Construction method of coal mining subsidence land sponge field

Abstract

The invention discloses a construction method for a coal mining subsidence land sponge field, and belongs to the technical field of sponge field construction. The high-strength geogrid is laid at the bottom of the backfill layer, the gangue filling layer bonded by Portland cement is combined, a rigid framework and flexible reinforced composite foundation structure is formed, differential settlement of a subsidence area is restrained, the gangue filling layer consolidated by cement prevents secondary collapse, the permeable material layer is arranged under the earth surface, and the water-permeable material layer is arranged under the earth surface. The water-permeable layer is formed by mixing modified coal gangue loaded compound fertilizer, broken stone and gravel, the water-permeable layer intercepts nutrients through the ion exchange effect of the modified coal gangue, graded pores of the broken stone and the gravel promote rapid infiltration of rainwater, waterlogging is avoided, and the surface layer is covered with a mixture of the modified coal gangue loaded compound fertilizer and local soil. A water retention-ventilation-fertilizer supply microenvironment is formed, the pore structure of the coal gangue improves the air permeability of the soil, the graft copolymer can retain water, slowly release and reduce water evaporation, and deep-root crops penetrate through roots to consolidate the soil and improve the erosion resistance.

Description

Technical Field

[0001] The invention belongs to the technical field of sponge field construction, and in particular relates to a method for constructing a sponge field in a coal mining subsidence area. Background Art

[0002] Coal mining subsidence is a special landform formed by surface subsidence caused by underground mining during the process of coal resource mining. Its typical characteristics include terrain fragmentation, soil structure destruction, hydrological system disorder and biodiversity loss. Especially in high-water mining areas (such as the Huaihe River and Huaibei regions in eastern my country), large areas of waterlogging often form after surface subsidence, leading to abandoned farmland and ecosystem degradation, which seriously restricts regional sustainable development. According to statistics, the area of ​​subsidence caused by coal mining in my country has exceeded 2 million hectares, of which about 60%-70% are waterlogged areas, and the maximum waterlogging depth can reach more than 20 meters. Such areas not only lose their agricultural production functions, but may also cause secondary disasters such as groundwater pollution and soil salinization.

[0003] Although traditional ecological restoration technologies (such as terrain reshaping, coal gangue filling, vegetation restoration, etc.) can partially restore land functions, they still have significant shortcomings:

[0004] Poor water and fertilizer retention capacity: When coal gangue is used directly for filling, its large pore structure easily leads to water and nutrient loss, requiring additional covering soil or adding improvers, which is costly and has unstable effects;

[0005] Low reclamation rate: The traditional "end-of-pipe treatment" model needs to be implemented after the surface has stabilized and settled, resulting in a long idle period for the land and a reclamation rate of less than 50%;

[0006] Insufficient structural stability: The foundation of the collapsed area is loose and prone to secondary collapse, which affects the long-term effect of the repair project;

[0007] Inefficient nutrient supply: Conventional fertilizers are easily leached and lost, making it difficult to meet the continuous growth needs of plants in the early stages of restoration.

[0008] As a new type of farmland ecosystem, sponge farmland emphasizes soil water regulation and nutrient recycling capabilities, but its application in coal mining subsidence areas faces technical bottlenecks:

[0009] Imbalance in water regulation: The destruction of soil structure in the subsidence area leads to an imbalance between rainwater infiltration and storage capacity, resulting in frequent droughts and floods;

[0010] Deterioration of soil microenvironment: after the collapse, soil organic matter is lost and microbial community is imbalanced, making it difficult to support crop growth;

[0011] Single material function: Existing restoration materials (such as ordinary coal gangue and fly ash) lack the synergistic functions of water retention and slow-release fertilizers.

[0012] Although the "mining and reclamation" technology proposed in recent years has improved the reclamation efficiency by dynamically predicting the subsidence boundary and zoning management, it still needs to combine material innovation and system design to achieve the goal of building sponge fields. Therefore, there is an urgent need for a coal mining subsidence restoration method that integrates material modification, structural optimization and ecological regulation, which can not only restore land productivity, but also build a sponge field system with water storage and nutrient slow release functions, achieving the dual goals of ecological restoration and agricultural utilization. Summary of the invention

[0013] In view of the above situation, in order to overcome the defects of the prior art, the present invention constructs a sponge farmland on coal mining subsidence land through the synergistic effect of coal gangue modification, foundation structure optimization and ecological regulation, so as to achieve the purpose of soil water and fertilizer conservation, foundation stability and rapid reclamation in the subsidence area.

