Construction method of scour prevention structure

Abstract

To provide a construction method of a scour prevention structure capable of efficiently constructing a scour prevention structure with high scour prevention effect using a foot protection unit provided with bags in which filling material is received.SOLUTION: A construction method of a scour prevention structure comprises steps of: with three units 3 at the same suspending level as one unit, setting suspending positions of the respective three units 3 at positions forming a regular triangle; making the gravity centers G of each unit of two of one units in a top view match with each other; suspending each of the units 3 at a time so as to become closer to each other as long as they do not overlap each other; repeating a process of installing each of the units 3 on a water bottom ground B to form a filter layer 2 by bringing a plurality of units 3 adjacent to each other into contact with each other in a top view; suspending a plurality of units 7 at a time so as to become closer to each other as long as they do not overlap each other; and repeating a process of installing each of the units 7 over the units 3 adjacent to each other in a tip view to form an armor layer 6.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for constructing a scour prevention structure, and more specifically, to a method for constructing a scour prevention structure that can efficiently construct a scour prevention structure with high scour prevention effect by using a foot protection unit in which a filling material is contained in a bag body. [Background technology]

[0002] Fixed-bottom offshore wind power generation facilities and the like have monopiles erected on the water bottom. It is known that a scour prevention structure is constructed on the water bottom around an underwater structure erected on the water bottom, such as a monopile (see, for example, Patent Document 1).

[0003] In the method proposed in Patent Document 1, crushed stone is poured into the water bottom ground through a tremie pipe, and the poured crushed stone is leveled to construct a filter layer. Next, a monopile is driven into the water bottom ground by penetrating the filter layer. Next, a large number of crushed stone units (foot protection units) in which crushed stone is filled in a bag are installed on the filter layer, and a scouring prevention structure is constructed by laying a large number of crushed stone units around the monopile. In this scouring prevention structure, adjacent crushed stone units are installed so as to overlap each other when viewed from above. In the process of suspending a plurality of crushed stone units from a hanging jig to install the crushed stone units in this manner, the plurality of crushed stone units are arranged so as to overlap each other when viewed from above.

[0004] In the above-mentioned method, if the multiple crushed stone units that are suspended do not reach the bottom at the same time, the center of gravity of the suspended units will change, and the positions of the other crushed stone units in a top view relative to the crushed stone unit that first reached the bottom will also change, causing a change in the bottom landing position. Therefore, if the multiple crushed stone units are arranged so as to overlap each other in a top view when suspended, there is a concern that the amount of overlap between the crushed stone units will be excessive or excessive gaps will be generated when the units are installed on the bottom ground (filter layer). In the invention proposed in Patent Document 1, it is not essential to install a filter layer under the crushed stone units (paragraph 0104 of Patent Document 1), so if a filter layer is not formed, gaps will be generated between the crushed stone units, reducing the scouring prevention effect. On the other hand, when a filter layer is formed, a large-scale leveling operation is required to level the crushed stone that has been put into the bottom ground, which is an obstacle to improving work efficiency. Therefore, when constructing a scouring prevention structure using a foot protection unit in which a filling material is stored in a bag body, there is room for improvement in order to further improve work efficiency and scouring prevention effect. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2022-19515 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for constructing a scour prevention structure that can efficiently construct a scour prevention structure with high scour prevention effect by using a foot protection unit in which a filling material is contained in a bag body. [Means for solving the problem]

