The proposed multi-storey building was to be located on a site which slopes steeply towards the River Avon. The site was close to one, at a lower level, which had shown evidence of local instability, and which formed the subject of an investigation by Skempton & Henkel (1959). The previous work showed that it was possible for material lying above a clay layer to slide obliquely outwards towards the Avon Gorge. A new site investigation was therefore undertaken to discover the nature, extent and frequency of other clay layers which might be present, to assess the condition of the limestones, and to discover the site groundwater conditions. Stability analyses were made using the sliding model postulated by Skempton & Henkel. Since porewater pressure is zero or nearly so the results of these analyses can be simply presented.
It was concluded that high level foundations were not suitable for this building on this site, and that the foundation loads should be transmitted by means of piers of variable lengths up to a maximum of 140 ft, through the interbedded clay layers to sound limestone. The same basic analysis was used to investigate the stability of the excavated faces (about 30 ft deep) at the rear of the site.