JPH03183813A - Creation of tideland - Google Patents

Abstract

PURPOSE:To construct a strong revetment and to improve sea environment by a method wherein construction members made of bags filled with sea bottom materials in the coastal area and hardening materials are stacked, the sea bottom materials are laid and sand are further laid thereon after reinforcing treatment is made on the upper layer of the sea bottom materials. CONSTITUTION:A construction member 3 is made by filling a synthetic resin bag 2 with a mixture made of sea bottom materials and hardening materials, and the bags are laid over the seabed 5 while filling materials 1 in the bags are still unhardened. After the filling materials 1 solidify, other construction members 3 whose filling materials 1 are still unhardened are stacked one after another over the construction members 3 that are already laid. A bottom layer 6 is then formed with the sea bottom materials laid up to a specified thickness, and a middle layer 7 is formed thereon with unhardened or hardened materials made of the sea bottom materials and hardening materials laid up to a specified thickness. An upper layer 8 is then formed by covering the underling layer with sand or the like up to a specified thickness. Thereby a tideland can be prevented from washing-away or breakdown that occur by currents and waves and, at the same time, the sea bottom materials can be utilized effectively as construction materials.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for creating tidal flats by reclaiming coastal sea areas, lakes, etc. (collectively referred to as coastal sea areas in this specification). The present invention relates to a method for creating tidal flats by effectively utilizing soft mud and dredged soil (herein referred to collectively as bottom sediment).

[Conventional technology] In Japan, a country with a small land area and few resources, the vast marine space that surrounds it is a valuable national land resource. Therefore, marine environment conservation and appropriate advanced utilization of coastal waters are important issues. ing.

Improving bottom sediment, which is part of marine environmental conservation, is essential because the amount of sediment deposited in inner bays and inland sea areas is enormous. Microbiological methods are being proposed and developed. However, a definitive solution has not yet been found.

Conventionally, methods of improving bottom sediment have been attempted by adding soil (covering soil), tilling, and dredging. This is a method of covering the soil with soil. In addition, tillage is a method of turning over, crushing, or stirring seabed soil using bulldozers or ships, targeting areas with hardened bottom sediment.Dredging is a method of removing accumulated garbage and bottom sediment. However, the target area is the removal of accumulated sediment that obstructs the flow of seawater within the fishing grounds.
This method involves removing bottom sediment containing a large amount of organic matter and digging into the seabed to maintain the appropriate water depth for aquatic life.

In addition, proposals have been made regarding the advanced use of coastal sea areas, and among them, many requests have been made to reclaim coastal sea areas to create tidal flats and establish breeding grounds for shellfish, mainly for clams and clams. has been done. Traditionally, tidal flats have been created by constructing a stone wall at the outer edge (tip) of the area where it is planned to be created, filling in the area from there to the coast, and then covering it with sand. ing.

[Problems to be solved by the invention] Sediment has (1) a large amount, (2) contains a large amount of water and is difficult to dry naturally, and (3) produces a foul odor due to the decay of organic matter. There are other problems. Therefore, the present invention aims to preserve the marine environment and make advanced use of coastal waters by effectively utilizing the bottom sediment.

Conventional problems in creating tidal flats by extending breeding grounds offshore are as follows. In other words, (1) the tip of the offshore tip of a tidal flat is likely to be washed away or damaged by external forces such as tidal currents and waves, so it is necessary to make the tip a particularly strong revetment; (3) Measures (1) and (2) require a large amount of money and are therefore impractical.

[Means for Solving the Problems] Therefore, in order to solve the problems in the conventional tidal flat creation methods described above, the present inventor focused on the use of bottom sediment and proposed the present invention.

That is, according to the present invention, when creating a tidal flat in a coastal sea area, the steps are: (a) providing a seawall made by treating the bottom sediment in the tidal flat construction area to increase its strength; (b) injecting sediment into the tidal flat creation area. (c) a step of treating the upper layer of the sediment that has been put into the tidal flat construction area to increase its strength; (d) a step of laying sand on top of the upper layer that has been treated to increase its strength. A method for creating tidal flats is provided.

