Question

In railroad industry,

Describe the tradeoffs to be assessed between using a "broadly" or a "narrowly" graded ballast.

Answer 1

Ballast form trackbed upon which sleepers are laid. The ballasts are capable of bearing the load from the railroad ties. And they facilitate drainage of water. It also prevents the growth of vegetation, that might interfere with the track structure.

On the basis of the grain size distribution, the ballasts can be classified as narrowly graded ballast and broadly graded ballast.

Narrowly graded ballast

It provides superb drainage and fouling material storage if these ballasts are adequately compacted. These ballasts are stiffer due to the dominating effect of the interlock of the large particles.

Broadly graded ballast

Broadly graded ballast can provide more strength and resistance to deformation due to the denser packing arrangement of the particle than narrowly graded ballast. But is has a lower void volume than narrowly graded ballast. But more broadly graded ballast can provide high resistance to deformation and has the desired drainage and fouling storage capacity.

Hope this explanation is enough about narrowly and broadly graded ballast. Thank you.