The B 215 is an important feeder road to the trunk road network for the town of Verden in Lower Saxony. North of the historic old town, it crosses the river Aller and an old arm of the Aller. Since the load-bearing capacity of the existing bridges from 1934 is no longer given, a new, approximately 264-metre-long bridge structure is being built. It consists of two separate three-span bridges with spans between 38 and 54 metres and a pier on the island between the two arms of the river. The slender, blue-painted steel composite construction is intended to blend sensitively into the scenery and interfere as little as possible with nature. When building in a river landscape, the construction of watertight excavations goes without saying. Stump-Franki secured the contract for the construction of around 1,200 m2 of low-lying DSV sealing pads for six excavation pits to provide horizontal protection against water pressure and to reinforce the sheet pile boxes. The tried and tested "Stump-Jetting" jet grouting method, which has been approved by the building authorities, was used. Stump-Franki Planung was responsible for the execution planning.
Test columns confirm planned column geometry
The sealing bases, which were at least 1 metre thick, were drilled to depths of approx. 4 to 15 metres. Test columns had been constructed on all construction sites in advance to confirm the injector parameters such as pumping rate, pressure and drawing speed for the planned column diameters of 3.2 metres. An external foundation engineering laboratory monitored the measurements. As each column was stored with a GPS coordinate in the final piercing plan, the piercing points were precisely marked out even in difficult ground conditions.
Focus on economic efficiency and safety
For the client, the focus was on the need for an economical and safe execution. As an experienced partner for unerring and economical execution, the experienced foundation engineering team fulfilled this requirement one hundred percent. Stump-Franki's Regional Manager North Markus Wenke was highly satisfied with the course of the project: "Reconciling economy, quality and safety in every contract is one of our great strengths. Here on the B 215, too, we benefit from decades of experience in special civil engineering."
Quality monitoring and documentation during construction
The actual production process was also closely monitored and documented by means of various key figures. Among other things, this included verticality measurements during the sinking of the borehole, continuous recording and logging of the drilling and injecting parameters for each column, as well as checking and logging the density of fresh slurry and return slurry. In order to check the setting behaviour and compressive strengths, various reserve samples were taken.
