Sand and gravel mixture packed into bags

Abstract

The objective of this invention is to provide a technology that can stabilize the ground in coastal areas and other similar locations. [Solution] The present invention provides a sand and gravel mixture packed into a bag, wherein the sand and gravel mixture contains calcium-containing sand and gravel and iron powder, the content of the iron powder is 2 to 12 v / v% relative to the sand and gravel mixture, the content of the sand and gravel mixture is 70 v / v% or more relative to the volume of the bag, and the bag is permeable to water.

Description

Technical Field

[0001] The present invention relates to a gravel mixture packed in a bag.

Background Art

[0002] Due to the effects of sea - level rise and abnormal weather caused by recent global warming, coastal erosion and retreat are becoming apparent. Therefore, the importance of stabilizing coastal areas and other regions and measures against wave erosion is increasing.

[0003] As such measures, various methods have been proposed that can achieve ground stabilization and the like without adversely affecting the natural ecosystems in coastal areas and the like. For example, Patent Document 1 describes a method for forming a gravel solidified body using a predetermined mat - shaped agglomerate.

[0004] Also, as a simple countermeasure method against wave erosion, the use of sand - filled sandbags in a bag can be mentioned.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] On the other hand, there is a need for a technology that can more stably stabilize the ground in coastal areas and the like.

[0007] The present invention has been made in view of the above circumstances, and an object thereof is to provide a technology capable of stabilizing the ground in coastal areas and the like.

Means for Solving the Problems

[0008] The inventors of the present invention have discovered that the above problems can be solved by using calcium-containing sand and gravel solidified by a predetermined method to reinforce the ground, and have completed the present invention. Specifically, the present invention provides the following:

[0009] (1) A mixture of sand and gravel packed in a bag, The aforementioned sand and gravel mixture contains calcium-containing sand and gravel and iron powder. The iron powder content is 2 to 12 v / v% relative to the sand and gravel mixture. The content of the aforementioned sand and gravel mixture is 70 v / v% or more relative to the volume of the bag, The bag body has water permeability. gravel mixture.

[0010] (2) The gravel mixture according to (1), wherein the calcium-containing gravel includes coral gravel.

[0011] (3) The sand and gravel mixture according to (1) or (2), wherein the sand and gravel mixture contains 0.01 to 15 v / v% of a foaming agent relative to the sand and gravel mixture.

[0012] (4) The sand and gravel mixture according to any one of (1) to (3), wherein cyanobacteria and / or green algae are in contact with the surface of the bag.

[0013] (5) The sand and gravel mixture according to any one of (1) to (4), wherein the average particle size of the iron powder is 20 to 500 μm.

[0014] (6) The sand and gravel mixture according to any one of (1) to (5), wherein the bag is biodegradable.

[0015] (7) A method for solidifying the ground, comprising the step of placing the sand and gravel mixture described in any of (1) to (6) on the ground surface.

[0016] (8) A method for growing plants, comprising growing plants on and / or inside the sand and gravel mixture described in any of (1) to (6). [Effects of the Invention]

[0017] According to the present invention, a technique capable of stabilizing the ground in coastal areas and the like is provided.

Brief Description of the Drawings

[0018] [Figure 1] It is a diagram showing the strength of the surface layer and the inside of the gravel mixture in the embodiment. [Figure 2] It is a diagram showing the strength of the gravel mixture according to the blending amount of the foaming agent in the embodiment.

Mode for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments.

[0020] (1) Gravel mixture packed in a bag The gravel mixture packed in a bag according to the present invention (hereinafter, also referred to as "the gravel mixture of the present invention") satisfies the following requirements in one aspect. · The gravel mixture contains calcium-containing gravel and iron powder. · The content of iron powder is 2 to 12 v / v% with respect to the gravel mixture. · The content of the gravel mixture is 70 v / v% or more with respect to the volume of the bag. · The bag has water permeability.

[0021] The ground is a surface geology very close to the ground surface and includes soil, gravel, sediment, consolidated rock, etc. In particular, the ground in coastal areas and the like is easily affected by sea level rise, waves, etc., and its strength is likely to decrease, leading to collapse, subsidence, etc. Therefore, it is important to stabilize the ground in coastal areas and the like. In the present invention, "stabilization of the ground" includes suppressing a decrease in ground strength, improving ground strength, and the like.

[0022] As a result of diligent research by the inventors, it was discovered that a sand and gravel mixture satisfying the above requirements solidifies through a reaction described later, and that the solidified material has good strength and can be used as part of the ground. Furthermore, it was found that the strength of this solidified material is maintained regardless of the installation location (on land or at sea). For example, by installing the sand and gravel mixture of the present invention on the ground surface in a coastal area (land and / or sea), solidification of the sand and gravel mixture will occur over time, and this is expected to reinforce the ground in the coastal area.

[0023] In this invention, "strength (of the ground or solidified sand and gravel mixture)" includes the strength specified in JIS A1216:2020. According to the present invention, for example, by placing a solidified mixture of sand and gravel on the ground surface, the above-mentioned strength is improved compared to a case where the solidified mixture is not placed.

[0024] The composition of the sand and gravel mixture of the present invention will be described in detail below.

[0025] (1-1) Solidification of sand and gravel mixture The sand and gravel mixture packed into the bag solidifies upon contact between the calcium-containing sand and gravel and the iron powder contained within. More specifically, when calcium-containing sand and gravel come into contact with iron powder, the reactions shown in equations (1) through (4) below occur in a stepwise manner. As these reactions progress, the iron powder oxidizes, and the entire sand and gravel mixture gradually solidifies and becomes harder. Typically, solidification due to this reaction begins within a few days and becomes fully solidified in about two weeks.

[0026] [Table 1]

[0027] Furthermore, the inventors' investigations revealed that the sand and gravel mixture packed into the bag does not solidify uniformly. Specifically, the solidified sand and gravel mixture packed into the bags exhibited relatively high strength in the surface layer (near the surface in contact with the bag) and relatively low strength in the interior (near the center of the sand and gravel mixture). The reason is not entirely clear, but one possible cause is that the amount of oxygen decreases from the surface of the bag towards the interior, making it more difficult for the iron powder to oxidize.

[0028] Due to this characteristic of having different strengths in the surface layer and the interior, the sand and gravel mixture of the present invention can be expected to have the following effects, for example. - Due to the action of waves and other forces in the ocean, the contents of the bag deform to conform to the natural topography and slowly solidify as a whole, contributing to the stabilization of the ground in coastal areas. • The sand and gravel mixture has a self-healing function that allows it to re-solidify while maintaining its shape if it undergoes rapid deformation due to the effects of waves, etc. However, in all of the above cases, after a long period of time (for example, several decades or more), sufficient solidification will proceed even within the sand and gravel mixture, and it is possible that the surface layer and the interior will eventually have equivalent strength.

[0029] In one embodiment of the present invention, in a sand and gravel mixture two weeks after the start of solidification, the strength of the surface layer (the surface in contact with the bag) is 1.5 to 5 times higher than the strength of the interior of the sand and gravel mixture (the center of the sand and gravel mixture). Note that "the point at which solidification begins" refers to the point at which the sand and gravel mixture is packed into the bag.

[0030] (1-2) Calcium-containing sand and gravel In this invention, the "calcium-containing sand and gravel" can be any sand or gravel that contains calcium as a component. The calcium-containing sand and gravel may be a single type or a combination of multiple types.

[0031] In this invention, "gravel" includes mixtures of stones and sand. These stones and sands may contain materials that do not contain calcium.

[0032] In one aspect of the present invention, the calcium contained in calcium-containing sand and gravel is in the form of calcium carbonate. In a preferred embodiment of the present invention, the calcium contained in calcium-containing sand and gravel is in the form of calcium carbonate.

[0033] In a preferred embodiment of the present invention, the sand and gravel may satisfy the definition of "sand and gravel" in the "River Earthwork Manual" (April 2009, Japan Institute of Land and Infrastructure Management).

[0034] In a more preferred embodiment of the present invention, the sand and gravel is a mixture of stones and sand having an average particle size preferably in the range of 1 μm to 30 mm, more preferably in the range of 50 μm to 2 mm. The average particle size is determined according to "JIS A1204:2020 Method for testing particle size distribution of soil".

[0035] Calcium-containing sand and gravel are not particularly limited as long as they contain calcium, and examples include the following embodiments. • Sand and gravel derived from calcium-containing organisms (corals, shellfish, etc.) • Sand and gravel derived from calcium-containing rocks • Gravel that does not contain calcium and to which calcium-containing components (such as calcium carbonate) have been added.

