Memory surface hardening model for granular soils under repeated loading conditions

The prediction of the stress-strain response of granular soils under large numbers of repeated loading cycles requires subtle changes to existing models, although the basic framework of kinematic hardening/bounding surface elasto-plasticity can be retained. Extending an existing model, an extra memory surface is introduced to track the stress history of the soil. The memory surface can evolve in size and position according to three rules which can be linked with physical principles of particle fabric and interaction. The memory surface changes in size and position through the experienced plastic volumetric strains but it always encloses the current stress state and the yield surface; these simple rules permit progressive stiffening of the soil in cyclic loading, the accurate prediction of plastic strain rate accumulation during cyclic loading, and the description of slightly stiffer stress-strain response upon subsequent monotonic reloading. The implementation of the additional modelling features requires the definition of only two new constitutive soil parameters. A parametric analysis is provided to show model predictions for drained and undrained cyclic loading conditions. The model is validated against available tests on Hostun Sand performed under drained triaxial cyclic loading conditions with various confining pressures, densities, average stress ratios and cyclic amplitudes.