Characteristics of Acoustic Emissions from Soil Subjected to Confined Uniaxial Compression

Abstract

Core Ideas Acoustic emissions (AEs) reveal information on soil deformation processes. We studied AEs during loading–unloading–reloading cycles under confined compression. The number of AE hits reflected well the soil deformation regimes. Soil compression and swelling indices correlate with AE parameters. The Gutenberg–Richter power law b value varied with wet soil yield stress. Application of mechanical stresses to soil results in deformation, microfracturing, particle motion, and liquid reconfiguration that may release measurable amounts of stored elastic energy in the form of acoustic emissions (AEs). This study aimed to systematically study AE characteristics during confined uniaxial compression of soil samples and link various AE parameters to soil deformation regimes. We hypothesized that variations in AE characteristics could offer new insights into the transition between elastic and plastic soil deformation and noninvasively identify the onset of yield stress. We subjected soil samples at known water contents to a loading–unloading–reloading cycle under uniaxial compression using an oedometer coupled with an AE monitoring system. The soil was a sandy loam equilibrated with two initial gravimetric water contents (12 and 25%) and two initial bulk densities (1.3 and 1.55 Mg m−3) for each water content. Observed AE event numbers (hits) and their energy content (E) varied during stress application to soil samples. Close agreement was found between soil yield stress deduced from normalized cumulative AE parameters and measured stress–void ratio curves (precompression stress, σpc) for the dry soil; however, the yield stress deduced from AE parameters was significantly larger than σpc for the wet soil. Swelling and compression indices were strongly correlated to AE hits and E, respectively. The preliminary results illustrate the potential of monitoring passive AE during load application to characterize soil mechanical parameters (potentially in situ). Nevertheless, additional studies with controlled pore water pressure and a range of soil types would be required to generalize these findings to offer a robust AE‐based method.