World's Biggest Tunnel Boring Machines

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Tunnel boring machines develop large tunnels all around the world. Since the first use of a tunnel boring machine back in 1853, these machines have seen a growth in use to complete underground constructions for tunnels and highways. There are many significantly sized tunnel boring machines that have helped in developing major constructions to date. The world’s biggest tunnel boring machines include:

  1. Tuen Mun-Chek Lap Kok
  2. Bertha
  3. Santa Lucia
  4. Martina

Read on to find out more about these impressive machines!

What is a tunnel boring machine?

A tunnel boring machine is a machine used to excavate tunnels below the ground. Tunnel boring machines take on a cylindrical shape to bore through hard and soft ground, as an alternative to the process of drilling and blasting methods. Tunnels can range anywhere from diameters of 1 metre to 17.5 metres. Tunnel boring machines are favourable as they produce smooth tunnel walls and limit the disturbance in the surrounding areas to predominantly underground. Unfortunately, due to their significant size, tunnel boring machines are very expensive to assemble and can be difficult to transport.

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What types of tunnel boring machines are there?

Tunnel boring machines can be categorised within two types: hard rock or soft rock machines. As the name suggests, hard rock tunnel boring machines are designed to bore through solid ground and hard rock with the use of aggressive disc cutters mounted in the cutter head that chip away at the rock. Soft ground tunnel boring machines drill through materials of a shifting nature, such as sand, gravel, mud or clay.

More specifically, there are three types of soft ground tunnel boring machines: earth pressure balance (EPB), slurry shield (SS) and open-face type. Both EPB and SS machines use thrust cylinders to advance forward through the soil, while open-type tunnel boring machines use a gripper system that allows the machine to push against the side walls of the tunnel to advance forward.

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What are the biggest tunnel boring machines?

1. Tuen Mun-Chek Lap Kok

The largest tunnel boring machine in the world is known as the Tuen Mun-Chek Lap Kok tunnel boring machine. This enormous slurry shield machine has a diameter of 17.6 metres, making it slightly larger than the previous holder of the biggest tunnel boring machine, Bertha. The tunnel boring machine is being used to drill a 5km tunnel in Hong Kong, known as the Tuen Mun Check Lap Kok link. The tunnel boring project began in October 2018 and was completed by the end of 2020.

2. Bertha

Prior to Tuen Mun-Chek Lap Kok’s arrival, the Bertha claimed the title as the biggest tunnel boring machine in the world. Now taking the title as the second largest tunnel boring machine, the Bertha was named after Seattle’s first female mayor, Bertha Knight Landes, and measures a massive 17.5 metres wide. This machine was designed and constructed in Osaka, Japan. It later arrived in Seattle during April 2013 to begin underground tunnel development for a double-decker highway, which was scheduled to be completed by December 2015. But as with many projects, unexpected events caused a two-year delay to the great tunnel boring project. Bertha resumed its duties on December 2015 and despite a few more halts, the tunnel boring process was completed in April 2017 and the highway was finally opened for use in February 2019.

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3. Santa Lucia

The Santa Lucia tunnel was developed by a mega-tunnel boring machine, measuring 15.8 metres in diameter - the third largest tunnel boring machine ever built. This tunnel boring machine was designed and constructed in Schwanau, Germany by Herrenknecht manufacturing company with no name given. This tunnel boring machine created the impressive 7.5km, three-lane tunnel in Santa Lucia, Italy on the Autostrada A1 between Bologna and Florence. The tunnel development process began in July 2017 and was completed in June 2020 for public use.

4. Martina

The Martina is considered the world’s largest hard rock tunnel boring machine with a diameter of 15.6 metres, allowing it to hold the title of the fourth largest tunnel boring machine in the world. The Martina was built in Germany by the same manufacturer of the Santa Lucia tunnel boring machine. This machine began work in August 2011 in Italy to develop the double barrel motorway known as the Sparvo tunnel, also located on the Autostrada A1. Boring of the two tunnels was completed by July 2013, making it one of the quickest development timeframes for tunnel boring.

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