people at both large and small construction companies. In many cases, when they are designing or upgrading roadways, engineers don’t have a lot of leeway on the depth of construction. A utility line may be only 3 feet underground and the design subgrade needs to maintain a specified clearance above the line. “It’s very, very important for them to know depths when they’re reconstructing these roadways,” Kuxhausen said. “In a lot of places, clients are forced to do Level A excavation. They may need data every 10 feet along the road, which makes for a lot of potholing. It can be very costly. The idea behind this technology is wonderful for them. We are able to use the SPAR system to reduce the frequency of the Level A excavations. We could make a Level A excavation, say, every 50 feet, and then use the SPAR information in between those Level A excavations. It’s a faster and more cost-efficient approach.” In addition to road construction, Kuxhausen sees potential clients in a variety of industries. He cited airports as a good example, where operators need accurate data on the complex web of underground pipes, wires, and conduits. “We repeatedly receive requests to perform mapping and subsurface utility engineering (SUE) services to support the redesign or relocation of navigation equipment,” he said. “For instance, we’ve completed work for airports where they might be deconstructing a control tower or some other site. Our crews will go out and locate the existing utilities, both active and decommissioned, so that no lines are damaged when the deconstruction takes place.” Kuxhausen said additional business comes from highway departments that like to see all the existing utilities in their transportation corridors for design mapping purposes. There has been some specialized work as well. “We’ve also performed locations prior to setting geodetic control marks for the National Geodetic Survey or the Federal Aviation Administration. For a Class C monument we need to dig a 4-foot hole, and a Class B monument is a stainless steel rod driven to refusal. So, the utilities are required to be designated on those sites.” He noted that “Call Before You Dig” location services often might not be responsive on airports or private property, especially for design mapping surveys when construction is not imminent. As a result, it’s important that Woolpert be able to provide SUE services. At the end of the day, Kuxhausen is looking for productivity and the ability to meet the needs of Woolpert’s clients. “It comes down to how we can streamline our processes,” he said. “We need to ask how we can quickly, safely, and accurately locate utility data and have accurate data that could be implemented into the larger infrastructure mass. I think this is a solution for that. Taking all the information that comes out of the SPAR/GNSS system and coupling it with the GIS database and additional attribution could be invaluable for any client that has a large inventory of underground assets.”
Four levels of accuracy and cost There are four generally accepted classification levels of a buried pipeline’s location; the levels reflect decreasing degrees of accuracy and reliability. The most accurate, Level A, requires the pipe to be physically exposed, typically via digging or hydro or pneumatic excavation (a process known as “potholing”). Survey teams can then use GNSS or total stations to accurately measure the 3D position of the exposed pipe. Techniques for Level B location include using electromagnetic sensors to detect a pipe; the position is marked on the ground using paint or small pin flags that can then be measured by surveyors. Conventional electromagnetic detectors are fast and can reveal a pipe’s location horizontally but they offer little information on its depth. Additionally, surveyors must coordinate with the pipeline location crew so that markings can be measured before they fade or are removed. It’s not unusual for survey crews to make multiple visits to a site to capture needed information. Level C location is based on visible evidence of underground assets such as manholes, meters, valve covers, or utility pedestals. Surveyors can capture accurate location on these features, but the approach provides no data on what is out of sight below ground. Level D locations are based on existing utility plans, as-built drawings, or “tribal knowledge.” While this is a common approach, it’s difficult to assess if the information on older maps is accurate or complete. In particular, data on the depth of a pipeline is subject to question and may be affected by surface changes such as grading, cultivation, or paving. The different location classifications provide a striking illustration of the costs associated with accurate information. While Level A offers the best accuracy, the cost to find and measure pipelines is high, especially when seeking pipelines beneath paved surfaces. Level D location data is essentially free, but comes with low confidence. Despite the cost and challenges, demand for accurate locations is strong and extends across multiple types of assets. It has opened the door for technological solutions that combine the speed and flexibility of electromagnetic detection with instruments and software for precise positioning and mapping. Companies are putting the technology to work — and keeping it busy.
ERIK DAHLBERG is a writer specializing in the geomatics, civil engineering, and construc- tion industries. Drawing on extensive training and industry experience, Dahlberg focuses on applications and innovation in equipment, software, and techniques.
62
csengineermag.com
april 2018
Made with FlippingBook Annual report