No-recess concrete slab
The high speeds trains on the HSL will be travelling with a top speed of 300km/hour. Those speeds demand a lot of the railway construction. A traditional railway embankment with rails on sleepers and ballast (a foundation of rocks) could subside in many places, due to the soft Dutch soil, and would require a lot of maintenance and readjustments. Therefore a no-recess concrete slab construction was the foundation of choice at many points of the HSL route. The slab ensures that the railway cannot subside.
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A no-recess concrete slab is supported by a great number of long, thin piles. Typical for this construction is that there is virtually no setting, which means subsiding before becoming stable. In places the piles supporting the slabs, the piles are partly overground and therefore visible.
Places where no-recess concrete slabs have been applied:
- Haarlemmermeerpolder
- Nieuwe Wetering - Hoogmade
- Hazerswoude-Dorp - Zoetermeer
- Berkel en Rodenrijs - Rotterdam N209
- Rotterdam tussen A20 - emplacement CS
- Barendrecht - Oude Maas
- Oude Maas - Dordse Kil
- Dordse Kil - Hollandsch Diep
- Hollandsch Diep - Zevenbergschen Hoek
- at De Mark river
Digging a ditch
A ditch was dug to a depth of around a metre, making the definitive HSL track practically level with the ground. The released earth was transported elsewhere.
Applying layer of sand with drainage
The bottom of the ditch was covered with a 30-50 cm layer of sand, and this layer contained a vertical drainage system. Such a system consists of 10 cm wide synthetic strips, which were stuck into the ground to a depth of 5 to 7 metres. The drainage system allows water from the subsoil to flow upward, and spread out through the layer of sand. This vertical drainage helps to speed up the setting of the body of sand.
Raising the ground
On top of the layer of sand (at the sides) a layer of earth was applied, which varied in height depending on the local situation: in low-lying parts only 50 centimetres, and at mounds up to a height of 9 metres. This soil will be covered with grass, so that the HSL will have a natural aspect.
Consolidation
It took more than a year for the earthen body to consolidate (bedding down/setting); in this period it subsided a little. For this reason the earthen body was raised once more to the required height. The vertical drainage system speeded up the process.
Finishing at height
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As soon as the earthen body had consolidated sufficiently, it was finished at the right height. This concluded the groundwork, after which the concrete work could start.
Driving concrete piles
Then it was time to lay the foundation of the slab construction. Concrete piles were driven into the ground: 8 rows of 4 piles at 30-35 metre intervals. This phase also included piling for the overhead wire masts and the side elements.
Freeing the reinforcement
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At the top of all the piles, 50 cm of concrete was drilled off to free the reinforcement. After this the construction floor could be poured.
Pouring the construction floor
Instead of working in the sand, a thin layer of concrete was poured to obtain a clean, hard construction floor.
Braiding the reinforcement
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The steel reinforcement for the concrete slabs were put in place and fixed to the freed-up reinforcement of the foundation piles.
Applying formwork
Metal formwork was applied to pour the concrete in. Afterwards, the formwork could be removed easily.
Pouring concrete slabs
_1024x685_tcm112-11472.jpg&alt=Constructie van de zettingsvrije plaat waar de HSL-Zuid gebundeld is met de A4 (januari 2004)&text=Constructie van de zettingsvrije plaat waar de HSL-Zuid gebundeld is met de A4 (januari 2004)&width=813&height=541 )
On site, the concrete slab construction was poured. The concrete slabs are 30-35 metres long, 3 metres wide and 50 centimetres thick.
Mounting the side beams
Beside the no-recess concrete slab, piles were driven to support the side beams. From the top of these beams the concrete was drilled away. On top of this, a construction was poured, which formed the base for the prefabricated side beam. The superstructure contractor will install fences or sound barriers on this side beam.
Foundation of overhead wire masts
The foundations for overhead wire masts were put in place between the no-recess concrete slab and the side beam construction.