Composite base material for ecological slope protection, preparation method of composite base material and slope protection method

Abstract

The invention discloses a composite base material for ecological slope protection, a preparation method of the composite base material and a slope protection method, and the composite base material comprises sandy loam serving as a matrix of the composite base material; the polyacrylamide forms a continuous cementation network on the surfaces of the sandy loam particles and solidifies the sandy loam particles, and the mixing amount of the polyacrylamide is 0.6%-1.0%; the coal ash is filled in sandy loam soil pores and hydrated to generate C-S-H gel covering the surfaces of sandy loam soil particles, and the doping amount of the coal ash is 1.0%-3.0%; the palm fibers are of a three-dimensional net-shaped reinforced structure in the sandy loam soil, and the mixing amount of the palm fibers is 0.6%-1.2%; the polyacrylamide, the fly ash and the palm fibers jointly form a composite base material containing cementing, filling and reinforcement in the sandy loam soil; according to the scheme, slope protection and ecological restoration are achieved, the composite base material is innovatively designed, the scheme with both ecological benefits and economical efficiency is provided for ecological restoration of the rock slope in the high-cold and high-altitude area, and the scheme has important reference value for sustainable development of ecologically fragile areas in China.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ecological slope protection, and particularly relates to a composite substrate for ecological slope protection, a preparation method thereof and a slope protection method. BACKGROUND

[0002] The rock slope in the alpine high-altitude region faces the dual challenges of ecological restoration and slope stability due to extreme climatic conditions (such as low temperature, freeze-thaw cycle, strong ultraviolet radiation) and special geological environment. The traditional slope protection technology mainly includes three types of engineering slope protection, simple ecological slope protection and comprehensive ecological slope protection, but all have significant defects: 1. The engineering slope protection technology (such as cement finishing and mortar rubble) can stabilize the slope in the short term, but it hinders water and soil exchange, inhibits plant growth, and has poor landscape coordination and low long-term ecological benefits.

[0003] 2. The simple ecological slope protection technology (such as spraying grass seeds and planting bags) has weak erosion resistance, fast nutrient loss, and is difficult to resist freeze-thaw and storm erosion, resulting in low vegetation coverage and unsustainable ecological function.

[0004] 3. The comprehensive ecological slope protection technology combines engineering and plant measures, but the existing substrate relies on a single additive (such as cement, lime or high polymer material), which is difficult to balance mechanical strength and ecological function. For example, high polymer materials (such as polyacrylamide and polyacrylamide) can improve soil cohesion and water retention, but the shear strength is insufficient when used alone; industrial waste (such as fly ash) can improve soil structure, but lacks cementing ability; plant fibers (such as palm fibers) can be reinforced to enhance shear performance, but have limited resistance to freeze-thaw and ultraviolet radiation.

[0005] In addition, the existing technology has poor adaptability in the alpine high-altitude environment, which is manifested in the following aspects: poor freeze-thaw resistance: repeated freeze-thaw leads to cracking and peeling of the substrate; weak erosion resistance: storm runoff easily causes soil erosion; insufficient vegetation conditions: poor soil, poor water and fertilizer retention, and difficult long-term survival of vegetation.

[0006] Although domestic and foreign scholars have tried to improve the performance through composite substrates, they have focused on single materials or local properties, and lack systematic research on the synergistic mechanism of multiple materials, especially the correlation mechanism of microstructure evolution and macro mechanical-ecological performance; therefore, developing a composite substrate with high strength, erosion resistance, weather resistance and vegetation function has become a key technical problem for ecological restoration of alpine high-altitude rock slopes. SUMMARY

[0007] In view of the above deficiencies of the prior art, the present application provides a composite substrate for ecological slope protection and a preparation method and protection method thereof, which optimizes multi-material proportioning and micro-macro synergistic mechanism, aims to solve the technical problems mentioned in the background art, and provides an innovative solution for high-cold high-altitude slope protection.

[0008] A composite substrate for ecological slope protection and a preparation method and protection method thereof.

