Making Measurement Float

October 8, 2010
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Teamwork and technology enable Parametrix to successfully complete a challenging survey on one of the world’s largest floating bridges.

Brones, senior party chief, completes the mapping of a girder after placement.


In a region characterized by majestic snow-capped peaks, rugged saltwater beaches and peaceful rainforest valleys lies a masterpiece of human engineering: The Hood Canal Bridge. Originally opened in 1961, the 7,869-foot-long structure (composed of two independent spans) is the longest floating bridge in the world located in a saltwater tidal basin and the third longest floating bridge overall. Each day, an estimated 15,000 to 20,000 vehicles cross the pontoon-supported concrete structure, which provides a vital link between the Olympic and Kitsap Peninsulas in Washington. 

Although vital, the bridge hasn’t always been completely reliable. In 1979, a severe storm with wind gusts approaching 120 mph caused the western half of the bridge to sink. The bridge was rebuilt and reopened to traffic in 1982. In 1997, the Washington State Department of Transportation (WSDOT) began working on replacing the east half of the structure, which was near the end of its useful structural life.

In 2004, the project ground to a halt with the discovery of a 2,700-year-old Native American village and burial ground at the Port Angeles graving dock, where the floating pontoons were to be constructed. Engineering documents that had been completed 20 years earlier during the west-half replacement were no longer adequate. WSDOT was facing potentially huge claims from the contractor, and other large projects throughout the state were causing internal labor and resource shortages. WSDOT began searching for a new way to deliver the project.

“Layout of a superstructure is challenging enough, but add to that a floating pontoon on tidal waters, influences from wind and waves, and the staged construction loading of the structures, and things quickly become more complicated,” says Norm Brones, senior party chief for Parametrix, a multidisciplinary firm with engineering, planning and environmental expertise. As one of a few local firms that could manage the survey of a floating superstructure, Parametrix was recruited to join the project team in 2005. The sheer magnitude of the project, combined with the need to have multiple teams at remote sites and build components on floating pontoons required clear expectations and goals for everyone involved. The team had to commit to resolving conflicts at the lowest possible level.

Ultimately, it was this commitment, along with the team’s expertise and the use of appropriate technology, that led to the success of the project.

Pontoons are floated out of Tacoma and headed to the pier in Seattle where the superstructure will be constructed. 

Rolling with the Changes

Following the archaeological discoveries in Port Angeles, the work there was discontinued in December 2004, and the bridge replacement date was reset to 2009. Pontoon construction began offsite in 2006, and the bridge parts began arriving in January 2009 in Port Gamble Bay, where they were moored in preparation for construction work. The bridge was closed in May, and Parametrix began its survey work alongside the construction crews.

Since the Hood Canal Bridge is a floating structure, standard survey procedures could not be implemented. Instead, the team had to use specialized survey equipment that established its own work plane and create an XYZ coordinate system within the plane. “Because the pontoons moved with the tides, waves, boat wakes and wind, the instrument could not remain level,” Brones explains. “The superstructure was built ‘perpendicular and parallel’ to the work plane rather than ‘plumb and level’ to the world. To simplify the coordinate system, the X-value used stationing, the Y-value was 10,000 feet at centerline, and the Z-value was the distance above the pontoon bottom with 1,000 feet added so that even the anchor positions were positive values.”

Led by Brones, the survey team laid out the elements of each structure. Each pontoon was 60 feet wide by 300 feet long. These pontoons were then joined lengthwise in groups of three, creating a single 900-foot assembly. Two of these 900-foot assemblies were built along with a third 400-foot section comprising eight pontoon pieces that formed the floating drawspan.

Once the pontoons were assembled, the superstructure construction began. Layout included columns, girder pads, girders, decking, rails for concrete paving--essentially everything needed to construct a 2,000-foot-long elevated roadway in three sections. Precise dimensional control was critical to the assembly of the components--a requirement that quickly became clear during construction, when three of the pontoons were submerged as part of the process. The surveyors drew on their detailed knowledge of the construction sequencing and coordination to re-establish control.

A completed road section waits to be moved to the bridge site.

To enable the construction team to continue working on the upper levels of pile bents, girders and the eventual road deck, the surveyors added three layers of control in sequence during the construction process. These layers of control were then carried to the road deck, which varied from about 15 feet to more than 50 feet above the pontoon deck. Each layer was visible for only a limited time. A minimum of four points had to be observed within the immediate working area to establish the pontoon surface plane; six to ten points were preferred.

The survey crew used a Leica TDM5005 Industrial Total Station for layout and set the rod heights as low as possible. “Under 18 inches was ideal, although the average was closer to 33 inches,” Brones says.

To compensate for the error caused by attempting to plumb over a point that was not sitting on a level plane, the survey technician used a procedure called “meaning the roll,” in which he sat on a bucket with his elbows braced on his knees to steady the rod while watching the bubble move back and forth with the roll of the pontoon. “The rod height could not be changed within the orientation, so the rod choice and height setting had to account for all variables in the control to minimize layout visibility challenges,” Brones says.

