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SFMTA’s Central Subway will connect San Francisco’s southeast neighborhoods to downtown and Chinatown. Whether you’re a concerned citizen, business owner, Muni customer, or just stumbled onto our blog, we welcome your questions and encourage you to connect with us. Follow us for the latest Central Subway news and information.

01 August 2013 ~ 1 Comment

Tunneling crews assemble Big Alma, the Central Subway’s second TBM

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Late in the night last month, crews installed the cutter head of tunnel boring machine (TBM) Big Alma. The massive machine’s cylindrical shield was already in place below.

Big Alma has arrived. The massive tunneling machine — the identical twin of recently launched Mom Chung — is now under assembly underground. Last month, tunneling crews lowered large sections of Big Alma into the tunnel launch box, the major excavation under 4th Street between Harrison and Bryant where tunneling begins. After about two months of assembly, Big Alma will begin building a tunnel parallel to Mom Chung’s, extending the Muni Metro T Third Line through SoMa, Union Square and Chinatown.

The photos in this post show the installation of Big Alma’s cutter head. The cutter head, a spinning excavator at the front of the machine, will dig through bedrock, clay and sand as Big Alma travels north beneath 4th Street, Stockton Street and Columbus Avenue. This major component of the TBM is about 20 feet in diameter and weighs about 143,000 pounds. While tunneling is underway, the cutter head will pump out an environmentally safe, soap-like foam to condition the ground as it cuts through the earth like a cheese grater. Once loosened, spoils pass through holes in the cutter head for transport out of the tunnel.

To learn more about the TBMs and their tunneling journey, follow them on Twitter. They’re @BigAlmatheTBM and @MomChungtheTBM.

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A large red crane, called a gantry crane, lifts the cutter head from the ground.

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When Big Alma tunnels, these wheels will spin to loosen the ground, aided by an environmentally safe, soap-like foam that conditions it.

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Operated by our tunneling crews, the crane lifts the cutter head into a vertical position to allow for installation.

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Crews help stabilize the cutter head before lowering it underground.

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The crane moves the cutter head into position over the tunnel launch box, where Big Alma’s cylindrical shield awaits.

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The shield, already underground, will stabilize the tunnel and form a watertight barrier while mining is in progress. Concrete tunnel segments are installed within the back of the shield and bolted together by tunneling crews.

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Above the shield, the cutter head descends into the excavation.

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The front of the shield, before the cutter head is installed. During tunneling, excavated ground spoils will pass through the hole at the bottom for transport out of the tunnel.

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The cutter head continues its descent into the excavation.

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Once the cutter head is lowered, crews work to connect it to the shield.

 

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To connect the TBM segments, crews bolt them together. Later, they will reinforce the connections with welding.

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The TBM assembly team poses in front of Big Alma. We thank our dedicated crews for all their hard work.

 

26 July 2013 ~ 4 Comments

TBM Mom Chung launches, beginning tunnel construction beneath SF


This video shows some of the first ground spoils excavated after our first TBM, Mom Chung, launched this week.

This week tunnel boring machine (TBM) Mom Chung started digging, kicking off construction of San Francisco’s first new subway tunnel in decades.  Over the next 10 months, the 350-foot-long, 750-ton machine will excavate and construct the tunnel that southbound T Third Line trains will use when the Central Subway opens in 2019.

As Mom Chung travels, you can follow her on Twitter — she’s @MomChungtheTBM. Her twin sister, Big Alma, recently arrived in San Francisco. After about six weeks of assembly underground, she will begin constructing a tunnel parallel to Mom Chung’s. (You can follow Big Alma at @BigAlmatheTBM.)

The tunnels are a key component in extending the Muni Metro T Third Line through SoMa, Union Square and Chinatown, vastly improving transit in these neighborhoods.

The Tunneling Journey

Mom Chung and Big Alma will excavate and construct the 1.5-mile-long tunnels at a pace of approximately 40 feet per day, though their pace will vary based on ground conditions and other factors. Most of their journey will be through two major ground formations: the Franciscan complex, a bedrock formation that forms Nob Hill; and the Colma formation, a dense mixture of sand and clay.

The TBMs will be so far beneath the surface – between 40 and 120 feet underground – that no vibration or noise will be felt above ground when they pass below.


In this video, a welder works on the TBM’s trailing gear.

How TBMs Work

The machines consist of three main sections: 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).

