The Authors discuss the results of seismic reflection profiling, borings and geotechnical, hydrogeological and mineralogical tests carried out to set up a geologic-structural model of clayey sediments crossed by a hydraulic tunnel. An appropriate survey campaign was impelled by the research of useful parameters for the choice of a suitable method of the tunneling works (boring and first face lining methods). The survey results allow to define: a) the tectonic conditions of the clayey sediments; b) the nature and the percentage distribution of clay minerals; c) the swelling characters of clay minerals; d) the correlation between mineralogy and geotecnical parameters; e) the hydrogeologic model. Besides traditional processing, reflection tomography was applied using some good reflecting layers to study the distribution of tectonic unconformity and to detect week or faulted zones.