[0007] In order to achieve the above object, the method for constructing a scour prevention structure of the present invention is a method for constructing a scour prevention structure having a filter layer and an armor layer laminated on this filter layer around an underwater structure erected on a water bottom ground, in which, when forming the filter layer, a filter layer footing unit having a filling material contained in a bag body is used, and a plurality of the filter layer footing units are hung at the same time by a hanging frame in such a manner that they are close to each other in a range where they do not overlap each other when viewed from above, and the steps of installing each of the filter layer footing units on the water bottom ground are repeated, and a large number of the filter layer footing units are installed on the water bottom ground with adjacent ones in contact with each other when viewed from above, and the filter layer footing units hung at one time are three filter layer footing units at the same hanging level. The method is characterized in that a filter layer is treated as one unit, and the hanging positions of each of the filter layer root strengthening units in each unit are set to positions that form an equilateral triangle when viewed from above, and at least one unit is hung at a time.When multiple units are hung at once, the center of gravity positions of each unit when viewed from above are aligned.When forming the armor layer, an armor layer root strengthening unit in which a filling material is contained in a bag is used, and multiple armor layer root strengthening units are hung at once by a hanging frame in close proximity to each other but not overlapping when viewed from above.The process of installing each armor layer root strengthening unit on the filter layer is repeated, and a large number of armor layer root strengthening units are installed on the filter layer so that they straddle adjacent filter layer root strengthening units when viewed from above. Effect of the Invention

[0008] According to the present invention, the filter layer and the armor layer are formed using the footing units, so that large-scale leveling work is not necessary, which is advantageous for efficiently constructing a scour prevention structure. In addition, a plurality of the filter layer footing units are hung at the same time in a range where they do not overlap each other when viewed from above, and the filter layer footing units hung at the same time are set to a position that forms an equilateral triangle when viewed from above, with three filter layer footing units at the same hanging level as one unit, and when a plurality of the units are hung at the same time, the center of gravity positions of the respective units when viewed from above are made to coincide with each other, so that even if the respective footing units hung at the same time do not reach the bottom at the same time, it is easy to stabilize the center of gravity position as viewed from above of the hanging footing units as a whole. Therefore, in the formed filter layer, the variation in the amount of overlap between the adjacent filter layer footing units can be suppressed. Accordingly, it is possible to prevent an excessively large gap from being generated between the adjacent filter layer footing units. Furthermore, since the armor layer footing unit is installed on the filter layer so as to straddle the adjacent filter layer footing units in a top view, even if a gap is generated between the adjacent filter layer footing units, the armor layer footing unit can close the gap. Therefore, it is possible to obtain a high scouring prevention effect. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram illustrating a front view of a scour prevention structure constructed according to the present invention. [Diagram 2] 2 is an explanatory diagram illustrating the scour prevention structure of FIG. 1 as viewed from above. [Diagram 3] 3A is an explanatory diagram illustrating an example of a root reinforcement unit, where FIG. 3A illustrates a front view of the unit placed on a flat surface, FIG. 3B illustrates a top view of the unit placed on a flat surface, and FIG. 3C illustrates a front view of the unit suspended from the ground. [Figure 4]FIG. 13 is an explanatory diagram illustrating the arrangement of a suspended filter layer root fixing unit from a front view. [Diagram 5] 5 is an explanatory diagram illustrating the arrangement of the foot fixing unit in FIG. 4 from a top view. FIG. [Figure 6] 5 is an explanatory diagram illustrating the state in which the foot fixing unit of FIG. 4 has been seated on the bottom. [Figure 7] 7 is an explanatory diagram illustrating the foot fixing unit of FIG. 6 as viewed from above. [Figure 8] FIG. 4 is an explanatory diagram illustrating the formed filter layer as viewed from the front. [Figure 9] 9 is an explanatory diagram illustrating the filter layer of FIG. 8 as viewed from above. [Figure 10] FIG. 9 is an explanatory diagram illustrating a front view of a monopile driven into the waterbed ground of FIG. 8. [Figure 11] FIG. 11 is an explanatory diagram illustrating the monopile and filter layer of FIG. 10 as viewed from above. [Figure 12] An explanatory diagram illustrating an armor layer formed on a filter layer from a top view. [Figure 13] An explanatory diagram illustrating the arrangement of suspended armor layer root reinforcement units from a front view. [Figure 14] 14 is an explanatory diagram illustrating the arrangement of the foot fixing unit in FIG. 13 from a top view. FIG. [Figure 15] 14 is an explanatory diagram illustrating the state in which the foot protection unit of FIG. 13 has been seated on the bottom. FIG. [Figure 16] 16 is an explanatory diagram illustrating the foot fixing unit of FIG. 15 as viewed from above. FIG. [Figure 17] FIG. 13 is an explanatory diagram illustrating a modified example of the arrangement of a suspended filter layer root fixing unit from a front view. [Figure 18] 18 is an explanatory diagram illustrating the arrangement of the foot fixing unit in FIG. 17 from a top view. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, a method for constructing a scour prevention structure of the present invention will be described based on the embodiment shown in the drawings.

