Caractérisation mécanique des sols très hétérogènes avec les ondes de surface

Characterizing highly heterogeneous soils by means of geotechnical methods often proves difficult, or even impossible, when the size of heterogeneities exceeds a few decimeters. Geophysical methods based on seismic wave propagation could help the engineer when it comes to mechanically characterizing such media. Surface waves and refracted compression waves will be used herein to determine the mechanical properties of an equivalent homogeneous medium; numerical results obtained with the finite element method will be featured as well. It will be shown that when surface wavelengths exceed 7.5 times the heterogeneity radius, for inclusion concentrations of less than 50%, wave propagation is governed by specific propagation equations within a homogeneous medium equivalent to the heterogeneous soil. In order to validate these results, a number of experimental campaigns have been conducted on reduced-scale controlled physical models. The phase velocity dispersion curves have been inverted to generate a vertical shear-wave velocity profile, and compression wave propagation velocities will be derived using the seismic refraction method. The volume wave velocities correspond with those calculated from a classical homogenization model. Lastly, this article will present the results from a full-scale experiment.