Introductory consideration supporting the idea of the release of unloading elastic waves in the steady state response of hysteretic soil

Abstract

Unintended and unwanted high frequency oscillation motion is commonly observed in small-scale experiments and in numerical simulations when soil is subjected to harmonic input motions. This high frequency motion has been often attributed to the drawbacks of actuating systems in experimental setups and to numerical noise in computational analyses. This work presents introductory consideration supporting the hypothetical idea that the recorded and the computed high frequency oscillation motion can possibly be the consequence of an unrecognized before physical phenomenon of soil elastic waves released upon unloading due to soil inherent hysteretic stress-strain behaviour and affecting the steady state response to harmonic excitation. To this aim, simplified numerical studies representative of the most basic soil mechanical properties are carried out. The results reveal the presence and the potential importance of soil-released unloading elastic waves when understanding soil free field response and structural response in numerical simulations of small-scale experimental setups. Chosen numerical cases are compared with available examples of experimental works on dry sand from the literature. The discussion provides further comments, including the potential importance of the soil-released elastic waves in real earthquakes of large magnitudes.