Method for producing solidified calcium-containing sand and gravel, and method for solidifying the ground.

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 method for producing a solidified product of calcium-containing sand and gravel, the method comprising the steps of: obtaining iron powder-containing sand and gravel by mixing calcium-containing sand and gravel and iron powder; and contacting the iron powder-containing sand and gravel with cyanobacteria and / or green algae, wherein the iron powder content in the iron powder-containing sand and gravel is 2 to 12 v / v%.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a solidified product of calcium-containing gravel and a method for solidifying ground.

Background Art

[0002] Due to the influence 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 taking countermeasures against wave erosion is increasing.

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

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] On the other hand, there is a need for a technology that can more stably stabilize the ground in coastal areas and the like.

[0006] 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] (1) A method for producing solidified calcium-containing sand and gravel, The aforementioned manufacturing method A process to obtain iron powder-containing sand and gravel by mixing calcium-containing sand and gravel with iron powder, The process of bringing the iron powder-containing sand and gravel into contact with cyanobacteria and / or green algae, Includes, The iron powder content in the aforementioned iron powder-containing sand and gravel is 2 to 12 v / v%. Manufacturing method.

[0009] (2) The method for producing the calcium-containing sand and gravel according to (1), wherein the calcium-containing sand and gravel is coral sand and gravel.

[0010] (3) A method for solidifying the ground, The solidification method described above is A process of creating layers of calcium-containing sand and gravel and iron-containing sand and gravel containing iron powder on the ground surface, The process involves bringing the iron powder-containing sand and gravel into contact with cyanobacteria and / or green algae, Includes, The iron powder content in the aforementioned iron powder-containing sand and gravel is 2 to 12 v / v%. Solidification method.

[0011] (4) The solidification method according to (3), wherein the calcium-containing sand and gravel is coral sand and gravel.

[0012] (5) The solidification method according to (3) or (4), wherein the thickness of the layer of iron powder-containing sand and gravel provided on the ground surface is 3 to 30 cm.

[0013] (6) The solidification method according to any one of (3) to (5), wherein the average particle size of the iron powder is 20 to 200 μm.

[0014] (7) The cyanobacteria and / or green algae are attached to a sheet-like material, The aforementioned contact is the contact between the iron powder-containing sand and gravel and the sheet-like material. The solidification method described in any of (3) to (6).

[0015] (8) The solidification method according to (7), wherein the sheet-like material is made of a biodegradable material.

Advantages of the Invention

[0016] According to the present invention, a technique for stabilizing the ground in coastal areas and the like is provided.

Brief Description of the Drawings

[0017] [Figure 1] It is a diagram showing the strength of iron powder-containing gravel in contact with cyanobacteria and green algae in an example. [Figure 2] It is a diagram showing the strength of a layer of iron powder-containing gravel in contact with cyanobacteria and green algae in an example. [Figure 3] It is a diagram showing the change in ground elevation in an example.

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments.

[0019] (1) Method for producing a solidified product of calcium-containing gravel The method for producing a solidified product of calcium-containing gravel according to the present invention (hereinafter, also referred to as "the production method of the present invention") satisfies the following requirements in one aspect. · A step of obtaining iron powder-containing gravel by mixing calcium-containing gravel and iron powder, and a step of bringing the obtained iron powder-containing gravel into contact with cyanobacteria and / or green algae. · The content of iron powder in the iron powder-containing gravel is 2 to 12 v / v%.

[0020] 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, stabilizing the ground in coastal areas and other similar locations is crucial. In this invention, "ground stabilization" encompasses suppressing the decrease in ground strength, improving ground strength, and so on.

[0021] As a result of diligent research by the inventors, it was found that the solidified calcium-containing sand and gravel obtained through the above process 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 whether it is in a land or sea area. For example, by implementing the manufacturing method of the present invention on the ground surface in a coastal area (land and / or sea), solidified calcium-containing sand and gravel can be placed on the ground surface, thereby reinforcing the ground in coastal areas.

[0022] In this invention, "strength (of the ground or solidified calcium-containing sand and gravel)" encompasses the strength specified in JIS A1216:2020. According to the present invention, for example, by placing a solidified calcium-containing sand and gravel obtained by the manufacturing method of the present invention on the ground surface, the above strength is improved compared to when the solidified material is not placed.

[0023] The configuration of the manufacturing method of the present invention will be described in detail below.

