After successfully delivering the massive retaining walls for Stratford International station on the Channel Tunnel Rail Line in East London, Cementation Foundations Skanska is now taking its specialist knowledge to the Netherlands to embark on a similar scheme.
This time, the company is applying its specialist skills on a £26 million (€38 million) joint venture scheme awarded by the City of Amsterdam to create the foundations for three new underground stations at Rokin, Vijzelgracht and Ceintuurbaan.
The 17-month project marks the start of construction work for the long-awaited new North-South metro line, a €1 billion project, due to open in 2011.
Working in a 50-50 joint venture with locally based Franki Geotechnics, Cementation Foundations Skanska will be constructing diaphragm wall foundations at three locations across the city centre. In total, the Amsterdam project is on a scale similar to that of the mammoth Stratford Box, the largest foundations contract ever awarded in the UK, which Skanska’s team completed last autumn.
This latest contract involves installing some 70,000 square metres of retaining wall totalling 1.7 kilometres in length, 1.2 metres thick and as deep as 45 metres.
All of the work will be within confined, narrow streets – made more complex by the canals that criss-cross the city. Working in variable ground conditions, with a water table only one metre below the existing ground level, Cementation Foundations Skanska and its partners will be using piling and mix-in-place techniques to remove existing wooden quay walls and pre-treat the upper soft Holocene clay, silt and peat layers.
The diaphragm walls will be excavated using hydraulic excavator grabs adapted with specialised rotator attachments for working in tight conditions, to depths of up to 45 metres. In total, some 85,000 cubic metres of concrete and 15,000 tonnes of steel will be used to create the underground boxes containing the new stations.
Rokin and Vijzelgracht both lie along the path of a former canal, which has since been filled in. Substantial obstructions left over from the old quay walls, including piles and grillage, have been removed to allow foundation work to get underway.
The team will work with the City of Amsterdam Adviesbureau Noord/Zuidlijn and main contractor Max Bögl under a Stelpost agreement, an innovative form of partnering incorporating agreed unit rates and target costs, under which the Client assumes responsibility for risk.
Project director Julian Crawley, for Cementation Foundations Skanska, said: “Following our successful completion of the work at Stratford Box, this new project maintains our foremost position working on strategic infrastructure schemes on behalf of major clients.”