[0036] From the viewpoint of ensuring that the effects of the present invention are stably achieved, the calcium-containing sand and gravel preferably includes coral sand and gravel, and more preferably consists of coral sand and gravel. In this invention, "coral gravel" refers to gravel derived from corals (organisms belonging to the class Anthozoa of the phylum Cnidaria), and includes, for example, crushed coral material.

[0037] The amount of calcium-containing sand and gravel in the sand and gravel mixture can be appropriately set according to the amount of iron powder, etc., as described later. In one embodiment of the present invention, the calcium-containing sand and gravel content is preferably 40-98 v / v%, more preferably 50-98 v / v%, and even more preferably 80-98 v / v%, relative to the sand and gravel mixture.

[0038] In a preferred embodiment of the present invention, the content of calcium-containing sand and gravel may be defined in terms of calcium carbonate (CaCO3) equivalent. In such cases, the calcium carbonate content is preferably 30 v / v% or more, more preferably 50-70 v / v%, and more preferably 80-95 v / v% relative to the sand and gravel mixture.

[0039] In one embodiment of the present invention, the sand and gravel mixture can come into contact with water (such as seawater). In such cases, the composition of the calcium-containing sand and gravel may be adjusted so that the amount of calcium (calcium ions) that dissolves in water is preferably 100 mg / L or more, more preferably 300 mg / L or more, and more preferably 300 to 500 mg / L.

[0040] (1-3) Iron powder In this invention, "iron powder" refers to an aggregate of iron (Fe) particles.

[0041] Iron powder is classified into reduced iron powder, atomized iron powder, and electrolytic iron powder depending on its manufacturing method, but any type of iron powder can be used in this invention. Furthermore, the iron powder of this invention consists of artificially manufactured iron particles and is clearly distinguishable from the iron components contained in calcium-containing sand and gravel.

[0042] In a preferred embodiment of the present invention, the average particle size of the iron powder is preferably 20 to 500 μm, more preferably 80 to 300 μm, and particularly preferably 100 to 200 μm. The average particle size is determined according to "JIS A1204:2020 Method for testing particle size distribution of soil".

[0043] The iron powder content in the sand and gravel mixture is 2-12 v / v% relative to the sand and gravel mixture. When the iron powder content is within the above range, the solidification of the sand and gravel mixture progresses. In a preferred embodiment of the present invention, further good solidification can be achieved by contacting the sand and gravel mixture containing iron powder within the above range with cyanobacteria and / or green algae, as described later.

[0044] From the viewpoint of easily achieving sufficient solidification, the lower limit of the iron powder content is 2 v / v% or more, preferably 5 v / v% or more, and more preferably 7.5 v / v% or more, relative to the sand and gravel mixture. The upper limit for the iron powder content is 12 v / v% or less, preferably 10 v / v% or less, and more preferably 7.5 v / v% or less, relative to the sand and gravel mixture, because sufficient solidification can be easily achieved even without excessive amounts.

[0045] (1-4) Other components added to the gravel mixture The sand and gravel mixture may or may not contain components other than those mentioned above, as long as they do not hinder the effects of the present invention.

[0046] In a preferred embodiment of the present invention, the sand and gravel mixture includes a foaming agent. In this invention, "foaming agent" includes any agent that generates oxygen gas. When a sand and gravel mixture containing a foaming agent is used, oxidation in the sand and gravel mixture is promoted, making it easier to increase the internal strength of the solidified sand and gravel mixture.

[0047] A typical reaction brought about by a foaming agent contained in a sand and gravel mixture is shown in equation (5).

[0048] [Table 2]

[0049] Examples of foaming agents include calcium peroxide.

[0050] The form of the foaming agent is not particularly limited and may be in powder, tablet, or other forms. In a preferred embodiment of the present invention, the foaming agent is in the form of a powder with an average particle size of 0.3 to 10 mm. The average particle size is determined according to "JIS A1204:2020 Method for testing particle size distribution of soil".

[0051] The foaming agent content is preferably 0.01 to 15 v / v%, more preferably 0.01 to 1 v / v%, relative to the sand and gravel mixture. When the foaming agent content is within this range, the oxidation reaction is moderately promoted, making it easier to increase the internal strength while maintaining a state where the surface strength of the solidified sand and gravel mixture is higher than the internal strength.

