Advanced Scanning Technology Produces Complete 3D Model to Transform Underground Utility Maintenance

By Linda Duffy

A network of 100-year-old underground passageways containing heating systems, electrical wires and other utilities in upstate New York was starting to show its age. With access by third parties restricted for security reasons, conducting maintenance and making repairs on the aging network presented a real challenge without existing paper or digital documentation.

To enhance efficiency, the administrators believed an accurate 3D model that showed sizes, locations and spatial relationships of everything in the system would be a key part of the solution. A comprehensive digital model of the infrastructure would help identify areas requiring attention and pre-plan work in the office to limit the time spent by contractors in the tunnels. Still, data collection would be difficult in the underground environment.

3D Model Provides a Clear View

There was a time when a large project involving intricate underground utility infrastructure with tunnels and pipes of various sizes would have required months of painstaking conventional surveying, with teams of surveyors measuring and documenting every inch. Instead, Colliers Engineering & Design (CED), a highly experienced A&E firm, applied advanced 3D scanning technology. The coordinated effort involved scanning over 10,000 linear feet, with some portions located five stories underground, using a variety of scanning systems, including the Trimble X7, NavVis VLX and Leica RTC 360.

“Without scanning, we would have relied heavily on hand sketching and manual measurements, then an office person would have tried to combine all the parts into a map,” said Lucas Boyer, geographic discipline leader survey, CED. “The process would have been very difficult and time consuming given the wide variety of utility infrastructure and space constraints in some areas.”

After considering all options, CED experts chose to leverage the power of 3D scanning technology to complete this project in a fraction of the time compared to conventional methods. Ultimately, fieldwork required two-and-a-half weeks to collect scans, rather than two to three months recording manual measurements, and two weeks for traverse, plus two weeks for registering and processing survey data.

“We needed to develop a methodology to survey a long tunnel system with minimal access that met the client requirements, both coverage and tolerance,” said Boyer. “Scanning enabled us to collect millions of data points much faster than traditional methods, and the comprehensive data will be useful in the future for projects that haven’t even been considered.”

Multiple Scanning Approaches Are Key to Success

The team at CED employed a multi-tool approach, utilizing a variety of scanning solutions to capture the most comprehensive and accurate data possible. The Trimble X7, a high-speed 3D laser scanner that delivers a very dense 360-degree point cloud and panoramic color images, was central to their strategy. In addition, CED employed a NavVis VLX backpack scanning system, which excelled at capturing a large volume of data while walking, as well as a Leica RTC 360 scanner used by a subcontractor.

Although originally planning to use the NavVis SLAM technology for the majority of data capture, the team made adjustments after gaining a better understanding of the conditions. After conducting tests, they determined the VLX was most suitable for large/long square areas, collecting up to 100,000 square feet in 20- to 30-minute scans. The X7 collected a significantly denser point cloud from stationary spots in four-minute scans, successfully capturing small details like valves and elbows and filling in gaps in the VLX data.

“The Trimble X7 is considerably more user-friendly than the other scanners we’ve tried,” said Boyer. “The field crews can see the data in real-time on the Trimble T100 tablet, and the X7 is faster and more reliable compared to older systems.”

The X7’s automatic self-leveling, a feature that helps ensure accurate data collection even in challenging environments, proved invaluable for the project. “We found it really made a difference in the tight, confined spaces of the tunnels,” Boyer explained.

Thinking Outside the Box

This project posed several challenges for the CED team, ranging from 100-plus degree temperatures in some tunnels to crawl spaces and vertical shafts too small to accommodate the NavVis backpack.
Given that the project was underground, establishing accurate control was not straightforward, and a mechanical room in the middle of the tunnels prevented traversing directly from end to end. Instead, they began at one end in a parking garage and did traverse work going five stories down along the ramps, setting control points above ground using the Trimble R12i GNSS receiver, and below ground with a Trimble S7 robotic total station with a Trimble TSC7 data collector and a Trimble DiNi digital level. At the opposite end, the team descended through a building, running a traverse through multiple narrow hallways and then up through another doorway. Trimble Business Center (TBC) was used to process the GPS and traverse work, which was then exported as a CSV file and brought into Trimble RealWorks.

Each scanning system was independently tested and registered, and QAQC comparisons were performed prior to cloud-to-cloud registration. The team also ran two independent traverses and checked cloud-to-cloud at the overlap areas within one inch prior to cloud-to-cloud registration of all scan data.

Due to the large volume of data, CED first registered the X7, RTC 360 and NavVis VLX data sets separately, then divided the data into project sections, such as hot and cold tunnels, before integrating the data from these various scanning systems. The ability to blend data from a variety of sources into a single point cloud offered them the flexibility to apply the tool most suitable for each given space and environment.

Using Trimble RealWorks and TBC software, they combined the data from three different scanning technologies with extremely accurate control network data and produced a single, congruent, cohesive recreation of the real world. The LAS 3D point cloud containing over 26 billion points was delivered to the client with the free Trimble RealWorks Viewer, which allowed even non-technical stakeholders to visualize each set-up.

“Managing such a large volume of data presented a significant challenge—we’re talking about 609 individual scans and over one terabyte of data in a single project,” said Boyer. “I was worried that my computer was going to crash, but the Trimble software made it possible to process and integrate everything, giving us an incredibly detailed and accurate 3D model of the entire tunnel system.”

Scanning Success

“We were extremely happy with the excellent outcome after combining three different scanning technologies and two traverses, trying to make it all work together by thinking outside the box,” said Boyer. “After data registration, we achieved a quarter-inch tolerance scan-to-scan and 3 inches end-to-end, which was well within our one-foot requirement for the entire 10,000 linear feet.”

Using 3D scanning technology, CED was able to complete this complex project in a fraction of the time it would have taken using traditional surveying methods, while also delivering a more comprehensive and accurate dataset for the client. The 26 billion data points provide a level of detail that allows owners to thoroughly understand the condition and layout of the utilities without always having to physically access the tunnels. This innovative approach transforms the way maintenance and repair work will be conducted in the future, providing significant benefits in efficiency.

Linda Duffy is a freelance writer and market researcher at Apropos Research, an independent firm providing marketing services to the geospatial and remote sensing community since 2003. Contact: lduffy@aproposresearch.com.