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9 This chapter describes technologies that use geophysics to detect and interpret the location of utilities already in the ground, reference utilities to a position on the earth, and store and retrieve utility information. The detection meth- ods detailed below are commercially available and broadly applicable. The relative merits and applicability of these tech- nologies are described, but not the theories behind them or instructions on how to use them. (Information on theory and use can be found in many of the references in the Appendices.) The technologies that are currently available include geo- physical sensors, survey equipment, CADD and GIS software tools, portable field computers, wireless communications, Radio Frequency Identification (RFID), Global Positioning System (GPS)-enabled cameras, and software. Some of the more recent and advanced technologies are integrated with multiple sensors and survey capabilities in a single platform (Young 2010). Technologies for detecting, tracing, position- ing, and depicting utilities are constantly improving. This results in an increasing number of options available to identify the location of utilities. Geophysical Detection Geophysical detection analyzes energy fields to find anoma- lies with the surrounding environment that might indicate the presence of a utility. Successful detection is a function of the utility material, the way that material is connected to other portions of the same system, the way that material is connected to the ground, and properties of the ground itself. There are many types of energy available (Sterling 2000). Sometimes field engineers will apply an energy field or use one that is applied by others or occurs naturally. Some of these energies are limited in power and amplitude owing to safety and interference issues. Some utilities can be detected by several methods, some can only be detected by one method, and some cannot be detected by any method other than exposure (Sterling 2009). A recent TRB product that assists in determining which type of geophysics is useful in a particular situation is the Selection Assistant for Utility Locating Technologies (SAULT), which can be found on the Internet at http://188.8.131.52/sault/ home.asp (Sterling et al. 2011). This tool was developed in part for project owners so that they could understand the broad toolbox necessary for the utility-mapping professional. electromagnetic pipe and cable locators Electromagnetic pipe and cable locators (EML) have been in common use since the 1960s. Recent advances in technology make it possible to measure and display current flow direc- tion, in addition to EMLâs traditional function of displaying signal amplitude. Advances also include multiple antennas and frequencies. EML devices come in a variety of available frequencies ranging from 50 HZ to 500 kHZ. The range of frequencies is essential in order to detect utilities in a variety of situations (TSA 2011). Most EML devices allow the operator to interpret the signal as being utility-related, mark the position of that sig- nal on the ground, and subsequently survey that mark. New devices can be equipped with mapping grade GPS capabili- ties. This positional data can be transmitted wirelessly to another computer or stored within the unit for later output. Most devices come with attachments that allow a signal to be better coupled to a known and exposed utility. Such attach- ments include cables, magnets, and inductive clamps. EML devices are limited to the possible detection of con- tinuously metallic structures or structures that can be made to act as if they are metallic (see Figure 3). Installation of a metal tape or âtracer wireâ directly above the utility during construction is one way to allow a non-metallic utilityâs loca- tion to be inferred. There are also metallic insertion devices for situations where pipes or conduits, typically empty and/ or out-of-service, can be accessed. Pipe diameter, material, number of bends and their proximity to one another, pipe con- strictions, and check-valve placement all affect capabilities. EML devices can also utilize sondes, or small radio trans- mitters, which are inserted into an accessible pipe or conduit. By detecting the sonde at numerous points as it is pushed through the pipe or conduit, the user can infer the position of the utility. Cameras can be inserted at the front of a sonde so that a video can be taken of the inside of the pipe or con- duit. This can be useful for condition assessment as well as location interpretation. Radio Frequency identification A type of miniature sonde, called RFID, has been employed more frequently over the last several decades (see Fig- ure 4). RFID âtagsâ are installed on or near the utility during chapter two state oF the technoloGy
10 construction or exposure for maintenance or other purposes. Some of these devices can be programmed to include infor- mation about the utility, such as ownership, type, size, and depth. Newer RFID devices are almost unlimited in the amount of data they can contain. Some devices transmit data when âinterrogatedâ on a particular frequency. The data can be encoded so that only proprietary devices can read them, but any device on that frequency can get a signal indicat- ing the utility is close by. Other manufacturers are using protocols that can be read by nonproprietary devices. RFID devices that have internal batteries can be detected deeper underground than devices that have no batteries and use the energy from the above-ground receiver. One drawback for a device with batteries is that it will eventually lose power. Just as with an inserted sonde, the user can use RFIDs to infer the position of the utility by âconnecting-the-dots.