Still this phrase a few times - what is the limiting factor on track life: is it profile change due to wear, or fracture risk due to fatigue?
Well, the phrase as used is 'life expired track' - I'm making the assumption that re-ballasting would be covered by the term 'track maintenance'.Do you mean 'track' or 'rails'? Your question looks as if it means only the rails, but track includes the sub-base, ballast, sleepers and so on as well as the rails.
All things being equal, and assuming that there's no deficiency in construction, which is likely to be life-expired first: rail or sleepers?
Thanks. So on a heavily used and/or tightly curved line, the rails will go first, followed by ballast and then sleepers?It depends on the traffic and the curvature...
Thanks to you as well. I hope nobody minded the 'stupid question' for the sake of some complete explanations of a term that gets used a lot.Without being too flippant, life expired track is simply when some or all of the track system is beyond economic repair, and it is easier to replace...
Thanks to you as well. I hope nobody minded the 'stupid question' for the sake of some complete explanations of a term that gets used a lot.
Sleepers - if the odd one breaks that's a maintenance job. Timber sleepers, particularly softwood, will normally rot more quickly than a concrete sleeper will decay.
I know that hardwood sleepers were much in use in the 19th century on certain lines and a particular type of Australian timber called Jarrah (Eucalyptus Marginata) was also very popular as use for sleepers with those early railway companies (Many of these redundant Jarrah ones are now readily available for purchase for use in gardening projects, in particular).
Without being too flippant, life expired track is simply when some or all of the track system is beyond economic repair, and it is easier to replace.
There are 5 main components (top first)
Rails
Fastenings
Sleepers (bearers in point work)
Ballast
Formation including drainage
Rails can last a long time - I've pulled out rail over 100 years old. Equally, some needs renewing every few years, particularly on rails with high tonnage, high speed and high cant deficinecy (eg WCML and ECML). Rerailing is classed as a renewal once you go above a certain length (can't remember how long).
Replacing fastenings is a maintenance job. However some fastenings are more prone to failure than others (eg Pan 8) and are considered life expired, and the whole track system will be replaced at the same time.
Sleepers - if the odd one breaks that's a maintenance job. Timber sleepers, particularly softwood, will normally rot more quickly than a concrete sleeper will decay. However some types of concrete sleeper are known to decay more quickly basically due to either their reinforcement wires corroding, and/or the concrete mix being less than ideal. Again, this will happen more quickly on high tonnage / high speed routes.
Ballast loses its angularity over time, partly through small movement under the passage of trains, and partly through tamping. Tiny pieces break off, creating fines (essentially sand) which clog the ballast causing it to lose its drainage properties. Rounded ballast is also not so good at locking sleepers into place, so more minor movement occurs and then the problem escalates. There are some locations around the country where limestone ballast was used; this is less hard than granite and will become, a problem much more quickly.
Formation life depends on the geology underneath. Decent rock or sand formation is great, clay and peat / fen is not. Clay is well know for pumping up through the ballast causing a 'wet spot' which causes all sorts of geometry and track defects. Digging out a wet spot on a wet Tuesday night in February is (in my experience) the hardest job on the railway. Any replacement of ballast and formation more than an occasional wet spot is a renewal.
Putting all the above together, life expired track can be any or all of the above, but usually means rail, sleepers, ballast and fastenings together, with formation / drainage done in about 20% of cases.
However once you have to renew the ballast, it is almost always more efficient in whole life terms to renew the sleepers and rails as well, as the cost of the new materials is a relatively small proportion of the job. In fact it is usually actually cheaper in initial cost terms to replace rails and sleepers with new than save the old ones. The process of dismantling and temporarily storing the old stuff takes longer and needs more plant and manpower than it does to simply cut the old track into 20 metre panels, chuck it on a train, and get it away. If the old sleepers have any life in them they can be reused elsewhere; rail will typically be scrapped unless it is in in very good condition. (The scrap value is generally more than the cost of unloading and reloading the rail at a depot, plus doing the necessary ultrasonic checks to ensure the rail is fit for reuse).
If I may tag along to this thread, how is rounded (worn) ballast collected and disposed of?
I know that hardwood sleepers were much in use in the 19th century on certain lines and a particular type of Australian timber called Jarrah (Eucalyptus Marginata) was also very popular as use for sleepers with those early railway companies (Many of these redundant Jarrah ones are now readily available for purchase for use in gardening projects, in particular).
Thanks to you as well. I hope nobody minded the 'stupid question' for the sake of some complete explanations of a term that gets used a lot.
I know that hardwood sleepers were much in use in the 19th century on certain lines and a particular type of Australian timber called Jarrah (Eucalyptus Marginata) was also very popular as use for sleepers with those early railway companies (Many of these redundant Jarrah ones are now readily available for purchase for use in gardening projects, in particular).
If I may tag along to this thread, how is rounded (worn) ballast collected and disposed of?
Or, for big jobs, using the High-Output Ballast Cleaner (trivia: the longest train formation regularly seen on the UK network).As Bald Rick says, if it's too far gone (full of slurry, etc.) then you take the track up and load the ballast into rail wagons using diggers.
However, to compensate for that, they've found another way of achieving long-running lane closures: coversion to "smart" motorways.One thing I meant to say earlier. The Highways Agency has learnt a thing or two from the railways recently. Until around 10 years ago, motorway resurfacing was typically done by installing lane closures and a contra flow, which would be in place for a couple of months on a 5-10 mile stretch.
Now, they throw plant and labour at it overnight in 7-8 hour lane closures, and will resurface a few hundred lane metres per night. Very similar production process to the high output kit, and much more friendly to traffic flow.
One thing I meant to say earlier. The Highways Agency has learnt a thing or two from the railways recently. Until around 10 years ago, motorway resurfacing was typically done by installing lane closures and a contra flow, which would be in place for a couple of months on a 5-10 mile stretch.
Now, they throw plant and labour at it overnight in 7-8 hour lane closures, and will resurface a few hundred lane metres per night. Very similar production process to the high output kit, and much more friendly to traffic flow.
Or, for big jobs, using the High-Output Ballast Cleaner
Or, for big jobs, using the High-Output Ballast Cleaner (trivia: the longest train formation regularly seen on the UK network).
[youtube]UgsHycXWOU0[/youtube]
However, to compensate for that, they've found another way of achieving long-running lane closures: coversion to "smart" motorways.
Well, that's embarrassing.* cough * that's a relaying train, which is the longest formation. the BCS trains aren't.
But they normally manage to keep the same number of lanes by narrowing them and reducing the speed, avoiding the lane closures and contraflows that used to cause huge tailbacks a few years ago. Shame the railway can't do that.
How does a railway achieve narrow lanes, pray tell? There is only (normally) 300mm between trains on adjacent lines.
Granted that reducing the speed would allow you to review the track interval, but the lower limit is 100mm irrespective of speed.
We often have contraflows, but the legislation that your elected representatives have enacted means the railway has to deploy significant safety measures which generally make doing it less than cost effective.
We had a contraflow through Farnworth, but it was there for so long it made sense. The "good old days" of single line working on a Sunday afternoon with a pilotman seems not to be widely favoured these days but I spent 8 years working like that (and being careful which side of the Tamper I got out of ...)
How does a railway achieve narrow lanes, pray tell?
How does a railway achieve narrow lanes, pray tell? There is only (normally) 300mm between trains on adjacent lines.