Feasibility of surface waves analysis to characterize the damaged zone of an underground gallery (EDZ)

ed by seismic phases velocity analysis. In this aim, we performed an experimental study in the experimental platform of Tournemire (Aveyron, France), which is a site that is operated by IRSN (Institute for Radiological Protection and Nuclear Safety). A comparison between the hammer source and a vibrator source showed the efficiency of the vibrator that improved the accuracy of evaluation of the phases velocity. A numerical study showed that the phases velocity of seismic surface waves is sensitive to the EDZ characteristics under the layer of concrete. In this way we have been able to invert the phases velocity picked between 200 Hz and 480 Hz. The inversed velocity profile includes an EDZ layer 60 cm thick with a velocity gradient from 300 m/s to 600 m/s. However, introducing the second mode in the inversion process does not give satisfactory results. This disagreement is probably due to the artifact introduced by the way we calculate the dispersion diagram that can lead up to define “effective mode”.