The acoustic emission (AE) technique can be used to locate failure-induced AE sources and provides an alternative to continuously visualise the development of failures inside stressed materials; however, a literature review reveals almost no studies regarding its application for source location in granular materials. Yet the visualisation of ubiquitously observed strain localisation and shear banding is critical to an in-depth understanding of the progressive failure mechanism of granular materials. In this paper, an original AE source three-dimensional (3D) tracing code based on the idea of ‘time difference of arrival’ (TDOA) was developed using Matlab programming, for the first time, to continuously visualise particle-scale interactions involved in saturated granular soils. After validating its feasibility through a series of pencil lead break (PLB) tests, the developed AE source 3D tracing code was applied to saturated granular soils subjected to drained triaxial shearing. Both the results of PLB tests and drained triaxial shearing tests demonstrate a good consistency between the traced AE source and actual PLB/particle interaction-induced sources. This suggests that the developed AE source 3D tracing code could be used to visualise the initiation and evolution of strain localisation and shear banding in saturated granular soils subjected to drained triaxial shearing.

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.