The integral bridge design concept for the third runway at Heathrow, UK

The Heathrow expansion project proposals comprise major works around Heathrow airport to allow the construction of new terminal buildings and the third runway. Owing to the critical nature of uninterrupted operation of both runway and the M25 motorway, the preliminary design had to be developed to minimise maintenance operations. At over 140 m in the total length, the adoption of an integral bridge of this length is in excess of most integral bridges in the UK, particularly where full-height abutments are being utilised. The maximum predicted expansion length also lies outside the limit equilibrium method set out in PD6694-1. As such, it was agreed that a full soil–structure interaction study should be carried out to assess the impacts of the structural behaviour of the bridge and its abutments. This paper looks at the calibration work for that study, the derivation of the earth pressures behind the walls, the behaviour of the abutment and how this compares with the predictions set out in PD 6694-1.