Acoustic Emission of Sand during Creep under Oedometric Compression

Abstract

Abstract Creep of sand is a consequence of micromechanical processes within the granular soil skeleton. These processes are known sources of acoustic emissions. Therefore, acoustic emission analysis provides additional information about the time-dependent mechanisms, even if conventional deformation measurements reach their limit of applicability (i.e., resolution, accuracy). The present study investigates the relationship between acoustic emission events and creep deformation. For this purpose, multistage creep tests at axial stresses up to 6,000 kPa are conducted on loose and dense quartz sand under oedometric conditions. During creep acoustic emission are recorded and processed and the results are compared to conventional displacement measurements. The deformations during creep are measured using a highly accurate displacement transducer. The creep behavior is characterized by the creep-coefficient C relating the change of the strains with the logarithmic increment of time. The experimental results show that the time-evolution of the acoustic emissions and the evolution of strain during creep are qualitatively similar. In analogy to the coefficient of C, a coefficient CAE relating the cumulated number of acoustic emissions with the logarithm of time is defined. In the conducted experiments, we observe that both the coefficients of C and CAE show a dependence on stress, the initial density, and the strain rate at the beginning of creep. Nevertheless, the influence of the initial strain rate on C and CAE reduces over time and both quantities approach constant values for increasing time.