Use of Multi-Shaft Deep Soil Mixing for Seismic Mitigation At Agnews Campus Project-Video

Video Transcription

Video Summary

The Agnews campus project redeveloped a 55-acre former state hospital site in San Jose into an elementary, middle, and high school campus. Because the 18 buildings sit on variable alluvial soils with significant liquefaction and settlement potential, deep soil mixing (DSM) was used to support shallow foundations and meet California seismic requirements. Over six months in 2019, crews installed about 235,000 cubic yards of DSM to depths of roughly 40 feet. Grids beneath the buildings achieved area replacement ratios of 43–47%, exceeding the 40% design target. Quality assurance included cores from 3% of the elements, more than 1,300 strength tests, wet-grab samples, and optical televiewer inspections. Average unconfined compressive strength exceeded the 250-psi design requirement; only 2% of test breaks fell below 150 psi. Supplemental sampling helped confirm material quality where gravel made coring difficult. DSM improved bearing capacity and reduced anticipated static and seismic settlement.

Keywords

Agnews campus project

deep soil mixing

liquefaction mitigation

seismic foundation support

San Jose school campus