Why are there little stones in between the railway tracks?

There's nothing more fun than shovelling ballast...

I had a shift not long ago where on a re-rail, the dozer decided to leave a huge incline in the ballast so when the sleepers were dropped, lined up and the rail clipped up, one rail was a ridiculous amount higher than the other one. Cue us mugs having to jack up one side of the track, and shovel ballast out from under the sleeper until it lay properly, then move down a bit to the next section and so on.
 
The engineering reasons are as follows, there are quite a few:
primarily, it spreads the weight of the train out very well and very evenly. If you laid the track on the soft topsoil it'd sink into it and vanish.
It's dead easy to renew, you just pour more on.
It's a lot cheaper and easier to work with and transport than alternatives such as concrete. Note the track is on a camber leaning into corners, try getting concrete to set on an even slant - won't happen.
The sleepers can't be rigidly fastened to the ground, due to the massive lengths of steel needing to expand and flex as one object. If you bolted them down you would find that after a few years the rail between sleepers would sag with the weight of the trains.
There are more but I think those are the major ones.
 
Skidilliplop said:
The engineering reasons are as follows, there are quite a few:
primarily, it spreads the weight of the train out very well and very evenly. If you laid the track on the soft topsoil it'd sink into it and vanish.
It's dead easy to renew, you just pour more on.
It's a lot cheaper and easier to work with and transport than alternatives such as concrete. Note the track is on a camber leaning into corners, try getting concrete to set on an even slant - won't happen.
The sleepers can't be rigidly fastened to the ground, due to the massive lengths of steel needing to expand and flex as one object. If you bolted them down you would find that after a few years the rail between sleepers would sag with the weight of the trains.
There are more but I think those are the major ones.
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Nice post - sounds good to me, but I'm no engineer.

Welcome to OcUK, by the way.

ps - claimed ;)
 
You can't really claim that as I've been on here before with over 1500 posts. I just thought I'd make a new account with new email address etc as getting mail forwarding to work was a pain in the ass.

But it's a semi claim cos it's the first post i've made in over 2 years. :P

I think it's all probably on Wikipedia but if not, paste that post :D

Skidilliplop BEng CCNA lord of the interwebs!
 
The gravel allows a little necessary movement in the system - ever watched a particular piece of rail/sleeper moving about as a train goes over it?

Without the movement the rail/sleeper would crack up quite quickly and I guess the ride in the train would be rougher too.
 
Skidilliplop said:
You can't really claim that as I've been on here before with over 1500 posts. I just thought I'd make a new account with new email address etc as getting mail forwarding to work was a pain in the ass.

But it's a semi claim cos it's the first post i've made in over 2 years. :P

I think it's all probably on Wikipedia but if not, paste that post :D

Skidilliplop BEng CCNA lord of the interwebs!
Click to expand...

I would contact an admin about that incase they ban you for having two accounts.
 
friddela said:
http://blogs.nlb.gov.sg/ask/anything-everything/302
Click to expand...

“The stone materials are described as ballast, and their functions are more fully outlined in this extract below:Ballast is the granular material, mostly uniformly graded stone aggregate of not less than 40 mm size, laid under and around the rail sleepers, to transmit the load on sleepers to a large area of formation.Ballast also imparts the much needed longitudinal and lateral stability to tracks by preventing the movement of sleepers under dynamic loads of moving trains. Indeed ballast with stood it all by a property called internal friction of aggregates (stone chips).

Internal friction of aggregates depends on the texture, shape and size of aggregates. So, hard and strong stones like granites, quartzite, trap, basalt etc are used. When such stones are not available sandstones, lime stones etc., may also be used. The only criterion is they should be cubical or angular instead of flaky and rounded.
If you ever happened to go to a construction site, make two small heaps one each of sand and stone aggregate (used for concrete) with equal height. Then try pushing the sand heap in one go with hands. It might move easily. Then try pushing the aggregate heap with hands. It offers disproportionately high resistance. You may even fail to move it fully or need much effort to slide it. Thats internal friction for you.

Similarly, stand on a sand heap it would flatten easily. Next stand on an aggregate heap, it will not budge much! Again it is the internal friction at work. So, the densely packed good quality ballast under, in between and around the sleepers gives much resistance to the movement of sleepers under dynamic loads of moving trains. The ballast packing on tracks would be checked regularly, say weekly once or so, to pack the slipped aggregate closely under and around sleepers. However, it is the humans and cattle straying on to tracks that cause more disturbance than dynamic loads.

Besides, the ballast also serves the following:
- It helps in draining the rain water easily off the track.
- It prevents capillary rise of surface water to track due to large voids.
- It helps prevent weed growth on track.
- It gives some elasticity to track structure.
- Loose nature of ballast helps easy maintenance and adjustment of track levels.
- It protects the form of top surface of formation.
Click to expand...

Interesting stuff.
 
Skidilliplop said:
Note the track is on a camber leaning into corners, try getting concrete to set on an even slant - won't happen.
The sleepers can't be rigidly fastened to the ground, due to the massive lengths of steel needing to expand and flex as one object. If you bolted them down you would find that after a few years the rail between sleepers would sag with the weight of the trains.
There are more but I think those are the major ones.
Click to expand...

lol, you wouldn't try getting the concrete to set like that, the concrete would be moulded in sections then positioned and assembled on site, but it would cost a fortune - the skytrain in Bangkok must have cost a fair whack as its all concrete afaik
 
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