[0009] To achieve the above-mentioned purposes, the technical scheme adopted by the present application is as follows: In a first aspect, a composite substrate for ecological slope protection is provided, comprising: sandy loam soil as the matrix of the composite substrate; polyacrylamide forming a continuous cementation network on the surface of the sandy loam soil particles and solidifying the sandy loam soil particles, the dosage of polyacrylamide being 0.6% to 1.0%; fly ash filled in the pores of the sandy loam soil and hydrated to generate C-S-H gel covering the surface of the sandy loam soil particles, the dosage of fly ash being 1.0% to 3.0%; palm fiber presenting a three-dimensional network reinforcement structure in the sandy loam soil, the dosage of palm fiber being 0.6% to 1.2%; polyacrylamide, fly ash and palm fiber together forming a composite substrate containing cementation, filling and reinforcement in the sandy loam soil.

[0010] Further, the dosage of polyacrylamide is 0.8%, the dosage of fly ash is 3.0%, and the dosage of palm fiber is 0.9%.

[0011] Further, the polar groups in the polyacrylamide are combined on the surface of the sandy loam soil particles through hydrogen bonds, and the polyacrylamide forms a continuous film wrapping the sandy loam soil particles after water absorption and swelling, and the polyacrylamide and the ions in the sandy loam soil are chemically cross-linked to form a three-dimensional cementation network.

[0012] Further, the maximum dry density of the sandy loam soil is 1.62 g / cm³, and the optimum moisture content is 12.1%.

[0013] Further, the polyacrylamide is a non-ionic polyacrylamide with a molecular weight of 30 million and a hydrolysis degree of 30%.

[0014] In a second aspect, a preparation method of a composite substrate for ecological slope protection is provided, comprising the following steps: S1: After the sandy loam soil is dried, it is passed through a 5 mm sieve, the required amount of water is calculated according to the optimum moisture content, and a portion of the water is added for pre-wetting, while the corresponding dosages of polyacrylamide, fly ash and palm fiber are weighed; S2: First, the sandy loam soil is uniformly mixed with fly ash, and then the palm fiber is manually uniformly dispersed in the mixed soil body; S3: The polyacrylamide is dissolved in the remaining water to form a solution, which is then stirred with the mixed soil body until uniform. S4: curing the mixed soil body in an environment of 25 DEG C and 95% humidity for 28 days until the composite substrate is formed.

[0015] In a third aspect, a slope protection method for the composite substrate of the ecological slope protection is provided, comprising the following steps: A1: cleaning the slope surface from top to bottom, removing loose pumice and floating soil one by one, and making the slope surface flat; A2: installing pegs on the slope surface and laying the net, and the net is fixed to the pegs through the connecting piece; A3: spraying the mixture of the composite substrate and grass seeds on the netted slope surface, and the spraying thickness is not less than 12 cm; A4: covering the sprayed slope surface with non-woven fabric, and compacting the non-woven fabric with fine soil at the top and bottom of the slope; A5: regularly watering and maintaining until the non-woven fabric is removed after the grass grows to a certain extent.

[0016] The beneficial effects of the present application are: 1. The present application innovatively proposes a polyacrylamide-fly ash-palm fiber composite substrate system, which can significantly enhance the mechanical properties of the composite substrate through the solidification mechanism of polyacrylamide, the reinforcement mechanism of palm fiber and the structure optimization mechanism of fly ash, and at the same time form a three-dimensional network structure inside the composite substrate, form an environment with water retention performance and ventilation function, and the minerals contained in the fly ash can provide the necessary nutrients for plant growth, promote plant development and ecological community construction; in addition, the composite substrate can fully reduce the material cost and reduce the environmental load by using industrial waste materials.

