Acoustic emission and energy dissipation in soils during triaxial shearing

Acoustic emission (AE) monitoring offers the potential to sense particle-scale interactions that lead to macro-scale responses of granular materials. However, there remains a gap in fundamental understanding of how particle-scale mechanisms and properties influence AE generation, which limits the application of AE monitoring and interpretation of AE measurements. Addressing this gap in knowledge was the principal focus of this study. A  benchmarking study was conducted first whereby a programme of seven 3D DEM simulations of drained triaxial tests with energy tracking were performed and compared with experimental measurements, which ensured the adopted simulation approach captured realistic behaviour. Dissipated plastic energy was influenced in the same way as measured AE by imposed confining pressure, displacement rate, and load-unload-reload compression and shearing. A parametric analysis was subsequently conducted using a programme of 25 3D DEM simulations. The findings show that sliding and rolling friction were the dominant mechanisms in plastic energy dissipation and hence particle-scale properties that influence sliding and rolling friction have the most significant influence on AE generation (e.g., particle shape, surface roughness, hardness). Relationships have been established to quantify how changes in particle-scale properties in DEM (sliding and rolling friction coefficients, normal and shear stiffness and their ratio, and local damping coefficient) lead to changes in dissipated plastic energy (R2 of 0.99); however, it should be noted that the relations in the sensitivity analysis cannot be interpreted as representative of specific granular materials. This new knowledge enables improved interpretation of AE and underpins the development of theoretical and numerical approaches to model and predict AE behaviour in particulate materials.