EP2700750B1 - Foundation pile for offshore structures and method for constructing a foundation pile for offshore structures - Google Patents

Description

The invention relates to a foundation pile for offshore structures, for example as drilling or production platforms or to accommodate wind turbines. The invention further relates to a method for producing a foundation pile.

For certain foundation types for offshore structures, in particular for offshore wind turbines, a pile foundation in the seabed is required. Such foundation types are, for example, so-called monopiles, jackets, tripods or tripiles. For this purpose, one or more steel piles are first rammed into the seabed, then on the steel piles, for example, a steel grid structure / tubular steel structure is placed on a jacket foundation, which receives a so-called transition piece above the sea level. The transition piece then takes on the actual structure, for example in the form of a steel tower. The tower receives at its uppermost end the wind power generator with a rotor.

Ramming of foundation piles (piles) is known to be associated with noise emissions, which are particularly undesirable because they cause damage and behavioral disturbance of marine mammals. It is therefore known and sometimes required to carry out offensive measures and / or noise abatement measures before carrying out pile driving to ensure that no marine mammals are present in the vicinity of the pile work and / or that sound is reduced to the permitted limit.

Since the penetration depth of the rammed steel piles and the progress of such piling depends on the strength of the seabed, the setting of steel piles has the disadvantage that the piles of a foundation placed on several piles are not always anchored with the same depth of penetration in the seabed. Finally can not be ruled out that results in the execution of pile driving a misalignment of one or more piles. As a result, costly measures to compensate for differences in level are required when placing the foundation or when mounting a connecting structure.

It is basically known in the art to sink steel piles by drilling or flushing in the seabed or to anchor foundations in the form of so-called caisson foundations in the seabed, for example from the DE 103 022 94 A1 ,

From the DE 10 2007 000 328 A1 as well as from the GB 231516 A a pile construction is known, comprising a tube made of glass fiber reinforced plastic, at the lower end of a cutting shoe is arranged, which has an overcut. The preparation of this pile construction can be carried out in a first step by ramming, shaking or flushing. After sinking the lower part of the tube in the underground, the material located inside the tube is drilled and drilled out through the soul of the tube even further below the cutting shoe and filled the drilled cavity including the pipe with concrete. The tube made of glass fiber reinforced plastic used for this purpose serves as a lost formwork. However, the pile construction described above only allows the use of small-sized pipes with diameters in the order of 0.3 m.

The aforementioned methods are advantageous in that the ramming of steel piles into the seabed is avoided.

The known types of foundations, however, are for the most part subject to the disadvantage that expensive measures for connecting and leveling the structure to be erected on the foundation are required.

The invention has for its object to provide a foundation pile for offshore structures that can be anchored both while avoiding ramming in the seabed, as well as the simplest possible Connection / transition to a building to be constructed, in particular to a tower construction for offshore wind turbines forms.

Furthermore, the invention has for its object to provide a suitable method for producing a foundation pile for offshore structures.

The object is achieved by a foundation pile according to the invention for offshore structures, which is modularly composed of individual pipe sections, of which at least one pipe section is anchored as lost borehole casing in the seabed, wherein the pipe sections are designed as concrete pipes, which are connected to each other by means of clamping elements.

The idea underlying the invention can be summarized in that the principle of separate pile foundation by means of steel pipes and also created separately made of steel tower construction is abandoned and instead a foundation pile for offshore structures is provided, which consists entirely of reinforced concrete components. This not only has the advantage that, for example, a foundation in the form of a monopile can be made entirely in reinforced concrete and can be composed throughout or predominantly over long lengths from the foundation tip to the wind turbine generator made of reinforced concrete pipe sections of approximately the same kind, but also the advantage of a relatively simple deconstruction. When using steel structures, such a readjustability is difficult or impossible to accomplish, since the connections of the pile section located in the seabed would have to be separated from above in the water body and in the air space to a pile section at the seabed level. This would be very expensive, for example, in a rammed Monopilegründung due to the large diameter and the wall thickness of the steel pipe.