[0017] 2. The polyacrylamide of the present application mainly forms a bridge between soil particles to enhance the bonding force, builds a stable network in the cycle, improves the pore structure, reduces water migration damage, and resists freeze-thaw degradation; by absorbing ultraviolet rays, protecting other components, blocking the penetration of ultraviolet rays through the cementing structure, delaying the performance decline and resisting ultraviolet radiation. Fly ash mainly optimizes the structure by filling the pores, reduces the frost heaving force, enhances the interfacial bonding after multiple cycles, and improves the stability to resist freeze-thaw degradation and ultraviolet radiation; palm fiber mainly forms a three-dimensional network to increase toughness, disperse stress concentration, limit particle displacement, and maintain structural integrity to resist freeze-thaw degradation and ultraviolet radiation.

[0018] 3. The scheme can determine and analyze the pH value, nutrient content and water content of the composite substrate. The fly ash content has the greatest impact on the pH value, making the composite substrate weakly alkaline, which can meet the needs of plant growth. In terms of nutrients, fly ash significantly improves the content of organic matter and available phosphorus, and polyacrylamide has a greater impact on the content of total nitrogen and available potassium. The composite substrate realizes efficient retention of nutrients through various effects. The water content and water evaporation rate are most affected by polyacrylamide. Polyacrylamide, palm fiber and fly ash synergistically improve water retention, but excessive polyacrylamide content can have a negative impact. Therefore, the optimal mass ratio of the composite substrate is determined as follows: polyacrylamide content 0.8%, fly ash content 3% (considering the actual application requirements for plant height), and palm fiber content 0.9%. Under this ratio, the composite substrate can significantly promote seed germination, plant growth and vegetation coverage.

[0019] 4. The polyacrylamide, fly ash and palm fiber of the scheme cooperate with each other in sandy loam soil to jointly improve the mechanical properties of the sandy loam soil. Polyacrylamide provides a bonding network, fibers enhance toughness, and fly ash optimizes density to form a "bonding-reinforcing-filling" composite system. The three synergistically change the soil structure from a micro level and significantly improve the strength, stability and deformation resistance of the sandy loam soil on a macro level, providing a solid theoretical basis for engineering applications.

[0020] 5. When the composite substrate slope of the scheme is eroded by rainfall, the polyacrylamide molecular chain absorbs water and swells, forming a dense gel film on the material surface. This film reduces the kinetic energy transmission efficiency of raindrops, reduces the direct impact of raindrops on the soil, and also blocks water infiltration to prevent the soil from becoming saturated due to rapid and large water absorption. The internal palm fiber forms a three-dimensional network structure, effectively dispersing runoff energy and dispersing concentrated water flow into multiple fine streams, reducing local scouring force and intercepting suspended particles in runoff, reducing the sand-carrying capacity. At the same time, fly ash fills soil pores, reducing the number of large pores, reducing soil aeration, improving water retention, and making the soil structure more stable. In addition, after planting plants on the slope, the roots can effectively anchor the soil, further improving the stability of the slope. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 Table of results analysis of compressive strength tests of different composite substrate ratios.

[0022] Figure 2 Table of results analysis of cohesion tests of different composite substrate ratios.

[0023] Figure 3 Table of results analysis of internal friction angle tests of different composite substrate ratios.

[0024] Figure 4 Table of quality loss rate analysis of freeze-thaw tests of different composite substrate ratios.

[0025] Figure 5 The quality loss rate analysis table of the different proportion composite base material ultraviolet irradiation test.

[0026] Figure 6 The strength loss rate analysis table of the different proportion composite base material ultraviolet irradiation test.

[0027] Figure 7 The result analysis table of the different proportion composite base material plant on the germination rate test.

[0028] Figure 8 The result analysis table of the different proportion composite base material on the plant height test.

[0029] Figure 9 The result analysis table of the different proportion composite base material on the vegetation coverage test.

[0030] Figure 10 The result analysis table of the different proportion composite base material on the PH test. DETAILED DESCRIPTION

[0031] The specific embodiments of the present application are described below to facilitate the understanding of the present application for those skilled in the art, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, it is obvious that various changes are within the spirit and scope of the present application defined and determined by the appended claims, and all the inventions utilizing the concept of the present application are within the scope of protection.

