Red soil area expressway slope vegetation synergistic type soil base material improvement method

Abstract

The invention relates to the technical field of red soil area expressway slope vegetation synergistic type soil base material improvement, in particular to a red soil area expressway slope vegetation synergistic type soil base material improvement method which comprises the following steps: S1, base material formula and function collaboration, S2, layered structure design, S3, pre-burying screened and configured plants, and S4, carrying out vegetation synergistic type soil base material improvement. The biochar and the modified ardealite have a synergistic effect, the pH value of the red soil is stably adjusted to 5.8-6.5, the long-term stability problem of traditional base material acidity neutralization and nutrient supply is solved, the alkaline buffer effect of the biochar and the slow calcium release mechanism of the modified ardealite form a long-acting pH adjusting system, the violent fluctuation of the pH value caused by lime adjustment is avoided, and the pH value of the red soil is stably adjusted to 5.8-6.5. The modified ardealite continuously releases sulfur elements in the degradation process, the nitrogen fixation efficiency of leguminous plants is improved by 30%-40%, meanwhile, nutrients are adsorbed and stored through the high specific surface area of the biochar, continuous supply of the nutrients is guaranteed, and rapid recovery of slope vegetation and stability of plant communities are achieved.

Description

Technical Field

[0001] This invention relates to the field of vegetation-soil substrate improvement technology for highway slopes in red soil areas, specifically a method for vegetation-soil substrate improvement for highway slopes in red soil areas. Background Technology

[0002] As is well known, red soil is widely distributed in southern China. Its strong acidity, heavy compaction, and poor water retention make it difficult to restore vegetation on highway slopes.

[0003] In existing technologies, substrate improvement often focuses on a single function, such as water retention or short-term pH adjustment, lacking a dynamic synergistic mechanism. For example, traditional formulations rely on lime to neutralize acidity, but the pH value fluctuates within a range of ±1.0, resulting in poor long-term stability. Water-retaining agents are prone to failure due to compaction in heavy clay soils. After heavy rain, the substrate erosion rate can reach as high as 1.2 kg / m², far exceeding the ecological protection standard. At the same time, the plant growth requirements are disconnected from the substrate nutrient supply. For example, sulfur deficiency in legumes leads to a 30%-40% decrease in nitrogen fixation efficiency. In grass-shrub mixed sowing, the nutrient competition problem has not been optimized through stratified structure, resulting in a vegetation coverage rate of less than 70%.

[0004] The mismatch between existing engineering materials and ecological restoration cycles further exacerbates technical deficiencies. For example, synthetic fiber mesh has an excessively long degradation cycle, hindering the expansion of plant roots and reducing tensile strength by more than 40%. Organic covering materials, such as straw mats, degrade rapidly in the high temperature and humidity environment of red soil, requiring frequent replacement and increasing maintenance costs by 25%-30%. In addition, the layered structure design of the substrate is not suitable for slope scenarios in red soil areas. For example, the "bottom planting soil + surface water-retaining agent" scheme results in a slippage rate of 15%-20% on steep slopes due to weak interlayer bonding. Single thick-layer spraying causes a root rot rate of 35% due to poor air permeability. Summary of the Invention

[0005] Technical problems to be solved

[0006] To overcome the problems of strong soil acidity (pH≤5.5), heavy compaction, poor erosion resistance, and difficulty in vegetation restoration in existing methods for improving highway slopes in red soil areas through vegetation synergy, this invention provides a method for improving highway slopes in red soil areas through vegetation-substrate-structure synergy optimization.

[0007] Technical solution

[0008] To achieve the above objectives, the present invention provides the following technical solution: a method for improving soil substrate through vegetation synergy on highway slopes in red soil areas, comprising the following steps:

[0009] S1: Substrate formulation and functional synergy: Prepare a bottom mixed layer and a surface composite layer. The bottom mixed layer is composed of planting soil, coconut powder and wood powder mixed in a weight ratio of 40:10:8. The surface composite layer is composed of biochar, modified phosphogypsum, humic acid, water-retaining agent and adhesive.

[0010] S2: Layered structure design: The contact surface between the bottom mixed layer and the slope surface is provided with grooves, the surface composite layer is embedded with coconut fiber mesh, and a transition layer is provided between the bottom mixed layer and the surface composite layer.

[0011] S3: Pre-buried vegetation configuration: Sow bermudagrass seeds and plant leguminous seedlings to form a synergistic protection system of herbaceous plants and shrubs.

[0012] Preferably, the planting soil has a clay content of ≤35% and a particle size of ≤5mm, the coconut fiber has a length of 5-10cm, and the wood powder is pine sawdust with a particle size of 2-5mm.

[0013] Furthermore, the biochar has a specific surface area ≥300m² / g and a pH value of 8.0-9.0, and the modified phosphogypsum, after calcination at 600℃, has a CaSO4 content ≥90% and a particle size of 80-100 mesh.

[0014] Furthermore, the thickness of the bottom mixed layer is 15-20cm, the thickness of the surface composite layer is 5cm, and the transition layer is a mixture of the planting soil and the coconut powder in a 3:1 weight ratio, with a thickness of 3-5cm.

[0015] In a further embodiment, the groove depth is 2-3cm and the spacing is 10cm.

[0016] Based on the aforementioned scheme, the tensile strength of the coconut fiber mesh is ≥8kN / m, the pore size is ≤10cm, the degradation period is 2-3 years, the warp and weft intersections of the coconut fiber mesh are fixed by biodegradable fiber lines, and the anti-slip strength of the mesh nodes is ≥5kN / m.

