Method for improving water retention and soil conservation performance of coarse-grained rock ballast slope through combination of W-OH and SAP

Abstract

The invention discloses a method for improving the water holding and soil conservation performance of a coarse-grained rock ballast slope through combination of W-OH and SAP. Coarse-grained rock ballast is a granular discrete material and does not have any cementing performance, soil particles are easily eroded by water flow under the hydraulic erosion action of surface runoff or underground water flow, and water and soil loss is caused. According to the invention, firstly, modified hydrophilic polyurethane W-OH is used for effectively cementing a material of soil particles, so that the connection among the particles is enhanced, and the capability of resisting hydraulic erosion is further enhanced. Meanwhile, the coarse-grained rock ballast is high in water permeability, relatively large in pore and weak in water holding capacity, and is not beneficial to plant growth. The additive for improving the water holding capacity of the waste residues by adopting the super absorbent resin SAP is used for improving the water holding and soil conservation performance of the waste residues, and then conditions are created for direct recovery of slope vegetation after improvement. According to the method, the water retention and soil conservation performance of the rock ballast slope surface is improved in a simple mode, and vegetation recovery is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of environmental geotechnical engineering, and in particular relates to a method for retaining water and soil on the surface of a slag slope. Background Art

[0002] With the development of society, the construction of a large number of highways and railways (such as the Sichuan-Tibet Railway), underground projects, etc. requires the excavation of a large number of tunnels and underground spaces, which will produce a large amount of coarse-grained slag composed of broken rocks. The amount of these coarse-grained slag is huge, and it is difficult to use them in a timely, sufficient and effective manner, so they need to be piled up in the waste dump. The waste dump will cause a series of environmental impacts on the surrounding ecosystem, such as surface vegetation destruction, soil erosion and topsoil erosion. There are currently no strict compaction specifications for the filling of waste dumps, which makes their structure loose. Under the action of groundwater, surface water and rainfall infiltration, soil erosion is very likely to occur, causing surface erosion and even geological disasters, causing harm to society and the environment. Due to the weak water and soil retention capacity of the coarse-grained waste dump, it may cause serious hydraulic erosion and it is also difficult to restore vegetation. Therefore, it is necessary to seek environmentally friendly methods to improve the water and soil retention performance of coarse-grained slag to create conditions for later vegetation restoration.

[0003] Defects and shortcomings of existing technologies (imported soil or complex artificial vegetation layer): The restoration of vegetation on coarse-grained slag slopes in areas with a lack of soil on the surface is currently a difficult problem to solve. At present, the main method used to improve or reconstruct slag slopes before vegetation restoration is the imported soil method, which requires that there is ready-made soil suitable for plant growth in the local area. However, in high-altitude or rocky desertification areas, it is difficult to find a soil layer on the surface, so the imported soil method cannot be applied. Other methods to improve slope planting conditions mainly involve the configuration of a special vegetation layer. For example, in the patent number ZL 201310746146.6, entitled Soil and Water Conservation Method for High-altitude Large Temperature Difference Arid Dry-hot Valley High Steep Slope Abandoned Slag Body, the soil at the construction site is used as the covering soil, cement is added to it as a binder, and the plant ingredients, mixed materials and grass seeds obtained by cutting plants are mixed to form a mixed material as a vegetation layer. The patent with publication number CN 202010802888.6 and titled Soil matrix for waste dump reclamation and its preparation method and application proposed a method for preparing soil matrix for waste dump reclamation using 40-75% original soil, 10-50% engineering waste, 3-8% organic fertilizer and 3-7% pine needles. The patent with publication number CN 202111140032.8 and titled Ecological Protection Waste Dump in Rocky Mountain Area designed a rocky mountain ecological protection waste dump that includes a topsoil stripping layer, a waste body and an ecological restoration layer from bottom to top. The ecological restoration layer used on its slope is in the form of stepped terraces, which include a matured slag layer, a geotextile, a stripped topsoil reconstruction layer and a potential waste recovery layer from bottom to top. The mature slag soil layer is a waste rock that needs to be placed on the surface for more than 3 months after adding biological agents; the stripped topsoil reconstruction layer is paved with a mixture of waste rock, stripped topsoil, agricultural and forestry waste compost and biological agents; the potential waste recovery layer is paved with a mixture of waste rock, agricultural and forestry waste and biological agents. The patent with the publication number of CN 202311616469.3 and the name of a method for ecological restoration of high-altitude waste piles proposes a method for ecological restoration of high-altitude waste piles, which obtains sludge or soil, cow dung, slag and forage fiber in situ, crushes them, adds polyacrylamide and sodium polyacrylate to them, and mixes them to obtain a guest soil matrix. The patent with the publication number of CN 202410300646.5 and the name of a method for soil reconstruction of waste slopes proposes to set a permeability barrier layer, a vegetation layer, a crust layer, a shrub planting pit and a tree planting pit on the surface of the waste pile to achieve the reconstruction of the waste slope soil.

