Ottawa Rapid Transit Network developments

[Franky]

Originally Posted by Dado

You mean the consultant?

And that doesn't hold any water for regular LRT vehicles. Double decker buses are higher than low-floor LRVs. Even Calgary's high-floor LRVs fit into tunnels with far less clearance than 5 m:


Source: LRT in Calgary

A clear 5 m height would also allow GO Train bilevels to clear a bridge since they're 4.85 m in height, bearing in mind that these are heavy rail vehicles:
http://en.wikipedia.org/wiki/Bombardier_BiLevel_Coach


The requirement for 5 m at St. Laurent is related to something other than standard LRVs...


Probably completely unrelated, but didn't we just acquire 3 double-decker buses? I wonder what would happen to a 4.25 m high double-decker bus passing under a bridge if it happened to hit a pothole or something? Sure would be nice to have some extra clearance for that. But like I said, probably completely unrelated.

Overhead wires. Go-transit is diesel (I guess).

Thanks for the link but they aren't LRV. How would that work or are we saying an LRV would likely be the same size?

[Dado]

Originally Posted by Franky

Actually, they said cut&cover was needed in the soft ground conditions of sandy hill area - no other way.

Yes, but that's on the east bank of the Canal where the tunnel comes back up at the UoO, out of the way of the direct concerns of the downtown businesses. From the sounds of it, the entire transitway from Laurier to Lees is going to be dug up.

East and west of the Canal are quite different and therefore the techniques to be employed will have to be quite different. From LeBreton eastwards under downtown and the Canal and up to about Laurier it'll be bored. South of there as the tunnel rises and the bed rock falls off cut&cover will have to be the rule. That's what I gathered from it all.

Perhaps Richard can confirm this impression?

The guy was not a decision maker, he said shafts for stairs and air shafts needed to be bored from the surface even for mined stations.

Yes, but still less disruptive than taking out the whole street.

I did not get the feeling a decision was made to mine the stations.

Interesting, because that's pretty much what you wrote a couple pages back.

I found a website for "BART Extension" which states
"
- Mined stations present greater risk to
construct (heaving of city streets & sidewalks)
- Significant cost penalty of $50 million more a
station
- Surface disruption of traffic not eliminated
(piping for freezing must be drilled & calcium
chloride brine solution continuously circulated
to maintain freeze)
- VTA recommends cut & cover method as
safest, “tried & proven technique” based on
experience constructing Vasona tunnel"
https://www.communicationsmgr.com%2Fproj...%2520Council%2520Workshop%255B1%255D.pdf
Granted, this is a specific case (I might look for more).

The most economically cost-effective (minimizing direct and indirect costs) in Ottawa given the shallow bedrock would probably be shallow bored tunnels and cut&cover stations. The two can be done concurrently with minimal interference between either operation and no requirement for one to be done before the other.

[Dado]

Originally Posted by Franky

Overhead wires. Go-transit is diesel (I guess).

Thanks for the link but they aren't LRV. How would that work or are we saying an LRV would likely be the same size?

I think you're missing the point of this bit of the discussion. Richard was saying that they want the clearance at St. Laurent Station to be 5 m for the regular trains. I say that's rubbish because standard LRVs can get through a lot less clearance than that and that even a bilevel GO Train can go under a 5 m bridge. It's the railway rhetorical equivalent of saying that someone is building a door so big one could drive an elephant through it. The point being that something other than a need to get standard LRVs through is driving this supposed requirement at St. Laurent Station.

But to answer your question, an electrified heavy-rail bilevel would require a bit more than 5 m clearance, though an electrified light-rail bilevel might not, if such a thing existed yet. So 5 m clearance would still be a good idea, but I don't think their concern at St. Laurent is about getting bilevel light rail vehicles through in the future.

[Franky]

We're in agreement for the most part.

Originally Posted by Dado

Interesting, because that's pretty much what you wrote a couple pages back.


The most economically cost-effective (minimizing direct and indirect costs) in Ottawa given the shallow bedrock would probably be shallow bored tunnels and cut&cover stations. The two can be done concurrently with minimal interference between either operation and no requirement for one to be done before the other.

If it wasn't clear, a deep tunnel seemed decided, but whether to mine or cut&cover stations was not (as I understand it). He seemed worried when I pointed to the 6 m minimum to building foundation said "that's a MINIMUM" meaning it will have to be quite a bit more. Blasting/mining close to buildings seems a bit risky?

http://ottawa.ca/residents/public_consult/transit_tunnel/op_1/segments/09_tunnel_const_en.html

Can a shallow bored tunnel dig between building foundations like under Albert or Slater? A also presume a shallow station would not take as long to construct as a deep one?

[Richard Eade]

A bored tunnel is preferred because it is not as disruptive to build as a Cut & Cover tunnel.

