supports a translucent membrane of Teflon-coated fiberglass at a height of 165 feet (50 meters) at the center.

See also

Bedouin tents

Further reading

Nervi, Pier Luigi. 1957. The Works of Pier Luigi Nervi. New York: Praeger.

Power, Mark. 2000. Superstructure. London: Harper-Collins Illustrated.

Temko, Allan. 1962. Eero Saarinen. New York: Braziller.

Thames Tunnel

London, England

The Thames Tunnel was designed by the French-born engineer Marc Isambard Brunel and supervised by his son Isambard Kingdom Brunel between 1825 and 1843. The approximately 1,200-foot-long (365-meter) structure runs under the River Thames between Wapping on the north bank and Rotherhithe on the south in east London. Originally used for foot traffic, it now forms part of the London Underground system. The first tunnel ever built through the soft ground under a river, and the forerunner of modern tunneling techniques (including that used for the Channel Tunnel), it is widely recognized as a landmark feat of civil engineering.

In 1798 one Ralph Todd had tried to build a tunnel under the Thames, further downstream between Gravesend and Tilbury, but the venture failed for financial and other reasons. In 1807, Robert Vazie and Richard Trevithick also attempted to construct a timbered tunnel. In January 1808 the river broke through. The hole was plugged with clay, the tunnel cleared, and work restarted, but a similar accident occurred a month later, when excavation was almost complete. Fearing that more clay dumping would endanger shipping, the authorities called a halt to the project. By about 1815 most of London’s docks were near Rotherhithe, while industry was springing up around Wapping. The nearest fixed crossing was London Bridge, about 2 miles (3.2 kilometers) upstream, and by about 1815 nearly 4,000 people a day were ferried in small boats; goods had to be taken on a costly, time-wasting detour over the bridge.

In 1818 Marc Brunel patented his tunneling shield, enabling tunnels to be excavated by a technique commonly employed in coal mines, that is, by sinking vertical shafts and digging from within the shield. The 88-ton (80-tonne) cast-iron structure, built by Henry Maudley, consisted of twelve 3-foot-wide (0.9-meter) sections, each with, three compartments in which a man could work. It had a closed face, and at the front, angled jacks held horizontal timber boards in place. The tunneler removed the boards one by one and dug out 4.5 inches (11 centimeters) of soil, replacing the jacks against the board in a forward position. When the entire face had been excavated, the shield assembly was edged forward by the use of screw jacks, and brickwork lining was built behind it. Most contemporary tunnels were built using the “cut and cover” method, that is, by digging a deep trench and roofing it; clearly such a technique was impossible underwater.

Marc Brunel secured financial backing to form the Thames Tunnel Company, and work started in March 1825. Until 1828 his son Isambard Kingdom Brunel, was engineer in charge of construction. The project, undertaken in perilous and testing conditions, did not proceed without problems: there were several roof falls and at least five floodings (in the second, the younger Brunel almost drowned), ten workers lost their lives, and others suffered injury and disease. The work was suspended between 1828 and 1835 because of failing finances, and Marc Brunel was almost bankrupted. The Thames Tunnel was completed in April 1840, but it was not until March 1843 that Queen Victoria officially opened it to the public. Estimated to take three years to build, it had taken, eighteen.

The brick structure had a rectangular outer profile measuring 22.25 by 37.5 feet (6.8 by 11.5 meters), pierced by a pair of side-by-side horseshoe inner tunnels lined with terra-cotta tiles. The tubes were horizontally linked by 64 brick-lined passages with classical arches at about 18-foot (5.5-meter) centers that were cut through the partition wall between them. It was little more than 20 feet (6 meters) below the riverbed in places, passing through mostly alluvial deposits. Seepage water ran to sumps in the tunnel floor and was pumped to the surface. The red