The ongoing construction of the $587 million SR 520 Evergreen Point Floating Bridge and Landings Project in Seattle, Wash. — the longest floating bridge in the world to date — is a complex and sophisticated project. It is bringing together underwater and surface construction techniques and the utilization of a wide variety of equipment to ensure that the delivery date is met.
The project, commissioned by the Washington State Department of Transportation (WSDOT), is being constructed via a joint venture consisting of Kiewit Corporation, General Construction and Manson Construction (KGM). Work began in September 2011, with completion expected in 2015.
“We’re probably running about $20 million worth of equipment on a daily basis,” said KGM Equipment Manager Bill Forgey. “Just focusing on utilization of the equipment has been a big job.”
The bridge that spans the north section of Lake Washington is approximately 7,000 ft. (2,133 m) long, but the project also includes road construction and land-based infrastructure.
The design-build bridge brings together many architectural aspects. There are 77 pontoons — big concrete hollow boxes (with cells inside) that are joined together to provide a floating platform for the elevated roadway to be built on. They are anchored down to the lakebed with 4 in. (10 cm) diameter steel cable to a series of large concrete anchors and shafts which are driven into the lake bottom. The six lane roadway deck is elevated on columns that are roughly 10 ft. (3 m) above the pontoons. Upon exiting the floating bridge, motorists will enter a 700 ft. (213 m) land-based bridge before joining back to the existing roadway surface at grade.
“There’s also a 19,000-square-feet four-story maintenance facility that’s being constructed,” said Erik Nelson, KGM’s project manager.
While WSDOT specified the design of the pontoons, Kiewit was responsible for the remainder of the project’s design.
“A floating bridge is quite technical and complex — there are a lot of load conditions that must be considered and a lot of different and unique criteria associated with it,” said Nelson. “Some of the pontoons are being furnished by WSDOT via another contract and being manufactured in Aberdeen, Washington — a four-day ocean tow that presents us with a lot of challenges — timing, weather conditions and seascapes.
“The remaining pontoons are being built under this contract at a facility in Tacoma,” he added, “so we have to coordinate the construction and towing of the pontoons and get them to the lake to join them in their corresponding final alignment. There is also an adjacent contract on the existing SR 520 highway on the east side, so there is a lot of coordination and timing requirements associated with the project that have to be accounted for.”
Planning for the bridge project was extensive and required nearly a year to determine the overall design, the delivery and work schedule, and the amount and type of equipment that would be needed for the multi-year project, as well as accounting for unexpected delays and potential surprises.
“So far our planning has been excellent and we’ve gotten off to a good start,” said Nelson.
The underwater portion of the project is complex and diving teams with solid construction experience have been brought in to work at the 200-ft. (61 m) depths. Diving to that depth requires special equipment, including a compression chamber.
“When we designed the anchors we had to take into account the soil conditions and properties,” said Nelson. “It requires a lot of planning to coordinate the underwater and above-water construction and ensure that all safety concerns are met.”
The marine equipment employed by KGM includes barges, derrick barges and tug boats – quite the flotilla.
“Most of the time we have six to eight derrick barges working,” said Forgey. “The largest one is a 400-ton DB 24 crane that is owned by Manson. The other derricks we’re using are owned by General and have a lifting capability of 150-ton and 100-tons.”
The DB Columbia and DB LA barges are owned by General. The tugs were supplied by Manson and Westar.
The anchors are being cast at Kiewit’s site at Kenmore, 20 mi. (32 km) north of the bridge. The gravity anchors (when filled with rocks) weigh over 560 tons (508 t), while the fluke anchors weigh 112 tons (101 t).
“We’re picking up the fluke anchors with a 120-ton shuttle lift and moving them out on a trestle and loading them on the barges,” said Forgey.
At the Tacoma site, Forgey is employing a 150-ton (136 t) Liebherr crawler crane and two Liebherr 44-ton (40 t) tower cranes help build the pontoons in a dry dock.
“We’re also using a lot of other gear to aid the work such as hydraulic cranes and smaller forklifts at our facility in Kenmore,” he said. “We have two crawler cranes — a 240-ton American 9310 and a 300-ton LR1280. We have a 30 ton gantry crane that will be doing some of our smaller pre-cast work, which includes a 120 — shuttle lift.” He added that nearly 95 percent of the equipment to be used on the project is owned by the joint venture.
Xtreme Manufacturing built two types of pick and carry extended boom forklifts — 10,000 and 15,000 lbs. (4,536 and 6,804 kg).
“We bought five new ones for the job,” said Forgey. “The forklifts pick and carry forms, deliver small tools, and can transport supplies to job locations.”
Maximizing equipment use and scheduling maintenance are critical to the success and schedule of the project. Forgey is using job equipment maintenance system software to ensure that there are no unexpected breakdowns, that regular maintenance is done, and that this work is taken care of during off-hours and downtime.
“All our repairs and maintenance are based on hours of use and we focus on getting all our hours into the computer program to stay on schedule,” he said. “One key to success of our job scheduling is to maintain a five week look-ahead schedule and communicate that on a weekly basis to everyone on the project team in a project meeting.”
Nelson noted that this project is providing a valuable experience and lessons that can be applied on future projects.
“Not only is this project unique,” he said, “but so is the variety of equipment. In addition to marine equipment, we have traditional land-based equipment as well as loaders, dozers, cranes, forklifts, etc. It’s important to us that we are building a project that really benefits the public and are performing well in meeting the needs of client.”
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