How Crossrail stopped the earth moving

Compensation grouting has been one of the great successes of the UK’s £14.8bn Crossrail project. Since 2009, 42km of new rail tunnels have been scooped out from under London with virtually no damage to existing buildings and infrastructure.

Compensation grouting at Crossrail’s Bond Street site.
Compensation grouting at Crossrail’s Bond Street site.

One of the first detailed reports of compensation grouting on the project appears in the latest issue of the ICE Geotechnical Engineering journal. Ruaidhri Farrell of Laing O'Rourke describes the work undertaken at the Bond Street station, where a large shallow tunnel was constructed using sprayed concrete lining under grade II listed buildings.

'The risk of damage to overlying listed buildings from tunnel-induced settlement was mitigated through compensation grouting,' he says. 'The grouting array consisted of 92 'tubes à manchette' (TAM) and was installed using a wet-flush drilling method.'

'Hugely successful'

Despite the 3m grout exclusion zones around existing and new tunnels, Farrell says, 'compensation grouting proved to be hugely successful in reducing differential settlements and limiting the amount of damage to overlying buildings.'

However, the installation of the grouting array itself was found to cause settlements of up to 18 mm, though this was subsequently corrected by grouting. 'The extent and spacing of the array should therefore be designed to target regions of large differential settlements, and caution should be exercised when considering installing TAMs in regions were settlements are less than 10 mm,' says Farrell.

For further information, please contact ICE Proceedings editor Simon Fullalove, email, telephone +44 (0)20 7665 2448.