â Another highly important use of RFID is to confirm the interpretation of a utility as a particular one, since the RFID is unique to that utility (Dziadak 2009). RFID tags have been proven to play a significant role in utility damage prevention (Anspach 2011). Magnetics Magnetics (MAG) technology has not changed appreciably in decades. It is useful for finding buried steel or iron â single-pointâ structures such as buried manhole lids and valves. Although there are several types of MAG methods in use, the one that is most used for utility detection is a gradient-field magnetometer (see Figure 5). As with EML, once a utility has been detected with MAG technology, marks are usually placed on the ground for later survey. elastic Waves (sound) There are three separate techniques that are currently in use to trace utilities using elastic waves (additional techniques are currently in development). A pipe under mechanical stress may deform and generate noise. This noise can be measured. The noise should be loudest directly over the pipe because the elastic waveâs travel distance is the shortest at this point. However, the type of surface (e.g., soil vs. concrete), the type Figure 3 eML device in use to designate electric lines. (Photo courtesy of Cardno.) Figure 4 A marker ball rFiD/Sonde being programmed prior to emplacement. (Photo courtesy of VDOT.) Figure 5 gradiometer. (Photo courtesy of Schonstedt instrument Co.)
11 of fill (e.g., rock vs. clay), the degree of compaction, and ground moisture may affect the noise distribution, as may other sources such as aircraft, automobiles, trains, and elec- trical transformers (see Figure 6). As with EML, marks are usually placed on the ground for later survey once the loca- tion has been inferred. The following excerpt from CI/ASCE 38-02 (2002) fur- ther describes methods for using sound waves to detect sub- surface utilities: One method involves inducing a sound onto or into a pipe. This can be accomplished by striking the pipe at an exposed point or by introducing a noise source of some kind into the pipe. This may work for metallic, nonmetallic, empty, or filled pipes. A noise source may have the advantage of moving within the pipe for some distance, thereby getting the sound closer to the detec- tion point. By marking or measuring the loudest points, a trace of the utility may be accomplished. This method is sometimes known as âactive sonics.â A second method relies on the pipeâs product being able to escape the pipe. This method is sometimes known as âpassive sonics.â For instance, water escaping a pipe at a hydrant or service petcock will vibrate the pipe. This vibration will carry along the pipe for some distance before attenuation. Factors such as product pres- sure, shape and size of orifice, and type of pipe material will affect the initial sound generation. Pipe material, surrounding material, compaction, and product will affect the distance the sound travels along the pipe. Factors such as those already mentioned affect the sound detection between the receiver and the pipe. The third method relies on the pipeâs product containing a non- compressible fluid (water in most cases). Interfacing the fluid surface (e.g., at a hydrant) and generating a pressure wave in the fluid will in turn create vibrations in the pipe that can be detected. This method is sometimes known as âresonant sonics.â It has the advantage of being able to tune the oscillatorâs fre- quency to one (or more) of the resonant frequencies of the pipe, usually resulting in more tracing distance. A disadvantage is the need for many different types of fluid or oscillator interfaces. electromagnetic terrain conductivity Terrain conductivity methods create and measure eddy currents caused by differences in the average conductivity from the ground surface to an effective penetration depth of 5 m or so. Utilities (and/or the product they convey) may exhibit conduc- tivities that are different enough from the average soil conduc- tivity that they can be differentiated using this method. In areas of high metallic utility congestion, there is usually too much noise to interpret results. Similarly, surface metals (e.g., cars, fences, etc.) and reinforced concrete will distort results. There are two basic antenna configurations for electromag- netic terrain conductivity (EMTC). One is long and linear; the other is square. Both instruments have the capability to store collected data for download. Each instrument has its advan- tages. The long linear antenna measures average conductivity in a cone-shaped space from the ground surface to a depth of about 20 feet (see Figure 7). The antennaâs linearity can both augment and hinder a utility investigation. If interpretation of the data is in âreal-time,â the operator can view a difference in signal strength as the antenna is rotated and/or dipped. The resultant signal can give clues as to a utilityâs depth and direc- tion of travel, and can also give clues as to interfering nearby structures (Geonics 2000). It is recommended that real-time interpretation be used for utility detection with this device, as using an intersection survey point grid and collecting data only at these points can result in incomplete data (ASCE 2002). Isolated metallic utilities, underground storage tanks, wells, and vault covers are usually detectable by means of this method. Under some conditions, large non metallic water pipes in dry soils or large nonmetallic empty and dry pipes in wet soils may be imaged. Once a utility is identified, a mark is typically placed on the ground for later survey. Figure 6 resonant sonics receiver. (Photo courtesy of So-Deep, inc.) Figure 7 Terrain conductivity device. (Photo courtesy of So-Deep, inc.)
