GNGTS 2015 - Atti del 34° Convegno Nazionale

116 GNGTS 2015 S essione 3.2 representation has been chosen in order to put into evidence all the most interesting depth levels in a synthetic way. The GPR surveys allowed us to highlight the presence of several anomalies (in particular, those in the red colors in Fig. 3) linked to buried critical zones. In such areas, in fact, instability events occurred, due to small voids, cavities and areas were previous artificial changes had been done. It can be noted that, as expected, in many houses the presence of wells and/or tanks, some of which partially filled with debris materials, was detected. Conclusions. Inthiscontributionwehaveshownageophysicalcasehistory,wheregeoresistivity, spontaneous potentials and ground penetrating data have been gathered in the historical center of the town of Mesagne, damaged by an exceptional storm that probably caused, among other things, the breaking of a water pipe of the aqueduct. The performed study demonstrates, one more time, the wide range of applicability of the geophysical methodologies. The results of the 3D ERT measurements showed the presence of a highly “disturbed” subsoil and a phase of adjustment still going on at the time of the measurements (March 2014). The SP data showed probable direction of flux of lose materials at the time of the prospecting. The GPR survey campaigns allowed to highlight the presence of several anomalies linked to buried critical zones. According with the achieved results, it is possible to deem that the instability events have been caused by: 1) losses within both the water supply networks and the drainage systems. 2) The uncontrolled condition of several wells (in particular their high number and above all their state of these wells had never been systematically monitored). 3) Rainwater that infiltrates into the subsoil. In particular, the flowing fluids can saturate the soil and reduce its mechanical resistance. Moreover, the infiltration of superficial runaway water, even in small quantity, can increase the foundation base plastic material quality, lowering the load capacity. Finally, indeed, also modern volumetric changes performed on some houses (e.g. perforation of load bearing walls) have made the structures more prone to damages, but this does not seem to be the main cause of the occurred problems. Fig. 3 – GPR slices at the apparently most “interesting” depths. The estimated depths are: A-B-C: 1.9-2.11 m; D: 0.61-0.78 m; E: 0.37-0.54 m; F: 0.25-0.42 m; G: 0.50-0.67 m; H:0.22-0.37 m; I: 0.25-0.42 m; L: 1.24-1.41 m; M: 0.69-0.78; N-O-P: 1.37-1.54 m.