05 Sep 2022
By Shan Wei
Phase II environmental site assessment – ordering a GPR survey?

Phase II environmental site assessment – ordering a GPR survey?

Geophysical Survey, Ground Penetrating Radar, Underground Storage Tank Locating, ,
During a geophysical survey for a Phase II environmental site assessment, some underground storage tanks (USTs) were located. The size of the survey area was less than 1/3 of an acre and 7 steel USTs were detected. The ground penetrating radar (GPR) profiles showing these USTs are shown in the following picture. The first example in the picture (the one at the top left of the picture) is a very good example of using GPR locating USTs. GPR profiles similar to this one are often used by GPR manufactures and GPR service providers to show that GPR is an amazing tool for UST locating. Although this kind of nice profiles could be very impressive, they can create a wrong impression…
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07 Jun 2022
By Shan Wei
Electrical conduits embedded in concrete have been marked through scanning — can we drill/core in cleared spaces near them?

Electrical conduits embedded in concrete have been marked through scanning — can we drill/core in cleared spaces near them?

Concrete Scanning, Construction, Ground Penetrating Radar, Underground Utility Locating, ,
The answer to the question seems to be obvious. Since the electrical conduits have been marked through scanning, why can't we drill/core in those cleared areas? We will keep a few inches away from those marked conduits, isn't it good enough? Unfortunately, it might not be. Are you telling us that the conduits are not marked accurately? Well, ground penetrating radar (GPR) can be as accurate as within an inch in finding conduits and other objects embedded in concrete. However, GPR accuracy is not the main issue here. The main issue lies in the limitations of scanning technologies. Due to the nature of scanning methods including GPR and cable/pipe locators, generally there are no guarantees that all conduits can be…
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30 Mar 2022
By Shan Wei
How are underground utility surveys affected by snowfalls?

How are underground utility surveys affected by snowfalls?

Underground Utility Locating,
Whether it's during or after snowfalls, or whether the snow has been plowed or not, usually snowfalls affect underground utility surveys in negative ways. If the snowfall is a safety issue and your site is closed due to the snowfall, then we cannot do underground utility surveys. Let's just leave it as that. Otherwise the survey might be able to be conducted, but often the results are less ideal. To decide whether you should go ahead to schedule an underground utility survey when a snowfall is a factor, there are several snow-related issues to be considered. You should consider them along with other factors such as survey purposes, budgets, project time lines, etc. Spray painting Spray painting doesn't work well…
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10 Dec 2021
By Shan Wei
Ghost rebar in ground penetrating radar concrete scanning

Ghost rebar in ground penetrating radar concrete scanning

Concrete Scanning, Ground Penetrating Radar, ,
Whether for embedded utility detecting or non-destructive testing (NDT) of concrete slabs, ground penetrating radar (GPR) interpretation involving rebar is often unavoidable. Understanding how GPR waves travel in reinforced concrete, and consequently what corresponding GPR profiles look like, are very important for appropriate GPR data interpretation. This article is about a "ghost rebar" phenomenon often encountered during GPR scanning of concrete slabs. These ghost rebar are not real but can show up and look real in GPR profiles. Even in theory this phenomenon can be easily understood, ghost rebar can cause confusion for data interpretation in real situations, especially when the concrete is not homogeneous or there are complex rebar patterns. Let's take a look at a GPR profile as…
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18 Nov 2021
By Shan Wei
Cross-polarized GPR scanning – a useful technique for locating utilities embedded in reinforced concrete

Cross-polarized GPR scanning – a useful technique for locating utilities embedded in reinforced concrete

Concrete Scanning, Construction, Ground Penetrating Radar, Underground Utility Locating, , ,
Above is an image showing two concrete ground penetrating radar (GPR) scanning profiles along the same line with normal and cross-polarized antenna orientations, respectively. Although the electrical conduit is visible in both profiles, it's easier to spot it in the cross-polarized profile than in the normal orientation profile. In the cross-polarized profile, the reinforcement's signature pretty much disappear; the conduit's signature also dials down, but remain very noticeable. So their differences are greatly amplified in the cross-polarized profile compared to the normal orientation profile. This tells us that the two signatures most likely represent two different objects, and it's most likely caused by the difference in their diameters. Of course, there are other possibilities such as differences in orientations or…
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28 Oct 2021
By Shan Wei
An Oil Tank Sweep Example – Why Should We Use Ground Penetrating Radar

An Oil Tank Sweep Example – Why Should We Use Ground Penetrating Radar

Ground Penetrating Radar, Underground Storage Tank Locating,
This underground heating oil tank was detected under a concrete floor using a ground penetrating radar (GPR) unit (See figure above). If only a metal detector was used, at best it would be suspected as a potential candidate for an oil tank. Exploratory digging would be difficult due to the concrete floor. However, Since the oil tank footprint occupied almost the whole concrete floor and there were steel stairs/fences and brick walls nearby, the metal detector responses could be easily disregarded as interferences from aboveground objects and reinforcement in the concrete. As a result, the oil tank could be missed if only a metal detector was used. Fortunately, we always use a GPR with a metal detector for oil tank…
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23 Sep 2021
By Shan Wei
A GPR Data Simulation on A Fiberglass UST

A GPR Data Simulation on A Fiberglass UST

Geophysical Survey, Ground Penetrating Radar, Underground Storage Tank Locating, Underground Utility Locating,
Ground penetrating radar (GPR) data can be complicated and difficult to interpret. GPR data simulation is a great way to help interpretation. Fiberglass underground storage tanks (USTs) have been more and more popular. Unlike a traditional steel UST, the top of a fiberglass UST is "transparent", making it possible to see liquid level and the tank bottom in GPR data, providing more underground information. But at the same time,  the GPR data is more complicated and can be easily misinterpreted. So a GPR data simulation is done here to minimize the chance of misinterpretation There are 3 simulated situations: an empty tank, a tank with some gasoline, and a half full tank. We can see from the simulation that both…
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04 Sep 2021
By Shan Wei
GPR scanning for voids underneath concrete slabs

GPR scanning for voids underneath concrete slabs

Concrete Scanning, Geophysical Survey, Ground Penetrating Radar,
Ground penetrating radar (GPR) is a great tool for checking potential voids beneath concrete slabs. The concrete on the ground surface may look fine, but the void might already be developing and it's just a matter of time before it collapses. If you have a large area of concern for potential underground voids, scanning with GPR and doing test holes in GPR anomaly areas might be the best option. Geophysicists in Quark Scan are highly experienced in concrete scanning and underground void locating. Give us a call!
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