Renaissance becomes virtual reality
28 Oct 2009
From the base of the Battersea Power Station chimneys, the view north-eastwards is a stark contrast between the shabby industrial units of the Thames' south bank and the stone and brick facades of Pimlico on the northern shore. At the south-western end of a strip of land, guarded by high-rise towers at Vauxhall Cross and hemmed in on three sides by river and railway viaducts, the power station has become the focal point of long-overdue efforts to regenerate this neglected area of London. A private developer's visions have been made flat-screen visual by architect and engineer.From the Vauxhall rail and tube interchange, the power station is a long hike or swaying bus ride along the deserted Nine Elms Lane. A brisk walk to the south through the ageing façade of Battersea Park Station is the alternative connection to the rail network.
Transport planners concluded that bus and rail improvements would not provide sufficient extra capacity to serve major development in the area. The preferred option for major new transport infrastructure is the extension of the Northern Line from Kennington to Battersea Power Station. This could be carrying 60,000 passengers daily by 2015 and would provide direct links into London's transport network.
In July 2008, Parsons Brinckerhoff, with help from architects Studiodare and cost consultants Corderoy, was commissioned by REO (Powerstation) Ltd to carry out a study to determine the engineering feasibility of constructing the proposed new tube line. The study was commissioned by the development manager for the Battersea Power Station site, Treasury Holdings Ltd.
Route options developed
The scope of the study included engineering feasibility, conceptual station designs to RIBA Stage B and high-level cost estimates, sufficient to enable the formulation of a business case and selection of a preferred route. REO's objective is to proceed to a Transport and Works Act Order for the development of the tube extension - the current timetable assumes an autumn 2010 application.
Three route options were developed in consultation with the key stakeholders, in particular LUL. All routes start at the south-west corner of the power station site at a proposed new station which would have a crossover immediately to the east. Both would be constructed in open-box excavations from which the tunnels would be driven by tunnel boring machines.
The routes connect into the Charing Cross branch of the Northern Line on either side of the Kennington Loop which is currently used to turn trains at Kennington Station. The horizontal alignments are laid out to avoid potential deep foundations and to pass under likely sites for ventilation and intervention shafts which are required at 1km intervals.
The vertical alignments are constrained by several tunnels immediately to the east of the proposed Battersea Station. Over a distance of 300m, the 4.4m diameter tunnels pass a few metres above the Thames Water Ring Main beneath the power station site, one metre above a power cable tunnel and two metres below a deep sewer. The tunnels also make their way under the Victoria and Northern Lines and intersect the shafts at low points in order to facilitate drainage.
Challenging engineering
The stations at Battersea and Nine Elms are designed with island platforms which would be built within deep open boxes. At Vauxhall, platform tunnels mined at depth would allow the tracks to pass beneath the Victoria Line. A high-level interchange would connect with the existing ticket hall.
The layout of the platforms and crossover at Battersea is constrained by the requirement to provide two banks of three escalators at points equidistant along the island platform and the need to avoid construction of open-box excavation above the Thames Water Ring Main. The subsequent limitation on length of the space available has resulted in curved platforms and a maximum 68km/h over curved turnouts within a diamond crossing. With 75m long overrun tracks and a well-run stepping-back operation, LUL should be able to operate 28 trains per hour.
At the start of the feasibility study it was assumed that, in order to protect the operation of the Northern Line, the Kennington Loop must remain active during construction. Thus, the connections into the loop tunnel provide the most challenging engineering aspect of the scheme. Two turnouts have to be constructed in caverns (step-plate junctions) up to 11m across and 18m below residential properties.
As the project proceeds towards TWAO, a further review will be carried out to consider alternative methods of connecting into the existing Northern Line tunnels. The selected route will be studied again in more detail with further investigation, consultation and appraisal of the various station and shaft sites.
With the necessary funding and, perhaps more importantly, the required political will, an extended tube line can become the catalyst for development in the shadow of the landmark chimneys, only a river bend away from the centre of British government.
Rory McKimm is Geotechnical Delivery Manager Tunnels - Europe & Africa for Parsons Brinckerhoff.