New construction to replace the Main Bridge, Mainflingen

The Main Bridge in Mainflingen on the BAB 45 is now being replaced with an elegant bridle bridge, also known as a false suspension bridge. Construction work is scheduled to begin in 2024. To ensure the load bearing capacity of the deep pylon foundations was sufficient, our Düsseldorf branch worked under contract to Autobahn GmbH North Bavaria to conduct test drilling procedures. The technical adaptation and planning works were conducted in close consultation with PORR Spezialtiefbau Planung and using our in-house measuring equipment. The need to drill down to 50m, difficult soil conditions and enormous test loads of up to 25MN demanded top performance from both team members and equipment.

Variety both above and beneath the earth

At the bridge site, the Main River forms the boundary between Mainhausen in Hessen and Kleinostheim in Bavaria. A slender steel composite construction and the low height of the false suspension system of the new bridge will ensure that the replacement structure blends harmoniously into the diverse river landscape. The subterranean geology of the site is equally diverse, and presents great challenges in terms of the specialist civil engineering for the project. The bridge’s location in a diluvian section of the Main represents one such challenge. Investigation of the earth before works began indicated that the subsoil layers progress from quaternary high flood loams and quaternary Main terrace

through settlement-prone tertiary clays and sands to sands with sufficient load bearing capacity, these last located at depths ranging from approximately 25m to 50m. The columns must therefore be built on large-scale bored pile foundations extending approx. 50m into the soil, in order to reach the bedrock far below.

Perfect cooperation between all competence areas

To ensure the load bearing capacity and settling process are satisfactory, the team used cased and slurry-supported reaction and testing piles with diameters of 1,200mm and pile lengths of up to 50m to conduct two static pile tests involving test loads of up to 25MN. The presence of an approx. 26m-thick clay layer interspersed with timber and coal remnants necessitated constant quality control to prevent any untoward reaction with the bentonite slurry used in the process. The bentonite was adapted precisely to suit the geology of the site in the construction site laboratory. Once the piles had been manufactured and cured, the test piles were subjected to test loads between up to 25MN and a breaking load – a situation that called for experts in measurement technologies. The employer was very pleased with the results, as was branch manager André Schürmann: “It is an invaluable advantage, on this kind of ambitious project, for various competence areas – from planning and quality control to civil engineering and measurement – to be able to work together seamlessly.”