Soil covering and reclamation technology for loess plateau coal gangue filling area

Abstract

The invention discloses a soil covering and reclamation process for a coal gangue filling area, provides a coal gangue filling treatment method of'from inside to outside, from bottom to top, reducing an overhead and performing layered compaction ', and can solve the problems of large slope exposure surface, difficulty in slope compaction and the like of a filling afforestation area in an existing treatment method. The invention mainly aims to realize comprehensive treatment and reutilization of environmental protection treatment and ecological restoration by utilizing development and construction of a modern agricultural base. The treatment speed and the ecological restoration process of the mining area are accelerated, the development mode of a mineral resource type region is changed, land utilization is restored, and secondary industrial construction and development of the mining area land are achieved; the problem of comprehensive utilization of the coal gangue can be solved, the damage of the coal gangue to the ecological environment is reduced, and the cost of coal enterprises for treating coal-based solid wastes is reduced; meanwhile, waste ditches become fertile farmland, the land utilization degree is improved, and crop planting cultivated land can be provided for local farmers.

Description

Technical Field

[0001] This invention belongs to the field of ecological governance and land reclamation technology for coal gangue backfilling. Background Technology

[0002] Coal gangue is mainly composed of carbonaceous shale, mudstone, and sandstone, with SiO2 and Al2O3 as its main chemical components, mixed with pyrite and a small amount of coal. Since pyrite is primarily FeS2, its oxidation produces acid, which hinders the absorption of phosphorus and calcium by plants, harming plant roots and affecting plant growth and development. The intense oxidation of pyrite can also lead to spontaneous combustion of the coal gangue.

[0003] Every year, a large amount of gangue is generated in the coal-producing area. Due to the lack of planning and scientific treatment methods, the large amount of gangue produced in the coal production process has accumulated in the region for a long time. This not only occupies the land but also causes disasters such as wind erosion and dust, leaching water pollution, landslides and debris flows, and landscape damage, posing a threat to the regional environment and becoming an important constraint on the high-quality development of the regional economy and society.

[0004] Domestic and international practical experience has proven that using a layered compaction method for stockpiling gangue is a relatively practical and feasible approach. Based on practical experience, the gangue removal process can be summarized as "from the inside out, from the bottom up, reducing voids, and compacting in layers." This method not only ensures a certain degree of compaction of the gangue, reducing porosity, but also minimizes the exposed surface area of ​​the slope in the afforestation area, as slopes are difficult to compact. After one layer of gangue is piled up, the next layer is then removed, resulting in a well-sealed, soil-covered monolith when the entire gangue yard is no longer in use. Summary of the Invention

[0005] To address the aforementioned problems that may occur with coal gangue filling, this invention proposes a method of "compacting from the inside out, from the bottom up, reducing gaps, and layering."

[0006] The specific stacking steps are as follows:

[0007] Step 1: Use a truck to transport the loose gangue to the bottom of the gully. During the loading process, be careful to prevent landslides caused by the upper gangue to avoid loss of life and property.

[0008] Step 2: Use a bulldozer to level the gangue, and compact it after each 1m thick layer of gangue. It can effectively prevent gangue from settling;

[0009] Step 3: Cover every 2.0m thick layer of gangue with a 50cm thick layer of loess to isolate it from the air and prevent spontaneous combustion caused by heat buildup inside the gangue.

[0010] Step 4: Construct a walkway every 5 meters of height on the slope until the highest platform is reached. The walkways should be 5 meters wide, and drainage ditches should be built on the walkway platforms to prevent water from the slope from eroding the platform.

[0011] Step 5: The slope of the filling area is formed with a gradient of 1:2.0;

[0012] Step 6: Take steps 2-5 for the newly delivered gangue;

[0013] Step 7: When the site is piled up to the elevation, cover the top platform with 1m thick loess and carry out greening and afforestation.

[0014] The key technologies for site construction and backfilling are as follows:

[0015] I. Collection and Storage of Topsoil

[0016] Before implementing land reclamation projects, first collect topsoil approximately 0.5 meters thick from the surface to the subsoil layer. The excavated topsoil should be specially piled up for later reclamation. This topsoil can be placed in woven bags and piled on the outside to form a barrier. After the soil collection is completed, cover the topsoil with soil for reclamation, providing a nutrient base for the next stage of reclamation work and improving the survival rate of planted crops.

