[Robert Stokes]

Yesterday morning I was at Doncaster station collecting my wife from a weekend away with our son and his family. This did not mean that I had an unfettered weekend of railway modelling. She went because I was undulging my other hobby by playing in a chess competition. (Did quite well actually - three wins and a draw out of five matches.)

Whilst waiting on the platform for her train to arrive, I noticed that the ballast shoulder was much more pronounced than I had imagined. This got me thinking as to why it was there at all and I have to confess to having no idea. Can anyone enlighten me?

Thank you, Robert.

 

[Brian Considine]

I could be wrong, but my understanding is that it helps to keep the track in place & in line.

 

[John Webb]

The diagrams from the Midland Railway shown in Bob Essary's book "Railway Signalling and Track Plans" (Ian Allan 2007) show that for bull-head track on wooden sleepers the ballast was about twice the depth of the sleepers as a minimum. On modern welded track with heavier flat-bottom rail, I understand that the depth of ballast is greater to help hold the track more firmly. Also the concrete sleepers are greater in depth? And on a curve the super-elevation on the outside of a bend also creates a deeper layer of ballast.
The shoulder is normally a 45 degree (1 in 1) slope. I presume this is an angle which the ballast holds easily but does not require excessive ballast to form.

Regards,
John

 

[Richard Johnson]

[quote name='John Webb' date='6 Nov 2007, 20:23' post='38824']
The diagrams from the Midland Railway shown in Bob Essary's book "Railway Signalling and Track Plans" (Ian Allan 2007) show that for bull-head track on wooden sleepers the ballast was about twice the depth of the sleepers as a minimum. On modern welded track with heavier flat-bottom rail, I understand that the depth of ballast is greater to help hold the track more firmly. Also the concrete sleepers are greater in depth? And on a curve the super-elevation on the outside of a bend also creates a deeper layer of ballast.
The shoulder is normally a 45 degree (1 in 1) slope. I presume this is an angle which the ballast holds easily but does not require excessive ballast to form.

*** Hi John
Actually a small correction if I may - the usual angle is appx 60 degrees, which is the natural angle of repose for ballast (the angle at which it forms a stable slope)

The trackbed and ballast itself is raised to provide natural drainage, which allows fines to pass through and keeps the ballast stable and cleaner. The ballast is also the "suspension" for the track, which was very important in steam days with very heaviy single axle loads and the "hammerblow" of the wheel as it rotated - having some suspension given by the track was very important to lower wear on the locos themselves, as without it key frame parts and bearings would have worn and broken much more frequently.

Incidentally the fact that steam loco's are very hard on the track is one of the reasons why use of steam on certain ines is not permitted these days - and where it is OK, speeds are often tightly controlled. The fact that diesel is also much gentler on track, so lowering costs of maintenance was also yet another reason why steam was replaced so fast!

Today the science is far more precise and the laying is done to very exact tamping (compression of the ballast) and depth to give a long term low maintenance track bed - this allied to the existence of continuous welded rail which needs a much firmer and stronger ballast bed, plus deeper and far stronger sleepers to control it under expansion/contraction is why it now looks so deep.

As a matter of interest this is amazing in reality - for example the new main line laid in Australia recently is thousands of kilometers long through deserts and tropical heat with NO breaks in the rail - its potential expansion if left free is massive (way, way more than a full kilometer of expansion potential ) so its held by very strong sleepers and fixings in a very firm ballast bed and controlled/held so tightly that all expansion is forced to happen in width not length!!

The rail is not pre-stressed but is laid at a specific "average temperature" for the region it is laid in to keep the expansion/compression as even as possible.

Regards

Richard Johnson

 

[Robert Stokes]

Thank you for the answers. However, I would humbly point out that neither of the last two actually answered my question of why the shoulder is there. I'm not talking about the depth of the ballast under the sleepers. As I saw it the ballast was roughly level with the top of the sleepers along their length but was significantly higher along a line about a foot wide just beyond the ends of the sleepers. That is what I meant by the shoulder and what I was particularly asking about. Has dbclass50 got the answer in one line?