[0014] In order to achieve the above-mentioned purpose, the following technical scheme is adopted: The present invention provides a method for constructing a sponge field in coal mining subsidence, comprising the following steps:

[0015] S1. Preparation of modified gangue-loaded compound fertilizer, specifically comprising:

[0016] The gangue is crushed, screened and dried in sequence to obtain gangue powder, the gangue powder is mixed with a sodium hydroxide solution for alkali treatment, and then the solid is filtered out, washed with deionized water to neutrality, and dried at 60° C. to constant weight to obtain activated gangue powder;

[0017] Add cellulose to deionized water under ice bath conditions, stir to dissolve, then add hydrogen peroxide and 98% concentrated sulfuric acid in sequence, stir for 10 minutes, adjust the pH of the reaction solution to 2.5-3.0 with glacial acetic acid, then react at 4-8°C for 6-12 hours, centrifuge to separate the precipitate, wash with deionized water and vacuum dry at 60°C to constant weight to obtain carboxylated cellulose, then dissolve the carboxylated cellulose in deionized water, stir until dissolved, add acrylamide under nitrogen protection, then add ammonium persulfate for initiation, react at 60°C for 4-6 hours, and freeze-dry to obtain a cellulose-acrylamide graft copolymer;

[0018] The cellulose-acrylamide graft copolymer solution is added to form a 5%-20% graft copolymer solution, and then the activated coal gangue powder and the graft copolymer solution are mixed in a mass ratio of 1:3-5, reacted at 50-80° C. for 3-8 hours under nitrogen protection, filtered, washed with deionized water and vacuum dried at 60° C. to constant weight to obtain grafted modified coal gangue;

[0019] The modified coal gangue is immersed in a compound fertilizer solution, and then centrifuged and spray-dried to obtain the modified coal gangue loaded compound fertilizer;

[0020] S2. Terrain reshaping and foundation stabilization, including:

[0021] Use coal gangue to fill cracks and depressions, then backfill, and control the surface slope at 1%-3% after compaction;

[0022] Lay a grid with a soil tensile strength of ≥50kN / m at the bottom of the backfill layer, and cover the surface with a mixture of modified coal gangue loaded with compound fertilizer and local soil with a thickness of 20-50cm;

[0023] S3. Construction of sponge structure farmland system, including:

[0024] Laying a 10-20 cm thick permeable material layer 20-40 cm below the ground surface, wherein the permeable material is composed of a mixture of modified coal gangue loaded with compound fertilizer, crushed stone and gravel;

[0025] The modified gangue-loaded compound fertilizer is evenly spread on the ground surface at a rate of 2-5 t / mu, with a tillage depth of ≤20 cm;

[0026] Mixed seeds of drought- and flood-resistant crops ryegrass and alfalfa and economic crop rapeseed are sown in rows with a row spacing of 30-50cm. After sowing, cover with shallow soil and straw to retain moisture.

[0027] Furthermore, in step S1, the mass concentration of the sodium hydroxide solution is 8%-12%, the mass ratio of the coal gangue powder to the sodium hydroxide solution is 1:5-8, the alkali treatment stirring reaction temperature is 70-85°C, and the reaction time is 3-5h.

[0028] Furthermore, the cellulose ether is carboxymethyl cellulose ether and / or hydroxypropyl methyl cellulose; the added amount of the initiator is 0.5%-2% of the total mass of the monomers of carboxylated cellulose and acrylamide; and the total concentration of monomers in the graft copolymer solution is 5%-20%.

[0029] Furthermore, the compound fertilizer solution contains a nitrogen source, a phosphorus source and a potassium source, wherein the mass ratio of nitrogen, phosphorus and potassium is 1:0.3-0.8:0.5-1.2, and the concentration of the compound fertilizer solution is 10%-40%.

[0030] Furthermore, in step S1, the coal gangue is crushed by a jaw crusher, the particle size of the coal gangue powder after screening is 80-150 mesh, the drying temperature is 80-120° C., and the drying time is 2-6 hours.

