Abstract
The experimental results reported in this paper were obtained performing monotonic, cyclic and dynamic torsional shear tests on a stiff Italian clay in the pre-failure stress-strain range. The experimental clearly demonstrate that the small strain values of shear stiffness and damping ratio are significantly affected by strain rate : while the initial shear modulus G0 continuously increases with strain rate, the equivalent viscous damping ratio D0 initially decreases with strain rate, then it reaches a minimum constant value and thereafter it increases significantly. The experimental data also demonstrate that, if the strain rate is properly accounted for, a linear behaviour for the soil is no longer distinguishable, even at strain levels as low as 10-4%. As a whole, these effects could have meaningful practical implications, thus requiring to be accounted for in modelling soil behaviour in those problems where the rate of loading varies significantly.
