Factory for offshore wind turbines, Cuxhaven

Electronics group Siemens has invested 200 million euros in the construction of a new factory in Cuxhaven. The company has been producing nacelles for offshore wind turbines in the immediate vicinity of the harbour since mid-2017. The factory was erected on a site covering 130,000 square metres – roughly the size of 24 football pitches. The factory’s location directly on the Elbe River means that the company can have its heavy components delivered directly by ship, thus avoiding expensive overland routes. Up to 1,000 jobs have been created at the Cuxhaven site. The plant is one of Siemen’s largest new production buildings to be built in Germany in the past few years. PORR was awarded the contract for the deep foundation as part of a consortium.

Geotechnical challenges

The new turbine plant was erected on a spoil area at the mouth of the Elbe. The waterfront location poses a number of geotechnical challenges: the tidal area is covered by a soft layer of clay of varying thickness. Ground conditions like this can lead to significant differential settlements in the later structure. Underneath this clay layer are medium-density mudflat sands. Below these is load-bearing ground. On top of the clay layer there is a densely bedded layer of washed-up sand, which had to be penetrated. The factory hall was designed so that the large, concentrated loads could be transferred to the piles under the columns.

Deep foundation of the columns

Siemens put out a tender for a deep foundation to carry the high concentrated loads under the columns of the future factory hall. Due to the large quantity of piles required for the project, The Special civil engingeering entered a bidding consortium with Kurt Fredrich Spezialtiefbau GmbH for the project – and was awarded the contract. Precisely 1,839 Simplex piles were used. Peak output reached 550 metres per day. The team produced 1,056 Simplex piles of up to 25 metres long and with diameters of 46, 51, and 61 centimetres using the KBM 02 pile driver alone. The consortium partner produced the remaining piles with two units. These were mostly raking piles, which took considerably more time. The consortium used a total of 520 tonnes of reinforcing steel and 12,000 cubic metres of pile concrete.

Test loads made all the difference

Three preliminary test loads with up to 9,500 kN pressure and the assistance of Spezialtiefbau Planung in processing the bid were the deciding factors that led to the awarding of the contract. The bidding consortium was ultimately able to eliminate 140 of the originally planned number of piles without substitution and reduce the circumference of numerous other piles from 51 to 46 centimetres in diameter.

Pile driving began at the start of March 2016. The consortium completed the work on time at the end of a twelve-week construction period.