Wave propagation in the soil: theoretical background and application to traffic induced vibrations

This paper reviews the direct stiffness method for the calculation of harmonic and transient wave propagation in horizontally layered media. Developed in the early eighties by Kausel and Roësset, this method has become a standard tool for the computation of the Green’s functions in layered media. As it is based on a superposition of plane harmonic waves in the frequency-wavenumber domain, it is very useful as a didactical tool for elastic wave propagation. The Green’s functions are subsequently used in a boundary element formulation to compute the dynamic impedance of the soil in a subdomain formulation for dynamic soil-structure interaction. This is illustrated for the case of road traffic induced vibrations, where the invariance of the problem domain in the longitudinal direction is exploited by working in the wavenumber domain. A numerical example demonstrates the influence of the soil stratification on free field vibrations during the passage of a two-axle truck on a traffic plateau.