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What Do Utilities Look Like With GPR?

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Understanding Ground Penetrating Radar

Ground Penetrating Radar (GPR) is a powerful tool for identifying subsurface features, including buried utilities such as water pipes, gas lines, and electrical cables.  

GPR uses electromagnetic waves to penetrate the ground and reflect off subsurface features, producing images that can be interpreted to identify the location, size, and depth of utilities. 

This article will provide a detailed overview of GPR technology and how it can be used to detect utilities.

What is GPR and How does it work?

GPR is a non-destructive testing method that uses high-frequency electromagnetic waves to penetrate the ground and reflect off subsurface features. 

The GPR equipment consists of an antenna, which transmits the electromagnetic waves, and a control unit, which records the reflections and processes the data. 

Antenna component of GPR
Antenna of GPR
Control Unit component of GPR
Control Unit of GPR

The antenna is typically pushed or towed along the ground, and the reflections are recorded in real-time.

The electromagnetic waves used by GPR are typically in the range of 10 MHz to 2.6 GHz. 

How GPR works in finding Underground Utilities service provided by Geoscope
Waves reflect off subsurface features

Although the ideal GPR antenna frequency for utilities is around 400-500MHz, which allows the signal to penetrate the ground to a depth ranging from around 0–2 metres

The waves reflect off subsurface features, producing a time-domain or frequency-domain signal that can be interpreted to identify the location and depth of features such as utilities.

If you want to learn more about what is GPR and how it works to find underground utilities, you can check out this article below written by Sydney’s GPR experts!

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How is GPR Used for Locating Utilities?

GPR is a valuable tool for identifying buried utilities, as it can detect a wide range of utility types and provide information on their location, depth, and condition. GPR can be used for the following: 

GPR is used for Utility Mapping

GPR can be used for utility mapping, which involves creating a comprehensive map of all utilities within a specific area. 

Once utilities have been identified with GPR and EM locating methods, these findings can be surveyed and mapped to the Australian Standard.

This is particularly useful for cities and local governments in Sydney, as it allows for better management of planning when working around utilities and can help prevent accidental damage during construction or excavation. 

If you are interested to know more about how GPR is used for Utility Mapping, you can check out Sydney’s Best Utility Locating and Utility Mapping service provider, they are one of the leaders in Sydney.

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GPR is used for Locating Buried Utilities

GPR can also be used to locate buried utilities. 

The GPR equipment is used to scan the ground in a systematic grid pattern, with the data collected and analysed in real-time to identify the location and depth of buried utilities. 

This information can then be used to plan excavation or construction projects, avoiding accidental damage to the utilities and reducing the risk of injury or property damage.

Geoscope Utility GPR Detection Service search work site construction Sydney, NSW
GPR used to map out underground utilities

GPR is used for Identifying Potential Obstructions when trenching and excavating

GPR can also be used to identify potential obstructions and prevention of damage to utilities. By detecting changes in the subsurface material, such as layers of asphalt, concrete, road base, clay, and rock. GPR can provide information on potential obstructions or damage to buried utilities.

The use of GPR for utilities has several advantages, including the ability to detect utilities without excavation or disruption to the surface – this minimises the impact on the environment, reduces costs, and saves time.

The speed of data collection – this allows for rapid mapping and location of utilities. And the ability to detect utilities in a wide range of soil conditions, including dry and wet soils, makes it a versatile technology.

If you are interested to learn more about the Advantages of GPR in Utility Locating, this article is for you!

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However, there are also some limitations to the use of GPR for utilities, including the need for proper ground conditions, the need for trained analysts to interpret the data, and the potential for false positives or false negatives.

How to Interpret GPR Data Results

Interpreting GPR data results is a critical step in identifying utilities and other subsurface features. Trained analysts can interpret data in real time or use specialised software to help refine the process and interpret the data, identifying hyperbolic reflections and layers that correspond to subsurface features such as utilities.

There are several types of GPR data, including time-domain and frequency-domain data. 

Ground Penetrating Radar GPR Service Locating Sydney Geoscope
Interpreting GPR Results

Time-domain data provides information on the depth and location of subsurface features, while frequency-domain data provide information on the material properties of subsurface features.

To interpret GPR data for utilities, utility locating professionals must be familiar with the expected characteristics of utilities in GPR images, such as their size, shape, and orientation. 

They must also be able to recognise hyperbolic reflections that correspond to utilities of different materials and shapes to estimate the depth of utilities from the time-domain data.

Radargrams, which are two-dimensional slices of the subsurface created by GPR data, are an important tool for interpreting GPR results. Analysts use radargrams to visualise the subsurface features and determine their location, depth, and orientation.

