Why are stones placed in and around railway tracks?

 The stones placed in and around railway tracks are technically called `ballast'. The railway track, named `Permanent Way' in rail lingo, is a multi-entity structure which comprises the pair of rail lines running parallel, the spaced sleepers, the ballast and the formation.The force exerted by the wheels of the train is transmitted successively in a proportionally diminishing extent down the rails, the sleepers and the ballast to the formation, a well prepared and consolidated road bed.

The ballast consists of broken stones of specific dimensions. The stability of the track depends on the depth of the ballast which imparts a cushioning effect to the track. The standard depth of ballast for trunk route is 25 cms ,for the Broad Gauge and 20 cms, for the Metre Gauge.Besides distributing the pressure on the track, as stated earlier, the ballast provides a foundation for the sleepers holding them in position albeit the shear produced on the rails by the moving train and protects the formation by diverting rain water to the cess, the exposed top portion of the formation.

Railway maintains periodical screening and packing of ballast. Currently, high-tech Ballast Regulating Machines are employed for the purpose supplanting the human agency.The depth of ballast under the ties has been increased in recent years to accommodate increasingly heavy trains. On some lines this layer is now laid 60.9 cm or even 76.2 cm. thick.

Source : The Hindu