Design method for soil layer structure of open pit coal mine dumping site in western arid and semi-arid region

Abstract

The invention belongs to the technical field of strip mine dumping design and ecological restoration, and discloses a design method for a soil layer structure of an open pit coal mine dumping site in a western arid and semi-arid region. The invention aims to solve the problem of poor permeability of the viscous surface soil layer of the dumping site at present by optimizing the design of the soil layer structure of the open pit coal mine dumping site in the western arid and semi-arid region from bottom to top by taking low-cost industrial solid wastes as raw materials and designing a geologic structure of'water-resisting layer-water-bearing layer-surface soil layer '. And the later ecological reclamation of the waste dump is facilitated.

Description

Technical Field

[0001] The invention belongs to the technical field of open-pit mine dumping design and ecological restoration, and in particular relates to a soil layer structure design method for an open-pit coal mine dumping yard in arid and semi-arid areas in western China. Background Art

[0002] Water is a key factor affecting the ecological reclamation effect of western mines. The mining of open-pit coal mines has caused serious damage to the original topsoil and shallow aquifers, and formed a large amount of rock and soil stripping. At the same time, the thermal power plants in the coal-fired power and chemical industrial parks also produce a large amount of industrial solid waste, such as fly ash and desulfurized gypsum. In order to reduce the adverse effects of open-pit coal mining on the geological and ecological environment, the rock and soil stripping produced by open-pit coal mining and the solid waste fly ash and desulfurized gypsum of coal-fired power plants are rationally stacked in the spoil dump to construct a "water-proof layer-aquifer-topsoil layer" reclamation soil layer structure that is conducive to the construction of the ecosystem, improve the water retention and permeability of the shallow soil in the open-pit mine spoil dump, and lay a good foundation for the near-natural ecological reclamation of the spoil dump.

[0003] At present, there are three ways to reconstruct and improve soil layers: physical, chemical, and biological. In the process of land reclamation, the type of matrix that is conducive to ecological restoration is generally reconstructed first, and topsoil substitutes are selected according to local conditions to effectively improve the physical and chemical properties and biological activity of the soil, thereby quickly restoring vegetation and improving ecological and environmental benefits. With the purpose of restoring the surface soil in the area damaged by mining, engineering and physical, chemical, and biological improvement measures are applied to rebuild a soil profile that can improve land productivity in a relatively short period of time. Soil reconstruction is the core of mining ecosystem restoration, and many scholars at home and abroad have conducted comparative studies on soil reconstruction models. The soil permeability of open-pit coal mine dumps in Northwest my country is low and the water conservation capacity is weak, resulting in poor ecological restoration effects. However, there is currently no effective solution, and there is still a lack of mature theoretical guidance for soil reconstruction and improvement in the reclamation of mining dumps.

[0004] CN114109389A discloses an aquifer in an open-pit mine dump and a reconstruction method thereof. During the stripping operation, the reconstructed aquifer rock and soil are selected, wherein the mechanical properties of the first type of rock and soil materials and the second type of rock and soil materials are similar to those of the original aquifer, and the particle size of the second type of rock and soil materials is larger than that of the first type of rock and soil materials; the third type of rock and soil materials have water-isolating properties. CN112982449A discloses an ecological reconstruction model of an open-pit mine dump, wherein a 100-200 cm water-isolating layer is set from bottom to top, with a permeability coefficient of 0.35-0.7 m / d and a compaction degree of 1200-1400 KPa; a 150-250 cm aquifer, with a permeability coefficient of 10-20 m / d and a compaction degree of 800-900 KPa; and a 40-60 cm topsoil ecological layer, which can utilize the topsoil layer stripped before mining or the topsoil layer with organic matter added.

[0005] Through the above analysis, the problems and defects of the prior art are as follows: the prior art CN114109389A aims to reconstruct a closed confined aquifer at a certain depth in the mining area. The three-layer sponge ecological structure and platform-slope structure described in CN112982449A are mainly aimed at preventing water from eroding the slope and reducing soil erosion. The synergistic effect of geological and ecological factors is not taken into account, and the reconstruction of the shallow soil structure and shallow hydrological circulation system (atmospheric precipitation-vadose zone-groundwater aquifer system) in the reclamation area is not considered. The actual difficulties of excessive clay in the stripped rock and soil in some mining areas in the northwest and the difficulty in absorbing solid waste (fly ash, desulfurized gypsum) in the adjacent industrial parks are not taken into account. It is necessary to adapt to local conditions, while quickly establishing a shallow water circulation system and improving soil structure, by adding an appropriate amount of industrial solid waste with high organic matter content to improve soil fertility, promote plant growth, and absorb industrial solid waste. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a method for designing the soil layer structure of an open-pit coal mine dump in arid and semi-arid areas in western China.

[0007] The present invention is implemented in this way: a soil layer structure design method for an open-pit coal mine dump in arid and semi-arid areas in western China comprises:

[0008] Step 1: Test the stripped soil layer to understand basic conditions such as soil type, soil physical properties, soil chemical properties, etc.

