A composite improvement material for loess slope erosion resistance and a treatment method thereof

Abstract

The application discloses a kind of composite improvement material for loess side slope erosion resistance and its treatment method.The composite improvement material is composed of mature compost and inorganic modifier;The mature compost is made of engineering waste residue crushed material, forest branch crushed material, straw compost and dewatered sludge by aerobic composting with dry basis mass ratio 3:2:3:2;The inorganic modifier is composed of quicklime, gypsum and polyacrylic acid sodium type water retaining agent with mass ratio 4:3:1;The addition amount of the inorganic modifier is 8% of the mass of the mature compost.The treatment method includes: according to the slope, accurate spraying, ploughing and mixing with 2.0-3.0 kg per square meter, and vegetation restoration.The application significantly improves the shear strength and water retention capacity of loess through organic-inorganic synergistic effect, reduces the soil erodibility factor, realizes the resource utilization of waste and efficient erosion resistance, and is suitable for loess plateau transmission and transformation project tower foundation slope treatment.

Description

Technical Field

[0001] This invention belongs to the field of soil and water conservation and geotechnical engineering technology, specifically relating to a composite improvement material for loess slope erosion resistance and its treatment method. Background Technology

[0002] The Loess Plateau region of my country is one of the areas in the world most severely affected by soil erosion. The loess soil widely distributed in the Loess Plateau of northern Shaanxi has inherent characteristics such as loose structure, extremely low organic matter content (usually below 0.6%), poor water and fertilizer retention capacity, and easy disintegration when exposed to water. Under rainfall conditions, loess slopes are highly susceptible to soil erosion phenomena such as slope erosion, shallow landslides, and gully erosion.

[0003] Power transmission and transformation projects (especially ultra-high voltage projects) are being constructed extensively on the Loess Plateau in northern Shaanxi. Construction activities such as tower foundation excavation and access road construction severely disturb the surface and destroy original vegetation, resulting in numerous exposed loess slopes. These slopes exhibit the following typical characteristics: short and steep slopes, typically between 15° and 35°; the surface loess is Holocene aeolian loess, with a loose structure and low shear strength; the surface soil is further fragmented after construction disturbance, making it highly erodible; and rainfall in northern Shaanxi is concentrated in summer downpours, resulting in surface runoff with extremely strong erosive force on the slopes. This soil erosion not only causes land degradation but, more seriously, can lead to instability of tower foundation slopes and deformation of tower foundations, directly threatening the safe operation of the power grid.

[0004] Existing governance technologies are mainly divided into three categories: The first category is engineering measures, such as constructing intercepting ditches, drainage ridges, and retaining walls, which reduce erosion by altering the surface runoff path. These measures are quick to take effect, but they cannot improve the physical and chemical properties of the loess itself, and facilities such as concrete are prone to aging and damage under freeze-thaw cycles and alternating wet and dry conditions, resulting in high maintenance costs. The second category is vegetation restoration measures, which involve artificially planting herbs or shrubs to utilize plant roots to stabilize the soil and intercept rainfall through the canopy. However, the soil in the Loess Plateau of northern Shaanxi is infertile, with an organic matter content of less than 0.6% and poor water retention capacity. This results in an initial germination rate of less than 40%, a low survival rate, and extremely slow coverage growth, often requiring 2 to 3 years to achieve effective coverage, during which time the slopes remain in a state of severe erosion. The third category is soil improvement measures, including the application of organic fertilizers, water-retaining agents, and soil structure modifiers. Existing technologies have attempted to use organic waste such as urban sludge and straw for soil improvement. For example, uncomposted or simply piled organic materials are directly applied to the soil, which has the following problems: lack of standardized aerobic composting process, low material maturity, secondary fermentation and seedling burn after application, and potential presence of pathogens and weed seeds; lack of scientific ratio for the compounding of organic materials with inorganic amendments (such as cement, lime, and water-retaining agents), resulting in poor synergistic effects; lack of formulation optimization for the specific physicochemical properties of Loess Plateau in northern Shaanxi, limiting the effectiveness of general-purpose amendments on Loess Plateau; and fragmented treatment measures, with drainage, soil improvement, and vegetation restoration implemented separately, without forming an integrated technical system.

