Acoustic emission behaviour at soil–metal interfaces during shearing: micro to macro insights

The study of acoustic emissions (AE) at soil-metal interfaces has gained increasing attention in geotechnical engineering due to its potential for developing acoustic-based early warning systems for structural stability and safety monitoring. Existing studies have paid limited attention to the fundamental mechanisms underlying soil-metal interface shearing across micro to macro scales and their associated acoustic emissions (AE). This study investigated the soil-metal interface shear and their AE responses through systematic tests using macromechanical and micromechanical interface shear testing apparatus, critically analyzing the shear response, geotribological aspects, and AE responses in the time and frequency domains to gain deeper insights and understand their interrelationships. The results revealed that soil-metal interface shear response and AE intensity (amplitude and frequency content) increased as normal stress and particle angularity increased. Unlike the shear response, the increase in displacement rate leads to a considerable increase in AE. Furthermore, the analysis of the test results reveal that the AE of soil-metal interfaces are strongly affected by the hardness of the continuum material, which, in turn, governs particle breakage and shear-induced surface changes during shearing. The novel micromechanical shear tests revealed that there is no AE during plowing, strain softening, or hardening; emissions are only observed when asperity breakage occurs, followed by micro-tapping during shearing. The findings of this study significantly advance the understanding of soil-structure interaction from an AE perspective and contribute to the design of efficient AE-based early warning devices.