New Tacoma Narrows Bridge Washington State DOT | 2003-2004
The new Tacoma Narrows Bridge Project is a suspension bridge design that requires two foundation caissons to be installed in 150 feet of water. These foundations are required to withstand tidal flows of 8 to 12 knots. Associated Underwater Services, Inc. was selected to provide the subsea interventions for Tacoma Narrows Constructors, a Kiewit / Bechtel JV.
The subsea work included: installation and removal of 64 main anchorage systems, capable of generating 600,000 pounds of holding force each; inspection and service of the anchor wire and chain; installation and removal of slider beams; and the removal of 30 false bottoms.
AUS also provided ROV services and designed and built site- specific camera sleds for both internal and external inspections. AUS initially installed the main anchor blocks in the Tacoma harbor and were an integral part of the team during the towing and anchorage phase of the caisson placement. The caissons were held in position with 5 tractor tugs while the main anchors were attached. Subsequent tasks required dive intervention from 10 to 190 feet of water. Maintenance and repair on the anchor systems in the substantial tidal exchange proved to be a challenge that was overcome by initiative and careful planning.