Foundations in Gault Clay

Abstract

Aspects of Gault Clay geology are reviewed with particular reference to engineering characteristics and a qualitative engineering geology assessment scheme for Gault Clays in foundations is presented. Geotechnical parameters including index, strength and compressibility properties are summarized. Results from a full-scale foundation load test in weathered Gault Clay are analysed. Site investigation techniques for Gault Clays are discussed and some of the most appropriate methods identified.Although the total area of outcrop of the Gault Formation is rather limited and typically restricted to non-urban areas in southern England, a number of important structures are founded in it and many, more modest, buildings are built on Gault. The Gault is the youngest of the Cretaceous stiff over-consolidated clays in Britain and typifies an argillaceous deposit on the boundaries between a soil and a weak rock in terms of its engineering behaviour. This requires both soil mechanics and engineering geology techniques to be applied to the understanding and prediction of its behaviour in foundations.The paper reviews the geology of the Gault Formation, with particular reference to its engineering geological characteristics and examines geotechnical parameters of relevance to foundations.The results of a full-scale field foundation load test on weathered Gault Clay are presented and compared with aspects of other reported case histories of foundations in Gault. These case histories provide useful pointers to the choice of site investigation techniques and selection of strength and deformation parameters for the construction of foundations on Gault Clay sites.