[0032] The composite base material for ecological slope protection comprises: sandy loam soil as the matrix of the composite base material; polyacrylamide forming a continuous cementation network on the surface of the sandy loam soil particles and solidifying the sandy loam soil particles, the polyacrylamide content being 0.6%-1.0%; fly ash filled in the pores of the sandy loam soil and hydrated to generate C-S-H gel covering the surface of the sandy loam soil particles, the fly ash content being 1.0%-3.0%; palm fiber presenting a three-dimensional network reinforcement structure in the sandy loam soil, the palm fiber content being 0.6%-1.2%; the polyacrylamide, fly ash and palm fiber together forming a composite base material containing cementation, filling and reinforcement in the sandy loam soil.

[0033] The particle size distribution of the sandy loam soil in the scheme is mainly fine gravel (23.47%) and coarse sand (30.82%), and the gradation is poor; the relationship between the compactness and the water content of the sandy loam soil can be determined through the compaction test, specifically, first, take about 15 kg of the sandy loam soil, pass it through a 5 mm sieve, and take about 3 kg of the soil each time, add water to prepare soil samples with water contents of about 8%, 10%, 12%, 14% and 16%, and seal for 24 hours; load the soil samples into a compaction cylinder in three layers, and perform 27 compactions for each layer; after the compaction of the last layer is completed, trim the excess soil at the top of the compaction cylinder to make the soil sample flush with the top surface of the compaction cylinder; after the compaction is completed, remove the compaction cylinder from the base plate, and use a soil pusher to push the compacted soil sample out of the cylinder, weigh the mass of the compacted soil sample, and calculate the water content thereof; thus, the relationship curve between the water content of the sample and the dry density is obtained, as shown in the figure; therefore, the maximum dry density of the sandy loam soil is 1.62 g / cm³, and the optimum water content is 12.1%.

[0034] The scheme also provides a preparation method of a composite substrate for ecological slope protection, which comprises the following steps: S1: dry the sandy loam soil, pass it through a 5 mm sieve, calculate the required amount of water to be added according to the optimum water content, and add a part of the water to pre-wet, and meanwhile, weigh the corresponding amounts of polyacrylamide, fly ash and palm fiber; S2: first, uniformly mix the sandy loam soil and the fly ash, and then manually uniformly disperse the palm fiber in the mixed soil body; S3: dissolve the polyacrylamide in the remaining water to form a solution, and then stir the mixed soil body until it is uniform; S4: store the mixed soil body in an environment with a temperature of 25°C and a humidity of 95% for 28 days until the composite substrate is formed.

[0035] The scheme preferably has a polyacrylamide content of 0.8%, a fly ash content of 3.0%, and a palm fiber content of 0.9%; the polyacrylamide is a non-ionic polyacrylamide with a molecular weight of 30 million and a hydrolysis degree of 30%, which enhances the cohesion and anti-scouring capacity of the composite substrate; the chemical composition of the fly ash is SiO2, Al2O3 and Fe2O3; the palm fiber has a length of 2 cm, which enhances the shear strength and anti-deformation capacity of the substrate through three-dimensional network reinforcement, and improves the air permeability and plant growth performance of the substrate.

[0036] The performance of the composite substrate with the optimal mass ratio is verified and illustrated through the following test: (1) The scheme can perform a composite substrate unconfined compressive strength test on composite substrates with different ratios, such as Figure 1As shown in the compression strength analysis table, polyacrylamide has a greater impact on the compression strength. With the increase of polyacrylamide, the compression strength of the substrate first increases and then decreases. The main reason is that the strength of the sample depends on the stable cementation network structure formed by the cementing material and soil particles. This network structure can effectively bond the particles of the substrate together, disperse and transfer external load, and improve the compression resistance of the substrate. When the polyacrylamide content increases, the amount of cementing material increases first, which can fill the pores and bond the particles, resulting in an increase in compression strength. However, when it exceeds a certain limit, excessive cementing material will cause some negative effects, such as agglomeration and pore blockage, which will hinder the improvement of material performance and lead to a decrease in compression strength. The impact of palm fiber is less, but it also shows a trend of first increasing and then decreasing. Palm fiber can effectively inhibit this deformation and maintain the integrity of the soil structure. However, when there is too much palm fiber, the fibers tend to overlap and entangle, forming agglomerates and weak structural planes in the soil, which reduces the compression strength.

