Methods for controlling slope erosion

Abstract

This invention provides a method for suppressing slope erosion that can control slope erosion from the initial stages of construction over a long period of time. [Solution] A method for suppressing slope erosion, comprising the steps of: mixing a soil fixation agent capable of fixing the surface of the soil by being sprayed onto the soil with seeds for greening; and spraying the mixed soil fixation agent and seeds onto the slope. The soil fixation agent mainly consists of, for example, a poorly soluble polyion complex produced by mixing a cationic polymer and anionic polymer.

Description

Technical Field

[0001] The present invention relates to a slope erosion suppression method for suppressing slope erosion.

Background Art

[0002] As a slope erosion suppression method for suppressing slope erosion, there are known methods such as spraying seeds or a base material on a slope (for example, see Patent Document 1) and laying a vegetation sheet (mat) on a slope (for example, see Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the method of spraying seeds or a base material on a slope, there is a concern that if the slope is exposed to high-intensity rainfall before the seeds germinate and take root, the slope may be eroded by scouring or the seeds may flow out. On the other hand, in the method of laying a vegetation sheet on a slope, there is a problem that resin-made materials such as the sheet remain in the environment for a long time.

Means for Solving the Problems

[0005] The present invention was created for the purpose of solving these problems in view of the above circumstances. The invention according to claim 1 is a slope erosion suppression method for suppressing slope erosion, comprising a step of mixing a soil immobilizing agent capable of immobilizing the surface of soil by spraying on the soil and seeds for greening, and a step of spraying the mixed soil immobilizing agent and the seeds on a slope. The invention of claim 2 is a method for suppressing slope erosion as described in claim 1, characterized in that the soil immobilizer mainly consists of a sparingly soluble polyion complex produced by mixing at least one cationic polymer selected from cationic polymers such as cationic cellulose and cationic starch with at least one anionic polymer selected from carboxymethylcellulose, carboxymethylamylose, ligninsulfonic acid and its salts, polyacrylic acid and its salts, and polysulfonic acid and its salts. The invention of claim 3 is a method for suppressing slope erosion as described in claim 2, characterized in that the cationic polymer is polydiallyldimethylammonium chloride and the anionic polymer is polycarboxymethylcellulose. The invention of claim 4 is a method for suppressing slope erosion according to any one of claims 1 to 3, characterized in that the bearing capacity strength of the slope to which the soil fixation agent has been applied is 0.1 MPa or more. The invention of claim 5 is a method for suppressing slope erosion as described in claim 1, characterized in that the mixed soil fixative and seeds are sprayed onto the slope using a truck-mounted spraying machine. [Effects of the Invention]

[0006] According to the invention of claim 1, a soil fixation agent capable of fixing the soil surface by being sprayed onto the soil is mixed with seeds for greening and then sprayed onto the slope. In the initial stages of construction, until the seeds germinate and take root, the soil fixation effect of the soil fixation agent suppresses erosion of the slope due to rainfall. Furthermore, although the bearing capacity strength of the soil due to the soil fixation agent may decrease over time, the germinated plants grow and take root on the slope, so it is possible to suppress slope erosion and achieve slope greening from the initial stages of construction over a long period of time. According to the invention of claim 2, a slope can be easily fixed using a poorly soluble polyion complex. According to the invention of claim 3, since the cationic polymer is polydiallyldimethylammonium chloride and the anionic polymer is polycarboxymethylcellulose, the slope can be fixed with a highly versatile and safe material. According to the invention of claim 4, the bearing capacity of the slope to which the soil fixative has been applied is 0.1 MPa or more, so even in the early stages of construction, when the seeds have germinated and taken root, erosion of the slope due to rainfall and other factors can be effectively suppressed. According to the invention of claim 5, the mixed soil fixative and seeds are sprayed onto the slope using a truck-mounted spraying machine, thereby ensuring the same level of ease of construction as conventional seed spraying methods while suppressing slope erosion over a long period of time. [Brief explanation of the drawing]

[0007] [Figure 1] This is a photographic diagram of a test specimen of a simply reinforced road surface. [Figure 2] This table shows the different levels of the experimental examples. [Figure 3] This table shows the results of the experimental examples. [Figure 4] This graph shows the germination rate at each level in the experimental example. [Figure 5] This graph shows the vegetation cover rate at each level in the experimental example. [Figure 6] These images show the changes over time at each level in the experimental example. [Modes for carrying out the invention]

[0008] The embodiments of the present invention will be described in detail below.