The reason Ottawa's tunnel will be so deep is due to our geology. We have good rock to bore through, but it starts about 10-15 metres down. Because buildings are generally built on solid foundations, you will find that most newer buildings are built on piles which go right down to the bedrock level. If there is any doubt about the tunnel being too close to a foundation, then the tunnel should be 1 to 1.5 tunnel diameters under the foundation; in this case, the start of bedrock. Thus, for a 6 metre tunnel, it needs to be 6-9 metres under the start of the bedrock. The bottom of the tunnel will therefore be 15+9+6=30 metres down. This is not an unheard of depth. There are many subways which are at, or deeper than this. (Of course, if the power goes out, you are walking up the equivelent of 9 stories.)



In this diagram, the bedrock has been bored for the tunnel deep enough to be well under the foundation of the building.

The white station area has been mined out, as well as the beginning of the stairwell/elevator shafts. This will likely be done with road headers. I don't think that it would be economical to try to mine through the looser material above the bedrock, this part of the shafts will be dug from above (the fuchia area).

The reason digging shafts is less disruptive is just size. This does, however bring up the point that if the station accesses are to be far away from the stations, longer cuts will need to be made.

Incidently, the fact that buildings are built on piles is a good reason not to go under the north part of the Rideau Centre. Recall that there is an underground valley in that area, thus plies are quite long there.



Notice that the station/tunnel will cut many of the piles in this area. Significant underpinning will be required.

[Franky]

"Open House Display Boards #1" are up:
http://ottawa.ca/residents/public_consult/transit_tunnel/op_1/overview_en.html

[Dado]

Originally Posted by Franky

Can a shallow bored tunnel dig between building foundations like under Albert or Slater?

I see what you're asking now... good question. I can see why they wouldn't if they're going to mine a station like in the graphic, but if they're not... but that's just asking the same question again in a different way.

It would be an issue of the lateral forces exerted by the building foundations and whether or not the lining of a tunnel can resist them, or even if it would need to. But if you do cut&cover for either a station or the tunnel itself, you have this problem in a lot bigger way anyway and it's never been suggested that cut&cover isn't doable. I've also seen buildings downtown have an entire face of their underground foundations exposed when another building is being put up next to it. So while I don't know, the real-life evidence doesn't suggest it's that big an issue.

I might be able to answer this question later since my father is a structural engineer.

A also presume a shallow station would not take as long to construct as a deep one?

One would presume not.

[Richard Eade]

A couple of points:

Dado: For the double decked buses, they have had to make some modifications at the St. Lairent station, even moving the sprinkler heads, to make room.

Absolutely, I meant consultant, not contractor; thanks. The consultant would like a clear 5 metre height because things have not been settled as to what vehicles are being used. To have that (arbitrary) envelope in mind ensures that the possibilities stay open. I am not saying that 5 metres will be needed in the end, just that it is a desire now.

Franky: Boring tunnels can easily be done during the winter, while Cut & Cover are generally done during the summer construction season. If it would take four or five seasons to do the Cut & Cover (judging by how much of Bank they do each year), then it is quite possible that the boring could be finished faster, with only the station shafts being done during the summers. And, while the boring and mining is being done, there should be no surface disruption.

Dado: As far as Halcrow (the tunneling specialist Delcan brought in) is concerned, a mixed face boring machine should be able to bore south under the Transitway if it is kept close to the rock interface. Their opinion is that it is doable. This will probably result in a slightly deeper Campus station if the tunnel is continued to Mann (Which I think I heard support for last night).

[Dado]

Originally Posted by Richard Eade

A bored tunnel is preferred because it is not as disruptive to build as a Cut & Cover tunnel.

The reason Ottawa's tunnel will be so deep is due to our geology. We have good rock to bore through, but it starts about 10-15 metres down.

But the display graphics show that bedrock is nowhere more than 10 m down in downtown Ottawa (except the pit under the Rideau Centre), and in much of the west end of downtown it's less than 3 m down:



That means the rest of your calculations are off, because the top of the tunnel can be about 12-15 m - not 30 m - down. Only once near the Canal do we have to go deeper, and there we've got lots of other problems that will likely call for a cut&cover tunnel anyway.

But it sure seems like a good idea to avoid going north of the Rideau Centre if at all possible. We could just go through the basement of the Rideau Centre at Daly

[Franky]

So a shallow bored depth tunnel could use a soft-soil boring machine for the whole length? It would probably tunnel faster and cost less because the stations could be cut&cover?

[Richard Eade]

There is a tendancy to avoid a lot of up and down motion when a rail tunnel is made. It would be possible to bore at a shallower depth through a lot of the west end, but how would you get there?

The rail top at LeBreton is about 15 metres below the surface of the road at Albert and Bronson and almost 20 metres below the park at the end of Queen. Would you suggest raising the train from LeBreton to half way up the escarpment?

