Connaught Tunnel surface rail approaches settlement mitigation

The London Docklands section of the Crossrail railway line which runs between Custom House Station and North Woolwich Portal, passes beneath the Royal Docks through the rehabilitated Connaught Tunnel (ref. Figure 1). The Crossrail Act of 2008 incorporated the tunnel and its approaches into the south-east branch of the new Crossrail line between Whitechapel Station and Abbey Wood which is due to open to the public in 2018. While the new track either side of the approaches to the existing tunnel, is at grade and follows the alignment of the defunct North London Line, a ballasted track was deemed unsustainable given the requirement for frequent interventions and track tamping to maintain its functionality throughout the mandated 120 year design life. Furthermore, given that the rest of this section of Crossrail is on slab track, it would have been an impracticable proposition to mobilise the essential tamping equipment for such a relatively short stretch of track. Therefore, an alternative track support system was proposed here comprising a granular load transfer platform (“LTP”) bedded on a grid of vibro-concrete columns (“VCC”), and it is the design of this track slab foundation that is the subject of this paper.