Building in the Heart of Hamburg

Anyone visiting the heart of Hamburg – HafenCity – usually looks at the impressive new and historic buildings or out across the wide water. Yet it is also worth taking a look at the ground beneath. Only those who understand the subsoil can successfully build in a harbour environment shaped by sand, storm surges and occasional water ingress.

Hamburg’s HafenCity is a place of superlatives. It is the largest urban development project in a European city centre, and only a few comparable projects exist worldwide. By 2025, residential and office space will be created here on an area of around 157 hectares. The district will also provide space for shops, schools and even a university.

In the heart of this new quarter, directly next to HafenCity University, three striking buildings were completed in 2017: the IQ Towers. The most prominent of them is the 70-metre-high office tower, which features not only 18 upper floors but also two basement levels. All three buildings are connected by a two-storey underground car park – a particular challenge on a harbour site. In addition, the U4 underground line runs directly beneath the underground parking structure. Located close to the mouth of the Elbe River, the construction works were also exposed to tidal influences and potential storm surges.

As a result, major challenges had to be addressed even before construction began: how could the excavation pit be secured and kept dry?

Stefan Reich, head of the Hamburg branch of HPC, took on this task together with his team. The civil engineer has more than 30 years of experience in building critical infrastructure next to – and sometimes even within – water. Together with his team, he develops concepts for island sewage treatment plants, flood protection systems, bridges and naval facilities.

A Trained Eye Meets the Riverbed

On behalf of the client, ECE Projektmanagement GmbH & Co. KG, HPC AG carried out geotechnical, hydrogeological and waste-management investigations and planning. The HPC specialists found hardly any contaminants. This is mainly due to the site’s particular history. Until the end of the 19th century, the area was part of the harbour basin of the former timber port. When the basin was no longer required and additional storage space was needed, it was simply filled with clean sand and enclosed by quay walls. The reclaimed harbour land was subsequently developed with sheds and warehouses and used for cargo handling and storage until the 1990s. As a result, any contamination remained largely limited to near-surface layers.

The results of the soil and groundwater investigations reflected this history. By analysing historical boreholes and cone penetration tests, the investigation team determined that the subsoil consists of loose sand down to a depth of around ten metres, underlain by organic material and silt layers from the former harbour floor.

The IQ Towers: Built on Sand – Yet Secure

At this location, the difference between high and low tide normally exceeds 3.6 metres. Several times a year, storm surges can further raise these tidal high-water levels.

This meant that within a confined construction site, and under the influence of ebb, flood and potential storm surges, the excavation pit had to be secured and kept dry in order to construct the foundations of the buildings. To prevent groundwater from breaking through the base of the excavation pit, automatically controlled wells were installed. At the same time, neither too much nor too little water could be pumped out. The required pumping volume had been calculated in advance by HPC.