Secondary Compression in the Shear of Clays

The amount of secondary deformation measured when shear-testing a laboratory sample of kaolin depends largely on its effective stress state, which may vary from a hydrostatic state of stress to stresses causing incipient failure in the specimen. Such deformation does not, however, appear to influence the basic stress-strain curve for the material, as this is essentially independent of load duration. Thus, in a limited sense, the stress-strain relationship may be considered as time-independent, Secondary deformation data from drained shear tests are decomposed into volumetric and shear components. In this way, creep in shear is interpreted as a stress-dilatancy phenomenon, and as such may be contrasted with similar relationships which describe the process of primary deformation in shear tests.