Thursday, December 11, 2014

TBM: Tunnel Boring Machines

On the left in photo above, the Northbound tunnel sits empty after TBM Big Alma’s removal. On the right, TBM Mom Chung continues to be disassembled in the Southbound tunnel.

Tale of Two Tunnels
(Excerpt) "The [San Francisco] Central Subway’s two tunnels – one for northbound trains and one for southbound trains – were constructed using state-of-the-art excavators known as tunnel boring machines. Each TBM consisted of a rotating cutter wheel (the cutter head), a cylindrical steel shell (the shield) and a 300-foot train of tunnel-building contraptions (the trailing gear). The two TBMs moved through the ground at an average rate of about 40 feet per day, with a maximum speed of around 120 feet in a day.

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.

TBM "Big Alma" named for the sake of...
'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.

TBM "Mom Chung" named for the sake of...
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.'"
Source: Meet the TBMs

GIVE ME A MOMENT a lifestyle
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