[0011] The scour prevention structure 1 illustrated in Figures 1 and 2 is constructed according to the present invention. This scour prevention structure 1 has a filter layer 2 and an armor layer 6 laminated on the filter layer 2, and is formed so as to cover the periphery of a monopile (underwater structure) 14 erected on the water bottom ground B. Examples of the underwater structure 14 include pile-shaped bodies such as monopile structures and jacket-type structures that constitute bottom-mounted offshore wind power generation facilities, and support piles erected on the water bottom ground B to support various structures.

[0012] The filter layer 2 is installed mainly for the purpose of preventing scouring of the bottom ground B (preventing the suction of ground soil). The armor layer 6 is installed mainly for the purpose of preventing the filter layer 2 from moving due to tides, etc. (functioning as a weight).

[0013] The filter layer 2 is formed by a number of filter layer footing units 3 (hereinafter referred to as units 3) as shown in Fig. 3, and the armor layer 6 is formed by a number of armor layer footing units 7 (hereinafter referred to as units 7). As shown in Fig. 3, the unit 3 is configured by containing a filler material 5 in a bag body 4. The unit 7 is also configured by containing a filler material 9 in a bag body 8.

[0014] Stones such as broken granite (JIS G 5006) or equivalent materials are used for the filling materials 5, 9. Mesh bags made of synthetic or natural fibers are used for the bags 4, 8. Locking parts 4a, 8a are attached to the upper ends of the bags 4, 8. The main difference between the units 3 and 7 is the size, and the unit 7 is larger than the unit 3. As illustrated in Figs. 3A and 3B, when placed on a flat surface in an unloaded state, the units 3, 7 are circular in top view, and the unit 3 has an outer diameter D1 of, for example, 1.5m to 2.5m and a height H1 of, for example, 0.5m to 0.8m, and the unit 7 has an outer diameter D1 of, for example, 2.5m to 3.5m and a height H1 of, for example, 0.8m to 1m. The size of the units 3, 7 is appropriately set according to the on-site marine environmental conditions, the state of the bottom ground B, the size of the underwater structure 14, and the like, and is not limited to the illustrated size.

[0015] As illustrated in Fig. 3C, when the units 3 and 7 are suspended via the locking portions 4a and 8a, the bags 4 and 8 extend in the vertical direction due to the weight of the inner filling materials 5 and 9. Therefore, it has been confirmed that the height H2 of the units 3 and 7 becomes larger (H2 > H1) and the outer diameter D2 in the top view becomes smaller (D2 < D1) compared to when they are placed flat. In the process of forming the filter layer 2, a plurality of units 3 are suspended via their respective locking portions 4a at one time, and in the process of forming the armor layer 6, a plurality of units 7 are suspended via their respective locking portions 8a at one time.

[0016] Specifically, as illustrated in Figs. 4 and 5, a plurality of suspension cables 11 are connected to a suspension frame 10 connected to a suspension wire 13. Hooks 12 are connected to the lower ends of the respective suspension cables 11. By locking the locking portion 4a of one unit 3 (3A, 3B) to one hook 12, the unit 3 is suspended. As the hook 12, various known specifications that can release the locking with the locking portion 4a by an operation from above the water are adopted. The suspension wire 13 is paid out and wound by the operation of a crane. The unit 7 is also suspended in the same manner as the unit 3.

[0017] Next, an example of the procedure for constructing this scour prevention structure 1 will be described.

[0018] First, after forming the filter layer 2 using the unit 3 on the underwater ground B, the monopile 14 is driven into the underwater ground B through the filter layer 2. Then, one or more layers of the armor layer 6 are formed using the unit 7 on the filter layer 2, and the scour prevention structure 1 is completed. For installing the units 3 and 7, a crane mounted on a barge or the like is used, for example.

