GeoDefinition Limited

Near surface geophysics and specialist surveying


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Electrical Resististivity Tomography (ERT)

A very versatile method for producing images that represent a 2 dimensional slice into the ground.  A line of electrodes are used to inject small electrical currents into the ground and the measured currents are used to calculate apparent resistivity.  If required, multiple images can be assembled into a 3 dimensional model.  A powerful method for a wide range of investigations into ground conditions from natural geology to tunnels and voids.

Induced Polarisation

A specialist method that can also be undertaken by the FlashRes system as an add-on to an ERT survey.  Essentially this is an electrical method that measures the extent to which ground holds onto electrical charge.  It is primarily sensitive to clays and sulphides.  Useful for mineral exploration, hydrogeology, contamination studies and the study of graves.

Rapid migration pathway for water via a natural fault.  This data was collected using a FlashRes 64 system with an electrode spacing of 2 metres.

A buried animal carcass at a depth of about 1.5 metres below ground level.

The data was collected using a FlashRes 64 system with an electrode spacing of 40 cm.

Electro-Magnetics

This method maps an area very close to surface and produces 2 independent data sets known as the quadrature and the in-phase data.  These are sensitive to apparent ground conductivity and magnetic susceptibility, respectively.  There are many applications such as the detection of backfilled ground or changes in soil type.  This has a wide range of uses from detecting backfilled shafts and ditches to specialist archaeology.

A landslip showing as a major fault just below surface but visible as only a couple of small holes at the surface.

Data was collected using a GSSI EMP-400 electro-magnetic profiler.

Geo-Referencing

Finding something with geophysics is only really helpful if the PRECISE location of what has been found can be established.  GeoDefinition uses genuine surveyors with the skills and equipment to establish a point in space to within the volume of a small matchbox.  We use a Trimble R2 GNSS system and a Nikon Nivo total station.

Geophysical data mapped across a large site.  Positions were established using a Trimble R2 smart rover to an accuracy or around 10 mm.

Additional Methods

The bulk of our work is accomplished using the techniques listed above, all using our in-house equipment.  However, from time to time there is a requirement for alternative methods and we also have a specialised piece of ground penetrating radar equipment that can be used as an aid to interpreting anomalies beneath rough or open ground.

We are also experienced in the conduct and processing of of magnetic surveys, both total field and vertical magnetic gradient.

Our range of experience is considerable and includes surveys underground, surveys over water and coastal engineering work.


Our aim is always to do a great job.  We are not afraid of a challenge but if we are not the right people for a job then we will say so.  We may even be able to suggest a more appropriate alternative company.  We also recognise that most people are unlikely to know what sort of geophysical survey is the most appropriate for their project.  We love what we do and are always happy to discuss a project and provide unbiased guidance on the best approach.  An email costs nothing but could be invaluable.  If you think geophysics might be what you need, drop Neill an email:


neill@geodefinition.co.uk

 

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For more information about the use of geophysical methods in site investigation, click on the photograph below.

We use a variety of geophysical methods in our work often combining several methods for maximum effect.  For instance, it can sometimes be helpful to use one method for a site wide reconnaissance and then follow up with a second method to further investigate areas of particular interest.