[0017] Furthermore, based on the aforementioned scheme, the sowing density of the bermudagrass seeds is 20g / m², the planting density of the legume seedlings is 5 plants / m², and the legume seedlings are either Leucaena leucocephala or Eriobotrya spp., with a plant height ≥20cm and a root length ≥15cm.

[0018] Furthermore, based on the aforementioned scheme, the components of the surface composite layer, by weight, include: 5 parts biochar, 3 parts modified phosphogypsum, 3 parts humic acid, 1.5 parts polyacrylamide water-retaining agent, and 0.5 parts sodium carboxymethyl cellulose binder.

[0019] Furthermore, based on the aforementioned scheme, the modified phosphogypsum is calcined for 2 hours, crushed, and sieved through an 80-mesh screen, with an effective sulfur release period of 6-12 months.

[0020] Furthermore, based on the aforementioned scheme, the biochar is prepared by pyrolyzing bamboo under anaerobic conditions at 500-600℃, and has a porosity of 70-85%.

[0021] Beneficial effects

[0022] A method for improving soil substrate through vegetation synergy with highway slopes in red soil areas:

[0023] 1. Dynamic pH adjustment: The synergistic effect of biochar and modified phosphogypsum stabilizes the pH of red soil to 5.8-6.5, solving the long-term stability problem of acid neutralization and nutrient supply of traditional substrates. The alkaline buffering effect of biochar and the slow calcium release mechanism of modified phosphogypsum form a long-term pH adjustment system, avoiding the drastic pH fluctuations caused by lime adjustment.

[0024] 2. Synergistic nutrient supply: Modified phosphogypsum continuously releases sulfur during degradation, increasing the nitrogen fixation efficiency of leguminous plants by 30%-40%. At the same time, the high specific surface area of ​​biochar adsorbs and preserves nutrients, achieving a continuous supply of nutrients and promoting vegetation growth.

[0025] 3. Optimized anti-erosion structure: The coconut fiber mesh and the surface composite layer form a "physical + biological" soil stabilization structure, which reduces the slope slip rate to ≤5% and the rain erosion to ≤0.5kg / m². The bottom groove design enhances the bonding force between the substrate and the slope and reduces the risk of interlayer delamination.

[0026] 4. Material and ecological cycle matching: The degradation cycle of coconut fiber mesh matches the root development cycle of vegetation, avoiding the persistent interference of traditional synthetic fiber mesh on the root system. At the same time, it is gradually transformed into organic matter during the degradation process, improving soil structure.

[0027] 5. Improved project economics: The use of coconut flour and wood flour to replace expensive water-retaining agents reduces material costs by 30%, and the maintenance cycle is extended to more than 3 years through long-term structural design, which significantly reduces maintenance costs and improves project economics.

[0028] 6. Vegetation synergy effect: Bermuda grass seeds quickly cover the ground surface, forming short-term protection, while leguminous plants with deep roots stabilize the slope, achieving long-term stability, forming a synergistic protection system of "herbaceous plants + shrubs", increasing the vegetation coverage rate to ≥90%. Attached Figure Description

[0029] Figure 1 This is a side view of the structure of the present invention;

[0030] Figure 2For the present invention Figure 1 A magnified schematic diagram of the local structure at point A;

[0031] Figure 3 This is a schematic diagram of the coconut fiber mesh structure of the present invention;

[0032] Figure 4 For the present invention Figure 3 A magnified view of the structure at point B in the middle;

[0033] Figure 5 This is a comparative data table of side views of leguminous seedlings during planting, as presented in this invention.

[0034] Figure 6 A comparison table of construction time consumption for the improved substrate of this invention;

[0035] Figure 7 This is a comparison table of anti-slip performance test data for the present invention;

[0036] Figure 8 This is a comparison table of pH value dynamic adjustment data for the present invention.

[0037] In the diagram: 1. Bottom layer; 2. Top layer; 3. Coconut fiber mesh; 4. Transition layer; 5. Groove; 6. U-shaped nail. Detailed Implementation

[0038] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0039] See Figures 1-8 A method for improving the soil substrate of highway slopes in red soil areas through vegetation synergy is proposed. Through the integrated design of "functional layered substrate + grass-shrub synergy vegetation", the soil structure improvement and ecological restoration of red soil slopes are synergistically optimized. The core scheme is as follows: a double-layer substrate structure of bottom mixed layer 1 and top composite layer 2 is prepared. The bottom mixed layer 1 improves the clay and compaction characteristics of red soil by mixing planting soil, coconut powder and wood powder. The top composite layer 2 uses biochar, modified phosphogypsum and other materials to adjust the soil pH and provide long-term nutrients. Combined with the interface design of groove 5 and coconut fiber mesh 3, the interlayer bonding force is enhanced. Bermuda grass and leguminous plants are pre-embedded to form a herbaceous-shrub synergistic protection system. This method solves the problems of strong acidity, poor water retention and difficulty in vegetation restoration of red soil, improves the slope erosion resistance by more than 60% and the vegetation coverage rate reaches 90%, and achieves long-term unity of engineering protection and ecological restoration.

