NO20092241L - Subsoil foundations, as well as methods for installing the foundation - Google Patents

Description

The invention relates to constructions for supporting offshore wind turbines and similar equipment. More specifically, the invention relates to a foundation for installation on a seabed under a body of water, as stated in the introduction to the independent patent claims.

The ever-increasing demand for the utilization of renewable energy sources increases the demand for offshore wind power. This is because the offshore wind conditions are more favorable than the conditions on land, and the environmental impact is much smaller. There is a constantly increasing need for structures that can safely and reliably support heavy wind turbines at a considerable height above sea level. The support structure generally includes a shaft or tower that is attached to the seabed, either directly by means of a foundation, or the structure floats and is connected to the seabed by means of a mooring arrangement. The present invention relates to the first-mentioned type, namely fixed support structures.

Typical fixed support structures for wind turbines currently in use, planned for use and/or patented and described in available publications are generally characterized as follows: 1. Due to feasibility limitations, the entire support structure is divided into two parts, namely a foundation and a tower, and the tower is assembled in situ on the pre-installed foundation. 2. The foundation is fixed in the seabed by driving down or drilling piles (either several piles or large-diameter monopiles), or the foundation is placed directly on an artificial gravel layer that transfers the load from the wind tower structure to the seabed.

Existing methods of delivering foundations from some delivery locations cannot satisfy the need for a high manufacturing and installation rate, i.e. the number of units that must be manufactured and installed during one installation season. Existing solutions that use gravity to fix the foundation on the seabed instead of using piles have significant application limitations related to the weight, the water depth at the installation site, as well as the water depth at the unloading site and along the transport route. These solutions use gravity as the only reaction against the operational and environmental loads that are transferred via the construction's horizontal contact with the seabed. As a rule, the upper foundations at a contact point will be weak, and must therefore be replaced with better materials, such as gravel.

Moreover, as the seabed is most often uneven and can also be sloping, there is a need for seabed preparation (levelling and planing).

EP 1 429 024 describes a support structure for an offshore wind turbine, including a lowering box which is supported by several columns in the seabed and subjected to tensile and compressive loads. Some columns are set down at an oblique angle to the vertical. The sump is supported below the water surface, but above the seabed.

WO 03/080939 describes a foundation structure for a wind turbine tower or the like, for installation on the seabed. The foundation structure can be brought to its offshore position using a vessel and separate (and removable) buoyancy aids. These buoyancy aids must be relatively large in order to provide stability. In position, the structure is lowered to the seabed, and a pumping mechanism is used to lower the lower part of the structure (eg skirt) into the seabed. Once the foundation structure has been anchored (or piled) in place on the seabed, it can be used to support the wind turbine tower. 1 themselves, the aforementioned solutions tend to entail high total capital investments, i.e. total costs for manufacturing, unloading, transport, seabed preparations and installation.

According to the invention, a foundation is proposed for installation on a seabed under a body of water, with a bottom part, a main body and a connecting part for a support structure and/or an equipment unit, characterized by a first ballast space and a second ballast space, with part of the first ballast space in the area at its upper end has an opening between the first and the second ballast space, and in that a channel runs between an area above the second ballast space and into the first ballast space.

In one embodiment, the second ballast space is arranged above the first ballast space, and a part of the first ballast space extends by a first length into the second ballast space.

In one embodiment, a line runs between the second ballast room and the outside of the foundation.

In one embodiment, the second ballast space includes a central ballast space, and the first ballast space includes a ballast space around the second ballast space, preferably in the form of an annular space around the central space.

In one embodiment, a lower channel part is connected to the channel via a link, the lower channel part extending into the first ballast space. Advantageously, the foundation includes controllable means for movement of the lower channel portion in the first ballast space.

In one embodiment, the line has a valve and a first opening on the outside of the foundation, and a second opening in the second ballast space, at a second distance above the first opening.

In one embodiment, the foundation includes a spreader element which is arranged under a lower channel part of the channel, so that the ballast material coming out of the lower channel part will go towards the spreader element. The spreader element may include a conical surface and a number of plates which are arranged around the conical surface, a part of each plate projecting above the conical surface.

The bottom part includes, preferably around its circumference, a skirt element which extends downwards and thereby forms a chamber under the bottom part, the skirt element being designed for at least partial penetration into the seabed. The foundation further includes openings between the chamber formed by the skirt and the outside of the foundation.

In one embodiment, the foundation includes a number of load resistance and leveling means which are arranged around and outward from the foundation. The load resistance and leveling means include, in one embodiment, outer skirt elements which are arranged at regular intervals around the bottom circumference and extend downwards, whereby respective separate chambers are formed under each skirt element. The outer skirt elements are designed for at least partial penetration into the seabed, and each outer skirt element further includes respective openings between the chamber formed by the outer skirt and the outside of the foundation, so that thereby a filling material can be injected and direct contact between water in the skirt elements and the porous seabed sediment.

In one embodiment, the foundation includes a number of stop means which are arranged around the circumference of the bottom part, and can be moved selectively from a retracted position where the stop means do not extend below the bottom part, and to a projecting position where the stop means extend down below the bottom part.

In one embodiment, the bottom portion includes a bottom plate having a raised peripheral wall. The base plate and the upstanding wall are mainly made of concrete or a similar castable and heavy material, while the rest of the foundation is mainly made of steel or a similar metal material.

Also provided is a method for providing a number of the foundations according to the invention at a coastal, inland or near-inland location, characterized by the steps: a) prefabrication of modules, possibly in one or more locations other than the aforementioned location; b) assembling the modules at said location to thereby provide a number of foundations; c) any storage of finished foundations in a floating state at a coastal site, ready for installation; d) towing one or more foundations to an offshore installation site; and

e) installing said foundations on a seabed.

