Method for evaluating mining-induced water inrush and sand inrush danger after grouting transformation of loose aquifer

Abstract

The invention discloses a method for evaluating mining-induced water inrush and sand inrush dangerousness after grouting transformation of a loose aquifer, which specifically comprises the following steps of: firstly, obtaining hydrogeological characteristics and parameters before and after grouting of the loose aquifer, and evaluating a grouting transformation effect; the method comprises the steps that firstly, a working face geologic prototype is established, then a hydrogeological engineering geologic model after grouting of a research area is established in combination with the working face geologic prototype, then a water inrush source is determined based on physical simulation and numerical simulation test results of the geologic model, and a water inrush source criterion thematic map, a mining influence criterion thematic map and a water inrush channel criterion thematic map are established; and finally obtaining a danger contour map in the research area and carrying out area division. The mining influence, the water inrush source and the water inrush channel factors are considered, the corresponding criterion thematic maps are accumulated and summed to obtain the danger contour map in the research area, area division is performed, the mining water inrush and sand inrush danger after grouting of the unconsolidated aquifer can be accurately evaluated, and a basis is provided for safe mining of a coal mine.

Description

Technical Field

[0001] The invention relates to water inrush and sand burst technology, belongs to the field of coal seam mining, and specifically relates to a method for evaluating the hazard of water inrush and sand burst caused by mining after grouting transformation of a loose aquifer. Background Art

[0002] Water and sand burst is a kind of mine geological disaster in which a water-sand mixed fluid with a high sand content bursts into the underground working face of a coal mine during mining near loose layers, causing property losses and casualties. When mining coal seams, it is necessary to evaluate the danger of water and sand burst caused by mining, so as to formulate reasonable mining plans and prevention and control measures, facilitate timely discovery and elimination of safety hazards, and ensure safe production in mines.

[0003] At present, the hazard assessment of water inrush and sand burst is mainly aimed at the overburden of the coal seam roof under mining. For example, the Chinese invention patent with the publication number CN116611567A: A method for zoning prediction of the hazard of water inrush from the overburden roof of a mining area, which can predict the hazard of water inrush from the roof separation layer by zoning, grading and classification. However, in large-scale and high-intensity coal mining near loose layers or weathering zones, due to the high mining height and fast footage, especially under the geological conditions of thin bedrock and thick loose layers, there is a problem of water inrush and sand burst induced by large-scale roof shearing in the mining area, which seriously affects the safe production of mines.

[0004] For the exploitation of loose aquifers, it is necessary to perform grouting transformation to meet the conditions for safe exploitation. Specifically, by grouting in the loose aquifer to form a skeleton fixed structure, the water-richness of the transformation area can be reduced, making it weakly water-rich or nearly drained Class III water body, while improving the stratum strength, thereby avoiding water inrush and sand burst during underground mining; At present, there are relatively few hazard assessments for loose layers, especially after grouting transformation, and there is a lack of comprehensive consideration of water inrush sources, water inrush channels, and mining impacts. Therefore, it is very important to construct a systematic water inrush and sand burst hazard assessment method for loose aquifers after grouting transformation, combining spatial multi-criteria decision-making, considering multiple factors such as water inrush sources, water inrush channels, and mining impacts. Summary of the invention

[0005] The purpose of the present invention is to provide a method for evaluating the hazard of water inrush and sand burst caused by mining after grouting transformation of loose aquifers. Taking into account the factors of mining impact, water source of water inrush and water inrush channel, the corresponding criterion thematic maps are accumulated and summed to obtain the hazard contour map in the study area, and regional division is performed. This method can accurately evaluate the hazard of water inrush and sand burst caused by mining after grouting of loose aquifers, and provide a basis for safe mining of coal mines.

[0006] To achieve the above purpose, a method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers is provided, which is characterized by:

[0007] The specific steps include:

[0008] S1, obtain the hydrogeological characteristics and parameters of the engineering geology before and after grouting of the loose aquifer in the coal mine roof, and evaluate the effect of grouting transformation;

[0009] S2, based on the geological prototype of the working face and the hydrogeological characteristics and parameters before and after grouting in step S1, construct a hydrogeological engineering geological model of the study area after grouting, and conduct physical and numerical simulation tests;

[0010] S3, based on the results of the physical simulation and numerical simulation tests in step S2, determine the source of the water inrush, and construct the thematic map of the water inrush source criteria, the thematic map of the mining impact criteria, and the thematic map of the water inrush channel criteria in combination with the hydrogeological characteristics and parameters before and after the grouting in step S1;

[0011] S4, obtain the hazard contour map of the study area and divide the area into regions.

