Power transmission and transformation project surface soil improvement and ecological restoration method based on alkali modified fly ash and composite modifier

Abstract

The invention belongs to the technical field of environmental protection and ecological restoration, and particularly relates to a power transmission and transformation project surface soil improvement and ecological restoration method based on alkali-modified fly ash, which comprises the following steps: stripping surface soil in a layered manner, preparing a composite modifier from alkali-modified fly ash, covering the surface soil in a layered manner, and supplementing with a water-retaining agent and vegetation restoration. And a soil structure with fertile top, stable bottom, water retention and air permeability is constructed. The alkali-modified fly ash has high specific surface area (greater than or equal to 25 m / g) and pore volume (greater than or equal to 0.09 cm / g), and the agglomeration, erosion resistance and water retention capacity of soil are remarkably improved. According to the method, the synergistic interaction of coal ash resource utilization and surface soil ecological restoration is achieved, and the method is suitable for rapid ecological restoration of the high abrupt slope and has remarkable environmental protection and economic value.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of environmental protection and ecological restoration, and particularly relates to a method for topsoil improvement and ecological restoration of power transmission and transformation projects based on alkali-modified fly ash and a composite improver. BACKGROUND

[0002] As a linear project, power transmission and transformation projects span a wide range of regions, and in the construction process, a large amount of topsoil will inevitably be disturbed and stripped, leading to vegetation damage and soil erosion. Topsoil is a valuable natural resource, rich in nutrients and seed banks. At present, there are the following outstanding problems in the protection and ecological restoration of topsoil in power transmission and transformation projects: Extensive utilization of topsoil resources: The conventional approach is to mix and strip, which destroys the soil structure and vertical distribution of the seed bank, resulting in a decrease in soil fertility after re-covering and weak natural recovery ability of vegetation.

[0003] Difficult to repair high and steep slopes: Tower foundations are often located in hilly and mountainous areas, forming high and steep slopes of 45°-75°. In such areas, water evaporates quickly and nutrients are easily lost, resulting in poor vegetation restoration.

[0004] High pressure on industrial solid waste disposal: Power plant fly ash occupies a large amount of land and poses an environmental risk. Although there have been studies on the use of fly ash in agriculture, direct application is common, which is limited by its alkalinity, low adhesion, and potential heavy metal risks, among other issues.

[0005] Lack of systematic technology: Existing topsoil stripping and re-covering technologies fail to combine graded utilization of topsoil resources, solid waste resource utilization, and ecological restoration of difficult site conditions.

[0006] For example, existing technologies disclose that alkali modification can improve the specific surface area and adsorption performance of fly ash and use it for sandy soil improvement. However, there is currently no technology or method that integrates alkali-modified fly ash as a multifunctional improver with the unique topsoil layering, stripping, and re-covering technology of power transmission and transformation projects, as well as the high and steep slope water retention technology, to solve the ecological restoration problems in specific site conditions of power transmission and transformation projects. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application aims to provide a method for topsoil improvement and ecological restoration of power transmission and transformation projects based on alkali-modified fly ash. This method can realize the resource utilization of fly ash, and through systematic technology coupling, significantly improve the physicochemical properties of re-covered topsoil, especially the water and fertilizer retention capacity, erosion resistance, and the ability to promote rapid vegetation recovery of high and steep slope topsoil, forming an ecological restoration mode of "waste treatment with waste, synergistic effect". To achieve the above-mentioned purpose, the present application adopts the following technical solutions: Specifically, a method for topsoil improvement and ecological restoration of power transmission and transformation projects based on alkali-modified fly ash is provided, comprising the following steps: S1. Topsoil stripping and grading: Before the construction of the tower foundation of the power transmission and transformation project, the original topsoil of the construction area is stripped in layers. The top 0-10cm layer of topsoil, which is rich in seed bank and organic matter, is stripped off separately and stored. S2. Alkali modification treatment of fly ash: Power plant fly ash and sodium carbonate (Na2CO3) are mixed evenly at a mass ratio of 1:(0.5-1) and calcined at 800±50℃ for 2±0.5 hours to obtain alkali modified fly ash; S3. Preparation of topsoil-fly ash composite modifier: The alkali-modified fly ash obtained in step S2 is mixed with the topsoil (not the uppermost layer) stripped in step S1 at a mass ratio of 1:(9-19) to obtain the topsoil-fly ash composite modifier. S4. Topsoil backfilling and improvement on steep slopes: On the slopes or disturbed areas formed by the tower foundations of power transmission and transformation projects, the bottom topsoil is backfilled first, and then the topsoil-fly ash composite improver prepared in step S3 is used as the improvement layer for backfilling. S5. Eutrophic topsoil layer backfilling and water retention treatment: On top of the improved layer in step S4, backfill the 0-10cm topsoil rich in seed bank that was separately stripped and stored in step S1; during or after backfilling, apply a high-molecular water-retaining agent accounting for 0.5‰-1.5‰ of the dry weight of the topsoil to the soil. S6. Vegetation restoration: Based on local climate and soil conditions, select suitable plant species for sowing or planting to promote the rapid restoration of vegetation communities.

