A method for constructing a key layer of full mining under a building
By constructing a key layer and utilizing grouting reinforcement technology, the problems of resource waste and low mining efficiency in coal seam mining below buildings were solved, enabling full mining of coal resources while ensuring ground safety, and improving resource recovery rate and mining efficiency.
Patent Information
- Application Number
- CN202510276215.4
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2025-03-10
- Publication Date
- 2025-12-12
- Estimated Expiration
- 2045-03-10
AI Technical Summary
When mining coal seams beneath buildings using existing technologies, large coal pillars need to be reserved to ensure the safety of the surface buildings, resulting in resource waste. Furthermore, traditional mining methods are inefficient and complex, making it difficult to effectively release coal resources.
By constructing a key layer and using grouting reinforcement technology to enhance the stability of the rock strata, the coal seam mining process is optimized and ground subsidence is reduced. Grouting is carried out by directional horizontal drilling on the ground, and the optimal geometric dimensions and mechanical properties of the key layer are determined by discrete element numerical simulation to ensure that the key layer effectively supports the overlying rock strata during the mining process.
It significantly improves the recovery rate of coal resources, simplifies the mining process, reduces mining costs, reduces construction risks and surface subsidence, and improves mining efficiency and safety.
Smart Images
Figure CN120105742B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of mine strata control, and particularly relates to a method for constructing a key layer for full mining of coal under a building. BACKGROUND
[0002] With the exhaustion of coal resources, it has become an important issue to liberate the coal resources under buildings, such as the coal seams under ground buildings. On the one hand, due to the requirement of safety, the settlement of the ground building needs to be controlled, which results in the need to leave a large coal pillar under the building, thereby causing waste of resources. On the other hand, the mining of such coal seams generally uses the method of entry-type filling of small cross-section and small disturbance to recover the ore body, which not only has high process requirements, but also consumes time and effort, and has low efficiency. At present, there is an urgent need for a mining anti-disturbance technology that can ensure the safety of the ground building and liberate as much coal resources under the building as possible.
[0003] The key layer theory proposed in the prior art is used to guide the control of mine pressure, strata movement and surface subsidence in coal mining. In the key layer theory, the strata are divided into a main key layer and a sub-key layer. The main key layer refers to the strata that play a full control role in the process of overburden strata movement and destruction, and the sub-key layer plays a local control role on the upper strata movement. The key layer has a significant influence on the deformation and destruction of the overburden strata through its mechanical properties, thereby affecting the mine pressure behavior, overburden movement and surface subsidence. When the strength of the key layer rock is not enough or the water resistance performance is poor, a large coal pillar needs to be left under the building to prevent excessive ground settlement during the mining of the coal seam under the building, thereby causing waste of resources. SUMMARY
[0004] In view of the deficiencies in the prior art, the purpose of the embodiments of the present application is to provide a method for constructing a key layer for full mining of coal under a building. By constructing the key layer, the stability of the strata during the coal mining process is optimized, the ground settlement is reduced, the recovery rate of coal resources is improved, and the coal resources under the building are liberated under the premise of ensuring small ground settlement.
[0005] To achieve the above-mentioned purpose, the embodiments of the present application provide the following technical solutions:
[0006] A method for constructing a key layer under a building during full mining of coal, comprising the following steps: based on geological and surveying investigation, combined with coal seam occurrence, mining conditions and overburden geology data, a numerical model of coal seam mining under composite strata is constructed; based on the upper three zone theory, key layer theory and caving observation data, combined with the numerical model, the reasonable position of the key layer is determined; the lithology and grouting property of the rock mass where the key layer is located are analyzed to determine the grouting reinforcement method, and the geometric size and mechanical index of the key layer are determined by using discrete element numerical simulation; according to the mining range, mining conditions, stratum lithology and grouting diffusion, a grouting hole arrangement scheme is designed, ground directional horizontal drilling is used to reach the target horizon for grouting, and the key layer is constructed; through drilling and geophysical prospecting verification, whether the thickness, density and strength of the key layer meet the standards are analyzed.
