Bridge renewal in the Höllental valley
B+H Bau employs PASCHAL formwork solutions in Deutsche Bahn works
In Breitnau on the B31 in the Black Forest, Deutsche Bahn is renewing a road bridge over the Höllental railway line. The contractor is B + H Bau, which is constructing the abutments and bored pile retaining wall with the help of PASCHAL formwork solutions.
Since April, a 12-strong team from B+H Bau has been renewing an overpass in Breitnau, around 30 kilometres east of Freiburg, on behalf of Deutsche Bahn. The bridge is built over railway line 4300: home to the 'Höllentalbahn' service, this track crosses the Black Forest from west to east and is considered the steepest railway line in Germany.
The new bridge in the Höllental valley is six metres high, 13 metres long and five metres wide. PASCHAL formwork solutions were used to construct the bored pile retaining walls and the abutment wings. The abutment is the part of the foundation of the bridge that forms the transition between the bridge structure and the railway embankment. The Wehrle engineering office in Regensburg was responsible for the construction documentation. Construction work started at the beginning of April and is expected to last until the end of 2024. Deutsche Bahn is investing a total of 2.2 million euros to ensure a robust railway in the Breisgau-Hochschwarzwald district.
The formwork of the rounded walls of the abutments used 150 m2 of LOGO.3 and circular trapezoidal girder formwork with clamp connection (TTK). The radii employed to pre-round the formwork at the PASCHAL factory in Steinach ranged from 2.05 m to 18.15 m.
Ground conditions make construction work difficult
At the end of May/beginning of June this year, train services were closed for a week in order to demolish the old bridge. In addition, a bored pile retaining wall was constructed from 39 bored piles set 15 metres deep. It serves to protect the track on one side of the slope over an area of around 600 m² and to support the slope itself. Nick Meiners is the responsible project manager at B+H Bau. He recalls: 'The ground conditions on site – the ground consists of rock and granite – made the drilling work more difficult. The limited space also required us to have a high degree of organisation and planning.' Meiners therefore liaised closely with the project manager at Deutsche Bahn, Alexander Schmidt.
The abutments with walls that are six metres tall at the highest point were then erected from June to August. Twelve foundation piles were driven into the ground under the abutments in order to increase stability and make the structure earthquake-proof. 'To create these foundation piles, which are nine metres deep, we drove a 75-tonne drilling rig into the track area during that period', explains the B+H Bau project manager. The LOGO.3 formwork solution from PASCHAL was used to concrete the pile head plates.
The organisation also involves adapted traffic management on the busy B31. 'The alternative route was about one kilometre long. This means that, while the building work is going on, transport to and from the construction site must be carefully planned', says Meiners, explaining another challenge of the bridge construction project. In addition, both abutments were constructed while trains were running, i.e. in the immediate vicinity of the track, which required a number of safety measures. For example, all the machines that are used in the immediate vicinity of the track have a turning radius limitation.
The two abutments each have a height of six metres. As a protection against earthquakes, they stand on nine-metre-deep foundation piles.
1000 cubic metres of concrete
80 m² of PASCHAL modular formwork were used for the 1.25-metre-high foundation of the abutments. 110 m² of wall formwork LOGO.3 were used for the straight walls of the abutment, while the curved walls were constructed using LOGO-3 in combination with the circular trapezoidal girder formwork with clamp connection, TTK for short. A surface area of around 150 m² was required because the formwork was moved to construct the second abutment. Eugen Schmidt is the formwork consultant coordinating the project on the PASCHAL side. He says: 'For the curved walls, the TTK was pre-rounded at the factory in Steinach; in total, there were five different radii ranging from 2.05 m to 18.15 m. However, it would also be possible to adapt the formwork on site without too much effort.' The B+H Bau project manager, Nick Meiners, is very satisfied with the preparation by the PASCHAL formwork planners and the use of the formwork solutions: 'We were able to erect the formwork panels on the construction site according to the plans drawn up by PASCHAL without any major prior expenditure. This saved us valuable construction time, which has enabled us to speed up progress in other areas.'
What's next? 'During the summer, the remaining header beams will be constructed in the abutment connection area, including the caps on the header beams, followed by the retaining wall to secure the embankment in the autumn', says Meiners, outlining the next stages of the project. The railway line will also be closed twice for three nights. During this time, B+H Bau employees will use a mobile crane to lift in three prefabricated parts for the superstructure and four prefabricated edge caps. Traffic is expected to be able to freely cross the bridge and therefore the Höllentalbahn railway again from January 2025.