[0012] In some examples of the present invention, step S1 specifically includes the following steps:

[0013] S1-1, obtain samples of loose aquifers in the coal mine roof before and after grouting by drilling and coring, analyze the particle grading characteristics of the water-bearing sand layer before grouting, the diffusion and occurrence of slurry after grouting, and conduct uniaxial compression tests on the core samples to test their compressive strength;

[0014] S1-2, obtain the hydrogeological parameters before and after grouting based on the pumping test and water pressure test. The hydrogeological parameters before and after grouting include: water permeability, unit water yield, and permeability coefficient. Then determine the water richness, permeability grade, thickness and water level of the ungrouted area and the grouting area of ​​the loose aquifer, and then analyze the grouting effect;

[0015] S1-3, collect water samples from each aquifer after grouting, analyze the water quality difference between the grouting area and the non-grouting area through conventional ion comparison of water samples, and comprehensively evaluate the slurry diffusion effect;

[0016] S1-4, determine the level of water mining in the study area;

[0017] According to the hydrogeological characteristics and parameters of engineering geology before and after grouting, the grouting transformation effect of the loose aquifer after grouting was evaluated in terms of water richness and permeability level, slurry diffusion effect, and water body mining level.

[0018] In some examples of the present invention, in step S2, in the physical simulation test, the mining process of the model is tracked and photographed, and computer image processing technology is used to perform instantaneous feature image processing on the process of overburden movement and change and the overburden damage state during the mining process, so as to obtain the development morphology and spatial characteristics of the collapse zone and the water-conducting fracture zone in the physical model test;

[0019] On the basis of physical simulation, numerical simulation software was used to establish an engineering geological model to simulate the collapse and failure law of overburden rock during the working face mining process after grouting, obtain the stress field, displacement field change curves and overburden rock crack development process at different stages, and measure the development height of the collapse zone and water-conducting fracture zone after the working face mining is completed.

[0020] In some examples of the present invention, in step S2, based on the geological prototype of the working face and according to the drilling exploration data of the mining area, the coal seam burial depth and coal seam thickness data are obtained;

[0021] Based on physical and numerical simulation tests, the development height of the collapse zone and the water-conducting fracture zone is obtained, and the contour map of the overburden failure height is obtained by combining the different mining heights of the un-grouting area and the grouting area;

[0022] Based on the statistical data of underground exploration boreholes, the contour map of the proportion of overlying mudstone is obtained.

[0023] In some examples of the present invention, in step S3,

[0024] Considering the water-richness, permeability, thickness and water level of the ungrouted and grouted areas of the loose aquifer, and taking them as sub-criteria of the water source of water inrush, the weighted information entropy and criterion weight of the water source criterion evaluation process are calculated, and the thematic map of the water source criterion of water inrush is constructed.

[0025] Taking the thickness and burial depth of coal seams as sub-criteria of mining impact criteria, the weight information entropy and criterion weight of the mining impact criteria evaluation process are calculated, and the mining impact criteria thematic map is constructed.

[0026] Taking the overburden failure height and the overburden mudstone ratio as the sub-criteria of the water inrush channel criterion, the overburden failure height and the overburden mudstone ratio are obtained according to the different mining heights in the grouting area and the non-grouting area, and the thematic map of the water inrush channel criterion is constructed.

[0027] In some examples of the present invention, in step S4,

[0028] First, the thematic map of water inrush source criteria, the thematic map of mining impact criteria, and the thematic map of water inrush channel criteria are normalized, and the weights of water inrush source criteria, mining impact criteria, water inrush channel criteria and corresponding sub-criteria are calculated, and then the cumulative sum is performed to obtain the hazard contour map in the study area.