[0009] Step 2: Determine the depth range of the dumping site that needs to be optimized for three-dimensional design of the dumping scheme based on the constraints of the local ecological water level on vegetation growth;

[0010] Step 3: according to the permeability characteristics of the stripped soil layer, clay with low permeability is laid as a waterproof layer at the bottom of the target depth range, and compacted;

[0011] Step 4: Based on the permeability and water holding capacity characteristics of the stripped soil layer, a mixed soil with good permeability and water holding capacity is laid above the aquifer as an aquifer;

[0012] Step 5: Based on the drainage system characteristics of the dump, sand with good permeability is laid every 100m above the aquifer as an enhanced infiltration channel;

[0013] Step 6: Based on the permeability and physical and chemical characteristics of the stripped soil layer, a mixed soil with good permeability and sufficient fertility is laid above the aquifer as the topsoil layer;

[0014] Step 7: Set up a clay dam based on the scope of the spoil dump.

[0015] Further, in step 1, the content of sand particles in the stripped sandy soil is 84.7%, the content of silt particles is 3.52%, the content of clay particles is 11.78%, and the soil texture is sandy soil; the content of sand particles in the stripped red soil is 11.4%, the content of silt particles is 27.9%, the content of clay particles is 62.7%, and the soil texture is clay;

[0016] In step 1, the bulk density of the stripped sand is 1.66 g / cm 3 , moisture content is 4.31%, specific gravity is 2.5; stripping red soil bulk density is 1.40g / cm 3 , moisture content is 16.45%, specific gravity is 2.61.

[0017] Further, in step 1, the stripped sand has an electrical conductivity of 78 us / cm, a pH of 8.9, an organic matter content of 2.0 g / kg, an alkaline nitrogen content of 40 mg / kg, an effective phosphorus content of 6.1 mg / kg, an available potassium content of 176 mg / kg, and a total nitrogen content of 0.65 g / kg; the stripped red soil has an electrical conductivity of 81 us / cm, a pH of 8.9, an organic matter content of 2.8 g / kg, an alkaline nitrogen content of 14 mg / kg, an effective phosphorus content of 6.8 mg / kg, an available potassium content of 150 mg / kg, and a total nitrogen content of 0.63 g / kg.

[0018] Furthermore, in step 2, the optimal ecological water level in the arid mining areas of Northwest China is generally 1.5 to 3 meters. Combined with the thickness of the aquiclude, the depth range of the three-dimensional design optimization of the soil discharge scheme is within 3 meters.

[0019] Furthermore, in step 3, a clay waterproof layer is laid at a depth of 3 m from the ground surface and compacted, with a thickness of 0.6 to 1 m and a permeability coefficient of less than 0.001 m / d.

[0020] Furthermore, in step 4, an aquifer is laid on the aquiclude with a thickness of 1 to 2 m, and the permeability coefficient of the aquifer should be greater than 1 m / d. The aquifer can be made of a mixture of crushed sandstone and clay in a certain proportion, which has good water retention;

[0021] The clay particles contain 85% to 90% of clay particles, which is the clay layer stripped by mining, and the particle size of the crushed sandstone is 0 to 5 mm; the clay is air-dried and crushed and mixed with the crushed sandstone, and the bulk density of the mixed soil in the aquifer is 1.6 g / cm 3 ; The weight percentage of broken sandstone is 60% to 80%, and the weight percentage of clay is 20% to 40%.

[0022] Furthermore, in step 5, sand with good permeability is laid every 100 m above the aquifer as an infiltration channel with a thickness of 0.5 to 1 m, which is consistent with the topsoil layer.

[0023] Furthermore, in step 6, a topsoil layer is laid on the aquifer with a thickness of 0.5 to 1 m. The topsoil layer can be made of fly ash, desulfurized gypsum, stripped sand and clay mixed in a certain proportion, and is required to have sufficient fertility and good air permeability and permeability.

[0024] Furthermore, the clay content of the clay particles is 85% to 90%, which is the clay layer stripped from mining; the clay is air-dried and crushed, mixed with sand, and then fly ash and desulfurized gypsum are added. The bulk density of the mixed soil of the topsoil layer is 1.45g / cm 3 The weight percentage of sand is 40% to 60%, the weight percentage of clay is 20% to 40%, the weight percentage of fly ash is 10% to 30%, and the weight percentage of desulfurized gypsum is 10% to 30%.

[0025] Furthermore, the fly ash and desulfurized gypsum are industrial solid wastes generated by coal-fired power bases, and the content of toxic and harmful elements does not exceed the soil environmental quality standard GB 15618-2018 "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)";

[0026] In step 7, a clay dam is set at the edge of the spoil dump to connect the waterproof layer, and the material of the clay dam is consistent with that of the waterproof layer.

[0027] In combination with the above technical solutions and the technical problems solved, please analyze the advantages and positive effects of the technical solutions to be protected by the present invention from the following aspects:

[0028] First, in view of the technical problems existing in the above-mentioned prior art and the difficulty of solving the problems, the technical solutions to be protected by the present invention and the results and data during the research and development process are closely combined to analyze in detail and deeply how the technical solutions of the present invention solve the technical problems, and some creative technical effects brought about after solving the problems. The specific description is as follows:

