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Formwork Vibrators for Concrete Compaction at "Tunnel Luise Kiesselbachplatz" Munich
The Tunnel “Luise Kiesselbach” in Munich is the last but current tunnel construction within the scope of the ring-road tunnel constructions of the “Mittlerer Ring” in Munich after having finished “Petuel-Tunnel (2008)” and Richard-Strauss-Tunnel (2011)”. It is currently constructed by the consortium “Arge Tunnel Luise-Kiesselbach-Platz”, consisting of the partners “Wayss & Freytag Ingenieurbau AG (technical management), Berger Bau GmbH (commercial management) und Bauer Spezialtiefbau GmbH”. A citizens´ decision of the city of Munich led to the resolution to reroute the enormous traffic of the traffic junction “Luise-Kiesselbach-Platz” to a tunnel below the ground. The completion of this tunnel is planned for the year 2015.
The tunnel is constructed in cut-and-cover method and has a length of 1.53 km, running from the northern tunnel portal at the end of highway A96 along the “Garmischer Street” southwards to “Luise-Kiesselbach-Platz” located at the end of the highway to “Garmisch-Partenkirchen”. For a short distance of 400 m the driving lanes between “Luise-Kiesselbach-Platz” and “Högelwörtherstreet” will be directed through an open trough with sound protection walls at both sides, followed by another 620 m long tunnel construction running eastwards from “Heckenstallerstreet” to “Passauer-Street”. End of may 2013 the tunnel excavation work had been finished. At the moment the tunnel walls, especially the tunnel center walls, are being completed. The walls are poured in two sections due to the fact that the height of each center wall is different. The concrete of the first few meters of the center wall, that is up to 4.0 m height, is poured and compacted conventionally from above with the help of internal vibrators. In a second step the formwork for the wall section below the ceiling is set up. In this case, it is no longer possible to use internal vibrators, so that compaction can only be achieved by help of external formwork vibrators.
Mooser pneumatic formwork vibrators proved to have important impact to gain excellent compacted concrete surfaces at the former Munich tunnel constructions “Petueltunnel” and “Richard-Strauss-Tunnel”, so that it was quite obvious to use them again for the concrete compaction of this current tunnel project at “Luise-Kiesselbach-Platz”. The Mooser pneumatic vibrators type VR* reach their nominal speed at once by switching on the air supply and they quickly pass through the critical resonance frequency of the formwork. A quick acceleration of the vibration and an almost lossless transmission of vibrating energy to the concrete results in excellent concrete surfaces and in great concrete compaction depths. The external vibrators are mounted onto the mounting clamp type STA including formwork specific adaptors for the H20 formwork girders. Thanks to the adaptor-pair the vibrators can be attached to the formwork in a way that is optimized for vibration and gentle to the girder. The concrete compaction of the walls with a height of 1.50 m and thickness of 60 cm is completely done by one single row of vibrators, which are mounted onto only one wall-side of the formwork. At the walls of the lateral tunnel sections with a thickness of 90cm, which are partly running from the main tunnel in direction to the A95 highway, the external vibrators are clamped onto a single-faced Meva Mammut formwork. In order to mount them onto the Meva Mammut formwork joint, the adapter-pair for the H20 girder simply has to be replaced by the adapter-pair for the Meva Mammut formwork joint. In order not to exceed the defined vibrator distances, the vibrators partly also have to be mounted onto some cross girders of the Mammut formwork. In this case, the STA clamp cannot be mounted onto the formwork girder with help of formwork specific adapters. In order to achieve a tight lock between vibrator and cross girder anyhow, a piece of wood can be put between the cross girder and the brackets of the STA clamp. The piece of wood prevents that the STA clamp slipps of the steel cross girder.
An air compressor and a central air distributor provide the necessary air supply (air volume and air pressure) for the vibrators. With help of the air distributor one single person is able to operate all connected vibrators one after another and is able to compact the concrete all by his own. The external vibrators are always operated at those positions, where concrete is being poured. Thus a standard construction-site air compressor with an air volume 4-6m³/min and an air pressure 6-10 bar is enough to provide sufficient air for all vibrators. Simultaneously the stress onto the formwork, caused by normal vibration, is minimized. For the concrete compaction of the tunnel technique rooms, Mooser vibrators are mounted onto a Streif Light aluminium formwork. The wall thickness that has to be compacted is 60 cm – 90 cm. The little weight of 12.5 kg of the vibrating unit, consisting of the vibrator and the STA clamp is a great advantage, if vibrators are to be relocated onto the formwork according to the pouring process. Relocation of this pneumatic vibrators is a quick process. It takes about one minute per vibrator. Furthermore the construction-site saves additional costs by relocating the vibrators, instead of having them all mounted onto the complete formwork face.
The compaction results of the formwork vibrators at “Luise-Kiesselbach-Platz” are excellent. Thus it can be proved that also small devices like external vibrators attribute to a quick and successful construction process, as long as they are working reliable and powerful and as long as the compaction concept is adjusted to the formwork and the concrete.
According to the project leading construction team, the tunnel construction “Mittlerer-Ring West” (this is the official name) is on schedule. For a project of this size this is not always a matter of fact. It can be ascribed to the experience, the competence and the good collaboration of all companies involved.