Regional Rail (RUR) & North-South Rail Link (NSRL)
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Re: North-South Rail Link
????
Given slurry walls that go down to bedrock, and a tunnel that's far above bedrock, by definition they often had to dig out between the slurry walls and re-fill with dirt from the top of the bedrock to the bottom of the tunnel.
That means there was lots of loose fill below every tunnel and under the greenway.
????
Given slurry walls that go down to bedrock, and a tunnel that's far above bedrock, by definition they often had to dig out between the slurry walls and re-fill with dirt from the top of the bedrock to the bottom of the tunnel.
That means there was lots of loose fill below every tunnel and under the greenway.
JumboBuc
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Re: North-South Rail Link
???
They had to dig out the space for the slurry walls themselves all the way down to bedrock, but not the space between the slurry walls. One of the main virtues of slurry wall construction is that you can dig them deep while leaving the dirt around them more-or-less undisturbed. It's perfectly plausible that the slurry walls of the tunnel were excavated to bedrock but the full footprint of the travel lanes between the slurry walls wasn't.
Look at One Dalton for an example; that building has foundation elements that go all the way down and tie into bedrock, but the "basement" doesn't go down that deep (i.e., they didn't dig the full footprint of the building all the way down, just the limited area for the actual structural elements that tie into bedrock).
I don't know what method they used in the Big Dig, but either is perfectly plausible. If they did actually dig out the space between the slurry walls, wouldn't it have made just as much sense to pour a rail tunnel floor and roof below the auto lanes than it would have to refill that space with clean backfill? This makes me suspect that ceo is correct, and the space between the slurry walls was not fully excavated and then backfilled. It's still likely "clean" in the sense that you won't find active utilities buried under the roadway (the slurry walls would have cut them off), but not in the sense that it was purposely filled in during the 90s.
???
They had to dig out the space for the slurry walls themselves all the way down to bedrock, but not the space between the slurry walls. One of the main virtues of slurry wall construction is that you can dig them deep while leaving the dirt around them more-or-less undisturbed. It's perfectly plausible that the slurry walls of the tunnel were excavated to bedrock but the full footprint of the travel lanes between the slurry walls wasn't.
Look at One Dalton for an example; that building has foundation elements that go all the way down and tie into bedrock, but the "basement" doesn't go down that deep (i.e., they didn't dig the full footprint of the building all the way down, just the limited area for the actual structural elements that tie into bedrock).
I don't know what method they used in the Big Dig, but either is perfectly plausible. If they did actually dig out the space between the slurry walls, wouldn't it have made just as much sense to pour a rail tunnel floor and roof below the auto lanes than it would have to refill that space with clean backfill? This makes me suspect that ceo is correct, and the space between the slurry walls was not fully excavated and then backfilled. It's still likely "clean" in the sense that you won't find active utilities buried under the roadway (the slurry walls would have cut them off), but not in the sense that it was purposely filled in during the 90s.
Re: North-South Rail Link
My dudes: the NSRL tunnel would only be below the artery for about 3000 ft between rowes wharf and North Station. All the cost and complexity is going to be in the stations and the portals anyway.
My dudes: the NSRL tunnel would only be below the artery for about 3000 ft between rowes wharf and North Station. All the cost and complexity is going to be in the stations and the portals anyway.
JeffDowntown
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Re: North-South Rail Link
They *did* dig more than they needed, either below the road tunnels or between them (and ar Federal reserve an "alongside-and-below")
Lacking money for a tunnel they built a defined TBM corridor beneath (passing under Red & Blue and Road) with no utilities or archeological barriers (or pipes pilings such as stalled Bertha)) ) filled it with clean fill.
It is wide enough for a 4 track railroad and a Central Station, but requires very steep grades to get down to and up from, and left limited choices for approach tunnels and portals.
It left open all kinds of questions on bore diameter and tracks (2? 3? 4?) and station location (Dewey Sq vs Dot Ave Ft Pt Channel and Central Y/N? Or a big Haymarket-and North and long accessed)
They *did* dig more than they needed, either below the road tunnels or between them (and ar Federal reserve an "alongside-and-below")
Lacking money for a tunnel they built a defined TBM corridor beneath (passing under Red & Blue and Road) with no utilities or archeological barriers (or pipes pilings such as stalled Bertha)) ) filled it with clean fill.
It is wide enough for a 4 track railroad and a Central Station, but requires very steep grades to get down to and up from, and left limited choices for approach tunnels and portals.
