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Lookup NU author(s): Rosa Maleki, Dr Paul Wilkinson, Dr Jessica HolmesORCiD, Dr Ross Stirling, Professor Jonathon Chambers
This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).
This study underscores the need for subsurface imaging and monitoring techniques to offer timelyinformation on railway embankment condition and to contribute to the decision-making processesneeded to minimise the risks of catastrophic slope failure. We investigate electrical resistivitytomography (ERT) as a means of providing railway earthwork asset condition assessmentinformation through the deployment of a bespoke ERT monitoring system (PRIME – the ProactiveInfrastructure Monitoring and Evaluation system), which has been specifically developed forgeotechnical monitoring applications.We focus on two test sites, Botley and Withy Beds, which are situated on mainline railwayembankments in the UK near Southampton and London respectively. Both embankments havelong histories of slope instability and are constructed from London Clay (a high plasticity claywidely associated with ground deformation problems). Long-term ERT monitoring infrastructurehas been deployed across both sites to enable imaging of subsurface heterogeneity and tomonitor subsurface moisture content variations. At Botley a grid of electrodes extending from theembankment shoulder to toe, over an area of ~20 by 30 m, was deployed to enable time-lapse 3Dimaging of a progressive rotational failure at the site, whilst at Withy Beds a line of electrodes wasdeployed along the embankment toe to enable time-lapse 2D imaging for a ~300m length ofsusceptible embankment. Manual geodetic (total station and LiDAR) monitoring of the slopegeometry and electrode positions, and conventional geotechnical monitoring using temperature,soil moisture and matric suction sensors have also been used at the sites to validate the results ofthe ERT monitoring. In additional, laboratory petrophysical testing of samples from the sites hasbeen used to establish relationships between resistivity, moisture content and matric suction.More than three-years of ERT monitoring data have been collected from the sites. Initial analysesof the results have shown strong correlations between the conventional geotechnical monitoringresults and ERT derived estimates of soil moisture. At the site scale, a remarkably clear low-resistivity layer can be seen in the middle embankment segment of Botley, which suggests a highclay content and likely limited hydraulic permeability. The properties of this layer, in conjunctionwith time-lapse ERT observations made during periods of heavy rainfall, have revealed thehydrological functioning of the slope and the strong influence of evapotranspiration associatedwith clusters of mature trees. On the other hand, the Withy Beds embankment shows less intensedrying and wetting patterns, even though noticeable fluctuations in resistivity suggest thepresence of localised zones of moisture build-up. The sandy sections at the Withy Beds site areconsistently dry even after rainfall, which permits water to seep into the clay layer beneath. On theother hand, the clay lands have higher moisture content and exhibit summertime surface drying.In this study we have provided unprecedented insights, in terms of ERT monitoring duration andspatiotemporal resolution, into the structure and moisture dynamics of mainline railwayembankments. ERT has been demonstrated as novel means of providing operationally relevantcondition monitoring information to support the management of vulnerable railway earthworksassociated with complex ground conditions.
Author(s): Maleki ZR, Wilkinson P, Swift R, Meldrum P, Harrison H, Camacho XKC, 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: EGU General Assembly 2024
Year of Conference: 2024
Pages: EGU24-20436
Online publication date: 11/03/2024
Acceptance date: 07/03/2024
Date deposited: 22/05/2024
URL: https://doi.org/10.5194/egusphere-egu24-20436
DOI: 10.5194/egusphere-egu24-20436
