Mechanical characterization of heterogeneous soils with surface waves: experimental validation on reduced‐scale physical models

Abstract

The characterization of heterogeneous soils using common geotechnical techniques often proves impossible when the size of the heterogeneity is larger than a few tens of centimetres. Geophysical investigation techniques based on seismic wave propagation can help engineers to characterize the mechanical properties of such materials. In this paper, both refracted and surface waves are used to estimate the mechanical properties of an equivalent homogeneous medium.A summary of the main results obtained numerically using finite-element computations and homogenization theory is presented. It is shown that, for first-mode surface-wave wavelengths larger than 7.5 times the nominal size of the heterogeneity and within certain heterogeneity concentration ranges (up to 50% for matrix dominant soils), surface waves homogenize the soil in accordance with classical homogenization theory.To validate these numerical results, a reduced-scale model was built and seismograms, generated with a falling weight, were recorded. The phase-velocity dispersion curve of the generated surface waves is inverted in order to obtain the shear-wave velocity of the heterogeneous layer. The compressional-wave velocity is calculated by means of seismic refraction analysis. Velocities obtained on the reduced-scale model correspond to those predicted by homogenization theory from individual measurements of matrix and inclusion velocities.

Near-offset effects on Rayleigh-wave dispersion measurements: Physical modeling

“…As regards the purely numerical aspects of this work, a complete parametric study has ensured the stability of these FDM in surface-wave analyses (Bodet, 2006). In this particular parametric study, FDM are targeted for comparison with finite element models that have previously been validated in several studies (Semblat and Brioist, 2000;Chammas et al, 2003;Abraham et al, 2004;Bodet et al, 2004). Two examples of synthetic data computed from the homogeneous and two-layer FDM are presented in Fig.…”

Characterisation of soils with stony inclusions using geoelectrical measurements

“…By simulating via finite-element analysis, several random distributions of inclusions made of limestone or sandstone in a sandy matrix, Chammas et al (2003) evinced the increase of the shear wave velocity Vs with the concentration of stiff inclusions (for velocity contrasts ranging from 2.4 to 5.5). This relationship, validated using a small-scale model (Abraham et al, 2004) at two different concentrations (19% and 35%), allows one to estimate the concentration of inclusions present in a soil using only seismic measurement techniques.…”

Identification of lateral discontinuities via multi‐offset phase analysis of surface wave data

“…The experimental information is extracted from seismograms as multi‐modal curves representing the dependence of phase‐velocity on frequency (e.g., Socco and Strobbia 2004). Different approaches to describe and handle surface wave propagation in non‐1D media have been described and investigated in the literature (Keilis‐Borok et al 1989; Abraham et al 2004; Socco et al 2006) but the existing practice is strongly limited to the inversion of data in terms of 1D shear velocity profiles.…”