It left open all kinds of questions on bore diameter and tracks (2? 3? 4?) and station location (Dewey Sq vs Dot Ave Ft Pt Channel and Central Y/N? Or a big Haymarket-and North and long accessed)
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tangent
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Re: North-South Rail Link
And by the time it gets geared up again all the people that know anything about all the stuff they did during the big dig to prepare for NS rail-link will be retired and the documents will be deep in the state archives right behind the ark of the covenant.
And by the time it gets geared up again all the people that know anything about all the stuff they did during the big dig to prepare for NS rail-link will be retired and the documents will be deep in the state archives right behind the ark of the covenant.
Re: North-South Rail Link
Yes, this is what I thought I have read that happened. BTW, probably should put "clean fill" in quotes - this was the big dig so gods only know what will really be found down there should the NSRL proceed.
Yes, this is what I thought I have read that happened. BTW, probably should put "clean fill" in quotes - this was the big dig so gods only know what will really be found down there should the NSRL proceed.
ceo
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Re: North-South Rail Link
I want a source for that. It makes no sense at all to dig further than you need to and fill it back up with dirt. They'd have to dig it out anyway to build the NSRL, so what good would it do?
And yes, slurry wall construction lets you only dig out the space for the wall itself. You dig a narrow trench down to bedrock, filling it with a clay slurry as you go to keep the walls from collapsing. Then drop in a rebar cage and fill it with concrete from the bottom as you pump out the slurry from the top. They did that along the entire length of the Central Artery tunnel, then transferred the weight of the elevated Artery onto the walls, so they could take out the old supports and dig under it between the walls.
I want a source for that. It makes no sense at all to dig further than you need to and fill it back up with dirt. They'd have to dig it out anyway to build the NSRL, so what good would it do?
And yes, slurry wall construction lets you only dig out the space for the wall itself. You dig a narrow trench down to bedrock, filling it with a clay slurry as you go to keep the walls from collapsing. Then drop in a rebar cage and fill it with concrete from the bottom as you pump out the slurry from the top. They did that along the entire length of the Central Artery tunnel, then transferred the weight of the elevated Artery onto the walls, so they could take out the old supports and dig under it between the walls.
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Re: North-South Rail Link
Page 4.6 (pdf page 72)
https://static1.squarespace.com/sta...80/NSRL+Tech+Report+No.5-Operations+Study.pdf
The NSRL will be re-dug in the dirt between the slurry walls and below the roadway of the Northbound tunnel from Rowe's Wharf to the Zakim's approach. I don't know if they excavated and refilled before or after the floor of the tunnel was installed, but he idea was that they were making a "no surprises" medium for a future TBM.
Knowing that your TBM has a clear path through a consistent medium is a very big deal, but they didn't have the $ or plan of what to build down there. Maybe they just core-sampled the heck out of most of it before pouring the tunnel floor, but the idea was that they assured that only clean fill lay between the slurry walls at railbed depth fairly far below the tunnel floor and above bedrock.
Page 4.6 (pdf page 72)
https://static1.squarespace.com/sta...80/NSRL+Tech+Report+No.5-Operations+Study.pdf
The NSRL will be re-dug in the dirt between the slurry walls and below the roadway of the Northbound tunnel from Rowe's Wharf to the Zakim's approach. I don't know if they excavated and refilled before or after the floor of the tunnel was installed, but he idea was that they were making a "no surprises" medium for a future TBM.
Knowing that your TBM has a clear path through a consistent medium is a very big deal, but they didn't have the $ or plan of what to build down there. Maybe they just core-sampled the heck out of most of it before pouring the tunnel floor, but the idea was that they assured that only clean fill lay between the slurry walls at railbed depth fairly far below the tunnel floor and above bedrock.
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ceo
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Re: North-South Rail Link
The report you linked to says nothing about the CA/T tunnel having been excavated and backfilled for the NSRL. It's also from 1997, which was early in the Big Dig construction process. Mind you, they definitely took lots of core samples, for the slurry walls if nothing else.
The report you linked to says nothing about the CA/T tunnel having been excavated and backfilled for the NSRL. It's also from 1997, which was early in the Big Dig construction process. Mind you, they definitely took lots of core samples, for the slurry walls if nothing else.
DominusNovus
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Re: North-South Rail Link
Unrelated to the current discussion, but I had an idea in the Reasonable Transit Thread that got me thinking about the Commuter Rail, and it occurs to me that a lot of our Commuter Rail lines are single tracks, aren't they? From what I can tell with satellite maps, we have single tracks on most of the lines once you get far away enough from the city (but my eyes have started going cross after zooming in and out over and over)
With that in mind, whats the NSRL plan for dealing with that? Won't it be pretty tricky to run trains against rush hour, which we will have to do if only to get them out of the way. Is it pretty much just 'run the trains through the system as far as we have double tracks' or is doubling up more of the tracks part of the pln? (or some combination of the two). Or is there some more clever train shuffling stuff that I have overlooked?