[0009] [Soil fixative] First, the soil fixation agent used in the slope erosion control method of this embodiment will be described. The soil fixation agent used in this embodiment can fix the surface of the soil by being sprayed onto the soil, and can be used, for example, as a dust suppressant to suppress the generation of dust from the soil, or as a simple paving agent to easily pave the soil.

[0010] The soil stabilizer of this embodiment contains a cationic polymer and an anionic polymer. The cationic polymer adopted in the soil stabilizer of this embodiment is at least one selected from cationic polymers such as polycationic cellulose and polycationic starch. Specifically, poly(diallyldimethylammonium chloride) (hereinafter referred to as "DADMAC") can be exemplified. However, DADMAC is a polymer adopted in many fields such as fiber processing, paper and pulp, paints, and inks, and is known as a polymer that hardly affects the human body and the environment.

[0011] [Chemical formula] Poly(diallyldimethylammonium chloride) (DADMAC)

[0012] Moreover, the anionic polymer is at least one selected from polycarboxymethyl cellulose, polycarboxymethyl amylose, poly(liguinic acid sulfonate) or its salt, and polyacrylic acid or its salt. Specifically, the sodium salt of polycarboxymethyl cellulose (hereinafter referred to as "CMC") and sodium polyacrylate can be exemplified. However, these CMC and PAAcNa are also polymers adopted in many fields such as food, medicine, and cosmetics, and are known as polymers that hardly affect the human body and the environment.

[0013] [Chemical formula] Sodium salt of polycarboxymethyl cellulose

[0014] [Chemical formula] Sodium polyacrylate

[0015] Furthermore, the soil immobilization agent of this embodiment immobilizes the soil by forming a poorly soluble complex (polyion complex) when an aqueous solution of anionic polymer and cationic polymer is permeated into the soil. For example, when the soil immobilization agent of this embodiment is used as a simple paving agent, a strong, simple paved road surface can be created.

[0016] While theoretically it is preferable to mix anionic and cationic polymers in an equal ratio of 1:1, in practice, the ideal ratio of cationic to anionic polymers in soil immobilization agents is in the range of 1:1 to 5. The reason for the higher proportion of anionic polymers is that the soil to which the mixture is applied in Japan is generally acidic. This ensures that the cationic and anionic polymers react to form a sparingly soluble polyion complex.

[0017] When creating a simple paved road surface using the soil fixative of this embodiment, the required bearing capacity strength of the simple paved road surface varies depending on the weight and frequency of travel of the vehicles. However, in a previous study by Kono et al. (Maiko Kono et al., Performance evaluation of dust dispersion suppressants for roads by indoor wheel load running tests, Proceedings of the 78th Annual Conference of the Japan Society of Civil Engineers, VI-1311, 2023), it was proposed that the installation pressure applied via the wheels should be 0.6 MPa as the condition for a wheel load running test machine when 200 10-ton class dump trucks were running for about one month. This installation pressure of 0.6 MPa can be set as a convenient target value for the bearing pressure strength of the simple paved road surface. In the experimental examples described later, the bearing capacity strength was measured by measuring the hardness index of the simple paved road surface using a commercially available Yamanaka soil strength meter, and the bearing pressure strength was calculated from this.

[0018] In this embodiment, the soil immobilizer preferably uses only water as the solvent. However, if necessary, a water-soluble organic solvent, such as alcohols like methyl alcohol, ethyl alcohol, or 2-propanol; ethers like diethyl ether or tetrahydrofuran; or ketones like acetone, methyl ethyl ketone, or cyclohexanone, can be used in combination with water. When using these organic solvents, ethyl alcohol is preferred to minimize the impact on the human body and the environmental burden.

