The stones you see scattered and compacted alongside train tracks are called ballast. The purpose of ballast is to hold the wooden track ties in place, and without it we would have some seriously wonky train tracks that would cause major problems for train infrastructure worldwide.
When you think about it, imagine running miles and miles of narrow steel tracks on top of normal dirt ground: the train tracks are subject to heat expansion and contraction, ground movements and also vibrations, and lastly weeds and plants growing from underneath. These are just the natural elements at work. If you couple that with massive freight trains running over the top of them too then you can only imagine what these skinny steel rails actually go through. Luckily all these problems were solved nearly two hundred years ago. They haven’t been changed since.
The job isn’t easy and requires a lot of labour to get it done. Let’s go through the process though. Usually they start on bare ground, and from there the goal is to build up a solid foundation to raise the tracks high enough to avoid flooding. On top of this solid foundation is when the ballast, aka crushed stone comes into play. Then come the sturdy wooden beams that sit on top of the ballast, followed by a lot more ballast to securely lock the beams in place.
The wooden beams are made of hardwood, in most cases either oak or hickory, and dosed with a chemical called creosote to make it weather proof. In the United States they call them “cross ties” and in Australia they are commonly referred to as “sleepers”. While most of today’s sleepers or ties are made of wood, heavily trafficked modern railway tracks are experimenting with alternatives, including plastic, steel and concrete.
Finally, the steel tracks come into play. Before they were usually joined by bolting an extra piece of steel across the joins, but today they are usually welded to create one seamless track. Yes, a lot of labour intensive work!
There you go: a very old process that is still used today due to its effectiveness. To sum it all up, the ballast distributes the load of the sleepers (or ties) across the foundation which allows for ground movement, expansions and contractions, and finally the weight variances allow rain and snow to drain through the track which prevents the growth of weeds and vegetation that would essentially take over the train tracks. Thank goodness for ballast!