During the next 10 days, Central Subway work continues at sites in SoMa, Union Square, Chinatown and North Beach. This section contains brief updates about what is happening in each neighborhood. For more detailed information click here or on the links below. You can also find construction, traffic detour, and Muni impact information on our project Google Map. For safety reasons, we encourage the public to follow all traffic and pedestrian notifications posted at the work sites.
Southern SoMa (Harrison to King/Berry): Potholing for utilities continues next week on 4th Street between Bryant and King. On Brannan between 4th and 5th Streets, work on utilities continues. Temporary walkways are in place around the construction zones.
Northern SoMa (Market to Harrison): At 4th and Folsom, work to build the Yerba Buena/Moscone Station continues. This includes construction of the station walls within the work site and water line replacement at the intersection of 4th and Folsom. Until Monday, July 28, 4th Street from Howard to Folsom streets will have one traffic lane. This area will continue to have a lane reduction overnight from 7 p.m. to 5 a.m.
Union Square: Stockton Street between Ellis and Geary is closed to vehicular traffic to allow for construction of the Union Square/Market Street Station. Work is underway for pile installation to construct the station walls. For the month of July, Stockton Street between Post and Geary will be closed to vehicular traffic. Please use alternate routes and follow construction signs.
Pile installation takes place at the southwest intersection of Stockton and O’Farrell streets until August 18. One lane of travel will be open. Expect delays and please use alternative routes.
Muni service impact:
Until August 1, the bus stop at Geary and Stockton will be temporarily discontinued. Please board bus at Geary and Powell. Please check back on our weekly Construction Update for the most current information on the re-opening of this stop.
Chinatown: The contractor started station wall construction at the future station site and on the adjacent section of Washington Street. Work to replace high pressure water pipeline and install new fire hydrant on Washington is ongoing. A section of the sidewalk at the northeast corner of the Washington and Stockton intersection will be demolished in order to install a new fire hydrant.
North Beach: Work continues at 1731-1741 Powell. Sustainable Streets is constructing bulbs on Columbus Avenue between Filbert and Union streets, and widening the sidewalk on both sides of the street for this block. Street restoration work is expected to be completed by the end of August. More information is available in this notice.
We thank the businesses, residents, shoppers, and commuters of San Francisco for their continued engagement with this significant investment in the extension of our public transportation system.
Tunnel boring machine Big Alma, shown here, will cross under BART and Market Street this week.
This week the Central Subway’s second tunnel boring machine (TBM) will pass beneath Market Street and the existing Bay Area Rapid Transit (BART) and Muni Metro tunnels, crossing from SoMa and into Union Square. The tunnel, one of two being constructed as part of the Central Subway Project, will allow T Third Line trains to travel quickly beneath 4th Street and Stockton Street, cutting transit travel times by more than half along this busy corridor.
The SFMTA has worked in close coordination with BART and an independent panel of top tunneling experts to plan and carry out this key phase of tunnel construction. To pass beneath Market Street and the existing transit tunnels, TBM Big Alma will turn slightly left beneath 4th Street just south of Market Street. The machine will then veer right to head north under Market Street and then Stockton Street. The new T Third Line tunnels will be about 10 feet below the existing BART tunnels.
This graphic shows the path the Central Subway TBMs will take when they pass under Market Street. The second TBM, Big Alma, is making this crossing this week.
Starting today, Big Alma will be in operation 24 hours a day to build the approximately 425 feet of new tunnel beneath the Market Street tunnels. Late last year the first TBM, called Mom Chung, safely and successfully completed the same undercrossing, using the same techniques and interagency coordination. Mom Chung is now beginning to tunnel under Nob Hill, heading toward Chinatown. Including both tunnels, tunneling contractor Barnard Impregilo Healy (BIH) has constructed more than 6,900 feet of tunnel under 4th Street and Stockton Street so far.
In preparation for the crossing, the contractor has injected a ground-stabilizing grout underground near the BART tunnels, accessing this subterranean area via a deep shaft they constructed on Ellis Street. About 150 monitoring devices installed in the Powell Street Station and on neighboring buildings will provide live data feeds about tunneling conditions to web applications that the SFMTA, the contractor, BART and an independent panel of tunneling experts can view at all times. Similar devices are installed along the entire tunneling path, from 4th and Bryant in SoMa to Columbus and Powell in North Beach. The readings of these instruments and others on the TBMs themselves allow the tunneling contractor to respond rapidly to ground conditions around the machines as they move forward.