[0007] Further, when constructing the numerical model, the mining conditions, goaf characteristics, number of overburden rock layers, lithology of each layer, thickness of each layer, and total thickness of the overburden rock are determined through geological and surveying investigation; the physical and mechanical properties of the rock samples are tested by drilling and extracting rock samples from typical profiles, and the physical and mechanical property parameters of the rock samples are determined; and the overburden rock geology numerical model is constructed based on the above information.
[0008] A comprehensive geological survey of the mining area is conducted, including coal seam burial depth, coal seam thickness, lithology distribution, groundwater conditions, and other geological obstacles. Accurate geological exploration data, such as drilling logs, groundwater levels, and seismic exploration data, are obtained.
[0009] Based on the actual exploration data, the stratum units are divided, and particular attention is paid to the characteristics of the overlying and underlying rock layers of the coal seam. Based on these geological data, a composite stratum model is constructed, taking into account factors such as lithology variation, rock strength, elastic modulus, porosity, and permeability.
[0010] A mechanical model of coal seam mining is established using the discrete element method (DEM). The model should include factors such as the mining process of the coal seam, stress-strain relationship, and pressure changes. Combined with actual geological data, the surface subsidence, deformation, and potential rock collapse risks after coal seam mining are simulated to provide a basis for subsequent steps.
[0011] Further, when determining the position of the key layer, the thickness of the caving zone and the fractured zone formed by the deformation and displacement of the overburden rock caused by coal seam mining is calculated using the numerical model, and the range of the bending subsidence zone is determined.
[0012] Through the key layer theory, the stability of the rock layers at the top and bottom of the coal seam is analyzed. The key rock layers that may be damaged during coal seam mining are determined, and their impact on surface subsidence, building stability, and other factors is evaluated.
[0013] Based on the upper three zone theory (i.e., caving zone, fractured zone, and bending subsidence zone) and key layer theory, the stability of key layers at different positions is evaluated by simulating different mining parameters.
[0014] Further, in determining the location of the key stratum, the deformation process of the surrounding rock during mining is simulated using discrete element numerical simulation software, the plastic failure range is determined, and the theoretical calculation results are combined to determine the structural location of the key stratum based on the safety principle of surrounding rock.
[0015] Further, in determining the key stratum parameters, the lithology of the rock mass where the key stratum is located is analyzed, including the mechanical properties, porosity, and fracture distribution of the rock mass, the injectability of the rock mass is analyzed, and the type and performance of the grout to be used are determined. These factors directly affect the grouting effect and the stability of the reinforced layer.
[0016] Based on the porosity and permeability of the rock mass, the grouting injectability of the rock mass is evaluated. For rock masses with high permeability, high flowability and low viscosity grouting fluid needs to be selected; while for dense rock masses, grouting fluid with higher viscosity needs to be used. Based on the injectability and lithological characteristics of the rock mass, a reasonable grouting reinforcement method is determined. For loose or broken rock layers, chemical grouting or cement grouting can be selected; while for relatively hard rock layers, resin grouting or expansion grouting can be selected.
[0017] Further, in determining the key stratum parameters, the discrete element numerical simulation software is used to construct a simulation of the coal mining process under the influence of the artificial key stratum, and multiple sets of variables are set for the key stratum size to study the influence of key strata with different physical and mechanical parameters on the settlement of ground buildings during coal mining, and finally determine the key stratum size and strength index.
[0018] Further, in building the key stratum, the key stratum size determines the grouting range, the construction conditions determine the drilling density, the stratum lithology determines the grouting fluid type and horizontal drilling method, and the grouting diffusion radius determines the drilling spacing to determine the final drilling and grouting scheme.
[0019] Further, in building the key stratum, the mining range and depth of the ore body are determined according to the coal mining plan; and the specific location of the grouting layer and the drilling density are determined based on the thickness, inclination and mining method of the coal seam.
[0020] Considering the geological conditions, environmental constraints, and construction equipment at the construction site, a reasonable drilling scheme is designed. In areas with high construction difficulty, the drilling density and depth should be increased to ensure that the grouting fluid can effectively penetrate the target layer.
