Frequency dependence of acoustic emission with particle interaction and failure process in dry sands during triaxial compression

To investigate the behaviour of sands at the particle-scale during shear failure, a series of triaxial compression tests was conducted on dry sands with varying confining stresses and relative densities. These tests were complemented by acoustic emission (AE) monitoring to analyse the frequency-dependent AE signals and characterise particle interactions in terms of crushing (>100 kHz) and rearrangement (<100 kHz). The results reveal a linear relationship between the relative breakage index (B_r) and the logarithm of cumulative high-frequency AE hits, regardless of the relative density. With this, particle crushing, as well as particle rearrangement, is demonstrated to occur throughout the entire shearing. Particle crushing increases more rapidly to prevail from the very beginning to the general yield, thereafter at a slower increasing rate to become less predominant. Its evolution in the post-peak regime is related to the failure pattern, which accumulates at a constant and most rapid rate when the specimen is ‘barrelling’; however, it decays rapidly in the presence of shear banding and eventually reaches an equilibrium state with particle rearrangement once the critical stress state is attained. Accordingly, two types of approximate evolution trends are suggested to estimate particle crushing upon shearing depending on the failure patterns.