JP2005226256A - Reclaimed tideland and reclaimed shallow place creating method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily reinforce the ground at the bottom of the water and prevent a load from being imposed on the nature, when a reclaimed tideland and a reclaimed shallow place are created on the soft bottom of the water. <P>SOLUTION: A sheet laying step of laying a biodegradable synthetic resin sheet 4 on the soft bottom of the water, and an earth covering step of applying an earth cover 5 onto the laid sheet 4 are performed. The sheet laying step and the earth covering step are performed after a reclamation step of reclaiming the bottom of the water by using dredged soil 3, so as to form the soft bottom of the water. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an artificial tidal flat and a method for creating a shallow field where a tidal flat and a shallow field are artificially created on a soft water bottom.

  In recent years, many of the tidal flats and shallow areas have decreased due to land reclamation accompanying the development of coastal sea areas, and the number of organisms that live there and play a role in purifying the sea areas has also decreased. Therefore, the creation of artificial tidal flats and shallow areas has been attempted for the purpose of restoring the natural environment of coastal waters.

  On the other hand, most of the dredged soil generated by dredging in coastal waters is discarded, and it is required to make effective use of it because it costs money to secure land for treatment.

  Then, the method of constructing an artificial tidal flat using the earth and sand dredged for a channel dredging and sludge purification is considered (for example, refer patent document 1). That is, Patent Document 1 discloses that dredged soil is used only for the bottom layer of an artificial tidal flat, and artificial tidal flats are formed by covering mountain sand and sea sand in layers on the surface layer.

  However, it was difficult to create a tidal flat by reclaiming dredged soil and covering it with sand in layers, without improving or reinforcing the ground, because the dredged dredged soil was extremely soft. .

On the other hand, a naturally decaying bag containing light weight materials such as pumice and foamed concrete is placed on the tidal flat, slurry and water slurry is injected into the bag, and the top of the bag is covered with sand to increase the tidal flat area. Such an artificial tidal flat formation method has been considered (see, for example, Patent Document 2). According to this method, there is a possibility that an artificial tidal flat can be created on soft ground.
JP 2003-268745 A (paragraph number 0002) Japanese Patent Laid-Open No. 11-336043

  However, in the artificial tidal flat formation method of Patent Document 2, it takes time to put a lightweight material into the bag body and time and labor to inject earth and sand into the bag body after being placed on the tidal flat, and depending on the area of the tidal flat to be created, Requires a high cost. Moreover, the weight-reduced bag body is for suppressing subsidence, and the ground below the bag body is not compacted, and a soft state is maintained over a long period of time. And after a bag body rots, there exists a possibility that an upper sand layer may enter into the soft ground of a lower layer, and may sink.

  An object of the present invention is to make it possible to easily reinforce the bottom of the seabed and not to give a load naturally when constructing an artificial tidal flat and a shallow field on a soft bottom.

  In order to solve the above problems, the invention described in claim 1 is an artificial tidal flat and shallow field creation method for artificially creating a tidal flat and a shallow field on a soft water bottom, for example, as shown in FIG. A sheet laying step for laying the biodegradable synthetic resin sheet 4 on a soft water bottom and a soil covering step for covering the soil 5 on the laid biodegradable synthetic resin sheet 4 are characterized.

  In this way, the soft water bottom is reinforced by the biodegradable synthetic resin sheet 4, so that the covering soil 5 can be easily formed on the water bottom. Moreover, by covering the biodegradable synthetic resin sheet 4 with the cover 5, the soft bottom ground can be evenly consolidated and the bottom bottom can be strengthened.

  Here, the biodegradable synthetic resin sheet 4 is made of polylactic acid made from corn as a main raw material, and possesses a predetermined tensile strength, while hydrolysis and enzymatic degradation by microorganisms in an artificial tidal flat or an artificial shallow field, It is characterized by being decomposed and returned to natural products over 10 years. For this reason, it is possible to reinforce the soft underwater ground and create artificial tidal flats and shallow fields in a situation where no load is naturally applied, and the underwater ground can be strengthened by compaction for about 10 years. Moreover, the biodegradable synthetic resin sheet 4 is formed into a sheet shape as a woven fabric, a nonwoven fabric, a knitted fabric, or the like using, for example, a biodegradable resin as a fiber. In this case, a uniform sheet having the required strength can be easily manufactured at a low cost as compared with a sheet made of biodegradable natural fibers.

  The invention according to claim 2 is the artificial tidal flat and shallow field creation method according to claim 1, for example, as shown in FIG. 1, after the reclamation process in which dredged soil 3 is buried in the bottom of the water to form a soft bottom. The sheet laying step and the soil covering step are performed.

  Thus, in order to form a water bottom at a depth near the surface of the water, the dredged soil 3 can be used for the creation of artificial tidal flats and shallow fields by reclamation using the dredged soil 3.

