Geospatial data used to identify geohazards for site investigations – Ground Engineering

10 October, 2023 By Nia Kajastie
Consultant Card Geotechnics (CGL) has applied aerial laser surveying to pinpoint natural hazards on development sites across the UK.
CGL is using geospatial data from aerial survey and geographic data company Bluesky. The data has formed part of the investigation stage on projects ranging from proposed residential developments to long, linear overhead powerlines.
High-resolution aerial photography, specialist imagery and lidar terrain maps provided by Bluesky have been used to identify areas of high geological hazards and associated risks. These include sinkholes in chalk and other soluble rocks, saturated soft ground and peat deposits presenting compression hazards, and areas with slope instability and landslides.
The data has helped CGL to provide an initial interpretive scan of a site to assess and target more intrusive surveys for additional investigation and detailed design.
CGL technical director David Giles said: “The UK has many diverse landscapes with a wide spectrum of geological hazards, each of which can present challenges for development.
“Using geospatial data from Bluesky we have developed a digital imagery consultancy provision to offer the visualisation, analysis and interpretation of data for site investigations.”
The consultancy has used the data, for example, in the identification of natural and anthropogenic hazards associated with chalk bedrock, which is highly susceptible to dissolution. It is widely found across northern, central and southern England.
This dissolution makes the development and presence of karstic topography, characterised by underground drainage systems including sinkholes and caves, a widespread occurrence. The features are hazardous because they provide possible pathways to the underlying aquifer and therefore demonstrate potential site-specific contamination, as well as posing significant risks to housing and commercial development. Many areas of the chalk bedrock have also been historically mined leaving a legacy of ground subsidence that can be identified on the digital imagery.
The Bluesky data used by CGL includes traditional aerial photographs, which, when combined with simultaneously captured near infrared (NIR) wavelength data, can be used to produce colour infrared (CIR) images. CIR photography can be used to assess the health of vegetation, as healthy plants reflect more of the NIR wavelength and therefore appear brighter in the image. It can also be used as a tool to evaluate water quality, as water absorbs the NIR wavelength while sediment and suspended particle reflect it.
“The Bluesky images can be processed to enable classification and effective broad-scale mapping of different ground surface conditions allowing us to differentiate between rock and soil types, thick peat cover, water bodies and water courses as well as vegetation cover,” Giles added.
CGL is also using Bluesky’s lidar data, which is processed to produce both digital surface models that include vegetation cover and digital terrain models, also known as bare earth models. Lidar can assist with various aspects of site assessment, including flood hazard, geomorphological assessment and geological hazard identification.
“Lidar models provide a highly accurate yet low-cost first development site scan which can identify construction and development risks at an early stage in the investment process,” said Giles. “Ground related issues can be interpreted from the imagery, delineating hazards that may not be possible to see or detect at the ground surface.”
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Tagged with: Bluesky CGL data digital imagery geospatial lidar site investigation
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