[0004] In summary, most of the existing methods for treating gravel slopes focus on restoring vegetation. The soil-importing method not only has the problem that the surface soil is more susceptible to soil erosion, but also cannot be used in areas with high altitudes and rocky desertification where there is a lack of land. Vegetation restoration can also be achieved by artificially configuring vegetation or reconstructing soil layers, but the processes are relatively complicated, and the processes of some methods are too complicated to be implemented on site. Summary of the invention

[0005] The purpose of the present invention is to provide a method for improving the water-retention and soil-retention performance of coarse-grained ballast slopes by combining W-OH and SAP in order to improve the water-retention and soil-retention performance of ballast slopes in a simple way, thereby facilitating vegetation restoration.

[0006] The concept of the present invention is: first, coarse-grained slag is a granular bulk material without any cementing properties. Under the hydraulic erosion of surface runoff or groundwater flow, soil particles are easily eroded by water flow, causing soil and water loss. The present invention first uses modified hydrophilic polyurethane W-OH to effectively cement soil particles, strengthen the connection between particles, and then enhance its ability to resist hydraulic erosion. At the same time, coarse-grained slag has strong water permeability, large pores, and weak water holding capacity, which is not conducive to plant growth. The present invention uses a highly absorbent resin SAP additive to improve the water holding capacity of the slag to improve its water holding and soil conservation properties, thereby creating conditions for the direct restoration of vegetation on the improved slope.

[0007] W-OH is an eco-friendly high molecular weight hydrophilic polyurethane resin curing material. Its main component is modified hydrophilic polyurethane resin with a density of 1.18 g / cm 3 , pH value is 6-7. W-OH organic binder is a light yellow oily liquid, which can react and gel with water in any proportion to form a milky white porous elastic gel with good mechanical properties and stability.

[0008] SAP is a polymer water-absorbent resin, a highly absorbent polymer material. It is a powdery solid crystal before absorbing water, and becomes an elastic hydrogel after absorbing water. It can absorb 100 to 300 times its own weight of water, and the water absorption speed is very fast.

[0009] Based on the above concept, the method provided by the present invention for improving the water-retaining and soil-retaining performance of coarse-grained slag by combining W-OH and SAP includes the following contents: Highly absorbent resin SAP is mixed into the coarse-grained slag to improve its water holding and water retention capacity, the evenly mixed mixture is spread on the surface of the slag slope, and then the modified hydrophilic polyurethane resin W-OH solution is poured in situ on the slag slope to improve the erosion resistance (soil retention performance) of the slag slope, and an improved slag planting layer is formed in situ on the slag slope for vegetation restoration.

[0010] The present invention also provides a method for restoring vegetation on a gravel slope, comprising the following steps: Highly absorbent resin SAP is mixed into the coarse-grained slag to improve the water holding and water retention of the coarse-grained slag, and the evenly mixed mixture is spread on the surface of the slag slope to form a slag layer. Then, about 70% of the total amount of modified hydrophilic polyurethane resin W-OH solution is poured on the slag layer in situ to improve the erosion resistance (soil retention performance) of the slag slope, and a modified slag planting layer is initially formed in situ on the slag slope. Finally, grass seeds or other plant seeds for vegetation restoration are mixed into the remaining part of the modified hydrophilic polyurethane resin W-OH solution, and while the slag planting layer is formed in situ, the plant seeds flow into the pores on the surface of the slope with the slurry and are evenly sown in the improved slag planting layer to achieve vegetation restoration on the slope.

