JP2024007487A - Method for arranging foundation in underwater bottom part from vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for arranging a foundation in an underwater bottom part from a vessel.

SOLUTION: There is provided a method for arranging a foundation in an underwater bottom part from a vessel. The underwater bottom part includes an upper layer, and a rock layer positioned below the upper layer. The method includes a step of arranging a first foundation pile having an internal cavity on the rock layer through the upper layer, and the first foundation pile is supported on the rock layer. Subsequently, a shaft is excavated into the rock layer through the first foundation pile. The shaft has a transverse dimension smaller than an internal transverse dimension of the first foundation pile. Subsequently, a second foundation pile is arranged up to a depth of the rock layer in the shaft, and the outer surface of the second foundation pile extends in the shaft, and overlaps with the outer surface of the first foundation pile over an overlapping length. Finally, the outer surface of the second foundation pile is connected to a shaft wall and the outer surface of the first foundation pile over substantially the overlapping length.

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present invention relates to a method for placing a foundation into an underwater bottom from a ship. The underwater bottom includes at least an upper layer and an underlying rock layer. The foundation includes in particular an offshore wind turbine foundation, more particularly in the form of a monopile. However, the foundation can also be applied to form the foundation for other marine structures such as landing or landing sites, radar towers and other towers, artificial islands. In such applications, the foundation may optionally comprise a number of monopiles arranged in the desired pattern within the submerged bottom.

The foundation of an offshore wind turbine or other structure must compensate for the height difference with the water bed and absorb the significant loads acting on the wind turbine. The loads acting on the foundation can be considerable, inter alia due to wave forces acting on the foundation and wind forces acting on wind turbines projecting above the water surface. Due to the increasing dimensions of wind turbines, foundations are becoming increasingly larger, heavier and therefore increasingly difficult to handle.

Frequently applied foundations for wind turbines comprise a monopile, which can be provided with a flange at its upper outer end, to which, for example, a wind turbine (mast) can be attached. It is also possible to install on the monopile a transition piece that forms a connection with a wind turbine (mast) located on the monopile. If a transition piece is used, the monopile generally also has a flange and/or may be provided with a tapered outer end. The transition piece can be slid over this outer end, and then a cement mixture (cement/water mixture or grout) is applied between the tapered outer end of the monopile and the transition piece that slides over it. ) and curing it, the transition piece and monopile are connected to each other. It is also possible to connect the transition piece to the cylindrical monopile by providing the intermediate space with a hardened cement mixture. Monopiles generally have two open outer ends, usually made of steel or concrete, which can be over 50 m in length, have a diameter of e.g. 6 m or more, and can weigh over 800 tonnes. It comprises a hollow tubular element. In use, a monopile driven into the underwater bottom is located mostly underwater, but with a certain amount above the water surface to facilitate connection to the wind turbine or other structure placed above it. It can also stand out due to its length.

The placement and fixing of the monopile in the underwater bottom is carried out according to the prior art by lifting the monopile from the vessel by its upper outer end with lifting means, e.g. a lifting crane, placing it in a substantially vertical position and lifting it from the lifting means. It can be carried out by lowering a suspended monopile onto or into the submerged bottom under water. The monopile is then driven further into the underwater bottom by impact with an impact hammer on the upper outer end or by other pile driving techniques that utilize ultrasonic vibrations, for example.

It is possible to carry out this method from a floating vehicle. It is also possible to carry out such a method from a jack-up platform. Such jack-up platforms are provided with legs, by means of which the platform can be placed on the seabed, so that it assumes a relatively stable position. When traveling, the legs of the jack-up platform are raised to avoid contact with the seabed.

When placing the monopile, it must be ensured that the monopile maintains its desired angular position. This angular position is preferably substantially vertical, especially if the monopile is placed on the ground over a certain length. However, monopiles suspended from the lifting means are subject to wave forces generated by water currents and/or vessel movement. This has proven difficult to maintain the desired angular position of the monopile, with the result that the monopile may be installed in an undesirable angular position, for example in a non-vertical orientation.

For this reason, US Pat. No. 5,001,301 proposes the use of a template placed on the seabed. The monopile is lowered and received within the relatively short sleeve of the template. In order to keep the monopile vertical, the angular position of the sleeve relative to the underwater bottom can be varied by positioning means. This allows the monopile to be biased into a somewhat vertical angular position. A disadvantage of the method described in this patent is that a template must be placed at the bottom of the water to place each monopile, which is time consuming and expensive. The template is a more complex device and requires controlled positioning means to keep the monopile vertical. It should also be taken into account that the template can be subjected to large forces, since the bending moment of a monopile subjected to wave forces is highest at the location of the sleeve.

