Greening soil covering material

Abstract

To provide a greening soil covering material excellent in greening function while improving erosion resistance of the soil covering material.SOLUTION: The greening soil covering material 1 is obtained by mixing soil 2 with a solidifying material using only blast furnace slag fine powder 3 without using cement to form treated soil, and blending the treated soil with a void forming means 5. By using only the blast furnace slag fine powder 3 without using cement as a solidifying material, the pH of the greening soil covering material 1 is kept from neutral to weakly alkaline, and since a solidifying speed is delayed, an environment for easily performing the initial growth of plants can be maintained. By blending the void forming means 5 with the treated soil, an increase in viscosity during kneading can be suppressed, and a gas phase necessary for plant growth can be secured. As the void forming means 5, any of beads composed of a bead-like water-absorbing polymer, a foaming agent and a biodegradable resin is used.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a greening soil cover material that has improved erosion resistance and excellent greening function. [Background technology]

[0002] In recent years, the increasing intensity and concentration of rainfall has led to frequent floods that far exceed the capacity of flood control facilities, and according to the Non-Patent Document 1 listed below, flooding caused by Typhoon No. 19 of 2019 (the 2019 East Japan Typhoon) resulted in the collapse of river levees in 142 locations across the country (86% of which were caused primarily by overflowing), and caused extensive damage, including the inundation of approximately 35,000 hectares. It is expected that flood damage will become even more frequent and severe due to climate change in the future, and there is a need to prevent and mitigate this damage.

[0003] In order to prevent and mitigate flood damage, the basic principle will remain the same as it has been in the past: to lower river water levels as much as possible during floods by dredging and widening river channels and constructing flood control facilities such as dams and floodplains. However, there is an increasing need to implement efficient and effective measures to reduce damage caused by flooding as much as possible, even in the case of floods that exceed the capacity of flood control facilities, and the Ministry of Land, Infrastructure, Transport and Tourism has indicated that it is necessary to consider measures to strengthen river levees against overflows.

[0004] For this reason, there is a need for river levees with a resilient structure that is less likely to collapse even if the water overflows, and that has the effect of reducing disasters by lengthening the time until the levees collapse ("resilient river levees" even if they are overflowed).

[0005] As shown in Figure 2, the mechanism by which river levees collapse due to overtopping occurs when water overflows the top of the levee and flows onto the backside of the river (Figure 2(A)). This causes erosion by scouring the toe of the slope on the backside of the river (Figure 2(B)), which then causes the backside slope to collapse (Figure 2(C)), leading to the collapse of the top of the levee.

[0006] As a method for preventing erosion of slopes and other surfaces, for example, Patent Document 1 listed below discloses the formation of a permeable improvement body made mainly of cement-based materials on part of the backside slope, including the bottom of the slope, and Patent Document 2 listed below discloses the construction of the surface of a levee body with improved soil made from a mixture of local soil and sand, cement material, short fiber material, water-blocking material, and water. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2020-133311 [Patent Document 2] Japanese Patent Application Publication No. 2022-62469 [Non-patent literature]

[0008] [Non-Patent Document 1] Technical Review Committee on Strengthening River Levees, Reference Material 1, Report of the Technical Review Committee on River Levees in light of the damage caused by Typhoon No. 19 of 2019, August 2020 Summary of the Invention [Problem to be solved by the invention]

[0009] Conventional erosion prevention methods disclosed in Patent Documents 1 and 2, etc., use cement-based solidification materials in the cover soil to improve the erosion resistance of the embankment surface (cover soil) against overflowing, thereby increasing the effectiveness of slowing surface erosion.

[0010] However, when cement-based solidification materials are used to cover the embankment, the following problems arise. (1) The amount of cement-based solidification material added makes the improved soil too hard, preventing plant roots from taking root. (2) Generally, a slightly acidic to neutral pH (pH 5.2 to 8.5) is most suitable for plant growth, but the use of cement-based solidification materials makes the soil highly alkaline, inhibiting plant growth. (3) A gas phase ratio of 20 to 30% is most suitable for plant growth, but in cement-based solidification materials, the gas phase ratio is less than 10%, which has a negative impact on plant growth. (4) Depending on the characteristics of the local soil and its compatibility with the cement-based solidification material being mixed, there is a risk that hexavalent chromium may leach out in amounts exceeding environmental standards.

[0011] In this way, when cement-based solidification materials are used to cover the embankment, the growing environment for plants is significantly reduced, making it difficult for plants to grow, and when used on river embankments, etc., there are problems such as damage to the natural environment and scenery.

[0012] Therefore, a main object of the present invention is to provide a greening soil cover material that has excellent greening function while improving the erosion resistance of the soil cover material. [Means for solving the problem]

[0013] In order to solve the above problems, the present invention according to claim 1 provides treated soil in which a solidification material using only ground granulated blast furnace slag without using cement is mixed with the soil, A greening soil covering material is provided, characterized in that a void-forming means is blended into this treated soil.

