Neckar Weir

Weir in Horkheim repaired with SCHWING truck-mounted concrete pump

After the devastating flood catastrophes in the middle of last year, the flood protection issue was back on the agenda of public discussion in Germany. More than 10 years after the last great flood event, also the politicians began to engage in lively discussions about the future measures to be taken in order to protect the people living in areas threatened by flooding.

This is the case also for Horkheim, the souhernmost quarter of the town of Heilbronn, which was repeatedly affected by flooding in the past as the place lies only a few meters above ground-water level and is located only approximately 250 m away from the river Neckar. For this reason and also to ensure the protection at the workplace and the safety of operation it was decided in 2012 to tackle the basic renovation of the Horkheim weir – the first renovation measure since the construction of the weir 86 years ago.

The weir installation is located separately from the sluice, the penstock and the power plant at the beginning of the old branch of the river Neckar and evens out the old course of the river over a height of almost 6.80 m. The weir is 29.50 m wide and approximately 120 m long. The 4.50 m-wide piers were realized a the time of construction of the plant with non-reinforced rammed concrete. Due to its low resistance and high pore volume, this concrete is prone to the ingress of water with the result of frequently recurring frost damage. The closures of the weir are moreover corroded to an extent normal for their age and must therefore be urgently replaced by new ones.

The contract for the renovation work was awarded to the company Heberger from Schifferstadt. In one of the primary steps, two mooring posts of approx. 40 m³ were concreted on both sides of the river Neckar. A steel rope stretched between these mooring posts serves the purpose of securing the various pontoons and the equipment that will be used for the construction work.

The challenge of this pour consisted in the fact that the placing site on the right bank of the river was inaccessible for truck mixers. For this reason, the company BPD Saussele Betonpumpen GmbH from Besigheim in charge of the concreting work laid an approx. 170 m-long pumping line across the weir from one bank of the river Neckar to the other.

The concrete placing operations were carried out with the tried-and-proven S 28 X truck-mounted concrete pump from SCHWING. The machine was connected directly at the beginning of the pumping line at the weir head.

The SCHWING pump S 28 X is a truly universal machine which – thanks to the roll-Z folding concept of the placing boom and the single-sided attachment of the pumping line on the boom – has excellent sliding and threading capabilities. With its unfolding height of only 5.85 m and its reach of more than 17.40 m, the machine can also be used in halls or in tunnels. Another important advantage is the steep angle of slope and the short wheelbase of only 3.60 m which make the machine suitable for driving also off ordinary roads. The S 28 X is generally equipped with pumpkits with a stroking length of 2 m. In the basic variant with a pumping piston diameter of 200 mm, this pumpkit can generate a maximum concrete pressure of 108 bars so that also pumping jobs over greater distances like the one here in Horkheim can be handled without any problems.

The concrete is supplied by the company Godel from their mixing plant in Weinsberg. For the mooring posts a water-stop concrete (WU) of class C25/30 with 330 kg of cement and a largest round aggregate size of 16 mm was used which does not need any mineral admixtures as, for instance, fly ash. The pumping job was started with approx. 1 m³ of cement slurry in order to minimize the risk of plug formation in the line. Cleaning of the system was performed in the classical way with two cleaning balls and compressed air pushing the concrete in the direction of the placing site. Thus, it was possible to utilize also the normally remaining “residual concrete” in the foundations.

The transport of the concrete was effected by several Stetter AM9 FHC LightLine truck mixers of the new C3 series. These LightLine mixers are characterized by high transport capacity and very long service life.

To this day, two pours have been effected on the weir without any problems. The company Heberger was rather satisfied with the successful operation of the SCHWING truck-mounted pump used by Saussele for the work.

The completion of the weir renovation is planned for 2018.