Slope ecological restoration base material based on multistage synergistic solidification and layered spray-seeding method

Abstract

The invention discloses a slope ecological restoration base material based on multistage synergistic solidification and a layered spray-seeding method, and belongs to the technical field of geotechnical engineering and ecological restoration. The invention provides a three-layer collaborative base material system and a dynamic construction process. In the base material, the bottom layer takes modified volcanic ash and nano silica sol as cementing materials, so that rock surface permeation and adhesion are enhanced; the middle layer adopts chitosan slow-release particles and gradient moisture content design, so that nutrient stage release and interlayer stress buffering are realized; the surface layer is combined with the 3D honeycomb-shaped biochar carrier and the degradable PLA grid, grass seeds and mycorrhizal fungi are synchronously loaded, and a physical-biological composite anchoring structure is formed. The construction method comprises high-frequency micro-vibration permeation, layered gradient spray-seeding and photosensitive non-woven fabric covering processes, and it is ensured that the base material is resistant to rainstorm scouring and rapid in vegetation covering. The method has both mechanical stability and ecological compatibility, is suitable for repairing the high and steep rock slope, and remarkably reduces the maintenance cost and the environmental pollution risk.

Description

Technical Field

[0001] The present invention relates to the technical fields of geotechnical engineering and ecological restoration, and particularly relates to a slope ecological restoration base material based on multi-level collaborative solidification and a layered spraying method. Background Art

[0002] Slope ecological restoration technologies are mainly divided into methods such as soil spraying, vegetation concrete, and ecological bags. The core goal is to achieve soil stability and vegetation restoration through base material improvement. In recent years, related research has focused on the following directions: 1) Using cement-organic polymer composite cementitious materials to improve the strength of the base material in the short term, but excessive cement usage (>15%) is likely to cause soil alkalization (pH>9.0), inhibiting the development of plant roots; 2) Proposing "fiber-reinforced spraying base materials", and improving the tensile strength by adding polypropylene fibers (0.5-1.5%), but the interfacial bonding force between the fibers and the base material is insufficient, and it is easy to delaminate and peel under heavy rain scouring; 3) Designing a layered spraying process (bottom bonding layer + middle nutrient layer), but the moisture content of each layer is the same, and the curing shrinkage difference causes interlayer cracking, resulting in a cracking rate of >30% in 60 days.

[0003] In the field of slope ecological restoration base materials, seeking cementitious materials to replace cement helps to reduce the cost and adverse effects of ecological restoration. However, the base materials currently used in this field are still dominated by cementitious systems. Pozzolan is a material with low cost and wide sources. In the similar field of concrete, there are studies on partially replacing cement with pozzolan and silica sol, or using them as concrete additives to improve performance. For example, the Chinese invention patent with the publication number CN114477828A provides a concrete waterproof and compacting shrinkage reducing agent and its preparation method, which uses nano-silica sol, pozzolan, zeolite powder, sodium carbonate, sodium silicate, nano-aluminum oxide, and water as raw materials to improve the impermeability of concrete and reduce the early shrinkage of concrete. Another example is in the Chinese patent with the publication number CN118851682A, which uses pozzolanic active substances as auxiliary cementitious materials, and at the same time utilizes the coagulation effect of silica sol and the filling and sintering effects of nano-particles, combined with fiber toughening materials, to improve the impermeability of cement base materials. However, conventional pozzolan has low cementitious activity, poor adhesion strength, and underdeveloped pore structure, making it difficult to completely replace cement materials. And considering slope repair applications and ecological factors, in addition to meeting the physical and chemical performance indicators of the base material, specific plant compatibility, heavy metal adsorption, carbon emission reduction and other functions also need to be considered. The above targeted design requirements further increase the difficulty of developing corresponding slope ecological restoration base materials.

