Using Ground Penetrating Radar to locate Plastic Gas Pipes


Ground penetrating radar works really well at locating gas pipes when we have the ideal soil conditions.

Geoscope's Utility Locating Ground Penetrating Radar Services                 Ground Penetrating Radar (GPR) Service in Locating Sydney Geoscope

GPR works really well when you have highly contrasting materials compared to the soils on site. 

Ground Penetrating Radar works by pulsing electromagnetic energy into the ground which travels through the subsurface. 

As the energy passes through the soil it will come into contact with materials of differing properties such as rocks, boulders, and even underground gas pipes which then reflects back to the GPR antenna.

The ideal conditions for ground penetrating radar in locating underground services is to have two highly differentiating materials which show up as distinct radar images. 

For example, a copper pipe with a dielectric constant of infinity buried in dry sandy soil will give the best results to produce a clean GPR hyperbola target.

The reason for this is light or radar energy cannot pass through metallic objects such as underground services and the like. 

Radar energy can travel through sandy soils a lot easier than it could through wet, saturated soils. That’s why we get the clear signals of buried pipes a lot easier with dry, sandy soils

Gas pipes made of nylon and polyethylene are not as highly contrasting as metal pipes in the ground, although in ideal conditions, the pipes can still be traced with ground penetrating radar.

As the pipe is filled with a gas, which has a similar dielectric property as air, this now becomes a high contrasting difference to wet soils. 

When you have contrasting materials, you generally get clearer images of buried targets. 

We can never know exactly what soils are buried but we can take very educated guesses with the results we collect by GPR over the years in various parts of Sydney and New South Wales.

Ground penetrating radar works really well in locating gas pipes when the area to be investigated has flat ground or pavement

Geoscope Ground Penetrating Radar Utility Locating Services in Sydney, NSW                        Ground Penetrating Radar (GPR) Service Locating in Sydney

If I had to choose between scanning the ground penetrating radar on some flat service like an asphalt road, rough paddock, or an existing excavated construction site, I will choose the flat surface any day of the week.

By having a smooth surface to run the radar over, we can eliminate the possibilities of bumps and humps disturbing the collected data and the GPR encoder wheel skipping, which can lead to data being missed or misinterpreted.

Flat surfaces like roads and grass fields are ideal as these surfaces are usually prepped quite well and backfilled to a standard that comprises sand, gravel, etc.

When you have these soil conditions available and the buried pipes are backfilled with these materials, it makes our job of locating these gas pipes with the ground penetrating radar so much easier.

Ground penetrating radar works really well in locating gas pipes  when the trench is backfilled with sand

As we discussed above, when we have the right material backfilled in the trench, the ground penetrating radar works well to differentiate the contrasting materials between the utilities and the ground.

Backfill trenches with sand give us great results to see not only the reflection off the pipes but also the possible extents of the trench.

Identifying the excavation cut in the existing soil, which could be clay or rock, also allows us to see that something has been dug below and we can make some deductions on site from the data we had collected.

Any information and data we can collect on-site on subsurface utility information is a win in our book. This leads to easier confirmation with further investigations.

Ground penetrating radar struggles to locate gas pipes in highly conductive soils such as wet clay

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Wet soils can, at times be advantageous for locating gas pipes due to the contrasting dielectric constant between the air and the wet soils.

Although, Highly conductive soils such as wet clay can restrict the amount of electromagnetic energy that can be posted into the soil.

If the GPR energy cannot penetrate through the ground, it has little chance of returning back to the antenna to show any data or reflections of pipes on our screens.

We are not saying it is impossible to see a pipe and highly conductive soils like wet clay, but it can be hard.

Things, as we mentioned before with the pipes being backfilled in sand and gravel road base, will always make our job easier.

We use Ground Penetrating Radar on every job possible.

We literally never know how effective the ground penetrating radar will be until can you turn it on and push it over the ground which you suspect a pipe to be.

I am always wary of individuals that can tell how the ground will react before they have even taken the GPR out of the truck. Let alone the guys who don’t bother trying.

We will never know how effective GPR is until you have completed your Ground Penetrating Radar scans.

Ground penetrating radar struggles to locate gas pipes in areas with congested underground services 

Gesocope Utility Gas Pipe Locating Service in congested area in Sydney, NSW              Geoscope Gas Pipe Locating Service in congested area in Sydney, NSW

No matter what type of soil you have below the surface, if you have many targets such as pipes and cables very close together in a localised area, you going to have a tough time differentiating which pipe is which.

When completing utility investigation and utility surveys which can include potholing and slit trenches to verify the buried services on our work sites, it is not uncommon for the gas main to be buried underneath existing underground services such as electrical conduits.

Many times we uncover the gas pipe which has been buried underneath Telstra cables, electricity ducts, or right next to underground water mains.

When you are working in the Sydney CBD, it is a spaghetti junction in terms of underground services. 

Geoscope Utility Gas Pipe Utility Locating Service in Sydney

                         Geoscope Utility Gas Pipe Locating Service in Sydney, NSW

Nothing is a surprise and pipes and cables are twisting up and over each other which does make our job as utility locator quite interesting.

The job can be hard at times, but the team at Geoscope love what we do.

Ground penetrating radar struggles to locate gas pipes in tight spaces.

If you have good knowledge and understanding of the ground penetrating radar data we are collecting when trying to locate underground gas pipes it is ideal to have a large data collection versus a small data collection.

When we collect all this data, we can make better decisions on what we have found and What the radar is telling us.

Sometimes we are asked to scan small areas and can only complete a small run-up with the radar. This is less than ideal although we work with what we are given and make our recommendations based on what data we are able to collect.

Geoscope Underground Utility Gas Pipe Locating Service

                    Geoscope Underground Utility Locating Service in Sydney, NSW

That’s a wrap on ground penetrating radar and locating underground gas pipes.

I hope this article has helped clear up some of the ideas you may, or may not have had about using ground penetrating radar to locate underground gas pipes.

At the end of the day, our teams would not be as successful as they are right now without the use of ground penetrating radar.

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                                Ground Penetrating Radar (GPR) Service in Sydney

As we’ve discussed, you are never going to know whether or not you are able to detect an underground utility with GPR until you have pushed it over the given work area.

Yes, there is Blacktown, Mount Druitt and the heart of Sydney‘s west which struggles with dense clay soils, but given the chance, I would always attempt to scan the area with ground penetrating radar before calling it a day.

If you have any questions about ground penetrating radar and its effectiveness in locating underground utilities or underground services, get in touch with the team at Geoscope and let’s work out if ground penetrating radar is the right piece of equipment to help you with your utility investigation.

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