Success Story Details
Offshore wind farm EnBW Baltic 2: Solid foundations on the sea bed using Putzmeister technology
After a planning and manufacturing period of three years, the first foundation for the new offshore wind farm EnBW Baltic 2 was laid in August 2013, marking the start of the construction phase. Monopiles or three-legged jackets were used as foundations, depending on the depth of the water. During the first stage of construction, the monopiles and foundation piles for the jackets were driven into the sea bed by a ship equipped with a special ram. The joint venture consortium JV HGN (HOCHTIEF, GEOSEA and NORDSEE NASSBAGGER) selected concreting equipment from Putzmeister to carry out the subsequent injection process for connecting the piles to the vertical foundation structures (transition pieces and jackets).
The arm assemblies for the stationary booms were hoisted onto the ship in the Port of Rostock...
Before the start of the project, Hamburg based company Betonlift (a service provider with more than 80 concrete pumps, distributor booms and machines) carried out a series of tests together with Putzmeister Niederlassung Nord. Betonlift rented a total of four stationary booms to the consortium, including a MX 24-4 and two MX 32-4, and trained employees from JV HGN to operate the distributor booms. At the Port of Rostock, service staff from NL Nord installed the booms on the ships – the MV Goliath and MV Abis Duisburg. The Goliath is what is referred to as a jack-up vessel, which means that after sailing out to sea, it can be anchored to the sea bed via four stationary piles and then raised hydraulically above the water line. In order to ensure maximum safety at sea, all ships working on wind turbines must be jack-up vessels.
...and then secured safely to a girder
Special ultra high-performance concrete
As a leading manufacturer of UHPC (Ultra High-Performance Concrete) for foundations in the offshore sector, Danish company ITW Engineered Polymers (formerly Densit) supplied a total of eight type P 715 concrete pumps, a concrete mixing plant and raw materials for manufacturing concrete. The aggregate was delivered to the ships in flexible bulk containers called "big bags". The two ships were each equipped with four concrete pumps, a DVH 5/2 transfer tube and distributor booms. Two of the pumps on each ship were intended as stand-by pumps.
Approx. 30 m of type SK 75 pipeline was laid between the P 715 and the distributor booms. A delivery hose with a 40 m long lance attached to the end was used instead of an end hose. During the injection process, a separate crane gradually withdrew the lance from the monopoles or foundation piles for the jackets. This process is called the "tremie method" – the outlet nozzle is located under the surface of the concrete at all times during concreting to prevent the fresh concrete from mixing with the water above. One special feature during subsequent cleaning: a catch basket attached permanently to the end of the lance. The volumes of concrete required for each pile were different: The standard fill volume for the three jacket grout connections was 70 two-ton big bags or approx. 61 m³. The fill volume for a monopile connection was 17 two-ton big bags or approx. 15 m³. The delivery rate was approx. 5.8 m³ per hour, limited by the minimum mixing time of the processed material. The delivery pressure ranged from 10 to 40 bar but also reached 60 bar on occasions. The material used was Densit Ducorit S5, a concrete that quickly reaches a high strength and demonstrates good pumping characteristics and processing qualities. The compressive strength of the material with a grain size of 4-5 mm is approx. 130 N/mm² (average cube compressive strength of standard offshore cubes with edge lengths of 75 mm).
There were a total of eight type P 715 concrete pumps on board the two ships
Special task: Cleaning the delivery line out at sea
Special attention was paid to the washing out process because it was imperative that concrete was not ejected into the sea. The delivery line was cleaned out in a forwards direction towards the placement location using sponge balls and water. The catch basket located at the end of the lance caught the sponge balls. Water escaping from a bore in the top section of the catch basket indicated that the pipeline was clean. A gate valve positioned between the delivery hose and lance was closed once the sponge balls arrived in the catch basket. The foundation work was performed between mid 2014 and February 2015.
Joint venture consortium(HOCHTIEF/GEOSEA/NORDSEE NASSBAGGER), client
Betonlift Hamburg, concrete equipment provider
ITW Engineered Polymers Denmark, concrete equipment provider