Graphic By the Author
Graphic By the Author

At Thursday’s meeting of Sound Transit’s Capital Committee, Executive Director for Construction Management Ahmad Fazel revealed that problems with tunnel boring machine Pamela are worse than previously thought. Mike Lindblom has more of the technical details ($) in his piece filed last night.

The machine had been stalled since December 28th near 47th & Brooklyn, roughly 650′ north of the future UDistrict Station, but Sound Transit restarted Pamela yesterday and was able to advance enough to fix one concrete ring. Pamela’s sister machine Brenda also struggled through the hard glacial till of the UDistrict, needing cutterhead repairs before continuing on to UW Station, but Pamela’s damage has been revealed to be much more severe. Meanwhile, Brenda is cruising along, entering UW property last week and is currently underneath Kane Hall nearly halfway between UDistrict Station and UW Station. (see graphic at right).

Sound Transit’s primary plan is to try to coddle Pamela but keep the machine in use – using lower torque and mining only about 10′ per day – taking 2 months to bore the final 650′ into UDistrict Station, which will serve as a makeshift repair site before continuing south to UW Station.

While these developments are worrying, it absolutely cannot be stressed enough how this situation differs from any tempting comparison to Bertha and the waterfront tunnel project, both in structural characteristics and in responsible project management.

TBM Comparison-01First and foremost, Pamela and Brenda (and Balto and Togo before them) are standard machines the likes of which are used all over the world, unlike the precedent-busting, one-of-a-kind, 2,500 sq ft beast that is Bertha. If Pamela fails completely, Sound Transit can refurbish Brenda to complete the 2nd bore from UDistrict to UW, it can also use Brenda to bore northward to reach Pamela for repairs,  and “Sequential Excavation Mining” would likely be used to reach Pamela. In a bit of great project management that stands in stark contrast to Bertha, Sound Transit’s contract also required a 3rd TBM be available for backup.

It should also be repeatedly stressed that this is the first major setback since the Beacon Hill tunnel for Central Link. In the combined 14 miles of tunneling for ULink and North Link, Sound Transit has already mined roughly 12 miles without a hitch until Pamela’s troubles. When it comes to Bertha, we talk in feet instead of miles.

Because of this foresight and planned redundancy, Fazel stressed to the committee that even a tunneling delay is 3-8 months is not estimated to impact overall deliverables, and that Northgate Link is still estimated to be on time and on budget. Current costs are running roughly ~$100m below the 2016 budget, giving Sound Transit breathing room for contingencies and repairs.

66 Replies to “Pamela Stalls, But She’s No Bertha”

  1. How long have we been anthropomorphizing tunnel boring machines? Does it go back a long way? Just curious.

    1. The machines that dug the bus tunnels in the 1980s were named the “Mighty Mole”. This was followed up by the “Emerald Mole” used on Beacon Hill, and the University Link TBMs.

    2. “According to Linea Laird, WSDOT’s tunnel project administrator, the tradition and practice of naming tunneling machines dates back to the earliest mining traditions.

      ‘Originally, it was part of the patron saints of protection of underground workers,’ she said. ‘There would be even a little shrine that would be established there for the workers.’

      Laird says the name of the saint gave the miners something personal that they could relate to as they did their dangerous work. Paying homage to their saints evolved into naming tunneling machines.”

      http://www.wnyc.org/story/286543-the-tradition-of-naming-tunneling-machines/

      1. If we ever have to tunnel through rock hard enough we need explosives, I think one of our machines should definitely be named “Barbara”.

        After St. Barbara, the patron saint of miners, artillerymen, and any other workers whose work tools feature explosions, as did her life story.

        Mud doesn’t count, but for creatures as pathetic as our poor Waterfront creature, I’m sure Barbara would arrange a detonation to free her.

        And also miraculously restore the Waterfront Streetcar, and then provide a Holy van full of nitrate fertilizer to miraculously blend the car-barn into the footbridge originally designed to withstand a bunker-busting bomb.

        Mercifully not pulverizing the monstrosity into railroad gravel as it deserves, but miraculously creating a world-amazing art-piece. For SAM to demolish for a huge roll of white-out to match the eraser.

        Though I think she’d take a pass on getting joint-ops straightened out before Judgment Day, I mean when Tunnel blocks solid and they take out the trains. Blessed St. Barbara…I beg you, one more stick of gelatin….!

        Mark

  2. I wonder, assuming Pamela can reach open air, if it might not be faster, easier, and possibly cheaper to remove and replace the entire drive section using the spare TBM?

