A - Alternative Track, Track forms Flashcards
What are the advantages and disadvantages of the traditional track structure
It is cheap
It is quick to install
It is easy to repair when necessary
It needs repairing often
Access is required to the track, reducing operating time
Ride quality becomes uneven over time
When do problems occur with the traditional structure
When high speeds are reached, demanding high ride quality
Traffic frequency is high, restricting access for maintenance
Loads are high, resulting in rapid damage to track
What is a ladder track and what makes it advantageous?
A ladder track places reinforced concrete beams under the rail and has ballast surrounding
Using beam on elastic foundation equation it can be seen the maximum deflection is less as this is proportional to lambda, and so reducing the stress under the track
If settlement is now more uniform due to the concrete beam what does this mean for maintenance?
Maintenance is required less frequently
However an adapted stone blower is required
What is a cast-in sleeper track?
What is the result and problem?
The track is built and a concrete slab is poured around the sleepers
This creates a very strong track with small settlements
However it is expensive and if repair is required it is hard to do
What is a booted sleeper?
Similar to Cast-in sleeper but here a rubber pad is between the concrete pour and the sleeper bottom
What does the rubber pad do in a booted sleeper?
They give the correct amount of resilience
With a smooth ride and little settlement, and the rubber absorbs sound
If water gets in however the sleeper can become loose
Why do no tracks use baseplate directly on a slab?
Demands a very high level of accuracy
Can cut down the number of construction processes but can not be done by slip-form paving
Have to grind down the concrete to exact level then grout out to fix baseplate
Very expensive
What is an embedded rail, and what advantages and disadvantages does it have?
Rail is set in a recess in the base slab surrounded by tough durable resin
Good for use where road traffic must pass over it
Excellent rail support
Rail depth reduced
Minimum overall thickness of track structure
Rail can work loose
Why is floating slab railway good/bad?
Thick expensive railway which lasts a long time
Problem in the cement-asphalt mortar layer which must be formed is poured through holes in the precast slab
Explain asphalt base railways?
Constructed like a road, with sleepers installed into milled grooves in the surface of the asphalt
Only needs conventional technology which degrades slowly
Asphalt can deform and so doesn’t hold the sleeper well, can be repaired easier than concrete
What are the key points affecting design?
How do you get the levels right?
Conventional - Build as best then tamp
Other - dependent on alternative track
What about long-term maintenance?
Conventional - Just keep tamping
Other - Initially get earthworks right so not to get differential settlement
Can you turn a conventional track into one of these alternatives?
Not economically feasible atm
Need a track that can be built quickly whilst trains are not running
Is it worth it?
Balance investment with customer satisfaction, ride quality and maintenance required
