Non-Linear Behavior of Sands under Longitudinal Resonance Testing

Abstract

One of the fundamental features needed to evaluate soil response during earthquakes, is the study of controllable external variables that may affect the instability phenomena of granular materials under vibration, such as acceleration, frequency, the interaction of grains and their arrangements. Despite previous researches in this field, an understanding of these phenomena is still incomplete. A more accurate description of one of the phenomena that we will see, is how the resonance curve changies and how the jump occurs with the frequency change. For this purpose, a series of longitudinal resonance excitation laboratory tests were carried out on dry sandy soils with different grain size distributions (spread and tight) and different densities to identify the instability zone.This type of test may be assimilated to a system subjected to a forced excitation with damping. The test results confirm the existence of a non-linearity zone represented by a "jump" just after the resonance for tight-grained sand. Moreover, this study shows that the grains interact with the contact forces. Indeed, a slight local density increase induces more collisions and friction, and therefore more dissipation, creating a pressure drop that attracts the neighboring particles and finally a low damping.