Construction methods

Abstract

To provide a construction method and offshore structure that can improve the constructability of monopiles for supporting offshore wind turbines. [Solution] The construction method comprises an installation step for installing the offshore structure and a lowering step for lowering the monopile that supports the offshore wind turbine to the seabed using a crane vessel. In the lowering step, the monopile is guided by the offshore structure when it is lowered by the crane vessel.

Description

Technical Field

[0001] The present disclosure relates to a construction method and an ocean structure.

Background Art

[0002] Conventionally, as disclosed in Patent Document 1, a casing guide device used for driving a casing is known. This casing guide device includes a guide roller that can abut against the casing being driven, and can guide the casing in the driving direction.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the construction of a monopile for supporting an offshore wind turbine, conventionally, it has been necessary to use a construction ship equipped with a pile gripper. That is, in the construction of a monopile, the monopile is guided using the pile gripper provided on the construction ship. There is room for improvement in improving the workability of monopile construction.

[0005] The present disclosure has been made in view of the above circumstances, and an object thereof is to provide a construction method and an ocean structure capable of improving the workability of monopile construction for supporting an offshore wind turbine.

Means for Solving the Problems

[0006] A construction method according to one aspect of the present disclosure comprises an installation step for installing an offshore structure and a lowering step for lowering a monopile supporting an offshore wind turbine to the seabed using a crane vessel, wherein in the lowering step, the monopile is guided by the offshore structure when it is lowered by the crane vessel.

[0007] An offshore structure according to one aspect of the present disclosure is an offshore structure having a truss section, configured to receive and guide monopiles driven into the seabed, and comprising a plurality of guide sections arranged vertically, wherein at least two of the plurality of guide sections are positioned above the lower end of the truss section. [Effects of the Invention]

[0008] According to one aspect of this disclosure, a construction method and an offshore structure can be provided that can improve the constructability of monopiles for supporting offshore wind turbines. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows a monopile and an offshore wind turbine supported by the monopile according to the first embodiment. [Figure 2] This is a diagram showing a jacket structure according to the first embodiment. [Figure 3] This is a diagram showing the guide section according to the first embodiment. [Figure 4] This is a diagram showing the guide section according to the first embodiment. [Figure 5] This is a diagram illustrating the construction method according to the first embodiment. [Figure 6] This is a diagram illustrating the construction method according to the first embodiment. [Figure 7] This is a diagram illustrating the construction method according to the first embodiment. [Figure 8] This is a diagram illustrating the construction method according to the first embodiment. [Figure 9] This is a diagram illustrating the construction method according to the first embodiment. [Figure 10] It is a diagram for explaining the construction method according to the first embodiment. [Figure 11] It is a diagram for explaining the construction method according to the second embodiment. [Figure 12] It is a diagram for explaining the construction method according to the second embodiment. [Figure 13] It is a diagram for explaining the construction method according to the second embodiment. [Figure 14] It is a diagram for explaining the construction method according to the third embodiment. [Figure 15] It is a diagram for explaining the construction method according to the third embodiment. [Figure 16] It is a diagram for explaining the construction method according to the third embodiment.

Mode for Carrying Out the Invention

[0010] <First Embodiment> Hereinafter, referring to the drawings, the construction method and the offshore structure according to the first embodiment of the present disclosure will be described.

[0011] The construction method according to the present embodiment is a method for constructing a monopile MP. As shown in FIG. 1, the monopile MP is, for example, a steel pipe for supporting an offshore windmill WM by being connected to the lower end of the offshore windmill WM. The monopile MP is connected to the lower end of the offshore windmill WM via a transition piece TP. That is, the monopile MP supports the offshore windmill WM via the transition piece TP. The monopile MP is, for example, a cylindrical member. Hereinafter, in the present embodiment, the monopile MP will be described as a cylindrical member. However, it is not limited thereto, and the monopile MP may be, for example, a square tubular member. Accordingly, each configuration described later may be appropriately corresponded.

[0012] The offshore structure according to the present embodiment is a jacket structure 1 which is a pile-type structure and is installed on the seabed. The jacket structure 1 is used for guiding the monopile MP during construction. Note that the offshore structure may be a gravity structure. As shown in FIG. 2, the jacket structure 1 has a plurality of legs 11, a plurality of braces 12, a mudmat 15, and a plurality of guide portions 20.

[0013] The leg 11 is a cylindrical member extending in the vertical direction. Although details will be described later, when the jacket structure 1 is installed on the seabed, a pile TS is inserted through the leg 11. By driving the pile TS into the seabed in this state, the jacket structure 1 is fixed to the seabed. In the present embodiment, the jacket structure 1 includes four legs 11. Note that the number of legs 11 is not limited to this, and three or more legs may be provided.

[0014] The brace 12 is a steel pipe connecting adjacent legs 11 to each other. By providing the brace 12, the jacket structure 1 is reinforced. In the present embodiment, by connecting the legs 11 and the braces 12 to each other, a substantially rectangular parallelepiped frame body having four side surfaces is formed.

[0015] The brace 12 has a horizontal brace 13 and a diagonal brace 14. The horizontal brace 13 is arranged to be horizontal when the jacket structure 1 is arranged on the seabed. The diagonal brace 14 is arranged to be diagonal with respect to the horizontal direction when the jacket structure 1 is arranged on the seabed.

[0016] The mudmat 15 is connected to the lower end of the leg 11. When the jacket structure 1 is installed on the seabed, the mudmat 15 contacts the seabed. The mudmat 15 increases the contact area of the jacket structure 1 with the seabed and suppresses the surface pressure acting on the seabed due to the weight of the jacket structure 1. In the present embodiment, the mudmat 15 is rectangular, and the four corners of the mudmat 15 are respectively connected to the lower ends of the four legs 11. The shape of the mudmat 15 may be appropriately set according to the number of legs 11 and the soil properties of the seabed where the jacket structure 1 is installed.