[0021] Based on the stratum lithology and grouting fluid diffusion characteristics, the diffusion range of the grouting fluid under different grouting conditions is simulated to ensure that the grouting fluid can effectively reinforce the key stratum and prevent its collapse. Considering the different permeability of the rock mass, the grouting holes should be arranged in the favorable diffusion path.
[0022] The ground directional horizontal drilling technology is adopted to accurately reach the target layer for grouting through horizontal drilling.
[0023] After grouting is completed, the grout is fully coagulated and reaches the expected strength (usually 50%-70% of the initial setting strength), ensuring that it can effectively support the overlying rock and soil during coal mining.
[0024] Further, when detecting the key layer, drilling core sampling uses laboratory mechanical test analysis means, and geophysical means use transient electromagnetic method, direct current method, optical fiber micro-motion method, and microseismic monitoring technology combined with geophysical technology to verify the thickness, density, and strength of the key layer.
[0025] Using drilling technology, the key layer position is sampled and analyzed to detect the actual thickness, density, and strength of the key layer. Through laboratory testing of the drill core samples, it is confirmed whether the strength of the key layer meets the design requirements.
[0026] The transient electromagnetic method, direct current method, optical fiber micro-motion method, and microseismic monitoring technology combined with geophysical technology are used to verify the key layer, and the geophysical verification of the grouting layer is carried out. Through geophysical data analysis, it is confirmed whether the distribution and thickness of the key layer meet the design scheme.
[0027] Further, when detecting the key layer, if the verification result shows that the strength of the key layer is insufficient or the thickness does not meet the standard, the grouting scheme is adjusted, and the amount of grouting liquid is increased or the grouting hole position is adjusted.
[0028] The one or more technical solutions provided in the embodiments of the present application have at least the following technical effects or advantages:
[0029] By constructing an artificial key layer, the grouting reinforcement technology is used to enhance the mechanical properties of the rock layer, thereby reducing the coal pillar setting under the premise of ensuring the safety of the ground buildings, realizing the full mining of the coal seam under the buildings, and solving the problem of waste of coal resources caused by the setting of protective coal pillars in traditional mining methods, significantly improving the recovery rate of coal resources.
[0030] The discrete element numerical simulation software is used to optimize the key layer parameters to determine the optimal geometric size (length, thickness) and mechanical indicators (tensile, compressive strength, etc.) of the key layer, so that the key layer can effectively support the overlying rock layer during coal mining and reduce surface subsidence. For example, in the application example of a certain coal mine, by optimizing the key layer parameters, the maximum ground settlement is controlled within 0.23 meters, significantly reducing the risk of building damage.
[0031] By analyzing the lithology and grouting characteristics of the rock mass where the key stratum is located, selecting appropriate grouting materials and reinforcement methods, and enhancing the stability of the key stratum, the overlying strata can be effectively supported, reducing the occurrence of roof caving, rib spalling and other accidents during mining, thereby significantly improving the safety of mine exploitation.
[0032] By constructing an artificial key stratum, the full-mining process is allowed, avoiding the use of traditional access-type filling and other complex processes, simplifying the mining process, improving the mining efficiency, reducing the mining cost, and reducing the construction risks caused by complex processes.
[0033] Through geological and measurement investigation, combined with the coal seam occurrence conditions and the characteristics of the overlying strata, a numerical model for coal seam mining under composite strata is constructed. The model is used to analyze the deformation law of rock strata under different geological conditions, so as to optimize the parameter design of the key stratum. The design of the key stratum can be flexibly adjusted according to different geological conditions to ensure its effectiveness and stability in various complex geological environments.
[0034] By discrete element numerical simulation, the optimal position and parameters of the key stratum are determined, the damage to the overlying strata during mining is reduced, the development height of the fractured zone is reduced, the risk of groundwater connection is effectively reduced, the groundwater resources are protected, and the damage to the ecological environment on the ground is reduced.
[0035] By reducing the coal pillar, the coal resource recovery rate is improved, the mining process is simplified, and the mining cost is reduced. In addition, by effectively controlling the ground subsidence, the maintenance cost caused by building damage is reduced, the resource recovery rate is improved, the mining cost is significantly reduced, and significant economic benefits are obtained.