[0031] Furthermore, the modified coal gangue is mixed with the compound fertilizer solution in a mass ratio of 1:2-10, immersed for 12-48 hours and then centrifuged; the spray drying temperature is 50-80° C., and the moisture content of the product after drying is ≤5%.

[0032] Furthermore, in step S3, when coal gangue is used to fill cracks and depressions, the particle size of the coal gangue is 10-50 mm, the compaction degree is ≥90% of the Proctor coefficient, and 10-15% of silicate cement is additionally added as a binder, so that the permeability coefficient after filling is ≤1×10 -3 cm / s.

[0033] Furthermore, the mixture of the modified gangue-loaded compound fertilizer and local soil is composed of the modified gangue-loaded compound fertilizer and local soil mixed in a mass ratio of 1:2-5.

[0034] Furthermore, the permeable material is composed of modified coal gangue loaded with compound fertilizer, crushed stone and gravel mixed in a mass ratio of 1:3-5:1-2.

[0035] Furthermore, the mixed seeds are composed of ryegrass: alfalfa: rapeseed in a sowing mass ratio of 2-5:1-2:1-2.

[0036] The beneficial effects of the present invention are:

[0037] (1) The present invention lays a high-strength geogrid at the bottom of the backfill layer, combined with a coal gangue filling layer bonded with silicate cement, to form a composite foundation structure with a rigid skeleton and flexible reinforcement. The geogrid disperses the foundation stress and suppresses uneven settlement in the collapsed area; the cement-consolidated coal gangue filling layer improves the overall compressive strength and prevents secondary collapse. The present invention also sets a permeable material layer 20-40 cm below the surface, which is composed of a mixture of modified coal gangue loaded with compound fertilizer, crushed stone, and gravel. The permeable layer The ion exchange effect of modified coal gangue intercepts nutrients, while the graded pores of crushed stone and gravel promote rapid infiltration of rainwater to avoid waterlogging. The surface is covered with a mixture of modified coal gangue loaded with compound fertilizer and local soil to form a microenvironment of water retention, air permeability and fertilizer supply. The pore structure of coal gangue improves soil aeration, and the water retention and slow release function of grafted copolymers reduces soil moisture evaporation. Deep-rooted crops such as ryegrass and alfalfa penetrate the soil through their roots to improve erosion resistance.

[0038] (2) The present invention uses hydrogen peroxide / concentrated sulfuric acid to oxidatively modify cellulose, introduce a large number of carboxyl groups and hydroxyl groups, and endow it with strong hydrophilicity and negatively charged surface. After grafting with acrylamide, a three-dimensional network structure with comb-like branches is formed, and the water retention capacity is synergistically improved through hydrogen bonding and capillary action. At the same time, the cross-linked structure enhances hydrolysis resistance, allowing it to exist stably in the soil for a long time;

[0039] (3) The negatively charged surface of carboxylated cellulose fixes ammonium nitrogen through electrostatic adsorption, while the porous structure of the grafted copolymer can physically coat the compound fertilizer particles, forming a synergistic slow-release system of chemical adsorption and physical encapsulation, which significantly prolongs the nutrient release cycle, improves fertilizer utilization, and reduces loss;

[0040] (4) The present invention activates the surface hydroxyl groups of coal gangue through alkali treatment, and forms a stable complex with the graft copolymer through chemical bonding. The porosity of the modified coal gangue is significantly improved, and the adsorption capacity of water and nutrients is enhanced. At the same time, its ion exchange capacity is simultaneously optimized, and the balance of cations in the soil can be dynamically regulated. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 The soil saturated water holding capacity test results of each embodiment of the present invention, the comparative example and the blank control group;

[0042] Figure 2 The soil porosity measurement results of each embodiment of the present invention, the comparative example and the blank control group;

[0043] Figure 3 The soil permeability coefficient test results of each embodiment of the present invention, the comparative example and the blank control group are shown;

[0044] Figure 4 The average organic matter content of the soil in each embodiment of the present invention, the comparative example and the blank control group is measured;

[0045] Figure 5 The average contents of available nitrogen, phosphorus and potassium in the soil of each embodiment of the present invention, the comparative example and the blank control group are measured;

[0046] Figure 6 The cation exchange capacity measurement results of the soils of various embodiments of the present invention, comparative examples and a blank control group;

[0047] Figure 7 The total amount of soil microorganisms in the embodiments of the present invention, the comparative examples and the blank control group are measured.

