DC-Electrical Resistivity Imaging for embankment dike investigation: A 3D extended normalisation approach

Abstract

Levee, dike and earth embankment dam structures are difficult to assess because of their length and complexity. Managers often include geophysical investigations in the overall dike condition assessment and the DC-Electrical Resistivity Imaging (ERI) method is particularly applicable owing to its costeffectiveness and its potential sensitivity to internal erosion. However, due to the truly 3D nature of embankment dikes, implementing inline longitudinal tomographies along with conventional 2D inversion is likely to yield image artifacts. 3D effects from external causes (geometry, water reservoir) can be predicted and therefore we present a new approach based on redefining the normalisation principle to derive apparent resistivities from the measured data. The aim is to provide a set of pre-processed apparent resistivities that are not contaminated by external 3D effects and that yield more reliable results when processed within a 2D conventional inversion scheme. The presented approach is successfully applied to synthetic and real data sets, proving superior to the conventional 2D approach, although data acquisition

A cost‐effective 3D electrical resistivity imaging approach applied to dike investigation

“…In this paper, we were particularly interested in the integration of the presence of the river. As noted previously, even with low resistivity contrast, it is always necessary to take into account a volume more or less conductive, whether solid or liquid, outside the studied object but in electrical continuity with it (Fargier et al ). Note that the variability of resistivity within the water volume is not considered here, although its implementation in the forward problem is possible.…”

“…On one hand, their inner structure may exhibit strong longitudinal and transverse variability (e.g., presence of a clay core or repaired zones). On the other hand, embankment topography and high water‐level fluctuations adjacent to the dike have 3D effects on the resistivity measurements leading to image artefacts (Hennig, Weller, and Canh ; Sjödahl, Dahlin, and Zhou ; Oh ; Fargier et al ; Cho et al ). In order to account for the full 3D attributes of the problem, one would normally recommend the use of a complete 3D ERI procedure (e.g., Chambers et al ).…”

3D assessment of an underground mine pillar by combination of photogrammetric and geoelectric methods

“…Results in this paper imply that for the common practice of performing a DTM, one has to take particular care during a geophysical survey. For the example of volcano surveys (Finizola et al, 2002;Brothelande et al, 2014Brothelande et al, , 2015, or engineering applications (hydraulic structures [Fargier et al, 2014]), the desired ERI resolution is often weaker than the DTM variations between two adjacent electrodes. In this case, our experience shows that the use of a very accurate surface description must become of major importance when the variation between interelectrode spacing and surface electrode spacing (at the same scale) is greater than 30%.…”

“…However, conventional 2D and 3D imaging techniques are mainly applied to flat surface surveys (Dahlin, 1996) or to surfaces with moderate topography (Fox et al, 1980;Günther et al, 2006;Erdoğan et al, 2008;Demirci et al, 2012;Fargier et al, 2014). Interesting results can be obtained using a 3D forward model (using a complex geometry) and performing a 2D inversion (Lesparre et al, 2014).…”

Reservoir assessment using non-invasive geophysical techniques

“…An examination of the literature discussing geophysical techniques applied to surveying flood embankments have shown the use of electrical resistivity tomography (ERT) to be common, due in part to the suitability of the construction materials (normally compacted, fine grained soils) and its sensitivity to changes in moisture as well as its ability to detect discontinuities in the material (Fargier et al 2014;Seokhoon 2012). ERT has been found as a good nondestructive technique, which gave the possibility of detecting internal erosion processes and to detect anomalous seepage (Sjödahl et al 2006(Sjödahl et al , 2010Cho and Yeom 2007;Lin et al 2014), at an early stage before the stability of the dam was compromised.…”