  The invention according to claim 3 is the artificial tidal flat and shallow field construction method according to claim 1 or 2, wherein, for example, as shown in FIG. 3, in the sheet laying step, a plurality of biodegradable synthetic resin sheets 4 are provided. And using the floating work stage 6 that can float and move even on a shallow water surface, and sequentially join the biodegradable synthetic resin sheets 4 on the floating work stage 6 and move the floating work stage 6, A plurality of biodegradable synthetic resin sheets 4 connected to each other are spread and arranged on the water surface.

  In this way, using the floating work stage 6 that can float and move even on a shallow water surface, a plurality of biodegradable synthetic resin sheets 4 are placed, and the biodegradable synthetic resin sheets 4 are sequentially joined together, By arranging a plurality of biodegradable synthetic resin sheets 4 connected to each other on the surface of the water, the biodegradable synthetic resin sheets 4 can be joined on the surface of the water, making it easy to create artificial tidal flats and shallow areas with large areas. Can be created.

  Invention of Claim 4 is the construction method of the artificial tidal flat and shallow field as described in any one of Claim 1 to 3, For example, as shown to FIG. 1 and 2, the earth and sand covered in the said soil covering process First, the outer peripheral part 5a on the laid biodegradable synthetic resin sheet 4 is covered with soil, and then the interior surrounded by the outer peripheral part 5a is covered with a lattice 5b, The step of covering the portion 5c covered with the grid 5b with a soil is provided.

  Thus, using at least a part of the earth and sand to be covered, first, the outer peripheral portion 5a on the laid biodegradable synthetic resin sheet 4 is covered with the soil, and then the interior surrounded by the outer peripheral portion 5a is covered. Covering the grid 5b, and then covering 5c between the portions covered by the grid 5b, covering the soil 5 while dispersing the load of the cover 5 on the biodegradable synthetic resin sheet 4 laid. It is possible to prevent the biodegradable synthetic resin sheet 4 from partially sinking together with the covering soil 5.

  In addition, when covering the remaining earth and sand after covering the soil 5 with a load dispersed to a certain height by the above-described method, the above-mentioned method is not used and the soil is covered by an arbitrary method. For example, the remaining earth and sand may be covered sequentially from one end of the range where the tidal flat is created to the other end.

  According to the first aspect of the present invention, the soft water bottom is reinforced by laying the biodegradable synthetic resin sheet on the soft water bottom and covering the earth and sand on the laid biodegradable synthetic resin sheet. As a result, it is possible to easily cover the bottom of the water, and the soft bottom ground is evenly consolidated and the bottom bottom can be strengthened.

  According to the second aspect of the present invention, the dredged soil can be effectively used for the creation of artificial tidal flats and shallow fields by reclaiming dredged soil to form a soft bottom.

  According to the invention described in claim 3, a biodegradable synthetic resin sheet is mounted on a water working stage that can float and move even on a shallow water surface. Resin sheets are joined together and the water work stage is moved, and multiple biodegradable synthetic resin sheets connected to each other are placed on the surface of the water so that artificial tidal flats and shallow fields with large areas can be placed on the surface of the water. Can be easily created.

  According to the invention described in claim 4, first, the outer peripheral portion on the biodegradable synthetic resin sheet laid is covered with at least a part of the earth and sand to be covered, and then, the outer peripheral portion is covered with the outer peripheral portion. Covering the enclosed interior in a grid, and then covering between the parts covered with the grid 5 while covering the soil while dispersing the load on the biodegradable synthetic resin sheet laid. The possibility that the biodegradable synthetic resin sheet partially sinks with the covering soil can be reduced.

Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.
FIG. 1 shows a state where an artificial tidal flat has been created in a portion surrounded by an existing revetment 1 and an existing submerged dike 2. In the present embodiment, a landfill process in which a soft water bottom is formed by reclaiming dredged soil 3 in the bottom of the water surrounded by the existing revetment 1 and the existing submerged dike 2, and a biodegradable synthetic resin sheet on the soft water bottom. 4 includes a sheet laying process for laying 4 and a soil covering process for covering the soil 5 on the laid biodegradable synthetic resin sheet 4.

  First, in the reclamation process, dredged soil 3 transported by an earth ship or the like is put into a portion surrounded by the existing revetment 1 and the existing submerged dike 2 and is set to a predetermined height (basically slightly above the water surface). Landfill to the depth below). And after filling up the clay 3, the soft water bottom is formed.

  Next, in the sheet laying step, the biodegradable synthetic resin sheet 4 is laid on the soft water bottom formed by reclaiming the clay 3.

