Scour prevention device, foundation structure for offshore wind turbine and construction method

Abstract

To provide a scouring-prevention device, a foundation structure for an ocean windmill and a construction method which can prevent overflow due to waves and tidal currents during construction.SOLUTION: A scouring-prevention device 10 that is provided so as to prevent scouring in a ground 12 around a structure 14 installed at a sea bottom, a river bottom or a lake bottom includes: a first bag body 16 which is annularly arranged on the ground 12 around the structure 14, is packed with a filter material 20 having a predetermined particle size, has a net shape and is flexible; and second bag bodies 18 which are arranged so as to be adjacent to each other or partially overlap each other in a circumferential direction along the first bag body 16 while being adjacent to or partially overlapping the radial outside of the first bag body 16, are packed with a filter material 20 having a predetermined particle size, have net shapes and are flexible.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a scour prevention device, a foundation structure for an offshore wind turbine, and a construction method. [Background technology]

[0002] Traditionally, offshore wind power generation has the lowest carbon dioxide emissions among renewable energies, and has been promoted by the government in several areas off the coast of Japan, with multiple operators competing to install it. Monopile-type foundations, as shown in Figure 3, are widely used for wind turbine foundations. In general, when such large-diameter pile foundations 1 (monopiles) are installed in the sea, scouring occurs around them due to waves and tidal currents, so scouring countermeasures are taken by pouring rubble 2 around the periphery of the foundation 1 to cover the seabed 3. Figure 4 shows an example of this scouring countermeasure work. As shown in this figure, the scouring countermeasure work 4 is composed of a fine-grained filter layer 5 and a coarse-grained armor layer 6 to prevent the filter layer 5 from being washed away.

[0003] The filter layer 5 has a small particle size of about 10 mm, so if it is thrown into the sea from a work boat 7 as shown in Figure 5, there is a concern that it may be washed away by waves or currents, so the armor layer 6 must be constructed soon after the construction of the filter layer 5. In addition, in order to secure the finished shape of the filter layer 5, a leveling work is required after it is thrown into the sea, which requires a process.

[0004] Conventional methods for implementing scouring countermeasures around pile foundations are known, for example, as shown in Patent Documents 1 and 2. Patent Document 1 involves sinking a pile driving template with an asphalt mat attached to its underside into the bottom of the water, positioning the pile foundation using the template, and then driving the pile foundation, and then detaching the asphalt mat from the template and pulling up the template, thereby simultaneously laying the asphalt mat on the bottom of the water and driving the pile foundation. Patent Document 2 involves paving the riverbed surface around the foundation with a block mat structure, in which a large number of unit blocks are joined together in a plane, in one or more layers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-204863 A [Patent Document 2] Special Publication No. 2005-508464 Summary of the Invention [Problem to be solved by the invention]

[0006] However, if the wind turbine assembly process is prioritized in Figure 4, the process of connecting the submarine cable will come after the monopile installation, making it difficult to install two layers, filter layer 5 and armor layer 6, after the monopile installation. Therefore, it is possible to install filter layer 5 before the monopile installation and armor layer 6 after the monopile installation. In this case, it is expected that the surrounding ground will subside due to the installation of the monopile, disturbing the filter layer 5 that was installed earlier, and there is also a risk that the filter layer 5 will be washed away by waves and tides during the period until the armor layer 6 is installed.

[0007] The present invention has been made in consideration of the above, and aims to provide a scour prevention device, a foundation structure for an offshore wind turbine, and a construction method that can prevent washout due to waves and tides during construction. [Means for solving the problem]

[0008] In order to solve the above-mentioned problems and achieve the object, the scour prevention device of the present invention is a scour prevention device provided to prevent scouring in the ground surrounding a structure installed on the seabed, riverbed or lakebed, and is characterized in that it comprises a flexible mesh-like first bag body that is arranged in a ring shape on the ground surrounding the structure and has a filter material of a predetermined particle size packed inside, and a plurality of flexible mesh-like second bag bodies that are adjacent to or partially overlapping the radial outside of the first bag body and adjacent to or partially overlapping each other in the circumferential direction along the first bag body, and have a filter material of a predetermined particle size packed inside.

[0009] Furthermore, the foundation structure for an offshore wind turbine according to the present invention is a foundation structure for a wind turbine installed offshore, and is characterized in comprising a pile foundation-type structure installed on the seabed, and the above-mentioned scour prevention device arranged on the ground surrounding this structure.