For the purposes of the present application, the term seabed hereinafter refers to the interface between the overlying body of water and the underlying mountains / sediment, which is referred to in this application as the subsoil.

A erfindunsgemäße construction has over other constructions in particular the advantage that due to the fully modular construction of the foundation pile, the underwater length of the foundation pile including the penetration depth in the seabed is adaptable, even during the foundation process, which is not the case when setting steel piles. These must be provided with a given length, which can not be changed. When reaming steel piles, exploration drillings are first drilled to determine the strength of the subsoil. After carrying out appropriate strength calculations, the pile depth is determined, after which the length of the prepared steel piles is finally measured, the length of which can not be adapted on site. Ramming may cause difficulties due to local heterogeneities of the seabed so that the full piling depth may not be achieved. Furthermore, the calculation of the required pile length is complicated and due to the cyclic load of the piles due to waves and wind with increased uncertainties afflicted.

Due to the fact that the foundation pile according to the invention is made up of a plurality of reinforced concrete pipe sections, misalignments of the foundation pile can already be compensated during its installation. For this purpose, different fittings can be kept for use as the top module, which compensate for a misalignment of the foundation pile so that a horizontal position of the turbine-generator shaft can be achieved within the manufacturing tolerances.

Further advantages of such a foundation pile construction composed of concrete pipe sections are greater safety against the effect of scoring, a smaller proportion of steel and, last but not least, the possibility of a low-noise creation of the foundation pile. Another advantage of the foundation pile construction according to the invention can be seen in the fact that the bond length in the seabed increases without problems so can be, that even after a later Kolkbildung still a sufficiently secure anchoring in the seabed is given. In isolated cases, an outcrop may have a depth of 7 to 10 meters below the seabed level.

Finally, the corrosion potential is lower, since no unprotected steel structure is exposed to the seawater.

In an advantageous expedient variant of the foundation pile according to the invention, provision is made for the pipe weft arranged at the bottom of the wellbore to be provided with a circumferential cutting shoe which can form an overcut or overhang relative to the diameter of the relevant pipe weft.

In an advantageous variant of the foundation pile according to the invention it is provided that the foundation pile from the seabed extends at least to the waterline and preferably well beyond the waterline and is composed at least over this length of approximately identical pipe sections.

Identical within the meaning of the invention means that the pipe sections are compatible in terms of compatibility or composability and bracing, but that the pipe sections above the seabed need not necessarily have all the same diameter over the entire height. This means that the pipe sections are not necessarily all cylindrical, but rather several pipe sections can form a tower / mast or pile with a hyperboloid or trapezoidal contour.

The foundation pile may, but need not necessarily, be partially filled within the wellbore. The foundation pile is advantageously circumferentially frictionally and / or positively anchored in the designated hole in the seabed.

A particularly advantageous variant of the foundation pile according to the invention is characterized by at least one Ortbetonfuß extending in the seabed below the cutting shoe in a borehole extension. This Ortbetonfuß can be designed in the manner of an elephant foot and be overlapped with respect to the concrete pipes. This means that the Ortbetonfuß at least partially has a diameter which is greater than the diameter of the cutting shoe. The foot can also have several overcuts or thickenings.

1. a) Absetzen von mehreren vorzugsweise gleichartigen Betonschüssen auf dem Meeresboden zu einer senkrecht stehenden Rohrtour,
2. b) Einbauen einer Bohrgarnitur in die Rohrtour,
3. c) Abteufen eines Bohrlochs innerhalb der Rohrtour,
4. d) Nachführen der Rohrtour in das Bohrloch mit dem Bohrfortschritt unter Ausnutzung der Gewichtskraft der Rohrtour und
5. e) Aufstocken der Rohrtour mit weiteren Rohrschüssen und
6. f) Wiederholen der Schritte c) bis d) bis zum Erreichen einer vorgesehenen Endteufe der Rohrtour im Meeresuntergrund.

