Abstract: Natural foundation usually contains irregular interfaces between the soil layers. Therefore, this paper proposes a thin layer method to calculate the three-dimensional (3D) dynamic response of stratified soils with irregular interfaces. Based on the double Fourier transform, the system of equations in terms of thin layer elements for the elastic medium are obtained in the frequency-wavenumber domain. The stiffness matrices of the semi-infinite thin-layer elements and the finite-length thin-layer elements are derived through the modal superposition principle. The perfectly matched layers (PMLs) are subsequently introduced to simulate the wave propagation in the bottom half-space. By using the semi-infinite and the finite-length thin-layer elements as well as the PMLs, a calculation model is finally developed to obtain the 3D fundamental solution for a harmonic point load acting on a layered half-space with irregular interfaces. The accuracy of the proposed method is verified by comparing with the existing methods. Finally, the dynamic responses induced by a harmonic load acting on a two-layer foundation with an inclined interface are investigated. The results show that the inclination of the inclined interface exhibits a significant influence on the dynamic response. The difference in the vibration level increases as the inclination and the load frequency increase. The irregular interface needs to be considered in the evaluation of dynamic response of natural foundation.

Key words: dynamic response, layered foundation, fundamental solution, thin layer method, perfectly matched layer