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Underground void detection survey will determine the location and extent of underground void, sinkhole, and subsidence.

An underground void detection survey using Ground Penetrating Radar (GPR) is a low-risk method to scan an area of ground to determine the location and extent of underground voids, sinkholes, and subsidence.

This can form part of a risk reduction process that checks the integrity of the ground before moving or using heavy equipment and cranes.

Underground void detection survey can also be used to determine the extent of potential underground voids and subsidence to aid in remediation planning.

topographic map with water contour lines

What are the benefits of GPR survey for detecting voids and subsidence?

GPR survey can help you easily detect underground voids and subsidence. Without Ground Penetrating Radar (GPR), they can be difficult to identify as they do not always show any signs on the surface but are present below the ground. 

By using a GPR survey and identifying a void, you can safely evacuate an area, so no one is hurt of injured. In many cases you can resolve the problem before the sinkhole opens. This can be done by first exposing the void and them pumping material into it until it is filled, however this may only work in certain circumstances.

For voids below concrete slab the typical infill material would be old-time cement slurry (cement, sand and water mix) or more recent- high-density polyurethane foam.

A sinkhole in a field or yard can be filled with fill dirt or soil or concrete.

Overall, the GPR void detection survey is the ideal method to determine the extent of an issue and help you work out what your best plan of action is moving forward.

GPR is fully non-destructive and non-intrusive, making it ideal for checking the property as it requires no digging. 

Why use GPR for underground void detection survey?

As mentioned previously, GPR is fully non-destructive and non-intrusive technique. The equipment is lightweight and can be used to scan areas of any size and it does not cause any damage to the surface being surveyed.

Using GPR for a void detection survey is also a cost-effective way to scan a large area safely. Digging or drilling would require specific construction equipment that would be more expensive to hire and possibly too heavy to go over the area with potential void underneath. It is also more time consuming digging the surface up and would result in damaging it.

Our GPR void detection survey will help save you time and money.

What causes underground voids and subsidence?

Underground voids

Voiding can be caused by several reasons including:

-geological (gaps in settlement and regularly occurring expansion and shrinkage of clay and silt in soil)

-man-made (wash out due to broken and leaking water pipes or faulty guttering which prevent rainwater to drain properly; old sewers, buried basements, disused mine shaft which have been compromised).

-washouts due to the underground water movement which carries some material with it (typical in costal promenades and car parks, masonry arch structures and docks and retaining walls).

-tunnelling animals such as badgers, moles, and rabbits.

-natural subsidence in which the ground itself is moving and settling over time (some foundation settlement in a normal occurrence; under the wight of a building the soil beneath will get compacted over time. The amount of settlement will depend largely on the type of the soil the building was erected on).

Detecting voids, sinkholes and subsidence using GPR

Ground Penetrating Radar (GPR) works by transmitting and electromagnetic signal into the ground and recording reflections. Those reflections are caused by any change in the below surface environment. GPR can detect most types of underground features including sinkholes, voids, and subsidence (provided the voids are large enough to be detected within the resolution and penetration capabilities of the GPR being used).

How a GPR survey to detect sinkholes, voids and subsidence is performed?

Detecting voids, sinkholes and subsidence is usually performed using handheld equipment which is mounted on a small trolley. Parallel lines of GPR data are collected in two axes to form an orthogonal grid. Each line represents a vertical cross-section through the ground at that specific location. These lines of data are then recorded so they can be processed and interpreted off-site.

In the office, the data is loaded into our advanced GPR post-processing and imagining software, by compiling the vertical cross-sections together a 3D picture is formed. Using this 3D image, underground features as voids, sinkholes and subsidence can be detected and traced from the scan to produce a CAD drawing.

Examples of GPR void, subsidence and sinkhole detection surveys

Some examples of void detection surveys include:

A GPR survey to detect underground sinkholes in Manchester (link). In this case, large voids and areas of subsidence were present beneath a surface layer of reinforced concrete, they caused a sinkhole 4m deep and were expanding. We were able to successfully detect and map them in our post-processing part of GPR survey even though they were not visible in the data on-site.

We also have experience detecting shallow voids and sinkholes in concrete and road structures. As well as badger tunnels and chambers, and man-made voids such as underground tanks, basements, culverts, mine shafts, gas pipes etc.

In this example, KB Surveys was asked to survey floor in a church and detect the location, depth and extent of an underground void which was identified as a disused crypt.

In these two examples, retaining walls were surveyed to detect potential voids caused by material washout. In one case voids were detected- in the other, the retaining wall was confirmed to be sound.

Sinkhole, underground void detection and subsidence survey deliverables

The results from a GPR survey of underground voids and subsidence will usually take the form of CAD drawings and/or a report. The final output may vary depending on the best way to represent the information.

If you require a void detection survey or a survey to detect sinkholes or subsidence, please contact KB Surveys by filling out the ‘Contact form’ at the bottom of this page or click on the ‘Quote Request’ in the main menu bar and we will get back to you with a free estimate.

Benefits of GPR for void location survey

NDT method

GPR will not affect scanned ground, concrete slab or retaining wall

Efficient

Small GPR survey usually take less than a day on site

Quick answers

You can know about the potential void on the day of your survey

Safety first

GPR survey will conclude the extend of void, sinkhole or subsidence

Why choose us for your void location survey?

check icon We use custom made equipment for best results
check icon Our surveyors have over 20 years of expertise
check icon We work with local councils
check icon We put emphasis on customer relationship

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