In one embodiment, the collection of modules includes:

a) extending a lower perimeter wall from the base plate to form a foundation bottom, which lower wall has a vertical extent dimensioned in accordance with the buoyancy requirements imposed on the finished support structure; b) placing the bottom part in a floating position on the surface of the body of water; c) further assembly of the foundation with successive assembly of prefabricated units.

There is also provided a method for installing the foundation according to the invention on a seabed under a body of water, characterized by the following steps: a) enabling water from the body of water to flow into the second ballast space through the line until part of the foundation is at least partially penetrated into the seabed, as water inside the space as determined by the section is pushed out via outlet; c) activation of selected leveling means, so that the foundation is thereby placed on the seabed in an essentially leveled condition; and d) placement of the ballast material in the main ballast compartment and possibly in the second ballast compartment.

In one embodiment, step b) of the installation method is repeated until a certain depth of penetration is reached, and a land face of the foundation has made contact with the seabed and the foundation's sinking has stopped. In one embodiment of the installation method, before step a) a step of movement of the stopping means from a retracted state to a locked state in the extended position is carried out. Optionally, before step a) a predetermined amount of particulate ballast material is placed in the main ballast space, which ballast material includes dry or naturally moist material such as sand, gravel or iron ore. In one embodiment, step c) of the installation method includes at least partially filling selected outer skirt spaces with grout.

In one embodiment, step a) of the installation method ends when the water in the second ballast compartment has reached a level which causes it to flow into the first ballast compartment via an internal line.

In one embodiment, step a) of the method ends when the water in the first ballast compartment has reached a level where it flows into the second ballast compartment via an internal conduit.

If necessary, the installation method may include a movement of the foundation to a mainly horizontal state during the introduction of the skirts into the seabed, by applying a corrective load or a corrective moment to the foundation or structure, so that any unevenness in the seabed, slope seabed or uneven ground conditions. The moment/load is provided by means of different water pressures in individual skirt spaces. The skirt design and the associated installation method also result in the provision of sufficient foundation stability over a certain period of time, until trapped water in the skirt space above the mud level is pushed out with the injection mass.

By providing a number of possible solutions can

the wind farm development project with its special conditions is optimized in an efficient way, for example to achieve the lowest costs for installed units, the greatest possible manufacturing and installation rates, use of available vessels, etc.

The present invention introduces a number of parameters and structural compatibility with the use of different material types that can be used to optimize the provision of ready-to-operate structural support structures for offshore wind farms. The following advantageous aspects are achieved: 1. A large part of completion, commissioning and unloading work can take place at the manufacturing site instead of at the offshore installation site. 2. Possible designs may allow integration of the tower with the foundation, cabling and the like.

3. A greater choice of materials and a greater range of structural dimensions.

4. Transport to the site on board barges and vessels is eliminated or can be significantly reduced. 5. There is no need for separate buoyancy elements under the discharge, even with special designs. 6. Placement in position (transfer from the transport position to the operating position) by adding ballast, and not by lifting. 7. No preparation of the seabed or exchange of material on the seabed.

8. No piling, except in weak ground.

9. Designs and equipment for removal can be easily implemented.

10. The use of large offshore cranes is avoided.

In addition to the low total costs, the present invention will also remove problems that are known from known solutions: 1. The possibility of delivering the foundations from the assembly site allows the execution of works in moderately sized areas and the use of vessels with a small draft, so that the selection possibilities for manufacturing sites increases.

2. Increased manufacturing and installation rate.

3. Reduction of hazards due to bad weather conditions in connection with the installation.

4. Reduction of the need for special vessels.

5. Possibility that superstructures (tower, wind generator, etc.) can be placed on the foundation structure at or near land, before towing to the installation site. 6. The foundation structure can be leveled during or after installation on the seabed, in order to thereby avoid an unforeseen tilting of the installed carrier.

7. Resistance to large ice loads.

The aforementioned and other properties of the invention will emerge from the subsequent description of a preferred form of execution. The designs are only intended as pure examples. The description is given in connection with the drawing, where: Fig. 1 is a schematic side view of an embodiment of the foundation according to the invention, installed on a seabed,

Fig. 2 is a ground plan of the foundation in fig. 1,

Fig. 3 is a vertical section through the foundation in fig. 1, in accordance with the section line A-A in fig. 2, and shows ballast chambers and equipment for placing solid ballast, Fig. 3a and 3b are respectively a plan view and a side view of an embodiment of a spreader element,

Fig. 4 is an enlarged section from fig. 3, and shows the ballast spreading device,

Fig. 5 is a plan of the ballast spreading device in fig. 4,

Fig. 6-11 is a side view showing the main steps in the assembly of the foundation according to the invention, Fig. 12 is a side view of a temporary mooring arrangement for a number of foundations,

Fig. 13 is a plan view of the mooring arrangement in fig. 12,

Fig. 14-20b are cross-sectional side views in accordance with the line A-A in fig. 2, and shows the main steps in installing the foundation according to the invention on the seabed, Figs. 21 and 22 are side views showing a possible collection and unloading method for the bottom section of the foundation, using a submersible barge, Figs. 23 and 24 are side views of the foundation according to the invention, in fig. 23 placed on an embodiment of a stabilization device that floats in the water, while the foundation in fig.