[0052] (1-5) Bag body The bag contains any container that is permeable to water and capable of holding a sand and gravel mixture inside.

[0053] In the present invention, "water-permeable bag" includes bags made of a material that allows water molecules (H2O) to pass through, bags that partially contain a material that allows water molecules (H2O) to pass through, and bags made of a material that does not allow water molecules (H2O) to pass through, with holes made in it. Because the bag is permeable to water, water molecules can move from the outside to the inside of the bag, or from the inside to the outside of the bag. Water molecules entering the bag from the outside to the inside come into contact with the sand and gravel mixture and contribute to the solidification reaction described above (equations (2), (3), etc.) and the reaction in the presence of cyanobacteria and / or green algae, which will be described later.

[0054] The material of the bag is not particularly limited as long as it is permeable to water. In a preferred embodiment of the present invention, from the viewpoint of reducing environmental impact, examples of materials for the bag include biodegradable materials (polylactic acid, polycaprolactone, polyglycolic acid, etc.) and plant fibers (hemp, coconut, cotton, etc.).

[0055] In a preferred embodiment of the present invention, the bag is made of a biodegradable material or plant fiber (preferably a biodegradable material). In this embodiment, the bag breaks or decomposes over time, exposing the contents of the bag, i.e., the solidified sand and gravel mixture. In such a case, the solidified sand and gravel mixture comes into direct contact with the ground and becomes more likely to integrate with the ground, thus potentially increasing the ground stabilization effect.

[0056] The size and shape of the bag are not particularly limited. In a preferred embodiment of the present invention, the size of the bag is such that one side or diameter is 50 to 150 cm. In a preferred embodiment of the present invention, the shape of the bag is square, triangular prism, cylindrical, etc.

[0057] In a preferred embodiment of the present invention, the bag has the shape and size of a large bag-type container known as a "flexible container bag."

[0058] In a preferred embodiment of the present invention, the bag has the shape and size of conventional sandbags. Common basic sizes for sandbags include "approximately 48 cm x approximately 60 cm" and "approximately 60 cm x approximately 100 cm".

[0059] The sand and gravel mixture of the present invention is a bag in which the sand and gravel mixture is packed inside. The content of the sand and gravel mixture in the bag is 70 v / v% or more, preferably 70 to 85 v / v%, relative to the volume of the bag, from the viewpoint of facilitating sufficient solidification of the sand and gravel mixture.

[0060] There are no particular limitations on the method of filling the inside of the bag with the sand and gravel mixture; any method using manual labor or machinery can be employed.

[0061] (1-6) Production of the sand and gravel mixture of the present invention In one embodiment of the present invention, a sand and gravel mixture is obtained by mixing or stirring each component constituting the sand and gravel mixture using any means. In a preferred embodiment of the present invention, the sand and gravel mixture is thoroughly stirred before being packed into a bag. After packing the sand and gravel mixture into the bag, the opening of the bag is closed as needed to obtain the sand and gravel mixture of the present invention.

[0062] (2) Contact with cyanobacteria and / or green algae In a preferred embodiment of the present invention, cyanobacteria and / or green algae may be brought into contact with the surface of the bag of the sand and gravel mixture of the present invention. According to this configuration, the solidification of the sand and gravel mixture (especially near the surface in contact with the bag) proceeds well, resulting in high strength in the surface layer of the bag's contents and low strength in the interior.

[0063] The reactions in equations (1) to (4) described above are accelerated under the oxygen supply of cyanobacteria and / or green algae, while equations (6) and (9) below also proceed, further solidifying the surface of the sand and gravel mixture (near the surface in contact with the bag). Such reaction systems also proceed in marine areas. More specifically, oxygen supply by cyanobacteria and / or green algae (equation (6)) promotes carbon dioxide consumption on the gravel surface through their photosynthesis and the production of calcium carbonate (crystallization) through carbonate ion generation (equations (7) to (9)). These reactions further solidify the surface of the gravel mixture, increasing its strength. Typically, this reaction results in a very good strength for the sand and gravel mixture within about six months.

[0064] [Table 3]

[0065] (2-1) Cyanobacteria and / or green algae Cyanobacteria and / or green algae may be present individually or in combination of two or more species.

