Netherlands: high-tech fastening for high-speed track ... - Hilti

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Engineering Page 16 of the temperature-dependent displacement of the concrete slab relative to the substructure, the Hilti engineers specified rectangular guides, also made from stainless steel, to be placed over the connecting dowels. The expansion space within the guides is filled with polystyrene foam. Two of these outer dowels are positioned at each end of the concrete slabs. Both types of dowel, the Hilti HCD-C for the central area of the slab and the Hilti HCD-O for the ends, are set in the substructure with Hilti HIT-RE 500 adhesive mortar. Both types are equipped with a rubber O-ring at their top ends, designed to absorb initial loads and thus prevent the dowel punching through the concrete surface. The O-ring is held in place by a plastic cap on the dowels at the center section. This technology, the brainchild of experienced specialists, proved itself in tests that continued even over the 2003 Christmas holiday period. Thanks to many years of experience gained in road tunnel tests, the Hilti engineers were also able to meet the corrosion resistance requirements without difficulty. After a development period of only seven months, the Hilti system for concrete to concrete connection was ready for implementation and was given preference over other proposed solutions. The story now takes a leap forward in time to May 2005. Engineer Harry Kolk, responsible for construction of the railway, has returned to his office. Being an engineer, words are generally not enough for him – he needs drawings. Harry Kolk’s pen darts to and fro on the plans pinned to the white board on the wall. He mentions the poor subsoil and makes a sketch of the various layers: peat or clay with a layer of sand between. Even a cow running across the meadow generates ground oscillations. That’s how the ground behaves here below sea level. This work of modern engineering thus began with the time-honored technique of driving piles into the ground – to a depth of up to 30 meters. The track, and its dynamic behavior, can thus in many ways be compared to a bridge or viaduct. Read more about this in the box “Switch to dowels” on page 15. “Safety, quality and construction progress – that’s the order of my priorities”, explains Harry Kolk. The Infraspeed consortium founded by technology leaders Siemens, planners and contractors Fluor Daniel and the BAM construction company, has not only planned and built the high-speed rail track, it has also Harry Kolk: “We need a dependable system that offers a simple application.” been contracted by the Dutch authorities to look after its maintenance. “We need a dependable system. Maintenance will otherwise be very costly,” Harry Kolk continues, laughing mischievously. “But these dowels are expected to last a hundred years!” Harry works for Rheda 2000 vof, a joint venture of BAM, the Dutch construction giant and Pfleiderer, the German specialist in concrete rail sleepers and originator of the Rheda 2000 slab track system. In comparison with conventional methods employed in the construction of maintenance-free slab track, use of the Hilti dowels has allowed the thickness of the concrete layer in the superstructure to be reduced by 10 cm to only 24 cm. “We had to optimize the thickness of the slab track in order to meet requirements for the free-space profile of the new high-speed line,” explains Harry Kolk. “In total, only 24 cm remains for the thickness of the Rheda slab. The challenge, on the one hand, was to come up with a method of fastening the Rheda slab to the engineered substructure and, on the other, to optimize the construction process required with this fastening system. If you consider that the task is to lay a concrete band with a length of 160,000 meters, the importance of a highly efficient logistic process becomes obvious. Use of a high-tech product not only simplifies the job, it also reduces the time-related risks and costs tremendously.” The next day, Jan Valstar, one of the team from a subcontractor of Rheda 2000 vof, also has time for a chat. He and his two colleagues are well ahead with their dowelsetting work and have now established quite a lead over the next workgroup in the process. His job is to drill the 44 mm holes, to blow out the holes with compressed air and to then inject Hilti HIT-RE 500
Magazine Fall/Winter 2005 Engineering Page 17 Images at left: the upper part of the dowel, for the center section of the superstructure slab, is covered with plastic so that super- and substructure do not have direct contact. Adhesive mortar is injected into the holes and the dowels are twisted in. Images below: the dowels for the edges of the slabs are flattened on the side. Thanks to the expansion space, longitudinal expansion of the connecting dowels is possible. The sleepers and rebar for the superstructure of the left rail bed are in place and the dowels have been set. On the right, the superstructure has already been poured. The expansion joints are visible.
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Netherlands: high-tech fastening for high-speed track ... - Hilti

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