Method for removing cover members and offshore structures

Abstract

This cover member is to be attached when collapsing an offshore structure comprising a columnar section fixed to the seafloor and extending upward and a heavy section disposed on the upper end of the columnar section. The cover member has a first cover member which has a main surface portion facing water surface when the offshore structure collapses toward the water surface and which at least partially covers the heavy section from outside with a space therebetween.

Description

【Technical Field】 【0001】 The present disclosure relates to a cover member and a method for removing an offshore structure. 【Background Art】 【0002】 Various structures are constructed offshore, including, for example, lighthouses and oil drilling rigs. In many cases, these offshore structures have a columnar portion extending from the seabed towards the water surface and an upper structure as a weight portion provided at the upper end of this columnar portion. That is, an offshore structure can be regarded as having a tower shape in which the weight of the weight portion is borne by the columnar portion. 【0003】 When removing this type of offshore structure, it is common to adopt a method of cutting the columnar portion at the root and causing it to collapse onto the water surface (see, for example, Patent Document 1 below). 【Prior Art Documents】 【Patent Documents】 【0004】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2007-327301 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0005】 However, if an offshore structure is allowed to collapse without taking any measures, for example, the oil and fat content contained in the weight portion may leak into the sea, or the members constituting the weight portion may scatter into the sea. As a result, there is a problem that the environmental load increases. 【0006】 The present disclosure has been made to solve the above problems, and an object thereof is to provide a cover member capable of reducing the environmental load and a method for removing an offshore structure. 【Means for Solving the Problems】 【0007】 To solve the above problems, the cover member according to the present disclosure is a cover member that is attached when a marine structure having a columnar portion fixed to the seabed and extending upward, and a weight portion provided at the upper end of the columnar portion is to collapse, wherein the cover member has a main surface portion that faces the water surface when the marine structure collapses toward the water surface, and a first cover member that covers at least a part of the weight portion. 【0008】 The method for removing a marine structure according to this disclosure is a method for removing a marine structure to which the above-mentioned cover member is attached is to be collapsed into the water, and includes the steps of: attaching the cover member to the marine structure; cutting the base of the columnar portion; and using the base of the cut columnar portion as a fulcrum, collapsing the marine structure from the main surface side toward the water surface. [Effects of the Invention] 【0009】 This disclosure provides a cover member that can reduce environmental impact, and a method for removing offshore structures. [Brief explanation of the drawing] 【0010】 [Figure 1] This is a longitudinal cross-sectional view showing the configuration of a marine structure and a cover member according to the first embodiment of this disclosure. [Figure 2] This flowchart shows the steps of the method for removing a marine structure according to the first embodiment of this disclosure. [Figure 3] This is a longitudinal cross-sectional view showing a first modified example of a cover member according to the first embodiment of this disclosure. [Figure 4] This is a longitudinal cross-sectional view showing a second modified example of the cover member according to the first embodiment of this disclosure. [Figure 5] This is a longitudinal cross-sectional view showing a third modified example of the cover member according to the first embodiment of this disclosure. [Figure 6] This is a longitudinal cross-sectional view showing an example in which a cover member is applied to a sea lighthouse, which is a sea structure according to the second embodiment of this disclosure. [Figure 7]This is a longitudinal cross-sectional view showing an example in which a cover member is applied to an offshore wind turbine as a marine structure according to the third embodiment of this disclosure. [Modes for carrying out the invention] 【0011】 <First Embodiment> Hereinafter, the offshore structure 1, the cover member 2, and the method for removing the offshore structure 1 using the same according to the first embodiment of this disclosure will be described with reference to Figures 1 and 2. 【0012】 (Composition of offshore structures) In this embodiment, the offshore structure 1 refers to a tower-like structure constructed on the ocean, such as a lighthouse, oil drilling rig, steel tower, or offshore wind turbine. To illustrate these schematically, the offshore structure 1 will be described below as having a columnar section 11 and a weight section 12. As shown in Figure 1, the columnar section 11 has its lower end fixed to the seabed and its upper end protruding above the water surface. The columnar section 11 extends in the vertical direction. The weight section 12 is fixed to the upper end of the columnar section 11. The weight section 12 is a member that has a greater weight than the columnar section 11. In the example in Figure 1, the columnar section 11 is a columnar shape extending in the vertical direction, and the weight section 12 is, for example, a rectangular parallelepiped. Note that the shape of the weight section 12 is not limited to a rectangular parallelepiped, and various shapes can be adopted depending on the use, purpose, and function of the offshore structure 1. 