Assuming that the train is to be kept under ground from LeBreton, the west end of the tunnel will be deep. As you point out, we need to be fairly deep under the canal. There is no real point in starting low, rising up only to go back down within a kilometre.

If there was a desire to, the tunnel could be run level under Albert at about 15 metres down, but that would be the minumim for a level tunnel, assuming 15 metres was deep enough in the canal area.

If you didn't care about the roller-coaster effect, then you could rise and fall as desired, but to go under any buildings would probably require you to drop down.

The benefit of having less dirt over the bedrock will not be that the tunnel can be less deep so much as it will allow more mining and shallower shafts dug from the surface. This will result in shorter surface disruptions.

Just for reference, the LeBreton rail is at an elevation of about 54 metres, and the bottom of the major sewer under the western edge of the canal is at about 48 metres. We need to get under the sewer by at least 6 metres.

[Franky]

Originally Posted by Richard Eade

There is a tendancy to avoid a lot of up and down motion when a rail tunnel is made. It would be possible to bore at a shallower depth through a lot of the west end, but how would you get there?

The rail top at LeBreton is about 15 metres below the surface of the road at Albert and Bronson and almost 20 metres below the park at the end of Queen. Would you suggest raising the train from LeBreton to half way up the escarpment?

Assuming that the train is to be kept under ground from LeBreton, the west end of the tunnel will be deep. As you point out, we need to be fairly deep under the canal. There is no real point in starting low, rising up only to go back down within a kilometre.

If there was a desire to, the tunnel could be run level under Albert at about 15 metres down, but that would be the minumim for a level tunnel, assuming 15 metres was deep enough in the canal area.

If you didn't care about the roller-coaster effect, then you could rise and fall as desired, but to go under any buildings would probably require you to drop down.

The benefit of having less dirt over the bedrock will not be that the tunnel can be less deep so much as it will allow more mining and shallower shafts dug from the surface. This will result in shorter surface disruptions.

A 5% grade would require 200 m to get to 10 m (bottom of the tunnel). Isn't the "roller coaster effect" overstated? Buses go over a bridge to cross the canal and the approach to Albert or Slater is probably a steeper than 5% grade. Since there are so many stations downtown, it's not like the trains will get any speed. Also, if the elevation changes are close to stations, trains have to stop at those stations anyway so they will be going slowly.

I had suggested a cut&cover across the canal, thought the sewer pipe would need to be addressed. A bridge is the other possibility.

[p_xavier]

Originally Posted by Richard Eade

If you didn't care about the roller-coaster effect, then you could rise and fall as desired, but to go under any buildings would probably require you to drop down.

Recent subways are now made with the roller-coaster effect, just because it uses the gravity to pull down the trains down and up to the next station. So it is actually recommended to have shallow stations. At 30m depth, the auxilliary structures (fans, escape stairs), cost about the same as the subway stations. The engineers said it was the first time in MTL that they did these sorts of structures, due to new security codes, and if they would have to redo the plans, they would have put more stations instead.

[Richard Eade]

Originally Posted by Franky

A 5% grade would require 200 m to get to 10 m (bottom of the tunnel). Isn't the "roller coaster effect" overstated? Buses go over a bridge to cross the canal and the approach to Albert or Slater is probably a steeper than 5% grade. Since there are so many stations downtown, it's not like the trains will get any speed. Also, if the elevation changes are close to stations, trains have to stop at those stations anyway so they will be going slowly.

I had suggested a cut&cover across the canal, thought the sewer pipe would need to be addressed. A bridge is the other possibility.

Yup, there are different levels of tolerance for going up and down. I think also, the consultant is trying to keep the grades at about 3% so ups and downs would be less noticable but it would take 333 metres to change 10 metres in height. Yes, it can be done. It is just not what is preferred.

There appears to be about 8-10 metres between the bottom of the canal and the sewer so, yes, it could be Cut & Covered across the canal. But where would you go from there? To the west isn't too much problem since there is a general drop of about 6 meters from Elgin to the canal surface. I am assuming you came along under Queen to avoid the NAC.

But on the east side, where would you Cut & Cover to, since you would be pretty much just below the surface? The best option would be under Daly which might work. Assuming you can get around the point of the NAC with enough clearance that they won't be bothered by noise and rumble. There should be no piles supporting buildings in the middle of Daly so that shouldn't be a concern. Nor should the valley be a problem since you are not using a TBM.

East of Daly, out from under the Rideau Centre, I'm not sure where you would go at that depth. Presumably, you would find some way over to Waller (maybe just following Daly and turn under the green space at the corner) and to just get under Laurier and surface.

Yes, it could probably be done. Yes, it would be less expensive. It might not be faster, though.

