Slope preservation method and program for slope preservation method

Abstract

[Problem] To provide a novel civil engineering technique that incorporates measures against flood damage caused by heavy rain on slopes. [Solution] A slope preservation method characterized in that a ditch that guides running water is formed in the slope of a site, and a water-permeable material is placed in the ditch. The water-permeable material is filled into a mesh bag of predetermined size and shape, and is placed continuously or at a predetermined intervals in the ditch.

Description

Slope preservation methods and programs for slope preservation methods

[0001] The present invention relates to a slope preservation method and a program for the slope preservation method.

[0002] In recent years, record-breaking torrential rains have occurred frequently in both mountainous and plain areas, resulting in significant human and economic losses. Transmission towers, which are representative of social infrastructure, are particularly susceptible to the collapse of their main lines, which run through mountainous areas, causing power outages for hundreds of thousands of households. Therefore, site preservation measures that can adapt to the current weather conditions are also required for the sites where transmission towers are located.

[0003] Until now, site conservation has mainly been achieved by using greening methods, but there have been frequent incidents where erosion has increased due to heavy rainfall that exceeds expectations, resulting in the site being washed away along with the greenery.One conventional greening method is to apply a mixture of soil and cement to the slope and then spray on an asphalt emulsion.

[0004] However, in the case of a method in which a soil and cement mixture is laid on a slope and then asphalt emulsion is sprayed on, there is a problem in that rainwater seeps in between the cement mixed layer and the slope, causing the cement mixed layer to easily peel off and collapse. Therefore, a method has been proposed in which a vegetation net is laid on the slope to cover it and prevent the topsoil from sliding off.

[0005] However, when covered only with a net, rainwater penetrates the topsoil layer during rainfall, making it susceptible to scouring, and there are limits to its ability to secure the topsoil in place. Therefore, a construction method has been developed in which a frame is laid on the slope to prevent the topsoil from sliding off. However, because there is nothing to secure the topsoil to the slope within the frame, there is insufficient adhesion between the slope and the topsoil layer, which creates the problem of the topsoil easily sliding off.

[0006] As such, in conventional slope greening methods, the adhesion between the topsoil and the slope is insufficient, which causes the topsoil to slide off or be eroded by collected and infiltrated rainwater, and the actual situation is that the intended purpose is not achieved from the perspective of slope conservation.

[0007] On the other hand, one method of utilizing coal ash in a greening construction method for slopes is disclosed in which a retaining mat member is laid on the slope of a steel flat block and fixed in place with anchor members, and then soil containing a binder is applied until the retaining mat member is covered to form a layer of added soil, and then soil mixed with plant seeds, fertilizer, and an erosion prevention agent is sprayed on top to form a plant growth layer, in which the binder and erosion prevention agent contain fly ash and have water permeability and water retention properties (see Patent Document 1).

[0008] Japanese Patent Application Laid-Open No. 2001-90012

[0009] However, the above-mentioned prior art only mentions water permeability (good drainage) and weed control properties that suppress the germination of plants such as weeds, and does not address water retention. For example, there is no disclosure or suggestion of civil engineering technology that takes measures against flood damage caused by heavy rain.

[0010] An object of the present invention is to provide a new slope preservation method that also takes measures to protect slopes from flood damage caused by heavy rain.

[0011] In order to achieve the above object, the present invention relates to a slope preservation method characterized by forming a trench for guiding running water on the slope of a site and disposing a water-permeable material in the trench.

[0012] The present invention also relates to a slope conservation method program that allows a computer to perform calculations to select the position, number, length, and depth of the grooves to be constructed on the slope and / or the number and type (particle size of the water-permeable material) of the mesh bags to be placed, and optimize the layout, based on information related to the soil and shape of the slope, information related to the shape, position, and falling water of structures on the slope, and / or weather information such as rainfall.

