BART Earthquake Safety Program on "fast track" to construction
BART issues 1st annual "Earthquake Safety Media Progress Report"
One year ago this month, nearly 70% of voters approved Measure AA – a $980 million bond that will help fund BART's $1.3 billion, 10 year Earthquake Safety Program. The program is designed to strengthen BART stations, elevated train tracks and the Transbay Tube to withstand a massive earthquake. (More information about the program is on BART's website: www.bart.gov/earthquakesafety.)
Today BART is issuing its first annual "Earthquake Safety Media Progress Report Card" news release. BART is pleased to announce that during the year since Measure AA's passage, BART has taken a number of swift steps to expedite the process needed to get BART into the construction phase of the Earthquake Safety Program.
Construction will first begin on the Transbay Tube. It is tentatively scheduled for mid 2007.
U.S. Geological Survey researchers and scientist predict a 67% chance that at least one or more magnitude 6.7 or greater earthquakes will strike the Bay Area. That's why BART is in a race against time to strengthen the system before the next big one hits.
PROGRESS ON "FAST TRACK"
During the past year BART has shaved months off the essential pre-construction process of selecting the right retrofit methods for the Transbay Tube, stations and elevated tracks. Under normal circumstances the process would take many more months, but these are not normal circumstances. BART is now about to enter into the last and shortest stage, called final design, before the physical work begins.
Here are some of the significant accomplishments BART has made in the year since Measure AA's passage on November 2, 2004:
- Completed Global Modeling and Analysis of Transbay Tube
- Completed the Environmental Analysis for the Transbay Tube and Related Work
- Accelerated Design of the Retrofits
- Awarded Numerous Design and Construction-Related Contracts to Strengthen the Transbay Tube & Other Structures
- Held more than 50 briefings for Elected Officials, Key Stakeholders and Other Community Members
TRANSBAY TUBE STRENGTHENING METHODS
The Transbay Tube, which carries nearly half of BART's 330,000 daily riders, tops the priority list of BART structures to strengthen. The overall goal is to both thicken the soil surrounding the Tube so it won't liquefy in an earthquake as well as tie the Tube down so it won't budge during a quake. BART engineers will likely use a combination of the following different strengthening methods to secure the Tube:
VIBRO-COMPACTION: This method involves using a device that will densify the soil around the Tube so that it essentially thickens up. The process is roughly similar to what happens to cake mix when you turn on the cake mixer and the mix starts to compact along the edge of the bowl. This method would prevent the soil from liquefying in an earthquake.
VIBRO-REPLACEMENT: This method is virtually the same as the vibro-compaction except that gravel is added to the hole created by the mixer. This method would prevent the soil from liquefying in a quake.
MICROPILES TIE-DOWN: This method is essentially like using a giant thumbtack to pin the bottom of the Tube to the bay floor. Crews would pierce the bottom of the Tube, sink a pile through it and push it deep into the bay floor. This would limit the Tube's movement in a quake.
PILE STITCHING: This method is essentially like stapling the Tube to the bay floor. Crews would insert giant piles into the bay floor on either side of the Tube and then attach a bar across the tops of the piles to form what would look like a giant staple over the Tube. This would limit the Tube's movement in a quake.