[0017] The jacket structure 1 has a truss section 16. The truss section 16 has an upper truss section 17 and a lower truss section 18 located below the upper truss section 17. The upper truss section 17 and the lower truss section 18 are formed by two diagonal braces 14 and one horizontal brace 13 arranged in a triangle.

[0018] Multiple guide sections 20 are arranged vertically. The guide sections 20 are positioned between adjacent legs 11. The guide sections 20 are attached to the horizontal brace 13. In a plan view, the multiple guide sections 20 are positioned outside the area enclosed by the multiple legs 11.

[0019] In this embodiment, two guide sections 20 are provided. The two guide sections 20 are provided on one side of the substantially rectangular parallelepiped frame. The two guide sections 20 are positioned above the lower end of the truss section 16. Note that there may be three or more guide sections 20. Multiple guide sections 20 may be provided on one side, or they may be provided on two or more sides. At least two of the multiple guide sections 20 are positioned above the lower end of the truss section 16.

[0020] Of the multiple guide sections 20, the uppermost guide section 20A is positioned to correspond to the upper part of the truss section 16 (upper truss section 17). Of the multiple guide sections 20, the lowermost guide section 20B is positioned to correspond to the upper and lower intermediate part of the truss section 16, more specifically, to the connection section that connects the upper truss section 17 and the lower truss section 18.

[0021] The guide section 20 has a pair of arm sections 21 and a plurality of contact members 22. As shown in Figure 3, each of the pair of arms 21, in a plan view, has one end attached to the horizontal brace 13 and extends from one end toward the other, forming a J-shape where the other ends move closer together. However, the shape of the arms 21 is not limited to this and may be semicircular or the like.

[0022] The pair of arms 21 are rotatably mounted on the horizontal brace 13 around a pivot axis 21a that extends vertically. This allows the pair of arms 21 to be switched between an open state, as shown in Figure 3(a), where the other ends of the pair of arms 21 are spaced apart from each other, and a closed state, as shown in Figure 3(b), where the other ends of the pair of arms 21 are in contact with or close to each other.

[0023] The contact member 22 has a fixed portion 23 that is fixed to the arm portion 21, and a movable portion 24 that is movable relative to the fixed portion 23. The movable portion 24 is configured to be movable toward the center of the internal space surrounded by the pair of arms 21 in the closed state. As a result, the contact member 22 is configured to be able to contact the outer circumference of the monopile MP. For example, a jack such as an electric jack or a hydraulic jack can be used as the contact member 22. When a hydraulic jack is used as the contact member 22, a biodegradable oil can be used as the hydraulic fluid.

[0024] The guide section 20 is configured to accept and guide the monopile MP. The guide section 20 is configured to be switchable between an acceptable state in which the monopile MP can be accepted, an accommodating state in which the monopile MP is housed inside, and a gripping state in which the monopile MP is gripped. Multiple guide sections 20 are configured to be switchable independently between the acceptable state, the accommodating state, and the gripping state.

[0025] Specifically, as shown in Figure 4(a), when the pair of arm portions 21 are in the open position, the guide portion 20 is in a receptive state that can receive the monopile MP. In this embodiment, the guide portion 20 is configured to be able to receive the monopile MP from the side.

[0026] As shown in Figure 4(b), by closing the pair of arms 21 from the state in Figure 4(a), the guide portion 20 enters a housing state in which the monopile MP is housed inside. At this time, the contact member 22 is not in contact with the outer circumference of the monopile MP. The pair of arms 21 are formed to have a portion that follows the outer circumference of the monopile MP when closed. In the illustrated example, the pair of arms 21 are formed to be U-shaped along the outer circumference of the monopile MP when closed. The pair of arms 21 may also be formed in a polygonal or annular shape along the outer circumference of the monopile MP.

[0027] As shown in Figure 4(c), by moving the movable part 24 from the state in Figure 4(b) toward the center of the internal space surrounded by the pair of arm parts 21, the contact member 22 comes into contact with the outer circumference of the monopile MP. By bringing multiple contact members 22 into contact with the outer circumference of the monopile MP, the guide part 20 enters a gripping state in which it grips the monopile MP.

[0028] Returning to Figure 2, the jacket structure 1 has a first passageway 31 for workers. The first passageway 31 is provided on the horizontal brace 13. The first passageway 31 may be provided separately from the horizontal brace 13. A first handrail 32 is provided around the first passageway 31.

[0029] The guide section 20 has a second passageway 33 for workers and a second handrail 34 (handrail) provided around the second passageway 33. The second passageway 33 is provided on the arm section 21. The first passageway 31 and the second passageway 33 are connected so that workers can move between them.

[0030] Next, the construction method for the monopile MP will be described with reference to Figures 5 to 12. In the construction method of this embodiment, the monopile MP is constructed using a jacket structure 1 and a first crane vessel 40 and a second crane vessel 50. The first crane vessel 40 has a slewing first crane 41. The second crane vessel 50 has a slewing second crane 51. Note that the first crane 41 may be a fixed crane. Also, the second crane 51 may be a fixed crane.

[0031] The construction method of this embodiment comprises a jacket structure transport step, an installation step, a fixing step, an inclination adjustment step, a switching step, a monopile transport step, a suspension step, a concrete pouring step, a recovery step, an attachment step, and an injection step.

[0032] In the jacket structure transport step, the jacket structure 1 is transported to the installation site using the first crane vessel 40.

[0033] In the installation step, the jacket structure 1 is installed on the seabed at the installation site using the first crane vessel 40. In the installation step, the jacket structure 1 is installed only in the locations where the monopile MP will be driven.