[0029] The present invention provides a soil layer structure design method for an open-pit coal mine dump in arid and semi-arid areas in western China. The method aims to solve the problem that the current dump simply mixes the stripped soil and then piles it up, resulting in an unreasonable geological structure of the shallow soil layer in the dump, excessive clay content in the surface layer, poor permeability, and inability of irrigation and precipitation to effectively infiltrate, thereby forming surface runoff and causing the risk of engineering geological problems. In addition, since the soil layer in the dump is relatively homogeneous, there is no soil layer that can effectively store water below the surface soil layer, which has a serious impact on ecological construction. The present invention classifies the stripped soil according to its permeability by performing physical and chemical analysis on the soil quality of the stripped soil, and lays the clay with poor permeability as a waterproof layer in a deeper position. Since the thickness of the aeolian sand on the surface of the mining area is unevenly distributed and the total volume is not large, the sand material with good permeability is insufficient. Sandstone is crushed and mixed with clay in a certain proportion to replace the sand material as an aquifer. The two layers of soil can be regarded as a small "underground reservoir" for water storage; sand, clay, fly ash and desulfurized gypsum are mixed in a certain proportion to prepare the topsoil material, improve the permeability of the original clay topsoil, and promote irrigation and rainfall infiltration; the addition of fly ash causes the soil to be too alkaline, and the mixed addition of desulfurized gypsum can react with the fly ash to adjust the pH value. The combined action of the two can enhance soil fertility, increase soil nutrients, and improve soil structure; infiltration channels are laid at intervals in the topsoil layer to reduce the impact of surface runoff; clay dams are set at the edge of the soil layer range of the spoil dump to prevent excessive water infiltration from affecting the slope.

[0030] Among them, the purpose of the present invention is to use low-cost industrial solid waste as raw materials, optimize the soil layer structure design of open-pit coal mine dumps in arid and semi-arid areas in the west, and design a geological structure of "water-proof layer-aquifer-topsoil layer" from bottom to top, so as to solve the problem of poor permeability of the current clay topsoil layer in the dump, and facilitate the ecological reclamation of the dump in the later stage. Reconstructing the topsoil layer can not only meet the moisture conditions required for plant growth, but also serve as a good water infiltration channel; reconstructing the aquifer can stably maintain the groundwater level in a range suitable for plant growth, promote the benign circulation of groundwater and topsoil moisture, store moisture in the rainy season, and provide moisture for the topsoil layer in the dry season; the water-proof layer prevents the infiltration of shallow groundwater, which has an adverse effect on mining production and environmental safety.

[0031] Second, the expected benefits and commercial value after the technical solution of the present invention is as follows: first, after the technical solution of the present invention is transformed, the irrigation cost of the spoil dump reclamation area can be reduced, the shallow water circulation system can be quickly rebuilt in the early stage of reclamation, and the ecological restoration can be accelerated; secondly, it can solve the disposal problem of some mining solid wastes, reduce land pollution, and reduce its treatment cost; the reconstructed soil profile configuration has better soil water retention performance and better vegetation growth conditions than the soil profile configuration of the original landform. Through soil improvement, restoration and adjustment, the quality and suitability of the land can be improved, making it more suitable for the construction and operation of energy projects in mining areas, thereby greatly enhancing its commercial value.

[0032] Does the technical solution of the present invention solve the technical problem that people have been eager to solve but have never succeeded in solving: ecological restoration and governance in arid and semi-arid areas in the northwest are limited by the natural environment, especially the influence of water resources, and are technically difficult, require large capital investment, and have a long implementation cycle. It is urgent to develop a systematic, fast, low-cost, and easy-to-maintain ecological greening technology to coordinate the consumption of mine water and spoil dump substrates to form a self-sustaining three-dimensional ecological carbon sink area. The soil layer structure of the reclamation area can be redesigned to rebuild the shallow groundwater circulation system to improve the soil quality of the reclamation area and restore its ecological function, thereby promoting the construction and development of a three-dimensional ecological carbon sink area.

[0033] Third, the present invention proposes a soil layer structure design method suitable for open-pit coal mine dumps in arid and semi-arid areas in western China, and its main parameters include:

[0034] 1) Soil texture and physical parameters of stripped sand and stripped red soil:

[0035] The content of stripped sand is 84.7%, the content of silt is 3.52%, the content of clay is 11.78%, and the bulk density is 1.66g / cm 3 , specific gravity 2.5, water content 4.31%, conductivity 78us / cm, pH 8.9.

[0036] The stripped red soil has a sand content of 11.4%, a silt content of 27.9%, a clay content of 62.7%, and a bulk density of 1.40 g / cm 3 , specific gravity 2.61, water content 16.45%, conductivity 81us / cm, pH 8.9.

[0037] 2) Hydrological and permeability characteristics:

[0038] The optimal ecological water level in the arid mining areas of Northwest China is 1.5 to 3 meters, and the optimized design depth range of the soil discharge scheme is within 3 meters.

[0039] The permeability coefficient of the clay aquifer should be less than 0.001m / d, and the laying thickness should be 0.6 to 1m.

[0040] The permeability coefficient of the aquifer should be greater than 1m / d. It is a mixture of crushed sandstone and clay. The particle size of the crushed sandstone is 0-5mm. The bulk density of the aquifer is 1.6g / cm 3 , sandstone content is 60% to 80%, and clay content is 20% to 40%.

[0041] 3) Topsoil ratio and thickness:

[0042] The topsoil layer is 0.5 to 1 m thick and is a mixture of fly ash, desulfurized gypsum, stripped sand and clay in proportion; 40% to 60% sand, 20% to 40% clay, 10% to 30% fly ash and 10% to 30% desulfurized gypsum.

