Geology Rocks, but it still has its faults!
Prior to starting a construction and infrastructure project, it can be worthwhile characterising the site’s subsurface as part of a wider geotechnical investigation, to avoid any unexpected problems and associated costs.
This can include anything from the depth of drift cover to bedrock to the extent of sinkhole formation. As a first step, a non-invasive survey can therefore provide invaluable information, prior to intrusive (and expensive) site investigation works involving boreholes and sampling.
SUMO’s engineering geophysics team utilise a combination of the latest survey techniques, including Ground Conductivity, Magnetic Survey, Electrical Resistivity Tomography (ERT) and Ground Penetrating Radar (GPR) to understand more about the natural features below the ground, including:
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Alluvial channels/paleochannels
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Bedrock depth
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Large discontinuities i.e. faults, major joints/fractures
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Mineralised veins
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Mineshafts (in mineralised areas)
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Sinkholes/solution features
Ground Conductivity
Ground conductivity surveys are well suited to some of these applications, notability sinkholes/solution features. The example below shows a solution feature in weathered chalk on the site of a former quarry. The feature has been filled from the ground above, causing the ground to collapse.
Above : Photograph of a solution feature in weathered chalk.
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The Ground Conductivity data collected on site, which is shown as a plan view below, identified a further three anomalies potentially associated with solution features C4, C5 and C6 shown below.
Above : Ground Conductivity data showing potential sinkholes - C4, C5 and C6. Anomaly C1 is likely to be related to a buried metal pipeline. The cluster of three very strong discrete anomalies C2 are associated with the rusting remnants of a scrap car abandoned on the site. C3 is a high value negative conductivity anomaly that is also likely to be associated with a buried metal feature.
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Magnetic Survey
Magnetic Surveys, which are quick and cost effective, are a useful tool for geological applications.
Above : Magnetic Survey data collection. Above Right : Magnetic Survey data showing the underlying dykes and sills of the bedrock geology on a site in Cornwall. This provided a greater understanding of the complex geology of the site.
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Electrical Resistivity Tomography (ERT)
This technique is suited to locating larger features at depth and can penetrate to depths of 20 - 30m.
Above : A Resistivity Imaging section view showing near surface geological faults/fissures penetrating to approximately 9m depth (low resistance in blue) and bedrock (High resistance – brown and red areas) at depths between 2m and 20m.
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Ground Penetratng Radar (GPR)
GPR has the capacity to work through a wide variety of surface materials, from soft landscaping, to hard surfaces such as tarmac and concrete. Ground Penetrating Radar is particularly adept at not only mapping buried features but approximating their depth, which provides an all-important extra level of detail.
Above : A Ground Penetrating Radar (GPR) survey in progress using a dual frequency system consisting of 300MHz and 800MHz antennas.
Above : A GPR Section view showing areas of granite at approximately 2m depth.
With a range of methodologies and techniques penetrating to depths of 30m+, SUMO has a solution to help you understand more about your site’s geology without the need for intrusive investigations.
So, why not contact SUMO, before starting your next construction or infrastructure project and make sure that you take the subsurface features of your site into account at the design stage, and thereby avoid any costly surprises?
Geophysical Engineering Surveys
Air Raid Shelters
Cellars & Basements
Post Tension Cables
Underground Storage Tanks
Air Voids
Chimney Flues
Rebar
Water Engineering
Badger Setts
Earthing Installations
Sinkholes
Burials
Geological Application
Soil Thermal Resistivity Testing
Buried Foundations
Landfills
Structural Investigations
Buried Manholes
Mineshafts