[0005] Therefore, developing a systematic treatment solution that can fundamentally improve the structure of loess soil, rapidly enhance its erosion resistance, realize the resource utilization of engineering and agricultural waste, and adapt to different slope gradients is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a composite improvement material for loess slope erosion resistance and a treatment method thereof, so as to overcome the problems of poor treatment effect, low utilization of waste and lack of slope adaptation scheme in the existing technology.

[0007] The core concept of this invention lies in mixing construction waste (earth, rock, and stone debris) and felled tree branches generated during power transmission and transformation projects with crop straw compost and dehydrated urban sludge in a precise dry-basis mass ratio of 3:2:3:2. This mixture is then processed using a standardized aerobic composting process to produce highly decomposed compost with high organic matter content, serving as the organic matrix. Simultaneously, quicklime, gypsum, and sodium polyacrylate water-retaining agent are compounded in a specific mass ratio of 4:3:1 to form an inorganic modifier, which is added at 8% of the compost mass, creating an organic-inorganic composite modifier. The proportions of each component can be adjusted within a certain range; optimal ratios can achieve better synergistic effects.

[0008] The mechanism of action of this material is as follows: The humus, cellulose, and other organic components in well-rotted compost provide long-lasting nutrients, improving soil aggregate structure and increasing soil organic matter content; hydrated quicklime produces calcium hydroxide, which reacts with active silicate minerals in loess to form hydrated calcium silicate and other cementing substances, enhancing soil strength; on the other hand, calcium ions promote clay flocculation, forming stable micro-aggregates; gypsum provides calcium and sulfate ions, further strengthening the aggregate structure and regulating soil pH; the water-retaining agent has a three-dimensional network structure, capable of absorbing more than 300 times its own weight in water, rapidly absorbing and storing water during rainfall and slowly releasing it during drought, regulating soil moisture conditions. These three mechanisms (organic cementation, inorganic cementation, and moisture regulation) work synergistically to systematically improve loess in four dimensions: structure, strength, moisture, and nutrients.

[0009] Based on this, the present invention also provides a precise treatment method adapted to different slopes: Different application rates (2.0, 2.5, and 3.0 kg per square meter) are set according to the slope angle (15°, 25°, and 35°), the composite amendment material is evenly spread, then tilled and mixed to a soil layer of 0 to 30 cm, and finally vegetation restoration is carried out. This treatment method achieves the integration of "source water interception—soil improvement—vegetation soil stabilization".

[0010] This invention provides a composite amendment for loess slope erosion resistance, comprising well-rotted compost and an inorganic amendment. The well-rotted compost is prepared by aerobic composting of crushed engineering waste, crushed tree branches, straw compost, and dewatered sludge in a dry basis mass ratio of (2-4):(1-3):(2-4):(1-3). The inorganic amendment is composed of quicklime, gypsum, and sodium polyacrylate water-retaining agent in a mass ratio of (3-5):(2-4):(0.5-2). The amount of inorganic amendment added is 5%-12% of the mass of the well-rotted compost.

[0011] Preferably, the dry basis mass ratio of the pulverized engineering waste, pulverized timber branches, straw compost, and dehydrated sludge in the mature compost is 3:2:3:2; the mass ratio of quicklime, gypsum, and sodium polyacrylate water-retaining agent in the inorganic modifier is 4:3:1; and the amount of inorganic modifier added is 8% of the mass of the mature compost.

[0012] Preferably, the particle size of the crushed engineering waste is less than or equal to 5 mm, and the particle size of the crushed timber branches is 2 cm to 3 cm.

[0013] Preferably, the effective content of calcium oxide in the quicklime is greater than or equal to 90%, the gypsum is calcium sulfate dihydrate, and the water absorption rate of the sodium polyacrylate water-retaining agent is greater than or equal to 300 times.