    1. ST mentioned this as an additional possibility, using Sequential Excavation Mining (SEM) to reach Pamela. The closer she is to UDistrict station when she breaks down, the likelier that they’d use SEM.

    2. I wonder how long it would take them to get the third TBM up and running. My understanding is that TBM No. 3 is one of the ones used in the University Link tunnels (either Balto or Togo) and was being refurbished for its role as standby. The latest available progress report (November, pg 35) says that the contractor had ceased work on TBM No. 3, presumably as they no longer thought it was needed. The question is, how far along did they get before stopping, and how long will it take to get that work finished? It might be easier to simply replace the broken parts in TMB No. 2 with those from TBM 3, as that way they don’t have to move two whole TBMs into and out of the tight confines of the U District construction site.

    3. Oops, misread your post as saying to replace the entire TBM with the spare. I was basically suggesting the same swap of parts that you did.

  3. “First and foremost, Pamela and Brenda (and Balto and Togo before them) are standard machines the likes of which are used all over the world.”
    “Sound Transit’s contract also required a 3rd TBM be available for backup.”

    Good work, folks. Cheers to the engineering team who wrote specs! There is something to be said for planning redundancy into a project and for using standard, off-the-shelf materials and equipment. Thinking out of the box can be good, but one should also assess what the risk is. The risk was probably not worth it on the SR 99 project.

  4. To be clear, it wasn’t so much “hard glacial till” that did the damage as it was what was imbedded in the till.

    Brenda hit an erratic on the same stretch between Roosevelt and U-Dist, and then she went on to discover that apparently erratics are gregarious. Basically she hit a boulder field and had to take several breaks for dental work.

    Pamela hit the same boulder field. Unfortunately her damage was a bit worse than some worn out teeth. The plan is to limp her into U-Dist and make repairs, but if she can’t make it they will probably SEM back from U-Dist to clear her path.

    The big question is the segment under UW. By agreement ST only has 10 months to complete the mining on both bores. ST has multiple options on this, but if Pamela can’t meet her launch schedule, then one option would be to bring Brenda back to U-Dist and re-launch her SB back to Husky Stadium. This is what they did with Brenda between Cap Hill and Westlake — she dug both bores.

    Also, Pamela is not on the critical path, so none of these delays are impacting the overall schedule.

    1. How tight is this ten-month limit? If Brenda continues at its current speed, how long would it take for her to bore to Husky Stadium, be brought back to U-District, and re-bore to Husky Stadium?

      (Also, how’s the geology just south of U-District – could either TBM get in another slowdown there?)

      1. Hmm, then, ST would have two months to disassemble her, bring her back, and reassemble her. Sounds tight but doable.

  5. Fundamentally, drilling tunnels is difficult work. Geology is uncertain and breakdowns can happen suddenly. If Pamela was drilling where Bertha was drilling, maybe it would be better, but I don’t think it would be all sunshine and rainbows. Luck certainly plays a factor as well. For whatever reason Brenda made it through and her twin didn’t.

    Also, I’m not sure how useful a 3rd TBM would be in practice. Clearly ST hasn’t required it yet, and Pamela is already badly delayed. If this isn’t reason enough to deploy the spare, when does that time come?

    1. I would just take Brenda on a reverse journey when she reaches husky station and meet up with her sister in the middle!

      1. All the support infrastructure is at U-Dist. They would bring Brenda back to U-Dist, reassemble her and run her SB on the second bore.

        That is exactly what Brenda did between Cap Hill and the DSTT stub.

  6. “…and that Northgate Link is still estimated to be on time and on budget.”

    Isn’t that what they kept saying about Bertha for years? *ducks*

    I joke of course.

    1. Project accounting is a good point to raise, Rapid. Waterfront or LINK, you’re skyscraper height and highway length underground. So even if the bore underneath and behind you were already paved, you’d still be running a machine many times the size of a truck. With no windshield.

      Also a map mainly a guess based on instruments, and on holes bored different places around the digging. Northbound up Third Avenue, in front of Century Square, one of the DSTT machines found out how Spring Street got its name, and the course of its river. Undiscovered in a place with over a century’s experience of digging.

      Accounting ink starts running long before engineering starts. But with the first turn of the cutter, whatever happens next, to whose-ever credit or blame, column sheet turns red for a long time ahead. For result that could turn out either disaster or unexpected benefit. Same for next step ahead. Same with next, say, mile of steps, some killing people. An electrician at Pioneer Square. Two crewman at Beacon Hill.