[0013] According to the present invention, it is possible to provide a new civil engineering technology that takes measures against flood damage caused by heavy rain on slopes, and it is possible to ensure site conservation that corresponds to the weather environment at the site of a transmission tower, which is a representative social infrastructure facility. It is also possible to establish an innovative site conservation method that contributes to the conservation of mountain ecosystems by promoting the recovery of vegetation and helps to achieve carbon neutrality.

[0014] FIG. 2 is a plan view schematically showing the slope conservation method of the present invention. FIG. 3 is a cross-sectional view taken along line A-A in FIG. 1. FIG. 4 is a graph of flow velocity attenuation by grain size. FIG. 5 is a graph of flow velocity attenuation by grain size. FIG. 6 is a graph of flow velocity attenuation by grain size. FIG. 7 is a table showing the step attenuation effect. FIG. 8 is a graph showing the step attenuation effect. FIG. 9 is a graph showing the water volume attenuation effect over time. FIG. 10 is a diagram showing the conservation points in the field test. FIG. 11 is a diagram explaining the conservation method in the field test using woven fence construction. FIG. 12 is a diagram showing the area after conservation in the field test.

[0015] The present invention will be described below based on an embodiment. Figure 1 is a plan view for explaining a slope preservation method of the present invention, and Figure 2 is a cross-sectional view of the plan view shown in Figure 1 taken along line A-A.

[0016] In the slope preservation method of the present invention, grooves 11 are formed on a slope 10, as shown in Figures 1 and 2. The number of grooves 11 may be one or more in the direction of rainwater flow indicated by the arrows in the figures, but from the viewpoint of disposing a relatively large amount of water-permeable material to effectively maintain the flood damage prevention measures associated with heavy rainfall of the present invention, it is preferable to have more than one groove 11. Specifically, at a slope angle between 20 and 40 degrees, it is preferable to have two to four grooves per 10 meters of width, and furthermore, at a slope angle of 40 degrees or more, it is preferable to have five to six grooves per 10 meters.

[0017] The width and depth of the groove 11 itself can be set appropriately from the viewpoint of disposing a water-permeable material in the groove 11. From the viewpoint of fixing the water-permeable material in the groove 11, it is preferable that the water-permeable material be disposed so as to fit into the groove 11 in the width direction of the groove 11, and it is also preferable that the width of the groove 11 be set to satisfy this requirement.

[0018] Next, in the slope preservation method of the present invention, a water-retentive material 13 is placed in the trench 11. Because the water-retentive material 13 is generally granular or powdery, it is filled into the mesh bag 12 and then placed, preferably fitted, in the trench 11. The mesh bag 12 can have a mesh size of 1 mm to 4 mm, and be rectangular in shape, with a width of 15 cm to 50 cm and a length of 30 cm to 100 cm. By setting the mesh size of the mesh bag 12 within this range, rainwater flowing into the mesh bag 12 through the mesh due to heavy rain or the like reaches the water-retentive material 13 with large particle sizes filled in the mesh bag 12, where its momentum is first reduced, and then is guided sequentially to the mesh bags 12 filled with water-retentive material 13 with smaller particle sizes, where it loses momentum and is absorbed into the porous material, and some of it is gradually absorbed into the slope.

[0019] The width and length described above are preferable from the viewpoint of facilitating handling of the net bag 12. That is, as explained in this embodiment, the slope preservation method of the present invention involves forming a trench 11 directly on-site and disposing the net bag 12 in the trench 11, but if the width and length of the net bag 12 are within the above-mentioned ranges, i.e., if the size of the net bag 12 is determined by the above-mentioned width and length, handling becomes easy and the slope preservation method of the present invention can be easily carried out.

[0020] The material that constitutes the mesh bag 12 is not particularly limited, but if it is to be solidified, it is preferable that it be made of a biodegradable material. This allows the mesh bag 12 to decompose within several months to several years, leaving only the water-permeable, retaining substance 13 in the groove 11. This eliminates the need to dispose of the mesh bag 12 as waste. After the mesh bag 12 disappears, the water-permeable, retaining substance 13 remains in the groove 11, providing the above-mentioned effects permanently.