[0019] When forming the filter layer 2, as illustrated in Figures 4 and 5, a plurality of units 3 are hung at once using a hanging frame 10 so that they are close to each other but do not overlap when viewed from above, and the process of installing them on the water bottom ground B is repeated until many units 3 are installed on the water bottom ground B with adjacent units 3 in contact with each other when viewed from above. The state in which the suspended units 3 are close to each other but do not overlap when viewed from above means that the gap (minimum gap) between adjacent units 3 when viewed from above is, for example, more than 0 cm and less than 10 cm.

[0020] The units 3 hung at one time are three units 3 at the same hanging level, which form one unit. In this unit, the hanging positions of the units 3 are set to positions that form an equilateral triangle when viewed from above. At least one unit is hung at a time. When multiple units are hung at once, the center of gravity G of each unit when viewed from above is made to coincide with each other.

[0021] In this embodiment, two units are hung at the same time. That is, one unit composed of three units 3A and one unit composed of three units 3B are hung at the same time. The dashed line illustrated in FIG. 5 connects the hanging positions of the three units 3A constituting one unit in a top view. This dashed line forms an equilateral triangle, and the center of gravity G of this unit in a top view is shown. The two-dot chain line illustrated in FIG. 5 connects the hanging positions of the three units 3B constituting the other unit in a top view. This dashed line forms an equilateral triangle, and the center of gravity G of this unit in a top view is shown. The center of gravity G of the two units in a top view is the same. The center of gravity G of each unit is the same means that the distance between the center of gravity G of each unit in a top view is within 5 cm, for example, and the center of gravity G is substantially the same.

[0022] When multiple units are hung at once, the center of gravity G of each unit in top view should be aligned, and the units 3 should be close to each other without overlapping each other in top view. The number of units 3 hung at once is not particularly limited, but is about three to twelve. In this embodiment, the equilateral triangle formed by the hanging positions of each unit in top view is rotated 180° around the center of gravity G. That is, the equilateral triangle formed by the hanging positions of one unit (units 3A, 3A, 3A) in top view and the equilateral triangle formed by the hanging positions of the other unit (units 3B, 3B, 3B) in top view are oriented in opposite directions around the center of gravity G, and six units 3 are hung at once.

[0023] The hanging level is the hanging length of the units 3 from the hanging frame 10. In other words, it is the vertical position of the lowest point of the units 3 in a hanging state. And the same hanging level means that the vertical positions of the lowest points of the units 3 in a hanging state are substantially the same (within ±10 cm).

[0024] When multiple units are suspended at once, it is preferable to make the suspension level of the unit 3 different for each unit. In this embodiment, the suspension level of the unit 3A of one unit is lower than the suspension level of the unit 3B of the other unit. The difference S in the suspension level between the units adjacent vertically is, for example, about 0.3 m to 0.5 m. In this embodiment, two units with different suspension levels are used, but three or four units with different suspension levels can also be used.

[0025] As shown in Figures 6 and 7, each unit 3 suspended at one time is landed on the water bottom ground B by moving the suspension frame 10 downward. This allows each unit 3 to be installed on the water bottom ground B with adjacent units in contact when viewed from above. Adjacent units 3 that have been installed are butt-butted and in contact, and more preferably are in contact with each other with some units overlapping vertically.

[0026] In this embodiment, the units 3 suspended at one time are grouped into one unit of three units 3 at the same suspension level, and the suspension positions of each unit are set to positions that form an equilateral triangle in top view. The units 3 suspended at one time are suspended by the suspension frame 10 close to each other without overlapping each other in top view, so that the units 3 suspended at one time are closely spaced in top view. Therefore, when installed on the water bottom ground B, the gap between adjacent units 3 in top view can be minimized, and excessive overlap between the units 3 can be avoided.

