One of New Zealand’s engineering marvels turned 60 this week. The Rimutaka rail tunnel, a railway tunnel through New Zealand’s Rimutaka Ranges (in the Waiarapa), began service on 3 November 1955 and is still going strong today.
The tunnel replaced the existing above ground rail line (the Rimutaka Incline). The Rimutaka Incline was the steepest railway line in New Zealand at the time, dropping 265m in less than 5km (an average gradient of 1 in 15, which is very steep for a railway). Due to its steepness, it would take around three hours and 20 minutes to get between Featherston and Wellington on the incline. In addition to its slowness, the Incline was also very expensive to run. Plans to replace the Incline began in the 1920’s, but construction was delayed due to two World Wars and the 1930’s depression.
In 1948, the Public Works Department started work on the replacement tunnel with bores of 321m at the western end and 250m at the eastern end. The tunnel was then completed by a joint venture between American firm Morrison Knudsen Inc and local company Downer and Co. Contractors from these two companies worked 24 hours a day, six days a week, for two years to drill through 8.8 kilometres of rock. This hard work meant that the tunnel was completed a year earlier than anticipated.
The size of the tunnel is very impressive given the technology available at the time, boasting an internal height of 5.18 metres and a width of 4.68 metres. It is lined with concrete with a minimum thickness of 38 cm inside the face of the excavation.
The tunnel is still used to carry passengers as well as freight, such as wood, which is not suited to the narrow and winding roads in the Rimutaka region. Kiwirail’s head of civil engineering, Daniel Headifen, said those who worked on the tunnel have left ‘a valuable legacy’ and that the tunnel is a ‘massively significant piece of infrastructure work.’
You can view the moment where the two shafts of the Rimutaka tunnel met here: