Yerba Buena Island Tunnel

Seismic Analysis

The Yerba Buena Island Tunnel was built in 1936 during construction of the San Francisco - Oakland Bay Bridge.  The bridge connects Oakland and San Francisco via Yerba Buena Island.  The bridge consists of two distinct segments: a cantilevered steel truss segment connecting Oakland to Yerba Buena Island (SFOBB East), and a double suspension segment connecting the island to downtown San Francisco (SFOBB West). Both bridges carry 5 lanes of traffic in each direction via double deck roadway system. Two bridge segments are connected to each other via the mined tunnel through Yerba Buena Island. It is still the largest diameter, single bore tunnel in the world with five lanes of traffic going each way, one above the other, and each high enough to accommodate large trucks in any lane.

SC Solutions’ responsibilities included creation of the 3D finite element model of the Yerba Buena Tunnel Portal section to evaluate seismic vulnerabilities of the concrete structure during the design seismic event. Originally, the tunnel was bored through solid rock of Yerba Buena Island and a concrete liner was installed on the surface of the borehole. This liner has a lip along the arch at each portal. Two additional arches were also built at the portals, but they are isolated from the tunnel liner, and therefore were not included in the analysis. A nonlinear time history analysis with multiple support excitations was conducted, and the structural integrity of the tunnel was evaluated. Nonlinear effects simulated in these models included representation of the construction sequence, global geometric effects, and liner/rock interaction. Specifically, effects of the seismic wave passage on the structural integrity of the tunnel were thoroughly examined.