The first tunnel under a navigable river took the Brunels eighteen years
Experts had declared a tunnel under the Thames impossible after Cornish miners flooded out twice. Marc Brunel disagreed, patented a shield that let 36 men dig in protected cells, and with his son Isambard spent from 1825 to 1843 boring 400 metres from Rotherhithe to Wapping.
London's growing docks on both banks badly needed a crossing in the early 1800s. Ralph Dodd failed to tunnel between Gravesend and Tilbury in 1799, and between 1805 and 1809 a team including Richard Trevithick drove a narrow pilot passage, meant as a drain for a larger tunnel, some 300 metres of a planned 370 before the river broke in twice. Used to hard rock, the miners never adapted to soft clay and quicksand, and engineers concluded such a tunnel could not be built.
Marc Brunel, an Anglo-French engineer, had already pitched a tunnel under the Neva to Russia's Alexander I in 1814, only to see a bridge chosen. He patented his tunnelling shield in January 1818 and drew up the Rotherhithe to Wapping plan in 1823. Private investors, the Duke of Wellington among them, backed a company created by an 1824 Act, and work began in February 1825.
First came a shaft on the south bank. Workers built a 15-metre iron ring topped by a brick tower carrying a steam pump engine, around 1,000 tons in all, then dug out soil beneath it so the whole thing sank like a pastry cutter. It jammed partway and needed 50,000 bricks piled on as extra weight; the later Wapping shaft was made slightly wider at the base to avoid the same problem. The shield itself, built at Henry Maudslay's works in Lambeth, had twelve iron frames of over 7 tons each, split into three levels. Each miner removed one board at a time, dug a short way, replaced it, and screws pushed the frame forward while bricklayers lined the space behind.
Conditions were grim. Sewage seeped from the river, sickening many workers and Marc Brunel himself, and methane from it could ignite in the miners' lamps. When resident engineer John Armstrong fell ill in April 1826, 20-year-old Isambard Kingdom Brunel took charge. The finished tunnel, 11 metres wide and 23 metres below high tide, was meant for carriages but drew mainly walkers and sightseers, and in 1869 it became a railway tunnel, now carrying London Overground trains.
Source: Thames Tunnel