They must also be able to recognise hyperbolic reflections that correspond to utilities of different materials and shapes to estimate the depth of utilities from the time-domain data.

The shape and orientation of these reflections can provide valuable information on the size, depth, and condition of the utilities. 

Analysts also examine the amplitude of the reflections, which can indicate the relative strength of the reflection and the material properties of the subsurface feature. 

To ensure an accurate interpretation of GPR results, analysts must be familiar with the software used to process the data and must have a thorough understanding of the expected characteristics of subsurface features. 

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Hyperbolas on GPR Radargram

They must also be able to differentiate between false positives, such as rocks or other natural features, and true utilities. Interpreting GPR results for utilities requires specialised knowledge and skills. 

If you’re in need of a proficient team for interpreting GPR data, Geoscope has the expertise to identify underground utilities and hyperbolic reflections that correspond to subsurface features. They are professionally trained to estimate the depth and location of these features, as well as determine their size, shape, and orientation. For more information about their services, please refer to the link below.

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By understanding the expected characteristics of utilities in GPR images and the factors that can affect GPR utility detection, analysts can provide accurate and reliable results to their clients.

What Do Utilities Look Like in GPR?

When viewing GPR data on a screen, utilities appear as hyperbolic reflections, which correspond to the shape of the utility and the angle at which the GPR antenna transmits and receives the electromagnetic waves. The shape and orientation of utilities in GPR images can provide valuable information on their size, depth, and condition. 

Ground Penetrating Radar GPR Service Locating Sydney Geoscope
Hyperbolic reflections shown on GPR

Hyperbolic reflections are a result of the energy wave being reflected off an object. The result is a hyperbolic curve which typically has either a positive, negative, positive response or vice versa a negative, positive, negative response.

When we get different colour wave bands, returning with the GPR. It generally tells us that the energy wave is speeding up as it travels through different materials, or slowing down when it hits an object that is different to the surrounding materials.

Plastic water pipes, for example, typically appear as a series of hyperbolic reflections with a circular or oval shape. This occurs because the non-metallic pipe allows radar energy to pass through, which then reflects off multiple boundaries such as the top and bottom of the plastic pipe, as well as the water.

Plastic gas lines may appear as a single hyperbolic reflection with a faint reflection as the pipe is typically at a similar relative dielectric constant to the surrounding soil material and is filled with a gas which generally causes the ground penetrating radar energy to speed up as it passes through the pipe.

Electrical cables may appear as a series of hyperbolic reflections which repeat or cause a ringing type response. This is due to the energy from the radar being reflected multiple times through the electrical assets which is also emitting its own Electric Fields.

GPR screens also display time-domain and frequency-domain data, which provide information on the depth, location, and material properties of subsurface features. 

Time-domain data shows the depth and location of hyperbolic reflections, while frequency-domain data shows the material properties of these reflections, such as their dielectric constant and attenuation.

In addition to hyperbolic reflections from utilities, GPR screens may also display reflections from other subsurface features, such as rocks, soil layers, and voids.

Ground Penetrating Radar (GPR) Equipment service provided by Geoscope
GPR screen displaying properties of subsurface features

Utility locators must be able to distinguish between these reflections and those from utilities to accurately identify and locate subsurface features.  To interpret GPR data on a screen, utility locators must be trained in the use of specialised software that processes and displays the data. 

They must also be familiar with the expected characteristics of utilities in GPR images and the factors that can affect the accuracy of GPR utility detection, such as soil conditions, the material, and orientation of the utility, and equipment settings.

Furthermore, they must also be able to distinguish between reflections from utilities and those from other subsurface features to accurately locate and identify utilities. 

Factors that Affect GPR Utility Detection

Several factors can affect the accuracy of GPR utility detection,

  • Soil conditions, 
  • The material of utility, 
  • Orientation of the utility, and 
  • The equipment settings. 

 

Analysts must be aware of these factors and take them into account when interpreting GPR data for utilities. 

Soil Conditions

Soil conditions can affect the accuracy of GPR utility detection, as different soil types have different electrical properties that can impact the propagation and reflection of electromagnetic waves. 

For example, wet, moist, or compacted soil may produce weaker reflections and make it harder to detect utilities, as the energy has difficulty penetrating through these conductive soils. 

Ground Penetrating Radar equipment being used in semi-wet soil NSW Sydney, Australia service provided by Geoscope
GPR on wet soil

The main areas of Western Sydney typically have wet or moist, clay-type soils. 

This makes it generally harder to detect underground utilities, especially nonmetallic gas pipes.

Conversely, dry or sandy soil has the potential to generate stronger reflections as the energy can penetrate easily and reflect off objects with contrasting electrical properties, such as utilities, rocks, and tree roots. This can result in false positives.