[0040] Preparation of the bottom mixed layer 1: Planting soil, coconut powder and wood powder are mixed in a weight ratio of 40:10:8, wherein the planting soil has a clay content of ≤35% and a particle size of ≤5mm, the coconut powder has a fiber length of 5-10cm, and the wood powder is pine sawdust with a particle size of 2-5mm. Sodium carboxymethyl cellulose of 0.5% of the total weight is added during mixing, and the mixture is mechanically stirred for 20 minutes to form a bottom mixed layer 1 with a thickness of 15-20cm. This layer can improve air permeability and water retention.

[0041] The coconut fiber powder is made from coarse coconut shell fibers with a fiber length of 5-10cm. Its porous structure can increase soil porosity by 15%-20% and alleviate red soil compaction. The wood powder is made from pine wood chips with a particle size of 2-5mm. After decomposition, it forms an organic matter network and enhances the soil aggregate structure. After the three are mixed, the thickness of the bottom mixed layer 1 is controlled at 15-20cm. At the contact point with the slope surface, there are grooves 5 with a depth of 2-3cm and a spacing of 10cm. Through mechanical interlocking, the adhesion between the substrate and the slope surface is enhanced, preventing the substrate from slipping under heavy rain. Through physical improvement, the stickiness of the red soil is reduced, providing a loose substrate for plant root growth. At the same time, the slow degradation of coconut fiber powder and wood powder can continuously release organic matter and improve soil fertility.

[0042] Preparation of surface composite layer 2: By weight, take 5 parts of biochar, 3 parts of modified phosphogypsum, 3 parts of humic acid, 1.5 parts of polyacrylamide water-retaining agent, and 0.5 parts of sodium carboxymethyl cellulose binder, mix them evenly to form surface composite layer 2, and cover it on the bottom mixed layer 1 with a thickness of 5cm. The biochar has a specific surface area ≥300m² / g and a pH value of 8.0-9.0. The modified phosphogypsum is calcined at 600℃ for 2 hours, with a CaSO4 content ≥90% and a particle size of 80-100 mesh. After crushing, it is screened through an 80-mesh sieve. The effective release period of sulfur element is 6-12 months.

[0043] The surface composite layer 2 is key to the functional improvement, comprising, by weight, 5 parts biochar, 3 parts modified phosphogypsum, 3 parts humic acid, 1.5 parts polyacrylamide water-retaining agent, and 0.5 parts sodium carboxymethyl cellulose binder. The biochar is prepared from bamboo through anaerobic pyrolysis at 500-600℃, with a specific surface area ≥300m² / g and a pH value of 8.0-9.0. It neutralizes the acidity of red soil through alkaline groups and adsorbs heavy metal ions through its porous structure. The modified phosphogypsum is calcined at 600℃ for 2 hours, with a CaSO₄ content ≥90%. With a particle size of 80-100 mesh, it slowly releases calcium ions and sulfur, which not only improves the soil aggregate structure but also provides sulfur for nitrogen fixation by leguminous plants. Humic acid and water-retaining agent form a network structure, increasing water holding capacity by more than 40%. The adhesive enhances the surface's resistance to erosion. The surface layer is 5cm thick and contains embedded coconut fiber mesh 3 with a tensile strength ≥8kN / m and a pore size ≤10cm. The intersections of the mesh's warp and weft lines are fixed with biodegradable fiber threads. The degradation cycle is 2-3 years. It provides structural support in the early stages, and its natural degradation in the later stages does not affect root expansion.

[0044] Layered structure design

[0045] Subbase treatment: grooves 5 are made at the contact surface between the subbase mixed layer 1 and the slope surface. The grooves are 2-3cm deep and spaced 10cm apart to enhance the anti-slip properties. When laying, the subbase mixed layer 1 is laid in layers with each layer being ≤10cm thick. The layer is compacted to the design thickness using a vibratory roller, and grooves 5 are reserved.

[0046] Mesh Embedding: Coconut fiber mesh 3 is embedded in the surface composite layer 2. The mesh has a tensile strength ≥8kN / m, a pore size ≤10cm, and a degradation period of 2-3 years. The intersections of the warp and weft threads of the coconut fiber mesh 3 are fixed with biodegradable fiber threads, and the anti-slip strength of the mesh nodes is ≥5kN / m. During installation, the coconut fiber mesh 3 is laid flat and fixed with 304 stainless steel U-shaped nails 6. Humic acid mortar is applied to the joints.

[0047] Transition layer 4 is set between the surface composite layer 2 and the bottom mixed layer 1. The transition layer 4 is made of planting soil and coconut powder in a weight ratio of 3:1, with a thickness of 3-5cm. It is embedded in the bottom groove 5 with an embedding depth of ≥2cm. It is compacted twice with a plate rammer (frequency 2800 times / minute) to achieve a density of ≥88%.

[0048] The transition layer 4 is located between the bottom and top layers. It is a 3-5cm thick mixture of planting soil and coconut powder in a 3:1 ratio. The transition layer reduces the interlayer permeability resistance through particle size gradient changes, while buffering the migration of functional materials from the surface composite layer 2 to the bottom mixed layer 1. The vegetation configuration adopts a "herbaceous + shrub" synergistic system: the sowing density of Bermuda grass seeds is 20g / m², and its creeping root system can quickly cover the slope and control soil erosion in the short term. The planting density of leguminous plants (leek or edamame) seedlings is 5 plants / m², with a plant height ≥20cm and a root length ≥15cm. The nitrogen fixation by rhizobia improves soil nitrogen and forms a nutrient complement with Bermuda grass. The deep root system of leguminous plants (main root depth ≥50cm) can penetrate the red soil plow layer and form a three-dimensional protection with the shallow root system of Bermuda grass (fibrous root depth 10-20cm), improving the stability of the slope.

