Leica HDS Used for Automated Laser Scanning for Near-Real-Time Geotechnical Monitoring

Debut on Seattle Light Rail Project — Leica Geosystems HDS™ Technology Enables Project

(Norcross, GA., 21 June 2010) Geo-Instruments implemented one of the industry’s first automated laser scanning systems using Leica Geosystems technology for near-real-time geotechnical monitoring to support construction of the Puget Sound Regional Transit Authority‘s (Sound Transit) University Link (U-Link) light rail extension in Seattle, WA.

The U-Link light rail extension will connect the three largest urban centers in the state of Washington. Beginning in 2011, the tunnel boring machines will excavate a 3.5-mile, twin-bored tunnel from downtown Seattle to the University of Washington. Key to the success of this project is the ability to tunnel under Interstate 5, a major artery near downtown Seattle, without impact to the aging infrastructure, deep foundations and existing utility lines.

Prior to excavation, Geo-Instruments installed a laser scanner-based fixed monitoring system to track fractional movements of the walls and highway surrounding the intersection during pit excavations and tunnel boring machine passage.

The monitoring system includes two Leica ScanStation 2 scanners from Leica Geosystems positioned on either side of I-5 to scan the horizontal arrays and surrounding infrastructure along with tiltmeters, linked beam sensors arrays and angled laser scan targets. The ScanStation 2 scanner includes survey-grade duel-axis compensation, a built-in high resolution camera for fast scene selection and auto-rectified photo overlays, and a high speed pulsed laser with a maximum scan speed of  50,000 pts/sec.

For the U-Link monitoring project, the laser scanners are fitted with a lightweight carbon fiber cover (fabricated in the Geo-Instruments factory) to protect the units from weather and vandalism. The scanner’s onsite computer is fitted with a locked protective cover, wireless evolution data optimized (EVDO) modems and a wired digital subscriber line (DSL) as redundant communications paths.

Twice per day, a custom computer program directs the scanners to automatically scan infrastructure elements potentially impacted by the construction under and adjacent to I-5 to within 2 millimeters along owner-defined scan lines of 1 inch x 1 inch. Each 360-degree scan covers a swath of 4 feet x 4 feet at a distance of 380 feet. The total data load is greater than 1 gigabyte per day.

Pierre Gouvin, president of Geo-Instruments, explains, “The laser scanners provide the flexibility to collect data and allow the team to analyze unexpected areas as needed. One of the benefits is the ability to pick up measurements at locations where the specifications did not call for sensors or where sensors are not practical.”

With the automated laser scanning monitoring system in place, contractors have begun preparation for the tunnel boring, which is scheduled to begin in 2011. The monitoring system will stay in place until contsruction of the U-Link in the vicinity of the I-5 is complete.

For more information on the HDS™ technology please click HERE

For more information on Geo-Instruments click HERE

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