[0014] A method for erosion control of loess slopes using the aforementioned composite modified material includes the following steps: uniformly applying the composite modified material to the surface layer of the loess slope according to a predetermined application amount based on the slope gradient; the application amount is determined based on the slope gradient: when the slope gradient is 15° to 35°, the application amount is 2.0 to 3.0 kg per square meter, and the application amount increases with the increase of the slope gradient; for intermediate slopes, the specific application amount is determined using a linear interpolation method.

[0015] Preferably, the method further includes the step of: tilling and mixing the applied composite amendment material with the soil at a depth of 0 to 30 cm on the surface of the slope.

[0016] Preferably, before applying the composite improvement material, a slope pretreatment step is also included: removing loose soil and weeds from the slope surface, and backfilling and compacting gullies with a depth greater than 20 cm using the composite improvement material.

[0017] Preferably, the method also includes a step of vegetation restoration on the slope after spreading and tilling the mixture.

[0018] Preferably, the vegetation restoration includes planting grass and shrub vegetation, watering thoroughly for the first time after planting, and then not applying artificial fertilizer.

[0019] Preferably, the method also includes the step of constructing interception and drainage facilities on the slope.

[0020] Beneficial effects

[0021] Significant synergistic anti-erosion effect: Indoor simulated rainfall tests showed that after using the composite amendment material of this invention, the shear strength of the surface soil of loess slopes increased from 18.6 kPa to 36.8 kPa, an increase of 97.8%; the soil erodibility factor K value decreased from 0.28 to 0.11, a reduction of 60.7%; and under a heavy rainfall intensity of 90 mm / hour, soil erosion decreased from 895.2 g / m² to 158.6 g / m², a reduction of 82.3%. These data are far superior to the effect of applying compost alone, proving that an unexpected synergistic effect occurred between the organic and inorganic components.

[0022] Fundamental improvements in soil physicochemical properties: After application, soil organic matter content increased from 0.62% to 2.78%, an increase of 348.4%; saturated water content increased from 22.5% to 35.8%, an increase of 59.1%; soil bulk density decreased from 1.52 g / cm³ to 1.25 g / cm³, a decrease of 17.8%; and permeability coefficient increased from 0.15 mm / min to 0.42 mm / min, an increase of 180%. These improvements create a favorable soil environment for vegetation growth.

[0023] Waste Resource Utilization and Low Cost: The engineering waste, timber branches, straw compost, and sludge used in this invention are all waste materials from power transmission and transformation project construction sites or surrounding areas, achieving on-site resource utilization. Raw material costs are reduced by more than 60% compared to commercially available soil conditioners. Construction requires no large equipment and is suitable for the field conditions in the hilly and gully areas of northern Shaanxi.

[0024] Precise slope adaptation: The three application rates of 15°, 25° and 35° (2.0, 2.5 and 3.0 kg per square meter) provided by this invention have been verified by experiments to be scientific and effective, avoiding material waste or insufficient application, and have good engineering adaptability.

[0025] Rapid vegetation recovery: Planting native grass-shrub combinations on the improved soil resulted in a vegetation coverage of 78.5% in 60 days and 82.5% in 180 days, significantly higher than the unimproved control area. The vegetation root system enhanced the soil's shear strength and erosion resistance, forming a dual protection of "improved materials + vegetation".

[0026] Green and environmentally friendly: The aerobic composting process kills pathogens and weed seeds, and the heavy metal content meets national standards, with no secondary pollution. Attached Figure Description

[0027] Figure 1 This is a schematic diagram illustrating the basic aerobic composting model and main influencing factors used to prepare the composite modified material of this invention.

[0028] Figure 2 This is a comparison chart of soil organic matter content, saturated water content and bulk density in each experimental group in Example 1 of the present invention.

[0029] Figure 3 This is a comparison chart of soil shear strength and permeability coefficient in each test group in Example 1 of the present invention.

[0030] Figure 4 This is a comparison chart of soil erodibility factors and vegetation germination rate in each experimental group in Example 1 of the present invention.