[0027] When the unit 3 hits the bottom, the weight of the unit 3 no longer acts on the suspension frame 10, so the balance of the suspension frame 10 is lost and it becomes easy to swing. As a result, it is disadvantageous to arrange the unit 3 at a desired position. In this embodiment, the units 3 to be suspended at one time are set as one unit of three units 3 at the same suspension level, and the suspension positions of each unit 3 are set to positions that form an equilateral triangle in a top view. Therefore, even if each unit 3 of one unit does not hit the bottom at the same time, the other units 3 of this unit can be immediately hit the bottom and the suspension frame 10 can be prevented from swinging significantly. Therefore, since each unit 3 can be easily arranged at a desired position, it is advantageous to construct a scour prevention structure 1 having an excellent scour prevention effect.

[0028] In this embodiment, one unit (units 3A, 3A, 3A) and the other unit (units 3B, 3B, 3B) land on the bottom in sequence. The center of gravity positions G of one unit (units 3A, 3A, 3A) and the other unit (units 3B, 3B, 3B) in top view coincide with each other. Therefore, even when one unit has landed on the bottom and the other unit has not yet landed on the bottom, the center of gravity position G in top view hardly changes compared to before one unit landed on the bottom, so that the hanging frame 10 can be prevented from swinging significantly.

[0029] In this embodiment, one unit (units 3A, 3A, 3A) is disposed closer to the center of gravity G in a top view than the other unit (units 3B, 3B, 3B), and is disposed in a narrower range. If the units 3B, 3B, 3B are disposed in a wider range, as in the other unit (units 3B, 3B, 3B), they are difficult to reach the bottom at the same time. In other words, the units 3A, 3A, 3A of one unit, which are disposed in a narrower range, are easily allowed to reach the bottom at the same time. Therefore, when suspending a plurality of units with different suspension levels, in order to suppress the swinging of the suspension frame 10, it is preferable to first allow the unit disposed in a narrower range to reach the bottom. Therefore, when suspending at once, it is preferable that the unit to be suspended at the lowest suspension level is the unit (units 3A, 3A, 3A) disposed in the narrowest range in a top view, as in this embodiment.

[0030] After each unit 3 is installed on the water bottom ground B, the hooks 12 engaged with the respective engaging portions 4a are released by an operation from above the water. The units 3 are installed starting from an area close to the preset driving position of the monopile 14 and proceeding toward an area farther away. Since the driving position of the monopile 14 is stored in the computing device, the position of each unit 3 as viewed from above is adjusted based on the data of the driving position, and the unit 3 is installed on the water bottom ground B. In this way, as illustrated in Figures 8 and 9, a circular filter layer 2 is formed with the driving position of the monopile 14 at the center as viewed from above. The shape of the filter layer 2 as viewed from above is not limited to a circle. The installation positions of each unit 3 may be stored in the computing device.

[0031] Next, as shown in Figures 10 and 11, the monopile 14 is driven into the water bottom ground B at a preset driving position, penetrating the filter layer 2. The monopile 14 may be driven into the water bottom ground B by a known method. Note that in Figure 10, the unit 3 is omitted, as in Figure 2.

[0032] Next, the armor layer 6 illustrated in Fig. 12 is formed. When forming the armor layer 6, as illustrated in Figs. 13 and 14, a plurality of units 7 are hung at once by a suspension frame 10 in such a manner that they are close to each other but do not overlap each other when viewed from above, and the process of installing each unit 7 on the filter layer 2 is repeated to install a large number of units 7 on the filter layer 2. Each unit 7 is installed so as to straddle adjacent units 3 when viewed from above, forming one to multiple armor layers 6.

[0033] The state in which the suspended units 7 are close enough to each other so as not to overlap when viewed from above means that the gap (minimum gap) between adjacent units 7 when viewed from above is, for example, about 50 cm. Since the main purpose of the units 7 is to prevent the units 3 from moving, the gap between adjacent units 7 suspended at one time can be set slightly larger when viewed from above compared to the units 3 suspended at one time. When units 7 overlap each other, excessive gaps tend to form above and below, so it is preferable to arrange adjacent units 7 in contact with each other so as to butt against each other.