24 is detached from the stabilization device,

Fig. 25 is a plan of the foundation and the stabilization device in fig. 23,

Fig. 26 is a side view showing a second embodiment of a floating stabilization device, connected to the foundation, Fig. 27 is a side view of the foundation and the stabilization device in fig. 26, and shows the method of assembling the floating stabilization device and the foundation, Fig. 28 is a plan view of an element of the floating stabilization device in fig. 27, connected with a foundation, and

Fig. 29a-j shows a possible assembly method for the foundation.

Figs. 1 and 2 show an embodiment of the foundation according to the invention, here generally denoted by the reference number 1. This embodiment is mounted on a seabed B which has an uneven surface (often referred to as "mud line") M, under a body of water W. Although it is not essential to the invention, it would be advantageous to give the foundation 1 a circular cross-section which can effectively withstand environmental loads in various directions and phases during manufacture, transport and operation; typical hydrostatic water pressure and wave loads.

The foundation 1 has a main body 5 and a bottom part 6. The bottom part 6 includes a bottom plate 4, a circumferential skirt 7 around the bottom part, and a number of outer skirt spaces 8a,b,c which are connected to the bottom part at regular distances around the base part's circumference.

Fig. 3 shows three such outer spaces 8a-c. A number of fins 9a-f may be arranged at mutual distances around the circumference of the bottom part.

The bottom part 6 also includes a number of extendable dowels 10a,b,c which are arranged at intervals around the circumference of the bottom part. In fig. 1, the dowels are shown in an extended state, and protrude into the seabed B below the lower edge of the skirt 7. Fig. 1 also shows how the skirt 7, the outer skirt spaces 8a-c and any fins 9 are embedded in the seabed B.

The outer skirt spaces 8a-c represent a significant improvement on known technology. This is because they enable the following: (a) means for leveling the foundation 1 during installation on the seabed,

which will be described in more detail below,

(b) in situ stability in the temporary phase between the placement of the foundation on

seabed B and the foundation are supported over the entire bottom area, for example by means of mass injection, which will be explained in more detail below,

(c) resistance to torques, for example as induced as a result of operation

of a wind turbine placed on a structure resting on its foundation, (d) resistance to horizontal loads in any phase (ie transport,

installation, operation), and

(e) additional resistance to overturning moments.

It should be mentioned that the resistance to torques and the resistance to horizontal loads (c and d in front) are uncoupled. They are therefore not additive (ie one room cannot at the same time be fully utilized to resist torques and at the same time take horizontal loads).

The main body 5 has a lower, mainly vertical circumferential wall 11. This wall 11 is connected to the bottom plate 4 and in the upward direction the wall is followed by one or more frustoconical sections 12a,b,c, as well as a column 14 which has a connecting part 15 to which the tower (not shown) for carrying a turbine (not shown) can possibly be connected.

Fig. 3 is a section in accordance with the section line A-A in fig. 2, and fig. 3 shows several details of the foundation 1 and its equipment for transport and installation. The main body 5 has an internal ballast space 13, 16.1 the embodiment shown, the vertical wall 11 and the first obtuse conical section 12a form a main ballast space 13. The second and third obtuse conical sections 12b,c and the column 14 form a second ballast space 16. This secondary ballast space 16 is placed above the main ballast compartment 13, and is separated from this by a bulkhead 17.

A line (a pipe or the like) 18 runs between a first opening 18a on the outside of the foundation (advantageously at a lower part, as shown in Fig. 3) and a second opening 18b inside the secondary ballast space 16 (preferably close to the bulkhead 17, as shown in Fig. 3).

A channel (runway or similar) 20 for filling solid ballast in the main space 13 runs from an upper area of the main body, advantageously from a funnel-shaped element 2 in the column 14, through the secondary space 16 and into the main space 13. As shown in Fig. . 3, an inner wall 16' in the secondary ballast space 16 limits a cavity 20' (in Fig. 3 a cylindrical and elongated cavity). An overflow opening 19 in the inner wall 16', between the secondary room 16 and the main room 13, is arranged at a suitable distance above the bulkhead 17.

When the foundation is lowered towards the seabed during installation, water will flow from the water mass W through the pipe 18 and into the secondary ballast space 16. The geometry of the secondary ballast space only allows for a very small water plane area, so that the ballast water will not affect the buoyancy stability during the foundation's lowering towards the seabed. The pipe 18 is provided with a valve (not shown) which can, for example, be remotely operated, or advantageously operated with an ROV (Remotely Operated Vehicle). As the water continues to flow into the secondary ballast space while moving down through the water, the water will eventually (determined for a final stage of the movement down towards the seabed) reach the overflow opening 19 and flow into the main ballast space 13 through the tube cavity 20'. When the water begins to flow into the main ballast compartment 13, both the depth of the foundation and the stabilizing arm will have increased to such an extent that the large water plane area formed in the permeable ballast material in the main ballast compartment 13 will not disturb the floating stability of the foundation. Alternatively, the foundation will hit the seabed B before the water begins to flow into the main ballast space 13, so that support is thereby achieved so that the floating stability is not compromised.

As described above, the foundation 1 includes an arrangement for filling solid ballast from the top of the column 15 into the main ballast space 13, through a run 20.1 in some cases it may be advantageous to at least partially fill ballast into the main space 13 before towing to the installation site begins. In such a case, it is important to place the ballast so that the center of gravity will lie mainly centrally in construction 1, and so that any displacements of the center of gravity as a result of wave-induced movements of the foundation will be as small as possible.

