The weight is distributed to the subgrade to avoid damaging the subgrade. For good water permeability and simple laying, it is very important to lay stones on the rails.
Paving stones also have such shortcomings:
Need frequent maintenance.
When the train passes by, it will bring vibration, and long-term vibration will mix the soil and ballast on the subgrade. The soil mixed with ballast will weaken the strength of subgrade and lead to the settlement and unevenness of rail surface. Therefore, on trunk railways, screening, ballast replacement and compaction are required every year.
Smoothness and ballast splash.
No matter how smooth the ballast is, it is impossible to reach the level of concrete monolithic ballast bed. Moreover, because the sleeper is not rigidly fixed on the track bed, when the train passes by, the rail between the wheels will drive the sleeper to bend upward together, which is visible to the naked eye on the heavy-haul railway. In addition, when the train passes by at high speed, there will be the problem of ballast splashing.