[0048] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0050] Unless otherwise defined, all professional and scientific terms used herein have the same meanings as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein may be applied to the present invention. The preferred implementation methods and materials described herein are for demonstration purposes only and are not intended to limit the content of this application.

[0051] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are purchased from commercial channels unless otherwise specified.

[0052] Example 1

[0053] A method for constructing a sponge field in coal mining subsidence land comprises the following steps:

[0054] S1. Preparation of modified coal gangue loaded compound fertilizer:

[0055] The gangue is crushed by a jaw crusher, and after screening, a gangue powder with a particle size of 150 mesh is obtained, which is dried at 120° C. for 6 hours; the gangue powder is mixed with a sodium hydroxide solution with a mass concentration of 12% in a mass ratio of 1:8, and the mixture is stirred and reacted at 85° C. for 5 hours for alkali treatment, and then the solid is filtered out, washed with deionized water until neutral, and dried at 60° C. until constant weight to obtain activated gangue powder;

[0056] The cellulose was added to deionized water under ice bath condition, and hydrogen peroxide and 98% concentrated sulfuric acid were added in sequence after stirring to dissolve, and after stirring for 10 minutes, the pH of the reaction solution was adjusted to 3.0 with glacial acetic acid, and then reacted at 8°C for 12 hours, and then centrifuged to separate the precipitate, washed with deionized water and vacuum dried at 60°C to constant weight to obtain carboxylated cellulose; the carboxylated cellulose was dissolved in deionized water, and after stirring until dissolved, acrylamide was added under nitrogen protection, and then ammonium persulfate accounting for 2% of the total mass of the monomer carboxylated cellulose and acrylamide was added for initiation, and the reaction was carried out at 60°C for 6 hours, and the cellulose-acrylamide graft copolymer was obtained after freeze-drying;

[0057] A 20% graft copolymer solution was prepared from the cellulose-acrylamide graft copolymer, and the activated coal gangue powder and the graft copolymer solution were mixed in a mass ratio of 1:5, reacted at 80° C. for 8 h under nitrogen protection, filtered, washed with deionized water, and vacuum dried at 60° C. to constant weight to obtain graft-modified coal gangue;

[0058] The modified coal gangue is mixed with a compound fertilizer solution having a concentration of 40% and a mass ratio of nitrogen, phosphorus and potassium of 1:0.8:1.2 at a mass ratio of 1:10, immersed for 48 hours, centrifuged, and then spray-dried at 80°C. The moisture content of the dried product is ≤5%, thereby obtaining a modified coal gangue-loaded compound fertilizer;

[0059] S2. Terrain reshaping and foundation stabilization:

[0060] Use coal gangue with a particle size of 50mm to fill cracks and depressions, add 15% of silicate cement as a binder, and compact the cracks to a degree of ≥90% of the Proctor coefficient, so that the permeability coefficient after filling is ≤1×10-3cm / s, and then backfill. After compaction, the surface slope is controlled at 3%;

[0061] A geogrid with a soil tensile strength of ≥50kN / m is laid at the bottom of the backfill layer, and a mixture of modified coal gangue loaded with compound fertilizer and local soil in a mass ratio of 1:5 is covered on the surface with a thickness of 50cm;

[0062] S3. Construction of sponge structure farmland system:

[0063] A 20cm thick permeable material layer composed of modified coal gangue loaded with compound fertilizer, crushed stone and gravel in a mass ratio of 1:5:2 is laid 40cm below the ground surface;

[0064] The modified gangue loaded compound fertilizer was evenly spread on the ground surface at 5t / mu, and the tillage depth was 10cm;

[0065] Mixed seeds consisting of ryegrass, alfalfa and rapeseed in a sowing mass ratio of 5:2:2 are sown in rows with a row spacing of 50 cm. After sowing, cover with shallow soil and straw to retain moisture.

