High Frequency Acoustic Emissions Observed during Model Pile Penetration in Sand and Implications for Particle Breakage Behavior

Abstract

Particle breakage has a significant impact on the mechanical properties of soils and has drawn continuous concerns among researchers. This study aims to deepen the current understanding on the particle breakage phenomenon through insights of high frequency acoustic emission (AE) signals. Two series of physical model pile tests were performed with AE instrumentation, using two different materials: silica sand and coral sand. The AE signals were digitalized continuously throughout the tests with a sampling interval of .5 μs (2 Mps), which enabled the signals with a maximum frequency of 1 MHz to be captured, and the AE signals with a frequency higher than 1 kHz were interpreted to be associated with particle breakage mechanism. Results show that the high frequency AE (i.e., particle breakage) occurred throughout the tests. An initial period of rapid rising and a following period of relatively stable high frequency AE signals were observed in all tests. Based on AE characteristics, the extent of particle breakage was found to be related to the material property, the pile penetration depth, and the ground density. In general, silica sand was found to be more emissive, although coral sand was more prone to break, and the dense ground was more emissive and more prone to break than the loose ground. In conclusion, the asymptotic evolving trend is suggested for simplified estimation of particle breakage during the pile penetration process.