【0013】 (Construction of the cover component) The cover member 2 is a component that protects the offshore structure 1 itself from the impact force when it enters the water when the offshore structure 1 is to collapse toward the water surface. The cover member 2 has a first cover member 21 that covers at least a portion of the heavy part 12 from the outside with gaps in between, and a sheet member 22. 【0014】 The first cover member 21 has a main surface portion 31 which is the surface facing the water surface when the marine structure 1 collapses towards the water surface, and a cylindrical portion 32 which is integrally formed with the main surface portion 31 and covers the weight portion 12 from the vertical and horizontal directions. That is, the main surface portion 31 faces one of the side surfaces of the weight portion 12 with a gap therebetween. The cylindrical portion 32 extends horizontally from the edge of the main surface portion 31. Also, the cylindrical portion 32 extends only to the midpoint position of the extending dimension of the weight portion 12 in the horizontal direction. These weight portion 12 and cylindrical portion 32 are integrally formed of a metal such as a steel material, CFRP (Carbon Fiber Reinforced Plastics), GFRP (Glass Fiber Reinforced Plastics), or the like. 【0015】 The sheet member 22 is a member that covers the portion on the opposite side of the above-described main surface portion 31. As an example, the sheet member 22 has a bag shape connected to the edge of the cylindrical portion 32. As the sheet member 22, for example, a sheet-like member formed of a resin or cloth is preferably used. That is, the sheet member 22 can be freely deformed according to the contour shape of the weight portion 12. Also, it is desirable that the sheet member 22 has the performance (waterproofness) of not allowing water to penetrate. 【0016】 The first cover member 21 is supported by a support member 33 connected to a structural member (not shown) provided inside the weight portion 12. That is, one end of the support member 33 is fixed to the structural member, and the other end is fixed to the inner surface of the first cover member 21. The space formed between the first cover member 21 and the weight portion 12 may be filled with a cushioning material such as a foamed resin or rubber. 【0017】 (Method for removing a marine structure) Next, a method for removing the marine structure 1 will be described with reference to FIG. 2. As shown in the figure, this removal method includes a step S1 of attaching the cover member 2 (first cover member 21), a step S2 of cutting the columnar portion 11, and a step S3 of collapsing the columnar portion 11. 【0018】 In step S1, a part of the weight part 12 is covered from the outside by the first cover member 21. Specifically, the first cover member 21 is fixed to the weight part 12 by the support member 33 described above. At this time, it is desirable that the portion covered by the first cover member 21 is appropriately selected as a portion that is relatively strong against the impact when colliding with the water surface. Also, at this time, the remaining portion of the weight part 12 is covered by the sheet member 22 described above. Subsequently, in step S2, the columnar part 11 is cut along the cut surface X near the base of the columnar part 11 (it may be above or below the water surface). Then, in step S3, the columnar part 11 and the weight part 12 are toppled so that the main surface part 31 described above faces the water surface side. Finally, the marine structure 1 after toppling is towed to land by a tugboat or the like. Or, the marine structure 1 is loaded onto a ship and transported to land. Thus, all the steps related to the method for removing the marine structure 1 are completed. 【0019】 (Function and effect) Here, when removing the marine structure 1, it was common to adopt a method of cutting the columnar part 11 from the base and simply toppling it onto the water surface. However, if the marine structure 1 is toppled without taking any measures, for example, the weight part 12 may be damaged by the impact, and the oil and fat content contained in the weight part 12 may leak into the sea, or the members constituting the weight part 12 may scatter into the sea. As a result, there was a problem that the load on the marine environment would increase. Therefore, the cover member 2 described above is used in this embodiment. 【0020】 According to the above configuration, at least a portion of the weight section 12 is covered by a first cover member 21 having a main surface portion 31. As a result, when the weight section 12 collides with the water surface from the main surface portion 31 side when the offshore structure 1 is to collapse, the first cover member 21 comes into contact with the water first, thereby mitigating the impact on the weight section 12. In particular, a gap is formed between the first cover member 21 and the weight section 12. This makes it difficult for the impact force upon hitting the water to be directly transmitted to the weight section 12 itself. Therefore, the probability of damage to the weight section 12 is reduced, and the possibility of large and small parts constituting the weight section 12 scattering into the sea or pollutants such as oils contained inside leaking into the sea can be reduced. Consequently, it becomes possible to remove the offshore structure 1 without burdening the marine environment. 