It’s been almost 70 years in the making, but the longest rail tunnel in the world is due to open this month.

Conceived in 1947, the Gotthard Base Tunnel in Switzerland is the longest rail tunnel in the world. It runs through the Swiss Alps for 57km (35.4miles) so travel time between Zurich and Milan will be an hour faster than pre-tunnel time.

This great feat of engineering began 17 years ago. It involved cutting through 28.2 million tonnes of rock at a depth of about 22.9km (13miles). Eight workers died during the construction phase of the $17 billion project.


Opening for traffic in 1978 at a length of 8.879km (5.5miles), the longest rail tunnel in New Zealand cuts through the Kaimai Range in the North Island. The Kaimai Tunnel is part of the 24km (14.9 miles) Kaimai Deviation, which was constructed on the East Coast Main Trunk Railway to bypass the old route through the Karangahake Gorge, part of which is now the Goldfields Railway.

The Kaimai Deviation was a major public works project as it involved forming several major cuttings, embankments and viaducts.


On the 2nd of October 1965 work began on the massive project to shorten the rail distance between New Zealand’s two fastest growing provincial cities of Hamilton and Tauranga by 51km (32miles). It would also shorten the rail distance between Tauranga and Rotorua by 100km (62miles). Most of the work was carried out by the Ministry of Works, whose main responsibility was the creation of the tunnel. It was hoped the newly developed Tunnel Boring Machine (TBM), which had been successfully used in Australia the previous year, could make the job easier. Rock samples were sent to the American manufacturers, the Jarva Company, to assess the suitability of the machines for the New Zealand project. The Americans believed their machine would be able to handle the eastern end of the tunnel, but they were less confident in its ability to handle the fractured rock at the western end. After a number of government meetings were held in Wellington, it was decided to try the Tunnel Boring Machine. It was imported from America in 1970 at a cost of $1.4 million. The decision was a risk as a TBM had not been used on this type of geology before. Despite concerns about starting at the western portal, it was considered to be the better option because of the 1:300 ascending grade from west to east. Also, the tunnel was to terminate at the eastern end at the Whatakao Stream Viaduct which had yet to be built.


Construction of the tunnel started at the western end on 15 January 1969 with the excavation of the approach cutting reaching 25 metres (82 feet) deep at the portal. A layer of soft earth meant that the tunnel face had to be excavated by hand. While the pilot tunnel was being formed a cave-in, caused by seepage, resulted in the loss of four lives. The rescue operation was able to save eight other workers who were trapped with those that perished.

Because of the tragedy, tunnelling was delayed for several months, but by 1971 the Tunnel Boring Machine was ready to commence work. It soon became apparent that the rock at this end of the tunnel was too fractured for efficient operation of the massive machine resulting in the cutter and extraction systems being continually blocked by rock. After just 12 weeks, the TBM had only advanced 106 metres (347 feet) and was wearing out far more quickly than was hoped, so it was decided to dismantle it and move it to the eastern portal.


Work at the western end of the tunnel was now undertaken with traditional drill and blast methods. The profile of the western portal had been circular to accommodate the TBM, but this was changed to a horseshoe shape to better suit conventional tunnelling methods. By the time the tunnel was finished, almost half the length of it had been bored using conventional methods.

The TBM was reassembled at the eastern end in April 1972 and more satisfactory progress was made from that time. Wear on the machine from its use at the western end caused numerous mechanical problems. Despite this, and the fact continuous pumping was required to clear the water flow in the tunnel, 15 metres (49 feet) of tunnelling was achieved daily. The closer the excavation got to the midway point, the hotter it was for the workers. To combat this, the shifts were shortened and three refrigeration plants were installed to cool the atmosphere down in the western end with another plant installed at the eastern end.


The eastern and western boring teams met in the centre on 4 June 1976 when two pilot tunnels were drilled through to the other side to check the alignment. Mr. L. Dillon, a project supervisor, became the first person to walk the tunnel end-to-end on 21 June 1976. A Silver Fern railcar departed Hamilton for Tauranga on the 12th September 1978 and became the first train to travel through the Kaimai Tunnel. Today, the tunnel is used by 36 freight trains daily. They transport inter-port container traffic, timber, coal, manufactured goods, and petrol. Recently, 13 million dollars was spent to upgrade the tunnel to allow heavier loads to use it.


The 8,529 metre (5.2 miles) Otira Tunnel is the longest rail tunnel in the South Island and was the longest in the British Empire at the time of its construction.

In 1866, a road was formed over Arthur’s Pass through the Otira Gorge connecting the east and west coasts of the South Island. The gruelling, uncomfortable trip between Christchurch and Hokitika in a Cobb and Company bullock hauled coach took 36 hours with an overnight stay in Arthur’s Pass. It was not until the early 20th century that a tunnel 5 miles long became feasible.

Driven through wet shale and rock of the Southern Alps, this massive feat of engineering was opened on the 4th August 1923 without the help of the technology that made the Kaimai Tunnel. It is amazing to us today to understand that teams of men literally used pick and shovel to hack their way through the longest mountain range in New Zealand. With the tunnel’s opening, the rail link known as the Midland Railway, connected Christchurch on the east coast to Greymouth on the west coast.

Otira Tunnel Construction 1907 (

An Abt rack rail system (also known as a cog railway) was initially considered but soon rejected as a rack rail engine could only haul its own weight. As the railway was intended for heavy rail traffic, another option would need to be adopted.

In 1907, the job of building the Otira Tunnel was awarded to John McLean and Sons, the most experienced contractors in New Zealand. They were given 5 years to complete the tunnel for the sum of £599,794. It ended up taken them 15 years to finish the job with the final cost being double the original price.


Labour troubles bedevilled the job. Ongoing strikes encouraged by various trade unions contributed to a chronic shortage of suitable labour. This resulted in poor productivity, a rise in accidents, and not least, the rise of the parliamentary Labour Party. John McLean and Sons petitioned Parliament to be released from their obligations which was approved towards the end of 1912. The company went out of business soon after, financially destroyed by the Otira Tunnel contract.

The Public Works Department took over the monumental task but World War One intervened which again slowed work on the much-delayed project. Eventually on the 20th July1918 tunnel workers from the east and west ends met in the centre. Remarkably, the surveyor lines produced from each end were found to vary by only 19mm for line and 29mm for level, amazing accuracy before the days of lasers. It took another three years to line the tunnel and set the profile so it was not until September 1921 that the tunnel was complete but there was still no working railway.


During the first decade of the 20th century, electric railway traction became a practical and economic proposition. It would be particularly useful in a long tunnel with the inherent problems of smoke and furnace gases from steam engines. These issues would create undesirable and dangerous situations in the long Otira Tunnel. In 1920, tenders were called for a generating plant at Otira, along with six electric locomotives and 14km (8.6 miles) of electrified line. Once the English Electric Company of London completed the work, the Midland Railway was finally opened for through traffic in August 1923 after almost 40 years in the building. The Midland Railway, formed to build the whole rail/tunnel system, ceased to exist along with New Zealand’s largest contracting company, a heavy price to pay but the railway was complete. Amazingly, despite the use of explosives and the dust this generated in the tunnel and the freezing winter temperatures, the hazardous working conditions killed only one worker during the entire construction period.

Today, the TranzAlpine Railway is billed as one of the world’s most scenic train journeys. Trains depart daily from Christchurch for the 4 hour trip to Greymouth – all thanks to the South Island’s longest rail tunnel at Otira.

Ceidrik Heward

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