[0066] Example 2

[0067] A method for constructing a sponge field in coal mining subsidence land comprises the following steps:

[0068] S1. Preparation of modified coal gangue loaded compound fertilizer:

[0069] The gangue is crushed by a jaw crusher, and after screening, a gangue powder with a particle size of 80 mesh is obtained, which is then dried at 80° C. for 2 h; the gangue powder is mixed with a sodium hydroxide solution with a mass concentration of 8% in a mass ratio of 1:5, and the mixture is stirred and reacted at 70° C. for 3 h for alkali treatment, and then the solid is filtered out, washed with deionized water until neutral, and dried at 60° C. until constant weight to obtain activated gangue powder;

[0070] The cellulose was added to deionized water under ice bath condition, and hydrogen peroxide and 98% concentrated sulfuric acid were added in sequence after stirring to dissolve, and after stirring for 10 minutes, the pH of the reaction solution was adjusted to 2.5 with glacial acetic acid, and then reacted at 4°C for 6 hours, and then the precipitate was separated by centrifugation, washed with deionized water and vacuum dried at 60°C to constant weight to obtain carboxylated cellulose; the carboxylated cellulose was dissolved in deionized water, and after stirring until dissolved, acrylamide was added under nitrogen protection, and then ammonium persulfate accounting for 0.5% of the total mass of the monomer carboxylated cellulose and acrylamide was added for initiation, and the reaction was carried out at 60°C for 4 hours, and the cellulose-acrylamide graft copolymer was obtained after freeze-drying;

[0071] A 5% graft copolymer solution was prepared from the cellulose-acrylamide graft copolymer, and the activated coal gangue powder and the graft copolymer solution were mixed in a mass ratio of 1:3, reacted at 50°C for 3 hours under nitrogen protection, filtered, washed with deionized water, and vacuum dried at 60°C to constant weight to obtain graft-modified coal gangue;

[0072] The modified coal gangue is mixed with a compound fertilizer solution with a concentration of 10% and a mass ratio of nitrogen, phosphorus and potassium of 1:0.3:0.5 in a mass ratio of 1:2, immersed for 12 hours, centrifuged, and then spray-dried at 50°C. The moisture content of the dried product is ≤5%, thereby obtaining a modified coal gangue loaded compound fertilizer;

[0073] S2. Terrain reshaping and foundation stabilization:

[0074] Use coal gangue with a particle size of 10mm to fill cracks and depressions, add 10% of silicate cement as a binder, and compact to a degree of ≥90% of the Proctor coefficient, so that the permeability coefficient after filling is ≤1×10-3cm / s, and then backfill, and control the surface slope at 1% after compaction;

[0075] A geogrid with a soil tensile strength of ≥50kN / m is laid at the bottom of the backfill layer, and a mixture of modified coal gangue loaded compound fertilizer and local soil in a mass ratio of 1:2 is covered on the surface with a thickness of 20cm;

[0076] S3. Construction of sponge structure farmland system:

[0077] A 10cm thick permeable material layer composed of modified coal gangue loaded with compound fertilizer, crushed stone and gravel in a mass ratio of 1:3:1 is laid 20cm below the ground surface;

[0078] The modified gangue loaded compound fertilizer was evenly spread on the ground surface at 2t / mu, and the tillage depth was 10cm;

[0079] Mixed seeds consisting of ryegrass, alfalfa and rapeseed in a sowing mass ratio of 2:1:1 are sown in rows with a row spacing of 30 cm. After sowing, cover with shallow soil and straw to retain moisture.

[0080] Example 3

[0081] A method for constructing a sponge field in coal mining subsidence land comprises the following steps:

[0082] S1. Preparation of modified coal gangue loaded compound fertilizer:

[0083] The gangue was crushed by a jaw crusher, and after screening, a gangue powder with a particle size of 120 mesh was obtained, which was dried at 100° C. for 4 hours; the gangue powder was mixed with a sodium hydroxide solution with a mass concentration of 10% in a mass ratio of 1:6.5, and stirred at 78° C. for 4 hours for alkali treatment, and then the solid was filtered out, washed with deionized water until neutral, and dried at 60° C. to constant weight to obtain activated gangue powder;

[0084] The cellulose was added to deionized water under ice bath condition, and hydrogen peroxide and 98% concentrated sulfuric acid were added in sequence after stirring to dissolve, and after stirring for 10 minutes, the pH of the reaction solution was adjusted to 2.7 with glacial acetic acid, and then reacted at 6°C for 9 hours, and then the precipitate was separated by centrifugation, washed with deionized water and vacuum dried at 60°C to constant weight to obtain carboxylated cellulose; the carboxylated cellulose was dissolved in deionized water, and after stirring until dissolved, acrylamide was added under nitrogen protection, and then ammonium persulfate accounting for 1.2% of the total mass of the monomer carboxylated cellulose and acrylamide was added for initiation, and the reaction was carried out at 60°C for 5 hours, and the cellulose-acrylamide graft copolymer was obtained after freeze-drying;

