Abstract
Provided is a method of installing a Gravity Based Structure (GBS). The method involves installing a substructure at a position to be below the GBS, the substructure providing a foundation upon which to support the GBS when installed, and installing the substructure to define at least an annular support region for the GBS. The method further involves installing the GBS above the substructure with the annular support region therebelow, and pre-installing the substructure in advance of the GBS, with the GBS being installed above the substructure subsequent to the substructure's installation.
Claims
1. A method of installing a Gravity Based Structure (GBS), the method comprising; installing a substructure at a position to be below the GBS, the substructure providing a foundation upon which to support the GBS when installed, the method comprising installing the substructure to define at least an annular support region for the GBS; and installing the GBS above the substructure with the annular support region therebelow; wherein the method comprises pre-installing the substructure in advance of the GBS, with the GBS being installed above the substructure subsequent to the substructure's installation.
2. The method of claim 1, wherein the substructure comprises at least one skirt element, the skirt element comprising a vertically-oriented cylinder with a central longitudinal axis of the cylinder being vertically oriented when installed, each cylinder comprising an open central portion for accommodating foundation material therein when installed.
3. The method of claim 2, wherein the skirt element comprises at least one of: a metal cylinder and a concrete cylinder.
4. The method of claim 2, wherein the substructure comprises a plurality of skirt elements and the method comprises arranging the plurality of skirt elements circumferentially to define the annular support region for the GBS.
5. The method of claim 4, wherein each of the plurality of skirt elements is individually installed, the substructure being installed incrementally.
6. The method of claim 4, wherein the method comprises simultaneously installing the plurality of skirt elements.
7. The method of claim 2, wherein, at least during installation, the skirt element is open at its upper end, the upper end being below the GBS when installed.
8. The method of claim 2, wherein the skirt element is enclosed at an upper end, the upper end being below the GBS when installed.
9. The method of claim 8, wherein the substructure comprises a plurality of skirt elements and each skirt element is enclosed at an upper end by a respective end wall; the method comprising enclosing the skirt element prior to installation of the skirt element.
10. The method of claim 8, wherein the substructure comprises a plurality of skirt elements and the plurality of skirt elements is enclosed at their respective upper ends by a common end wall, the common end wall being configured to correlate to the arrangement of the skirt elements when installed.
11. The method of claim 8, wherein the skirt element is enclosed at the upper end by a concrete end wall.
12. The method of claim 1, wherein the method comprises providing the substructure below the GBS such that the substructure falls within a footprint of the GBS when installed; and wherein a central axis of the substructure is vertically aligned with a central axis of the GBS when installed.
13. The method of claim 1, wherein installing the substructure comprises inserting or lowering the substructure at least partially into the formation below; and wherein the method comprises installing the substructure using one or more of: vibration, piling, oscillation, pumping, suction.
14. The method of claim 1, wherein the method comprises: transporting the substructure to the location for installation separately from the GBS; providing a gap between the substructure and the GBS thereabove; and providing a gravel bed between a top of the substructure and a bottom of the GBS, the gravel bed being applied after installation of the substructure and prior to the installation of the GBS.
15. The method of claim 1, wherein the method comprises connecting the substructure to the GBS subsequent to installing the substructure.
16. The method of claim 1, wherein the substructure effectively comprises one or more stiffeners such that the method comprises providing an improved stiffness of foundation for the GBS, the improved stiffness being relative to the formation prior to the installation of the substructure; and wherein the method comprises providing a consistent stiffness of support around at least the annular support region for the GBS, the consistent stiffness of support being provided at least partially by a consistency of stiffness of the substructure.
17. A substructure for supporting a GBS, the substructure providing a foundation upon which to support the GBS when installed, wherein the substructure comprises at least an annular support region to define an annular support for the GBS when installed; and wherein the substructure comprises a pre-installed substructure configured to be installed in advance of the GBS.