[0011] In the above technical solution of the present invention, the usage of the super absorbent resin SAP is 0.04-0.05% of the mass of the slag used in the entire improved slag planting layer.

[0012] In the above technical solution of the present invention, the mass concentration of the W-OH solution is 4%, and the volume usage of the W-OH solution is 9.0-12.0% of the volume of the laid slag layer that needs to be cemented (calculated according to the thickness and area required to be cemented).

[0013] In the above technical solution of the present invention, the slag is mainly composed of sand, gravel and stone with a particle size greater than 0.1 mm and less than 200 mm, which is a coarse-grained slag with poor water holding performance. For example, coarse-grained waste slag composed of broken rock blocks produced by the construction and excavation of tunnels and underground spaces in highways, railways, underground projects, etc.

[0014] The invention also provides a water-retaining and soil-retaining agent, which comprises a highly water-absorbent resin material SAP and a modified hydrophilic polyurethane resin W-OH.

[0015] The present invention also provides a combined application of a highly water-absorbent resin material SAP and a modified hydrophilic polyurethane resin W-OH in improving the water-retaining and soil-retaining properties of coarse-grained slag. The highly water-absorbent resin SAP is a granular material before and after water absorption. If it is added to the soil alone, it is easily washed away by the water flow under the action of seepage, and it does not play the role of positioning and enhancing the water-retaining properties of the soil. The gel formed after the W-OH is poured can wrap and connect the soil with the SAP particles, avoiding the loss of SAP particles in the improved slag layer under the action of seepage, and ensuring the effect of water-retaining improvement and the durability of the improved slag water-retaining properties.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The method of the present invention does not require any topsoil or other soil suitable for plant growth. It adopts an improved method of adding organic cementing materials and water-retaining materials in situ to improve the water-holding performance of coarse-grained slag, making it suitable for plant growth, which is conducive to the full and effective use of coarse-grained waste generated by engineering excavation, and avoids a series of environmental impacts such as surface vegetation destruction, soil erosion and topsoil erosion. The method of the present invention is particularly suitable for areas with high altitudes and rocky desertification where topsoil is scarce.

[0017] 2. In the method of the present invention, W-OH gel with cementing properties is used to achieve the connection of coarse-grained slag particles, thereby improving the slag's anti-hydraulic erosion performance, i.e., soil retention performance; at the same time, SAP with extremely strong water absorption is added to improve the slag's water holding and water retention performance. By simply adding two environmentally friendly materials, the in-situ improvement of the coarse-grained slag's water holding and soil retention performance is achieved at the same time, providing conditions for the restoration of vegetation on the coarse-grained slag slope.

[0018] 3. The method of the present invention has a simple process and can improve the slag by only using ordinary mixing and pouring processes. It does not require the preparation of complex artificial materials and is easy to implement on site. In addition, the method uses a small amount of added materials and is low in price, making it suitable for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The electron microscope scanning photos of the slag after W-OH modification (a is magnified 500 times, b is magnified 5000 times) Figure 2 The change process of volumetric moisture content of coarse-grained slag before and after improvement in the water absorption-drying cycle; Figure 3 The maximum water absorption rate of coarse-grained slag after drying varies with the number of cycles before and after improvement; Figure 4 Changes of infiltration rate of coarse-grained gravel slope with flow rate before and after improvement; Figure 5 Photos before and after planting grass on the improved slag (a is before planting grass, b is after grass seedlings emerge). DETAILED DESCRIPTION

[0020] The present invention is further described below by way of examples. It is necessary to point out that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Those skilled in the art may make some non-essential improvements and adjustments to the present invention according to the above-mentioned invention content and implement the invention specifically, which still falls within the scope of protection of the invention.

