For practically the entire HSL route (with the exception of the connections to existing tracks and the section in North Brabant up to the Belgian border), it was decided to use a so-called ballast-free rail system as a stable base for the rails. The ballast-free rail system differs from regular railways, in that the rails do not rest on sleepers and a base of rock metal, but are anchored in concrete slabs that are poured on top of the no-recess slabs. This makes the rail system strong and rigid. Other advantages of ballast-free rail are: extended life, low maintenance and less wear of rails and wheels because dust and rubble are virtually absent.
This ballast-free construction, with the rails anchored in concrete, is laid out using the 'Rheda-2000' method. The building consortium Rheda 2000 v.o.f. (comprising Bam Civiel, Bam Rail and the German firm Pfleiderer, which has a patent on the rail system) has a patent on this construction method (the name of Rheda-2000 refers to the German town of Rheda, where a type of ballast-free rail system, the predecessor of the system used on the HSL, was first applied in 1972).
The contractor who in the end has responsibility for the superstructure of the HSL, including the ballast-free rail, is Infraspeed.
On the no-recess slab, a synthetic felt is laid to separate the substructure concrete from the superstructure concrete. This felt is used to:
At places specified in advance, holes are bored in the no-recess slab (the concrete base). At a later stage, builders can place the dowels (steel pins) that anchor the rail construction to the substructure.
Then the sleepers (made of steel and concrete) are laid out. The sleepers for Rheda-2000 rails differ from the regular wooden or concrete sleepers used in ballast rail systems: they consist of two concrete parts that are connected with reinforcement steel. They are approximately 2 metres wide. On top of both of the sides there is a U-shaped concrete element. In these elements, the rail clamps that will hold the rails have already been fitted already in the factory. A gripper lays out the sleepers, five at a time, at specified intervals of 60 to 65 centimetres.
The sleepers are cast into the concrete. This concrete slab is then fixed with the dowels to the floating slab.
Temporary rails (a construction rail) are placed on top of the sleepers. After fitting the temporary construction rails, the complete track construction is aligned both vertically and horizontally by means of spindle bolts that carry the entire track construction. A computer laser check quarantees the proper alignment.
After this, steel benders put in reinforcement steel lengthwise along the track, both under and above the sleepers. At transversal slopes (in curves) clamps are also fitted at the sides of the slab. These are fixed to the reinforcement of the sleepers. In this way, two concrete elements are connected to each other, creating a single whole and a rectangular pattern of reinforcement steel.
The next step is placing and anchoring (green) metal plates on beams, serving as formwork, on both sides of the sleepers. This is done with a machine.
After every tenth sleeper, a traverse partition (a so-called dilatation joint) is placed, thus creating sections of approximately 6 metres. Like the felt between substructure concrete and superstructure concrete, these sections with dilatation joints that will used to absorb stretch and shrinkage caused by temperature changes.
After all these preparations, the extremely intensive definitive measuring work starts to set the rails at the right height and longitudinal direction. The setting is accurate to within two tenths of a millimetre. As soon as the rails have been set definitively, the concrete can be poured.
A type of modified concrete is used. The concrete is poured between the sleepers and over and between the reinforcement. In this process, the reinforcement gradually disappears under the concrete and part of the sleeper is cast in the concrete.
After the concrete has been poured, the track is temporarily covered, so that the hardening process is not affected by weather conditions. The concrete is smoothend out meticulously by hand. The total hardening process takes four weeks. During this period, the concrete already can sustain certain controlled loads.
Thanks to the doweling and the reinforcement steel, the hardened concrete forms an extremely rigid and strong construction, which is capable of absorbing the enormous forces of the high speed trains.
Once the concrete has hardened, the formwork and temporary construction rails (15 metres long) can be removed.
Now the definitive rails, measuring 120 metres, weighing 7.2 tons each and known as longrails, can be laid out. The longrails have steel heads, while in curves the rails are made of tempered steel, requiring little or no maintenance.
First the so-called 'mustard pots' are laid out, which are used to roll out the longrails.
After this, the longrails are rolled out from a work train that rides backwards and lays its own rails, as it were. The rails are screwed tight to one out of every 10 sleepers.
The longrails are heated to a neutral temperature, so that they reach their nominal length. Then they are welded together without joints, by heating and melting the heads. As a result, a so-called jointless railway is created. Now the longrails are anchored to the sleepers at intervals of around 60 centimetres. As a consequence, the rails can scarcely expand or shrink, and comfortable travelling is guaranteed - even at 300 km/hour.