  Here, the biodegradable synthetic resin sheet 4 is made of polylactic acid made from corn as a main raw material, and possesses a predetermined tensile strength, while hydrolysis and enzymatic degradation by microorganisms in an artificial tidal flat or an artificial shallow field, It is characterized by being decomposed and returned to natural products over 10 years. Moreover, the biodegradable synthetic resin sheet 4 is formed into a sheet shape as a woven fabric, a nonwoven fabric, a knitted fabric, or the like using, for example, a biodegradable resin as a fiber.

Polylactic acid is a hydrolyzable biodegradable resin produced by a direct condensation method of lactic acid using lactic acid obtained by fermenting starch or saccharides produced from corn or the like as a raw material. The high molecular weight polylactic acid obtained by the direct condensation method has sufficient strength as compared with polyethylene and polyethylene which are general-purpose resins. In addition, it is highly transparent compared to other biodegradable plastics, and has the characteristic that mold does not grow even in damp environments. Polylactic acid has a structure in which the above hydroxyl group (OH) and carboxyl group (COOH) OH are dehydrated and bonded, and has “—CH ₃ CH (CH ₂ ) OCO—”.

  Hydrolysis is the decomposition of polymer bonds by the action of water. Since polylactic acid is made by chemically dehydrating polycondensation of lactic acid, it is decomposed when water is absorbed. The polylactic acid poly represents a polymer state in which many molecules are gathered and bonded. In the enzymatic decomposition, microorganisms secrete a degrading enzyme and decompose lactic acid more finely. The decomposed lactic acid becomes water and carbon dioxide.

  The biodegradable synthetic resin sheet 4 is previously sewed into a specified dimension, for example, a width of about 10 m, at a factory in advance, and an on-site joint is sewn to the end of the biodegradable synthetic resin sheet 4. This biodegradable synthetic resin sheet 4 is carried near the site and loaded on a hoist ship.

  Also, the water work stage 6 is assembled in advance, carried near the site, loaded onto a trolley by a hoist ship or the like, and towed to the site by tug.

  As shown in FIG. 4A, the floating work stage 6 has a width of about 31 m and a width of about 12 m, for example, a steel pipe 7 a that forms a rectangular frame 7 on the outer periphery thereof, and the frame 7 It consists of the reinforcing material 8 (aluminum square tube 8a) connected by the inside of a grid | lattice form. A float (float) such as foamed polystyrene 7c for imparting buoyancy is attached to the steel pipe 7a, and a hook 7b for pulling the water work stage is attached to the outer periphery. This water work stage 6 can make the draft extremely shallow, and can move on the water without any problems even if there is a buried clay 3 just below the water surface. Further, the amount of float to be attached can be adjusted, and the loading amount can be changed.

  And as shown in FIG.4 (b), the assembled frame is mounted on the water-impervious sheet 9, and the outer peripheral edge part of the water-impervious sheet 9 is folded and welded so as to cover the outer peripheral part of the frame. Moreover, as shown in FIG.4 (c), the rubber sheet 8b is welded to a water shielding sheet so that the aluminum square tube 8a may also be covered. The floating work stage 6 is floated on a portion surrounded by the existing revetment 1 and the existing submerged dike 2.

  As shown in FIG. 3, a carry dump 11 equipped with a winch 13 and a small backhoe 12 are arranged on the existing revetment 1, and a hoist ship 10 equipped with the winch 13 is arranged on the submerged dam side. The biodegradable synthetic resin sheet 4 placed on the hoisting ship 10 on the submerged dam side is suspended and loaded on the water work stage 6 as much as necessary for one row.

  Then, the biodegradable synthetic resin sheet 4 is laid while pulling the water work stage 6 in a direction perpendicular to the existing revetment 1 by the winch 13 disposed on the existing revetment 1 and sliding on the water work stage 6. And if the edge part of the biodegradable synthetic resin sheet 4 laid near the edge part of the floating work stage 6 has moved, the next biodegradable synthetic resin sheet 4 and its edge parts are bound with a rope or the like. Join sequentially. After that, when the water work stage 6 is pulled and moved to the existing revetment 1 side, the back work 12 is pulled in a direction parallel to the existing revetment 1 to move the water work stage 6 and the hoist ship 10 on the existing submerged dike 2 side. The water working stage 6 is pulled back to the existing submerged dike 2 side by the winch 13.

  Again, the necessary amount for one row is suspended and loaded on the water work stage 6, and the above-described towing and laying operations are repeated in the same manner. At that time, the sheet end portion of the existing biodegradable synthetic resin sheet 4 in the adjacent row is newly laid on and adjacent to the end portion of the biodegradable synthetic resin sheet 4 so as not to be caught on the water work stage. The ends of the biodegradable synthetic resin sheet 4 are bound. By repeating the above operation, the biodegradable synthetic resin sheet 4 is laid on the entire portion surrounded by the existing revetment 1 and the existing submerged dike 2.

