The San Jose BART extension and making changes to cut costs

[Taunton]

Ironically one of the few US city centres with similar urban density to European ones is San Francisco. But even there they managed to put two decks of tunnel under Market Street in the 1970s - BART below and MUNI streetcars above - by cut and cover I presume.

It was a mixture. Stations were cut & cover, running tunnels between them were bored by TBM. Photos and an article about the construction, and why a mixture of methods were used here:

Building San Francisco's BART tunnels - FoundSF

www.foundsf.org

 

[MarkyT]

Ironically one of the few US city centres with similar urban density to European ones is San Francisco. But even there they managed to put two decks of tunnel under Market Street in the 1970s - BART below and MUNI streetcars above - by cut and cover I presume.

As Taunton says, stations were cut & cover trenches under the street which was restored to road traffic during excavation using a wooden decking after an initial heading had been established. Stations were joined by bored sections through the soft earth. High air pressure was maintained at the cutting face so workers had to go through controlled decompression after a shift to avoid the bends, like their transbay tube diving colleagues.

 

[Taunton]

I first went to San Francisco in 1971, whilst still at (UK) school. The excavations were in full progress. PCC cars on the Market Street route were picking their way through the works. Went back in 1974, BART was open (though I think not the Transbay tunnel), but the Muni Metro tracks above were not, so the PCC cars were still in full swing on the reinstated street tracks above. There were still substantial excavations for the Muni tunnels around Duboce, after BART turns off. For whatever reason it took further years to get the Muni tunnels going, I think after 1980. Next there in 1983, it was all finished, but the street tracks were still in situ. Amazingly the street service came back, after various special events, in 1995, with those original PCC cars, and still runs today. I think these wonderful old cars have now run for longer in this reinstated all-day service than they did in their original mainstream life. They have been painted up in the liveries of various other USA cities, but the cars themselves are mainly the old San Francisco fleet.

 

[stuu]

It was a mixture. Stations were cut & cover, running tunnels between them were bored by TBM. Photos and an article about the construction, and why a mixture of methods were used here:

Building San Francisco's BART tunnels - FoundSF

www.foundsf.org

Thanks for posting, that's a fascinating article. Having used it a few times I'm surprised it was tunnelled rather than cut and cover, there doesn't seem enough vertical space between the two rail levels

 

[MarkyT]

I first went to San Francisco in 1971, whilst still at (UK) school. The excavations were in full progress. PCC cars on the Market Street route were picking their way through the works. Went back in 1974, BART was open (though I think not the Transbay tunnel), but the Muni Metro tracks above were not, so the PCC cars were still in full swing on the reinstated street tracks above. There were still substantial excavations for the Muni tunnels around Duboce, after BART turns off. For whatever reason it took further years to get the Muni tunnels going, I think after 1980. Next there in 1983, it was all finished, but the street tracks were still in situ. Amazingly the street service came back, after various special events, in 1995, with those original PCC cars, and still runs today. I think these wonderful old cars have now run for longer in this reinstated all-day service than they did in their original mainstream life. They have been painted up in the liveries of various other USA cities, but the cars themselves are mainly the old San Francisco fleet.

Their Wheels of the World collection also includes examples from Melbourne and Milan amongst others, and an open car from Blackpool.

San Francisco’s Historic Streetcars

San Francisco Market Street Railway | We keep San Francisco's Vintage Streetcars on Track

www.streetcar.org

 

[Gag Halfrunt]

They now operate two Blackpool "boats" and have acquired a third.

Help us bring the original "Love Boat" back to San Francisco

San Francisco Market Street Railway | We keep San Francisco's Vintage Streetcars on Track | www.streetcar.org

www.streetcar.org

 

[Taunton]

Curiously, the most recent San Francisco PCC car I saw was in the tram museum in Sydney, Australia. They seem to have been shipped both ways.

https://www.sydneytramwaymuseum.com.au/tramway/wp-content/uploads/2020/09/BP-1014testrun.jpg

 

[edwin_m]

It was a mixture. Stations were cut & cover, running tunnels between them were bored by TBM. Photos and an article about the construction, and why a mixture of methods were used here:

Building San Francisco's BART tunnels - FoundSF

www.foundsf.org

Thanks for this link. However, I'm still a bit confused about how this works. TBMs are stated to have been 18ft in diameter, probably not enough for a double track once segment thickness is included. Twin tunnels are mentioned for but that appears to be for the BART-only section on Mission Street. Considering the rule of thumb that bored tunnels should be separated by at least two diameters, four such under Market Street would have been very wide and deep and I wonder if this part might have been fully cut and cover, not just the stations.

 

[Taunton]

No, at the time there were only excavations at the stations. I think the separation standards have probably come along since - which among other things stop tunneling under the street line, unless the latter is extremely wide. Obviously there's a lot of heritage tunneling out there which has run for a century at less than this separation, without issue.

Did the "two diameters" guidance follow the Heathrow Express construction collapse in the early 1990s?

The BART cars are very broad, 10ft 6in I seem to recall (though still just 2+2 seating), so you won't get two in a tunnel done with an 18ft TBM once its lined up! Possibly the Muni Metro tunnels are not the same size.