[0004] In summary, the existing technology has three core defects: 1) Poor ecological compatibility of cementitious materials: traditional cement or chemical binders cause soil compaction (porosity <35%) and pH imbalance (8.5-10.0), resulting in a vegetation survival rate of less than 50%; 2) Single anti-scour structure: relying on surface covering nets or random distribution of fibers, unable to form a "physical-biological" synergistic anchoring system, and the substrate loss under a 50 mm / h rainstorm is >10 kg / m 2 ; 3) Mismatch between nutrient supply and plant demand: Ordinary slow-release fertilizers have a fixed release cycle (such as 30 days), which cannot match the nutrient requirements of plants in different growth stages (such as high nitrogen in the budding stage and high phosphorus in the root expansion stage). Therefore, developing a slope ecological restoration substrate without cement addition can reduce construction costs, solve the problem of easy loss of traditional substrates, and take into account the effects of rapid greening and zero pollution, which is of great significance to the field of slope ecological restoration. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, in the first aspect of the present invention, a slope ecological restoration substrate which is not easy to be lost, has rapid greening, is degradable and low-cost is provided, comprising a bottom layer substrate, a middle layer substrate and a surface layer substrate; in parts by weight, each layer of the substrate comprises raw materials in the following proportions: (a) The bottom substrate comprises 25-35 parts of modified volcanic ash, 3-7 parts of nano silica sol, 45-55 parts of crushed stone aggregate, 3-7 parts of humic acid, and 0.5-1.5 parts of pH regulator; wherein the modified volcanic ash is calcined basalt volcanic ash; (b) The middle layer substrate comprises 15-25 parts of coconut shell fiber, 8-12 parts of chitosan slow-release particles, 20-30 parts of bentonite, 10-20 parts of organic fertilizer, and 3-7 parts of water retaining agent; (c) The surface substrate comprises the following components in parts by weight: 10-20 parts of 3D printed honeycomb biochar carrier, 2-5 parts of plant seeds, 1-3 parts of arbuscular mycorrhizal fungus powder, and 8-12 parts of vermiculite.

[0006] Preferably, in the bottom substrate, the modified volcanic ash is basalt volcanic ash calcined at 600-800 °C, with a specific surface area of ​​≥200 m 2 / g.

[0007] Preferably, in the bottom substrate, the SiO2 content of the nano-silica sol is 20 wt.%-30 wt.%, and the particle size is 10-50 nm.

[0008] Preferably, the pH of the bottom substrate is 6.5-7.2, and the porosity is 45%-50%.

[0009] Preferably, in the middle-layer substrate, the chitosan sustained-release granules are made by blending and granulating chitosan and humic acid at a weight ratio of 1.5-3:1, the particle size of the granules is 2-5 mm, and the sustained-release period is 60-90 days.

[0010] Preferably, in the surface-layer substrate, the 3D printed honeycomb biochar carrier is made by carbonizing crop straw under anoxic conditions at 500-600 °C, the pore diameter is 0.5-2 mm, and the porosity is ≥70%.

[0011] In the second aspect of the present invention, a layered spraying method for slope ecological restoration that is convenient, easy to implement, and has a low construction cost is provided. Using the slope ecological restoration substrate of the first aspect of the present invention, it includes the following steps: (1) Clean the surface of the slope, spray the bottom-layer substrate to a thickness of 3-5 cm, and apply high-frequency micro-vibration to form a bottom-layer substrate penetration and solidification layer; (2) After the bottom-layer substrate starts to set, spray the middle-layer substrate in two times; the gradient moisture content design of the middle-layer substrate is divided into a lower-layer water-containing layer and an upper-layer water-containing layer. Among them, the moisture content of the lower-layer water-containing layer is 20%-25%, and the moisture content of the upper-layer water-containing layer is 35%-40%; spray 50%-60% of the total amount of the middle-layer substrate for the first time to prepare the lower-layer water-containing layer, let it stand for 3-5 h to form a semi-solidified layer, and then spray the remaining part to a total thickness of 5-8 cm to prepare the upper-layer water-containing layer, and finally form a middle-layer gradient water-retaining layer; (3) Synchronously spray the surface-layer substrate and the biodegradable polylactic acid (PLA) fiber grid, and implant deep-rooted shrub seedlings at the grid nodes to form a surface-layer biochar-plant symbiotic layer; (4) Cover with a photosensitive degradation non-woven fabric to complete the construction of the slope ecological restoration structure.

[0012] Preferably, in the step (1), the high-frequency micro-vibration is realized by an eccentric wheel vibrator attached to the spraying equipment, and the vibration direction forms an angle of 10°-30° with the normal direction of the slope surface; the application frequency of the high-frequency micro-vibration is 20-40 Hz, the amplitude is 0.5-1 mm of high-frequency micro-vibration, and the duration is 5-15 min.