[0008] Preferably, in step S1, the total thickness of the layered stripping is determined according to the national topsoil stripping grading map: for the Class 1 stripping area with soil organic matter content greater than 10g / kg, the stripping thickness is 30-50cm; for the Class 2 stripping area with soil organic matter content less than 10g / kg, the stripping thickness is 20-30cm.

[0009] Preferably, in step S2, the fly ash is fly ash produced by a coal-fired power plant, and its Fe2O3 content is not less than 15%. A high Fe2O3 content helps to enhance the stability of soil aggregates through the cementing effect of iron oxides after modification.

[0010] Preferably, in step S3, the preferred mixing mass ratio of the alkali-modified fly ash to the topsoil (not the uppermost layer) is 1:9.

[0011] Preferably, in step S5, the polymeric water-retaining agent is a potassium polyacrylate type water-retaining agent, and its optimal addition amount is 1.0‰ of the dry weight of the topsoil.

[0012] Preferably, in step S4, the slope of the slope is between 45° and 75°. The method of this invention is particularly suitable for the stabilization and ecological restoration of such steep slopes.

[0013] Preferably, the topsoil stripped in step S1 shall be stored and protected for no more than 3 months, and the restoration and vegetation restoration work in steps S4 to S6 shall be completed before the arrival of the main rainy season in the region, so as to maximize the preservation of soil activity and the utilization of natural precipitation.

[0014] This invention also provides a topsoil-fly ash composite amendment for ecological restoration of power transmission and transformation projects. The amendment is composed of alkali-modified fly ash and non-topsoil mixed at a mass ratio of 1:(9-19), wherein the alkali-modified fly ash has a specific surface area ≥25 m² / g and a total pore volume ≥0.09 cm³ / g. This microstructural characteristic is imparted through a specific "sodium carbonate medium-temperature calcination" process, which not only gives the amendment a strong ability to adsorb and retain moisture and nutrients, but more importantly, its well-developed porous surface and stable weak alkalinity allow it to form an extremely stable "aggregate-pore" composite structure with soil particles through hydrogen bonding and cementation. This structure exhibits excellent erosion resistance and stability on steep slopes (soil cohesion can be increased by nearly 8 times), while creating an ideal "water-retaining, aerated, and temperature-stable" microenvironment for plant roots and soil microorganisms. This achieves a functional upgrade from simple physical filling to actively constructing and maintaining a healthy soil ecosystem, which is unparalleled by conventional soil amendment materials.

[0015] Preferably, the alkali-modified fly ash is obtained by calcining a mixture of fly ash and sodium carbonate at a mass ratio of 1:(0.5-1) at a temperature of 800±50℃ for 2±0.5 hours. This specific parameter combination constitutes a precise "thermal-alkali synergistic activation" window: within this window, sodium carbonate is sufficient to effectively disrupt the glassy silica-alumina network of the fly ash, exposing a large number of internal pores, thereby achieving a leap in specific surface area and pore volume; at the same time, the temperature of around 800℃ avoids excessive volatilization or sintering of sodium salts, ensuring the stable formation of the amorphous silica-alumina gel skeleton and fixing alkali metal ions in a slow-release form. This endows the fly ash with extremely high surface activity and adsorption sites, and fundamentally avoids the risk of soil salinization caused by conventional strong alkali modification, achieving a unity of "highly efficient activation" and "environmentally friendly"—a synergistic effect that is difficult to achieve by directly using raw fly ash or other alkali modification methods.

