Imaging of Moisture Dynamics within an Operational Railway Cutting – The Effects of Vegetation

The British railway network is one of the busiest in the world. A major part was constructed more than a century ago, prior the advent of modern soil mechanics theories. Today about 50% of the earthworks are in poor or marginal condition. There is a need for cost-effective, remote condition monitoring technology to evaluate their state. A novel Proactive Infrastructure Monitoring and Evaluation (PRIME) system has been developed, which employs electrical resistivity tomography monitoring. We present data obtained from an operational railway cutting over the time of more than one year. At site a now grass-covered relict landslide is in contrast to the otherwise densely vegetated cutting, offering the opportunity to study the effect of vegetation on the shallow moisture dynamics in infrastructure earthworks. Our results show that evapotranspiration and canopy lead to strongly increasing resistivities in summer, indicative for a significant loss in moisture, followed by a fast saturation in winter, when biological activities are at their minimum and no canopy exists. Resistivity, and thus moisture dynamics show significantly higher amplitudes in the vegetated than in the grass-covered part. These insights into the moisture dynamics will aid engineers in designing infrastructure slopes and intervention strategies for unstable slopes.