I don't think that's true: the slurry walls go down to bedrock, but I'd be surprised if they dug any deeper than they had to to build the road tunnel.
????
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.
???
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.
I don't think that's true: the slurry walls go down to bedrock, but I'd be surprised if they dug any deeper than they had to to build the road tunnel.
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)
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?
Is the new Wollaston design even planning for the possibility of a second commuter rail track through that station?
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.