The invention relates to a method for mounting a super structure on a foundation pile. The invention relates to a method for mounting a super structure over a top end of a foundation pile, for forming a slip joint between the super structure and the said top end of the foundation pile. The invention further relates to structures for use in such mounting.

In for example onshore and offshore structures slip joints are used for mounting super structures on foundation piles, such as monopiles driven into a land surface or a sea bed. This means generally that a super structure having a suitable mounting opening is slipped over a truncated conical shaped upper end of a pile. The opening has an inner surface which is shaped according to said conical upper end, such that it can be slipped over said end and forced onto said end by force of gravity. Such joints rely on gravity and friction between the outer surface of said upper end of the pile and the inner surface of the super structure for maintaining the super structure in position, even at high loads working on the super structure and foundation, such as for example due to waves and/or wind. Such slip joint is for example known from W02020/106146 or WO2018/070868.

When installing a super structure onto a top end of a foundation pile, for forming a slip joint, the super structure is traditionally lifted by a crane to a position above the top end of the foundation pile, such that the opening of the super structure can be lowered over the top end of the foundation pile. This requires relatively high precision since the opening is generally not much larger than the cross section at the top of the top end of the foundation pile over which said opening has to be fitted. During mounting of the super structure, such as for example a platform, the super structure will be suspended from the crane and hence will be susceptible to external forces, such as wind. Moreover, if the super structure is an off- shore structure which is to be placed using a lifting vessel, also waves will effect the precision with which the structure can be lowered onto the foundation pile. This means that the mounting of the super structure is highly dependent on good weather conditions, with for example no or only limited winds and no or only limited waves. Which limits the time frame during which such mounting operations can be performed significantly and may lead to relatively long waiting periods for personnel and equipment, which can be highly cost inefficient. This may even make such projects only possible during relatively short seasons. Moreover, during such mounting operations damage may occur to the super structure and/or the foundation pile, because of for example sudden gusts of wind or waves which may result in the suspended super structure making sudden and non-controllable movements relative to the foundation pile, which may result in collisions.

In off-shore mounting it is known to use installation platforms which are fixed at the sea bed near the foundation pile, in order to avoid influence of waves to a high extend. This is however time consuming and costly because of the equipment and personnel necessary. Moreover, even if using such platforms the influence of wind on the suspended super structure will not be eliminated.

There is a need for an improved method and equipment for mounting of a super structure onto a foundation pile.

In the present disclosure in one aspect a method is disclosed for mounting a super structure over a top end of a foundation pile, wherein the top end has a truncated conical shape and the super structure has an opening fitting over said top end. In an aspect of the present disclosure a guide structure is placed at said top end, comprising at least one sloping guide surface. Thereafter said super structure is lowered over the guide structure onto the top end of the foundation pile. During lowering of the super structure onto the foundation pile the guide surface of the guide structure can guide the super structure, such that wind and/or waves will have less impact on the positioning of the super structure.

The opening preferably has a truncated conical peripheral surface fitting over said top end of the foundation pile.

When using a method according to the disclosure a side ways movement of the super structure relative to the foundation pile will be prevented or at least limited by the guide surface of the guide structure. By the sloping guide surface upon further lowering of the super structure the guide surface will increasingly center the super structure relative to the top end of the foundation pile, making positioning of the super structure more easily possible, even at relatively high winds and/or waves.

Preferably in a method according to the disclosure after mounting of the super structure the guide structure is removed from the foundation pile. The guide structure can for example be reused for mounting a further super structure to a further foundation pile. Furthermore by removing the guide structure the top end of the foundation pile, especially the top surface of said top end comes available again, for example for mounting a further super structure, such as for example but not limited to a tower of a wind turbine generator, as for example disclosed in W02020/106146.

In an aspect according to the disclosure a guide structure can be used having an upper part with a cross section increasing in dimensions, especially diameter, in a downward direction, i.e. in a direction during use towards the foundation pile. Preferably the said upper part is substantially conical or truncated conical. In an aspect according to the disclosure such guide structure can be used having a lower part, connected to the upper part, which lower part has a decreasing cross section in a direction away from the upper part. The lower part preferably has a substantially conical or truncated conical configuration.