The first of these two requirements is satisfied by providing the barrel 20 with a lower pipe section 22 which is pivotally connected to the barrel 20 by means of a joint connection 21, as shown in fig. 3. The lower pipe section 22 has a cross-section which, compared to the cross-section of the cavity 21', will enable a movement of the pipe section 22 - mainly in a horizontal plane - in the cavity 20'. Fig. 4 shows these relative dimensional differences and shows how the lower pipe section 22 has been moved from its central position to an extreme position in contact with the inner wall 16'. Fig. 4 and 5 show suitable means for moving the lower pipe section 22, here in the form of hydraulic cylinders 23. These cylinders can be remote-controlled and actuated to move the lower pipe section in a suitable way, for steering the solid ballast into the main ballast space in the desired way.

The second requirement is satisfied by spreading the solid ballast in the main space 13 without thereby forming one or more large piles with sloping sides that approach the internal friction angle of the solid ballast. Such placement of the solid ballast is achieved with a spreader 24 which can consist of a number of plates 24b which are inclined at different angles and are arranged radially in the horizontal plane corresponding to a fan. Fig. 3a is a ground plan of an embodiment of a spreader element 24, here with a conical surface 24a and raised surfaces or plates 24b. Fig. 3b is a side view of the embodiment in fig. 3a and shows how the plates 24b are lifted above the conical surface 24a. When falling solid ballast hits these plates, the fall path will change by several angles, so that a distribution of the ballast material is thereby achieved. Model tests carried out with a spreader also indicate that due to the speed of the ballast material particles and the inclined paths, the angle of placement of the material in the outward direction will tend to be lower than the internal friction angle, which will improve the resistance of the placed solid ballast material by consideration of shifts of the center of gravity in the case of movements in waves.

The new manufacturing, transport and installation method will now be described in more detail with reference to fig. 6-20.

Fig. 6 shows an initial assembly phase where the bottom part 6 rests on a dock 26, on carriers 27a,b,c. The sections which make up the main body 5, and which may have been prefabricated elsewhere, are brought to the assembly point and put together in an efficient manner to form a suitably large part of the whole structure. The bottom part 6 is designed for lifting and with buoyancy. In a preferred embodiment, the construction is designed as a uniform or partially double steel shell.

In fig. 7, the combined bottom part 6 is lifted free from the carriers on the quay 26. This happens, for example, with the help of a suitable lifting arrangement L, and the part 6 is ready for placement in a liquid state in the body of water W. Fig. 8, see arrows C, shows concrete casting on the bottom part 6 bottom plate 4. The concrete can stiffen the bottom plate and represent heavy ballast in the lower part of the foundation, so that a low center of gravity and better flow stability is thereby achieved. Fig. 9 shows the lifting and assembly of the lower sections 12a,b as a unit on the bottom part 6. The sections 12a,b can also be assembled individually, or they can include extra sections up to the upper part of the foundation. Fig. 10 shows the lower sections 12a,b integrated with the bottom part 6, and the upper section 12c, the column 14 and the connecting part 15 being lifted as a unit onto the top of the finished part of the structure. The elements can also be collected individually.

Fig. 11 shows a finished foundation 1 floating in the water, ready for discharge.

During the construction, assembly and hauling out of the foundation 1, the dowels 1 Oa-c are retracted, i.e. they do not extend below the lower edge of the skirt 7. This is shown, for example, in fig. 6-11. When the foundation is to be installed at the calculated place on the seabed, the dowels are lowered and locked in a position in which they extend down below the lower edge of the skirt 7, as shown for example in fig. 1 and 15. This will be explained in more detail below.

In situations where a number of foundations 1 are to be used, it may be advantageous to pre-fabricate a number of foundations and store these on land or in satisfactorily protected waters, until installation is to begin. The storage can take place in relatively shallow water, so that you get a larger selection with regard to possible storage locations. Fig. 12 shows this situation, and shows a series of finished foundations la,b,c which are moored in the area protected from wind, waves and hazards. Each foundation is moored by means of mooring cables 30a-f, for example scattered cables, connected to the buoys 31a-d, which in turn are connected by means of mooring cables 32a-f to the anchor 33a-d and thereby to the seabed B.

Fig. 13 shows this mooring arrangement in a ground plan. Each anchor cable

32a-c are provided with anchors 33a-d. The mooring arrangement in the figure is advantageous for several reasons: it takes up less space per moored construction, the constructions can be connected and released from the mooring in any desired sequence, the construction la-f is connected to the mooring by means of cables 30a-f which are also used during

the towing. This mooring arrangement enables any of the foundations la-f to be connected or disconnected from the foundation row. For example

the foundation lb can be removed without it being necessary to alter or in any way disturb the moorings of any of the other foundations in

the mooring arrangement. Using the towing cables 3Oa-f instead of ordinary anchoring cables between each foundation and the buoys will reduce the amount of necessary cables and enable faster preparation for the tow. The respective mooring cables are used when towing the foundation to the installation site.

