When a hole in the ground started to appear in a playing field in Buckinghamshire, UK, a rapid assessment of the site and the newly appeared sinkhole was needed.
Geoterra was appointed by the local Parish Council to carry out a 3D laser subsurface scan and video survey, and Managing Director Mark Hudson knew his GeoSLAM device was the only option to quickly and most essentially, the safest way, to find out the size and depth of the sinkhole.
The site had been used to excavate clay for brick making, and when it was decommissioned the area was backfilled with waste, and covered with soil. The land was then turned into a playing field.
The depth of the sinkhole was unknown, but clearly a hazard.
A survey was needed to assess the depth, size and extent of the sinkhole and bell pit. A full geophysical survey of the playing field was also carried out to locate any further sinkholes or old mining features.
The solution
Geoterra used a handheld SLAM device, with a ZEB cam to carry out a surface laser scan. The same device was then lowered down into the centre of the void with access provided by a long reach boom arm from a portable MEWP. Using a bespoke shaft bracket, complete with high powered lighting, the scanner was lowered to a depth of 45m in order to fully survey the sinkhole and bell pit. The survey was geo-referenced to OSGB OSTN15 National Grid.
The deliverables
Geoterra provided the local parish council with a combined geo-referenced 3D laser scan point cloud and HD video of both the surface and void. The laser scans were provided in RCS/RCP & LAS formats for viewing as a 3D model. A mesh model was created and a volume of the void was also calculated. The results from the laser scan survey and geophysics survey were then analysed by consultant engineers to determine the best remediation solution for the sink, and it could be returned as a safe site.
Mark commented “Geoterra are constantly pushing the boundaries and limitations of all of our survey equipment, to push them into areas where others tend not to enter. The sinkhole and deep bell pit in Sappers Field was one those areas where we believed was perfect for our GeoSLAM solutions. Lowering the mobile mapping laser scanner into the centre of the deep abyss revealed a subsurface structure which surprised everybody involved with the project. The GeoSLAM tool was the only way we could safely carry out this laser scan survey and has produced a truly stunning 3D point cloud model, the likes of which we have never seen before”
Find out more about Geoterra here: https://www.geoterra.co.uk/
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