The collapse of NATM tunnels at Heathrow Airport - the full story
Professor R.J. Mair
CUED
On the night of 20th October 1994 three large tunnels under construction collapsed beneath Heathrow Airport's Central Terminal Area. The event has been described as one of the worst civil engineering disasters in the UK in the last quarter of a century. By good fortune no one was injured, but major disruption to the airport ensued. The consequent costs of the collapse has been estimated to be around £80 million.
Publication of the technical reasons for the collapse has been delayed for many years,
because of court proceedings arising from prosecutions by the Health and Safety Executive. Now that the court proceedings have been completed, the full technical background is in the public domain and this will be presented and discussed in the Colloquium.
The tunnels were being constructed using sprayed concrete as a temporary lining - a technique often referred to as the New Austrian Tunnelling Method (NATM). The thickness of the temporary linings supporting the 9m diameter tunnels in London Clay at a depth of 26m was 250mm.The measurements of the tunnel performance prior to their collapse will be presented and discussed, together with subsequent analyses of the soil-structure interaction. The principal causes of the disaster, and the lessons learned, will be presented.