[0043] As industrial solid wastes, the content of toxic and harmful elements in fly ash and desulfurized gypsum complies with GB 15618-2018 "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standards".

[0044] Technical problems of existing technologies:

[0045] 1) The soil texture is simple and the permeability is poor:

[0046] Traditional spoil dumps do not fully utilize the physical and chemical properties of stripped sand and stripped red soil, resulting in poor water retention in the soil of the spoil dumps, which is prone to soil erosion or surface runoff.

[0047] 2) Ecological restoration is difficult:

[0048] A spoil dump without a layered design cannot form a topsoil layer suitable for plant growth. The soil is insufficiently fertile and has poor air permeability, making it difficult to restore vegetation cover.

[0049] 3) Hydrological conditions do not match:

[0050] The optimized design of the spoil dump does not fully consider the groundwater level and aquiclude, resulting in insufficient or excessive permeability, which affects water storage and regional hydrological balance.

[0051] 4) Low utilization rate of industrial solid waste:

[0052] The insufficient recycling of industrial solid wastes such as fly ash and desulfurization gypsum not only causes waste of resources but also increases the burden on the environment.

[0053] The method for solving the technical problem of the present invention is as follows:

[0054] 1) Layered optimization design of soil structure:

[0055] According to the texture difference between stripped sand and stripped red soil, combined with parameters such as water holding capacity and permeability, a multi-layer structure including a water-proof layer, an aquifer and a topsoil layer is designed within a depth of 3m to optimize the water balance of the dump.

[0056] 2) Introducing clay aquiclude:

[0057] A clay aquiclude with a thickness of 0.6 to 1 m is laid 3 m from the ground surface, with a permeability coefficient of less than 0.001 m / d, to avoid excessive groundwater leakage and form a stable ecological water level.

[0058] 3) Constructing aquifers:

[0059] The aquifer is a mixture of crushed sandstone and clay in proportion (60% to 80% sandstone, 20% to 40% clay), with a permeability coefficient greater than 1m / d, providing a lasting water supply for vegetation growth.

[0060] 4) Using industrial solid waste to improve topsoil:

[0061] Fly ash (10% to 30%) and desulfurized gypsum (10% to 30%) are added to the topsoil layer to improve fertility and air permeability, while increasing the environmental friendliness of the topsoil layer.

[0062] 5) Setting up permeable channels and clay dams:

[0063] Permeable sand is laid every 100m to form an infiltration channel to enhance the water replenishment capacity of the aquifer.

[0064] A clay dam connected to the aquiclude is constructed at the edge of the dump to prevent water loss at the boundary.

[0065] Significant technological advancements:

[0066] 1) Improve water storage and utilization efficiency:

[0067] Through the coordinated design of aquicludes, aquifers and permeable channels, water infiltration and storage can be effectively regulated, the appropriate ecological water level in the spoil dump can be maintained, and the moisture conditions required for vegetation restoration can be met.

[0068] 2) Improve soil fertility and ecological environment:

[0069] Industrial solid waste (fly ash, desulfurized gypsum) is introduced to improve the topsoil layer. At the same time, the characteristics of stripping sand and clay are combined to enhance the water holding capacity, air permeability and fertility of the topsoil layer, providing an ideal soil environment for plant growth.

[0070] 3) Reduce environmental burden and promote resource recycling:

[0071] Make extensive use of industrial solid waste from coal-fired power bases to reduce solid waste emissions, lower environmental pollution risks, and achieve efficient recycling and reuse of resources.

[0072] 4) Improve the stability and anti-erosion ability of the dump:

[0073] The optimized soil structure and clay dam design significantly improve the permeability and erosion resistance of the spoil dump, effectively preventing soil erosion and surface collapse.

[0074] 5) Provide universal design solutions for arid and semi-arid areas in western China:

[0075] The optimized design based on regional hydrological conditions and soil characteristics provides a soil structure construction method suitable for arid and semi-arid areas, and provides a technical reference for similar ecological restoration projects.

[0076] 6) Comprehensive ecological and economic benefits:

[0077] While improving the ecological environment, it also reduces restoration costs, increases the sustainable utilization value of coal mine spoil dumps, and provides strong support for local economic development.

[0078] The present invention rationally utilizes stripped sand, red soil and industrial solid waste, and combines the layered optimization design of the soil structure to effectively solve the shortcomings of traditional technologies in water regulation, soil fertility, and industrial solid waste utilization, and provides an efficient and low-cost solution for the ecological restoration of open-pit coal mine spoil dumps in arid and semi-arid areas in western China. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Figure 1 It is a flow chart of a soil layer structure design method for an open-pit coal mine dump in arid and semi-arid areas of western China provided by an embodiment of the present invention;

[0080] Figure 2 It is a soil profile schematic diagram of a soil layer structure design scheme for a spoil dump provided by an embodiment of the present invention;

[0081] Figure 3 It is a top view of the soil layer structure design scheme of the spoil dump provided by an embodiment of the present invention;

[0082] Figure 4 It is a schematic diagram of making aquifer mixed soil provided by an embodiment of the present invention;

[0083] Figure 5 This is a schematic diagram of making mixed soil for the topsoil layer provided by an embodiment of the present invention;

[0084] Figure 6 This is a schematic diagram of a small-scale on-site test provided by Example 2 of the present invention;

[0085] Figure 7 This is a small-scale field test data diagram provided by Example 2 of the present invention;