The crossing under BART may last up to six days. Tunneling may cause BART to run at slower speeds in the area.
More information is available in this press release from the SFMTA.
Using time-lapse cameras installed underground, we’ve condensed the first months of tunneling into this captivating two-minute video. In the video, Central Subway crews assemble tunnel boring machine (TBM) Mom Chung and drive the state-of-the-art tunnel builder north under 4th Street to build San Francisco’s first new subway line in decades. The video shows the TBM assembly process, installation of the first tunnel rings, removal of excavated ground spoils and other aspects of the complex tunneling operation.
By the end of the video, Mom Chung has tunneled from her launch box south of 4th and Harrison to 4th between Folsom and Howard. Since we captured this footage, she has mined much farther north, crossing successfully and safely under Market Street and the existing BART and Muni tunnels last weekend.
We thank our tunneling crews and tunneling contractor Barnard Impregilo Healy for their hard work to build the Central Subway, extending the Muni Metro T Third Line through SoMa, Union Square and Chinatown. Stay tuned for more time-lapse videos as construction proceeds.
Tunnel boring machine Big Alma, shown here on the right, began tunneling under 4th Street. On the left is the entrance to the parallel tunnel being built by TBM Mom Chung.
There are now two 350-foot-long, 750-ton tunnel boring machines mining under 4th Street to construct the Central Subway’s pair of parallel tunnels. Our second TBM, named Big Alma, recently launched. She’s building the tunnel that northbound T Third Line trains will use when the Central Subway opens in 2019.
Over the coming months, Big Alma will travel north under 4th Street and Stockton Street, building tunnel at an average pace of 40 feet per day. Her tunnel will be just east of the tunnel that her twin, named Mom Chung, began building in July. Big Alma will move more slowly during the first 500 feet of tunneling, as Central Subway crews test the TBM and calibrate its many functions.
Big Alma is named for “Big Alma” de Bretteville Spreckels, a 19th century 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.
The photos below show Big Alma the TBM during her assembly and launch. To learn more about Big Alma and her underground journey to build San Francisco’s first new subway line in decades, check out this press release from the SFMTA. You can also follow the machine on Twitter. She’s @BigAlmatheTBM.
This section of Big Alma’s “shield,” the portion of the machine that puts in place the tunnel segments, was among the first to be lowered into the launch box.
Known as the “cutter head,” this part is on the front of the machine, attached to the shield. It excavates the earth to make room for the new tunnel.
The cutter head is lifted by a crane and lowered into the launch box.
Underground, crews connect the cutter head to the shield.
A welder welds together two sections of Big Alma’s shield.
After the shield and cutter head were assembled, crews moved them to the northern end of the launch box, where tunneling begins.
Crews work in the launch box, preparing to move Big Alma forward.
In the launch box, Mom Chung is on the left, tunneling, and Big Alma is on the right, being assembled.
Crews assemble the trailing gear of Big Alma. This 300-foot train of tunnel-building mechanisms performs a variety of important functions.
Once assembled, the trailing gear stretches almost the full length of the launch box.
A welder works on Big Alma’s shield in the weeks before launch.
Tunnel segments are lowered into the launch box for installation by the TBMs.
After Big Alma’s launch, a tunneling crewman walks out the back of the machine. We thank our crews for their hard work as they build San Francisco a new subway line.
In the operating cabin of TBM Mom Chung, two TBM operators monitor tunneling conditions provided from a variety of state-of-the-art instruments.
Next week our first tunnel boring machine, Mom Chung, will pass beneath Market Street and the existing BART and Muni Metro tunnels, crossing from SoMa and into Union Square. The tunnel, one of two being constructed as part of the Central Subway Project, will allow T Third Line trains to travel quickly beneath 4th Street and Stockton Street when the Central Subway opens, cutting travel times by more than half along this busy corridor.
The SFMTA has worked in close coordination with BART and an independent panel of top tunneling experts to plan and carry out this key phase of tunnel construction. To pass beneath Market Street and the existing transit tunnels, TBM Mom Chung will turn slightly left beneath 4th Street just south of Market Street and travel partially under 801 Market Street, home to Old Navy. The machine will then veer right to head north under Market Street and then Stockton Street. The new T Third Line tunnels will be about 10 feet below the existing BART tunnels.
