Posey Webster Tunnel Ground Improvement Demonstration Project Cities of Alameda and Oakland, California Back to Project List Vibratory Ground Improvement Jet Grout Columns are installed at the Posey Tube in the Jack London Square site, Oakland. Vibro stone column installation with fixed lead at Webster Tube section, Mariner Square, Alameda. Project Overview: Determination of the most appropriate ground improvement method was necessary for planning one of the most difficult seismic retrofit projects by the State of California Department of Transportation. Two submerged vehicular tunnels were constructed during the 1960's, utilizing different construction techniques and underwater backfill materials. Layne GeoConstruction was selected to perform two demonstration trials using two distinct ground improvement techniques- jet grouting and stone columns. Interconnected jet grout columns, forming a cut-off wall to reduce liquefaction, were constructed beside the Posey tunnel. Vibro replacement stone column technique was performed at the Alameda Tunnel to densify loose sand backfill around the tubes..     Value of Work Performed: $995,000 Project Duration: 2 months Project Completion Date: October 2000 Project Reference: Owner: CALTRANS Oungkar Narine (510) 286-1300