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GPR Geophysical Services
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The following case studies illustrates the uses of the technologies employed in the services we provide. Further information can be found in the our publications for various international conferences.

EM-31 Survey of a large industrial area

A soil electrical conductivity (or resistivity) survey was used to detect and plot areas within an industrial complex, which were affected by chemical contamination.

Using this totally non-intrusive method meant that the affected areas could be quickly and accurately defined. This (EM 31) survey meant that the complete area, approximately 1000m by 450m, could be carried out and completed on-site in 3 days.

Soil samples were subsequently taken from the identified areas for laboratory analysis to determine the precise nature of the chemicals involved.

Using this technique represented a significant cost saving for the client over the traditional multiple borehole investigation of the whole site.

 

 

 

 

 

 

 

 

GPR survey of historic burial sites

Ground penetrating radar has been used to successfully locate and plot many different types of subsurface targets.

An example is plotting the layout of old unmarked graves at cemeteries and Maori urupa sites. A burial site is normally characterised by the void or uncompacted soil resulting from the presence of the buried body and/or decomposed remains. Some of the gravesites detected date back to the 1860’s The radargram shows a typical distinctive response seen from old burial sites.

Many hundreds of gravesites have been found and plotted using this technique.

 

 

 

 

 

 

 

UXO survey using EM-61

This type of survey is used to detect, both ferrous and non-ferrous, buried metal objects.

A typical example would be a survey to detect and plot the location of buried UXO (unexploded ordnance). The EM61 used for this type of survey is mounted on a small handcart, which is pulled behind the operator along grid lines laid out to cover the survey area.

The example is a survey of an area near Manilla Airport which was heavily bombed during WW2. Detected targets can be seen as the red coloured anomalies on the adjacent plot of the surveyed area.

In a similar manner to the EM31 survey these investigations area carried out at walking pace and can therefore cover a large area during the course of a normal survey day.

The picture shows a recovered ex military airborne bomb most likely from the WW2 era.

 

 

 

 

 

 

 

 

 

 

Ground Penetrating Radar in environmental studies

Ground penetrating radar can be used to detect and plot a wide range of subsurface conditions including buried waste dumpsites.

This example shows a survey carried out over the site of an old sawmill site. Buried waste material left behind under the surface can create problems for later generations. Gradually rotting buried organic matter can cause subsidence problems and lead to ground instability.

In the example shown a long since buried sawdust pit can be clearly seen as the circled dark homogenous area on the radargram. The top of the pit is situated around 1.0 to 1.5m below the surface.


 

Ground Penetrating Radar in stuructural engineering

Dropping levels of the local water table caused a collapse in the soils underneath a concrete floor slab at an industrial site. This in turn caused distortion of the slab and a serious problem to operation of the plant.

Using non-intrusive Radar the voids beneath the concrete slab could be detected and plotted. A scaled layout drawing was then produced allowing repairs to the voided areas to targeted and carried out with minimal disruption to the concrete floor slab.

A detailed discussion can be found in one of our publications