The influence of dynamic properties of ground soil on vibration characteristics of rigid body on sand ground

This study aims to investigate the influence of dynamic properties of the ground soil on vibration properties of a rigid body placed on the sand ground surface to clarify the vibration behavior of a structure in terms of the interaction between the structure and the ground. A series of cyclic triaxial tests and three types of model vibration tests were performed. The dynamic properties of ground soil were clarified using cyclic triaxial tests. It was found that the equivalent shear modulus markedly depends on confining pressure and relative density, and that the hysteresis-damping ratio also depends on confining stress but not upon relative density. In model vibration tests, rigid body models with variable masses, inertial moment, base size and base shape were prepared and their vibration behaviors were observed. Vibration characteristics were estimated from the observed behavior, and the period and damping ratio were examined. It was found that the period depends on not only the mechanical properties of the rigid body and the relative density of ground, but also upon the magnitude of the vibration amplitude. A simple model of a spring and a dashpot was used to correlate period and damping ratio of ground soil in a model vibration test with equivalent shear modulus and hysteresis damping ratio by cyclic triaxial testing. The relationship between normalized inverse squares of the period and rotation amplitude was similar to the relationship between the normalized equivalent shear modulus and the shear strain amplitude. Normalized damping ratio also showed good agreement with the normalized hysteresis-damping ratio. The calculated equivalent shear modulus from the simple model linearly increased with increased average contact pressure, as the equivalent shear modulus of the cyclic triaxial test 1 inearly increased with effective confining pressure on a log-log scale.