Assessing electrical resistivity tomography (ERT) to detect soil pipes: theoretical modelling and field experiments

Soil erosion research is essential for sustainable development due to its significant impact on soil health through different erosive processes. One of these processes is subsurface erosion by soil piping, which is often overlooked in research. Recently, some progress has been made in detecting surface piping features using UAVs, while the identification of underground pipes remains challenging. Therefore, this study focuses on the innovative geophysical approach in studying subsurface soil erosion. The main aim is to assess the effectiveness of electrical resistivity tomography (ERT) in detecting soil pipes. Field experiments were conducted in the Bieszczady Mountains (Carpathians, SE Poland), alongside theoretical modelling using Resistivity 2D software. The findings were compared with existing research and validated through trenching. We evaluated different measurement settings, including array configurations (Wenner – W, Wenner-Schlumberger – WS and dipole-dipole – DD), electrode spacing, and measurement directions along the pipe system, to assess their effect on detecting pipes regarding their size, shape, and depth. We performed six ERT profiles in the field and we modelled the electrical response of a theoretical void at various subsurface positions, assuming the root-mean-squared error (RMS) of 0% and 5%. The results revealed that higher resistivity anomalies correspond to pipes, with the DD configuration showing lower resistivity (105 Ωm) compared to the W and WS configurations (268–427 Ωm). A comparison with other studies suggests that there is no universal threshold for confirming the presence of soil pipe; rather, a clear electrical contrast with the surrounding area is crucial. Our findings suggest that while all tested configurations effectively detect pipes, the choice of configuration impacts image quality. We recommend using the WS configuration for detecting both vertical and horizontal features. The number of anomalies influences the RMS and should be critically evaluated during surveys. These findings can help researchers and practitioners in designing more effective ERT studies in different environments to detect subsurface soil pipes.

The study is supported by the National Science Centre, Poland within the first author’s project SONATINA 1 (UMO-2017/24/C/ST10/00114).