Lasers, Software and the Devil's Slide

New system lets engineers safely dig tunnel beneath landslide-prone coastal highway.

This image depicts the point cloud of the tunnel beneath Devil's Slide made with a laser-scanning system and visualized with gVT.
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Running for more than 620 miles along picturesque coastline, California's Highway 1 is easy prey for many of the natural hazards plaguing the region, including landslides. At one of the route's particularly rough spots—Devil's Slide—the California Department of Transportation (Caltrans) is at work building a half-mile-long tunnel to let drivers safely avoid the landslide-prone stretch.

It's not the first time crews have dug their way through a dangerous pass, but this time Caltrans is using a new 3-D visualization software that lets them work more safely and efficiently. Called "geotechnical Visualization Tool," or gVT, the software, converts imagery of millions of rock-surface points collected at a safe distance by a laser scanner into an easily manipulated web of information. The data become a permanent digital record of the newly exposed material.

Part of a suite of engineering tools and software critical to the tunneling beneath Devil's Slide, gVT is the product of a two-year collaboration between civil engineers and computer scientists. The Devil's Slide application is the first use of gVT in a true construction environment.

"Geologic maps have traditionally been made using manual measurements taken by geologists directly on the rock," said Virginia Tech's Joseph Dove, gVT's lead developer. "Laser scanning is revolutionary for underground mapping because it allows direct collection of digital data in 3 dimensions at high resolution."

At resolutions of mere fractions of an inch, the scan data provides information the software program packages into enormous visualizations incorporating up to 30 feet of excavated tunnel. Engineers then use gVT to spot potential hazards to both the tunnel and the construction crews before weaknesses in the rock have a chance to trigger a collapse.

The information is so detailed that researchers can observe where rock layers are separating and how fractures are oriented. They can even recreate sections of rock after they have fallen, providing a critical asset for determining where and how to safely drill. And, because the data is portable, engineers can conduct all of the analyses from their home base at any time, far from the danger of the tunnel.

"These 3-D visualizations enhance geological documentation and an engineer's ability to make decisions," said Jeramy Decker, a co-developer of gVT who is now working at Kiewitt Pacific Company, the contractor excavating the tunnels.

Decker presented the new technique June 29th at the U.S.-Canada Rock Mechanics Symposium in San Francisco. gVT was developed as part of a National Science Foundation Information Technology Research Initiative project.

By Josh Chamot/NSF

This report is provided by the National Science Foundation, an independent federal agency that supports fundamental research and education across all fields of science and engineering, in partnership with U.S. News and World Report. For more information, go to www.nsf.gov.