homeWelcome, sign in or click here to subscribe.login
     


 

 

Architecture & Engineering


print  email to a friend  reprints add to mydjc  

February 9, 2026

Best in State - Gold Award: Complexity

Photo courtesy of ACEC
Juniper Apartments and Block 6 Private Access Drive were built on the Jackson Street landslide zone above I-5.

GeoEngineers
Yesler Terrace Block 6 PAD & Juniper Apts
Seattle Housing Authority

The Block 6 Private Access Drive (PAD) and Juniper Apartments represent the most technically complex and consequential phase of the Seattle Housing Authority’s (SHA) multi-year effort to redevelop historic Yesler Terrace. Located on the Jackson Street landslide zone — an environmentally critical area shaped by early-20th-century regrades and long considered too unstable for construction — this portion of the site had been intentionally left for last. As SHA’s geotechnical consultant, GeoEngineers designed the landslide-retention system and performed all geotechnical modeling, analysis, and design for both the Block 6 PAD and the seven-story Juniper Apartments, enabling safe development on ground once considered unusable.

Building in a landslide zone required engineering solutions that balanced seismic demands, long-term stability, and the unusual challenge of designing two independent structures only inches apart. GeoEngineers used advanced, performance-based seismic modeling to understand how the slope and future structures would behave under real earthquake motions.

This work led to a robust landslide-retention solution centered on a wall of 48 large-diameter cylinder piles, each 8.2 feet in diameter and socketed into undisturbed Lawton clay. Structurally tied together with a heavy header beam and topped with a mechanically stabilized earth wall, this system stabilized the landslide mass, supported the PAD, and provided permanent support for the future Juniper excavation.

Because the cylinder pile wall would ultimately sit immediately adjacent to a seven-story building, GeoEngineers also established a carefully calibrated seismic “air gap”—wide enough to prevent structural pounding during an earthquake, but narrow enough to maintain efficient site layout and building design. When the Juniper building was built years later, the predicted seismic behavior and wall performance held true, validating the early modeling and future-ready approach.

For the Juniper Apartments, GeoEngineers designed an isolated foundation system of auger cast piles, drilled shafts, and lightweight fills to avoid adding weight to the landslide mass while also managing complex interactions with neighboring retaining walls and existing foundations.

The Block 6 PAD and Juniper Apartments now serve as the final structural link in SHA’s broader redevelopment vision, delivering affordable housing, reconnecting street grids, and demonstrating how innovative geotechnical engineering can reclaim even the most challenging urban ground for public benefit.


Other Stories:



Email or user name:
Password:
 
Forgot password? Click here.