This is an 11-story apartment building with underground parking and street level retail space. The loads were substantial with maximum 2,100 kips on the isolated columns and wall loads as high as 100 kips per lineal foot in the elevator core.
The subsurface conditions consisted of loose to medium dense sand with occasional silt seams below foundation level to depths of 70 feet. The Geotechnical Engineer, Braun Intertec Corporation, determined that compression settlements from these soils would be excessive and recommended ground improvement to increase the bearing pressure and maintain settlements within a tolerable range.
Vibrocompaction was considered for this project but ultimately the Geopier Densipact® system was chosen as the best, most economical solution. The Densipact system was designed to heavily densify the upper sands to provide an allowable foundation design bearing pressure of 14,000 pounds per square foot. The project team relied on real-time Cone Penetrometer Testing to confirm the effectiveness and refine the improvement process.
Over 540 Densipact elements were installed in eleven days to complete the soil densification.
Geotechnical Engineer: Braun Intertec Corporation, Minneapolis, MN
General Contractor: Stevens Construction, Madison, WI
Geopier Densipact Installer: Peterson Contractors, Inc.
Geopier Designer: Ground Improvement Engineering, Minneapolis, MN