Greathead

Greathead was a brand of tunnelling shield developed by James Henry Greathead in the late 19th century. The Greathead shield was a significant advancement in tunnelling technology, allowing for the construction of tunnels through soft ground and under waterways with greater safety and efficiency than previous methods.

The key innovation of the Greathead shield was its use of a pressurized face to support the excavation. Compressed air was introduced into the working chamber of the shield, counteracting the pressure of the surrounding soil and water and preventing collapse. This allowed miners to excavate the tunnel face with reduced risk.

The shield itself was a cylindrical structure, typically made of iron or steel, which was advanced through the ground by hydraulic jacks. The excavated material was removed through the shield, and the tunnel lining, usually consisting of cast iron segments, was erected behind the shield.

Greathead shields were used in numerous major tunnelling projects around the world, including the London Underground, the Tower Subway, and the City and South London Railway. The technology pioneered by Greathead significantly contributed to the expansion of urban infrastructure and the development of modern tunnelling techniques. The Greathead shield is considered a precursor to modern tunnel boring machines (TBMs).