San Francisco Municipal Transportation Agency (SFMTA) Twin Peaks Tunnel and Sunset Tunnel Vulnerability Study - San Francisco, CA
To perform vulnerability study of two SFMTA tunnels, identify their potential deficiencies under a major seismic event, and develop and recommend remedial retrofit concepts. The Twin Peaks Tunnel, running under the Twin Peaks and connecting the Castro neighborhood and the West Portal neighborhood, was built by the San Francisco Department of Public Works and began service operations in the late 1910s. The tunnel consists of approximately 9,000-feet of mined tunnel and 1,500-feet of open-cut tunnel. The Sunset Tunnel, beneath Buena Vista Park and the hill that the park is located on, was built by the San Francisco Department of Public Works and began service operations in the late 1920s. The total length of the Sunset Tunnel is approximately 4,100-feet. The tunnel is mostly under the rock line according to the original Test Boring drawings and is an arch section (horseshoe shape) throughout the whole route.
As part of ANV/BCA team, AMC was responsible for the evaluation of the tunnel sections. AMC first searched for as-built drawings through all possible City document depositories to establish the as-built conditions. Secondly, AMC performed site visits and identifies the current structural conditions. Response-spectrum-compatible rock motion time histories were developed along the tunnel alignment. The rock motions were propagated towards the surface to obtain the free-field deformation at the centerline of the tunnels. A simplified two-dimensional raking analysis was performed on different cross-sections of the tunnel by imposing free-field deformation at far boundaries and the force/displacement capacities of the local structural members of the tunnels were evaluated. Conceptual retrofit schemes were also developed.