12 A recent advance in EMTC is the use of the square antenna (see Figure 8). This antenna shape is more efficient than the linear one and alignment of the antenna with the utility is not a factor in detection. Some technicians combine multiple anten- nas for a broader swath of coverage, decreasing the time spent collecting data, and increasing the density of the data returned. Improved data density allows for a more robust interpretation, and can be used to âseeâ utility trenches as well as the utility. The square antenna is usually coupled to some sort of survey equipment and the data are downloaded and plotted on plans without using markings on the ground. Quality control of the positioning is critical as there are no marks on the ground for correlation (Young 2010). Ground penetrating Radar Ground penetrating radar (GPR) is a sub-class of electro- magnetic methods. GPR is an established technology that until recently had a poor reputation. This reputation was the result of âover-sellingâ of GPR capabilities, difficulty of data inter- pretation by typical utility locating personnel, and unreliability of components. That has changed within the last decade, and GPR has become widely accepted within the subsurface utility engineering market. However, âcontract locatingâ or One-Call providers still find the equipment too expensive and compli- cated for their purposes (Sterling 2007). The main benefit of GPR is that it can detect virtually anything that contrasts with the surrounding underground environment, such as non-metallic pipes, edges of trenches, and plastic conduits. Another significant advantage is that when an image is received, its depth can be determined fairly accu- rately, and accuracies can be increased through calibration of the signal velocity over targets of known depths. This con- trasts with EML methods, which provide a less reliable depth measurement. GPR does have limitations. In conjunction with other technologies it can be used to interpret a very accurate pic- ture of the subsurface environment (TSA 2011). Approxi- mately 50% of the land area of the United States has soils that are unsuitable to obtain any meaningful data on utilities regardless of size, contrast, or depth (USDA 2009). Local use of pavement de-icing salts can also increase soil conduc- tivities where the salt washes off, rendering GPR less reliable at the edges of paved areas in northern climates. Surface con- ditions such as uneven ground and physical obstacles may limit survey coverage. Additionally, the depth of penetration is inversely proportional to the size of the utility that can be imaged. This implies that small pipes and cables can be difficult or impossible to see at greater depths. Sometimes a utility can be inferred through seeing the edges of a trench, even when the utility is deep (Sterling 2009). There are different types of GPR that involve permuta- tions of single or multiple frequencies, numbers of antennas, orientations of antennas, types of data storage, and display capabilities. Each has its advantages and disadvantages. For the purposes of this study, we will classify them into two main groups: basic GPR and advanced GPR (Green 2006). Basic GPR has a transducer that sends out an electro- magnetic signal (see Figure 9). Electromagnetic waves are Figure 8 Multiple square antenna eMTC with integrated survey. (Photo courtesy of uiT.) Figure 9 Basic gPr unit. (Photo courtesy of So-Deep, inc.)