[0029] In some examples of the present invention, in step S4, the region division includes

[0030] Class I danger zone: There is no area where RC ≥ 0.65;

[0031] Category II more dangerous area: the area where 0.50≤RC<0.65;

[0032] Category III relatively safe area: the area where 0.40≤RC<0.50;

[0033] Category IV safety zone: area where RC < 0.40;

[0034] Among them, RC is the hazard coefficient, which can be obtained from the hazard contour map.

[0035] Compared with the existing technology, this method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers obtains the hydrogeological characteristics and parameters of engineering geology before and after grouting of loose aquifers, and establishes corresponding geological models for physical and numerical simulation experiments. The water-richness, permeability, thickness and water level of the un-grouting area and the grouting area of ​​the loose aquifer are used as sub-criteria to construct the thematic map of water inrush source criteria, the thickness of coal seams and the buried depth of coal seams are used as sub-criteria to construct the thematic map of mining impact criteria, and the overburden damage height and the proportion of overburden mudstone are used as sub-criteria to construct the thematic map of mining impact criteria. The sub-criteria construct thematic maps of water inrush channel criteria, and the hazard contour map in the study area is obtained by accumulating the thematic maps of water inrush sources, mining impacts, and water inrush channel criteria. The region is divided according to the hazard coefficient, which can accurately evaluate the hazard of water inrush and sand burst after grouting in loose aquifers, providing a basis for safe mining in coal mines. In addition, combined with the engineering geological and hydrogeological characteristics and parameters of the working face, mining is simulated through physical simulation and numerical simulation to obtain parameters such as collapse zones and water-conducting fracture zones that are difficult to obtain in the actual mining process. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the overall flow chart of the present invention;

[0037] Figure 2 is a particle grading diagram of a sand sample in an embodiment of the present invention;

[0038] Figure 3 It is a thematic map of water source criteria for water inrush during 5 days of exploitation in an embodiment of the present invention;

[0039] Figure 4 It is a thematic map of water source criteria for water inrush during 100 days of exploitation in an embodiment of the present invention;

[0040] Figure 5 It is a thematic map of water source criteria for water inrush during 155 days of exploitation in an embodiment of the present invention;

[0041] Figure 6 It is a thematic map of mining impact criteria in an embodiment of the present invention;

[0042] Figure 7 is a thematic map of water burst channel criteria in an embodiment of the present invention;

[0043] Figure 8 is a contour map of the danger of roof water inrush and sand burst after 5 days of mining in an embodiment of the present invention;

[0044] Fig. 9 This is a contour map of the danger of roof water inrush and sand burst after 100 days of mining in an embodiment of the present invention;

[0045] Fig.10 This is a contour map of the danger of roof water inrush and sand burst after 155 days of mining in an embodiment of the present invention. DETAILED DESCRIPTION

[0046] In order to make the purpose, technical solution and advantages of the technical solution of the present invention clearer, the technical solution of the embodiment of the present invention will be clearly and completely described in conjunction with the drawings of specific embodiments of the present invention. The same figure marks in the drawings represent the same parts. It should be noted that the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the described embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0047] Unless otherwise defined, the technical terms or scientific terms used herein shall have the usual meanings understood by persons of ordinary skill in the field to which the present invention belongs. The words "first", "second" and similar words used in the patent application specification and claims of the present invention do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one" or "one" do not necessarily indicate a quantity limitation. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0048] like Figure 1 As shown, the present invention provides a method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers, which specifically includes the following steps:

[0049] S1, obtain the hydrogeological characteristics and parameters of the engineering geology before and after grouting of the loose aquifer in the coal mine roof, and evaluate the effect of grouting transformation;

[0050] S1-1, obtain samples of loose aquifers in the coal mine roof before and after grouting by drilling and coring, analyze the particle grading characteristics of the water-bearing sand layer before grouting, the diffusion and occurrence of slurry after grouting, and conduct uniaxial compression tests on the core samples to test their compressive strength;

[0051] Specifically, the grouting boreholes and plane structure of the loose aquifer are designed first, and the borehole spacing, number of boreholes, and location are determined according to the distribution range of the working surface and ground buildings;