[0013] After the bottom layer is sprayed, high-frequency micro-vibration is applied to make the gelling material penetrate into the rock mass fissures, and the penetration depth is increased by 2.3 times compared with the conventional process.

[0014] In the middle-layer substrate, the moisture content of each layer is controlled by a water-retaining agent (such as polyacrylamide-attapulgite complex, etc.) and gradient water spraying volume. The middle-layer substrate is sprayed in two times. First, a semi-solidified layer is formed and then the remaining part is sprayed, which helps to avoid overall shrinkage and cracking.

[0015] Preferably, in the step (3), the degradation period of the degradable polylactic acid fiber grid is 150 - 200 days, the degradation products are carbon dioxide and water, the grid spacing is 15 cm × 15 cm to 25 cm × 25 cm, the grid tensile strength is ≥50 MPa, planting holes with a diameter of 3 - 5 cm are provided at the nodes, and the degradable polylactic acid fiber grid forms a spatial staggered anchoring network with the roots of the deep-rooted shrub seedlings, and the anchoring depth is ≥30 cm.

[0016] Preferably, in the step (4), the degradation condition of the photosensitive degradable non-woven fabric is that the cumulative ultraviolet irradiation reaches 200 - 300 MJ / m 2 , and the degradation period is 25 - 35 days.

[0017] In the third aspect of the present invention, a slope ecological restoration structure is provided, which is made by using the slope ecological restoration stratified spraying method of the second aspect of the present invention.

[0018] Preferably, the substrate loss amount of the slope ecological restoration structure under the rainstorm scouring of 50 mm / h is ≤3.5 kg / m 2 , and the time when the vegetation coverage rate reaches more than 80% is 60 - 90 days.

[0019] Based on the above technical solutions, the design concept and principle of the present invention are as follows: In the present invention, a modified volcanic ash and nano-silica sol are used in the bottom substrate to form an inorganic-nano composite cementitious system without adding cement, which enhances the rock surface penetration adhesion and forms a bottom substrate penetration curing layer with indexes such as pH and porosity within the set target range, reserving expansion space for plant roots. In the middle substrate, chitosan slow-release particles are combined with the gradient moisture content design, and the gradient moisture content is used to reduce the interlayer shear stress difference, so that the interlayer bonding strength is increased to 45 - 50 kPa, realizing the staged release of nutrients and the buffering of interlayer stress. The 3D printed honeycomb biochar carrier and the degradable PLA grid are synchronously loaded with arbuscular mycorrhizal fungi and drought-tolerant grass seeds, combined with photosensitive degradation synergistically, forming a "physical-biological" composite anchoring structure, taking into account the application requirements of fast vegetation coverage and strong ecological compatibility, and realizing rapid greening and zero pollution. The modified volcanic ash / straw biochar replaces high-price materials, combined with the stratified vibration spraying process, reducing the rework rate and maintenance frequency, and having good economic benefits.

[0020] To replace the use of cement materials, the present invention designs a gelling system formed by modified volcanic ash and nano-silica sol, whose gelling strength is significantly improved and cannot be replaced with ordinary volcanic ash. The modified volcanic ash exhibits higher gelling activity, with its activity index (28 days) ≥ 85%, while that of ordinary volcanic ash is ≤ 65%. Calcination can destroy the crystal structure of basalt, releasing more gelling active substances; and high-temperature calcination can remove volatile impurities, optimize the pore size distribution, and reduce defects. In addition, when synergistically acting with nano-silica sol, the adhesion strength reaches 3.0 - 3.5 MPa, which is higher than that of ordinary volcanic ash; while when using volcanic ash alone as a gelling material, the adhesion strength is as low as < 1.5 MPa. The modified volcanic ash has unique multi-level pores (micropores + mesopores), with a porosity of 45% - 50%, while the pore size distribution of ordinary volcanic ash is single and the porosity < 35%, which does not meet the indicators for slope ecological restoration.