Unrelated to the current discussion, but I had an idea in the Reasonable Transit Thread that got me thinking about the Commuter Rail, and it occurs to me that a lot of our Commuter Rail lines are single tracks, aren't they? From what I can tell with satellite maps, we have single tracks on most of the lines once you get far away enough from the city (but my eyes have started going cross after zooming in and out over and over)
With that in mind, whats the NSRL plan for dealing with that? Won't it be pretty tricky to run trains against rush hour, which we will have to do if only to get them out of the way. Is it pretty much just 'run the trains through the system as far as we have double tracks' or is doubling up more of the tracks part of the pln? (or some combination of the two). Or is there some more clever train shuffling stuff that I have overlooked?
Re: North-South Rail Link
I would imagine you'd pair the line that are double tracked (say Worcester to Salem, Providence to Lowell, and Fairmont to Fitchburg) and have the other lines continue terminating at the surface terminals.
I would imagine you'd pair the line that are double tracked (say Worcester to Salem, Providence to Lowell, and Fairmont to Fitchburg) and have the other lines continue terminating at the surface terminals.
The EGE
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Re: North-South Rail Link
Providence, Fairmount, Worcester, and the entire northside are largely 2+ tracks. Most effectively single-track areas just need additional platforms on multi-track mainlines.*
*Easy projects to modify as-needed: TFG and WJ platforms, Worcester platform, the Newton stations, Readville, Waltham, Fitchburg and Wachusett platforms, a section north of Reading, the Wildcat Branch, Andover and Ballardvale stations, Lawrence station, and the branches past Ipswich and Gloucester.
Needham needs to get pushed to rapid transit, as endlessly discussed. Franklin would be very easy to double-track, and I've heard rumors that it's the next line due for major upgrades. The three Old Colony branches are largely single with well-spaced passing sidings, and they can mostly get additional sidings and platforms as needed.
The three sticking points are the inner NEC, the Salem Tunnel, and the Old Colony mainline. The NEC can buy time with OLX-Needham, pushing additional Franklin trains to the Fairmount, and axing Hyde Park. The Salem Tunnel is near-impossible to modify, but it's short and BLX-Lynn could help. The Old Colony mainline, with huge sections of single track, is by far the biggest limitation on the system.
Providence, Fairmount, Worcester, and the entire northside are largely 2+ tracks. Most effectively single-track areas just need additional platforms on multi-track mainlines.*
*Easy projects to modify as-needed: TFG and WJ platforms, Worcester platform, the Newton stations, Readville, Waltham, Fitchburg and Wachusett platforms, a section north of Reading, the Wildcat Branch, Andover and Ballardvale stations, Lawrence station, and the branches past Ipswich and Gloucester.
Needham needs to get pushed to rapid transit, as endlessly discussed. Franklin would be very easy to double-track, and I've heard rumors that it's the next line due for major upgrades. The three Old Colony branches are largely single with well-spaced passing sidings, and they can mostly get additional sidings and platforms as needed.
The three sticking points are the inner NEC, the Salem Tunnel, and the Old Colony mainline. The NEC can buy time with OLX-Needham, pushing additional Franklin trains to the Fairmount, and axing Hyde Park. The Salem Tunnel is near-impossible to modify, but it's short and BLX-Lynn could help. The Old Colony mainline, with huge sections of single track, is by far the biggest limitation on the system.
Joel N. Weber II
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Re: North-South Rail Link
Is the new Wollaston design even planning for the possibility of a second commuter rail track through that station?
Is the new Wollaston design even planning for the possibility of a second commuter rail track through that station?
DominusNovus
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Re: North-South Rail Link
Doesn’t it currently?
Edit: I was looking at N Quincy. Told you guys my eyes started to cross.
Doesn’t it currently?
Edit: I was looking at N Quincy. Told you guys my eyes started to cross.
Charlie_mta
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Re: North-South Rail Link
I'm pretty sure that the soil between the deep slurry walls is the original in-situ soil. They were under the gun to get the new slurry walls and tunnel built underneath the old Central Artery viaduct, plus they were faced with ever-increasing cost overruns. For these reasons, I cannot imagine them taking the time and expense to excavate out the material beneath the Central Artery tunnel floor.
