DK2796620T3

DK2796620T3 - MAKING foundation pile FOR OFFSHORE STRUCTURES AND foundation pile FOR OFFSHORE STRUCTURES

Info

Publication number: DK2796620T3
Application number: DK14165646.2T
Authority: DK
Inventors: Daniel Bartminn
Original assignee: Rwe Innogy Gmbh
Priority date: 2013-04-26
Filing date: 2014-04-23
Publication date: 2016-08-22
Also published as: EP2796620A3; EP2796620B1; DE102013007237A1; EP2796620A2

Description

Method for constructing a foundation pile for offshore constructions and foundation pile for offshore structures

The invention relates to a method for producing a foundation pile for offshore structures. The invention further relates to a foundation pile for offshore structures as well as an offshore structure with a pile foundation.

Offshore structures for the purposes of the present invention include wind turbines, transformer substations or drilling or production platforms. A pile foundation in the seabed is required for certain types of foundations for offshore structures, especially for offshore wind turbines. Common types of foundations are, for example, so-called monopiles, jackets, tripods or tripiles. To anchor these foundations in the seabed one or more steel piles are initially driven into the seabed. A steel grid structure/steel tube structure is then placed, for example, on the steel piles in a jacket foundation to receive a so-called "transition piece" above the surface of the sea. The transition piece then receives the actual structure, for example in the form of a steel tower. The tower receives the wind power generator with a rotor on its uppermost end.

The driving of the foundation piles, also referred to as "piles", is accompanied by noise emissions, which are particularly undesirable because they cause harm and behavioral disorders among marine mammals. It is therefore known and partly prescribed to implement deterrent measures and/or sound reduction measures before carrying out pile driving to ensure that no marine mammals are in the vicinity of the pile driving and/or that the sound is reduced to the permitted level.

Since the penetration depth of the pile-driven steel piles and the progress of such piledriving depends on the resistance of the seabed, the setting of steel piles suffers from the disadvantage that piles among multiple foundation piles do not always penetrate to the same depth in the seabed.

Depending on the nature of the seabed, the piles must be driven to a considerable depth in the seabed, as the structural stability of the piles is only ensured when the piles are driven into a load-supporting soil horizon in the seabed. Under certain circumstances, the actual stress on the piles may be higher than the presumed load-supporting requirements, and this may ultimately lead to the foundation piles failing. It is possible that the stress and fatigue caused by the pile-driving may exceed the predicted and calculated measurements so that the pile must be either simply scrapped or be subject to a reduced life expectancy. The greater the foundation depth, the higher is the risk of local structural failure, for example by buckling.

The connection of the underwater structures of the foundation with the foundation piles requires the casting of the material using casting materials that may be cured under water, or other costly connection techniques.

The setting of the piles must be carried out at a predetermined distance, which is ensured via so-called "prepiling" using corresponding templates. This assumes that the condition of the seabed is such that all the piles to be set may be driven to the predetermined soil horizon.

There are no possible variations with respect to the distance or positions for setting the piles.

When setting larger piles, undersea currents may scour the seabed in the area of the piles. In this case, further measures must be provided to prevent scouring of the seabed. WO 2011/147476 A1 describes a method for producing a foundation pile for offshore structures.

The invention therefore has the object of providing a particularly simple method for producing a foundation pile for offshore structures, which are not particularly subject to the aforementioned restrictions.

The object is achieved by a method for producing a foundation pile for offshore structures according to claim 1.

By shot channel for the purposes of the present invention, is meant the displacement channel produced by the drop anchor upon introduction in the sediment of the seabed.

The invention is based on the concept of a drop anchor and at least an anchor cable attached to the drop anchor and at least an anchor point in the seabed to which the anchor cable is attached.

The drop anchor is so dimensioned, for example, with respect to its mass and with respect to its geometry, that it penetrates to a predetermined depth in the seabed due to its kinetic energy in free fall.

This entrains the attached anchor cable with it. One or more casting material lines may be attached to the anchor cable, which are likewise entrained by the drop anchor. This casting material lines enable a curable casting material, for example a curable underwater concrete, to be pressed into the shot channel, wherein the anchor cable serves to reinforce the casting material column simultaneously produced in situ. A drop anchor according to the present invention means, for example, a drop anchor which has a torpedo-shaped body comprising a penetrating tip and provided at its end with several stabilizing torpedo vanes.

