The West Approach Bridge North (WABN) Project was a construction phase of the SR 520 Bridge Replacement and HOV Program for the Washington State Department of Transportation. The new approach bridge extends the bridges three westbound lanes from the new floating bridge to the Montlake interchange in Seattle. The existing west approach bridge was a fixed structure connecting the floating bridge to the Montlake interchange. The hollow columns supporting the existing approach bridge were determined to be vulnerable to a catastrophic earthquake, and its four-lane roadway had narrow shoulders and lacked transit/HOV lanes and had no bicycle/pedestrian path.
The new west approach bridge will be built as two separate structures; a north bridge and a south bridge. The new West Approach Bridge North will carry westbound cars, trucks, and buses from the new floating bridge to the Montlake area and features a new 14-ft-wide regional bicycle/pedestrian path and a dedicated transit/HOV lane. The project also involved local street improvements in the Montlake area, a new stormwater treatment facility at the site of the old Museum of History and Industry (MOHAI), and a wider bicycle/pedestrian path on 24th Avenue East in Montlake. The benefits to the community include things like a new, seismically sound structure designed to modern earthquake standards, a connection between Montlake and the Eastside with new transit/HOV lanes, bicycle and pedestrian connection across Lake Washington with a new, regional shared-use path, and environmental improvements such as a new Arboretum trail, a public park north of SR 520.
The West Approach Bridge North project is fully funded by state and federal sources. The overall construction of this phase of construction was awarded a $199.5 million. PPM was responsible for installation of over 1.3 mile long pile-supported support trestle, drilled shafts, and large diameter drilled caisson installation, and associated support services. Installation required complex sequencing and materials had to be staged per installation with limited lay down area in order to meet the schedule.
The support trestle called for 18-in dia. x .375t, 24-in dia. x .500t, and 30-in dia. x .500t steel pipe pile. Pile was installed using various cranes including a 9310 American Crawler Crane, Manitowoc 4100 series II , 218 Hylab Crawler Crane. Also called for various hammers including a D46 and D62 Diesel Impact Hammers; an APE 200-6 Vibratory Hammer; and an ICE 44-50 Vibratory Hammer with Caisson Clamp.