The project team gathers just before completion of the Hood Canal Bridge. This photo includes blended team members from WSDOT, Parametrix and Kiewit-General. 

Scanning for Conflicts

Another project requirement was providing an as-built survey of the “knuckle” of a 900-foot-long pontoon that had been previously constructed. “The knuckle was a large (10-foot-diameter) circular fitting with corresponding male and female parts that came together to keep the pontoons aligned,” Brones explains. “The pontoons flex and rotate about the knuckle. Laser scanning was an obvious choice--except that the pontoon was floating in Port Gamble Bay near the bridge.”

To overcome this challenge, the team built a coffer dam around the structure and pumped out the water. The surveyors used the Leica TDM5005 total station to meticulously place control into the dam and then scanned the knuckle using a Leica ScanStation 2. 917,000 points were collected and processed through Leica's Cyclone software. “Lowering the $65,000 scanner into the coffer dam by ropes was hair raising,” Brones recalls.

The scanning and control for the scanning were completed in two days. A 3D model of the knuckle was developed from the scan and delivered to the contractor’s engineers for construction of the corresponding new mating element to the knuckle. 

The Hood Canal Bridge nears completion.

Blending Teams to Ensure Success

Throughout the project, WSDOT and Parametrix used a “blended team” approach in which staff from both groups worked side by side out of the same office. This arrangement allowed both the owner and consultants to work as a single unit without regard to the traditional static lines of communication. Each position was filled by the person who had the most experience with the type of work being performed and who could provide the greatest contribution to the success of the project, regardless of whether that person was employed by WSDOT or was a consultant. For example, state inspectors reported directly to a consultant construction manager who, in turn, reported to the state project engineer.

Conflicts were reduced by a clear understanding of responsibilities and expectations. If a conflict persisted to a point where it interrupted delivery elements or expectations, the issue was elevated to the next level. In general, most conflicts were effectively handled at the lower levels of the team, but occasionally they were elevated to the construction or group manager level.

The Parametrix surveyors worked hand-in-hand with Kiewit-General, WSDOT and other Parametrix staff to communicate goals and assignments each day. This level of communication included providing daily downloads of staking and layouts to Kiewit-General’s engineers for analysis. If challenges were encountered, they were immediately addressed at the lowest possible level.

This blended-team approach worked so successfully that WSDOT has since implemented it on other projects, including the SR520 and Seattle Alaskan Way Viaduct replacement projects. 

Driving Future Design

The Hood Canal Bridge was closed to traffic on May 1, 2009, and old components were taken away. New components were brought in and assembled in conditions that included 16-foot tidal swings and three-knot tides. On June 3, 2009, the new bridge reopened to traffic--approximately one week ahead of schedule.

The success of the project was due largely to the new teaming and contracting approaches that WSDOT was willing to try. The level of teamwork, problem solving and coordination set a high standard of performance that should be a benchmark for future projects.

Blair Prigge, PLS, has more than 25 years of experience in surveying and is registered in both Oregon and Washington states. As the survey division manager at Parametrix (www.parametrix.com), Prigge is responsible for leading 25 surveyors across four offices in the Puget Sound region. Prigge served as the survey project manager for the Hood Canal Bridge project. For more information about the Hood Canal Bridge project, click here

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Restoring an Ancient Burial Ground

The discovery of a Native American village dating back an estimated 2,700 years at the original graving dock site in Port Angeles had a significant impact on the bridge replacement project as well as on the Lower Elwha Klallam Tribe.

In August 2003, when materials of archaeological interest were first discovered, no one envisioned the significance or extent of the discovery. Work at the site was temporarily stopped. In March 2004, after further investigation, numerous consultations and much deliberation among WSDOT, other state agency representatives, tribal leaders, federal officials, consultants and advisors (including archaeologists and attorneys), an agreement was reached to resume work at the graving dock within the framework of the so-called “inadvertent discovery” procedures of Section 106 of the National Historic Preservation Act. Simultaneously, an archaeology excavation and construction of a graving dock were to take place. However, the construction process soon began inadvertently unearthing human remains. What had been discovered was the location of Tse-whit-zen Village, one of the oldest and largest Indian villages in Washington, which included an extensive burial ground.

WSDOT made the decision in December 2004 to permanently end construction at the Port Angeles graving dock site and return the sacred ground to the tribe. Parametrix helped to expedite closure and restoration of the site in support of tribal efforts to repatriate remains to the area. On March 29, 2007, Parametrix completed the permitting of the site closure, and the firm completed the design on May 29, 2007. The project was finished four months ahead of schedule and 10 percent under budget through the use of innovative and creative solutions that expedited the permitting process.

In 2008, Lower Elwha Klallam tribal members reburied the remains of more than 300 ancestors at the site. The tribe hopes to build a longhouse and museum at the site, where artifacts that were discovered will be displayed.

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