[0049] Pre-buried vegetation configuration

[0050] Seed sowing: Sow the Bermuda grass seeds in layers at a density of 20g / m² between the bottom mixed layer 1 and the top composite layer 2, and cover with 1-2cm of soil.

[0051] Seedling planting: Select Leucaena leucocephala or Edamame as leguminous seedlings with a plant height ≥20cm and root length ≥15cm. Plant at a density of 5 plants / m². When planting, fix the leguminous plant roots through the coconut fiber mesh 3 with polypropylene straps (2cm wide, tensile strength ≥500N). Bury the roots 15-20cm deep.

[0052] Slope pretreatment

[0053] Remove loose soil layers from the slope. When the slope is greater than 1:1.5, excavate a stepped platform with a step width of 30cm and a height difference of 50cm to enhance the bonding force between the substrate and the slope. Preparation of bottom mixed layer 1: Mix planting soil, coconut powder and wood powder in a weight ratio of 40:10:8. The planting soil has a clay content of ≤35% and a particle size of ≤5mm. The coconut powder has a fiber length of 5-10cm. The wood powder is pine sawdust with a particle size of 2-5mm. Add sodium carboxymethyl cellulose at a weight of 0.5% of the total weight during mixing. Mechanically stir for 20 minutes to form a bottom mixed layer 1 with a thickness of 15-20cm. This layer can improve air permeability and water retention.

[0054] first, Figure 1 This is a cross-sectional structural diagram of the present invention, showing the overall layered structure of the improved method. The diagram shows the slope surface, bottom mixed layer 1, transition layer 4, surface composite layer 2, coconut fiber mesh 3, bermudagrass seed layer, and legume seedlings. The bottom mixed layer 1 has grooves 5 at its contact surface with the slope surface, 2-3 cm deep and spaced 10 cm apart. This structure enhances the bonding force between the substrate and the slope through mechanical interlocking. The transition layer 4, 3-5 cm thick, is embedded in the grooves 5 of the bottom mixed layer 1 and is composed of planting soil and coconut powder mixed in a 3:1 weight ratio. Its function is to buffer the migration of functional materials from the surface composite layer 2 to the bottom mixed layer 1 and reduce interlayer seepage. The surface composite layer 2, 5cm thick, covers the transition layer 4. Coconut fiber mesh 3 is embedded within it to form an anti-erosion structure. The coconut fiber mesh 3 has a tensile strength ≥8kN / m, a pore size ≤10cm, and a degradation cycle of 2-3 years. The intersections of the warp and weft lines are fixed by biodegradable fiber threads. Bermuda grass seed layer is sown between the surface composite layer 2 and the transition layer 4 at a sowing density of 20g / m². Leguminous seedlings are planted in the surface composite layer 2 with a plant height ≥20cm and a root length ≥15cm. The roots penetrate the coconut fiber mesh 3 and extend to the bottom mixed layer 1 at a planting density of 5 plants / m². The varieties are Leucaena leucocephala or Eriocaulon buergerianum.

[0055] Then, Figure 2This is an enlarged schematic diagram of the groove 5 at the contact surface between the bottom mixed layer 1 and the slope surface. The bottom surface of the bottom mixed layer 1 has grooves and protrusions, with a groove depth of 2-3 cm and a spacing of 10 cm. This groove 5 structure increases the contact area between the bottom mixed layer 1 and the slope surface by 40%, forming a mechanical interlocking structure. After anti-slip testing, under a rainfall of 120 mm / h for 2 hours, this structure can increase the bonding force between the substrate and the slope surface by 60%, effectively preventing the substrate from sliding along the slope. The bottom mixed layer 1 is composed of planting soil, coconut flour, and wood flour mixed in a weight ratio of 40:10:8. The planting soil is screened to have a clay content of ≤35% and a particle size of ≤5 mm. The coconut flour has a fiber length of 5-10 cm, and the wood flour is pine sawdust with a particle size of 2-5 mm. This mixing ratio can increase the porosity of the bottom layer by 18%, alleviating the heavy and compacted characteristics of red soil. At the same time, after the coconut flour and wood flour decompose, they form an organic matter network, improving the soil aggregate structure by 30%.

[0056] Secondly Figure 3 The diagram shows the structure of the coconut fiber mesh 3. The coconut fiber mesh 3 is woven from warp and weft threads, and the intersections of the warp and weft threads are fixed with biodegradable fiber threads. The mesh is fixed to the surface composite layer 2 with stainless steel U-shaped nails 6. The longitudinal spacing of the U-shaped nails 6 is 50cm and the transverse spacing is 80cm. Humic acid mortar is applied to the joints to enhance the integrity of the mesh. The anti-slip strength of the mesh nodes is ≥5kN / m, and the degradation period is 2-3 years. It can provide structural support in the early stage, and the natural degradation in the later stage does not affect the root expansion. According to the simulated rain erosion test, the erosion resistance of the surface composite layer 2 with this mesh is reduced by 70% compared with the unmesh layer. Under the condition of rainfall of 150mm / h, the loss of the surface composite layer 2 is ≤0.3kg / m², while the loss of the traditional solution is 1.2kg / m².

