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TerraDat is a UK based specialist geophysical ground exploration company that operates worldwide. Geophysical surveys provides a rapid, non-invasive ground investigation tool that has many applications ranging from locating buried manmade structures through to characterising geological and hydrogeological features. This TerraDat Technical Note deals with how geophysics can benefit ground engineering problems encountered when planning or constructing pipeline and cable routes. A particular application is river crossings
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Geophysics for Pipelines and Cable RoutesP
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Pipelines and cable routes present a set of unique developmental and geotechnical challenges. TerraDat has designed an integrated geophysical survey approach, providing data that is useful to all stages of a project.
Archaeological assessments and UXO detection; Due to the large distances covered by pipelines and cable routes, the chance of encountering archaeological features is high. in order to mitigate this, TerraDat use a 4m wide magnetometry rig towed behind a 4x4 vehicle or ATV, this system provides corridors of archeological geophysical; data that can be interpreted by our in-house archaeologist to provide detailed maps of archaeological remains along the proposed route. Using this system up to 50km per day of pipeline can be surveyed, depending on site conditions. This system will also detect shallow ferrous metallic items, useful in areas where UXO is of concern
Bedrock profiling and geological structure surveys; Resistivity tomography surveys effectively map buried geological structures. This technique can be adapted to gather data for a range of depths and profile lengths. Measuring the electrical properties of the subsurface enables identification of structures such as bedrock variation, fault zones and weathered / clay-rich layers. The models can be calibrated with the help of physical observation of direct samples. Seismic surveys provide information on the depth and strength (rippability) of underlying ground materials. Seismic data can be acquired using surface-based P and S-wave refraction and /or MASW techniques. On sites with limited survey area or variable geology, seismic data can be obtained via boreholes. By combining the derived seismic P and S-wave velocities with density information, it is possible to calculate Poisson’s Ratio along with a range of elastic moduli (Shear, Young’s and Bulk).
River crossings; Seismic refraction and resistivity tomography surveys provide detailed cross sections along the routes of proposed pipelines or cables. These can be of particular benefit in areas where the opportunity for intrusive investigations are limited, such as river road or railway crossings, or in environmentally sensitive areas where the presence of a drill rig may be prohibited.
Soil Resistivity/Corrosistivity Testing; Resistivity tomography surveys are used to provide information on the shallow geology and soil electrical properties for earthing design. This approach is more accurate than the traditional 4-pin method as it is possible to derive more reliable resistivity values. Thermal properties of the soil can be analysed by using a thermal resistivity meter to acquire data either at surface, or within trial pits.
Archaeological Surveys
Rock Head Detection Surveys
TechnicalNote
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TerraDat (UK) Ltd - Tel (08707 303050)www.terradat.co.uk
Resistivity tomography Section
UXO survey plan
Existing buriedservice
Magnetic anomalies- possible UXO
General scatter of smallmagnetic anomalies
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Upper resistive layer Conductive clay-rich layer
Resistive Siltstonestrata
Lower resistive Siltstone Layer
Localised conductive bedrock feature - fracture zone
Seismic refraction profile over a river valley
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Geotechnical information
Earthing Measurements
Unexploded Ordnance Detection,
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Archaeological survey data and interpretive CAD drawing
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Contact Simon Hughes for more info; [email protected]
