The seismic retrofit of the Bayshore Viaduct in San Francisco, California, included strengthening of the existing pile foundations. This required installing piles around the existing structure and then tying those piles into an enlarged pile cap. These photos are from work during 2000-01.
An APE-8 pile driving hammer (24,000 foot-pound) was used to drive the piles adjacent to existing pile foundations. There was very limited working room with the viaduct being immediately above the hammer in this photo. The pile was driven in segments, with each segment welded onto the preceeding segment.
The square plates are resting on top of the open ends of the newly-installed pipe piles. The existing pile cap is at the top of the photo. Shoring is used around this excavation, within which the enlarged pile cap will be constructed.
The reinforcement cage for the enlarged pile cap fills the excavation.
This close up view shows a worker tying rebar in position in preparation for the concrete pour.
Look closely, and you can see the open end of one pipe pile beneath the main reinforcing cage. Several reinforcing bars extend from well within the pipe pile up into the pile cap’s reinforcing cage, tying the piles to the pile cap. This connection is essential for carrying the tensile (uplift) loads that may be imposed on the piles during earthquake loading.
The lower portion of the enlarged (retrofitted) pile cap has been poured.
This view shows several columns along the alignment of the viaduct. Retrofit of the pile foundations for the columns in the background have been completed, while one additional concrete pour is needed to complete the above-ground portion of the cap for the column in the foreground.