GB2524460A

GB2524460A - Offshore foundation

Info

Publication number: GB2524460A
Application number: GB1320041.5A
Authority: GB
Inventors: Ioannis Anastasopoulos
Original assignee: University of Dundee
Current assignee: University of Dundee
Priority date: 2013-11-13
Filing date: 2013-11-13
Publication date: 2015-09-30
Also published as: GB201320041D0; WO2015071634A1

Abstract

A foundation for an offshore structure comprises a footing 12 for mounting on the seabed 26 and a pile 14 for insertion into the seabed. The pile extends at least partially through the footing. The footing is free to move in the vertical direction around the pile while maintaining an effective engagement with the pile in the lateral direction. The footing may comprise pockets formed by an outer wall extending above the footing and ballast material placed in the pocket.

Description

OFFSHORE FOUNDATION

FIELD OF THE INVENTION

The present invention relates to a foundation and a method of installation for an offshore structure.

BACKGROUND TO THE INVENTION

There are many circumstances when a structure may need to be installed in an offshore environment. These structures often are securely supported on offshore foundations resting on the seafloor.

Offshore wind power generators are installed in bodies of water such as lakes, and seas for producing electricity from wind. Offshore wind power, despite its growth, remains relatively more expensive than onshore wind power, partly because of the massive foundation required to support a wind power structure in an offshore environment.

An offshore wind power foundation supports the wind power plant which typically includes a tower and a nacelle which includes a turbine and a rotor. The foundation must resist a challenging combination of large horizontal forces and moments generated by waves, wind and the motion of the nacelle. Several different foundations are currently employed for offshore wind power plants depending on site conditions and water depth.

In shallow waters, gravity foundations are mainly used. Gravity foundations typically consist of a cement foundation ("footing") that rests on top of the seafloor simply by gravity. The footing provides support for a pile or tower extending vertically above the sea surface on top of which the wind power tower is fixed. Another foundation structure, the so-called guyed" system, combines a central tower secured with the help of a plurality of pre-stressed cables anchored at a distance from the tower. Through such an arrangement, the moment forces are mainly undertaken by the cables thus reducing the overall tower requirements. The guyed systems are more suitable for land wind power but may also be used in shallow waters.

In medium water depths, a single elongated pile, commonly referred to as a monopile, is hammered into the seafloor. The wind power tower is fixed on top of the monopile. Monopiles are well accepted in the industry mainly due to their proven track record from oil and gas offshore installations. For instance, in the UK the vast majority of offshore wind power generators are supported on monopiles. Typical monopile dimensions may range from about 30 to about 40 meters in length, and from about 4 to about 6 meters in diameter. The process of hammering such large monopiles into the seafloor entails great engineering difficulties. These difficulties increase considerably as the dimension requirements for the monopile increase for larger wind power generators or applications in even deeper bodies of water.

Another foundation, often used in medium depths is the so-called suction caisson". A suction caisson is typically a skirted circular footing which is installed into the seafloor by pumping water out from the footing to create a vacuum force that drives the vertical wall of the footing into the seafloor. Suction caissons reduce the need for hammering, but require heavy, airtight structures and rather involved installation procedures.

In deeper waters, multi-footing structures are typically employed consisting of a plurality of piles and/or suction caissons. Such foundations can resist the increased forces and moments due to wind and wave loading experienced in deeper waters but they are generally more expensive to build and install.

Various other foundations have been proposed in the literature.

Examples of proposed monopile foundations are described in patent documents, DE202005004739, CN2002265837, and KR2O1 20001384.