International Publication No. 2019/057827 pamphlet

The present invention has the object of providing a method for locating a foundation in an underwater bottom from a ship, which at least partially obviates the above-mentioned and other disadvantages. Another object of the invention is a method for placing a foundation in an underwater bottom from a ship, which always requires additional equipment, appliances or devices to adapt the desired angular position of the foundation to that purpose. The purpose is to provide a method that can be achieved without

The invention provides for this purpose a method according to claim 1. In particular, a method is provided for placing a foundation in an underwater bottom from a ship, the underwater bottom including an upper layer and an underlying rock layer. This method is
- placing a first foundation pile with an internal cavity through the upper layer and onto the rock formation, the first foundation pile receiving support on the rock formation;
- drilling a shaft through the first foundation pile into the rock formation by lowering the excavation means provided with a cutting tool into the internal cavity of the first foundation pile and rotating the excavation means; the step, the shaft having a transverse dimension smaller than an internal transverse dimension of the first foundation pile;
- arranging a second foundation pile in the shaft to the depth of the rock layer, the outer surface of the second foundation pile extending into the shaft and overlapping length with the outer surface of the first foundation pile; Overlapping steps and
- connecting the outer surface of the second foundation pile to the shaft wall and the outer surface of the first foundation pile over a substantially overlapping length;
including.

The method of the invention proposes an improved solution for locating the foundation pile in the desired angular position, which takes advantage of the stratification of the underwater bottom, where this bottom is separated by at least the upper layer and the underlying layer. including the rock formations in which it is located. A significant portion of the underwater floor on Earth is actually covered by loose or less consolidated materials such as soil, clay, sludge, sand, gravel, and rock. This so-called topsoil (or cover layer, also called top layer) can have a depth that varies widely from a few centimeters to, for example, 100 meters or even hundreds of meters. The top layer may also include multiple sublayers with different properties. In the context of the present invention, it can be stated that the upper layer is not a rock layer or does not include a rock layer.

According to the invention, the first foundation pile, which ultimately also forms part of the placed foundation, has a dual function.

Firstly, the first foundation pile prevents the upper layer material from falling behind the excavation means and returning into the excavated shaft. Such accumulation of top layer material within the drilled shaft can make it more difficult to pull the drill string through the drilled shaft again. The voids and porosity in the upper layer also prevent the circulation of the optionally applied flushing medium, thereby allowing the flushing medium to be used to move the excavated comminution section upwardly through the excavated shaft. It can make transport more difficult. This problem is also avoided by the first foundation pile.

Secondly, the first foundation pile acts as a guide for the excavation means. This achieves that the longitudinal direction of the excavation shaft is substantially parallel to the longitudinal direction of the first foundation pile. In other words, the excavated shaft and the first foundation pile are longitudinally aligned with each other. The second foundation pile is placed in a shaft that is excavated into the rock formation, so that the longitudinal direction of the second foundation pile also extends substantially parallel to the longitudinal direction of the first foundation pile. . The second foundation pile is thus also automatically aligned longitudinally with the first foundation pile, the longitudinal direction generally extending substantially vertically.

It is known per se to place a foundation pile in an excavated shaft, the intermediate space between the foundation pile and the excavated shaft being filled with a cement mixture and then hardened. Such a method is described, for example, in FR 3107908. This patent describes a mechanism in which a number of radially extensible fingers are provided which are placed within the foundation pile and pressed against the shaft wall excavated through the foundation pile. In this way, the foundation pile can be placed relative to the excavated shaft. Such an arrangement allows the cement mixture placed in the space between the foundation pile and the drill shaft wall to harden or harden without being subjected to forces and displacements that could actually change the geometry of the intermediate space. It is essential to be able to solidify. This can cause fractures and tears in the still fresh cement mixture. The method described in FR 3107908 requires the use of that mechanism. Furthermore, the angular position of the foundation pile with its mechanism is set relative to the excavated shaft, so that it is assumed that the excavated shaft extends to the desired angular position. Deviations in the angular position of the excavated shaft likewise cause deviations in the angular position of the foundation pile.

