Thin layer covering sand method and covering sand establishment bucket

Abstract

To solve the problem in which molding of thin layer covering sand securing a plan requirement is previously performed on a covering sand unloading bucket, on a covering sand work ship as a large-scale thin layer covering sand method, the bucket is lowered to a sea bottom, an automatic opening / closing type bottom plate is opened, the molded covering sand is quietly unloaded, which proceeds development of a method preventing occurrence of pollution, but as for cost performance, a construction cost of a large-sized covering sand work ship becomes a burden.SOLUTION: In a thin layer covering sand method, a covering sand establishment bucket having an automatic opening / closing type bottom slab has a diving / floating function. The function reduces a buoyancy of a barge integral with the bucket to the self weight of the bucket and the weight of a covering sand material by introduction of sea water, dives the barge, and floats the bucket due to the buoyancy generated by unloading of the covering sand material. The function is operated by only a hydraulic pressure. Cost performance is greatly enhanced, without requiring a large-sized dedicated work ship. In a thin layer covering sand method, a top end of a covering sand material loaded on the covering sand establishment bucket has both scattering of an eelgrass seed package and establishment of an eelgrass bed.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a thin layer sand-capping method, which is a main method for purifying bottom sediment environments such as the seabed, and a sand-capping bucket used for this method.Furthermore, it relates to the development of thin layer sand-capping into the creation of seaweed beds. [Background technology]

[0002] Today, climate change caused by global warming has made it imperative to move towards a decarbonized society. SDG 13 calls for concrete measures to combat climate change, and SDG 14 calls for protecting and sustaining the life of the oceans and seas. Seaweed beds have been shown to reduce carbon dioxide emissions, purify water, and contribute to marine products. Carbon absorbed as carbon dioxide by marine plants living in seaweed beds is called "blue carbon," and the diverse effects of blue carbon are attracting attention.

[0003] Sludge-filled seabeds are widespread throughout Japan's coastal waters. Sludge-filled waters are carbon dioxide emitters. On the other hand, coastal waters with vegetation, such as seagrass beds, are carbon dioxide sinks. Converting these sludge-filled coastal waters into vegetated coastal waters would significantly contribute to climate change countermeasures. Bottom sediment improvement is required to transform these sludge-filled seabeds into seaweed beds. Current bottom sediment improvement methods include dredging and sand-capping. The principle of sand-capping is to contain the sludge and prevent direct contact between the sludge and seawater, thereby preventing the release of harmful chemicals and nutrients that leach from the sludge into the seawater. As eutrophication progresses, large amounts of red tide plankton emerge, eventually dying and sinking. This sludge accumulates on the seabed. Bacteria actively decompose the organic matter in the sludge, consuming large amounts of dissolved oxygen in the water and causing the bottom water to become hypoxic. This vicious cycle continues. The sand covering is intended to maintain good water quality and aquatic ecosystems in the water area.

[0004] Sand-capping methods tend to use thin layers of sand, minimizing the thickness required, in order to reduce public works costs and conserve sand-capping materials. A common challenge for thin-layer sand-capping methods is achieving a uniform and accurate sand thickness. Furthermore, minimizing contamination during construction is essential, especially if the bottom soil is contaminated. The thinner the sand, the more advanced the technology and management required. Traditionally, sand-capping materials were dumped directly from the water surface using backhoes or grab boats. However, in recent years, slit dumping has been introduced, which creates slits in the pollution prevention frame to reduce the impact of the material dumping. Furthermore, a blind sand-capping method has been developed to improve the accuracy of sand thickness. This method involves installing a blind sand-capping device on the side of a sand-spreading barge, spreading and leveling sand in the device, and then opening the bottom of the device to perform sand-capping, aiming to achieve uniform sand-capping. A further development of this method is the slurry-type blind sand-capping method. This involves lowering a blind sand-capping device directly above the sand-capping location in the water, spreading the sand sent in a slurry form evenly over the device, reducing the occurrence of contamination when the sand falls and ensuring that the sand is reliably covered in the designated position (see Non-Patent Document 1).