[0031] Figure 5 This is a roadmap for the vegetation restoration experiment in Embodiment 2 of the present invention. The diagram illustrates the complete technical process from the preparation of composite amendment materials, slope clearing, application of amendment materials, tilling and mixing to vegetation planting. Detailed Implementation

[0032] The present invention will be described in detail below with reference to specific embodiments and accompanying drawings. These embodiments are only for explaining the present invention and do not constitute a limitation on the scope of protection of the present invention. Any equivalent substitutions or modifications made by those skilled in the art without departing from the principles of the present invention shall fall within the scope of protection of the present invention.

[0033] Example 1: Preparation of composite modified materials and verification of their indoor performance

[0034] This embodiment describes in detail the complete preparation process of the composite modified material and verifies its modification effect through indoor simulated rainfall tests.

[0035] 1. Material preparation

[0036] Construction waste material: earth, rock, and soil debris from a tower foundation construction site of the Shaanxi-Yulin-Henan UHVDC project. The waste was crushed using a jaw crusher and then screened using a vibrating screen to collect particles with a diameter of 5 mm or less.

[0037] Timber branch shreds: These are branches of poplar, willow, and other miscellaneous trees felled in the same construction area. The branches are naturally dried until the moisture content is below 15%, then shredded using a wood shredder and sieved to collect coarse powder with a particle size of 2 to 3 centimeters.

[0038] Straw compost: Purchased from an agricultural waste treatment center in northern Shaanxi, this commercial organic fertilizer is made from corn stalks as the main material, with the addition of cow manure, and has been aerobically composted for 90 days. The organic matter content is greater than or equal to 45%.

[0039] Dewatered sludge: Taken from a wastewater treatment plant in Yulin City, with a moisture content of 75%, and naturally air-dried to a moisture content of approximately 60% before use. The heavy metal content meets the limit requirements of "Sludge Quality for Land Improvement in the Disposal of Sludge from Urban Wastewater Treatment Plants" (GB / T 24600-2009).

[0040] 2. Preparation of well-rotted compost

[0041] The following materials are weighed precisely according to a dry basis mass ratio of (2-4):(1-3):(2-4):(1-3), preferably 3:2:3:2: engineering waste slag, timber branch slag, straw compost, and dewatered sludge. For example, to prepare 100 kg of the dry basis mixture: 30 kg of engineering waste slag slag, 20 kg of timber branch slag, 30 kg of straw compost, and 20 kg of dewatered sludge. The four materials are then added to a twin-shaft paddle mixer and mixed for 10 minutes.

[0042] Add 0.5% lignin (i.e., 0.5 kg of lignin per 100 kg dry basis mixture) to the mixture as a compost conditioner.

[0043] The carbon-to-nitrogen mass ratio of the mixture was adjusted to 25:1: the initial carbon-to-nitrogen ratio was approximately 32:1, which was reduced by adding urea, resulting in a measured value of 24.8:1. The moisture content was adjusted to 60% and measured using a portable moisture analyzer, with an error controlled within ±2%.

[0044] A forced-ventilation static composting system was used, with a ventilation rate of 0.2 cubic meters per cubic meter per hour. The mixed materials were piled into long strips, 1.2 meters high and 2.0 meters wide. The surface of the pile was covered with waterproof and breathable non-woven fabric.

[0045] During the composting process, the temperature of the compost pile rose to 55 degrees Celsius on day 5, remained between 58 and 65 degrees Celsius from day 6 to day 20, and gradually decreased to below 45 degrees Celsius from day 21 to day 28. The pile was turned over every 7 days. On day 28, the compost was dark brown, loose, and odorless. Testing showed an organic matter content of 32.5%, total nitrogen of 1.86%, total phosphorus of 0.89%, total potassium of 1.25%, a pH of 7.2, and a seed germination index of 92%, indicating that the compost was fully decomposed.

[0046] 3. Compounding of inorganic modifiers

[0047] Weigh quicklime, gypsum, and sodium polyacrylate water-retaining agent precisely according to a mass ratio of (3-5):(2-4):(0.5-2), preferably 4:3:1. For example, to prepare 10 kg of inorganic modifier: 5 kg quicklime, 3.75 kg gypsum, and 1.25 kg water-retaining agent. Mix the three materials in a V-type mixer for 15 minutes.

