Geophysical Research

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Geophysical Research

Geophysical research  maps the subsurface and constructions in the subsurface, usually without having to drill or dig. The depth of the investigation can vary from a few centimetres to many kilometres.

Why T&A for geophysical surveys?   

  • T&A provides clear and independent information about the possibilities of geophysical research.   
  • T&A has dozens of geophysical measuring instruments and is therefore able to use the optimum technique or combination of techniques to deliver the best results for every problem.   
  • Solutions to problems regular methods are unable to solve.
  • Reduced risks of unexpected deviations (objects) in the subsurface, which can cause extra costs and delays.
  • The use of on-destructive techniques reduces inconvenience to the surroundings.
  • T&A maintains intensive contacts with universities and scientific institutions, combining theoretical knowledge with practical experience.

Dike inspections

Weak spots in dikes can be detected quickly and efficiently with geophysical dike research. This can be done from ground level, but also from the air with the help of a drone. Possible applications of geophysical techniques in dike research are:    

  • Deformation measurements    
  • Seepage (water) detection: each dike allows water to pass through under normal circumstances. If a dike is overloaded by extreme conditions, it will let more water through than normal.    
  • Piping: these are sand tracks in or under the dike, through which a lot of water can flow. As a result, there is a chance that soil will be washed away, weakening the dike.    
  • Detecting presence of and damage caused by muskrats.

Geo-electrical measurements

Geo-electrical measurements (resistance measurements) are an electrical research technique that determines the resistance of the subsurface in a non-destructive way. This technique can be used in dike inspections if the subsurface has to be accurately mapped in order to record geological structures with a high resistance or a resistance that deviates from the surroundings. The depth range of the measurements varies from a few meters to a depth of more than 500 meters.

Dike inspections with Drone technology

T&A Survey Drone Services performs dike inspections with a drone equipped with various techniques such as infrared (IR) thermography and photogrammetry. Read more about Dike inspections with drones.

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Cables, pipes and foreign objects

Geophysical survey can be used to detect foreign objects in the ground, for example in infrastuctural and archaeological projects or landfill investigations. Foreign objects in the subsurface can usually be detected because they have different properties than the surrounding material. Possible applications of geophysical techniques in the research of foreign objects in the subsurface are:

  • detection of cables and pipes, 
  • detection of foundation piles,
  • detection of metal objects such as oil barrels and tanks,
  • archaeological research of roads, foundations, tools and canals or ditches,
  • forensic investigation,
  • mapping of the thickness of rubble and waste layers and embankments,
  • detection of cavities or basements,
  • detection of Unexploded Ordnance (UXO),
  • dertermine the position of conductive horizonal and vertical boreholes or boreholes with metal casings,
  • dertermine the position of non-conductive horizontal and vertical boreholes or boreholes without metal casings.

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Road construction

Geophysical techniques are frequently used to evaluate of the composition of a (concrete) construction or asphalt quality.

Possible applications of geophysical techniques in road contstruction are:

  • determination of thickness of asphalt or concrete on roads and constructions,
  • mapping of cracks and cavities,
  • detection of mesh tracks and reinforcement bars,
  • mapping of the complete road foundation.

Project: Detection of sink holes and cavities under a road

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Borehole research

Borehole research takes place if geophysical research from ground level is not possible. T&A performs measurements with logging equipment and maps the properties of the borehole and its immediate surroundings. Examples of possible applications of geophysical techniques in borehole research are:

  • scanning the borehole wall, for example to detect micro fractures,
  • determining salinity and other physical properties of the soil surrounding the borehole
  • dermination of physical properties of subsurface material 
  • detecting aquifers
  • detecting impermeable layers
  • detecting of geological transitions
  • detecting of deeper laying (foreign) objects
  • detecting pollution

TISA 2D Borehole Radar

The TISA® 2D Borehole Radar developed by T&A is a simple, safe and clear way to collect data about the subsurface. The TISA 2D can be used in various shallow and deep underground applications where surface radar is not possible.