[0034] In this embodiment, four units 7 at the same suspension level are suspended at once, and the suspension positions of each unit 7 are set to positions that form a diamond when viewed from above. That is, when the suspension positions of each unit 7 are connected when viewed from above, a diamond (a shape formed by connecting two adjacent equilateral triangles) is formed. The number of units 7 suspended at once is not limited to four, and for example, three units 7 may be suspended at once close to each other without overlapping each other when viewed from above, and the suspension positions of each unit 7 when viewed from above may be set to positions that form an equilateral triangle when viewed from above.

[0035] The units 7 suspended at one time can have different suspension levels, but as in this embodiment, the suspension levels may be the same. The number of units 7 suspended at one time is not particularly limited, but is about two to eight. In this embodiment, the suspension frame 10 for suspending the units 3 and the suspension frame 10 for suspending the units 7 are separate from each other, but they can also be shared.

[0036] As shown in Figs. 15 and 16, each unit 7 suspended at one time is landed on the filter layer 2 by moving the suspension frame 10 downward. In this way, each unit 7 is installed on the filter layer 2 so as to straddle adjacent units 3 when viewed from above. It is preferable that adjacent units 7 when installed are butted against each other in top view so as to be in contact with each other. Even if a gap occurs between adjacent units 3 forming the filter layer 2, this gap can be blocked by the units 7. This makes it possible to ensure a high scouring prevention effect.

[0037] After each unit 7 is installed on the filter layer 2, the hooks 12 that are engaged with the respective engaging portions 8a are released by operating from above the water. The units 7 are installed starting from the area close to the monopile 14 and proceeding toward the area farther away. In this way, as exemplified in Figs. 1 and 2, a circular filter layer 2 is formed with the monopile 14 cast position as the center in top view as seen from the outside. If the monopile 14 cast position and the installation positions of each unit 3 are stored in the computing device, the suspended units 7 can be precisely installed so as to straddle adjacent units 3 as seen from above by adjusting the positions as seen from above based on the stored position information.

[0038] According to this embodiment, the filter layer 2 and the armor layer 6 are formed using the above-mentioned units 3 and 7, respectively. The installation positions of the units 3 and 7 can be roughly controlled, so large-scale leveling work is not required. This is advantageous for efficiently constructing the scour prevention structure 1. The units 3 and 7 are less likely to move due to tides and the like compared to individual crushed stones, etc. This is advantageous for maintaining the filter layer 2 and the armor layer 6 for a long period of time. In addition, as described above, the units 3 that are suspended at one time are closely arranged, which is advantageous for quickly forming a high-quality filter layer 2.

[0039] Furthermore, even if the units 3 suspended at one time do not reach the bottom at the same time, the center of gravity G of the suspended units 3 as a whole in a top view can be easily stabilized. Therefore, the swinging of the suspension frame 10 is suppressed, and each unit 3 can be easily installed in a desired position, so that the variation in the amount of overlap between adjacent units 3 in the formed filter layer 2 can be suppressed. Accordingly, the occurrence of excessively large gaps between adjacent units 3 can be prevented. Even if gaps occur between the units 3 forming the filter layer 2, they can be closed by the units 7 installed later. Therefore, the constructed scour prevention structure 1 can obtain a high scour prevention effect.

[0040] As illustrated in FIG. 17 and FIG. 18, a linearly arranged unit group having three units 3C at the same suspension level and the suspension positions of the units 3C are set on a straight line in top view can be added as the units 3 to be suspended at one time. In this embodiment, one unit (units 3A, 3A, 3A) and the other unit (units 3B, 3B, 3B) are suspended from the suspension frame 10 with their center of gravity G aligned in top view. The dashed line illustrated in FIG. 17 connects the suspension positions of the three units 3A constituting one unit in top view. This dashed line forms an equilateral triangle, and the center of gravity G of this unit in top view is shown. The two-dot chain line illustrated in FIG. 18 connects the suspension positions of the three units 3B constituting the other unit in top view. This dashed line forms an equilateral triangle. The suspension level of one unit (units 3A, 3A, 3A) is lower than the suspension level of the other unit (units 3B, 3B, 3B).

