If you’re walking between the DLR and the Waterloo and City Line platforms at Bank Underground Station, at one point you’ll come across something that was left behind in 1898 and found 100 years later.
What could it be? A tool, some graffiti? Well, it’s this:
That red ring going around the tunnel is part of a ‘Greathead’ Tunnelling Shield, which was used in the construction of the Waterloo and City Line in the 1890s. It protected the construction workers by supporting the tunnel they were excavating. They would work in the shield, digging away the soil by hand. When they dug far enough, the shield was moved forward and the tunnel lined with metal plates.
The name Greathead comes from James Henry Greathead, who devised the shield building upon previous designs by Sir Marc Brunel and Peter W. Barlow. Brunel’s design, the first of its kind, was rectangular in shape. Barlow changed this to be round. The round shape was better at keeping the surrounding soil at bay, as the pressure was distributed all around the shield, rather than just the top and bottom as would be the case with Brunel’s shield.
When the Waterloo and City Line was completed in 1898, the tunnelling shield was left behind. It was found in 1987 during excavation work for the Bank extension of the Docklands Light Railway and later integrated into the foot tunnel when the DLR opened.
James Henry Greathead is commemorated in statue form outside Bank station. Just along the south side of the Royal Exchange in Cornhill is a statue of Greathead, be-hatted and looking down at a set of plans. Apparently the plinth the statue is on is hollow and acts as a ventilation shaft for the Underground. Also on the plinth, you can see an engraving of a tunnelling shield in use.
The same general idea of a tunnelling shield is still in use today. The tunnel boring machines making their way across London, carving out the tunnels for Crossrail operate on the same principal.