[0036] The advantages of the additional aspects of the present application will be given in the following description, some of which will become apparent from the following description, or will be understood by those skilled in the art through practice of the present application. BRIEF DESCRIPTION OF DRAWINGS
[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or the prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments described in the present application, and those skilled in the art can also obtain other drawings according to these drawings without creating any creative labor.
[0038] Figure 1 is a schematic diagram of the overall method of the present application;
[0039] Figure 2 is a stress model diagram of the key stratum of the present application;
[0040] Figure 3 is a schematic diagram of the horizontal drilling and grouting of the present application;
[0041] Figure 4 is a schematic diagram of the key layer structure horizon of the present application;
[0042] Figure 5 is a numerical model diagram of the coal seam mining of the embodiment;
[0043] Figure 6 is a diagram of the influence of the coal seam mining on the surrounding rock displacement of the embodiment;
[0044] Figure 7 is a numerical model diagram of the coal seam mining under the influence of key layers of different sizes of the embodiment;
[0045] Figure 8 is a diagram of the overburden deformation displacement caused by the coal seam mining under the influence of key layers of different sizes of the embodiment;
[0046] Figure 9 is a column diagram of the maximum ground subsidence under the influence of key layers of different sizes of the embodiment;
[0047] Figure 10 is a numerical simulation diagram under the condition of zero ground subsidence of the embodiment.
[0048] In the figure: 1, uniform load of overburden; 2, key layer; 3, lower rock mass support; 4, horizontal borehole; 5, rock layer where the key layer is located; 6, coal seam. DETAILED DESCRIPTION
[0049] It should be noted that the following detailed description is exemplary and is intended to provide further explanation of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. In addition, it should also be understood that the terms "comprise" and / or "include" as used in this specification indicate the presence of a feature, step, operation, device, component and / or combinations thereof.
[0050] Explanation of terms:
[0051] Upper three-zone theory: refers to the three different deformation characteristic rock layer regions formed in the overburden due to the influence of mining, namely, the caving zone, the fractured zone and the bending subsidence zone. This theory is an important theoretical basis for analyzing and predicting the surface subsidence, rock movement and groundwater resource protection, etc. caused by coal seam mining.
[0052] Caving observation data refers to the data and information obtained by monitoring and recording the deformation, damage and collapse of the overlying strata during coal mining. These data provide important support for theoretical analysis, key layer position determination, numerical simulation verification, mining plan optimization and safety assessment, and are indispensable basic data in coal mining engineering.
[0053] The embodiment proposes a method for constructing a key layer for full mining of coal under a building, which includes the following steps (as shown in Figure 1
[0054] In the first step, based on actual geology and survey, combined with geological data, coal seam occurrence, coal seam mining and overburden conditions of coal seam roof, a numerical model of coal seam mining under composite strata is constructed;
[0055] In the second step, based on the "upper three zones" theory, key layer theory and coal mining caving observation data, theoretical analysis and numerical simulation of coal mining are carried out to determine the reasonable position of the key layer 2 to be constructed;
[0056] In the third step, the lithology and grouting characteristics of the rock mass at the position of the key layer 2 are analyzed, the grouting reinforcement method is determined, and the influence law of different key layer 2 parameters is explored by using discrete element numerical simulation software to determine the geometric size (length, width, thickness, etc.) and mechanical indexes (tensile, compressive strength and deflection, etc.) of the key layer 2;
[0057] In the fourth step, according to the mining range of the ore body, the coal mining conditions, the stratum lithology and the grouting diffusion, the grouting hole arrangement scheme is designed, the ground directional horizontal drilling technology is used to reach the target horizon for grouting, and the key layer 2 is constructed;
[0058] In the fifth step, the key layer 2 is inspected and detected, and the thickness, density and strength of the key layer 2 are analyzed to determine whether they meet the standards through drilling and geophysical prospecting verification.
[0059] In the first step, a comprehensive geological survey of the mining area is carried out, including coal seam burial depth, coal seam thickness, lithology distribution, underground water conditions and other geological obstacles. Accurate geological exploration data such as drilling log, underground water level, seismic exploration data, etc. are obtained.