In a very suitable configuration a guide structure is used in which an upper part is provided, having a conical or truncated conical shape and a lower part is used also having a conical or truncated conical shape, the upper and lower part having decreasing cross sections in opposite directions. Said upper and lower part in such embodiment preferably meet at an interface plane, wherein the upper part extends radially outward relative to the lower part, such that a support element is provided with which the guide structure can be supported on the upper end of the foundation pile, the lower part extending into an open upper end of said foundation pile, the upper part extending upward from said end.

With such embodiment of a guide structure the advantage can be obtained that the guide structure can be self-centering when being lowered to the foundation pile. Preferably the lower part in such embodiment has a maximum cross section at or near the interface plane between the upper and lower parts which is substantially equal to the inner cross section of the open end of the foundation pile.

In an aspect of the disclosure a method is further characterized in that at least during use the guide structure and the super structure are suspended from a support frame, wherein preferably the guide structure is suspended such that it extends at least partly below the super structure. With such method the super structure and the guide structure can be lifted together, and be lowered onto the foundation pile together. This will further reduce the time involved in mounting the super structure. In such method when suspended from the support frame preferably the guide structure extends partly below the super structure, such that said part of the guide structure is mounted to, especially entered into an open end of the open end of the foundation pile, before the super structure is moved over said top end of the foundation pile.

In embodiments of a method according to the disclosure the guide structure and the super structure, suspended from the support frame, are lifted to a position above the upper end of the foundation pile, such that the guide structure, especially a lower part thereof, is suspended directly above the top end of the foundation pile, especially an open top end of said foundation pile. Thereafter the support frame is lowered such that the guide structure is at least partly inserted into said open top end of the foundation pile, where after the support frame is lowered further, such that the super structure is lowered over an outer surface of the top end of the foundation pile, forming a shp joint with the foundation pile. Then the super structure is released from the support frame and the support frame is lifted again, pulling the guide structure away from the foundation pile.

A method according to the disclosure is especially but not exclusively suitable for mounting a platform with an upper side and a lower side, and wherein the said opening extends through the platform, from the upper side to the lower side. In such method the guide structure can easily be suspended from a suspension element extending through said opening, said suspension element being connected to a support frame extending above the platform and the guide structure.

In embodiments according to the disclosure the guide structure can be a relatively open structure, such that wind can pass largely through said guide structure.

The present disclosure is further directed to a novel guide structure for use in mounting a super structure onto a foundation pile.

In an aspect of the disclosure a guide structure is provided which comprises an upper part and a lower part, wherein the upper part comprises or forms a guide surface and the lower part is designed for engaging a top end of a foundation pile, such that during use the lower part enables centering of the guide structure relative to the top end of the foundation pile and the guide surface extends above the top end of the foundation pile for guiding a super structure during lowering of the super structure onto the top end of the foundation pile.

The present disclosure is further directed to an assembly of a guide structure according to the disclosure and a super structure, wherein the assembly further comprises a support frame, wherein the super structure and the guide structure are supported by, preferably suspended from the support frame.

The present disclosure is further directed to a foundation pile for supporting at least one super structure, especially a monopile for mounting at least a platform by a slip joint, wherein the foundation pile is provided at a top end with a removable guide structure for guiding said super structure relative to the top end during mounting of said super structure.

Embodiments of methods, structures and assemblies according to the disclosure will be discussed hereafter, with reference to the drawings, which are only given by way of example and should by no means be understood as limiting the scope of the disclosure or protection in any way or form. These examples are given in order to better understand the invention and are not restrictive. In these drawings:

Fig. 1 - 4 schematically show four steps in mounting a super structure, here shown by way of example as a platform, to a foundation pile;

Fig. 5 shows schematically, partly in cross section, a guide structure mounted to a top end of a foundation pile;

Fig. 6A and B show schematically in 3D view a guide structure and a guide structure mounted to an top end of a foundation pile;

Fig. 7 shows schematically an off-shore application of a method cq assembly according to the disclosure; and

Fig. 8A - D show schematically a general configuration of embodiments of a guide structure according to the disclosure;

Fig. 9A - D schematically show a guide structure and a platform being aligned using a guide structure according to an embodiment of the disclosure.

