A New Mexico highway alignment project (U.S. 82) still in the design phase has already saved taxpayers more than $500,000 by automating much of the subsurface utility engineering (SUE) field work. SUE locating crews mapped 1.2 million linear feet of underground utility lines in just eight weeks, in less time and at lower cost than it would have taken had the work been completed using traditional methods.
And the savings isn’t likely to end there. The automated mapping technology enabled the SUE services provider to deliver infrastructure location details more quickly to the project design company. In turn, the designer was able to resolve potential conflicts and line relocations earlier in the process when such issues are less expensive to address.
“In highway construction, making a minor change in design [to accommodate a utility conflict] costs about 100 times less than making a change in the field,” said Sean Wolfe, Region Manager and Vice President at CobbFendley & Associates, the Texas-based civil engineering and survey firm that performed the SUE work.
“Accurately mapping buried pipelines and other assets early in a highway alignment project is critical to keeping construction on time and on budget,” Wolfe added. This gives the designers time to coordinate with infrastructure owners to determine the best ways to deal with conflicts. Pipelines and electric lines are usually moved, but sometimes it’s less expensive to tweak the roadway design. The worst-case scenario is finding an underground asset once construction has begun.
“Inaccurately mapped utilities can lead to change orders and potential project shutdowns,” said
Wolfe, adding that either can blow the timeline and the budget on a taxpayer-funded project.
The U.S. 82 project is currently the largest highway alignment underway in New Mexico. The two-lane route runs 62 miles from Artesia to Lovington in the southeast part of the state where oil and gas production activities are extensive. As a result, the east-west route sees heavy traffic from trucks carrying hydrocarbon products and equipment. Due to safety concerns over two lanes carrying so much traffic, New Mexico DOT (NMDOT) put the alignment project on the fast track.
NMDOT selected WSP Parsons Brinckerhoff as the prime design consultant on the project. The company’s Albuquerque office was tasked with performing an initial alignment study and suggesting a series of preferred alternatives, such as adding extra lanes or building passing and climbing lanes. This study involved locating underground infrastructure, which included water, gas and petroleum pipelines, as well as electric lines and fiber optic cable, either crossing beneath the roadway or buried beside it within the right-of-way.
Parsons subcontracted this SUE work to CobbFendley. Typically, this work is performed by multiple crews and mobilizations. The first uses electromagnetic utility line locators and ground
penetrating radar to find the pipes and conduit, and then mark their subsurface locations with paint stripes on the ground. Next, a separate crew follows behind to survey the paint marks with GNSS receivers or traditional equipment.
CobbFendley condensed the two-step process into one by equipping its field crews with automated mapping gear. The field software selected for this project, UtiliMapper, connects a GNSS enabled datalogger to the underground utility line locator via Bluetooth to capture incoming sensor data instantly and map it with precision GNSS accuracy, usually to within three to five centimeters. This resulted in major cost reductions for the project.
Mapping U.S. 82
Before heading into the field, CobbFendley identified more than 45 utilities and other organizations with infrastructure in the U.S. 82 corridor and contacted them with requests for any information they had pertaining to their buried lines. Some had relatively accurate GIS maps, while others provided only decades-old sketches or nothing at all. In most cases, the location information provided had to be taken with a grain of salt because the data was based on design plans, not as-built maps.
Once it had a relatively good idea of the various types of pipes, cables and wires that would be mapped, CobbFendley worked with Tri-Global to customize smart menus in the software that was pre-loaded with a database of nearly all common utility assets and their attributes, allowing locate crews to select appropriate pipe sizes and cable types as they map. Tri-Global converted some asset nomenclature to match naming standards required by the designers for that specific project.
From the outset, CobbFendley knew the lion’s share of the line locating would be done with an electromagnetic utility line locator. A utility locate crew uses such a device by first transmitting a unique frequency on the suspect utility which then can be detected and traced aboveground, allowing the user the ability to mark the route of the pipe or cable.
“The locator strength and quality of the signal can sometimes be interpreted by the device to give
approximate depth of the feature,” said Wolfe. The software linked the utility location and attribute information with each asset and created a record for each feature being mapped. Preloaded attribute details, such as asset type and owner name, were attached to the appropriate record as well. The crew members had the opportunity to key field notes directly into the software file using the keypad on the field GNSS datalogger.
A function within the software called Multiline allowed the field crews to traverse a section of
the corridor, mapping one asset for a short distance and then turn around to begin mapping a
second walking in the other direction. The software automatically kept track of the different assets and allowed them to switch back-and-forth between lines when necessary.
Processing SUE Data
Field crews downloaded data nightly from the data collection unit to the centralized office software suite, where the data was processed for output. Although the GNSS receiver and UtiliMapper products were both capable of receiving real-time data correction in the field, CobbFendley opted instead to rely on post-processing.
“We post-processed the captured location data in Tri Global’s DataView using online correction data from the U.S. government’s Continuously Operating Reference Stations (CORS),” said Wolfe. “Due to the east-west direction of the project, we had to introduce six different conversion factors to stay within the project coordinate system.”
He said the SUE contract called for mapping underground assets to within plus or minus one foot horizontally, but the final deliverables were accurate to within about three to six inches.
At the request of WSP Parsons Brinckerhoff, CobbFendley output the data as AutoCad Civil 3D
files, which contain layers of attributes associated with each utility feature. Parsons received the SUE information during the alignment study phase of the project and was able to include the utility location data as an overlay on the preferred alternative plans provided to NMDOT.
Utility location information often isn’t available so early in a project of this type, according to Rod Adams, Senior Transportation Engineer at Parsons Brinckerhoff. That enabled the designers to begin contacting asset owners earlier in the process, giving them more time to figure out how to deal with potential conflicts. This extra time lessened the possibility of unexpected design changes later in the process. “With its new approach [to SUE mapping], we were able to provide more accurate, higher quality data at a lower price point… that will help us meet the aggressive schedule,” said Adams. “That’s a value to New Mexico DOT and taxpayers.”
Dennis Heath is Managing Partner with Tri-Global. He can be reached at Dennis.Heath@triglobal.net.