      Present new sinkhole could either stop or permanently end the digging. The same with votes and recalls. If not, the next one either might- or not. But all events leaving question of what do do next. And drain, car-sewer, or bullet train track, all above same-same.

      Right now, Deep Bore thing I like worst has to do with present litigation- itself same order as any other tunneling problem. I’ve read that just before the heavy-duty Rotary Litigator switched on, the State Legislator summarily dissolved a citizen fact-finding committee. Necessary legal tactic- maybe. Ugly damage- no question.

      For me, strongest reason for, aside from human death or injury, settling as many disputes out of court until Tunnel operations- or storm-sewer- are dedicated. Especially on a project with so much bad blood as this one, you don’t, don’t, don’t kill a fact-finding group to make a lawsuit easier. No court award can undo that kind of damage.

      Mark Dublin

  7. Not surprising, actually more in keeping with expectations. I wondered what Pamela would do when she hit the same area that Brenda did, especially since Pamela seemed to be a touchier machine, being a little slower and taking a little longer to dig her side. (This from the ST Agency Progress Reports on Northgate Link)

    That Brenda, though, what an iron maiden. Digging through bores between Cap Hill and Westlake, coming within 15ft of some of the pilings of I-5, and possibly having to do the same thing in the U District. Any plans for MOHAI to buy out some of the pieces of her after this whole thing is done?

    1. @baselle,

      I saw somewhere that some city had taken the cutterhead off their machine after the tunnel was done, cleaned it up, and then mounted it in a little park as sort of an abstract piece of art. I’ve never been a fan of abstract art, but I must admit it did look pretty good. Sort of like a little bit of SiFi in a natural setting.

      So could ST save money on it’s “!% for Art” budget by creatively mounting a cutter head or two instead of paying some artist to stack blocks or something? You know, kill two birds with one stone while saving money????

      1. Careful. Better read the contract carefully. For company reputation, manufacturer may have stipulated that their cutter be recycled as iron filings rather than displayed in certain unfitting anti-transit Sculpture Gardens.

        However, since donations like this happen so seldom, I think those cutters are generally fitted onto machines for other projects. They have to be literally worth a fortune.

        But if not…seriously, wonderful idea! I’d also love to see one converted into the face of a clock. With serious legal consequences for leaving it filthy, non-repaired, and stuck still for 20 years, like the wonderful ones with project tools to mark hours in a station that starts with a “P”.

        Faces, incidentally, on one are left-over materials for the new station, the other, bricks and stones found on site when digging started. Like the Benson cars and equipment, not even decently thrown away, just forgotten-in-place!

        Feds actually almost took back their money over the sequestration of the streetcars. Transit here has a bad habit of wasting valuable things. Which should once or twice cost the system painfully enough to send a message.

        Instead of black or red, column for this category should be neither red or black, but fresh-feedlot-yellow-brown.

        Mark

    2. If they’re the right sort of machines… I’d say send Bertha and “Number 3” right back to work on the Bellevue tunnel.

  8. I believe ST over WSDOT, but it is important to know that at various times WSDOT has said that Bertha’s mes isn’t going to impact the project’s budget.

    1. I’m no attorney, but isn’t Seattle Tunnel Partners an LLC ( Limited Liability Corp).
      If the state thought the DBT would cost X, but it comes in costing 2X or 3X, then the state/city/fed can pony up most of that, or STP can do the math, close up shop, and declare bankruptcy of the LLC.
      In other words, those big corporations aren’t stupid enough to accept unlimited risk of letting their own holdings come crashing down because one mega project went horribly wrong.
      Anyone know the real answer for either STP or ST’s contractor?

      1. I’m not involved, but in a construction project like the DBT, there are significant performance bond requirements. A performance bond is insurance that the contractor is required to take out ensuring if they go out of business, the contract will be completed at no additional cost to the owner. Now, I know that STP have claimed that many of the Bertha repairs are not a part of their base contract. If STP were to declare bankruptcy, any bonding company would take the same path, trying to avoid any and all expenses that they could.

        But as for STP declaring bankruptcy and leaving the owners high and dry, there is at least some insurance coverage for that eventuality.

        I’m not sure what the deal is with STP, but companies like STP are often created to bid on a given project due to the bidding requirements of that project. Sometimes there is a requirement in projects like this that the work be bid on by local companies, but the local companies who would like to bid lack the bonding capacity for the job. Basically they aren’t big enough to get a performance bond for a $2B project. So, they combine with a bigger company.

