The US$3.4 million Washington State Department of Transportation project will take until next spring to complete.
One end of each cable is attached inside a bridge pontoon; the cables then extend at an angle in to the wate where the other end is hooked to a large anchor embedded in floor of the lake. Cables range in length from 113m to 227m.
The cables, which prevent the bridge from undulating, are frequently exposed to strong winds and pounding waves. In some instances, the individual steel strands that twist together to create each cable are now broken after up to 29 years in use.
“Worn cables pose a higher risk of breaking during a windstorm,” said Archie Allen, Washington State Department of Transportation bridge superintendent. “Broken cables increase the risk that the bridge could be damaged, resulting in a long-term closure.”
There are 108 cables attached to the I-90 bridges and 15 were replaced in 2010.
Replacing the cables will have very little impact on drivers because most of the work will take place on the lake bottom, inside the floating pontoons and from a work barge anchored on Lake Washington. Commercial deep-sea divers will disconnect existing cables and attach new ones, at depths of up to 55m.
After a diver has disconnected a cable from the anchor on the lake bed, the cable will be winched to the surface. A second diver will descend to the lake bed with a new cable to fasten to the underwater anchor. The new cable is attached inside the bridge pontoon and tightened.