[0019] Next, we will describe the experiments conducted to confirm the effectiveness of the soil fixation agent (simple paving agent) according to this embodiment.

[0020] Using stock solutions of DADMAC as the cationic polymer and CMC as the anionic polymer, these were mixed in an equal ratio of 1:2. These mixtures were then pre-diluted with water as the solvent to 2x, 5x, 7x, and 10x by weight, thereby creating aqueous solutions of the soil fixative.

[0021] Soil collected from a construction site in Japan was air-dried, then passed through a 4.5 mm mesh sieve. The soil was spread to a thickness of 86 mm, and then compacted to a bearing capacity of 0.2 MPa to create a test soil layer 70 mm thick. A diluted solution of the prepared soil fixative was then sprayed onto the surface of the test soil layer.

[0022] For the application conditions, the mixed aqueous solutions with dilution ratios of 2x, 5x, 7x, and 10x were used, and the application rate of the soil fixative was 2-5 L / m². 2 The soil was adjusted accordingly, and the hardness index of the soil surface was measured two and five days after application (with the application day being day zero) using the Yamanaka soil hardness meter described above, and the bearing capacity strength was calculated. The results are shown in the following table.

[0023] [Table 1]

[0024] These results show that on the second day after application, no samples exceeding the target bearing capacity of 0.6 MPa were observed. However, on the fifth day, even with a high concentration of 5 times or less dilution and a spray rate of 3 L / m², 2 The bearing capacity strength of the above materials exceeded 0.6 MPa, confirming the creation of a simple paved road surface that met the target. Figure 1 shows a photograph of a section of the solidified pavement, serving as a substitute for a drawing. This shows that the created simple reinforced road surface solidified while incorporating the soil well, demonstrating its effectiveness.

[0025] These findings suggest that the chemical reaction between the raw materials, DADMAC and CMC, to form a sparingly soluble polyion complex progressed over time. Therefore, even if the bearing capacity strength did not reach 0.6 MPa on the fifth day, it is estimated that the reaction would continue to progress over time, eventually reaching the required bearing capacity strength.

[0026] [Methods for controlling slope erosion] Next, the slope erosion control method of this embodiment will be described. The slope erosion control method of this embodiment comprises the steps of mixing the aforementioned soil fixation agent, which can fix the surface of the soil by being sprayed on the soil, with seeds for greening, and spraying the mixed soil fixation agent and seeds on the slope.

[0027] Seeds that have traditionally been used for slope greening can be used as seeds for greening to be mixed with soil fixatives. For example, introduced plants such as perennial ryegrass, tall fescue, Kentucky bluegrass, and Bermuda grass, as well as native plants such as Lespedeza cuneata, Japanese knotweed, and Zoysia japonica can be used. Note that the seeds used are not limited to one type, and multiple types of seeds may be mixed together.

[0028] The mixed soil fixative and seeds are spread onto the slope using, for example, a truck-mounted spraying machine (hydroseeder). This ensures the same level of ease of application as conventional seed spraying methods.

[0029] According to the slope erosion control method described above, since the seeds for greening are mixed with a soil fixative and scattered on the slope, erosion of the slope due to rainfall can be suppressed in the initial stages of construction, until the seeds germinate and take root, due to the soil fixative's soil-fixing effect. For example, if the bearing capacity of the slope where the soil fixative has been scattered is 0.1 MPa or higher, it is considered that erosion of the slope due to rainfall can be effectively suppressed even in the initial stages of construction, until the seeds germinate and take root. Furthermore, although the bearing capacity of the soil due to the soil fixative may decrease over time, the germinated plants grow and take root on the slope, so slope erosion can be suppressed and slope greening can be achieved over a long period from the initial stages of construction.

[0030] Next, we will explain the experiments conducted to confirm the effectiveness of the slope erosion suppression method according to this embodiment, with reference to Figures 2 to 6.