[0010] Furthermore, the construction method for a foundation structure for an offshore wind turbine according to the present invention is a method for constructing the above-mentioned foundation structure for an offshore wind turbine, characterized in that after a first bag body of the scour prevention device is installed on the seabed, a pile foundation-type structure is installed on the seabed within the annular interior of the first bag body.

[0011] Furthermore, another construction method for a foundation structure for an offshore wind turbine according to the present invention is a method for constructing the above-mentioned foundation structure for an offshore wind turbine, characterized in that after a pile foundation-type structure is installed on the seabed, a first bag body of a scour prevention device is installed on the seabed surrounding the structure. Effect of the Invention

[0012] According to the scour prevention device of the present invention, the scour prevention device is provided to prevent scouring in the ground around a structure installed on the seabed, riverbed, or lakebed, and includes a mesh-like flexible first bag body arranged in an annular shape on the ground around the structure and filled with a filter material of a predetermined particle size, and a plurality of mesh-like flexible second bags arranged adjacent to or partially overlapping each other in the circumferential direction along the first bag body while being adjacent to or partially overlapping the radial outside of the first bag body, and filled with a filter material of a predetermined particle size, so that the filter material inside the bag body is not separated and diffused to the outside by waves or tidal currents. Therefore, it is possible to prevent the scour prevention device being washed away by waves or tidal currents during construction.

[0013] Furthermore, the foundation structure for an offshore wind turbine according to the present invention is a foundation structure for a wind turbine installed offshore, and comprises a pile foundation-type structure installed on the seabed and the above-mentioned scour prevention device placed on the ground surrounding this structure, thereby achieving the effect that the scour prevention device can be quickly constructed even after the pile foundation-type structure has been installed.

[0014] According to the construction method of the foundation structure for an offshore wind turbine of the present invention, the first bag body of the scour prevention device is installed on the seabed ground, and then a pile foundation type structure is installed on the seabed ground inside the annular part of the first bag body, so that it is possible to prevent the scour prevention device installed prior to the pile foundation type structure from being washed away by waves or tides. Even if the surrounding ground sinks and deforms due to the installation of the pile foundation type structure, the first bag body installed first can deform in accordance with this deformation.

[0015] Furthermore, according to another construction method for a foundation structure for an offshore wind turbine of the present invention, which is a method for constructing the above-mentioned foundation structure for an offshore wind turbine, after a pile foundation-type structure is installed on the seabed, a first bag body of the scour prevention device is installed on the seabed surrounding the structure, thereby achieving the effect that the scour prevention device can be quickly constructed even after the pile foundation-type structure has been installed. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic plan view showing an embodiment of a scour prevention device, an offshore wind turbine foundation structure, and a construction method according to the present invention. [Diagram 2] FIG. 2(1) is a schematic perspective view showing the position of the second bag body, and (2) is a plan view of the second bag body. [Diagram 3] FIG. 3 is a schematic perspective view showing a conventional offshore wind power generation system (monopile type). [Figure 4] FIG. 4 is a side cross-sectional view showing an example of a conventional scouring prevention work around a monopile. [Diagram 5] FIG. 5 is a side cross-sectional view showing an example of a construction status of a conventional scouring prevention work. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, embodiments of a scour prevention device, a foundation structure for an offshore wind turbine, and a construction method according to the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to these embodiments.

[0018] (Scouring prevention device) First, an embodiment of a scour prevention device according to the present invention will be described. 1 and 2, a scour prevention device 10 according to this embodiment is provided to prevent scouring in the ground 12 around a monopile 14 installed on the seabed, riverbed or lakebed ground 12, and includes a doughnut-shaped (annular) first bag body 16 and a sector-shaped (fan-shaped) second bag body 18 arranged around the outside of the first bag body and divided into a plurality of pieces in the circumferential direction. The monopile 14 is a pile-shaped (pile foundation-type) structure with a circular cross section erected in the vertical direction, with its lower part driven into the supporting layer beneath the ground 12 and its upper part extending above the sea, river or lake surface.

[0019] The first bag body 16 is disposed in a doughnut shape (annular shape) on the ground 12 around the monopile 14, and is a mesh-like (net-like) flexible bag body filled with a filter material 20 of a predetermined grain size inside. More specifically, the first bag body 16 is located in the radially inner compartment of the compartments obtained by concentrically dividing a ring 24 having a through hole 22 in the center into two in a plan view. The annular inner diameter D of the doughnut is desirably set to approximately the diameter of the monopile 14 so that the monopile 14 can penetrate inside the annular shape.

