Alaskan Way Viaduct Replacement Tunnel

[jakeroot]

Here's a video from WSDOT demonstrating how the exterior concrete ring is constructed:

https://youtu.be/XQxtJb4fbdY

As well, here's another video (from WSDOT) showing the filling of the access pit:

https://youtu.be/YF-dJiG9YLI

There's also one more video (from WSDOT -- surprise!) showing the parts of the tunnel not related to Bertha:

https://youtu.be/qaEvjXhxHOQ

[Rothman]

The Interstate Bridge on I-5 between Portland, OR and Vancouver, WA needs to be replaced with something.  There is a clearance constraint below for shipping traffic and a clearance constraint above for PDX flight traffic which together don't leave much space for a bridge.  Tunnel boring might be an option.  It would certainly make the airport and the shipping companies happy.  With a need for five lanes in each direction, that would require two double-stacked bores (probably two full-height lanes below for trucks and buses and three limited-height lanes above for cars).  Bore diameter would be similar to Bertha's.

Dear heavens.  Tunnels that size would never be built in that area.  The cost would simply be too prohibitive.

The cost of tunnel boring continues to decline.  The TBMs are becoming more efficient, more capable, more automated, etc.  So the labor costs are going down as the crews get smaller and the overhauls become less frequent. 

Yeah, but cost reductions from billions to fewer billions doesn't matter much.  What's incredible to me is that ever since the Big Dig -- which had a wide variety of critics -- tunnel proposals have popped up with greater frequency. 

I've had opportunity to be more informed than most on the tunnel alternative for the I-81 viaduct in Syracuse, for example.  Although the alternative is being thoroughly considered due to political pressures, the result is the same:  The cost of tunnels is still in the range of adjectives like "ludicrous," "absurd," or "idiotic" and projects like the Seattle project are only pursued when there's immense political will for such, which is rare.

Also remember that there were some well-intentioned but ignorant boosters for a tunnel option to the Tappan Zee Bridge.  Again, ridiculously high cost estimates killed that idea fairly quickly.

Anyway, tunnels are attractive in a Jetson-flying-car kind of way.  However, reality always brings things back above ground.

[Bruce]

The next big hurdle for Bertha:

The next leg in Bertha's journey by Washington State Dept of Transportation, on Flickr

This rendering shows the path that Bertha, the SR 99 tunneling machine, will take from the pit where she was repaired to an underground maintenance stop 450 feet to the north. After moving the machine forward 8 feet in late December 2015, Seattle Tunnel Partners, the SR 99 tunnel contractor, was preparing to tunnel toward the maintenance area beginning in January 2016.

[english si]

Also, when the machine is planned to cross under the viaduct in March, the latter will have to close for two weeks.

Is the viaduct that unstable? I thought Seattle was an earthquake-prone area and ought to cope with underground disturbances like a TBM passing under it - even with Bertha being big and heavy. Or is it boring through the foundations (dangerous)?


Crossrail sent one of it's TBMs through a gap between an escalator bank and platforms with a vertical gap about 4ft (1'2" above, 2'10" below) more than the tunnel diameter. They put someone one each platform to keep an eye on things and some high tech stuff to measure vibrations and so on, but they left both things open and 900 tons passed through 'the eye of a needle' without any bother. They didn't expect travellers to notice (and hoped they didn't), though when the platform was empty you could hear it. watch this to see it go through.

---

Both the Big Dig, and the issues with this scheme, will create an impediment to more road tunnels replacing old viaducts. That said, Stockholm and Oslo have recently built a lot, and London has looked into it (the big issues being cost and many people's pathalogical dislike of spending money on roads, meaning that it is politically easier to replace a rotting concrete viaduct with a new concrete viaduct, rather than build a long tunnel and get the extra benefits wrt severance, air quality, etc) to replace life-expired elevated structures.

[jakeroot]

Also, when the machine is planned to cross under the viaduct in March, the latter will have to close for two weeks.

Is the viaduct that unstable? I thought Seattle was an earthquake-prone area and ought to cope with underground disturbances like a TBM passing under it - even with Bertha being big and heavy. Or is it boring through the foundations (dangerous)?

In short, yes, the viaduct is very unstable. There are a couple of problems at the moment:

1) The 2001 Nisqually earthquake beat the shit out of it. Though it was repaired, its stability in the long run was compromised.

1 a) As a result of the 2001 quake, another good "shaking" could do serious, irreperable damage.

2) The land that the viaduct sits on is fill. It's not very stable. It's good material for a tunnel because (as I understand it) the tunnel is able to move with the land as it shakes, but things above it liquify and fall apart. The waterfront of Seattle is also being completely rebuilt to handle earthquakes because of how unstable the current situation is, even without the viaduct.