[0060] According to the actual exploration data, the stratum units are divided, and the characteristics of the overlying and underlying rock layers of the coal seam are particularly concerned. Combined with these geological data, a composite stratum model is constructed, considering factors such as lithology change, rock strength, elastic modulus, porosity, permeability, etc. A mechanical model of coal mining is established by using the discrete element method (DEM), laying a theoretical foundation for the subsequent steps.
[0061] The second step determines the position of the key layer.
[0062] Using the physical and mechanical properties of each rock stratum obtained in the first step, calculate the collapse zone H formed by the deformation and displacement of the overlying rock mass caused by coal mining. K and fracture zone H li The height is used to determine the range of the bending subsidence zone. Relevant calculation formulas are shown in Tables 1 and 2. Where ∑M represents the cumulative mining thickness; the formula applies to single-layer mining thicknesses of 1–3 m, with a cumulative mining thickness not exceeding 15 m; the ± sign in the calculation formula represents the mean square error.
[0063] Table 1. Formulas for calculating the caving zone height in layered mining of thick coal seams.
[0064]
[0065] Table 2. Formulas for calculating the height of water-conducting fracture zones in layered mining of thick coal seams.
[0066]
[0067] The distance range between key layer 2 and coal seam 6 is:
[0068] H g ≥H k +H li (I)
[0069] Based on the numerical model constructed in the first step, a numerical simulation of the coal seam mining process is performed to obtain the range of the plastic failure zone. If the maximum distance from the upper boundary of the plastic zone to the coal seam is H1, then to ensure the safety of the critical stratum, considering both the numerical simulation and theoretical calculation results, the distance range between the critical stratum and the coal seam is as follows:
[0070] H g ≥max(H k +H li ,H1)(II)
[0071] Based on the theory of elasticity, such as Figure 2 As shown, the stress on the key layer is simplified to a uniformly distributed load 1 from the overlying rock and a thin plate (lower rock mass support 3) with rectangular supports on all four sides. The expression for its maximum deflection is:
[0072]
[0073] in The flexural stiffness of the plate is the sum of the loads from the overlying rock layers. a, b, and h represent the length, width, and thickness of the key layer, respectively. E represents the elastic modulus of the rock layer, and v represents Poisson's ratio of the rock layer.
[0074] The maximum stress value is:
[0075]
[0076] Generally, the key layer is placed in a rock formation with high porosity, which ensures good injectability and improves the strength of the rock formation to a great extent, reducing the impact of ground deformation. The original thickness, strength, and surrounding rock properties are good.
[0077] The third step is to determine the grouting parameters and key layer size. First, conduct a detailed analysis of the rock mass where the key layer is located, considering factors such as rock strength, brittleness, porosity, and fracture development. These factors directly affect the grouting effect and the stability of the reinforced layer.
[0078] Based on the porosity and permeability of the rock mass, evaluate the grouting injectability of the rock mass. For rock masses with high permeability, high-flowing and low-viscosity grouting fluid is required, while for dense rock masses, grouting fluid with higher viscosity is needed. Based on the injectability and lithological characteristics of the rock mass, determine the appropriate grouting reinforcement method. For loose or broken rock layers, chemical grouting or cement grouting can be selected, while for harder rock layers, resin grouting or expansion grouting can be chosen.
[0079] Set multiple variables for key layer size, use discrete element numerical simulation software (such as UDEC) to simulate coal seam mining, study the influence of key layer with different physical and mechanical parameters on the settlement of ground buildings during coal seam mining, and finally determine the appropriate key layer size and strength index.
[0080] The fourth step is to design the grouting scheme. The key layer size determines the grouting range, the construction conditions determine the drilling density, the stratum lithology determines the type of grouting fluid and the horizontal drilling method, and the grouting diffusion radius determines the drilling spacing. Based on the comprehensive conditions, determine the final drilling and grouting scheme.