[0005] Sediment improvement aimed at combating climate change is a large-scale project. To make it sustainable, it is necessary to consider cost-effectiveness while taking the environment into account. In large-scale projects using current construction methods, bottom sludge dredging is a problem due to the lack of final disposal sites. In any case, a major challenge is how to utilize the economies of scale of large-scale projects to improve cost-effectiveness. The ideal thin-layer sand-capping method would minimize the occurrence of pollution and the sinking of the sand into the bottom ground, maintain the planned shape and condition of the thin-layer sand, and construct the thin-layer sand in a short period of time. However, current thin-layer sand-capping methods are only at the stage where they are intended to minimize the occurrence of pollution and spread sand evenly.

[0006] In February 2024, a patent application was filed for a thin layer sand capping method as a new technology for purifying bottom sediment environments such as the seabed, taking into account social and global environmental factors. In this method, a thin layer of sand is formed in a sand capping loading and unloading bucket on board a sand capping work vessel, ensuring the sand configuration, thickness, and density conditions required for the plan. Next, the bucket loaded with the formed sand is lowered to the bottom of the water and gently lands, and the automatic opening and closing bottom plate is opened as the bucket is raised to the height of the sand capping thickness, and the formed sand is gently unloaded. This method does not actually cause the formed sand to fall into the water, suppresses the occurrence of pollution, and maintains the shape and condition of the sand capping, constructing a thin layer of sand in a short period of time (see Patent Document 1).

[0007] Although not a sand-capping method, there are examples of significant reductions in initial costs. This method, for which a patent application was filed in August 2023, involves the use of a submersible soil-carrying vessel to lower soil to the seabed. The background to this method is the existence of numerous large dredged depressions in Tokyo Bay and other areas where soil was extracted for landfill construction. Due to factors such as the occurrence of hypoxic water masses, red tides and blue tides have become chronically more likely to occur. This is believed to be due in part to the large-scale dredged depressions of the past. To improve the marine environment, shallow basin creation projects are underway to backfill these dredged depressions with construction waste soil. The current method involves using a dedicated work vessel equipped with a double-pipe tremie device and a backhoe to lower the soil (construction waste soil) transported by the soil-carrying vessel, creating shallow basins. In contrast, the method of unloading soil using a submersible soil carrier involves a soil carrier loaded with soil and submerging, then turning over at a specified seabed surface to unload the soil, and the empty soil carrier automatically rises to the surface as its buoyancy overcomes gravity, and no dedicated special work vessel is required (see Patent Document 2).

[0008] Although it is not a sand-capping method, there is an example where a work boat moving device is installed. This is a submerged ground upside-down turning method and a dedicated work boat for which a patent application was filed in February 2024. This upside-down turning method was developed as a large-scale bottom sediment improvement method. This method is mounted on a dedicated work boat and uses a turning bucket to vertically rotate the bottom sediment collected in the bucket 180 degrees, making the sludge layer on the surface the lower layer and the good soil layer the upper layer. This method does not require the sludge to be transported outside the work area as in the dredging method, nor does it require the transport of covering material from outside the work area as in the soil-capping method. The dedicated work boat used for this method is equipped with a work boat moving device using a double-acting hydraulic cylinder (see Patent Document 3). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent application 2024-42888 [Patent Document 2] Patent application 2023-139354 [Patent Document 3] Patent application 2024-26982 [Non-patent literature]

[0010] [Non-Patent Document 1] Civil Engineering and Construction Technology Symposium 2003 Proceedings pp.61-68, 2003, Japan Society of Civil Engineers, Thin layer sand covering technology on contaminated bottom sediment "Slurry type blind sand covering method" Summary of the Invention [Problem to be solved by the invention]

