Volume Change Behavior of Vibrated Sand Columns

Densification of granular soil during vibration was investigated using laboratory experiments. Longitudinal vibration was applied to cylindrical columns of sand. The apparatus simplified the boundary conditions of the specimen from those acting on specimens of soil in rigid molds, previously used to investigate vibration effects on granular soil. An analytical model was derived to help interpret laboratory test results. The maximum acceleration, stress, and strain all occurred at the resonant frequency for low base accelerations. As the base acceleration increased in magnitude, the specimen experienced large permanent strains at low frequencies instead of at the resonant frequency where the acceleration of the top cap and the stress were greatest. The analytical model revealed that strain was related only to the elastic component of stress, and that for increased viscous damping, the combined stress (elastic plus viscous) was not greatest at the same frequency as the strain. Knowledge of the stress states alone is not enough to predict permanent strains during vibration. Knowledge of the dynamic strains or the soil damping would be required.