EDZ characterization with surface wave analysis: Experimental and numerical study for defining feasibility in the context of the Tournemire Platform (France)
LEPAROUX ; COTE ; GELIS ; CABRERA
Type de document
ARTICLE A COMITE DE LECTURE REPERTORIE DANS BDI (ACL)
Langue
anglais
Auteur
LEPAROUX ; COTE ; GELIS ; CABRERA
Résumé / Abstract
The assessment of an Excavating Damaged Zone (EDZ) due to underground works is important in the context of radioactive waste disposal within a geological formation. Seismic surveys can pro- vide, in a non-destructive manner, information directly related to the mechanical properties of this damaged zone. However, the classical refraction method is unusable for galleries where a concrete layer caps the top surface. Moreover, other possible seismic methods like surface wave analysis can become complex to implement in such a context since guided waves are present and pass through a high-velocity concrete layer. For these reasons, the present paper will focus on an experimental feasibility study of the MASW (Multi Channel Analysis of Surface Waves) method for assessing an EDZ below a concrete layer in the specific context of the Tournemire experimental platform, which was drilled into an argillaceous formation in the Aveyron department of central France. This facil- ity is operated by IRSN (French institute for Radiological Protection and Nuclear Safety). This experimental study has been conducted in conjunction with a modelling results analysis. During an initial stage, the measurements carried out in situ are analysed and it is demonstrated that a receiv- ing profile longer than 8 m is required to distinguish the various modes. Moreover, the comparison of a hammer source and a sweep signal generated by a vibrator source shows that the latter is more appropriate when building the dispersion diagram, particularly for fundamental and first higher mode curves. A second stage shows that according to the analysis of theoretical curves for profiles with similar seismic velocities of the Tournemire platform medium, the dispersion curves are sensi- tive to EDZ characteristics. In the paper's final part, the dispersion curves obtained from the experimental seismic data are inverted using a global approach. Results of the inversion of the fundamental mode only and of both the fundamental mode and the first higher mode are com- mented upon, evidencing an improved quality for this last approach.
Source
Near Surface Geophysics, num. 5, pp. 401-411 p.
Editeur
Eage Publications
