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Tunnel boring machine

What is a TBM? 

A tunnel boring machine is a machine that can excavate tunnels in a single operation, called full-face drilling. It has a rotating head with cutting parts and runs on hydraulic or electric motors, though its power supply is 100% electric. 

The TBM is also used for shoring. Shoring is a temporary containment system used in construction and civil engineering works to support excavations or structures.

What types of tunnel boring machines are there? 

There are two large groups: moles and shields.

Shields: these are tunnel boring machines designed to excavate in soft rocks or friable terrain; they require setting up support. They have an outer metal casing that temporarily holds the ground from the front, allowing the final shoring to be placed to ensure the tunnel’s stability. These tunnel boring machines can be open face or closed face, have a mechanical seal, be pressurized with compressed air, made of bentonite (or hydro-shield), or have earth pressure balance (EPB).

Moles: these tunnel boring machines are designed to excavate high or medium-hard rocks. The thrust force is transferred to the cutter head by the thrust cylinders. Unlike shields, moles don’t have a steel cylinder behind the cutting wheel, so they don’t serve as temporary shoring.

There are also tunnel boring machines known as double shield, a kind of mixed model capable of working as a mole or as a shield as needed.

When was the TBM invented?

The first successful TBM was built in 1863, and improvements were made to it in 1875 by Frederick Beaumont. It was later updated by Thomas Thomas in 1880. In 1875, an English TBM was authorized to carry out tests to build a tunnel under the English Channel. 

What benchmarks are there in terms of tunnel boring machines in Spain?

There are many large companies worldwide that specialize in building tunnels for transport infrastructure. In Spain, one of the most important ones is Ferrovial.

Among particularly notable projects carried out by Ferrovial over the last decades are the tunnels for the Lisbon Metro, Heathrow Airport, and Madrid’s M-30. Ferrovial was also part of a consortium of companies in charge of developing the largest section of the Crossrail, a new means of underground transport that will cross the city of London from East to West.

The Herrecknecht EPB S-120 TBM (9.36 meters in diameter) was the first used by Ferrovial in Spain in 1997. By then, Ferrovial had already used a Kawasaki shield (9.71 meters in diameter) in building the Lisbon Metro. In 2005, Dulcinea (15.20 meters in diameter) arrived, the largest tunnel boring machine it has used to date. Dulcinea was used to build the Madrid M-30 ring road.

Fun facts about tunnel boring machines

  • Some models of tunnel boring machines can work 24 hours a day, stopping only for maintenance.
  • On average, a TBM can build 40 meters of tunnel during a 24-hour work shift.
  • The first successful TBM was invented in 1863 and improved in 1875 by Frederick Beaumont, then updated in 1880 by Thomas Thomas. In 1875, an English TBM was approved for carrying out tests to build a tunnel under the English Channel.
  • The largest TBM in the world is called Bertha. It was designed by Dragados and manufactured by Japan’s Hitachi Zosen in Sakai, Osaka.

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