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.
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
Why choose us for geological GPR survey
Our surveyors have used all types of low frequency GPR | |
Experienced surveyors have worked in multiple locations | |
Detailed drawings and clearly presented results | |
GPR and Geophysical survey experts |