Buried infrastructure suffers from “out of sight, out of mind” until a backhoe takes out a line, and now a community is without electricity or water or cable.
A line strike can add thousands to tens of thousands of dollars in project costs and can sometimes be dangerous or even deadly.
Underground utilities include the following:
- Pipelines (natural gas, oil)
- Steam and oxygen lines
- Telecommunications lines (phone, TV, coaxial, fiber optics)
- Electrical lines
- Water and irrigation lines
- Sewer, storm, and sanitary laterals
- Printed maps are sometimes old, inaccurate, and incomplete. It can be more cost-effective to “scan” a project site for underground utilities than to find out by digging. Through the use of radar and other non-destructive technologies, what is in the subsurface can be known without ripping things up.
What lies in the subsurface of a job site? Where is it? How deep is it? What is it? Underground utility location helps reduce the guesswork.
Techniques and Technologies
Electromagnetic utility location is one of the most common and cost-effective techniques, and it is quite accurate up to 10–15 feet. The locating equipment generates an electromagnetic radio signal that is directed onto the utility line. Metallic pipes will be detected, and all non-metallic material is ignored. It is used to locate gas, electric, telephone, cable, propane, water, sewer, storm, and irrigation lines that are made of metal or have conductive tracer wire.
According to utility location original equipment service provider multiVIEW Locates, there are three types of signal application techniques: straight induction, direct connection, and induction clamp. When using straight induction, the transmitter is placed over the target and emits an electromagnetic field without connection to utility hardware. When using direct connect, a signal lead cable connects the transmitter to a piece of utility hardware that is connected to the target. When using induction clamp, the clamp is placed on exposed cables and then energized by the transmitter, and produces a magnetic field that then gets transferred onto the cable.
Since this technology can’t locate non-metallic items, sometimes a metallic tracer wire gets laid along a pipeline when it is installed so that it, which is composed of non-magnetic material, can be located using electromagnetic utility detection technology.
Besides not being able to locate non-metallic materials, the technology doesn’t accurately reveal an object’s depth.
Ground penetrating radar (GPR) is an effective and non-destructive technology that transmits high-frequency radio waves into the ground and then analyzes the reflected energy to create a profile of the subsurface features. GPR waves reflect off different materials and compositions in the subsurface. Each transmission (or pulse) emitted by the transmitter results in reflected energy that gets recorded; recordings are called traces. Traces are placed side by side to create a cross-sectional image (or profile) of the subsurface.
Since it can locate non-metallic material, it often gets used in applications where the previous electromagnetic methods aren’t well suited.
A Sensors & Software client obtained the necessary information to design a new water line installation that avoids existing utilities.
“GPR is a complementary technology. It complements other locating technologies. It’s very important for people to know to understand what GPR can and cannot do. Its performance will vary depending on your soil conditions,” says Troy De Souza, training manager, Sensors & Software Inc.
GPR is divided into three frequency categories: high, medium, and low. High-frequency GPR (1000 MHz or greater) is not great for utility locates in soil because the signal doesn’t reach as far as lower frequencies, but it does provide a clearer picture (less distortion) than lower frequencies. It is are most frequently used to locate objects within or below concrete structures, such as rebar or electrical lines. Medium frequency GPR (500–250 MHz) is used for subsurface utility mapping, as well as for archaeology and forensics. It can penetrate several feet deep while offering a good resolution (which means little distortion). Low-frequency GPR (250 MHz or lower) is used for deeper subsurface utility mapping, as well as geologic mapping and geotechnical applications.
GPR has several limitations: it can’t function at optimum levels when locating narrow-diameter objects at greater depths, when working in a congested area, and when working in soils that have high conductivity, such as shale or clay. GPR also requires greater training to use.
Utility locating contractor GeoScan achieves a more complete picture of subsurface utilities by combining GPR data with electromagnetic data. They also champion a process called subsurface utility engineering (SUE).
According to the company, SUE involves collecting existing utility records, applying geophysical methods to determine the presence of subsurface utilities and then leveraging techniques such as GPR or vacuum excavation to verify the horizontal and vertical positions of objects. The process applies four quality levels (records research, field investigation, utility locating, and daylighting) to gather precise information on underground utilities.
All the data is digitally mapped; when viewed alongside a utility conflict matrix, evaluating, and comparing collected utility information with proposed plans becomes much easier.
Underground utility location technologies are categorized as either active and passive. Active locating is searching for a known utility. Passive locating is searching for an unknown utility.
Technology and Equipment
For the last few years, utility equipment has made incremental changes that have really improved upon existing technologies, such as providing a clearer signal, more power, or adding GPS capabilities so locates can be tied to specific GPS.
