Crews working for the Washington State Department of Transportation began fieldwork in Lake Washington July 23 to study the lake bed where support columns and anchors will be placed for a new SR 520 bridge.

Crews plan to use barge-mounted drill rigs alongside the floating bridge between Medina and the west end of the floating bridge. Nearly 40 borings will be completed, with a depth of 60 feet to more than 100 feet into the lake bed. The results of the fieldwork will be shared with potential design-build teams as WSDOT moves closer to construction. Smaller efforts were conducted previously on the preliminary anchor design. This more robust geotechnical work allows WSDOT to advance the design of the anchors prior to issuing the contract documents for the floating bridge.

“Learning the strength and composition of the underwater soils is a key step to properly designing the columns and anchors for the new bridge,” said SR 520 Program Director Julie Meredith.

Daytime traffic slowdowns are possible on the floating bridge if distracted drivers watch the work. The work is scheduled 7 a.m. to 7 p.m. in 10-day shifts, with four days off in between shifts. Crews plan to complete this phase of work by the end of September, and then will move to other sites within the corridor.

WSDOT is completing environmental review of the I-5 to Medina Bridge Replacement and HOV Project, which proposes to replace the floating bridge with a six-lane facility and reconstruct the Seattle interchange. Construction on a new floating bridge is scheduled to begin in 2012, and a new floating bridge is scheduled to open to traffic in 2014.

For more information about the SR 520 Bridge Replacement and HOV Program and the fieldwork, visit www.wsdot.wa.gov/Projects/SR520bridge/.