What's the construction (ties? cement foundation? ...) for street-running railroad segments?
Example (turn down volume before clicking):
https://youtu.be/2X8rEckbdjg?t=79
https://www.youtube.com/watch?v=UoQczWetlRw&t=859s
Never too old to have a happy childhood!
Totally depedendent on train frequency and tonage, traffic density, overloaded trucks, intersections, vehicle speeds and environmental factors (esp drainage)...
There is no one size fits all solution.
mudchickenThere is no one size fits all solution.
I'm surprised by several aspects of this in a section of track that would be difficult to service.
1. Using joint bars instead of welding track.
2. Wood ties where drainage could be a problem. I didn't see any dedicated way to drain the railbed.
3. Ballast base where it would be difficult to tamp.
Perry Babin1. Using joint bars instead of welding track.
They may be insulating joints for track circuits.
Perry Babin2. Wood ties where drainage could be a problem. I didn't see any dedicated way to drain the railbed.
Unless there's a high water table or a known drainage issue, wood ties will be fine. They are a known quantity. Concrete is fine until it's not (ie, breaks).
Perry Babin3. Ballast base where it would be difficult to tamp.
When they rehabbed our line, they tamped it at a class higher than we will be using it. I'm sure they are doing the same.
Larry Resident Microferroequinologist (at least at my house) Everyone goes home; Safety begins with you My Opinion. Standard Disclaimers Apply. No Expiration Date Come ride the rails with me! There's one thing about humility - the moment you think you've got it, you've lost it...
Perry Babin I'm surprised by several aspects of this in a section of track that would be difficult to service. 1. Using joint bars instead of welding track.
Those joints are probably temporary. Typical procedure when replacing track with new track panels:
1.) Cut existing track into pieces short enough to move easily with the equipment you have on hand, by torch cutting the rail. You can see the removed track stacked up off to the side in the video.
2.) Once the old track is gone, remove as much of the ballast as you want, and make sure that what you have is relatively smooth without big humps or dips. How deep to dig depends on track and drainage condition, but you at least have to get down below the loose rock into stuff that you can run equipment over with it rutting up too much.
3.) Place new track panels in place. Bar them together.
4.) Dump ballast. If you've got all the joints barred up, the track should be perfectly usable at walking speed, so you can do this off-track (using an end dump as shown in the video, or a loader) or on-track (from a high-rail end dump or directly from ballast cars). Use whatever off-track equipment you've got to knock down any big piles of ballast to below the rails. When dumping directly from a ballast cars, this may be done during dumping with a retractable plow on the bottom of the car or with a crosstie on top of the rail moved along by the wheel of the car. Do this step wrong and something will derail.
5.) Run the ballast regulator through a couple times to get the ballast evenly distributed.
6.) Run the tamper through to give the track a first lift.
At this point, you may be ready to run a train or two at low speed if desperately needed, but more typically you've repeat steps 5, 6, and possibly 4 a few more times, then move on to:
7.) Use the regulator to dress the ballast and broom off the ties.
At this point, at least when I was a track construction supervisor, we would usually apologize for overstaying our window, clear off the track, debrief, write a report explaining why we overstayed the window, and go home for the night. (In theory, you could start welding up some of the joints if you have time.)
Next day (or two days later), surface it one more time. Follow that up with several days of welding all the joints and destressing the track (i.e. getting the rail in the right state of tension so that it won't buckle in extreme heat).
For a long street-running section like in Lagrange, that road is probably closed for a week or more.
Three reasons for barring up the joints and saving the welds for last, in order of importance:
- Barring is much quicker, you can start running trains sooner
- The destressing process involves removing or (rarely) adding rail. You want to leave some joints in place until you're done destressing, otherwise you wind up having to go and cut your brand new rail anyways and do additional welds. You don't destress until the rail has been brought to it's final surface, because taking crooked, bumpy track and making it smooth shortens the rail and reduces the tension, thereby undoing your careful efforts to "destress" the rail into just the right amount of tension.
- If your ties are spaced well (not a problem for the joints connecting track panels together), welds are easier to do on smooth, surfaced track. When you weld stuff together out of track, you have to do more shimming to get the rails to line up exactly right.
Drainage is definitely a problem for embedded track. Watch a new light-rail construction project in the street and you'll see all sorts of storm drain infrastructure installed to keep the track drained. That was not the state of the practice when the track was laid through Lagrange, and it's costly and VERY time-consuming (in terms of track outages) to retrofit. So you just accept the fact that everything will degrade faster and you'll have shorter asset life.
BUT... compared to concrete, timber ties actually perform better in areas with drainage problems. This is primarily because a poorly-supported or unevenly-supported timber tie will bend and flex, gradually accumulating fatigue damage, while a concrete tie that tries to bend will crack and expose the prestressing tendons, which can then corrode in that wet, muddy environment. A secondary factor is that concrete ties tend to impose higher loads in the subgrade, which may cause the subgrade to fail faster if it is wet and therefore weak.
Hence why street-running light rail tends to use ballastless track. But it takes far too long to build track like that for an active freight rail line. (As far as I know, there aren't any ballastless track systems proven to work well with North American axle loads at faster-than-walking speed... although that may be a bit of a self-fulfilling complaint.)
Dan
Additional video
To fellow field engineer Mr. Peltier, THANKS!
(#3 Comment: pre-cast Pac-Trak is a bear to properly set-up even in a crossing situation. Doing that for street running would be an absolute nightmare)
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