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| The plaque at Rotherhithe station. |
London is a city layered with history, and some of the most fascinating stories lie beneath its surface. One such story belongs to the Thames Tunnel, an engineering marvel that was the first tunnel ever successfully built beneath a navigable river and a project so ambitious it took nearly two decades to complete.
Today, you might speed through it on the London Overground, barely giving a second thought to the brick arches passing by your window. But, in the 19th century, this passageway connecting Rotherhithe and Wapping was the scene of drama, innovation, and, for a short time, one of the city's most popular tourist attractions.
By the early 1800s, London's docks were booming, but the River Thames created a huge bottleneck. Building a new bridge downstream of London Bridge would have blocked the passage of tall-masted sailing ships. The only solution was to go under the river.
Several attempts to tunnel beneath the Thames had failed disastrously. The soft, treacherous ground beneath the riverbed made traditional mining techniques impossible. Enter the brilliant French-born engineer, Marc Isambard Brunel.
Brunel’s genius lay in his invention of the tunnelling shield. The idea, allegedly inspired by watching a shipworm bore through wood, was a revolutionary concept in civil engineering.
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| Keilyn at the bottom of the tunnel shaft. Notice the soot mark, from steam trains, still on the wall. |
Patented in 1818, the shield was essentially a massive, rectangular, cast-iron frame divided into 36 compartments. Miners would work inside these individual cells, digging away a small section of earth in front of them while the surrounding frame held the unstable ground in place. Once a small segment was dug, the shield would be moved forward, and bricklayers would immediately line the new section of the tunnel behind it. This method was the key to conquering the soft, wet subsoil.
Work began in 1825, but the project was far from smooth sailing. It was a harrowing 18-year ordeal, plagued by financial crises, poor air quality, and most terrifyingly, repeated floods as the river burst through the thin crust of ground above.
