THE YIELDING OF BOTHKENNAR CLAY

The Paper describes the yielding characteristics of Bothkennar clay, as shown by stress-path triaxial tests. Computer-controlled equipment and high resolution instrumentation were used to obtain a detailed picture of the behaviour of the undisturbed clay at very small and large strains. The results confirm an earlier hypothesis that the soil's behaviour at small strains can be described by two kinematic sub-yield surfaces existing within an initial bounding surface. Consolidation beyond the initial bounding surface is shown to bring about a progressive breakdown of the clay's initial sedimentary structure. Once this has occurred the soil's stress-strain and undrained strength characteristics become highly dependent on the stress conditions under which consolidation takes place.