The immediate proximity to the Elbe, whose tidal water levels in Hamburg fluctuate by more than 3.6 meters several times a day, presents a number of challenges. For example, the tides influence the groundwater level, which is therefore also subject to regular fluctuations. As a result, old foundations could only be gradually replaced with sand during low tide conditions to prevent water ingress and soil erosion.

To ensure safe working conditions, Ginger HPC regularly produced water level forecasts. These were used to define time windows during which excavation work could be carried out at low tide. For deeper excavation of the construction pit, including up to two basement levels, groundwater lowering was required. This had to be carefully regulated in line with the constantly rising and falling groundwater levels.

As flood protection coordinator, Ginger HPC also developed a comprehensive flood protection concept:

At a water level of 4.4 meters, the construction pit would be flooded from above by the Elbe, making protective measures and precise forecasts essential. Ginger HPC focused on several key criteria: ensuring the safety of people and machinery, and preventing contamination of the Elbe. To achieve this, a dedicated on-call team produced storm surge forecasts at least twice a week and defined corresponding measures. For example, once certain Elbe water level thresholds were expected to be exceeded, building materials were moved to flood-safe elevations or work was temporarily halted.

“Flood protection measures cost time and money—but our top priority is that people, machinery, and the environment are not harmed.”

Gerson Schramm

Logistics in confined spaces

A major challenge in this project is the limited space and accessibility. On both the western and eastern sides, the daycare building directly borders neighboring buildings still under construction. To the north and south, the construction pit adjoins public areas: on one side, there is a tartan track where neither construction vehicles can drive nor materials can be stored. On the other side, the only site access is a one-way street with adjacent cycling and pedestrian paths. This means that extensive work, such as excavation, must be managed within a one-way traffic system.

This creates significant logistical challenges, particularly when installing the water treatment system required for groundwater lowering. Due to the limited space around the construction pit, the system was installed 250 meters away on a nearby undeveloped plot. A complex task in which Ginger HPC was closely involved in both planning and execution. This contributed significantly to preventing contamination of the Elbe and the groundwater.

In the meantime, the structural buoyancy of the new building is ensured through its own weight and additional loads, allowing the groundwater management system to be successfully dismantled.

Looking ahead: sustainability for the future

The southern retaining structure is planned to be backfilled under the professional supervision of Ginger HPC using liquid soil up to 1.5 meters below ground level. The sandy fill above will be installed using water flushing techniques, while the timber sheeting will be gradually removed.

Finally, public areas such as roads, sidewalks, and cycle paths, as well as infrastructure like wastewater and stormwater pipelines, will be inspected through comprehensive elevation measurements, compaction testing, and CCTV inspections. Ginger HPC is responsible for planning and initiating these verification measures, carrying them out in part, and evaluating the results.