[0011] The thin layer sand-capping method, for which a patent application was filed in February 2024, can fully utilize economies of scale to improve cost-effectiveness in large-scale projects. However, in medium-scale projects, the cost of building a sand-capping work vessel becomes a burden. If the initial cost can be significantly reduced, it will be possible to further improve cost-effectiveness in large-scale projects. Furthermore, because the bottom sediment of sludge-filled coastal waters is improved by covering with sand, it is possible to turn these into vegetated coastal waters. If bottom sediment improvement projects using sand covering are carried out in combination with seaweed bed creation projects, the total cost can be significantly reduced. This will make a significant contribution to climate change countermeasures. Challenge 1 is to significantly reduce the initial cost of the thin layer sand-capping method. Challenge 2 is to progress towards a blue carbon project that combines bottom sediment improvement using sand covering with seaweed bed creation. Means for the invention to solve the problems

[0012] The solution to Problem 1 of the present invention is to provide a sand-capping bucket with a bottom plate that is automatically opened and closed with submergence and floating functions. These functions allow the sand-capping bucket to submerge by reducing the buoyancy of the floating barge, which acts as a floating body against the gravity of the weight of the sand-capping bucket itself and the weight of the loaded sand-capping material, by inflowing ballast water, and then the buoyancy overcomes and the sand-capping bucket floats when the sand-capping material is loaded or unloaded. The submergence and floating functions of the sand-capping bucket are simply operated hydraulically. In other words, there is no need for a large sand-capping work vessel like that in Patent Document 1. This results in a significant reduction in initial costs.

[0013] The sand capping bucket used in the thin layer sand capping method of this invention consists of a box-shaped sand capping bucket with an open top, a pair of barges several times taller than the sand capping bucket, and a pair of side walls. The sand capping bucket is surrounded by these barges and side walls and is fixed horizontally at the vertical midpoint, forming a sand capping bucket with upper and lower spaces above and below the sand capping bucket. The sand capping bucket's structure is such that its height corresponds to the minimum thickness of the sand capping, and the internal space is divided into a lattice pattern by vertical plates, and an automatic opening and closing bottom plate with a width half the division width is hinged to the bottom of the vertical plates so that it opens on both sides. The internal structure of the barge is also divided into a space dedicated to the floating body and a ballast space. The sand-capping bucket used in the thin layer sand-capping method is characterized by its submersible function, which allows ballast water (seawater) to be introduced into the ballast space, its ability to load and unload sand-capping material by opening the automatically opening and closing bottom plate, and its ability to float when buoyancy is overcome by the reduction in gravity equal to the weight of the sand-capping material.

[0014] The sand-capping bucket of the present invention has an upper space and a lower space above and below the sand-capping bucket, and the height of the sand-capping bucket corresponds to the minimum thickness of the sand. The sand-capping thickness in the thin-layer sand-capping method is not a fixed thickness, but is approximately 30 cm to 50 cm. For example, if the thickness of the sand-capping bucket is 30 cm, sand with a thickness exceeding 30 cm will occupy the upper space and be loaded. This makes it easy to accommodate different planned sand-capping thicknesses. In addition, the lower space has an automatically opening and closing double-opening bottom slab that opens when loading and unloading sand-capping material, but a height equivalent to the width of the bottom slab is ensured.

[0015] In the structure of the sand-capping bucket, the standard height of the barge is approximately three times that of the sand-capping bucket. The position at which the sand-capping bucket is fixed to the barge is determined by the size of the barge's dedicated floating space and ballast space so that when the barge's ballast space is empty and the sand-capping bucket is loaded with the specified sand-capping material, the top of the sand-capping bucket is positioned above the flotation surface. This facilitates accurate construction when leveling the top of the loaded sand-capping material. The barge is also equipped with multiple seawater inlets with automatic opening and closing lids. When the required amount of seawater is introduced into the ballast space of the barge with the specified sand-capping material loaded, the top of the sand-capping bucket becomes the flotation surface, and seawater flows into the space above the sand-capping bucket from the undercut portion of the top of the sand-capping bucket's side wall. This allows the sand-capping bucket to submerge stably. Here, the required amount of seawater is determined by the planned sand covering thickness, which is not a fixed thickness but varies depending on the situation, and therefore the amount of seawater to be introduced will also vary.

