GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 ___ GNGTS 2023 VMD -1.5 HMD -1.5 VMD -2.5 HMD -2.5 VMD -4.5 HMD -4.5 VMD&H MD CMD measured 2.39 9 6.51 3 3.62 3 2.69 0 3.12 2 1.67 0 3.336 CMD calibrated 1.34 9 1.85 9 1.06 0 1.69 6 1.33 7 1.66 3 1.494 DUALEM-642 performed a better solution than CMD-Explorer. This related to the greater depths of investigation, which allowed us to identify substantial discontinuity related to sand intrusions. Before the calibration, results show, compared to the considered true or accurate conductivity: more conductive measurements for the DUALEM HCP and PRP modes, more resistive values for the VMD mode from CMD-Explorer; and more conductive measurements from the HMD of the CMD-Explorer 4. CONCLUSION Our experiment on levees context in the presence of sand intrusions revealed the importance of calibrating measurements from different EM instruments in order to obtain absolute values of electrical resistivity. Integration of different geophysical methods is essential to obtain a satisfactory model. Geophysical surveys represented by ERT and EM methods have proved to be fast, accurate, and useful in identifying and mitigating levee failures. EM measurements from different instrumentation and depth of investigation showed excellent results in shallow detail for the CMD-Explorer, and in greater depth, for the DUALEM-642. Comparing the calculated and measured EM curves, the use of shift values allowed us to calibrate the data. The shift values obtained can be used in future acquisitions over larger areas close to the test area where geotechnical and ERT data are unavailable. Acknowledgments This research was partially funded by Ministero dell'Ambiente e della Tutela del Territorio e del Mare, Italy, project DILEMMA – Imaging, Modeling, Monitoring and Design of Earthen Levees (2018-2020). REFERENCES Cosenza, P., Marmet, E., Rejiba, F., Cui, Y. J., Tabbagh, A., & Charlery, Y.; 2006: Correlations between geotechnical and electrical data: A case study at Garchy in France . Journal of Applied Geophysics, 60(3-4), 165-178. DUALEM;2008: DUALEM ‐421s User's Manual . Milton, Ontario, Canada: DUALEM Inc.