London’s early Underground projects taught engineers valuable lessons about tunnelling. Mike Chrimes reports as the Tube celebrates its 150th anniversary.
Celebrations are now well underway to commemorate the 150th anniversary of the world’s first urban underground railway - the Metropolitan Line.
It is an anniversary which engineers can celebrate with pride, and the intervening period has seen constant innovation in construction and service provision thanks to succeeding generations of engineers.
The mastermind behind the Met was John Fowler, who engineered the line in his early 40s, but had been planning it since his mid-30s. Its funding and parliamentary sanction owed much to Fowler’s tenacity and ability. As one director told his biographer: “I never met anyone who so often was able to convince me that things which I had all my life regarded as white were really black.”
“Tunnelling through a town is a risky operation, and settlements may occur years after the completion of the works”
Sir Benjamin Baker
The Met was intended to link the main passenger terminals north of the Thames with the City, but an inner circle linking the southern railway termini was always part of Fowler’s grand scheme. Progress was slow, and the “circle” was not completed for nearly 20 years. The costs were enormous - about £5M for the Met and £6M for the (Metropolitan) District Line and £3M for the final section, including £1M for street works. The level of local disruption caused by the current Crossrail project gives a hint of what was involved.
Fowler was engineer for almost all of the work.
Experience was limited at first. Benjamin Baker, Fowler’s chief assistant on the District line, noted: “With the utmost precautions, tunnelling through a town is a risky operation, and settlements may occur years after the completion of the works.
“Water mains may be broken in the streets and in the houses, stone staircases fall down, and other unpleasant symptoms of small earthquakes alarm the unsuspecting occupants.”
One way in which construction changed was to build retaining walls for the cuttings and covered way in trenches before excavating the “dumpling” between the walls.
“I never met anyone who so often was able to convince me that things which I had all my life
regarded as white
were really black”
By 1900 Baker could state: “It is now known what precautions are necessary to ensure the safety of valuable buildings near to the excavations; how to timber the cuttings and keep them clear of water without drawing the sand from under the foundations of adjoining houses; how to underpin walls…how to drive tunnels, divert sewers over or under the railway, keep up the numerous gas and water mains, and maintain the road traffic when the railway is being carried underneath; and how to construct the covered way, so that buildings of any height and weight may be erected over the railway without risk of subsequent injury from settlement or vibration.”
Fowler and Baker, with all their experience, were involved with the early tubes - the City and South London Railway, and the Central Line. But a key contributor to both was James Greathead, a South African engineer who developed the tunnelling shield, invented by Peter William Barlow in the 1860s, into a successful form utilised largely unchanged down to the Second World War. With grouting pan and compressed air working it proved ideal for London’s geology. Greathead died in 1896 and Baker brought in Basil Mott as his partner on the Central line.
The early 20th century saw a frenzy of subterranean activity. Over 40km of Tube were opened from 1903-1907, notably the Piccadilly and Bakerloo lines and the Charing Cross branch of the Northern Line. Known as the Yerkes tubes because of the notorious financier behind them, the engineer responsible for their delivery, James Russell Chapman, was an American who had worked with Yerkes in Chicago on the electrification of its tramways and urban railways.
The engineer largely responsible for the tunnelling was Dalrymple-Hay, who had developed the use of clay pocketing and the hooded shield before 1900. It was he who installed the first escalator at Earls Court station in 1911.
The arrival of these new lines demanded a response from the earlier companies and the enlargement and extension of the City Branch of the Northern Line in the early 1920s. The tunnels had been built of three different diameters and to bring them up to the standard diameter involved hand excavation behind cast iron segments, line closures and complex temporary support. This kind of complexity was the rule at Piccadilly Station where Sir Harold Harding cut his teeth in the late 1920s.
“I never met anyone who so often was able to convince me that things which I had all my life regarded as white were really black”
As Barker and Robbins noted in their History of London Transport, nearly 40 years ago, in discussing the gestation and delivery of the Victoria line between 1948 and 1969: “We have seen how up to the First War the underground railways had been promoted and hopefully financed as profit-making commercial activities…we shall now see how the area of debate was progressively widened until a proposal for an underground railway became the subject of cost/benefit analysis involving total concepts of urban organisation and planning, and soincurred the risk of getting no decision at all.”That final sentiment must have been shared by many engineers involved in major British infrastructure schemes since then. Of course the rapid development of the early tubes was financed with difficulty, with the keen competition of the tram and motor bus deterring investors, but they were a great engineering success.