GNGTS 2015 - Atti del 34° Convegno Nazionale

us to define the pinch-out of marine clays and in the north the covering is in direct contact with the Flysch altered. Due to the low resistivity of the marine clays, ERT measurements did not allow sufficient penetration to image the underlying Flysch. The advantage of using this method of investigation was to identify the geometry of marine clays in the southern part of the area, clays from 5 m depth coastal seabed that now lie on the surface due to the pressure of the industrial landfill that with it weight has squirt marine sediments upwards. The ERT survey has also allowed the identification the underground power line high-voltage located in the north part of the area. The major problem in the analysis of electrical tomographic data was the presence of salty sea water that increases the conductivity and hides the differences lithological. The refraction seismic survey has extended the exploration at depth allowing to define, with the calibration of the drillings, the interface between the marine clays and the Flysch bedrock. The transition between the marine clays and the Flysch shows a gradual velocity rise with increasing depth, with a continuous variation of soil properties resulting in a curvature of seismic rays. The correlation between the velocity model obtained from the inversion of seismic data and the boreholes stratigraphies helped define the top of the altered Flysch, corresponding to an average seismic velocity of about 2300 m/s. The bedrock Flysch outcrops on the southern slopes of Mount San Pantaleone. The top of the Flysch deepens towards the sea, with a variable slope varying between 6° and 15°, reaching a depth of 19 m from the sea level in the borehole E3, located south of the site. This formation continue to deepen, deduced by drillings made in 1987 that intercept the top of the Flysch at the depth of 55 m below ground level. From marine seismic surveys performed by OGS, the maximum depth of the top of the Flysch in the Zaule Valley reaches the depth of about 80 m. Ground flow simulations. The ground water flow modeling relative to the Ex-Esso area was conducted using MODFLOW, awell-established software produced by the US Geological Survey. This is a 3D finite difference code that reproduces the flow of water in confined and unconfined saturated porous media. In the specific case, MODFLOW was used in stationary conditions to reproduce the piezometric data measured on the site and then to evaluate the effect that would, in the same conditions of external hydraulic loading, the presence of the planned waterproof excavation as designed in the plan of intervention for the site reclamation. The model was built by reproducing the three-dimensional geometry obtained from the geophysical and geological surveys, which identifies three main formations (from top to bottom): Fig. 3 – Geological section that summarizes the results of geological and geophysical study of the industrial site Ex-Esso (Trieste, Italy): the Flysch in brown, the altered Flysch in orange, the marine silty clay in blue, continental deposits and anthropogenic fills in green. 74 GNGTS 2015 S essione 3.2