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Ground Penetrating Radar – A GPR Expert’s Guide

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The Breakdown of Ground Penetrating Radar's Applications and Uses for Locating Utilities

Have you ever wondered what is below the ground?

You might be digging a trench or planning an excavation. How would you know what’s down there? Would it be safe to just dig it up?  It seems like it could be a lot of work to figure out.

Luckily, there’s some equipment to help guide us called Ground Penetrating Radar also known as GPR.

GPR Services in Sydney service provided by Geoscope
Ground Penetrating Radar (GPR)

What is Ground Penetrating Radar?

GPR Services in Sydney service provided by Geoscope
Ground Penetrating Radar being used on-site

Ground penetrating radar (GPR) is a non-invasive survey method that uses the pulsing and reflection of electromagnetic radio waves to create images of objects buried underground. 

GPR has three main components – the transmitter and receiver antenna, and the display monitor.

GPR is used in many different geotechnical investigations but works well and is commonly used for finding underground services and utilities.

Here's how ground-penetrating radar works

The utility surveyor collects and records data by walking with the GPR instrument across the surface of the ground or structure to be investigated. 

GPR Services in Sydney service provided by Geoscope
Ground Penetrating Radar being used by utility locator

The electromagnetic waves of signal energy from the transmitter antenna penetrate down into the ground and onto the buried objects or utilities and then these waves are reflected back to the receiver.

The receiver measures the returning signals and records data which is then translated into images of the objects within the subsurface. 

By understanding the GPR data we can work out how to map structures and utilities buried in the ground, concrete or man-made structures.

What type of materials can ground-penetrating radar detect?

With Ground Penetrating Radar, you can detect a wide range of objects whether it’s metallic or non-metallic materials. However, this subsurface tool performs at its highest level of efficiency, when there is a significant difference between the dielectric properties of the target. 

Ground Penetrating Radar being used on site
Ground Penetrating Radar being used to detect metallic and non-metallic materials

The following items are some of the most common targets: 

  • Metallic pipes and cables
  • Pvc pipes and conduits
  • Plastics pipes
  • Void or space
  • Rebar
  • Conduit
  • Concrete

Is GPR the best way to find plastic water pipes?

Detected underground utility plastic water pipes
Detected plastic water pipes using Ground Penetrating Radar

There are multiple ways to locate poly water pipes, some more effective than others with different confidence levels.

Ideally, the poly service has a trace wire that is intact the whole way through the work area which can be connected to the pipe riser or valve box with the direct connection method, although in our experience this is a rarity in the plumbing industry.

When there’s no trace wire to locate the plastic water pipe, another method that can be effective at locating poly water lines is Ground Penetrating Radar. 

Depending on the site conditions, ground surface, and the types of soils in the proposed work area, GPR could be the answer to finding poly-blue stripe pipes.

Ground Penetrating Radar works by pulsing electromagnetic energy into the soil and showing differences in the dielectric permittivity of materials such as differences in buried utilities and soil.

How accurate is the GPR method?

Ground Penetrating Radar (GPR) accuracy check
GPR being tested on accuracy of locating utilities on-site

I am in the right hands, they can be millimetres accurate.

I am in the wrong hands, they can be head-shaking and wild guesses being thrown around.

Most modern-day GPR systems allow the user to hyperbola fit against potential utilities buried underground.

This amazing feature allows us to estimate the radar energy’s velocity through the soils and calibrate the GPR in real time to the soils we are experiencing from site to site. 

To hyperbola fit accurately, we need to make sure we have run the GPR perpendicular to the service we are trying to measure. This is important as if the pipe is on a slight angle it will throw out our depth estimation. If we hit the buried utility at any other angle, the shape of the hyperbola will be wider or possibly displayed as near horizontal lines.

After careful calibration of your GPR tuning the time zero, hyperbola fitting and energy velocity we have found the depth and position of underground services to be within millimetres 

In some cases, where we have ideal soils with utilities made, GPR can be more effective at depth estimation than electromagnetic locating.

That’s why we always recommend using GPR in conjunction with electromagnetic locating to overcome the limitations of each piece of equipment.

How would you prove how accurate GPR is at locating utilities? You would need to pothole to confirm the findings that are!

How do I know if my project needs GPR?

Utility locating site where Ground Penetrating Radar (GPR) can be used
Project required using GPR to locate underground utilties

The main factors that determine if you require Ground Penetrating Radar on your project are whether on not you plan to dig around underground services, or plan to in the near future.

GPR is another tool in the kit of underground service locating and utility surveying professionals. 

When it comes to Geoscope, we highly recommend using both electromagnetic and GPR locating methods on all job sites so we are able to combat the limitations of one method with the advantages of the other.

Geoscope Utility Detection Ground Penetrating Radar Sevices
Certified Utility Locator using Ground Penetrating Radar (GPR) on-site

If you are after a complete Subsurface Utility Investigation at your site before you dig, you want to leave no stone unturned. This means using all available resources, plans, materials, equipment (including GPR), and last but not least, quality personnel experienced in all aspects of utility locating.

When you use GPR to scan the ground before you begin any groundbreaking projects, you ensure that you won’t encounter unexpected obstacles and possibly cause damage to your equipment or everyone onsite by doing all that you possibly could do. Especially when you’re conducting potentially hazardous work like excavation, concrete cutting, trenching or coring.

If you think Ground Penetrating Radar would be beneficial on your site or would like to discuss how Geoscope can help with GPR, get in contact with our team today.

You may also want to consider the advantages of using Ground-penetrating radar on your project.

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