[0021] Examples of biodegradable materials that can be used include natural products such as hemp, cotton, starch, and cellulose, as well as general-purpose biodegradable plastics such as polylactic acid, polycaprolactone, polybutylene succinate, polyethylene succinate, polyvinyl alcohol, polyglycolic acid, poly(caprolactone / butylene succinate), and poly(butylene succinate / adipate).

[0022] Examples of the water-permeable material 13 include porous materials such as clinker ash, volcanic gravel, pumice, and bora soil. Clinker ash is particularly preferred from the viewpoints of effective waste utilization and water absorption / retention. However, it goes without saying that it can also be a material obtained by mixing and solidifying a cement-based solidification material and water. In this case, the porous material functions as the main body of the water-permeable material, and the cement-based solidification material and water function as connecting materials for the main body of the water-permeable material.

[0023] When using a connecting material as described above, it becomes necessary to transport a mixer or other equipment directly to the work site. Therefore, in such cases, it is preferable to premix the porous material with a cement-based solidification material, fill the mesh bag 12 with this, and then spray water on it to solidify it. This eliminates the need to transport a mixer or other equipment to the work site, improving work efficiency.

[0024] Clinker ash in the present invention refers to ash obtained by recovering, dehydrating, and pulverizing lumps of coal ash that fall to the bottom of a boiler, among the coal ash generated when coal is burned in a thermal power plant, etc. As the coal ash, clinker ash that has been crushed or sieved and classified to particle sizes of about 0 mm to 40 mm is preferably used.

[0025] The weight ratio of porous material to connecting material is clinker ash 1m ３To prepare the water-permeable material 13, 200 to 300 kg of cement-based solidification material and 120 to 140 liters of admixture are mixed in a mixer. Examples of the cement-based solidification material include, but are not limited to, Tufflock (product name: manufactured by Sumitomo Osaka Cement Co., Ltd.). The cement-based solidification material refers to a powder that hardens over time when mixed with an admixture such as water. Examples of suitable cement-based solidification materials include calcined gypsum, magnesia cement, hydraulic gypsum, natural cement, Portland cement, and alumina cement. While the mesh bags 12 filled with the water-permeable material 13 are spaced apart in FIGS. 1 and 2, the spacing between them can be adjusted appropriately, taking into account the amount of rainfall, such as during heavy downpours. In cases of heavy rainfall, the mesh bags 12 can also be arranged continuously in the vertical, horizontal, and height directions.

[0026] As shown in Figures 1 and 2, the number of mesh bags 12 arranged in each groove 11 can be varied or the same. Furthermore, the amount and type (grain size) of water-retentive material 13 filled in the mesh bags 12 can be varied or the same for each mesh bag. When the water-retentive material 13 filled in the mesh bags 12 is divided by grain size, for example, the force of raindrops or running water can be reduced by mesh bags 12 filled with water-retentive material 13 having large grain sizes, and the water can be gently guided in the desired direction by passing through mesh bags 12 filled with water-retentive material 13 having medium grain sizes arranged underneath. Furthermore, when mesh bags 12 filled with very fine water-retentive material 13 are brought into contact with the ground, the behavior of water due to capillary action can be utilized to control water permeation and water retention, allowing rainwater to be freely guided in any direction, vertically, horizontally, or vertically.

[0027] Although not specifically shown in Figures 1 and 2, a permeability control sheet can also be placed on the bottom of the trench 11, specifically on the lowest surface or deeper. This prevents rainwater from seeping through the trench 11 and into the slope 10, even in the unlikely event that the water-permeable, water-retentive material 13 in the mesh bag 12 placed in the trench 11 is unable to absorb rainwater from a torrential downpour. This more reliably prevents the site having the slope 10 from collapsing due to rainwater, ensuring the preservation of the site. Examples of permeability control sheets that can be used include general-purpose vinyl sheets and nonwoven fabric civil engineering sheets. Using an impermeable vinyl sheet prevents rainwater from seeping vertically and instead moves it horizontally to a lower level. Nonwoven fabric civil engineering sheets can be used to control the rate at which they permeate the ground by varying their thickness or by layering them.

