Effect of cyclic loading on clay behaviour : Andersen, K H; Brown, S F; Foss, I Paper to Design and Construction of Offshore Structures Conference, London, 27–28 Oct 1976

Abstract

Offshore gravity platforms exert enormous forces on the foundation soil, both static forces from the submerged weight of the platform and cyclic forces from wave action on the platform. This paper concentrates on one important foundation design problem: the effect of cyclic loading on clay behaviour. It is based on the results from a comprehensive joint research project involving laboratory testing of clay samples under cyclic loading and summarizes some of the main conclusions of this work. Foundation behaviour for a gravity platform subjected to cyclic wave loading may be separated into an undrained short-term condition and a long-term condition in which drainage occurs. Using the laboratory test data, explanations are given of how cyclic displacements may increase and stability decrease during the undrained short-term condition. It is also shown that for a foundation on normally consolidated clay, the long-term effect of cyclic loading may be beneficial with respect to stability and cyclic displacement. However, if overconsolidated clay is involved, the long-term effect of cyclic loading may be unfavourable.