【0021】 Furthermore, with the above configuration, the surface of the cover member 2 opposite to the main surface portion 31 is open, which reduces the amount of material required to manufacture the cover member 2. Therefore, it is possible to lower the manufacturing cost by the amount of material that would otherwise be required for the opening. As a result, the cost required to remove the offshore structure 1 can be reduced. In addition, since the opening is covered with the sheet member 22, it is possible to reduce the risk of seawater entering the interior of the cover member 2 through the opening after the offshore structure 1 is collapsed. In other words, since the heavy portion 12 is sealed by the cover member 2 and the sheet member 22, it is possible to prevent seawater from entering the interior and oil and grease from leaking to the outside. This makes it possible to further reduce the possibility of marine pollution. 【0022】 Furthermore, according to the above removal method, since at least a portion of the offshore structure 1 is covered by the cover member 2, when the offshore structure 1 is to collapse, the impact is mitigated by the cover member 2 when the heavy part 12 hits the water surface from the main surface 31 side. This reduces the possibility of parts of the heavy part 12 scattering into the sea or pollutants such as oil contained inside leaking into the sea. In addition, this eliminates the need to lay oil fences or the like around the offshore structure 1 before and after removal, making it possible to remove the offshore structure 1 easily and inexpensively. 【0023】 The first embodiment of this disclosure has been described above. It is possible to make various changes and modifications to the above configuration and method without departing from the gist of this disclosure. 【0024】 As a first modification, as shown in Figure 3, the cover member 2 can also be configured to further include a cone member 23 in addition to the first cover member 21. The cone member 23 is integrally provided on the main surface portion 31 of the first cover member 21 and protrudes from the main surface portion 31 in the direction normal to the main surface portion 31. The direction normal to the main surface portion 31 is the direction perpendicular to the outer surface of the main surface portion 31, and when the main surface portion 31 is curved, it coincides with the direction in which it enters the water surface when the offshore structure 1 collapses. Viewed from this direction normal to the main surface portion 31, the cross-sectional area of ​​the cone member 23 gradually decreases as it moves away from the main surface portion 31. In other words, the cone member 23 is pointed. With this configuration, by providing the pointed cone member 23 on the main surface portion 31 side, the entry speed of the cone member 23 into the water surface can be gradually reduced. In other words, after the tip of the cone member 23 touches the water, the cross-sectional area of ​​the part that is submerged in the water gradually increases, causing the water resistance to gradually increase and the entry speed to gradually decrease. As a result, the impact of the water hitting the heavy part 12 is mitigated, and the heavy part 12 can be protected more stably. 【0025】 As a second modification, as shown in Figure 4, the cover member 2 may also have a configuration in which, in addition to the first cover member 21, a second cover member 24 is further included. The second cover member 24 covers a part of the columnar portion 11 from the outside, rather than the weight portion 12. In other words, the second cover member 24 is semi-cylindrical in shape to match the cross-sectional shape of the columnar portion 11. A gap may be formed between the second cover member 24 and the columnar portion 11, or they may be in close contact. If a gap is formed, a cushioning material may be filled into the gap, as in the case of the first cover member 21. With this configuration, since the columnar portion 11 is covered by the second cover member 24, damage to the columnar portion 11 due to impact with the water surface when the offshore structure 1 is collapsed can be avoided. As a result, the original shape of the columnar portion 11 is maintained as much as possible, and the possibility of floating debris being generated in the sea can be reduced. 【0026】 Furthermore, as a third modification, as shown in Figure 5, the cover member 2 can also be configured to have a bulging member 25 in addition to the first cover member 21 and the second cover member 24. The bulging member 25 extends from the upper end of the first cover member 21 to the lower end of the second cover member 24. The bulging member 25 protrudes in a curved shape so as to be convex from the main surface portion 31 side of the first cover member 21, thereby forming a space between the first cover member 21 and the second cover member 24. Moreover, it is desirable that the radius of curvature of the bulging member 25 decreases as it goes downwards and increases as it goes upwards. With this configuration, when the offshore structure 1 collapses, the bulging member 25 first touches the water surface, and then the collapse progresses as it rolls on the water surface. In particular, when the radius of curvature of the bulging member 25 is set as described above, in the initial stages of collapse, the bulging member 25 tends to immediately roll in the direction of collapse based on the small radius of curvature. Therefore, the possibility of damage occurring due to impact being transmitted to the offshore structure 1 itself is greatly reduced. Furthermore, because a space is formed between the bulging member 25 and the cover member 2, a large buoyancy is generated, allowing the offshore structure 1 to float stably on the water surface after it has collapsed. This makes subsequent towing operations and other processes smoother. As a result, the efficiency of the removal work and the cost reduction can be achieved. 