Editing Tunnelling shield (section)

==History==
{{unreferenced section|date=April 2025}}
The first successful rectangular tunnelling shield was developed by [[Marc Isambard Brunel]] and patented by him and [[Thomas Cochrane, 10th Earl of Dundonald|Lord Cochrane]] in January 1818. Brunel and his son [[Isambard Kingdom Brunel]] used it to excavate the [[Thames Tunnel]] beginning in 1825 (though the tunnel was not opened until 1843).<ref name=becket-10>Becket, Derrick (1980). ''Brunel's Britain''. Newton Abbot: [[David & Charles]]. {{ISBN|0-7153-7973-9}}. Chapter 10: "Tunnels".</ref> Brunel is said to have been inspired in his design by the shell of the [[shipworm]], a mollusc whose efficiency at boring through submerged timber he observed while working in a shipyard.<ref name=becket-10/> The shield was built by [[Henry Maudslay|Maudslay, Sons & Field]] of Lambeth, London, who also built the steam pumps for de-watering the tunnel.

In 1840, [[Alfred Ely Beach]], editor of ''Scientific American'' journal, was the first to suggest a circular design would be superior to Brunel's rectangular design. In 1868 Beach built a circular shield - a picture of which was printed in a New York news article about his pneumatic tunnel system idea. The design was based upon Brunel's shield lattice and screw-jacked forwards as the face advanced manually.

In 1864 [[Peter W. Barlow]] applied for a design patent that had a circular cross-section. Theoretically this made the shield easier to build and better able to support surrounding soil; theoretically, because no shield was ever built using this design. The 1864 Barlow patent was further improved and given a provisional patent in 1868 but never ratified as Barlow died a short time afterwards.

Brunel's original design was substantially improved upon by [[James Henry Greathead]] who was granted three patents for different shield designs. Additionally, he invented the concept of sprayed concrete grout to stabilise earthworks with injected concrete, a gritting pan that hydraulically injected reinforcing grout into the cavities between the constructed lining and the circular tunnel wall.

Greathead was the first to ever use a cylindrical tunnelling shield, which he did in the course of the construction of the [[Tower Subway]] under the River [[Thames]] in central [[London]] in 1869. The Greathead shield was {{convert|7|ft|3|in}} in diameter. Similarly, [[Alfred Ely Beach]] opened his tunnel to the public on March 1, 1870.

Greathead also used one in the construction of the [[City and South London Railway]] (today part of [[London Underground]]'s [[Northern line]]) in 1884, with tunnels {{convert|10|ft|2|in}} in diameter. His shield was also used in the driving of the {{convert|12|foot|1+3/4|inch}} diameter running tunnels for the [[Waterloo & City line|Waterloo & City Railway]] which opened in 1898. The station tunnels at the City station (now known as Bank) were the largest diameter tunnelling shields in the world at the time, measuring {{convert|23|feet}}.

An original Greathead shield used in the excavation of the deep London Underground lines remains in place in disused tunnels beneath [[Moorgate station]].<ref>{{cite web |url=https://www.bbc.co.uk/iplayer/episode/b01sjtzw/The_Tube_An_Underground_History/ |title=The Tube: An Underground History, broadcast 16 May 2013 |publisher=bbc.co.uk |year=2013 |access-date=17 May 2013 |archive-date=28 July 2023 |archive-url=https://web.archive.org/web/20230728205407/https://www.bbc.co.uk/programmes/b01sjtzw |url-status=live }}</ref>

Most tunnelling shields are still loosely based on Greathead's design.<ref name = gillham>John C Gillham, ''The Waterloo & City Railway'', The Oakwood Press, Usk, 2001, {{ISBN|0 85361 525 X}}</ref>