[0057] again, Figure 4This is a schematic diagram of the connection structure between the surface composite layer 2 and the transition layer 4. The transition layer 4 is made of planting soil and coconut powder mixed in a 3:1 weight ratio, embedded in the groove of the bottom mixed layer 1, with a thickness of 3-5 cm, and tightly bonded to the grooves 5 of the bottom mixed layer 1. The surface composite layer 2 covers the transition layer 4, and the coconut fiber mesh 3 is partially embedded in the surface composite layer 2 and the transition layer 4, forming a multi-layer synergistic anti-erosion structure. The components of the surface composite layer 2, by weight, include: 5 parts biochar, 3 parts modified phosphogypsum, 3 parts humic acid, 1.5 parts polyacrylamide water-retaining agent, and carboxymethyl methacrylate. The binder contains 0.5 parts of sodium cellulose, in which biochar is prepared by pyrolysis of bamboo under anaerobic conditions at 500-600℃, with a specific surface area ≥300m² / g and a pH value of 8.0-9.0. Its alkaline groups can neutralize the acidity of red soil, and its pore structure has an adsorption rate of heavy metal ions ≥85%. After calcination at 600℃ for 2 hours, the modified phosphogypsum has a CaSO4 content ≥90%, a particle size of 80-100 mesh, and an effective sulfur release period of 6-12 months. It can slowly release calcium ions and sulfur, improve soil aggregate structure, and provide sulfur for leguminous plants.

[0058] Figure 5 This diagram illustrates the planting structure of leguminous seedlings. The roots of the leguminous seedlings penetrate the coconut fiber mesh 3 and extend into the bottom mixed layer 1. The roots are fixed to the coconut fiber mesh 3 with polypropylene straps to prevent the seedlings from lodging. The leguminous seedlings are ≥20cm tall and have root lengths ≥15cm to ensure a synergistic slope stabilization effect with the herbaceous plants. The planting density is 5 seedlings / m². The varieties are Leucaena leucocephala or Eriocaulon buergerianum, whose rhizobia nitrogen fixation capacity can reach 180-220kg / hm²·year. The sowing density of Bermuda grass seeds is 20g / m², and its fibrous root depth is 10-20cm. The main root depth of the leguminous plants is ≥50cm. The two form a three-dimensional root system structure, which increases the shear strength of the slope soil by 45% and improves the slope stability by 3 times compared to slopes covered by a single herbaceous vegetation.

[0059] Figure 6 The comparison of construction process time for substrate improvement methods demonstrates the complete construction process from slope pretreatment to vegetation planting. The first step is slope pretreatment, which involves cleaning debris from the slope surface and chiseling grooves 5 at a depth of 2-3cm and a spacing of 10cm to ensure that the surface roughness meets the requirements of mechanical interlocking. This process takes 2 hours per 100㎡, which is 45% more efficient than the traditional hydroseeding process of 4 hours per 100㎡ (manual cleaning + irregular chisel marks). The advantage lies in the fact that mechanized operation reduces labor costs and standardized grooves enhance interface interlocking.

[0060] The second step is to lay the bottom mixed layer 1. The planting soil, coconut powder and wood powder are mixed in a weight ratio of 40:10:8 and then applied using the high-pressure spraying method. The thickness is controlled at 15-20cm. The moisture content of the spraying material needs to be maintained at 25%-30% to ensure adhesion. The time taken is 3h / 100㎡, which is 47% more efficient than the traditional spraying process of 6h / 100㎡ (manually spreading a single planting soil and compacting it in layers). Because high-pressure spraying makes the material mix more evenly, and the groove structure can be formed in one go.

[0061] The third step is to lay the transition layer 4. The planting soil and coconut powder are mixed at a weight ratio of 3:1 and then laid with a thickness of 3-5cm. When laying, it is necessary to ensure that it is tightly filled with the bottom groove 5. The time taken is 1 hour / 100㎡, which is 50% more efficient than the traditional hydroseeding process (no transition layer or simple soil covering, which takes 2 hours / 100㎡). Its gradient structure can reduce the interlayer seepage resistance and improve the overall stability.

[0062] The fourth step is to install the coconut fiber mesh 3. Use stainless steel U-shaped nails 6 to fix it at a spacing of 50cm in the longitudinal direction and 80cm in the transverse direction. Apply ≥2mm thick humic acid mortar to the joints to ensure sealing. The time taken is 1.5h / 100㎡, which is 55% more efficient than the traditional spraying process of 3h / 100㎡ (wire binding of synthetic fiber mesh, no sealing treatment). The biodegradable fixing method reduces later maintenance, and the mortar sealing enhances the overall integrity.

[0063] The fifth step is to lay the surface composite layer 2. Biochar, modified phosphogypsum, humic acid, water-retaining agent and adhesive are mixed in proportion and then laid with a thickness of 5cm. During the laying process, coconut fiber mesh 3 needs to be embedded at the same time. The time taken is 2h / 100㎡, which is 33% more efficient than the traditional hydroseeding process of 3h / 100㎡ (single water-retaining agent surface spraying, uneven thickness). The functional materials work synergistically to achieve pH adjustment and nutrient supply at the same time.

[0064] The sixth step is to sow the Bermuda grass seeds, sowing them in layers at a density of 20g / m². After sowing, cover them with a 0.5cm thick surface composite layer of fine material. This process takes 0.5 hours per 100 square meters, which is 50% more efficient than the traditional hydroseeding process of 1 hour per 100 square meters (which involves broadcasting without covering and resulting in uneven density). Precise sowing combined with covering and protection improves the germination rate and ensures that the nutrients are compatible with the substrate.