[0021] The present invention adopts a gelling system of modified volcanic ash and nano-silica sol, which is a specific choice for the ecological benefits of slopes. Considering the plant compatibility of slopes, the modified volcanic ash is more conducive to promoting root development. In practical applications, the root length can increase by up to 40%; while the alkaline environment and harmful impurities of ordinary volcanic ash are likely to inhibit the growth of plant roots. In terms of heavy metal absorption, the pore structure of the modified volcanic ash has an adsorption rate of > 90% for ions such as Pd 2+ , Cd 2+ etc., while that of ordinary volcanic ash is < 50%. Ordinary volcanic ash needs to be mixed with cement materials for use, and the emission reduction effect is poor. The gelling system designed by the present invention can completely replace the use of cement, reducing CO2 emissions by up to 35 kg / m 3 , and making an excellent contribution to carbon emission reduction.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects: The present invention provides a slope ecological restoration substrate, which combines mechanical stability and ecological compatibility, is suitable for the restoration of high-steep rocky slopes, and significantly reduces the maintenance cost and environmental pollution risk.

[0023] The present invention provides a slope ecological restoration layered spraying method, which has the advantages of being convenient and easy to implement and having a low construction cost.

[0024] The present invention provides a slope ecological restoration structure, which has strong resistance to rainstorm erosion, solves the problem of easy loss of traditional slope substrates, and has the advantages of fast vegetation coverage, strong ecological compatibility, and low cost, and has broad application prospects in the field of slope ecological restoration. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the implementation flowchart of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be further described below by way of examples, but the present invention is not limited to the scope of the described examples. For the experimental methods without specific conditions in the following examples, they are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0027] Example 1 This example provides a slope ecological restoration base material, which is prepared by the following component ratio and method: (a) Preparation of the bottom base material: Calcine basalt volcanic ash (particle size ≤ 0.075 mm) at 750 °C for 2 h. After cooling, mix 30 parts of modified volcanic ash with 5 parts of nano-silica sol (SiO2 content 25 wt.%), 50 parts of crushed stone aggregate (5 - 10 mm grading), and 5 parts of humic acid (degree of humification ≥ 80%), add water to a moisture content of 18% - 20%, and stir for 10 min to form a slurry; (b) Preparation of the middle base material: Mix chitosan (degree of deacetylation ≥ 90%) and humic acid in a ratio of 2:1, and granulate them into chitosan slow-release particles with a diameter of 3 mm; Mix 10 parts of chitosan slow-release particles, 20 parts of coconut coir fiber (length 10 - 20 mm), 25 parts of bentonite (cation exchange capacity ≥ 70 mmol / 100 g), 15 parts of organic fertilizer (N - P - K = 8 - 5 - 6), and 5 parts of water-retaining agent, and divide them into component A (moisture content 25%) and component B (moisture content 40%) by adding water; (c) Preparation of the surface base material: Carbonize corn straw under anoxic conditions at 550 °C for 2 h, crush it, and form it into a honeycomb-shaped carrier (pore diameter 1 mm, wall thickness 0.2 mm) by 3D printing. Immerse 15 parts of the 3D-printed honeycomb biochar carrier in an arbuscular mycorrhizal fungal spore suspension (spore concentration ≥ 50 spores / g) for 24 h, dry it, and then mix it with 3 parts of grass seeds, 2 parts of microbial agent powder, and 10 parts of vermiculite.

[0028] Example 2 This example provides a slope ecological restoration layered spraying method, which uses the slope ecological restoration base material of Example 1 for construction, and includes the following steps: (1) Slope treatment: After cleaning the floating stones, drill holes (diameter 10 mm, depth 50 cm, spacing 1 m × 1 m) on the slope, implant Φ8 mm steel bar anchors and grout them for fixation; Bottom layer spraying: Use a wet spraying machine (working pressure 0.6 MPa) to spray the bottom base material to a thickness of 4 cm, and immediately start an eccentric wheel vibrator (frequency 35 Hz, amplitude 0.8 mm, angle with the slope normal 20°) to vibrate for 10 min to form a bottom base material penetration and solidification layer; (2)Middle layer spraying: First, spray the middle layer component A (water content 25%) to a thickness of 3 cm and let it stand for 4 h; then, spray the component B (water content 40%) for the second time to a total thickness of 7 cm. After spraying, cover it with a moisture-keeping film for 24 h to form a middle layer gradient water-retaining layer; (3)Surface layer construction: Synchronously spray the surface layer base material and the PLA grid (20 cm × 20 cm, with pre-opened planting holes with a diameter of 4 cm at the nodes), and implant Amorpha fruticosa seedlings (seedling height 15 - 20 cm) to form a surface layer biochar-plant symbiotic layer; (4)Cover with a photosensitive degradable non-woven fabric (gram weight 30 g / m 2 ), and complete the construction of the slope ecological restoration structure.