In this description the same or similar parts will be referred to by the same or similar reference signs. Though different embodiments or parts thereof are shown also combinations of embodiments of the methods and structures or parts thereof should be considered having been disclosed herein.

In this description an offshore structure should be understood as at least including any structure founded in or on the bottom of a body of water, including but not limited to the bottom of a sea or ocean. In this disclosure an offshore structure can for example be a wind mill, drilling rig, electrical unit such as a transformer, or the like, preferably supported at least partly above a water surface of the body of water where the structure is positioned. On-shore structures can be the same or similar constructions, but then provided on land.

In this description a platform mounted or to be mounted on a pile as disclosed should be understood as meaning at least but not limited to a platform surrounding at least partly the pile. Preferably the platform forms a slip joint with the pile, but alternatively the platform can be mounted differently, for example bolted to the pile. Such platform can be suitable for landing of a vessel for transferring people and/or products to and from the offshore structure, and/or for people to move around the pile and/or tower or leg mounted on the pile safely. In the present disclosure if used with a tower mounted on the pile too, a platform is mounted prior to fixing a tower to the pile, such that personnel can enter onto the platform and assist in positioning and fixing, such as for example bolting the tower to the pile.

In this description words like substantially or about should be understood as meaning that for a given value or aspect this word is used with small deviations considered allowable, for example deviations of less than 20% of such given value, such as less than 15%, for example less than 10%, or at least deviations due to normal tolerances, such as for example manufacturing tolerances.

In this description embodiments are disclosed and discussed, wherein it should be understood that parts of the disclosed and discussed embodiments can also be combined for forming different embodiments. In this description a foundation pile should be understood at least as meaning a pile, such as for example but not limited to a monopile commonly known and used as a foundation pile for for example on-shore or off-shore wind turbine generators, landing platforms, artificial islands or the like. Preferably a foundation pile according to the disclosure has a truncated conical top end with an open upper end, wherein the pile more preferably is a substantially hollow monopile, for example made primarily of metal and/or concrete. In this description a slip joint should be understood in its common meaning. A slip joint can be formed directly between an inner surface of an opening of the super structure and an outer surface of the foundation pile or a transition piece of said foundation pile. A slip joint can also be formed between such surfaces, wherein at least one filling element is provided between said surfaces, for example adhered to one of such surfaces, which at least one filling element can for example be made of a material more compressible that the materials of the super structure and of the foundation pile, such as for example a plastic material, such as for example but not limited to PU.

Fig. 1 - 4 show schematically four steps in mounting a super structure, here shown as a platform 1, to a top end 2, which can also be referred to as an upper end 2, of a foundation pile 3. The foundation pile 3 in this embodiment is shown as a monopile, formed generally as a hollow pile, for example made of metal, such as steel, with a top end 2 which is substantially truncated conical, such that it has a truncated conical outer surface 4, the said surface 4 sloping at an angle a relative to the longitudinal axis X - X of the pile 3, which preferably extends substantially vertically. In this embodiment at the upper side 5 of the top end 2 a rim 6 is provided, extending substantially parallel to the lower part 7 of the pile 3. Such rim 6, considered forming part of the top end 2, can also be omitted or be provided extending radially inward, as for example shown schematically in fig. 5. In fig. 1 and 2 the platform 1 is suspended from a support frame 8 by a series of first suspension elements 9, which can for example be wires, ropes, chains, rods or the like. These suspension elements 9 can be flexible elements or can be relatively stiff elements. Preferably these elements 9 are sufficiently flexible or pliable such that when the platform 1 is lowered onto the top end 2 of the pile 3, the support frame 8 can be lowered further towards the pile 3. As can be seen in for example fig. 7, by way of example, the support frame 8 can be suspended from a crane by a suitable suspension element or elements 10, and can be lifted and lowered by the crane C.

The platform 1 has an opening 13 extending through the platform 1, from an upper side 1A to a lower side IB, which opening 13 in this embodiment has a truncated conical inner peripheral surface 14, which can form a slip joint with the outer surface 4 of the top end 2 of the pile 3, in a known manner.

