Its 60 years since the Rimutaka Rail Tunnel opened. Due to its solid construction it has required minimal maintenance over its life and is set to last for another 100 years.
THE RIMUTAKA RAIL TUNNEL, which runs under the Rimutaka Range between the Hutt Valley and the Wairarapa, opened in late 1955. It is the longest, single-track rail tunnel in New Zealand through which both freight and passenger trains operate. At just over 8.7 kilometres long it is only superseded by the Kaimai Tunnel north-west of Tauranga, which is just under 8.8 kilometres long, but caters only for rail freight.
The tunnel replaced the tortuous and lengthy rail route over the Rimutakas, which, due to the steepness of the terrain, utilised the famous ‘Fell’ steam engines to slowly haul passenger carriages and freight wagons over the incline. These unique engines, which began operating in 1878 over the route, ran on a track comprising three rails, with the centre rail slightly raised to couple with two pairs of horizontal grip wheels mounted beneath the engine to provide extra grip when climbing the steep incline. Special brake vans helped control the descents.
The tunnel was a long time coming and was fraught with delays. In 1898, surveyor and engineer J Dobson completed several surveys for the Public Works Department (forerunner of the Ministry of Works and Development), however it was not until the mid-1920s that any advancement was made and a number of feasibility studies and routes explored.
Due to lack of funding and the Depression it was not until 1936 that the government announced its intention to proceed with the tunnel, and while detailed plans were made the project was abandoned due to the advent of WW2.
By 1945/46 it was becoming urgent, as the incline route was in bad shape and the Fell engines were in need of expensive maintenance. Work began in 1948 with exploratory bores of up to 321 metres, and in July/August 1951 a consortium comprising American company Morrison Knudsen and Downer and Co commenced work at both ends.
‘Carved’ from solid rock the tunnel construction took three years to break through. Workers toiled 24 hours a day, six days a week, using explosives, drilling, boring and pick and shovel to excavate the portal. The spoil material was carted out by wagons on temporary rails, with some of it used as ballast for the railway line. The tunnel excavation was shored-up by wooden framing and was built with a semi-circular roof and near vertical walls in what was then known as the ‘American system’ with concrete casing up to 38-centimetres thick lining the tunnel and culverts providing for water seepage.
There was one fatality during construction, the result of a rock fall on September 9, 1952, when 27 men were trapped for over nine hours underground before being rescued.
When the tunnel broke through on April 20, 1954 the survey error was only 44.5mm astray, which was quite a feat given the length and gradient of the tunnel.
It took another year to build the approach formations and bridge piers, lay track and install the signalling equipment, with the first train passing through on November 3, 1955.
The tunnel is 4.68 metres wide and 5.18 metres high. It rises at 1-in-400 from the western portal to the highest point, which is approximately midway through, before descending to the eastern portal at 1-in-180. A 117-metre high vertical ventilation shaft was bored up to the surface from the midway point to allow fumes to escape. Over 299,258 kilograms of gelignite and 26,163 tonnes of concrete were used and around 87,800 metres of aggregate removed.
Due to smoke build up, coal/steam driven locomotives were unable to use the tunnel, resulting in the Wellington to Wairarapa line becoming the first to utilise the ‘new’ diesel locomotives. To this day, when ‘commemorative’ steam trains use the line, diesel locomotives have to haul them through the tunnel. Electrification was provided for (though not operative) by way of a 1500-volt DC line.
According to KiwiRail, the Rimutaka Rail Tunnel still has plenty of life ahead of it, with head of civil engineering, Daniel Headifen saying the tunnel and those who constructed it left a valuable legacy.
“It is still a massively significant piece of infrastructure for both KiwiRail and for New Zealand,” he said in a recent Radio NZ interview.