Kaimai Tunnel facts for kids

The Kaimai Tunnel is a long railway tunnel in New Zealand. It goes through the Kaimai Range mountains on the North Island. Since it opened in 1978, it has been the longest railway tunnel in New Zealand. It is about 9.025 kilometres (5.608 mi) long.

This tunnel is part of a bigger railway project called the Kaimai Deviation. This project created a new, shorter path for the East Coast Main Trunk Railway. It helped trains avoid an older, more difficult route through the Karangahake Gorge. The Kaimai Deviation is 24.01 kilometres (14.92 mi) long in total. The tunnel makes up a big part of this distance.

History of the Tunnel

In the early 1900s, the old railway route through the Karangahake and Athenree gorges caused many problems. It was a very difficult path for trains.

Why a New Tunnel Was Needed

The old railway line had many issues:

• It was very long.
• It had steep hills (up to 1:50, which means for every 50 meters forward, it went up 1 meter).
• It had sharp turns.
• The tracks were not strong enough for the most powerful diesel trains.
• Landslides often blocked the route, causing delays.

Because of these problems, people started looking for a better way to connect places like Auckland and Tauranga by train.

Early Ideas for the Tunnel

People first suggested building a railway line over the Kaimai Range in 1911, but this idea was quickly thought to be too hard. In 1913, a shorter tunnel of about 3.2 km was suggested. By 1920, people were asking for a survey to find a good route for a Kaimai railway. However, it took many years for this to happen.

In 1955, there was a new idea to build a road and rail link to Mount Maunganui from the Waikato area. This plan included a 4 km tunnel. Farmers and local newspapers really liked this idea. This led to the creation of the Kaimai Tunnel Committee.

However, in 1958, the project was put on hold. A report said there weren't enough goods to transport by train to make the project worthwhile at that time. The report did suggest a 24 km route between Waharoa and Apata, which would include a 9 km tunnel. This is very similar to what was eventually built. This new route was estimated to cost at least NZ$10.5 million. Officials felt the old line could still handle the current train traffic. They decided to review the idea later when more trains were needed.

Official Investigation and Approval

Local groups were not happy with the delay. They kept asking the government to build the new line. In 1960, a group met with the Minister of Railways to explain how important a new route was. Because of this, an official investigation, called a Commission of Inquiry, was set up in August 1962. Its job was to look into "Improved Access by Land to the Port of Tauranga and Bay of Plenty." During the hearings, many people and groups shared their opinions and facts.

The investigation concluded that train traffic to the Bay of Plenty would double by 1982. This actually happened much sooner, by 1966! The commission suggested:

• Building the new railway line from Waharoa to Apata through the Kaimai Range.
• Closing the old section of the East Coast Main Trunk between Paeroa and Apata.

After this report came out in 1963, the government allowed a survey of the new route. The project was finally approved in September 1964. It was expected to cost about $11.4 million. Construction was delayed for another six months until funding was approved in 1965. At that time, people thought the project would be finished by October 1970.

Construction of the 24 km railway line, including the 8.85 km tunnel, officially began on 2 October 1965. The new section of railway opened on 12 September 1978. The old route closed the very next day.

Building the Tunnel

At the start of construction in October 1965, the Minister of Works, Percy Allen, spoke at the ceremony. He said the new railway line would help the entire North Island railway system. It would make the train journey between Tauranga and Hamilton 51.5 km shorter. It would also shorten the trip between Rotorua and Tauranga by 100 km. He believed the money spent on building the line would be saved later through lower running costs.

Most of the work was done by government engineers, who were in charge of drilling the tunnel. Other jobs, like building the tunnel entrances and laying the track bed inside the tunnel, were done by private companies.

In 1966, engineers thought about using a special machine called a Tunnel Boring Machine (TBM). This machine drills through rock much faster than traditional methods. They talked to people in Australia who had used or studied TBMs. Rock samples were sent to the TBM manufacturer (Jarva Company) to see if their machines would work for the Kaimai Tunnel. They thought the TBM could handle the eastern side of the tunnel, but the western side might be too rocky.

A Jarva TBM was bought from the United States in 1970 for $1.4 million. This was a big decision because a TBM had not been used on this type of rock before. Even though there were worries about starting at the western end, it was decided to do so. This was because the tunnel would go uphill from west to east, and starting there would help with water drainage. Also, the eastern end of the tunnel would finish on a bridge over the Whatakao Stream, which was not yet built.

Tunnel construction began at the western end on 15 January 1969. Workers first dug a deep trench leading to the tunnel entrance. The very beginning of the tunnel had soft, wet soil, so this part had to be dug by hand.

