Webster Street and Posey Tubes

Description

The cities of Oakland and Alameda are linked by two historically significant traffic corridors that traverse beneath the Oakland Estuary: the Posey Tube and the Webster Street Tube.
Completed in 1928, 3200 ft long Posey Tube designed by Alameda County Engineer George A. Posey was the first pre-cast immersed tube structure of its kind.
By 1962, the two-lane tube carried approximately 30,000 vehicles per day. To increase vehicle capacity, the Webster Street Tube was constructed parallel to and 500 ft west of the Posey Tube in 1965.
Each tube consists of twelve 200 ft long sections, joined by collars, which were set in trenches cut into the estuary floor.
The Posey Tube was backfilled with the excavated silts, soft clay and loose sand.
The Webster Tube was backfilled with imported sand.
Both tubes were set on layers ofloose sand during construction.
Crushed iron slag was dumped over each submerged tube to protect it from possible damage and to add weight to resist hydrostatic uplift. Today the estuary may be up to 40 ft deep, depending on the tide. (excerpted from "Seismic retrofit..." linked below.)

Seismic retrofit of the Posey and Webster Street tubes in Oakland, California...(May 2005)
Jet Grouting Experience at Posey Webster Street Tubes Seismic Retrofit Project

You Tube video (thanks to "gregory g" gives a real feel for the Posey Tube - away from Alameda.

Also see, Alameda Info on Tubes