Why is crushed stone paved beside the tracks?

If you look at the railroad tracks, you will notice that gravel and crushed stones are spread all over the rails and sleepers. For those unfamiliar with railways, the railway company AlphaRail explains about these crushed stones (ballasts) that are likely to raise the question of ``why is it?''.

Why do railway tracks have crushed stones alongside them? - Alpha Rail

Under the rails of the track, or beside the rails, finely crushed stones are laid over almost the entire line. These stones are mainly used to keep sleepers and rails level, prevent slippage of sleepers, suppress plant growth, and prevent tracks from being flooded.

Ballast is characterized by very rough and sharp edges. If you use smooth stones, such as those found on riverbeds or the sea, trains may roll or slide as they pass, but sharp stones are fixed by colliding with each other, so sleepers and rails are effectively used. can be stabilized.

When laying long tracks, it is important to keep the tracks parallel and even. Ballast and sleepers are used there. Traditionally, wood has been used, but on modern railway lines with heavy traffic, man-made materials such as synthetic resin, steel, and prestressed concrete are often used.

Ballast is laid to support the sleepers and rails, and moves slightly each time a train passes to keep the rails level. However, ballast becomes dirty and breaks into small pieces under load, so regular maintenance is essential.

AlphaRail says, “Ballast has been used for centuries. Without ballast, railroads cannot withstand the weight of trains and the effects of expansion and contraction. When you see it rumbling, you will have more respect for the ballast's role in getting you safely to your destination.'