[0066] Cyanobacteria are not particularly limited to oxygen-producing photosynthetic bacteria classified as blue-green algae, but examples include Leptolyngbya sp., Dichothrix sp., and Oscillatoria sp.

[0067] Algae are not particularly limited to oxygen-producing photosynthetic organisms other than mosses, ferns, and seed plants, but examples include Ulva prolifer, Spirogyra sp., and Chlorokybus sp.

[0068] (2-2) Contact conditions The conditions for bringing the sand and gravel mixture of the present invention into contact with cyanobacteria and / or green algae are not particularly limited. Any conditions can be adopted that do not inhibit the growth of cyanobacteria and / or green algae, and allow some or all of the surface of the components of the sand and gravel mixture of the present invention (bags and their contents) to come into contact with some or all of the cyanobacteria and / or green algae. In one preferred embodiment of the present invention, for efficiency of operation, part or all of the surface of the bag is brought into contact with part or all of the cyanobacteria and / or green algae.

[0069] The method for bringing the sand and gravel mixture of the present invention into contact with cyanobacteria and / or green algae is not particularly limited, but includes placing the cyanobacteria and / or green algae in a liquid (such as a culture medium) that does not inhibit their growth, and then spraying, coating, or immersing the resulting solution on part or all of the surface of the components of the sand and gravel mixture of the present invention (bags and their contents). Cyanobacteria and / or green algae may be shredded or otherwise processed as needed. In this embodiment, the amount of cyanobacteria and / or green algae contained in the solution is preferably 1 to 10 g / L. The amount of cyanobacteria and / or green algae contained in the solution can be determined based on the total surface area of ​​the bag, etc. For example, if the surface area of ​​the bag is 3000 cm² 2 For a size of 60cm x 50cm, 0.5 to 3 liters of a suspension of cyanobacteria and / or green algae (1 g / L) may be sprayed so that the surface of the bag is sufficiently moistened.

[0070] The location where the sand and gravel mixture of the present invention comes into contact with cyanobacteria and / or green algae is not particularly limited as long as it does not inhibit the growth of cyanobacteria and / or green algae, and may be on the ground surface, in marine areas, in freshwater areas, etc.

[0071] The contact time between the sand and gravel mixture of the present invention and cyanobacteria and / or green algae is not particularly limited and may be, for example, 24 hours or more.

[0072] As a result of sufficient contact between the sand and gravel mixture of the present invention and cyanobacteria and / or green algae, a solidified sand and gravel mixture with good strength is obtained.

[0073] (3) Method of solidifying the ground As described above, according to the present invention, a solidified sand and gravel mixture with high strength can be obtained by utilizing solidification by reaction of calcium-containing sand and gravel and iron powder, solidification by the action of a foaming agent, and solidification by the action of cyanobacteria and / or green algae. The present invention also includes, as an example of the application of such solidified materials, a method for solidifying ground (hereinafter also referred to as "the solidification method of the present invention"). In the solidification method of the present invention, the above-described configuration can be appropriately adopted.

[0074] (3-1) Step of applying a sand and gravel mixture to the ground surface. The solidification method of the present invention includes the step of providing the sand and gravel mixture of the present invention to the ground surface.

[0075] The method for providing the sand and gravel mixture of the present invention to the ground surface is not particularly limited, and for example, conditions similar to those for conventionally known sandbags can be employed. One such method involves, for example, placing the sand and gravel mixture of the present invention, in its bags, onto any surface of the ground and leaving it undisturbed.

[0076] In a preferred embodiment of the present invention, the sand and gravel mixture of the present invention is left to stand in any outdoor location where ground reinforcement is required. Such locations include coastal areas (land and / or sea), within sea areas, outside river embankments, slopes, and the like.

[0077] In one embodiment of the present invention, after the sand and gravel mixture of the present invention is placed on the ground surface, the contents are exposed when the bag decomposes or breaks. Subsequently, over time, the solidified sand and gravel mixture and the ground surface assimilate, and the solidified sand and gravel mixture can become part of the ground. Since the solidified material has good strength, the ground can be stabilized effectively.