[0037] (2) This scheme can test the shear resistance of different proportioning composite substrates, such as Figure 2 As shown in the cohesion analysis table, with the increase of polyacrylamide content, the number of soil aggregates increases significantly, and the cohesion increases significantly. The cohesion first increases and then decreases, and when the polyacrylamide content is 0.8%, the cohesion is maximum, which is 46.8 kPa. When the content exceeds 0.8%, the polyacrylamide molecular chain agglomerates, and the molecules are not easy to diffuse and convect in the soil layer, forming a high-molecular cemented soil film layer on the soil surface, which prevents water from entering the soil aggregate voids and reduces the effective bonding between soil particles. When the fiber content is low, the cohesion of the soil has a certain improvement, but the improvement is low. With the continuous increase of the content, the palm fiber forms an effective spatial structure network structure in the soil, which enhances the constraint and connection of soil particles and effectively prevents the relative movement of soil particles, greatly improving the ability of sandy loam soil to resist external damage and significantly improving the cohesion. Fly ash can optimize the soil structure by filling pores and partial cementation, but its contribution to cohesion is relatively small. When the fly ash content is 3.0%, the cohesion reaches a higher value (38.0 kPa), but its range is only 3.70 kPa, indicating that its contribution to cohesion is limited.

[0038] As shown in the cohesion analysis table, with the increase of polyacrylamide content, the number of soil aggregates increases significantly, and the cohesion increases significantly. The cohesion first increases and then decreases, and when the polyacrylamide content is 0.8%, the cohesion is maximum, which is 46.8 kPa. When the content exceeds 0.8%, the polyacrylamide molecular chain agglomerates, and the molecules are not easy to diffuse and convect in the soil layer, forming a high-molecular cemented soil film layer on the soil surface, which prevents water from entering the soil aggregate voids and reduces the effective bonding between soil particles. When the fiber content is low, the cohesion of the soil has a certain improvement, but the improvement is low. With the continuous increase of the content, the palm fiber forms an effective spatial structure network structure in the soil, which enhances the constraint and connection of soil particles and effectively prevents the relative movement of soil particles, greatly improving the ability of sandy loam soil to resist external damage and significantly improving the cohesion. Fly ash can optimize the soil structure by filling pores and partial cementation, but its contribution to cohesion is relatively small. When the fly ash content is 3.0%, the cohesion reaches a higher value (38.0 kPa), but its range is only 3.70 kPa, indicating that its contribution to cohesion is limited. Figure 3As shown, according to the internal friction angle analysis table, with the increase of the polyacrylamide content, the internal friction angle of the soil body presents a trend of first increasing and then decreasing. The polyacrylamide enhances the cementation force between soil particles through the bridging effect of its high molecular chain, and indirectly improves the internal friction angle. When the polyacrylamide content is 0.8%, the internal friction angle reaches a peak value of 46.8°; excessive polyacrylamide (1.0%) reduces the internal friction angle due to the entanglement of molecular chains, which leads to the agglomeration phenomenon; the soil body first increases and then decreases with the increase of the palm fiber content, and when the palm fiber content is 0.9%, the internal friction angle reaches a peak value of 46.8°; the incorporation of fibers has a strong influence on the internal particle distribution of the soil body; this is mainly because the fibers act as a filler in the soil body, reducing the pores between the particles, thereby improving the density and stability of the soil body. During the compaction sample preparation process, the interaction between the fibers and the soil particles may cause deformation and local damage to the surface of the fibers, and some soil particles are embedded into the surface of the fibers. This embedded structure enhances the close connection between the soil particles and the fibers, significantly increasing the internal friction of the soil body. This effect not only improves the mechanical properties of the soil body, but also promotes the stability of the overall structure; fly ash mainly fills the voids of the soil body, reduces the void ratio and optimizes the grading, thereby increasing the internal friction angle, and with the increase of fly ash, the internal friction angle of the soil body continues to increase.