In efforts to reduce the size requirements for the monopile structures, hybrid, monopile-type foundations have been proposed. For example, a hybrid, monopile-type foundation which combines a single pile with a very rigid and heavily loaded foundation, made of reinforced concrete is proposed in Stone KJL, Newson Ta and Sandon J. (2007), "An investigation of the performance of a hybrid monopile-footing foundation for offshore structures", Proceedings of 6th International Conference on Offshore Site Investigation and Geotechnics, London: SUT, 391-396. See also, Stone KJL, Newson Ta and El Marassi M. (2010), "An investigation of a monopiled-footing foundation, International Conference on Physical Modelling in Geotechnics, ICPMG2O1O, Rotterdam: Balkema, 829-833.

Also, European patent application EP19881219A1 of Jaroszewicz describes a hybrid monopile type foundation which includes a single pile, a resistance plate surrounding the single pile, and gravel or other loose and hard material fill into the space between the external surface of the single pile and the internal surface of the resistance plate. Jaroszewicz recommends that the resistance plate be made of heavy concrete.

Both hybrid structures proposed by Stone et al. and Jaroszewcz remain large and heavy and thus expensive to transport and install.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided an offshore foundation for supporting a structure, the offshore foundation comprising a footing and an elongated pile. When installed at the offshore location, the footing may rest on the seafloor with the pile extending vertically through the footing. The footing may be free to move in the vertical direction around the pile. This freedom of movement or decoupling in the vertical direction of the two main structures of the foundation is advantageous because it may allow repositioning of the footing on top of the seafloor to accommodate long-term consolidation seftlements of the seafloor.

However, the footing and the pile may maintain an effective engagement in the lateral direction to permit adequate transmission of horizontal or lateral loads and moments from the footing to the pile thus reducing the structural requirements for the footing. Through such decoupling of vertical and horizontal loads, the accumulation of rotation during long-term cyclic loading can be effectively reduced, allowing for a substantial reduction of the length of the pile. Since the vertical loads are undertaken directly by the surface foundation, the soil around the pile is subjected to limited initial plastic deformation, and hence there is less accumulation of plastic deformation.

Moreover, the resistance of the pile may be increased due to the increase of vertical stresses, and hence of the horizontal as well, directly underneath the footing. Through such an arrangement, the footing may roughly undertake 100% of the vertical loads, and 30% to 50% of the lateral loads.

The footing may include a mounting section for positioning a structure to be supported thereon. The footing may be constructed to support substantially all vertical loads of the structure of a complete offshore wind power installation, including a tower and a nacelle. Thus, unlike monopile foundations, the loads of the structure, such as dead loads or any vertical forces generated by the nacelle, may be supported substantially entirely by the footing and not by the pile. Therefore, one important function of the footing is primarily to support the vertical loads of the structure. As a result, the dimensions and/or other structural requirements for the pile may be reduced substantially.

The footing may comprise a base structure defining a bore to accommodate the pile. A bore wall structure may surround the bore and may extend above the base structure in a vertical or substantially vertical orientation. The bore wall structure may comprise a bore plate. The bore wall structure may provide additional contact surface for lateral engagement with the pile. The height of the bore wall structure may be selected in order to provide optimum contact suiface with the pile in the lateral direction. The bore wall structure may comprise a plurality of sections and may comprise a top section having a mounting section for positioning the structure to be supported thereon. The bore wall structure may extend above the water surface which may permit a structure to be supported to be readily mounted thereon.

The bore wall structure may extend below the base structure to provide a section that may be inserted into the seafloor.

The mounting section of the footing may comprise an annular section surrounding the bore wall structure and may abut the bore wall structure or be an integral part of the bore wall structure.

The mounting section may be placed away from the bore wall structure to allow for the diameter of the base of the structure that is supported on the footing to be larger than the diameter of the bore. This may be advantageous in allowing a reduction in the diameter of the pile without limiting the design requirements of the overall structure.

The footing may comprise an outer wall structure defining the outer perimeter of the footing. The bore wall structure, the base structure, and the outer wall structure may form a compartment or pocket within which ballast material may be added to increase the weight of the footing and securely anchor it on the seafloor.