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Geotechnical surveys in UXO suspect areas

T&A performs geotechnical research, depth detection, the determination of the length of sheet piling or the location of anchor rods using a magnetometer cone. A CPT (Cone Penetration Test) rod with a built-in magnetometer is pressed into the ground in a controlled manner using a CPT truck or CPT platform. Probings can be set up to many tens of meters and can be used on land as well as in water.

Magnetometer CPT

Magnetometer CPT is a magnetic technique that can detect deep ferrous metal objects. Applications include:
  • Detection of deep, large metal objects (UXO).
  • Determining the depth of a sheet pile wall.
  • Locating reinforced piles.
  • Locating anchor rods.
  • Geotechnical probes in suspected area.

Project: Mapping of grout anchor locations with magnetometer CPT

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Application in geological and hydrological investigation

Geophysical survey techniques make it possible to map the geological structure of the subsurface to a depth of several kilometres. A continuous image of the underground is created without having to do numerous deep drillings or probings.

Possible applications of geophysical techniques in geological investigation are:

  • mapping the geological structure of the subsurface,
  • mapping dike composition,
  • mapping of impermeable (clay)layers,
  • mapping of aquifers,
  • determination of pleistocene-holocene transitions, 
  • detection of salt domes or caverns,
  • detection of deep oil and gas reservoirs,
  • Detection of conductive structures as for example mineral ores,
  • surveying of salty seepage water.

Project: Mapping a salt dome

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Geophysical techniques

There are various techniques for mapping the subsurface or constructions. Based on our knowledge and practical experience we determine which technique will be most succesful for each investigation. Important factors to take into consideration are for example depth, specific circumstances, precision, measurement speed and costs.

Performing a detection

The measurements are taken by moving the equipment on foot or with a a quad or boat, over the research area. Sometimes the research equipment has to be brought closer to the research goal, for example by using a borehole. All geophysical techniques used are non-destructive, making the location immediately accessible afterwards. Sometimes locations are partially cordoned off.

UXO detection techniques

The geophysical techniques used for UXO detection respond to changes in the soil caused by the presence of metallic objects. All our detection techniques have been tested worldwide and found suitable for the detection of explosives.

Measurement results

The results are usually not immediately available on site. The data is analyzed in the office and then reported. Depending on the purpose of the research, this is done in an overview map, a cross section or a contour map of the subsurface.

(UXO) Detection techniques commonly used by T&A are:

  • TISA 2D Borehole Radar
  • TISA 3D Borehole Radar 
  • 3D Radar
  • Borehole magnetometer (CPT) 
  • Borehole metaldetector 
  • EM-61 Metal Detector 
  • Ground Penetrating Radar 
  • Manual metal detector  
  • Magnetometer and Gradiometer 
  • Multisonde gradiometer 
  • NanoTEM 
  • Sidescan sonar 
  • Sub-Bottom Profiler 

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Geophysiscal survey projects

Detection of sinkoles and hollow spaces under a trajectory

On behalf of TNO Geological Survey of the Netherlands, T&A conducted a GPR investigation along a route in South Limburg. The aim of the survey was to detect sinkholes and hollow spaces under a 1 km trajectory. The cavities are created by local solution of the limestone (marl) in dolines (solution depressions).

Determining the location of the groutanker locations

T&A has mapped the location of 22 grout anchor locations in the Buiksloterkanaal in Amsterdam for a client. 38 pile foundation pairs (76 piles in total) will be placed at the location of these grout anchor locations.

Mapping the transition between sewage sludge and water bottom

A lagoon in the Manchester area has been filled with sewage sludge from a nearby water treatment plant for the past 50 years. To enable a good planning of the dredging and soil improvement activities, information about the exact depth of the lagoon was needed. T&A was commissioned to map the transition between the sewage sludge and the actual water bottom, consisting of glacial clay.

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Benieuwd wat T&A Survey voor u kan betekenen?

Onze onderzoeken worden uitgevoerd door een deskundig, multidisciplinair team en T&A heeft de nieuwste geofysische meettechnieken in huis. Hierdoor bieden wij altijd de hoogste kwaliteit tegen een gunstige prijs!