[Operation] In the present invention, when creating a tidal flat in a coastal sea area, after forming a seawall by treating the bottom sediment at the outer edge (tip) of the tidal flat creation area to increase its strength, the area from this seawall to the coast is The bottom layer of the bottom layer is then treated to increase the strength of the upper layer of the bottom layer, and then sand or the like is coated on top to provide habitat for shellfish.

By using the bottom sediment in combination with these strength-enhancing treatments, the outer edges of the tidal flats are protected by the bottom sediment strength-increasing treatments, so they are protected from being washed away or damaged by ocean currents, waves, etc. Moreover, since a large amount of bottom sediment from the ocean floor is used, the bottom sediment that causes many harmful effects can be removed and used effectively, which can help improve the sea environment.

In the present invention, the strength of the bottom sediment introduced into the outer edge of the tidal flat construction site and the planned tidal flat area is increased by adding various solidification agents to the bottom sediment and throwing it into the sea in an uncured state (hardening in the sea). Either method may be used, such as increasing the strength (increasing the strength) or hardening it into a predetermined shape and then inserting it into the sea.

In addition, if the outer edge of a tidal flat site requires a strong revetment due to the influence of tidal currents, etc., the bottom sediment added with a solidification material is filled into a bag in an unhardened state to form a rod-like structure. It is preferable to harden the rod-shaped products after putting them into the sea, and then stack them to create a seawall. The seawall formed in this way becomes strong and protects the outer edge of the tidal flat. The shape, height, and strength of the hardened part of the seawall are determined by tidal currents, waves,
Determined based on local conditions such as depth and topography.

The material of the bag described above is not particularly limited, and various materials may be used.For example, as the fiber material, natural fibers, recycled fibers, semi-synthetic fibers, synthetic fibers, and inorganic fibers are used. As the plastic material, a synthetic or semi-synthetic polymer sheet is used. These materials can be processed into a shapeable bag either singly or as a composite.

The solidifying agent used for hardening the bottom sediment in the present invention is usually a cement-based solidifying agent, but if the bottom sediment contains a small amount of cement setting inhibitors such as organic matter and phosphates (generally less than 2% organic matter). For this purpose, cement specified by JIS standards can be used. Note that the cement-based solidifying material is not specified by JIS standards or the like, but is developed for special purposes.

In the present invention, the most suitable hardening materials for hardening the sediment include those whose main materials are gypsum, pozzolan materials, and cement materials. This has the characteristic that even if the sediment contains organic substances and phosphates that inhibit the setting reaction of Portland cement, it reacts effectively and achieves the purpose.This solidification material is mixed with the bottom sediment. Then, (a) ion exchange reaction of fine soil particles, (b) formation reaction of ettringite, and (c) formation of tobelmonite mineral-like layer between the various constituent materials of the solidification material and the bottom sediment and the water and fine soil particles contained therein. Pozzolanic reaction (d) Calcium carbonate production reaction (e) Production reaction of amorphous gel-like substances by various reactions occur in parallel, and skeletons and sticky amorphous substances necessary for soil stability are deposited in the sediment. The bottom sediment is chemically improved and hardened (increased strength).

In addition, a filler may be added as an additive in addition to the solidifying material. When a filler is mixed as an additive for the strength increasing treatment of the sediment, it is preferable because the tensile strength of the resulting strength increasing treated product is improved. Various fillers are used, among them steel fiber, glass 11 carbon fiber,
Using aramid fiber as a filler has a great effect.

What kind of sediment is used to create tidal flats for the growth of shellfish?

Contaminant elution tests are carried out using the elution test described in "Sediment Investigation Methods" (Kanmokukan No. 127, dated September 8, 1986), and safety is confirmed before use. By the way, the elution test method is Environmental Agency Notification No. 13 (prescribing methods for testing hazardous substances contained in industrial waste) and No. 14 (Marine Pollution Prevention) based on the Marine Pollution Prevention Act regarding waste dumping in the ocean. There is a test method based on waste to be discharged to a landfill site etc. (determining the testing method for hazardous substances contained) as stipulated in Article 5, Paragraph 1 of the Law Enforcement Order. The elution time and pH adjustment of the eluate are slightly different.