[0016] This invention further claims protection for the application of the above-mentioned topsoil-fly ash composite modifier in the ecological restoration of slopes in power transmission and transformation projects.

[0017] Beneficial effects 1) Outstanding Creativity: This invention is the first to systematically integrate and innovate a cross-domain, multi-technology approach by combining a specific alkali modification process for fly ash (Na2CO3 calcination method) with topsoil layering and backfilling technology and water retention technology for steep slopes, which are unique to power transmission and transformation engineering. It does not simply use fly ash as a soil filler, but rather modifies it to create a novel composite amendment for constructing a soil intermediate layer (amended layer) with excellent physical and chemical properties. This represents a completely new application scenario and technological concept.

[0018] 2) Significant synergistic effects: Synergistic effects of waste resource utilization and soil improvement: A specific alkali modification process not only stabilizes some heavy metals in fly ash but also activates nutrients such as silicon, calcium, and iron. The modified fly ash has a high specific surface area (up to 25.75 m² / g or more) and a porous structure, significantly enhancing the soil's adsorption capacity and water retention capacity.

[0019] Synergistic use of topsoil grading and ecological restoration: Through layered stripping and layered backfilling, the seed bank and fertility of the topsoil are preserved to the maximum extent, laying the foundation for natural vegetation restoration. Placing the soil conditioner below the nutrient-rich topsoil layer avoids the risk of direct contact between fly ash and plant roots in the early stages of modification, while providing a stable water and fertilizer support layer for the growth of upper plants.

[0020] Synergistic improvement of physical structure and chemical properties: The addition of fly ash improves the pore structure and permeability of the soil; the cementing effect of Fe2O3 and the hydroxyl groups on the surface of modified fly ash significantly enhance the stability of soil aggregates and shear strength (cohesion can be increased by nearly 8 times) through hydrogen bonding; the addition of water-retaining agent further strengthens the drought resistance of topsoil on steep slopes.

[0021] 3) Quantifiable technical effects and strong practicality: This method makes full use of the topsoil generated by the project itself and the solid waste (fly ash) of the power industry, resulting in low cost and strong operability. The proposed basis for topsoil stripping thickness, fly ash modification parameters, and water-retaining agent addition are all supported by clear experimental data (such as specific surface area, cohesion, and germination rate improvement), making it easy to promote and apply in power transmission and transformation engineering construction and meeting the requirements of green power grid construction. Attached Figure Description

[0022] Figure 1 This is a flowchart of the overall process of the method of the present invention.

[0023] Figure 2 This is a schematic diagram of the topsoil backfilling structure in the tower foundation area of ​​a power transmission and transformation project. Detailed Implementation

[0024] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments.

[0025] Example 1: Ecological Restoration of Tower Foundations for an Ultra-High Voltage Transmission Project in the Loess Plateau Region Project Overview: This project takes the construction of tower foundations for an ±800kV ultra-high voltage direct current transmission project in a Loess Plateau region as an example. This area belongs to Level 2 in the national topsoil stripping classification, and the soil organic matter content is low.

[0026] S1. Topsoil stripping and grading: Before construction, the tower base area was surveyed, and the total topsoil removal thickness was determined to be 30cm. A combination of mechanical and manual methods was used: first, the 0-10cm topsoil layer was removed separately, transported to a designated area, and covered with fine-mesh netting for curing. Then, the 10-30cm bottom layer of topsoil was mixed and removed, and piled separately. All removed topsoil was reused within two months.

[0027] S2. Alkali modification treatment of fly ash: Fly ash (Fe2O3 content approximately 21%) taken from a nearby power plant was mixed with anhydrous Na2CO3 at a mass ratio of 1:1, placed in a muffle furnace, heated to 800℃ at a rate of 5℃ / min, and calcined at this temperature for 2 hours. After natural cooling, the mixture was removed to obtain alkali-modified fly ash. Testing showed that the alkali-modified fly ash had a specific surface area of ​​25.75 m² / g and a total pore volume of 0.0968 cm³ / g. These precise process parameters constitute a synergistically optimized "thermal-alkali activation" system: a precise 1:1 ratio creates the optimal solid-liquid reaction interface at 800℃, ensuring effective destruction of the fly ash vitreous structure while avoiding harmful alkali metal residues; a slow, programmed heating of 5℃ / min acts like a gentle simmer, orderly draining bound water and oxidizing residual carbon, providing kinetic support for building a well-developed and stable microporous-mesoporous structure (specific surface area of ​​25.75 m² / g, total pore volume of 0.0968 cm³ / g); and 2 hours of isothermal calcination provides ample window for the activation of Fe₂O₃ (content 21%), transforming it into a natural "iron-based cementing agent" that enhances soil cohesion. Finally, natural cooling stabilizes the highly active amorphous gel network, collectively endowing the amendment with excellent water retention, permeability enhancement, and mechanical strengthening functions.