[0017] II. Seepage Prevention Project

[0018] According to the "Standard for Pollution Control of Storage and Filling of General Industrial Solid Waste" (GB18599-2020): 5.2.1 When the saturated permeability coefficient of the natural foundation layer is not greater than 1.0 x 10⁻⁵ cm / s and the thickness is not less than 0.75 m, the natural foundation layer can be used as the seepage-proof lining. 5.2.2 When the natural foundation layer cannot meet the seepage-proof requirements of clause 5.2.1, a modified compacted clay lining or other material seepage-proof lining with equivalent or higher water-proofing effect can be used, and its seepage-proof performance should be at least equivalent to a natural foundation layer with a permeability coefficient of 1.0 x 10⁻⁵ cm / s and a thickness of 0.75 m.

[0019] This invention uses compacted clay for seepage prevention, and its seepage prevention performance is equivalent to a natural foundation layer with a permeability coefficient of 1.0×10-7cm / s and a thickness of 0.75m.

[0020] III. Retaining Wall Project

[0021] To prevent waste rock and some of the topsoil from flowing downstream during slope stabilization and to ensure slope stability, a 5m high masonry retaining dam was constructed at the gully mouth. Designed for a seismic fortification intensity of 8.0 degrees, with a safety level of II, the dam foundation bearing capacity is required to be no less than 160 kPa. The dam body is 5.0m high above ground, with a crest width of 2.0m, a face slope ratio of 1:0.5, and a back slope ratio of 1:0.2. It is constructed using M7.5 cement mortar and MU30 rubble masonry. The retaining dam is approximately 24.8m long.

[0022] The foundation is supported by a 100mm thick C10 concrete pad, extending 100mm on each side; a 300mm thick 3:7 lime-soil mixture is placed under the pad, extending 100mm on each side; the extended foundation uses C25 concrete, with HRB335 reinforcing steel and HPB235 distribution steel, and a 40mm thick protective layer; the exposed surface of the retaining dam is reinforced with M10 cement mortar joint tape.

[0023] IV. Drainage Engineering

[0024] 1. Intercepting ditches and transverse drainage ditches

[0025] Drainage ditches are constructed on both sides of the slope near the retaining dam. The ditches have a trapezoidal cross-section, with a top width of 1.0m, a bottom width of 0.4m, and a height of 0.6m. The ditches are 2965m long and are constructed using mortar-grouted masonry, with a thickness of 0.4m and a 10cm crushed stone cushion layer underneath. Expansion joints with a width of 25mm are installed every 15m and filled with asphalt.

[0026] The slope of the drainage ditch shall not be less than i = 0.01.

[0027] A transverse drainage ditch is laid along the horse trail. The transverse drainage ditch has a trapezoidal cross section with a top width of 0.5m, a bottom width of 0.4m, and a height of 0.4m. The transverse drainage ditch is 242.3m long and is constructed using a mortar-grouted rubble masonry structure. An expansion joint with a width of 25mm is set every 15m and filled with asphalt. The slope of the drainage ditch is not less than i = 0.005.

[0028] 2. Stilling basin

[0029] A stilling basin is set at the end of the drainage ditch outside the retaining dam. The water from the flood discharge culvert and the drainage ditch enters the stilling basin, which is a masonry structure with a length of 11.6m, a width of 3.0m, and a depth of 2.5m.

[0030] V. Waste Disposal Road Engineering

[0031] The road surface is made of mud-bound gravel, and the waste disposal road is about 400m long and 4m wide.

[0032] VI. Backfilling Work

[0033] For every 2m thick layer of waste rock piled up, a 50cm thick layer of loess is placed between the piles and on the slopes. When the pile reaches its maximum height, the top platform is covered with 1.0m of soil. The soil covering design of the filling area is itself a soil and water conservation project. When the pile reaches the design elevation, the slopes and walkway platforms are sealed off and greened by planting shrubs and grasses. The top platform is covered with soil and reclaimed as woodland. These measures will effectively prevent landslides, debris flows, and other soil erosion hazards in the filling area. The soil covering design not only achieves the goals of soil and water conservation, greening, environmental protection, and increasing the area's forest area, but also helps prevent spontaneous combustion of the waste rock pile.

[0034] VII. Slope Protection Engineering

[0035] 1. Project Layout

[0036] The maximum slope ratio in this design is 1:2. A horse trail will be built for every 5m of height, and the trail will be 5m wide. Drainage ditches will be installed at the toe of the slope on the inner side of the trail. The slope will be protected by vegetation measures. First, the slope will be covered with soil to a depth of 0.5m.