[0016] When looking at the vertical position of the barge as a floating body relative to the sand-capping bucket, it can be divided into three spaces, each of which is the same height from top to bottom: the upper space, the sand-capping bucket, and the lower space. This makes it easy to adjust the height of the flotation surface of the sand-capping bucket by adjusting the amount of ballast water introduced. If the vertical volume positions of the barge and the sand-capping bucket are the same, it would be impossible to adjust the height of the flotation surface.

[0017] In addition, the sand-capping bucket's structure opens an automatically opening and closing double-hinged bottom plate when loading and unloading sand-capping material. The lower space of the sand-capping bucket is ensured to be high enough to allow the bottom plate to open. Furthermore, when loading and unloading sand-capping material, multiple drainage ports with screens are installed on the barge and side walls to allow seawater from the lower space to escape, preventing the spread of pollutants such as floating mud.

[0018] An example of an automatic open-close double-opening bottom plate for a sand-capping bucket is the bottom plate support girder system. In this system, multiple bottom plate support girders are attached to the bottom of the sand-capping bucket, and are perpendicular to the open-close double-opening bottom plate. These bottom plate support girders move up and down in the lower space below the sand-capping bucket by the height of the bottom plate width. This is powered by a double-acting hydraulic cylinder. When the bottom plate is closed, the weight of the bottom plate and the load weight are supported by these bottom plate support girders, and when the bottom plate support girders are lowered, the bottom plate opens and the sand-capping material is gently unloaded. When the bottom plate support girders are then raised, the necessary rotational moment in the closing direction is generated around the hinge, causing the bottom plate to close.

[0019] The vertical and horizontal bucket movement device attached to the sand-capping bucket is a two-beam portal structure fixed to the upper and lower ends of the barge. The upper and lower beams correspond to double-acting hydraulic cylinders, and the columns correspond to the spuds. The columns, or spuds, are separated from the barge, but are hingedly connected to the rods of the upper and lower cylinders, providing structural strength and optimizing the horizontal ground reaction force acting on the tip of the spud during barge movement. This suppresses horizontal displacement of the spud tip, changing the distribution of ground reaction force from triangular to trapezoidal, thereby increasing the ground reaction force. Functionally, the spud function reduces the impact of waves, facilitating vertical diving of the bucket at the designated position, and the operation of two double-acting hydraulic cylinders allows for precise horizontal movement of the bucket. This sand-capping bucket equipped with a vertical and horizontal bucket movement device is characterized by the following features:

[0020] The thin-layer sand capping method creates sand by moving an area of ​​the seabed equal to the area of ​​the sand capping bucket. The sand capping method can be broadly divided into the sand capping process and the sand capping bucket movement process. In the sand capping process, first, the sand capping bucket loaded with sand capping material is placed in a designated position at sea, and all spuds of the bucket's vertical and horizontal movement device are extended to thrust it into the seabed and maintain its position. Next, ballast water is introduced into the barge, and all spuds are retracted, allowing the sand capping bucket to submerge and install on the seabed. Next, the automatic double-opening bottom slab is opened to unload the sand capping material, creating sand on the seabed. As the weight of the capping sand decreases, buoyancy overcomes gravity, causing the sand capping bucket to float. At this point, all spuds must be extended to accommodate the floating. If the buoyancy is too great, the floating speed will increase. If the swath cannot keep up and breaks free of the seabed before it can keep up, the sand-capping bucket will not be able to maintain its position. Therefore, care must be taken to avoid introducing too little ballast water. Next, in the bucket movement process, the floating sand-capping bucket pulls the spud of the moving device on the direction of travel out of the seabed, extends the cylinder of the moving device by the distance traveled, and thrusts the spud into the seabed to maintain its position. Next, the spud of the moving device on the opposite side is pulled out of the seabed, and the cylinder of the moving device on the direction of travel is retracted. The sand-capping bucket is then moved to the next designated position, thrusting the spud into the seabed to maintain its position. The ballast water is then discharged, and the sand-capping material is loaded into the sand-capping bucket. The thin-layer sand-capping method involves repeating the sand-capping process and bucket movement process to load and unload a specified planned thickness of sand on the seabed, creating a thin layer of sand of a specified thickness in a specified area.