[Richard Eade]

Originally Posted by d_jeffrey

Recent subways are now made with the roller-coaster effect, just because it uses the gravity to pull down the trains down and up to the next station. So it is actually recommended to have shallow stations. At 30m depth, the auxilliary structures (fans, escape stairs), cost about the same as the subway stations. The engineers said it was the first time in MTL that they did these sorts of structures, due to new security codes, and if they would have to redo the plans, they would have put more stations instead.

I know that Montreal used the 'station on a hill', but are there others? With regenerative breaking (which I don't believe Montreal has but we will), it doesn't make sense to 'waste' generating capacity to gravity - unless you can get a bigget boost from the down-hill start.

Yes, I agree, the extra stuff will be expensive to install and run. The 60 metres of escalators alone are going to be expensive to run. I have in my mind that I've seen an estimate of about $550,000 per year for operating the stuff, but I might have dremt that. Has anyone else come across an estimated operating cost?

[Franky]

Originally Posted by Richard Eade

Yup, there are different levels of tolerance for going up and down. I think also, the consultant is trying to keep the grades at about 3% so ups and downs would be less noticable but it would take 333 metres to change 10 metres in height. Yes, it can be done. It is just not what is preferred.

A bunch of rail advocates keep telling me LRV can do 9% grades no problem. Either the salesmen are lying or somebody has a hidden agenda. Wouldn't be the first time.

Originally Posted by Richard Eade

There appears to be about 8-10 metres between the bottom of the canal and the sewer so, yes, it could be Cut & Covered across the canal. But where would you go from there? To the west isn't too much problem since there is a general drop of about 6 meters from Elgin to the canal surface. I am assuming you came along under Queen to avoid the NAC.

If you go under the canal, I imagine you could follow through to Daly and put a station near the rideau centre somewhere (near the new congress centre). The curve around waller to the transitway. Keep it short and simple and pop out for the University station or keep going further as you suggested.

My original idea was the BeamTrain route which would start elevating after University station, follow the route above, station on top of the rideau centre, bridge across the canal and into the hill near the NAC, bored tunnel with cut&cover stations to the west side, rest is the same.

Originally Posted by Richard Eade

But on the east side, where would you Cut & Cover to, since you would be pretty much just below the surface? The best option would be under Daly which might work. Assuming you can get around the point of the NAC with enough clearance that they won't be bothered by noise and rumble. There should be no piles supporting buildings in the middle of Daly so that shouldn't be a concern. Nor should the valley be a problem since you are not using a TBM.

Exactly.

Originally Posted by Richard Eade

East of Daly, out from under the Rideau Centre, I'm not sure where you would go at that depth. Presumably, you would find some way over to Waller (maybe just following Daly and turn under the green space at the corner) and to just get under Laurier and surface.

Seems right.

Originally Posted by Richard Eade

Yes, it could probably be done. Yes, it would be less expensive. It might not be faster, though.

Faster? To build you mean? Slightly faster because no mined stations are needed and they would be closer to the surface. I wonder if the cut&cover station debris can be sent out on the tunnel bore conveyor? Don't see why not.

[MalcolmTucker]

The Toronto streetcars might be able to do 9% (I believe I heard 10% quoted on the replacement RFP)

The LRVs Calgary uses max out at about 7%. Spec sheets I have seen for other models are pretty much in the 4 - 7% zone. that being said, I don't think many trackways are designed to test the maximum specs.

Usually stations are cut out before the tunnel is bored (digging down to a stable finished tunnel is a less logical work flowm for reasons you can probably imagine), so you can't really send the debris down the line. Anyways, if you did that the cut and cover it would only be for a short while or else you would say the station was mined out, no?

[Franky]

Originally Posted by kyle_olsen

Usually stations are cut out before the tunnel is bored (digging down to a stable finished tunnel is a less logical work flowm for reasons you can probably imagine), so you can't really send the debris down the line. Anyways, if you did that the cut and cover it would only be for a short while or else you would say the station was mined out, no?

You'll have to spell this last part out for us dunces. What "work flow reason"?

[p_xavier]

Originally Posted by Franky

You'll have to spell this last part out for us dunces. What "work flow reason"?

Because when you dig after the tunnel is finished, you risk more sending debris in the tunnel, thus causing some structural issues. When you bore when the stations are dug out, your tunnel is basically finished.

[Franky]

Originally Posted by d_jeffrey

Because when you dig after the tunnel is finished, you risk more sending debris in the tunnel, thus causing some structural issues. When you bore when the stations are dug out, your tunnel is basically finished.

Somebody wrote it didn't matter. The guy at the open house said the mining starts after the tunnel is bored, so it's not "impossible", it may not even be difficult to C&C the stations after the tunnel bore. Are air shafts dug before or after tunnel bore?