The footing may comprise one or more stiffener elements that are used to increase its rigidity. The shape and/or size of the stiffener elements and/or their number may vary depending upon the requirements of each installation. The footing may comprise a plurality of stiffener elements that may be spaced apart at regular intervals around the bore wall structure and may extend radially from the bore wall structure to the outer wall structure. The stiffener elements may be in the form of vertical or substantially vertical plates that together with the bore wall structure, the base structure, and the outer wall structure may define a plurality of compartments or pockets within the top surface of the footing. Ballast material may be added inside one or more of these compartments.

The bottom surface of the base structure of the footing may comprise a flat or substantially flat portion in order for the footing to establish good contact with the seafloor. The footing may be installed directly on the soil surface, or on a levelled gravel bed of appropriate thickness. As the footing is free to move freely in the vertical direction any settlement or change on the surface of the seafloor below the footing will cause the footing to move to re-establish contact with the seafloor.

The bottom surface of the base of the footing may comprise one or more protruded sections that may be shaped to provide additional anchoring or binding to the seafloor. For example, the bottom surface of the footing may comprise a plurality of short protrusions, spikes or similar devices that may be inserted into the seafloor. Such spikes may be advantageous in securely positioning the footing, and reducing the overall lateral load exerted on the pile via its engagement with the footing.

When the footing is positioned on the seafloor the base structure may rest on the seafloor with the pile disposed in a vertical or substantially vertical orientation through the bore. The shape, dimensions and structural requirements of the pile may vary based on the design considerations of each installation. Partly because the pile is not required to support all or a significant proportion of the vertical loads of a supported structure the overall size of the pile may be significantly reduced. Also, the structural requirements of the pile may be reduced allowing for a lighter and more flexible foundation. Reductions in the required length of the pile, all other factors being the same, of at least 10, preferably of at least 20, and more preferably of at least 40 percent may be achieved. Reducing the length of the pile may be advantageous as it may reduce the overall material, construction, and transportation costs relating to the pile. Also, installation by hammering may be easier facilitated due to the smaller length, thus substantially reducing the installation cost.

The pile may be an elongated pipe (i.e., a thin-walled section) or a solid rod.

The pile may have a substantially cylindrical cross section but other cross sectional shapes may be employed such as oval, tear drop, or polygonal.

The diameter of the cross section of the pile may be substantially constant along the entire length of the pile. Alternatively, the pile may include a taper becoming gradually narrower toward an end, for example a bottom end thereof. The pile may have a more pronounced tapered lower end to facilitate insertion into the seafloor. The pile may have an upper section that is sized to fit within the bore of the footing.

The length of the pile may be sufficient to provide for an adequate length of the pile to be inserted within the seafloor to provide an effective anchoring and support for the tooting so that the overall foundation may withstand any lateral forces and moments exerted on the foundation. The upper portion of the pile may extend above the seafloor inside the bore of the base structure of the footing and the bore wall structure.

The upper portion of the pile may extend above the top of the bore wall structure to provide lateral engagement with the tower structure.

The upper portion of the pile may comprise a section that may be configured to facilitate connecting the pile with machinery to hammer the pile into the seafloor.

A clearance may be maintained between the pile and the bore wall structure to permit substantially free movement of the footing around the pile in the vertical direction while maintaining an effective lateral engagement between the pile and the footing. Thus, no significance interference may be present in the vertical direction between the footing and the pile.

The clearance may be sufficiently small to prevent relative displacement and rotation between the pile and the footing, as well as foreign materials such as sand, or gravel to enter inside the clearance. Such foreign matter may overtime damage the foundation.

According to one embodiment the clearance has to be very tight and may range from about 0.5 to about 3 millimetres, and more preferably between 0.5 and 1 millimetres.

According to one embodiment of the present invention, the pile may be sized to allow the footing to slidably move around the pile in the vertical direction while obtaining maximum engagement in the lateral direction.