18. The substructure of claim 17, wherein the substructure comprises a plurality of substructure elements, the plurality of substructure elements arranged circumferentially when installed to define the annular support region for the GBS; and wherein the plurality of substructure elements comprises a plurality of skirt elements, the skirt elements each comprising a vertically-oriented cylinder, with a central longitudinal axis of the cylinder being vertically oriented when installed, each cylinder comprising an open central portion for installation for accommodating foundation material therein when installed; wherein each skirt element comprises a cylinder, the cylinder being configured for insertion into the formation when installed, such that the open central portion is filled with formation and an upper end of each skirt element is adjacent an upper surface of the formation.
19. An installation comprising the GBS and the substructure of claim 17.
20. The installation of claim 19, comprising a gap between the substructure and the GBS thereabove, the gap comprising a gravel bed between a top of the substructure and a bottom of the GBS.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.
[0045] An embodiment of the present disclosure will now be described by way of example only and with reference to the accompanying drawings, in which:
[0046] FIG. 1 shows three examples of support structures for offshore installations: FIG. 1a shows a monopile structure 3; FIG. 1b shows a tripod structure 5; and FIG. 1c shows a Gravity-based structure 7 (GBS).
[0047] FIG. 2 shows an example of a method according to the present disclosure;
[0048] FIG. 3 shows an example of a substructure according to the present disclosure;
[0049] FIG. 4 shows an analysis model of the substructure of FIG. 4;
[0050] FIG. 5 shows another example of a substructure according to the present disclosure;
[0051] FIG. 6 shows schematic plan and side views of another example of a substructure according to the present disclosure;
[0052] FIG. 7 shows schematic plan and side views of another example of a substructure according to the present disclosure;
[0053] FIG. 8 shows schematic plan and side views of another example of a substructure according to the present disclosure;
[0054] FIG. 9 shows schematic plan and side views of another example of a substructure according to the present disclosure;
[0055] FIG. 10 shows a schematic side view of the substructure of FIG. 8 prior to installation;
[0056] FIG. 11 shows a schematic side view of the substructure of FIG. 8 after installation;
[0057] FIG. 12 shows schematic plan and elevation views of the substructure of FIG. 6;
[0058] FIG. 13 shows an example of a transit of a support element;
[0059] FIG. 14 shows a schematic example of a further transit of a plurality of support elements;
[0060] FIG. 15 illustrates an example of an installation step of a support element; and
[0061] FIG. 16 shows an example of a portion of an installation positioned above a substructure.
DETAILED DESCRIPTION
[0062] Referring firstly to FIG. 1, there is shown three examples of support structures for offshore installations, such as a wind turbine. FIG. 1a shows a monopile structure 3; FIG. 1b shows a tripod structure 5; and FIG. 1c shows a Gravity-based structure 7 (GBS). The monopile structure 3 of FIG. 1a and the tripod structure 5 of FIG. 1b have been penetrated into the formation therebelow, which is a seabed formation 9 as shown here. Each of the monopile structure 3 of FIG. 1a; the tripod structure 5 of FIG. 1b; and the GBS 7 of FIG. 1c includes a scour protection 11 in the examples shown here.
[0063] Referring now to FIG. 2, there is depicted an example diagram of a method 2 according to the present disclosure. Initially, a plurality of skirt elements are fabricated in a first step 4. Thereafter the skirt elements are positioned in a subsequent step 4. As outlined in detail below, the skirt elements are individually positioned incrementally in a series of sub-steps; or the skirt elements are positioned in unison in a single step. Likewise, where the GBS is positioned upon the skirt elements in a subsequent step 8, in at least some examples the two positioning steps 6, 8 can be effectively combined with a single GBS being positioned along with the plurality of skirt elements in a single step. Accordingly, in contrast to embodiments whereby a single skirt is positioned beneath a single structure, such as a single skirt under a single GBS; the method here provides a plurality of skirt elements beneath a single structure. Where a skirt may have previously been employed, a single skirt has been associated with a single construction element, such as providing a single skirt for a single monopole or three skirts for a tripod (a single respective skirt for each respective leg). In contrast, here, multiple skirt elements 16 are provided for a single substructure 10 for a single GBS.