According to the invention, by aligning the second foundation pile with the first foundation pile without using additional equipment, instruments or devices, the gap between the first foundation pile and the second foundation pile is achieved. The intermediate space of is clearly defined. The method of the invention maintains a constant intermediate space between the outer surfaces of the second foundation pile and the first foundation pile by at most 2 mm to 3 mm, more preferably at most 1 mm, and most preferably at most less than 1 mm during the connection of the outer surfaces. It was found that it is possible to maintain

According to the invention, the outer surface of the second foundation pile is connected to the shaft wall on one side and the first foundation pile on the other side over a substantial overlap length between the first foundation pile and the second foundation pile. connected to the outside surface of the foundation pile. The connection can be performed in one step or in several steps separated in time as required. Thus, for example, it is possible to connect the outer surface (optionally a part thereof) of the second foundation pile to the shaft wall and then only to the outer surface of the first foundation pile.

In one embodiment, a suitable connection method includes a cement mixture in the intermediate space between the outer surface of the second foundation pile and the shaft wall and between the outer surface of the second foundation pile and the first foundation pile. and then curing the cement mixture. Cement mixtures are understood to mean water/cement mixtures known per se, also referred to as grouts.

Although the second foundation pile can be placed around the first foundation pile, in one embodiment the outer surface of the first foundation pile is the inner outer surface and the outer surface of the second foundation pile is the outer outer surface. It is preferable that there be. Thus, in this embodiment, the second foundation pile is arranged within the first foundation pile over a portion of the length of the second foundation pile, ie over the overlapping length.

In one embodiment, a further advantage of the invention may be that the first foundation pile placed on the rock formation is held in place by support from the upper layer of the underwater bottom. This is especially true if the top layer extends over a sufficient depth, for example 5 m. Due to the support from the upper layer, the angular position of the first foundation pile changes little during the various steps of the method after placing the first foundation pile on the rock layer, and the first foundation pile Receives support on rock formations. In this embodiment, the wave forces actually have little influence on the angular position, especially the verticality, of the first foundation pile.

If the depth of the top layer is insufficient to hold in place (desired angular position) the first foundation pile placed on the rock layer, in one embodiment, the first foundation pile placed on the rock layer is The first foundation pile may be held in place by supporting it with a gripping structure suspended downwardly from the vessel. Such a gripping structure is connected to a support structure mounted on the vessel, for example a rudder suspended in the water and optionally suspended up to a rock formation. The ladder is provided with a gripping member configured to engage the peripheral edge of the first (or second) foundation pile suspended downwardly from the lifting means. If desired, multiple gripping members can be placed at different depths of the ladder. The gripping member is movable in a horizontal plane relative to the support structure, for example a ladder. It is also possible to make the support structure itself movable in the horizontal plane, in particular the rudder. It is also possible to dampen and/or compensate for movements of the gripping member relative to the vessel such that the foundation pile received within the gripping member remains arranged in a substantially constant position relative to the underwater bottom. .

In one embodiment of the method of the invention, the angular position of the first foundation pile is determined by moving the gripping member in a horizontal plane relative to the underwater bottom before fixing the first foundation pile in the upper layer and the rock layer. Optionally adjusted by letting. This allows the first foundation pile placed on the rock formation to be in approximately the correct angular position, preferably in a vertical position. The angular position is determined by the angle between the longitudinal direction of the foundation pile and the vertical direction.

In the context of this application, vertical direction refers to a direction extending substantially perpendicular to the water surface. In the context of this application, horizontal direction refers to a direction extending substantially parallel to the water surface.

The gripping structure may be used only when placing the first foundation pile until the first foundation pile receives support on the rock formation. It is also possible to continue using the gripping structure in further steps of the method. Thus, for example, it is possible to use the gripping structure to engage the second foundation pile when it is lowered and placed into the drill shaft. The gripping structure is preferably only used to engage the first foundation pile during placement of the first foundation pile until it receives support on the rock formation.

Excavation of the shaft can be performed in any known manner. Suitable drilling means include, for example, an elongated drill string that rotates within the arranged first foundation pile such that ground material is removed by the cutting action of the cutting tool. The removed ground material is generally removed using a flushing agent (e.g., without limitation, water, mud, air), optionally through an intermediate annular space between the drill string and the first foundation pile. It is discharged upwards.

The method of the invention can be carried out using any drilling means, such as a conventional drill string, preferably a hollow drill string, constructed of segments. It is advantageous to apply excavation means that can be fixed both in the longitudinal direction of the first foundation pile and in the direction perpendicular to it (radial direction) against the inner wall of the first foundation pile using the fastening means. , and the excavation forces are effectively absorbed by transmitting these forces to the first foundation pile.