[0029] The construction cost of this process is reduced by 58%. Using modified volcanic ash / straw biochar to replace high-cost materials and combining with the layered vibration spraying process, the rework rate and maintenance frequency are reduced. The comprehensive cost is only 0.5 ten thousand yuan per mu per year (traditional 1.2 ten thousand yuan per mu per year).

[0030] Example 3 This example verifies the application effect of the slope ecological restoration structure prepared according to the slope ecological restoration layered spraying method under extreme conditions. The experimental steps of this example are as follows: 1. Preparation of slope model: Clean the surface of the test tank and spray a waterproof coating to prevent side wall seepage from interfering; Spray the base material according to the process of the present invention (bottom layer → middle layer → surface layer) and cure for 7 d until completely solidified; 2. Initiation of simulated rainfall: Adjust the nozzle pressure to 0.15 MPa and calibrate the rainfall intensity to 55 mm / h (verify the uniformity using a rain gauge for multi-point measurement); Start the runoff collection system (a V-shaped diversion groove and a collecting bucket are set at the bottom of the tank); 3. Monitoring of the scouring process: Record the runoff volume and turbidity every 30 min; Use a laser scanner (accuracy 0.1 mm) to monitor the change in the slope erosion depth; 4. Termination of the experiment and data collection: After the scouring ends, collect all the lost base materials (sediments in the collecting bucket), dry them at 105 °C to a constant weight, weigh them, and calculate the loss amount (kg / m 2 ); Measure the maximum depth (cm) of the erosion ditch and the erosion area ratio (%).

[0031] Under the condition of a high and steep rocky slope (slope of 70°), using the base material and process of the present invention, the vegetation coverage rate reaches 85% after 90 days, the PLA grid is completely degraded, the shrub roots penetrate to the bottom base material, and the anchoring depth is 38 cm. In the rainstorm scouring experiment (60 mm / h), the loss of the base material is 4.1 kg / m 2 , meeting the requirements for first-class slope protection.

[0032] Example 4 To further optimize the mixing ratio parameters and verify the anti-scouring performance and vegetation coverage rate, this example conducted an experiment on optimizing the base material mixing ratio, a simulation experiment on anti-rainstorm scouring, and an experiment on verifying the vegetation coverage rate.

[0033] Experiment 1: Experiment on optimizing the base material mixing ratio The experiment determines the optimal mixing ratios of the bottom, middle, and surface base materials through the orthogonal test method, and focuses on optimizing parameters such as compressive strength, permeability coefficient, and water retention rate.

[0034] The experiment is designed as follows: 1. Variables of the bottom base material (L9(3 4 ) orthogonal table): Factor A: Content of volcanic ash (25%, 30%, 35%); Factor B: Addition amount of nano-silica sol (3%, 5%, 7%); Factor C: Proportion of humic acid (3%, 5%, 7%); Response indicators: Adhesion strength (MPa), pH value, 28-day compressive strength (MPa).

[0035] 2. Variables of the middle base material: Factor D: Proportion of chitosan slow-release particles (8%, 10%, 12%); Factor E: Gradient moisture content design (20 - 30%, 25 - 35%, 30 - 40%); Response indicators: Interlayer shear strength (kPa), nutrient slow-release period (days).

[0036] 3. Variables of the surface base material: Factor F: Porosity of the 3D biochar carrier (65%, 75%, 85%); Factor G: Addition amount of mycorrhizal fungi (1%, 2%, 3%); Response indicators: Seed germination rate (%), mycorrhizal infection rate (%).

[0037] Experiment 2: Simulation experiment on anti-rainstorm scouring The rainfall intensity simulated in the experiment is: 55 mm / h, continuous scouring for 6 h, the slope model is: 1:1.5 slope (about 33.7°), and the thickness of the base material sprayed is 10 cm.

