Response to soil compaction of the electrical resistivity tomography, induced polarisation, and electromagnetic induction methods: a case study in Belgium

Context Soil compaction acts at different scales and is challenging to measure on field scales.Aims To evaluate soil compaction under a controlled traffic experiment, using three different geophysical methods.Methods Electrical Resistivity Tomography (ERT), Electromagnetic Induction (EMI), and Induced Polarisation (IP) were selected to map soil compaction. Two different ERT arrays and EMI geometries were selected with different spacings. The influences of configuration, electrode spacing, and the Depth of Investigation Index (DOI) were evaluated. Soil physical properties were measured in the Laboratory and in the field. Error models were developed to assess the accuracy of the ERT profiles and later correlated with EMI and soil physical results.Key results Penetration resistance measurements identified a compacted layer at 25 to 35 cm depth with a maximum value of 5 MPa under fixed tracks and bulk density of 1.52 Mg m-3, while lowest values were 1.4 MPa and 1.36 Mg m-3. The dipole-dipole (DD) 10 cm array was more accurate towards both soil properties and locating the zones of high resistivity. The IP method identified chargeability anomalies at the same depth as the resistivity anomalies, possibly indicating a similar origin. The EMI test was less successful in accurately determining the locations of the conductive areas.Conclusions A clear relationship between the absolute value of the resistivity/conductivity signals with the level of compaction was not found, yet patterns of lateral variations in resistivity were identified.Implications Further studies are needed to establish the concrete relationship between soil compaction and geophysical signals. Soil compaction was studied in this research using three different geophysical tools. We created a controlled traffic farm in Belgium that contains different zones of soil compaction and used geo-electrical methods to find out whether soil compaction can be accurately estimated using geophysics. Laboratory data were also assessed complementary to the geophysical data. We found resistivity variations and realised that soil compaction does indeed affect geophysical signals, yet a straightforward relationship is yet to be found.