The clearance may have a special low-friction coating to allow relative displacement in the vertical sense, minimizing relative horizontal displacement and rotation. Lubrication may be provided in the clearance area to ensure the proper functioning of the foundation and also prevent foreign matter from entering into the clearance. A gasket, made of rubber or any other suitable material, may be installed at the top of the clearance to protect the interface.

The footing and the pile may be made of any suitable material that may be used in offshore foundations including steel, steel alloys, stainless steel alloys, aluminium, aluminium alloys, steel or fibre reinforced concrete, or any synthetic based material such as a carbon based synthetic material. Preferred materials may include high strength steel typically used with for offshore structures. The foundation may be used to support many different types of offshore structures including wind power installations, drilling rigs, natural gas platforms and oil platforms.

Another aspect of the present invention relates to an offshore structure comprising: a foundation according to any of the aspects of the present invention; and an offshore structure mounted on the foundation.

The offshore structure may include a tower mounted on top of the footing of the foundation. The tower may be placed on a mounting section of the footing especially designed to receive the wind tower. The tower may be securely fixed on the mounting section of the footing using any type of conventional connectors. The connection may be made below or above the sea level.

The tower may be an integral part of the bore wall structure. A nacelle including a turbine and a rotor may be securely mounted on top of the tower at a desired height.

Yet another aspect of the present invention is directed to a method for installing the foundation according to any other aspect of the present invention in an offshore location such as a seafloor or the floor of a lake.

The method may comprise positioning the foundation at the seafloor with the pile positioned through the footing and driving the pile into the seafloor in a substantially vertical orientation.

The footing and the pile may be lowered at the desired seafloor location with the help of a derrick from a vessel. Divers or ROVs may assist in the exact positioning of the footing and the pile at the seafloor. The pile may be driven into the seafloor before or after the footing is positioned on the seafloor.

The footing may be assembled onshore or on the vessel before lowered to the seafloor. The footing may be assembled around the pile with the help of divers and/or ROVs.

Ballast material may be added inside the footing before and/or after the footing is securely positioned on the seafloor.

After the foundation is installed in place a structure to be supported, such as a tower of a wind power installation, may be positioned on top of the footing. The remaining components of an offshore structure such as a nacelle of a wind power structure, may then be fixed on the tower.

The present invention method is advantageous compared to existing methods and may be employed in shallow, medium depth and deeper bodies of water. The present invention method is simpler and more economical than heretofore methods partly because the foundation may be significantly bulky, and lighter than existing foundations capable to support the same level of vertical and lateral loads. Therefore, the foundation is simpler and more economical to transport and install.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the present invention will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which: Figure 1A is a diagrammatic illustration of a foundation for an offshore wind power generator, according to one embodiment of the present invention; Figure lB is a diagrammatic top view of the foundation of Figure 1k Figure 2 is a diagrammatic illustration of a portion of an offshore installation showing a portion of the foundation of Figure 1A with a portion of a tower positioned thereon; Figures 3A and 3B show the finite element models used to computationally compare the performance of a conventional monopile foundation 100 (Figure 3A) with an embodiment of the present invention foundation 10 (Figure 3B); Figure 4 is an illustration of a finite element model of the embodiment of the present invention foundation 10 shown in Figure 3B; Figures 5A and SB is a comparison of the conventional monopile toundation (Figure 5A) with the embodiment of the present invention foundation 10 (Figure SB) in terms of deformed tinite element mesh with plastic strain contours after 60 cycles of cyclic wave-induced loading; and Figure 6 is a comparison of the moment-rotation response of the conventional monopile foundation (line 102) with an embodiment of the present invention foundation (line 110).

DETAILED DESCRIPTION OF THE DRAWINGS

The present invention provides a foundation which may be employed to support many different offshore structures and may not be limited to the support of wind power installations. An exemplary application of the present invention foundation is provided herein in respect with an offshore wind power installation.

