered in the construction of the Otira Tunnel.

He predicted that the only rocks to be encountered would be slate and very hard sandstone (greywacke), with no economic minerals except possibly small amounts of graphite. My first job when I started as a voluntary worker at Canterbury Museum several years ago was to sort and catalogue several hundred rock specimens collected during the construction of the tunnel in the early part of this century. It is hard to ■imagine a more monotonous collection of rocks — greywacke, greywacke and greywacke.

Nothing unexpected. Tunnelling through 8.5 kilometres of hard rock was a major achievement, but there were other problems in completing the Canterbury-Westland rail link. Nearly 60 years elapsed between the first proposal for a tunnel and its completion in 1923.

The discovery of gold on the West Coast had led to public

demand in Christchurch for a better route to the goldfields than the rough, roundabout route via the Hurunui Saddle (Harper Pass). In 1865, Edward Dobson, provincial engineer, was asked to make a feasibility study for a road over the alps. He chose Arthur’s Pass, discovered a year before by his son, Arthur. Dobson realised the treacherous

nature of the Otira route and thought the only satisfactory solution was a tunnel between the upper and lower gorges. A tunnel was out of the question at the time, not just because tunnelling technology was insufficiently advanced but because the energies of the Canterbury settlement were directed elsewhere — the Lyttelton rail tunnel. The Otira road was completed in March, 1866. The abolition of provincial governments in 1875 meant that Canterbury was forced to lobby the Government to keep the idea of a trans-alpine rail link alive. For the next decade or more, a number of syndicates were formed to build the line, and all experienced varying degrees of failure. The syndicates were to raise money, build the line, then hand it over to the Government in exchange for land along the route.

The Greymouth-Brunner line was completed in 1876. Springfield was reached in 1880, but from then on it was a story of piecemeal development of the line, which was to take over 40 more years to complete. The New Zealand Midland Railway Company, Limited was registered in London in 1886. But the company was under-capi-talised, and they laid the easiest sections of the route first without any over-all plan. By the end of 1891, only 66km had been laid, mostly on the West Coast. Only 6km had been laid beyond Springfield. It was obvious the contract was not going to be honoured, and the Government took over in 1895. The Government resumed work near Springfield in March, 1898. By 1902, only another 6km had been laid, albeit a very difficult section with six tunnels.

By December, 1899 the western line had reached Otira and the question loomed: how was the divide to be crossed? A committee of engineers

up in 1900 which eventually agreed on a tunnel with a gradient of 1 in 33. From this time to the construction start in 1907, political considerations dominated. South Island interests had to compete with the North Island main trunk line for funds, and there was strong opposition in the North Island to the Otira Tunnel. The tunnel’s problems were not over when the contract was let to a New Zealand company, John McLean and Sons, in July, 1907. They signed a five-year contract to build what at the time was the sixth longest tunnel in the world. A “Firing the First Shot” ceremony was arranged after the

tunnel work started,.But on the day — May 5, 1908 —63 mm of rain fell in the Otira region. Only a few hundred people made it to the festivities at the Otira entrance. Atrocious conditions east of the divide also spoiled the celebrations, and Christchurch officials were forced to hold their celebrations at. the Bealey

Hotel because the Waimakariri was so high. Many factors contributed to delay tunnel progress after work started. One delay was surveying the route, a survey that was extremely difficult and took two years. A line had to be cut through the scrub and a series of trig stations established. The survey! was done in at least five portions because of the steepness of the country. At one stage, six months were lost when a delicate theodolite had to be sent to England for repair. It was a tribute to the surveyors’ accuracy that when the two ends of the tunnel met, they were only 2.9 cm out in level and I.9cm in alignment. ; ,< From 1914. oh, there was a labour shortage due to the war. Progress was delayed by areas of rotten rock which needed extra timbering, and water in the tunnel often made working conditions unbearable. However, the tunnel was finally opened in 1923 — 16 years after ; the contract had been signed.

By

HOWARD KEENE