Making better use of your ballast

Many railways have huge amounts of surplus ballast on their linesides, and a new machine developed by Plasser & Theurer finally allows it to be used, saving money and speeding track maintenance. Wolfgang Nemetz, of Austrian Federal Railways (ÖBB), explains his railway’s experience with the new technology.

MODERN track machinery and technology enable the efficient processing of material for re-use. Such machinery ranges from ballast cleaners to formation rehabilitation machines which process reclaimed ballast material - and there is further potential for reducing the quantity of new material needed to maintain track.

With conventional technology, it was impossible to determine the exact amount of ballast required, so large quantities of ballast were deposited, for example during tamping, in areas where it seemed to be lacking, often according to the maxim that too much is better than too little. Since the excess ballast could not be moved elsewhere efficiently, huge amounts of unused ballast can accumulate alongside the tracks over the years.

With the development of Plasser’s ballast distribution system (BDS), it is finally possible to transfer these unused resources efficiently and cut the amount of new ballast required during maintenance. The excess ballast is collected during ballast regulation and stored in an integrated ballast hopper, from where it can be returned to the track in areas where ballast is needed. The machine can handle large quantities of ballast and is equipped with a front plough, shoulder ploughs and, most importantly, a multi-section centre plough enabling a variety of ballast transfer movements to be carried out.

The front plough is mainly used on work sites for distributing and regulating accumulations of ballast, while the shoulder ploughs can pick up ballast from the toe of the ballast bed thanks to its flexible configuration. A slewing limitation means traffic on adjacent tracks need not be affected when the machine is being used. The diagram below shows the various ballast transfer movements possible when using the centre plough. The centre plough can also be used on lines electrified with third-rails.

The surplus ballast is stored in an integrated ballast hopper with a capacity of 40 tonnes and this can be expanded in multiples of 100 tonnes by adding MFS100 units. The ballast can be placed accurately by conveyor belts and distribution chutes.

In combination with modern high-performance tamping machines, ÖBB benefited from the high output of the BDS. This meant fewer track possessions were needed compared with other systems. In order to reap the full benefit of BDS in terms of ballast relocation, a procedure had to be developed that could determine what quantities of ballast were actually in the track and not used.

For this purpose, the EM-SAT 120 track measuring system was equipped with a ballast profile measuring system and the required target profiles were added to the existing infrastructure geometry database. The target data for level and line, and now the required ballast profile, are read from the infrastructure geometry database and then compared with the measurements. During the automated evaluation it is possible to determine ballast levels and decide exactly where and how much ballast is needed to produce the required ballast profile.

	The BDS 2000 ballast distributing and regulating machine is generating significant cost savings in service.

Depending on the working direction of the mechanised maintenance train (MDZ), the excess quantity of ballast (collected in the BDS) is compared with the requirements, thus establishing the actual amount of new ballast required. During operation of the MDZ, the necessary quantity of new ballast can be added immediately by the BDS.

An ÖBB study compared the cost of ballast management, using the BDS 2000 system, with the costs incurred when using traditional ballasting methods during tamping. No financial evaluation was conducted in the study concerning the increased working speed, which leads to shorter track possession times for the main work, or with regard to the additional track possession times no longer required for pre-depositing ballast according to traditional work methods.

The comparison shows that the BDS system is more economical, reducing the quantity of new ballast required by 38% or more. Taking into account the cost of track possessions, the economies actually achieved are likely to be significantly higher.

An analysis of the measuring data now available has shown that the quantities of new ballast required by ÖBB during pre-ballasting in the course of tamping can currently be reduced by an average of 60% by using the BDS ballast management system in combination with the measuring system.

Due to the rapid increase in the working speed of the latest tamping machines, ballast regulating using conventional ballast distributing and profiling systems has become the limiting factor in terms of the working speed of the overall system. The BDS enables a significant increase in the productivity of the overall process, with a distinctly higher quality of ballast profiling.

Generally, an additional track possession for pre-depositing ballast is no longer required when the optimised ballast management system is used. BDS 2000 is a milestone in the development of ballast handling that achieves not only significantly higher productivity, but also offers a previously unknown and extremely economical method of ballast management.

ÖBB now relies on integrated ballast management in the course of tamping. The excess quantities of ballast lying in the tracks are detected by the ballast profile measuring system during EM-SAT surveying, and with the help of this analysis, there is often no need to supply new ballast for tamping over extensive areas because the surplus ballast to be found in many areas is picked up and stored in the material conveyor and hopper units of the BDS to be returned to the track wherever it is needed.

The advantage of integrated ballast management is that the requirement for new ballast can be determined before starting maintenance tamping and then supplied as required in the course of tamping without the need for the additional track possession that was previously necessary. Evaluations so far have shown that due to this technology the amount of new ballast required has been reduced by more than 50% and this has not only enabled the costs for tamping to be reduced, but has also helped to conserve the environment by encouraging a more economical use of valuable raw materials.