        One famous example of this is the Hoover Dam, which was won by the Six Companies Construction Company, a joint venture of six western construction companies who couldn’t meet the bonding requirements on their own.

      2. Aren’t performance bonds tied somewhat to the original estimates of cost, and not a blank check to be endorsed by XYZ Insurance Company? They have good lawyers too.
        I have this image of all the attorneys for all sides in a big circle pointing guns at each other, wondering who’ll pull the trigger first.

      3. Circular duel among lawyers great image, Mic. But instead of shooting each other, which is still within rules of war, they’d certainly bill the time in same manner, billing each others’ firms and their own more and more as the papers got passed around with multiplying speed.

        Like the great book I read at age 5, when I found out what an Interurban was, this little jungle resident my same age tricked a bunch of tigers to chase each other around a palm tree until they melted into butter. Though
        pancakes here would taste worse than melted tiger.

        However, what tastes worse is time and money spent litigating instead of working- especially to repair a problem that hasn’t or won’t kill anybody- and then head for court soon as the ribbon is cut.

        Because, as I was told by one of Metro’s attorneys in DSTT preliminary engineering days, most civil lawyers encourage their clients, for their own financial interests, to settle.

        But also, while criminal defendants are often eager to cut a deal, civil litigants would rather be either murdered or shot by the police, or both, than to let that [hurtful to male puppies and their mothers] get the better of them.

        So unfortunately, your postulated duel could never happen. One, even though bullets often don’t ricochet in predictable directions, only way for circle of lawyers to all get shot is for somebody impartial, maybe the judge, standing inside the circle to swing a firearm on full automatic around the circle on a rope.

        But more important, in the days of dueling, a gentleman was not obliged, or even permitted, to fight a duel with anyone who was not also a gentleman. You see the impossibility here.

        Mark

    2. The only addition to the budget is the cost of repairs and additional costs related to idling equipment. Outside that, the scope of work hasn’t changed significantly which is the killer on megaprojects. Most of the other work has been going just fine and hasn’t experienced spirals in cost. All things considered, the “mess” cost, assuming the project finishes, sounds to be about $150M on a $3.1B project. That’s a 6% overrun, which isn’t all too bad in the world of megaprojects.

  9. Thanks for the boring dimension graphic! The general public sometimes doesn’t understand that bores have to be circular and that adding a few feet can mean a much larger hole.

    Isn’t a heavy rail bore even smaller than a light rail bore? Having the additional height required for light rail catenaries adds some dimension but I’m not sure how much.

      1. Another point of tunneling. Boring, I think technically called “mining”, in addition to less surface disruption gives you a round, and therefore stronger, tunnel.

        But at an point where the amount of earth above the bore becomes less than the diameter of the tube, you’ll get a cave-in if you don’t cut open the ground.

        Reason DSTT had to cut open Pine Street from Third to Convention Place. And also for all three underground stations. Must-read for every STB reader, pro-or-anti tunnel, and squared for Seattle Subway.

        Good thing you can’t put it down. “The Chunnel” by Drew Fetherston

        http://www.amazon.com/The-Chunnel-Amazing-Undersea-Crossing/dp/0812921984

        Mark

    1. @Al S,

      I don’t think you can say that LR tunnels are larger than heavy rail tunnels. If anything it is probably the other way around.

      Heavy rail vehicles are a lot larger than LR vehicles, and double stacks are running about 20 ft tall. This is measured from the top of the rail, so if you add the invert to that value the inside of the bore for heavy rail is substantially larger than even 20 ft.

      Additionally, the 21 foot diameter of the ST TBM’s is OD — the actual interior diameter is less. So the LR tunnel is most likely smaller in most cases.

      Note: Older tunnels might have less clearance. Hence the general dearth of double stacks on older European railroads and the notching of many tunnels on American railroads.

      So generally speaking, LR tunnels are smaller.

      1. Al S. was probably talking about traditional 3rd rail-powered subways (New York Subway, Chicago L, BART), so… no double-stacks.

        Though it wouldn’t surprise me if at some point Chicago stacked L cars on top of eachother, to board from station roofs. Not much crazier than some of the other stuff the L has seen.

      2. Al Diamond is right. I use ‘heavy rail’ to describe the third-rail track design like BART, MARTA and DC Metro.

      3. Oh, for God’s sake. “Heavy rail” does not mean “double stacks”. You are thinking of “commuter rail”. And freight trains.