This graphic shows the path the Central Subway TBMs will take when they pass under Market Street. The first TBM, Mom Chung, is expected to begin this crossing on Monday.
Starting yesterday, Mom Chung is in operation 24 hours a day to build the approximately 425 feet of new tunnel beneath Old Navy and the Market Street tunnels. Mom Chung is expected to begin crossing beneath the Market Street tunnels on Monday, Nov. 25. The tunneling methods used during this key crossing will be the same that are in use along the rest of the tunneling route. As the TBM moves forward, it installs tunnel segments within the section known as the “shield,” a 20-foot-diameter cylinder at the front of the machine. The shield and the newly installed tunnel lining create a watertight barrier that holds the ground outside in place. Using these methods, tunneling contractor Barnard Impregilo Healy (BIH) has constructed more than 2,100 feet of tunnel under 4th Street so far.
“We’re thrilled at the progress our tunneling contractor and tunnel boring machines are making to build this essential new subway line for San Francisco,” said SFMTA Director of Transportation Edward D. Reiskin. “We are using state-of-the-art technology and the country’s top expertise to ensure the entire tunneling process safeguards the city as well as the region’s critically important transportation infrastructure. We thank BART for the excellent partnership in this process.”
With the help of TBM Mom Chung, Central Subway crews have now built a new subway tunnel under 4th Street from Harrison and Stevenson.
In preparation for the crossing, the contractor has injected a ground-stabilizing grout underground near the BART tunnels, accessing this subterranean area via a deep shaft they constructed on Ellis Street. They will inject additional grout as needed while Mom Chung is mining below BART.
About 150 monitoring devices installed in the Powell Street Station and on neighboring buildings will provide live data feeds about tunneling conditions to web applications that the SFMTA, the contractor, BART and an independent panel of tunneling experts can view at all times. Similar devices are installed along the entire tunneling path, from 4th and Bryant in SoMa to Columbus and Powell in North Beach. The readings of these instruments and others on the TBM itself allow the tunneling contractor to respond rapidly to ground conditions around the machine as it moves forward.
BART may run at lower speeds between Powell and Montgomery stations while tunneling is in progress under BART. Please visit BART on the web at www.bart.gov/alerts or call 511 to get up-to-date service information.
For more about this major tunneling milestone, check out this press release from the SFMTA.
This building in Chinatown will be demolished soon to make way for the Central Subway Chinatown Station.
Last month, we started the first construction activities to build the Central Subway’s stations, tracks and operating systems. This work will extend the Muni Metro T Third Line underground to improve public transit in some of San Francisco’s busiest neighborhoods. Once in operation, the Central Subway will cut travel times in half along congested Stockton Street and 4th Street while enhancing connections to BART, Muni Metro and Caltrain.
The first construction activities are preparatory in nature and include installing monitoring devices, putting up fences and removing hazardous materials at future subway station sites in Chinatown and SoMa. After completing this work, contractor Tutor Perini will demolish the existing structures at the sites of the future Chinatown Station (933-949 Stockton Street) and Yerba Buena/Moscone Station (260-266 4th Street). Station construction will follow.
At other locations, construction will commence later this year or in 2014. Construction timelines and impacts will vary significantly at the various project sites (more details below). Construction is expected to finish in 2018.
Over the next few years, we will build the Union Square/Market Street Station on Stockton Street. This rendering shows the station entrance that will be built in Union Square Plaza, at the corner of Stockton and Geary.
The construction is part of SFMTA Contract 1300 (Stations, Track and Systems), awarded to Tutor Perini, a leading California-based construction firm, earlier this year. As part of this contract, Tutor Perini will construct three subway stations, one surface-level station, 1.7 miles of train tracks and the operating systems for the T Third Line extension.
Tutor Perini has extensive experience in building public infrastructure in the Bay Area and around the country. Tutor Perini improved the seismic reliability of the Richmond Bridge and is currently building the expansion of the Caldecott tunnel in the East Bay, among numerous other major projects.