  Moreover, in the place where the water depth is deep, a buoy is put so that the edge part of the biodegradable synthetic resin sheet 4 after laying may not sink, and the edge part of the biodegradable synthetic resin sheet 4 is floated. This buoy is removed when it is bound to a new biodegradable resin sheet 4 next to it and transferred to its end. In addition, grasp tide level fluctuations and install buoys as necessary.

  The end of the biodegradable synthetic resin sheet 4 on the existing revetment 1 side and the existing submerged dike 2 side is fixed, for example, by attaching a single pipe to the end of the biodegradable synthetic resin sheet 4. Insert a reinforcing bar into the top of 2 and fix it with a rope. Thereafter, the biodegradable synthetic resin sheet 4 is folded back to the artificial tidal flat side after completion of the first layer covering to be described later, the single pipe attached to the end is removed, and the first layer and the second layer of the covering soil 5 are removed. Try to pinch. In addition, when there is a water depth, it is turned back after the covering 5 is completed and pressed with a sandbag.

  In the soil covering process, the soil covering 5 is divided into four layers for construction. The first layer is first covered with the outer peripheral portion 5a on the laid biodegradable synthetic resin sheet 4, and then the interior surrounded by the outer peripheral portion 5a is covered with a grid 5b, Covering 5c between the portions covered with the shape 5b. In the soil covering of the outer peripheral portion, the soil is covered to the height of the second layer.

  Next, in the second layer, the interior already surrounded by the outer peripheral portion 5a is again covered with the lattice 5b, and then, similarly to the first layer, the portion 5c between the portions covered with the lattice 5b is covered. Do it. And the 3rd layer and the 4th layer cover the remaining earth and sand sequentially from one end of the range which constructs an artificial tidal flat to the other end.

  As a method of covering soil, for example, sea sand is brought in by a gut ship, soil transport is brought into contact with a hoist ship, the hoist is put into a tank pit of a micropump-equipped base ship, and water is transported by a micropump-equipped base ship. Perform construction at Then, the land piping is moved manually, and the sea sand is uniformly sprinkled on the biodegradable synthetic resin sheet 4 to secure the work scaffold and perform the construction while extending the piping. In addition, the sand and sand to be sprinkled may be mountain sand instead of sea sand.

In the above embodiment, the biodegradable synthetic resin resin sheet 4 is made of polylactic acid as a main raw material. Any material other than polylactic acid may be used as long as it has strength and does not decompose during the period until the water bottom ground is consolidated and strengthened.
Further, although the cover 5 is divided into four layers, the present invention is not limited to this, and may be divided into two or three layers, or may be divided into five or more layers. In the case of other than four layers, at least the first lower layer is covered with soil so as to disperse the load as described above.
In addition, it is needless to say that specific detailed structures and the like can be appropriately changed.

It is sectional drawing which shows the construction method of the artificial tidal flat of embodiment to which this invention is applied. It is a top view which shows the soil covering condition of the 1st layer in the construction method of an artificial tidal flat. It is a top view which shows the laying condition of a biodegradable synthetic resin sheet. The water working stage for laying a biodegradable synthetic resin sheet is shown, (a) is a plan view, (b) is a cross-sectional view taken along the line AA, and (c) is a cross-sectional view taken along the line BB. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Existing revetment 2 Existing submerged dike 3 Dredging 4 Biodegradable synthetic resin sheet 5 Cover soil 6 Water work stage

Claims (4)

Artificial tidal flat and shallow field construction method that artificially creates tidal flats and shallow fields on a soft water bottom,
A sheet laying step of laying a biodegradable synthetic resin sheet on the soft water bottom;
A method for constructing an artificial tidal flat and a shallow place, comprising a soil covering step of covering soil on a biodegradable synthetic resin sheet laid.   The artificial tidal flat and shallow ground creation method according to claim 1, wherein the sheet laying step and the soil covering step are performed after the landfilling step of reclaiming dredged soil to form a soft water bottom.   In the sheet laying step, a plurality of biodegradable synthetic resin sheets are placed on a floating work stage that can float and move even on shallow water surfaces, and the biodegradable synthetic resin sheets are sequentially placed on the water work stage. 3. Construction of artificial tidal flat and shallow field according to claim 1 or 2, wherein a plurality of biodegradable synthetic resin sheets connected to each other are moved and joined to each other and moved to move on the surface of the water. Method.   In the soil covering step, using at least a part of the earth and sand to be covered, first, the outer peripheral portion on the biodegradable synthetic resin sheet laid is covered, and then the interior surrounded by the outer peripheral portion is latticed. The method for creating artificial tidal flats and shallow fields according to any one of claims 1 to 3, further comprising a step of covering the soil between the portions covered in a lattice shape.

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