【0027】 <Second Embodiment> Next, a second embodiment of the present disclosure will be described with reference to Figure 6. Components similar to those in the first embodiment described above are denoted by the same reference numerals, and detailed descriptions are omitted. 【0028】 As shown in Figure 6, in this embodiment, the above-described cover member 2 is applied to a lighthouse 50 at sea as a specific example of a marine structure 1. The lighthouse 50 has a base portion 51 as a columnar portion 11 and a lighthouse body portion 52 as a weight portion 12 provided at the upper end of the base portion 51. A light source such as a searchlight is arranged inside the lighthouse body portion 52. The base portion 51 is fixed to the seabed. 【0029】 Figure 6 shows an example in which the first cover member 21 is attached to the lighthouse body 52. ​​With this configuration, by cutting the base 51 near the root, the lighthouse 50 can be stably collapsed with a low environmental impact, with the same effects as described in the first embodiment. 【0030】 The second embodiment of this disclosure has been described above. It is possible to make various changes and modifications to the above configuration without departing from the gist of this disclosure. For example, the sheet member 22, second cover member 24, cone member 23, and bulging member 25 described in the first embodiment and each of the modified examples can be appropriately combined and applied to the lighthouse 50 of this embodiment. 【0031】 <Third Embodiment> Next, a third embodiment of this disclosure will be described with reference to Figure 7. Note that components similar to those in the above embodiments are denoted by the same reference numerals, and detailed descriptions are omitted. 【0032】 As shown in Figure 7, in this embodiment, the above-described cover member 2 is applied to a wind turbine 60 at sea as a specific example of the offshore structure 1. The wind turbine 60 has a columnar section 11, a nacelle 61 fixed to the upper part of the columnar section 11, and a propeller 62 fixed to the end of a shaft extending from the nacelle 61. The propeller 62 has a plurality of blades 63 that extend radially from the shaft and are arranged at intervals in the circumferential direction. The nacelle 61 and the propeller 62 constitute the weight section 12. 【0033】 In the example shown in Figure 7, the first cover member 21 is attached to the nacelle 61. A hole 34 is formed in the edge of the first cover member 21 opposite to the main surface portion 31 (the edge of the cylindrical portion 32), through which each blade 63 is inserted. It is desirable that a sealing member (not shown) be provided between the inner circumferential surface of this hole 34 and the surface of the blade 63. With this configuration, by cutting the columnar portion 11 near the base, the wind turbine 60 can be stably collapsed with a low environmental impact, with the same effects as described in the first embodiment. 【0034】 The third embodiment of this disclosure has been described above. It is possible to make various changes and modifications to the above configuration without departing from the gist of this disclosure. For example, the sheet member 22, second cover member 24, cone member 23, and bulging member 25 described in the first embodiment and each of the modified examples can be appropriately combined and applied to the lighthouse 50 of this embodiment. Furthermore, in addition to the nacelle 61, the blade 63 can also be covered by the first cover member 21. 【0035】 <Note> The method for removing the cover member 2 and the offshore structure 1 described in each embodiment can be understood, for example, as follows. 【0036】 (1) The cover member 2 according to the first embodiment is a cover member 2 that is attached when a marine structure 1 having a columnar portion 11 fixed to the seabed and extending upward, and a weight portion 12 provided at the upper end of the columnar portion 11 is to collapse, wherein the cover member 2 has a main surface portion 31 that faces the water surface when the marine structure 1 collapses toward the water surface, and a first cover member 21 that covers at least a part of the weight portion 12 from the outside with a gap in between. 【0037】 With the above configuration, at least a portion of the weight section 12 is covered by the first cover member 21 having a main surface portion 31. Therefore, when the weight section 12 collides with the water surface from the main surface portion 31 side when the offshore structure 1 is to collapse, the impact is mitigated by the first cover member 21. This reduces the possibility of parts of the weight section 12 being scattered into the sea or contaminants such as oils contained inside leaking into the sea. 【0038】 (2) The cover member 2 according to the second embodiment is the cover member 2 of (1), wherein the cover member 2 further comprises a second cover member 24 that covers the columnar portion 11. 【0039】 With the above configuration, since the columnar portion 11 is covered by the second cover member 24, damage to the columnar portion 11 can be avoided when the offshore structure 1 is collapsed. This reduces the possibility of floating debris being generated in the sea. 【0040】 (3) The cover member 2 according to the third embodiment is the cover member 2 of (1) or (2), wherein the first cover member 21 comprises a first cover member 21 body having the main surface portion 31, and a cone member 23 that protrudes from the main surface portion 31 and whose cross-sectional area as viewed from the normal direction of the main surface portion 31 gradually decreases as it moves away from the main surface portion 31. 