[0024] (1-1) Process for obtaining iron powder-containing sand and gravel In the process of obtaining iron powder-containing sand and gravel, an iron powder-containing sand and gravel mixture, which is a mixture of calcium-containing sand and gravel and iron powder, is obtained. The iron powder content in such iron powder-containing sand and gravel is 2 to 12 v / v%.

[0025] When calcium-containing gravel comes into contact with iron powder, the reactions shown in equations (1) to (4) below occur in a stepwise manner. As this reaction progresses, the iron powder oxidizes, and the entire mixture of calcium-containing gravel and iron powder gradually solidifies and hardens. Typically, solidification due to this reaction begins within a few days and becomes fully solidified in about two weeks.

[0026] [Table 1]

[0027] (1-1-1) 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.

[0028] In this invention, "gravel" includes mixtures of stones and sand. These stones and sands may contain materials that do not contain calcium.

[0029] 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 the calcium-containing sand and gravel is in the form of calcium carbonate.

[0030] 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).

[0031] 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".

[0032] 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.

[0033] 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.

[0034] (1-1-2) Iron powder In this invention, "iron powder" refers to an aggregate of iron (Fe) particles.

[0035] 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.

[0036] In a preferred embodiment of the present invention, the average particle size of the iron powder is preferably 20 to 200 μm, more preferably 80 to 120 μm, and particularly preferably about 100 μm. The average particle size is determined according to "JIS A1204:2020 Method for testing particle size distribution of soil".

[0037] (1-1-3) Sand and gravel containing iron powder Iron powder-containing sand and gravel can be obtained by mixing calcium-containing sand and gravel with iron powder.

[0038] The method for mixing calcium-containing sand and iron powder is not particularly limited as long as the calcium-containing sand and iron powder can come into contact with each other, and any stirring means can be used.

[0039] The iron powder content in iron powder-containing sand and gravel is 2-12 v / v%. When the iron powder content is within the above range, the solidification of the iron powder-containing sand and gravel progresses, and furthermore, sufficient solidification can be achieved through contact with cyanobacteria and / or green algae, as described later.

[0040] 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 iron powder-containing sand and gravel. 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 iron powder-containing sand and gravel, because sufficient solidification can be easily achieved even without excessive amounts.

[0041] The amount of calcium-containing sand and gravel in iron powder-containing sand and gravel can be appropriately set according to the amount of iron powder, etc. In one embodiment of the present invention, the content of calcium-containing sand and gravel in the iron powder-containing sand and gravel is preferably 40 to 98 v / v%, more preferably 50 to 98 v / v%, and even more preferably 80 to 98 v / v%.

[0042] 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 in the iron powder-containing sand and gravel is preferably 30 v / v% or more, more preferably 50 to 70 v / v% or more, and more preferably 80 to 95 v / v%.

[0043] In one embodiment of the present invention, the iron powder-containing sand and gravel 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 to 400 mg / L, and even more preferably 400 mg / L or more.

[0044] The iron powder-containing sand and gravel may or may not contain other components, as long as they do not hinder the effects of the present invention.

[0045] The resulting iron powder-containing sand and gravel may be immediately subjected to a step in contacting cyanobacteria and / or green algae, or it may be subjected to a step after a period of time (e.g., within 24 hours).

[0046] (1-2) A step of bringing iron powder-containing sand and gravel into contact with cyanobacteria and / or green algae. The iron-containing sand and gravel obtained by mixing calcium-containing sand and gravel with iron powder is brought into contact with cyanobacteria and / or green algae.

[0047] The reactions in equations (1) to (4) described above are accelerated under the oxygen supply of cyanobacteria and / or green algae, while equations (5) and (8) below also proceed, further solidifying the iron powder-containing sand and gravel. Such reaction systems also proceed in marine areas. More specifically, oxygen supply by cyanobacteria and / or green algae (Equation (5)) promotes carbon dioxide consumption on the gravel surface through their photosynthesis and the production of calcium carbonate (crystallization) through carbonate ion generation (Equations (6)-(8)). These reactions further solidify the iron powder-containing gravel, increasing its strength. Typically, this reaction results in the iron powder-containing sand and gravel becoming very strong within about six months.

[0048] [Table 2]

[0049] (1-2-1) Cyanobacteria and / or green algae Cyanobacteria and / or green algae may be present individually or in combination of two or more species.

[0050] 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.