[0021] The principle of sand capping is to contain sludge by covering it with sand, preventing direct contact between seawater and the sludge and preventing the release of harmful chemicals or nutrients that would otherwise leach from the seabed sludge into seawater. Therefore, the sand capping method can be implemented without causing seawater pollution, and the sand capping material can be any material that can prevent the release of nutrients and is not easily washed away after construction. In other words, it does not have to be sand. For leaching prevention, clayey soil is a good choice. For washout prevention, gravel is better than sand. Overall, the most suitable sand capping material is one that contains a moderately sized mixture of clay, sand, and gravel. The thin-layer sand capping method of the present invention loads and unloads the sand at the seabed, rather than at the sea surface, thereby preventing seawater pollution. Furthermore, the sand capping material is loaded and unloaded by opening an automatic opening and closing base plate, making this method easily adaptable to a wide range of sand capping materials.

[0022] The second objective of this invention is to advance a blue carbon project that combines bottom sediment improvement through sand capping with the creation of seaweed beds. Steel slag has been confirmed to purify eutrophic bottom sediments by suppressing the generation of sulfur and phosphates. It has also been confirmed to have the ability to adsorb harmful substances in water. For these reasons, steel slag is extremely effective as a sand capping material for the thin-layer sand capping method intended for creating eelgrass beds. The thin-layer sand capping method for creating eelgrass beds involves simultaneously creating eelgrass beds and creating a thin layer of sand. After loading the sand capping material into a sand capping bucket and leveling the top, an additional step is added: scattering numerous eelgrass seed packages on top of the sand capping material to prevent the eelgrass seeds and seed soil material from being washed away. The eelgrass seed packages are, for example, soil mixed with eelgrass seeds, formed into balls approximately 5 cm in diameter, and bags containing gravel to serve as weights. The blue carbon project, which combines bottom sediment improvement through sand covering with the creation of seaweed beds, simply adds the process of scattering eelgrass seed packages to the thin layer sand covering method. There is a significant difference in the cost-effectiveness when compared to a standalone seaweed bed creation project. The thin layer sand covering method, which is intended to create eelgrass beds, restores coastal waters that are a source of carbon dioxide and are filled with seabed sludge to vegetated coastal waters that act as a carbon dioxide sink. Effects of the invention

[0023] The thin layer sand capping method of the present invention provides the sand capping bucket of the automatically opening and closing bottom slab with submergence and floating functions. These functions are achieved by reducing the buoyancy of the floating barge, which acts as a floating body, by the inflow of ballast water relative to the weight of the sand capping bucket itself and the weight of the sand capping material, allowing it to submerge, and by reducing gravity when the sand capping material is loaded and unloaded, allowing it to float. The submergence and floating functions of the sand capping bucket can be operated simply by hydraulics, and no large sand capping work vessel is required. This method therefore has the effect of significantly reducing initial costs.

[0024] The thin layer sand-capping method of the present invention loads and unloads sand-capping materials on the seabed, not on the sea surface. This prevents seawater pollution. Furthermore, loading and unloading of sand-capping materials is carried out by opening the automatic open-close bottom slab, making it easy to accommodate a wide range of sand-capping materials. Therefore, the sand-capping material is not limited to sand, and any useful sand-capping material can be selected according to the purpose.

