GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 691 The detection of bombs is based on two important conditions: 1) the object must be associated with a low resistive volume; 2) the object must be characterized by high chargeability anomaly (Snyder et al. , 2004; Wynn & Roberts, 2009). In Fig. 2, the volumes with 2 Ω·m ≤ ρ ≤ 40 Ω·m are shown and overlapped to the volumes with high chargeability, correlated with metallic object, between 50 mV/V and 201 mV/V. From a first analysis, chargeability anomalies (A1, A2, A3, A4; yellow circles in Fig. 2) seems to be not comparable, by linear and vertical position, to the low resistivity anomalies and, thus, not correlated to the presence of landmines. For a better view, four visualizations along different orientations was provided. In Fig. 2, high chargeability values overlapped to low resistivity ones are shown; they exclude the presence of metallic object. Conclusions. In this paper, we present a joined investigation between 3D resistivity and induced polarization tomography surveys in urban area (Trento, north Italy) with the aim to check of the presence of metallic object in order to help a demining operation. Despite of the logistic impediments, the surveys along fixed measurement lines, parallel to the railway lines was lead on. This configuration allows to avoid noise due to the railway lines and give a good detailed three – dimensional visualization of the volume under the railway tracks. We chose the electrodic and the spreads spacing considering both the investigation depth and the horizontal detail, respectively. The resistivity and chargeability data were analysed through different ranges of values to better identify the contribution derived from lithologies, urban services and metallic object. More specifically, the presence of bombs is marked by very low values of resistivity volumes overlapped to very high chargeability volumes. Joining the results, we excluded with certain the presence of bombs and landmines. Thus, focusing on the very detailed results obtained, we can affirm that an optimal configuration of spreads in urban areas could give a very detailed investigation defining the dimensions, the depth and the shape of eventually anomaly bodies, reducing the noise due to the presence of metal artefacts (in this case, railway tracks). Moreover, a joined investigation between resistivity and chargeability values, conducted with the optimal spreads and electrodes spacing, could detect the presence or not of bombs and landmines. References Alile O.M., Aigbogun C.O., Enoma N., Abraham E.M. and Ighodalo J.E.; 2017: 2D and 3D electrical resistivity tomography (ERT) investigation of mineral deposits in Amahor, Edo State, Nigeria. Nigerian Research Journal of Engineering and Environmental Science, 2 , 1, 215-231. Chávez R.E., Cifuentes-Nava G., Hernández-Quintero E. and Vargas D.; 2014: Special 3D electric resistivity tomography (ERT) array applied to detect buried fractures on urban areas: San Antonio Tecómitl, Milpa Alta, México . Geofísica Internacional, 53 , 4, 425-434. Lecocq T. and Camelbeeck T.; 2017: Electrical resistivity tomography data across the Hockai Fault Zone (Ardenne, Belgium) . Data in brief, 11 , 1-4. Metwaly M., El-Qady G., Matsushima J., Szalai S., Al-Arifi N.S.N. and Taha A.; 2008: Contribution of 3-D electrical resistivity tomography for landmines detection . Nonlin. Processes Geophys., 15 , 977–986. Oyeyemi K. D, Aizebeokhai A. P, Adagunodo T. A, Olofinnade O. M, Sanuade O.A. and Olaojo A. A.; 2017: Subsoil characterization using geoelectrical and geotechnical investigations: Implications for foundation studies. International Journal of Civil Engineering and Technology, 8 , 10, 302-341. Petrit K., Klamthim P. and Duerrast H.; 2018: 3D resistivity survey for shallow subsurface fault investigations. E3S Web of Conferences, 34 , 01007. Snyder D.D., Mac Innes S.C., La Brecque D. and Sharpe R.; 2004: Detection of UXO in Underwater Sites Using Towed Array Resistivity/IP Measurements . SERDP Project UX-1325. Final technical report. Rossi M., Dahlin T., Olsson P.I. and Gunther T.; 2018 . Data acquisition, processing and filtering for reliable 3D resistivity and time-domain induced polarisation tomography in an urban area: field example of Vinsta, Stockholm . Near Surface Geophysics, 16 , 220-229. Wynn J.C. and Roberts Will.; 2009 : The application of induced polarization techniques to detect metal-bearing offshore anthropogenic waste and unexploded ordnance. Symposium on the Application of Geophysics to Engineering and Environmental Problems., pp. 1104-1113. DOI: 10.4133/1.3176681.