[0085] A 12% graft copolymer solution of cellulose-acrylamide graft copolymer was prepared, and activated coal gangue powder and the graft copolymer solution were mixed in a mass ratio of 1:4, reacted at 65°C for 5.5h under nitrogen protection, filtered, washed with deionized water and vacuum dried at 60°C to constant weight to obtain grafted modified coal gangue;

[0086] The modified coal gangue is mixed with a compound fertilizer solution with a concentration of 25% and a mass ratio of nitrogen, phosphorus and potassium of 1:0.55:0.85 in a mass ratio of 1:6, immersed for 30 hours, centrifuged, and then spray-dried at 65°C. The moisture content of the dried product is ≤5%, thereby obtaining a modified coal gangue-loaded compound fertilizer;

[0087] S2. Terrain reshaping and foundation stabilization:

[0088] Use coal gangue with a particle size of 30mm to fill cracks and depressions, add 12.5% ​​of silicate cement as a binder, and compact to a degree of ≥90% of the Proctor coefficient, so that the permeability coefficient after filling is ≤1×10-3cm / s, and then backfill, and control the surface slope at 2% after compaction;

[0089] A geogrid with a soil tensile strength of ≥50kN / m is laid at the bottom of the backfill layer, and a mixture of modified coal gangue loaded with compound fertilizer and local soil in a mass ratio of 1:3.5 is covered on the surface with a thickness of 35cm;

[0090] S3. Construction of sponge structure farmland system:

[0091] A 15cm thick permeable material layer composed of modified coal gangue loaded with compound fertilizer, crushed stone and gravel in a mass ratio of 1:4:1.5 is laid 30cm below the ground surface;

[0092] The modified gangue loaded compound fertilizer was evenly spread on the ground at 3.5t / mu, and the tillage depth was 10cm;

[0093] Mixed seeds consisting of ryegrass, alfalfa and rapeseed in a sowing mass ratio of 3.5:1.5:1.5 were sown in rows with a row spacing of 40 cm. After sowing, the seeds were shallowly covered with soil and straw to retain moisture.

[0094] Comparative Example 1

[0095] The difference between this comparative example and Example 3 is that the grafting modification step in step S1 is omitted, and the unmodified alkali-treated coal gangue is directly used to load the compound fertilizer. The rest is the same as Example 3.

[0096] Comparative Example 2

[0097] The difference between this comparative example and Example 3 is that the geogrid laying in step S2 and the water-permeable material layer construction in step S3 are omitted, and the rest are the same as Example 3.

[0098] Comparative Example 3

[0099] The difference between this comparative example and Example 3 is that ordinary coal gangue powder and conventional fertilizers are used instead of modified coal gangue loaded compound fertilizers, and the conventional fertilizers include urea, superphosphate, and potassium chloride, wherein the total amount of nitrogen, phosphorus, and potassium elements is the same as that in Example 3, and the rest are the same as that in Example 3.

[0100] Results Analysis

[0101] Land in a coal mining subsidence area was selected and divided into test fields of 10m×10m. Sponge fields were constructed for the test fields using the methods of the embodiments and comparative examples. A blank control group was set up at the same time. The blank control group did not perform any operation. Ten test fields were set up in each group for parallel experiments. After 30 days, the following indicators of each test field were tested.

[0102] Test Example 1

[0103] Soil physical properties testing

[0104] The saturated water holding capacity of the soil was determined by the dry-wet weight method, the porosity of the soil was determined by the pycnometer method, and the permeability coefficient of the soil was determined by the double-ring infiltrator. The results are shown in Figure 1-3 .

[0105] From the above test results, it can be seen that the water holding capacity of Examples 1-3 is significantly higher than that of the comparative example and the blank group. This is because the present invention utilizes the unique three-dimensional network structure of cellulose-acrylamide graft copolymer, which has a large number of sites for water molecules to attach, and can efficiently absorb water through hydrogen bonding. At the same time, after a series of treatments, the pore structure of the modified gangue is optimized, further increasing the space for water storage. The application of modified gangue loaded with compound fertilizer, and the reasonable matching of materials during the construction process, such as the mixing of modified gangue loaded with compound fertilizer, crushed stone, and gravel in the permeable material layer, form a more reasonable pore distribution between soil particles. This optimized structure does not lead to a significant increase in the permeability coefficient, and still controls it at a low and reasonable level. Therefore, the present invention enables the soil to quickly allow rainwater to infiltrate, avoiding surface water accumulation and waterlogging, while effectively maintaining a certain amount of water in the soil, providing a continuous water supply for crop growth.