[0064] Accordingly, here, the method comprises providing a support pre-structure in the form of a substructure 10 for supporting a construction thereabove. As shown in FIG. 6, the construction above here comprises a Gravity Based Structure 12 (GBS 12). The substructure 10 effectively comprises a pre-structure for locating below the GBS 12 thereabove. As shown in FIG. 3, the method comprises installing the substructure 10 at a position to be below the GBS 12. Accordingly, the substructure 10 provides a foundation upon which to support the GBS 12 when installed. The method comprises installing the substructure 10 to define at least an annular support region 14 for the GBS 12. The method comprises installing the GBS 12 above the substructure 10 with the annular support region 14 vertically below the GBS 12, being directly below the GBS 12 as shown here.
[0065] In the example here, there is provided a method of installing a Gravity Based Structure (GBS 12), the method comprising installing the substructure 10 at a position to be below the GBS 12, the substructure 10 providing a foundation upon which to support the GBS 12 when installed, the method comprising installing the substructure 10 to define at least an annular support region for the GBS 12; and installing the GBS 12 above the substructure 10 with the annular support region therebelow. It will be appreciated that the location installation here is a subsea marine location, with the substructure 10 being located at the seabed. Here, the method comprises installing the substructure 10 to be fully submerged once installed. Accordingly, the method in this example comprises installing the GBS 12 to be at least partially submerged once installed.
[0066] Referring now to FIG. 3, there is shown an example of a substructure 12 comprising a plurality of support elements in the form of circumferentially-arranged skirt elements 16. The substructure 10 comprises a support element. The support element comprises a tubular support. The tubular support comprises a circular profile. The tubular support comprises a skirt element 16. The skirt element 16 comprises a cylindrical profile. The skirt element 16 comprises a vertically-oriented cylinder with a central longitudinal axis of the cylinder being vertically oriented when installed. The cylinder comprises a hollow cylinder. The cylinder comprises an open central portion for accommodating foundation material therein when installed. The foundation material comprises formation material, such as in situ formation material (e.g. soil, ground, rock/s, etc.) at the location for installation of the substructure 10. Additionally, or alternatively, the foundation material for at least partially filling the support element's open central portion comprises ex situ material, such as supplied materials (e.g. ballast, gravel, concrete, etc.).
[0067] The skirt element 16 is open at the bottom, prior to and during installation. The skirt element 16 is open at the bottom for facilitating insertion of the skirt element 16 into the formation. The skirt element 16 comprises a thin-walled element. For example, the wall thickness of the wall defining the cylinder comprises a thickness of at least an order of magnitude less than a radius of the cylinder. The skirt element 16 here comprises a metal element formed from plate or sheet steel. Here, the method comprises prefabricating the skirt elements art a location remote from the location for installation.
[0068] The substructure 10 comprises a plurality of support elements. The method comprises arranging the plurality of substructure 10 support elements circumferentially to define the annular support region for the GBS 12. The plurality of substructure 10 support elements comprises a plurality of skirt elements. The plurality of skirt elements may each define a pocket or compartment within the skirt, such that a plurality of pockets or compartments are provided beneath a single GBS 12. The skirt may isolate the soil beneath the foundation/GBS 12. The skirt may encapsulate any water pockets within the soil.
