The Raurimu Spiral, is a single-track railway spiral, starting with a horseshoe curve, overcoming a height difference, in the central

North Island The North Island ( , 'the fish of Māui', historically New Ulster) is one of the two main islands of New Zealand, islands of New Zealand, separated from the larger but less populous South Island by Cook Strait. With an area of , it is the List ...

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

, 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 ser ...

railway (NIMT) between

Wellington Wellington 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 third-largest city in New Zealand (second largest in the North Island ...

and

Auckland Auckland ( ; ) is a large metropolitan city in the North Island of New Zealand. It has an urban population of about It is located in the greater Auckland Region, the area governed by Auckland Council, which includes outlying rural areas and ...

. It is a notable feat of

civil engineering Civil engineering is a regulation and licensure in engineering, professional engineering discipline that deals with the design, construction, and maintenance of the physical and naturally built environment, including public works such as roads ...

, 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 North Island Main Trunk, 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 t ...

to the east and the valleys and

gorge A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosion, erosive activity of a river over geologic time scales. Rivers have a natural tend ...

s 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 Kūiti and 55 km west of T� ...

, the

terrain Terrain (), alternatively relief or topographical relief, is the dimension and shape of a given surface of land. In physical geography, terrain is the lay of the land. This is usually expressed in terms of the elevation, slope, and orientati ...

is steep, but not unmanageable, with the exception of the stretch between Raurimu and

National Park A national park is a nature park designated for conservation (ethic), conservation purposes because of unparalleled national natural, historic, or cultural significance. It is an area of natural, semi-natural, or developed land that is protecte ...

, 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 f of several variables is the vector field (or vector-valued function) \nabla f whose value at a point p gives the direction and the rate of fastest increase. The g ...

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've been steeper than 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 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 station before going round a 200° bend to the left in a horseshoe curve, 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 more 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 further away as it revolves around the point. It is a subtype of whorled patterns, a broad group that also includes concentric objects. Two-dimensional A two-dimension ...

are relatively common in the

Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...

, particularly in

Switzerland Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...

, 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.

Folklore

Legend has it that a locomotive engineer once engaged the emergency brakes of his train upon mistaking the light of his own guard's van on a nearby part of the spiral for the rear of a different train directly ahead of him.

References

Citations

Bibliography

* (limited online search only) *

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 Heritage New Zealand Category 1 historic places in Manawatū-Whanganui Rail transport in Manawatū-Whanganui Ruapehu District Railway attractions in New Zealand Rail infrastructure in New Zealand