[0034] In the fixing step, the jacket structure 1 is fixed to the seabed by piles TS. Specifically, as shown in Figure 5, the piles TS are inserted through the legs 11 of the jacket structure 1. The first hammer 42 is attached to the first crane 41, and the piles TS are driven into the seabed by the first hammer 42. The piles TS are driven into the seabed through holes in the mud mat 15 (not shown). As a result, the jacket structure 1 is fixed to the seabed.

[0035] In the tilt adjustment step, the tilt of at least the portion of the jacket structure 1 (offshore structure) that guides the monopile MP is adjusted. If the offshore structure is a jacket structure 1 (pile structure), the tilt adjustment step may adjust the tilt of the entire jacket structure 1. For example, the tilt of the jacket structure 1 is adjusted by using the first crane 41 of the first crane vessel 40 to pull upward the portion of the jacket structure 1 that is sinking higher than the rest of the jacket structure 1. If the offshore structure is a gravity structure, the tilt adjustment step may adjust the tilt of only the guide portion 20. Furthermore, if the offshore structure is a pile-type structure, the tilt of only the guide section 20 may be adjusted in the tilt adjustment step, and if the offshore structure is a gravity-type structure, the tilt of the entire jacket structure 1 may be adjusted in the tilt adjustment step.

[0036] In the switching step, the pair of arms 21 of the guide section 20 are opened, thereby switching the guide section 20 to a state where it can accept the monopile MP. If the pair of arms 21 are already in the open state, the switching step may be omitted.

[0037] In the monopile transport step, the monopile MP is transported to the installation site. Specifically, as shown in Figure 6, the monopile MP is transported to the construction site by a transport barge 60. At the construction site, the lifting equipment 52 is attached to the monopile MP, and the monopile MP is erected by the second crane vessel 50. Alternatively, the monopile MP located on a quay on land may be erected by the second crane vessel 50 and then towed to the construction site by the second crane vessel 50. The monopile transport step may be performed in parallel with the jacket structure transport step, installation step, fixing step, tilt adjustment step, and switching step described above.

[0038] In the lowering step, as shown in Figure 6, the monopile MP is lowered to the seabed using the second crane 51 of the second crane vessel 50. At this time, the monopile MP is guided by the guide section 20 of the jacket structure 1. In the illustrated example, two guide sections 20 are used to guide the monopile MP. However, only one guide section 20 may be used. Multiple guide sections 20 may be selected to guide the monopile MP according to the water depth, etc.

[0039] Specifically, first, with the monopile MP suspended by the second crane 51, the monopile MP is brought close to the guide section 20. At this time, the guide section 20 is in the receiving state shown in Figure 4(a). The monopile MP is inserted into the inside of the guide section 20. In this embodiment, the monopile MP is inserted into the inside of the guide section 20 from the side of the guide section 20. In this case, the monopile MP can be easily inserted into the guide section 20 without raising the boom of the second crane 51 too much.

[0040] Subsequently, the guide section 20 is switched to the housing state shown in Figure 4(b). This positions the monopile MP inside the guide section 20. The monopile MP is guided by the guide section 20 and lowered into the sea by its own weight using the second crane 51, until it reaches the seabed. Specifically, the movable part 24 of the contact member 22 is brought into contact with the outer circumference of the monopile MP, and the guide section 20 is switched to the gripping state shown in Figure 4(c). With the movable part 24 of the contact member 22 in contact with the outer circumference of the monopile MP (switched to the gripping state), the monopile MP is sunk into the seabed while the verticality of the monopile MP is ensured by the guide section 20.

[0041] Next, the verticality of the monopile MP is measured. If the verticality of the monopile MP is greater than the specified value (i.e., the monopile MP is tilted), the monopile MP is reinstalled. If the verticality of the monopile MP is below the specified value, the concrete placement step is initiated.

[0042] The driving step is performed after the lowering step. As shown in Figures 7 and 8, in the driving step, the monopile MP is driven into the seabed by the first crane vessel 40. At this time, the guide section 20 remains in a gripping state, and the monopile MP is guided by the guide section 20.

[0043] Specifically, the lifting device 52 is recovered from the monopile MP. Then, the second crane vessel 50 is moved away from the jacket structure 1 and the monopile MP. Next, the second hammer 43 is attached to the first crane 41 of the first crane vessel 40. The second hammer 43 is a vibro-hammer. Then, the monopile MP is driven into the seabed by the second hammer 43 while being guided by the guide section 20. Note that the attachment of the second hammer 43 to the first crane 41 may be carried out in parallel with the monopile transport step and the lifting step.

[0044] The recovery step is performed after the driving step. In the recovery step, the jacket structure 1 is recovered by the first crane vessel 40. Specifically, as shown in Figure 9, the first crane 41 of the first crane vessel 40 is used to remove the pile TS from the leg 11 and release the jacket structure 1 from its fixation to the seabed. A vibro-hammer may also be used to pull out the pile TS. After that, the jacket structure 1 is recovered using the first crane 41 of the first crane vessel 40.

[0045] The installation step is performed after the recovery step. The injection step is performed after the installation step. As shown in Figure 10, in the installation step, the transition piece TP is attached to the upper end of the monopile MP using the first crane 41 of the first crane vessel 40, and in the injection step, grout is injected between the monopile MP and the transition piece TP. This fixes the transition piece TP to the monopile MP. The grout injection may be performed using the first crane vessel 40 or using a dedicated vessel for grout injection.