The torpedo body may, for example, be hollow and comprise one or more ballast chambers that may be filled with a ballast.

The method has the particular advantage over conventional pile foundations in that bracing of the structure being erected may take place with one or more anchor cables which naturally permits a certain leeway in the positioning of the offshore structure so that the setting of the foundation piles need not be determined by means of a template or the underwater structure.

Moreover, setting the piles by driving is eliminated. The process of setting the drop anchor is a one-off action, whereas the driving of piles is accompanied by a regularly recurring and frequent sound emissions in the marine environment.

An anchor line or an anchor chain or an anchor cable is provided as the tension element according to the present invention.

Of course, several tension elements/anchor lines, or anchor cables or anchor chains may be attached to a drop anchor, although reference hereinafter is to a tension element. A tension element according to the invention is, in any case, a flexible tension element that can only transmit tensile forces, and not, however, pressure forces.

In an advantageous variant of the method according to the invention, it is provided that the casting material is introduced through at least a partial length of the tension element into the shot channel, wherein the tension element remains in the cured casting material. On the one hand, the tension element serves for the reinforcement of the casting material, and for the bracing of the offshore structure to be built on the other. In this way, the depth to be achieved by the drop anchor is reduced because the frictional force at the tension element required for the bracing of the main structure is reduced and is supplied by the casting material body.

Appropriately, the tension element at the end remote from the drop anchor side is provided with at least a float, which is arranged at a predetermined distance from the drop anchor, wherein the distance is selected according to the planned penetration depth into the seabed of the drop anchor and the height of the surface of the sea above the seabed, so that the tension element and the casting material line connected to it may float, and so that these may be caught up by a support vessel.

Appropriately, the drop anchor is provided with ballast before being dropped, wherein the ballast mass is so selected that the drop anchor penetrates into the subsoil until it reaches a load-supporting soil horizon.

In a particularly advantageous variant of the method, it is provided that the drop anchor is suspended from a drop string and the dropping is effected by actuating a trigger mechanism on the drop string. In this dropping, the drop anchor is attached to both the drop string as well as to one or more tension elements.

In a favorable variant of the method according to the invention, it may be provided that the drop anchor is introduced into the seabed through a protective tube or a sheet piling enclosure, wherein the protective tube or the sheet piling enclosure will have been previously put in place.

In order to facilitate the penetration of the drop anchor into the seabed, it may be provided that the seabed beneath the protective tube or inside the sheet piling enclosure is fluidized by injecting compressed air or water before dropping the drop anchor.

Alternatively, for example, the use of a protective tube may be provided, wherein the protective tube is pumped out before dropping the drop anchor, so that the kinetic energy with which the drop anchor penetrates the seabed, may be significantly increased.

Alternatively, the protective tube, which may extend, for example, beyond the surface of the sea, may be pumped full of a liquid so that increased hydrostatic pressure is built up at the foot of the tube by the liquid column in order to facilitate the penetration of the drop anchor in the seabed. The liquid column may, for example, be adjusted accordingly in terms of its specific gravity. For example, a baryte solution may be used as the liquid.

The protective tube may, for example, be flushed into the seabed up to a certain depth before dropping the drop anchor.

The casting material line may, for example, be provided with a plurality of casting outlet openings or vents longitudinally spaced apart, so that the casting mass may be evenly distributed in the shot channel above the height of the tension element.

It is also possible that the casting materail line is pulled during the casting. It is thus not absolutely necessary to provide a plurality of outlet openings for the casting material. Pulling the casting material line may, however, also be provided when a casting material line has several outlet openings for the casting material that are distributed over its height and/or circumference.

The casting mass line may be lost, at least over a part section extending in the shot channel, i.e. above this section remains in the shot channel.

The object underlying the invention is further achieved by a foundation pile for offshore structures, which comprises a drop anchor to which is attached an anchor cable as a tension element, and a casting mass column cast in situ inside the seabed and extending over a length within the seabed, wherein the anchor cable extends over a partial length within the casting mass column and to at least the surface of the sea. The foundation pile according to the invention may comprise at least a protective tube, which only extends over a partial length of casting mass column.

Alternatively, the foundation pile may be provided with a sheet piling enclosure extending over a partial length of the casting mass column.

The object underlying the invention is finally achieved by an offshore structure with a pile foundation, comprising a plurality of drop anchors sunk into the seabed and a casting mass column cast in situ extending above the drop anchor, wherein the structure is braced via anchor cables that are attached to the drop anchors.

