I often get asked, “What is it that you do?” when I tell people I’m out in the middle of nowhere doing a recon.
The stability of the the railway is dependent on the rocks and dirt underneath the steel and sleepers. There are three layers to the rail, a stabiliser mix (basically rocks with a bit of concrete), a capping layer, then the ballast. The ballast is usually 40-70mm rocks that are shaped perfectly to fit together when weight is applied to it. The more weight, the tighter it grips to itself.
Occasionally parts of the rail line get filled with mud and water and that causes the whole section to sink and slide about which makes the track bumpy and dangerous. When that happens, it is time for a track recon.
How’s it work?
The first step is fairly easy, at either end of the section that needs to be fixed up the rail is physically cut and then dragged back up the track and out of the way. Then a bobcat with forks on comes along and scoops out all the sleepers to be stacked up neatly. Once the sleepers are out of the way the fun really begins.
Excavators start to dig out all the old ballast into Hydremas which tip it onto a spoil pile for recycling later on. Once the ballast is out they then keep digging down, usually at least another metre or so getting rid of the mud and water and unclean dirt (I know right). Once they are done a bulldozer and a roller will come in and even out the surface and make it hard and flat.
They will then roll out some geofab, this offers a layer of separation between the regular dirt and the stabiliser.
As it is brought in by the Hydremas it is leveled out, rolled, compacted, and generally winds up looking like a hardened dirt footpath. As the go along the length of the job the geotechs will measure it all with a nuclear density gauge to make sure it is capable of handling the weight of the trains and will also not absorb to much water.
Once completed a layer of capping is then laid out in the same process. The capping has a different amount of concrete mixed in to offer further protection from water and weight compaction.
At this point we start bringing in the base layer of ballast, this is set to a particular depth and covers the stabiliser and capping layers. It is leveled by a bulldozer and compacted with a roller to “lock” the stones into place.
Once that is completed the sleepers are then put back into place, usually with The Octopus. This is an attachment that goes on an excavator that can pick up 6 sleepers at a time from the neat stacks they were put into earlier, it will then spread them out to a predetermined spacing and drops them down onto the ballast base layer. When they are in place a loader will then drag the rail back down and fit it into place.
After the rail is put back into place it is time to clip it up. A crew of labourers will reconnect the rail with the clips, biscuits, pads, and often a small excavator is used to lift up the sleepers hard against the rail to assist with this process. Generally whilst clipping up the Hydrema drivers get to have a bit of a break.
When the rail is clipped into place it is time to flood the track with ballast. If you are lucky there will be a circuit you can do, you get on track at one end and drive towards the other, tipping off your load as you go along.
Between loads a bobcat will run along with a spreader bar to ensure an even layering of the ballast. Eventually the rail will wind up looking a lot like this.
As soon as the track is completely flooded it is time for the tamper and shaper crew to come through. These are specialised trains, one will move the excess ballast from the track and get it all to a uniform shape, then the tamper will come through and it picks up the rail, punches some prongs into the ballast, vibrates strongly, and locks the ballast and the sleepers into place.