A gigantic tunnel boring machine was bid farewell by San Francisco officials today as it soon begins its underground voyage to excavate and construct the city’s Central Subway project.

The subway project will create a new branch of the San Francisco Municipal Transportation Agency’s T-Third line between the South of Market and Chinatown neighborhoods, with stops also at Yerba Buena/Moscone and Union Square/Market Street stations.

Mayor Ed Lee and other city officials this morning signed their names on the tunnel boring machine named Mom Chung, which is set to begin excavating underneath Fourth and Harrison streets starting the week of June 10.

Lee said the Central Subway project is about “making sure that we connect up the north and south (ends of the city). A modern San Francisco will have a transportation system that reflects that.”


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He said, “It’s a reflection that our neighborhoods are here to stay and grow and prosper.”

SFMTA took the mayor, other city officials and the media on a tour of the excavation site and the tunnel boring machine, Mom Chung, which is longer than a football field and weighs 750 tons, according to SFMTA officials.

Sparks were flying as welders continued work this morning to assemble the large, cylindrical machine, which will use a rotating cutter wheel and 300-foot-long trailing gear to cut through the earth between 40 and 120 feet below ground.

The machine will move about 40 feet per day and take about 10 months to create the 1.5-mile tunnel, according to SFMTA officials, who say no vibration or noise will be felt above ground from the tunneling.

A second tunnel boring machine named Big Alma will also create a parallel tunnel starting this summer, with both machines ending up at the site of the former Pagoda Palace Theatre in Chinatown, SFMTA officials said.

Mom Chung is named after Dr. Margaret “Mom” Chung, the country’s first female Chinese-American physician, while the second machine is named after 19th century San Francisco socialite “Big Alma” de Bretteville Spreckels, according to SFMTA officials.

The names were chosen via an online poll held earlier this year.

“It’s important to honor the past while we build the future of San Francisco,” SFMTA director of transportation Ed Reiskin said.

The Central Subway is expected to open in 2019. Updates on the project can be found online at www.centralsubwaysf.com.

Dan McMenamin, Bay City News

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