The object on which the invention is based is furthermore achieved by a method for producing a foundation pile for offshore structures, comprising the following method steps:

1. a) depositing several preferably similar concrete shots on the seabed to a vertical tube tour,
2. b) installing a drill set in the pipe run,
3. c) sinking a borehole within the pipe run,
4. d) tracking the tube tour in the well with the drilling progress, taking advantage of the weight of the tube tour and
5. e) Upgrading the tube tour with other pipe sections and
6. f) repeating steps c) to d) until reaching a planned final depth of the pipe tour in the seabed.

According to the invention, the pipe sections of the foundation pile are provided as lost borehole piping. The bore is drilled at least initially in the protection of the wellbore wall stabilizing casing / tubing. The pipe tour remains after reaching the intended final depth in the borehole as actual support structure in the seabed. This piping forms above the seabed a structurally identical continuation, which can extend at least to just over the water surface or significantly beyond. The pipe run or piping is equipped at its leading end, ie at its foot with a cutting shoe and is from the inside working drilling tool, which dissolves the rock layer of the seabed in the protection of the piping and conveyors to the sea surface transported so undercuts that the pipe shots or Rohrtour sinks by its own weight in the well. During drilling, the piping is in each case increased by pipe sections defined length so that the top of the pipe tour is always sufficiently above sea level and thus on a mounting platform, for example on an auxiliary ship, a safe drilling activity including targeted Bohrgutaustrags is guaranteed.

During the drilling and pumping process, the pipe tour is filled with seawater via pumps in such a way that the water level within the pipe tour is sufficiently above the sea water level. This ensures that the hydrostatic pressure within the pipe run or within the borehole is so great that there is always an overpressure against approximately drilled groundwater horizons in the seabed, so that an influx of groundwater through the borehole wall and erosion of the borehole wall are reliably avoided.

The pipe sections are preferably braced against one another in terms of longitudinal force, preferably already during assembly to a pipe run. Alternatively, it is possible to provide a so-called flaccid reinforcement instead of a restrained clamping of the pipe sections with relatively large diameters or relatively large material cross-sections.

Conveniently, after completion of the borehole at least part of the pipe run, preferably in the region of the foot of the pipe run, filled.

Backfilling may be provided, for example, with cuttings and / or in-situ concrete, which backfill does not have to meet high strength requirements and is not necessarily required. An advantage of this approach is the fact that a costly landfill of drilled cuttings is not required.

In a particularly preferred variant, it is provided that the sinking of the borehole takes place in the air lifting boring method. Such a drilling technique requires no tubing stabilizing tubing, in contrast to the known Spülbohrverfahren no optimized in terms of density and sealing of the well drilling is used, but above the drilling tool compressed air is introduced into the production pipe or drill pipe, the cuttings due to the density difference to the surrounding water-bearing borehole raises and discharges. Such a drilling method is particularly suitable for the removal of large boreholes without piping.

In the method according to the invention can be provided that prior to discontinuation of concrete pipe shots a removable protective piping is set, which may include, for example, the seabed patch set steel pipe shots, which have a larger diameter than the concrete pipes and which does not necessarily penetrate into the seabed.

The concrete pipe route expediently extends before and during the sinking of the borehole above the seawater level. The individual concrete pipe sections can be sealed against each other to ensure the establishment of a sufficiently high hydrostatic pressure within the pipe run. Under sealing in the context of the invention is merely to be understood that the individual pipe sections are set in accordance with precisely fitting each other, so that a leakage water flow is kept as low as necessary at the joints. The pipe sections are expediently designed as precast concrete rings and set without Fugenvermörtelung and without Fugenverklebung each other.

In a variant of the method according to the invention, it is provided that after installation of the pipe sections until the intended end depth of the pipe run, an uncased extension of the borehole below the lowest pipe section is produced.

