Why are railroad tracks always surrounded by rocks?

Question

I assume it is slate, but I have no idea why it is there. Anyone know?

Answer 1

There are some places, in one particular swampy area from Hampton, Virginia, USA to Burkeville, VA, that had cypress or locust logs laid down in the swamp, then ballast on top. This was back at the turn of the century, and the Norfolk and Western is STILL using that old railroad line to get to Hampton and Norfolk, VA. So not all ballast or under-base is all rock. But mostly it is, to provide a stable base for the track and the weight of the trains upon it. And railroads will use whatever rock is handy locally if possible, to cut down on costs.

- The Gremlin Guy -

Answer 2

so that grasses or weeds won't grow on the tracks.

Answer 3

Most Ballast used in the US is either Granite, Limestone or Traprock.  The ballast does provide drainage for the track structure, but the primary purpose is provide for the transfer of the train load from the ties to the subgrade (earth).   Twelve (12) inches of ballast with twelve (12) inches of sub-ballast (ABC Stone) is a common track structure.  A machine called a Tamper compacts the stone under the tie to create a point to point bearing condition (density) in the stone.  Without the ballast, the ties could sink into the subgrade losing vertical track alignment and will decay faster.  The ballast also locks the ties longitudinally to provide resistance for braking.  Rails are anchored, often "box anchored", to the ties which transfer the braking forces from the rail to the tie and then into the ballast.

Answer 4

Crushed rock is used to stabilize the wooden "ties" which support & keep the rails properly spaced.

Called 'ballast' it provides some drainage & also keeps the ties from coming into contact with the soil which causes rot.

Been around since rails have been in use.

Answer 5

Those rocks are called Ballast.

Answer 6

It's limestone, granite, traprock, whatever is available locally.  The harder the better.  Jagged crushed stone is way better than round river rock.

It's there for drainage.  Get the water to move away from the ties so the ties don't rot or freeze.   It also makes the roadbed firm to carry the weight of trains.  The jagged rocks also interlock and keep the ties from moving around.

An example of bad ballast is a muddy area right around a track joint.  That joint is pumping up and down with the passage of trains, and dirt from below the track has squished up into the ballast.  Now that's making it pump even worse.  That ballast needs to be dug out, cleaned, and put back down.  Hard work, but there are giant machines which can do that, digging under the track, sifting the ballast from the dirt and throwing the ballast back down.  They fling the dirt 30 feet from the track, and you will see a furrow of dirt where such a machine has gone by.  It's something to see!

Answer 7

It's gravel, and it's to keep down weeds.

Answer 8

It's limestone and it's called ballast. It packs snugly around the ties to support them. The RR companies have machines that can repack the stones.

Answer 9

To give stability, prevent the tracks from being over grown and to keep the ground underneath and around the tracks from erosion.

Answer 10

ballast for drainage