A transformation on the fly: Excavation pits on a former military site

Frankfurt am Main, Germany – At one time, airships and military planes rolled down the runway and landing strip here day after day. Later on, the Rebstock site in Frankfurt am Main housed the Battelle Institute for Nuclear Physics until everything disappeared gradually in the 90s. Now this site will soon begin its new future after many years as a wasteland: in part as a residential quarter, and also as a site for a daycare center and an elementary school. But before the shell can be constructed, the Bauer Umwelt division of BAUER Resources GmbH in collaboration with BAUER Spezialtiefbau GmbH is constructing the 15,000 m² excavation pit for the last section of the district development.

In April 2022, a new chapter in the city's history was opened, or rather excavated. Due to the previous military history, the site first had to be scrutinized very carefully. “This is because former military sites often have a few surprises in the ground,” remarks site manager Raphael Werner from the Bauer Umwelt Division of BAUER Resources GmbH based on his experience. Once everything was painstakingly examined and recorded, the actual excavation could begin. Up to a depth of 5 m, 30,000 t of material has been excavated already – a wide range has been found from unpolluted, undisturbed soil all the way to highly polluted material in some places. After excavation, the material is removed and brought to a suitable disposal center in the region. “There, most of the polluted soil first undergoes a microbiological treatment, as it cannot be disposed of without treatment due to the presence of organic pollutants,” explains Raphael Werner. Around 4,000 truckloads are required for the total of 100,000 t from the excavation pit. This might seem simple, but it has to be executed under extreme time pressure. For this reason, many work steps and construction tasks are carried out simultaneously. “Everything has to mesh properly, and every move needs to be spot on,” emphasizes foreman Hans Kurschat from the Bauer Umwelt Division of BAUER Resources GmbH.

While excavation was still ongoing, BAUER Spezialtiefbau GmbH worked using heavy equipment on the partially tied back sheet pile wall with an area of approx. 7,000 m² as well as the secant pile wall with a diameter of 1,500 mm down to a depth of nearly 30 m. The dewatering system including groundwater treatment plant, comprising six containers and two active filters as well as two sand charcoal filters, was also positioned and installed at the same time within a period of two weeks. Since its commissioning in August 2022, the plant cleans to 50 m³ of water per hour – 300,000 m³ of water in total by the end of operations.

Raphael Werner and his team have already done an impressive job on the site. Until the conclusion of the project in January 2023, the rest of the material will be excavated and roughly 15,000 m² of excavation base will be profiled, and subsequently sealed by the Spezialtiefbau team with roughly 19,000 running meters of vibrated stone columns. In addition, lightning protection and a granular subbase will be constructed and finally the turnkey excavation pit will be handed over for the regular construction phase. Starting in 2027, the former brownfield site will finally begin its new life with 373 apartments, a large underground garage, a daycare center and an elementary school. With less history, but a whole lot of style to compensate.