[0106] Test Example 2

[0107] Soil chemical properties testing

[0108] The average content of organic matter in the soil was determined by potassium dichromate oxidation-external heating method, the average content of available nitrogen in the soil was determined by indophenol blue colorimetry, the average content of available phosphorus in the soil was determined by sodium bicarbonate extraction-molybdenum antimony colorimetry, the average content of available potassium in the soil was determined by ammonium acetate extraction-flame photometry, and the cation exchange capacity of the soil was determined by EDTA-ammonium salt rapid method. The above results are shown in Figure 4-6 .

[0109] from Figure 4-6It can be seen that the organic matter content of the embodiment increases the content of quick-acting nitrogen, phosphorus and potassium, respectively, which is higher than that of the comparative example and the blank control group. First, in the process of preparing the modified gangue-loaded compound fertilizer, the introduction of cellulose-acrylamide graft copolymer not only improves the physical structure of the soil, but also provides a rich organic carbon source for soil microorganisms, promotes the growth and metabolic activities of microorganisms, and thus accelerates the decomposition and transformation of organic matter in the soil. Secondly, after the gangue is treated with alkali, substances such as silicon aluminum oxide are released. These substances can interact with organic matter in the soil, promote the formation of organic and mineral complexes, and improve the stability of organic matter in the soil, which is not easy to be decomposed and lost. Carboxylated cellulose has a negatively charged surface and can effectively fix ammonium nitrogen through electrostatic adsorption, reducing the loss of nitrogen. The porous structure of the graft copolymer physically coats the phosphorus and potassium elements in the compound fertilizer particles, forming a slow-release system, so that the phosphorus and potassium elements can be slowly released in the soil, continuously providing nutrients for crops. In addition, the ion exchange capacity of the modified coal gangue itself is optimized after treatment, which can dynamically regulate the balance of cations in the soil, increase the cation exchange capacity of the soil, and further promote the soil's retention and supply of nutrients.

[0110] Test Example 3

[0111] Soil biological index detection

[0112] The plate count method was used to determine the number of microorganisms per gram of dry soil. The results are shown in Figure 7 .

[0113] from Figure 7 It can be seen that the total amount of microorganisms in the embodiment is significantly higher than that in the comparison example. This is because during the sponge field construction process, the optimized pore structure provides a suitable living environment for microorganisms. While the straw covering retains moisture, it also provides an additional carbon source for soil microorganisms, thereby stimulating the proliferation of microorganisms.

