Raurimu Spiral

The Raurimu Spiral is a single-track terminal loop structure with circular bend on the North Island Main Line North Iceland Main Trunk Railway of New Zealand, which connects the cities of Auckland and Wellington. The track here overcomes a height difference of 132 m, contains two tunnels ( 384 m and 96 m long) and 3 hairpin bends.

Background

During the construction of the central section of the North Iceland Main Trunk Railways between Auckland and Wellington, there was the problem that Raurimu between Flat and the central plateau near the national park at about 6 km as the crow a height difference of 218 m was overcome. The area was at the time of the survey work in the 1890s from a high, dense rainforest. A direct connection would have meant a slope of 1:24. For a long time a 19- km-long alternative route was followed, which would have required even nine viaducts and a slope of 1:50.

Construction

The solution finally executed was developed by the engineer RWHolmes 1898. He suggested the spiral route before with two tunnels and an average slope of 1:52. Long sections of the route, however, are also created with a gradient of 1:50. The lower hairpin curve has a radius of 198 m, the upper curves and the circular bend with a radius of 200 m. Overall, the route extended so that the distance between Raurimu and National Park about 11 km.

The spiral begins in Raurimu with a 180 ° turn to the left, followed by two sharp right turns, then moves through the route the two mentioned tunnel. In a complete circle bend to the right then the longer the tunnel is crossed before the route continues climbing the plateau. After another two kilometers each followed by a sharp right and a left turn.

Worth knowing

East of State Highway 4 branching from junction to a lookout point with a high point from which is visible from a part of the investment in Raurimu.