Earthquake Safety Program Technical Information
Seismic Vulnerability Study
One of the first and most critical undertakings of the Earthquake Safety Program was a systemwide vulnerability study — an assessment of how system components would perform during a major earthquake. Completed in 2002, the study was the most comprehensive evaluation of BART facilities since the original construction of the system. It involved one and one-half years of engineering and statistical analyses, which included developing earthquake scenarios, computer models, damage predictions, upgrade options, and cost-benefit analyses. The study also incorporated new information from the 1994 Northridge, California and 1995 Kobe, Japan earthquakes.
Results of the Seismic Vulnerability Study indicated that if the BART system is not strengthened, it will take years to restore service after a major earthquake. The study found that portions of the system most susceptible to earthquake damage include the Transbay Tube, aerial structures, stations and equipment. The study recommended that priority be given to the Transbay Tube, where soil backfill is prone to liquefaction. Though the consequences of liquefaction on the Tube are uncertain, a worst-case scenario could cause excessive movement of the seismic joints and structural stress that could result in significant damage.
Through the Seismic Vulnerability Study, upgrade design concepts were developed for vulnerable portions of the system. The concepts outlined below will be refined, allowing consultants to develop construction schedules. By carefully planning and monitoring upgrade work, BART aims to continue train operation during construction, with minimal impact to BART riders.
The highest priority for upgrades is the Transbay Tube, which connects Oakland to San Francisco. Preliminary upgrade concepts include the following:
- Vibro-replacement to compact soil backfill,
- Increasing seismic joint capacity and sealing around joints, and
- New concrete shear walls in the Oakland Ventilation Structure.
Potential aerial structure upgrade concepts are as follows:
- Enlarge or reinforce concrete foundations,
- “Jackets” around concrete columns,
- Additional shear keys, and
- Additional foundation piles (where poor soil conditions exist).
Station upgrades may include using similar aerial structure upgrade techniques as well as strengthening platform connections, canopies, and stairways. For mechanical, electrical, and other equipment, upgrades will consist of additional anchorage.
To ensure that lessons learned and technological advancements are applied to the program, BART has worked closely with advisors such as the California Seismic Safety Commission, California Department of Transportation (Caltrans), and independent panels of world-renowned experts in seismology, geotechnical engineering, risk analysis and upgrade design. The panels of experts reviewed and concurred with the findings of the Seismic Vulnerability Study and recommended that upgrade work begin as soon as possible.