[0069] It will be appreciated that the arrangement of the skirt elements 16 can improve poor soil conditions. Here, the plurality of skirt elements 16 (for forming the single support substructure for the single GBS) all comprise a similar type. Each of the plurality of skirt elements 16 comprises a similar configuration, including dimensions. Accordingly, the substructure 10 comprises a plurality of similarly-proportioned skirt elements 16, regularly arranged about the central longitudinal, vertical axis 18 for the GBS 12. In the example shown here, the substructure 10 comprise a total of fourteen skirt elements 16, each with a diameter of 7.9 m. The skirt elements 16 are arranged around the central longitudinal axis 18, to define the annular region with an inner diameter (global middle) of 36 m; and an outer diameter of 44 m. The substructure 10 here is configured to provide a skirt penetration of 5 m into the formation. The plurality of skirt elements 16 can be configured to transfer global base shear load through a soft top soil layer and down to competent soil. In the example shown here, the substructure 10 is configured for a soil zone 2B with a 2.4 m weak top layer. The skirt elements 16 are lift-installed prior to installation of GBS (e.g. 4 points lift). As shown here, a 0.5 m penetration (weight 1100 mT) is used; whereafter suction can be applied during installation. Accordingly, a maximum suction used during penetration can be around 180 kPa, as illustrated in FIG. 4, which shows an analysis model of the substructure of FIG. 4. Here, the load conditions of the skirt elements 16 are governed by the maximum suction (of 180 kPa) during penetration. In the example shown here, the weight of the skirts is 588 mT.
[0070] FIG. 5 shows another example of a substructure 110 according to the present disclosure The substructure 110 shown in FIG. 5 is generally similar to that shown in FIG. 3, with like features referenced by like numerals, incremented by 100. Accordingly, the substructure 110 comprises a plurality of skirt elements 116 arranged around a common central longitudinal axis 118. For conciseness, definitions of all like features are not duplicated in this description. Here, the four skirt elements 116 can be made from concrete, with an individual diameter of 15 m of each skirt element 116. A top slab 122 (shown here with a diameter of 36 m) can be positioned intermediate the plurality of skirt elements 112 and the single GBS to be positioned thereabove.
[0071] FIG. 6 shows schematic plan and side views of another example of a substructure according to the present disclosure. The substructure 210 shown in FIG. 6 is generally similar to that shown in FIG. 5, with like features referenced by like numerals, incremented by 100. Accordingly, the substructure 210 comprises a plurality of skirt elements 216 arranged around a common central longitudinal axis 218. Here, the four skirt elements 216 are modular; and can be made from steel, defining an outer diameter of the skirt elements 218 as 15 m in the example shown. The skirt elements 216 here are modular, being individually transported and installed sequentially, prior to placement of the GBS 212 thereabove, with a gravel pad 224 being applied here intermediate the installation of the skirt elements 216 and the GBS 212. The annular support region defined by the arrangement of the plurality of the skirt elements 216 is larger than any individual support element 216. For example, the diameter of the annular support region is more than twice that of an individual skirt element 216. The elevation view of FIG. 6 clearly shows the arrangement of skirt elements 216 installed into the formation 209 to a depth corresponding to the height of each skirt element 216.
[0072] FIG. 7 shows schematic plan and side views of another example of a substructure according to the present disclosure. The substructure 310 shown in FIG. 7 is generally similar to that 210 shown in FIG. 6, with like features referenced by like numerals, incremented by 100. Accordingly, the substructure 310 comprises a plurality of skirt elements 316 arranged around a common central longitudinal axis 318. Here, FIG. 7 shows an example of a substructure 310 comprising a plurality of pre-installed modular skirts 316 connected to the GBS 312. As shown here, a total of eight steel skirts 316 are inter-connected by a circular concrete skirt slab 322 with a ring beam 324. The circular concrete slab 322 here has a central opening (6 m in diameter), providing access to the centre of the substructure 310. The example of a skirt slab 322 here is filled with a layer of crushed stone and cement slurry before installation on the seabed. Accordingly, there is ensured an evenly distributed gravity load between the GBS 312 and the skirt slab 322. A horizontal gap between the GBS periphery and the ring beam 324 can be filled with an underwater concrete cast (not shown) to ensure fixity between the GBS 324 and the skirt slab 322. However, in other examples, no such filling is provided, with no such additional fixity required.