[0039] Through the above tests, it is known that the polyacrylamide content is the main control factor of the compressive strength, and the optimal mass ratio is A2B3C2 (polyacrylamide content 0.8%, fly ash content 3%, fiber content 0.9%). The compressive strength of the experimental group 5 after 28 days of maintenance reaches 328 kPa, which is 286% higher than that of the soil; the cohesion reaches 46.8 kPa, which is 96.1% higher than that of the soil (23.87 kPa); the internal friction angle reaches 46.8°, which is 74.6% higher than that of the soil (26.8°), and the compressive strength and shear resistance of the remaining experimental groups are also improved to different degrees compared with the soil; and the strength and shear resistance of the samples increase with the increase of the maintenance time.

[0040] (3) The scheme can perform freeze-thaw degradation tests and ultraviolet aging tests on different proportioning composite substrates, such as Figure 4 , Figure 5 and Figure 6As shown, the quality loss rate of test group 5 after 28 days of maintenance and 20 freeze-thaw cycles at ±20°C is less than 0.94%, and the strength loss rate is less than 5.8%; the optimal mass ratio during the ultraviolet aging test is A2B3C2 (polyacrylamide content 0.8%, fly ash content 3%, fiber content 0.9%), and the quality loss rate of test group 5 after 28 days of maintenance and 20 days of ultraviolet radiation is less than 1.68%, and the strength loss rate is less than 6.2%. The optimal mass ratio of the freeze-thaw degradation test is different from other experiments, because when the fly ash content is 2%, it can fill the pores and optimize the structure, and it will not be too serious due to the excessive amount of pore structure degradation under the impact of frost heaving force. The best mass ratio of this scheme is polyacrylamide content 0.8%, fly ash content 3%, and fiber content 0.9%).

[0041] The polyacrylamide of this scheme mainly forms a bridge between soil particles to enhance the cohesive force, builds a stable network in the cycle, improves the pore structure, reduces water migration damage, and resists freeze-thaw degradation; by absorbing ultraviolet rays, protecting other components, cementing structure to block ultraviolet rays, delaying performance decline to resist ultraviolet radiation. Fly ash mainly fills the pores to optimize the structure, reduces the frost heaving force, enhances the interface bonding after multiple cycles, and improves the stability to resist freeze-thaw degradation and ultraviolet radiation. Palm fiber mainly forms a three-dimensional network, increases toughness, disperses stress concentration, limits particle displacement, maintains structural integrity, and resists freeze-thaw degradation and ultraviolet radiation.

[0042] (4) This scheme gives the influence test of different ratio of composite base material on plant germination rate, plant height, vegetation coverage, and PH, such as Figure 7 、 Figure 8 、 Figure 9 and Figure 10As shown, polyacrylamide has the greatest impact on each index, followed by fly ash on germination rate, and palm fiber on plant height and coverage rate, with the least impact on germination rate; at the same time, the polyacrylamide content should not be too high, otherwise the increased viscosity will inhibit the air permeability, resulting in a decrease in each index of the plant growth performance, and finally the optimal mass ratio of the composite substrate is determined as 0.8% of the polyacrylamide content, 3% of the fly ash content (considering the actual application requirements for plant height), and 0.9% of the palm fiber content. Under this ratio, the composite substrate can significantly promote seed germination, plant growth and vegetation coverage; the pH value, nutrient content and water content of the composite substrate are determined and analyzed. The fly ash content has the greatest impact on the pH value, making the composite substrate weakly alkaline and meeting the growth needs of plants; in terms of nutrients, fly ash significantly improves the content of organic matter and available phosphorus, and polyacrylamide has a greater impact on the content of total nitrogen and available potassium, and the composite substrate realizes efficient retention of nutrients through various effects; the water content and water evaporation rate are most affected by polyacrylamide, and polyacrylamide, palm fiber and fly ash synergistically improve the water retention, but too high a polyacrylamide content will have a negative impact.

