East-half Pontoon Construction
WSDOT and Kiewit-General (K-G) of Poulsbo constructed 14 new pontoons in Tacoma, Wash. inside a 150-foot wide by 465-foot long Concrete Technology Corporation graving dock. Construction (CTC) was completed over four cycles, or phases. Crews built in three pontoons in the first cycle, five pontoons in the second cycle, four pontoons in the third cycle and are constructing two pontoons in the fourth cycle.
The completed pontoons were floated out of the graving dock and towed to Todd Pacific Shipyards in Seattle, Wash. for assembly and outfitting. The completed east-half pontoon roadway sections and fully assembled east-half draw span will be floated into place during the bridge closure in May-June 2009.
You can watch the how work progressed from the pontoon construction Web camera or browse the photo gallery.
See time lapse camera footage of the final concrete pour for new pontoon construction and the fourth cycle float-out of the Hood Canal Bridge Project.
Pontoon Construction Cycles
||Start of cycle one pontoons (PA, PB, Q) |
||Float-out of cycle one pontoons|
||Start of cycle two pontoons (NA, NB, YD, YE and YF) |
||Float-out of cycle two pontoons|
||Start (prefabrication outside the graving dock) of cycle three pontoons (ZC, ZD, V and X)|
||Float out of cycle three pontoons|
||Start of cycle four pontoons (W and U)|
||Float out of cycle four pontoons|
A bird's-eye view of what the new east half of the Hood Canal Bridge will look like when complete.top
Building Pontoons in a Graving Dock
Each cycle of pontoons will be floated out of the graving dock and taken up to the Seattle area for outfitting. Here is how the process works (pdf, 147 KB):
- Empty all water from the graving dock
- Build pontoons in dry graving dock
- Attach flexi floats to the sides of the pontoons. The flexi floats help the pontoons detach from the graving dock floor and give the pontoons extra buoyancy to float out of the shallow graving dock.
- Open the valve on the gate at low tide. As the tide rises, the graving dock fills with water.
- Float the gate out of the way with a tug boat.
- Pull the pontoons out of the graving dock with tug boats.
- Remove the flexi floats and float the pontoons to Seattle for pontoon outfitting, assembly and testing.
All the pontoons will be floated to the bridge site before the May-June 2009 bridge replacement. The bridge will be closed to traffic during that time.
Pontoon Construction by the numbers…
- 150 feet wide x 465 feet long, size of Concrete Technology Corporation graving dock
- 14, number of pontoons to be built at Concrete Technology
- 30,000+ cubic yards, concrete used to make all 14 pontoons
- 70, approximate miles that completed pontoons will travel from Concrete Technology Corporation, to Todd Pacific Shipyards to Hood Canal
- 10,358 tons, the weight of the heaviest pontoon
- 12 feet, how deep water needs to be to float a pontoon