Introducing G.RE.T.A. – an innovative geo-resistivimeter for long-term monitoring of earthen dams and unstable slopes

Abstract

Nowadays there is an increasing interest in introducing techniques capable of monitoring the internal conditions of embankments and slopes in order to develop early warning alarm systems. Geophysical methods have been widely used in geotechnical risk mitigation studies to evaluate the stability conditions of dams, embankments and slopes. Geophysical methods have the advantage of investigating large volumes of subsurface in a non-invasive manner. Among different geophysical techniques, geo-electrical methods are more frequently used for this purpose.In previous decades, electrical resistivity tomography (ERT) technique has been widely used in a variety of problems such as engineering investigations, groundwater studies, landfill surveys, mineral exploration, glaciological applications, hydrogeological risk mitigation (e.g. landslides), and monitoring of embankments, earthen dams and tailings dams. Commercial resistivity instruments are portable devices which are generally capable of investigating the subsurface down to depths of a few hundred metres with high injected currents. These instruments are not customised for long-term installations in remote places. In this paper, we present the design, installation and testing of a new geo-electrical monitoring system customised for long-term monitoring projects.In the first step, the feasibility of using time-lapse ERT method to study the saturation and de-saturation processes and to monitor anomalous seepage paths in a levee was demonstrated. Then, a long-term geo-electrical monitoring system, G.RE.T.A. (Geo REsistivimeter for Time-lapse Analysis), was designed based on the information obtained in the first step. The G.RE.T.A. system is capable of being programmed remotely and working autonomously In order to monitor anomalous seepages in levee structures that can lead to the levee breach, two installations of G.RE.T.A. have been completed along two river embankments in northern Italy. In order to develop the system to monitor landslides, laboratory studies are in progress to monitor rainfall-triggered landslides. The results have proved the capability of ERT measurements in delineating inhomogeneous infiltration zones during precipitation and detecting weak zones before collapse.

An Iterative 3D Correction plus 2D Inversion Procedure to Remove 3D Effects from 2D ERT Data along Embankments

“…In recent decades, there has been an increasing interest in integrating geophysical monitoring techniques with other technologies to assess the stability of slopes and embankments to mitigate hydrogeological risks [ 1 , 2 ]. Most long-term monitoring systems have been developed using microseismic networks to detect the seismic energy released by unstable slopes [ 3 , 4 , 5 , 6 ] or geoelectrical methods to monitor the hydrogeological conditions of slopes and embankments [ 7 , 8 , 9 , 10 , 11 , 12 , 13 ]. Among different geophysical techniques, electrical resistivity tomography (ERT) method has a long history in solving a variety of engineering, environmental and hydrogeological problems [ 14 , 15 , 16 ].…”

“…This paper specifically addresses ERT monitoring of earthen embankments like river levees, earthen dams, tailings dams and transportation embankments [ 1 , 11 , 12 , 13 , 32 , 39 ]. Two-dimensional ERT monitoring systems can be installed along the main axis of such structures with the aim of providing real-time measurements to highlight the internal heterogeneities of the embankments and, if required, activate early-warning alarm systems to promptly plan mitigation actions.…”

“…I also present two examples from long-term monitoring data measured along a river levee after rainy and dry periods to underline the importance of 3D effects. We have different projects where customized ERT monitoring systems are permanently installed along a river levee or a tailings dam—e.g., [ 13 , 47 , 48 ]. In most projects, the earthen embankment has an approximately homogeneous body and the main inhomogeneity that can be considered for resistivity values is a layered situation due to rainy or dry seasons that result in a decrease or increase in the resistivity values of the superficial part of the embankment.…”

“…Sensors 2024, 24, x FOR PEER REVIEW 2 of 20 risk mitigation strategies, thanks to its potential to monitor changes in water saturation of the subsurface material and to detect seepage zones [30][31][32][33][34][35][36][37][38][39][40][41]. This paper specifically addresses ERT monitoring of earthen embankments like river levees, earthen dams, tailings dams and transportation embankments [1,[11][12][13]32,39]. Two-dimensional ERT monitoring systems can be installed along the main axis of such structures with the aim of providing real-time measurements to highlight the internal heterogeneities of the embankments and, if required, activate early-warning alarm systems to promptly plan mitigation actions.…”