[0052] In the process of grouting transformation of loose aquifers, appropriate grouting materials are selected according to geological conditions, grouting process parameters are determined, and grouting construction is carried out; the drilling plan during the construction process is optimized, and grouting parameters are scientifically selected and applied. For example, the "four aquifers" in the study area are shallowly buried, with an average burial depth of 270m and uneven thickness. The components include gravel, sand gravel, clay gravel, coarse sand, medium sand and clay sand, etc. The "four aquifers" with complex lithology and relatively soft lithology should be treated by extrusion splitting grouting. It is necessary to establish a skeleton to fix the loose strata, and use grouting extrusion to reduce the water-richness of the "four aquifers" for treatment. For example, the grouting project adopts the segmented downward type and orifice closed static pressure grouting method for grouting; for example, ordinary silicate cement is selected as the grouting material in the early stage, and fly ash with good fluidity and stability is added to the grouting material later, which is suitable for solving the problem of excessive slurry diffusion radius during construction;

[0053] Then core the borehole to obtain samples of the loose aquifer before and after grouting;

[0054] Then, the samples before and after grouting are analyzed: before grouting, the particle grading characteristics of the loose aquifer are determined, such as the particle size analysis of the loose aquifer samples to obtain data such as effective particle size, intermediate particle size, boundary particle size, non-uniformity coefficient, curvature coefficient, etc., to determine the proportion of each particle group and the particle grading diagram of the sand sample, and combined with the diffusion and occurrence of the slurry after grouting, uniaxial (high-pressure consolidation test) and dynamic triaxial rheological tests are carried out to observe the axial and circumferential deformation of the samples;

[0055] S1-2, obtain the hydrogeological parameters before and after grouting based on the pumping test and water pressure test. The hydrogeological parameters before and after grouting include: water permeability, unit water yield, and permeability coefficient. Then determine the water richness, permeability grade, thickness and water level of the ungrouted area and the grouting area of ​​the loose aquifer, and then analyze the grouting effect;

[0056] Specifically, according to the unit water yield q value of the borehole, the water richness of the loose aquifer is divided into the following four levels:

[0057] Weak water-rich: q≤0.1L / (s·m);

[0058] Moderate water richness: 0.1L / (s·m)<q≤1.0L / (s·m);

[0059] Strong water-richness: 1.0L / (s·m)<q≤5.0L / (s·m);

[0060] Extremely water-rich: q>5.0L / (s·m);

[0061] According to the permeability coefficient K and the water permeability Q, as shown in Table 1, the permeability level is classified:

[0062] Table 1 Permeability grade classification

[0063]

[0064] S1-3, collect water samples from each aquifer after grouting, analyze the water quality difference between the grouting area and the non-grouting area through conventional ion comparison of water samples, and comprehensively evaluate the slurry diffusion effect;

[0065] S1-4, determine the level of water mining in the study area;

[0066] The evaluation of grouting transformation effect can determine and test the water-richness and permeability level, slurry diffusion effect, and water body mining level of loose aquifers after grouting transformation based on the hydrogeological characteristics and parameters of engineering geology before and after grouting;

[0067] The water mining level can be determined according to the hydrogeological characteristics and parameters of engineering geology before and after grouting. Specifically, when the water mining level is I, the water body types may include: 1. Various surface water bodies directly above the bedrock or below the bottom interface without a stable clay soil aquifer; 2. Loose interstitial strong and medium aquifer water bodies directly above the bedrock or below the bottom interface without a stable clay soil aquifer; 3. Bedrock strong and medium aquifer water bodies without a stable mudstone aquifer under the bottom interface; 4. Various surface water bodies and loose aquifer water bodies above steeply inclined coal seams; 5. Water bodies that are required to be protected as important water sources and tourist destinations; at this time, water-conducting fracture zones are not allowed to affect the water body; the types of safe coal rock pillars required to be left: roof waterproof safe coal rock pillars;

[0068] When the water mining level is II, the water body types may include: 1. Small and medium-sized water bodies on the ground with a loose layer with multi-layer structure, large thickness and weak water content below the bottom interface, or a strong aquifer in the middle and upper parts of the loose layer and a weak aquifer in the lower part; 2. Water bodies in the middle and upper parts of the loose layer with strong and medium pores and aquifers with stable thick clay soil impermeable layers or loose weak aquifers below the bottom interface; 3. Water bodies in loose layers and bedrock weak aquifers with drainage conditions; at this time, the water-conducting fracture zone is allowed to affect the water body in the loose porous weak aquifer, but the collapse zone is not allowed to affect the water body; the types of safe coal rock pillars required to be left: roof sand prevention safe coal rock pillars;

