Encouraging Innovation in Locating and Characterizing Underground Utilities (2009) / Chapter Skim
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Pages 22-37
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22C H A P T E R 4 Utility Locating TechnologiesIntroduction "While it is hard to find a black cat in a dark coal bin by optical means, it is easy to distinguish its furry outline from hard coal by touch" (1)
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23Designating The process of using a surface geophysical method or methods to interpret the presence of a subsurface utility and to mark its approximate horizontal position (its designation) on the ground surface.
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24Table 4.1. Utility Locating Terminology (continued)
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25Frequency Range Acronym Common Name Type of Instrumentation 30 GHz – 300 GHz EHF Extremely high frequency (microwaves) None yet 3 GHz – 30 GHz SHF Super high frequency (microwaves)
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26imposed on the wires by the consumer using the power. As the load changes, so does the signal strength.
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27maximize utility detection and tracing, and for safe opening of utility appurtenances. Practitioners employ several pieces of equipment with direct connect wire and toroid clamps.
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28better in those situations in which the utility is metallic but its joints are not, precluding a good circuit for the pipe and cable locator method. A small clay sewer pipe is not much different in dielectric constant than the surrounding soil.
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29snow on the ground above it is melting because of the temperature difference. Some utilities -- including steam lines, energized power cables, sanitary sewer lines, and industrial process lines -- give off significantly more heat than others, but the deeper a utility is buried, the less chance there is that the heat signature can be detected at the surface.
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30is selected, wave propagation through the earth or the utility is beyond the technician's control. Receiving the elastic wave is also largely out of the technician's control, although various types of ground surfaces can enhance or decrease the signal.
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31decreasing tracing distance. There is at least one commercial manufacturer of equipment using this technique.
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32interpretations to be immediately cross-checked through other field measurements. Geophysical diffraction tomography (GDT)
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33type, or just a cautionary message. A disadvantage of a tracer tape is that once it is broken, it is difficult to splice the tape back into a continuous conductor, rendering future detection by geophysical means highly improbable.
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34fying buried assets. The report concluded, "These trials show the need for substantial improvements in equipment performance" (4)
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35apply CDF's properties to the advantage of surface imaging could be further explored. For the time being, knowing whether the CDF (or concrete)
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36Tracking Heads (Sondes) During Installation One system for controlling an underground boring tool involves the use of gyroscopes, accelerometers, magnetometers, or all of these to track the movements of the boring tool.
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37Record Updates Utilities are exposed for reasons other than initial installation. Typical reasons may include ongoing maintenance activities such as repairs, new service connections, and anode emplacement.
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