Temporary Soil Nail Walls

THE BRAVERN
BELLEVUE, WA


The Bravern - Phase I & II project, developed by Schnitzer Northwest was begun in 2005 and completed in 2009 and is a mixed-use commercial and residential development located in the heart of downtown Bellevue, Washington. The project encompasses 3 city blocks bounded by NE 8th Street to the north, 112th Ave NE along the east, NE 6th Street along the south, and 110th Ave NE to the west. The development includes several high-rise office and residential towers, and a 9-level below grade parking structure that required an excavation that reached up to 87 feet below the adjacent city streets.

Skanska USA was the Prime Contractor for the project and Malcolm Drilling provided the Design-Build shoring system with ourselves as designer. The parking garage excavation for both phases of the project required a total of roughly 155,000 SF of wall face that was temporarily shored with soil nailing. The existing Meydenbauer Center was located on the city block to the southeast of the site and required direct underpinning by the temporary shoring wall. The temporary soil nail wall at the north end of the site was up to 87 feet deep and is considered the deepest known temporary soil nail wall in the United States. The deflection of this wall was roughly 1-1/4" at the completion of construction, well within the expected performance.




Figure 1. View of Bravern Excavation toward Meydenbauer Convention Center.

Along the southeast wall, the existing Meydenbauer Center was directly under-pinned through the use of small diameter vertical elements that were drilled adjacent to the existing footing and connected via steel brackets attached to the beams (Figure 1). The soil nail wall in this area was 60-ft deep and was designed using an earth-pressure approach with a no-load zone and fully prestressed soil nails in the upper part of the wall, resulting in less than 1/4" of movement to the existing structure.