The Tunneling Machines That Are Expanding the London Underground

Did you know that back in the 1860s, the cut-and-cover method was employed to dig London’s underground tunnel? This construction ran for a mere 3.75 miles (6 km) and saw workers dig trenches by hand to build it.

Luckily, today we have a much simpler technology: tunnel boring machines or TBMs. TBMs feature a cutter-head at the front and a series of trailers behind that carry the mechanical and electrical equipment.

TBMs also feature an array of dozens of disc cutters that continually rotate and dig away at the earth ahead. The loosened material is then removed from the cutter head using a screw conveyor.

Finally, TBMs possess a tunnel shield, a cylindrical assembly that’s pushed forward to secure the excavated area until the concrete tunnel lining is built. Once each section is cut, a concrete ring is placed above it with its segments brought into the tunnel on flatbed rail cars and lifted into place using a vacuum hydraulic system, then bolted into position.

This is how London’s underground lines are now built, much safer and easier.

How do TBMs guarantee the workers’ safety? How are they more agile and more convenient? What else are TBMs used for? We answer all these questions and more in our video.