Western Railroad Discussion > Where does the ballast go?

So, running across some MOW threads...how much ballast is removed, destroyed or otherwise "displaced" to required some heaving dumping of new ballast with MOW work?

I have seen pictures of what was described as routine track work, but requiring a few cars of ballast to be dumped. The before and after pictures appeared that the grading was the same.

Unless ants are walking off with rocks...

?

Over time the rock breaks down into smaller pieces and fines, this reduces the ability of the ballast to transmit the load from the ties to the subgrade, it also cause more water to be retained in the ballast layer lead to tie rot and in colder climates to frost heaves during winter. So when a ballast undercutter comes throught the ballast is passed through a screen and any pieces that are too small are discard to the side of the ROW.

Indeed, the above explanation covers it quite well. If you beat on rocks long enough, they become smaller rocks, smaller rocks become sand, sand is not as useful for holding track.


TCS - lather, rinse, repeat

And to add to it, the cars weight is more now and it needs to be wider and deeper then 20 years a go, so just add more till its higher and wider. And it ends up getting pushed down over time to.

I figured that was most of it, just not by the amount of rock that I have seen bought in an dumped to replace said pebbles..

This article may be of help:

http://en.wikipedia.org/wiki/Track_ballast

Fred Harrison
Central Point, OR
CORPpower/JSS/EORS

Sometimes the subgrade (the dirt, clay or fill part under the ballast) sinks and the ballast is tamped (crammed) under the ties to raise/level the track properly. Rocks, dirt, gravel, and even cinders were used as fill in low areas. In some cases, as with old roadbeds built a century ago by cash strapped fledgling railroads, shortcuts were made in the subgrade. Old logs and tree stumps were sometimes used by contractors when railroad officials were not monitoring closely. If other factors, such as springs, creeks, etc, were mitigated properly, the afore mentioned fill material was usually sufficient. In perpetually wet areas and areas with poor draining clay, the continuous up - down motion of the track could cause pumping. Moisture and mud will actually get sucked up from the subgrade and 'contaminate' the ballast. This further reduces the ballast's ability to stabilize the load and it's ability to drain properly. There have been successful experiments where an asphalt 'road' is laid down on top of the subgrade and the ballast (1 1/2'-2 1/2') is laid directly on top of the asphalt. Sheets of barrier material (kind of like a big roll of plastic) have been in regular use for years in attempts to drain rain away, and keep subgrade mud from pumping up. Aside from mud, other things can contaminate the ballast, like coal dust in the Powder River Basin, causing derailments. Periodic cleaning and adding of material is necessary.

There are places North of Westwood CA, on the BNSF Gateway Sub. that get a dose
of ballast and a tamping at least 3 or 4 times a year !! Mind you, this has been
going on since the rails were laid down by the late, lamented WP !!!

DaveL

TopcoatSmith Wrote:
-------------------------------------------------------
If you beat on rocks long enough, they
> become smaller rocks,


"Back on the Chain Gang" -- Chrissie Hynde

BobE

A lot of trackwork is an upgrade: wider ballast shoulders to better restrain welded rail, deeper ballast under the ties, etc.

As the above explanations note, ballast gradually gets crushed and is "fouled" with the fine particles.
When we excavate a track section it is like archeology: various layers of ballast through the years, getting smaller the deeper you go, until you get to the native soil. On some SP lines you can find copper slag, steel slag, granite from Logan, and green rock from Ione, and more.

Laying ballast on pavement?--this has been advocated for the Metro Orange Line in the San Fernando Valley (section of Los Angeles). Metro took over the SP Burbank Branch, removed all the track, and paved it over for a busway, much to the displeasure of local rail advocates. So it's not too farfetched to envision a light rail line built on top of the busway asphalt, but it's still in the "I should live so long!" category.

Though there is no real substitute for a subgrade constructed with suitable, compacted, well-draining material, when applied properly, asphalt pavement has proven to achieved the desired results in main line heavy axle load conditions. http://findarticles.com/p/articles/mi_m0BFW/is_1_98/ai_82134975 What politicians, and other 'public servants', will do with their taxpayer's dollars is anyone's guess.