[0031] In this experiment, test seeds were sown in test soil treated with a soil fixative (sometimes referred to as the base material in diagrams), and the germination status of the seeds was observed. The experimental procedure is as follows. 1) As shown in Figure 2, the test soils used were horticultural black soil (levels 1 and 3) and excavated soil (levels 2 and 4). 2) For the test, we used perennial ryegrass, which is commonly used in sowing methods (slope greening work). 3) The test soil was placed in 100mm x 100mm square pots. Three pots were used for each level. 4) No soil fixative was applied to the test soils of levels 1 and 2. A 10-fold diluted soil fixative (concentration 0.7%) was applied to the test soils of levels 3 and 4 at a rate of 2 L / m². 2 The spray was applied using the specified amount. 5) The seeding rate on the test soil should be 10g / m². 2 The pot area is 0.01m². 2 Therefore, the sowing rate is 0.1g / 0.01m 2 Therefore, since perennial ryegrass has 500 seeds / g, I sowed 0.1g x 500 seeds / g = 50 seeds. 6) Under watering conditions that resulted in a soil moisture content of 60%, germination rates and vegetation cover were evaluated every 7 days up to 28 days after the initial assessment. 7) The germination rate was calculated as a percentage based on the ratio of germinated seeds to the number of seeds sown (50 seeds). 8) For vegetation cover, the images taken for each sample were binarized to create grayscale images, and the vegetation cover rate was calculated from the ratio of the white to black areas.

[0032] Figures 3 to 6 show the experimental results. As shown in Figures 3 and 4, when a soil fixative was applied to the field soil (level 4), the initial germination rate (one week after sowing) was lower compared to the other levels, but thereafter the germination rate became similar to the other levels. Also, when a soil fixative was applied to black soil (level 3), the initial germination rate was similar to levels 1 and 2, where no soil fixative was applied. Therefore, it was confirmed that although the effect of soil type and the application of a soil fixative was somewhat lower in the initial stages in some cases, the difference disappeared over time. Furthermore, since the germination rate of perennial ryegrass is usually said to be 70-90%, good germination rates were shown at all levels in this experiment.

[0033] As shown in Figures 3 and 5, the vegetation cover rate was approximately 10% higher at levels 1 and 3, which used black soil, than at levels 2 and 4, which used on-site soil, regardless of whether or not soil fixatives were applied. This is thought to be because the on-site soil had inferior water retention compared to black soil, hindering the growth of grasses that require a lot of water during their growth. Since the current vegetation work is mainly checked visually, the determination of the vegetation cover rate is prone to differences depending on the subjectivity and experience of the assessor. Therefore, in this study, the vegetation cover rate was calculated from the area ratio of black and white images obtained by binarization, but with this method, the vegetation cover rate did not exceed 30% at any level. This study was conducted over a one-month observation period and was an experiment to confirm whether or not the application of soil fixatives inhibited plant growth. The initial objective was achieved in that no growth inhibition by soil fixatives was confirmed by checking the germination rate. It is thought that the vegetation cover rate may improve if observations are continued for about three months.

Claims

1. A method for suppressing slope erosion, A process of mixing a soil fixation agent, which can fix the soil surface by being sprayed onto the soil, with seeds for greening, A method for suppressing slope erosion, characterized by comprising the step of scattering a mixture of the soil fixative and the seeds onto a slope.

2. The soil immobilizer is, A cationic polymer selected from cationic polymers such as cationic cellulose and cationic starch, The method for suppressing slope erosion according to claim 1, characterized in that it mainly comprises a poorly soluble polyion complex produced by mixing at least one anionic polymer selected from carboxymethylcellulose, carboxymethylamylose, ligninsulfonic acid and its salts, polyacrylic acid and its salts, and polysulfonic acid and its salts.

3. The method for suppressing slope erosion according to claim 2, characterized in that the cationic polymer is polydiallyldimethylammonium chloride and the anionic polymer is polycarboxymethylcellulose.

4. The method for suppressing slope erosion according to any one of claims 1 to 3, characterized in that the bearing capacity strength of the slope to which the soil fixation agent has been applied is 0.1 MPa or more.

5. The method for suppressing slope erosion according to claim 1, characterized in that the mixed soil fixative and seeds are sprayed onto the slope using a truck-mounted spraying machine.

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