[0078] (3-2) Application Examples The solidification method of the present invention can be used for the following purposes, for example. • Measures to counter erosion caused by rising sea levels, storm surges, and waves associated with global warming. • A substitute for artificial breakwaters. • Long-term stabilization of structures using conventional sandbags and flexible containers. • Restoration, re-solidification, and stabilization of ground deformed by the effects of waves, etc. • The growth base of a plant.

[0079] (4) Plant growth methods As described above, according to the present invention, a solidified sand and gravel mixture with high strength can be obtained by utilizing solidification by reaction of calcium-containing sand and gravel and iron powder, solidification by the action of a foaming agent, and solidification by the action of cyanobacteria and / or green algae. Such solidified materials can also be used as a growth base for plants. Therefore, the present invention also includes a method for growing plants (hereinafter referred to as "the growth method of the present invention") as an example of the application of solidified materials. The above-described configuration can be appropriately adopted in the growth method of the present invention.

[0080] The conditions for the growth method of the present invention are not particularly limited, and examples include attaching plant seeds or any part of a plant (such as roots) to the surface of the bag or placing it inside the bag, and then sprinkling water as appropriate.

[0081] The plants to be grown in the cultivation method of the present invention are not particularly limited and include any plants that can adapt to the environment of the site where the sand and gravel mixture of the present invention is installed. For example, when the sand and gravel mixture of the present invention is installed in a coastal area, preferred plants to grow on are coastal plants (such as mangrove species (e.g., Rhizophora stylosa, Calystegia soldanelloides, Crinum asiaticum, Pandanus oxyphyllus, etc.)). [Examples]

[0082] The present invention will be described more specifically below based on examples, but the present invention is not limited to these examples.

[0083] <Test 1: Solidification of sand and gravel mixture packed in bags - 1> The following method was used to prepare a mixture of sand and gravel packed into bags, and the effects of exposure to seawater on its physical properties were investigated.

[0084] (1) Preparation of the bag A biodegradable bag (made of hemp, 15 cm long x 10 cm wide) was prepared as the bag material. This bag is permeable to water, and when the bag is immersed in water, water enters the inside from the surface of the bag.

[0085] (2) Preparation of sand and gravel mixture First, coral gravel (coral fragments, equivalent to calcium-containing gravel) with a median particle size (D50) of approximately 1.3 mm was collected from sandy and gravelly beaches in Japan. It was confirmed that this coral gravel contained almost no iron. Iron powder (pure iron powder, average particle size 100 μm) was mixed with this coral sand and gravel to prepare sand and gravel containing 5 v / v% iron powder.

[0086] (3) Preparation of the sand and gravel mixture packed into bags The sand and gravel mixture was placed in a bag to fill it with at least 60 v / v% of its volume, thereby obtaining the sand and gravel mixture packed into the bag.

[0087] (4) Creation of a simulated coastal environment A tank filled with seawater was set up inside the room. The sand and gravel mixture, packed in bags, is placed at the bottom of this tank so that the entire contents are submerged in seawater. The tank is then exposed to tidal changes (approximately 3 hours of exposure per day and night) and light (light intensity: 1000-2000 μmol / m²). 2 They were exposed to / s) for 60 days.

[0088] (5) Measurement of the strength of the sand and gravel mixture packed in the bag During the exposure period, the sand and gravel mixture packed into bags was removed from the water tank, and the strength of the contents of the bags was measured in the surface layer (near the surface in contact with the bag) and the interior (approximately 15 mm from the surface) using the needle penetration test method (Japanese Geotechnical Society standard). The results are shown in Figure 1.

[0089] As shown in Figure 1, the surface layer developed an intensity of approximately 2 MPa from 28 days after the start of exposure, but the intensity in the interior was less than 1 MPa. The reason for the difference in strength between the surface and the interior is thought to be that while the solidification of the sand and gravel mixture requires oxygen, insufficient oxygen is supplied to the interior. Given these properties of the sand and gravel mixture, it is expected that the contents of the bag will slowly solidify as they deform to conform to the natural topography due to the action of waves and other forces in the sea, contributing to the stabilization of the ground in coastal areas. Furthermore, if the sand and gravel mixture undergoes rapid deformation due to the effects of waves or other forces, it is expected to have a self-healing function that will allow it to solidify again while maintaining its shape.