[0028] Furthermore, in the slope conservation method of the present invention, a woven fence 15 is installed at the foot of the trench 11. As a result, when the slope 10 is steep, even if the mesh bag 12 slides down inside the trench 11, the mesh bag 12 will not be released outside the trench 11, and the mesh bag 12 filled with the water-permeable material 13 will not be lost if it flows away with the rainwater. On the other hand, when the slope 10 is gently inclined, the desired effect of controlling rainwater can be achieved by simply digging a side trench and pouring the water-permeable material 13 into it without installing the woven fence 15.

[0029] As described above, in the slope preservation method of the present invention, the above operations can be carried out directly on-site, and can always be carried out under the best conditions through so-called in-situ construction. That is, the position, number, length, and depth of the grooves 11 to be constructed on the slope 10 and / or the number, type (particle size of the water-permeable material) and layout of the mesh bags 12 to be installed can be optimized based on information on the soil and shape of the slope 10, information on the shape, position, and falling water of structures (such as steel towers) on the slope 10, and / or weather information such as rainfall.

[0030] In addition, the above optimization can be performed by storing information obtained from the relationship between information related to the soil and shape of the slope, information related to the shape, position, and falling water of structures (such as steel towers) on the slope, and / or weather information such as rainfall, and the position, number, length, and depth of the grooves to be constructed on the slope and / or the number, type (particle size of the water-retentive material) of the mesh bags to be placed, and the layout, in a computer, and then, based on this information, the position, number, length, and depth of the grooves to be constructed on any slope and / or the number, type (particle size of the water-retentive material) of the mesh bags to be placed, and the layout can be determined by calculation using the computer.

[0031] Specifically, information regarding the soil and three-dimensional shape of the slope 10, as well as the shape and location of structures on the slope 10 (e.g., the presence and location of steel towers), is first input into a computer (step S1). Next, the expected amount of water falling on the slope 10 and the expected amount of rainfall are input into the computer based on, for example, information such as the annual precipitation at the location (step S2). Next, based on the information obtained in steps S1 and S2, the positions, number, length, and depth of the grooves 11 to be constructed on the slope 10 are set to initial values, such as forming multiple rows of wide and deep grooves on a steeply sloping slope with a deep valley shape. Furthermore, the number, type (particle size of the water-permeable material), and layout of the mesh bags 12 to be placed in the grooves 11 are determined (step S3).

[0032] At this time, if the water volume cannot be sufficiently attenuated in the grooves 11 and mesh bags 12, the weighting is updated again in step S3 by changing the coefficients of the formula, and the positions and number of grooves 11 are adjusted, and the optimum number of mesh bags 12 is updated. This operation is repeated until the water volume attenuates by 50% or more after 30 minutes, and the positions and number of grooves 11 and the number of mesh bags 12 that satisfy the requirements are input into the computer as conditions sufficient to protect the slope 10 from rainwater, etc. (step S4).

[0033] These conservation conditions are obtained for the types of soil and shape of various slopes 10 in step S1 described above, as well as for the shapes and positions of structures on the slopes 10, and are also obtained for the amounts of water falling on the slopes 10 and rainfall in step S2, and are input into the computer. Therefore, for any given slope 10, appropriate conservation conditions can be selected from the conservation conditions stored in the computer based on information on the soil and shape of the slope 10, information on the shapes and positions of structures on the slope 10, and the amounts of water falling on the slope 10 and rainfall, or based on optimal values ​​calculated from these, the positions, number, length, and depth of trenches 11 to be constructed on the slope 10 can be determined, and the number, type (particle size of the water-permeable material), and layout of the mesh bags 12 to be placed in the trenches 11 can be determined.