Figure 1A illustrates a foundation 10 for an offshore wind power generator (not shown) according to one embodiment of the present invention. The foundation 10 comprises a footing 12 and a pile 14. The footing 12 comprises a base structure 16 having a centrally located bore 18, a bore wall structure 20, an outer wall structure 22 and stiffener elements 24 which extend radially between the bore wall structure 20 and the outer wall structure 22.

The base structure is resting on top of the seafloor 26. The pile 14 is inserted into the seafloor 26 for anchoring the foundation 10 at the seafloor 26. A top portion 14a of the pile 14 extends above the seafloor 26 through the bore 18 and the bore wall structure 20. The tooting 12 is tree to move around the pile 14 in the vertical direction thus allowing the footing 12 to reposition itself on top of the seafloor 26 to accommodate any long-term settlements of the seafloor 26. The footing 12 and the pile 14 maintain an effective engagement in the lateral direction to ensure adequate transmission of any horizontal or lateral forces and moments from the footing 12 to the pile 14. This is advantageous as it may reduce the overall size and structural requirements for the footing 12, and the length of the pile 14.

Figure lB shows a top view of the foundation 10 of Figure 1A. The stiffener elements 24 are spaced apart at regular intervals around the bore wall structure 20 and extend radially from the bore wall structure 20 to the outer wall structure 22. The stiffener elements 24 comprise vertical plates and define together with the bore wall structure 20 and the outer wall structure 22 a plurality of compartments 30 within the top surface of the footing 10.

A clearance 28 is allowed between the pile 14 and the bore wall structure 20.

The clearance 28 to be effective should permit substantially free movement of the footing 10 around the pile 14 in the vertical direction while maintaining sufficient engagement between the pile and the footing in the lateral direction.

Figure 2 is side view of a portion of the foundation 10 shown in Figures 1A and 1 B. Figure 2 shows a portion of a wind power generator tower 32 positioned on top of the bore wall structure 20. Thus the wind power generator tower 32 rests on the footing and not on the pile. This is advantageous as it may significantly reduce the size and structural requirements for the pile. Besides the material savings, and transportation costs associated with a reduced size pile, significant advantages arise with respect to the installation of the pile. Smaller size piles are substantially easier to hammer into the seafloor. Thus, the foundation may be employed in applications that were heretofore limited by the installation limitations of very large piles.

The single pile 14 extends within the bore wall structure 20 all the way up to the top of the bore wall structure 20 to provide sufficient contact area for an effective engagement in the lateral direction with the footing 12.

Ballast material 34 such as rocks and/or gravel is placed within compartments formed between the stiffener elements 24 the bore wall structure 20 and the outer wall structure 22. The ballast material 34 provides adequate weight to the footing 12 forcing it to establish good contact with the seafloor 26. The ballast material 34 renders the footing structure heavier, more solid, and resistant to horizontal forces and moments. Besides rocks and gravel other materials can be used as ballast material including cement bricks, metal bars, and sand.

Comciarative Examcde A foundation 10 according to one embodiment of the present invention as shown in Figure 1 is compared with a conventional monopile foundation employing finite element analysis. In accordance of this comparative example, the foundation 10 of Figure 1 is designed for supporting a 3.5 MW wind turbine. The wind turbine and related structure, i.e. the wind tower, and the nacelle have a total mass of 420 tons.

The rotor of the wind turbine is positioned at a height of 80 m from the foundation level.

A typical clayey soil of undrained shear strength S = 60 kPa is considered for simulating the seafloor 26.

A conventional solution consisting of a monopile foundation 100 would require a pile having a 5 meter diameter and 30 meters length based on the analysis. The hybrid foundation 10 embodiment as shown in Figures 1A and lB requires a pile 14 having the same diameter of 5 m as the conventional solution but with a reduced length of only meters. Therefore a reduction of 50% in the overall length of the pile is achieved.

