Slurry Wall that was built for the North/South Rail Link.

Where exactly is the slurry wall built that would have provided a North/South Station Rail Link.

I read something, somewhere a while ago which said the floor of the new Central Artery tunnel was constructed so that a two-track rail tunnel could be deep-bored in the future just underneath it. In other words, a rail tunnel, two tracks only, could be bored just under the floor of the expressway tunnel.

I don't see how this could be done without a lengthy shut down of at least one direction of the expressway tunnel to traffic, which would never be allowed to happen I'm sure.

I still think it would be easier to convert the Grand Junction railroad through Cambridge to a passenger/commuter rail link: 2 tracks for passenger rail and 1 track for freight rail. It would require a new tunnel under the Charles River just east of the BU Bridge, but it would be a lot cheaper than trying to do another Big Dig under the Central Artery tunnel.

From what I've read, it's like this:



but the space where the rail link would be isnt empty, it's filled, so you'd still have to excavate.

dudeursistershot wrote:but the space where the rail link would be isnt empty, it's filled, so you'd still have to excavate.

Excavating there is pretty easy, the hardest part in that section is already done.

Charliemta wrote:I still think it would be easier to convert the Grand Junction railroad through Cambridge to a passenger/commuter rail link: 2 tracks for passenger rail and 1 track for freight rail. It would require a new tunnel under the Charles River just east of the BU Bridge, but it would be a lot cheaper than trying to do another Big Dig under the Central Artery tunnel.

Not necessarily, considering that it would have to be a deep-bored tunnel under the Charles, and a tunnel or boat section through East Cambridge.

It also wouldn't work for through-routing of commuter rail, due to the long detour. Intercity rail would be able to through-route, but it wouldn't be enough of an improvement to be worth it.

Interchanging it with the northside rail system would be tricky too. You'd have to route it out the Haverhill Line, which would then require double-tracking to handle pretty much any traffic increase (this is why the Downeaster goes out the Lowell Line to the Wildcat Branch). All in all, if you're going to spend big bucks on the Grand Junction, better to use it for the Urban Ring.

Yeah, you're probably right. It would only be useable for through-routing of Amtrak trains to points north, but would be too expensive for just that one use.

Also, the remaining ROW for the Grand Junction in Cambridge gets very narrow through the MIT area. Plus there would be the problem of tunneling under Main Street in Cambridge which already has the Red Line under it. That section would require a deep tunnel to dip below the Red Line tunnel.

However, a downtown north-south connector under the Big Dig would also have to have a deep-bored tunnel under the Charles River. I don't think there's any room east of North Station for the rail connector to emerge from beneath the Big Dig to cross the Charles River on a bridge.

Are these the same slurry walls that are springing leaks in the existing tunnel? I think John Businger may need to add wall inspections and patches to his budget estimates if they are.

Charliemta wrote:However, a downtown north-south connector under the Big Dig would also have to have a deep-bored tunnel under the Charles River. I don't think there's any room east of North Station for the rail connector to emerge from beneath the Big Dig to cross the Charles River on a bridge.

Correct. The plan for the Rail Link calls for a deep-bored tunnel with two branches at each end: on the south, one connecting to the Framingham & Providence lines and one coming up in the area of the Southampton St. yard. On the north, the tunnel continues under the Charles and comes up near BET, with inclines connecting to the Fitchburg and Lowell & Haverhill lines.

Pete wrote:Are these the same slurry walls that are springing leaks in the existing tunnel? I think John Businger may need to add wall inspections and patches to his budget estimates if they are.

Yes, they are. But the problem with the Big Dig tunnels is that they decided to use the rough slurry walls as permanent walls, when the normal construction technique calls for using the slurry walls just for excavation, and enclosing the tunnels in a yard-plus-thick concrete box. Due to the very limited amount of space in the area, enclosing the tunnels in the normal concrete box would have caused them to allow only three lanes of traffic on each side, which would result in no benefit in terms of capacity from the elevated structure.
I would assume that there would be enough room in a rail tunnel to enclose it in concrete, so the rail tunnel would have little or no problems with leakage.