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Lookup NU author(s): Dr Ross StirlingORCiD, Professor Jonathon Chambers
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This project aimed to demonstrate the value of Electrical Resistivity Tomography (ERT) for remote condition monitoring of earthwork assets in live mainline railway settings. To this end, BGS PRIME ERT monitoring systems were installed on two rail embankments to provide near-real-time information on variations of subsurface moisture conditions over a continuous period of over two years. The outputs of PRIME can be delivered to end-users via a web dashboard to provide engineers with direct access to near-real-time subsurface images, alongside other geotechnical data streams, thereby enabling enhanced decision support. The two test sites are known as Botley and Withy Beds, located in England near Southampton and London respectively. Both are mainline UK railway embankments constructed from London Clay which is known for being highly plastic and prone to deformation. Two types of installation were trialled, a grid of electrodes to monitor a local rotational failure in 3D at Botley, and a line of electrodes to monitor an extended region of embankment in 2D at Withy Beds. The Botley grid covered the full extent of the slip between the shoulder and toe of the embankment, an area of approximately 20 by 30 m. The Withy Beds installation comprised one line of electrodes covering a stretch of embankment approximately 325 m long. The line was not straight as it had to avoid obstacles and was installed in a zig-zag pattern to improve the resolution of local off-line structure. To validate and complement the ERT monitoring outputs, traditional geotechnical monitoring, such as temperature, moisture and suction sensors, were manually installed in both sites. Both field and laboratory testing data can also be used to establish petrophysical relationships between geophysical parameters (e.g., resistivity), and geotechnical characteristics (e.g., moisture content and soil suction). Preliminary analyses revealed strong correlations between ERT-derived soil moisture estimates and traditional geotechnical measurements. At Botley, a distinct low-resistivity layer was identified in the mid-embankment, indicating a high clay content and probable low hydraulic permeability. Time-lapse ERT data collected during periods of heavy rainfall revealed the slope's hydrological dynamics and the significant role of evapotranspiration, influenced by clusters of mature trees (Figure 1). Withy Beds revealed somewhat different behaviour. Previous slip failures had been remediated using sandy material. These sections of the embankment consistently remained drier, even after rainfall, allowing water infiltration into the underlying clay layers, which exhibited higher moisture content and seasonal surface drying. This study offers unprecedented insights into the structure and moisture dynamics of mainline railway embankments through long-term, high-resolution ERT monitoring. The findings demonstrate the potential of ERT as a novel and operationally relevant tool for condition monitoring, providing critical data to support the management of vulnerable railway earthworks affected by complex ground conditions.
Author(s): Maleki ZR, Wilkinson P, Swift R, Dashwood B, Meldrum P, Harrison H, Ngui J, Kuras O, Harms J, Jessamy G, Donohue S, Holmes J, Stirling R, Chambers J
Publication type: Conference Proceedings (inc. Abstract)
Publication status: Published
Conference Name: 7th International Workshop on Geoelectrical Monitoring (GELMON)
Year of Conference: 2025
Pages: 42-43
Acceptance date: 15/11/2024
Publisher: Vienna University of Technology
URL: https://repositum.tuwien.at/bitstream/20.500.12708/216950/1/Jochum-2025-GELMON%202025%20-%207th%20International%20Workshop%20on%20Geoelectrical%20Mon...-vor.pdf