[0046] As described above, the construction method according to this embodiment comprises an installation step of installing the jacket structure 1 (offshore structure) and a lowering step of lowering the monopile MP supporting the offshore wind turbine WM to the seabed using a second crane vessel 50 (crane vessel). In the lowering step, the monopile MP is guided by the jacket structure 1 when it is lowered by the second crane vessel 50. According to the above configuration, when lowering the monopile MP to the seabed, the jacket structure 1 can be used to guide the monopile MP that supports the offshore wind turbine WM. Therefore, a construction vessel equipped with a pile gripper is not required, and the constructability of the monopile MP is improved.

[0047] Furthermore, the construction method according to this embodiment includes a fixing step for fixing the jacket structure 1 to the seabed by pile TS. According to the above configuration, the jacket structure 1 can be securely fixed to the seabed, and the monopile MP can be guided more reliably using the jacket structure 1.

[0048] Furthermore, the construction method according to this embodiment includes a tilt adjustment step for adjusting the inclination of at least the portion of the jacket structure 1 that guides the monopile MP. According to the above configuration, by adjusting the inclination of at least the part of the jacket structure 1 that guides the monopile MP, the verticality of the monopile MP can be more reliably ensured when lowering the monopile MP to the seabed.

[0049] Furthermore, in the installation step, the jacket structure 1 is installed only in the locations where the monopile MP is to be driven. The above configuration further improves the workability of the monopile MP.

[0050] Furthermore, in the installation step, the jacket structure 1 is installed by the first crane vessel 40, and in the lowering step, the monopile MP is lowered by the second crane vessel 50. According to the above configuration, the construction period can be shortened because the monopile MP is constructed using the first crane vessel 40 and the second crane vessel 50.

[0051] Furthermore, the lowering step guides the monopile MP being lowered by the second crane vessel 50. The above configuration further improves the workability of the monopile MP.

[0052] Furthermore, the construction method according to this embodiment includes a driving step in which, after the suspension step is performed, the monopile MP is driven into the seabed by the first crane vessel 40. According to the above configuration, the monopile MP can be securely fixed to the seabed. Furthermore, since the first crane vessel 40 used in the installation step is also used for driving the monopile MP, the constructability of the monopile MP is further improved.

[0053] Furthermore, the construction method according to this embodiment includes a recovery step in which the jacket structure 1 is recovered by the first crane ship 40 after the concrete pouring step has been performed. According to the above configuration, the jacket structure 1 can be recovered and used, for example, in the construction of a new monopile MP. In addition, since the first crane vessel 40 used in the installation step is also used to recover the jacket structure 1, the constructability of the monopile MP is further improved.

[0054] Furthermore, the construction method according to this embodiment includes an installation step in which, after the concrete pouring step is performed, a transition piece TP is attached to the upper end of the monopile MP by the first crane vessel 40. According to the above configuration, a transition piece TP can be attached to the upper end of the monopile MP. Furthermore, since the first crane vessel 40 used in the installation step is also used for attaching the transition piece TP, the constructability of the monopile MP is further improved.

[0055] Furthermore, the construction method according to this embodiment includes an injection step in which grout is injected between the monopile MP and the transition piece TP after the installation step has been performed. According to the above configuration, the transition piece TP can be securely fixed to the monopile MP by injecting grout.

[0056] The jacket structure 1 according to this embodiment is configured to receive and guide monopile MPs driven into the seabed and includes a plurality of guide sections 20 arranged in the vertical direction. At least two of the plurality of guide sections 20 are positioned above the lower end of the truss section 16. With the above configuration, the monopile MP can be guided using the guide section 20 of the jacket structure 1 during construction. Therefore, a construction vessel equipped with a pile gripper is not required, improving the constructability of the monopile MP. In addition, since at least two of the multiple guide sections 20 are positioned above the lower end of the truss section 16, the monopile MP can be guided in a stable state by the guide sections 20.

[0057] Furthermore, the lowest of the multiple guide sections 20, the guide section 20B, is positioned to correspond to the upper and lower intermediate section of the truss section 16. With the above configuration, the monopile MP can be guided in a stable state by the guide section 20B at the lowest end.

[0058] Furthermore, the uppermost guide section 20A among the multiple guide sections 20 is positioned to correspond to the upper part of the truss section 16. With the above configuration, the monopile MP can be guided in a stable state by the uppermost guide section 20A.

[0059] Furthermore, the jacket structure 1 includes a plurality of legs 11. The plurality of guide sections 20 are located outside the area surrounded by the plurality of legs 11 in a plan view. According to the above configuration, since the guide section 20 is positioned outside the area surrounded by the multiple legs 11 in a plan view, guiding the monopile MP using the guide section 20 becomes easier.

[0060] Furthermore, the jacket structure 1 comprises multiple legs 11. The guide section 20 is positioned between adjacent legs 11. With the above configuration, the guide section 20 can guide the monopile MP in a more stable state.

[0061] Furthermore, the jacket structure 1 comprises a plurality of legs 11 and a mud mat 15 connected to the lower ends of the plurality of legs 11. According to the above configuration, by providing the mud mat 15, the contact area of ​​the jacket structure 1 can be increased, and the surface pressure acting on the seabed due to the weight of the jacket structure 1 can be reduced.

[0062] Furthermore, the guide section 20 is configured to be switchable between a state in which it can accept the monopile MP and a state in which it grips the monopile MP. With the above configuration, by switching the guide section 20 between a receivable state and a gripping state, guiding the monopile MP using the guide section 20 becomes easier.

[0063] Furthermore, the multiple guide sections 20 are configured to be able to be switched independently between a receiving state and a gripping state. According to the above configuration, for example, by independently switching between a receptive state and a gripping state depending on the water depth, it is possible to select the guide section 20 to be used for guiding the monopile MP from among the multiple guide sections 20.

[0064] Furthermore, the guide section 20 is configured to be able to receive the monopile MP from the side. With the above configuration, even if the monopile MP is heavy, for example, the monopile MP can be easily placed inside the guide section 20.