[0025] The thin layer sand capping method for creating eelgrass beds simply adds the process of scattering eelgrass seed packages to the sand-covering process of the thin layer sand capping method. Its economic effect is far superior to that of a standalone seaweed bed creation project in terms of cost-effectiveness. Furthermore, this thin layer sand capping method for creating eelgrass beds has the effect of restoring coastal waters that were once a source of carbon dioxide, filled with seabed sludge, into vegetated coastal waters that act as a carbon dioxide sink. [Brief explanation of the drawings]

[0026] [Figure 1] Plan view of the sand-covering bucket of the present invention [Figure 2] Side view of the same short side [Figure 3] Cross section of line AA in Figure 1 [Figure 4] Cross section of line BB in Figure 1 [Figure 5] Enlarged cross-sectional view of the sand-capping bucket with the bottom plate of the double-opening door closed [Figure 6] Enlarged cross-sectional view of the sand-capping bucket with the bottom plate open [Figure 7] An explanatory diagram of the sand-capping process in the thin-layer sand-capping method of the present invention. [Figure 8] An explanatory diagram of the bucket movement process in the thin layer sand capping method DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of the present invention will be described with reference to FIGS.

[0028] Figure 1 is a plan view of the sand-capping bucket of the present invention, Figure 2 is a side view of the short side of the same, Figure 3 is a cross-sectional view taken along line AA in Figure 1, and Figure 4 is a cross-sectional view taken along line BB in Figure 1. In the figures, 1 is the sand-capping bucket, 2 is the sand-capping bucket, 21 is a vertical plate in the long side direction, 22 is a vertical plate in the short side direction, 23 is an automatically opening and closing double-opening bottom plate, 24 is a bottom plate support girder, 25 is a support girder up and down movement device, 3 is a barge, 4 is a side wall, 5 is a bucket vertical and horizontal movement device, 51 is a spud, 52 is a cylinder, 6A is the sea surface, 6B is the seabed, and 6C is the seabed ground.

[0029] As shown in Figures 1 to 4, the sand capping bucket 1 is composed of a box-shaped sand capping bucket 2 with an open top, a pair of barges 3 several times taller than the sand capping bucket 2, and a pair of side walls 4. The sand capping bucket 2 is surrounded by the barges 3 and side walls 4 and is fixed horizontally at the vertical midpoint between them, forming the sand capping bucket 1 with an upper space and a lower space above and below the sand capping bucket 2. As shown in Figure 4, the internal space of the sand capping bucket 2 is divided into a grid pattern by vertical slabs 21 in the long side direction and vertical slabs 22 in the short side direction, and an automatically opening and closing double-opening bottom slab 23 with a width half the width of the division is hinged to the bottom of the vertical slabs so that it opens on both sides. Figure 4 shows an example in which the double-opening bottom slab 23 is hinged to the bottom of the vertical slab 21 in the long side direction.

[0030] Figure 5 is an enlarged cross-sectional view of the sand-capping bucket 2's automatically openable, double-hinged bottom slab 23 in a closed position, and Figure 6 is an enlarged cross-sectional view of the sand-capping bucket 2's open, double-hinged bottom slab 23. The example shown in the figure uses a bottom slab support girder system. In this system, multiple bottom slab support girders 24 are attached to the bottom of the sand-capping bucket 2, perpendicular to the openable, double-hinged bottom slab 23. These bottom slab support girders 24 move up and down in the lower space below the sand-capping bucket 2 by the width of the double-hinged bottom slab 23 using a support girder lifting device 25. This is powered by a double-acting hydraulic cylinder. When the double-hinged bottom slab 23 is closed, the weight of the bottom slab and the load are supported by the bottom slab support girder 24. When the bottom slab support girder 24 descends, the double-hinged bottom slab 23 opens, allowing the sand-capping material to be gently unloaded. When the bottom slab support girder 24 subsequently rises, the necessary rotational moment is generated around the hinge in the closing direction, closing the double-hinged bottom slab 23.