So, for the NSRL, a TBM will need to bore through the Boston blue clay which sits between the deep slurry walls. Probably two parallel TBM tunnels, two tracks each. The new highway tunnel being bored under downtown Seattle by a TBM is 4 lanes wide, and is probably the largest you'd want to go with a TBM. Four tracks wide would require a larger diameter tunnel than 4 traffic lanes.
I'm pretty sure that the soil between the deep slurry walls is the original in-situ soil. They were under the gun to get the new slurry walls and tunnel built underneath the old Central Artery viaduct, plus they were faced with ever-increasing cost overruns. For these reasons, I cannot imagine them taking the time and expense to excavate out the material beneath the Central Artery tunnel floor.
So, for the NSRL, a TBM will need to bore through the Boston blue clay which sits between the deep slurry walls. Probably two parallel TBM tunnels, two tracks each. The new highway tunnel being bored under downtown Seattle by a TBM is 4 lanes wide, and is probably the largest you'd want to go with a TBM. Four tracks wide would require a larger diameter tunnel than 4 traffic lanes.
Re: North-South Rail Link
Guys, we're barking up the wrong tree with this soil thing. Here's why:
1. The presence of the slurry walls is at least as important as the consistency of the soil/clay between them, because the walls mean that pressure & water flow in the soil/clay around the TBM will be much more stable & predictable than if they were not present. ... and my understanding is the changes in pressure and water around the TBM are at least as much of a complication for boring as rocks and boulders in the clay in front of the cutting head would be...
2. There's really not that much TBMing to be done anyway - especially if Central Station stays in the plan (which is shouldn't but whatever). Central Station & North Station would both include essentially full excavation between the slurry walls, for a distance of ~1000 feet each. That leaves only a short distance to actually bore out - a small multiple of the length of a TBM. Might make more sense just to excavate, rather than set up a machine. The one complication might be the section under the charles, but even that's not a clear cut case for a TBM.
...plus you have to create space to get a TBM into the ground (and sometimes out, too). That's probably not going to happen @ rowes wharf, so you're looking at sinking it on the north side of the charles and then leaving it below the Channel (after you somehow get it through the existing slurry wall and under the hotel?)
3. If you're going for more than 2 tracks, it especially doesn't make sense to use a TBM. 3 or 4 tracks would essentially take the entire width between the walls, so might as well just excavate it. As you go for larger diameters, you end up with more 'wasted' excavation because the profile of a train is essentially a rectangle, and you're trying to fit 3 or 4 of those efficiently inside a circle. (There are advanced TBMs that do two overlapping circles but this is too short for those to be cost effective). Just dig between the walls, lay some tracks and calling it a day.
Guys, we're barking up the wrong tree with this soil thing. Here's why:
1. The presence of the slurry walls is at least as important as the consistency of the soil/clay between them, because the walls mean that pressure & water flow in the soil/clay around the TBM will be much more stable & predictable than if they were not present. ... and my understanding is the changes in pressure and water around the TBM are at least as much of a complication for boring as rocks and boulders in the clay in front of the cutting head would be...
2. There's really not that much TBMing to be done anyway - especially if Central Station stays in the plan (which is shouldn't but whatever). Central Station & North Station would both include essentially full excavation between the slurry walls, for a distance of ~1000 feet each. That leaves only a short distance to actually bore out - a small multiple of the length of a TBM. Might make more sense just to excavate, rather than set up a machine. The one complication might be the section under the charles, but even that's not a clear cut case for a TBM.
...plus you have to create space to get a TBM into the ground (and sometimes out, too). That's probably not going to happen @ rowes wharf, so you're looking at sinking it on the north side of the charles and then leaving it below the Channel (after you somehow get it through the existing slurry wall and under the hotel?)
3. If you're going for more than 2 tracks, it especially doesn't make sense to use a TBM. 3 or 4 tracks would essentially take the entire width between the walls, so might as well just excavate it. As you go for larger diameters, you end up with more 'wasted' excavation because the profile of a train is essentially a rectangle, and you're trying to fit 3 or 4 of those efficiently inside a circle. (There are advanced TBMs that do two overlapping circles but this is too short for those to be cost effective). Just dig between the walls, lay some tracks and calling it a day.
odurandina
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Re: North-South Rail Link
i wish i could see a 3d map of the future site.
even 2 tracks would be amazing but 3 sounds much better.
4? well we can't spend 7 trillion in iraq and then build a 4th track.
come on guys/ gals be reasonable.
i wish i could see a 3d map of the future site.
even 2 tracks would be amazing but 3 sounds much better.
4? well we can't spend 7 trillion in iraq and then build a 4th track.
come on guys/ gals be reasonable.