Simplified Calculation of Horizontal Dynamic Impedance of Piled Raft Foundation on Layered Soil

This paper develops a simplified calculation method for evaluating the horizontal dynamic impedance of a piled raft foundation on a layered soil medium. The proposed method combines a model of wave propagation that considers the reflection and refraction phenomena at the layer boundaries and a calculation method for estimating the dynamic impedance of a piled raft foundation on homogeneous soil. Numerical analyses of a piled raft foundation on layered soil subjected to harmonic horizontal loading are performed to investigate the effect of soil stratification on the frequency-dependent characteristics of dynamic impedance. The results show that the initial phase angle of propagating waves in layered soil related to the dynamic impedance of the piled raft foundation is slightly smaller than that for a spread foundation. Based on the analysis results, the calculation model is developed for the propagating waves that re-enter the foundation through reflection and refraction phenomena at the layer boundaries.