【0041】 With the above configuration, the cone member 23 is provided on the main surface portion 31 side, which allows the entry speed of the cone member 23 into the water surface to be gradually reduced. This reduces the impact of water contact transmitted to the weight portion 12, thereby providing stable protection for the weight portion 12. 【0042】 (4) The cover member 2 according to the fourth embodiment is a cover member 2 according to any one embodiment of (1) to (3), wherein the cover member 2 further has a sheet-like member that covers an opening formed on the surface facing the opposite side from the main surface portion 31. 【0043】 According to the above configuration, since the side of the cover member 2 opposite to the main surface portion 31 is open, the amount of material required to manufacture the cover member 2 is reduced, making it possible to significantly lower manufacturing costs. Furthermore, since the opening is covered with the sheet member 22, it is possible to reduce the risk of seawater entering the interior of the cover member 2 through the opening after the offshore structure 1 collapses. 【0044】 (5) The cover member 2 according to the fifth embodiment is the cover member 2 of (2), further comprising a bulging member 25 that extends from the upper end of the first cover member 21 to the lower end of the second cover member 24 and protrudes in a curved shape so as to be convex from the main surface portion 31 side, thereby forming a space between the first cover member 21 and the second cover member 24. 【0045】 According to the above configuration, when the offshore structure 1 is to collapse, the bulging member 25 first touches the water surface, and then the collapse progresses as it rolls across the water surface. As a result, the possibility of the impact being transmitted to the offshore structure 1 itself and causing damage is greatly reduced. Furthermore, because a space is formed between the bulging member 25 and the cover member 2, a large buoyancy is generated, allowing the offshore structure 1 to float stably on the water surface after it has collapsed. 【0046】 (6) A method for removing a marine structure 1 according to the sixth embodiment is a method for removing a marine structure 1 to which a cover member 2 according to any one embodiment of (1) to (5) is attached is to be toppled into the water, the method comprising the steps of: attaching the cover member 2 to the marine structure 1; cutting the base of the columnar portion 11; and using the base of the cut columnar portion 11 as a fulcrum, topple the marine structure 1 from the main surface portion 31 side toward the water surface. 【0047】 According to the above method, since at least a portion of the offshore structure 1 is covered by the cover member 2, when the offshore structure 1 is to collapse, the impact is mitigated by the cover member 2 when the heavy part 12 hits the water surface from the main surface 31 side. This reduces the possibility of parts of the heavy part 12 being scattered into the sea or contaminants such as oils contained inside leaking into the sea. [Industrial applicability] 【0048】 In the above method of removing the cover member 2 and the offshore structure 1, at least a portion of the offshore structure 1 is covered by the cover member 2. This prevents damage to the offshore structure 1 when it is to collapse into the water, thereby reducing the environmental impact. [Explanation of symbols] 【0049】 1...Maritime structure 2…Cover component 11...Columnar part 12...Parts by weight 21…First cover component 22…Sheet material 23... Cone component 24…Second cover component 25...bulging member 31...Main surface part 32...Cylindrical part 33…Support member 34...hole 50…Lighthouse 51...Base 52...Lighthouse main body 60...Windmill 61… Nasser 62... Propeller 63... Blade X…Cut surface

Claims

[Claim 1] A cover member attached when collapsing a marine structure having a columnar portion fixed to the seabed and extending upward, and a weight portion provided at the upper end of the columnar portion, The cover member has a main surface portion that faces the water surface when the offshore structure collapses toward the water surface, and a first cover member that covers at least a portion of the heavy portion from the outside at intervals. [Claim 2] The cover member according to claim 1, further comprising a second cover member that covers the columnar portion. [Claim 3] The first cover member is The first cover member body having the main surface portion, A cone member that protrudes from the main surface and whose cross-sectional area, as viewed from the normal direction of the main surface, gradually decreases as it moves away from the main surface, A cover member according to claim 1 or 2, having the following characteristics: [Claim 4] The cover member according to claim 1, further comprising a sheet-like member that covers an opening formed on a surface facing the opposite side of the main surface. [Claim 5] The cover member according to claim 2, further comprising a bulging member that extends from the upper end of the first cover member to the lower end of the second cover member and protrudes in a curved shape so as to be convex from the main surface side, thereby forming a space between the first cover member and the second cover member. [Claim 6] A method for removing a marine structure, wherein the marine structure to which the cover member described in claim 1 is attached collapses into the water, The steps include attaching the cover member to the offshore structure, The steps include cutting the base of the columnar portion, The steps include: using the base of the severed columnar portion as a fulcrum to collapse the offshore structure toward the water surface from the main surface side, A method for removing offshore structures, including [specific type of structure].