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This conveyor belt on top of Mom Chung’s trailing gear will help transport ground spoils out of the tunnel. In the background you can see the cutter head of our second TBM, Big Alma.

The cutter head, a spinning excavator at the front of the machine, pumps out an environmentally safe, soap-like foam to condition the ground as it cuts through the earth like a cheese grater. Once loosened, spoils pass through holes in the cutter head and onto a large screw. The screw carries the spoils onto a series of conveyors for transport out of the tunnel.

To launch, Mom Chung pushed off of a steel frame as her cutter head began to spin.

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The large concrete segments shown here are what will form the Central Subway tunnels. The TBMs will install them, and crews will bolt them together, as the machines move forward.

As she tunnels, Mom Chung will stop every five feet to install the concrete segments that make up the tunnel’s lining. The concrete segments are installed within the back of the TBM’s cylindrical shield. The machine lifts the segments into place, and then crews bolt them together. Hydraulic jacks within the shield then push off of the newly installed tunnel lining, propelling the massive machine forward.

These concrete rings, already installed, are held in place by hydraulic arms (seen on the left) as the machine moves forward.

A crew of about 10 people operates the machine and bolts the tunnel segments together. Crews will be at work 24 hours a day, six days a week to build the Central Subway’s tunnels.

Learn More

Want to find out more about the Central Subway’s complex, high-tech tunneling machines? Check out the following documents:

12 July 2013 ~ 2 Comments

Construction Update | July 13-22

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People pass by our Stockton Street construction site on a sunny day earlier this week.

During the next 10 days, construction to prepare for tunneling will continue in SoMa and Union Square. In North Beach, demolition of the Pagoda Palace is planned to begin. No Central Subway construction is planned in Chinatown.

For descriptions of construction impacts in each neighborhood, click here or on the links below. We also post construction, traffic detour and Muni impact information on our project Google Map.

Construction impacts are planned to change at these locations by July 22:

  • Southern SoMa (Harrison to King/Berry): Full closure of 4th Street between Harrison and Bryant will continue some evenings and weekends, including all day Saturday, July 13. Two lanes of traffic will remain open at all other times. Contact us at central.subway@sfmta.com if you have questions about the closure schedule. On Bryant Street at 5th Street, the left lane and several parking spaces will remain closed.
  • North Beach: Demolition of the Pagoda Palace Theater is scheduled to take approximately four weeks to complete. For more information about construction at this site, check out this fact sheet.

At these locations, current construction impacts are planned to continue until July 22:

  • Northern SoMa (Market to Harrison): Two lanes of traffic will remain closed on 4th Street between Howard and Folsom. On 4th Street between Market and Stevenson, the sidewalk and two traffic lanes will remain closed on the eastern side of the street.
  • Union Square: Stockton Street between Geary and Ellis will remain closed to vehicle traffic. Ellis Street between Stockton and Powell will remain closed to westbound traffic.
  • Chinatown: No construction planned

We appreciate your patience and support while we build this essential upgrade to San Francisco’s public transportation system.

11 July 2013 ~ 0 Comments

Construction Details | Pagoda Palace Demolition

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The Central Subway tunnel will end at this site in North Beach, now home to the old Pagoda Palace Theater.

Since last summer, the SFMTA has worked closely with the North Beach community and multiple city agencies to relocate the retrieval site of the Central Subway’s tunnel boring machines (TBMs) from its original site on Columbus Avenue. After a series of community meetings and based on feedback from the community, the TBMs will now be retrieved at 1731-1741 Powell Street, known as the Pagoda Palace.

The first phase of construction at this site is the demolition of the Pagoda Palace. We expect this activity to take approximately four weeks to complete, including mobilization and site clean-up.

The building will be demolished using specialized equipment called a nibbler and crusher. This equipment is like a scissor that cuts the building into small pieces of rubble. Working from the sidewalk and parking lane in front of the Pagoda Palace, the contractor will take down the facade of the building, starting with the tallest point. Once there is enough clearance, the contractor will move inside the property line and complete the demolition from within.

After demolishing the building, we will construct a retrieval shaft within the property lines at 1731-1741 Powell Street. The retrieval shaft is an excavation of about 45 ft. by 49 ft., with a depth of approximately 42 ft. We will provide additional details about retrieval shaft construction before it begins.

The SFMTA is working closely with local contractor MH Construction to minimize construction impacts as much as possible while demolition is underway. For more information, check out this fact sheet. Construction details are below.

