Crossrail Sprayed Concrete Lining Depressurisation at Stepney Green Caverns

Crossrail is a new railway currently under construction in London and when completed will significantly reduce journey times across the capital. It includes approximately 10 km of Sprayed Concrete Lining (SCL) tunnels at station, ventilation shaft and junction locations. One of the largest of these tunnels is being constructed at Stepney Green, East London, to facilitate construction of a sub-surface junction. This will allow Crossrail trains from Maidenhead and the west to travel to Shenfield and Woolwich in the east. The excavation and installation of primary sprayed concrete lining at Stepney Green was completed in August 2013.

The east- and west-bound cavern crowns lie 17 m and 21 m respectively below ground level in a constrained urban site and are situated within the London Clay and underlying Lambeth Group formations. The Lambeth Group is a variable series of clays, silts and sands and the higher permeability sands contain high pore pressures which are hazardous to SCL construction (CIRIA, 2004). Depressurisation of these high pore pressures was crucial to the safe construction of the caverns and compliance with the zero harm Crossrail ethos.