MASW 2D Seismic Survey in Urban Areas - The Case of the Turin Metro 1 Line

The present article discuss the results of seismic investigation conducted in Turin, Italy, to assess the geological and geotechnical modeling related to the planned extension of the underground Metro Line 1 from Collegno to Cascine Vica (about 4 km of length, from Collegno to Cascine Vica). The specific objectives were to map the thickness of the man-made ground lying upon alluvial soil made of gravel and sand and evaluate the stiffness property of the subsoil. To overcome the typical obstacles of the urban ambient (electromagnetic and vibrational noise, hard traffic management, high energy source required) we applied the shallow wave technique with a continuous profiling (MASW 2D) by means of a customized system of geophones array on a land streamer and a controlled source of energy mounted on a vehicle. The surveys were performed overnight in two sessions (two days), with a fast data acquisition for a total length 2000 m. The results of the survey, calibrated with boreholes positioned all along the survey line, has precisely mapped the contact between the shallow reworked ground and the alluvial deposits. Moreover, the survey results have highlighted many lenses of cemented gravel (conglomerate bodies) inside the alluvial deposits.