Ultra Wide Band GPR Survey using DXG1820

As part of runway rehabilitation program works, our client instructed us to undertake a Ultra Wide Band GPR survey of the areas. The objectives of the survey were to identify the depths and positions of utilities, individual asphalt layers, the presence of significant cracks, depths and extent of any voids/delamination and the depth and extent of any reinforcement.

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The survey was situated within the pavement area of the Northern Runway. Additionally, the project includes Main Runway, Northern Runway, Connecting Taxiways and a 10m swathe around the grassed areas. This image shows final coverage achieved.

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Using an UTV survey vehicle, the GPR system was towed along each block with overlaps to provide maximum coverage. Parameters of the equipment were tailored accordingly prior to survey commencement. The distance measuring wheel (DMI) was calibrated to the survey vehicle used and parameters were set to trigger samples of 7.5cm intervals. During the first visit to the airfield, 7 known control points were located and surveyed using RTK GNSS to compare accuracy of GPR data collection positioning.

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All surveys were undertaken using the following method: M4P.

No EML was to be applied to the survey at this time therefore a maximum QL-B2P was achievable and quality levels within the survey data for each utility would range from B2P to B3P in line with PAS128 specification.

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All detected / potential utility infrastructure had been cross referenced against the client’s provided records where positions of detected utilities matched client records, the Utility had been designated to the appropriate layer. Instances where evidence did not support the positioning of buried assets from surveyed or available records were plotted as unknown.

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Identified utilities were annotated onto the drawing and modelled as B2P, or B3P if an accurate depth of the utility could not be determined. The client’s Utility Records did not show the same amount of utilities detected. Utility density is far greater. Particularly the AGL network within the asphalt layers. Along utilities, all structural findings and delamination targets were plotted to the CAD drawings. The average visible depth achieved was 3m.

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Beside utilities and structural findings, the scope also included detecting all layers that make up the runways and taxiways. Old core hole records were used to identify the layers and to calibrate the GPR data.

Lines were created where the scope called for long sections. These lines were brought in to Examiner and they were moved, onto the layers, then exported back to CAD, where the longsections were created.

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Processing and Final Output Images

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This image shows one block processed in Examiner, before adding any targets.

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Here is the same image after plotting utilities, concrete slab edges, metal mashes, etc.

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This is what this area looks like after editing it CAD.

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This is an example of the PDF version of the final deliverable, plan view.

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Example of pavement damage/debonding in Examiner.

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Example of long sections / Pavement Profiles final output.

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Example of Reflected Energy Profiles. It was a special request from the client to produce these profiles. In order to maintain high quality, the tracing lines were broken up to no longer then 50m. These lines were used in Examiner to open virtual long-sections, images then were exported, and stitched together in AutoCAD.

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22 shifts – on site
~176 hours – surveyed
~850 hours – post processing divided between 3 people done in 7 weeks, 4 of those were parallel processed while site works were carried out. This gave us 3 weeks to deliver the final package after site works finished.

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Reflected Energy Profile and Pavement Profile has been presented through 50.1km on this project. Dowel bars, Cracks, Bay Patterns and surface features (e.g. Slot Drains) are not included in the statistic.