[0051] 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.

[0052] (1-2-2) Contact conditions The conditions for bringing iron powder-containing sand and gravel into contact with cyanobacteria and / or green algae are not particularly limited, and 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 iron powder-containing sand and gravel to come into contact with some or all of the cyanobacteria and / or green algae.

[0053] One method for bringing iron powder-containing sand and gravel into contact with cyanobacteria and / or green algae is to place a sheet-like material (mat, cloth, sheet, etc.) on which cyanobacteria and / or green algae are attached on the surface of the iron powder-containing sand and gravel.

[0054] From the viewpoint of promoting oxygen production from cyanobacteria and / or green algae, sheet-like materials made of plant fibers (hemp, coconut, cotton, etc.) or biodegradable materials (polylactic acid, polycaprolactone, polyglycolic acid, etc.) are preferred.

[0055] There are no particular limitations on the method for attaching cyanobacteria and / or green algae to a sheet-like material, but examples include placing 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 sheet-like material with the resulting solution.

[0056] The location where iron powder-containing sand and gravel come 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 the ground surface, in marine areas, in freshwater areas, etc.

[0057] The contact time between the iron powder-containing sand and gravel and the cyanobacteria and / or green algae is not particularly limited and may be, for example, 24 hours or more.

[0058] (1-3) Solidified calcium-containing sand and gravel As a result of sufficient contact between iron powder-containing sand and gravel and cyanobacteria and / or green algae, a solidified product of calcium-containing sand and gravel is obtained.

[0059] Solidified calcium-containing sand and gravel possess good strength. In a preferred embodiment of the present invention, when contact is made with the ground surface, as time passes, the solidified calcium-containing sand and gravel assimilates with the ground surface, and the solidified calcium-containing sand and gravel can become part of the ground.

[0060] (2) Method of solidifying the ground As described above, according to the present invention, a solidified material with high strength can be obtained by utilizing solidification through the reaction of calcium-containing sand and gravel with iron powder, or 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 conditions in the manufacturing method of the present invention can be appropriately adopted.

[0061] (2-1) Process of creating a layer of iron powder-containing sand and gravel on the ground surface. The solidification method of the present invention includes the step of providing a layer of iron powder-containing sand and gravel on the ground surface (however, the manufacturing method of the present invention also includes embodiments that include such a step).

[0062] The thickness of the layer of iron powder-containing sand and gravel placed on the ground surface is not particularly limited, but from the viewpoint of easily achieving a high ground stabilization effect, it is preferably 3 to 30 cm, more preferably 10 to 15 cm. Furthermore, the layer of iron powder-containing sand and gravel is placed on the outermost surface of the ground. Therefore, "the thickness of the layer of iron powder-containing sand and gravel placed on the ground surface" refers to the thickness from the outermost surface of the ground to the outermost layer of the iron powder-containing sand and gravel layer (on the opposite side from the outermost surface).

[0063] The required amount of calcium-containing sand and gravel and iron powder can be calculated based on the area and thickness of the ground, as well as the area and thickness of the iron powder-containing sand and gravel layer to be constructed.

[0064] In a preferred embodiment of the present invention, the following are examples of methods for providing a layer of iron powder-containing sand and gravel on the ground surface. These methods and means may be used individually or in combination. (Method 1) Mix iron powder into the surface of the ground containing calcium-containing sand and gravel (for example, ground containing naturally deposited coral sand and gravel). (Method 2) Mix calcium-containing sand and gravel and iron powder onto any ground surface (for example, a ground surface that contains little to no calcium-containing sand and gravel).

[0065] The following are examples of "Method 1" mentioned above. After scattering iron powder on the ground surface, the ground surface is stirred. After sprinkling iron powder on the excavated ground surface, the ground surface is stirred.

[0066] The following are examples of "Method 2" mentioned above. • After spreading a mixture of calcium-containing sand and gravel and iron powder on the ground surface, the ground surface is stirred. • After scattering a mixture of iron powder onto the surface of an existing gravel zone (containing calcium), the surface of the ground is stirred.

[0067] Any mixing method can be used for excavating or stirring the ground surface. Such agitation methods can be appropriately set according to the scale of the ground surface, and may be manual, mechanical, or water-based.

[0068] Manual tools include rakes, hoes, shovels, spike rollers (rollers with protrusions on the surface), pitchforks (tools with multiple teeth on a long handle), and tamping sticks.