[0090] <Test 2: Solidification of sand and gravel mixture packed in bags - 2> As shown in Test 1, it was confirmed that the solidification of the sand and gravel mixture is accelerated in seawater. As mentioned above, the solidification of the sand and gravel mixture requires the oxidation of iron by oxygen. In actual marine environments, such a reaction can be promoted by oxygen supply from cyanobacteria and green algae. Therefore, in this example, the same test as in Test 1 was conducted by applying a suspension containing cyanobacteria and green algae to the surface of a sand and gravel mixture packed into a bag using the following method.

[0091] A sand and gravel mixture packed into bags was prepared using the same method as in Experiment 1. Next, 100-300g (total amount) of cyanobacteria (Leptolyngbya sp., etc.) and green algae (Ulva prolifera, etc.) were added to 1L of seawater and mixed in a blender to obtain a suspension. The resulting suspension was diluted with seawater to an algal content of 1-10g / L and sprayed onto the surface of the sand and gravel mixture packed into the bag (the surface of the bag).

[0092] The sand and gravel mixture, obtained by the method described above and packed into bags, was placed in a simulated coastal environment using the same method as in Experiment 1. As a result, similar to Test 1, the strength of the outer layer of the bag's contents was high, while the strength of the inner layer was low. Furthermore, when the amount of algae on the surface of the sand and gravel mixture packed into the bags (the surface of the bags) was calculated, it was observed that algae proliferated over time.

[0093] <Test 3: Solidification of sand and gravel mixture packed in bags - 3> As shown in tests 1 and 2 above, it was confirmed that solidified material with different strengths could be obtained in the surface layer and the interior. On the other hand, when using sand and gravel mixtures packed into bags as sandbags or the like, there may be a need for a configuration in which the strength differs between the surface and the interior, but with higher internal strength. Therefore, in this example, we attempted to promote oxidation within the solidified material by adding a foaming agent (an oxygen-generating agent) to the sand and gravel mixture using the following method.

[0094] A commercially available solid foaming agent (tablet type) was crushed to a diameter of approximately 1 to 10 mm and mixed with the sand and gravel mixture prepared in the same manner as in Test 1, at concentrations of 2.5, 5, or 10 g / L. Next, similar to Test 1, a sand and gravel mixture was prepared in bags and left to stand in a simulated coastal environment. After that, the internal strength of the contents of the bags was measured. The results are shown in Figure 2.

[0095] As shown in Figure 2, the internal strength was increased by incorporating a foaming agent. However, although the data is not shown, in all examples the strength of the surface layer was 3 to 5 times higher than the strength of the interior.

[0096] <Test 4: Solidification of sand and gravel mixture packed into bags - 4> Instead of leaving the sand and gravel mixture, obtained using the same method as in Experiment 1, in a simulated coastal environment, we planted Rhizophora stylosa, a mangrove species belonging to the Rhizophoraceae family, on the surface of the bags and allowed it to grow for 120 days while periodically sprinkling it with seawater. As a result, the roots and plant bodies of Rhizophora stenocephala grew stably on the surface and / or within the solidified sand and gravel mixture. Therefore, it was confirmed that the solidified sand and gravel mixture can serve as a suitable ground for plant growth.

Claims

1. A mixture of sand and gravel packed into a bag, The aforementioned sand and gravel mixture contains calcium-containing sand and gravel and iron powder. The iron powder content is 2 to 12 v / v% relative to the sand and gravel mixture. The content of the aforementioned sand and gravel mixture is 70 v / v% or more relative to the volume of the bag, The bag body has water permeability. gravel mixture.

2. The gravel mixture according to claim 1, wherein the calcium-containing gravel includes coral gravel.

3. The sand and gravel mixture according to claim 1, wherein the sand and gravel mixture contains 0.01 to 15 v / v% of a foaming agent relative to the sand and gravel mixture.

4. The sand and gravel mixture according to claim 1, wherein cyanobacteria and / or green algae are in contact with the surface of the bag.

5. The sand and gravel mixture according to claim 1, wherein the average particle size of the iron powder is 20 to 500 μm.

6. The sand and gravel mixture according to claim 1, wherein the bag is biodegradable.

7. A method for solidifying ground, comprising the step of installing the sand and gravel mixture described in any one of claims 1 to 6 on the ground surface.

8. A method for growing plants, comprising a method for growing plants on and / or inside a sand and gravel mixture according to any one of claims 1 to 6.

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