The California Maritime Academy, a California State University campus, sits on the south side of Vallejo and fronts San Pablo Bay near the Carquinez bridge at Morrow Cove. The site served as the ferry terminal up to the 1920’s for the Carquinez strait to Crocket. The site has been filled since the 1920’s to its present state to expand the campus for the growth of the California Maritime Academy. In the late 1990’s, a seismic upgrade project was performed to improve the shoreline against liquefaction and lateral spread, but not in the western portion of the site near the new dining hall.
The geotechnical engineer performed 4 borings and observed old fill, sandy gravel and rocky colluvium, and then loose sand layers and soft bay mud at depths of 15 to 30 feet. The soil mantle was underlain by bedrock to depths of 38 feet that slopes toward the bay. Lateral spread and liquefaction were major design problems with up to 10 inches of calculated liquefaction settlement and sloping bedrock toward the bay.
Cal Maritime needed a solid foundation to go vertical with the project. Farrell collaborated with Forell Elsesser and KC Engineering to provide a well-defined, compaction grouted column, ground improvement using the Drill Displacement Column (DDC) system. Considerable design effort was required by Farrell to gain approval for the CSU peer review requirements. We installed over 500 DDC to depths of 38 feet to improve and reinforce the loose fill and soft bay mud. The DDC displacement and pressure grout effect resulted in considerable cavity expansion in the loose soil. The site elevation was raised by 6 inches with DDC construction, which proved the maximum ground improvement possible at depth. Farrell completed this project on time in October 2012 for McCarthy and Cal Maritime.
The project and site performed well during and after the magnitude 6.0 South Napa earthquake in 2014. Peak ground accelerations near the site at the Crockett – Carquinez Bridge Geotechnical Array #1 measured median PGA = 0.7g. The DDC ground improvement performed very well during this earthquake.
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