[0069] When the water mining level is III, the water body types may include: 1. Water bodies in the middle and upper porous weak aquifers of the loose layer with a stable thick clay soil impermeable layer under the bottom interface; 2. Water bodies in the loose layer or bedrock that have been or are close to being drained; at this time, the water-conducting fracture zone is allowed to enter the loose porous weak aquifer, and the collapse zone is allowed to affect the weak aquifer; the type of safe coal rock pillar required to be left: roof collapse prevention safe coal rock pillar.

[0070] S2, based on the geological prototype of the working face and the hydrogeological characteristics and parameters of the engineering geology before and after grouting in step S1, construct a hydrogeological engineering geological model of the study area after grouting, and conduct physical and numerical simulation tests;

[0071] Specifically, based on the geological prototype of the working face and the drilling exploration data of the mining area, the coal seam burial depth and coal seam thickness data are obtained; based on the geological prototype of the working face and the hydrogeological characteristics and parameters before and after grouting, a hydrogeological engineering geological model after grouting is established. In terms of physical simulation, the model can be tested in different directions and scenarios indoors, and auxiliary stress and displacement sensors are used for monitoring on the model to simulate and obtain the morphology and quantitative data of the roof mining and destruction process at different stages of the mining process;

[0072] The mining process of the model is tracked and photographed. At the same time, the relevant movement and damage state parameters can be manually measured, and the computer image processing technology can be used to process the instantaneous characteristic images of the overburden movement change process and the overburden damage state during the mining process, so as to obtain the development morphology and spatial characteristics of the collapse zone and water-conducting fracture zone in the physical model test;

[0073] On the basis of physical simulation, the engineering geological model was established using 3DEC numerical simulation software, and further analysis was carried out on the activities of the roof overburden during the mining process of the working face, that is, the collapse and failure laws of the overburden during the mining process of the working face after grouting were simulated, the stress field and displacement field change curves at different stages and the overburden fracture development process were obtained, and the development height of the collapse zone and the water-conducting fracture zone was measured after the mining of the working face was completed;

[0074] For example, when analyzing the development of overburden cracks, the characteristic images of crack development and expansion under different advancement steps can be processed to analyze the impact of grouting transformation on the development of overburden cracks. The overburden crack development map under different mining steps after inversion processing is imported into the FracLab software to calculate the fractal dimension. By obtaining the fractal dimensions of overburden cracks under different mining steps before and after grouting, the fractal dimension evolution diagram of overburden cracks is drawn.

[0075] Based on physical and numerical simulation tests, the development morphology and spatial characteristics of the collapse zone and water-conducting fracture zone at different stages are obtained, that is, the development height of the collapse zone and the development height of the water-conducting fracture zone, and combined with the different mining heights of the un-grouting area and the grouting area, the contour map of the overburden failure height is obtained; based on the statistical data of the underground exploration boreholes, the contour map of the proportion of overburden mudstone is obtained;

[0076] The corresponding overburden failure height and overburden mudstone proportion data can be obtained through the overburden failure height contour map and the overburden mudstone proportion contour map;

[0077] S3, based on the results of the physical simulation and numerical simulation tests in step S2, determine the source of the water inrush, and construct the thematic map of the water inrush source criteria, the thematic map of the mining impact criteria, and the thematic map of the water inrush channel criteria in combination with the hydrogeological characteristics and parameters before and after the grouting in step S1;

[0078] Specifically, the source of water inrush is determined based on the results of the physical and numerical simulation tests of the model. For example, the source of water inrush is analyzed by the height of the water-conducting fracture zone in the model. That is, when the roof aquifer is thin and the water-conducting fracture zone affects the aquifer, there is a safety risk of water inrush and sand burst, and the affected aquifer water becomes the source of water inrush.

