Shoreline Stability - Seismic Retrofit of BART SFTS

Abstract eng:
This paper presents the shoreline slope stability analyses performed as part of seismic vulnerability studies for the San Francisco Transition Structure (SFTS) of the Bay Area Rapid Transit system Trans Bay Tube (TBT) system. The SFTS connects the TBT to the east with Bored Tunnels to the west via multiple degree-of-freedom seismic joints. For these analyses factor of safety and yield acceleration were evaluated by state-of-the-art 3-D finite difference model (FLAC3D) that incorporate both the 3-D variations in stratigraphy and the interactions with adjacent structures. Those analyses also provide critical insights into the mechanism of interaction between slope movement and the various buried structures. The project criteria required consideration of extremely high shaking levels (PGA of ~ 0.6 g) associated with an approximately 1,000-year return period event. The slope deformations were calculated by: a) a decoupled approach consisting of a 2-D equivalent linear site response analyses (QUAD4M) and Newmark-type analyses, and b) fully-coupled 2-D nonlinear finite element (PLAXIS) and finite difference (FLAC) analyses. The results of the analyses were used to develop inputs for a project global analyses and helped guide the selection/rejection of retrofit measures for the project.

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