Re: Cleaning Ballast - Why do they need to do this?

["Rod Gayford" <rjaygee@smartchat.net.au>]

They use geofab extensively in NSW. I have noticed that they often go back
in bad drainage areas and dig sumps and drains with flat agricultural
drainage pipe covered in geofab.  As for sleeper vs tie, the last NSW State
Rail tender I saw referred to quotes on concrete "crossties".

Cheers
RJG
Christopher_Martin GORDON <cmgord@ecr.mu.oz.au> wrote in message
7q1tli$7gs$1@mulga.cs.mu.OZ.AU">news:7q1tli$7gs$1@mulga.cs.mu.OZ.AU...
> : Ballast cleaning (as distinct from simply putting new ballast under the
> : sleepers) is done to remove some of the fine and dirty material from
under
> : the sleepers, thus lowering the track. By dirty material, I mean silts
and
> : organic soil; by fines I mean degraded ballast that is less than 25 mm.
Fine
> : and dirty material does not support the track well, and encourages the
> : growth of weeds that hasten the degradation of ballast and timber
sleepers..
>
> : Placing new ballast directly on to soft clays or other fine deformable
soils
> : is bad technique. Under the axle loads of trains, and especially with
the
> : assistance of rain, the fine soil will quickly work though the ballast.
It
> : will act like a lubricant between the stones, allowing movement to
occur.
> : The line and top will rapidly deteriorate. Ballast must be placed on a
finer
> : stone material that can (1) carry load without excessive deformation,
and
> : (2) will not break down or weaken under normal rainfall.
>
> I am not sure about NSW but it Victroia when they re-lay track like
station
> pits in the suburban area, they take out all the old ballast, and clean
back to
> level dirt, and before the first ballast is put down, something called
> Geofrabic, which basically stops the dirt/mud from coming up through the
> ballast.  Then (just to keep this complete) a layer of ballast is put
down,
> then the concrete sleepers, then tracks, then ballast to the top of the
> sleepers, then tamped, and then more ballast to the top of the sleepers
again
> (since the tamping will put almost all the ballast under the sleepers) and
the
> final grading, tamping.
>
>
>
> --
>
> Chris Gordon
> http://www.ecr.mu.oz.au/~cmgord