[0065] Furthermore, the guide portion 20 has a shape that includes a part that follows the outer circumference of the monopile MP. With the above configuration, the monopile MP can be guided more reliably using the guide section 20.

[0066] Furthermore, the jacket structure 1 is equipped with a first passageway 31 for workers. The guide section 20 has a second passageway 33 for workers. The first passageway 31 and the second passageway 33 are connected in such a way that workers can move between them. With the above configuration, workers can visually check the construction status. Furthermore, workers can inspect and repair the area around the guide section 20.

[0067] Furthermore, the guide section 20 has a second handrail 34 (handrail) provided around the second passage 33. The above configuration makes it easier for workers to move around.

[0068] Furthermore, the guide section 20 has a plurality of contact members 22 that can contact the outer circumference of the monopile MP. With the above configuration, the monopile MP can be guided more reliably using the guide section 20.

[0069] <Second Embodiment> Next, a construction method according to the second embodiment of this disclosure will be described with reference to Figures 11 to 13. In this embodiment, the same reference numerals are used for parts that are the same as those in the first embodiment, and their descriptions are omitted; only the differences will be described.

[0070] In this embodiment, multiple jacket structures 1 are used to construct multiple monopiles MP in parallel using multiple first crane vessels 40 and multiple second crane vessels 50. The number of first crane vessels 40, second crane vessels 50, and jacket structures 1 may be appropriately changed depending on the number of monopiles MP to be driven, the distance to the installation site, the size of the installation site, etc. For example, there may be two or more first crane vessels 40.

[0071] For example, in the installation step, as shown in Figure 11, multiple jacket structures 1 are installed by multiple first crane vessels 40. In the lowering step, as shown in Figure 12, multiple monopiles MP are lowered to the seabed by multiple second crane vessels 50. At this time, each of the multiple monopiles MP is guided by multiple jacket structures 1. In the driving step, as shown in Figure 13, multiple monopiles MP are driven into the seabed by multiple first crane vessels 40. At this time, each of the multiple monopiles MP is guided by multiple jacket structures 1.

[0072] As described above, in the construction method according to this embodiment, the installation step involves installing multiple jacket structures 1. According to the above configuration, multiple jacket structures 1 can be used to carry out the construction of multiple monopile MPs in parallel. Therefore, the construction period can be shortened.

[0073] In addition, during the installation step, multiple jacket structures 1 are installed using multiple first crane vessels 40. According to the above configuration, since multiple jacket structures 1 are installed using multiple first crane vessels 40, the construction period can be further shortened.

[0074] <Third Embodiment> Next, a construction method according to the third embodiment of this disclosure will be described with reference to Figures 14 to 16. In this embodiment, the same reference numerals are used for parts that are the same as those in the first embodiment, and their descriptions are omitted; only the differences will be described.

[0075] In this embodiment, multiple monopile MPs are constructed at multiple installation locations using a single jacket structure 1. The construction method according to this embodiment includes a moving step for moving the jacket structure 1 within the same wind farm or sea area. The construction method according to this embodiment also includes a second installation step, a fixing step, a tilt adjustment step, a switching step, a monopile transport step, a hoisting step, a driving step, a recovery step, an attachment step, and an injection step. In the following description, the second installation step, etc., will be referred to as the second installation step, etc.

[0076] Specifically, first, the first monopile MP1 (monopile MP) is constructed at the first installation site P1 using the jacket structure 1. The construction method in this case is the same as the construction method according to the first embodiment, so the explanation is omitted here.

[0077] Subsequently, in the moving step, the jacket structure 1 is moved by the first crane vessel 40 from the first installation location P1 to a second installation location P2, which is different from the first installation location P1.

[0078] Subsequently, the second monopile MP2 is constructed at the second installation site P2 using the jacket structure 1. The construction method in this case is the same as the construction method according to the first embodiment, except that the jacket structure transport step is not performed. For example, in the second installation step, as shown in Figure 14, the jacket structure 1 is installed at the second installation site P2 by the first crane vessel 40. As shown in Figure 15, in the second lowering step, the second monopile MP2 is lowered to the seabed at the second installation site P2 by the second crane vessel 50. At this time, the second monopile MP2 is guided by the jacket structure 1. As shown in Figure 16, in the second driving step, the second monopile MP2 is driven into the seabed by the first crane vessel 40. At this time, the second monopile MP2 is guided by the jacket structure 1.

[0079] As described above, the construction method according to this embodiment includes a moving step for moving the jacket structure 1 within the same wind farm or sea area. According to the above configuration, the jacket structure 1 can be used for the construction of multiple monopile MPs.

[0080] Furthermore, in the installation step, the jacket structure 1 is installed at the first installation location P1 by the first crane vessel 40, and in the lowering step, the first monopile MP1 (monopile MP) is lowered to the seabed at the first installation location P1 by the second crane vessel 50. In addition, the construction method according to this embodiment includes a second installation step in which, after the lowering step is performed, the jacket structure 1 is installed at a second installation location P2, which is different from the first installation location P1, by the first crane vessel 40, and a second lowering step in which, after the second installation step is performed, the second monopile MP2, which is different from the first monopile MP1, is lowered to the seabed at the second installation location P2 by the second crane vessel 50. According to the above configuration, the jacket structure 1 can be used for the construction of multiple monopile MPs.

[0081] It should be noted that this disclosure is not limited to the embodiments described above with reference to the drawings, and various modifications are possible within its technical scope.

[0082] For example, the number of guide sections 20 may be one or three or more. If the jacket structure 1 has two or more guide sections 20, the guide sections 20 may be provided on two or more sides at different heights. In this case, the guide section 20 to be used to guide the monopile MP can be easily selected from the multiple guide sections 20 according to the water depth, etc.

