Geotechnical Screening of Linear Earth Structures: Electric and Seismic Streamer Data for Hydraulic Conductivity Assessment of the Arignano Earth Dam, Italy

River embankments and small earth dams are linear retaining structures commonly used to protect densely populated areas from flood phenomena and to provide water reservoirs for human or agricultural use. Their continuity and uniformity are fundamental to their structural efficiency. Due to their significant length and the localized nature of potential weakness points, their characterization cannot rely only on local geotechnical investigations: it requires the application of efficient and affordable investigation methods. The need for new screening tools is becoming increasingly important worldwide because most river embankments and small earth dams are reaching their design life limit due to aging. This study used a new electric streamer and a seismic streamer for the combined measurement of resistivity and shear wave velocity to investigate the Arignano earth dam (Piedmont Region, northwestern Italy), a historical reservoir used for agricultural purposes. A procedure is also proposed to assess hydraulic conductivity from the measured geophysical parameters. The results of this assessment were compared with available geotechnical investigations and also used for calibrating the proposed procedure. Results are in good agreement when compared with local geotechnical investigations. The proposed procedure can therefore provide engineers and local authorities with information to plan maintenance or urgent measures for reducing flood risk.