The extension of the borehole can be created at least in sections with a larger diameter than the cased portion of the borehole. This uncased area of the borehole can then be cast with in-situ concrete and possibly with reinforcing elements.

The clamping of the pipe sections is advantageously carried out by tendons in the form of steel cables, which are performed either within the pipe run or within the pipe sections in the longitudinally extending sleeves. The tendons can be connected in sections, for example via corresponding couplings or via corresponding turnbuckles.

The discontinuation of the individual pipe sections to a pipe tour on the seabed, for example, carried out such that the pipe sections are guided over the longitudinal clamping elements to each other and deposited on a settling device by means of winds on the seabed.

The pipe sections, for example, by means of guide ropes, which rest against the outside of the pipe sections or against the pipe trip, be dropped by means of winds on the seabed. For this purpose, for example, a total of three provided over the circumference of the tube tour guide cables are used, which are posted in each case at the bottom pipe shot or engage under this.

Alternatively, several already pre-assembled to a tube tour pipe shots can be placed on the seabed.

The discontinuation of the pipe run and performing the drilling is advantageously carried out by a floating or elevated installation platform.

The invention will be explained below with reference to an embodiment shown in the drawings.

Figur 1:

eine erste schematische Darstellung eines Gründungspfahls gemäß der Erfindung als Monopile zur Aufnahme eines Turmbauwerks und eines Windkraftgenerators nach einer ersten Variante,

Figur 2:

eine Schnittansicht durch einen Rohrschuss nach der ersten Variante des Gründungspfahls,

Figur 3:

eine Draufsicht auf den in Figur 2 dargestellten Rohrschuss,

Figur 4:

eine Draufsicht auf einen Rohrschuss gemäß einer zweiten Variante des Gründungspfahls nach der Erfindung und

Figur 5:

eine schematische Darstellung, die den Einbau der Rohrschüsse innerhalb einer Schutzverrohrung zeigt.

Show it:

FIG. 1:

a first schematic representation of a foundation pile according to the invention as a monopile for receiving a tower structure and a wind power generator according to a first variant,

FIG. 2:

a sectional view through a tube shot according to the first variant of the foundation pile,

FIG. 3:

a top view of the in FIG. 2 shown pipe shot,

FIG. 4:

a plan view of a pipe section according to a second variant of the foundation pile according to the invention and

FIG. 5:

a schematic representation showing the installation of the pipe sections within a protective casing.

Although the invention is described below with reference to a so-called monopile, it should be mentioned at this point that the foundation pile 1 according to the invention and the method for producing the foundation pile 1 are suitable for the production of various foundation types for offshore structures of any kind. For example, a jacket foundation, a tripod foundation or a tripile foundation could be mentioned. Likewise, foundations for offshore drilling platforms, offshore production platforms or offshore supply platforms can be created in this way.

The in FIG. 1 illustrated foundation pile 1 comprises a plurality of pipe sections 2 made of reinforced concrete, which are joined together at the front end to form a pipe run 3. The pipe sections can for example have a diameter of 1 to 10 m. The individual pipe sections 2 are braced against each other via tension members 4, for example in the form of tendons or steel cables. The individual pipe sections 2 are provided with a reinforcement. The pipe sections 2 can also each be composed of segments.

The joints 5 between the individual pipe sections 2 are expediently neither glued nor mortared, but only accurately matched.

According to a first variant of the foundation pile 1 according to the invention, the tension members 4 extend within the lateral surface of the pipe sections 2, for example within cast-in sleeves.

At a second in FIG. 4 illustrated variant of the foundation pile 1, the tension members 4 are laid in the interior of the pipe sections 2, which can either be fixed by appropriate fasteners on the inner wall of the pipe sections 2 or, for example, at a provided above the seabed hyperboloid contour of the pipe run 3 completely free against the Inner wall of the pipe sections 2 or inner wall can rest.