[0083] Furthermore, in the above embodiment, a first crane vessel 40 and a second crane vessel 50 are used in the construction method. However, the disclosure is not limited thereto. Only a single crane vessel may be used in the construction method. In this case, in the installation step, the jacket structure 1 is installed by the crane vessel, and in the lowering step, the monopile MP is lowered to the seabed by the crane vessel. With the above configuration, the number of crane vessels to be used is reduced, so construction costs can be reduced.

[0084] Furthermore, in the above embodiment, the multiple guide sections 20 are located outside the area enclosed by the multiple legs 11 in a plan view. However, the disclosure is not limited thereto. The multiple guide sections 20 may be located inside the area enclosed by the multiple legs 11 in a plan view. The above configuration allows for a reduction in the installation space required for the jacket structure 1.

[0085] Furthermore, in the above embodiment, the guide portion 20 is configured to receive the monopile MP from the side. However, the disclosure is not limited thereto. The guide portion 20 may also be configured to receive the monopile MP from above. For example, by closing the pair of arm portions 21, the monopile MP can be received from above. In this case, after inserting the monopile MP into the guide portion 20 from above, the monopile MP can be guided using the guide portion 20. Furthermore, depending on the weight of the monopile MP and the water depth, it may be selected whether to insert the monopile MP from the side of the guide section 20 or from above the guide section 20.

[0086] Furthermore, it is possible to replace the components in the above embodiments with well-known components as appropriate, without departing from the spirit of this disclosure, and the above-described modifications may be combined as appropriate.

[0087] For example, the construction method according to the second embodiment and the construction method according to the third embodiment may be combined. In this case, multiple jacket structures 1 are used, and multiple first monopiles MP1 are constructed in parallel by multiple first crane ships 40 and multiple second crane ships 50. After that, the multiple jacket structures 1 are moved to another installation location by the multiple first crane ships 40, and multiple second monopiles MP2 are constructed at the other installation location.

[0088] (Note) The construction method and offshore structure according to the above embodiment can be understood, for example, as follows. <1> A construction method according to one aspect of the present disclosure comprises an installation step for installing an offshore structure and a lowering step for lowering a monopile supporting an offshore wind turbine to the seabed using a crane vessel, wherein in the lowering step, the monopile is guided by the offshore structure when it is lowered by the crane vessel. According to the above configuration, when lowering the monopile to the seabed, the offshore structure can be used to guide the monopile that supports the offshore wind turbine. Therefore, a construction vessel equipped with a pile gripper is not required, and the workability of the monopile is improved.

[0089] <2> the above <1> In the construction method relating to this, the offshore structure may be a pile-type structure.

[0090] <3> the above <2> The construction method may include fixing steps for securing the offshore structure to the seabed with piles. According to the above configuration, the offshore structure can be securely fixed to the seabed, and the monopile can be guided more reliably using the offshore structure.

[0091] <4> the above <1> In the construction method relating to this, the offshore structure may be a gravity-type structure.

[0092] <5> the above <1> from <4> In any one of the construction methods, the method may include a tilt adjustment step for adjusting the inclination of at least the portion of the offshore structure that guides the monopile. According to the above configuration, by adjusting the inclination of at least the part of the offshore structure that guides the monopile, the verticality of the monopile can be more reliably ensured when lowering the monopile to the seabed.

[0093] <6> the above <1> from <5> In any one of the construction methods, the offshore structure may be provided with a moving step for moving it within the same wind farm or sea area. According to the above configuration, the offshore structure can be used for the construction of multiple monopiles.

[0094] <7> the above <1> from <6> In the construction method relating to any one of the above, the offshore structure may be installed only in the location where the monopile is driven in the installation step. The above configuration improves the ease of installation of monopile.

[0095] <8> the above <1> from <7> In the construction method relating to any one of the above, the installation step may involve installing multiple marine structures. According to the above configuration, multiple monopiles can be constructed in parallel using multiple offshore structures. Therefore, the construction period can be shortened.

[0096] <9> the above <1> from <8> In the construction method relating to any one of the above, in the installation step, the offshore structure may be installed by a first crane vessel, and in the lowering step, the monopile may be lowered by a second crane vessel, which is the crane vessel. With the above configuration, the construction period can be shortened because the monopile is constructed using the first and second crane vessels.

[0097] <10> the above <1> from <8> In a construction method relating to any one of the above, the installation step may include installing the offshore structure at a first installation site using a first crane vessel, the lowering step may include lowering the first monopile at the first installation site to the seabed using a second crane vessel, after the lowering step has been performed, installing the offshore structure at a second installation site different from the first installation site using the first crane vessel, and after the second installation step has been performed, lowering the second monopile, different from the first monopile, to the seabed at the second installation site using the second crane vessel. According to the above configuration, the offshore structure can be used for the construction of multiple monopiles.

[0098] <11> the above <1> from <8> In any one of the construction methods, the installation step may involve installing the offshore structure using the crane vessel, and the lowering step may involve lowering the monopile to the seabed using the crane vessel. With the above configuration, fewer crane ships are needed, thus reducing construction costs.

[0099] <12> the above <8> In the construction method relating to this, in the installation step, multiple offshore structures may be installed by multiple first crane vessels. According to the above configuration, since multiple offshore structures are installed using multiple first crane vessels, the construction period can be further shortened.

[0100] <13> the above <9> In the construction method relating to this, the lowering step may guide the monopile being lowered by the second crane vessel. The above configuration improves the ease of installation of monopile.