Since the excavation means must be received in the first foundation pile during excavation, the first foundation pile has a somewhat larger transverse dimension than the excavation means. The first foundation pile is preferably of cylindrical form and the excavation means, which is also preferably substantially cylindrical, is inserted into the first foundation pile in a direction corresponding to the longitudinal direction of the first foundation pile. can be lowered to

During drilling, the drill head will eventually be pushed deeper into the underwater bottom than the lower outer edge of the first foundation pile, and the lower outer edge of the first foundation pile will eventually be on the rock formation. Posted. It is important to ensure that the rock layer is not weakened excessively during excavation into the rock layer, at least in the area located below the first foundation pile. It is actually undesirable for the first foundation pile to sink.

The first foundation pile is inserted into the top layer using known means such as rotary motors, pile drivers and/or mechanical or sonic oscillators that rotationally "thread" the first foundation pile into the top layer. can be placed in

In order to further be able to realize the desired angular position of the first and second foundation piles, the excavation means are supported by the first foundation pile in the method according to the embodiment, more preferably along the longitudinal axis of the excavation shaft. It is supported by the first foundation pile such that the direction is substantially the same as (corresponds to) the longitudinal direction of the first foundation pile.

A further improvement method according to an embodiment provides that the second foundation pile is supported by an excavation shaft, more preferably such that the longitudinal direction of the excavation shaft is substantially the same (coinciding) with the longitudinal direction of the second foundation pile. It has the feature of being supported by a drilling shaft.

The foundation is finally formed by first and second foundation piles connected to each other and the second foundation pile connected to a drill shaft in the rock formation, the first and second foundation piles being , preferably aligned with each other in the longitudinal direction of the first foundation pile. Therefore, the dimensions of the first and second foundation piles must be adapted to the design loads. This is because the foundation, optionally with further intervening transition pieces, carries the loads of structures placed above it, such as wind turbines. The drill shaft of the second foundation pile and its connection with the first foundation pile must also be compatible with the design loads. It will be obvious that how to size these foundation piles and connections is within the ordinary knowledge of those skilled in the art. A suitable first foundation pile has a wall thickness of a minimum of 50 mm, more preferably a minimum of 60 mm, even more preferably a minimum of 70 mm, even more preferably a minimum of 80 mm and most preferably a minimum of 100 mm. Suitable first foundation piles have a wall thickness of at most 200 mm, more preferably at most 180 mm, even more preferably at most 160 mm and most preferably at most 120 mm.

It is advantageous to provide a method according to an embodiment of the invention, in which the outer surface of the first foundation pile and/or the second foundation pile is provided with shear projections over at least the overlap length. It has been found that since the connection between the outer surfaces of the first and second foundation piles is primarily under shear loads, the shear projections significantly strengthen the connection. The shear projections preferably have an imaginary line connecting two successive shear projections of each of the first and second foundation piles to each other between 35° and 55°, more preferably between 40° and 50°, most preferably. are arranged to extend at an angle of approximately 45°.

In one embodiment, the second foundation pile is also hollow for weight reduction.

In a further embodiment of the invention, the upper outer end of the first foundation pile is located above the water level after connection to the second foundation pile, the upper outer end of the first foundation pile being , a transition piece is provided after connection with the second foundation pile, the method further comprising placing a wind turbine on the foundation, and a method is provided, wherein the vessel is equipped with a jack-up platform.

Finally, that the embodiments of the invention described in this patent application can be combined in any possible combination of these embodiments, and that each embodiment can separately form the subject of a divisional patent application. is stated.

Other details and advantages of the invention will become apparent from the following description of a device and method for placing foundations on an underwater bottom from a ship. This description is given by way of example only, without the invention being limited thereto. The reference numbers refer to the attached drawings.

