4D electrical resistivity tomography for assessing the influence of vegetation and subsurface moisture on railway cutting condition

Instability of slopes, embankments, and cuttings on the railway network is increasingly prevalent globally. Monitoring vulnerable infrastructure aids in geotechnical asset management, and improvements to transport safety and efficiency. Here, we examine the use of a novel, near-real-time Electrical Resistivity Tomography (ERT) monitoring system for assessing the stability of a railway cutting in Leicestershire, United Kingdom. In 2015, an ERT monitoring system was installed across a relict landslide (grassed) and an area of more stable ground on either side (wooded), to monitor changes in electrical resistivity through time and space, and to assess the influence of different types of vegetation on the stability of transportation infrastructure. Two years of 4-Dimensional ERT monitoring results are presented here, and petrophysical relationships developed in the laboratory are applied to calibrate the resistivity models in order to provide an insight into hydrogeological pathways within a railway cutting. The influence of vegetation type on subsurface moisture pathways and on slope stability is also assessed – here we find that seasonal subsurface changes in moisture content and soil suction are exacerbated by the presence of trees (wooded area). This results in shrink-swell behaviour of the clays comprising the railway cutting, resulting in fissuring and a reduction in shear strength, leading to instability. As such, it is proposed that on slopes comprised of expansive soils, grassed slopes are beneficial for stability. Insights into the use of 4-D ERT for monitoring railway infrastructure gained from this study may be applied to the monitoring of critical geotechnical assets elsewhere

Application of petrophysical relationships to electrical resistivity models for assessing the stability of a landslide in British Columbia, Canada

Landslides in the Thompson River Valley, British Columbia, Canada, threaten the serviceability of two railway lines that connect Vancouver to the rest of Canada and the US. To minimise the impact of slope instability on vital transport infrastructure, as well as on terrestrial and aquatic ecosystems, public safety, communities, local heritage, and the economy, and to better inform decision making, there is a need for monitoring. Since 2013, the Ripley Landslide – a small, slow-moving, translational landslide – has been the focus of monitoring efforts in the Thompson River Valley transportation corridor. In November 2017, a novel Electrical Resistivity Tomography (ERT) monitoring system was installed on the site, providing near-real-time data collection via a telemetric link. 4-Dimensional resistivity models are presented in the context of moisture content and soil suction, two parameters known to influence slope stability in the Thompson River Valley. Here, we discuss the development of laboratory-based petrophysical relationships that relate electrical resistivity to moisture content and soil suction directly, building on relationships developed in the field. The 4-D ERT models were calibrated using these petrophysical relationships to provide insights into the complex spatial and temporal variations in moisture content and soil suction. This study highlights the utility of geoelectrical monitoring for assessing slope stability in the context of moisture-driven landslides