Mechanical Uplifting Behavior of Belled Piles Embedded in Calcareous Sands: Insights from Acoustic Emission Monitoring

Abstract The uplift behavior of belled piles in crushable calcareous sand remains poorly understood due to limited research and a lack of suitable methods for quantifying particle-scale interactions. This study addresses this gap by supplementing the existing database with data from model uplift tests that integrate acoustic emission (AE) monitoring, considering effects of the base-to-shaft diameter ratio ( λ ) and overburden pressure ( σ O P ). A real-time method is proposed to quantify various modes of particle interactions based on frequency-dependent AE characteristics, overcoming a key limitation of current methods in isolating the contribution of particle crushing from other micromechanical behaviors. The present results reveal strong correlations between AE response and mechanical behavior: (1) proportional enhancements in uplift resistance and AE activity with increasing λ and σ O P ; (2) a linear correlation between traditional breakage indices and AE-based parameters; and (3) a three-stage evolution of frequency-dependent AE behavior that mirrors the load-displacement response. Furthermore, a quantitative analysis of distinct evolutionary patterns in AE characteristics is used to explain the pile–soil interaction and failure mechanisms governing the bearing capacity of both straight-shaft and belled piles. The proposed AE-based framework provides new micromechanical insights into uplift mechanisms, establishing a basis for potential improvements in foundation design in calcareous sand.