1 is a schematic perspective view of an embodiment of a device for placing a foundation on the underwater bottom; FIG. 1 is a schematic side view of the steps of an embodiment of a method according to the invention; FIG. 3 is a schematic side view of subsequent steps of an embodiment of the method according to the invention; FIG. 3 is a schematic side view of subsequent steps of an embodiment of the method according to the invention; FIG. 3 is a schematic side view of the steps of another embodiment of the method according to the invention; FIG. 3 is a schematic side view of subsequent steps of another embodiment of the method according to the invention; FIG. 3 is a schematic side view of subsequent steps of another embodiment of the method according to the invention; FIG. 1 is a schematic perspective view of a foundation according to an embodiment of the invention; FIG. FIG. 5 is a schematic cross-sectional view of the foundation shown in FIG. 4; FIG. 5 is a detailed schematic cross-sectional view of the foundation shown in FIG. 4;

Referring to FIG. 1, a device 1 for placing a monopile 3 on an underwater bottom 2 is shown. The device is likewise suitable for placing other objects having a longitudinal direction, such as for example the transition piece 4 of a wind turbine mast, on one another or on another ground. The illustrated device 1 comprises a jack-up platform 5 that can be navigated autonomously and placed and fixed in a desired position by lowering several spud poles 50 onto the underwater bottom 2. For this purpose, the spud pole 50 is moved downwards relative to the underwater bottom by means of a toothed wheel drive (or other mechanism), as shown in FIG. 1, whereby the platform 5 is also lifted out of the water. . In this position, the working deck 51 of the platform 5 may be located several meters above the water surface 20. The spud pole 50 is provided with legs 52 for preventing the spud pole 50 from penetrating into the underwater bottom 2.

On the working deck 51 of the platform 5 there are arranged components, such as for example several transition pieces 4, a first monopile 3 and a second monopile 7. The working deck 51 of the jack-up platform 5 is further provided with lifting means in the form of a crane 6 with a double boom (60a, 60b) for the purpose of absorbing considerable forces. The crane 6 is rotatable around a base 61 about a substantially vertical axis 62 . The crane 6 is provided with a set of lifting cables (63a, 63b) that can be moved in and out of the upper part 65 of the crane 6 using a winch (not shown), and this set of cables includes a free outer At the end there is provided a lifting block 66 with a hook from which the monopiles (3, 7) are suspended in use. The first monopile and the second monopile (3, 7) can optionally be provided with a removable lifting structure at the lifting point (33, 73) for this purpose. The angular position of the boom (60a, 60b) can be adjusted as required by a set of traction cables (64a, 64b) connecting the upper part 65 to the base 61. The traction cables (64a, 64b) can similarly be moved in and out using a winch (not shown).

The working deck 51 of the platform 5 may further comprise a gripping structure 10 separate from the crane 6. The gripping structure 10 is configured to engage the gripping arm 101 with one or more peripheral portions (32, 72) of the first and/or second monopiles (3, 7) suspended from the crane 6. . The gripping structure 10 is connected to (the working deck 51 of) the jack-up platform 5 by a ladder structure 100. The ladder structure 100 extends substantially vertically downward toward the submersible bottom 2 and optionally has a length sufficient to allow the ladder structure 100 to be supported on the submersible bottom 2. It is possible to have a The gripping arm 101 is placed at a determined depth of the ladder structure 100. If desired, a plurality of gripping arms can also be provided along the ladder structure 100, which are displaceable along the ladder structure 100 as desired. In this embodiment, the jack-up platform 5 serves as a stable support structure for the gripping structure 10.

Referring to FIGS. 2A-2C, several steps of the method of the present invention are illustrated, according to one embodiment thereof. It is important to mention that the underwater bottom 2 comprises an upper layer 2a and an underlying rock layer 2b. The upper layer 2a is made of a material softer than rock, such as clay, sand, screw, and loam. As shown in FIG. 2A, in a first step, the first foundation pile 3 is picked up by a crane 6 and placed through the upper layer 2a and onto the rock layer 2b. The feeding of the first base pile 3 with the internal cavity 3a through the upper layer 2a can be carried out in any manner known to the person skilled in the art, for example by pile driving. It has been found that since the upper layer 2a is relatively soft, there are no significant problems in arranging the first foundation pile 3. The first foundation pile 3 is lowered through the upper layer 2a until the first foundation pile 3 receives support on the rock layer 2b. Here, the lower outer end of the first foundation pile 3 is placed on the rock layer 2b. It is not excluded here that the first foundation pile 3 can penetrate into the rock layer 2b over a short distance, but this distance will be minimal. In the illustrated embodiment, the first foundation pile 3 can be supported by the gripping members 101 of the gripping structure 10, since the thickness of the top layer 2a is relatively limited. The ladder 100 of the gripping structure 10 now extends into the upper layer 2a. This is not essential; the rudder 100 may extend only into the water, or even above the rock formation 2b. The support of the first foundation pile 3 can take place not only during its descent through the upper layer 2a, but also during successive method steps, such as the excavation of the shaft 9 shown in FIG. 2B.