2 a) Due to the nature of the fill, the viaduct continues to settle, exacerbating the situation (by further compromising the integrity of the structure).

3) The viaduct wasn't built to withstand big shakings. I'm not sure what the maximum magnitude is before the viaduct would come crashing down, but I know it wouldn't last through "the big one". It was built during a period of poor earthquake research (supposedly).

[Bruce]

Also, when the machine is planned to cross under the viaduct in March, the latter will have to close for two weeks.

Is the viaduct that unstable? I thought Seattle was an earthquake-prone area and ought to cope with underground disturbances like a TBM passing under it - even with Bertha being big and heavy. Or is it boring through the foundations (dangerous)?


Crossrail sent one of it's TBMs through a gap between an escalator bank and platforms with a vertical gap about 4ft (1'2" above, 2'10" below) more than the tunnel diameter. They put someone one each platform to keep an eye on things and some high tech stuff to measure vibrations and so on, but they left both things open and 900 tons passed through 'the eye of a needle' without any bother. They didn't expect travellers to notice (and hoped they didn't), though when the platform was empty you could hear it. watch this to see it go through.

---

Both the Big Dig, and the issues with this scheme, will create an impediment to more road tunnels replacing old viaducts. That said, Stockholm and Oslo have recently built a lot, and London has looked into it (the big issues being cost and many people's pathalogical dislike of spending money on roads, meaning that it is politically easier to replace a rotting concrete viaduct with a new concrete viaduct, rather than build a long tunnel and get the extra benefits wrt severance, air quality, etc) to replace life-expired elevated structures.

The viaduct is very unstable, especially since it was damaged in the 2001 earthquake. During the digging of the recovery pit for Bertha, it sank 1.2 inches and caused quite a bit of concern.

The main reason for the closure is for WSDOT to monitor the viaduct's condition (vibrations mostly) without interference from traffic.

London has the distinct advantage of better soil conditions than our waterfront, which is mostly fill from the regrading of our hills.

[jakeroot]

The cost of tunnels is still in the range of adjectives like "ludicrous," "absurd," or "idiotic" and projects like the Seattle project are only pursued when there's immense political will for such, which is rare.

I bet tunnels will become more common in the future. People just don't like the look of freeways. All over Seattle, there are numerous lidding projects (including another proposed right in downtown Seattle) to cover up freeways to provide additional green space. The fact is, people like the function that freeways provide, but only the engineers among us can appreciate their beauty.

[Rothman]

The cost of tunnels is still in the range of adjectives like "ludicrous," "absurd," or "idiotic" and projects like the Seattle project are only pursued when there's immense political will for such, which is rare.

I bet tunnels will become more common in the future. People just don't like the look of freeways. All over Seattle, there are numerous lidding projects (including another proposed right in downtown Seattle) to cover up freeways to provide additional green space. The fact is, people like the function that freeways provide, but only the engineers among us can appreciate their beauty.

The public appreciates not paying for tunnels more than they do tunnels.

[jakeroot]

The cost of tunnels is still in the range of adjectives like "ludicrous," "absurd," or "idiotic" and projects like the Seattle project are only pursued when there's immense political will for such, which is rare.

I bet tunnels will become more common in the future. People just don't like the look of freeways. All over Seattle, there are numerous lidding projects (including another proposed right in downtown Seattle) to cover up freeways to provide additional green space. The fact is, people like the function that freeways provide, but only the engineers among us can appreciate their beauty.

The public appreciates not paying for tunnels more than they do tunnels.

That's for a cost/benefit analysis to decide.

[mcarling]

More than half of the North-South Expressway now in preliminary construction in Singapore will be underground.  My understanding is that TBMs will not be used i.e. the tunneling method will be cut-and-cover.  The two short "semi-tunnel" sections are expected to be lidded in the future.

http://www.lta.gov.sg/data/apps/news/press/2011/NSE%20Annex%20A.pdf

[TEG24601]

The original proposal for the tunnels was cut and cover the entire distance, under the roadway known as "Alaskan Way".  This project would have used the new, side-by-side tunnels as a new seawall as well.  The cap would then be used as a new roadway for Alaskan Way.


The thing I am confused about is why WSDOT went with the largest TBM ever to build a double decker tunnel, instead of two smaller tunnels side-by-side.  It just seems odd to get a custom build, single use machine, for that purpose, when alternatives would be much cheaper, and reusable.

