A foundation for a wind turbine installation The invention refers to a foundation for a wind turbine in ^¬ stallation, comprising a connection to one or more piles which can be driven into a seabed, and a connected pile- sleeve encasing the pile. In existent offshore wind turbine installations different foundations are common: monopole foundations consist of a steel pile which is driven into the seabed. Gravity founda ^¬ tions consist of a large base constructed from either con ^¬ crete or steel or a combination, which rests on the seabed. The wind turbine is dependent on gravity to remain erect.

Tripod foundations consist of three legs comprising piles on each end which are driven into the seabed. This type is gen ^¬ erally used at deeper depths. Usually the tripods are an ^¬ chored to the seabed and embedded into a pile sleeve by fill- ing the sleeve with concrete so that a bonding is effected by grouting .

A similar foundation is used for jacket foundations. In EP 2 067 914 A2 a jacket foundation consisting of a framework of tubes with different diameters is disclosed, which is fixed to a seabed by vertical tubes through which piles are driven into the seabed. For the connection of the piles and the tubes a grouting material is used, which requires curing be ^¬ fore subsequent installation steps can be performed.

It is therefore an object of the present invention to provide a foundation for a wind turbine tower which can be installed faster and easier. According to the present invention this object is achieved in the above defined foundation for a wind turbine tower in that the connection further comprises a clamp connection, whereby the pile comprises a pile-collar, securely fixed to the pile, and the pile-collar and the pile-sleeve are connected by a wedge joint with mating wedge surfaces.

The present invention is based on the idea that instead of using concrete or grouting material for establishing a connection of the foundation to an underground like a seabed a clamp connection can be used which can be installed easier. Due to the fact that no grouting material is needed which normally has to be cured, the installation procedure can be shortened substantially. Another advantage of the clamp con ^¬ nection of the inventive foundation for a wind turbine in ^¬ stallation is that it is possible to dismantle the connection without destruction. Therefore according to the invention the wind turbine installation or a foot of the wind turbine installation is connected to the seabed by vertical forces so that a wedge joint is established, whereby the pile-collar is wedged with the pile-sleeve.

In the inventive foundation it is preferred that the pile- sleeve comprises a sleeve-collar with an inclined wedge sur ^¬ face. The pile-sleeve which encases the pile-collar is equipped with the inclined wedge surface, which forms part of the wedge joint. The inclined wedge surface is arranged such that it has a smaller diameter towards the underground and a larger diameter towards the wind turbine tower. Therefore the inclined wedge surface can cooperate with another wedge surface which is fixed to the wind turbine installation or a foot of the wind turbine installation so that this second wedge surface can be moved towards the inclined wedge surface of the sleeve-collar in order to create the wedge joint.

According to a preferred embodiment of the inventive founda ^¬ tion a wedge with an inclined wedge surface may be arranged between the pile-collar and the pile-sleeve. This wedge com- prises the (second) inclined wedge surface which is needed for the wedge joint. According to a further development of the inventive founda ^¬ tion the wedge may be loosely inserted between the pile- collar and the pile-sleeve. The use of a loose wedge facili ^¬ tates the clamping procedure where a mechanical force is ex- erted upon the pile-collar which keys the wedge and the sleeve-collar. In order to obtain a very reliable connection the wedge of the inventive foundation may be fixed in posi ^¬ tion when locking, preferably by welding. The welding may be carried out when the wedge joint has been installed.

In the inventive foundation the wedge may have an outward flange for contacting the sleeve-collar in order to improve the transmission of forces during installation, when the wedge forces the sleeve-collar downward.

According to another embodiment of the inventive foundation the wedge may be segmented and comprise at least two wedge parts. Accordingly two, three, four or more separate wedge parts can be used, which are spaced from each other in circumferential direction.

In order to facilitate the installation procedure the pile- collar may have an outward flange, so that this flange can be impacted mechanically when the wedge joint is installed.

In order to obtain a wedge joint with improved clamping characteristics it can be envisaged that at least one surface of the pile-collar and/or at least one surface of the pile- sleeve and/or at least one surface of the wedge joint has an increased roughness, preferably through a surface treatment. The increased roughness leads to an increased friction be ^¬ tween the contact surface, so that a higher clamping force is achieved . In order to improve installation of the inventive foundation at least one distance piece may be used between sleeve-collar and wedge during installation. The distance piece ensures that the wedge does not key the sleeve-collar too early when the wind turbine installation or a foot of the wind turbine tower is forced into the seabed. Subsequently, when the pile-collar is in contact with the wedge the distance piece can be removed.

Further the invention comprises a wind turbine installation.

The inventive wind turbine installation comprises a founda ^¬ tion as described before.

The invention and its underlaying principle will be better understood when consideration is given to the following detailed description of preferred embodiments.

In the accompanying drawings :

Fig. 1 shows a detail of an inventive foundation in a sec ^¬ tional view during installation;

Fig. 2 shows the foundation of fig. 1 in a later stage for the installation;

Fig. 3 shows the foundation of fig. 1 in the installed

state; and

Fig. 4 shows an inventive foundation for a wind turbine installation during installation in a sectional view, whereby a distance piece is used.

Fig. 1 shows a detail of a foundation 1 for a wind turbine installation in a sectional view.