“With a buried utility product life often exceeding 50 years, a variety of site-specific practical difficulties arise due to different and evolving utility network structures. Equipment manufacturers are looking to meet this challenge with a combination of new locate technology innovations to provide more information and ways to help technicians make appropriate use of accumulated industry best practice methodologies,” says Richard Fling, utility locating product manager, Subsite Electronics.
Innovations such as the Subsite Utiliguard Ambient Interference Measurement (AIM) feature on the locator and the transmitter advanced impedance measurement information are innovations that provide additional and important information. “It then becomes most important to train operators how to make the best use of this information to identify the best locate settings as an actionable outcome and help diagnose the actual buried utility network configuration and help the technician achieve the best locate quality,” says Fling.
The above data can be integrated into an effective operations process that provides a qualitative measure of the best settings and mode of operation for each site. “This intelligence can act as an operations trigger, where poor locating conditions are identified, take alternative locating steps or notification to the supervisor, site managers, or utility owner,” says Fling. “The measure-taking results in a reduced risk of avoidable damage by other site operations equipment or other contractors.”
Sensors & Software manufactures ground penetrating radars that help in non-destructive utility detection. GPR can be deployed in a simple “Locate & Mark” mode for rapid onsite solutions. When carrying out SUE or controlled excavation in complex areas, GPR can be used to map an area for better defining subsurface infrastructure.
The company’s latest offering allows for different views of radar data. “Radar data can be visualized in different ways, so once you’re done, you can make depth slices, 3D images, or overlay the data onto Google Earth,” says De Souza. “There are different ways to visualize your data beyond just putting a paint mark on the ground.”
The MALÅ Easy Locator Pro WideRange HDR GPR boasts the widest GPR antenna bandwidth available for utility detection (80–950 MHz). It features fast, simultaneous data acquisition presented on a high-resolution display with a movable horizontal divider at the center of the screen that allows the user to view more or less by moving the divider on the screen up or down. The new locator also features ObjectMapper 2.0, a software for utility detection professionals, now updated with an improved and intuitive interface and support for online maps.
The new vLoc3 series locators from Vivax-Metrotech Corporation have new locate modes. “Distortion is the main culprit in determining whether the ‘locate’ is good or not,” says Richard Jordan, group marketing manager, Vivax-Metrotech Corporation. “There are elements above and belowground that can cause distortion. We have some great tools that warn if distortion is on the line.” One mode simultaneously uses two locate modes: a peak mode and a null mode. If the readings for peak mode and null mode are the same, then you’re good. If they’re off, then you have possible distortion. Then you have to pull out your bag of tricks to confirm everything.
“It’s a 3D world and previous locators have looked at things two-dimensionally,” says Jordan. “Our new vLoc3 series, we are using a set of 3D antennas, so we can locate cable without actually being directly on top of it. It could be off to the side and our new vLoc3 series could still locate it. It could be behind a fence, and our new vLoc3 series could still locate it.”
The Sensors & Software LMX200
ground penetrating radar system
Tips and Tricks
- Review project goals. Poorly planned locates can lead to incorrect/
incomplete data and more hours needed to complete the task. Review the job site area for safety and access issues. “Use visual clues,” says DeSouza. “Look at aboveground features for clues as to what is underground and where it is.” - Investigate the area. “Reconnaissance should include identifying evidence of utilities such as valve boxes, gas, telecom, water, or electrical street equipment cabinets. Identify surface scars or subterranean utility access chambers,” says Fling. “Identify where access difficulties might occur and request support from other site or utility owners to ensure that when arriving onsite that all likely steps can be taken effectively and without delay.”
- Use the right equipment. “If you’re in a cornfield and you’re locating a pipeline, it will be an easy locate, because there is only one utility there. If you’re in downtown New York, there are dozens of buried utilities, and this calls for a specialized locator.”
- Train your technicians. Don’t just hand them the machine and the manual, train them; operators should be trained on the technology and on how to perform successful locates. “For high-quality utility locating and reduced risk of utility damage or accident risk, it is essential for project managers to ensure that the necessary people and skills are identified and the correct individuals available to ensure that appropriate and correctly executed utility locating tasks are completed with confidence in the locating completeness accuracy of the outcomes,” says Fling.
- Obey local state laws and company practices.
- Get grounded. “In order to do a good location underground, it all has to do with grounding,” says Jordan. “When using frequency, you attach a transmitter to a utility (a pipe or a cable); you have a hot lead that is red, which goes to the utility, and you have a black lead goes to ground. It is important for that black wire to be well grounded. The better the ground the better the sound. You get the best locate that way.”
- Technique/method. “In an area with a lot of buried utilities, you want to use the lowest frequency possible, because low frequencies have a decreased chance of coupling onto another utility,” says Jordan. “Low frequency is ideal for locating cable TV and telephone, which have thin diameters and are insulated. But finding a six-inch cast iron or ductile water main with bell housings and rubber gaskets, you will want to use a high frequency for those locates.”
