History
The first successful tunnelling shield was developed by Sir Marc Isambard Brunel, and patented by him and 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 would not be opened until 1843). Brunel is said to have been inspired in his design by the shell of the shipworm Teredo navalis, a mollusc whose efficiency at boring through submerged timber he observed while working in a shipyard. The shield was built by Maudslay, Sons & Field, of Lambeth, London, who also built the steam pumps for de-watering the tunnel.
Brunel's original design was substantially improved by Peter W. Barlow in the course of the construction of the Tower Subway under the River Thames in central London in 1870. Probably the most crucial innovation of Barlow's design was that it had a circular cross-section (unlike Brunel's, which was of rectangular cross-section), which at once made it simpler in construction and better able to support the weight of the surrounding soil.
The Barlow design was enlarged and further improved by James Henry Greathead for the construction of the City & South London Railway (today part of London Underground's Northern Line) in 1884. To this day, most tunnelling shields are still loosely based on the Greathead shield.
Read more about this topic: Tunnelling Shield
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