Effects of Vibration History on Modulus and Damping of Dry Sand

Abstract

This paper describes an experimental program aimed at a close examination of the dynamic properties (shear modulus and damping ratio) of a normally consolidated dry sand as affected by the previous vibration. Tests were performed using a newly developed energy-injecting virtual-mass resonant column system. The new system allows the strain as well as the strain rate be kept constant concurrently throughout a test (hours of continuous vibration), irrespective of changes in soil properties. During the tests, modulus and damping values were monitored continuously without interrupting vibration. The test variables include strain amplitude, number of previbration cycles, confining pressure, and relative density. The results confirm that the damping ratio of dry sand is evidently dependent on the number of loading cycles when the shear strain exceeds a threshold, while the variations of shear modulus as number of loading cycles increases are relatively moderate. The test results also show that there exists an unequivocal signature of vibration history in the measured sand properties. This new finding may lead to certain applications.