[0065] The seventh step is to plant leguminous seedlings at a density of 5 seedlings / m². The roots of the seedlings must be in contact with the bottom mixed layer 1. After planting, the roots are fixed with polypropylene straps. This process takes 1 hour per 100 square meters, which is 67% more efficient than the traditional hydroseeding process of 3 hours per 100 square meters (random planting without fixing measures). Standardized planting ensures that the roots are in contact with the bottom layer, thus improving the survival rate.

[0066] The total construction period for the entire process is 11 hours per 100 square meters, while the traditional hydroseeding process has a total construction period of 22 hours per 100 square meters. The solution of this invention reduces the total time by 50% through the efficient connection of each process, realizes assembly line operation, and completes the configuration of functional materials and vegetation simultaneously, which significantly shortens the construction period.

[0067] Figure 7 To compare the anti-slip performance test data of the substrate under different slopes, the test was conducted by applying simulated rainwater erosion for 2 hours under a rainfall of 120 mm / h. The slip rate of the substrate was tested. The results showed that under steep slope conditions (slope ≥ 45°), the slip rate of the substrate of the present invention was ≤ 5%, while the slip rate of the traditional solution was 15%-20%. The substrate of the present invention did not show obvious interlayer separation after the test. The bottom mixed layer 1 and the groove 5 structure of the slope surface still maintained complete interlocking. Due to the lack of mechanical interlocking structure, the traditional solution is prone to overall slippage of the substrate under steep slope conditions, and the insufficient interlayer bonding force leads to delamination.

[0068] Figure 8 The table presents a comparison of the pH adjustment effects of the substrates. The figures compare the pH change curves of the method of this invention, the traditional lime adjustment method, and untreated red soil. The tests were conducted under the condition that the initial pH of the red soil was 4.5, and continuous monitoring was performed for 12 months. The results show that the method of this invention can stabilize the pH at 5.8-6.5 for more than 12 months. The synergistic effect of biochar and modified phosphogypsum continuously releases alkaline substances and calcium ions, forming a long-term pH adjustment mechanism. In contrast, the traditional lime adjustment method significantly reduced the pH from 6.0 to 5.6 after 3 months. Because lime is highly water-soluble and easily washed away by rainwater, it cannot continuously neutralize acidity. The pH of the untreated red soil remained ≤5.5, and the strongly acidic conditions were unfavorable for plant growth. In the method of this invention, the pH of the biochar was 8.0-9.0, and the alkalinity of the modified phosphogypsum increased after calcination. Both slowly released alkaline substances, making the soil pH adjustment effect more durable and stable.

[0069] Finally, in this example of ecological restoration of the Xuanhui Expressway in Yunnan:

[0070] Improvement of steep red soil slopes (slope ≥ 45°)

[0071] Layered construction:

[0072] After the slope is cleaned, grooves 5 are chiseled to a depth of 2-3cm, with the groove spacing reduced to 8cm to enhance the mechanical interlocking between the bottom layer and the slope.

[0073] The bottom mixed layer 1 is constructed using high-pressure spraying to ensure that the planting soil, coconut powder, and wood powder adhere evenly, with a thickness controlled at 20cm. After the bottom layer has initially set, the transition layer 4 is laid.

[0074] One part of adhesive is added to the surface composite layer 2, and the coconut fiber mesh 3 is densified to a pore size of 8cm. The mesh nodes are fixed by anchor bolts (anti-slip strength ≥5kN / m) to prevent slippage on steep slopes.

[0075] Vegetation optimization: Sow bermudagra seeds mixed with a water-retaining agent, select drought-resistant varieties of leguminous plants (such as edamame), and apply microbial agents to the roots during planting to promote root nodule formation and improve nitrogen fixation efficiency.

[0076] Improvement of acidic red soil (pH≤4.5)

[0077] Material adjustments:

[0078] The amount of biochar used was increased to 7 parts, and high-temperature pyrolysis bamboo charcoal with a pH of 9.0 was selected to neutralize the strong acidity. The calcination temperature of modified phosphogypsum was increased to 650℃, extending the sulfur release cycle to 12 months and continuously improving soil acidity.

[0079] Adding one part of dolomite powder to the surface composite layer 2, in synergy with biochar, increases the content of calcium and magnesium ions and reduces the toxicity of aluminum ions.

[0080] Vegetation management: Spray the surface with a microbial activator 7 days before sowing to promote the release of functional substances from biochar and modified phosphogypsum. After the bermudagrass sprouts, spray with a 0.2% potassium dihydrogen phosphate solution to enhance its acid resistance.

[0081] Biochar alternatives: Rice husk charcoal (specific surface area ≥200m² / g) or walnut shell charcoal can be used, reducing costs by 30% and suitable for low-intensity modification scenarios. Industrial waste activated carbon (such as activated carbon residue from sewage treatment plants) can also be used as an alternative after activation treatment, but the heavy metal content must be controlled to ≤0.1mg / kg.

[0082] Leguminous plant alternatives: In the hot and humid southern regions, it can be replaced by milkvetch, sclerotium brevicornu, etc., which are highly adaptable. In the arid red soil regions, pigeon pea, white-gray soybean, and pig manure bean are selected, as they have deeper root systems and outstanding drought resistance, and their nitrogen fixation capacity can reach 250 kg / hm²·year.

[0083] Multi-layer composite structure: For extremely unstable slopes, a 10cm thick crushed stone buffer layer (particle size 20-40mm) can be added between the bottom layer and the slope surface. The hydrostatic pressure is reduced by drainage through the pores, and together with the bottom groove 5, a double anti-slip structure of "crushed stone-groove" is formed.

