Abstract
This paper presents the experimental results of swaying and rocking vibration tests on small bodies resting on the surface of a foundation. The experiments were conducted for the purpose of clarifying the spring and damping effects of real soil in the horizontal and rotational directions, because the resonance of a vibration pickup mounted on the surface of the ground causes considerable error on the measurement of the ground surface vibration. The experiments were conducted on a foundation of Kanto loam. The results obtained are summarized below. The approximate expressions for the spring constant and the damping coefficient in the horizontal and rotational directions for an elastic half-space were introduced using the Groud Compliance given of Tajimi (Eqs. (9)-(12)). The measured swaying spring constant is proportional to the radius of the contact area and rocking spring constant is proportional to the third power of the radius, as theoretically predicted. The measured value of the swaying spring constant is nearly identical to that of the static spring constant assuming a uniform contact pressure distribution, and the value of the rocking spring constant lies between the two calculated values obtained assuming rigid base and triangular contact pressure distributions (Figs. 5 and 7). The measured values of the swaying and rocking spring constants increase as the average contact pressure increases (Figs. 6 and 8). The measured value of the dimensionless natural frequency of the coupled swaying and rocking vibration system lies between two calculated values, one of which was calculated assuming a rigid base pressure distribution both in the horizontal and rotational directions, while the other was calculated assuming a uniform distribution in the horizontal direction and a triangular pressure distribution in the rotational direction (Fig. 10). The influence of the soil viscosity on the damping effects was investigated. The expressions for the damping coefficient due to soil viscosity were introduced assuming the foundation to be a Voigt solid (Eqs. (21)-(25)). The measured value of the magnification factor is nearly identical to the value calculated using a damping coefficient assuming the soil to be a visco-elastic material (Fig. 11).
