The Challenge
The Naval Amphibious Base at San Diego recently built a squadron operations building. The soils underlying the site consisted of reclaimed dredge materials, liquifiable silts, shells and loose sands. In order to increase seismic stability, a liquefaction mitigation subcontract was let to Condon-Johnson & Associates (CJA) by General Contractor R.A. Burch Construction.

The Solution
The depth of treatment was limited to 25’, so stone columns, which are constructed by installing stone through a vibro probe to increase the density of the surrounding soils, were used for most of the project. These columns were installed with a device known as a stitcher, which can mount on a track hoe for ease of movement.

In areas where the vibration associated with the installation of stone columns was thought to threaten adjacent structures, the liquefaction mitigation as carried out by deep mixing utilizing the Geo-Jet® system. This system injects cement and water under high pressure while mechanically breaking the existing soil structure to ensure complete mixing.

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Geo-Jet®