[0114] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

[0115] The present invention and its implementation methods are described above, which is not restrictive. The drawings are only one of the implementation methods of the present invention, and the actual application is not limited thereto. In short, if ordinary technicians in the field are inspired by it and design methods and embodiments similar to the technical solution without creativity without departing from the purpose of the invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for constructing a sponge field in coal mining subsidence, characterized in that: The following steps are involved: S1. Preparation of modified gangue-loaded compound fertilizer, specifically comprising: The gangue is crushed, screened and dried in sequence to obtain gangue powder, the gangue powder is mixed with a sodium hydroxide solution for alkali treatment, and then the solid is filtered out, washed with deionized water to neutrality, and dried at 60° C. to constant weight to obtain activated gangue powder; Add cellulose to deionized water under ice bath conditions, stir to dissolve, then add hydrogen peroxide and 98% concentrated sulfuric acid in sequence, stir for 10 minutes, adjust the pH of the reaction solution to 2.5-3.0 with glacial acetic acid, then react at 4-8°C for 6-12 hours, centrifuge to separate the precipitate, wash with deionized water and vacuum dry at 60°C to constant weight to obtain carboxylated cellulose, then dissolve the carboxylated cellulose in deionized water, stir until dissolved, add acrylamide under nitrogen protection, then add ammonium persulfate for initiation, react at 60°C for 4-6 hours, and freeze-dry to obtain a cellulose-acrylamide graft copolymer; The cellulose-acrylamide graft copolymer solution is added to form a 5%-20% graft copolymer solution, and then the activated coal gangue powder and the graft copolymer solution are mixed in a mass ratio of 1:3-5, reacted at 50-80° C. for 3-8 hours under nitrogen protection, filtered, washed with deionized water and vacuum dried at 60° C. to constant weight to obtain grafted modified coal gangue; The modified coal gangue is immersed in a compound fertilizer solution, and then centrifuged and spray-dried to obtain the modified coal gangue loaded compound fertilizer; S2. Terrain reshaping and foundation stabilization, including: Use coal gangue to fill cracks and depressions, then backfill, and control the surface slope at 1%-3% after compaction; Lay a grid with a soil tensile strength of ≥50kN / m at the bottom of the backfill layer, and cover the surface with a mixture of modified coal gangue loaded with compound fertilizer and local soil with a thickness of 20-50cm; S3. Construction of sponge structure farmland system, including: Laying a 10-20 cm thick permeable material layer 20-40 cm below the ground surface, wherein the permeable material is composed of a mixture of modified coal gangue loaded with compound fertilizer, crushed stone and gravel; The modified gangue-loaded compound fertilizer is evenly spread on the ground surface at a rate of 2-5 t / mu, with a tillage depth of ≤20 cm; Mixed seeds of drought- and flood-resistant crops ryegrass and alfalfa and economic crop rapeseed are sown in rows with a row spacing of 30-50cm. After sowing, cover with shallow soil and straw to retain moisture.

2. A method for constructing a sponge field in coal mining subsidence according to claim 1, characterized in that: The mass concentration of the sodium hydroxide solution in step S1 is 8%-12%, the mass ratio of the coal gangue powder to the sodium hydroxide solution is 1:5-8, the alkali treatment stirring reaction temperature is 70-85°C, and the reaction time is 3-5h.

3. A method for constructing a sponge field in coal mining subsidence according to claim 2, characterized in that: The cellulose ether is carboxymethyl cellulose ether and / or hydroxypropyl methyl cellulose; the added amount of the initiator is 0.5%-2% of the total mass of the monomers of carboxylated cellulose and acrylamide; and the total concentration of the monomers in the graft copolymer solution is 5%-20%.

4. A method for constructing a sponge field in coal mining subsidence according to claim 3, characterized in that: The compound fertilizer solution contains a nitrogen source, a phosphorus source and a potassium source, wherein the mass ratio of nitrogen, phosphorus and potassium is 1:0.3-0.8:0.5-1.2, and the concentration of the compound fertilizer solution is 10%-40%.

5. A method for constructing a sponge field in coal mining subsidence according to claim 4, characterized in that: In step S1, the coal gangue is crushed by a jaw crusher, and the particle size of the coal gangue powder after screening is 80-150 meshes, the drying temperature is 80-120° C., and the drying time is 2-6 hours.

6. A method for constructing a sponge field in coal mining subsidence according to claim 5, characterized in that: The modified coal gangue and the compound fertilizer solution are mixed in a mass ratio of 1:2-10, immersed for 12-48 hours and then centrifuged; the spray drying temperature is 50-80°C, and the moisture content of the dried product is ≤5%.

7. A method for constructing a sponge field in coal mining subsidence according to claim 6, characterized in that: In step S3, when coal gangue is used to fill cracks and depressions, the particle size of the coal gangue is 10-50 mm, the compaction degree is ≥90% of the Proctor coefficient, and 10-15% of silicate cement is additionally added as a binder, so that the permeability coefficient after filling is ≤1×10 -3 cm / s.

8. The method for constructing a sponge field in coal mining subsidence according to claim 7, characterized in that: The mixture of modified coal gangue loaded compound fertilizer and local soil is composed of modified coal gangue loaded compound fertilizer and local soil mixed in a mass ratio of 1:2-5.

9. A method for constructing a sponge field in coal mining subsidence according to claim 8, characterized in that: The water-permeable material is composed of modified coal gangue loaded with compound fertilizer, crushed stone and sand gravel mixed in a mass ratio of 1:3-5:1-2.

10. A method for constructing a sponge field in coal mining subsidence according to claim 9, characterized in that: The mixed seeds are composed of ryegrass: alfalfa: rapeseed in a sowing mass ratio of 2-5:1-2:1-2.

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