Dynamic characterization of vertically loaded foundations on granular soils

By means of scaled modeling on a geotechnical centrifuge, a systematic experimental investigation was conducted to examine the vertical dynamic response of surface foundations on granular soils. From the results of more than 100 tests, it was found that the dynamic characteristics of such foundations can be well represented in the frequency domain by the homogeneous half-space analytical solution despite the gravity- and load-induced spatial variations of the soil's modulus. However, it was also revealed that the foundation response has a significant nonlinear dependence on the soil bearing pressure and footing dimension. To capture such aspects, a set of equivalent-homogeneous elastic parameters was determined from the physical measurements for a wide range of soil-foundation configurations. Through an analytical synthesis, it was found that the equivalent-homogeneous Poisson's ratio of the soil can be taken as 0.25 while the equivalent-homogeneous shear modulus of the soil can be related through a power law to the soil's void ratio, footing radius, and average foundation bearing pressure. The practical relevance and potential applications of the resulting semiempirical formula for the dynamic foundation compliance are discussed.