Futuristic Tunnel Portals on the A81 with alkus^® SF 3 Flex

Complex curves, concave recesses, and flowing transitions: During construction of the tunnel portals for a new noise protection enclosure near Böblingen and Sindelfingen, the 3 mm-thick alkus^® SF 3 Flex demonstrates what flexible solid plastic formwork facing can achieve when creating challenging concrete shapes.

A Distinctive Design for an Exceptional Structure

The approximately 850-meter-long noise protection enclosure on the A81 protects residents in Böblingen and Sindelfingen from traffic noise. While MEVA tunnel formwork travelers, support frames, and wall formwork systems were among the solutions used for the enclosure itself, the architecture of the tunnel portals presented additional challenges: curves, straight lines, and sloped surfaces intersect, while surfaces flow into one another to form distinctive concave recesses.

3 mm Flexibility for Concave Curves

The most demanding portal sections feature inward-curving, bowl-shaped recesses. To form them, precisely joined wooden elements of the special formwork were faced with alkus^® SF 3 Flex. At just 3 mm thick, the solid plastic formwork facing can conform to the formwork’s curved geometry. Before the formwork is closed, the erected formwork section reaches a height of approximately nine meters.

Special Formwork and Formwork Facing Working Together

MEVA developed custom special formwork for the portals’ complex intersecting surfaces. In addition to the special formwork, the project uses MEKit, the MT 60 and MEP shoring systems, and Triplex diagonal braces. Concrete is placed into the formwork through several filling ports. Cones with Dywidag threads on both ends accommodate the form ties.

The portal construction comprises four sections in total. The special formwork was designed for reuse in the remaining sections: it is rotated or tilted for this purpose.

The Result: Distinctive Architectural Concrete Shapes

The A81 project demonstrates how flexible formwork facing and custom-designed special formwork work together. alkus^® SF 3 Flex forms the direct concrete-contact surface and follows the formwork’s complex curves. This is how the noise protection enclosure’s distinctive, futuristic tunnel portal shapes are created.

“Where other materials reach their limits with complex geometries, that is often where new possibilities begin for us. Our solid plastic formwork facings open up new possibilities for demanding shapes, curves, and custom formwork solutions. This project clearly demonstrates how SF 3 Flex can be used to achieve even extraordinary geometries with precision,” says Daniel Keller, CEO of alkus AG.

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