Location: 400 Q Street, Sacramento, CA

The CalPERS project consisted of a six-story, above ground structure with two stories below ground for parking. This is the first structure in this area to accommodate a two-level below ground installation. It was the below ground challenges and remediation that were of particular interest. Due to its close proximity to the Sacramento River, ground water was perhaps the major obstacle since it was both high (15 feet below street grade) with significant seasonable fluctuations. Alluvial soils added to the complexity of the site. While dewatering was obvious, the affect to the proposed and buildings in close proximity was critical. A slurry cut-off wall served as both a ground water barrier and shoring support for the structure excavation. The wall was constructed to a depth of 120 feet below the adjacent ground surface.

Foundation support for the structure consisted of 17-inch diameter, 45-feet long augercast piles, which were drilled through the alluvium and seated in an underlying cemented soil stratum. To account for potential buoyancy affects in the event that the cut-off wall was breached, tiedown anchors were installed to depths of 50 feet below the lower parking level floor slab.

We served as the Geotechnical Engineer of Record and provided design and on-site support during the installation of all ground related improvements including the cut-off wall, sheet pile installation, tieback installation and stressing, augercast pile load installation and load testing, and tiedown anchor installation and testing.