Appropriately, the anchor cables each extend through a casting mass column and approximately in the longitudinal center.

The offshore structure according to the invention may comprise, for example, a monopile created in a conventional manner and comprising bracing via several anchor cables.

The offshore structure according to the invention comprises a pile foundation constructed according to the invention, wherein the pile foundation is effected using the method according to the invention.

The invention is explained below with reference to an embodiment shown in the drawings:

Fig. 1 shows a side view of a monopile foundation of an offshore structure according to the prior art,

Fig. 2 shows a corresponding view of an offshore structure established according to the invention,

Fig. 3 shows a plan view of the view according to Fig. 2,

Fig. 4 shows an illustration of a drop anchor according to the invention,

Fig. 4a to 4c show the drop anchor as shown in Fig. 4 in the plan view with four or five anchor cables, and

Fig. 5, 5a, 5b show the setting of the drop anchor according to the inventive method.

Reference is first made to Fig. 1, which shows a monopile 1 according to the prior art. A transition piece 2 with a platform 3 and a related structure (not shown) is fitted on the monopile 1. The transition piece 2 is referred to in the prior art as a "transition piece".

The monopile 1 according to the invention has a relatively large diameter and is set either by driving or flushing into the seabed 4.

Fig. 2 shows, in direct comparison to Fig. 1, an offshore structure according to the invention also comprising a monopile 1, a transition piece 2 and a platform 3.

The monopile 1 according to the invention, however, is shorter and slimmer than the monopile 1 according to the prior art. The former is braced by about four anchor cables 5, each of which is attached to a foundation pile 6 under the seabed 4. More specifically, each anchor cable 5 is fixed to a drop anchor 7 and extends through a casting mass column 8 arranged above the drop anchor 7, and which is cast in situ in the seabed. The casting mass column 8 is created without permanent formwork and without a stand pipe as described below. Thus, the casting mass column 8 has no regular outer contour.

Fig. 3 shows a plan view of the arrangement according to Fig. 2

One embodiment of the drop anchor 7 is shown in Fig. 4 The drop anchor 7 is a drop anchor within the meaning of the foregoing embodiment. This includes a torpedo-shaped body 9, which has a penetration tip 10 at its leading end and is provided with four vanes 11 at its trailing end.

An anchor cable 5 is attached to the trailing/rear end of the body 9 in the direction of dropping, and is arranged to be concentric with a casting mass line 12.

In the illustrated example, an extra concentric arrangement of the casting mass line 12 and the anchor cable 5 is provided, so that the anchor cable 5 extends within the casting mass line 12; alternatively, of course, it may also be provided to lay one or more casting mass lines 12 parallel to the respective anchor cable 5.

Of course, several anchor cables 5 may be connected to a drop anchor 7 as is suggested in Fig. 4b and 4c. These figures show, respectively, exactly as in Fig. 4a, a plan view of the drop anchor 7 according to Fig. 4.

In the method according to the invention, it is provided to introduce the drop anchor 7 in the seabed 4 by using a certain drop height and drop energy, wherein the drop anchor 7 entrains the anchor cables 5 as well as the casting mass line 12. Then, a casting material, for example, concrete, is pressed into the shot channel produced in the seabed 4 under the pressure of the drop anchor 7, to result in the casting mass column 8 extending above the drop anchor 7 as shown in Fig. 2. A concrete or an anchor grout is considered as a casting material. When the casting material is cured, this provides the foundation pile 6 shown in Fig. 2, from which the anchor cable 5 is led out. The setting of the drop anchor 7 is shown relatively simplistically in Fig. 5, 5a and 5b.

The drop anchor 7 is suspended from a crane 13 which is placed on a provisional platform 3 already built. The platform 3 may be a part of the offshore structure to be anchored.

On the one hand, the drop anchor 7 is attached to the anchor cable 5, and suspended from a drop string 14 on the other.

It should be noted, of course, that the drop anchor 7 may be dropped from a ship.

The reference numeral 15 designates a protective tube, whose diameter is slightly larger than that of the drop anchor 7. The protective tube is only slightly flushed into the seabed 4 and extends well above the surface of the sea 16.

