How well does the 'slab track' ballastless model hold welded rail in place as Moms Nature plays ambient temberaturs like a slide trombone?
Never too old to have a happy childhood!
mudchickenDRAINAGE-DRAINAGE-DRAINAGE
I thought that was Trump's line.
Norm
BaltACD mudchicken (*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch! In accordance with M/W Rule #1 is Rule #2 - all ground is not the same.
mudchicken (*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch!
In accordance with M/W Rule #1 is Rule #2 - all ground is not the same.
Waiting for Island Man to start singing the praises of PTC. ...Broad brush, "pie in the sky" approach is a very dangerous approach in this industry.
Jerry Rose will tell you about the fails along with the successes. (he's an AREMA fixture, especially with one of my committees.)...
Going back to the concrete tie analogy, you ought to see what happens with unconfined slab track in tension
Slab track is most commonly seen in at-grade road crossings and the results there are mixed. (Indiana DOT is in lust with it)...the fails aren't pretty and as stated above the subgrade is usually the culprit. Trying to add things like asphalt subgrades and geomats only drives up the cost$ and lengthen$ the proce$$.
mudchickenRailroaders M/W Rule #1 - Mother Nature Is A B__tch!
MC,
Based on what I learned from my (now retired) track foreman friend you are spot on. The Spring thaw was the worst in his opinion. Thaw/freeze/repeat wreaked havoc on the track. My having an interest in MOW and following his crew resulted in my gleaning a bit of knowledge. I still have far to go to catch up to what that man knew by heart. He hired on at age 18 and retired at 60. Took a lot of knowledge with him when he left. Waiting to see how the new track foreman performs, and so far the crossing repairs are not a good indication of his performance.
I'm sitting by waiting for indications of improvements. Signal maintainer friends say those improvements may be in the offing.
Asphalt under conventional ballast has been in use for many years. The following link gives the results of tests performed on asphalt sub-bases of various ages:
http://www.engr.uky.edu/~jrose/papers/Hot%20Mix%20Asphalt%20Railway%20Trackbeds.pdf
It perhaps depends on how near the surface the asphalt layer is. On a highway the asphalt is inherently exposed to the sun and is the perfect color for absorbing solar radiation! Under a couple of feet of crushed rock, or one-ton slabs of concrete, the asphalt will be protected from the sun, from UV and from extremes of temperature. Temperature change will also be more gradual.
It may be easier to adjust an asphalt-based system than one based on OPC. Some forms of concrete do reach maximum strength quite quickly, e.g. concrete based on calcium sulfoaluminate cement.
Top-down construction gives excellent results though like most ballastless track design it is aimed at producing very high quality track for high-speed lines. For freight lines with a design speed of <100 mph something simpler to build and cheaper might be better (Tubular Track seems about right).
If ballastless track starts to become more common it will be used for new construction, multi-tracking of existing routes and really deep reconstruction of existing lines, i.e. the sort of situation in which CWR with concrete ties is used at present. Short lines and regionals would probably stick to conventional track with spot replacement of ties, use of relay rail and ballast cleaning and tamping.
mudchicken(*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch!
Agree with PDN 200%
Might not be a big deal laying down slab track, but trying to get the S/G to near perfect grade and surface is going to eat your shorts.
With concrete ties, the subgrade had better be solid or you dig up half of your R/W in CO and NM like BN did in the 80's & 90's . (DC & I can remember the ATSF headache/disaster at and along the El Dorado KS line change, including a section of PacTrac/Slab track when the subgrade liquified under tonnage and multiple attempts at fly ash stabilization.)
OP bought the hype - hook, line & sinker. Slab track has a place (usually over relatively short distances), but it's hardly a universal option. IM might want to look at the documented fails in the AREMA proceedings, at the AAR/TTC test track fails & successes and ask himself how he is going to adjust that slab track after Ma Nature* decides to not play by the designer's rules and tonnage physics comes into play.
(*) Railroaders M/W Rule #1 - Mother Nature Is A B__tch!
Weak, marginal, or too-variable subgrade bearing capacity - including expansive soils, and the heavy loads, high impact, and vibrations caused by US railroad equipment at speed, are severe challenges to any of these systems.
Concrete ties - a good idea with some valid benefits - have demonstrated the sometimes-truism that "Every advantage has a disadvantage". A lot of money and faith was put into them, only to find out some years later that abrasion under the rail seat was causing wide gage and stability problems - and this weakness is ongoing. Not enough to completely negate their added value, but definitely a tarnish on it.
- PDN.
tree68A sub-roadbed will still be required. It's not going to be like putting together snap-track on your dining table.
Part of the premise is that all the necessary subgrading can be done continuously without 'finish precision', ultimately using good HA differential GPS to do finish grade directly with the field machines. MC has commented on this before, and I hope will do it again here...
