The Raurimu Spiral is a single-track

railway spiral A spiral (sometimes called a spiral loop or just loop) is a technique employed by railways to ascend steep hills. A railway spiral rises on a steady curve until it has completed a loop, passing over itself as it gains height, allowing the railw ...

, starting with a

horseshoe curve A horseshoe curve is a class of climbing curve in a roadbed which reverses turn direction (inflection) twice on either side of a single tight curve that varies through an angle of about 180 degrees or more. Such curves are more commonly found ...

, overcoming a height difference, in the central North Island of

New Zealand New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...

, on the

North Island Main Trunk The North Island Main Trunk (NIMT) is the main railway line in the North Island of New Zealand, connecting the capital city Wellington with the country's largest city, Auckland. The line is long, built to the New Zealand rail gauge of and se ...

railway (NIMT) between

Wellington Wellington ( mi, Te Whanganui-a-Tara or ) is the capital city of New Zealand. It is located at the south-western tip of the North Island, between Cook Strait and the Remutaka Range. Wellington is the second-largest city in New Zealand by metr ...

and

Auckland Auckland (pronounced ) ( mi, Tāmaki Makaurau) is a large metropolitan city in the North Island of New Zealand. The List of New Zealand urban areas by population, most populous urban area in the country and the List of cities in Oceania by po ...

. It is a notable feat of civil engineering, having been called an "engineering masterpiece." The Institute of Professional Engineers of New Zealand has designated the spiral as a significant engineering heritage site.IPENZ
/ref> Raurimu Railway Spiral from Helicopter - panoramio

Raurimu Railway Spiral from Helicopter - panoramio

Background

During the construction of the central section of the NIMT, a major obstacle arose: how to cross the steep slopes between the

North Island Volcanic Plateau The North Island Volcanic Plateau (often called the Central Plateau and occasionally the Waimarino Plateau) is a volcanic plateau covering much of central North Island of New Zealand with volcanoes, lava plateaus, and crater lakes. It contains ...

to the east and the valleys and gorges of the

Whanganui River The Whanganui River is a major river in the North Island of New Zealand. It is the country's third-longest river, and has special status owing to its importance to the region's Māori people. In March 2017 it became the world's second natur ...

to the west? Raurimu Spiral map

South of

Taumarunui Taumarunui is a small town in the King Country of the central North Island of New Zealand. It is on an alluvial plain set within rugged terrain on the upper reaches of the Whanganui River, 65 km south of Te Kuiti and 55 km west of ...

, the

terrain Terrain or relief (also topographical relief) involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin word ...

is steep but not unmanageable, with the exception of the stretch between Raurimu and National Park, where the land rises too steeply for a direct rail route. A direct line between these two points would rise in a distance of some , a

gradient In vector calculus, the gradient of a scalar-valued differentiable function of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p is the "direction and rate of fastest increase". If the gr ...

of 1 in 24. The area was thoroughly surveyed during the 1880s in an attempt to find a route with a lesser grade, but the only viable possibility seemed to require a detour and nine massive viaducts. Even then, the gradient would have been over 1 in 50.

Construction

The problem was solved in 1898 by a surveyor in the employ of Robert Holmes,

Public Works Department This list indicates government departments in various countries dedicated to public works or infrastructure. See also * Public works * Ministry or Board of Public Works, the imperial Chinese ministry overseeing public projects from the Tang ...

engineer. He proposed a line that looped back upon itself and then spiralled around with the aid of tunnels and bridges, rising at a gradient of 1 in 52. Though costly and labour-intensive, the scheme was still cheaper than the previous plan by Browne and Turner which required 9 viaducts down the Piopiotea River. The most remarkable feature is that even today there is no place to view the complete line. By all accounts, Holmes visualised the layout in his imagination. The railway forms an ascending spiral southwards, with two relatively short tunnels, a circle and three hairpin bends. From the north, trains pass Raurimu before going round a 200° bend to the left in a

, climbing above the track on which they have just travelled. Two sharp bends to the right follow, after which the line passes through two short tunnels, the Lower Spiral Tunnel (384 m) and the Upper Spiral Tunnel (96 m). Trains then complete a full circle, crossing over the Lower Spiral Tunnel through which they have just passed which is below, before continuing towards Wellington. further on the line has two further sharp bends, to the right and then to the left. After the second of these bends a train has risen and travelled from Raurimu– the straight-line distance is . Some of the sharp curves are only 7½ chains (150 m) radius. Although

spirals In mathematics, a spiral is a curve which emanates from a point, moving farther away as it revolves around the point. Helices Two major definitions of "spiral" in the American Heritage Dictionary are:Alps The Alps () ; german: Alpen ; it, Alpi ; rm, Alps ; sl, Alpe . are the highest and most extensive mountain range system that lies entirely in Europe, stretching approximately across seven Alpine countries (from west to east): France, Sw ...

, particularly in

Switzerland ). Swiss law does not designate a ''capital'' as such, but the federal parliament and government are installed in Bern, while other federal institutions, such as the federal courts, are in other cities (Bellinzona, Lausanne, Luzern, Neuchâtel ...

, they generally involve extensive tunnelling inside mountainsides. A masterly feature of Holmes' layout is the way in which it uses natural land contours so that no viaducts are needed, and only two short tunnels. Legend has it that a locomotive engineer once put on the emergency brakes of his train in the night upon mistaking the light of his Guard's Van on a nearby part of the spiral as the rear of a different train directly ahead of him.

References

Citations

Bibliography

* *''By Design: A brief history of the Public Works Department Ministry of Works 1870–1970'' by Rosslyn J. Noonan (1975, Crown Copyright) Appendix XIV, The Raurimu Spiral by J. H. Christie (pages 312–315).

External links

1906 photo of cutting being excavated at what was then known as PukerimuNZ Engineering Heritage North Island Main Trunk line page''Raurimu Spiral'' (NZR Publicity pamphlet)
* *The New Zealand Railways Magazine, Volume 11, Issue 6 (1 September 1936

* {{coord, 39, 7.4, S, 175, 23.8, E, region:NZ-WGN_type:landmark, display=title Buildings and structures in Manawatū-Whanganui NZHPT Category I listings in Manawatū-Whanganui Rail transport in Manawatū-Whanganui Ruapehu District Railway attractions in New Zealand Rail infrastructure in New Zealand