Why is gravel used in laying railway tracks?

Question

Why is gravel used in laying railway tracks?

Answer 1

Also, the loose gravel is easily moveable for when there are low spots in the track. If some gravel gets washed away, its not too hard to replace it as it would be with just dirt or mulch.

Answer 2

let water drain away from wooden ties to prevent premature rotting!

Answer 3

The ballast is there to both support the rail structure and provide for drainage, though drainage is not its primary function for dealing with waterlogged or rotting ties.  The cross ties are treated with creosote to extend their useful life and drainage is provided to prevent washouts on the ground upon which the roadbed is constructed.

If you see conventional freight traffic passing by, notice how the rail flexes (up and down) as the wheels of the cars pass by.  This is necessary so that high levels of force imparted to the wheel / track interaction (also called track - train dynamics) can be absorbed by the roadbed and thereby reduce the level of force where wheel meets rail, much the same way that car race tracks, as well as many highway guard rails, are designed to absorb impact forces during a collision.

There is one drawback.  When the ballast has been disturbed, usually by maintenance of way crews, it requires several days for the structure to "consolidate", an engineering term meaning the ballast has compacted and the cross ties are firmly in place, resulting in a temporary speed restriction, uaually 10 MPH, for the length of the disturbace, sometimes many miles long.

When the ballast needs replacing, due to build up of mud and / or sand from locomotives, it is dispersed by a tyoe of work train, called a ballast train.  The hopper cars have side dump hatches as well as a center-dump capability.  There is usually a cross tie placed on the rail in front of trailing truck on the car being unloaded, and this acts like a leveling device.  In concrete work it is called a "screed",

The ballast cars are unloaded "on the fly", moving at walking speed so that the MOW emplyee can control the rate at which the ballast leaves the hopper, with an objective of keeping a nice, smooth average.

After the ballast has been unloaded, MOW employees come in with a piece of equipment called a "ballast regulator" that further levels the ballast and shapes the distinctive "shoulder" of the balast we see every day, followed by a "tamper", which actually lifts the rail and cross ties and squeezes the ballast under and around the ties.  At the same time, a track alignment is made via laser, to ensure level and equal spread of the ballast. crossties and rail that sits on it.

Answer 4

It stops weeds from growing on the tracks(its for more than just to make it look pretty, because if it weren't, the ballast rocks wouldn't be there).

Answer 5

It allows for drainage and minimizes the effects of heaving, expansion, and shrinking caused by freezing and thawing, as well as from the earth drying out.

Answer 6

It's called ballast

Answer 7

Two reasons, really. One is to hold the ties and keep them stable. The second is to allow rainwater and meltwater to drain away from the ties, helping to prevent rotting, subsidence and damage to the tracks.

In colder climes it also minimizes the effects of freezing and thawing on the ties and tracks.

Answer 8

It keeps the dirt in place, and the weeds down.

Answer 9

To revert rainwater and runoff from the railroad ties. If the gravel weren't there, the water would lay around the ties and rot them away. The gravel prevents them from rotting, or at least slows down the rotting cycle so workers don't have to replace them as often as it is a very tedious process.