The drop anchor 7 is introduced into the upper end of the protective tube 15, so that the drop anchor 7 is separated from the drop string 14 or dropped with the drop string 14 by using its kinetic energy. The drop anchor 7 falls through the protective tube 15 and penetrates into the seabed 4, wherein, in the simplest case, this only entrains the anchor cable 5 and the casting mass line 12. A float 17 is attached to the distal end of the anchor cable 5, which allows the anchor cable 5 to float. The anchor cable 5 may be supplied in this way from a supply ship and fastened, for example, to the offshore structure and tensioned.

The drop anchor 7 may be provided with an appropriate ballast before being dropped, which is why the main body 9 of the drop anchor 7 may be provided with corresponding chambers.

The mass of a drop anchor may be between ten and one hundred tonnes, and such a drop anchor may have, for example, a length of up to twenty meters and a diameter of up to one meter.

List of reference numerals 1 Monopile 2 Transition piece 3 Platform 4 Seabed 5 Anchor cables 6 Foundation pile 7 Drop anchor 8 Casting material column 9 Foundation pile 10 Penetration tip 11 Vane 12 Casting material line 13 Crane 14 Drop string 15 Protective tube 16 Surface of the sea 17 Floating body

Claims

MANUFACTURE OF FOUNDATION PELLETS FOR OFFSHORE CONSTRUCTIONS AND FOUNDATION PILE FOR OFFSHORE STRUCTURES

A method of manufacturing a foundation pile (6) for offshore structures comprising the following steps: - Providing and placing a fall anchor (7) at a predetermined height above the seabed (4), - attaching at least one anchor ridge (5) for the fall anchor, - attachment of at least one casting lead (12) to the anchorage (5), - throwing down the fall anchor so that this penetrates into the seabed due to its kinetic energy, and - introducing a curable casting mass into the shot channel produced by the fall anchor. via the seabed penetration.

Method according to claim 1, characterized in that the casting mass is introduced into the shot channel at least over a part of the length of the anchor truss, where the anchor truss is seated in the cured molding mass.

Method according to claim 1 or 2, characterized in that the anchor truss is provided with at least one float body (17) arranged at a predetermined distance from the drop anchor, the distance being chosen according to the planned depth of penetration of the anchor into the seabed and according to the water level ( 16) height above sea level.

Method according to claims 1 to 3, characterized in that the fall anchor is provided with ballast prior to the drop, the ballast mass being selected such that the fall anchor penetrates into the seabed to a sustainable subsurface horizon.

Method according to claims 1 to 4, characterized in that the drop anchor is suspended in a drop string (14) and the throw-off is effected via release of a release mechanism on the drop string.

Method according to claims 1 to 5, characterized in that the fall anchor is placed in the seabed through a protective tube (15) or through a baffle wall mount.

Process according to claim 6, characterized in that the protective pipe is flushed into the seabed prior to the throw-off of the waste tank.

Method according to Claim 6 or 7, characterized in that the seabed inside the protective pipe or inside the bunker wall casing is fluidized before injection of the fall anchor via injection of compressed air or water.

Method according to claim 6, characterized in that the protective tube is pumped empty before the drop of the fall anchor.

Method according to claims 1 to 9, characterized in that at least one molding line is used, which has a plurality of outlet openings for the molding and which are provided at a distance from one another in the longitudinal direction.

Method according to claims 1 to 10, characterized in that the molding line is drawn during the molding process.

Method according to claims 1 to 11, characterized in that the molding line is dropped at least over the sub-section extending in the firing channel.

The foundation pile (6) for offshore structures, manufactured according to a method according to one of claims 1 to 12, wherein the foundation pile comprises a casting column (8) cast in situ in the seabed (4) and extending in the seabed (4). ) over a certain length and where the anchor cluster (5) extends into the casting column (8) and at least up to the water level (16).

The foundation pile of claim 13, which has a protective covering extending over a portion of the length of the molding column (8).

The foundation pile according to claim 13, which has a pivot wall mount extending over a portion of the length of the molding column (8).

An offshore structure having a pile foundation comprising a plurality of foundation piles according to one of claims 13 to 15, which are lowered into the seabed (4) and in situ cast casting columns (8) extending over the fall anchors of the foundation piles ( 7), wherein the structure is supported by anchor trusses (5) which are attached to the drop anchors (7).

An offshore structure according to claim 16, characterized in that the anchor trusses (5) extend through the casting columns.

An offshore structure according to one of Claims 16 and 17, characterized in that it comprises a monopole (1) and a support in the form of a plurality of anchor trusses (5).