Dependency of the mechanical behaviour of granular soils on loading frequency: experimental results and constitutive modelling.

The paper shows some cyclic torsional shear test results obtained on dense Toyoura sand specimens. The dependency of the mechanical response of this material on both loading amplitude and frequency are discussed, to obtain a framework to analyze the mechanical behaviour of granular soils. The pseudo-elastic shear stiffness and the damping ratio are the variables taken into consideration; their evolution with the number of cycles performed at the different loading amplitudes is analysed to describe the mechanical irreversibility of the material response. The experimental data are then reproduced by means of a multiple mechanism elasto-viscoplastic constitutive model characterised by one viscoplastic mechanism and by an internal kinematic plastic mechanism capable of capturing the material mechanical response even when small cyclic tests are performed.