The tension members 4 were each partially extended during installation of the pipe sections 2 and connected to each other via couplings, not shown, or turnbuckles.

• Von einem Installationsschiff aus wird zunächst eine Schutzverrohrung 6 aus Stahl gesetzt. Wie eingangs bereits erwähnt, ist die Schutzverrohrung optional, deren Erforderlichkeit ist von den Strömungsverhältnissen und den Beschaffenheiten des Meeresbodens abhängig. Die Schutzverrohrung 6 besteht aus mehreren Stahlrohrsegmenten, die auf dem Meeresboden 7 abgesetzt werden und die einen etwas größeren Durchmesser als eine niederzubringende Bohrung aufweisen. Die Schutzverrohrung 6, ebenso wie die anschießend zu setzende verlorene Verrohrung erstrecken sich deutlich oberhalb des Meeresspiegels 8.

The production of the foundation pile 1 according to the invention is accomplished as follows:

• From an installation ship, a protective casing 6 made of steel is first set. As already mentioned, the protective casing is optional, the necessity of which depends on the flow conditions and the characteristics of the seabed. The protective casing 6 consists of several steel pipe segments which are deposited on the seabed 7 and which have a slightly larger diameter than a bore hole to be drilled. The protective piping 6, as well as the piping to be subsequently set, extend clearly above the sea level 8.

Preferably, the protective casing 6 extends approximately as high above the sea level 8 as the tube 3, so that no hydrostatic Imbalance between the annulus of the protective casing 6 and the interior of the tube 3 leads. At most, the tube 3 may extend in two parts above the protective casing 6.

Within the protective casing 6 several pipe sections 2 of reinforced concrete to a tube tour 3 are placed on each other, this tube tour 3 extends well above the sea level 8 and slightly above the protective casing 6, for example, to about 15 m above the sea level 8. The individual pipe sections 2 are all among themselves connected to each other via the tension members 4 and clamped in the erected state against each other restrained. The lowest in the installed position pipe section 2 is provided as a special construction with a cutting shoe, not shown.

When building the first section of the pipe run 3 from the seabed 7 to above the sea level 8 and above the protective piping 6, the individual pipe sections 2 can be maintained and stabilized, for example, with external guide cables 11, so that the vertical loads occurring in the end and added via the attachment of steel cables can be forwarded to the top. Depending on the diameter of the pipe sections 2, a plurality of guide cables 11 or groups of cables can be distributed uniformly over the outer circumference of the pipe sections 2. These can be laterally deflected, fixed and actuated via radially arranged deflection rollers 12 and winches on the assembly platform. In the illustrated embodiment, a total of three guided over guide rollers 12 guide cables 11 are arranged distributed over the outer circumference of the pipe run 3. The guide cables 11 engage under the lowest or in the installed position pipe shot 2 or the cutting shoe arranged thereon. If the pipe run 3 from the seabed 7 to the mounting platform above the sea level 8 completely drained or built, a drill set can be installed in the pipe run 3.

The FIG. 2 shows the pipe run 3 in already on the seabed 7 remote position. The discharge of the first pipe sections 2 to above the sea level is preferably suspended. In this example, a wellbore 9 is sunk in the air lifting drilling. The sinking of the hole takes place while maintaining a hydrostatic overpressure in the wellbore 9, which basically can be dispensed with other stabilization measures. Depending on the consistency of the seafloor or the seabed, however, initial drilling of the well may require conditioning of the seabed or suction of the upper strata.

When lowering the hole of the lowest installed pipe section 2 is undercut, the pipe trip 3 decreases with the Bohr progress in the hole 9, gradually with increasing drilling progress more pipe sections 2 are increased to the pipe tour, the tension members 4 are connected.

In this way, the pipe run 3 is performed as lost borehole casing to a designated depth, as in FIG. 1 is shown.