[0086] In the figure: 1. Mixed soil in the topsoil layer; 2. Water infiltration direction; 3. Mixed soil in the aquifer; 4. Phreatic level; 5. Clay dam; 6. Clay aquiclude; 7. Infiltration channel. DETAILED DESCRIPTION

[0087] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0088] In the reclamation area of ​​the Xiwan open-pit mine, the shallow water circulation system has been destroyed, resulting in a significant decrease in the permeability of the topsoil. Irrigation water or heavy rainfall cannot infiltrate effectively, and it is very easy to form surface runoff, which not only increases the demand for coal mine drainage facilities and energy consumption costs, but also weakens the soil's water conservation capacity, making the vegetation growth conditions in the reclamation area worse. In addition, the lack of sufficient water storage and regulation capacity in the topsoil has led to a tense water relationship in the reclamation area, high irrigation costs, and reduced soil carbon sequestration effects and ecological restoration efficiency.

[0089] In response to the above problems, this study intends to conduct innovative research and transformation of the soil structure in the reclamation area of ​​Xiwan open-pit mine. By fully considering multiple factors such as regional geology, climate, water resources and vegetation, it aims to reconstruct the near-surface soil layer, thereby repairing the shallow water circulation system in the mining area, improving water resource utilization efficiency, reducing drainage costs and energy consumption, enhancing the carbon sink function of the topsoil layer, and ultimately improving the ecosystem recovery capacity of the entire reclamation area.

[0090] The specific objectives of the research include: promoting the effective infiltration of precipitation and irrigation water through soil layer reconstruction, reducing surface runoff and drainage facility costs, and reducing the risk of soil erosion; improving soil moisture conservation capacity, constructing shallow aquifers near the surface, and realizing a hydrological regulation mechanism of water storage in the rainy season and water supply in the dry season, thereby reducing irrigation pressure and promoting vegetation growth; increasing soil organic matter and moisture content, enhancing carbon sequestration capacity, and allowing carbon dioxide in the atmosphere to be stored in soil organic matter through vegetation photosynthesis, thereby improving soil productivity and ecological restoration efficiency.

[0091] In the studied area, the red clay of the Neogene Baode Formation is widely distributed, with thickness ranging from several meters to more than 100 meters. This type of red clay has poor water permeability, is easy to stick when it rains, and is easy to become dry and compacted on sunny days, which poses a serious obstacle to the normal growth of crops in the reclamation area. Through the soil layer structure optimization and improvement measures of this study, it is expected to overcome the soil permeability and water retention problems brought by red clay, improve the ecological function and carbon sequestration capacity of the soil in the reclamation area, and thus achieve sustainable development of the region and overall improvement of environmental quality.

[0092] like Figure 1 As shown, a method for designing soil layer structure of an open-pit coal mine dump in arid and semi-arid areas in western China provided by an embodiment of the present invention comprises the following steps:

[0093] S101, test the stripped soil layer to understand the basic conditions such as soil type, soil physical properties, soil chemical properties, etc.;

[0094] S102, based on the constraints of local ecological water level on vegetation growth, determine the depth range of the dumping site that requires three-dimensional design optimization of the dumping scheme;

[0095] S103, according to the permeability characteristics of the stripped soil layer, laying clay with low permeability as a waterproof layer at the bottom of the target depth range, and compacting it;

[0096] S104, based on the permeability and water-holding characteristics of the stripped soil layer, a mixed soil with good permeability and water-holding properties is laid above the aquiclude as an aquifer;

[0097] S105: Based on the characteristics of the drainage system of the dump, sand with good permeability is laid every 100m above the aquifer as an enhanced infiltration channel;

[0098] S106, based on the permeability and physical and chemical characteristics of the stripped soil layer, a mixed soil with good permeability and sufficient fertility is laid above the aquifer as the topsoil layer;

[0099] S107, set up clay dam according to the scope of the spoil dump.

[0100] In S101 provided in the embodiment of the present invention, the content of sand particles in the stripped sandy soil is 84.7%, the content of silt particles is 3.52%, the content of clay particles is 11.78%, and the soil texture is sandy soil; the content of sand particles in the stripped red soil is 11.4%, the content of silt particles is 27.9%, the content of clay particles is 62.7%, and the soil texture is clay;

[0101] In S101, the bulk density of the stripped sand is 1.66 g / cm 3 , moisture content is 4.31%, specific gravity is 2.5; stripping red soil bulk density is 1.40g / cm 3 , moisture content is 16.45%, specific gravity is 2.61.

[0102] In S101 provided in an embodiment of the present invention, the stripped sand has an electrical conductivity of 78 us / cm, a pH of 8.9, an organic matter content of 2.0 g / kg, an alkaline nitrogen content of 40 mg / kg, an effective phosphorus content of 6.1 mg / kg, an available potassium content of 176 mg / kg, and a total nitrogen content of 0.65 g / kg; the stripped red soil has an electrical conductivity of 81 us / cm, a pH of 8.9, an organic matter content of 2.8 g / kg, an alkaline nitrogen content of 14 mg / kg, an effective phosphorus content of 6.8 mg / kg, an available potassium content of 150 mg / kg, and a total nitrogen content of 0.63 g / kg.

