What does the slope monitoring toolbox look like in 2025?
Reflections on recent case histories on transport corridors in New Zealand and Victoria
David Stewart and Simon Harbig
The options for slope monitoring continue to expand with advances in technology. The plethora of monitoring options and the large amount of data that can be generated are both an opportunity and a risk. The concept of a toolbox of methods is a useful one – the methods are tools to assist geoprofessionals to understand the behaviour of slopes, so that they can assess risks and present sound risk mitigation options / recommendations. Also, the challenge is to choose the right tools for the job, based on the understanding of expected and potential failure mechanisms. The use of UAVs has been a gamechanger in being able to both safely inspect and survey landslides. Installed instruments such as tilt sensors, extensometers, GNSS/GPS, rain gauges and CCTV cameras, as well as remote techniques from various types of spatial scanning, provide data on water content and deformation that can inform decisions on risk and the resultant actions. Trigger Action Response Plans (TARPs) are used to facilitate the decision process. This paper provides examples from monitoring of slope movements related to transport corridors in Victoria and New Zealand. Covered are the Bogong landslide which closed access to the Falls Creek Alpine Resort in Victoria, landslides threatening the North Island Main Trunk railway north of Wellington (Kapiti slope) and a rural road in the Wairarapa (Hinekura Road) and repeat multiple slope failures affecting SH1 road access to Northland, NZ (Mangamuka Gorge and Brynderwyns sites). A trial of InSAR for deformation of Northland roads is also presented. Examples of what went well and what didn’t are discussed to assist others with similar challenges. The importance of using multiple methods and having well trained staff involved in the choice of tools and data review is stressed.
About the speakers
David Stewart Technical Principal – Geotechnical. WSP, Wellington
David is a Technical Principal – Geotechnical, at WSP in Wellington, New Zealand, with over 35 years geotechnical experience. After completing an MSc in Engineering Geology from Canterbury University he had an OE in the UK which included experience working in geotechnical monitoring in the portal areas of the Channel Tunnel. The call for engineering geologists to work on the Cromwell Gorge landslide project (prior to filling of the Clyde Dam) brought him back to New Zealand in 1990, followed by work as an engineering geologist for GNS Science in Dunedin and then at the nearby Macraes open pit gold mine. When geology opportunities were scarce in the late 90s he obtained a Civil Engineering degree and he has been based in Wellington since 2002, mainly with Opus (now WSP).
David works across both engineering geology and geotechnical engineering disciplines and specialises mainly in risk management (including risk assessment and risk mitigation) related to slopes and occasionally tunnels, as well as site investigations. Most of his work relates to road and rail transport corridors. He is a keen advocate of technologies such as drones and remote monitoring to enhance our understanding of the behaviour of slopes. As part of this David has been a UAV (drone) pilot with WSP since 2014; and was the main author of an article in the 2018 ‘Digital Geotechnics’ special edition of the Australian Geomechanics journal (Vol. 53, No. 3) highlighting the use of UAVs and related digital data in geotechnical and natural hazard impact assessments.
The current presentation is based on the recently published follow-up article in the 2025 ‘Digital Geotechnics 2.0’ special edition of the Australian Geomechanics Journal (Vol. 60, No. 2) and available here; https://australiangeomechanics.org/papers/what-does-the-slope-monitoring-toolbox-look-like-in-2025/
Simon Harbig Associate Engineering Geologist. WSP, Melbourne
Simon is an Associate Engineering Geologist at WSP in Melbourne and has worked in the field for close to 10 years. Simon studied undergraduate engineering and geology at Monash University and has completed a UNSW Masters in geotechnical engineering and engineering geology. Simon works across both engineering geology and geotechnical engineering in Melbourne with a focus on field and digital geological modelling and landslide risk assessment.
During 2023 and 2024 Simon was heavily involved in the Bogong High Plains Road Landslip project, implementing and developing the onsite slope monitoring and trigger action response plan (TARP) for the project.
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