Planned construction (all dates approximate):

  • Disconnect utilities within building (week of July 8)
  • Set up pedestrian detour (week of July 15)
  • Mobilize demolition equipment (week of July 15)
  • Demolish building (approx. July 15-26)
  • Remove demolished building pieces (week of July 29)
  • Grade the site (week of July 29)
  • Construction hours will be Monday to Friday, 7 a.m. to 3:30 p.m.
  • Demolition takes approximately two weeks to complete, with two additional weeks required to prepare the site, remove the building pieces and grade the lot.

Traffic, transit and pedestrian impacts:

  • Area of impact: Powell Street and Columbus Avenue between Filbert and Union streets
  • The sidewalk in front of 1731-1741 Powell Street will be impacted
  • The Muni 39 Coit may be temporarily rerouted, but no stops will be impacted (see fact sheet for details)
  • Parking restrictions will be in effect in front of the Pagoda Palace on Powell Street and Columbus Avenue
  • Powell Street between Union and Columbus will remain open to traffic, but the traffic lane may be narrowed
  • The contractor will maintain access to adjacent businesses and facilitate the flow of traffic during work hours
  • Dust will be monitored and controlled, and noise will be kept within required decibel levels (see fact sheet for details)

We will provide additional updates via email and on our blog as work proceeds. Should you have any questions, please contact North Beach liaison Andrea Baker at 415.351.8427.

Thank you for your patience and support.

28 June 2013 ~ 0 Comments

Construction Update | June 29-July 15

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On Stockton Street, we are using this machine to construct underground walls. The walls will be incorporated into the Union Square/Market Street Station.


Note: Because of  the July 4 holiday, this construction update covers construction impacts through July 15. We will not send a construction update email next Friday, July 5; however, we will provide additional details about construction in North Beach early next week. Please contact us at central.subway@sfmta.com with any questions.


During the next 17 days, construction to prepare for tunneling will continue in SoMa and Union Square. In North Beach, Pagoda Palace demolition contractor MH Construction will perform surveys of the site. No Central Subway construction is planned in Chinatown.

In honor of the holiday, Central Subway construction will pause on Thursday, July 4.

For descriptions of construction impacts in each neighborhood, click here or on the links below. We also post construction, traffic detour and Muni impact information on our project Google Map.

Construction impacts are planned to change at these locations by July 15:

  • North Beach: Demolition of the Pagoda Palace Theater is scheduled to start Monday, July 8. For more information about construction at this site, check out this construction notice. We will provide detailed information about construction impacts next week, before demolition begins.
  • Northern SoMa (Market to Harrison): To allow for ground improvements, construction will be underway for 24 hours a day from June 28 until the morning of June 30 on 4th Street between Howard and Folsom (details in the Northern SoMa section). Two lanes of traffic will remain closed on 4th Street between Howard and Folsom. On 4th Street between Market and Stevenson, the sidewalk and two traffic lanes will remain closed on the eastern side of the street.

At these locations, current construction impacts are planned to continue until July 15:

  • Southern SoMa (Harrison to King/Berry): Full closure of 4th Street between Harrison and Bryant will continue some evenings and weekends. Two lanes of traffic will remain open at all other times. Contact us at central.subway@sfmta.com if you have questions about the closure schedule. On Bryant Street at 5th Street, the left lane and several parking spaces will remain closed.
  • Union Square: Stockton Street between Geary and Ellis will remain closed to vehicle traffic. Ellis Street between Stockton and Powell will remain closed to westbound traffic.
  • Chinatown: No construction planned

We appreciate your patience and support while we build this essential upgrade to San Francisco’s public transportation system.

21 June 2013 ~ 0 Comments

Construction Update | June 22-July 1

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Crews are continuing to assemble tunnel boring machine Mom Chung. The black roll of ribbon is her conveyor belt, where spoils will be transported out of the tunnel.

During the next 10 days, construction to prepare for tunneling will continue in SoMa and Union Square. In North Beach, Pagoda Palace demolition contractor MH Construction will perform surveys of the site. No Central Subway construction is planned in Chinatown.

For descriptions of construction impacts in each neighborhood, click here or on the links below. We also post construction, traffic detour and Muni impact information on our project Google Map.

