Volumetric Monitoring of Dynamic Moisture Distribution in an Aged Railway Embankment

The condition of aged embankments relates to the engineering geological properties of the source materials, the internal heterogeneity produced during construction and how these factors have affected long term processes leading to deterioration in integrity and performance. Remotely operated, automated monitoring systems providing non-invasive geophysical measurements provide insight into the processes driving long term deterioration compromising stability, such as dynamic moisture movement throughout embankments. Automated time Lapse Electrical Resistivity Tomography (ALERT) technology provides high resolution information relating to the internal structure of an embankment. The dynamic moisture distribution throughout the embankment can be interpreted from a series of time lapse, differential resistivity images based upon robust resistivity-moisture content relationships. A 3D ALERT system was installed to monitor moisture movement within a 22 m section of embankment operated by the Great Central Railway (Nottingham) Ltd. This included: 12 cables of 31 m length laid from toe to toe, across the transect of the embankment, spaced at 2 m, each comprising 32 electrodes with a 1 m spacing. This paper presents baseline 2D and 3D images of the resistivity distribution within a section of the embankment that will be used to assess the impact of vegetation and drainage characteristics upon moisture movement.