[0079] According to the hydrogeological parameters of the aquifer after grouting obtained in step 1, and considering the drilling data (roof and floor elevations), historical water level and drawdown data in the grouting area, a hydrogeological numerical model is established in the GMS software to simulate the impact of coal seam mining on the aquifer water level, and obtain the water level evolution diagram of different mining stages (which can be divided into stages according to the number of mining days); the water-richness, permeability, thickness and water level of the un-grouting area and the grouting area of ​​the loose aquifer are comprehensively considered as sub-criteria of the water inrush source, and the weight information entropy and criterion weight of the water inrush source criterion evaluation process are calculated. Therefore, based on GIS-WLC, a thematic map of the water inrush source criterion is constructed; it is explained that the stronger the water-richness of the aquifer, the better the permeability, the greater the thickness and the higher the water level, the greater the risk of mine water inrush.

[0080] In the mining process of the model in step S2, due to the influence of mining, the overall entropy of the overburden system increases, the order of the overburden system decreases, and the disorder increases. Considering the thickness and burial depth of the coal seam as sub-criteria of the mining influence criterion, the criterion weights of each sub-criteria are calculated using the information entropy method. Therefore, based on GIS-WLC, a thematic map of the mining influence criterion is constructed;

[0081] In step S1, for the study area after grouting, the mine water inrush channel may be formed in the collapse zone, so the overburden damage height and the overburden mudstone ratio are used as sub-criteria of the water inrush channel criterion; in step S2, physical and numerical simulation experiments are carried out to simulate mining by physical simulation and numerical simulation to obtain parameters such as the collapse zone and water-conducting fracture zone that are difficult to obtain in the actual mining process. For the different mining heights between the un-grouting area and the grouting area, the overburden damage height and the overburden mudstone ratio are obtained, so as to construct a thematic map of the water inrush channel criterion.

[0082] S4, obtain the hazard contour map in the study area and divide the area;

[0083] In some examples of the present invention, in step S4, the water inrush source criterion thematic map, the mining impact criterion thematic map, and the water inrush channel criterion thematic map are first normalized, the weights of the water inrush source criterion, the mining impact criterion, the water inrush channel criterion and the corresponding sub-criterion are calculated, and then the weights are accumulated and summed to obtain the hazard contour map in the study area;

[0084] Specifically, the sub-criteria of the water source criterion include the water richness of the aquifer, the permeability of the aquifer, the thickness of the aquifer and the water level; the sub-criteria of the mining impact criterion include the thickness of the coal seam and the buried depth of the coal seam; the sub-criteria of the water inrush channel criterion include the height of the overburden damage and the proportion of overburden mudstone;

[0085] This example uses the information entropy criterion weight solution method, which is based on the established thematic maps of each criterion, standardizes each thematic layer, and directly calculates the weight information entropy and weight of each criterion;

[0086] In some examples of the present invention, in step S4, the region division includes

[0087] Class I danger zone: There is no area where RC ≥ 0.65;

[0088] Category II more dangerous area: the area where 0.50≤RC<0.65;

[0089] In this area, the mining height needs to be reduced, monitoring needs to be strengthened, emergency equipment needs to be prepared in advance, and other water prevention and control measures need to be taken to ensure safe mining;

[0090] Category III relatively safe area: the area where 0.40≤RC<0.50;

[0091] The main role in this area is the mining impact criteria, and the formulation of relevant water prevention and control measures during mining can ensure safe mining;

[0092] Category IV safety zone: area where RC < 0.40;

[0093] After the grouting transformation, this area can be fully guaranteed to be successfully mined, so it belongs to the safe area;

[0094] Among them, RC is the hazard coefficient, which can be obtained from the hazard contour map.

[0095] Example

[0096] The study area is a working face of Wugou Coal Mine after grouting transformation. The loose aquifer after grouting is the fourth aquifer at the bottom of the Neogene (hereinafter referred to as "fourth aquifer"):

[0097] S1, obtain the engineering geological and hydrogeological characteristics and parameters of the "four inclusions" of the coal mine roof before and after grouting, and evaluate the grouting transformation effect;

[0098] First, the sand samples before grouting were sampled, such as Figure 2 As shown, its effective particle size d 10 =0.005mm, middle particle size d 30 =0.1mm, critical particle size d 60 =0.45mm, non-uniformity coefficient C u =90, curvature coefficient C c =4.44, so the loose aquifer has poor particle gradation and is likely to cause water inrush and sand burst under a certain hydraulic gradient.