The footing 12 used in the analysis has a diameter of 14 meters and it has 8 stiffener elements extending radially from the bore wall structure 20 to the outer wall structure 22. The stiffener elements 24, the bore wall structure 20 and the outer wall structure 22 all are vertical plates having a constant width cross section of 0.02 meters. The clearance between the pile 14 and the bore wall structure 20 is 1 mm. Ballast material 34 comprising gravel is used having a total weight of 240 tons (taking account of buoyancy).

All the components of the footing 10, i.e. the base structure 16, the bore wall structure 20, the outer wall structure 22, and the stiffeners are made of high strength steel, typically used for offshore structures.

The analysis comprised three steps: (a) application of vertical loads; (b) monotonic wind loading P = 1000 kN at 80 m height; and (c) cyclic wave loading application of forced controlled cyclic loading to simulate the cyclic wave loading P = ± 2000 kN at T = 10 sec, 60 cycles. The imposed wind loading of 1000 kN has been computed according to widely accepted design standards, such as the American Petroleum Institute Recommended Practice for Fixed Offshore Structures (API RP2A, 1993). The ±2000 kN wave loading has been computed according to the simplified procedure described in AASHTO 1992, assuming a water depth of 15 m.

The finite element models of a conventional monopile foundation 100 and the present invention hybrid foundation 10 of Figure 1 are shown in Figures 3A and 3B respectively. The soil 26 is modelled with hexahedral brick type elements. Details of the model of the hybrid foundation model are shown in Figure 4. The stiffener elements 24, the bore wall structure 20 and the outer wall structure 22 are modelled with shell elements, while the ballast material 34 is modelled with hexahedral brick type elements. The pile 14 is a thin-walled steel of 5cm thickness. The pile is modelled with beam elements, circumscribed by eight-noded hexahedral continuum elements of nearly zero stiffness. The nodes of the beam elements representing the pile are rigidly connected with the circumferential solid element nodes at the same height. Thus, each pile cross-section behaves as a rigid disc. Such a modelling technique allows direct computation of pile internal forces (through the beam elements), and realistic simulation of the 3D geometry of the soil-pile interface.

The results of the analysis are shown in Figures 5A, SB and 6. More specifically, Figures 5A and SB compare the results of the conventional monopile foundation 100 (Figure 5A) and the hybrid foundation 10 (Figure SB) in terms of deformed finite element mesh with plastic strain contours, after 60 cycles wave-induced loading.

Figure 6 compares the moment-rotation response measured in MNm of the two foundations. Line 102 shows the moment-rotation response of the conventional monopile 100 having a diameter of 5 meters and length of 30 meters, while line 110 shows that of the hybrid foundation having a pile with a diameter of 5 meters, length of meters and a footing of 14 meters in diameter. Wind loading (step 2 of the analysis) develops a moment of 80 MNm. The subsequent wave loading (step 3 of the analysis) leads to an alternating moment of + 16 MNm. As shown in Fig. 6, when subjected to wind loading the hybrid foundation 10 is characterized by a stiffer and more elastic response, compared to the conventional monopile foundation 100, and its rotation is roughly 20% lower. Thanks to this more elastic response, when subjected to subsequent cyclic wave loading, the hybrid foundation 10 accumulates smaller permanent rotation. Although in reality the wind turbine is subjected to millions of wave loading cycles, the finite element analysis results are indicative of the superior performance of the invention 10 compared to the conventional monopile 100.

Importantly, this performance is achieved with a 50% shorter pile. Depending on the hourly rental rates of the vessels used to carry and operate the hammering machinery for the installation of the pile, the reduction of the required pile driving by 50% may lead to significant cost savings. Generally, the installation usually constitutes more than 60% of the foundation cost. Hence, reducing the installation cost by 50% may lead to cost savings of the order of 30%.

It should be understood that the embodiments described herein are merely exemplary and that various modifications may be made thereto without departing from the scope of the invention as defined in the following claims.