When the foundation 1 is to be installed, the first operation is a placement of ballast in an amount derived from the available towing depth towards the installation site. However, this step can be omitted if the foundation has sufficient float stability with offshore ballasting at the same time as the installed structure has sufficient spatial stability in the temporary phase between installation and the filling of all voids between the bottom part and the seabed. The latter requirement can be simplified if the installation and filling is carried out as a continuous operation. The foundation 1 in fig. 14 is kept in place at the ballasting site. Unless the main ballast compartment 13 is provided with a water drainage system, the ballast is carried out with solid ballast, such as sand, gravel, iron ore, etc., which does not mix with water (ie the materials are dry or only have natural moisture). The ballast 35 is lifted to the top 34 of the foundation 1 by means of a conveyor belt, a crane or the like (not shown). The ballast 35 falls down through the barrel 20 and through the movable lower pipe 22, towards the spreader 24 and is finally deposited as a layer 36 in the main ballast space 13. The layer 36 is shown here schematically to indicate that the ballast deposited will not form large conical piles of the possibility of collapse, so that unwanted shifts in the center of gravity and associated tilting of the floating structure can be avoided. Fig. 15 shows the foundation 1 with the desired amount of ballast 36 upon arrival at the installation site, and after the dowels 10a,b,c have been released from a (retracted) transport position and into an (extended and locked) installation position, so that the dowels now protrude below the skirt's 7 lower edge. Fig. 16 shows the foundation 1 during the lowering towards the seabed B as the construction's weight is increased. A valve 18c, which controls the intake 18a of the pipe 18, is open, so that thereby water can flow into the pipe 18 and further into the secondary (upper) ballast space 16 through the opening 18b. When a level above the seabed B suitable for placement has been reached, the valve which controls the water intake 18a in the pipe 18 is closed. The lowering is then stopped, and the foundation can then be brought to the desired horizontal position and orientation with the help of a towing vessel (not shown). When the desired position has been reached, the ballast water intake 18 is opened again, so that more water can thereby flow into the secondary ballast space 16, whereupon the foundation will start to sink again, as a result of the increased weight. The foundation may be exposed to wave-induced movements, but these will gradually be counteracted and finally completely cease when the dowels 10a,b,c gradually penetrate the surface M and further into the seabed B. The dowels are dimensioned so that before the lower edge of the skirt 7 touches seabed B, the movements will either have been stopped or have been reduced to small and acceptable values. Fig. 17 shows the foundation 1 in an installation stage where the skirt 7 has partially penetrated into the seabed B as a result of the weight of extra water that has flowed into the secondary ballast space 16 and filled it, so that the water now flows through the overflow opening 19 and into the main ballast space 13. The increased weight of the foundation means that the skirt 7 penetrates into the seabed B so that sealed skirt spaces are thereby formed. The captured water is pushed out through openings 42a,b between the area enclosed by the skirt 7 and the water outside the foundation. These openings are appropriately provided with one-way valves (not shown).

In cases where the upper layer of the seabed consists of granular material, i.e. relatively permeable material such as sand, silt sand or gravel, as opposed to impermeable sediments such as clay and similar sediments, it will be necessary to prevent direct contact between the water that is trapped in the outer spaces and the water in the seabed. This is necessary to prevent water seepage as a result of pressure gradients generated to achieve the leveling described above. The seal can be achieved, for example, by means of membranes or bags that separate water inside and water outside, so that direct contact does not occur. In the preferred embodiment, the seal is achieved using a mass which can typically be a mixture of water, cement and sodium silicate. Fig. 18 shows a final step for the penetration of the skirt 7 into the seabed B. The outer skirt spaces 8a-c (only 8a and b are shown) are filled with mass 46 to thereby separate trapped water in the spaces from water in the porous bottom mass. Captured water exits through the outlets 44a,b until the water is fully replaced with mass 46, as shown in the skirt space 8b, after which the outlets 44 are closed. The ballasting is then resumed with a free flow of seawater into the foundation through the inlet 18a. Although the ballast water will increase the foundation weight, no penetration occurs before the outlets 44a,b are opened again, and some of the mass, still in a fluid phase, is pushed out from the outer skirt spaces 8a-c as a result of the foundation's increased weight. If at this time of installation there is a situation where the foundation has an unacceptable deviation from the horizontal, then this deviation is removed by limiting the mass flow from the suitable outer skirt spaces 8a-c. In this way, the foundation can be leveled in a very precise way. When the desired penetration has been achieved, the mass outlets 44 are closed, and the penetration into the seabed stops even when possibly not all the ballast water has flowed into the foundation's ballast chamber. During the penetration, water in the main skirt space 39 will exit through the outlets 43 and 42a,b. This happens under the influence of the foundation weight minus the penetration resistance of the foundation parts that go into the seabed, such as the dowels, the main skirt and the skirts of the outer skirt spaces. If there is a hard bottom layer, the weight of the foundation, including all the ballast water, will possibly not be sufficient to be able to penetrate the skirts and dowels into the ground. In such a case, the penetration is increased by pumping water out from the main skirt water 39 through a suction outlet 43, whereby a downward vertical force is provided on the foundation, a force which will overcome the penetration resistance of the skirts. The desired depth of penetration has been achieved when the landing surface 100 has made contact with the seabed and the sinking of the foundation has stopped. If the penetration is enhanced by means of suction, the achievement of the target depth will be marked by a sudden increase in the suction pressure. If the solution with a landing surface is not used, then visual observations of penetration markings or proximity detectors are used with regard to the mud line, in order to be able to identify the completed penetration in that way.

A water-filled cavity 45 between the mud line M and the bottom plate 14 is suitable for filling in pulp, as shown in fig. 19. At the end of this phase, when the outer skirt spaces 8 are filled with mass, the foundation will be able to withstand significant wave loads and current loads, until the next phase - the mass injection. This move has significant practical, cost and logistical implications; reduced need for the desired weather window, with the associated occurrence of suitable weather windows, and the possibility of carrying out the mass injection in another weather window.

Fig. 19 shows the mass injection. The mass 46 will push the water out from the skirt spaces 39 through the openings 42b.