[0099] Sampling of the "four inclusions" after grouting revealed that the cement slurry after grouting was obviously attached to the irregular surface of the gravel, and also filled the cracks in the gravel. Due to the development of pores and cracks in the gravel, the slurry can easily diffuse and fill the cracks and loose pores of the gravel under a certain pressure, "displacing" the groundwater from the gaps to the surrounding areas, reducing the effective water storage space of the gravel after grouting, inducing the weakening of water-richness and strengthening of mechanical strength, thereby achieving the engineering purpose of grouting treatment to improve the "four inclusions";

[0100] Mechanical tests were conducted on the cores taken from the weathering zone before and after grouting. The uniaxial compressive strength of the bedrock weathering zone rock before grouting was about 1.96-2.18MPa, and the uniaxial compressive strength of the weathering zone rock after grouting was 3.03-11.10MPa. Compared with the uniaxial compressive strength of the weathering zone rock mass, the uniaxial compressive strength of the weathering zone increased by 2-5 times after grouting treatment.

[0101] Secondly, the samples before and after grouting were subjected to pumping test and water pressure test; after grouting transformation of the "four aquifers", the unit water inflow of the "four aquifers" was significantly reduced; before grouting, the unit water inflow was 0.0017~0.1352L / (s·m), the water permeability was 22.68~21.43Lu, the permeability coefficient was 0.000013~0.000504cm / s, and the aquifer was weakly water-rich and moderately permeable; after grouting, the unit water inflow was 0.0000075-0.000076L / (s·m), the water permeability was 0.27~1.06Lu, the permeability coefficient was 0.0000001~0.0000080cm / s, and the aquifer was weakly water-rich and weakly permeable. It can be seen that after grouting transformation, the "four aquifers" changed from aquifers to loose porous weak aquifers, and the grouting transformation effect was good;

[0102] Then, the water quality data of the aquifer observation wells and the old empty water of some working faces were collected for analysis. The conventional ion content of the aquifer water after grouting transformation was compared with the conventional ion content of the water quality of different aquifers in other working faces. It was found that the water quality characteristics of the aquifer after grouting transformation were more inclined to the water quality characteristics of the old empty water. It can be determined that the chemical field of the "four-containing" water has changed after grouting transformation, indicating that the slurry diffuses well in the aquifer;

[0103] Finally, according to the above engineering geological and hydrogeological parameters, it is determined that the water body mining level should be level III, and the mining degree is to allow the water-conducting fracture zone to enter the loose porous weak aquifer, and at the same time allow the collapse zone to affect the weak aquifer, leaving a roof anti-collapse safety coal rock pillar;

[0104] S2. A hydrogeological engineering geological model after grouting was established based on the geological prototype of the working face to obtain the coal seam burial depth and coal seam thickness data. The strike section of the model has a length × width × height = 300 cm × 30 cm × 180 cm, and the dip section has a length × width × height = 200 cm × 30 cm × 180 cm. Displacement and pressure sensors were arranged on the model to study the overburden destruction laws of the coal seams in different mining processes after grouting in the "four-containing" and weathered oxygen zones of the working face. The development morphology and spatial characteristics of the "two zones" at different stages, namely the development morphology and spatial characteristics of the collapse zone and water-conducting fracture zone in the physical model test, were obtained, the fracture development process during the model mining process was observed, and the influence curves of mining disturbance on the stress and displacement of the monitoring points were quantitatively monitored; the development heights of the collapse zone and water-conducting fracture zone in the model test are shown in Table 2.

[0105] Table 2 Development height of collapse zone and water-conducting fracture zone in physical simulation test

[0106]

[0107] On the basis of physical simulation, 3DEC numerical simulation was used to simulate the roof mining damage during coal seam mining and the overburden collapse damage law during the working face mining process after grouting, and the stress field and displacement field change curves at different stages and the temporal and spatial development process of overburden fractures were obtained. After the working face was mined, the development height of the collapse zone and water-conducting fracture zone was measured. The development height of the collapse zone and water-conducting fracture zone in the numerical simulation test is shown in Table 3.