[0101] <14> the above <13> The construction method relating to this may include a driving step in which the monopile is driven into the seabed by the first crane vessel after the suspension step has been performed. According to the above configuration, the monopile can be securely fixed to the seabed. Furthermore, since the first crane vessel used in the installation step is also used for driving the monopile, the workability of the monopile is further improved.

[0102] <15> the above <14> The construction method relating to this may include a recovery step in which the offshore structure is recovered by the first crane vessel after the pouring step has been performed. According to the above configuration, offshore structures can be recovered and used, for example, in the construction of new monopiles. Furthermore, since the first crane vessel used in the installation step is also used for recovering offshore structures, the constructability of monopiles is further improved.

[0103] <16> the above <14> or <15> The construction method relating to this may include an attachment step in which, after the concrete placement step is performed, the transition piece is attached to the upper end of the monopile by the first crane vessel. According to the above configuration, a transition piece can be attached to the upper end of the monopile. Furthermore, since the first crane vessel used in the installation step is also used for attaching the transition piece, the constructability of the monopile is further improved.

[0104] <17> the above <16> The construction method relating to this may include an injection step in which grout is injected between the monopile and the transition piece after the installation step has been performed. According to the above configuration, the transition piece can be securely fixed to the monopile by injecting grout.

[0105] <18> the above <1> from <17> In any one of the construction methods, the offshore structure may be a jacket structure.

[0106] <19> An offshore structure according to one aspect of the present disclosure is an offshore structure having a truss section, configured to receive and guide monopiles driven into the seabed, and comprising a plurality of guide sections arranged vertically, wherein at least two of the plurality of guide sections are positioned above the lower end of the truss section. With the above configuration, the monopile can be guided using the guide section of the offshore structure during construction. Therefore, a construction vessel equipped with a pile gripper becomes unnecessary, improving the workability of the monopile. In addition, since at least two of the multiple guide sections are positioned above the lower end of the truss section, the monopile can be guided in a stable state by the guide section.

[0107] <20> the above <19> In the marine structure relating to this, the lowest of the multiple guide sections may be positioned in a location corresponding to the upper and lower intermediate portion of the truss section. With the above configuration, the monopile can be guided in a stable state by the guide section at the lowest end.

[0108] <21> the above <19> or <20> In the marine structure relating to this, the uppermost of the multiple guide sections may be positioned at a location corresponding to the upper part of the truss section. With the above configuration, the monopile can be guided in a stable state by the uppermost guide section.

[0109] <22> the above <19> from <21> In the case of an offshore structure relating to any one of the above, the offshore structure may be a jacket structure.

[0110] <23> the above <22> In the marine structure relating to this, a plurality of legs may be provided, and the plurality of guide portions may be located outside the area surrounded by the plurality of legs in a plan view. With the above configuration, the guide section is positioned outside the area surrounded by multiple legs in a plan view, making it easier to guide the monopile using the guide section.

[0111] <24> the above <22> In the marine structure relating to this, a plurality of legs may be provided, and the plurality of guide portions may be arranged inside the region surrounded by the plurality of legs in a plan view. The above configuration allows for a reduction in the installation space required for offshore structures.

[0112] <25> the above <22> from <24> In any one of the above, the offshore structure may have multiple legs, and the guide portion may be positioned between adjacent legs. With the above configuration, the guide section can guide the monopile in a more stable state.

[0113] <26> the above <22> from <25> An offshore structure relating to any one of the above may include a plurality of legs and a mud mat connected to the lower ends of the plurality of legs. According to the above configuration, by providing a mud mat, the contact area of ​​the offshore structure can be increased, and the surface pressure acting on the seabed due to the weight of the offshore structure can be reduced.

[0114] <27> the above <19> from <26> In a marine structure relating to any one of the above, the guide portion may be configured to be switchable between a receptive state in which the monopile can be received and a gripping state in which the monopile is gripped. With the above configuration, by switching the guide section between a receptive state and a gripping state, guiding the monopile using the guide section becomes easier.

[0115] <28> the above <27> In the marine structure relating to this, the multiple guide sections may be configured to be able to switch between the receiving state and the gripping state independently of each other. According to the above configuration, for example, by independently switching between a receptive state and a gripping state depending on the water depth, it is possible to select the guide section to be used for guiding the monopile from among the multiple guide sections.

[0116] <29> the above <19> from <28> In any one of the offshore structures, the guide section may be configured to receive the monopile from the side. With the above configuration, even if the monopile is heavy, for example, it can be easily positioned inside the guide section.

[0117] <30> the above <19> from <29> In any one of the offshore structures, the guide section may be configured to receive the monopile from above. With the above configuration, after inserting the monopile into the guide section from above, the monopile can then be guided using the guide section.

[0118] <31> the above <19> from <30> In the case of an offshore structure relating to any one of the above, the guide portion may have a shape that includes a portion along the outer circumference of the monopile. With the above configuration, the monopile can be guided more reliably using the guide section.

[0119] <32> the above <19> from <31> In any one of the offshore structures, a first passageway for workers is provided, the guide section has a second passageway for workers, and the first passageway and the second passageway may be connected in such a way that workers can move between them. With the above configuration, workers can visually confirm the construction status. Furthermore, workers can inspect and repair the area around the guide section.

[0120] <33> the above <32> In the marine structure relating to the above, the guide portion may have a handrail provided around the second passage. The above configuration makes it easier for workers to move around.

[0121] <34> the above <19> from <33> In a marine structure relating to any one of the above, the guide portion may have a plurality of contact members that can contact the outer circumference of the monopile. With the above configuration, the monopile can be guided more reliably using the guide section.

[0122] <35> the above <19> from <34> In the case of an offshore structure relating to any one of the above, the offshore structure may be a pile-type structure.