[0034] That is, by performing machine learning from steps S1 to S4 using a computer, appropriate conservation conditions can be selected and applied to any slope 10.

[0035] In view of the above-described embodiments, the present application also encompasses the following inventions. [1] A slope preservation method comprising forming a trench on a slope of a site to guide running water and disposing a water-permeable material in the trench. [2] The slope preservation method according to [1], wherein the water-permeable material is a porous material, or a porous material that is mixed or premixed with cement, and then water is sprayed on the porous material to solidify it. [3] The slope preservation method according to [2], wherein the porous material is at least one selected from the group consisting of clinker ash, volcanic gravel, pumice, and bora soil. [4] The slope preservation method according to any one of [1] to [3], wherein the water-permeable material is filled in a mesh bag having a predetermined size and shape and disposed continuously or at predetermined intervals in the trench. [5] The slope conservation method according to [4], wherein the mesh bag has a mesh size of 1 mm to 4 mm and is in the shape of a roughly rectangular bag with a width of 15 cm to 50 cm and a length of 30 cm to 100 cm. [6] The slope conservation method according to [4] or [5], wherein the mesh bag is filled with the water-permeable and water-retentive substances classified by particle size. [7] The slope conservation method according to any of [4] to [6], wherein the mesh bag is made of a biodegradable material. [8] The slope conservation method according to any of [4] to [7], wherein a water-permeability control sheet is disposed or buried in the lowest layer of the trench or deeper therein. [9] The slope conservation method according to any of [4] to [8], wherein a woven fence is installed at the foot of the trench.

[10] A slope preservation method according to any one of [4] to [9], which optimizes the selection and layout of the position, number, length and depth of the grooves to be constructed on the slope and / or the number and type (particle size of the water-permeable material) of the mesh bags to be placed, based on information on the soil and shape of the slope, information on the shape, position and falling water of structures on the slope, and / or weather information such as rainfall.

[11] A slope preservation method program which causes a computer to perform calculations to optimize the selection and layout of the position, number, length and depth of the grooves to be constructed on the slope and / or the number and type (particle size of the water-permeable material) of the mesh bags to be placed, based on information on the soil and shape of the slope, information on the shape, position and falling water of structures on the slope, and / or weather information such as rainfall.

[0036] (Measurement of flow velocity attenuation by particle size) A test was carried out on clinker ash by particle size at an inclination angle of 10 degrees and 30 degrees, with a rainfall equivalent to 48 mm for 1 hour. Figures 3 and 4 show the flow velocity attenuation effect using clinker ash samples of 0-40 mm, 0-7 mm, and 5-7 mm, compared with no sample.

[0037] As shown in Figure 3, when the angle is 10 degrees, after 20 minutes the flow rate is reduced by 69% for 0-40mm, 62% for 0-7mm, and 35% for 5-7mm. For 0-40mm, no drainage is performed for the first 10 minutes. After that, the water is retained and the drainage is slow. The more the particle size range is narrowed, the less water is retained. The results in Figure 3 also reveal that the flow rate reduction effect is high for clinker ash particle size 0-40mm (raw ash).

[0038] Furthermore, as shown in Figure 4, when the angle is 30 degrees, the flow velocity attenuation effect after 20 minutes is 50% for 0-40 mm and 37% for 5-7 mm compared to when there is no sample, and the 0-40 mm angle is 19% lower than the 10 degree angle, but there is no difference for 5-7 mm. On the other hand, it was found that the attenuation effect of 0-40 mm clinker ash remains 50% even when the inclination angle is increased to 30 degrees.

[0039] Tests were conducted on clinker ash at different particle sizes, with an inclination angle of 10 degrees and 30 degrees, equivalent to a rainfall of 1,000 mm per hour. Figures 5 and 6 show graphs of the flow velocity attenuation effect using clinker ash samples of 0-40 mm, 0-7 mm, and 5-7 mm, compared to no sample.

