Ballast fouling has a negative effect on its functions. Increases in fine particles reduce the inner friction angle of the ballast material. This reduces the resistance to shearing and lowers the load-bearing capacity. Moreover, the water permeability and durability of the track geometry are negatively affected.
One cause of ballast fouling is the daily traffic load. It leads to splintering of the ballast stones at the contact points, causes rearrangements of the stones and produces friction. As a result, the amount of fine particles in the ballast bed increases. The traffic load is the result of both high loads and the dynamic of high-speed traffic.
Rising material from the subsoil also leads to ballast fouling. In addition, fine particles from outside also find their way into the ballast bed by wind erosion or spilled freight. Even in newly placed ballast, the amount of fine particles is between 3 to 5%. Tamping works also cause wear on the ballast bed. However, operational loads cause much higher wear over the track’s service life.