Acoustic emission in calcareous subsoils: particle interaction quantification and bearing performance interpretation

The bearing capacity of foundations on crushable calcareous sands is governed by the interplay between particle crushing and rearrangement. However, these mechanisms are not sufficiently understood to support accurate design theories, largely due to the lack of effective techniques for real-time quantification of such particle-scale processes. This study investigates the bearing behavior of calcareous sand foundations with varying gradations using static loading model tests, integrating with high-performance acoustic emission (AE) and particle image velocimetry (PIV). A frequency-domain framework (100 kHz threshold) was used to decouple high-frequency crushing signals from low-frequency rearrangement. Results demonstrate a relationship between frequency-dependent AE activity and mechanical response, confirming the feasibility of AE to quantify particle-scale processes and characterize the load–settlement behavior of calcareous subsoils. Combining AE patterns with PIV data identifies two distinct substages within the traditional “linear compression” stage, revealing complex underlying micro-mechanisms. Regarding gradation effects, poorly graded soils exhibit general shear failure driven by unconstrained rearrangement, whereas well-graded soils undergo local shear failure, where cooperative crushing and rearrangement enhance interlocking to suppress strain localization. This study provides a novel AE-based framework for full-process monitoring and understanding the particle-scale origins of bearing capacity, offering fundamental insights for optimizing foundation design in carbonate sediments.