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evolutionsummer2013

Figure 1: Cover way on the Circle line showing the cast iron roof beams with recent Carbon Fibre Plate strengthening cuttings. Different maintenance regimes eliminate the final 30 structures with the The running tunnels for the trains were and approaches have been adopted longitudinal timber track support over the circular and accommodated relatively small over the years, however a proactive next 30 years. sized trains, which is the legacy to this preventative maintenance regime is now day determining why there are two sizes being promoted, which is having benefits in The introduction of the tube, of trains on the LU network. The small reducing the significant maintenance repairs 1890 to 1910 tunnels limit the capacity of new trains, and required across the network. The development of the circular so the capacity of each line. A further key tunnel shield by Barlow for use on the innovation introduced with this new tube Expansion of the subsurface network was construction of the Tower subway (1870), railway was electric traction. carried out in various stages, which also below the river Thames near the Tower of introduced other issues that have had London, enabled the construction of the To enable access to these deep level lines maintenance consequences. Many of the first tube railways in London. The first line that were, wherever practical, constructed Circle Line stations had high level roofs constructed entirely at deep level below in the underlying ‘stable’ London clay it was over the platforms and railways, and there the ground and opened in 1890 was the necessary to construct deep shafts with are many examples that remain to this day City & South London line from near King hydraulically powered lifts and helical stairs. including Notting Hill Gate and Paddington William Street in the City of London to Despite the development and introduction stations. Although these roof structures Stockwell. This innovative construction of escalators there are still many stations have lasted well they are now in need of technique coupled with bolted segmental that are to this day only served by lifts and major refurbishment and by their very cast iron linings remains the underlying helical stairs. It is ironic that following years nature are difficult to access and maintain basis of the tube network in London. of trying to introduce alternative vertical or repair. Over the last five years roofs have This approach proved to be cheaper and transportation to enable quicker exit to been refurbished at Earl’s Court, Notting less disruptive than the cut-and-cover street since the 1990s LU has been striving Hill Gate and Aldgate however this has had subsurface lines with routes following the to improve ‘step free’ access and look to to include additional measures to ensure line of streets to minimise claims from introduce new lifts where practical. LU provision of access for maintenance and properties above. For this early tube line has recently placed contracts to introduce compliance with 21st century health and the large station platform tunnels were the first inclined lift on the network at safety legislation. constructed in brick. Greenford. At locations where the subsurface railway emerges into the open the railway runs on elevated viaducts and bridges that cross the numerous streets and pathways. However, economies in construction left a legacy in a form of bridge construction that retains the use of timber bearers to support the running rails on steel bridge decks. These structures (also common on Network Rail) have been a constant ongoing expensive maintenance liability for both track and structures. Over the last 50 years LU has had a policy of removing these types of under bridge structures when funding permits. LU now has a programme to Figures 2 & 3: Early construction of the Central London Railway circ.1897 (now part of the Central line) 3


evolutionsummer2013
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