Construction of a wildlife bridge over the A7 near Northeim

With increasing landscape fragmentation, humans are encroaching more and more on nature and the habitat of wild animals. Green bridges or wildlife bridges allow wildlife to safely cross heavily used traffic routes such as highways and rail lines. They connect wildlife habitats that are dissected by traffic routes.

One such green bridge has been built on the A7 autobahn between Hanover and Kassel near Northeim. Construction of the 80 meter wide arched bridge took place in seven separate blocks. Due to the horizontal concrete pressure, the building work had to be carried out by the back-step method rather than continuously. An arched stationary scaffold made of Röro E 2000 scaffold girders was used.

When creating long, oversized concrete walls, the use of this method has construction and logistical advantages. The wall is divided into individual blocks. First, every second block is cast. Recesses are provided on the connecting sides to interlock with the gap elements cast later. The hydration heat generated during the setting of the concrete can dissipate more evenly. In the next step, the gaps are concreted, with the previously cast blocks making lateral formwork unnecessary. Thanks to this construction sequence, tensile stresses in the concrete and thus the risk of cracking in the support area above the piers can be reduced.

This method of construction meant that only 15 scaffold trusses were used, whereas 90 would have been required for construction in one piece. The back-step method was not only cheaper for the client, it also avoided lengthy road closures that would have resulted from the massive use of materials and corresponding setup times for single block construction. The scaffolding was moved to the next block in each case during the night. This was only possible with full closure of the A7 so major traffic disruptions could be avoided.