Combined Analysis of Geophysical and Geotechnical Data for Investigating the Alluvial Plain of Beyrouth

Geophysical methods are now increasingly used for sub-surface recognition. Geophysical and geotechnical tests were carried out on a site in -Beirut (Lebanon). The survey included 2 electrical tomography profiles and ambient vibration measurements using 2 passive seismic arrays with different apertures. The computed Rayleigh wave dispersion curves were inverted to derive vertical Vs profiles. Geological and geotechnical information was obtained through 14 boreholes with SPT tests. The combined interpretation of the different sets of data highlighted the strong lateral and vertical heterogeneity of the site, along with the relations between the geology, the geophysical parameters and the geotechnical properties (SPT). In particular, the combination of methods has allowed detecting a few m thick Low Velocity Zone (LVZ) of varying depth, corresponding to a soft clay layer embedded in coarser layers. Without prior information given by the other investigation techniques, the dispersion curve inversion would have led to erroneous interpretation in the Vs profiles.