      4. I researched the term.

        In the US, heavy rail is the term for third-rail electric power (APTA).

        In the UK, heavy rail is the term for the primary freight and passenger rail tracks.

      5. If you look at the shape of a London subway car- carefully rounded to fit its tube, you’ll see how compact a car like that is. But definitely a problem on the street.

        Again, probably not a hundred percent but close, overhead catenary and pantographs or poles on the roof necessitate a taller tunnel. Very likely there are some systems where on going underground, or along any stretch were intrusion is impossible, “pans” retract, and car has “shoes” to run on third rail.

        Third rail, incidentally, provides a much better contact. But can’t put that much electricity where anything alive can touch it- inadvertently or not.

        Maybe my own eccentric definition does not apply to the weight of the cars- I think the BART cars are fairly light- but to the degree the right of way absolutely has to be reserved. Heavily meaning totally, as with BART.

        LINK counts as “light” because line can be either heavily reserved, like on the Viaduct east of Tukwila, or lightly, like on MLK, or every DSTT station. The old Interurbans, which LINK most closely matches, often ran regular streetcar track along with car traffic. Before they got up to between 50 or 90 on their own rural track.

        In the interurban days here, and in Europe now, term “light rail” doesn’t exist. LINK would be a streetcar, literally “tracked road”. Two important lines in Stockholm are classified by their function: “Tverbana”, meaning, literally, Link. More honest definition than ours, because their purpose is to connect heavy-rail subway lines.

        Anyway, try those terms, and see if they fit,

        Mark

    2. @AlS,

      Sorry, I completely mis understood what you meant by “heavy rail”.

      But to answer your question, no the size of the tunnels for 3rd rail Metro type rail and for LR aren’t necessarily that different. The overall vehicle dimensions aren’t that different (although Metro type vehicles tend to be wider). Additionally, LR vehicles usually operate with their pantographs in a low, or partially retracted position, while in a tunnel. This is done to reduce tunnel size and thus construction costs.

      The high or fully extended LR pantograph position is used when the LRV is operating where a truck or some other vehicle might need to cross under thenLR cantenary.

  10. I had thought they were digging UW to U Dist after completing Montlake so it was hard to understand the map and the directions (north/south) until I looked at the legend and realized most of the tunnel work is complete between Northgate and the U Dist. 90 days to complete that stretch in limp mode isn’t so bad.

    What happened to the sled dogs? I know one was entombed near Westlake but wasn’t the other one free and clear at the end of it’s run? Maybe that is the back-up machine.

    If they back bore (SEM horizontally) will they need to dig a pit where they meet or can they extract both machines through the bored tunnel? That sounds a bit tricky. If they have to dig an access pit is maybe that could be turned into a connection/transfer point to a Ballard UW subway (the Yellow Line, “watch out where the Huskies go” :=).

    1. The TVMs go with the contractor. Brenda’s contractor is the one here. Togo and Balto’s are with that contractor and are presumably on another job.

  11. I had thought they were digging UW to U Dist after completing Montlake so it was hard to understand the map and the directions (north/south) until I looked at the legend and realized most of the tunnel work is complete between Northgate and the U Dist. 90 days to complete that stretch in limp mode isn’t so bad.

    What happened to the sled dogs? I know one was entombed near Westlake but wasn’t the other one free and clear at the end of it’s run? Maybe that is the back-up machine.

    If they back bore (SEM horizontally) will they need to dig a pit where they meet or can they extract both machines through the bored tunnel? That sounds a bit tricky. If they have to dig an access pit is maybe that could be turned into a connection/transfer point to a Ballard UW subway (the Yellow Line, “watch out where the Huskies go” :=).

  12. I realize that this is water under the bridge, but it’s too bad that the tunnels weren’t offset in elevation somewhere new UW or the U-District to allow for a future branch line to Ballard or Lake City.

    If ST does a similar twin bore for ST3, I hope that ST offsets the elevation in places to allow for future branch tracks!

      1. I first mentioned this in one of the early U-District Station open houses years ago. The station needs to be designed as expandable for a second crosswise platform, because 45th is the biggest east-west corridor outside downtown and this will become one of the biggest transfers in the system, so the station needs to be expandable or it will cause more work later. Or worse, people might have to go to the surface, cross a street at a stoplight, and go down to another station. That would depress ridership and cause visitors to think, “Seattle is supremely stupid and shortsighted.” Others have asked for a flying junction or spur, so that downtown – U-District -Ballard trains could use the station and then branch off.