[0073] In the example shown here, each steel skirt element 316 has a diameter of 8.9 m; and a height of 6 m; formed from steel plate with a 40 mm thickness. The skirt slab 322 has an outer diameter more than four times that of the individual skirt elements 316. The skirt slab 322 has an outer diameter around 42 m in the example shown. The skirt slab thickness of 1.1 m can be achieved with concrete/steel (e.g. reinforced concrete). Accordingly, the approximate dry weight is 3650 tons; with an approximate submerged weight of 3400 tons.
[0074] FIG. 8 shows schematic plan and side views of another example of a substructure 410 according to the present disclosure. The substructure 410 shown in FIG. 8 is generally similar to that shown in FIG. 7, with like features referenced by like numerals, incremented by 100. Accordingly, the substructure 410 comprises a plurality of skirt elements 416 arranged around a common central longitudinal axis 418. For conciseness, definitions of all like features are not duplicated in this description.
[0075] Here, FIG. 8 shows an example of a substructure 410 comprising a plurality of integrated skirt elements 416 connected to the GBS 412. As shown here, a total of six steel skirts 416 are integrated. It will be appreciated that the steel skirt elements 416 can be integrated in the GBS 412 at a construction site or pre-installed offshore.
[0076] FIG. 9 shows schematic plan and side views of another example of a substructure 510 according to the present disclosure. The substructure 510 shown in FIG. 9 is generally similar to that 410 shown in FIG. 8, with like features referenced by like numerals, incremented by 100. Accordingly, the substructure 510 comprises a plurality of skirt elements 516 arranged around a common central longitudinal axis 518. For conciseness, definitions of all like features are not duplicated in this description. The modular steel skirt elements 516 shown in FIG. 9 are generally similar to those 216 shown in FIG. 6. Here, the skirt elements 516 can be open-ended at their top ends, at least for installation. Rather than any slab or common enclosure, the plurality of skirt elements 516 can be covered by the gravel pad 524 intermediate the substructure 510 and the GBS 512 (following installation of the skirt elements 516 into the formation 509).
[0077] FIG. 10 shows a schematic side view of the substructure 410 of FIG. 8 prior to installation; whilst FIG. 11 shows a schematic side view of the substructure 410 of FIG. 8 after installation. As shown in FIG. 10, the plurality of skirt elements 416 are connected to the GBS 412 prior to installation at the installation, such as the seabed 409 shown in FIG. 11. Here, the skirt elements 416 are installed at the GBS fabrication yard and are fixed in the GBS base slab. The method here comprises pre-assembling the substructure 410 with the GBS 412 thereabove, such as illustrated in FIG. 10. The method comprises the substructure 110 being installed together with the GBS 412. The method comprises transporting the GBS 412 and substructure 410 as a combined pre-assembled unit to the location for installation. Accordingly, the integrated skirt elements 416 can be transported and installed integrally with the GBS 412. In other examples, the method comprises pre-assembling the substructure 410 at or adjacent the installation location prior to installation. In each of these cases, the method comprises connecting the substructure 410 to the GBS 412 prior to installing the substructure 410. In the example shown here, six cylindrical skirt elements 416 are provided, each with a diameter of 12 m made from plate steel (e.g. S355) with a thickness of around 38 mm. Accordingly, the substructure 410 comprising the six skirt elements 416 contributes around 432 mT to the weight of the GBS 412. The method here comprises simultaneously installing the plurality of skirt elements 416. Here the skirt elements 416 have a height of 6 m, with full penetration into the formation 409 (as shown in FIG. 11) ensuring that the substructure 410 penetrates the formation 409 to a corresponding depth of 6 m. As shown in FIG. 11, when installed, the GBS 412 can be directly connected to the substructure 410 directly therebelow. Accordingly, any intermediate layers or structures, such as a gravel pad, may be reduced or even eliminated.
