Why are train tracks always lined with gravel?

Question

with the exception of at railroad crossings [where cars pass over the tracks], train tracks always seem to be surrounded or lined with gravel underneath the tracks and on a few feet on either side. you don't see tracks laid on top of cement or dirt or sand or grass or asphalt... always gravel.

anyone have a logical explanation?

Answer 1

Im guessing cement would just crack anyway

Answer 2

Ballast is exactly right and for the reasons stated and a few more.

As rail heats and cools there is a lot of expansion and contraction, the ballast is there to hold the track from moving.

Crushed rock works best as it has countless sharp edges form the broken rocks that actually dig into the sides and bottom of the ties and hold it in place.

when the track moves and shifts, which is does constantly it is a relatively simple matter for the track crews to move it back into position. In the "good old days" it was done by hand, now by machines, but exactly the same way, pick the track up, put it where it belongs and tamp the ballast back in.

With a gravel ballast system, when ties need replaced it is also realitively easy, pull the spikes, push out the old one and push in a new one, concrete would not be nearly as versatile.

I have worked on tracks that were of such low density that grass was growing in and around the ties, that doesnt work very well but it looks rather quaint LOL.

Concrete would break, it simply cannot move as much as necessary, asphalt for the same reason, and once either started cracking, it would need replaced, it cannot be renewed as gravel can.

Answer 3

It is for support so the tract is where it is gravel  is the best and cost wise choice and easy to use. Concret whould crack under wieght of 1 train and water wlhould not drain of.

Answer 4

They have to have gravel for drainage, and a solid foundation that will "give".   If you ever see a train go over the tracks you will see how the rails "give".   It needs to do this in order to prevent damage to the rails themselves.

Answer 5

1st of all the gravel is called ballast,  ballast is there to prevent shifting in the ties, drainage, and weed control

Answer 6

so the water can drain away

Answer 7

It's called ballast and the stones are bigger than gravel.

Answer 8

Its not economical to use concrete or asphalt.If you didn't cover the dirt bed with gravel erosion would always be washing out the road bed.Its a combination of economics and drainage, erosion control that makes gravel most popular......George

Answer 9

the gravel has 100% compaction at all times wet or dry without being tamped or rolled into place...all the big pipes under the street are setting on a gravel bed as well for the same reason...

many years in the mining and construction industry

Answer 10

the gravel  makes for an excellent foundation for the tracks. The gravel foundation is larger than the actual tracks to avoid erosion under the tracks and to properly transmit the effort to the ground. Concrete foundations for hundreds of kilometers would be too difficult to make and the concrete should be much much thicker than for example in a road foundation. Even so, the concrete would brake if the ground settles  even a few centimeters. gravel is great for tracks ;)

Answer 11

For drainage, the railroad ties are made of wood.  If the ties were set on concrete or mud, the water would pool and cause the ties to rot at a faster rate.  I think I heard that on the History channels Rail Road Tech.

Answer 12

This photo shows tracks that are set in concrete:

http://i134.photobucket.com/albums/q119/...

It's a matter of cost. Track could be laid in concrete, like I showed you in the picture.

The "gravel" used by railroads is called "Ballast" and is rocks between 2 1/2 and 3 inches is size.

It is used for drainage, otherwise, the tracks would sink into mud when it rains.