Why do railway tracks have stones?  

On any train journey, all of us have seen those endless piles of stones that line up the train tracks. They might look like regular pebbles. However, there’s more to them. Those seemingly unnoticeable rocks are collectively called track ballast and it keeps the train tracks in place. Also, irrespective of the city or country you might be travelling in, the shape and texture of these stones are almost the same everywhere. Let us find out more about them. 

What is a track ballast? 
A track ballast is placed around railway tracks and constitute the track bed. It  serves as the foundation for railway sleepers, which are utilised to keep railway tracks level and spaced properly. The rectangular support piece perpendicular to the tracks is known as a railway sleeper. A railroad tie or a crosstie is another name for a railway sleeper. These stones are packed below, between and around the railroad ties. Previously, railway sleepers were built of wood, but currently they are mostly composed of pre-stressed concrete. The thickness of a track ballast is usually between 25 and 30 cm, but it varies depending on certain conditions related to the railway track's geographical location.  

What type of stone has to be used on railway tracks? 
Any type of stone cannot be used as a track ballast. When a train passes over the railway lines, smooth, round pebbles, such as those found on river beds or used for decoration, may roll over or slide against one another. The wrong type of stone would fail to perform the primary job of track ballast. Only stones that don't move around a lot are suitable for the purpose. Hence, sharp-edged stones are utilised as track ballast on railway tracks. These rocks interlock with each other and therefore stay in place. If circular or smooth rocks were used, they would slide over each other, compromising the track ballast's strength. This can have disastrous consequences. 

To put it in another way, crushed rocks or stones are commonly used for a track ballast. However, less suitable alternatives such as burnt clay are also utilised in some circumstances.  

What are the other functions of a track ballast? 
Apart from holding the railway lines in place and providing support for heavy trains, a track ballast also serves the following purposes:  

• It prevents vegetation from growing on railway tracks, which could damage the ground beneath the tracks. 
• A track ballast also keeps water from regularly reaching the track and softening the ground. It does not totally seal off the railway tracks from water, but it does allow for efficient drainage beneath or around the tracks to ensure that water does not accumulate on them.