InSAR for geotechnical infrastructure: enabling stakeholders to remotely assess environmental risk and resilience

The three stakeholders in this project, Transport Northern Ireland (TNI), Northern Ireland Rail (NIR) and the Department of Enterprise, Trade and Investment (DETI) all have one common need which this project addresses. They are required to monitor ground deformations across their geotechnical assets (e.g. embankments, cuttings and earth retaining structures) using the most efficient, cost effective methods, with a view to minimising and managing the geotechnical risk to their businesses and the road/rail users. The objective of the work therefore is to apply the methodologies that the British Geological Survey (BGS) have already developed through past research projects of assessing the deformation of geotechnical infrastructure, such as slope movement or ground subsidence, using Satellite Interferometric Synthetic Aperture Radar (InSAR). The project will validate this methodology through ground truthing, using geotechnical monitoring and high resolution photogrammetry developed by Queen's University Belfast (QUB). Through this project, the stakeholders will be able to monitor ground deformations in a more cost effective, efficient, more thorough and more robust way, and embed the use of this methodology across their organisations making a step change on how they approach assessment and manage the resilience of their geotechnical infrastructure.

TNI anticipate that the use of InSAR data will help form their strategies for monitoring their geotechnical assets and will feed into the existing GIS based risk assessment methods for their infrastructure assets. The site at Straidkilly is only one of many sections along the A2 coast road that is unstable and it is hoped that InSAR will give a much greater insight into the behaviour of a variety of geohazards that impact on the road and will inform their maintenance strategies and lead to more cost effective better targeted maintenance. TNI also are committed to having a better understanding of the mechanisms of failure on the slow moving failures on the Throne Bend in Belfast. The InSAR data will allow a much better correlation between slope movement and rainfall intensity and duration to be undertaken. InSAR data will also allow better mapping of the extent and magnitude of the instability.
NIR also hope to be able to correlate the slope instability against rainfall data on the Belfast-Bangor rail line. DETI anticipate that the project will validate new methods of monitoring and provide baseline data of ground motion to form the basis of future strategic decisions in regards to geohazards. The use of InSAR at sites in Carrickfergus will potentially provide greater knowledge of extent of subsidence boundaries and provide indicators to potential catastrophic collapse by analysing SAR data against periods of known rapid collapse of ground.

Keywords: geotechnical infrastructure, subsidence, slope instability, remote sensing, radar interferometry (InSAR), ground motion monitoring

TNI: The expected outcomes are an enhanced capability to monitor and assess landslide hazards across the whole 21,000km of road network by investing in this 'leapfrog' technology, moving from a traditional on site visual assessment, to state of the art, remote sensed, regional scale hazard mapping using InSAR technology. This will see huge benefits across TNI in mapping and understanding geo-hazards. Having a better understanding of the mechanisms and extend of soil movement also allows belter informed engineered remediation techniques to be considered. This also has the impact on the organisation of being able to target their limited resources at sites assessed at being at high risk.
NIR: In addition to similar benefits and impacts to TNI, an added value to NIR is the reduced requirement to have staff on active rail tracks inspecting geo-hazards.
DETI: New innovative monitoring technologies will complement past and current data in determining the risk associated with mine subsidence and the economic impact of infrastructure deformation. The InSAR technology offers the benefit of greater consistency and accuracy of ground motions with the capability of narrowing measurement intervals during periods of increased concern. The added benefit of this platform is it also provides remote monitoring methods reducing the risk to personal that previously monitored movement from within sites. The benefit of more accurate data will improve information delivered to stakeholders in the Planning Service, local Councils and Government agencies resulting in better regulation and information for decision making process. The project will also enhance and develop the relationship between DETI and scientific research in using innovative approaches in assessing risk associated with geological hazards.
The outcomes for DETI are opportunities to provide the greater capability to assess and communicate the risk posed by ground subsidence and support the planning process in determining 0m lines of subsidence with greater accuracy. This is crucial at Carrickfergus, an area of growing residential and commercial development which borders and encroaches many of the mine sites under review. This immediate outcome will form the basis of risk assessments and feed into the planning process with the anticipation of continuation of same technology for future monitoring. The main beneficiaries from the project outputs and increased knowledge with the planning authorities and the general public with increased knowledge and understanding of risk associated with ground motion.