Note that sewage sludge, incineration ash, fly ash, etc. can also be added to the bottom sediment of the present invention.

[Examples] Hereinafter, the present invention will be described in more detail based on illustrated examples, but the present invention is not limited to these examples.

FIG. 1 is a schematic cross-sectional view showing the tidal flat creation method of the present invention in coastal waters.

First, a mixture of sediment and solidifying material is synthesized into a bag made of Iam.
Next, the filling material 1 of the construction member 3 is placed in an uncured state in close contact with the seabed 5 on which the seawall 4 is to be constructed. After the filling l of the installed construction member 3 becomes a solidified body, the installed construction member 3
``Building members with uncured fillers'' produced under the same conditions as above are stacked one after another on top of the .

The curing period for the mixture of solidifying material and bottom sediment filled in the bag body 2 to harden can be selected arbitrarily, and the strength gradually develops while it is placed and laid on the seabed 5, increasing the strength of the hardened material. increases, so the work of stacking the construction members 3 may be carried out when the solidification strength of the filler reaches a predetermined strength.The predetermined strength at this time is determined by the cross-sectional size, shape, and specific gravity of the construction members. .

The final strength of this filling 1 is usually several tens of kilograms of axial compressive strength.
It is desirable that gf/C1 or more be set.

Further, although the work of filling the bag body 2 with the mixture 1 of solidifying material and sediment can be performed on the ground, it is usually performed underwater. When the filling operation is carried out underwater, there are advantages such as improved workability and operability due to effects derived from buoyancy, and a reduction in the load exerted on the bag body used in the present invention.

Next, the bottom layer is poured into the tidal flat area to a predetermined thickness to form the bottom layer 6, and then an uncured or hardened mixture of bottom sediment and solidification material is laid down to a predetermined thickness on top of the bottom layer 6 to form the middle layer. Part 7
form. The ultimate strength of this middle layer is the compressive strength of 0.
．． 5 to 5 kgf/am", and furthermore, the upper layer 8 is covered with sand or the like in which shellfish can live to a predetermined thickness. When covering the upper layer 8 with sand, at the same time Sprinkling pebbles the size of adzuki bean grains on the surface is effective for depositing young shellfish.

The thicknesses of the above-mentioned lower layer 6, middle layer 7, and upper layer 8 are determined in consideration of local conditions, soil conditions, etc.

[Effects of the Invention] As explained above, according to the tidal flat creation method of the present invention,
By using the bottom sediment and a strength-enhancing treatment obtained by hardening the bottom sediment with a solidifying agent, the tidal flat can be protected from being washed away or destroyed by ocean currents, waves, etc. Particularly at the outer edges of tidal flats where conditions such as ocean currents are severe, strong seawalls can be constructed by using bags filled with a mixture of bottom sediment and solidification material.

Furthermore, according to the tidal flat creation method of the present invention, it is possible to remove a large amount of bottom sediment from the ocean floor, which causes many harmful effects, and to effectively use the bottom sediment, which has no disposal site, as a material, and to create a vast tidal flat. This will effectively improve the marine environment by killing two birds with one stone.

Incidentally, artificial tidal flats provide fishing grounds that are suitable for the initial development and improvement of survival rates of benthic organisms, and can save labor in breeding and management.

In other words, the benefits of artificial tidal flats include first-order effects.

(a) It has an accumulation effect on floating larvae such as bivalves.

(b) In addition to bivalves, it serves as a settlement site for young prawns and crabs, and has a high survival rate after settlement.

(c) Growing and managing living things is easy.

(d) Others.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a tidal flat created according to the present invention. l...Filling material, 2...Bag body, 4...Revetment, 6...Low layer portion 7...Medium layer portion, 8...Surface layer portion.

Claims (1)

[Claims] (1) When creating a tidal flat in a coastal sea area, (a) a process of installing a seawall made by treating the bottom sediment to increase its strength at the outer edge of the tidal flat creation area; (b) a process of introducing bottom sediment into the tidal flat creation area. , (c) a process of increasing the strength of the upper layer of the sediment that has been put into the tidal flat construction area, and (d) a process of laying sand on top of the upper layer that has been subjected to the strength increase treatment. A tidal flat creation method characterized by