Jet Grouting Experience at Posey Webster Street Tubes Seismic Retrofit Project

This paper summarizes the construction experience of a seismic retrofit project for the Posey and Webster Street Tubes near Oakland, California. The Posey and Webster Street Tubes serve as the main tunnels for the California Route SR 722 along the city streets connecting cities of Alameda and Oakland. The retrofit work consisted, among other things, jet grouting and chemical grouting of the soils supporting the tubes. The primary purpose of the grouting work was to strengthen and densify the soils immediately surrounding the tubes to avoid liquefaction of the soils and loss of support for the tubes during major earthquakes with magnitude of M-7.5 or greater. Some of the criteria used for measurement of success of the work consisted of testing the soils after grouting. The tests included density, unconfined compressive strength field permeability tests and visual inspection of the grouted columns. Several construction difficulties were encountered during jet grouting. This paper summarizes materials, equipment, soil and groundwater conditions, grouting operation, rate of production, costs, and time requirements for jet grouting operation at Posey and Webster Street Tube Joint No. 1. The paper provides a summary of the experience gained from the jet grouting operation and presents conclusions and recommendations useful for similar applications.