GNGTS 2019 - Atti del 38° Convegno Nazionale

GNGTS 2019 S essione 3.2 721 period (Fig. 3a, 1April – 1 June 2019). Making the difference between data after (Fig. 3c) and before the event (Fig. 3b), the response to rainfall of the different parts of the embankment can be described (Fig. 3d). Both datasets have the same depth of burial of electrodes and the same 3D effects, since water is far from the structure in both cases, so to underline the difference we could individually invert the pseudosections and then subtract them without correcting for 3D effects. As can be seen, the variation in resistivity is not constant along the levee segment: the old part (lateral parts of the section) have a strong decrease in resistivity, due to higher permeability, while the re-built part (centre) has lower decrease due to less infiltration. Conclusions. We discussed the efficiency of long-term ERT monitoring systems to study the internal condition river levees. The first step is always the knowledge of the territory, thanks to the dialogue with managing authorities, such as Consorzi di Bonifica. Once having acquired a list of priority sites, geophysical methods, in this case ERT, used to assess the inner condition of critical sites and to select the high-risk one. Not only the condition of the structure, but also the exposure of the surrounding areas has to be considered to plan an installation of a long- term monitoring system. The real-time monitoring of the levee is useful to know the change of characteristics of the embankment soil, the communication part in the monitoring is thus really important. For the G.Re.T.A. monitoring device, a cloud base system is provided in order to remotely take under control the situation. It automatic data inversion and automatic control on crossing of thresholds. The Colorno study case is reported as a best practice example, with the description of the device, the installation and the data processing. 3D effects on resistivity data were studied with 3D and 2D forward modelling to remove the influence of geometry, not homogenous structure and boundary conditions. With time-lapse data analysis, since the boundary conditions in the study site are constant, data can be inverted without correction and variations in soil properties can be observed. An example of differential infiltration in the structure during a rainy period is reported. Acknowledgments. The research was partially funded by Ministero dell’Ambiente e della Tutela del Territorio e del Mare, grant DILEMMA. The authors want to thank Stefania Gherbi for 2D and 3D modelling; Consorzio di Bonifica Terre dei Gonzaga in Destra Po, Consorzio di Bonifica Est Ticino Villoresi and AIPO for the collaboration. The monitoring system has been developed with the technical support of LSI-Lastem. References Arosio D., Munda S., Tresoldi G., Papini M., Longoni L. and Zanzi L.; 2017: A customized resistivity system for monitoring saturation and seepage in earthen levees: installation and validation . Open Geosci., 9 , 457-467. Dahlin T., Johansson S., Sjödahl P. and Loke M. H.; 2008: Resistivity monitoring for leakage and internal erosion detection at Hällby embankment dam . J. of Appl. Geophys., 65 (3), 155-164. Hojat A., Arosio D., Ivanov V.I., Longoni L., Papini M., Scaioni M., Tresoldi G. and Zanzi L.; 2019a: Geoelectrical characterization and monitoring of slopes on a rainfall-triggered landslide simulator . J. of Appl. Geophys. https://doi.org/10.1016/j.jappgeo.2019.103844 Hojat A., Arosio D., Longoni L., Papini M., Tresoldi G. and Zanzi L.; 2019b: Installation and validation of a customized resistivity system for permanent monitoring of a river embankment . EAGE-GSM 2 nd Asia Pacific Meeting on Near Surface Geoscience & Engineering, Kuala Lumpur, Malaysia, https://doi.org 10.3997/2214- 4609.201900421. Jomard H., Lebourg T., Guglielmi Y. and Tric E.; 2010: E lectrical imaging of sliding geometry and fluids associated with a deep seated landslide (La Clapière, France) . Earth Surf. Process. Landforms, 35 , 588–599. Kuras O., Pritchard J. D., Meldrum P. I., Chambers J. E., Wilkinson P. B., Ogilvy R. D. and Wealthall G. P.; 2009: Monitoring hydraulic processes with automated time-lapse electrical resistivity tomography (ALERT) . Comptes Rendus Geosci., 341 , 10, 868-885. Loke M.H.; 2014: RES3DMODx64 ver. 3.04: 3-D resistivity and IP forward modeling using the finite-difference and finite-element methods . Geotomosoft Solutions. Loke M.H.; 2016: RES2DMOD ver. 3.03: Rapid 2D resistivity and I.P. forward modeling using the finite-difference and finite-element methods . Geotomosoft Solutions. Loke M.H.; 2018: Rapid 2-D Resistivity and IP inversion using the least-squares method. www.geotomosoft.com Loperte A., Soldovieri F., Palombo A., Santini F. and Lapenna V.; 2016: An integrated geophysical approach for water infiltration detection and characterization at Monte Cotugno rock-fill dam (southern Italy) . Eng. Geo., 211 , 162–170.