What kinds of ballast does IR use?
For all high-traffic lines, IR uses machine crushed hard stone ballast, usually from locally quarried granite stone, or crushed basalt. In the past, broken brick, slag from metal processing, cinders, and waste construction material were also used. For most sections with wooden sleepers, the ballast is of a 6.5cm nominal size (not more than 5% retained on a 65mm square sieve, 40%-60% retained on a 40mm square sieve, and at least 95% retained on a 20mm square sieve). In the past, ballast of 5cm nominal size was extensively used, and smaller ballast of 4cm – 2.5cm was used for iron or steel sleepered track, points, etc. The ballast layer is 0.15m-0.25m thick on most lines but is up to 0.3-0.35m in newer trackwork, especially for high-traffic lines with prestressed concrete sleepers. The sides of the ballast layer generally slope at a 1.5:1 incline. A few sections of IR have ballastless concrete bed track: much of the Calcutta Metro, a few sections of Konkan Railway, the second phase of th
