A - Trackbed Maintenance Flashcards
What maintenance is required?
Correct track levels Clean or replace ballast Restore shape of rail head Rerail
Briefly explain the process of tamping
It restores the line and level of the track by lifting the rails into their correct position and vibrating ballast underneath so that it re-forms itself to support the track at its new level
What is two advantages of tamping?
It restores the line and level of the track The process is automated and so is relatively quick (2km/hr)
What are disadvantages of tamping?
It leaves the ballast in a loosen state Some immediate settlement will therefore occur Stability of the track is reduced, required temporary speed restrictions Damages the ballast stones
What is stone blowing?
A pipe is inserted into the ballast alongside the sleeper and small stones are blown down into any gaps which exists between the bottom of the sleeper and the ballast
Why is stone blowing advantageous to tamping?
Does not disturb the ballast Little immediate settlement and no ballast damage
Why is tamping advantageous to stone blowing?
Stone blowing is a lot slower and expensive It cannot be done with steel sleepers
What is ballast compaction?
Dynamic Track Stabilisers grip the rails and shakes the whole structure, vibrating ballast stones and inducing some immediate settlement and restores some stability, which also avoids the need to speed restrictions
Explain with a diagram the process of ballast cleaning
A ballast cutter removes the ballast will sieves removing fine material and only large clean ballast being re-placed
What is necessary to remove corrugations?
Rail grinding This can be done up to a point where the rail is no longer strong enough
What three reasons explain why track bed is likely to return a previous state?
Sub-grade has a large influence on the track and tamping does not affect the sub-grade The ballast is not regularly cleaned and so damaged areas remain present The rail has built in stresses which lead to long term bending
How can design lift tamping improve sites?
Positions that after a few weeks would return to the same poor state, could be design tamped where the track can be lift in a state opposite to that in a few weeks, creating a flat track in the long run
