One of the recommendations from the SHRP 2 R01 study, Encouraging Innovation in Locating and Characterizing Underground Utilities, was “the development of locating technologies that target deep utilities that currently cannot be detected by surface-based approaches. These could include direct-path detection methods deployed from inside a utility or cross-bore techniques based on vacuum-excavated boreholes.” This recommendation garnered a low priority because of its expected technological difficulty and probable low return on investment. As a result, there was a slight realignment in goals to include the concept that it is not always deep utilities that prove difficult to locate; there are also utility systems that are hidden or masked by those utilities that reside on top of them. It is more likely that these shallower utilities, difficult to locate, would be more frequently impacted by highway construction. Therefore, the SHRP 2 R01C project proceeded with the concept that “innovations to improve the extent of the locatable zone” might produce a larger return on investment to the transportation community. The R01C project worked closely with the R01B project, Utility Locating Technology Development Using Multisensor Platforms, to avoid duplication and provide a complementary set of tools. Some activities of the two projects were conducted together and jointly analysed in order to be in harmony. Additionally, the two projects had a common technical expert task group (TETG) and user group for guidance and feedback on direction. One of the first activities undertaken by the projects was a literature search. The literature search discovered 24 possible technologies available to detect and map utilities. Some of these techniques require a large amount of development to make them usable for application in the field. The goal of this R01C project is development of near-term solutions. Therefore, techniques requiring technological breakthroughs were eliminated from consideration, as were technologies that are unsuitable for deep or stacked utilities. Factors that make them unsuitable include Federal Communications Commission (FCC) power and frequency restrictions, geometry restrictions, and terrain/environmental issues such as traffic. On the basis of the literature review and with guidance from the TETG and the user group, this project proposed research into developing fie complementary technologies: 1. Pipe mapping using inserted inertial navigation devices; 2. A scanning electromagnetic (EM) locator; 3. Seismic reflection location using an aboveground seismic generator; 4. Active acoustic location using an acoustic generator coupled to the pipe being located; and 5. Long-range (in excess of 10 ft) radio frequency identification (RFID) tags. Details on all fie technologies and their progress are included in this report. During the course of the project, these fie technologies were reduced to two for prototype development: * Smart tags detectable on utilities at depths of 20 ft. These can be read to obtain stored information such as pipe depth, date of installation, pipe size, and content. * Active acoustic technology that injects pulses of sound into a pipe utility. The sound propagates though the medium in the pipe and is detected at the ground surface. This technology uses lower frequencies than units on the market and uses time of flight (TOF) rather than amplitude detection. The same equipment can be used in a passive mode to detect certain utilities that cause vibrations, such as three-phase electric cables. RFID technology is a wireless technology that can provide both location and positive identification. A typical RFID system includes two components: a transceiver (equipped with an antenna) and a buried RFID tag that is programmed with unique information. The transceiver initiates the communication with the buried RFID tag. Commercial RFID readers typically incorporate the transceiver and the antenna into the same assembly. Commercial smart tags now in place can be detected in soils to a maximum of 6 ft. This limitation forces the placement of tags over, rather than directly on, facilities beyond this depth. Nearby excavation may destroy or relocate these “floating” tags. To overcome the depth limitation, it was necessary to develop active tags containing an internal battery. Long battery life and range are therefore the two critical components not yet found in commercial RFID systems. The smart RFID tag developed from this research project is suitable for utilities at 20-ft depths, with an expected 50-year battery life. This prototype tool builds on an existing device designed for the gas industry. It consists of a transmitter for acoustic signals and six receiving accelerometers. In application, the acoustic transmitter is coupled directly to a free end of the pipe being located. The array of six wireless sensors is deployed across the suspected path of the pipe. An acoustic signal is sent, and the signals from the sensors are correlated. The user receives feedback on where the signal strength is greatest. The user can move the sensors until the best signal is obtained and centered. The depth can then be estimated from the acoustic TOF. The solutions to locating deep and stacked utilities are not easy to come by with geophysics. Government policies, utility installation practices, geotechnical constraints, and physics all work against developing cost-effective and field-implementable solutions. Mandating accurate and reproducible records of utilities during installation is the recommended path forward to keep the problem from getting worse. Mandating placement of some type of RFID for every instance where a utility is exposed is a reasonable means to implement this recommendation. The R01C project tested two prototype tools that with further development may combine to provide solutions in certain situations. The project has also developed valuable information for future researchers on three technologies that did not reach the prototype stage. (Author/publisher)
Samenvatting