Ultrasound and acoustic wave propagation measurements in rocks and granular media made concurrently with In Situ synchrotron x-ray imaging

Abstract

Ultrasound transport through granular media has been of significant interest to physicists, civil engineers, and geophysicists studying soils and rocks for decades. Of particular interest are the features which govern wave speeds, dispersion, and attenuation in these materials. We will discuss experiments in which ultrasound waves were propagated through disordered 3D granular media while samples were imaged with x-ray computed tomography (XRCT) and 3D x-ray diffraction (3DXRD) – together, these measurements provide the particle contact topology and inter-particle forces. We show through data analysis and modeling that both contact topology and contact forces control the fastest measured wave speeds and dispersion in these materials, while contact topology alone explains most of the observed wave attenuation. We will also discuss ongoing studies of acoustic emissions (AE) generated in granular materials and sandstones during triaxial compression. These studies, also performed with in-situ XRCT and 3DXRD, aim to directly visualize changes in microstructure (fracture, flow) and fluctuations in stress associated with AE events.