Acoustic emission behaviour of dense sands

Interpretation of acoustic emission (AE) generated by particulate materials has to date been qualitative. The objective of this study was to move the discipline towards quantitative interpretation of AE to enable early warning of serviceability and ultimate limit state failures in the field, and to enhance the instrumentation of element and physical model tests in the laboratory. Results from a programme of drained triaxial tests on dense sands show that: AE generation is proportional to the imposed stress level, imposed strain rate, fabric coordination number and boundary work done; there are two types of AE response at the transition from contractive to dilative behaviour, which was governed by the mean particle size; and AE activity in particulate materials is negligible until the current stress conditions (compression and/or shear) exceed the maximum that has been experienced in the past. Relationships have been quantified between AE and boundary work (i.e. AE generated per Joule) for a unit volume of sand under isotropic compression and shear, and between AE and shear strain rate. An example interpretation framework demonstrates how AE measurements could be used to identify the transition from contractive to dilative behaviour, mobilisation of peak shear strength and quantify accelerating deformation behaviour that typically accompanies shear zone development.