San Francisco completes Central Subway tunnel portal entrance
The identical twin TBMs weighed-in at 750 tons each and were affectionately named Mom Chung — for Dr. Margaret “Mom” Chung, the nation’s first Chinese-American physician — and Big Alma — for San Francisco philanthropist and socialist “Big Alma” de Bretteville Spreckles.
Construction on the now-completed Central Subway Portal on 4th Street
2 min to read
Construction on the now-completed Central Subway Portal on 4th Street
The San Francisco Municipal Transportation Agency (SFMTA), which manages all transportation in the city, including the Municipal Railway (Muni), completed the Central Subway tunnel portal entrance, which was the final element to the overall tunneling contract. This portion of the Central Subway Project was completed on-time and on-budget.
The portal, at 4th and Harrison streets, was initially called the “launch box” because it served as the entrance site of two 350-foot-long boring machines (TBMs). Each TBM tunneled 8,500 feet beneath SoMa, Union Square and Chinatown creating the Central Subway tunnels. The identical twin TBMs weighed-in at 750 tons each and were affectionately named Mom Chung — for Dr. Margaret “Mom” Chung, the nation’s first Chinese-American physician — and Big Alma — for San Francisco philanthropist and socialist “Big Alma” de Bretteville Spreckles.
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Now that the TBMs have completed their 1.5-mile journeys, the launch box has been seismically and structurally reinforced creating the portal where the Muni Metro T Third Line Light Rail Vehicles (LRVs) will enter and exit the Central Subway.
The tunnel portal structure contract called for a final completion date of May 15. However, the crews met expectations by substantially completing the portal structure, constructing the twin tunnels and five cross passages a month earlier.
“It was not only imperative that the portal structure create San Francisco’s next generation of public transit,” said Ed Reiskin, SFMTA Director of Transportation. “It was crucial that we adhered to our commitment to the public. We promised to deliver on-time and on-budget, and the completion of this portion of the project is another milestone that demonstrates we deliver as promised.”
The project was complete within budget estimates of $241 million. The U.S. Department of Transportation announced approval of the Full Funding Grant Agreement of $942.2 million to fund nearly half of the Central Subway Project. The remaining budget is balanced by existing state and local grant funds.
The Central Subway is expected to open to the public in 2019 and will directly serve some of San Francisco’s most densely populated communities including: the Visitacion Valley in the Southeast, east to the Bayview/Dogpatch, and west to the city’s center.
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