[0041] The center of gravity of one linearly arranged unit group (3C, 3C, 3C) is aligned with the center of gravity G of each unit in top view. The suspension level of this linearly arranged unit group (3C, 3C, 3C) is made higher than the suspension levels of the two units. In other words, of the units 3 suspended at one time, the suspension level of the linearly arranged unit group (3C, 3C, 3C) is made the highest. Each of the nine units 3 (3A, 3B, 3C) is suspended at one time by the suspension frame 10 close to each other but not overlapping each other in top view.

[0042] In this way, even when one linearly arranged unit group (3C, 3C, 3C) is added and a plurality of units 3 are suspended at once, similarly to the previous embodiment, the suspension frame 10 is moved downward to land each unit 3 on the water bottom ground B. As a result, each unit 3 is placed on the water bottom ground B with adjacent units in contact with each other when viewed from above, forming the filter layer 2.

[0043] This embodiment also makes it possible to obtain the same effect as the previous embodiment. As shown in Fig. 18, many units 3 are closely arranged based on an equilateral triangle in top view, which is advantageous for minimizing the gap between adjacent units 3 in top view. In addition, the center of gravity G of one unit (units 3A, 3A, 3A), one unit (3B, 3B, 3B), and the linearly arranged unit group (3C, 3C, 3C) in top view coincide with each other, and one unit (units 3A, 3A, 3A) and the other unit (3B, 3B, 3B) land on the bottom in sequence, which can suppress the swinging of the suspension frame 10.

[0044] If the two single units are on the bottom, the swinging of the suspension frame 10 is suppressed to some extent even if the linearly arranged unit group (3C, 3C, 3C) is not on the bottom. Therefore, the linearly arranged unit group (3C, 3C, 3C) with a higher suspension level than the two single units can have a higher degree of freedom in arrangement to some extent.

[0045] 17 and 18 is the same as the hanging frame 10 used to suspend the unit 7 illustrated in Figs. 13 to 15. That is, the hanging frame 10 is shared when suspending the unit 3 and when suspending the unit 7. Sharing the hanging frame 10 is advantageous in minimizing the tools used when constructing the scour prevention structure 1.

[0046] The filter layer 2 may be formed as described above, and the armor layer 6 may be formed by using a tremie pipe or the like to pour crushed stones onto the filter layer 2. In this case, the poured crushed stones are placed on the filter layer 2 so as to fill the gaps between adjacent units 3 when viewed from above.

[0047] The present disclosure includes the following inventions. Invention 1: A method for constructing a scour prevention structure, comprising constructing a scour prevention structure having a filter layer and an armor layer laminated on the filter layer around an underwater structure erected on a water bottom, When forming the filter layer, a filter layer base fixing unit in which a filling material is contained in a bag body is used, and a plurality of the filter layer base fixing units are hung at once by a hanging frame in such a manner that they are close to each other in a range where they do not overlap each other when viewed from above, and the process of installing each of the filter layer base fixing units on the water bottom is repeated, and a large number of the filter layer base fixing units are installed on the water bottom ground by contacting adjacent units when viewed from above, The filter layer root strengthening units to be hung at one time are three filter layer root strengthening units at the same hanging level as one unit, and the hanging positions of each filter layer root strengthening unit are set to positions that form an equilateral triangle when viewed from above, and at least one of the units is hung at one time. When multiple units are hung at one time, the center of gravity positions of the units when viewed from above are aligned with each other. When forming the armor layer, a method for constructing a scouring prevention structure is performed by using an armor layer root reinforcement unit in which filling material is contained in a bag body, suspending a plurality of the armor layer root reinforcement units at one time using a hanging frame in close proximity to each other but not overlapping when viewed from above, and repeating the process of installing each of the armor layer root reinforcement units on the filter layer, thereby installing a large number of the armor layer root reinforcement units on the filter layer so that they straddle adjacent filter layer root reinforcement units when viewed from above. Invention 2: A method for constructing a scouring prevention structure as described in Invention 1, in which, when forming the filter layer, two of the units are hung at once, and the equilateral triangle formed by the hanging positions of each of the filter layer root reinforcement units in one of the units when viewed from above and the equilateral triangle formed by the hanging positions of each of the filter layer root reinforcement units in the other unit when viewed from above are rotated 180° around the aligned center of gravity position in opposite directions. Invention 3: 3. A method for constructing a scour prevention structure according to claim 1 or 2, wherein the suspension level of each of the units is made different. Invention 4: A method for constructing a scouring prevention structure as described in Invention 2 or 3, which includes adding one linearly arranged unit group having three filter layer root reinforcement units of the same suspension level as the filter layer root reinforcement units to be hung at one time, with the suspension positions of each of the filter layer root reinforcement units set in a straight line when viewed from above, and the center of gravity of the group being aligned with the center of gravity of each of the units when viewed from above, and making the suspension level of this linearly arranged unit group higher than the suspension level of each of the units. Invention 5: A method for constructing a scour prevention structure according to any one of Inventions 1 to 4, wherein each of the armor layer foot protection units is installed in contact with adjacent units. [Explanation of symbols]

