Innovations to Locate Stacked or Deep Utilities (2014) / Chapter Skim
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32 Combined Technical Assessment of SHRP 2 Projects R01B and R01C Executive Summary The objective of this project is to design, construct, and test prototype instruments for locating buried utilities. These prototypes will be based on new and emerging technologies.
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33 and returning to the surface. Examples include GPR and seismic reflection location.
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34 General Background on physics of detection Almost all subsurface measurements fall into four basic categories: 1. Electromagnetic.
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35 Table B.1. Potential Technologies to Detect and Map Utilities Technique Utility Material Property Measured Soil Type Detection Limit Critical Property Development Needed State of Development Acoustic holography Any Seismic velocity or attenuation Any Approximately 30 ft or less Seismic velocity or attenuation contrast High Low Active EM detection Conductive Radiated EM signal Any Less than 50 ft Radiated field strength -- imposed on line Available now NA Frequency-domain EM Generally conductive Induced EM field Nonconductive Less than 10 ft Conductivity contrast Available now NA Capacitive EM Any Low-frequency EM Any Less than 20 ft Dielectric contrast Moderate Low Gas detection -- chemical Gas filled or containing volatile Concentration Any Less than 50 ft Gas or contaminant concentration Moderate Low Ground-penetrating radar All Reflected EM field Nonconductive Less than 30 ft Conductivity/permittivity contrast Available, but modifications in progress High Induced polarization Conductive Electrical potential Any Approximately 30 ft Conductivity contrast High Low Infrared thermometry Any Temperature Any Approximately 10 ft Temperature contrast Available NA Leak detector Fluid filled Sound Any Less than 20 ft -- leaksize-dependent Radiated pressure field Available in several forms NA Magnetic field Magnetic Magnetic permeability Nonmagnetic Less than 25 ft Magnetic susceptibility contrast Available NA Metal detector Conductive Induced EM field Relatively nonconductive Less than 25 ft Conductivity contrast Available NA Nuclear magnetic resonance Contains polar molecules Spin resonance Relatively dry Unknown Variations in water content Moderate to high Existing systems are used on very large targets.
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36 Seismic refraction Large diameter Seismic velocity Any Approximately 30 ft or less Seismic impedance contrast Available but not for utility mapping High Seismic tomography Size dependent Seismic velocity or attenuation Any Approximately 30 ft or less Seismic velocity or attenuation contrast Available but not for utility mapping High Spontaneous potential Conductive Electrical potential Any Approximately 30 ft Conductivity contrast Available but not used for utilities Moderate Sonic Hollow pipe Sound Any Less than 50 ft Radiated pressure field Under development by Mapping the Underworld (MTU) Low to medium Sonic and subsonic acoustics Any, preferentially large diameter Seismic impedance or scattering Any Less than 150 ft Acoustic impedance contrast High Low Spectral analysis of surface waves (SASW)
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37 Electromagnetic Properties of Soils Electromagnetic wave propagation in soil is governed by Maxwell's equations. These equations can be solved in one dimension for a wave propagating into a conducting medium (5, 6)
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38 a superposition of the regression equation. Rough estimates for er can be made from the following general values for moisture content in soil.
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39 f fr r { }( )
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40 travels 6 ft, the attenuation is 5.1 × 6 × 0.5 = 15.3 dB [dB = 20 log (A/Ao)
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41 waves can have advantages. For example, in a soil with a longitudinal velocity of 280 ft/s, a wave with a frequency of 280 Hz will have a 1.0-ft wavelength, as indicated by the pink arrows.
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42 depth of penetration. The depth of the object is calculated by multiplying the travel time by the wave velocity.
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43 method can be skewed when interfering signals from adjacent pipe are present. In such cases, the peak and null signals do not occur in the same place.
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44 One version of this technology is being developed by Underground Imaging Technologies (UIT) as part of their digital multisensor system.
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45 active techniques can be implemented with the same sensors, signal-processing hardware, and readout display. The difference is that the active technique requires injection of a signal.
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46 Inertial Navigation Internal mapping starts at a known location of the buried utility, inserts an instrument into the pipe, and moves the instrument through the pipe. New and emerging inertial navigation system (INS)
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47 flowing in the pipe create temperature differences between the pipe and ground. These in turn create a temperature field at the surface of the ground, with the highest or lowest temperature above the pipe.
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48 the entry point. For this tool, GTI will work with Geospatial and their commercially available Smart Probe to make operational improvements in three areas.
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49 ground. These waves will propagate to the pipe and reflect to sensors on the surface of the ground.
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50 Seismic and Acoustic Compared One of the overall goals of the project is to develop a suite of complementary technologies. The seismic reflection method has the advantage at locations where the buried facility is inaccessible.
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51 to field methodology and data processing, it may be possible to improve the time efficiency and cost of S-wave seismic surveys to make them both functionally and economically useful for utility mapping. The use of multiple sensor, multiple antenna/transducer geophysical systems for improved mapping of buried utilities has been demonstrated and is used in the commercial market today.
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52 Table B.4. Locating Technologies Matrix Technology Horizontal Accuracy Vertical Accuracy Factors Effecting Accuracy Ease of Use Features Examples Comments Electromagnetic pipe and cable locators 2–12 in.
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53 nonplane Wave Bibliography Annan, A
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