[mcarling]

All TBMs sized for twin multi-lane tunnels are also custom built for the variety of soil conditions expected to be encountered along their path.  However, there may have been some components that would have been off-the-shelf that had to be custom fabricated for Bertha.

[noelbotevera]

Another thing that's even more questionable is: why destroy Bertha? It can be used for another projects that require tunneling like this, but if you will turn it into scrap, why build it in the first place, if you'll destroy it for its first job.

[mcarling]

At the end of a project like this, a TBM is not in great condition.  To be used again, it needs a major overhaul.  The cost of extraction, overhaul, and transportation to new site add up to something near the cost of a new TBM.  Again, as I wrote above, TBMs (except, as of several years ago, some smaller than 1 meter in diameter) are all custom designed to match the expected combination of soil conditions.  TBMs are substantially different for hard rock, soft rock, clay, sand, etc.  So, for all these reasons, and because reliability is so important, there is no market for used TBMs.

[Kacie Jane]

Another thing that's even more questionable is: why destroy Bertha? It can be used for another projects that require tunneling like this, but if you will turn it into scrap, why build it in the first place, if you'll destroy it for its first job.

mcarling explained it more thoroughly, but the short answer is no, it can't.  TBMs are, except in rare circumstances, one use only.  Individual parts can be re-used or recycled, but the machine as a whole is useless upon completion of the project.

[mgk920]

Another thing that's even more questionable is: why destroy Bertha? It can be used for another projects that require tunneling like this, but if you will turn it into scrap, why build it in the first place, if you'll destroy it for its first job.

mcarling explained it more thoroughly, but the short answer is no, it can't.  TBMs are, except in rare circumstances, one use only.  Individual parts can be re-used or recycled, but the machine as a whole is useless upon completion of the project.

I remember in articles from when the English Channel Tunnel was built, a couple of the TBMs were purposely driven off-course at the completion of their tasks and entombed in the chalk-marl under the Channel.

----------------

Also, before BNSF's ex GN tunnel was built, the original GN used street trackage on Alaskan Way, much like in Jack London Square on Oakland, CA.

Mike

[TEG24601]

Another thing that's even more questionable is: why destroy Bertha? It can be used for another projects that require tunneling like this, but if you will turn it into scrap, why build it in the first place, if you'll destroy it for its first job.

mcarling explained it more thoroughly, but the short answer is no, it can't.  TBMs are, except in rare circumstances, one use only.  Individual parts can be re-used or recycled, but the machine as a whole is useless upon completion of the project.

Which is odd, give that Sound Transit is using the same machines for their tunnels from Capitol Hill to the U District, and onward to Northgate (at least that is how the articles have been written to indicate).

[mcarling]

It's not odd at all.  It's the same project, with the same requirements, the same or similar soil conditions, and no need for disassembly, transport, and reassembly.  Metro projects often overhaul a TBM when it reaches a station box and then continue on to the next station box.  Once the metro line is finished, then the TBM is typically buried (though some parts are typically salvaged first).

[Bruce]

Bertha lurches forward another 6.5 feet and is poised to break out of its repair vault this week.

[kkt]

Bertha lurches forward another 6.5 feet and is poised to break out of its repair vault this week.

Is Vegas taking odds on completing the rest of the tunnel without further delays?

[Bruce]

Bertha lurches forward another 6.5 feet and is poised to break out of its repair vault this week.

Is Vegas taking odds on completing the rest of the tunnel without further delays?

Not yet, but there is an office pool on Reddit predicting where the next breakdown will be: https://www.reddit.com/r/Seattle/comments/3xwzs9/reddit_office_pool_on_how_far_bertha_makes_it/

[jakeroot]

Jokes aside, does it really have to break down again? I know, given the past two years, this sounds a little crazy, but I don't think it'll break down again. This is a critical time for Bertha -- she can't really get dug out again (not easily, at least). I get the feeling that WSDOT and STP have been doing their homework to prevent another issue.

[noelbotevera]

Quote from WSDOT:

"Bertha has 450 feet to go before reaching what's being called "Safe Haven 3." Where they do one more checkup on the machine before sending her along her way. It's approximately 7,300 feet to the finish from there."

Thanks to Bruce, it was in the reddit pool.

If a person gets it correct, WSDOT will give that person a tour of the tunnel (actual WSDOT comment)

Another 8180.5 feet to go with Bertha.

[Henry]

According to the article, 1,098 of the 9,270-foot project, or 11.8%, has already been bored through; although it's not exactly great progress since the project started, at least it's started moving forward once again. April 2018 is now the projected completion date for the tunnel, provided no further problems with Bertha or otherwise.

[The Ghostbuster]

Why do I have the feeling that date is optimistic?