[0069] Mechanical methods include vibrators (such as concrete vibrators), electric mixers, water jets, tillers (such as rotary tillers), harrows (machines attached to tractors that mix soil using plows or discs), and quad aerators.

[0070] As a means using water flow, for example, as in "Method 2" above, a method is used in which the mixture or iron powder is scattered and then the ground surface is agitated by spraying water. Examples of means for spraying water include hoses and spray nozzles. By spraying water, a water flow is created on the ground surface, which mixes the iron powder into the sand and gravel. The action of the water also agitates the sand and gravel, allowing the iron and sand to be uniformly mixed.

[0071] After laying the layer of iron powder-containing sand and gravel, the ground surface may be compressed and compacted. Examples of such methods include using a vibrating plate (compactor).

[0072] (2-2) Step of contacting cyanobacteria and / or green algae The layer of iron powder-containing sand and gravel is brought into contact with cyanobacteria and / or green algae.

[0073] In a preferred embodiment of the present invention, a sheet-like material on which cyanobacteria and / or green algae are attached is laid on the ground surface to bring the layer of iron powder-containing sand and gravel into contact with the cyanobacteria and / or green algae.

[0074] After the above contact, as time passes, the layer of iron-containing sand and gravel becomes part of the ground. Since the iron-containing sand and gravel has good strength, it can stabilize the ground on which the layer of iron-containing sand and gravel is provided. [Examples]

[0075] The present invention will be described more specifically below based on examples, but the present invention is not limited to these examples.

[0076] <Test 1: Solidification of iron powder-containing sand and gravel - 1> The following method was used to prepare iron powder-containing sand and gravel, and the effects on its physical properties in the presence of cyanobacteria and green algae were examined.

[0077] (1) Preparation of sand and gravel containing iron powder 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 50 μm) was mixed with this coral sand gravel in a ratio of 1.25, 2.5, 5.0, or 10.0 v / v% to prepare iron powder-containing gravel. Each type of iron powder-containing sand and gravel was packed into a molded tube with a diameter of 50 mm (height of 10 cm). The molded tubes used had open ends.

[0078] (2) Creation of a simulated coastal environment A tank filled with seawater was set up inside the room. A molded tube filled with iron powder-containing sand and gravel was placed vertically at the bottom of the tank, and seawater was then introduced into the molded tube. Next, a mat containing coconut and hemp components (10 mm thick, biodegradable) was placed directly on the opening of the molded tube (the opening on the opposite side from the bottom of the tank). Cyanobacteria (such as Leptolyngbya sp.) and green algae (such as Ulva prolifera) were pre-attached to this mat. This arrangement resulted in contact between the iron powder-containing sand and gravel, the cyanobacteria, and the green algae. While maintaining the above configuration, the system was exposed to the tidal cycle of seawater every 12 hours for two weeks.

[0079] (3) Measurement of the strength of iron powder-containing sand and gravel After the exposure period, the molded tubes were removed from the water tank, broken open, and the iron powder-containing sand and gravel were recovered. Each of the recovered iron powder-containing sand and gravel had formed into a concrete-like mass. Next, the strength of the obtained iron powder-containing sand and gravel was measured using the needle penetration test method (Japanese Geotechnical Society standard). The results are shown in Figure 1.

[0080] As shown in Figure 1, when the iron powder content was 2.5 v / v% or higher, it solidified only partially. When the content was 5.0 v / v% or higher, it solidified completely, and a stable strength of approximately 1 to 1.2 MPa was observed. This was presumed to be because the oxidation of the iron powder was promoted by oxygen supplied by cyanobacteria and green algae, resulting in the acquisition of a strong oxide.

[0081] Although data is not shown, when using mats without cyanobacteria or green algae attached using the above method, sufficient solidification was not observed regardless of the iron powder content (below 0.6 MPa).

[0082] <Test 2: Solidification of iron powder-containing sand and gravel - 2> As shown in Experiment 1, it was confirmed that the solidification of iron powder-containing sand and gravel is accelerated in the presence of cyanobacteria and green algae. Therefore, in this example, we conducted a test similar to Test 1 in a coastal area to confirm whether it is possible to solidify the coral sand and gravel on the coast.

[0083] The following tests were conducted in a naturally occurring area of ​​coral sand and gravel in the intertidal zone of a coastal region in Japan.