[0048] The quicklime contains 92% effective calcium oxide, the gypsum is calcium sulfate dihydrate (purity ≥95%), and the water-retaining agent is sodium polyacrylate with a water absorption rate of 350 times.

[0049] 4. Formulation of composite modified materials

[0050] Using the aforementioned well-rotted compost as the basic organic component, the aforementioned inorganic amendment is added at a ratio of 5%-12% of the mass of the well-rotted compost, preferably 8%. For example, take 100 kg of well-rotted compost and add 8 kg of inorganic amendment. Mix and stir for 15 minutes using a twin-shaft paddle mixer to obtain the composite amendment material of the present invention.

[0051] 5. Indoor simulated rainfall test

[0052] The experiment was conducted in the artificial rainfall simulation hall of the State Key Laboratory of Soil Erosion and Dryland Agriculture in the Loess Plateau, Northwest A&F University. The experimental trough was 5 meters long, 1 meter wide, and 0.8 meters high, with a 10-centimeter-thick layer of graded sand and gravel at the bottom and a slope of 25°. The tested soil was Loess soil from northern Shaanxi, with the following basic physicochemical properties: organic matter 0.62%, natural moisture content 8.3%, bulk density 1.52 g / cm³, erodibility factor K value 0.28, permeability coefficient 0.15 mm / min, and shear strength 18.6 kPa.

[0053] Three treatment groups were set up: CK group (undisturbed soil control, without any amendments); T1 group (only well-rotted compost was applied at a rate of 2.5 kg / m²); and T2 group (the composite amendment of this invention was applied at a rate of 2.5 kg / m², including approximately 2.3 kg / m² of well-rotted compost and approximately 0.2 kg / m² of inorganic amendment). Each group was replicated three times.

[0054] Each treatment group premixed the improved material with the top 0-30 cm layer of yellow cotton soil and then filled the soil trenches in layers of 10 cm each, controlling the compaction at 1.52 grams per cubic centimeter. After filling, a combination of grasses and shrubs (sea buckthorn, alfalfa, and long-grass grass) was sown and allowed to cure for 30 days.

[0055] Artificial rainfall simulations were conducted, with three rainfall intensities set at 25 mm / h, 45 mm / h, and 90 mm / h, lasting 66 minutes. Initial runoff time, runoff volume, and soil erosion were measured. Soil physicochemical properties and vegetation indicators were measured after 60 days of curing.

[0056] The experimental results are shown in Table 1.

[0057] Table 1. Results of indoor test indicators for each treatment group

[0058]

[0059] As shown in Table 1, all indicators of group T2 (the present invention) are significantly better than those of group T1 (single compost). The shear strength of group T2 is 45.5% higher than that of group T1, the erosibility factor K value is 42.1% lower, and the soil loss under a rainfall intensity of 90 mm / hour is only 32.6% of that of group T1. These data demonstrate that adding 8% of a specific ratio of inorganic amendment to the base of well-rotted compost produces an unexpected synergistic effect, resulting in a significant secondary improvement in erosion resistance on the basis of compost.

[0060] Example 2: Field Engineering Application Verification

[0061] This embodiment applies the composite modified material and treatment method prepared in Example 1 to the field treatment of loess slopes in a tower base area of ​​the Shaanxi-Yan'an-Anhui UHV project.

[0062] 1. Project Overview

[0063] The test site was located in Wuqi County, Yan'an City, Shaanxi Province, which is a key national-level soil and water conservation area in Northwest China. The test slope was a loess slope formed by the excavation of the tower foundation, with a length of 12 meters, a height of 8 meters, and a slope of 28°. The soil type was loess, and its basic physical and chemical properties were consistent with those of Example 1. The test period was 180 days.