The borehole continues to be bored below the lowest installed pipe section without piping, expanded at the end and filled with in situ concrete, so that the in FIG. 1 Ortbetonfuß 10 shown results, which is also provided with cast-in tension members 4.

After completion of the foundation pile 1, the protective casing 6 can be removed. The foundation pile 1 can be completely or partially filled with the drilled cuttings, if necessary, this can be solidified with cement.

A building can now be erected on the foundation pile. The structure can, for example, as a monopile with pipe sections 2 of the same design as those underwater.

At 13 is in FIG. 1 denotes the thickening of Ortbetonfußes.

Reference numerals:

1

foundation pile

2

pipe sections

3

pipe string

4

tension members

5

Put

6

protective casing

7

Seabed

8th

Sea level

9

well

10

Ortbetonfuß

11

guide ropes

12

guide rollers

Claims (16)

1. Foundation pile (1) for offshore structures which is composed in a modular manner of individual pipe sections (2), of which at least one pipe section (2) is anchored as a permanent borehole casing in the subsoil, wherein the pipe sections (2) are formed as concrete pipes which are connected to one another via clamping elements in a longitudinally force-locked manner.
2. Foundation pile according to Claim 1, characterized in that the pipe section (2) arranged at the very bottom in the borehole (9) is provided with a circumferential cutting shoe.
3. Foundation pile according to either of Claims 1 and 2, characterized in that the foundation pile (1) extends from the subsoil at least as far as the water line and is composed of approximately structurally identical pipe sections (2) at least over this length.
4. Foundation pile according to one of Claims 1 to 3, characterized in that it is filled at least partially within the borehole (9).
5. Foundation pile according to one of Claims 1 to 4, characterized by at least one in situ concrete base (10) which extends in a borehole continuation below the cutting shoe in the subsoil.
6. Foundation pile according to Claim 5, characterized in that the in situ concrete base (10) has, at least in certain regions, a diameter which is greater than the diameter of the cutting shoe.
7. Method for producing a foundation pile (1) for offshore structures, comprising the following method steps:

   a) depositing a plurality of pipe sections (2) preferably in the form of concrete pipes on the seabed (7) to form a vertical pipe string (3),

   b) installing a drill string into the pipe string (3),

   c) sinking a borehole (9) within the pipe string (3),

   d) feeding the pipe string (3) into the borehole (9) as boring advances while using the weight force of the pipe string (3) and

   e) stacking further pipe sections on top of the pipe string (3) and

   f) repeating steps c) to e) until reaching an intended end depth of the pipe string (3) in the subsoil (7).
8. Method according to Claim 7, characterized in that the pipe sections (2) are braced against one another in a longitudinally force-locked manner, preferably even during assembly or directly after assembly to form a pipe string (3).
9. Method according to Claim 7 or 8, characterized in that, after completing the borehole (9), at least part of the pipe string (3) is filled.
10. Method according to Claim 9, characterized in that a filling with drillings and/or in situ concrete is provided.
11. Method according to one of Claims 7 to 10, characterized in that the borehole is sunk while maintaining a hydrostatic overpressure in the borehole (9).
12. Method according to one of Claims 7 to 11, characterized in that the sinking of the borehole (9) takes place by the airlift boring process.
13. Method according to one of Claims 7 to 12, characterized in that, prior to depositing the pipe sections (2), a dismantleable protective casing (6) is put in place.
14. Method according to one of Claims 7 to 13, characterized in that the pipe string (3) extends above the sea level (8) before and during the sinking of the borehole (9).
15. Method according to one of Claims 7 to 14, characterized in that, after installing the pipe sections (2) and until reaching the intended end depth of the pipe string (3), an uncased extension of the borehole is produced below the lowest pipe section.
16. Method according to Claim 15, characterized in that the extension of the borehole (9) is produced, at least in certain portions, with a greater diameter than the cased region of the borehole (9).

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