13 reflected, refracted, and diffracted in the subsurface by changes in electrical conductivity and dielectric properties. Travel times of reflected, refracted, and diffracted waves are analyzed to give depths, geometry, and location information. The energy returned to the antenna is processed within the control unit and displayed on a screen. Round targets (typical of a utility) are of a distinctive shape and therefore easy to interpret. The operator usually places a mark on the ground where a target is identified, and then moves to the side and repeats the process until a series of marks can be interpreted as a probable utility. An analogy is that of a fish-finder on a boat, but instead of identifying schools of fish, the field engi- neer looks for long linear features. The marked utilities are then surveyed to record their location. Advanced GPR has multiple sensors for better data den- sity, and integrated positioning hardware to correlate the equipmentâs location to the data associated with that loca- tion (see Figure 10). Real-time analysis is usually not pos- sible, and interpretation of the data is done at the office by highly skilled technicians. One advantage of advanced radar is the speed at which data can be collected, which reduces the amount of time spent on roads, aprons, taxiways, and runways. The higher data density allows better interpreta- tion, and for some radar configurations, the multiple frequen- cies can increase the ability to see utilities at greater depths. Instead of the operatorâs stopping every few seconds to place a paint mark on the ground, he/she uses a small tow tractor. Another advantage is that the data delivered is more compre- hensive than with basic GPR. A cross section through any part of the data will yield depth information at that point, rather than the interpolated depth information gained through basic radar. Another significant advantage of advanced GPR is that other subsurface characteristics such as paving thickness, bedding thickness, voids, thrust blocks, depth to bedrock, depth to water table, soil lenses, and contamination plumes can be detected as well (see Figure 11). This increases the value of the utility mapping process. Both EMTC and GPR methods can gather this type of data (Young 2010). positioninG MethoDs The state of the technology for mapping the positions of exposed or remotely sensed underground utilities is con- stantly and rapidly changing. Surveying methods and tech- niques have embraced new technologies such as total stations, spatial stations, and GPS to make it faster and cheaper to col- lect more accurate data. total stations Total stations can be divided into two basic types: mechani- cal and servo-autolock-robotic. Mechanical total stations are useful for surveying lines (paint marks representing utilities) and structures. Robotic total stations are useful for surveying the locations of advanced geophysical instruments as they are traversing a site. Total stations are oriented to known ground control points, and generally require a survey team of several persons, survey control identification, and processing of the survey data. spatial stations Spatial stations are relatively new. They combine the precision of traditional point surveying with the ability to capture shapes and details, and coordinates with integrated video and 3D scan- ning (see Figure 12). Global positioning system GPS comes in many different forms and is rapidly chang- ing. For the purposes of this study, GPSs are divided into mapping grade and survey grade. The differences are in cost, accuracy, and procedure. Further details on this technology can be found at many GPS manufacturersâ websites.Figure 10 Advanced gPr. (Photo courtesy of uiT.) Figure 11 Output from an advanced gPr. (graphic courtesy of uiT.)
14 ences between the surveyed position and the initial position are used to calculate inertial drift. If the variance is unaccept- able, the distance of travel may be shortened and the process attempted again. The inertial device produces a read-out that plots its location as it travels through the pipe (Sterling 2007). electRonic inFoRMation stoRaGe, RetRieval, anD analysis Utilities data have traditionally been recorded on engineering drawings and related documents. Years ago, these drawings were hand-drafted on parchment material, paper, or Mylar. Because these historic records can still be of significant value, they are often scanned and saved as electronic images in TIF or PDF format. Interviews with some airport staff indicated that this can amount to tens or hundreds of thousands of drawing sheets that can be stored, searched, viewed, copied, and backed up much more efficiently than their hard copy equivalents. Electronic data about utilities can also be disseminated more easily than hard copy drawings. Advances in Internet security, the growing use of mobile computing devices, cloud computing (i.e., Internet) resources, and other advances have made it easier to exchange data with less fear of sensitive data getting into the wrong hands. computer automated Design and Drafting Over the last few decades, airport engineering drawings have been developed predominately using CADD software. Because they are produced electronically, the original draw- Real-Time Kinematic (RTK) GPS equipment can yield absolute positions of 1â2 cm horizontal accuracy in real time without post-processing. RTK surveys require few obstruc- tions in the field area, ideal for airfield settings (see Figure 13). Less accurate GPS is useful for some related utility appli- cations. An example of this is the GPS-enabled camera, which can take a picture and associate the location of that picture with a particular geographic spot, indicate the direc- tion the camera is pointing, and insert an icon into a CADD or GIS system that will, when clicked, bring up the photo- graph for viewing while you are looking at the CADD or GIS drawing (see Figure 14). ineRtial MappinG Inertial mapping methods use the same technology as sub- marines to track positions through the use of gyroscopes. A survey reading is taken with traditional means at the open- ing to a conduit or empty pipe. The inertial device (called a âsmart pigâ by the oil and gas industry) then travels through the pipe to either an end point or to its tethering limit and then retrieved. Its location is surveyed again and the differ- Figure 12 Spatial total station. (Photo courtesy of Trimble.) Figure 14 rTK gPS on 3-D advanced gPr array. (Photo courtesy of Cardno.) Figure 13 rTK gPS positioning on eMTC System at airport. (Photo courtesy of uiT.)
