Local Information

SR 520 pontoons readying for a busy summer

Thursday, June 6, 2013 - 13:38

Debera Carlton Harrell, SR 520 Communications 206-770-3554, 206-819-7230 (cell)

Pontoon arrivals, repairs at the top of construction to-do list

SEATTLE – The State Route 520 summer construction season heats up along with the weather as crews move pontoons on and off Lake Washington during June and July.

One pontoon will arrive from Grays Harbor on Friday, June 7, while four others from Cycle 1 are prepared for repairs. The repairs will be made at an offsite drydock or on Lake Washington using a coffer cell – a steel box attached to the underside of pontoons. The repairs, endorsed by an expert review panel, are necessary to ensure that the new floating bridge meets its 75-year design life.

Washington State Department of Transportation contractor Kiewit/General/Manson, A Joint Venture, will tow one pontoon to a drydock in Portland, Ore., and another to a drydock on Harbor Island in Seattle. The remaining two pontoons will be repaired on Lake Washington.

The repairs (pdf 436 kb) will address cracks that developed in the keel slabs and end walls on four of the first six pontoons built in Aberdeen. Crews will seal cracks in these pontoons by injecting epoxy, adding post-tensioning across the ends of the pontoons and applying a carbon-fiber wrap to portions of the keel slabs. Post-tensioning is a common construction process in which steel cables are placed through the concrete and tightened to increase strength.

Pontoon A arrives on Lake Washington
Sometime Friday afternoon or evening, tugboat “Alaska Mariner” towing cross Pontoon A is expected to arrive through the Hiram M. Chittenden Locks in Ballard on its way to Lake Washington from Grays Harbor. Pontoon A is the second of two cross pontoons that will form the ends of the new floating bridge. Pontoon A will be moored temporarily at the east-end staging area, where crews will build columns atop the pontoon. It will later be moved into its permanent location on the west end of the new bridge. The public has a variety of viewing locations (pdf 2.4 mb) for watching the pontoon’s arrival.

Pontoon T leaves for drydock in Portland
Depending on weather conditions, longitudinal Pontoon T is expected to leave Lake Washington early next week for drydock repairs in Portland. This facility was one of two drydocks chosen based on availability and capacity to support the 11,000-ton pontoons. Using drydocks allows work to proceed on two pontoons while a coffer cell is being constructed for use on Lake Washington later this year for the remaining two pontoons.

Pontoon W headed to drydock in Seattle in July
Crews will tow Cross Pontoon W from its moorage on the north side of the current SR 520 floating bridge mid-July to a Seattle drydock for repairs, then return the pontoon to its permanent location at the east end of the new bridge.

Pontoons U and V will be repaired on Lake Washington
Both longitudinal pontoons U and V will remain on Lake Washington for repairs. A coffer cell will be brought to the lake later this year to create the dry environment needed for the repairs on the bottom of these pontoons. Additional details will be provided as coffer-cell construction proceeds.

Project information
Modifications were made to Cycle 2 pontoons in Aberdeen to include post-tensioning across ends, and Cycles 3-6 include this change in design. WSDOT is negotiating the cost of repairs and potential schedule effects with the contractor.

Details about the new SR 520 floating bridge can be found at www.wsdot.wa.gov/projects/sr520bridge.

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