News | February 14, 2019

San Francisco’s Transbay Tube will receive a seismic retrofit

The 3.6-mile transit tunnel, which runs under the Bay, will be worked on for the next three years

San Francisco’s Transbay Tube will receive a seismic retrofit

Image source: Bay Area Rapid Transit

The San Francisco Bay area has become almost notorious for its high cost of living and the plethora of out-of-town commuters who may work in the city but can’t afford to live there. One major artery that aids such commuters is the Transbay Tube, the Bay Area Rapid Transit’s 3.6-mile transit chord that connects San Francisco with the city of Oakland under the bay itself.

 

Unfortunately, this tunnel has been determined to be vulnerable to seismic activity, a common issue in California, and therefore a project to retrofit the tunnel with added safety features in presently underway.

 

According to the San Francisco Chronicle, the retrofit will consist of attaching, welding and grouting steel plates along the tube’s concrete inner surface in order to create a liner. The tube system’s gallery walls also will be fitted with flat steel plates, and crews will waterproof the tunnel’s concrete floors with a waterproofing polymer membrane. Each night, workers will remove a small section of track, level the concrete beneath it and coat it with the membrane. They will then pour new concrete on top and restore the track. In the final stage, workers will install new pumps that can flush out at least 3,000 gal of water per minute (three times current capacity), plus an emergency generator that can power the pumping system for 48 hours.

 

The pricetag for the update is approximately $313 million, and work is expected to run through 2022. At present, the tunnel is vulnerable to earthquakes of an 8.0 magnitude or above. The purpose of the retrofit is to give those people who may be in the tube in the event of such an earthquake time to get out before it floods.

 

Though commutes will be disrupted for thousands of riders, officials are adamant that the repairs are crucial and necessary. “We want to make sure that workers and patrons who happen to be in the tube during a major event have enough time to exit” before the structure floods, Zecharias Amare, BART’s group manager of capital projects, told reporters.

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