[0040] As shown in Figure 5, when the angle is 10 degrees, compared to no sample, the 0-40 mm sample had a damping effect of 44% after 5 minutes and 11% after 10 minutes, and 33% of the retained water was slowly discharged after 5 minutes. The 0-7 mm sample had a damping effect of 36% after 5 minutes and 10% after 10 minutes. The 5-7 mm sample had a damping effect of 4% after 5 minutes and 1% after 10 minutes, and the clinker ash flowed almost completely along the floor surface.

[0041] Furthermore, as shown in Figure 6, when the angle is 30 degrees, the 0-40 mm specimen is 16% after 5 minutes and 4% after 10 minutes compared to no sample, which is about one-third of the 10-degree inclination angle. The 5-7 mm clinker ash specimen is 8% after 5 minutes and 0% after 10 minutes, which suggests that the water temporarily held in the voids was drained by gravity after 5 minutes.

[0042] (Tests measuring flow velocity attenuation by stage number) Under conditions equivalent to a rainfall of 34 mm per hour and an inclination angle of 30 degrees, 0-40 mm clinker ash was used and compared by stage number. The attenuation effect 20 minutes after the rainfall (Figure 7) was 59% for stage 1 and 96% for stage 2. Discharge stopped 26 minutes after the water was stopped for stage 1, but 45 minutes later for stage 2. After 45 minutes, the attenuation effect was 54% for stage 1 and 76% for stage 2. Two stages showed the greatest attenuation effect, demonstrating the effectiveness of mitigating the flow velocity of concentrated flowwater in proportion to the amount of clinker ash used (Figure 8). Furthermore, no overflow occurred even at an inclination angle of 30 degrees.

[0043] The drainage volume from this test is shown in time series in Figure 9. The results clearly show that the second stage temporarily retains concentrated precipitation and then slowly drains it away.

[0044] From the above, it can be seen that in order to preserve the slope, it is essential to control the damping effect by adjusting the particle size and number of layers of clinker ash.

[0045] (Field Test) <Verification Test of Drainage Control Using Clinker Ash at a Tower Site> Field tests were conducted at four tower sites. Clinker ash was selected based on the results of basic tests on porous materials. To verify its workability and on-site effectiveness, it was installed at four high-slope ultra-high-voltage tower sites and a demonstration test of its drainage control effectiveness was conducted. Several types of polyethylene mesh bags with 1-4 mm mesh, 20-40 cm wide, and 20-100 cm long were fabricated and placed on slopes prone to runoff concentration. Cylindrical 90 cm long, 4 mm mesh, and clinker ash granularity 5-40 mm were placed on top of the woven fence to verify the dispersed drainage effect of the permeable and water-retaining properties of concentrated runoff. The results showed that the concentration of runoff was reduced, but the water retention capacity was less than that of raw ash, so the water retention effect was not significant. However, the effectiveness of preventing water concentration was confirmed by the condition of the vegetation and topsoil below the installation (Figure 10).

[0046] Based on the above results, the specifications of the mesh bags were changed. Materials with a width of 30 cm, length of 70 cm, and mesh of 1 mm, made of clinker ash with a particle size of 0 to 40 mm, were placed continuously on a single slope (Fig. 11). The results confirmed that the dispersed drainage effect prevented the vegetation below from being washed away and allowed it to grow normally. The woven fence construction was placed on steep slopes where runoff tends to concentrate. To disperse and drain concentrated runoff, two or more layers of clinker ash bags were used, so a construction method was devised that combined them with reinforced woven fence construction (Fig. 12).