[0103] In S102 provided in the embodiment of the present invention, the optimal ecological water level in the arid mining area in Northwest China is generally 1.5 to 3 meters. Combined with the thickness of the aquiclude, the depth range of the three-dimensional design optimization of the soil discharge scheme is within 3 meters.

[0104] In S103 provided in the embodiment of the present invention, a clay waterproof layer is laid at a depth of 3 m from the ground surface and compacted, with a thickness of 0.6 to 1 m, and a permeability coefficient of less than 0.001 m / d.

[0105] In S104 provided in the embodiment of the present invention, an aquifer is laid on the aquiclude with a thickness of 1 to 2 m, and the permeability coefficient of the aquifer should be greater than 1 m / d. The aquifer can be configured by mixing crushed sandstone and clay in a certain proportion, and has good water holding capacity;

[0106] The clay particles contain 85% to 90% of clay particles, which is the clay layer stripped by mining, and the particle size of the crushed sandstone is 0 to 5 mm; the clay is air-dried and crushed and mixed with the crushed sandstone, and the bulk density of the mixed soil in the aquifer is 1.6 g / cm 3 ; The weight percentage of broken sandstone is 60% to 80%, and the weight percentage of clay is 20% to 40%.

[0107] In S105 provided in the embodiment of the present invention, sand with good permeability is laid every 100m above the aquifer as an infiltration channel with a thickness of 0.5 to 1m, which is consistent with the topsoil layer.

[0108] In S106 provided in the embodiment of the present invention, a topsoil layer with a thickness of 0.5 to 1 m is laid on the aquifer. The topsoil layer can be a mixture of fly ash, desulfurized gypsum, stripped sand and clay in a certain proportion, and is required to have sufficient fertility and good air permeability and permeability.

[0109] The clay provided in the embodiment of the present invention has a clay particle content of 85% to 90%, which is a clay layer stripped from mining; the clay is air-dried and crushed, mixed with sand, and then fly ash and desulfurized gypsum are added. The bulk density of the mixed soil in the topsoil layer is 1.45g / cm 3 The weight percentage of sand is 40% to 60%, the weight percentage of clay is 20% to 40%, the weight percentage of fly ash is 10% to 30%, and the weight percentage of desulfurized gypsum is 10% to 30%.

[0110] The fly ash and desulfurized gypsum provided in the embodiment of the present invention are industrial solid wastes generated by coal-fired power bases, and the content of toxic and harmful elements does not exceed the soil environmental quality standard GB 15618-2018 "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard (Trial)";

[0111] In S107 provided in the embodiment of the present invention, a clay dam is set at the edge of the spoil dump to connect the waterproof layer, and the material of the clay dam is consistent with that of the waterproof layer.

[0112] The present invention is specifically implemented:

[0113] In one embodiment, the present application provides a soil layer structure design method for an open-pit coal mine dump in arid and semi-arid areas in western China, which can be used for surface restoration of mining areas, including the following contents:

[0114] like Figure 2 , Figure 3As shown, a waterproof layer 6 is laid at a depth of 3m at the bottom of the spoil dump. The waterproof layer 6 is made of clay material stripped from the open-pit mine and is constructed by mechanical rolling consolidation during spoil discharge. The thickness of the waterproof layer is not less than 0.6m. The waterproof layer effectively blocks the infiltration of shallow surface water, helps to achieve phased reclamation of open-pit mines, and restore surface vegetation and the ecological environment.

[0115] like Figure 4 As shown, above the aquifer 6, a mixed material of clay and crushed sandstone is used to construct an aquifer 3 with a thickness of 1 to 2 m, and a water infiltration channel 7 is set up on the aquifer 3 at intervals of 100 to 150 m using sand material. In the rainy season, the infiltration channel 7 can prevent surface runoff caused by rainfall exceeding the absorption limit of the topsoil layer, and can help water to effectively infiltrate into the aquifer 3, so that the water is evenly distributed, and the aquifer 3 can improve the water storage efficiency; when the topsoil layer is dry, it can allow the water in the lower layer to penetrate into the upper soil layer through the aquifer through capillary action, providing the necessary water for vegetation growth.

[0116] like Figure 5 As shown, above the aquifer 3, a topsoil layer 1 with a thickness of 0.5 to 1 m is constructed using a mixture of clay, sand, fly ash and desulfurized gypsum. Sand is added to the clay to increase the porosity and permeability of the topsoil reconstruction material, thereby avoiding surface soil erosion and flood disasters. Fly ash can increase soil fertility, improve water retention, and promote plant water absorption. Desulfurized gypsum can regulate the increase in soil pH caused by excessive fly ash content and promote plant growth.

[0117] A clay dam 5 is set up according to the scope of the spoil dump to prevent the lateral loss of groundwater, reduce the adverse impact of groundwater on the slope of the spoil dump, and reduce safety hazards.

[0118] Example 1: Aquiclude-aquifer-topsoil integrated structure soil layer reconstruction method

[0119] As for the impermeable layer, according to the results of the investigation of the mine dumping process, the general principle of the current dumping process is to keep the rock stripping material at the bottom of the dumping site, lay a thick red clay (about 50m) on the bottom layer, and then lay a layer of sand (about 3m) on its surface. The thickness of red clay is much greater than the general impermeable layer thickness requirement (generally the impermeable layer thickness is required to be no less than 2m), and has a good impermeable effect. The double ring seepage test results of the dumping site soil showed that the soil permeability coefficient of the dumping site was 2.55×10 -5 cm / s~1.02×10 -3 cm / s. In the plane, the soil permeability of the spoil dump varies greatly. A small permeability coefficient indicates that there is more clay, resulting in poor regional permeability. A large permeability coefficient indicates that there is more sand and good permeability. The soil type of the spoil dump varies significantly in space, resulting in permeability differences, which also indirectly indicates the low permeability and good water-repellent properties of the clay layer.

