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A series of approximately 40 controlled-deformation, torsional shear tests in sinusoidal oscillation was performed on a Georgia Kaolin clay at moisture contents ranging from slightly below to considerably above the liquid limit. The tests were done with a rotational viscometer using a cone-and-plate sample holder to provide reasonable homogeneity of strains and stresses. The results are expressed in terms of complex viscoelastic response parameters, and some aspects of the limitations and usefulness of viscoelastic relations to describe soil response are examined by (a) study of the strain dependence of the response parameters and (b) comparison of energy dissipation as calculated by viscoelastic relations with that measured directly from hysteresis loops.
The magnitude of the complex modulus was found to vary exponentially with the moisture content and to vary as the -1.3 power of the strain amplitude. The phase lag between stress and strain had no discernible dependence on the moisture content for moisture contents above the liquid limit, but was found to vary as the 0.4 power of the strain amplitude. Despite the marked nonlinearity of the material, the calculation of energy dissipation according to viscoelastic relations agrees comparatively well with the observed data.
shear behavior, soil dynamics, dynamic loads, viscoelasticity, clay, clay soils, energy dissipation, phase angle, hysteresis, evaluation, tests
Associate Professor of Civil EngineeringPersonal Member, Northwestern UniversityASTM, Evanston, Ill.
Assistant Professor of Civil Engineering, Northwestern University, Evanston, Ill.