[0028] S3. Preparation of topsoil-fly ash composite amendment: The alkali-modified fly ash obtained in step S2 is mixed evenly with the 10-30cm bottom topsoil stripped in step S1 in a mixer at a mass ratio of 1:9.

[0029] S4. Topsoil backfilling and improvement on steep slopes: After the tower foundation construction is completed, the resulting 45°-60° slopes are leveled. First, a layer of approximately 10-15cm of topsoil (not the uppermost layer) is backfilled onto the slope as a base course (corresponding to...). Figure 2Middle layer 2). Then, a topsoil-fly ash composite amendment of about 10-15cm thickness is applied as the amendment layer (corresponding to...). Figure 2 Intermediate level 3).

[0030] S5. Eutrophic topsoil layer backfilling and water retention treatment: Above the improved layer, a 10cm thick layer of nutrient-rich topsoil (0-10cm) that was separately stripped and stored in step S1 is backfilled (corresponding to...). Figure 2 Middle layer 4). When backfilling this layer, mix the potassium polyacrylate water-retaining agent with the topsoil at a ratio of 1.0‰ (based on the dry weight of the backfilled soil). Figure 2 Component 5).

[0031] S6. Vegetation Restoration: After the response is completed, select suitable native grass species (such as liriope, crested wheatgrass, etc.) for hydroseeding or planting (corresponding to...). Figure 2 Intermediate level 6). Figure 2 In this invention, 1-Original Foundation / Engineering Foundation: The original slope or foundation after the tower foundation construction is completed; 2-Non-Uppermost Backfill Topsoil / Subsoil: The backfilled bottom soil, mainly serving a leveling and transitional function; 3-Topsoil-Fly Ash Composite Improvement Layer: The core layer of this invention. It is composed of alkali-modified fly ash mixed with the bottom topsoil, playing a key role in enhancing erosion resistance, water and fertilizer retention, and stabilizing the structure; 4-Nutrient-Rich Topsoil Layer with Seed Bank: The most fertile topsoil that has been separated and stored separately, rich in seeds and organic matter, forming the basis for natural vegetation restoration; 5-High Molecular Water-Retaining Agent: Mixed with this nutrient-rich topsoil layer, further improving the drought resistance of the topsoil; 6-Vegetation: The restored vegetation community.

[0032] Proper watering and maintenance are necessary.

[0033] Effect verification: The slope at the base of the tower, repaired using this method, achieved a vegetation coverage of over 85% after three months, significantly higher than the traditional mixed backfill method (approximately 50%). Soil moisture content increased by about 15%-20%, and soil cohesion increased to 3.1948 kPa, nearly eight times higher than the original soil, demonstrating significant soil and water conservation effects. Simultaneously, it consumed fly ash from the power plant, achieving a win-win situation for both environmental and economic benefits.

[0034] Example 2: Comparative application of different alkali-modified fly ash composite amendments This embodiment illustrates the differences in ecological restoration effects of composite modifiers prepared from fly ash using different modification methods.

[0035] Following the steps in Example 1, steps S3 to S6 were performed using the following three modifiers respectively: Control group A: Unmodified raw fly ash (FA, specific surface area 1.50 m² / g) was mixed with the bottom topsoil at a ratio of 1:9.

[0036] Control group B: Fly ash-based material (JFA1, specific surface area 7.28 m² / g) prepared by room temperature modification with Na2CO3 solution was mixed with the bottom topsoil at a ratio of 1:9.

[0037] Experimental Group C (Invention): The fly ash modified by Na2CO3 calcination in Example 1 (specific surface area 25.75 m² / g) was mixed with the bottom topsoil at a ratio of 1:9.

[0038] All groups were implemented in adjacent areas on the same slope, with the same water-retaining agent dosage of 1.0‰ and the same vegetation restoration measures.

