07 March 2013 ~ 3 Comments

Introducing Big Alma and Mom Chung, the Central Subway’s tunnel boring machines


Mom Chung, shown here, will construct the tunnel for southbound trains. More photos of both TBMs are available on our Flickr page. (Photo courtesy of The Robbins Company)

We are excited to introduce Big Alma and Mom Chung, the tunnel boring machines (TBMs) that will excavate and construct the Central Subway tunnels. Named Big Alma, after “Big Alma” de Bretteville Spreckels, and Mom Chung, after Dr. Margaret “Mom” Chung, the machines will begin tunneling later this year, starting in SoMa and heading north under 4th Street and Stockton Street through Union Square, Chinatown and North Beach. A press release about the TBMs is available online here.

The first of the machines, Mom Chung, is expected to arrive in San Francisco in April. The 300-foot-long machine will be assembled within an excavation on 4th Street between Harrison and Bryant streets and will start building the tunnel for southbound trains about two months later. Big Alma will arrive soon after Mom Chung to construct the northbound tunnel.

As tunneling proceeds, updates about the TBMs, including photos of the machines and the tunnels, will be posted on Twitter at the usernames @BigAlmatheTBM and @MomChungtheTBM. You can learn more about them on our website, at www.centralsubwaysf.com/tbm-name.

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The front of the TBM, called the cutter head, spins as it excavates. In this photo Mom Chung is being tested before being disassembled for transport to San Francisco. (Photo courtesy of Barnard Impregilo Healy)

The names were selected by the public in an online poll held in January. Participants could select up to two names, one for each TBM. Of the 1,453 responses, Big Alma was the top vote-getter at 682 votes. Mom Chung took second place with 487 votes, closely followed by Firebelle Lil (451 votes), Mary Ellen (437 votes) and Juana (148 votes).

In tunneling tradition, the custom of naming TBMs is believed to bring good luck to tunneling projects. The names will remain in official use by the SFMTA and the tunneling contractor throughout the duration of the project.

“Big Alma and Mom Chung will construct San Francisco’s first new subway tunnel in decades, bringing together neighborhoods of our city that have long been in need of improved public transit,” said SFMTA Director of Transportation Ed Reiskin. “We are happy to have included the public in this exciting part of tunneling tradition. We thank everyone who voted for contributing to this important project.”


Big Alma, shown here, is still being assembled. She will arrive in San Francisco after Mom Chung to construct the northbound tunnel.

Each TBM consists of a rotating cutter wheel (the cutter head), a cylindrical steel shell (the shield) and a 300-foot train of tunnel-building mechanisms (the trailing gear). The TBMs will arrive in several parts, to be assembled at the site on 4th Street between Harrison and Bryant streets where tunneling will begin.

About the Winning Names:

“Big Alma” de Bretteville Spreckels (1881-1968): Known as “Big Alma” (she was 6 feet tall) and “The Great-Grandmother of San Francisco,” Alma de Bretteville Spreckels was a wealthy socialite and philanthropist who, among her many accomplishments, persuaded her first husband, sugar magnate Adolph B. Spreckels, to fund the design and construction of the California Palace of the Legion of Honor at Land’s End in San Francisco.  A model in her youth, Spreckels was the inspiration for the “Victory” statue atop the Dewey Monument in the center of Union Square.

Dr. Margaret “Mom” Chung (1889-1959) was the country’s first female Chinese-American physician, practicing in the heart of San Francisco’s Chinatown. During World War II she “adopted” more than a thousand “sons,” most of them American servicemen, mentoring them, sending them presents and sharing meals with them during and after the war. She was also one of the earliest supporters of women in the Navy. When one of her “sons” became a congressman, he filed the first legislation to create a female branch of the Navy in response to a phone call from “Mom Chung.”

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3 Responses to “Introducing Big Alma and Mom Chung, the Central Subway’s tunnel boring machines”

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