The most terrible tunnel

Labourers working at the face of the Thames Tunnel were protected by Marc Brunel’s newly-invented “Shield”; behind them, other gangs hurried to roof the tunnel before the river could burst in. Nineteenth century lithograph.

At the beginning of the 19th century, the port of London was the busiest in the world. Cargoes that had traveled thousands of miles, and survived all the hazards of the sea, piled up on the wharves of Rotherhithe—only for their owners to discover that the slowest, most frustrating portion of their journey often lay ahead of them. Consignments intended for the southern (and most heavily populated) parts of Britain had to be heaved onto creaking ox carts and hauled through the docklands and across London Bridge, which had been built in the 12th century and was as cramped and impractical as its early date implied. By 1820, it had become the center of the world’s largest traffic jam.

It was a situation intolerable to a city with London’s pride, and it was clear that if private enterprise could build another crossing closer to the docks, there would be a tidy profit to be made in tolls. Another bridge was out of the question—it would deny sailing ships access to the deepwater dock known as the Pool of London—and ambitious men turned their thoughts to driving a tunnel beneath the Thames instead.

This was not such an obvious idea as it might appear. Although demand for coal was growing fast as the industrial revolution hit high gear, working methods remained primitive. Tunnels were dug by men wielding picks in sputtering candlelight. No engineers had ever tunneled under a major river, and the Thames was an especially tricky one. To the north, London was built on a solid bed of clay, ideal tunneling material. To the south and east, however, lay deep strata of water-bearing sand and oozing quicksand, all broken up by layers of gravel, silt, petrified trees and the debris of ancient oyster beds. The ground was semi-liquid, and at depth it became highly pressurized, threatening to burst into any construction site. Continue reading