[0047] Steel pipe piles 48.6 mm in diameter and 1,100 mm long were driven into the woven fence at 50-70 cm intervals, and inside this was a 14 mm mesh plastic strip cross-woven net with iron wire reinforcing, with a nonwoven fabric sheet (civil engineering sheet) on top of it, installed in an L shape to a height of 400 mm. In the space between the woven fence net and the slope, polyethylene mesh bags 35 cm x 60 cm filled with porous material (coal ash) were stacked three high, which retained water running from above and dispersed drainage (runoff suppression), thereby protecting the vegetation below the woven fence and the surface.

[0048] A follow-up survey was then conducted for one year. Rainfall data was taken from the Japan Meteorological Agency observation station near the test site and the Ume Observatory in Saiki City, Oita Prefecture, and a time-lapse camera was installed to conduct monthly follow-up surveys. Results showed that the maximum rainfall was 479 mm in August 2021, with a maximum of 68 mm in one hour and a maximum of 15 mm in 10 minutes, but the vegetation and surface layer below the equipment were confirmed to be healthy. The camera also confirmed that runoff from the main legs of the tower was concentrating, flowing into the woven fence and being absorbed. Furthermore, progress observations showed that there was no exposed topsoil and vegetation below the woven fence was thriving, indicating that the dispersion and drainage effect was evident.

[0049] To date, permeable, water-retentive flat plates made from coal ash have been used to protect steel towers from raindrops. However, a method was devised and tested to eliminate the manufacturing process by encasing coal ash in a mesh bag to prevent raindrop scouring. Two methods were used: one with a 4mm mesh and clinker ash granularity of 5-40mm, and the other with a 1mm mesh and clinker ash granularity of 0-40mm. Figure 13 shows a pattern using clinker ash granularity of 0-40mm, with artificial turf installed on the surface to mitigate raindrop impact and improve aesthetics. Both methods proved to be easy to install, even on steeply sloping sites. One year later, there was no scouring or vegetation decline due to raindrops or concentrated rainwater at the site.

[0050] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims.

[0051] 10 Slope 11 Groove 12 Mesh bag 13 Water-permeable material 15 Woven fence

Claims

1. A slope preservation method characterized by forming a trench on the slope of a site to guide running water and placing a water-retentive material within the trench.

2. A slope preservation method as described in claim 1, wherein the water-retentive substance is a substance made of a porous material, or a substance made by kneading or premixing cement into a porous material and then spraying water on it to solidify it.

3. The slope preservation method according to claim 2, wherein the porous material is at least one selected from the group consisting of clinker ash, volcanic gravel, pumice, and bora soil.

4. A slope preservation method as described in claim 1, in which the water-permeable material is filled into mesh bags of a specified size and shape and arranged continuously or at specified intervals within the trench.

5. A slope preservation method as described in claim 4, wherein the mesh bag has a mesh size of 1 mm to 4 mm, and is an approximately rectangular bag shape with a width of 15 cm to 50 cm and a length of 30 cm to 100 cm.

6. A slope preservation method as described in claim 4, wherein the mesh bag is filled with the water-permeable material classified according to particle size.

7. A slope preservation method as described in claim 4, wherein the mesh bag is made of a biodegradable material.

8. A slope preservation method as described in claim 4, in which a water permeability control sheet is disposed or buried in the lowest layer of the trench or deeper therefrom.

9. A slope preservation method as described in claim 4, in which a woven fence work is provided at the foot of the trench.

10. A slope conservation method as described in claim 4, in which the position, number, length and depth of the grooves to be constructed on the slope and / or the number and type (particle size of the water-permeable material) of the mesh bags to be disposed are selected and layout are optimized based on information relating to the soil and shape of the slope, information relating to the shape, position and falling water of structures on the slope and / or weather information such as rainfall.

11. A program for a slope conservation method, characterized in that it causes a computer to perform calculations to select the position, number, length and depth of the grooves to be constructed on the slope and / or the number and type (particle size of the water-permeable material) of the mesh bags to be placed, and optimize the layout, based on information relating to the soil and shape of the slope, information relating to the shape, position and falling water of structures on the slope, and / or weather information such as rainfall.

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