According to FIG. 2B, a shaft 9 is then drilled into the rock formation 2b through the arranged first foundation pile 3. This is done by lowering the drilling means 8, which is provided with a drill head 80 (equipped with a cutting tool) into the internal cavity 3a of the first foundation pile 3. By rotating the drill head 80, a shaft 9 is formed, which extends into the rock formation 2b over the desired depth. The drill head 80 is placed through the first foundation pile 3 so that the transverse dimension 90 of the drilled shaft 9 is smaller than the internal transverse dimension of the first foundation pile 3. Thereby, the first foundation pile 3 remains supported on the rock layer 2b and does not sink downward. In the method step shown in FIG. 2B, the first foundation pile 3 can also be supported with a gripping structure 10.

According to FIG. 2C, a second foundation pile 7 is placed in the excavated shaft 9 in the next step. This is done to a depth 70 of the rock layer 2b, the outer surface of the second foundation pile 7 extending into the shaft 9 but also overlapping the outer surface of the first foundation pile 3 over an overlap length 71.

As also schematically shown in FIG. 2C, the outer surface of the second foundation pile 7 is preferably prepared by placing a cement mixture in the space between the outer surface of the second foundation pile 7 and the shaft wall 9. It is connected to the wall of the shaft 9 over a length 70. The cement mixture is also inserted into the space between the outer surfaces of the second foundation pile 7 and the first foundation pile 3 over the overlapped length 71. The cement mixture is then hardened such that the first foundation pile 3 and the second foundation pile 7 are structurally connected to each other over the overlapped length 71. Thereby, the second foundation pile 7 is also structurally connected to the inner wall of the drill shaft 9. The result is a foundation constructed from two nested foundation piles (3, 7) structurally connected to each other. The transmission of forces from the foundation thus formed to the underwater bottom 2 takes place at different levels. In addition to the shear stresses generated by the external surfaces of the first and second foundation piles (3, 7) and the drill shaft wall, the first foundation pile 3 receives support on the rock layer 2b and the second The foundation pile 7 can receive support on the underside of the drill shaft 9. Force transmission also takes place between the first foundation pile 3 and the top layer 2a via shear stresses between the outer surface of the first foundation pile 3 and the top layer 2a.

Another embodiment of the method is shown in FIGS. 3A-3C. In this embodiment, the depth of the upper layer 2a of material softer than rock is deep enough to hold the first foundation pile 3 in place by support from this upper layer 2a of the underwater bottom 2; Gripping structure 10 is not used. This position is preferably substantially vertical.

As shown in FIG. 3A, in a first step, the first foundation pile 3 is picked up by a crane 6 and placed through the upper layer 2a and onto the rock layer 2b. In this embodiment, moving the first base pile 3 with internal cavities 3a through the upper layer 2a can also be carried out in any manner known to the person skilled in the art, for example by pile driving. . Since the upper layer 2a is known to be relatively soft, placing the first foundation pile 3 poses fewer problems even though the upper layer 2a is thicker than in the example of FIGS. 2A-2C. I know it won't cause it. The first foundation pile 3 is lowered through the upper layer 2a until the first foundation pile 3 receives support on the rock layer 2b. Here, the lower outer end of the first foundation pile 3 is placed on the rock layer 2b. It is not excluded here that the first foundation pile 3 can also penetrate over a short distance into the rock layer 2b, but this distance will be minimal. In the illustrated embodiment, due to the relatively large thickness of the upper layer 2a, the first foundation pile 3 does not need to be supported by the gripping members 101 of the gripping structure 10, which are submerged by the ladder structure 100. is carried to a certain depth. It is only necessary to hold the first foundation pile 3 on the upper side by means of the positioning structure 11 in the position of the platform 5 and with gripping elements 111 on its sides. The first foundation pile 3 is engaged with the gripping member 111 only on its upper side, so that the desired angular position, in particular the verticality, of the first foundation pile 3 can be set. For this purpose, the gripping member 111 can be moved in a horizontal plane, preferably in such a way that its position can be kept stable with respect to the underwater bottom 2. Any movement of the platform 5 relative to the underwater bottom 2 is thus compensated. The support of the first foundation pile 3 can take place not only during its descent through the upper layer 2a, but also during successive method steps, such as the excavation of the shaft 9 shown in FIG. 3B. The advantage of the positioning structure 11 is that it can be removed in a simple manner after the first foundation pile has been placed on the rock layer 2b and no longer needs to be used, for example during excavation.