Claims

CLAIMS: 1. A foundation for an offshore structure, the foundation comprising: a footing for mounting on the floor of a body of water; and a pile for insertion into the floor of the body of water, the pile extending at least partially through the footing; wherein the footing is free to move in the vertical direction around the pile while maintaining an effective engagement with the pile in the lateral direction.
2. The foundation according to claim 1, wherein the footing comprises a mounting section for positioning a structure to be supported thereon.
3. The foundation according to any of the preceding claims, wherein the footing comprises a base structure having a bore that is sized to accommodate the pile.
4. The foundation according to claim 3, wherein the footing comprises a bore wall structure extending above the base structure of the footing around a periphery of the bore.
5. The foundation according to claim 4, wherein the bore wall structure is adjustable to permit variable lateral support by the pile.
6. The foundation according to any of the claims 3 to 5, wherein the footing comprises an outer wall structure extending above the base structure at an outer perimeter of the base structure.
7. The foundation according to claim 6, wherein the footing comprises a pocket formed between the outer wall structure and the bore wall structure.
8. The foundation according to claim 7, wherein the footing comprises ballast material disposed within the pocket.
9. The foundation according to any of the preceding claims, wherein the footing comprises a plurality of stiffener elements.
10. The foundation according to any of the claims 6 to 8, wherein the footing comprises a plurality of stiffener elements comprising vertical plates spaced apart at regular intervals around the bore wall structure and extending radially from the bore wall structure to the outer wall structure.
11. The foundation according to claim 10, wherein the stiffener elements together with the bore wall structure, the base structure and the outer wall structure define a plurality of compartments within the top surface of the footing.
12. The foundation according to claim 11, wherein the plurality of compartments are filled with ballast material.
13. The foundation according to any of the claims 3 tol2, wherein the base structure has a substantially flat bottom surface.
14. The foundation according to any of claims 3 to 13, wherein a clearance is allowed between the pile and the bore of the bore wall structure to permit substantially free movement of the footing around the pile in the vertical direction while maintaining an effective engagement of the footing with the pile in the lateral direction.
15. The foundation according to claim 14, wherein the clearance between the pile and the footing is sufficiently small to prevent relative rotation between the pile and the footing and to prevent intrusion of extraneous objects therein.
16. The foundation according to any of the preceding claims, wherein the pile comprises an elongated element having a cross section of a cylindrical, oval, tear-drop, or polygonal shape.
17. The foundation according to any of the preceding claims, wherein the pile comprises an elongated pipe or solid rod.
18. The foundation according to any of the preceding claims, wherein the pile includes a tapered portion.
19. The foundation according to any of the preceding claims wherein the pile includes an upper portion that is configured to facilitate connection with a driving device for driving the pile into the floor of the body of water.
20. An offshore installation, comprising: a foundation according to any of the preceding claims; and a structure mounted on the footing of the foundation.
21. The offshore installation according to claim 20, wherein the structure comprises a tower that is mounted on the footing.
22. The offshore installation according to any of the claims 20 to 21, wherein the structure comprises a nacelle.
23. A method for installing the foundation or the offshore installation according to any of the claims ito 22 in an offshore location, the method comprising: positioning the foundation at the floor of a body of water with the pile positioned through the footing; and driving the pile into the floor of a body of water in a substantially vertical orientation.
24. The method according to claim 23, wherein the footing and the pile are lowered at the desired location from a vessel.
25. The method according to claims 23 or 24, wherein the pile is driven into the floor of the body of water before the footing is positioned on the floor of the body of water.
26. The method according to claims 24 to 25, wherein the footing is assembled onshore or on the vessel before lowered to the floor of the body of water.
27. The method according to any of the claims 23 to 26, wherein the footing is assembled around the pile with divers or subsea robots.
28. The method according to any of the claims 23 to 27, wherein ballast material is added inside the footing.
29. The method according to any of the claims 23 to 28, comprising mounting a structure to be supported on top of the footing of the foundation.