Non-invasive time-lapse imaging of moisture content changes in earth embankments using electrical resistivity tomography (ERT)

Earth structures, such as embankments, require ongoing monitoring and maintenance to identify potential failure zones and to compensate for the effects of settlement. Extreme weather events leading to prolonged periods of desiccation or saturation are becoming more frequent and threaten embankment stability. In this paper the development of electrical resistivity tomography (ERT) as a non-invasive tool for characterizing and monitoring earth embankments is described. A study is presented in which ERT was applied alongside conventional intrusive techniques to investigate and monitor a section ofVictorian era embankment on the Great Central Railway. ERT electrodes were permanently installed as a series of linear 2D arrays, both parallel and perpendicular to the long-axis of the embankment. The resulting ERT images, when calibrated using intrusive sampling methods, revealed the spatial variability of the embankment soils and were used to identify major discontinuities between material types at locations associated with poor track geometry. Subsequently time-lapse ERT images were used to monitor moisture content changes in the embankment; these images revealed both the spatial extent and magnitude of water content variations, and were used to assess the effect of an exceptionally prolonged and heavy period of rainfall during the summer of 2007