Construction impacts are planned to change at these locations by July 1:

  • Northern SoMa (Market to Harrison):  Two lanes of traffic will remain closed on 4th Street between Howard and Folsom, but the traffic configuration will change (details in the Northern SoMa section). Construction will be underway on Saturdays until further notice. On 4th Street between Market and Stevenson, the sidewalk and two traffic lanes will remain closed on the eastern side of the street.
  • North Beach: Pagoda Palace demolition contractor MH Construction will perform surveys of 1731-1741 Powell Street. For more information about construction at this site, check out this construction notice. We will provide detailed information about construction impacts before demolition begins.

At these locations, current construction impacts are planned to continue until July 1:

  • Southern SoMa (Harrison to King/Berry): Full closure of 4th Street between Harrison and Bryant will continue some evenings and weekends. Two lanes of traffic will remain open at all other times. Contact us at central.subway@sfmta.com if you have questions about the closure schedule. On Bryant Street at 5th Street, the left lane and several parking spaces will remain closed.
  • Union Square: Stockton Street between Geary and Ellis will remain closed to vehicle traffic. Ellis Street between Stockton and Powell will remain closed to westbound traffic.
  • Chinatown: No construction planned

We appreciate your patience and support while we build this essential upgrade to San Francisco’s public transportation system.

14 June 2013 ~ 2 Comments

Construction Update | June 15-24

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About 80 feet below Ellis Street, we’re installing pipes into the ground around this shaft. We’ll use the pipes to inject grout into the ground, improving soil conditions near the existing Muni and BART tunnels.

During the next 10 days, construction to prepare for tunneling will continue in SoMa and Union Square. No Central Subway construction is planned in Chinatown or North Beach.

For descriptions of construction impacts in each neighborhood, click here or on the links below. We also post construction, traffic detour and Muni impact information on our project Google Map.

Construction impacts are planned to change at these locations by June 24:

  • Northern SoMa (Market to Harrison):  Two lanes of traffic will remain closed on 4th Street between Howard and Folsom, but the traffic configuration will change (details in the Northern SoMa section). Construction will be underway on Saturdays until further notice. On 4th Street between Market and Stevenson, the sidewalk and two traffic lanes will remain closed on the eastern side of the street.

At these locations, current construction impacts are planned to continue until June 24:

  • Southern SoMa (Harrison to King/Berry): Full closure of 4th Street between Harrison and Bryant will continue some evenings and weekends. Two lanes of traffic will remain open at all other times. Contact us at central.subway@sfmta.comif you have questions about the closure schedule. On Bryant Street at 5th Street, the left lane and several parking spaces will remain closed.
  • Union Square: Stockton Street between Geary and Ellis will remain closed to vehicle traffic. Ellis Street between Stockton and Powell will remain closed to westbound traffic.
  • Chinatown: No construction planned
  • North Beach: No construction planned before June 24, but demolition of the Pagoda Palace is scheduled to begin in June. For more information, check out thisconstruction notice.

We appreciate your patience and support while we build this essential upgrade to San Francisco’s public transportation system.

07 June 2013 ~ 0 Comments

Construction Update | June 8-17

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Crews continue to prepare tunnel boring machine Mom Chung for launch.

During the next 10 days, construction to prepare for tunneling will continue in SoMa and Union Square. No Central Subway construction is planned in Chinatown or North Beach.

For descriptions of construction impacts in each neighborhood, click here or on the links below. We also post construction, traffic detour and Muni impact information on our project Google Map.

Construction impacts are planned to change at these locations by June 17:

  • Northern SoMa (Market to Harrison):  Two lanes of traffic will remain closed on 4th Street between Howard and Folsom, but the traffic configuration may change (details in the Northern SoMa section). Construction will be underway this Saturday, June 8, and next Saturday, June 15, on this block. On 4th Street between Market and Stevenson, the sidewalk and two traffic lanes will remain closed on the eastern side of the street.

At these locations, current construction impacts are planned to continue until June 17:

  • Southern SoMa (Harrison to King/Berry): Full closure of 4th Street between Harrison and Bryant will continue some evenings and weekends. Two lanes of traffic will remain open at all other times. Contact us at central.subway@sfmta.com if you have questions about the closure schedule. On Bryant Street at 5th Street, the left lane and several parking spaces will remain closed.
  • Union Square: Stockton Street between Geary and Ellis will remain closed to vehicle traffic. Ellis Street between Stockton and Powell will remain closed to westbound traffic.
  • Chinatown: No construction planned
  • North Beach: No construction planned before June 17, but demolition of the Pagoda Palace is scheduled to begin in June. For more information, check out this construction notice.

