Formation reinforcement on the Austrian line Timelkam-Redl Zipf using the AHM 800-R

Austrian Federal Railways (ÖBB) introduced mechanised methods of formation rehabilitation very early on using the available ballast cleaning machines as a basis. At the beginning of the nineties the call for a powerful track machine for installation of a protective layer became louder. One of the main demands was the incorporation of a recycling process for the track ballast.

Consequently the developing engineers at Plasser & Theurer designed the AHM 800 R excavating machine which incorporated for the first time a process for material recycling into a heavy-duty machine. This machine has been in service for the rehabilitation of existing lines on ÖBB since 1994. The results can certainly be termed as very good.

No hindrance to adjacent track even during operations

• Removal of the top layer of ballast using excavating chain 1 and transport to the crushing plant
• Excavation of the remaining ballast bed material using excavating chain 2 and transport of the spoil
• Smoothing the formation crown
• Breaking the ballast material in the crushing plant and transport to the mixer
• Production of a sand-gravel mixture for the formation protective layer in the mixing plant adding new FPL material and water
• Continual adjustment and checking of the water content of the sand-gravel mixture for an ideal degree of consolidation of the FPL
• Insertion of geotextiles, geogrid or PVP formation rehabilitation slabs is possible
• Insertion of the sand-gravel mixture for the formation protective layer in the required thickness
• Regulating and consolidating the sand-gravel mixture to the prescribed degree using large plate compactors
• Supply of the required material using towed MFS material conveyor and hopper units

The AHM 800 R is capable of performing a large proportion of the protective layers required by the ÖBB. For quality control the operations are recorded as follows giving the results as a foundation for acceptance:

• Excavation depth, thickness of layer and formation crossfall are measured at all marking points
• At least once a day the stone size distribution and water content of the protective layer are checked in the laboratory section of the machine
• Roughly every 200 m, load plate tests are made on the substructure formation and on the protective layer to determine the resiliency modulus
• Occasional tests of the thickness using the isotope probe as per Troxler.

All results can be considered as very good. Not least, during the operations together with the SUZ 500 high-speed relaying train, finished metre outputs of up to 250 metres per day (previously not thought possible) were achieved in two-shift operation. This figure relates to the insertion of a protective layer and track renewal on existing lines!

Geo-radar instruments mounted on the machine

The application of geo-radar systems to determine the subsoil conditions is gaining increasing importance. This process is also used in conjunction with formation rehabilitation and complements the localised soil investigation by taking probes. Geo-radar enables a continuous and fast survey of the geotechnical state of the railway line.

The objective of this method of investigation is to determine the pollution within the ballast bed and the mixture of ballast with the subsoil. It is also possible to locate water traps. The qualitative measurement of the water content in the subsoil enables the existing drainage quality to be assessed. By comparing the condition before and after the rehabilitation, it was possible to make a quality assessment of the formation rehabilitation work performed.

The AHM 800 R itself enables considerable savings during formation rehabilitation, for example:

• Installation of a protective layer without removing the existing track.
• Recycling of the old track ballast, thus fewer transport costs, savings of up to 50% new material, fewer costs for transport to and from the site, dumping, specialist disposal, recultivation and energy.
• Option for simultaneous insertion of geotextiles in one operation.
• Working output of 40 to 80 m/h, depending upon the thickness of the new protective layer
• Rail services not hindered on the adjacent track.
• Reduction of track possessions by up to 50%, thus reduction of operational hindrance costs.
• Complete worksite operation including transport of material to and from the worksite only in the track under repair, thus less environmental damage, no construction of temporary access roads, no road traffic.

Besides these advantages which come directly from the application of the machine, the installation of a high quality formation protective layer such as that produced by the AHM 800 R, has wide-ranging positive effects on the maintenance costs. The properly installed protective layer with geotextiles brings a high initial quality of the track with an additional quality reserve. The maintenance expenses are minimised and the service life of the track extended.

This quality reserve has been proven on the basis of the evaluations of the MDZ quality figures of the track recording car runs: the previously usual tamping intervals of approx. 2 years have been extended considerably which has brought a drop in the maintenance costs.

AHM 800 R

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