SUBSURFACE UTILITY DETECTION
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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.
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 ONE: LARGE SCALE SITE CHARACTERISATION, PORT FAIRY
A large commercial factory site (~4 hectares) that has been in place for over 50 years was in need of a ‘site characterisation’ for locations of ALL underground services (including redundant 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. Throughout the whole survey site, an incredible amount of services were found and can be seen in figure 3. The linear features indicate the presence (and depth) of underground services. The resulting data is available as a .dxf file (CAD or simliar comaptible GIS file) 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. CASE STUDY TWO: SHOPPING CENTRE UTILITY INVESTIGATION, WA A busy Perth shopping centre had plans to clear existing shopfronts and refit the entire area. Electrical pits were cluttered and there were no clear plans of the subsurface utility setup. New shopfronts were to require electricity and in order to accommodate the developers required as-built plans of the current service layout. A 1300MHz 3D instrument was deployed in a hand pushed custom cart. As GPS reception was not possible, a laser tracking total station was used to position the project and track the GPR. The GPR was successful in locating a large network of subsurface linear features. These reults were provided to further work in conjuncton with qualified cable locators to determine location/depth and type of service for the entire shopping centre. Such a process would not be as tidy or efficient without the aid of non destructive imaging instruments. |
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