We appreciate your patience and support while we build this essential upgrade to San Francisco’s public transportation system.

06 June 2013 ~ 0 Comments

Mayor Lee, public officials, community members celebrate TBM Mom Chung and upcoming start of tunneling

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A tour group visits tunnel boring machine Mom Chung beneath busy 4th Street.

Tunnel boring machine Mom Chung is almost assembled and just about ready for launch. This summer, the 350-foot-long, 750-ton tunnel-building behemoth will begin her journey north beneath the streets of San Francisco, constructing the city’s first new subway tunnel in decades.

Last week we celebrated Mom Chung’s upcoming journey with an event at the site where tunneling will begin. After speeches by Mayor Edwin M. Lee, Democratic Leader Nancy Pelosi’s Chief of Staff Robert Edmonson, Board of Supervisors President David Chiu, District 6 Supervisor Jane Kim and others, guests toured the underground site where Mom Chung is being assembled. They sent her off by signing their names on her cylindrical shield, wishing her a safe and successful voyage beneath SoMa, Union Square, Chinatown and North Beach.

The photos below are of the event, held last Thursday on and below 4th Street. For more photos, visit us on Flickr. To find out more about the event, check out this press release from the SFMTA.

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Before the event, the stage was set with safety gear for special guests and honored speakers.

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Reporters set up cameras, preparing for the arrival of Mayor Lee and other special guests.

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A cheerful Mayor Lee talks about the many benefits of the Central Subway — reducing travel times, connecting San Francisco’s neighborhoods and preparing for the growth expected in the city in coming years and decades.

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Supervisors Jane Kim and David Chiu listen to Mayor Lee’s speech. The Central Subway (and Mom Chung) will travel through their districts.

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Mayor Lee prepares to cut the cake decorated with TBM Mom Chung. Thanks to Victoria Pastry for creating this delicious treat.

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Central Subway Program Director John Funghi leads the first tour of the excavation, known as a launch box, where Mom Chung is being assembled and will begin tunneling.

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At the entrance to the launch box, tour goers look with awe upon Mom Chung.

 

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Mayor Lee signs Mom Chung. The TBM will help build “our future San Francisco.”

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Others, including Supervisor Chiu, sign their names and messages on the TBM.

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Gina Low Weiss, grandniece of Dr. Margaret “Mom” Chung, after whom the TBM is named, signs her name and writes her message on the machine.

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This section of Mom Chung, known as the trailing gear, performs a variety of functions, including carrying excavated spoils out of the tunnel and bringing concrete tunnel segments in.

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After the tour, participants exited the launch box, returning outside to a warm, sunny day.

 

24 May 2013 ~ 1 Comment

Construction Update | May 25-June 3

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Pedestrians cross the street near the Union Square construction site.

During the next 10 days, construction to prepare for tunneling will continue in SoMa and Union Square. No Central Subway construction is planned in Chinatown or North Beach.

For descriptions of construction impacts in each neighborhood, click here or on the links below. We also post construction, traffic detour and Muni impact information on our project Google Map.

Construction impacts are planned to change at these locations by June 3:

  • Northern SoMa (Market to Harrison): On 4th Street between Market and Stevenson, the sidewalk and two traffic lanes will remain closed on the eastern side of the street except from 8 p.m. Thursday, May 30, to 6 a.m. Friday, May 31. At that time, three lanes will be closed. Two lanes of traffic will remain closed on 4th Street between Howard and Folsom, but the traffic configuration may change (details in the Northern SoMa section). Construction will be underway this Saturday, May 25, and Sunday, May 26, on this block.
  • Union Square: Construction will be underway this Sunday, May 26, from 6 a.m. to 4 p.m. Stockton Street between Geary and Ellis will remain closed to vehicle traffic. Ellis Street between Stockton and Powell will remain closed to westbound traffic.

At these locations, current construction impacts are planned to continue until June 3:

  • Southern SoMa (Harrison to King/Berry): Full closure of 4th Street between Harrison and Bryant will continue on some evenings and weekends. Two lanes of traffic will remain open at all other times. Please contact us at central.subway@sfmta.com if you have questions about the closure schedule. On Bryant Street at 5th Street, the left lane and several parking spaces will remain closed.
  • Chinatown: No construction planned
  • North Beach: No construction planned before June 3, but demolition of the Pagoda Palace is scheduled to begin in June. For more information, check out this construction notice.

We appreciate your patience and support while we build this essential upgrade to San Francisco’s public transportation system.