[0064] 2. Preparation of composite modified materials

[0065] The preparation method is exactly the same as in Example 1. Based on the slope area of ​​96 square meters and the slope angle of 28° (which falls within the range of 15° to 35°), the application rate was calculated using linear interpolation. With 2.5 kg / m² corresponding to 25° and 3.0 kg / m² corresponding to 35° as the benchmark, the application rate for 28° was calculated to be 2.65 kg / m². Taking 2.7 kg / m², the total application rate was approximately 259 kg.

[0066] 3. Construction Steps

[0067] Slope clearing: Remove loose soil, gravel, and weeds from the slope surface. Level any gullies on the slope surface, and for gullies deeper than 20 cm, backfill with composite amendment material and compact.

[0068] Material application: The composite amendment material is manually and evenly applied to the surface of the slope, with the total amount controlled at 2.5 kg per square meter.

[0069] Tillage and mixing: A small rotary tiller is used to till and mix the top 0 to 30 cm layer of soil on the slope, ensuring that the composite amendment material is fully mixed with the loess. After tillage, the slope surface is compacted.

[0070] Planting: Plant sea buckthorn (seedlings 30 to 40 cm tall, transplanting spacing 1 m × 1 m), alfalfa and long-grass grass (seed weight ratio 3:4, sowing rate 20 g per square meter, sowing depth 1 to 2 cm).

[0071] Water catchment control facilities: Construct intercepting ditches at the top of the slope, set up transverse drainage ridges on the slope surface, and construct retaining embankments and sedimentation tanks at the foot of the slope.

[0072] Post-planting care: Water thoroughly after planting, and then water according to natural rainfall. Do not apply fertilizer artificially.

[0073] 4. Monitoring methods and results

[0074] Nine monitoring points were set up, with a blank control area set up simultaneously. After 180 days of maintenance:

[0075] Soil physicochemical properties: The organic matter content of the improved slope soil increased to 2.65% (control 0.58%), the saturated water content was 34.2% (control 21.8%), and the bulk density decreased to 1.28 g / cm³.

[0076] Soil erosion: The cumulative natural rainfall over 180 days was 528 mm, and the cumulative soil erosion on the improved slope was 1.25 kg / m², compared to 9.86 kg / m² in the control area, representing a reduction of 87.3%.

[0077] Vegetation restoration: Sea buckthorn survival rate was 86.7%, grass seed germination rate was 88.2%, and total vegetation coverage was 82.5% (compared to 12.3% in the control group), representing an increase of 570.7%.

[0078] Slope stability: Distributed fiber optic monitoring showed that the maximum micro-displacement of the deep soil in the improved slope was 0.8 mm, while that in the control area was 5.2 mm, indicating that the slope was stable.

[0079] Economic efficiency: Raw material costs are reduced by more than 60% compared to commercial soil conditioners, and no large equipment is required for construction.

[0080] Example 3: Verification of the suitability of application rate under different slope conditions

[0081] This embodiment verifies the adaptability of the method of the present invention for three slope angles: 15°, 25°, and 35°. The test method is the same as in Example 1, only the slope of the soil trench and the application rate are adjusted: 2.0 kg / m² for 15° slope, 2.5 kg / m² for 25° slope, and 3.0 kg / m² for 35° slope.

[0082] Experimental results: Under a rainfall intensity of 45 mm / hour, soil erosion on a 15° slope was reduced by 89.5% compared to the control, with vegetation coverage of 85.3%; on a 25° slope, it was reduced by 83.3%, with coverage of 78.5%; and on a 35° slope, it was reduced by 78.6%, with coverage of 72.3%. This verifies the scientific validity of the correlation between slope and application rate.

[0083] Example 4: Analysis of Microscopic Improvement Mechanism

[0084] Soil samples from groups CK, T1, and T2 in Example 1 were collected after 60 days of curing and subjected to scanning electron microscopy, X-ray diffraction analysis, and mercury intrusion porosimetry analysis.

[0085] Scanning electron microscopy observation: The soil particles in group CK were loose and mainly in point contact; group T1 had organic coating and unstable aggregates; group T2 formed a large number of stable aggregates, with organic-inorganic composite cementing materials connecting the particles.