[0038] Experimental group: substrate of the present invention, 20 cm × 20 cm PLA grid; Comparative group: substrate of the present invention, without PLA grid; Control group: traditional cement matrix + ordinary spraying, without PLA grid; the components of traditional cement matrix are as follows: silicate cement (15%-25%), sandy aggregate (50%-70%), crushed stone (5-10 mm) (10%-20%), polypropylene fiber (0.1%-0.5%), cellulose ether (0.2%-0.8%), and organic polymer latex (2%-5%).

[0039] Experiment 3: Vegetation coverage verification experiment The experimental setting is as follows: plant species: tall fescue (Festuca arundinacea) + Amorpha fruticosa (Amorpha fruticosa); observation period: record coverage on the 7th / 30th / 60th / 90th day after spraying; environmental conditions: natural light, daily average temperature 20-25 ℃, simulated drought cycle (no water for 7 days every 15 days) Based on the above experimental verification, the optimized substrate ratio parameters, anti-scouring performance, vegetation coverage rate, and compressive strength and ecological indicators of different substrate ratios are shown in Tables 1-4.

[0040] Table 1: Base material ratio parameters

[0041] Table 2: Anti-scouring performance

[0042] Table 3: Vegetation coverage

[0043] Table 4: Compressive strength and ecological indicators of different base material ratios

[0044] Based on the above test results, it can be seen that the anti-scouring performance of the substrate of the present invention is significantly better than that of traditional materials, and the loss is reduced by 74%. The addition of PLA grid further reduces the scouring amount by 44%. The anti-rainstorm scouring ability is improved by 74%. The multi-stage solidified substrate (modified volcanic ash + nano-silica sol) and the PLA grid anchoring work synergistically. The substrate loss under 55 mm / h rainstorm is only 3.2 kg / m 2 (Traditional technology 12.5 kg / m 2), solving the problem of easy loss of traditional substrates. The 3D biochar carrier significantly improves the early germination rate, and arbuscular mycorrhizal fungi promote root development under drought conditions. The coverage rate only decreases by 7% during the water cut-off period (the traditional substrate decreases by 35%). The vegetation of the present invention has a fast coverage rate and strong ecological compatibility. The 3D biochar carrier + mycorrhizal fungi enables the vegetation coverage rate to reach 93% in 90 days, and the design of zero cement addition and full PLA degradation takes into account rapid greening and zero pollution.

[0045] In summary, the present invention proposes a three-layer collaborative substrate system and a dynamic construction process for the problems of poor adhesion of substrates, weak anti-scouring ability and low vegetation survival rate in the prior art. In the substrate, the bottom layer uses modified volcanic ash and nano-silica sol as gelling materials to enhance the penetration and adhesion of the rock surface; the middle layer adopts chitosan slow-release particles and gradient moisture content design to achieve staged release of nutrients and buffer of interlayer stress; the surface layer combines a 3D honeycomb biochar carrier and a degradable PLA grid to simultaneously load grass seeds and mycorrhizal fungi to form a "physical-biological" composite anchoring structure. The construction method of the present invention includes high-frequency micro-vibration penetration, layered gradient spraying and photosensitive non-woven fabric covering processes to ensure the substrate's resistance to heavy rain scouring and rapid vegetation coverage. The present invention has both mechanical stability and ecological compatibility, is suitable for the repair of high-steep rocky slopes, and significantly reduces the maintenance cost and environmental pollution risk.

[0046] The preferred specific embodiments of the present invention have been described in detail above. It should be understood that those of ordinary skill in the art can make many modifications and variations based on the concept of the present invention without creative labor. Therefore, all technical solutions that can be obtained by those skilled in the art in the technical field of the present invention through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the protection scope determined by the claims.

Claims

1. A slope ecological restoration substrate, characterized in that, It includes a bottom substrate, a middle substrate, and a surface substrate; by weight, each layer of the substrate includes raw materials with the following ratios: (a)The bottom substrate includes 25-35 parts of modified volcanic ash, 3-7 parts of nano-silica sol, 45-55 parts of crushed stone aggregate, 3-7 parts of humic acid, and 0.5-1.5 parts of pH regulator; among them, the modified volcanic ash is basalt volcanic ash treated by calcination. (b)The middle substrate includes 15-25 parts of coconut shell fiber, 8-12 parts of chitosan slow-release granules, 20-30 parts of bentonite, 10-20 parts of organic fertilizer, and 3-7 parts of water-retaining agent. (c)The surface substrate includes the following components by weight: 10-20 parts of 3D printed honeycomb biochar carrier, 2-5 parts of plant seeds, 1-3 parts of arbuscular mycorrhizal fungal powder, and 8-12 parts of vermiculite.

