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 sometimes observed in small-scale experimental works and in numerical
simulations when soil is subjected to simple harmonic input
motions. This high frequency motion has been often attributed to the
drawbacks of the 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 of soil
to harmonic excitation. To this aim, simplified numerical studies representative
of the most basic soil mechanical properties are carried out.
The results reveal potential importance of soil-released unloading elastic
waves and their reflections inside a soil column when understanding
free field response in numerical simulations representative of small scale
experimental setups. Chosen numerical cases are compared with
available examples of experimental works from the literature. In addition,
two further cases are analyzed, including a case showing the potential
importance of soil-released elastic waves in the response of soil
to real earthquakes, and a case showing the response of structural elements.