The strength of the subgrade is often not enough to bear so much pressure. Though the sleeper undertakes quite an amount of pressure, the ballast is needed to scatter pressure by increasing the functional area and reducing the pressure of per unit area.
When the train is running, the wheels on the track generates not only vertical and lateral forces but also the rolling and longitudinal sliding of the wheels, making the rail undulate under the action of dynamic load.
This longitudinal horizontal thrust can cause the longitudinal displacement of the rail and sometimes drive the sleeper to move together. This movement is called track creep. The movement of the track can be reduced by making the ballast packed the sleepers.
The train runs on the steel rail with a steel wheel. Because the wheels are not perfectly round, they will cause considerable impact when passing the rail joint. The instantaneous pressure on the track can be up to twice the static weight, and there is no rubber to absorb the impact. Such instantaneous impact, if acted directly on the subgrade, will cause subgrade settlement, as well as pumping the phenomenon of repeated impact water flowing out of the surface, which can be simulated by stomping on the wet ground.
If the reaction is directly on the track, it can cause fasteners, rails and even sleepers to break. Drainage is by no means a matter of gutters alone. Good ballast is essential to drainage. One may ask whether drainage is the primary or secondary function of ballast. Assuming that poor drainage will not affect the strength of the subgrade, then ballast need not have drainage function, but this is not the case. Ballasts laid also help in reducing water logging in train tracks.
When water comes on the tracks during the rainy season, it goes down to the ground through ballasts. At the same time, stones bigger than this do not even flow in the flow. Does Drinking Lemon Water actually reduce your weight? Know the truth here. Read: Why Nose Hairs should not be Cut , these are the main reasons. This person has been living in the forest for the last 17 years, know why? In this weird village people live underground ,know the reason here. Leave A Reply Cancel Reply.
Save my name, email, and website in this browser for the next time I comment. Notify me of follow-up comments by email. Notify me of new posts by email. Home Offbeat Know why Stones are laid on train tracks, you will be surprised to know the reason. Know why Stones are laid on train tracks, you will be surprised to know the reason Offbeat. By Nandini Naamdev Last updated Aug 14, Related Posts. Oct 22, Oct 21, Look here for new government jobs: Bumper chance for 8th 10th 12th pass to apply for government job.
Being made of metal though, steel sleepers are inappropriate for certain types of electric trains and train signalling. Plastic sleepers are typically the most expensive.
Recycled plastic sleepers are becoming more popular however. Trains have to slow down or suffer through a bumpy ride if the ballast or sleepers are not maintained.
This is because of:. When ballast wears away, trains have a bumpy ride. Trains can also derail if the condition of ballast, sleepers, and rail deteriorate too much. We analysed a few years of derailment data to identify what the most common causes of train derailment are, and track related problems were on top. Maintaining ballast is about removing the gaps that form between the stones. Gaps can form gradually due to the movement of trains on the rails, or by water flowing through and eroding the stones.
To do this, a machine picks up the rails and sleepers, and re-settles ballast to close the gaps in the rocks. This is also a good opportunity to replace stones that have eroded into rounder shapes. Sleepers crack or erode after being exposed to weather for many years.
To replace broken sleepers, the rails are first untied from the sleepers, then a machine picks up the rail, a new sleeper is inserted, and the rail is lowered back down and retied to the new sleepers.
We wrote recently about what is involved in track maintenance, and what sort of qualifications are needed for the work. Click here to check out that article:. There are many train lines that do not use ballast or sleepers.
Modern subway and metro lines typically use this alternative to sleepers. Concrete blocks have a better life-time performance under the load of frequent trains. Subway and metro lines are also typically in tunnels, the controlled conditions help prolong the life of the concrete which outweighs the greater initial costs. I used to work as an Alignment Engineer where I helped to design and build train lines.
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