[0039] Result comparison: Soil physicochemical properties: Experimental group C had the lowest soil bulk density (1.3953 g / cm³), the highest total porosity (53.32%), and the greatest cohesion (3.1948 kPa), which were significantly better than control groups A and B.

[0040] Vegetation restoration effect: 28 days after sowing, the germination rate of seeds in experimental group C reached 94%, with the tallest plant height and vigorous growth. The germination rate of control group A (original fly ash) was only 24%, and seedling death occurred. The effect of control group B was between the two.

[0041] This result demonstrates that the composite conditioner prepared by the specific alkali modification process (calcination method) used in this invention has unexpected advantages in improving soil structure and promoting plant growth.

[0042] Comparative Example: Traditional Hybrid Response Method In the same project area, a portion of the slope was selected and the traditional method was used: all the stripped topsoil (0-30cm) was mixed and then backed onto the slope in one go without adding any amendments or water-retaining agents, and then vegetation restoration was carried out in the same manner.

[0043] Results: Three months later, the vegetation cover in the area was only about 50%, the soil was significantly compacted, and fine gully erosion was visible on the slopes, with low soil moisture content. This highlights the significant advancement of the method of this invention in rapid ecological restoration and soil and water conservation.

[0044] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for topsoil improvement and ecological restoration in power transmission and transformation projects based on alkali-modified fly ash, characterized in that, Includes the following steps: S1. Topsoil stripping and grading: The original topsoil in the construction area is stripped in layers, and the top 0-10cm layer of topsoil, which is rich in seed bank and organic matter, is stripped off and stored separately. S2. Alkali modification treatment of fly ash: fly ash and sodium carbonate are mixed at a mass ratio of 1:(0.5-1) and calcined at 800±50℃ for 2±0.5 hours to obtain alkali modified fly ash; S3. Preparation of composite amendment: Alkali-modified fly ash and bottom topsoil are mixed at a mass ratio of 1:(9-19) to obtain topsoil-fly ash composite amendment; S4. Topsoil backfilling and improvement: Backfill the bottom topsoil and topsoil-fly ash composite amendment sequentially on the slope or disturbed area. S5. Eutrophic topsoil layer backfilling and water retention treatment: Backfill the topsoil layer that was stripped separately in step S1 on top of the topsoil-fly ash composite amendment, and apply a high-molecular water-retaining agent accounting for 0.5‰-1.5‰ of the dry weight of the topsoil; select plants for sowing or planting.

2. The method according to claim 1, characterized in that, In step S1, the total thickness of topsoil stripping is determined according to the national topsoil stripping grading map: 30-50cm for Grade 1 areas with organic matter content >10g / kg; 20-30cm for Grade 2 areas with organic matter content <10g / kg.

3. The method according to claim 1, characterized in that, In step S2, the fly ash is fly ash from a coal-fired power plant, and its Fe2O3 content is not less than 15%.

4. The method according to claim 1, characterized in that, In step S3, the mixing mass ratio of the alkali-modified fly ash to the topsoil (excluding the uppermost layer) is 1:

9.

5. The method according to claim 1, characterized in that, In step S5, the polymeric water-retaining agent is a potassium polyacrylate type water-retaining agent, and the addition amount is 1.0‰ of the dry weight of the topsoil.

6. The method according to claim 1, characterized in that, In step S4, the slope of the slope is 45° to 75°.

7. The method according to claim 1, characterized in that, The topsoil stripped in step S1 shall be stored for no more than 3 months and the backfilling and vegetation restoration shall be completed before the main rainy season.

8. A topsoil-fly ash composite conditioner, characterized in that, The improver is made by mixing alkali-modified fly ash and non-topmost topsoil at a mass ratio of 1:(9-19), wherein the alkali-modified fly ash has a specific surface area ≥25 m² / g and a total pore volume ≥0.09 cm³ / g.

9. The topsoil-fly ash composite conditioner according to claim 8, characterized in that, The alkali-modified fly ash is obtained by calcining fly ash and sodium carbonate at a mass ratio of 1:(0.5-1) at a calcination temperature of 800±50℃ for 2±0.5 hours.

10. The topsoil-fly ash composite conditioner as described in claim 8, characterized in that, It is applied in the ecological restoration of slopes in power transmission and transformation projects.

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