To inform local businesses, residents, property owners and community groups about construction timelines and impacts, the SFMTA and Tutor Perini will work in partnership to disseminate information and host community meetings before major work begins. The public may learn about Central Subway community meetings and construction by signing up for the project’s weekly construction emails. An online signup form is available at http://eepurl.com/oOs-b.
Construction will take place at the sites of the four new stations, an on 4th Street south of the 1-80 overpass.
The following provides an overview of the work included in this major construction undertaking. More information is available in this press release from the SFMTA.Timeline
Construction will be in progress at various sites from September 2013 to February 2018. Timelines will vary significantly at each site. Additional information will be provided in the coming months.Locations and Scope of Work
Father John Takahashi and Central Subway Program Director John Funghi stand beside concrete blocks that once formed the foundation of a historic North Beach church.
Earlier this month, construction crews demolishing the Pagoda Palace unearthed a long-lost piece of San Francisco history: the foundations of a church that stood on these grounds more than a century ago.
The Holy Trinity Orthodox Cathedral, now located at 1520 Green Street, once stood in North Beach at the corner of Powell Street and Columbus Avenue. Built in 1888, the dramatic onion-domed structure was completely destroyed by the great San Francisco earthquake and fire of 1906. All that remained were five bronze bells – and they survived because they were off site at the time, being repaired. The church relocated to the Green Street location soon after, opening in 1909.
Last week a concrete block from the old church’s foundations joined the bells at the Green Street cathedral. After construction crews unearthed the foundations, we contacted Father John Takahashi, the senior priest of the Holy Trinity Orthodox Cathedral, to inform him of our discovery. We also invited him to visit the construction site and see the newly uncovered relics of his church’s past.
The Holy Trinity Cathedral on Powell Street, circa 1890.
Once on site, Father John spoke with Central Subway Program Director John Funghi, and the Central Subway team gave Father John a block of concrete from the old foundations. The block will now live in the garden of the Green Street cathedral.
Central Subway crews discovered the historic foundations while dismantling the thick concrete slab that formed the base of the Pagoda Palace Theatre. Once the slab was removed, the outlines of the foundation revealed themselves amidst dirt and rubble.
Archeologists and construction personnel examined the unearthed foundations and concluded that they were consistent with building practices in the late 19th century. The absence of rebar, the consistency of the concrete and the size of the aggregate in it helped support this conclusion.
With a piece of the old church now safely preserved, crews then broke apart what remained of the foundations to make room for the next phase of Central Subway construction, and the next chapter in the life of this storied North Beach site.
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.
A large red crane, called a gantry crane, lifts the cutter head from the ground.
When Big Alma tunnels, these wheels will spin to loosen the ground, aided by an environmentally safe, soap-like foam that conditions it.
Operated by our tunneling crews, the crane lifts the cutter head into a vertical position to allow for installation.
Crews help stabilize the cutter head before lowering it underground.
The crane moves the cutter head into position over the tunnel launch box, where Big Alma’s cylindrical shield awaits.
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.
Above the shield, the cutter head descends into the excavation.
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.
The cutter head continues its descent into the excavation.
Once the cutter head is lowered, crews work to connect it to the shield.
To connect the TBM segments, crews bolt them together. Later, they will reinforce the connections with welding.
The TBM assembly team poses in front of Big Alma. We thank our dedicated crews for all their hard work.
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).
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.
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:
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):
Traffic, transit and pedestrian impacts:
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.
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 month, 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.
Before the event, the stage was set with safety gear for special guests and honored speakers.
Reporters set up cameras, preparing for the arrival of Mayor Lee and other special guests.
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.
Supervisors Jane Kim and David Chiu listen to Mayor Lee’s speech. The Central Subway (and Mom Chung) will travel through their districts.
Mayor Lee prepares to cut the cake decorated with TBM Mom Chung. Thanks to Victoria Pastry for creating this delicious treat.
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.
At the entrance to the launch box, tour goers look with awe upon Mom Chung.
Mayor Lee signs Mom Chung. The TBM will help build “our future San Francisco.”
Others, including Supervisor Chiu, sign their names and messages on the TBM.
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.
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.
After the tour, participants exited the launch box, returning outside to a warm, sunny day.
Construction of the Union Square/Market Street Station, shown here, is included in the major contract awarded earlier this week.
