Machines quietly tunneling in Muni's Central Subway project
Visitors get a peek at the progress in the northbound tunnel of Muni's Central Subway project in San Francisco.
A transport vehicle emerges from the northbound tunnel of Muni's Central Subway construction project in San Francisco, Calif. on Saturday, March 8, 2014. Two large boring machines, Big Alma and Mom Chung, are grinding their way north from Fourth and Bryant streets towards Chinatown and North Beach.
....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.
Imperceptible on surface
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.
"You could be in the Nike store shopping and you wouldn't feel a thing," Funghi said. "We've been very fortunate. Nothing on the surface has moved. We crossed under BART without stopping or even disrupting service."
The machines excavate and build about 50 feet of tunnel a day, Funghi said. Big Alma is quicker at 54 feet a day compared to Mom Chung's 44-foot average, but Mom Chung holds the performance record of 96 feet in a single day.
....The tunneling may be done this summer, but it will be another 4 1/2 years before passengers can ride the Central Subway in 2019....
Metro system connector
"This will be the Metro system connecting north and south, which has not been connected by rail so far," said Paul Rose, an MTA spokesman. "It's connecting Chinatown, one of the densest areas not only in the city but in the state and country."
He said the project is on schedule and on budget.