According to FIG. 3B, a shaft 9 is drilled into the rock formation 2b through the arranged first foundation pile 3. This is done by lowering the drilling means 8, which is provided with a drill head 80 (equipped with a cutting tool) into the internal cavity 3a of the first foundation pile 3. By rotating the drill head 80, a shaft 9 is formed, which extends into the rock formation 2b over the desired depth. The drill head 80 is placed through the first foundation pile 3 so that the transverse dimension 90 of the drilled shaft 9 is smaller than the internal transverse dimension of the first foundation pile 3. Thereby, in this embodiment, the first foundation pile 3 also remains supported on the rock layer 2b and does not sink downward. In the method step shown in FIG. 3B, the upper outer end of the first foundation pile 3 can also be supported by the positioning structure 11 if required.

According to FIG. 3C, a second foundation pile 7 is placed in the excavated shaft 9 in the next step. This is done to a depth 70' of the rock layer 2b, the outer surface of the second foundation pile 7 extending into the shaft 9 but also overlapping the outer surface of the first foundation pile 3 over an overlap length 71'. The length 70' by which the second foundation pile 7 is inserted into the rock layer 2b may be smaller than the insertion length 70 in the embodiment shown in FIGS. 2A to 2C, which is equal to the thickness of the upper layer 2a. is larger than in FIGS. 2A-2C, thereby providing more support.

Also shown schematically in FIG. 3C, the outer surface of the second foundation pile 7 is preferably prepared by placing a cement mixture in the space between the outer surface of the second foundation pile 7 and the shaft wall 9. , connected to the wall of the shaft 9 over a length 70'. The cement mixture is also inserted into the space between the outer surfaces of the second foundation pile 7 and the first foundation pile 3 over the overlapped length 71'. The cement mixture is then hardened such that the first foundation pile 3 and the second foundation pile 7 are structurally connected to each other over the overlapped length 71'. Thereby, the second foundation pile 7 is also structurally connected to the inner wall of the drill shaft 9. As in the embodiment shown in FIGS. 2A-2C, this creates a foundation constructed from two nested foundation piles (3, 7) that are structurally connected to each other. The transmission of forces from the foundation thus formed to the underwater bottom 2 takes place here too at different levels, as already explained above in the context of FIGS. 2A to 2C.

An embodiment of a foundation formed in this way is further illustrated in FIGS. 4 and 5. FIG. 4 shows a foundation formed as an assembly of first foundation piles 3, into which a second foundation pile 7 is received and fixed, for example by a grout connection as described above. If desired, the foundation can be provided with a transition piece 4, which is slid over the outer end of the first foundation pile 3 and fixed thereto, for example with a grout connection 43. The transition piece 4 can be provided with a platform 40 in a known manner.

The cross-section in FIG. 5 shows that the diameter 74 of the second foundation pile is smaller than the diameter 34 of the first foundation pile 3. As further illustrated in FIG. 6, the first foundation pile 3 is supported on the rock layer 2b because the diameter 90 of the drill shaft 9 is smaller than the inner diameter 34 of the first foundation pile 3. The diameter 74 of the second foundation pile 7 is furthermore smaller than the drill shaft diameter 90 (and therefore smaller than the internal diameter 34 of the first foundation pile 3). As a result, an intermediate space 79 is created between the second foundation pile 7 and the drill shaft wall 9 on the one hand, and on the other hand between (the peripheral wall of) the second foundation pile 7 and the first foundation pile 3 (of the An intermediate space 37 is created between the inner peripheral wall and the inner peripheral wall. The two intermediate spaces (79, 37) are at least partially, preferably completely, filled with a cement mixture that is subsequently hardened. Furthermore, in FIG. 6, the second foundation pile 7 (outer peripheral wall of) and the first foundation pile 3 (inner peripheral wall) have a structure between the first foundation pile and the second foundation pile (3, 7). It can be seen that respective shear projections 75 and 35 are provided to increase shear strength. FIG. 6 further shows that the relatively soft upper layer 2a can also be composed of sublayers (2a', 2a'') whose properties may differ. Thus, for example, the sublayer 2a'' is more flexible than the sublayer 2a'. It is also possible to be stiff.