[0021] In the following examples, W-OH and SAP were purchased from the market.

[0022] Example 1 This embodiment includes the following contents: (1) a method for determining the reasonable amount of additional water-retaining agent - super absorbent resin SAP; (2) a method for applying SAP; (3) determining the applicable concentration of W-OH solution; and (4) a reasonable amount and addition method of W-OH.

[0023] Since SAP has a strong water absorption capacity, if the amount is too large, it will cause the soil to expand and destroy the structure of the soil; if the amount is too small, the pore space in the coarse-grained slag that can store water cannot be fully utilized. Therefore, it is necessary to determine the reasonable amount of SAP. The principle of determination is to maximize the use of the pore space between the slag particles to store water, but to ensure that the structure of the soil is not destroyed. According to the lower limit of the free expansion rate in the judgment conditions of expansive soil is 25%, considering a certain margin, the free expansion rate of the slag after adding SAP is limited to less than 15% when it is saturated with water. The amount of SAP added obtained by the free expansion rate test is 0.05% by mass.

[0024] After fully mixing the coarse-grained slag with 0.05% SAP by mass, the mixture was spread on the filled slag slope with a thickness of 30 cm to meet the growth depth requirement of plant roots.

[0025] Experimental studies have found that after the binder W-OH solution is poured into the coarse-grained slag, W-OH gel will form between the coarse particles, connecting and wrapping the soil particles. Figure 1 The anti-erosion ability of soil increases with the increase of binder concentration and dosage. However, when the concentration of W-OH solution exceeds 4%, the gel formed is hard, which is not conducive to plant growth. Therefore, a 4% mass concentration of W-OH solution (binder) is used when improving shallow slag on the slope.

[0026] Through the soil column slurry injection test, it can be seen that when the volume dosage of W-OH binder is 9.4% of the volume of the laid slag material that needs to be bonded (calculated according to the thickness and area required to be bonded), it can effectively bond the soil particles of coarse-grained slag to form cemented slag with strong anti-erosion ability.

[0027] According to the concentration of W-OH binder determined above, mix the W-OH stock solution with water and stir thoroughly to make the two react fully. Then quickly and evenly pour the prepared W-OH solution onto the slope surface with a watering can. When a 30 cm thick gravel slope with SAP water retainer added needs to be cemented, 28.2 L of 4% concentration W-OH solution needs to be poured per square meter of slope surface.

[0028] The irrigation can be implemented in two stages. In the first stage, 18.2 L of pure 4% concentration W-OH solution is poured per square meter. In the second stage, grass seeds can be mixed with the remaining 10 L W-OH solution for irrigation, so that the grass seeds can flow into the surface pores of the slope along with the slurry to achieve vegetation restoration on the slope.

[0029] The permeability of the slag slope treated with W-OH binder with a volume dosage of 9.4% and a mass concentration of 4% increased from 10% to 20% of the untreated slag. -3 cm / s reduced to 10 -5 cm / s, which is reduced by 2 orders of magnitude. The permeability of the treated slag is similar to that of ordinary silt sand or silt soil, and the water holding and water retention performance is significantly enhanced, which is beneficial to plant growth.

[0030] The modified slag layer obtained by combining SAP and W-OH was subjected to a water absorption-drying cycle test, and the unmodified slag was used as a comparison. The results are as follows: Figure 2 , Figure 3 . Figure 2 In order to improve the volumetric moisture content of coarse-grained slag before and after the change in the water absorption-drying cycle, Figure 3 The maximum water absorption rate of coarse-grained slag after drying changes with the number of cycles before and after improvement. Figure 2 , Figure 3 It can be seen that the initial water absorption rate of the unimproved coarse-grained slag is only 7.6%, while the initial maximum water absorption rate of the improved slag can reach 20.0%, indicating that the improved slag can absorb more water. Moreover, after two drying processes, the maximum water absorption rate of the unimproved slag is only 6.3%; the maximum water absorption rate of the improved slag can still be maintained at 16.2%, which has a strong water absorption capacity. At the same time, the water release rate of the improved slag is significantly reduced. The soil sample of the slag before improvement will completely lose water after 30 days at 30°C, while the improved soil sample still retains 60% of water after 35 days, and the water release rate of the improved slag gradually decreases with the extension of time. It can be seen that the time for the slag to completely dry after the improvement method of the present invention will be significantly longer than before treatment, that is, the water retention time can be significantly increased, which is conducive to the continuous supply of water required for plant growth in the dry season.