[0014] In the invention described in claim 1, first, treated soil mixed with a solidifying agent consisting only of ground granulated blast furnace slag is used as a covering material, so that the ground granulated blast furnace slag undergoes a hardening reaction and the soil solidifies. Therefore, when used as covering soil for embankments, etc., erosion due to scouring is unlikely to occur even if the soil overflows due to flooding, and it is possible to prevent the embankment from collapsing.

[0015] Furthermore, by using only blast furnace slag powder as a solidification material without using cement, the pH of the greening soil cover material is maintained at a neutral to slightly alkaline level, and the solidification rate is slowed (strength development proceeds slowly), which maintains an environment that is favorable for the initial growth of plants, such as germination, rooting, and root spread.As the surface of the cover soil is covered with plants, the natural environment and landscape can be preserved, and the strength of the cover soil can be improved as the roots of plants spread within the cover soil.

[0016] Furthermore, by incorporating a void-forming means into this treated soil, the increase in viscosity during mixing is suppressed and the gas phase (air and voids) necessary for plant germination, root development and growth is secured. This means that the surface of the covering soil is covered with plants, preserving the natural environment and landscape, and the strength of the covering soil is improved as the plant roots grow within the covering soil.

[0017] A second aspect of the present invention provides the greening soil covering material according to the first aspect, wherein the void-forming means is a bead-shaped water-absorbent polymer.

[0018] The invention described in claim 2 uses a bead-shaped superabsorbent polymer as the void-forming means. The superabsorbent polymer absorbs water and swells during kneading, gradually releasing the absorbed water as the covering material hardens, forming voids in the areas where the polymer is absorbed.

[0019] A third aspect of the present invention provides the greening soil covering material according to the first aspect, wherein the void-forming means is a foaming agent.

[0020] In the invention described in claim 3, by using a foaming agent as the void forming means, voids are reliably formed inside the soil covering material.

[0021] A fourth aspect of the present invention provides the greening soil covering material according to the first aspect, wherein the void-forming means is beads made of a biodegradable resin.

[0022] The invention described in claim 4 uses beads made of biodegradable resin as the void-forming means. The beads made of biodegradable resin are decomposed by microorganisms, and as the decomposition progresses, voids are formed in the decayed parts. [Effects of the Invention]

[0023] As explained above in detail, according to the present invention, it is possible to provide a greening soil cover material that has excellent greening function while improving the erosion resistance of the soil cover material. [Brief explanation of the drawings]

[0024] [Figure 1] 1 is a diagram showing a manufacturing procedure for the greening soil covering material 1 according to the present invention. [Figure 2] This is a cross-sectional view showing the mechanism of river levee collapse due to overflow. DETAILED DESCRIPTION OF THE INVENTION

[0025] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0026] As shown in Figure 1, the greening soil covering material 1 of the present invention is a treated soil made by mixing soil 2 with a solidification material made only of blast furnace slag powder 3 without using cement, and mixing this treated soil with a void-forming means 5.

[0027] The soil 2 is not particularly limited, and a wide range of soils such as clayey soil, silty soil, sandy soil, and gravel can be used.

[0028] The solidification material does not contain any cement and is composed only of ground granulated blast furnace slag 3. Because no cement is used, the pH of the greening soil cover material 1 is maintained at a neutral to slightly alkaline level, and the setting and development of initial strength is slower than with cement, delaying the solidification rate (strength development proceeds slowly), maintaining an environment conducive to early growth such as plant germination, rooting, and root spread. As a result, the surface of the cover soil is covered with plants, preserving the natural environment and landscape, and the strength of the cover soil is improved as the plant roots spread within the cover soil.

[0029] The ground granulated blast furnace slag 3 is obtained by drying and pulverizing granulated blast furnace slag, which is a by-product of the process of producing pig iron in a blast furnace, and is known to hydrate and harden upon contact with water. Several types of ground granulated blast furnace slag 3 with different Blaine values ​​are available on the market, and any of them can be used without any particular restrictions.

[0030] The blend weight of the ground granulated blast furnace slag 3 is 1 / 3 of the soil. 3The weight of the ground granulated blast furnace slag 3 is 250 kg to 320 kg, preferably 270 kg to 310 kg per 1 m 3 On the other hand, if the weight is less than 250 kg, the strength of the greening soil covering material 1 is insufficient and scouring is likely to occur. On the other hand, if the weight exceeds 320 kg, the hardness of the greening soil covering material 1 increases, preventing plants from taking root sufficiently and making it unsuitable for vegetation.