[0043] The polyacrylamide of the present scheme solidifies the soil particles through four stages of physical adsorption, film coating, chemical cross-linking and structure stabilization, that is, the polar groups in the polyacrylamide are combined with the surface of the soil particles through hydrogen bonds, the polyacrylamide forms a dense film after water absorption and swelling, inhibits the migration of particles, the carboxyl groups are coordinated with Ca²⁺, and a "soil-polymer-soil" three-dimensional cementation network is constructed; finally, the stable structure is jointly constructed by the cementation product of fly ash; the fiber reinforcement mechanism can be divided into four kinds of soil-fiber interface action, quasi-cohesion action, bridging action and stress dispersion action, which improves the mechanical properties of sandy loam soil from multiple dimensions, and the fly ash particles are dispersed in the three-dimensional cementation network to form a "rigid skeleton-flexible matrix" structure, which enhances the network continuity and inhibits the sliding of polyacrylamide molecular chains; at the same time, the pore of the substrate is optimized, the structure is dense, the surface active hydroxyl groups form hydrogen bonds with the polyacrylamide molecular chains, the active SiO2 reacts with Ca²⁺ to generate C-S-H gel, covers the surface of the soil particles, cements the pores, and improves the interface strength.

[0044] The polyacrylamide, fly ash and palm fiber of the present scheme cooperate with each other in sandy loam soil to jointly improve the mechanical properties of sandy loam soil; the polyacrylamide provides a cementation network, the fiber enhances the toughness, and the fly ash optimizes the density, forming a "cementation-reinforcement-filling" composite system, which synergistically changes the soil structure from the micro level and significantly improves the strength, stability and anti-deformation ability of sandy loam soil on the macro level, providing a solid theoretical basis for engineering applications.

[0045] The present scheme also provides a slope protection method for the composite substrate for ecological slope protection, which comprises the following steps: A1: clean the slope surface from top to bottom, remove loose floating stones and soil, and make the slope surface flat; A2: install pegs on the slope surface and lay the net, and the net is fixed to the pegs through the connecting piece; A3: spray the mixture of composite substrate and grass seeds on the netted slope surface, and the spraying thickness is not less than 12 cm; A4: cover the sprayed slope surface with non-woven fabric, and compact the non-woven fabric with fine soil at the top and bottom of the slope; A5: regularly water and maintain until the non-woven fabric is removed after the grass grows to a certain extent.

[0046] When the composite substrate slope of the scheme is eroded by rainfall, the polyacrylamide molecular chain absorbs water and swells to form a dense gel film on the surface of the material. This layer of film reduces the kinetic energy transmission efficiency of raindrops, reduces the direct impact of raindrops on the soil, and also blocks the downward infiltration of water, preventing the soil from being saturated due to rapid and large water absorption. The internal palm fiber forms a three-dimensional network structure, effectively dispersing the runoff energy, dispersing the concentrated flow into multiple fine streams, reducing the local scouring force, and also intercepting suspended particles in the runoff, reducing the sand-carrying capacity. At the same time, the fly ash fills the soil pores, reducing the number of large pores, reducing the soil aeration, improving the water retention, and making the soil structure more stable. In addition, after planting plants on the slope, the roots can effectively reinforce and anchor the soil, further improving the stability of the slope.

[0047] The scheme takes a sandy loam slope in Shannan City, Tibet as the research object, uses polyacrylamide, fly ash and palm fiber composite substrate, and combines with the net hanging and spray seeding technology to implement comprehensive ecological slope protection engineering. After the implementation of the project, the vegetation coverage is significantly improved, reaching 90% after 6 months, the root depth is 15 cm, the soil moisture content increases from 6% to 18%, the organic matter content increases by 18%, the water and soil loss is reduced and the erosion resistance is enhanced. The detection content of heavy metals is lower than the national standard, and the deep migration is limited. Compared with traditional concrete slope protection, the cost is reduced by 41% (363 yuan / m²), which has both ecological and economic benefits. The research verifies the feasibility of polyacrylamide substrate in slope repair, and provides technical reference for similar comprehensive ecological slope protection engineering in the region.