[0086] X-ray diffraction: Characteristic peaks of hydrated calcium silicate and ettringite were observed in group T2, proving that quicklime reacted with active silica-alumina minerals in loess in a volcanic ash reaction.

[0087] Mercury intrusion porosimetry analysis: Group T2 shows a gradient distribution of "macropores-mesopores-micropores", which is conducive to permeation and water storage.

[0088] Summary of the mechanism of action: The three mechanisms of organic-inorganic composite cementation, mineral gelation, and moisture regulation work synergistically to make the improvement effect far exceed that of a single component.

[0089] The composite modified material and treatment method of this invention have widely available raw materials, mature preparation technology, and simple construction methods, making them particularly suitable for the treatment of loess slopes distributed in a point-to-line pattern, such as the tower foundation area of ​​power transmission and transformation projects. This invention can be widely applied in the treatment of soil and water loss in water conservancy, transportation, oil and gas pipeline projects in the Loess Plateau of northern Shaanxi and even the entire Loess hilly and gully region, with broad market prospects and significant social and ecological benefits.

[0090] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A composite amendment material for erosion resistance of loess slopes, characterized in that, It is composed of well-rotted compost and an inorganic amendment; the well-rotted compost is prepared by aerobic composting of engineering waste slag crushed material, forest branch crushed material, straw compost and dewatered sludge in a dry basis mass ratio of (2-4):(1-3):(2-4):(1-3); the inorganic amendment is composed of quicklime, gypsum and sodium polyacrylate water-retaining agent in a mass ratio of (3-5):(2-4):(0.5-2); the amount of inorganic amendment added is 5%-12% of the mass of the well-rotted compost.

2. The composite modified material according to claim 1, characterized in that, The dry weight ratio of the pulverized engineering waste, pulverized timber branches, straw compost, and dehydrated sludge in the mature compost is preferably 3:2:3:2; the weight ratio of quicklime, gypsum, and sodium polyacrylate water-retaining agent in the inorganic modifier is preferably 4:3:1; and the amount of inorganic modifier added is preferably 8% of the mass of the mature compost.

3. The composite modified material according to claim 1, characterized in that, The particle size of the crushed engineering waste is less than or equal to 5 mm, and the particle size of the crushed timber branches is 2 cm to 3 cm.

4. The composite modified material according to claim 1, characterized in that, The quicklime contains an effective calcium oxide content greater than or equal to 90%, the gypsum is calcium sulfate dihydrate, and the sodium polyacrylate water-retaining agent has a water absorption rate greater than or equal to 300 times.

5. A method for erosion control of loess slopes using the composite modified material according to any one of claims 1 to 4, characterized in that, The process includes the following steps: uniformly spreading the composite improvement material onto the surface of the loess slope according to a predetermined application amount based on the slope gradient; the application amount is determined based on the slope gradient: when the slope gradient is 15° to 35°, the application amount is 2.0 to 3.0 kg per square meter, and the application amount increases with the increase of the slope gradient; for intermediate slopes, the specific application amount is determined by linear interpolation.

6. The method for erosion control of loess slopes according to claim 5, characterized in that, It also includes the step of: tilling and mixing the applied composite amendment material with the top 0 to 30 cm depth of soil on the slope.

7. The method for erosion control of loess slopes according to claim 5, characterized in that, Before applying the composite improvement material, a slope pretreatment step is also included: removing loose soil and weeds from the slope surface, and backfilling and compacting gullies with a depth greater than 20 cm using the composite improvement material.

8. The method for erosion control of loess slopes according to claim 5, characterized in that, It also includes the step of vegetation restoration on the slope after spreading and tilling the mixture.

9. The method for erosion control of loess slopes according to claim 8, characterized in that, The vegetation restoration includes planting grass and shrub vegetation, watering thoroughly for the first time after planting, and then not applying artificial fertilizer.

10. The method for erosion control of loess slopes according to any one of claims 5 to 9, characterized in that, It also includes the step of constructing interception and drainage facilities on the slope.

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