[0031] On-site runoff infiltration tests and on-site slope scour tests were conducted on the slopes with improved slag layers. The test results showed that the runoff rate of the improved slopes increased significantly and the infiltration rate decreased by 56% to 68% (see Figure 4 ), indicating that the method of the present invention has a good effect on reducing slope water loss. At the same time, from the results of the on-site slope scour test, it can be seen that a relatively stable protective layer is formed on the improved slag slope, which has a certain protective effect on the slag particles and has a strong resistance to water erosion. Therefore, the runoff erosion rate of the improved slope is significantly lower than that of the unimproved slope.

[0032] In the laboratory, a grass planting experiment was carried out using improved coarse-grained slag. After sowing seeds of ryegrass and Amorpha fruticosa, the grass seedlings could germinate smoothly, grow and survive in the improved slag. Figure 5 .

Claims

1. A method for improving the water-retention and soil-retention performance of coarse-grained slag by combining W-OH and SAP, characterized in that: Includes the following: Highly absorbent resin SAP is mixed into coarse-grained slag, and the evenly mixed mixture is spread on the surface of the slag slope to form a slag layer. Then, a modified hydrophilic polyurethane resin W-OH solution is poured in situ on the slag layer to form an improved slag planting layer in situ on the slag slope surface for vegetation restoration.

2. The method according to claim 1, characterized in that: The amount of the highly absorbent resin SAP used is 0.04% to 0.05% of the mass of the slag used in the entire improved slag planting layer.

3. The method according to claim 1, characterized in that: The mass concentration of the W-OH solution is 4%, and the volume usage of the W-OH solution is 9.0-12.0% of the volume of the paved slag layer that needs to be cemented.

4. The method according to claim 1 or 2, characterized in that: The coarse-grained slag is a slag material composed of sand, gravel and stone with a particle size greater than 0.1 mm and less than 200 mm.

5. A method for restoring vegetation on a gravel slope, characterized in that: The following steps are involved: Highly absorbent resin SAP is mixed into coarse-grained slag, and the evenly mixed mixture is evenly spread on the surface of the slag slope to form a slag layer; then, a part of the modified hydrophilic polyurethane resin W-OH solution is poured on the slag layer in situ to preliminarily form an improved slag planting layer in situ on the slag slope surface; finally, grass seeds or other plant seeds for vegetation restoration are mixed into the remaining part of the modified hydrophilic polyurethane resin W-OH solution to form the slag planting layer in situ, and at the same time, the plant seeds are evenly sown into the improved slag planting layer to achieve vegetation restoration on the slope surface.

6. The method according to claim 5, characterized in that: The amount of the highly absorbent resin SAP used is 0.04% to 0.05% of the mass of the slag used in the entire improved slag planting layer.

7. The method according to claim 5, characterized in that: The mass concentration of the W-OH solution is 4%, and the volume usage of the W-OH solution is 9.0-12.0% of the volume of the paved slag layer that needs to be cemented.

8. The method according to claim 2, characterized in that: The coarse-grained slag is a slag material composed of sand, gravel and stone with a particle size greater than 0.1 mm and less than 200 mm.

9. A water-retaining and soil-retaining agent, comprising a highly water-absorbent resin material SAP and a modified hydrophilic polyurethane resin W-OH.

10. Combined application of highly absorbent resin material SAP and modified hydrophilic polyurethane resin W-OH in improving the water-retaining and soil-retaining properties of coarse-grained slag.

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