In fig. 20a, the voids between the bottom plate and the seabed are filled with injected mass 46 in the previous operation, and the structure is now filled with final ballast. It is shown that the main ballast space is already filled, and that the ballast material is placed in the upper ballast space 16. In the embodiment shown, the placement of the ballast material 35 takes place by means of a temporary pipe 48 that goes over the top of the foundation 1 34, and consists of a rigid pipe section 49, a flexible pipe section 50 and a coupling 51. An ordinary dredging boat (not shown) is connected by its own lines to the coupling 51, and pumps a mass mixture of water and solid ballast material through the temporary pipe 48 and into the funnel 2 at the top of the barrel 20.1 the in the first phase, the mixture of water and ballast material will enter the main ballast space 13.1 the figure shows a stage where the main space 13, the barrel and the funnel 20 are filled, and the mass goes over the edge of the funnel and into the secondary (upper) ballast space 16. Therefore, the whole the interior of the foundation is filled with ballast material. Surplus water from the mass can freely exit from the foundation through suitable pipes, for example the pipe 18 described above, which ends with the outlet 18a. As the retention time for water is long in the foundation, displaced water, which exits through the outlet 18a, will contain a reduced number of suspended solid particles. This is advantageous both for operational reasons and for environmental reasons.

The solid particles in the ballast mass will remain in the foundation, while excess water can flow freely through the line 18, the water outlet 18a and out from the foundation. At the end of the ballasting, the foundation will be filled with a desired volume of solid ballast, and voids between the particles in the solid ballast will be filled with water up to the seawater level 52 on the outside of the foundation 1. Finally, the valve that controls the outlet/inlet 18a is closed, the temporary the pipe 48 is removed and the installation of the structure will now be complete.

Fig. 20b shows another possible design of the foundation 1' with associated ballasting system. The interior of the foundation 1' is divided by means of a bulkhead 17b into a ballast space 13a, which is centrally located in the foundation, and a ballast space 13b, which has the shape of an annular space. When a valve is opened in the water inlet/outlet 18a, ballast water will flow into the central ballast space 13a through a line 18. The dimensioning of the central space is such that the free surface of the ballast water will not have a negative impact on the foundation's floating stability. When the water level in the central ballast space 13a has reached the top of the open conduits 18d and 18e, the water will flow into the annular ballast space 13b. The entire inner space is filled with water until the inner level corresponds to the water level W on the outside of the foundation. During the final ballasting with the sand mass, the filling can take place through a temporary pipe, as shown in fig. 20a. The ballast filling of the rooms takes place in the same way as the water filling described above.

In the embodiment in fig. 20b, the bottom plate 4 and the vertical wall 11 are made of concrete or of a similar castable and heavy material, while the rest of the foundation 1' is made of steel, so that an inert and relatively low center of gravity for the foundation is thereby achieved. It will therefore possibly not be necessary to use sand ballast in the foundation during towing to the offshore installation site, and the previously described ballast spreading element and associated parts, which are mentioned in connection with the first design, will be unnecessary. Fig. 21 shows a possible method for assembling the bottom part 6 of the foundation 1. This is based on the use of a submersible barge 53. The barge is moored using a mooring 54, preferably to a quay 26. Prefabricated sections are assembled as a bottom section 6 on the barge's 53 decks. Fig. 22 shows the discharge for finished female parts 6a,b to a liquid state. Depending on the depth conditions, both locally and on the tow route towards storage, it may be advantageous to be able to carry out as much collection work as possible before unloading. By dashed lines it is indicated that the conical section 28 and also the column section 29 can be assembled while the structure is on the deck of the barge, provided the depth conditions allow this. The barge 53 is shown submerged and resting on the seabed 3, and the female parts 6a,b have been floated free from the deck and can now be towed away, so that the barge can be de-ballasted and prepared for assembly of new foundations.

In some cases, depending on the designs, there may be an intermediate depth area where the foundation will require additional stabilization to achieve sufficient float stability. Fig. 23 is a side view showing a floating stability device 82 which supports the foundation 1 in a phase where the foundation is floated to a position between the columns 83a-d of the ballasted floating stability device 82 at a sufficient draft, after which the floating stability device is de-ballasted so that the foundation 1 rests on the floating stability device's 82 lower section 84.1 this condition, the foundation is prepared for ballasting and for transfer from a shallower depth to a greater depth, for towing to the installation site.

In the side frame in fig. 24, the foundation 1 is shown after complete ballasting and after the foundation has obtained the desired weight and draft, with ballasting of the float stability device 82 until sufficient clearance has been achieved between the foundation 1 and the lower part 84 for the execution of the foundation. In the position in fig.

24, the foundation is ready for towing and the float stability device 82 can be used again for the next foundation. Fig. 25 is a plan of the float stability device 82 and the foundation 1 as shown in fig. 23 and 24. The preferred application of this possible design is to support the foundation during the transfer from a shallow draft to a deeper lying condition during the ballasting, so that the need to design the foundation with float stability during such a vertical transfer due to the addition of weight can thereby be eliminated to the foundation. Savings can thereby be achieved as the foundation's 1 body size can be reduced. Another

possible use of the float stability device 82 is to use it both for the entire assembly of the foundation, thus replacing the use of the barge 53, and for the transfer to a larger draft position.

Figs. 26-28 show a modular flow stability device 90.

Fig. 26 shows a side view of the floating foundation 1 to which the modular float stability device 90 is connected. The connection between the modular device 90 and the foundation can, for example, be achieved by means of a flange element 91 on the lower part of the foundation, the modular device 90 moving towards this, thereby supporting the foundation. The modular device

90 has a number of columns 93 which extend above the water surface.

