How do you find something again after you’ve buried it? Pirates solved the problem with treasure maps. Cities that operate their own utilities have long used a similar methodology. They maintain maps — both digital and paper — to help them locate underground assets such as water pipes. Unfortunately, with these maps inaccuracies are common, so often a figurative “X” does not mark the spot to find an underground asset, limiting their usefulness. That’s especially true when multiple utilities have assets underground in the same area.
Inaccurate and incomplete data can cause problems when the time comes to maintain or update underground assets. Engineers don’t know exactly where changes will create interferences, so combing through multiple sets of CAD data and paper maps is often a first step in the planning and design process. Still, interferences can crop up and cause costly delays in the field.
When the City of Las Vegas experienced these problems, its leaders said, “Enough.” They decided to develop a 3D model of above- and below-ground infrastructure in Las Vegas’s core downtown area. Alan Riekki, surveyor for the City of Las Vegas, explained, “It’s frustrating to obtain survey and other information for subsurface utilities for a project only to have to revisit the area again six or seven years later for a new project and start all over again. We wanted a working 3D model of the existing infrastructure — not an archive, but a living model that could serve as an up-to-date source of information for planning, designing, and maintenance.”
“We decided to start with our core downtown area, and as we do projects elsewhere, grow the model to encompass more of the city,” Riekki said. “As we talked to other departments in the city, it became clear that there was a great unmet need for fast access to infrastructure and location information above and below ground. With a 3D model, we saw the potential to explore many aspects of projects — subsurface implications, sight lines, traffic — using a single resource.”
BIM for infrastructure
The city turned to VTN Consulting for help building the 3D model. VTN, a Las Vegas-based engineering, planning, and surveying firm, brought extensive experience with 3D models to the project. The firm is a longtime proponent of building information modeling (BIM) for infrastructure. Widely used in the architectural realm, BIM is the process of using intelligent, 3D models to explore projects before they are built. BIM for infrastructure extends the idea to civil engineering, public works, and planning.
“When you use BIM for infrastructure, you take a big-picture view and see projects, planning, and maintenance in the larger context of existing conditions,” said Keith Warren, BIM manager for VTN. “That’s exactly what the city wanted to do. It wasn’t about just one project, though. The city wanted the most accurate model possible of existing conditions above and below ground.”
BIM for infrastructure not only makes it easier to spot and address interferences in designs before getting into the field, it also helps to improve communication. People who are not accustomed to viewing traditional 2D designs and plans can more easily visualize how a project could impact them and their community by viewing a 3D model.
“You can take your laptop with a real-world, 3D city model to a community meeting and demonstrate how a project might look before it is even approved,” said Riekki. “Or you can demonstrate how you’ll be working to minimize the impact of a below-ground project on traffic. A 3D model can help win support for a project. People really see how their tax dollars could be used in ways that enhance service and make the city better.”
Bringing data together
The model needed to blend data from various sources, and the City of Las Vegas wanted it to be editable by authorized users. With these factors in mind, VTN and the city decided to use AutoCAD Civil 3D software as the core model-building tool. The software delivers direct access to geographic information system (GIS) data from a variety of sources, making it flexible enough to accommodate a number of file formats without time-consuming data translation. To help coordinate data, the team chose Autodesk Navisworks Manage software. Navisworks Manage can aggregate data in multiple formats and help spot clashes.
“We knew there would be interferences between different types of above- and below-ground assets,” said Warren. “For instance, there are clashes that were corrected in the field, but were not recorded as as-builts. Reviewing for conflicts and noting corrections allows for some accuracy enhancement without reviews in the field.”
Michael Kinney, land survey associate for the City of Las Vegas, added, “As maintenance or new projects take place, we will be able to update our information. It’s a system that makes it easier to improve data accuracy continuously. Because the city’s engineers design with the same software used to create the model, they’ll be able to import the model data as they start projects. And we’ll be able to incorporate new designs into the model just as easily.”
The City of Las Vegas and VTN consulted with Geodetic Analysis, LLC, to establish a coordinate system built on a custom mapping projection for Las Vegas and the surrounding area. As the team brought data from various sources into the model, they aligned the data to conform to the coordinate base. Then, using GIS and design data provided by the city along with aerial photos, the team began building the framework for the model. The aerial photographs provide a wealth of information about conditions and buildings above ground, and serve as a point of reference for underground infrastructure.
“We’re now bringing in underground utility information, which will be one of the key aspects of the model,” Warren said. “Soon, we’ll have more visibility into what’s underground. Some information we’re bringing in is quite old and may not perfectly reflect existing conditions. For every area in the model, we’re using American Society of Civil Engineers standards to help rank the quality of subsurface utility data on a scale of A to D, with ‘A’ being the most accurate level. Quality level ‘A’ denotes areas where the data is based on actual exposure and surveying; ‘D’ denotes data from unverified records or oral recollections.”
At the time of writing this article, the City of Las Vegas expected its 3D infrastructure model to be complete enough to use in a matter of a few weeks — and this has Riekki excited about the future. “The possibilities are endless,” he said. “We know the model can help us to drive inconsistencies and errors out of subsurface projects while allowing designers to get ramped up on existing conditions very quickly. But we also are beginning to think about a huge number of unexpected uses. For instance, planners will be better able to take more aspects of surrounding buildings into account as they explore projects for things like visibility, glare, or even shading. It seems that every discussion about the model inspires new ideas for uses and benefits.”
Teresa Elliot, an industry marketing manager for utilities for Autodesk, has spent 14 years working with CAD and geospatial solution providers on industry-focused marketing programs for infrastructure including electric, gas, water/wastewater, telecommunications, transportation, government, and photogrammetry. She can be contacted at firstname.lastname@example.org.