[0048] To sum up, the scheme innovatively proposes a polyacrylamide-fly ash-palm fiber composite substrate system. The composite substrate can significantly enhance the mechanical properties of the composite substrate through the polyacrylamide curing mechanism, the palm fiber reinforcement mechanism and the fly ash structure optimization mechanism. At the same time, a three-dimensional network structure is formed inside the composite substrate, forming an environment with water retention performance and ventilation function. The minerals contained in the fly ash can provide the necessary nutrients for plant growth, promote plant development and ecological community construction. The scheme research finds the optimal mass ratio between materials through indoor and outdoor tests and verifies the basic performance of the materials, reveals the synergistic mechanism between the material structures, and provides an ecological benefit and economic solution for the ecological restoration of rock slopes in high-cold and high-altitude areas. It has important reference value for the sustainable development of China's ecologically fragile areas.

Claims

1. A composite substrate for ecological slope protection, characterized in that: include: Sandy loam soil, which serves as the matrix for the composite substrate; Polyacrylamide, which forms a continuous cementing network on the surface of sandy loam particles and solidifies the sandy loam particles, and the polyacrylamide is added in an amount of 0.6% to 1.0%; Fly ash fills the pores of the sandy loam and hydrates to form CSH gel covering the surface of the sandy loam particles. The fly ash is added in an amount of 1.0% to 3.0%. Palm fiber, which presents a three-dimensional network reinforcement structure in sandy loam, and the amount of the palm fiber is 0.6% to 1.2%; The polyacrylamide, fly ash and palm fiber together form a composite matrix including bonding, filling and reinforcement in sandy loam.

2. The composite substrate for ecological slope protection according to claim 1, characterized in that: The content of the polyacrylamide is 0.8%, the content of the fly ash is 3.0%, and the content of the palm fiber is 0.9%.

3. The composite substrate for ecological slope protection according to claim 1, characterized in that: The polar groups in the polyacrylamide are bonded to the surface of the sandy loam particles through hydrogen bonds, and the polyacrylamide forms a continuous film wrapping the sandy loam particles after absorbing water and swelling. The polyacrylamide and the ions in the sandy loam are chemically cross-linked to form a three-dimensional cementation network.

4. The composite substrate for ecological slope protection according to claim 1, characterized in that: The maximum dry density of the sandy loam soil is 1.62 g / cm³, and the optimal moisture content is 12.1%.

5. The composite substrate for ecological slope protection according to claim 1, characterized in that: The polyacrylamide is a non-ionic polyacrylamide with a molecular weight of 30 million and a hydrolysis degree of 30%.

6. A method for preparing a composite substrate for ecological slope protection according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1: Air-dry the sandy loam soil and pass it through a 5 mm sieve. Calculate the required water content based on the optimal moisture content and add a portion of water for pre-wetting. At the same time, weigh the corresponding amounts of polyacrylamide, fly ash, and palm fiber. S2: Sandy loam and fly ash were first mixed evenly, and then palm fiber was artificially dispersed evenly in the mixed soil; S3: dissolving polyacrylamide in the remaining water to form a solution and then stirring it with the mixed soil until it is uniform; S4: Cure the mixed soil in an environment of 25°C and 95% humidity for 28 days until a composite substrate is formed.

7. A slope protection method using the composite substrate for ecological slope protection according to any one of claims 1 to 5, characterized in that: The following steps are involved: A1: Clean the slope surface from top to bottom, remove loose pumice and loose soil one by one, and make the slope surface smooth; A2: Install stakes on the slope and lay the net, and the net is fixed to the stakes with connectors; A3: Spray a mixture of composite substrate and grass seeds on the slope with the net hanging, with a thickness of not less than 12cm; A4: Cover the sprayed slope with non-woven fabric and compact it with fine soil at the top and bottom of the slope. A5: Water the grass regularly until it grows to a certain size, then remove the non-woven fabric.

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