[0084] (1) Mixing iron powder into coral gravel The entire surface of naturally deposited coral sand and gravel (approximately 4m 2 After sprinkling iron powder (average particle size 50 μm) onto the coral gravel, the surface layer was stirred using a concrete vibrator (manufactured by Makita Corporation) and an electric mixer (manufactured by Makita Corporation). Through both of these processes, it was possible to mix iron powder into the coral gravel at a concentration of 7.0-8.0 v / v% from the surface down to a depth of approximately 10 cm. In other words, this process made it possible to create layers of calcium-containing sand and gravel and iron-containing sand and gravel containing iron powder on the ground surface.

[0085] The amount of iron powder to be scattered was calculated based on the area of ​​the coral gravel, resulting in a value of 7.0-8.0 v / v% relative to the coral gravel. Specifically, the amount of iron powder to be scattered was calculated per 1 m of coral gravel. 2 The weight range was set to 13.5-27 kg per person.

[0086] (2) Installation of the mat Similar to Experiment 1, a mat containing coconut and hemp components (30 mm thick) was prepared and laid over the entire area of ​​coral sand and gravel that had been sprinkled with iron powder. This mat was pre-inoculated with cyanobacteria (such as Leptolyngbya sp.) and green algae (such as Ulva prolifer). This arrangement resulted in contact between the iron-containing sand and gravel and the cyanobacteria and green algae. As a control, a similar experiment was conducted in which the mats were arranged in the same way, except that cyanobacteria and green algae were not allowed to attach to them. The above configuration was maintained and left untouched for 1 year and 7 months (July 2022 to April 2024).

[0087] (3) Measurement of the strength of iron powder-containing sand and gravel The surface strength (uniaxial compressive strength) of each group was measured in accordance with JIS A1216:2020 at various points during and after the test period. The results are shown in Figure 2. Furthermore, at the end of the testing period, the mat had decomposed, and the gravel layer was exposed.

[0088] As shown in Figure 2, according to the method that satisfies the conditions of the present invention, solidification of the sand and gravel layer over time was observed, and its strength reached 1 MPa two weeks after the start of the test, 1.5 to 1.8 MPa after six months, and 1.8 to 2.0 MPa after one year. On the other hand, in the control group, almost no solidification of the sand and gravel layer was observed.

[0089] Furthermore, in the area where this example test was conducted (including the location where the test was performed), waves caused by typhoons and low-pressure systems were observed, and ground deformation of up to 15 cm was confirmed. However, as shown in Figure 3, when using the method that satisfies the conditions of the present invention, virtually no change in ground elevation was observed. Furthermore, algae and cyanobacteria were naturally growing on the surface of the sand and gravel layer.

[0090] From the above, it has been found that the present invention can solidify sand and gravel layers and achieve ground stabilization in coastal areas and other similar locations.

Claims

1. A method for producing solidified calcium-containing sand and gravel, The aforementioned manufacturing method A process to obtain iron powder-containing sand and gravel by mixing calcium-containing sand and gravel with iron powder, The process of bringing the iron powder-containing sand and gravel into contact with cyanobacteria and / or green algae, Includes, The iron powder content in the aforementioned iron powder-containing sand and gravel is 2 to 12 v / v%. Manufacturing method.

2. The manufacturing method according to claim 1, wherein the calcium-containing sand and gravel is coral sand and gravel.

3. A method for solidifying the ground, The solidification method described above is A process of creating layers of calcium-containing sand and gravel and iron-containing sand and gravel containing iron powder on the ground surface, The process involves bringing the iron powder-containing sand and gravel into contact with cyanobacteria and / or green algae, Includes, The iron powder content in the aforementioned iron powder-containing sand and gravel is 2 to 12 v / v%. Solidification method.

4. The solidification method according to claim 3, wherein the calcium-containing sand and gravel is coral sand and gravel.

5. The solidification method according to claim 3, wherein the thickness of the layer of iron powder-containing sand and gravel provided on the ground surface is 3 to 30 cm.

6. The solidification method according to claim 3, wherein the average particle size of the iron powder is 20 to 200 μm.

7. The cyanobacteria and / or green algae are attached to a sheet-like material, The aforementioned contact is the contact between the iron powder-containing sand and gravel and the sheet-like material. The solidification method according to claim 3.

8. The solidification method according to claim 7, wherein the sheet-like material is made of a biodegradable material.

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