Strain Rate Effect on the Young's Modulus of Augusta Clay

An experimental study was carried out using a triaxial cell in order to determine the undrained stress-strain behaviour of Augusta clay, with special attention being paid to the dependence of Young modulus on strain rate. A particular attention was paid to the stiffness assessment at small strains, for which the deformation of specimen in triaxial compression was measured locally over the central part with an accuracy of the strain measurement of about 0.001 %. The results obtained showed in the small strain range a little influence of strain rate on Young modulus. While the Young's modulus for medium and large strains is strongly influenced by the strain rate. The results obtained from triaxial tests were compared to those obtained from monotonic loading torsional shear tests (MLTST) performed in undrained conditions. Rate effects were evaluated by means of an empirical parameter. The rate dependence of the pore pressure increase in undrained, monotonic, triaxial, compression tests and MLTST was carefully examined.