Olive 8 Innovative Shoring Design

Overcoming challenging design constraints, GeoEngineers designed and modeled a unique combined shoring system to significantly reduce costs for a 39-story mixed use high-rise in downtown Seattle.

Approach

Removing and replacing the alley soils was impossible due to the presence of sensitive downtown electric and communication utilities, and with an adjacent 50-foot-deep basement wall across the alley, the only typically available alternative was expensive internal bracing. GeoEngineers challenged conventional thinking by:

• Designing a shoring system consisting of soldier piles with soil nails in the upper portion of the excavation and tiebacks below the adjacent building in the lower portion.
• Modeling the wall performance using a 2-D finite element model carefully calibrated to specific site conditions.
• Seismic design of this tall building was also a challenge. GeoEngineers worked closely with the structural engineer to develop a series of site-specific response spectra and acceleration records based on documented past experience for input into their 3-D dynamic model.

Results

The high-rise, consisting of 170 upscale condominiums atop a 343-room luxury hotel, was completed in 2007. The owner estimated that the innovative shoring approach saved more than $1.5 million.