 

[Richard Johnson]

QUOTE (Robert Stokes @ 6 Nov 2007, 21:25) <{POST_SNAPBACK}>Thank you for the answers. However, I would humbly point out that neither of the last two actually answered my question of why the shoulder is there. I'm not talking about the depth of the ballast under the sleepers. As I saw it the ballast was roughly level with the top of the sleepers along their length but was significantly higher along a line about a foot wide just beyond the ends of the sleepers. That is what I meant by the shoulder and what I was particularly asking about. Has dbclass50 got the answer in one line?

****Robert, the answer is there if you read it.

to quote "The trackbed and ballast itself is raised to provide natural drainage, which allows fines to pass through and keeps the ballast stable and cleaner.

if it is raised, it has to have a shoulder.

It could be made with NO shoulder by burying it, but that would reuire expensive and exxy to maintain drains as well.

Richard

 

[Robert Stokes]

Richard, from your last answer it appears that I did not make my original question clear enough. I wish that I could include a diagram here but I don't know how.

By the word 'shoulder' I did not mean the ballast falling at the ends of the sleepers to the slightly lower level of the land nearby. What I saw yesterday was that at the ends of the sleepers the ballast rose by a few inches to make a definite hump, distinctly above sleeper level, before falling again (by more than it rose) to the level of the land nearby. It is this hump that I meant by 'shoulder'. I have re-read your answer and I don't think that it addressses this point. Do they have these humps either side of the sleepers on Australian railways?

Cheers, Robert.

 

[Richard Johnson]

QUOTE (Robert Stokes @ 6 Nov 2007, 22:44) <{POST_SNAPBACK}>By the word 'shoulder' I did not mean the ballast falling at the ends of the sleepers to the slightly lower level of the land nearby. What I saw yesterday was that at the ends of the sleepers the ballast rose by a few inches to make a definite hump, distinctly above sleeper level, before falling again (by more than it rose) to the level of the land nearby. It is this hump that I meant by 'shoulder'. I have re-read your answer and I don't think that it addressses this point. Do they have these humps either side of the sleepers on Australian railways?

Cheers, Robert.

*** Hi Robert. Yes, the bump at the shoulder different to the shoulder . Re the difference between railways I think they all use the same sort of gear these days so the results look pretty well the same!

The "Bump" you saw is not usually there with totally relaid track but is there with maintained track quite often. ie, the shoulder normally doesn't have it but these bumps do exist sometimes on newly maintained areas.

What happens - sort of - is that when servicing and reballasting/ realigning or re-tamping track to restore it, without totaly lift and replace happening, more ballasting is just laid on top and the job completed by a machine which slightly lifts the existing track and tamps and packs the new ballast which is pushed directly under the old track. It does this in a continuous movement as it moves along and if there is excess ballast this will be heaped up a little at the sides as it is in excess of needs as "suspensiion and drainage"

(happy to stand corrected on this procedure - thats how it looks to me anyway)

In days gone by it may have been manually removed immediately but time is money now and closures really disrupt things a lot with the rail system under pressure so in busier places it will usually be left as you see it as to recover it and resore the "flat" profile to the edges costs a lot of time.

In time if someone doesn't make a decision to move it during quiet times will mostly eventually settle or disappear anyway as vibration moves and spreads it, so it falls into the "cess" making the "shoulder" area less tidy than that of new track.

Hope this is closer to your question.

kind regards

Richard

 

[alastairq]

I, too, have noticed this pronounced 'hump' on modern, flattybottom track...where teh ballast shoulders seem heaped up almost level with the rail heads, but away from the sleeper ends.

Re-reading Iain Rice's Finescale trackbook the other night..I like his style......I noticed he comments on how PW 'design' has changed in recent times......

Since the 80's or around there, PW started to be made a lot more 'rigid' and inflexible....with teh springing of locos/stock getting softer.....bit like a road and a car?

whereas in teh days of Bullhead, the PW was in fact very flexible and floaty...I often watch the considerable spring in the track under the trains of my local NYMR.
But then,it has/had to be, since loco and stock springing was incredibly stiff, and the track also had to resist hammer-blow shock from the locos.

His application of this in model terms was to create a floaty, insulated PW for smoother, reliable running?