Centrifuge Modeling to Evaluate the Seismic Response of Elastic and Inelastic Structures Embedded in Unsaturated Soil

Soil-structure interaction has recently been increasingly considered in the design of structures located in areas of high seismicity. Design codes typically assume the soil to be in either the dry or fully saturated states; however, dynamic soil properties such as stiffness and damping are influenced by the degree of saturation in the underlying soil. This paper presents some findings from two series of centrifuge tests to evaluate the performance of a mid-rise structure, shallowly embedded in sandy silt with varying water table depths. In one test series, the physical model was designed to remain within its elastic range, in another, the physical model was designed to behave inelastically during seismic loading. Results indicate that as the water table elevation decreased, the soil behaved stiffer, leading to reduced period lengthening and system damping. Reductions in period lengthening and system damping that were correlated with the depth of the water table, were also related to the behavior of the superstructure, with greater reductions observed during the experiments performed on the elastic structure.