Kinematic Soil-Structure Interaction Effect in Layered Liquefiable Soils on Foundation Input Motion

Abstract

The principal objective of this study is to make use of medium and strong motion data from instrumented shaking table tests to evaluate the effects of kinematic soil-structure interaction on foundation input motion (FIM). The shaking table tests consisted of a 2×2 pile group in two-and three-layered liquefiable soils (models 1 and 2). Each test model was subjected to three realistic earthquake motions with peak accelerations ranging from 0.13g to 0.50g, and time step ranging from 0.006 to 0.02 sec. The three input earthquake motion represented the realistic earthquake motion with high frequency, low frequency and high amplitude. The foundation/free-field ground motion variations were quantified in terms of acceleration time histories and Fourier amplitude spectrum. Preliminary analysis of the data suggests that (1) regarding the input motion with high frequency, the higher peak acceleration of the foundation indicates the structure feedback and kinematic interaction between the soil and foundation during shaking; soil layering has little effect on foundation input motion, (2) regarding the input motion with low frequency, the kinematic soil-structure interaction increases the foundation response for model 2 while reduces it for model 1. The soil profile has significant effect on the predominant frequency, (3) regarding the input motion with high amplitude, the higher response of foundation in model 1 indicates the stronger kinematic SSI effect. The small deviation between the free field and foundation in model 2 indicates the coherent motion of the foundation with soil and no obvious kinematic SSI effect, (4) soil liquefaction has significant effect on the values of peak acceleration and peak Fourier amplitude.