[0120] For the aquifer, considering the uneven thickness distribution and small total volume of aeolian sand on the surface of the mining area, the reconstruction of the shallow aquifer faces the dilemma of insufficient sand and soil materials. Sandstone is crushed and mixed with clay as a substitute for sand to prepare aquifer materials. The collected sandstone is dried and crushed, sieved into four particle sizes of <2mm, 2mm~5mm, 5mm~8mm, and 8mm~10mm, and mixed with clay in different proportions. The orthogonal test is used to simplify the mixing scheme, and the saturated water content and field water holding capacity of aquifer materials with different proportions are tested. The aquifer material ratio is determined in combination with the permeability test of the aquifer material, the bulk density of the aquifer material is determined by the direct shear test, and the thickness of the aquifer material is determined by the capillary rise test. Finally, the material ratio scheme and aquifer thickness for reconstructing the aquifer are comprehensively determined. The bulk density of the aquifer mixed soil is 1.6g / cm3; the weight percentage of crushed sandstone is 60%~80%, the weight percentage of clay is 20%~40%, and the thickness is 1~2m.

[0121] For the topsoil layer, clay, sand, fly ash and desulfurized gypsum are selected as soil reconstruction filling materials to improve the water holding capacity of the topsoil layer and provide fertility for plant growth. Fly ash should generally not exceed 50% in the reconstructed soil. Sand and clay are used as the main materials, and fly ash and desulfurized gypsum are used as auxiliary materials in different proportions. As shown in Table 2, the topsoil ratio is comprehensively determined based on the saturated water content of the topsoil and the field water holding capacity test, the saturated hydraulic conductivity test, the soil column infiltration test, the infiltration simulation of the Hydrus software fixed head conditions and rainfall conditions. The bulk density of the mixed soil for the reconstructed soil layer is 1.45g / cm3; the weight percentage of sand is 40% to 60%, the weight percentage of clay is 20% to 40%, the weight percentage of fly ash is 10% to 30%, and the weight percentage of desulfurized gypsum is 10% to 30%. The thickness is determined to be 0.6 to 1m according to the water level required for plant root growth.

[0122] Example 2: On-site small-scale test results

[0123] The reconstructed soil layer structure in Example 1 was used to conduct a small-scale field test. The implementation diagram is shown in FIG. Figure 6 , moisture probes were installed at different depths in each soil layer, and two months of test data were selected for analysis as follows:

[0124] Aquitard: The sign of dividing aquifer and aquitard does not lie in whether the rock and soil layer contains water or the water content is high or low. The clay layer contains almost all bound water. Bound water is very difficult to move under natural conditions and has extremely poor permeability. Therefore, it is called an aquitard or a weakly permeable layer. Aquifers with relatively large pore size / aperture mainly contain gravity water, which can penetrate or discharge water under the action of gravity. From the aquifer (120, 180cm) to the aquitard (220, 260cm), water infiltrates from 120cm to 180cm in the aquifer, and the water content in the aquitard from 220 to 260cm does not change significantly, indicating the effectiveness of the aquitard. Figure 7 .

[0125] Aquifer: Due to the strong precipitation during the backfilling process of the field test, the experimental group used the stripped soil taken in the early stage, and the control group used the accumulated soil (red clay) affected by rainfall on site, resulting in inconsistent water content with the original soil of the dumping site. And because the consolidation degree of the refilled soil is low, and the natural consolidation of the soil lasts for a long time (generally several years), while the monitoring time is short, the current water content gradually decreases with the change of monitoring time. The water content of the experimental group increased from the topsoil layer to the aquifer, and the water content of the control group did not change significantly from the topsoil layer to the aquifer, and was basically stable. The water content of the shallow part of the aquifer is about 17% at this stage, and the water content of the deep part is about 43% at this stage, which is more than 31.38% higher than the water content of the original dumping site soil of 12.94%. The water content of the deep part of the aquifer is much greater than that of the shallow part. The water content above the field water holding capacity of the soil is not firmly adsorbed by the soil particles and can move under the action of gravity. Therefore, it can be considered that these water can flow freely. Therefore, it is shown that the reconstructed aquifer has the ability to store and conserve water. Since the implementation of the field test, the amount and intensity of atmospheric precipitation have been limited, the infiltration efficiency under unsaturated conditions is not high, the recharge to the aquifer is limited, and the water content of the aquifer does not change significantly with rainfall. Figure 7 .

[0126] Topsoil layer: From the monitoring data of the topsoil layer, it can be seen from the data of the experimental group and the control group in the figure that in precipitation weather, within the same period of time, the fluctuation range of the water content in the experimental group was significantly greater than that in the control group, and the overall water content in the experimental group was less than that in the control group, indicating that the reconstruction of the topsoil structure is more conducive to water infiltration than the original soil in the dumping site; at the same time, the monitoring data showed that rainfall had no significant effect on the soil layer below 40 cm in depth, and the control group was basically unaffected by rainfall. The moisture content of the 40 cm soil layer in the experimental group was affected to a certain extent, and the fluctuation was not as significant as that of the 20 cm layer, indicating that the precipitation intensity was limited, and the water migrated downward in an unsaturated state, with limited migration efficiency. The effect of the topsoil layer was Figure 7 .

