Machines quietly tunneling in Muni's Central Subway project

Traveling from South of Market, past Moscone Convention Center and to the far end of Union Square on Saturday morning was an other-worldly experience: no cars, no stores, no tall buildings, no crowded sidewalks, no panhandlers.

Everything was gray. And noisy - a loud constant buzz bordering on a roar mixed with the incessant metallic hammering sound interspersed with occasional beeps. Even the weather was odd. It was warm and humid, yet dry. Still, the pavement underfoot was covered in a sticky layer of mud.

This trip, seemingly out of a science fiction novel, was a tour of the under-construction northbound bore of the Central Subway - the Municipal Transportation Agency's $1.6 billion transit link between the Caltrain station and Chinatown.

The line will stretch 1.7 miles, with a twin-bore tunnel going underground where Interstate 80 crosses Fourth Street. An above-ground station will be built at Fourth and Brannan streets with subterranean stations near Moscone Center at Fourth and Folsom streets, at Union Square and in Chinatown at Stockton and Washington streets, where the tracks will end.

But the tunnel will extend to Powell Street and Columbus Avenue, the site of the old Pagoda Palace Theater in North Beach, where the two tunnel-boring machines will be plucked from the ground and an extension might someday be built.

For now, the two machines - each longer than a football field and weighing 750 tons - are steadily and surreptitiously gnawing 20-foot wide tunnels beneath one of the most-congested parts of the city. Tunneling crews work five days a week, 12 hours a day, with maintenance work taking place when they're not digging.

Mom Chung, the machine named for the nation's first American-born female Chinese physician, got a head start in July and is now at Stockton and Clay streets in Chinatown. Big Alma, dedicated to socialite and philanthropist Alma de Bretteville Spreckels, started work in November and has made it past Union Square. She's now sitting beneath the Nike store.

Mike Sinon, safety manager for contractor Barnard Impreglio Healy, said it's a tradition as well as a safety precaution to name the tunneling machines - usually after women.

"It's bad juju to not name tunnel-boring machines," he said. "It's done all over the world."

So far, it seems to be working. John Funghi, the MTA's Central Subway project manager, said the work has been imperceptible on the surface, even when passing beneath some of the city's busiest areas, such as Fourth and Market streets, where the boring machines had to dig beneath Old Navy and Forever 21.

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Machines quietly tunneling in Muni's Central Subway project