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GPR is reliable way of detecting geological features and deep layers.

Ground Penetrating Radar (GPR) can be used for geological surveys to detect features such as the bedrock, water table, and stratigraphic layers. GPR can also be used to measure the thickness of ice sheets, and the profile of river or canal beds with some penetration into the soil beneath – which is not possible using only a sonar-based system.

For the detection of the bedrock, water table and the stratification of the ground, the use of a very low frequency antenna is required. This could be anything between 25MHz and 100MHz. In the right conditions such GPR have penetration into the tens of meters. Such GPR have very poor surface resolution and are of little use for typical applications, but they can detect very large features and interfaces (layers) which are located deeper in the ground.

topographic map with water contour lines

GPR survey to detect bedrock and layers

Due to building works necessitating a cut into a hillside, a GPR survey was requested to locate the depth from the surface to the bedrock, this would allow the engineers to decide to what extent the ground needed to be pinned to prevent future landslides.

We attended site and collected a series of cross sections which saved for office-based processing and compilation into a report and a table of offsets. Because the surface resolution of such a low frequency antenna is poor, the results were challenging to produce, however we identified the bedrock approximately 2m below the surface (shallower than expected) which was sufficient information for the engineers to work from.

On a similar survey, we identified bedrock within 3-5m of the surface.

GPR survey to detect deep layers at disused landfill sites near London Heathrow Airport

There are many disused landfill sites scattered around the UK. At each of these, the thickness of the waste can vary from just a few meters to tens of meters deep. In the past the sites would have been left open and once the land had been filled to capacity, the waste was compressed and capped.

Over the years many of those landfill sites have been left unmanaged and become scrub land, whilst the surrounding areas have been developed. As land prices increase, it has become economical to reclaim a disused landfill, clean the waste, and develop it.

Our client had speculatively purchased some of those sites and was looking for a method to cost effectively determine which ones had the most development potential. Sites with a relatively thin layer of waste could be cleaned much more easily and economically than sites with a thicker layer of waste.

We achieved a maximum penetration of 11m but were unable to positively identify the bottom of the landfill. Although we were unable to answer our customers ultimate question of how deep the landfill is, we could inform them that the depth of fill was greater than 11m and using the area of the site, our customer could calculate a minimum volume of fill and therefore a minimum cost to reclaim the land from which they could make an informed decision about further site investigation.

Low frequency GPR survey to identify deep voids and karsts

We were asked to survey a large area of fields using GPR, to check for signs of voids, sinkholes or subsidence, and potentially the deeper underlying cause of those issues being karsts in limestone bedrock.

We attended site with a multi frequency, 70MHz and 300MHz antenna. This antenna is particularly useful because the shallow resolution (in the first few meters) of a low frequency antenna is particularly poor, but the 300MHz data helps to overcome that. This provides quality data of both deeper features and those in the first few meters.

We surveyed the site and confirmed that there was no evidence of voids or subsidence within the survey area, however, a sinkhole was located to one side of the site.

Benefits of using GPR surveys to detect deep layers

Non-intrusive and NDT

GPR is entirely non-intrusive and non-destructive (NDT)

Deep survey without drilling

Low frequency GPR can investigate up to tens of meters deep

Time and cost saving

Minimise borehole requirements with a GPR survey

Understand the big picture

A GPR survey can provide a wide overall picture of the site

Why choose us for geological GPR survey

check icon Our surveyors have used all types of low frequency GPR
check icon Experienced surveyors have worked in multiple locations
check icon Detailed drawings and clearly presented results
check icon GPR and Geophysical survey experts

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