[0127] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A soil layer structure design method for open-pit coal mine dumps in arid and semi-arid areas of western China, characterized in that: The following steps are involved: Step 1: Test the stripped soil layer to understand basic conditions such as soil type, soil physical properties, soil chemical properties, etc. Step 2: Determine the depth range of the dumping site that needs to be optimized for three-dimensional design of the dumping scheme based on the constraints of the local ecological water level on vegetation growth; Step 3: according to the permeability characteristics of the stripped soil layer, clay with low permeability is laid as a waterproof layer at the bottom of the target depth range, and compacted; Step 4: Based on the permeability and water holding capacity characteristics of the stripped soil layer, a mixed soil with good permeability and water holding capacity is laid above the aquifer as an aquifer; Step 5: Based on the drainage system characteristics of the dump, sand with good permeability is laid every 100m above the aquifer as an enhanced infiltration channel; Step 6: Based on the permeability and physical and chemical characteristics of the stripped soil layer, a mixed soil with good permeability and sufficient fertility is laid above the aquifer as the topsoil layer; Step 7: Set up a clay dam based on the scope of the spoil dump.

2. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 1, characterized in that: In the step 1, the content of sand particles in the stripped sandy soil is 84.7%, the content of silt particles is 3.52%, the content of clay particles is 11.78%, and the soil texture is sandy soil; the content of sand particles in the stripped red soil is 11.4%, the content of silt particles is 27.9%, the content of clay particles is 62.7%, and the soil texture is clay; In step 1, the bulk density of the stripped sand is 1.66 g / cm3, the moisture content is 4.31%, and the specific gravity is 2.5; the bulk density of the stripped red soil is 1.40 g / cm3, the moisture content is 16.45%, and the specific gravity is 2.

61.

3. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 1, characterized in that: In the step 1, the stripped sand has an electrical conductivity of 78 us / cm, a pH of 8.9, an organic matter content of 2.0 g / kg, an alkaline nitrogen content of 40 mg / kg, an effective phosphorus content of 6.1 mg / kg, an available potassium content of 176 mg / kg, and a total nitrogen content of 0.65 g / kg; the stripped red soil has an electrical conductivity of 81 us / cm, a pH of 8.9, an organic matter content of 2.8 g / kg, an alkaline nitrogen content of 14 mg / kg, an effective phosphorus content of 6.8 mg / kg, an available potassium content of 150 mg / kg, and a total nitrogen content of 0.63 g / kg.

4. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 1, characterized in that: In step 2, the optimal ecological water level in the arid mining areas of Northwest China is generally 1.5 to 3 meters. Combined with the thickness of the aquiclude, the depth range of the three-dimensional design optimization of the soil discharge scheme is within 3 meters.

5. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 1, characterized in that: In step 3, a clay waterproof layer is laid at a depth of 3 m from the ground surface and compacted, with a thickness of 0.6 to 1 m and a permeability coefficient of less than 0.001 m / d.

6. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 1, characterized in that: In step 4, an aquifer is laid on the aquiclude with a thickness of 1 to 2 m, and the permeability coefficient of the aquifer should be greater than 1 m / d. The aquifer can be made of crushed sandstone and clay mixed in a certain proportion, which has good water holding capacity; The clay particles contain 85% to 90% of clay particles, which is the clay layer stripped by mining, and the particle size of the crushed sandstone is 0 to 5 mm; the clay is air-dried and crushed and mixed with the crushed sandstone, and the bulk density of the mixed soil in the aquifer is 1.6 g / cm 3 ; The weight percentage of broken sandstone is 60% to 80%, and the weight percentage of clay is 20% to 40%.

7. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 1, characterized in that: In the step 5, sand with good permeability is laid every 100m above the aquifer as an infiltration channel with a thickness of 0.5 to 1m, which is consistent with the topsoil layer.

8. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 1, characterized in that: In step 6, a topsoil layer is laid on the aquifer with a thickness of 0.5 to 1 m. The topsoil layer can be made of fly ash, desulfurized gypsum, stripped sand and clay in a certain proportion, and is required to have sufficient fertility and good air permeability and permeability.

9. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 8, characterized in that: The clay content of the clay particles is 85% to 90%, which is the clay layer stripped from mining. The clay is air-dried and crushed, mixed with sand, and then fly ash and desulfurized gypsum are added. The bulk density of the mixed soil in the topsoil layer is 1.45g / cm 3 The weight percentage of sand is 40% to 60%, the weight percentage of clay is 20% to 40%, the weight percentage of fly ash is 10% to 30%, and the weight percentage of desulfurized gypsum is 10% to 30%.

10. The soil layer structure design method for open-pit coal mine dump in arid and semi-arid areas of western China as claimed in claim 8, characterized in that: The fly ash and desulfurized gypsum are industrial solid wastes generated by coal-fired power bases, and the content of toxic and harmful elements does not exceed the soil environmental quality standards; In step 7, a clay dam is set at the edge of the spoil dump to connect the waterproof layer, and the material of the clay dam is consistent with that of the waterproof layer.

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