The lecture will cover mainly the importance of stiffness parameters of crushable type of foundation sands in the perspective of the state of the art of soil testing and its new developments.

Any soil structure interaction model (SSI) can be deployed successfully or can fail depending on the reliability of the estimations of the soil structure interaction stiffness parameters. The stiffness evaluation of the engineered materials' structural elements and their combined role in the structure itself, commonly can be evaluated rather easily. However, the key issue and the much more problematic interaction parameters in any successful SSI analysis are linked to the soil stiffness, at the relevant strain levels, of the specific interacting soil layers under the corresponding structural loading conditions.