In the eastern suburbs of Sydney, close to the coastline, or in the southern highlands with raised elevations, we typically get the sandy soils that are favourable for GPR. 

You never quite know which site is going to be favourable until you start running the GPR, but having an idea before you start is part of the experience of knowing what to expect.

The Material of the Utility

The material of the utility is another factor that affects GPR utility detection. For example, metal utilities may produce stronger reflections than plastic utilities. This is because metal is a better conductor of electricity, which means that it reflects more electromagnetic waves.

Moreover, the thickness of the utility wall can also impact the strength of the reflection if the pipe is made of a non-metallic pipe, such as a concrete, stormwater drain, a clay, sewer pipe, or a plastic PVC water main.

GPR used to detect stormwater pipes in Sydney, service provided by Geoscope
GPR detects stormwater pipes

Orientation of the Utility

The orientation of the utility also plays a role in GPR utility detection. When a utility is oriented parallel to the GPR antenna, it doesn’t produce a hyperbola at all. The typical response we get when we are running the GPR parallel to a pipe or layer is a horizontal band-type response.

This is because when we are moving the direction of the GPR over the pipe, we don’t deviate off the pipe at all. This causes the radar energy to reflect up and down and giving that straight line or horizontal response.

The Equipment Settings

Finally, the equipment settings can significantly impact GPR utility detection accuracy. 

Ground Penetrating Radar Services by Geoscope Utility Locating GPR Services in Sydney
GPR Locator adjusting GPR frequency settings

Adjusting the frequency, gain, and sampling rate can affect the quality and resolution of the data. 

A lower frequency may penetrate deeper into the ground, but may also produce lower-resolution data. 

In contrast, a higher frequency may produce higher-resolution data, but may not penetrate as deeply into the ground.

Getting the antenna frequency right from the start is key to target in utilities at certain depths.

Other factors that might affect the GPR utility detection:

Depth of Utility

The depth at which the utility is buried can also affect GPR utility detection. 

The deeper the utility, the more difficult it can be to detect it with GPR as radar energy needs to return to the surface, so we are able to interpret the signal. 

If the energy does not return to the entertainer, we are unable to determine what utilities are buried beneath.

GPR used before the Non-destructive Utility Potholing service provided by Geoscope
Depth of utility affecting GPR utility detection

Signal Frequency

The frequency of the GPR signal can also impact utility detection. Higher frequencies can provide better resolution but have less penetration depth, while lower frequencies can penetrate deeper but with less detail.

Antenna Type

Different antenna types are suitable for different types of surveys. For example, ground-coupled antennas can be used for high-resolution surveys of shallow depths, while air-launched antennas can be used for deeper surveys.

Antenna component of GPR
Antenna component of GPR

Interference

The presence of other electromagnetic signals in the area, such as power lines or radio signals, can interfere with GPR detection and reduce the accuracy of the results.

Operator Expertise

The experience and expertise of the GPR operator can also affect utility detection. Experienced operators can interpret data more accurately and adjust settings for optimal results.

The team and Geoscope are trained to detect utilities using the latest methods in electromagnetic and ground, penetrating radar locating methods.

GPR Services by Geoscope

Geoscope Utility Detection Services are the experts when it comes to finding buried utilities and locating underground services using ground penetrating radar in the Sydney area.
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Survey Design

The design of the GPR survey, including the survey grid and line spacing, can also affect utility detection. A well-designed survey can improve accuracy and reduce the risk of missing utilities.

Again, utility detection using GPR is influenced by several factors that need to be taken into account to achieve accurate results. Utility locators need to be aware of these factors and apply appropriate measures to ensure reliable results.

If you want to know more about the limitations of GPR, feel free to check out this article!

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Ground Penetrating Radar is a valuable technology for identifying subsurface features such as buried utilities. By using electromagnetic waves to penetrate the ground and reflect off subsurface features, GPR can produce detailed images that provide valuable information on the location, size, and depth of utilities.

However, interpreting GPR data for utilities requires specialised knowledge and training, as several factors can impact the accuracy and reliability of the results. Overall, GPR is an invaluable tool for utility mapping and management, providing a non-destructive and efficient means of detecting and identifying buried utilities, reducing the risk of damage to utilities and enhancing public safety.

If you have any questions, concerns, or feedback regarding this article, please feel free to either comment below or directly contact us at info@geoscopelocating.com.au. Or if you are looking to avail the most reliable GPR Services in Sydney, New South Wales, you can fill out our contact form below or directly get in touch with our customer service at 1300 750 350.

 

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Patricia Cupiado

Co-Author of this Article

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