[0031] In addition, alkaline compounds such as calcium hydroxide, sodium hydroxide, potassium hydroxide, sodium carbonate, etc. may be mixed as an alkaline stimulant. The greening soil covering material 1 according to the present invention does not use cement as an alkaline stimulant either, and does not contain any cement, including this alkaline stimulant.

[0032] The void forming means 5 may be any means configured to generate a porous body with numerous voids formed inside the solidified covering material 1, and in particular, it is preferable to use a means that incorporates the void forming means 5, which can suppress an increase in viscosity during mixing and ensures that the gas phase (air and voids) necessary for plant germination, root growth, and root establishment is maintained inside the covering material 1.

[0033] The amount of the void forming means 5 mixed is adjusted to provide a void ratio of 20 to 30% relative to the solidified soil covering material 1. A void ratio of 20 to 30% is most suitable for plant growth.

[0034] Specifically, a first embodiment of the void forming means 5 is a bead-shaped (granular) water-absorbent polymer. The water-absorbent polymer is a polymer material that can absorb and retain water in an amount of several hundred to several thousand times its own weight, and any commercially available water-absorbent polymer can be used without limitation as long as it is formed into a granular shape, specifically, has a particle size of 1 mm or more in a dry state.

[0035] This water-absorbing polymer is added when mixing the soil 2, ground granulated blast furnace slag 3, and water, and absorbs water during mixing, swelling and dispersing throughout the treated soil. At this time, the water-absorbing polymer acts as a lubricant, suppressing an increase in viscosity during mixing and ensuring fluidity during pouring.

[0036] After pouring, as the soil covering material 1 sets and hardens, the water-absorbing polymer gradually releases the absorbed water, reducing its volume and forming voids. This makes the soil covering material 1 porous, ensuring the gas phase (air and voids) necessary for plant germination, root development, and growth.

[0037] The amount of the water-absorbing polymer blended is adjusted so that the volume when swollen is 20 to 30% of the total volume of the soil covering material 1. This allows voids to be formed in the solidified soil covering material 1 at a rate of approximately 20 to 30%, ensuring an air phase ratio (void ratio) that is optimal for plant growth.

[0038] Next, a foaming agent can be mentioned as a second example of the void forming means 5. As the foaming agent, a foaming agent that is mixed into aerated soil mixtures mainly for the purpose of reducing weight is suitable. By adding a foaming agent to the treated soil, the fluidity is increased, making pouring easier and forming a large number of bubbles inside the soil cover material 1.

[0039] The foaming agent is mixed by adding a specified amount of water to the mixer that mixes the soil 2 and the ground granulated blast furnace slag 3, and then adding the foaming agent to form a slurry.

[0040] Beads made of biodegradable resin can be mentioned as a third example of the void forming means 5. The beads made of biodegradable resin are decomposed by microorganisms, and voids are formed in the decayed parts as the decomposition progresses.

[0041] Biodegradable resin beads are formed by molding biodegradable resins, which are decomposed into water, carbon dioxide, and other substances by the action of microorganisms, into granular shapes such as spheres or pellets. Examples of biodegradable resins include polylactic acid-based resins and polyester-based resins. Examples of suitable synthetic resins include polylactic acid (PLA), polyhydroxyalkanoate (PHA), biopolybutylene succinate (PBS), polybutylene adipate terephthalate (PBAT)-polylactic acid (PLA) compounds, starch polyester resins, cellulose acetate (diacetate), polyvinyl alcohol (PVA), polyglycolic acid (PGA), polybutylene succinate (PBS), polybutylene succinate (PBSA), polybutylene adipate terephthalate (PBAT), and polyethylene terephthalate succinate (PETS). Beads made of biodegradable resins that decay within approximately 1 to 5 years are used.

[0042] Next, we will explain the manufacturing method of the greening soil covering material 1. The greening soil covering material 1 is manufactured by putting soil 2, blast furnace slag powder 3, and void forming means 5 into a mixing device such as a mixer and stirring and mixing them for a certain period of time.

[0043] The greening soil covering material 1 thus produced is pumped by a compressed air pumping device and sprayed onto the surface of river banks, slopes, and embankments. Note that transportation by heavy machinery such as a backhoe or by a belt conveyor may also be used. [Explanation of symbols]

[0044] 1...greening soil covering material, 2...soil, 3...granulated blast furnace slag, 5...void forming means

Claims

1. The soil was treated by mixing a solidification material made only of blast furnace slag powder without using cement. A greening soil covering material characterized in that a void-forming means is blended into the treated soil.

2. 2. The greening soil covering material according to claim 1, wherein the void-forming means is a bead-shaped water-absorbent polymer.

3. 2. The greening soil covering material according to claim 1, wherein the void-forming means is a foaming agent.

4. 2. The greening soil covering material according to claim 1, wherein said void-forming means is beads made of a biodegradable resin.

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