[0123] <36> the above <19> from <21> and <27> from <34> In the case of an offshore structure relating to any one of the above, the offshore structure may be a gravity-type structure. [Explanation of Symbols]

[0124] 1. Jacket structure (offshore structure) 11 Legs 15 Mud Mat 16 Truss section 20 Guide section 22 Contact Member 31 1st aisle 33 2nd aisle 34. Second handrail (handrail) 40 First hoist ship 50 2nd hoist ship MP Monopile TP Transition Piece TS piles WM offshore wind turbine

Claims

1. Installation steps for installing offshore structures, A lifting step for lowering the monopile supporting the offshore wind turbine to the seabed using a crane ship, Equipped with, In the aforementioned lowering step, the construction method involves guiding the monopile with the offshore structure when it is lowered by the crane vessel.

2. The construction method according to claim 1, wherein the offshore structure is a pile-type structure.

3. The construction method according to claim 2, further comprising a fixing step for fixing the offshore structure to the seabed with piles.

4. The construction method according to claim 1, wherein the offshore structure is a gravity-type structure.

5. The construction method according to any one of claims 1 to 4, further comprising a tilt adjustment step for adjusting the inclination of at least a portion of the offshore structure that guides the monopile.

6. The construction method according to any one of claims 1 to 4, comprising a moving step for moving the aforementioned offshore structure within the same wind farm or sea area.

7. The construction method according to any one of claims 1 to 4, wherein in the installation step, the offshore structure is installed only in the location where the monopile is driven.

8. The construction method according to any one of claims 1 to 4, wherein the installation step involves installing a plurality of the offshore structures.

9. In the installation step, the offshore structure is installed by the first crane vessel, The construction method according to any one of claims 1 to 4, wherein in the lowering step, the monopile is lowered by the second crane vessel, which is the crane vessel.

10. In the installation step, the offshore structure is installed at the first installation site by the first crane vessel. In the aforementioned lowering step, at the first installation site, the first monopile is lowered to the seabed by the second crane vessel, which is the crane vessel. After the lowering step is performed, a second installation step is performed in which the offshore structure is installed at a second installation location different from the first installation location using the first crane vessel. After the second installation step is performed, a second lowering step is performed in which a second monopile, different from the first monopile, is lowered to the seabed by the second crane vessel at the second installation site, A construction method according to any one of claims 1 to 4, comprising the above.

11. In the installation step, the offshore structure is installed by the crane vessel, The construction method according to any one of claims 1 to 4, wherein in the lowering step, the monopile is lowered to the seabed by the crane vessel.

12. The construction method according to claim 8, wherein in the installation step, the multiple offshore structures are installed by multiple first crane vessels.

13. The construction method according to claim 9, wherein the lowering step guides the monopile being lowered by the second crane vessel.

14. The construction method according to claim 13, further comprising a driving step in which the monopile is driven into the seabed by the first crane vessel after the suspension step has been performed.

15. The construction method according to claim 14, further comprising a recovery step of recovering the offshore structure by the first crane vessel after the pouring step has been performed.

16. The construction method according to claim 14, further comprising an attachment step in which, after the pouring step is performed, a transition piece is attached to the upper end of the monopile by the first crane vessel.

17. The construction method according to claim 16, further comprising an injection step of injecting grout between the monopile and the transition piece after the installation step has been performed.

18. The construction method according to any one of claims 1 to 4, wherein the offshore structure is a jacket structure.

19. An offshore structure having a truss section, It is configured to receive and guide monopiles driven into the seabed, and is equipped with multiple guide sections arranged in the vertical direction. An offshore structure in which at least two of the multiple guide sections are located above the lower end of the truss section.

20. The marine structure according to claim 19, wherein the lowest of the multiple guide sections is positioned to correspond to the upper and lower intermediate portion of the truss section.

21. The marine structure according to claim 19, wherein the uppermost of the multiple guide sections is positioned at a location corresponding to the upper part of the truss section.

22. The offshore structure is a jacket structure, according to any one of claims 19 to 21.

23. Equipped with multiple legs, The marine structure according to claim 22, wherein the plurality of guide portions are arranged outside the region surrounded by the plurality of legs in a plan view.

24. Equipped with multiple legs, The marine structure according to claim 22, wherein the plurality of guide portions are arranged inside the region surrounded by the plurality of legs in a plan view.

25. Equipped with multiple legs, The marine structure according to claim 22, wherein the guide portion is arranged between adjacent legs among a plurality of legs.

26. Multiple legs, A mud mat connected to the lower end of multiple legs, The marine structure according to claim 22, comprising:

27. The offshore structure according to any one of claims 19 to 21, wherein the guide portion is configured to be switchable between a receptive state in which the monopile can be received and a gripping state in which the monopile is gripped.

28. The marine structure according to claim 27, wherein the plurality of guide portions are configured to be switchable independently between the receiving state and the gripping state.

29. The offshore structure according to any one of claims 19 to 21, wherein the guide portion is configured to receive the monopile from the side.

30. The offshore structure according to any one of claims 19 to 21, wherein the guide section is configured to receive the monopile from above.

31. The marine structure according to any one of claims 19 to 21, wherein the guide portion has a shape that extends along the outer circumference of the monopile.

32. Equipped with a first passageway for workers, The aforementioned guide section has a second passage for workers, The offshore structure according to any one of claims 19 to 21, wherein the first passage and the second passage are connected in such a way that workers can move between them.

33. The marine structure according to claim 32, wherein the guide portion has a handrail provided around the second passage.

34. The marine structure according to any one of claims 19 to 21, wherein the guide portion has a plurality of contact members that can contact the outer circumference of the monopile.

35. The offshore structure is a pile-type structure, according to any one of claims 19 to 21.

36. The aforementioned offshore structure is a gravity-type structure, according to any one of claims 19 to 21.

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