This week the SFMTA awarded the contract to construct the Central Subway’s stations, train tracks and operating systems to California-based firm Tutor Perini. Tutor Perini’s bid of $840 million was the lowest of three bids received for the contract, SFMTA Contract No. 1300, the largest and final major construction contract for the Central Subway Project.
After review, Agency staff determined that the bid meets contract solicitation requirements and recommended approval. At their meeting Tuesday, the SFMTA Board of Directors voted unanimously to approve the award.
With 25 percent of the contract amount going to certified Small Business Enterprise (SBE) firms, Tutor Perini significantly exceeded the SBE participation goal of 20 percent. In addition, Tutor Perini will set aside at least 50 percent of the contract’s trucking and hauling work for certified SBE firms, invest at least $1.5 million in hiring socially and economically disadvantaged individuals for entry-level jobs, and provide socially and economically disadvantaged individuals with at least 40,000 hours of on-the-job training for construction management positions.
Under Contract 1300, Tutor Perini will construct the following elements of the Central Subway:
In the coming weeks and months, Tutor Perini and the SFMTA will mobilize to begin the major construction associated with the contract. Construction will continue through 2018, with the Central Subway scheduled to open in 2019.
This time lapse video — our first ever — shows the first steps of installing and assembling tunnel boring machine Mom Chung.
For the past few weeks, Central Subway crews have worked day and night to install and assemble our first tunnel boring machine, Mom Chung, underground beneath 4th Street.
We’ve documented the process on three time lapse cameras installed at this major construction site. The cameras took photos every two minutes, and we compiled and edited the images to create the video above.
In it, you’ll see our crews construct a specialized crane, called a gantry crane, over 4th Street to prepare for Mom Chung’s arrival. Then hundreds of tons of massive Mom Chung are lowered underground and assembled by Central Subway workers. The segments seen here make up Mom Chung’s shield (the part that builds the tunnel) and cutter head (the part that excavates). At the end of the video, we install an auger screw, which is used to transport dirt and spoils through the front of the TBM and onto a series of conveyors.
We’ll post more time lapse videos soon, including one of the entire TBM assembly process, as we continue to document construction of this essential improvement to San Francisco’s public transportation system.
San Francisco Mayor Edwin M. Lee takes a look at tunnel boring machine Mom Chung in the excavation under 4th Street where tunneling will begin.
Yesterday, Mayor Edwin M. Lee paid a visit to the construction site where tunneling will begin and saw Mom Chung, the 350-foot-long tunnel boring machine currently being assembled underground.
Speaking to reporters in front of the digging cutter head of Mom Chung, Mayor Lee said he was excited about the Central Subway, calling the T Third Line extension “one of the most important projects for the future of San Francisco.”
SFMTA Board Chairman Tom Nolan, SFMTA Director of Transportation Edward D. Reiskin, Central Subway Program Director John Funghi, key city officials and members of Central Subway team accompanied Mayor Lee under 4th Street to show him the major excavation where tunneling will begin. Check out the photos below for more on the Mayor’s visit to this important construction site.
The tour group heads down the ramp near 4th and Bryant and into the excavation beneath the roadway.
The tour group makes its way through the excavation and toward Mom Chung. From left to right: Director Reiskin, Mayor Lee, John Funghi, tunnel contract Resident Engineer Sarah Wilson.
Sarah Wilson, the engineer overseeing construction of the Central Subway tunnels, explains the details of the tunneling process to Mayor Lee. From left to right: SFPUC Assistant General Manager Emilio Cruz, SFPUC General Manager Harlan Kelly, Jr., Mayor Lee, the Mayor’s Chief of Staff Steve Kawa, John Funghi, Sarah Wilson.
Mayor Lee responds to questions from reporters. From left to right: Director Reiskin, Chairman Nolan, Mayor Lee, John Funghi, SFMTA Board Vice Chairman Cheryl Brinkman, Sarah Wilson.
The tour group gathers around the front of Mom Chung. Called the cutter head, this spinning excavator will dig through the earth under 4th Street, Stockton Street and Columbus Avenue.
Representatives of tunnel construction contractor Barnard Impregilo Healy meet Mayor Lee and Director Reiskin. From left to right: Assistant Project Superintendent Andy Granger, Mayor Lee, Project Manager Ben Campbell, Director Reiskin.
Read more about the Mayor’s visit in today’s San Francisco Chronicle. Tunneling is slated to begin in June.