[0084] Intelligent monitoring integration: A humidity sensor and a pH sensor are pre-embedded in the surface composite layer 2. Data is transmitted remotely through an NB-IoT module. When the humidity is <15%, the water-retaining agent is automatically released. When the pH is <5.5, an early warning is issued and the biochar slow-release device is remotely controlled to achieve precise improvement.

[0085] Heavy metal pollution remediation: Add 5 parts of modified bentonite to the surface composite layer 2. Its layered structure adsorbs heavy metal ions (Pb²+, Cd²+ removal rate ≥90%), and forms a pollution barrier layer in synergy with biochar. It is suitable for the improvement of red soil slopes around mining areas.

[0086] Landscape and ecological integration: 80% of the seeds of native plants (such as ryegrass, zinnia, tall bulrush, etc.) are mixed into the surface composite layer 2, forming an ecological landscape that blends with the surrounding environment with plants such as bermudagrass, pigweed, and pigeon pea, enhancing the landscape of the highway slope. At the same time, native plants have strong adaptability and their developed root systems can further improve soil structure.

[0087] This method constructs an integrated solution for red soil slope improvement through a three-layer technical logic of "physical structure improvement - chemical function regulation - biological ecological synergy". The material ratio and groove design of the bottom mixed layer 1 fundamentally improve the heavy clay properties of red soil. The functional material system of the surface composite layer 2 achieves synergistic improvement of acidity neutralization, nutrient supply and erosion resistance. The configuration of grass and shrub vegetation forms a long-term protection mechanism through ecological niche complementarity. This method breaks through the limitations of traditional single improvement, enabling the pH value of red soil slopes to increase from 4.5 to 6.0-6.5 within 6 months, the organic matter content to increase by 1.2%, and the erosion resistance to below 0.5 kg / m², which is significantly better than traditional solutions. Its modular design allows for flexible adjustment of materials and structure according to slope gradient, soil acidity and vegetation requirements. It is applicable to different types of highway slopes in the red soil area of ​​southern China and provides a replicable technical paradigm for the green construction of transportation engineering in ecologically fragile areas.

[0088] Working principle:

[0089] This method for improving highway slope vegetation in red soil areas involves, firstly, the preparation of the substrate formulation and its functions in a synergistic manner.

[0090] Preparation of the bottom hybrid layer 1:

[0091] Mix planting soil (clay content ≤35%, particle size ≤5mm), coconut flour (fiber length 5-10cm), and wood flour (pine sawdust, particle size 2-5mm) in a weight ratio of 40:10:8. Add 0.5% sodium carboxymethyl cellulose by weight and mechanically stir for 20 minutes to form a bottom mixed layer 1 with a thickness of 15-20cm. This layer improves the heavy compaction of red soil and enhances air permeability and water retention through the porous structure of coconut flour and wood flour.

[0092] Preparation of surface composite layer 2:

[0093] Weigh out 5 parts by weight of biochar (specific surface area ≥300m² / g, pH 8.0-9.0), 3 parts by weight of modified phosphogypsum (calcined at 600℃ for 2 hours, CaSO4 content ≥90%, 80-100 mesh), 3 parts by weight of humic acid, 1.5 parts by weight of polyacrylamide water-retaining agent, and 0.5 parts by weight of sodium carboxymethyl cellulose binder. Mix them evenly to form a 5cm thick surface composite layer 2. Biochar neutralizes soil acidity, modified phosphogypsum slowly releases sulfur and calcium ions, humic acid and water-retaining agent enhance water retention capacity, and binder enhances erosion resistance.

[0094] Layered structure design and laying

[0095] Substrate and slope interface treatment:

[0096] A groove 5 with a depth of 2-3cm and a spacing of 10cm is opened on the contact surface between the bottom mixed layer 1 and the slope surface. The mechanical interlocking enhances the adhesion between the substrate and the slope surface and prevents the substrate from slipping due to rain erosion.

[0097] Transition layer 4 laying:

[0098] A transition layer 4 (planting soil and coconut powder mixed at a weight ratio of 3:1, with a thickness of 3-5cm) is laid above the bottom mixed layer 1 and embedded in the bottom groove 5. It is then compacted to a density of ≥88% using a plate rammer to reduce interlayer permeability resistance and buffer the migration of surface functional materials to the bottom layer.

[0099] Coconut fiber mesh 3 embedding:

[0100] A coconut fiber mesh 3 with a tensile strength ≥8kN / m and a pore size ≤10cm is embedded in the surface composite layer 2. The intersections of the mesh warp and weft lines are fixed with biodegradable fiber threads (node ​​anti-slip strength ≥5kN / m) and fixed with stainless steel U-shaped nails 6 (longitudinal spacing 50cm, transverse spacing 80cm). Humic acid mortar is applied to the joints to form a "physical + biological" soil stabilization structure, which initially provides erosion resistance and degrades into organic matter in the later stage.

[0101] Pre-buried vegetation configuration and synergistic protection

[0102] Bermuda grass seed sowing:

[0103] Bermuda grass seeds were sown in layers at a density of 20g / m² between the transition layer 4 and the surface composite layer 2, and covered with 1-2cm of soil. The creeping roots of Bermuda grass quickly covered the ground surface, controlling soil erosion in a short period of time and forming a short-term protective layer.

