Large Diameter Steel Pipe Piles Running under Self Weight in Soft Clay: Predicted vs. Observed Behavior — Richmond San-Rafael Bridge Seismic Retrofit

The Richmond San Rafael Bridge (Figure 1) is a 7 kilometer long major toll bridge span across northern San Francisco Bay. Tutor-Saliba/Koch/Tidewater (TSKT) conducted a comprehensive seismic retrofit, which was at the time Caltrans' largest-ever construction contract at $484 million. The robust foundation retrofit design of 11 bridge piers included the installation of 26 new, large diameter (3.20 to 4.11 m OD, wall thickness 38 to 57 mm) Cast-in-Drilled-Hole (CIDH) and Cast-in-Steel-Shell (CISS) piles, with steel pipe piles installed to tip elevations of Elev. –42.7 to –67.1 m, in water depths up to 21 m. The open-ended steel pipe piles had initial sections ranging from 21.6 to 52.4 m long, self weight of 880 kN to 2780 kN in air, with full lengths that extended to the bay bottom and then through 30.5 to 39.6 m of marine sediments to top of bedrock. The marine soils of most interest consisted mainly of soft to firm Young Bay Mud (YBM), a silty, moderately-sensitive clay common to SF Bay. A key constructability issue was prediction of pipe piles "running". The term "pile running" describes the penetration of the pile into the soil due to the self-weight of the pile only. This issue was critical because 1) there was limited head room under the bridge deck, and 2) if piles run too deep, the pile splicing on several piles would be problematic (the lowest desirable pile top elevation after running was +3 m). This paper discusses the running prediction under self weight for 26 piles, and the methodology used in developing the predictions. The prediction methodology was quite good, and no significant constructability problems were encountered. Another case is also presented using the same methodology. The paper presents the model, predictions, observations, and discusses important lessons learned.