15 enhances traditional CADD by providing sophisticated 3D models that can be used to assist facility designs and improve the efficiency of the design process. BIM also enables sophis- ticated analyses that can support cost estimating, material ordering, conflict detection, environmental efficiency, and other factors throughout a buildingâs life cycle. As the use of BIM grows, new tools are being developed to aid in the plan- ning and design of utilities networks (Ball 2011). technoloGy inteGRation The above-mentioned technologies are becoming increas- ingly compatible, so that the most appropriate software can be applied where and when it is most effective. International, national, or open (i.e., nonproprietary) commercial standards defining the structure and format of utilities data foster this compatibility. Many airports have defined GIS and CADD data standards that are compatible with one another so that software tools can migrate data from CADD to GIS and back again. These data standards also enable GIS and CADD data to be exchanged with other airport information systems, such as asset management and computerized maintenance management systems (CMMS). One large hub airport that has invested a great deal in CADDâGIS interoperability notes that while significant advances have been made, data exchange between CADD and GIS has plenty of room for improvement. Coordinate system transformations, differ- ences in how GIS and CADD data are traditionally structured, and divergent user preferences are all factors that need to be taken into consideration (Reid 2003). The benefits of exchanging data between different soft- ware applications on different hardware platforms are, how- ever, great. For instance, it is now possible for a professional with a single hand-held device to stand at a spot on the airport property, look at a screen that has an overlay of satellite imag- ery, have the location shown on that imagery, look at all the utility locations, change those locations if there is better infor- mation, receive information on those utilities from RFIDs, retrieve more detailed information from records stored in a database either on site or on the Internet, and send that infor- mation immediately to almost anyone, anywhere. Another example is combining GPS with laser scan- ning equipment to map utilities before they are buried. A 3D position of underground utilities constructed by open trenchless methods can be collected by a single per- son using integrated technologies within an accuracy of Â±450 mm (Â±1.5 ft). Furthermore, the positional data of a 30 m (100 ft) long utility line can be collected within approximately 15 minutes, including time taken for setup (Ariatnum 2010). ings can be stored, backed up, retrieved, and viewed much like scanned hard copies. To reduce their file size and to pre- vent alteration, CADD drawings are often converted to a TIF or PDF format for archival purposes. CADD drawings can also convey a great deal of infor- mation about components of a utilities network. Increas- ingly, these components are drawn accurately in 3D and in a known coordinate system so that other relevant data can be superimposed to yield a more informative map. Different types of utility components are drawn on specific layers that can be turned on or off and easily symbolized to distinguish between other types of utilities. Labels, dimensions, call- outs, and other annotations provide additional textual details. More advanced CADD software allows these details to be stored in a database format that supports queries and analy- sis. Metadata, or information about the data itself, is stored in the drawingâs title block, title/index sheets, and in letters of transmittal. Some advanced CADD software packages include or can be augmented with utility models that offer advanced analytic tools to support network capacity imaging and upstream/downstream tracing. Geographic information systems GIS has emerged over the last decade as a means to store engineering data. When GIS technology was first introduced in the 1960s it was not viewed as a precise enough tool for engineering applications. Advances in the precision of GIS data, as well as in the compatibility between GIS and CADD software, have allowed GIS to become a practical tool for engineering purposes. As a result, most utility companies and a growing number of airports are using GIS as a means of storing, retrieving and analyzing utilities data. One of the primary benefits enjoyed with GIS is the ability to perform advanced queries and analyses of detailed loca- tions, attributes, and metadata. Once specific utility compo- nents have been identified, linked drawings, specifications, and photos that provide further information can be easily retrieved. GIS also enables advanced models to be developed that carry information about the direction and capacity of products traveling through a utility network. These models offer additional analytic abilities such as capacity planning, what-if analyses, isolation of branches impacted by a break, and tracing the likely source of pollutants. Building information Modeling Building Information Modeling (BIM) has emerged as a technology to model and depict information about the struc- ture, utilities, furnishings, and other details of buildings. BIM