- Check your equipment. Check that equipment works as it should and is on the correct settings. Check the frequency. Treat equipment with respect. Don’t leave it somewhere it can get damaged. Also, bad weather can have a negative effect on your equipment’s ability to function normally.
- Establish a test point. Regularly test your equipment on a known pipe or line, so that if a problem arises in the field you can immediately rule out equipment failure. A marked location provides a go-to point every time you need to test your equipment.
- Collect a lot of data. Don’t just accept the readings from one line. “Collect a lot of data before making a conclusion,” says DeSouza.
The Vivax-Metrotech vLoc3-Pro utility
locator introduces new, innovative tools
for locating buried utilities, assuring
damage prevention while gathering
information for analysis.
Put Your Trust in SUE
Contractors are using more and more of the SUE process in their utility locates. Here are several examples where contractors employed that technique, as well as the results of using it.
Transit infrastructure: The number of rapid transit projects in Toronto is increasing. Although rapid transit can be great for moving large numbers of people quickly, they are often also built in highly congested areas. During the design phase, it must be determined whether the existing utilities can be accommodated or relocated.
Locate company multiVIEW Locates Inc. used subsurface utility engineering (SUE) when the company won the bid to perform utilities locates along the proposed rapid transit route. They were tasked with mapping all underground utilities along an 11-mile stretch of Finch Avenue, as well as on side streets and major intersections, in order to assist with siting layouts for proposed stations, alternative road designs, potential parking, and more while identifying utilities in need of relocation.
They were also tasked with mapping out along Eglinton Street all underground utility conflicts in order to assist with design services for the proposed twin tunnels, including bored tunnels, cut and cover structures, emergency exit buildings, tunnel crossing passages, tunnel boring machine launch shafts, and extraction shafts.
First, multiVIEW completed the physical delineation of the storm and sanitary sewer systems and surveyed water valves, then designated and mapped locatable underground utilities. Utility information was captured by survey-grade GPS measurements and plotted in digital format.
SUE includes records research, geophysical methods, land survey techniques, and hydro excavation in order to create the most accurate and complete subsurface information. This is then used to identify potential conflicts. An SUE engineer can then work alongside municipalities, ministries, private property owners, and other stakeholders to review and comment on utility accommodation plans.
In the end, the SUE process helped mitigate unplanned utility relocation costs and project schedule impacts.
Water infrastructure: A California city had planned the installation of a new water line that crosses several busy intersections. There was a lot of buried infrastructure beneath the intersections, but the drawings could not be trusted to be complete or accurate, so they followed the SUE process.
Through the use of GPR, the city obtained the necessary information to design a new water line installation that avoids existing utilities.
The contractor used the Sensors & Software LMX200 GPR system, which provides for both real-time and post-survey display and analysis of buried targets.
According to a case study published by the company: “Three parallel lines of data were collected in Line Scan mode starting from the same baseline. GPR targets were marked out in real-time using field interpretations [color-coded dots placed at the apex of the hyperbolas (inverted V’s) on the screen] with associated position and depth information.”
Data were downloaded into Sensors & Software’s EKKO_Project software, which gets used to organize and process collected data and generate reports.
Since GPS was integrated with the GPR, the MapView window of EKKO_Project displayed the path traveled, as well as the field interpretations. This information was then overlaid on a site image to help provide the perspective of where the data were collected and correlated with ancillary site data and surface features; in this case, a Google Earth image was used.
In this situation, GPR demonstrated it can be used quickly to provide high-quality data. Using GPR, the city obtained the necessary information to design the new water line installation in a way that avoids existing utilities. “This approach not only prevented possible costly damage to existing infrastructure, but it also allowed optimization of the new installation with minimized costs and surface disruptions,” states the study. “Further, the digital records are available for future projects in the same area. Incorporating the LMX200 to carry out SUE for the city’s water line installation provided many benefits and the approach will be an integral component of future city projects.”
Healthcare infrastructure: Utility locate company GeoScan was contracted by a general contractor to perform underground utility locates for a project. The city of New Westminster in British Columbia (BC), Canada, required accurate underground utility information in order to plan for the construction of a new hospital wing, as well as upgrade the surrounding water and drainage utilities.
GeoScan used the SUE process. According to the company, SUE “provides the platform for successful design; it reduces the risk of expensive extras during construction and ensures a safer working environment as the unknown is eliminated.”
When the locate was complete, GeoScan crated a digital GPS-plotted utility composite of the entire project area, which allowed the city to design the new hospital wing with confidence that plans and schedules will not be jeopardized by what may lay beneath.