        The ST rep I talked to at the open house said that ST couldn’t incorporate a transfer stub when the east-west line wasn’t voter-approved yet, and that some of alternatives may not go to UW Station at all. He cited the Northlake Way – Pacific Street – 520 option as one that wouldn’t use the station. (This was before the 2014 cross-lake study was done. ST stopped talking about 520 after that, at least for ST3.)

        I repeated my concern at later open houses, in written feedback to ST, and in emails to the board. So far ST has not acknowledged it as a problem, which I find astounding. But it will come to a head when ST pursues the 45th line, which could be in the ST3 system plan this spring.

      2. Thanks for making this plea when you did, Mike.

        I would love to see some sort of independent design panel reviewing ST’s work. ST hires major engineering firms to design things — which is great because of their experience — but they are not going to risk their design contracts by suggesting that there is any design problem with the project. (cough — FHSC — cough)

        ST doesn’t seem to publicly utilize independent rail operations and rail design experts who could keep them from future design problems. There are those out there — a few national firms and many retirees (whose talent is sitting their wasting while they leave the Weather Channel on all day). I would love to see some promise to have a panel like this in ST3.

      3. Thanks for telling the story again, Mike. I appreciate it.

        Anyone who has any doubt about whether there are serious problems with Sound Transit can read that story. In isolation it is not the worst problem in the world, but it is part of a larger pattern of just doing the minimum. Ever ask a lazy, obnoxious 8 year old to empty the dishwasher? You will find the dishes all over the place, and a kid who says “But you told me to empty them — how was I supposed to know the silverware doesn’t belong inside the bowls?”. ST kind of reminds me of that.

        Oh well, at least the folks they contract to dig tunnels can really dig them.

    1. We could still branch north of Northgate somewhere… Might be especially useful if it turns out we don’t need a train every three minutes to Lynnwood after all…

      1. Not if they don’t plan for it. Seriously; ST will not allow a level junction, so if there is no “wide spot” left for the away side track to descend (or ascend) and join, no junction can be created. Remember the right of way is going to be cheek by jowl with I-5 all the way to Lynnwood.

      2. Lots can happen over time. What the current administration won’t do doesn’t mean a future administration will also not do.

        Tell someone who came to Seattle from the CTA that their primary junction on the Loop can’t possibly be a level junction and have trains every 30 to 45 seconds or so.

  13. Good graphics and good report. It helps put things in perspective (the Seattle Times article did as well). Anytime they basically start talking about digging the old fashioned way (albeit with sprayed on concrete) it means you are very close. This thing is almost done, and just encountered a little hiccup in what was otherwise a very smooth trip. It may still be built ahead of schedule, just not as far ahead as we would like.

    The contrast between it and the SR 99 project is huge. Not only because of the size of the boring machine, but because of the distance left. A graphic in that regard would also be telling, but it is obvious in the text — Bertha has barely started. It has a long ways to go — as in, almost all of it. It is already late, and likely to be very late when all is said and done (and lets hope that it will be done).

    1. The contrast between it and the SR 99 project is huge. Not only because of the size of the boring machine, but because of the distance left.

      Not to mention that Pamala isn’t below sea level. It would have been a major Ah Shucks if one of the TBMs decided to die under the Montlake Cut.

      1. No, but Pamela has been operating under water.

        Particularly the stretch just south of Northgate is basically one giant underground river. Neither Brenda nor Pamela had any trouble operating through these areas, but it is an issue for cross passage mining (done by hand). That is why they using more ground freezing on this project.

  14. A good example of an over-under subway is up in Vancouver- which lucked into not only an existing tunnel running exactly where SkyTrain needed to go through Downtown, but with extra room at the top to vent steam locomotives.

    Taking new lines over existing tubes or stations really depends on things like soils, but also underground utilities. And a couple of decades from now, tunneling technology will certainly improve.

    ButI believe there’s also a large-diameter sewer running along the north shore of the Ship Canal as it goes by the U-District. Extra wages for anybody who’s got to dig a machine out from a collision with that one!

    Mark

    1. The Dunsmuir Tunnel wasn’t really exactly where Skytrain needed to go. Skytrain went there because there was an existing tunnel to use. Although it did have to be expanded to accommodate the over-under design. If a new tunnel were to have been dug for Skytrain, it would have been under Georgia with a wider radius curve to the waterfront.

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