The use of near-surface geophysics for monitoring slopes that affect transport infrastructure

Abstract

Landslides on transportation networks are becoming increasingly prevalent in response to environmental change, at the same time as demand placed on road and rail infrastructure is growing in line with population growth and economic development. 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 remote-condition-monitoring systems to reveal processes that are precursors to slope failure. Here, the application of a novel electrical resistivity tomography (ERT) system (Proactive infrastructure Monitoring and Evaluation (PRIME)) for monitoring unstable slopes that affect transport infrastructure is examined. The system provides near-real-time data collection via a telemetric link. 4-Dimensional resistivity models (3-D with a time-lapse element) are presented in the context of moisture content and soil suction, two parameters known to influence slope stability. Building upon relationships evident in the field, the development of laboratory-based petrophysical relationships that relate electrical resistivity to moisture content and soil suction directly is also discussed. 4-D ERT models were calibrated using these petrophysical relationships to provide insights into complex spatial and temporal variations in moisture content and soil suction.

Two study areas are considered here, enabling different controls on electrical resistivity to be examined. The Ripley Landslide in the Thompson River Valley, British Columbia, Canada, threatens the serviceability of two national railway lines. Here, 4-D ERT models reveal complex hydrogeological pathways, providing new insights into the subsurface processes in an active, natural landslide. Freeze-thaw cycles also impact the subsurface resistivity here, which highlights the need to consider the impact of temperature when inferring changes in moisture content from ERT data. The Old Dalby Railway Cutting in Leicestershire, United Kingdom, is also considered in this thesis. Subsurface changes in resistivity at this site across both wooded and grassed areas of the slope enable an improved understanding of hydrogeological pathways and allow examination of the use of ERT for assessing the influence of vegetation on subsurface moisture pathways and on slope stability. This thesis highlights the utility of geoelectrical monitoring for assessing slope stability in the context of moisture-driven landslides. It aims to emphasise the benefits of 4-D geoelectrical monitoring and points towards the future incorporation of ERT monitoring in integrated decision support and early warning condition monitoring systems.

Thesis embargoed until 31 December 2024.

Date of Award	Dec 2021
Original language	English
Awarding Institution	Queen's University Belfast
Sponsors	Northern Ireland Department for the Economy & British Geological Survey
Supervisor	Vinayagamoothy Sivakumar (Supervisor), Shane Donohue (Supervisor) & Jonathan Chambers (Supervisor)