[0081] According to the coal mining plan, determine the mining range and depth of the ore body. Based on the thickness, inclination, and mining method of the coal seam, determine the specific location of the grouting layer and the drilling density. Considering factors such as geological conditions, environmental restrictions, and construction equipment at the construction site, design a reasonable drilling scheme. In areas with high construction difficulty, increase the drilling density and depth to ensure that the grouting fluid can effectively penetrate the target layer.
[0082] Based on the stratum lithology and grouting fluid diffusion characteristics, simulate the diffusion range of the grouting fluid under different grouting conditions to ensure that the grouting fluid can effectively reinforce the key layer and prevent its collapse. Considering the different permeability of the rock mass, the grouting holes should be arranged in the favorable diffusion path.
[0083] Use ground directional horizontal drilling technology (such as shown in Figure 3 ), accurately reach the target layer (the rock layer where the key layer is located 5) for grouting through horizontal drilling 4. This technology can reduce the impact on the surrounding stratum and buildings, improve construction precision and efficiency. Finally, a high-strength and dense key layer is formed in the target stratum,Figure 4 As shown.
[0084] The fifth step is to test the constructed key layer performance. After grouting is completed, the slurry is fully coagulated and reaches the expected strength (usually 50%-70% of the initial strength), ensuring that it can effectively support the coal seam during mining.
[0085] Using drilling technology, sample analysis is conducted on the key layer position to detect the actual thickness, density and strength of the key layer. Through laboratory testing of the drill core samples, it is confirmed whether the strength of the key layer meets the design requirements.
[0086] Geophysical exploration technology is used to verify the key layer, including transient electromagnetic method, direct current method, optical fiber micro-motion method and microseismic monitoring technology. Through geophysical data analysis, it is confirmed whether the distribution and thickness of the key layer meet the design scheme.
[0087] If the verification result shows that the key layer strength is insufficient or the thickness does not meet the standard, the grouting scheme is adjusted in time to increase the amount of grouting liquid or adjust the grouting hole position, ensuring the safety and stability of the key layer.
[0088] Example 1
[0089] Taking a certain coal mine as an example, through analysis of geological data, a mechanical model and numerical model of the influence of thick coal seam mining on ground subsidence are constructed to determine the position, thickness and size parameters of the key layer, and the influence of the constructed key layer on strata subsidence under coal seam mining conditions is studied. The main mineable coal seam in the coal mine is 3# coal, with an average thickness of 7m and an average burial depth of 889m, and there is a 517m soil layer.
[0090] A numerical model is established based on the simplified information of the coal mine strata. As shown in Figure 5 , the types of strata rock bodies from top to bottom are loose layer, siltstone, fine sandstone, sandy mudstone, 3# coal, fine sandstone and sandy mudstone.
[0091] According to the formulas provided in Table 1 and Table 2, H k = 16.58m and H li = 31.46m, so the distance between the key layer and the coal seam should be no less than 48.04m.
[0092] The numerical model is calculated to study the influence of coal seam excavation on ground subsidence, as shown in Figure 6 . The results show that coal seam excavation causes the overlying rock mass to collapse and deform, causing ground subsidence and forming a damage zone with an upper boundary distance of 128m from the coal seam. Based on the theoretical calculation results, the distance between the key layer and the coal seam should be no less than 128m.
[0093] According to the stratum information, the key layer is finally determined to be set at a distance of 142 m from the coal seam height, that is, at the junction of fine sandstone and siltstone, the porosity is larger, which is suitable for grouting, and the grouting improvement effect is better.
[0094] In this example, the length and thickness of the key layer are studied to affect the stability of the key layer. According to the length of the working face of 800 m, the length of the key layer is set to 960 m, 1120 m, 1280 m and 1440 m, and the thickness is 20 m, 40 m, 60 m and 80 m. Form 16 groups of working conditions, corresponding to f1, f2, f3, f4, f5, f6, f7, f8, f9, f10, f11, f12, f13, f14, f15 and f16, as shown in Figure 7 .
