Now that I feel better after having had my rant, I figure I should try to make some positive contribution to the site.
I would like to know the purpose/how it works for much of what goes on beneath the rails and ties. The rock ballast that we see that is made up of fairly large rocks and is on the surface, what does that do? I have heard that it helps the track keep its allignment, and helps with water drainage? Is it just the weight of the ballast on the side of the ties that holds the allignment? If it is more, please, do tell. Also, how does rock on the sides of the ties help with water drainage? Is there any other purpose?
Part of my confusion is, I remember reading a Trains article on the Blue Mountain and Reading ten years agao wherein the comment was made that the addition of ballast raised the track level 3 inches (good article by the way). Yet, when I see track laid, it seems like the ballast is put in after the track is in place.
I think I have seen road bed being laid on smaller rock (NS coal spur), blacktop (Transcon), and mounded dirt (Illinois Terminal main). What are the differences? When they lay the ties on dirt, do they generally try to take the top soil off first?
Are there any other significant aspects of road bed that have a major impact?
MC will, of course provide the definitive answer, but here’s a few points that I can recall…
A key feature of whatever is used for ballast is that it “interlocks.” That’s why you won’t see pea gravel used - It would just “squish” out. The rough texture of the crushed stone does the interlocking. Cinders do a nice job, but don’t have the hardness of rock.
Drainage, as we discussed a while back, is a HUGE factor. Ditching, culverts, you name it. MC will have to talk about the rationale of how high the ballast should be on the ties.
From what I’ve seen of trackwork in progress, the track structure is often built on the subgrade, then ballast is dumped over the track, after which the track is jacked up so the ballast falls through and under the track. Coverage of this year’s flooding on the Mississippi mentioned that at Fort Madison, BNSF had raised their track some two feet - I’m sure that’s how. When I saw it, they were jacking the track using jacks - I’m sure there is a mechanical method using on-track equipment.
We discussed the whole asphalt thing a while back, too. IIRC, it adds to the general stability of the entire structure and helps keep “fines” (dirt) from working up from below. Rock ballast is still used on top of the asphalt.
As for the title of the thread - dirt in the ballast is actually a bad thing as it undermines the stability of the ballast and hurts drainage. That’s why railroads are employing “ballast cleaners”. IIRC, coal dust is proving to be a problem on the Powder River lines.
I don’t think Gabe actually meant that he wants “dirt” on ballast, rather, he’d like the “scoop”, “skinny”, “411”, etc. on ballast. But, with his admitted low I.Q.; which I highly doubt, by the way, I suppose I could be wrong. [;)]
Yes ballast is important, it helps water drain through and can pretty much keep everything stable. On a modeling note, it certainly makes things look better.
The MILW used to use pit-run gravel in many spots. Those places are very poor now.
Cinders decompose after time. Some roads used cinders for fill material. They were free, just had to get them to the fill site. After a while, the cinders would break down, and a dip shows up in the track. So the road foreman would dump more ballast there. The added weight pressed down, and the cinders would give way more. Not a good deal.
This is a large subject - would take at least an intensive 1-day seminar to cover it in comprehensively - but here’s at least some of it:
The rock ballast up high between the ties bears against the sides of the ties. That does a couple things: 1) By being in the way and locking together in place, it provides resistance to help keep the track in place and not “run” longitudinally as it sometimes does under rail traffic - esp. 1-way or downgrade - and/ or from temperature expansion. 2.) Likewise, it provides resistance to any motion of the ties and track laterally, such as to get out of alignment fomr rail traffic on curves and sun kinks. The ballast against the ends of the ties does that, too, but if I recall correctly the ballast along the tie is more important. For example, a 7" thick x 9" wide (“#5 size”) x 8’-6" long wood mainline tie has only 7" x 9" = 63 sq. in. of area on each end = about 0.45 sq. ft. to resist the lateral motion, although that area can then engages a much larger wedge-shaped portion of the ballast shoulder. (I would have to sketch and calculate to give you an exact figure, but a quick estimate would be not more than the tie spacing horizontally - because the adjoining ties will be doing the same thing - x about 1 ft. vertically, so say about 2.0 sq. ft.) However, the sides of the ties - and both sides count for lateral restraint here - are 7" = 0.58 ft. high x 8’-6" long = 4.93 sq. ft. per side = 9.85 sq. ft. total - more than 20 times the area of the end of the tie. Similarly, for longitudinal restraint, the area of the side of the tie - here, only 1 side counts - is again 4.93 sq. ft., compared to 2 ends at 0.44 sq. ft. each = 0.88 sq. ft. total, or about 5.6 times as much area.
Another - and probably not appreciated - function of the deep ballast stone is to add weight on top of the stone underneath, lower down on the tie and underneath it
Please keep the dirt off of or in my ballast. (Don’t you dare foul my ballast.[swg])
Wait till Gabe finds out that there is sub-ballast under the 3 1/2’’ stuff and that the harder the stuff is, the better (why basalts trump limestone, degradation is not a good thing) Maybe Gabe ought to see how ballast can eat the side of the tie he doesn’t see by purely mechanical means.
I really like you, so I am going to try to resist my natural inclination to . . . well . . . I don’t get it . . . why? I was just attempting to inject some levity with a serious topic via I though a somewhat learned pun. My wife hates my puns, and I am sure she is laughing at my befudlement right now.
Still, I don’t think I would have qualified anything you have ever wrote with “poor”–even if you started a thread on white box cars. Sorry, if it was that bad . . .
