Prediction and observation of ground conditions following Heathrow Express tunnels collapse

The paper describes the methodology and objectives of the site investigation designed to characterise the ground conditions following the significant collapse of the sprayed concrete lined tunnels under construction at the Central Terminal Area, Heathrow in October, 1994. Details of the various exploratory techniques as well as comments on their suitability are given. The identification of the extent of the collapsed and disturbed ground utilising geostatistical techniques and the assessment of appropriate ground parameters using digital data handling software are discussed. Comparisons between these predictions, the geotechnical data obtained and the observations mad during construction from void infilling and ground treatment through piling and excavation are discussed and differences highlighted.