S10 Mühlviertler Highway, Construction Section 4.1, Section Bypass System Freistadt

With the S10, ASFINAG completed the long-planned connection of the A7 motorway from Linz in direction Czech Republic. For the awarding and completion the 22 km long section was divided into several construction sections. In January 2011, the contract for the construction section 4.1 - the bypass Freistadt - was awarded to PORR Tunnelbau GmbH as the best bidder. PORR Bau GmbH, subsidiary in Upper Austria, and PORR Bau GmbH, Infrastructure Department were integrated into the execution of the project in the form of a performance group.

The project consisted primarily of the construction of six bridge structures, two passageways, one underground road, a gallery, two tunnel structures in accordance with mining practice and several auxiliary bridges as well as the completion of two bridges from front construction section and the earthwork and road construction of a 4.5 km long construction section.

Due to the multiplicity of objects subdivisions or object families were formed for the production. The first group consisted of three bridges, each with two bearing structures for each directional roadway.

The first object, the gallery bridge F41, is a 3-field bridge structure with separate bearing structures with a length of about 95 meters and spans of up to 37 m. As cross-section a prestressed plate with low angle view including cantilever plates was used for execution. The production of the structures was carried out on a falsework and each in one casting, for each of which  about 1,400 cubic meters of concrete were installed. The two other bridges F37 and F38 were each separate 3-panel structures having a length of about 55 m and a span of up to 22 m. As a cross section a reinforced plate of double-sided cantilever plates in an integral construction was used for execution.

The second group consisted of the two passageways F30 and F35 for a service road and a stream and the two bridges F31 and F32. We started with the passageways as  closed, one-line rectangular cross sections.  For the slope stabilization parallel wings were arranged at the portals. The bridge F32 was completed in the form of two separate, oblique frames with support intervals of 22 and 32 m. Their cross-section is a plate structure with double sided cantilever arms. The support structure is reinforced with double sided coves. The bridge F31 was advertised as a 5-span structure with a length of 135 m and support intervals of up to 32 m. Their cross-section is a prestressed plate with double sided cantilever arms. The supporting structure has been divided into two concrete sections due to the length.

The two remaining  objects were carried out simultaneously with the other projects as their own production lines due to their penalised  interim deadlines.

The underground route F34 with a length of about 800 m was built as a tunnel with two carriageways using open construction method. With a block length of 25 m, the abutments and the three walls were build consecutively. Subsequently, the ceilings were concreted in weekly shifts with a slab formwork carriage. The gallery Brandstätter F40 / 42 was planned as an open reinforced concrete frame with horseshoe cross-section and a block length of 25 m. Consecutively, the abutments and a base member were concreted. Subsequently, the pillars and the vault were made in two 12.5 m long blocks with the tunnel formwork carriage. Finally, a spur for  noise reduction of the second directional roadway was implemented on the vault and fed in the building on one side. The vault was built with a thickness of 60 cm and a reinforced construction joint as white tank. The gallery is interrupted by the bridge F41. In order not to interrupt the noise protection, the gallery vault was built over the bridge in steel construction with panelling.

As a separate group the production of the five operational buildings and line collectors and the water protection systems for the operational phase were implemented at the portals of the tunnel sections.