A couple of years ago, Golden Spike needed a lot of new ballast which was obtained by some government purchasing agent somewhere. We got gravel instead of ballast. The size was right but the rock were mostly round (river run). It didn’t hold at all. This year, we let the rail contractor purchase the ballast and the track looks better and holds shape much better. We don’t have drainage issues (we rarely get rain) but we have a lot of foot traffic on some of the ballast and those round rocks rolled everywhere.
As he notes, one of the main purposes of ballast – besides holding track alignment and yet allowing some ‘give’ to the track – is to spread the load of the train over a larger area of soil. As he also notes, the engineering involved there is a bit complex (and gets really hairy up where I used to play, in the muskeg!) but the basic point is that, in general, ballast can withstand much heavier loads than the underlying soil, per square foot. Also in general, the worse the underlying soil, the more ballast (wider and thus deeper) is needed.
But… only if it is clean. If it gets dirt (we seem to keep coming back to that!) in it, two things, both bad, happen: first, the dirt holds moisture. Bad, when dirt is present, as wet dirt is slippery… Second, the dirt, if there is enough of it even if it is dry, reduces the ‘lock’ of the ballast stone to itself, and thus the load capacity.
One way to avoid such problems is to periodically clean the ballast, which is exactly what it sounds like (and the machinery involved is fun, if noisy, to watch). Another approach is to put something between the ballast and the underlying soil; on the Transcon asphalt is being used, as Gabe noted. In some areas, engineering fabrics which permit drainage but not movement of soil particles are used.
In 1903, the owners of the lumber company I work for moved their lumber yard off the Milwaukee Road line, to a spot they purchased where the Milwaukee and The Rock Island crossed. That way, they could receive lumber and coal from both railroads-very smart on their part. Being thrifty, the parcel they bought was a marsh along the river. My old boss, the son of the 1903 owner, said it was nothing but a shanty-town/red light district.[:O]
Upon purchase of the land, they proceded to bring it up to grade the cheapest way they could. They filled it with cinders and ash from the railroads. 105 years later, we have all kinds of old lumber and coal sheds that are sway-backed and droopy. The existing rails on 2 sides of the property still look pretty good.
Ballast is all about providing a stable medium for the rails and ties to sit in to carry the trains. There needs to be a sufficient amount to provide a way to distribute the load uniformly to the sudgrade (depth below the tie), ensure lateral stability (between the ties and on the shoulder) and it has to drain well.
The three most important things needed for good track: drainage, more drainage, more and better drainage
In Paul’s description of how track is built/raised/tamped, the next thing to consider is that even with several passes of the tamper squeezing rock under the ties, it is still going to go down when you start running trains over it. That is why you typically see a slow order on the track after such work until a certain amount of tonnage has gone over it, the track has been inspected and then, if okay, a higher speed is authorized.
On the heavy density lines, this is tough to live with so the railroads may go to the additional expense of a dynamic stabilizer which vibrates the whole track structure to duplicate trains running over it. Various numbers of passes equal X million gross tons of train traffic and you can get your track speed raised quicker.
Also, the resource for ballast specifications is the AREMA (American Railway Engineering and Maintenance of Way Association) Manual for Railway Engineering, Chapter 1. This is where the various gradation of rock sizes are listed (after many, many years of use of different variations and testing, there are just a few recommended gradations) along with material testing requirements. All very technical, but once a quarry is set up to produce rock for a railroad, they usually can continue to doso for many years, so long as the quality of the rock they are quarrying is consistent.
Resist transverse or longitudinal displacement of track under dynamic (train) or thermal load by absorbing transverse and longitudinal loads and transferring to subgrade.
Drain water away from track structure to minimize frost heave and water-influenced deterioration of ties, rail, and OTM.
Provide fluid medium that enables track to be economically maintained to correct cross, vertical, and horizontal alignment
Resist vegetation growth
Provide inexpensive method for track to be brought to correct cross, vertical and horizontal alignment regardless of variations in subballast or subgrade when constructed.
Distribute load onto subgrade without overloading subgrade.
Provide consistent-resistance insulating medium that enables track circuits to be properly tuned and to function.
All three come under the heading of “subballast.” The purpose of subballast is to distribute load from the ballast to the subgrade, drain water away from the subgrade, and prevent earth from working up into the ballast layer and clogging the ballast. On a low-capacity line with low capital availability, subballast may be dispensed with (your IT example). The railroad pays later with higher track maintenance costs, slow orders, reduced line capacity, reduced weight capacity, and higher train operating costs. Asphalt macadam is being used in some instances instead of the usual crushed rock and roller-compacted subballast. Not everyone is convinced it’s a good idea in all environments, but in a hot, dry environment it appears to work just fine. It can be much expensive than crushed rock subballast in some regions.
I was about to razz RWM on points #4 and #6 being redundant, but noticed that 6 was in regards to initial construction and 4 was in regards to maintenance. Pretty much the same process and equipment for both.
This is a very subtle and important advantage of railroads in comparison with roads. As an example, part of Calif Highway 52 was laid over filled in portions of the Miramar landfill, and the road gives a good approximation of a roller coaster ride. Fixing the dips would require tearing up the road (they’re a bit too deep to level by adding asphalt), where a railroad could simply drop more ballast and raise the tracks (e.g. the SP raising the track on the Great Salt Lake fill in the mid-1980’s).
This is likely a huge advantage for High Speed Rail over mag-lev technology. While the mag-lev guideway will probably require less day-to-day maintenance than a high speed rail line, there will still be problems with the earth moving under the guideway, and that will likely be a royal pain to fix.
Gabe, unless I have misunderstood both what Larry posted and his character, or unless I have missed an in-joke between you both, I believe his statement was a self-deprecation…not a lash at you.