[0095] The numerical simulation results are arranged as Figure 8 , the maximum ground settlement corresponding to each group of working conditions is plotted as Figure 9 , with the increase of the thickness and span of the key layer, the maximum ground settlement decreases, and the span has a greater impact than the thickness. Considering the construction cost and other factors, the thickness of 60 m and the length of 1280 m of the key layer size are the best, and the maximum ground settlement is 0.23 m.
[0096] The ground is required to have no settlement, and through numerical simulation, as shown in Figure 10 , the thickness of the key layer is 100 m, and the length is 1440 m.
[0097] Although the specific embodiments of the present application are described above in combination with the drawings, it is not a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.
Claims
1. A method for constructing a key layer under a building, characterized in that, The method comprises the following steps: Based on geological and surveying investigation, combined with coal seam occurrence, mining conditions and overburden strata geological data, a numerical model of coal seam mining under composite strata is constructed; Based on the upper three zone theory, key layer theory and caving observation data, combined with the numerical model, the reasonable position of the key layer is determined; when determining the position of the key layer, the numerical model is used to calculate the thickness of the caving zone and the fractured zone formed by the deformation displacement of the overburden strata caused by coal seam mining, so as to determine the range of the bending subsidence zone; And the discrete element numerical simulation software is used to simulate the deformation process of the surrounding rock of mining, to determine the plastic failure range, combined with the theoretical calculation results, to determine the structural position of the key layer according to the safety principle of surrounding rock; The lithology and grouting property of the rock mass where the key layer is located are analyzed, the grouting reinforcement mode is determined, and the geometric size and mechanical index of the key layer are determined by using discrete element numerical simulation, wherein the discrete element numerical simulation software is used to construct the simulation of the coal seam mining process under the influence of the artificial key layer, a plurality of variables are set according to the size of the key layer, the influence law of the key layer with different physical and mechanical parameters on the settlement of the ground building in the process of coal seam mining is studied, and finally the size and strength index of the key layer are determined; According to the mining range, mining conditions, strata lithology and grouting diffusion, a grouting hole arrangement scheme is designed, ground directional horizontal drilling is adopted to reach the target layer for grouting, and the key layer is built. Through drilling and geophysical prospecting verification, whether the thickness, density and strength of the key layer meet the standards are analyzed.
2. The method according to claim 1, wherein, When constructing the numerical model, the mining conditions, goaf characteristics, overburden strata layers, lithology of each layer, thickness of each layer, and total thickness of the overburden strata are determined through geological and surveying investigation; the physical and mechanical performance parameters of the ore rock sample are determined by testing the physical and mechanical performance of the ore rock sample extracted by typical profile drilling, and the geological numerical model of the overburden strata of the coal seam is constructed based on the above information.
3. The method according to claim 1, wherein, When determining the parameters of the key layer, the lithology of the rock mass where the key layer is located is analyzed, including the mechanical properties, porosity and fracture distribution of the rock mass, the grouting property of the rock mass is analyzed, and the type and performance of the grouting fluid used are determined.
4. The method of constructing a key layer for full-seam mining under a building as claimed in claim 1, wherein, When building the key layer, the size of the key layer determines the grouting range, the construction conditions determine the hole density, the strata lithology determines the type of grouting fluid and the horizontal drilling method, and the grouting diffusion radius determines the hole spacing, and the final drilling and grouting scheme is determined.
5. The method of constructing a key layer for full-seam mining under a building as claimed in claim 1, wherein, When building the key layer, the mining range and depth of the ore body are determined according to the coal mining plan; the specific position of the grouting layer and the hole density are determined according to the thickness, inclination and mining method of the coal seam.
6. The method of constructing a key layer for full-seam mining under a building as claimed in claim 1, wherein, When detecting the key layer, the drilling core is analyzed by laboratory mechanical test means, and the thickness, density and strength of the key layer are verified by using transient electromagnetic method, direct current method, optical fiber micro-motion method and microseismic monitoring technology combined with geophysical prospecting technology.
7. The method of constructing a key layer for full-seam mining under a building as claimed in claim 1, wherein, When detecting the key layer, if the verification result shows that the strength of the key layer is insufficient or the thickness does not meet the standards, the grouting scheme is adjusted, and the amount of grouting fluid is increased or the grouting hole position is adjusted.