[0031] To give an example of the dimensions of an actual large sand-capping bucket 1, the sand-capping bucket 2 is 30 cm high, 20 m wide, and 50 m long, while the barge is 100 cm high, 5 m wide, and 50 m long. The sand-capping bucket 1 is 100 cm high, 30 m wide, and 50 m long. The sand-capping bucket 1 is an extremely thin structure. For this reason, the scales of the sand-capping bucket 1 and sand-capping bucket 2 in Figures 1 to 8 have been changed for clarity. The spacing between the bottom slab support girders 24 is 10 m, and the spacing between the long-side vertical slabs 21 and the short-side vertical slabs 22 is 2 m. However, it is preferable to install additional vertical slabs 21 at 20 cm intervals 10 cm below the long-side vertical slab 21 to which the double-opening bottom slab 23 is attached. Therefore, the width of the double-opening bottom slab 23 is 10 cm. Now, let's assume that the sand-capping thickness is 30 cm. The bottom slab support girder 24 is slowly lowered by the support girder lifting device 25, and the double-opening bottom slab 23 also slowly opens. The first 10 cm of the 30 cm of sand-covering material is deposited relatively slowly, and the cross section of the deposit is a trapezoidal shape close to a triangle. However, for the remaining 20 cm of sand-covering material, the double-opening bottom slab 23 is fully open, and as the sand-covering material is unloaded, the buoyancy prevails and the sand-capping bucket 1 begins to rise. As a result, the sand-capping material falls off the double-opening bottom slab 23 evenly, and the top of the sand-capping material is leveled and becomes almost flat.

[0032] The thin-layer sand-capping method of the present invention creates seabed sand by moving the sand-capping bucket 2 over an area of ​​the seabed equal to its area. Figure 7 is an explanatory diagram of the sand-capping process, with 6D representing the seabed sand. In the sand-capping process, the sand-capping bucket 1 loaded with sand-capping material is placed at a predetermined position at sea, and all spuds 51 of the bucket's vertical and horizontal movement device 5 are extended to pierce the seabed 6C and maintain its position. This is the state shown in Figure 7a. Next, seawater is introduced into the barge 3, and the spuds 51 are retracted, allowing the sand-capping bucket 1 to submerge and install itself on the seabed 6B. This is the state shown in Figure 7b. Next, the automatic open-close double-opening bottom slab 23 is opened to unload the sand-capping material, creating a thin layer of sand 6D, and the sand-capping bucket 1 is raised to the surface. The spuds 51 are extended as the bucket rises to the surface. This is the state shown in Figure 7c.

[0033] Figure 8 is an explanatory diagram of the movement process of the sand-capping bucket 1. First, the floated sand-capping bucket 1 pulls the spud 51 of the vertical and horizontal moving device 5 of the bucket on the traveling direction side from the seabed 6C, extends the cylinder 52 of the moving device 5 by the movement distance, and thrusts the spud 51 into the seabed 6C to hold its position. This is the state shown in Figure 8a. Next, the spud 51 of the moving device 5 on the opposite side is pulled out from the seabed 6C, and the cylinder 52 of the moving device 5 on the traveling direction side is retracted to its original position. The sand-capping bucket 1 is then moved to the next predetermined position, and thrusts the spud 51 into the seabed 6C to hold its position. This is the state shown in Figure 8b. Then, ballast water is discharged, and sand-capping material is loaded into the sand-capping bucket 1. This is the state shown in Figure 8c. The thin layer sand capping method involves repeating the sand capping process and the moving process to load and unload a specified planned thickness of sand capping on the seabed surface 6B, creating a thin layer of sand capping 6D of a specified thickness in a specified area. [Explanation of symbols]

[0034] 1 Sand-covering bucket 2 Sand capping bucket 21 Long side vertical plate 22 Short side vertical plate 23 Double-sided bottom plate 24 Bottom support girder 25 Support girder up / down device 3 barges 4 side wall 5. Bucket vertical and horizontal movement device 51 Spud 52 cylinders 6A sea level 6B Seabed surface 6C Submarine ground 6D Seabed sand covering (thin layer sand covering)

