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Old 12-18-2017, 09:03 AM   #1
TheRifleman
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Big Dig Tunnel--

Anybody a Structural Engineer on this site?

I have a question: Driving into the big dig tunnel the other day I saw the developments above the tunnel near North Station. Looking above going through the tunnel those structures seem a bit heavy to be sitting on the tunnel.

Any thoughts?
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Old 12-18-2017, 09:26 AM   #2
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Re: Big Dig Tunnel--

I am certain the whole thing is going to collapse any day now.
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Old 12-18-2017, 09:58 AM   #3
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Re: Big Dig Tunnel--

1. The tunnel walls got to bedrock, and held up the old artery during construction.
2. There is a lot of steel bracing and truss work in the new buildings to distribute the loads onto the walls.
3. Think of the tunnels like a parking garage with big entrances and exits.
4. Beyond that - magic.
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Old 12-18-2017, 10:03 AM   #4
Arlington
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Re: Big Dig Tunnel--

I have a very clear recollection that all surface building sites were planned from the beginning, and that the necessary foundations for future buildings were incorporated during tunnel construction.

Where we see buildings, it is because they were provisioned

Where we see foundations capped off, buildings are yet possible.

Where no foundations were built (where none were planned) no buildings are possible.
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Old 12-18-2017, 11:00 AM   #5
TheRifleman
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Re: Big Dig Tunnel--

Quote:
Originally Posted by fattony View Post
I am certain the whole thing is going to collapse any day now.
That wasn't my point--- but because your arrogant post.

Tell that to the poor women's family that died driving through the tunnel.
http://www.nytimes.com/2007/07/11/us/11bigdig.html

Oh yeah did we forget about the arrests concerning the Cemet scam.
https://www.cbsnews.com/news/arrests...oncrete-fraud/
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Old 12-18-2017, 11:13 AM   #6
CSTH
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Re: Big Dig Tunnel--

Ok I see what youíre asking - how big is the bezel? Itís a difficult question; not even the bezzler knows for sure in a case like this...
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Old 12-18-2017, 01:26 PM   #7
TheRifleman
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Re: Big Dig Tunnel--

My point is with the additional developed buildings near North Station could the Big Dig tunnel become top heavy overtime? I believe most the highway is right under the Greenway so there is really not much built over it besides the beginning of the tunnel.
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Old 12-18-2017, 01:47 PM   #8
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Re: Big Dig Tunnel--

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Originally Posted by TheRifleman View Post
My point is with the additional developed buildings near North Station could the Big Dig tunnel become top heavy overtime? I believe most the highway is right under the Greenway so there is really not much built over it besides the beginning of the tunnel.
All that development at North Station (as well as a few other parcels over the tunnel) was planned for during the construction of the Big Dig foundation. Acceptable building envelopes (massing/height) were established so that the foundation could carry the planned load.

Same thing is true out in the Seaport district.
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Old 12-18-2017, 03:24 PM   #9
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Re: Big Dig Tunnel--

Yes I believe they are building a few building over the SL tunnel in the Seaport.
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Old 12-18-2017, 05:16 PM   #10
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Re: Big Dig Tunnel--

And city square fwiw
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Old 12-18-2017, 05:32 PM   #11
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Re: Big Dig Tunnel--

Is this thread for real? No, the structural loads aren't inflicted on the tunnel itself. They are transferred to columns attached to footings that are either between the highway lanes and/or outside the ROW. The friggin Prudential Center was built on air-rights in the 1960s and its doing just fine along with Copley Place from the 1980s. I can assure you: we've definitely figured out how to do air rights construction in 2017.
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Old 12-19-2017, 10:34 AM   #12
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Re: Big Dig Tunnel--

A slightly different question - I remember a couple years ago there was a flurry of articles about how the supposedly frozen soil under the MassPike Tunnel (Ted Williams) was thawing too fast. Any concerns over that still?
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Old 12-19-2017, 12:36 PM   #13
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Re: Big Dig Tunnel--

Quote:
Originally Posted by autonomy View Post
A slightly different question - I remember a couple years ago there was a flurry of articles about how the supposedly frozen soil under the MassPike Tunnel (Ted Williams) was thawing too fast. Any concerns over that still?
Why would soil be frozen under there? It would be well deep enough to not freeze in cold weather. All I can think of is that they did some trickery building it with freezing the soil to give it more rigidity while tunneling under the old elevated/south station/etc, but that wasn't permanent.
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Old 12-19-2017, 01:32 PM   #14
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Re: Big Dig Tunnel--

Yes, they did freeze the soil during part of the construction, but certainly that would not still be frozen today, nor would the engineers have planned on it being forever frozen.
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Old 12-19-2017, 01:49 PM   #15
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Re: Big Dig Tunnel--

Recall that Soil Freezing was used both for tunneling the SL under (then) Russia Wharf (now a more marketable "Atlantic Wharf"), and for freezing under the South Station approach tracks.

The soil under the South Station approach tracks was frozen so that the connector section could be dig between the old I-90@Artery and the large stretch of I-90 that was made in the Fort Point casting basin* So that under-the-tracks section is the part that we'd worry about in this thread.

Foam Tech, which insulated the exposed frozen faces as they were dug-through, has great pictures on their site, including this aerial view of the tunnel going under the tracks with frozen soil above:


I found this story from 2011 that said that afther the freeze plant was shut off in 2002, the thawing soil had taken longer and shrunk more than expected, leaving voids in that area (and that they expected that thawing would have ended by then, but would probably continue until 2013:
Quote:
When constructing the I-90 connector tunnel, an area of about 200-feet-by-160-feet was frozen to allow for excavation without disrupting train service above to depths of about 130 feet below the ground surface. The freeze plant was shut down in 2002, as engineers expected the clay soil to settle approximately the same amount it had swelled during the freezing process.
...
The highway department hired an independent engineering firm, STV Parsons, to analyze the tunnel structure in light of the settling, and DePaola said it was determined the tunnel, acting as bridge, is able to withstand the additional pressure being put on the structure from above even when assuming the void spans the entire length and width of the tunnel section.

*casting basin video shows the cast-float-sink sections of tunnel that the dug-through-frozen-soil connector tunnel was connecting to.
.
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