With all the bigger clearance projects going on here in the east I’ve often wondered exactly how much clearance do you need/get? Are we talking 6" on top, more on the sides? I would think that top clearance can be closer as rail cars may rock side to side but very few jump up and down.
John
Someplace I have copies of the proposed cross-sections of the ex-PRR tunnels at Gallitzin and Tunnel Hill, about 6 miles above/ beyond Horse Shoe Curve - when I can get hold of them, I’ll let you know the details of what ConRail did to them. The usually westbound now 2-Main Track Allegheny Tunnel was widened from 1 track and raised considerably, with a new circular arch installed. The usually eastbound single track New Portage Tunnel I’m not so sure about, as there the track had been moved into the center of the former 2-track bore some years before, so maybe the work there wasn;t as extensive.
When the clearances are improved by the ‘roof notching’ method as NS recently completed with many of the tunnels on its Heartland Corridor route, the clearances created are not so generous, as every additional inch is extremely expensive and runs the risk of getting into a total rebuild of the tunnel liner. I recall they can be as little as 6’’ above and outside of the upper corners of a double-stack, but again that’s putting a lot of faith into my memory . . .
It would be interesting to compare those with what UP just finished to the tunnels Doner Pass Route.
Keep in mind that the ‘maximum train’ would have 2 ea. 9’-6’’ high domestic containers stacked in a well car, so I’m recalling a basic train height of 21’-0’‘, and maybe 22’-0’’ for the top of the clearance envelope.
All of the above clearances are positively parsimonious when compared with what the Southern did to the CNO&TP’s ‘Rathole’ line’s few remaining tunnels for clearance back in the early 1960’s - something like 30 ft. to allow for possible future taller equipment and electrification, etc.
Here’s a link to a diagram from the NS Heartland Corridor Project that has diagrams of 4 different car types/ container combinations, and their height and the required clearances for them. The common factor is that in all cases 6’’ is provided for clearance above the top of the car - the highest of which is 20’-3’’ for a pair of 9.5’ doublestacks which requires a clearance of 20’-9’’ - and the High ‘Q-Car ‘Multi-Levels are only 1’’ less.
http://www.thefutureneedsus.com/latest-news/lightbox/160/
Now let me see what I can find for the side clearances. You’re right about side-sway from super-elevation, other minor-out-of-cross-level track conditions, springs, worn wheels and other car parts, etc. are likely to cause more variation in horizontal position and clearances at the top of the car than any vertical phenonmena.
Paul,
I haven’t had tome to read the information at the link, but I agree there should be tolerances for ‘out of level track’, etc. Notches may be helpful but I will rely on more informed opinions than mine. Just my humble, but I think vertical and ‘sway’ clearance would have to be considered by the civil engineers.
The ol’ mind is a little slow this morning - what we’re really talking about here is known as the ‘‘Dynamic Clearance Envelope’’, which is the space needed for a moving equipment while allowing for all of these possible influences - plus curvature, an ‘air gap’, etc.
This is one of those things where the proverbial drawing is going to save a lot of words - the link above has very few of them, and is just really a single diagram. Elsewhere on that site - http://www.thefutureneedsus.com/latest-news/media/category/heartland-corridor/ - are lots of photos. As you’ll see, the notches are in the upper corners of the rounded portions, and do allow for those motions.
Here’s another link to the ‘‘Proceedings of the Rapid Excavation and Tunneling Conference - 2007’’ at Google Books. The portion pertinent to this discussion is on page 1153 under Preliminary Investigations, where the proccess that NS used to develop its clearance diagram is described in an article titled ‘‘Heartland Corridor Tunnels’’ that begins on page 1152 :
And with all that careful planning for clearances…
Along comes the tie and surfacing gang and in tamping in fresh ballast raises the track 2 inches.
[swg] Oh, yeah . . . Sometimes it is indeed ‘‘Forgive them, Father, they know not what they do . . .’’. Which is precisely why one of the signs on the left side of the portal in this photo (not mine) - says:
BEFORE RAISING
TRACK
CALL DIVISION
ENGINEERING
http://www.railpictures.net/viewphoto.php?id=175249
But at least for NS’ Heartland Corridor tunnels, it should be a good while before that has to happen - I understand that the last major work was to basically replace the entire track structure, to get out all the debris th
About the time that double-stacks came into service, the former CA&E bridge over the C&NW Omaha main at Wheaton was found to clear the tops of double-stacks by two inches. Needless to say, a 10 MPH speed restriction was put in the Special Instructions. Several years later, the bridge, which is now part of the Illinois Prairie Path, was raised several inches to allow the restriction to be removed.
6" is typical and provides some cushion. Conrail dropped the tolerance to 4" when they started moving domestic stacks. There were places like the tunnel under West Point where it would have been very difficult to get 6" of clearance.
(1) Usually preceded by the knuckleheads in the operating and mechanical departments OK-ing loads that won’t fit what the roadheader carved out. The results can be expen$ively comical. Tell-tales and sensors don’t catch-em all of the time.
(2) you can pour/pump all the grout in the world and never fill the voids behind the tunnel liner (learned that lesson more than once)
(3) the tunnels I worked in 1989-90 cleared a 19-6 stack train by 4 inches. BNSF went back in later and added another foot, including cutting out and replacing several steel sets. Not cheap, but necessary.
Don’t be surprised is they go back in in the next few decades and open them up some more. The next new container / railcar will dictate the economics of that.
(4) Never completely trust what the geologist tells you.
Thanks for the answers guys.
I remember that one…don’t think it took “several years” to lift the restriction. It only involved raising one end (the north end) of the truss and putting some support under it. They were relieved at the time that no further work needed to be done to preserve the integrity of the Prairie Path. Right now, though, the bridge is closed again while they work on the structure to the north of the track (it was a smaller bridge utilizing the CA&E piers). The truss over the tracks appears intact, and I don’t know whether it’s involved at all. The old truss bridge for vehicular traffic, a short distance to the west, has been torn out and will be replaced by something with a higher weight limit.