This 123-ton ring was the first part of tunnel boring machine Mom Chung to be installed underground. Installation began late Friday night and continued through Saturday morning.
Mom Chung has arrived — all 750 tons of her — and soon she’ll start building San Francisco’s newest subway tunnel, the first constructed in the city since the 1970s.
Mom Chung is one of two tunnel boring machines (TBMs) built specially for the Central Subway Project. The massive machines consist of 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). Starting a few weeks from now, Mom Chung will excavate and construct the tunnel for southbound trains, digging at a rate of about 40 feet per day far beneath the surface of the city. Her twin sister, Big Alma, will begin building the tunnel for northbound trains about two months later.
On Friday, crews worked through the night to lower the first part of Mom Chung into the major excavation beneath 4th Street where tunneling will begin. The part, one of three rings that make up the shield, is 20 feet in diameter and weighs about 123 tons. Of the 750-ton TBM, this was the heaviest part, and one of the most complicated to install.
Crews will assemble Mom Chung underground over the next four to six weeks. She will then begin tunneling in June, traveling north under 4th Street and Stockton Street through SoMa, Union Square, Chinatown and North Beach. Once she starts tunneling, you won’t hear, see or feel her — she’ll be too far underground and will pass below without a trace above ground.
The photos below show the installation of the first part of Mom Chung both above and beneath 4th Street, from the middle of Friday night until well past sunrise Saturday.
If you would like to see Mom Chung in person, stop by our staging area on Bryant Street at 5th Street. Trucks will deliver pieces of her during the next few weeks. We’ll store the parts on Bryant Street before installing them underground.
After picking the ring up, the gantry crane maneuvered it into position over the opening of the excavation. The excavation is called a launch box.
The ring was then lowered into the launch box.
Now halfway down, here’s a view of the ring from the ramp entering the launch box.
Crews look on as the 123-ton TBM segment descends underground.
The crane turned the TBM segment to rest it on a cradle. The other two shield segments and the rotating, excavating cutter head will soon join this first part.
This is the machinery of Mom Chung — a state-of-the-art assemblage of tunnel-building motors and wires.
For more information about Mom Chung, and to see photos of her before she was disassembled for transport to San Francisco, check out our project website.
While the Stockton and Ellis entrance is closed, customers may use one of seven other entrances to access the Powell Street Station.
Starting Wednesday, April 24, the entrance to the Powell Street Station located at Stockton and Ellis streets will close to accommodate Central Subway construction. The closure of this entrance, also known as the Apple Store entrance, will be in effect for approximately five years to facilitate construction of the Central Subway tunnel and Union Square/Market Street Station.
When the Central Subway opens in 2019, this entrance will provide convenient access to the T Third Line at the future Union Square/Market Street Station. An underground concourse connection will link the Union Square/Market Street and Powell Street stations, allowing customers to transfer easily between the T Third Line and the BART and Muni Metro lines operating in the Market Street tunnel.
To facilitate access to Powell Street Station while the Apple Store entrance is closed, signage will direct customers to the nearest alternate entrance at 4th and Market streets.
We appreciate your continued patience while construction is in progress.
These renderings show the designs of the Central Subway’s three subway stations and one surface-level station.
Yesterday at the headquarters of the San Francisco Municipal Transportation Agency (SFMTA), bids were opened for the contract to construct the Central Subway’s stations, track and systems. The three bids for the contract, SFMTA Contract No. 1300, were submitted by the following firms:
The apparent lowest bidder is Tudor Perini with a bid of $840 million. Although the bids are higher than estimated, they fall within the project budget of $1.6 billion. We will work with our policy board and funding partners to move forward with this major contract.
This contract is the final construction contract for completing the Central Subway. After the contract is awarded, construction of the Central Subway’s stations, tracks and systems will commence in SoMa, Union Square and Chinatown.
We’ll keep you updated as the review process proceeds and a contractor is selected. You can view a PDF of the bids here. You may also download the full bid packages at the following links:
To view more design renderings of the Central Subway’s three subway stations and one surface-level station, check out our Flickr page.
The T Third Line, shown here at 4th and King streets, will travel underground through SoMa, Union Square and Chinatown once the Central Subway is complete.
Last week we received great news from our funding partners in Washington, D.C. As part of the federal budget for the current fiscal year, the Central Subway was awarded about $142 million through the Federal Transit Administration’s New Starts program.