Claims

1. A sand capping bucket used in the thin layer sand capping method is composed of a box-shaped sand capping bucket with an open top, a pair of barges and a pair of side walls that are several times taller than the sand capping bucket, and the sand capping bucket is surrounded by these barges and side walls and fixed horizontally at the vertical midpoint between them, forming a sand capping bucket with upper and lower spaces above and below the sand capping bucket.The sand capping bucket has a structure in which its height corresponds to the minimum thickness of the sand capping, and the internal space is divided into a lattice pattern by vertical plates, and at the bottom of the divisions, an automatically opening and closing double-opening bottom plate with a width that is half the width of the divisions is hinged to the bottom of the vertical plate.The internal structure of the barge is divided into a space dedicated to the floating body and a ballast space, and the sand capping bucket used in the thin layer sand capping method is characterized by having a submersible function by introducing ballast water into the ballast space, a function to load and unload sand capping material by opening the automatically opening and closing double-opening bottom plate, and a floating function due to a decrease in gravity.

2. In the structure of the sand-capping bucket of claim 1, the height of the barge is typically about three times that of the sand-capping bucket, and the position at which the sand-capping bucket is fixed to the barge is such that when the ballast space of the barge is empty and the sand-capping bucket is loaded with a predetermined amount of sand-capping material, the top of the sand-capping bucket is above the flotation surface, and the barge is provided with multiple seawater inlets with automatic opening and closing lids, so that when the predetermined amount of sand-capping material is loaded and the required amount of seawater is introduced into the ballast space of the barge, the top of the sand-capping bucket becomes the flotation surface, and seawater flows into the upper space of the sand-capping bucket from the undercut portion of the top of the side wall of the sand-capping bucket.

3. The structure of the sand-capping bucket of claim 1 is characterized in that, when loading and unloading sand-capping material, a plurality of drainage ports with screens are provided on the barge and side walls to allow seawater to escape from the lower space of the sand-capping bucket, thereby preventing the spread of pollutants such as floating mud.

4. In the vertical and horizontal movement device for the bucket equipped on the sand-capping bucket of claim 1, the device is a two-beam portal structure fixed to the upper and lower ends of the barge, the upper and lower beams being double-acting hydraulic cylinders and the pillars being spuds, the pillars being separated from the barge but the spuds being hingedly connected to the rods of the upper and lower cylinders making them structurally strong, and the horizontal ground reaction force applied to the tip of the spud when the barge is moving acts advantageously, and functionally the spud function reduces the effect of waves making it easier to vertically dive the bucket at the designated position, and the horizontal movement of the bucket is accurate by operating two sets of double-acting hydraulic cylinders.

5. In the thin layer sand capping method using a sand capping bucket equipped with a vertical and horizontal bucket movement device according to claim 1, the sand capping step involves placing the sand capping bucket loaded with sand capping material at a predetermined position, extending all the spuds of the bucket's vertical and horizontal movement device, and piercing the bucket into the seabed to maintain its position, then introducing ballast water into the barge and retracting all the spuds to submerge the sand capping bucket and install it on the seabed, then opening the automatic open-close double-opening bottom plate to unload the sand capping material and create seabed sand, and then floating the sand capping bucket due to the reduction in the weight of the capping sand and extending all the spuds to accommodate the floating, and then the bucket movement step involves moving the floated sand capping material to the bottom of the seabed. The sand creation bucket is constructed by pulling out the spud of the moving device on the direction of travel from the seabed, extending the cylinder of the moving device the distance of travel to insert the spud into the seabed and maintain its position, then pulling out the spud of the moving device on the opposite side from the seabed, retracting the cylinder of the moving device on the direction of travel to its original position, moving the sand creation bucket to the next designated position, then draining the ballast water and loading the designated sand creation material into the sand creation bucket.This is a thin layer sand creation method using a sand creation bucket equipped with a vertical and horizontal bucket movement device, characterized in that by repeating the sand creation process and bucket movement process, a designated planned thickness of sand is created in a designated area.

6. 2. The thin layer sand-covering method of claim 1, wherein the sand-covering bucket loaded with the sand-covering material in the sand-covering step further contains numerous eelgrass seed packages that are packaged to prevent the eelgrass seeds and seed soil material from being washed away, and the eelgrass bed and the thin layer sand-covering method are simultaneously created.

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