Another part of the premise is that automated tracklaying has now become a reasonable specialty, with companies able to supply both equipment and know-how in the way Rcrane can for bridges. But much of the equipment is just as 'happy' working with panelized stick track as it is with slab or fixed track systems, and as tree68 noted much automated track machinery works well at periodic line, surface, and maintenance in ways that might be more cost-effective overall than the equivalent for fixed systems that suffer subgrade problems, environmental damage, etc.
The replaceability will also be a factor. With a few gons worth of ties, some track, and some associated hardware, a line laid with wooden (or concrete) ties can be back in service in literally hours, given the appropriate machines, etc.
You seldom see the slab=track proponents discuss this; they like to concentrate on that 40 to 60 year 'life' without mentioning that there are things other than normal wear and tear that can damage track and grade structure...
Since I have been interested in this area since the early '70s (before getting out of high school) I'll jump in.
IslandManMany designs require a top-down method of construction in which the rails are held in the correct position while concrete is poured underneath to form a slab.
Both IVES and PORR are inherently top-down systems - but is there something supposed to be wrong with that? The Amtrak testing of Class 9 track was a bit more intensively top-down (geometry being much more critical for very high speed) and for a system intended to have zero or low maintenance in line and surface for many years, getting the geometry correct at the actual railheads and adjusting the support accordingly seems like highly sensible methodology.
I participated in one of the early 'asphalt in railroad construction' competitions in late 1975 or 1976, in which continuous paving of properly-subgraded ROWs figured largely as a design alternative -- the problem being that whether or not you think 'dowel pins' and heavy weight will keep the track laterally aligned, once you get a good hot day that asphalt layer can bite you. (I believe there were sections of the Transcon that were built using asphalt in the subgrade, as a sealing layer not dissimilar to its function in 'tarmac' roads, and when these got up to liquidus they sun-kinked like nobody's business...) This led me to discard asphalt comparatively early and look at some combination of RCC, concrete and tremie as a better solution to more 'permanent' alignment.
There was a sort of renaissance of investigation into actively sprung/suspended track at around that time, looking back into the German experiments just after WW1, and I thought at the time that very-high-speed track would require some form of suspension to be capable of absorbing all the reflected energy without permanent distortions or excessive resonance reflection back into the vehicles. This used a slip-cast or sectional trough, with appropriate reinforcement, post-tensioning tendons, etc. (with the ability to mud-jack the sections if needed to overcome earth changes) and continuous beams with elastomer and clamps for each rail and adequately robust gauge holding. The 'suspension' allowed at least some of the differential expansion in welded rail to be accommodated; lateral thrust was handled with elastomer between the running beams and hardpoints cast in the troughs. The beams were to be top-down aligned, and the suspension contact/support points were to be tremie'd in a manner similar to the PORR sections (although with much less volume of pumped concrete!) and only these comparatively few points would have to be adjusted to keep the track beams in correct line and surface if the trough settled or twisted.
I have liked the idea of the Tubular Track for many years, since I first saw it demonstrated in South Africa. It has an advantage in that trespassing anywhere near the rail, or crossing the lines, is extremely difficult! A potential problem with it, though, is that the gauge beams seem susceptible to damage from derailments or some kinds of dragging equipment, and I think it is particularly important to recognize all the potential drainage issues; perhaps more appropriate for North American use, the grade-crossing issues can be severe (compare the problems with road regrading in Biloxi, for example). I'm a bit surprised that some of the projects now being built with NTC machines haven't used this construction, particularly for projects that will have high-level platforms.
A sub-roadbed will still be required. It's not going to be like putting together snap-track on your dining table.
In the end, it will come down to dollars and cents. If the cost is less than conventional track over some period of time, it will gain acceptance.
Having to dig out and demolish a section of this stuff would probably put a line out of service for days.
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...
For 40+ years concrete slab track has been used in tunnels, for example to gain extra height for overhead wires when existing lines are electrified. It is also used extensively on light rail projects. Ballastless track has a low regular maintenance requirement compared to conventional track, especially for high-speed lines and tracks subject to fouling by drifting sand.
Ballastless track is expensive to install. Many designs require a top-down method of construction in which the rails are held in the correct position while concrete is poured underneath to form a slab. If a cheaper form of ballastless track were to become available it might become a serious competitor to conventional track.
The two links below might be of interest:
http://www.railengineer.uk/2014/06/24/asfordby-tunnel-trials/
https://www.railengineer.uk/2014/04/22/sand-ballast-dont/
The IVES system in the first link and the Tubular Modular Track in the second *might* become competitors to conventional track for new lines and for multi-tracking existing routes. In both cases, an asphalt base can be laid with adapted highway machinery and the prefabricated concrete slab/tie (IVES) or longitudinal concrete bearers (TMT) laid on top. Using asphalt and prefabricated concrete components should speed up construction rates (compared to using wet concrete).
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