 

[edwin_m]

No, at the time there were only excavations at the stations. I think the separation standards have probably come along since - which among other things stop tunneling under the street line, unless the latter is extremely wide. Obviously there's a lot of heritage tunneling out there which has run for a century at less than this separation, without issue.

Did the "two diameters" guidance follow the Heathrow Express construction collapse in the early 1990s?

The BART cars are very broad, 10ft 6in I seem to recall (though still just 2+2 seating), so you won't get two in a tunnel done with an 18ft TBM once its lined up! Possibly the Muni Metro tunnels are not the same size.

Much of the older tunneling is in better material such as London Clay. Your link mentions how poor the ground conditions were in San Francisco, and that TBMs were new to the USA, so I don't think they'd be taking any chances.

It's a long time since I visited Muni or BART but if the stations are between the running lines as illustrated, then that would give two diameters of horizontal separation assuming the tunnels don't converge elsewhere. Also the tunnels could be under the building line as long as the station boxes could reach them from the street excavation. Vertical is a bit more tricky - are the BART tunnels way way below the Muni ones? - but perhaps they have to be to get deep enough below the Bay.

Perhaps the historic disruption on Market, even just confined to station sites, was a reason they chose not to do the same in San Jose.

 

[stuu]

It's a long time since I visited Muni or BART but if the stations are between the running lines as illustrated, then that would give two diameters of horizontal separation assuming the tunnels don't converge elsewhere. Also the tunnels could be under the building line as long as the station boxes could reach them from the street excavation. Vertical is a bit more tricky - are the BART tunnels way way below the Muni ones? - but perhaps they have to be to get deep enough below the Bay.

BART and Muni have next to no vertical separation, at least in the stations, there's only the floor between them. The BART platforms are much wider though, so they are horizontally separated

 

[Jan]

Apart from Barcelona, I can't think of a metro in bored tunnel that has anything other than twin bores each containing one track. However, I think Grand Paris Express has two track side by side in the same bore.

The new Karlsruhe tram tunnel has twin track in a single bore.

 

[edwin_m]

The new Karlsruhe tram tunnel has twin track in a single bore.

Is this bored or cut and cover?

 

[Jan]

Is this bored or cut and cover?

Both: The east-west tunnel has been bored with a TBM, the north-south tunnel north of Ettlinger Tor conventionally bored (probably New Austrian tunneling method), and south of Ettlinger Tor cut-and-cover. The stations were all done in cut-and-cover.

 

[stuu]

There's lots of double track metro tunnels in the world. Spain almost always builds them that way, most of the French metros are, and most Italian metros. That also applies to places influenced by the those countries - Latin America especially.

 

[edwin_m]

There's lots of double track metro tunnels in the world. Spain almost always builds them that way, most of the French metros are, and most Italian metros. That also applies to places influenced by the those countries - Latin America especially.

I'm thinking of TBM bored tunnels - sorry if that wasn't clear previously. Karlsruhe is confirmed as such above, but are there any others TBM bored tunnels with double tracks side by side in the same bore?

The various mining techniques allow a lot of flexibility in cross-section but with a TBM it has to be circular, and a circular tunnel with two tracks side by side has much more cross-section than two circular tunnels with one track each.

 

[stuu]

I'm thinking of TBM bored tunnels - sorry if that wasn't clear previously. Karlsruhe is confirmed as such above, but are there any others TBM bored tunnels with double tracks side by side in the same bore?

The various mining techniques allow a lot of flexibility in cross-section but with a TBM it has to be circular, and a circular tunnel with two tracks side by side has much more cross-section than two circular tunnels with one track each.

Yes, all the current extensions in Paris are being built as double track tunnels. I believe all the recent new lines in France have used TBMs and built double track tunnels.... New lines in Sao Paulo and Santiago are currently being dug that way. Milan's newest metro lines definitely were, as was the first section of Line C in Rome, before they got to the historic bit. For whatever reason, Spain, France and Italy prefer double track tunnels, and are still building them that way

 

[Jan]

Specifically for Karlsruhe – it's only a tram tunnel, so vehicles are only 2.65 m wide, whereas heavy metros commonly utilise 3.00 or 3.20 m wide rolling stock, so that alone already shaves about a metre off the tunnel diameter. And the city and part of the interurban rolling stock are unidirectional, so side platforms are required. Two side-by-side tunnels plus side platforms would have taken up too much space, and stacked tunnels probably would have led to too many complications as well (length of the tunnel ramps; deeper stations at least in one direction; more space required for the central junction at Marktplatz, though at least it would have allowed for grade separation).

Paris also utilises relatively narrow rolling stock (approx 2.40 - 2.45 m I think). Taking a quick look through Wikipedia, French metros generally seem to be narrower than 3 m. Lyon is the widest at 2.89 m, but otherwise they tend towards 2.40 to 2.65 m, or in the case of the VAL metros even down to 2.06 or 2.08 m.

If by Milan's newest metro lines you mean lines 4 and 5, those utilise 2.65 m wide rolling stock I think. Line C in Rome is 2.85 m.