Geometrical characterization of urban fill by integrating the multi‐receiver electromagnetic induction method and electrical resistivity tomography: A case study in Poitiers, France

Abstract

A geophysical survey including electromagnetic induction (EMI) and electrical resistivity tomography (ERT) methods was applied and assessed with a 40‐trench sampling grid to delineate the geometry of an urban fill layer. Classical investigation techniques, such as excavation, offer localized information and suffer from time and budget constraints for environmental assessments. Near‐surface geophysics can provide the required spatial sampling to evaluate the coverage of anthropogenic soils in a time‐effective and quasi‐continuous manner. Fast‐acquisition and high‐spatial‐coverage EMI mapping and high‐vertical‐resolution ERT were implemented to delineate a suspicious urban fill on a 5‐ha site in a suburban region, which will host the buildings of a commercial complex. The ERT data and 40 trench excavations revealed an urban fill thickness ranging from 0.4 to 3.6 m overlying a calcareous substratum. After ERT–EMI calibration, a two‐layer model was introduced into the one‐dimensional (1‐D) inversion of the EMI data for estimating the geometry of the urban fill layer across the study site. The EMI 1‐D inversion results indicated that the predicted urban fill thicknesses were consistent with 70% of the measured values (27 out of 40 excavation sites). Resistive ground, large 3‐D structures and the heterogeneity of urban fill affected the EMI and ERT measurements and increased the difficulty of estimating its spatial distribution. In this paper, we present a measurement protocol that can guide land‐use development and be reproduced to investigate brownfield sites. Highlights Urban soils are poorly characterized by localized investigations for environmental assessments. Spatial EMI data from an urban fill context were calibrated by ERT for thickness inversion. The ERT–EMI inversion reconstructed the urban fill thickness for 70% of the excavation points. Geophysical techniques can reduce uncertainties for site rehabilitation and land‐use development.

Toward high‐resolution agronomic soil information and management zones delineated by ground‐based electromagnetic induction and aerial drone data

“…(2019) turn the sled‐based EC a to handle‐based values. When the data need to be quantitative for reliable inversion results to compute a subsurface model with layer/horizon depths, this can be obtained when calibrating the EC a against independent geoelectrical data (Binley et al., 2015; Cavalcante Fraga, Schamper, Noël, Guérin, & Rejiba, 2019; Heil & Schmidhalter, 2019; Lavoué et al., 2010; Mester, van der Kruk, Zimmermann, & Vereecken, 2011; von Hebel et al., 2014; Whalley et al., 2017) or when using an EMI system‐based numerical calibration procedure (Hunkeler, Hendricks, Hoppmann, Paul, & Gerdes, 2015; Minsley, Kass, Hodges, & Smith, 2014; Tan et al., 2018).…”

Calibration, Conversion, and Quantitative Multi-Layer Inversion of Multi-Coil Rigid-Boom Electromagnetic Induction Data

“…For the linear regression between predicted and measured σ a , the obtained rectangular ERT part was re-gridded to the positions of the EMI data, with a regular spacing of 0.5 m. This resulted in 41 vertical σ profiles with layer thickness increments between 3 and 25 cm increasing from surface up to 2.12 m depth. We inserted the layered subsurface models extracted at the collocated ERT and EMI positions [42], as well as the σ distribution obtained with the VES inversion into the Maxwell-based EMI forward model (Equations (5) and (6)) to obtain Q, which was converted into σ a using the EEC approach.…”

“…Also, a linear regression between independently obtained σ a values and those measured with the EMI system can be used by taking pointwise information of σ depth profiles along extracted soil cores [40] or by predicitng σ a values based on direct current ERT data [41]. This ERT-based calibration approach has successfully corrected σ a values measured with EMI and resulted in reliable inversion results in a range of studies [12,24,33,41,42,43,44,45]. Nevertheless, the calibration of σ a measured with EMI using direct current methods can be seen critically.…”

The role of electromagnetic induction in development planning: the case of the Grands Philambins enigma

“…(2008), and for brownfields in Cavalcante Fraga et al . (2019) and Guérin et al . (2004), for example.…”