[0020] The second bag body 18 is a flexible sector-shaped bag body arranged adjacent to each other in the circumferential direction along the first bag body 16 while being adjacent to the radial outside of the first bag body 16, and is filled with a filter material 20 of a predetermined particle size inside. More specifically, the second bag body 18 is located in a section obtained by equally dividing the radially outer section radially (in a sector shape) among sections obtained by concentrically dividing a ring 24 having a through hole 22 at the center in a plan view. Note that the second bag body 18 may be arranged so as to overlap partially in the up-down direction, instead of being arranged so as to be adjacent to each other in the circumferential direction. Also, instead of arranging the second bag body 18 so as to be adjacent to each other in the circumferential direction, the second bag body 18 may be arranged so as to overlap partially in the up-down direction.

[0021] The filter material 20 of the first bag body 16 and the second bag body 18 is of a grain size that can exhibit a predetermined scouring prevention function. The grain size may be fine. The type and grain size of the filter material 20 used may be the same for the first bag body 16 and the second bag body 18, or may be different. The material of the first bag body 16 and the second bag body 18 may be a metal, a resin, or the like that has a predetermined strength and flexibility. The first bag body 16 and the second bag body 18 may be made of the same material, or may be made of different materials. The size of the mesh of the first bag body 16 and the second bag body 18 is set to a size that prevents the filter material 20 packed inside from leaking out of the mesh. In other words, the size of the mesh is set to be smaller than the grain size of the filter material 20. This prevents the filter material 20 from flowing out due to waves and tides.

[0022] When constructing the above-mentioned scour prevention device 10, for example, the first bag body 16 is lowered into water (in the sea, river or lake) from a work boat and installed at the construction position of the monopile 14. After that, the multiple second bag bodies 18 are each separated and independently lowered into water from the work boat and installed in the circumferential direction on the outside of the first bag body 16. In this way, the scour prevention device 10 consisting of a net-type filter layer can be quickly and easily constructed on the ground 12 around the monopile 14.

[0023] The filter material 20 inside the first bag body 16 and the second bag body 18 does not separate and diffuse to the outside due to waves or tidal currents during construction. Therefore, it is possible to prevent the scour prevention device 10 from being washed away by waves or tidal currents during construction. In addition, since the scour prevention device 10 is composed of the flexible first bag body 16 and the second bag body 18 and can be easily deformed, it is possible to ensure a predetermined finished shape without leveling after construction. Since this scour prevention device 10 can be constructed in one go over a wide area, it does not put a strain on the process even if it is installed after driving the monopile 14.

[0024] In the above embodiment, the first bag body 16 and the second bag body 18 are used as an example. However, the present invention is not limited to this. Any configuration may be used as long as doughnut-shaped bags are arranged around the monopile 14 and sector-shaped bags are arranged on the outermost periphery. For example, in the above embodiment, another bag body may be arranged between the first bag body 16 and the second bag body 18. This bag body may be doughnut-shaped, or may be formed into a doughnut shape by arranging sector-shaped bags in the circumferential direction. In addition, another bag body may be arranged radially outside the second bag body 18. This bag body is preferably formed into a doughnut shape by arranging sector-shaped bags in the circumferential direction. Even in this case, the same effects as those described above can be achieved.

[0025] (Foundation structure for offshore wind turbines and its construction method) Next, an embodiment of an offshore wind turbine foundation structure and a construction method thereof according to the present invention will be described. As shown in Figures 1 and 2, the foundation structure 100 for an offshore wind turbine in this embodiment is a foundation structure for a wind turbine installed offshore, and comprises a monopile 14 (a pile foundation type structure) installed on the seabed, and the above-mentioned scour prevention device 10 arranged on the ground 12 around this monopile 14.

[0026] When constructing the foundation structure 100 for an offshore wind turbine, for example, (1) a method of installing the scour prevention device 10 before installing the monopile 14, or (2) a method of installing the scour prevention device 10 after installing the monopile 14 can be applied.

[0027] In the case of (1), the first bag body 16 of the scour prevention device 10 is installed on the seabed ground 12, and then the monopile 14 is driven into the seabed ground 12 inside the annular shape of the first bag body 16. After that, the second bag body 18 is installed outside the first bag body 16. This makes it possible to prevent the scour prevention device 10, which was installed prior to the monopile 14, from being washed away by waves or tidal currents. Furthermore, even if the surrounding ground 12 sinks and deforms due to the installation of the monopile 14, the first bag body 16, which was installed first, can deform in response to this deformation.

