UTILITY AND SERVICES MAPPING
One of the main modern applications for Ground Penetrating Radar is that of underground service and utility (pipe and cable) location. Common practice for locating underground services involves the use of an electromagnetic induction wand (eg Radiodetection RD8000). As Induction wands are handy and successful tools for locating metallic objects (eg telecoms), they are really only covering half or less of the potential underground services. In order to locate non metallic targets (eg poly pipe or terracotta pipe) as well as metallic objects, a Ground Penetrating Radar is required. As most services lie within the top 2m of subsurface, the ideal GPR antenna frequency (400-450MHz) is required for optimal depth penetration and data resolution. Such investigations for service location may range from single service locations for residential properties to complete site characterisations for large commercial/industrial sites. Therefore whether you require ‘locate and spray’ investigations or full data post processing and mapping, MALA GPR has the instrument to suffice within the Easy Locator HDR (2D), Easy Locator HDR PRO (2D), Ground Explorer HDR (2D) or MIRA (3D).
Service and utility location is never 100% and locators often tend to leave site doubting their interpretations and not completely understanding the full extent of the subsurface utility network. Use a MALA Ground Penetrating Radar, compliment it with an electromagnetic induction wand, and be certain!
CASE STUDY: LARGE SCALE INDUSTRIAL UTILITY MAPPING
Application – A large commercial factory site (~4 hectares) that has been in place for over 50 years was in need of a ‘site characterisation’ for ALL underground services. They had limited records of old inactive/active services that were believed to be varying in depth, some extremely shallow.
The MALA MIRA 400MHz antenna was used, being custom mounted to the front of a John Deere mower. With a 400MHz antenna running 16 GPR channels, the system was setup to require only a single pass over the surface to gather enough data for 3D modelling. Full RTK GPS was used in conjunction with the GPR survey for sub inch accuracy positioning. The entire rig arrived on site on a trailer and was pre-setup to virtually begin data collection immediately. The site was covered in a few days with an additional couple days designated for data analysis, post-processing, interpreting and reporting on the data/project. Figure 1 displays the approximate GPR coverage throughout the entire factory site, as monitored by RTK GPS.
A surprising amount of underground services were detected on site. Figure 2 outlines the GPR data response as seen in post processing software. The linear features indicate the presence (and depth) of underground services. Throughout the whole survey site, an incredible amount of services were found and can be seen in figure 3. Figure 3 displays interpretations made (Blue) on top of the total coverage area (Yellow). In addition, areas of voiding were discovered (Black) and marked on the site map. Figure 3 is available as a .dxf file delivered to the client that can further be imported in CAD and similar GIS software packages. The .dxf file includes the GPS positioning of the service/void interpretation markers which have a depth value attached to them.
The information was of high assistance and value to the client as they were able to locate their shallow (potentially dangerous) services as well as contribute the results to aid in rebuilding their site plans, which initially were completely unknown.
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