[0037] 2. Slope stability analysis

[0038] The slope stability calculation was performed using the "Slope Stability Calculation Software" from Lizheng Software Design Institute. The stability of the gangue slope was calculated using the following formula:

[0039]

[0040] Where: K—safety factor for anti-sliding stability of the gangue pile;

[0041] Φ—Angle of friction within the gangue pile, taken as 31.5°;

[0042] α—the angle between the straight sliding surface and the horizontal plane, with a slope ratio of 1:2.0 and a = 27°.

[0043] The calculation results show that the stability safety factor K of the gangue slope is 1.28, which is greater than 1.15, meeting the slope stability requirements. The gangue pile with a slope ratio of 1:2.0 is stable and safe.

[0044] VIII. Spontaneous Combustion Prevention Project

[0045] Each 1-meter-thick layer of gangue is compacted once with a bulldozer; every 2.0-meter-thick layer of gangue is covered with a 50-cm-thick layer of loess to isolate it from the air and prevent spontaneous combustion of the gangue due to heat accumulation inside.

[0046] IX. Soil Borrowing Works

[0047] The initial dam and the flood control earth dam that need to be compacted and filled, as well as the gangue piled up and covered with soil in layers, all use externally purchased soil. Therefore, this project does not involve borrow pits.

[0048] 10. Reforestation Project

[0049] When the gangue pile reaches the design elevation of the waste disposal site, the construction unit will level and cover the gangue pile with soil for land reclamation.

[0050] 1. Collection and storage of topsoil

[0051] Before implementing the coal gangue remediation project, a layer of mature soil approximately 0.5 meters thick from the ground surface to the topsoil layer should be collected and piled up nearby for future reclamation. The height of the soil pile should not exceed 5-10 meters.

[0052] 2. Afforestation by covering with soil

[0053] After the site is leveled, a layer of low-fertility topsoil of about 0.5m is laid first, followed by a layer of mature soil collected before construction of 0.5m, to meet the land requirements for planting trees.

[0054] The vegetation restoration of the slopes and top platforms formed after backfilling will be carried out by planting Amorpha fruticosa, with a planting standard of 2000 holes / hm2 and a spacing of 2m×2m. The horse trail will also be restored by planting Amorpha fruticosa, with a spacing of 2m×2m. Reclamation is required to be carried out in a terraced manner, with land reclamation in terraced sections. The reclamation direction is woodland (area 7.51hm2), and the slope protection is artificial grassland (area 0.5hm2).

[0055] After the entire filled area is covered with soil and afforested, it will be returned to the local villagers. Attached Figure Description

[0056] Figure 1 This is a process flow diagram.

[0057] Figure 2 A flowchart for land reclamation operations involving filling ditches. Detailed Implementation

[0058] To make the objectives, advantages, and technical features of the present invention clearer, specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments.

[0059] This invention proposes a method for treating gangue that involves "from the inside out, from the bottom up, reducing the size of the pile, and compacting in layers," the steps of which are as follows:

[0060] Step 1: Use a truck to transport the loose gangue to the bottom of the gully. During the loading process, be careful to prevent landslides caused by the upper gangue to avoid loss of life and property.

[0061] Step 2: Use a bulldozer to level the gangue, and compact it after each 1m thick layer of gangue. It can effectively prevent gangue from settling;

[0062] Step 3: Cover every 2.0m thick layer of gangue with a 50cm thick layer of loess to isolate it from the air and prevent spontaneous combustion caused by heat buildup inside the gangue.

[0063] Step 4: Construct a walkway every 5 meters of height on the slope until the highest platform is reached. The walkways should be 5 meters wide, and drainage ditches should be built on the walkway platforms to prevent water from the slope from eroding the platform.

[0064] Step 5: The slope of the filling area is formed with a gradient of 1:2.0;

[0065] Step 6: Take steps 2-5 for the newly delivered gangue;

[0066] Step 7: When the site is piled up to the elevation, cover the top platform with 1m thick loess and carry out greening and afforestation.

[0067] Furthermore, this invention provides a more detailed process for land reclamation operations involving ditch filling, such as... Figure 2 As shown.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A soil covering and reclamation technology for coal gangue backfilling areas in the Loess Plateau, characterized in that: It includes a coal gangue backfilling treatment method that "works from the inside out, from the bottom up, shrinks and lifts, and compacts in layers", as well as the backfilling process, land reclamation operation process and key technologies.

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