The method of the invention is particularly suitable for placing foundations in underwater floors, which have a relatively soft upper layer and an underlying rock layer. Such an upper layer is also referred to by the term cover layer or topsoil. By applying the method of the invention, it is possible to obtain a solid foundation within an underwater bottom that is itself not very hard.

The invention is not limited to the embodiments described herein, but many modifications may be made within the scope of the appended claims.

1 device, 2 underwater bottom, 2a upper layer, 2a', 2a'' sublayer, 2b rock layer, 3 foundation pile, monopile, 3a internal cavity, 4 transition piece, 5 jack-up platform, 6 crane, 7 foundation pile, monopile, 8 excavation means, 9 drill shaft wall, drill shaft, 10 gripping structure, 11 positioning structure, 20 water surface, 32 peripheral portion, 33 lifting point, 34 inner diameter, 37 intermediate space, 40 platform, 43 grout connection, 50 Spud pole, 51 work deck, 52 leg, 60a, 60b double boom, 61 base, 62 shaft, 63a, 63b lifting cable, 64a, 64b traction cable, 65 upper part, 66 lifting block, 70 depth, 70' Depth, 71 Overlapping length, 71' Overlapping length, 72 Peripheral portion, 73 Lifting point, 75 Shear projection, 79 Intermediate space, 80 Drill head, 90 Drill shaft diameter, transverse dimension, 100 Ladder structure, 101 Gripping member, Gripping arm, 111 Gripping member

Claims (17)

A method for placing a foundation in an underwater bottom from a ship, the underwater bottom including an upper layer and a rock layer located below the upper layer, the method comprising:
- placing a first foundation pile with an internal cavity through the upper layer and onto the rock layer, the first foundation pile receiving support on the rock layer;
- lowering an excavation means provided with a cutting tool into the internal cavity of the first foundation pile and driving a shaft through the first foundation pile into the rock formation by rotating the excavation means; excavating, the shaft having a transverse dimension that is less than an internal transverse dimension of the first foundation pile;
- placing a second foundation pile in the shaft to a predetermined depth in the rock formation, the outer surface of the second foundation pile extending into the shaft and overlapping lengths of the second foundation pile; A step that overlaps the outer surface of the foundation pile of No. 1,
- connecting the outer surface of the second foundation pile to the wall of the shaft and the outer surface of the first foundation pile substantially over the overlapped length;
including methods. The step of connecting includes applying a cement mixture in the space between the outer surface of the second foundation pile and the shaft wall and in the space between the outer surfaces of the second foundation pile and the first foundation pile. 2. The method of claim 1, carried out by placing a cement mixture and curing the cement mixture. 3. A method according to claim 1 or 2, wherein the outer surface of the first foundation pile is an inner outer surface and the outer surface of the second foundation pile is an outer outer surface. 4. A method according to any one of claims 1 to 3, wherein the first foundation pile placed on the rock formation is held in place by support from the upper layer of the underwater bottom. 5. According to any one of claims 1 to 4, the first foundation pile placed on the rock formation is held in place by support from a gripping structure suspended downwardly from the vessel. the method of. 6. A method according to claim 4 or 5, wherein the position is substantially vertical. 7. A method according to any preceding claim, wherein the excavation means are supported by the first foundation pile. 8. A method according to claim 7, wherein the excavation means is supported by the first foundation pile such that the longitudinal direction of the excavated shaft is substantially the same as the longitudinal direction of the first foundation pile. . 9. A method according to any preceding claim, wherein the second foundation pile is supported by the excavated shaft. 10. The second foundation pile is supported by the excavated shaft such that the longitudinal direction of the excavated shaft is substantially the same as the longitudinal direction of the second foundation pile. the method of. 11. The method according to any one of claims 1 to 10, wherein the outer surface of the first foundation pile and/or the second foundation pile is provided with shear projections over at least the overlap length. 12. A method according to any one of claims 1 to 11, wherein the second foundation pile is hollow. 13. The method of claim 12, wherein the first foundation pile has a wall thickness of 50 mm or more and 120 mm or less. 14. A method according to any one of claims 1 to 13, wherein the upper outer end of the first foundation pile is located above the water level after connection with the second foundation pile. 15. A method according to any one of claims 1 to 14, wherein the upper outer end of the first foundation pile is provided with a transition piece after connection with the second foundation pile. 16. A method according to any one of claims 1 to 15, further comprising the step of arranging a wind turbine on the foundation. 17. A method according to any preceding claim, wherein the vessel comprises a jack-up platform.