Why do the stones under the train tracks come and go?

While waiting on the train platform, attentive travelers often notice an interesting phenomenon: some tracks are covered with small stones, while others are bare with no stones visible. What exactly are these little rocks? Why does it come and go? Behind this lies the scientific wisdom of railway track design.

According to China Railway Popular Science,The scientific name of the small stones under the track is "ballast", which is made from strictly selected granite, basalt and other stones.Natural stone needs to go through multiple processes such as crushing, cleaning, and quality inspection before it can be "worked" until it meets the standards.

Whether there are stones under the track is the core difference between ballasted track and ballastless track.

Ballasted tracks are mainly composed of ballast and are mostly found on railways with speeds below 250 kilometers per hour.After the ballast is laid, it forms a buffer layer, which can evenly distribute the weight of the train to the roadbed through the rails and sleepers, playing a key role in dispersing stress.

There are gaps between the sharp-edged gravels. When the train passes by, the slight deformation caused by mutual compression and friction acts like a spring to absorb shock and improve ride comfort.

Ballastless track does not use ballast and is mainly used in high-speed railways with speeds of 250 kilometers per hour and above.It uses concrete to cast the overall load-bearing plate layer, and the rails are laid directly on the surface. This kind of structure has higher stability, can ensure the smoothness of the track and meet the operation requirements of high-speed trains.

More importantly, the ballastless track can avoid gravel splashing, effectively reduce noise, and provide passengers with a quieter travel environment.

Whether the ballasted track relies on the elastic buffering of the ballast, or the ballastless track relies on the stability and smoothness of the overall structure, they are the optimal solutions designed by railway engineers based on different speed requirements.