GNGTS 2022 - Atti del 40° Convegno Nazionale

450 GNGTS 2022 Sessione 3.2 of 94 meters, ensuring a depth of investigation of about 15 m. A mixed sequence Wenner Schlumberger 48 channels was adopted for the acquisition of electrical resistivity data for a total of 545 measurement quadripoles for each line. The ERT1 section (Fig. 3) is the most interesting for the purposes of lithostratigraphic characterization. As illustrated in Figure 3, an electro-stratigraphic sequence is highlighted characterized by an alternation of sandy levels (with electrical resistivity values ​between 70 and 100 Ω×m, shades of ocher-brown color) and sandy levels with a clayey matrix (with values​ of electrical resistivity between 30 and 70 Ω×m, green-ocher color tone). The most interesting element from a geological point of view is represented by the strong anomaly conductive visible under the access road to the building. This anomaly (with resistivity lower than 10 Ω×m, blue color tone) is localized around the building. From the lithological point of view - given the strong homogeneity of the subsoil found both in the rest of section ERT1 and in section ERT2 - this anomaly corresponds with soils probably saturated with a predominantly loamy-clayey matrix. Since there are no feeding areas from the overhanging slope, and since, on the other hand, a possible supply from the area of ​the building itself, it is believed that the presence of humidity both to be connected to the activity related to the building (gargoyles of the downspouts with direct discharge in the subsoil, direct discharges into the subsoil, rupture of water collection pipes, rupture of pipes of drinking water, etc.). The ERT2 section highlights an extremely homogeneous lithostratigraphic situation without anomalies attributable to the presence of water; this supports the hypothesis that infiltration of water occurs in the area of ​​the building. Conclusions . This note shows as the combination of geophysical methods can lead to a better comprehension of the failure mechanisms of unstable slope. Both cases studied show the identification of channelized groundwater flow into clayey soils by means of geoelectric surveys (ERT) requires an accurate and careful interpretation of the geophysical data integrated with a detailed geological survey and/or geotechnical tests for the calibration of the results. In details, in the first case study, the ERT survey has localized the saturated clay along which occurred the sliding. According to this information, a first remediation action (D in Fig. 2) was the re-profiling of the slope to remove the unstable mass upon the gliding surface (emergency action). Subsequently, the stabilization of the slope has included both drainage interventions (to control the water pressure), a more efficient re-profile of the ground surface (E in Fig. 2) and the positioning of retaining wall at the toe of the slope. In the second case history, the geoelectric survey showed that: i) the lithostratigraphic setting is rather homogeneous, characterized by a stratigraphic sequence with sandy levels alternating with sandy-clayey levels. There was no evidence of the presence of an aquifer or of localized occurrences of water seepage; ii) strong conductive anomalies were found around the building attributable to presence of fine matrix soils in conditions of high saturation. Such saturation seems to derive from superficial infiltrations located near the building. References Boni A., Boni, P. Braga G., Bruno G., Casnedi R., Corsi M., Gatto G.O., Gatto P., Mosna S., Motta E., Perotto G., Rampoldi R.; 1969: Foglio 69 “Asti”. Carta Geologica d’Italia alla scala 1:100.000, II ed., Serv. Geol. It., Roma. Barbero D., Boano P., Forno M.G.; 2014a: Fenomeni di instabilità di versante in un tratto Astigiano della valle del Fiume Tanaro che interessano forme fluviali sospese. In: Atti e contributi del convegno “L’alluvione del 5-6 Novembre 1994 in Piemonte: venti anni di attività nella previsione e prevenzione in ambito gelogico-idraulico”, 28-29 ottobre 2014, Torino, Regione Piemonte, Ordine Reg. Geol. Piemonte, CNR-IRPI, GEAM (Eds), 123-128. Barbero D., Doglione A., Forno M.G., Gattiglio M.; 2014b: The importance of stratigraphic and structural aspects in the mitigations of landslides involving slopes near Aguggia (San Damiano d’Asti) , In: Miscellanea INGV Abstract Volume AIQUA Congress 2015: “The Plio-Pleistocene continental record in Italy: highlight on stratigraphy and neotectonics”, 24-26 Febbraio 2015, Torino, Monegato, G., Gianotti, F., Forno, M. G. (Eds), AIQUA, 11-12.