Metro Karlsruhe: STB 450 support frame masters forces of 250 kN

Project: Marktplatz underground station with junction, Karlsruhe, Germany

Owner: KASIG, Karlsruhe

Contractor: BeMo Tunnelling GmbH, Innsbruck, Austria

MEVA systems: STB 450 support frame, Mammut 350 wall formwork, MevaFlex slab formwork, MT 60 shoring system

Engineering and support: MEVA Schalungs-Systeme, Nord and Berlin branches



Max. 2 cm Deflection in 10 m

Karlsruhe, a city with 300,000 inhabitants, is a technology hub in Germany’s Southwest. The city’s trams bring in passengers from all over the region to the city centre, yet heavy traffic plagues the central business district day in, day out. This is why cars are to be banned from the streets and trams relocated underground, serving the centre through a new 2.4 km tunnel, Karlsruhe’s first metro line. MEVA formwork is being used to pour the outer and intermediate walls of a new train station on the tunnel route.

Heavy loads on loose ground
Underground construction in this area is difficult, as the ground consists of layers of gravel. It was only after approx. 20 m deep slurry walls and temporary columns had been poured that the cover plate for the tunnel station could be poured and the earth below the plate excavated before pouring the tunnel floor. Reinforced concrete walls, 80 cm thick and up to 10.16 m high, are poured along the slurry walls using MEVA wall formwork. The high density of rebar requires the use of a flowable concrete that can be poured through the filling nozzles and pressed through the rebar without problem. This type of concrete exerts high pressure when setting, and the building specifications demand that the walls are straight and must not bend more than 2 cm over the total height of 10 metres. Hence, the contractor chose the most powerful systems for single-sided pouring available from MEVA: the Mammut 350 wall formwork that handles loads up to 100 kN/m², the STB 450 support frame and Triplex heavy-duty braces.

Two large forming unitsfor 10 m cycles
Each unit is 10 m long and over 10 m high with a forming area of 105 m². Ten 1 m wide panels are ganged next to each other and height-extended three times. The 4.50 m high support frames have four height extensions and are equipped with hydraulic devices and wheels that allow them to be wheeled from cycle to cycle without being disassembled

Tensile forces up to 250 kN
It had been clear from the start that high concrete pressure was a critical parameter that had to be considered when choosing the formwork and designing its setup. This was confirmed in practice when the pressure gauges on the tie rods measured peak tensile forces up to 250 kN. MEVA’s engineers had catered for the enormous pressure by additionally attaching dry ties to the support frames’ top extensions to fix them in place and by bracing and stabilising the extensions relative to each other using vertical tie rods to limit bending to a maximum of 2 cm.

Inside walls and intermediate ceilings
When the outside walls are finished, 6 m high inside walls will be poured to carry the 1 m thick intermediate ceiling between the platform and the shop levels. The slab will be poured using the conventional MevaFlex slab formwork and MEVA’s new MT 60 shoring systems.

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