Experimental observations relative to repeatability of wave propagation tests

Abstract

International audienceThe results of a prospective experimental study of wave propagation into granular materials using bender – extender elements are presented. The experiments mainly focus on the repeatability of the pulse tests into multiple samples, which has not been so much investigated until now, in order to assess the degree of relevance of a frequency analysis of the signals. The repeatability is first assessed by multiplying the pulse tests into one sample: that method is currently carried out to decrease the level of noise in the electrical signals. More interesting is the repeatability of pulse tests into two samples prepared in the same conditions and presenting the same macroscopic parameters (void ratio in particular). The interaction between the wave and the granular assembly induces two distinct parts in the output signals: (i) the coherent part, usually contained in the first period of the output signals, representative of the continuous effective medium and similar in different samples and (ii) an incoherent part attributed to differences into the fabric and evolution of the fabric of distinct samples. The main conclusion is that time analysis which doesnot consider the content of the output signals is highly repeatable whereas frequency analysis depends on the sample fabric