Wind turbines are provided with a rotor shaft which is part of an electrical generator producing electricity during move ^¬ ment of the rotor relative to a stator of the generator. The stator comprises a number of coils, the rotor comprises a number of permanent magnets so that an electric voltage is induced when the rotor is turned. The generator is mounted on top of a wind turbine tower which is supported by a foun ^¬ dation comprising feet which are placed on a seabed and fixed in position by piles which are driven into the seabed. Fig. 1 shows the lower part of a pile 2 of a foot of a wind turbine installation which is anchored to a seabed 3. On the outer side of the pile 2, which is made out of steel, a pile- collar 4 is securely fixed. With suitable tools the lower end of the pile 2 undergoes mechanical impacts so that the pile 2 is driven vertically into the seabed 3.

A pile-sleeve 5 which comprises a sleeve-collar 16, rests on the seabed 3 and encases the pipe-collar 4. The pile-sleeve 5 has a tubular shape and a larger diameter than the pile- collar 4, so that an annular area 6 separates pile-sleeve 5 from pile-collar 4.

The foundation 1 comprises the wedge joint with mating wedge surfaces. A first inclined wedge surface 7 is formed on the pile-collar 16 of the pile-sleeve 5. The wedge surface 7 is cone-shaped with a smaller diameter near the seabed 3 and a larger diameter in direction to the top of the pile 2.

The wedge joint further comprises a second inclined wedge surface 8, which is part of a tubular wedge 9, which is posi ^¬ tioned around pile-collar 4 during installation. As can be seen in fig. 1 wedge 9 is loosely inserted between pile- collar 4 and pile-sleeve 5. Fig. 1 shows the foundation 1 during installation. After installation of the pile-sleeve 5 on the seabed 3 the pile 2 which is surrounded by wedge 9 is inserted into the seabed 3 through pile-sleeve 5. On top of the pile 2 a vertical force is applied, as is indicated by an arrow 10. The pile-collar 4 comprises an outward facing flange 11 on which the impact force can be applied. Subsequently the pile 2 is driven into the seabed 3 together with the pile-collar 4. During the installation procedure the vertical distance be ^¬ tween flange 11 and pile-sleeve 5 is reduced until the wedge surface 8 of wedge 9 contacts the wedge surface 7 of the pile-sleeve 5.

Fig. 2 shows the state shortly before keying between wedge 9 and the inclined wedge surface 7 of pile-sleeve 5 starts.

The first wedge surface 7 and the second wedge surface 8 have undergone a surface treatment which has altered their rough ^¬ ness. Consequently friction between the two mating inclined surfaces is increased which supports the function of the clamp connection. The wedge 9 is provided with an outwardly facing flange 12 at its top so that the flange 11 contacts the flange 12 of the wedge 9 during installation. As the position of the pile- sleeve 5 comprising the first inclined wedge surface is fixed the wedge 9 is constantly driven vertically and forced against the outer surface of pile-collar 4, until the pile 2 with the pile-collar 4 is keyed to the pile-sleeve 5. In this state no further movement of the pile 2 relative to the pile-sleeve 5 is possible. This status is depicted in fig. 3. As can be seen the wedge 9 contacts the first wedge surface 7 of pile-sleeve 5 with its second wedge surface 8, in addition the inner surface 13 of wedge 9 contacts the pile-collar 4. The wedge 9 keys the pile 2 and the pile-sleeve 5 together, so that the foundation construction 1 is locked in position.

In the embodiment of fig. 1 to 3 the wedge 9 is shaped as a ring with the same cross-section as the pile-collar 4 and the pile-sleeve 5. However, other embodiments are possible where the wedge is segmented and comprises two, three or four wedge parts, which are spaced from each other in circumferential direction of the pile 2. After installation the wedge may be welded to the pile-collar 4 and/or the inclined wedge surface 7 of the pile-sleeve 5.

Fig. 4 shows a detail of another embodiment of a foundation for a wind turbine tower during installation in a sectional view. For like components as in the embodiment of fig. 1 to 3 like reference signs have been used.

In contrast to the first embodiment an annular distance piece 14 with a similar diameter as the pile-sleeve 5 is positioned between wedge 9 and the upper horizontal surface 15 of sleeve-collar 16. The distance piece 14 is used only during installation and ensures that the wedge 9 or wedge segments do not key the pile-collar 4 and the pile-sleeve 5 together too early when the pile-collar 4 is forced into the seabed 3. The distance piece 14 is only needed before the flange 11 of the pile-collar 4 is in contact with the wedge 9. In the present embodiment the distance piece 14 is made from plas ^¬ tics, in other embodiments it may be made of rubber, wood, etc. The distance piece 14 is removed manually or automati ^¬ cally when the flange 11 of the pile-collar 4 contacts the wedge 9. In many cases the impacts which are directed down ^¬ ward automatically push the distance piece 14 away. The foundation as shown in the embodiments of fig. 1 to 4 is advantageous in that the clamp connection is easy to estab ^¬ lish, the process of piling and locking the pile-collar 4 together with the pile 2 of the foundation is done in a single step. The installation method does not require curing of a grouting material, instead the foundation can be put into use as soon as it is established. On the other hand the clamp connection with the wedge joint makes it possible to disman ^¬ tle the connection without destruction.