In fig. 1 further a guide structure 11 is suspended from the support frame 8, in this embodiment by at least one second suspension element 12. The at least one second suspension element 12 in this embodiment extends through the opening 13. The guide structure 11 comprises at least one sloping guide surface 15 which slopes down and outward, at an angle B relative to said longitudinal axis X - X. In the embodiments shown in fig. 1 - 4 the guide structure comprises an upper part 11A and a lower part 11B. The upper part 11A comprises or forms said guide surface 15 and the lower part 11B is designed for engaging the top end 2 of the foundation pile 3. During use the lower part 11B enables centering of the guide structure 11 relative to the top end 2 of the foundation pile 3, whereas the guide surface 15 extends above the top end 2 of the foundation pile 3 for guiding the platform 1 during lowering of the platform 1 onto the top end 2 of the foundation pile 3.

The upper part 11A has a configuration with an increasing cross section towards the lower part 11B, and is in this embodiment shown as a substantially conical or truncated conical part 11A. Said upper part can have a circular cross section with an increasing, preferably constantly increasing diameter DA towards said lower part 11B with a top angle which is two times angle B. Said lower part 11B preferably has a configuration with a decreasing cross section in a direction away from the upper part 11A, and is in this embodiment shown as a substantially conical or truncated conical part 11B. Said lower part 11B can also have a circular cross section with a decreasing, preferably constantly decreasing diameter DB in a direction away from said upper part 11A. The lower part 11B also has a sloping outer surface 16, sloping inward and downward, with a top 17 facing downward. The outer surface 16 is also a guide surface and extends at an angle y relative to the axis X - X, such that the top 17 has an angle of two times Y- The angle 6 is, and preferably both the angles 6 and y are, preferably larger that the angle a, such that the outer surface 4 slopes steeper than at least the surface 15.

The upper part 11A interfaces with the lower part 11B at an interface plane 18, wherein at the interface plane 18 the upper part 11A extends radially outward from the lower part 11B, such that a support portion 19 is provided by an end 20 of the upper part 11A at the interface plane 18. In this embodiment the support portion 19 is substantially ring shaped with a width W defined by the maximum diameter DA(max) of the upper part 11A minus the maximum diameter DB(max) of the lower part 11B.

The guide structure 11 is suspended from the support frame 8 with the top 21 extending inside the opening 13 or below it, most or all of the guide structure extending below the lower side IB of the platform 1. The pile 3 has an open upper side 22. The rim 6 is ring shaped, with an inner diameter Din which is substantially the same or slightly larger than the maximum outer diameter DB(max) of the lower part 11B of the guide structure 11, and an outer diameter D _ou t which is preferably substantially the same as the maximum outer diameter DA(max) of the upper part 11A of the guide structure 11.

As can be seen in fig. 2 the support frame 8 can be lowered, towards the pile 3, whereby the lower part 11B of the guide structure 11 is lowered into the open upper side 22 of the pile, until the support 19 abuts the rim 6 of the pile 3. During said insertion the guide surface 16 will, or at least may abut the rim 6, such that the guide structure is forced to center inside the end 22, when being lowered further. This means that for example in case the guide structure 11 is not properly aligned with the axis X - X of the pile 3, for example due to wind pushing the guide structure 11 sideways, or waves influencing said alignment, or even when the crane is not properly positioned, the guide surface 16 will force the guide structure 11 to properly align, due to gravity.

As can be seen in fig. 2, when the guide structure 11 has been lowered properly into the pile 3, it will rest with the support portion 19 on the rim 6, whereas the upper or first part 11A will extend upward from the upper end 2 of the pile 3. In this position the platform is still suspended from the support frame 8, free from the pile 3.

When lowering the support frame 8 further, the platform 1 will be lowered further too, moving with the opening 13 over the upper part 11A of the guide structure 11, to a position as schematically shown in fig. 3, on the top end 2 of the pile 3. If the opening 13 of the platform 1 is not properly aligned relative to the axis X - X of the pile 3, for example because of wind pushing the platform 1 sideways, or waves influencing said alignment, or even when the crane is not properly positioned, the guide surface 15 will force the platform 1 to properly align, due to gravity. A part of the peripheral surface 14 of the opening 13 may engage with the guide surface 15 of the upper part 11A, wherein due to gravity the platform 1 will be forced to center relative to the guide structure 11, especially the upper part 11A thereof, and thus relative to the pile 3. Preferably the guide structure 3 stays attached to the support frame 8 by the at least one suspension element 12, as shown in fig. 3.

