Thames Tunnel

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 in 1824, the project beginning in February 1825.

The first step was the construction of a large shaft on the south bank at Rotherhithe, back from the river bank. It was dug by assembling an iron ring in diameter above ground. A brick wall high and 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 . 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:

Each of the twelve frames of the shield weighed over . 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 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 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. Provided by Wikipedia