[0104] Planting of legume seedlings:

[0105] Select seedlings of Leucaena leucocephala or Eriobotrya javanica (plant height ≥ 20cm, root length ≥ 15cm) and plant them at a density of 5 plants / m². After the roots penetrate the coconut fiber mesh 3, fix them with polypropylene straps and bury them at a depth of 15-20cm. Leguminous plants improve soil nitrogen through nitrogen fixation by rhizobia. The deep root system (main root depth ≥ 50cm) and the shallow root system of Bermuda grass (10-20cm) form a three-dimensional protection, which improves slope stability. At the same time, the supply of sulfur increases nitrogen fixation efficiency by 30%-40%.

[0106] Dynamic functional collaboration and long-term maintenance

[0107] pH value and nutrients are regulated in synergy:

[0108] Biochar and modified phosphogypsum work synergistically to stabilize the pH value of red soil at 5.8-6.5. Modified phosphogypsum continuously releases sulfur over 6-12 months, while biochar adsorbs and preserves nutrients, achieving a long-term supply.

[0109] Maintaining erosion resistance:

[0110] The coconut fiber mesh 3 is combined with the surface composite layer 2 to control the amount of rainwater runoff to ≤0.5kg / m². The bottom groove 5 and the transition layer 4 ensure the interlayer bonding force and the slope slip rate to ≤5%.

[0111] Vegetation ecological synergy:

[0112] The rapid coverage of bermudagrass and the deep root stabilization of leguminous plants form a "herbaceous + shrub" system, increasing the vegetation coverage to ≥90%. The degradation cycle of coconut fiber mesh (2-3 years) matches the root development cycle of vegetation, and it is later converted into organic matter, continuously improving the soil structure.

[0113] Special scenario adaptation (optional operation)

[0114] Steep slope improvement (slope ≥ 45°):

[0115] The spacing of the grooves 5 is reduced to 8cm, the surface composite layer 2 is increased by 1 part of adhesive, the pore size of the coconut fiber mesh 3 is increased to 8cm, drought-resistant varieties (such as edamame) are selected for legumes, and microbial agents are applied to the roots to promote root nodule formation.

[0116] Strongly acidic red soil (pH ≤ 4.5):

[0117] The amount of biochar was increased to 7 parts (pH 9.0), the calcination temperature of modified phosphogypsum was increased to 650℃, 1 part of dolomite powder was added to the surface, and a microbial activator was sprayed before sowing to promote the release of functional substances.

[0118] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for improving soil base material of a highway side slope in a red soil region in a vegetation coordination type, characterized by, The method comprises the following steps: S1: substrate formula and function synergy: preparing a bottom mixed layer (1) and a surface composite layer (2), the bottom mixed layer (1) is prepared by mixing planting soil, coconut powder and wood powder at a weight ratio of 40:10:8, the surface composite layer (2) is composed of biochar, modified phosphogypsum, humic acid, water retaining agent and adhesive; S2: layered structure design: the bottom mixed layer (1) is provided with concave-convex grooves (5) on the contact surface with the slope surface, the surface composite layer (2) is embedded with coconut fiber grid (3), and a transition layer (4) is arranged between the bottom mixed layer (1) and the surface composite layer (2); S3: pre-embedded plant configuration: according to the inverse relationship between grass seed density and shrub seed germination, shrub seeds are sown first in the slope under different climate conditions, and then grass seeds are sown after the shrubs grow for a period of time, forming a grass and shrub cooperative protection system.

2. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 1, characterized in that, The planting soil has a clay content of ≤35% and a particle size of ≤5 mm, the coconut powder has a fiber length of 5-10 cm, and the wood powder is pine sawdust with a particle size of 2-5 mm.

3. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 2, characterized in that, The biochar has a specific surface area of ≥300 m² / g and a pH value of 8.0-9.0, and the modified phosphogypsum has a CaSO4 content of ≥90% and a particle size of 80-100 mesh after calcination at 600°C.

4. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 3, characterized in that, The thickness of the bottom mixed layer (1) is 15-20 cm, the thickness of the surface composite layer (2) is 5 cm, and the transition layer (4) is prepared by mixing the planting soil and the coconut powder at a weight ratio of 3:1, with a thickness of 3-5 cm.

5. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 4, characterized in that, The concave-convex grooves (5) have a groove depth of 2-3 cm and a pitch of 10 cm.

6. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 5, characterized in that, The coconut fiber grid (3) has a tensile strength of ≥8 kN / m and a pore size of ≤10 cm, a degradation period of 2-3 years, and the warp and weft cross points are fixed by degradable fiber lines, with a grid node anti-sliding strength of ≥5 kN / m.

7. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 6, characterized in that, The sowing density of the dog tooth grass seeds is 20 g / m², the planting density of the legume seedlings is 49 plants / m², the legume seedlings are Albizia lebbeck or Millettia pinnata, with a plant height of ≥20 cm and a root length of ≥15 cm.

8. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 7, characterized in that, The components of the surface composite layer (2) include biochar 5 parts, modified phosphogypsum 3 parts, humic acid 3 parts, polyacrylamide water retaining agent 1.5 parts, and carboxymethyl cellulose sodium adhesive 0.5 parts by weight.

9. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 8, characterized in that, The calcination time of the modified phosphogypsum is 2 hours, and after crushing and sieving through an 80 mesh sieve, the effective release period of sulfur element is 6-12 months.

10. The method for improving soil base material of expressway slope vegetation in red soil region according to claim 9, characterized in that, The biochar is prepared by pyrolysis of bamboo under anaerobic conditions at 500-600°C, with a porosity of 70-85%.

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