Eli5: Why are railroads full of rocks?
In: Engineering
It is called ballast. The ballast is very stable and does not move whenever a train runs over it. So it will effectively transfer the weight of the train over a much larger area of the ground and preferably all the way into the bedrock. However the ballast is movable whenever there is constant forces. So if the ground moves the ballast will just adapt as the individual rocks will be able to fill any voids and get pushed away from any high spots. Similarly the rails gets longer and shorter depending on temperature and will move on top of the ballast. The ballast also helps with things like drainage and to keep the weeds away.
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