[0048] 1 Anti-scouring structure 2 Filter Layer 3 (3A, 3B, 3C) Footing unit for filter layer 4 Bag body 4a Locking part 5 Filling material 6 Armor Layers 7 Armor Layer Footing Unit 8 Bag body 8a Locking part 9 Filling material 10 Hanging frame 11 Suspension 12. Hook 13 Suspension wire 14 Monopile (underwater structure) B Underwater ground

Claims

1. A method for constructing a scour prevention structure, comprising constructing a scour prevention structure having a filter layer and an armor layer laminated on the filter layer around an underwater structure erected on a water bottom, When forming the filter layer, a filter layer base fixing unit in which a filling material is contained in a bag body is used, and a plurality of the filter layer base fixing units are hung at once by a hanging frame in such a manner that they are close to each other in a range where they do not overlap each other when viewed from above, and the process of installing each of the filter layer base fixing units on the water bottom is repeated, and a large number of the filter layer base fixing units are installed on the water bottom ground by contacting adjacent units when viewed from above, The filter layer root strengthening units to be hung at one time are three filter layer root strengthening units at the same hanging level as one unit, and the hanging positions of each filter layer root strengthening unit in one unit are set to positions that form an equilateral triangle in a top view, and at least one unit is hung at one time. When multiple units are hung at one time, the center of gravity positions of each unit as viewed from above are aligned with each other. When forming the armor layer, a method for constructing a scouring prevention structure is performed by using an armor layer root reinforcement unit in which filling material is contained in a bag body, suspending a plurality of the armor layer root reinforcement units at one time using a hanging frame in close proximity to each other but not overlapping when viewed from above, and repeating the process of installing each of the armor layer root reinforcement units on the filter layer, thereby installing a large number of the armor layer root reinforcement units on the filter layer so that they straddle adjacent filter layer root reinforcement units when viewed from above.

2. A method for constructing a scouring prevention structure as described in claim 1, wherein when forming the filter layer, two of the units are hung at once, and the equilateral triangle formed by the hanging positions of each of the filter layer root reinforcement units in one of the units when viewed from above and the equilateral triangle formed by the hanging positions of each of the filter layer root reinforcement units in the other unit when viewed from above are rotated 180° around the aligned center of gravity position in opposite directions.

3. 3. The method for constructing a scour prevention structure according to claim 1 or 2, wherein a suspension level is made different for each of the units.

4. A method for constructing a scouring prevention structure as described in claim 3, further comprising adding one linearly arranged unit group having three filter layer root strengthening units of the same suspension level as the filter layer root strengthening units to be hung at one time, the suspension positions of each of the filter layer root strengthening units being set in a straight line when viewed from above, and the center of gravity positions being aligned with the center of gravity positions of each of the units when viewed from above, and the suspension level of this linearly arranged unit group being set higher than the suspension level of each of the units.

5. The method for constructing a scour prevention structure according to claim 1 or 2, wherein each of the armor layer foot protection units is installed in contact with adjacent units.

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