As shown in the figures, the modular device 90 has a first section 90a and a second section 90b. These sections are connected to each other by means of a hook connection, wedges or the like. Each module has a respective hook element 92a,b, one hook element 82a being directed downwards while the other hook element 92b is directed upward. The modular device 90 is connected to the foundation 1 by first moving the first section 90a into contact with the foundation, preferably under the flange element 91, as shown in fig. 27. Next, the second section 90b is also moved towards the foundation in a ballasted state, after which the second section is de-ballasted, so that it thereby rises to abut against the flange element 91 and the hook elements 92a,b will interact with each other, whereby a rigid support structure is provided for the foundation. This embodiment enables the connection and release of the floating device 90 in relation to the foundation 1, while it rests on a seabed.

The sections 90a,b in the modular float stability device 90 are designed as hollow bodies, preferably with a shape that surrounds the foundation along the circumference, for example circular as shown in the figures. The body of each section 90a,b includes a lower section 94 resembling a pontoon, and a number of vertical columns 93. The first and second sections 90a,b of the modular flotation device 90 are designed for a free-floating condition (ie, not attached to the foundation) with a stable vertical position. In this step, the lower section 94 is filled with ballast water. Fine adjustments of draft, as necessary for adaptation to the foundation and release from it, are carried out by changing the amount of ballast water in a particular vertical column or columns 83. The lower section 94 can be designed so that it will be either filled or empty, so that there is no free surface of water during the operations. With the help of the design, wave-induced movements can also be reduced to a large extent.

Fig. 28 is a plan view of the foundation 1 associated with the first section 90a, similar to that shown in fig. 27. The purpose of the modular floating stability device 92 is to provide extra water plane area for the floating foundation 1 and thereby make the foundation stable during towing and installation.

The invention is particularly suitable for collection points with limited water depth or with limited depth along the tow route. Fig. 29a-j shows a possible assembly method based on the use of a buoyancy device and with some parts of the foundation built in concrete. In particular, it would be advantageous to construct the bottom part and the vertical part, or parts thereof, with normal or prestressed concrete. Fig. 29a is a plan view of a prefabricated bottom part 110 in the foundation, consisting of the perimeter skirt 7 with several skirt stiffeners 106, the outer skirt spaces 8a-c and the dowels 10a-c. As explained above, the foundation may possibly have fins (not shown in fig. 29a). The main skirt compartment is open at both ends while the outer skirt compartments 8a-c preferably have a waterproof upper hood. The circumferential path 7 can extend over the bottom of the future bottom part, thereby forming a kind of concrete mold. Fig. 29b is a section through the prefabricated bottom part 110 of the foundation, which bottom part rests on carriers 27a,b. One sees the circumferential skirt 7, and an outer skirt space 8b with a waterproof cap 107b. The prefabricated bottom part is ready for the next step, as shown in fig. 29d. Fig. 29c shows a float 108 which serves two purposes during the assembly of the foundation, namely as support for new and not yet hardened concrete in the perimeter skirt area, and as additional buoyancy during assembly. The upper side 109 of the float 108 is flat and forms a suitable interface against the concrete. Fig. 29d shows the lowering of the prefabricated bottom section 110 towards the float 108. The float 108 enters the circumferential skirt, as shown in fig. 29th The bottom section 110 can optionally be assembled from suitably sized parts on top of the float 108. Fig. 29e shows a vertical section through the float 108 and the bottom section 110 which rests on the float. It can be seen that the float 108 is divided into compartments 11 la-d and 112. The former are intended for ballasting with seawater, while the latter is always filled with air. The ballastable spaces 11 la-f are so small that the possible free water surface will not reduce the floating stability to an unacceptable degree.

In fig. 29f shows the situation after the completion of preparatory work, such as covering the area outside the upper surface 109 of the float 108 and inside the circumferential skirt, whereby a horizontal support surface 109 is provided with a separating membrane that will facilitate the removal of the float 108 in a next phase. Finally, steel reinforcements and other steel details will be embedded in the concrete. Furthermore, the figure shows concrete pouring as indicated by arrows C. If new concrete is used which has a relatively fluidized consistency, then the float 108 must be stabilized until the concrete has hardened. Fig. 29g shows the finished bottom part 112 and a section of the superstructure, consisting of a vertical wall 111 and a conical section 113 which is lowered onto the bottom part so that the two parts become one. Alternatively, the construction can also take place using commonly known methods, with the use of concrete that is cast in temporary forms.

Fig. 29h shows an installation of another section 114.

Fig. 29i shows the finished foundation 1 floating in the water and supported by the float 108, everything being prepared for removal of the float. Fig. 29j shows the float 108 resting on the seabed and the ballast with seawater. The ballasting has meant that the float no longer floats, and that it has therefore sunk towards the seabed from the main skirt compartment.

The float 108 in fig. 29a-j can be replaced with the one in fig. 21 and 22 showed the submersible barge 53.