After properly positioning the platform 1 onto the upper end 2 of the pile 3, forming a slip joint, the first suspension elements 9 can be released from the platform 1, where after the support frame 8 can be moved upward again, as shown in fig. 4, thereby lifting the guide structure 11 back up from the pile 3. The guide structure 3 can be removed and for example made available for further use, for example for mounting a further super structure such as a platform 1 onto a further pile 3. The upper end of the pile, especially the end surface 22 thereof moreover becomes available for mounting a further construction, such as for example but not limited to a tower of a wind power turbine, which can for example be mounted to the pile 3 by bolting or by a further slip joint.

Fig. 9A - 9D schematically show examples of forces acting on the guide structure 11 and platform 1 during lowering of the guide structure onto the pile 3 and lowering the platform towards and onto the pile 3.

Fig. 9A shows the platform 1 and guide structure 11 suspended from the support frame 8, wherein the center line 24 of the guide structure 11 and the center line 25 of the opening 13 of the platform 1 are not aligned with the axis X - X of the pile 3. They are shown in fig. 9A - 9C as moved to the right of the axis X - X. In fig. 9 A a position is shown in which the guide surface 16 of the lower part 11B is in contact with the inner side of the rim 6. Gravity force F _zw (ii) acting on the guide structure 11 forces the guide structure further down when lowering the support frame 8 in the direction M, which will result in a reaction force Fin on the guide structure 11. This will make the guide structure 11 move towards the axis X - X of the pile, such that the center line 24 of the guide structure 11 will align with the axis X - X.

Fig. 9B shows the guide structure 11 properly centered relative to the axis X - X and thus to the pile 3. In fig. 9B it is shown that the platform 1 is not properly aligned with the axis X - X and thus not with the pile 3. In this figure by way or example the center line 25 of the opening 13 is moved to the right of the axis X - X. If the platform were to be lowered from this position straight down, as it would in the prior art, without a guide structure 11 in position as shown, the lower side IB of the platform 1 would hit the rim 6 of the pile and would not be properly mounted. In such case it would have been necessary to apply an external force to the platform 1 to move it sideways, in fig. 9B to the left, in order to bring the opening 13 over the upper end of the pile 3. Providing for such external force in the prior art is very cumbersome, time consuming and costly, if even possible, whereas there would be a significant risk of damage to the platform and/or to the pile, and of improper mounting of the platform.

In a method according to the disclosure, by providing a guide structure 11, such problems are prevented in a surprising manner. As can be seen schematically in fig. 9C, when the platform 1 is lowered further, a part of the inner surface 14 of the opening 13 can engage the guide surface 15 of the upper part 11A of the guide structure 11. The force of gravity F _zw (i) acting on the platform 1 will then, when further lowering the support frame 8 in the direction M, result in a horizontal force Fhor pushing the platform 1 into alignment, in fig. 9C to the left, such that the center line 25 of the opening 13 comes into alignment with the axis X - X of the pile 3, as schematically shown in fig. 9D.

In fig. 5 schematically an embodiment of a guide structure 11 is shown, mounted on an upper end 2 of a pile 3. Fig. 6A and B show the same or a similar guide structure, in 3D view. In this embodiment the guide structure has a substantially open configuration, such that for example wind can pass through the guide structure relatively easy. It should be noted that obviously a guide structure 11 as shown in fig. 1 - 8 can have the same or a similar structure. In this embodiment the guide structure 11 is mainly constructed from profiles 30, such as metal profiles or beams or the like, which can for example be welded or bolted together for forming a solid structure.

In the embodiments shown in fig. 5 and 6A and B the guide structure comprises a central profile 30A, extending from the top 21 to a lower end 17, which is here also referred to as top 17. In these embodiments the guide structure comprises an upper part 11A which is conical, and a lower part 11B which is truncated conical. Each of the upper part 11A and lower part 11B comprise a series of sloping profiles 30B, which define substantially the respective guide surfaces 15, 16 of the upper and lower parts 11A, 11B respectively. The interface surface 18 is in these embodiments substantially formed by a ring shaped profile 30C provided with a series of radial spokes 30D connected to the central profile 30A. The suspension element 12 is connected to an upper end of the central profile 30A.