[0078] FIG. 12 shows schematic plan and elevation views of the substructure 210 of FIG. 6. It will be appreciated that the arrangement of pre-installed modular skirt elements 216 is without connection to the GBS 212. The skirt elements 216 here each comprise a steel cylinder with a respective concrete top slab 217. The skirt elements 216 have an individual diameter of 15 m; and are 6 m deepallowing a penetration of the substructure 210 into the formation 209 of a corresponding 6 m, as shown in the elevation view of FIG. 12.
[0079] Here, each of the four free-standing skirt elements 216 can be installed prior to installation of the gravel pad and GBS 212. There is no mechanical connection between the GBS 212 and the skirt elements 216. Accordingly, the fabrication and transport of the GBS 212 can be as for without such a substructure 210 (e.g. as for a conventional GBS fabrication and transportation). Furthermore, such installation can mitigate or even eliminate additional skirt offshore work after GBS 212 installation.
[0080] FIG. 13 through FIG. 15 show examples of a transit of a support element, such as the skirt element 316 of FIG. 7. FIG. 13 shows a respective front and end view of the skirt element 316 mounted on a rolling transport 330 (e.g. multiwheeler). Accordingly, the plurality of skirt elements 316 can be individually transported from the fabrication yard, such as for marine transport on a vessel 340 as shown n FIG. 14. Each skirt element 316 can be individually lifted onto the vessel 340, where it will be appreciated that the plurality of skirt elements 316 can be distributed along the vessel 340 as shown (or across other vessels, depending on dimensions). In at least some examples, all of the modular skirt elements 316 for forming a single substructure 310 for a single GBS 312 can be transported on a same vessel. In some instances, the GBS 312 can also be loaded on separately to the same vessel 340.
[0081] FIG. 15 shows a single skirt element 316 of the plurality for forming the single substructure 310, being lifted into position at the marine location. It will be appreciated that each individual skirt element 316 can be sequentially installed. Accordingly, each skirt element 316 can be inserted into the seabed, such as initially under weight and optionally vibro-hammering or the like. Once a sufficient penetration of the individual skirt element 316 into the formation 309 has been achieved, then a pump can be activated to use suction within the enclosed skirt element 316 (effectively acting as a suction bucket) to fully insert the individual skirt element 316 into the formation 309 to the desired penetration. This installation procedure can be repeated for each of the individual skirt elements 316 to provide the arrangement of the substructure 310 for receiving the GBS 312 thereabove. The skirt elements 316 are individually installed, with the substructure 310 being installed incrementally. It will be appreciated that an intermediate procedure, such as a gravel pad installation can be performed prior to installation of the GBS 312. Accordingly, the gravel pad can be installed after and on top of the skirt elements 316. The gravel pad can be levelled out and adjusted for any elevation differences between the top of the skirt elements 316 if present.
[0082] Once the GBS 312 has been installed, then the remaining structure can be completed. For example, as shown in FIG. 16, additional components of the installation 350, such as a wind turbine or the like, can be installed on or above the GBS 312.
[0083] It will be appreciated that the provision of such substructures below the GBS as shown can improve the stiffness of formation/soil below the GBS (prior to installation of the GBS). The installation methods provide a more uniform stiffness of substrate or region below the GBS (e.g. relative to the formation/soil prior to the installation of the substructureand relative to conventional soil remediation operations). Accordingly, the installation methods reduce or even eliminate remedial soil works to uniformize the soil stiffness.
[0084] It will be appreciated that, although schematic, the relative proportions of the skirt elements shown are shown to scale with the relative proportions of the slabs, GBS and annular regions shown.
[0085] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.
[0086] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.
[0087] The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The claims should not be construed to cover merely the foregoing embodiments, but also any embodiments which fall within the scope of the claims, including with equivalence.
