Dissipation of Elastic Wave Energy in Granular Soils

The dissipation of wave energy in the soil beneath a footing results from (a) dispersion of wave energy outward from the footing and (b) damping by energy losses within the soil. Following a brief illustration of a method for evaluating dispersion damping, the paper is primarily directed toward establishing numerical values of internal damping in granular soils. Laboratory tests using the vibration decay method permitted evaluation of the effects of confining pressure, amplitude of vibration, degree of saturation, and grain characteristics for four granular materials. The values of logarithmic decrement varies from 0.02 to approximately 0.20 for the various materials and test conditions used. It was found that the variation of logarithmic decrement with amplitude of vibration was appreciably affected by the degree of saturation and the grain characteristics of the material. The test results for a fine-grained quartz showed a marked dependence on time of loading and stress history, with the added complication that higher vibration amplitudes seemed to shake out the beneficial effects of prestress.