Measure

Geotechnical Observations installed SAA displacement monitoring equipment into the concrete retaining walls at Crossrail’s Tottenham Court Road Western Ticket Hall and monitored the deflections of the walls as the soil was removed from inside the resulting box.

Inform

The measured deflections were significantly smaller than those that had been predicted using the specified design parameters.

Decide

A decision was taken to remove the lowest supporting prop, which facilitated more room for excavating (11m as opposed to 3m) at the bottom of the excavation and reduced the programme by this saved 28 days on the programme. This brought about a saving of £715,000 after taking account of the cost of the monitoring (approximately £200,000).