GNGTS 2015 - Atti del 34° Convegno Nazionale

These data were rejected for the LCI approach, but remained in the 2D tomographic results (Fig. 3a). Conclusions. This research moved from one main question: how deep is the top of Miocene sediments below the Po River in the city of Turin? The answer would have implications in many fields: it would allow for a better knowledge of the structural geology of Turin Hill, a better understanding of the relationship between surface and groundwater and finally, being the top of Miocene a marly unit (the Baldissero Formation), an interesting indication, from a geotechnical point of view, for every engineering work across or below the river. Many water wells, drilled in the town, even nearby the left bank of the Po River, did not find the top of the marls, and the depth of the Miocene could only be guessed by outcrops in the hill and some rare information from deeper logs. The asymmetry of the Turin Hill anticline, according to these preliminary results, has been validated for the Miocene, from geophysical data, along a 5-km section parallel to the anticline axis. According to these preliminary results, the marls below the river are at depth ranging from 3 to 15 m. Only in some short stretches of the survey their depth exceeds the 20 m, a reasonable depth of investigation of CVES. These marls surely have different hydrogeological and geotechnical properties with respect to the Quaternary fluvial sediments. Marls will likely have cohesion and, even if they may have some secondary porosity due to tectonic fractures, a different hydraulic conductivity. They are the impervious bedrock below the alluvial plane and therefore, in the Turin area, they represent the bottom of the shallowest aquifer that drains into the Po River. Fig. 3 – Inversion results for the whole dataset. From (a) to (e) consecutive 1-km sections. The first line of each section is the result of the LCI approach, the second refers to the classical 2D tomography. The water layer has been blanked in both sections. Vertical dashed lines highlight the location of bridges. The simplified geological information nearest to the river are plotted in direct comparison with the geophysical results. GNGTS 2015 S essione 3.2 81