[0028] In the case of (2), after the monopile 14 is driven into the seabed 12, the first bag body 16 of the scour prevention device 10 is installed on the seabed 12 around the monopile 14. After that, the second bag body 18 is installed outside the first bag body 16. In this manner, the scour prevention device 10 can be quickly constructed even after the monopile 14 has been installed.

[0029] Furthermore, in some cases, the second bag body 18 may be installed before the installation of the first bag body 16. The final shape of the scour prevention device may be such that the first bag body 16 and the second bag body 18 are adjacent to each other around the pile foundation type structure, or are arranged so as to overlap each other partially in the vertical direction.

[0030] As described above, the scour prevention device according to the present invention is a scour prevention device provided to prevent scouring in the ground around a structure installed on the seabed, riverbed, or lakebed, and includes a mesh-like flexible first bag body arranged in an annular shape on the ground around the structure and filled with a filter material of a predetermined particle size, and a plurality of mesh-like flexible second bags arranged adjacent to or partially overlapping each other in the circumferential direction along the first bag body while being adjacent to or partially overlapping the radial outside of the first bag body, and filled with a filter material of a predetermined particle size, so that the filter material inside the bag body is not separated and diffused to the outside by waves or tidal currents. Therefore, it is possible to prevent a situation in which the scour prevention device being installed is washed away by waves or tidal currents.

[0031] Furthermore, the foundation structure for an offshore wind turbine according to the present invention is a foundation structure for a wind turbine that is installed offshore, and comprises a pile foundation-type structure installed on the seabed and the above-mentioned scour prevention device that is placed on the ground surrounding this structure. Therefore, the scour prevention device can be quickly constructed even after the pile foundation-type structure has been installed.

[0032] According to the construction method of the foundation structure for an offshore wind turbine of the present invention, the first bag body of the scour prevention device is installed on the seabed ground, and then a pile foundation type structure is installed on the seabed ground inside the annular part of the first bag body, so that the scour prevention device installed prior to the pile foundation type structure can be prevented from being washed away by waves or tides. Even if the surrounding ground sinks and deforms due to the installation of the pile foundation type structure, the first bag body installed first can deform to follow this deformation.

[0033] Furthermore, according to another construction method for a foundation structure for an offshore wind turbine of the present invention, which is a method for constructing the above-mentioned foundation structure for an offshore wind turbine, after a pile foundation-type structure is installed on the seabed, a first bag body of the scour prevention device is installed on the seabed surrounding the structure, so that the scour prevention device can be quickly constructed even after the pile foundation-type structure has been installed. [Industrial Applicability]

[0034] As described above, the scour prevention device, foundation structure for an offshore wind turbine, and construction method of the present invention are useful for constructing wind turbine foundations for offshore wind power generation, and are particularly suitable for preventing a situation in which the scour prevention device during construction is washed away by waves or tides. [Explanation of symbols]

[0035] 10 Scour prevention device 12 Ground 14 Monopile (structure) 16 First bag body 18 Second bag body 20 Filter Material 22 Through hole 24 Ring 100 Foundation structure for offshore wind turbines D Circular inner diameter

Claims

1. A scour prevention device provided to prevent scouring in the ground around a structure installed on the seabed, riverbed, or lakebed, comprising: A scouring prevention device comprising: a first flexible mesh bag body arranged in a ring shape on the ground around the structure, and having a filter material of a predetermined particle size packed therein; and a plurality of second flexible mesh bags arranged adjacent to or partially overlapping each other in a circumferential direction along the first bag body while being adjacent to or partially overlapping the radial outside of the first bag body, and having a filter material of a predetermined particle size packed therein, wherein the first bag body is annular in a plan view, and the second bag body is fan-shaped in a plan view, and is arranged so that the structure passes through a central through hole of the first bag body which is annular in a plan view.

2. A foundation structure for a wind turbine installed on the ocean, 13. A foundation structure for an offshore wind turbine, comprising: a pile foundation type structure to be installed on the seabed; and the scour prevention device according to claim 1, which is disposed on the seabed ground surrounding the structure.

3. A method for constructing the foundation structure for an offshore wind turbine according to claim 2, A construction method for a foundation structure for an offshore wind turbine, characterized in that the first bag body of the scour prevention device is installed in a ring shape in a planar view on the seabed, and then the pile foundation type structure is installed on the seabed within the ring shape of the first bag body.

4. A method for constructing the foundation structure for an offshore wind turbine according to claim 2, A construction method for a foundation structure for an offshore wind turbine, characterized in that after the pile foundation type structure is installed on the seabed, the first bag body of the scour prevention device is installed on the seabed surrounding the structure.

Images