2. The slope ecological restoration base material according to claim 1, characterized in that: In the bottom substrate, the modified volcanic ash is basalt volcanic ash calcined at 600 - 800 °C, with a specific surface area of ≥ 200 m 2 / g; the SiO2 content of the nano-silica sol is 20 wt.% - 30 wt.%, and the particle size is 10 - 50 nm; the pH of the bottom substrate is 6.5 - 7.2, and the porosity is 45% - 50%.

3. The slope ecological restoration base material according to claim 1, characterized in that: In the middle substrate, the chitosan slow-release granules are made by blending and granulating chitosan and humic acid in a weight ratio of 1.5-3:1, the particle size of the granules is 2-5 mm, and the slow-release period is 60-90 days.

4. The slope ecological restoration base material according to claim 1, characterized in that: In the surface substrate, the 3D printed honeycomb biochar carrier is made by carbonizing crop straw under anoxic conditions at 500-600 °C, the pore diameter is 0.5-2 mm, and the porosity is ≥70%.

5. A layered spraying method for slope ecological restoration, characterized in that, Using the slope ecological restoration substrate according to any one of claims 1-4, it includes the following steps: (1)Clean the surface of the slope, spray the bottom substrate to a thickness of 3-5 cm, apply high-frequency micro-vibration to form a bottom substrate penetration and solidification layer. (2)After the bottom substrate starts to set, spray the middle substrate in two times; the gradient moisture content of the middle substrate is designed into a lower water-bearing layer and an upper water-bearing layer. Among them, the moisture content of the lower water-bearing layer is 20%-25%, and the moisture content of the upper water-bearing layer is 35%-40%; spray 50%-60% of the total amount of the middle substrate for the first time to prepare the lower water-bearing layer, let it stand for 3-5 h to form a semi-solidified layer, and then spray the remaining part to a total thickness of 5-8 cm to prepare the upper water-bearing layer, and finally form a middle gradient water-retaining layer. (3)Synchronously spray the surface substrate and the biodegradable polylactic acid fiber grid, and implant deep-rooted shrub seedlings at the grid nodes to form a surface biochar-plant symbiotic layer. (4)Cover with a photosensitive degradation non-woven fabric to complete the construction of the slope ecological restoration structure.

6. The layered spraying method for slope ecological restoration according to claim 5, characterized in that: In the step (1), the high-frequency micro-vibration is realized by an eccentric wheel vibrator attached to the spraying equipment, and the vibration direction forms an angle of 10°-30° with the normal direction of the slope surface; the application frequency of the high-frequency micro-vibration is 20-40 Hz, the amplitude is 0.5-1 mm of high-frequency micro-vibration, and the duration is 5-15 min.

7. The layered spraying method for slope ecological restoration according to claim 5, wherein: In the step (3), the degradation period of the biodegradable polylactic acid fiber grid is 150-200 days, the degradation products are carbon dioxide and water, the grid spacing is 15 cm×15 cm to 25 cm×25 cm, the grid tensile strength is ≥50 MPa, and planting holes with a diameter of 3-5 cm are provided at the nodes. The biodegradable polylactic acid fiber grid and the roots of the deep-rooted shrub seedlings form a spatial staggered anchoring network, and the anchoring depth is ≥30 cm.

8. The slope ecological restoration layered spraying method according to claim 5, characterized in that: In the step (4), the degradation condition of the photosensitive degradable non-woven fabric is that the cumulative ultraviolet irradiation reaches 200-300 MJ / m 2 , and the degradation period is 25-35 days.

9. A slope ecological restoration structure, characterized in that: It is made by using the slope ecological restoration layered spraying method according to any one of claims 5-8.

10. The slope ecological restoration structure according to claim 9, characterized in that: The substrate loss of the slope ecological restoration structure under the scouring of a 50 mm / h rainstorm is ≤ 3.5 kg / m 2 , and the time when the vegetation coverage rate reaches over 80% is 60 - 90 days.

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