Claims (23)

1. Foundation (1) for installation on a seabed (B) under a body of water (W), with a bottom part (6), a main body (5) and a connecting part (15) for a supporting structure and/or an equipment unit, characterized by - a first ballast room (13; 13a) and a second ballast room (16; 13b), - where part (20') of the first ballast space (13; 13a) in an area at its upper end has an opening (19; 18d, 18e) between the first and second ballast space, and - by a channel (20) which extends between an area above the second ballast space (16; 13a) and into the first ballast space (13; 13a). 2. Foundation according to claim 1, characterized in that the second ballast space (16) is arranged above the first ballast space, and that a part (20') of the first ballast space (13) extends a first distance (d) into the second ballast space (16). 3. Foundation according to claim 2, characterized in that it further includes a line (18) which runs between the second ballast space (16) and the outside of the foundation (1). 4. Foundation according to claim 1, characterized in that the second ballast space (13a) includes a central ballast space and that the first ballast space (13b) includes a ballast space which surrounds the second ballast space, preferably in the form of an annular space around the central space. 5. Foundation according to claim 4, characterized in that it further includes a line (18) which runs between the first ballast space (13a) and the outside of the foundation (1). 6. Foundation according to one of claims 1-3, characterized in that a lower channel part (22) is connected to the channel (20) via a joint connection (21), the lower channel part (22) extending into the first ballast space (13). 7. Foundation according to claim 6, characterized in that it further includes controllable means (23) for movement of the lower channel part (22) inside the first ballast space. 8. Foundation according to one of the preceding claims, characterized in that the line (18) includes a valve (18c) and a first opening (18a) on the outside of the foundation (1) and a second opening (18b) in the second ballast space (16), at a second distance (e) above the first opening (18a). 9. Foundation according to one of claims 1-3 or 6-9, characterized in that it further includes a spreading element (24) arranged under a lower channel part (22) in the channel (20), so that thereby the ballast material coming out of the lower channel part (22) will go towards the spreading element (24). 10. Foundation according to claim 9, characterized in that the spreading element includes a conical surface (24a) and a number of plates (24b) which are arranged around the conical surface, a part of each plate (24b) being arranged lifted above the conical surface (24a). 11. Foundation according to one of the preceding claims, characterized in that the bottom part (6), preferably around its circumference, includes a skirt element (7) which projects down and thereby forms a chamber (45) below the bottom part, which skirt element (7) is designed for at least partial penetration into the seabed, the foundation further includes openings (42a,b) between the chamber (45), which is formed by the skirt, and the outside of the foundation. 12. Foundation according to one of the preceding claims, characterized in that it further includes a number of load resistance and leveling means (8a,c) which are arranged around and extend out from the foundation. 13. Foundation according to claim 12, characterized in that the load resistance and leveling means include outer skirt elements (8a,c) arranged at regular distances around the perimeter of the bottom part and projecting downwards, whereby they form respective separate spaces under each outer skirt element, the outer skirt elements (8a-c) being designed for i the least partial penetration into the seabed and each outer skirt element (8a-c) further includes respective openings (44a-c) between the chamber formed by the outer skirt and the outside of the foundation, whereby a filling material (46) can be injected and a direct contact between the water in the skirt elements and the porous seabed sediment is prevented. 14. Foundation according to one of the preceding claims, characterized in that it further includes a number of stopping means (10a,c) which are arranged around the circumference of the bottom part (6) and are selectively movable from a retracted position in which the stopping means do not extend down below the bottom part, and to an extended position in which the stopping means extends down below the bottom part. 15. Foundation according to one of the preceding claims, characterized in that the bottom part (6) includes a bottom plate (4) with a projecting peripheral wall (11), the bottom plate (4) and the projecting wall (11) being mainly made of concrete or a similar castable and heavy material, while the rest of the foundation is mainly made of steel or a similar metal material. 16. Procedure for providing a number of foundations in accordance with one of the claims 1-10 at a location by land, on land or near land, characterized by the steps: a) prefabrication of modules (6, 12a-c, 14), possibly at one or more locations than the aforementioned location, b) assembly of the modules at the mentioned location in order to thereby provide a desired number of foundations, c) any storage of finished foundations in a floating state at a location on land, ready for installation, d) towing one or more foundations to an offshore installation site, and e) installing said foundations on a seabed. 16. Method according to claim 15, characterized in that the collection of the aforementioned modules includes: a) extending a lower perimeter wall (11) from the bottom plate (4) to form a foundation bottom part (6), which lower wall has a vertical extent dimensioned in accordance with the buoyancy requirements of the finished support structure, b) placing the bottom part (6) in a floating position on the surface of the water mass, c) assembly of the foundation (1) with successive assembly of prefabricated units (12a-c, 14, 15). 17. Method for installing the foundation in accordance with one of claims 1-15 on a seabed under a body of water (W), characterized by the following steps: a) enabling water from the body of water (W) to flow into the second ballast space (16) or the first ballast space (13a) through the line (18), until a part (7) of the foundation (1) has penetrated it least partially into the seabed (B), as water inside the space formed by part (7) is pushed out via outlet (42a,b), b) activation of selected leveling agents (8a-c), so that thereby the foundation is placed on the seabed in an essentially leveled state, and c) placement of the ballast material (34) in the main ballast compartment (13) and possibly in the second ballast compartment (16). 18. Method according to claim 17, characterized in that step b) is repeated until a specific placement depth is reached, and a landing surface (100) on the foundation has made contact with the seabed and the sinking of the foundation has been stopped. 19. Method according to claim 17 or 18, characterized in that step a) follows a step with movement of the stopping means (10a-c) from a retracted state and to a locked state in an extended position. 20. Method according to one of claims 17 and 19, characterized in that before step a) a predetermined quantity of particulate ballast material is placed in the main ballast space (13), this ballast material including dry or naturally moist material, such as sand, gravel or iron ore. 21. Method according to claim 17, characterized in that step c) includes at least partial filling of certain of the outer skirt spaces (8a-c) with injection compound (46). 22. Method according to claim 17, characterized in that step a) ends when the water in the second ballast compartment (16) has reached a level where the water via an internal line (19) will flow into the first ballast compartment (13). 23. Method according to claim 17, characterized in that step a) ends when the water in the first ballast space (13 a) has reached a level where the water will flow into the second ballast space (13b) through an internal line (18d, 18e).