This is what $25 million looks like, a KiwiRail ballast machine recently parked up at Te Kūiti. Photo supplied
Unusual yellow rail wagons on the Te Kūiti siding recently are the working part of a ballast cleaning operation on the North Island Main Truck Line south of Te Kūiti.
The ballast cleaner (aka undercutter, shoulder ballast cleaning machine) specialises in cleaning the railway track ballast.
KiwiRail has had the ballast cleaner, which would cost around $25,000,000 to replace, for about 12 years, a spokesperson said.
KiwiRail owns one ballast cleaner, which can be transported between the North and South Islands via ferry.
The ballast cleaner can clean about 350 metres of railway line per hour and works a 10-month programme that covers sections of the network at a time.
The ballast cleaner will be undergoing maintenance in Hamilton for a few weeks then will return to Te Kūiti for a short while.
The machine works by using a cutter bar that runs beneath sleeper level excavating all of the ballast under the sleepers to a specified, variable depth.
A conveyor then moves the ballast into the cleaner, where it gets forced through a mesh by a shaking chamber.
Pieces of ballast which are smaller than the mesh size fall through and are rejected, those that are bigger than the mesh are returned to the track along with fresh ballast.
Some ballast cleaners have both ballast and spoil wagons attached to which the materials are fed by a series of conveyor belts.
The ballast bed distributes the loads of the trains uniformly onto the track substructure and assures a firm, unshifting position for the sleepers.
To withstand the dynamic impacts, the ballast bed has to be elastic.
An increase in the proportion of fines reduces the elasticity of the track, the water permeability and the durability of the track geometry.
This leads to irregular settling of the track which tamping can compensate only for short periods.
From a certain point it is more economical to clean the entire ballast bed.