In total, the FTA has committed $942.2 million in New Starts funds to construct the Central Subway, which will extend the Muni Metro T Third Line through SoMa, Union Square and Chinatown. The funds are awarded annually throughout the course of the project. Due to sequestration, this year’s award is about $8 million less than President Obama recommended; however, there is no change to the FTA’s total funding commitment.
For the upcoming fiscal year, President Obama’s budget, announced last Wednesday, recommends $150 million in New Starts funds for the project (see page 67 of this document).
Federal sources are providing about half of the funding for the entire Third Street Light Rail Transit Project, which includes the existing T Third Line and the Central Subway. The remaining half is from state and local sources. For more on funding for the Central Subway Project, visit our website.
We thank our federal funding partners for their continued support for the Central Subway, an essential upgrade to San Francisco’s public transportation system.
The Central Subway tunnels will end here, at the Pagoda Palace in North Beach, under a plan to relocate the retrieval site for the project’s tunnel boring machines.
In response to community concerns about Central Subway construction in North Beach, SFMTA staff and multiple city agencies have worked for the past few months to relocate the retrieval site of the project’s tunnel boring machines (TBMs) from Columbus Avenue to the Pagoda Palace (1731-1741 Powell Street).
As we complete the administrative steps required to finalize the site change, we would like to clarify the details of the plan and respond to questions that have been raised about it. These FAQs, posted on our website, include information about the Pagoda Palace construction plan, construction impacts, the reasoning behind the change and the community’s involvement in the process.
In addition, we have prepared a memo for the SFMTA Board and our partner agencies that describes our construction plan, the lease terms for the Pagoda site, and our process in pursuing the change. You can read the memo online here.
Should you have any further questions about the Pagoda Palace plan, don’t hesitate to contact our team at email@example.com or 415-701-4371. Thank you for your continued participation as we work to improve public transit in San Francisco.
Mom Chung, shown here, will construct the tunnel for southbound trains. More photos of both TBMs are available on our Flickr page. (Photo courtesy of The Robbins Company)
We are excited to introduce Big Alma and Mom Chung, the tunnel boring machines (TBMs) that will excavate and construct the Central Subway tunnels. Named Big Alma, after “Big Alma” de Bretteville Spreckels, and Mom Chung, after Dr. Margaret “Mom” Chung, the machines will begin tunneling later this year, starting in SoMa and heading north under 4th Street and Stockton Street through Union Square, Chinatown and North Beach. A press release about the TBMs is available online here.
The first of the machines, Mom Chung, is expected to arrive in San Francisco in April. The 300-foot-long machine will be assembled within an excavation on 4th Street between Harrison and Bryant streets and will start building the tunnel for southbound trains about two months later. Big Alma will arrive soon after Mom Chung to construct the northbound tunnel.
As tunneling proceeds, updates about the TBMs, including photos of the machines and the tunnels, will be posted on Twitter at the usernames @BigAlmatheTBM and @MomChungtheTBM. You can learn more about them on our website, at www.centralsubwaysf.com/tbm-name.
The front of the TBM, called the cutter head, spins as it excavates. In this photo Mom Chung is being tested before being disassembled for transport to San Francisco. (Photo courtesy of Barnard Impregilo Healy)
The names were selected by the public in an online poll held in January. Participants could select up to two names, one for each TBM. Of the 1,453 responses, Big Alma was the top vote-getter at 682 votes. Mom Chung took second place with 487 votes, closely followed by Firebelle Lil (451 votes), Mary Ellen (437 votes) and Juana (148 votes).
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 throughout the duration of the project.
“Big Alma and Mom Chung will construct San Francisco’s first new subway tunnel in decades, bringing together neighborhoods of our city that have long been in need of improved public transit,” said SFMTA Director of Transportation Ed Reiskin. “We are happy to have included the public in this exciting part of tunneling tradition. We thank everyone who voted for contributing to this important project.”
Big Alma, shown here, is still being assembled. She will arrive in San Francisco after Mom Chung to construct the northbound tunnel.
Each TBM consists of 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). The TBMs will arrive in several parts, to be assembled at the site on 4th Street between Harrison and Bryant streets where tunneling will begin.
About the Winning Names:
“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.
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.”