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GPR News - September 20

Locating Steel In Concrete - Webinar and White Paper

PCTE have recently produced a white paper, and are presenting a webinar on the topic "Locating Steel in Concrete".

The focus is on the reasons that users of NDT equipment may wish to locate steel in concrete, a comparison between the two most common technologies [GPR and Pulsed Eddy Current Covermeter] and some simple case studies of each systems output.

The intent is that either presentation is helpful to those who use location tools, or people who need to specify location or review the output of either technology. 

Please find links below to access the White Paper document and a video embedded for the webinar. 

Download the Locating Steel in Concrete whitepaper

 

Case Study- Random Walk Depth Slices

Grid Scanning or Depth/Time Slicing is a method of displaying Ground Penetrating Radar data.

It involves fitting together the usual 2D Line Scans (also called B-Scans) into a 3D solid and viewing the data in a plan view from above. The data is collected in a grid pattern over the area to allow for the 3D solid to be formed.

Conventional GPR Depth SliceFigure 1: Depth Slice Formation
The advantage of the technique is that the Plan view creates a map for the user to follow, with buried targets for a particular depth shown. It is especially helpful where targets are at differing angles and hence line scans are showing targets at multiple positions. The disadvantage of the technique is that for Utility Location GPR it is time consuming, relies on relatively unencumbered site and the image quality is constrained by the ability to follow the grid accurately.

The concept of random walk alleviates a large percentage of the disadvantages. Rather than being constrained to a grid, the GPR is connected to a GPS. The GPS tracks the position of the GPR and allows the Depth Slice to be formed without need for a highly regulated grid pattern. Instead the user can “Randomly Walk’ covering the area in any direction and allow the software and GPS to resolve the image. The idea is demonstrated below in Figure 2.

random walk B Scan
Figure 2: Path collated by GPS with GPR data fitting the actual path

During a recent demonstration of the process PCTE collected data at a local university shown on Google earth it can be seen that a rough grid was collected over the survey area.

random walk Google earth
Figure 3: GPR Path collected by GPS shown on Google Earth (left) and a projected grid (right)
Almost immediately the target horizontal to the image can be seen. The right image in Figure 3 shows these confirmed as interpretations from the Line Scan data.

random walk shallow deep
Figure 4: Depth Slices at increasing depths
The image on the left in Figure 4 shows the 3 pipes, whilst the image on the right shows a fourth target deeper and perpendicular to the path of the other three.
Overall the data collected took about 10 minutes and the processing shown an additional 10 minutes.

This demonstrates that the reluctance to Grid Scan caused by the time intensiveness of the process is almost completely alleviated and the project is probably completed faster and with a better deliverable than with Line Scan methods.

VIC:

Stuart McCurdy

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M: 0428 315 502

 

Monica Simhadri

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M: 0488 331 244

QLD:

Michael Dubery

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T: (07) 3040 6166

M: 0419 477 715

NZ:

Jun Han Lee

T: +64 9 377 6778

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M: +64 274 738 758

WA:

(Head Office)

T: (08) 9322 4020

Derek Burns

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M: 0498 800 373

Reuben Barnes

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M: 0408 034 668

NSW:

T: (02) 9453 9999

William Ward - NDT / Instruments

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M: 0418 381 709

Jeshwin Mohan - Lab / GPR 

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M: 0487 043 466

Warehouse / Service Centre

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T: (02) 9453 9941

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