In these embodiments the guide surfaces 15, 16 are formed by outward facing portions 31 of the sloping profiles 30B, which virtually form a conical or truncated conical surface as shown for example in fig. 1 and 2. Between the profiles 30A - 30D open areas 32 are provided, through which for example wind can pass, reducing the influence of the wind on the guide structure. Moreover this reduces the contact surface between the guide structure and the opening in the super structure such as but not limited to a platform 1. The surface portions 31 can be provided with friction reducing covering or coating or finishing, such as for example longitudinal ridges, plastic strips, paste, fluid or the like materials as known in the art of tribology.

Fig. 7 schematically shows an assembly 33 of a guide structure 11 and a platform 1 forming a super structure for use off-shore. The assembly 33 is suspended from a support frame 8, which is supported by a hoisting cable 10 and has been lifted by a crane C on a vessel 34, in a known manner. The assembly is suspended above the upper end 22, 2 of the pile 3, as schematically shown in fig. 1, to be lowered by the crane for mounting the platform 1 onto the pile 3, following for example the steps as shown in and described with reference to fig 1 - 4 and fig. 9.

Advantageously in a method according to the disclosure the guide structure 11 is only provided at the top end of the pile 3 after the foundation pile 3 has been driven into the ground, such as for example in a water bedding or on-shore into dry land. This allows for commonly known pile drivers or similar drive means to engage the top end of the pile for driving it into the ground, without the risk of damaging the guide structure. When using a pile which is not to be driven into the ground by engaging the top end, for example with a foundation pile build up from segments, a guide structure may be removably attached to the top end separately.

Fig. 8 A - D show schematically different configurations of a guide structure 11 according to the disclosure, by way of example only. Fig. 8A shows an embodiment as described here before, comprising an upper part 11A and a lower part 11B, both conically shaped. Fig. 8B shows an embodiment in which the lower part 11B is conical but the upper part 11B is substantially semi spherical or at least forms a curved guide surface 15. Fig. 8C shows an embodiment in which the lower part 11B again is conically shaped, but wherein the upper part 11A is substantially truncated conically shaped. Fig. 8D shows an embodiment in which both the upper part and the lower part 11A, B are substantially truncated conically shaped.

In the embodiments shown the pile 3 and the guide structure 11 have circular cross sections perpendicular to the axis X - X. This means that the guide structure 11 can be mounted to the top end 2 of the pile 3 in any rotation position around the longitudinal axis X - X cq center line 24. In embodiments however the pile 3, especially the rim 6 and the opening 6A defined thereby can be formed other than circular, for example oval or with a partially straight edge, wherein the guide structure, especially a lower part 11B thereof can be formed accordingly, such that by lowering the guide structure into the opening 6A it will be forced to rotate around the centerline 24 to a position in which it fits inside said opening. In such embodiment for example the opening 13 in the platform can accordingly be non-circular, the upper part 11A of the guide structure being formed again accordingly, such that also the platform is forced, when being lowered over the guide structure, to take the appropriate position relative to the guide structure and hence relative to the pile 3. This can for example be advantageous when a specific predefined rotational position of the platform relative to the pile is desired.

The embodiments as disclosed are shown by way of example only and should not be construed as limiting the scope of the disclosure. Many variations are possible within the scope of the invention as defined by the claims. For example the super structure mounted on the pile can be of a different structure and can for example be supported by a series of piles as disclosed. A guide structure can be formed differently, for example by using plates for forming a skeleton, instead of next to profiles as shown. A guide structure and a platform or other super structure may be placed in separate steps, for example by lifting the guide structure onto the pile first and then lifting the super structure onto the pile. This can for example be advantageous when the super structure does not have an opening extending all the way through it, such as a tower. The guide structure can be made such that it can easily be dismantled, such that it can be removed in parts.

These and other amendments, including but not limited to combinations of embodiments or parts thereof as disclosed are also considered to have been disclosed within the ambit of the claims.