Sadly, during this time, an accident happened due to high groundwater, and four workers lost their lives. Eight other workers who were trapped were rescued.

After a few months, tunnelling started again. By 1971, the TBM was ready to work. A three-month trial period was set to see if the TBM could handle the western end. It quickly became clear that the rock there was too broken up for the TBM to work well. The machine's cutters and systems kept getting blocked by rocks. After the trial, the TBM had only moved 106 meters and was wearing out too fast. So, it was decided to take it apart and move it to the eastern end of the tunnel.

Work at the western end continued using traditional drill and blast methods. The tunnel's shape at the western end was changed from round (for the TBM) to a horseshoe shape, which was better for this method. By the time the tunnel was finished, about 48% of its length had been dug using traditional methods.

Good progress was made from the eastern end once the TBM was put back together there in April 1972. Even though the machine had some problems from being used at the western end, it could dig up to 15 meters in an 8-hour shift. However, progress was much slower in wet areas. A lot of water (up to 600 cubic meters) flowed through the tunnel walls, so pumps had to run all the time to prevent flooding.

At first, fans were enough to keep the air fresh for the machine and workers. But as the digging got closer to the middle of the tunnel, the temperature inside increased. To help with this, work shifts were made shorter. Eventually, three cooling systems were installed at the western end and one at the eastern end to keep the air cool.

Finishing the Tunnel

The two ends of the tunnel met on 4 June 1976. Two small pilot tunnels were drilled through to check that the alignment was correct. The official "hole-through" ceremony was planned for 17 June, but the TBM got stuck again with loose rock. So, the important guests had to be happy with just shovelling some of the rubble. Mr. L. Dillon, a project supervisor, was the first person to walk through the entire tunnel on 21 June.

The original plan was to line the tunnel with concrete after all the digging was done. But the rock, especially at the western end, was getting worse. So, the plan had to change. The problem was solved by pumping concrete under high pressure behind strong steel liners. After this was done, a British company called Robert McGregor and Sons laid the concrete track bed. They had developed a special method for laying paved concrete track (PACT). This method was chosen instead of traditional railway sleepers and ballast. It was meant to lower the cost of maintaining the tracks inside the tunnel.

Opening Day

Front cover of a programme of ceremony of the opening of the Kaimai railway tunnel and deviation, Tuesday 12 September 1978. Attended by the Prime Minister, Rt. Hon. Robert Muldoon.

The very first official train to go through the Kaimai Tunnel was the Silver Fern railcar RM 3. It left Hamilton railway station for Tauranga on 12 September 1978. On board were railway officials and 50 school children with disabilities from the Waikato area.

After a lunch break in Matamata, the Prime Minister, Robert Muldoon, greeted the crowd and got on the train. The next stop was Hemopo, where another crowd had gathered. Speeches were given by local leaders and government ministers. Then, the Prime Minister gave a speech and unveiled a special plaque. This plaque honored the four workers who had lost their lives during the tunnel's construction. Finally, he cut a ribbon and officially declared the tunnel open. The train then continued to Tauranga with the official guests.

The project took eight years longer than planned and cost more money. The final cost was $43 million for the tunnel and $13 million for the rest of the railway line, making a total of $56 million.

The Kaimai Tunnel Today

Today, the Kaimai Tunnel is very busy. Up to 22 freight trains travel through it each weekday, and up to 19 trains on weekends. These trains carry many different goods, such as shipping containers, timber, coal, manufactured products, and petroleum.

Since it opened, the Kaimai Deviation has mainly been used by freight trains. Regular passenger trains to the Bay of Plenty had stopped in 1967. The old, long, and slow route was one reason why these services were no longer profitable. It wasn't until 9 December 1991 that a regular passenger service to the Bay of Plenty was brought back. This train was called the Kaimai Express, named after the tunnel. It ran between Auckland and Tauranga until it was stopped on 7 October 2001. It was always operated by Silver Fern railcars. Sometimes, special passenger trips are run on the line by groups like Mainline Steam and the Railway Enthusiasts Society.

A mountain peak directly above the tunnel was named Stokes Peak in 2010, after a geographer named Evelyn Stokes. However, in 2012, the peak's name was changed back to being unnamed.

Geology of the Tunnel

The Kaimai Tunnel goes through different types of rock, including pumice, breccia, andesite, and ignimbrite. These are mixed with softer rock called tuff. The rocks in this area are about 3 to 5 million years old.

Because the ground is soft and there is a lot of groundwater, empty spaces have formed under the tunnel floor. Repairs using a special resin were made in 2013 and 2018 to fix these issues.

See also

In Spanish: Túnel de Kaimai para niños