Evaluation of different methods for deriving geotechnical parameters from electric and seismic streamer data

Geotechnical parameters of linear earth structures, such as embankments and earth dams, are usually obtained from point-wise investigations through drilling or penetration tests, commonly time and cost consuming. Non-invasive geophysical investigations can be considered alternative for a preliminary screening of earth structures physical properties, given their surveying speed and their depth and length of investigation. Seismic and electrical methods can be also used, through specific correlations, for the estimation of geotechnical soil characteristics. Several methodologies have been developed over the years combining two or more geophysical techniques for the estimation of geotechnical parameters. In this paper, data from geophysical surveys were used for the comparison of geotechnical parameters forecasted with three different methods (with theoretical, statistical, and field based approaches respectively). Their strongpoints and limitations were also evaluated by comparison with available direct geotechnical investigations. Integrated seismic and electrical data from extensive surveying performed over seven retaining structures located in Piedmont Region (NW Italy) were used to forecast their fine content and hydraulic conductivity distributions. Geophysical data were acquired using seismic and electric streamers, useful for the simultaneous execution of the surveys in motion along the earth structures. The results of this study show the effectiveness of the proposed data acquisition approach and elaboration procedures as a first screening tool for earth retaining structure safety assessment. The increased capability of the theoretical method to better predict geotechnical parameters with respect to the other methodologies is also reported.