Design for the new San Francisco-Oakland Bay Bridge East Span, soil-structure interaction problems

This paper presents a brief summary of two aspects of soil-structure interaction studies conducted for the San Francisco-Oakland Bay Bridge East Span project. There was significant variability in the presence or absence of a very dense Merritt sand layer at shallow depths due to Paleochannel erosions of the Merritt sand strata. This resulted in the choice of battered pile groups for the skyway. A battered pile group has some advantages for the specific project condition. The SFOBB skyway contract is unique in the fact that the resultant design needs to be checked against both conventional response spectrum solution as well as time history solutions. A rigorous kinematic soil structure interaction (SSI) input motion approach was adopted in developing the theoretically rational acceleration response spectrum (ARS) criteria. This paper provides discussions of the kinematic SSI motion approach. Various site stability issues have surfaced historically at the Oakland Mole approach, due to the combination of poor soil condition and the relatively steep ground relief features at that location. Efforts were involved in the design to address potential ground movements and their implication to the Oakland Mole transition structures. The pinning effect of the large pile groups was found to be significant in stabilizing the ground against potential ground movements. This aspect is also addressed in this paper.