The Thames Tunnel is a tunnel beneath the River Thames in London, connecting Rotherhithe and Wapping. It measures 35 ft (11 m) wide by 20 ft (6.1 m) high and is 1,300 ft (400 m) long, running at a depth of 75 ft (23 m) below the river surface measured at high tide. It is the first tunnel known to have been constructed successfully underneath a navigable river. It was built between 1825 and 1843 by Marc Brunel, and his son, Isambard, using the tunnelling shield newly invented by the elder Brunel and Thomas Cochrane. The tunnel was originally designed for horse-drawn carriages, but was mainly used by pedestrians and became a tourist attraction. In 1869 it was converted into a railway tunnel for use by the East London line which, since 2010, is part of the London Overground railway network under the ownership of Transport for London.
History and development
Construction At the start of the 19th century, there was a pressing need for a new land connection between the north and south banks of the Thames to link the expanding docks on each side of the river. The engineer Ralph Dodd tried, but failed, to build a tunnel between Gravesend and Tilbury in 1799. Between 1805 and 1809, a group of Cornish miners, including Richard Trevithick, tried to dig a tunnel further upriver between Rotherhithe and Wapping/Limehouse, but failed because of the difficult conditions of the ground. The Cornish miners were used to hard rock and did not modify their methods for soft clay and quicksand. This Thames Archway project was abandoned after the initial pilot tunnel (a 'driftway') flooded twice when 1,000 ft (300 m) of a total of 1,200 ft (370 m) had been dug. It only measured 2–3 ft (0.6–0.9 m) by 5 ft (1.5 m), and was intended as a drain for a larger tunnel for passenger use. The failure of the Thames Archway project led engineers to conclude that "an underground tunnel is impracticable". The Anglo-French engineer Marc Brunel refused to accept this conclusion. In 1814 he proposed to Emperor Alexander I of Russia a plan to build a tunnel under the river Neva in St Petersburg. This scheme was turned down (a bridge was built instead) and Brunel continued to develop ideas for new methods of tunnelling.
Brunel patented the tunnelling shield, a revolutionary advance in tunnelling technology, in January 1818. In 1823 Brunel produced a plan for a tunnel between Rotherhithe and Wapping, which would be dug using his new shield. Financing was soon found from private investors, including the Duke of Wellington, and a Thames Tunnel Company was formed by the Thames Tunnel Act 1824 (5 Geo. 4. c. clvi), the project beginning in February 1825. The first step was the construction of a large shaft on the south bank at Rotherhithe, 150 ft (46 m) back from the river bank. It was dug by assembling an iron ring 50 ft (15 m) in diameter above ground. A brick wall 40 ft (12 m) high and 3 ft (0.9 m) thick was built on top of this, with a powerful steam engine surmounting it to drive the excavation's pumps. The whole apparatus was estimated to weigh 1,000 long tons (1,016 t; 1,120 short tons). The soil below the ring's sharp lower edge was removed manually by Brunel's workers. The whole shaft thus gradually sank under its own weight, slicing through the soft ground like a pastry cutter. The shaft became stuck at one point during its sinking, as the pressure of the earth around it held it firmly in position. Extra weight was required to make it continue its descent. 50,000 bricks were added as temporary weights. It was realised that the problem was caused because the shaft's sides were parallel. Years later when the Wapping shaft was built, it was slightly wider at the bottom than the top. This non-cylindrical tapering design ensured it did not get stuck. By November 1825 the Rotherhithe shaft was in place and tunnelling work could begin.
The tunnelling shield, built at Henry Maudslay's Lambeth works and assembled in the Rotherhithe shaft, was the key to Brunel's construction of the Thames Tunnel. The Illustrated London News described how it worked:
The mode in which this great excavation was accomplished was by means of a powerful apparatus termed a shield, consisting of twelve great frames, lying close to each other like as many volumes on the shelf of a book-case, and divided into three stages or stories, thus presenting 36 chambers of cells, each for one workman, and open to the rear, but closed in the front with moveable boards. The front was placed against the earth to be removed, and the workman, having removed one board, excavated the earth behind it to the depth directed, and placed the board against the new surface exposed. The board was then in advance of the cell, and was kept in its place by props; and having thus proceeded with all the boards, each cell was advanced by two screws, one at its head and the other at its foot, which, resting against the finished brickwork and turned, impelled it forward into the vacant space. The other set of divisions then advanced. As the miners worked at one end of the cell, so the bricklayers formed at the other the top, sides and bottom. Each of the twelve frames of the shield weighed over 7 long tons (7.1 t; 7.8 short tons). The key innovation of the tunnelling shield was its support for the unlined ground in front and around it to reduce the risk of collapses. However, many workers, including Brunel himself, soon fell ill from the poor conditions caused by filthy sewage-laden water seeping through from the river above. This sewage gave off methane gas which was ignited by the miners' oil lamps. When the resident engineer, John Armstrong, fell ill in April 1826, Marc's son Isambard Kingdom Brunel took over at the age of 20. Work was slow, progressing at only 1–8 ft (0.3–2.4 m) a week. To earn income from the tunnel, the company directors allowed sightseers to view the shield in operation. They charged a shilling for the adventure and an estimated 600–800 visitors took advantage of the opportunity every day. The excavation was hazardous. The tunnel flooded suddenly on 18 May 1827 after 549 ft (167 m) had been dug. Isambard Kingdom Brunel lowered a diving bell from a boat to repair the hole at the bottom of the river, throwing bags filled with clay into the breach in the tunnel's roof. Following the repairs and the drainage of the tunnel, he held a banquet inside it.
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