The deleted Language thread did teach that ballast "does not require lubrication, and its values include being unaffected by water, unless sufficient for a washout. Apparebntly, thisc was new knowledge to some readers. A deitailed discussion on this specific topic would bw helpful, including the cinder-ballast used for economy, etc.
What thread was that?
"Ballast" requires no more lubrication than muffler bearings do. And its being 'unaffected by water' presumes very careful, and very carefully maintained, drainage arrangements.
In fact, proper drainage goes way down into the subgrade structure, to make sure both that liquid doesn't "get where it shouldn't be" and that, if it does, it can be diverted without causing any of the material to settle, shift, or become displaced.
The issue with 'lubrication' in the water thread had exclusively to do with hydrostatic pressure "levitating" ballast particles under relatively rapid and severe loading -- the hydrostatic pressure peak will cause the ballast rocks to move apart from each other, and shift unpredictably, and repeated peaks may cause the ballast alignment to shift (or to provide improper support in different planes for the track structure itself). This is only more pronounced when fouling with fines or other material holds the 'incompressible' water in the spaces between the ballast rocks.
I'll leave it to one of the practicing and experienced civil engineers like diningcar to write a discussion of best practices in subgrade, grade, and ballasted track construction and maintenance.
I'll leave it to one of the practicing and experienced civil engineers like diningcar to write a discussion of best practices in subgrade, grade, and ballasted track construction and maintenance. But I ruefully note one seemingly very promising solution that turned out Not To Be Particularly Effective.
In the mid-Seventies, when I was involved in the transportation program at Princeton, the asphalt industry sponsored a student competition involving effective uses of asphalt and asphalt-bound aggregates in the railroad industry. Rather obviously this would have very little to do with anything involving modern track structure, especially at grade crossings -- but it did occur to me that a very useful thing would be a somewhat self-healing hydrophobic layer between grade and subgrade, keeping any water from invading 'lower' and directing it instead to the drainage system. (This is an application that I believe geotextiles are now used for).
When this was tried on a Western railroad, I believe UP, it worked just as swimmingly as expected -- until local heating conditions softened the asphalt down in *** bed. It partially liquefied, and became a more or less excellent lubricant -- for transverse shifting, including the sort of thing involved in sun kink. As I recall, some of the results were as spectacular as they were unanticipated, rapid, and disassembling...
I'm wondering if the main problem with asphalt between the grade and subgrade is that if the asphalt is too hard, then you lose shear strength between the grade and subgrade.
The problem was very much that the asphalt became much too soft, and that produced the loss of shear strength between grade and subgrade.
As I recall, there was some thought given to 'keying' the subgrade via some kind of RCC compacting with wavy rollers to solve any potential problems with the asphalt becoming excessively hard in cold weather. Whether that was done in practice, I have no firsthand knowledge.
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