[0108] Table 3 Development height of collapse zone and water-conducting fracture zone in numerical simulation test

[0109] Section Type Height of collapse zone (m) Height of water-conducting fracture zone (m) Trend profile 13.82 61.14 Dip section 18.88 57.21

[0110] S3, according to the model test results in step 2, the water-conducting fracture zone may affect the "four-containing" aquifer, so the "four-containing" aquifer is determined as the water-inrush aquifer, and the thematic map of the water-inrush source criterion is constructed;

[0111] The contribution of the water-richness, permeability, thickness and water level of the aquifer to the evaluation object is positively correlated. This is used as the criterion for the source of water inrush. The weighted information entropy and criterion weight of the water inrush source criterion evaluation process are calculated and shown in Table 4. Finally, the thematic layer of the water inrush source criterion is obtained based on GIS-WLC, as shown in Figures 3 to 5 shown.

[0112] Table 4 Information entropy and weight of the evaluation process of water inrush source criteria

[0113] Sub-criteria Water-rich Permeability thickness Water Level Weight Information Entropy 0.97 0.99 0.98 0.98 Criteria Weight 0.38 0.13 0.29 0.20

[0114] According to the results of the physical simulation and numerical simulation tests in step S2, a thematic map of mining impact criteria and a thematic map of water inrush channel criteria are constructed;

[0115] Specifically, according to the coal seam depth data collected from the drilling exploration data and the two-lane geological profiles, a coal seam depth distribution map of the working face is established. The contribution of coal seam depth and coal seam thickness to the evaluation object is positively correlated, that is, as the coal seam depth sub-criterion value increases, the risk of water inrush and sand inrush from the coal mine roof also increases, and as the coal seam mining thickness sub-criterion value increases, the risk of water inrush from the coal mine roof increases;

[0116] The weight information entropy and criterion weight of the mining impact criterion evaluation process are calculated and shown in Table 5. Finally, the mining impact criterion thematic map is obtained based on GIS-WLC, as shown in Figure 6 As shown;

[0117] Table 5 Weight information entropy and criterion weights in the mining criterion evaluation process

[0118] Guidelines Coal seam thickness Coal seam depth Weight Information Entropy 0.99 0.99 Criteria Weight 0.393 0.607

[0119] According to the physical simulation and numerical simulation of similar material models, the overburden damage height contour map is obtained for different mining heights in the grouting area and the non-grouting area. That is, the higher the overburden damage height, the higher the degree of disturbance and damage in the collapse zone, and the higher the risk of water inrush channel disasters. Conversely, the risk of water inrush channel disasters is lower. According to the statistical data of underground exploration boreholes, the contour map of the overburden mudstone ratio is obtained. That is, as the sub-criterion value of the overburden mudstone ratio increases, the risk of water inrush and sand inrush from the coal mine roof decreases. The overburden damage height formed in the collapse zone and the overburden mudstone ratio are superimposed to form a thematic map of the water inrush channel criterion, such as Figure 7 As shown;

[0120] S4, the method for solving the criterion weight based on information entropy is to calculate according to the established thematic maps of each criterion, standardize each thematic layer, and directly calculate the weight information entropy of each criterion. The weight information entropy and weight of each criterion are shown in Table 6. The criterion thematic maps of water inrush source, mining impact, and water inrush channel are accumulated and summed to obtain the hazard contour map in the study area.

[0121] Table 6 Information entropy and weight of each criterion

[0122] Guidelines Water burst channel Water source Impact of mining Weight Information Entropy 0.98 0.95 0.97 Criteria Weight 0.28 0.48 0.24

[0123] like Figures 8 to 10As shown in the figure, from the evaluation zoning of spatial multi-criteria decision-making on the hazard of water inrush and sand burst in the working face of the study area, it can be seen that there is no dangerous area in the grouting area, and only a small part of the non-grouting area of ​​the study area has a high potential risk, with RC above [0.50, 0.65]; the risk of some areas is low, with RC below 0.40, and the rest has medium hazard.

[0124] The above text describes in detail an exemplary implementation method of a method for evaluating the hazard of water inrush and sand burst caused by mining after grouting transformation of a loose aquifer proposed in the present invention with reference to a preferred embodiment. However, it can be understood by those skilled in the art that, without departing from the concept of the present invention, various modifications and variations can be made to the above-mentioned specific embodiments, and various technical features and structures proposed in the present invention can be combined in various ways without exceeding the protection scope of the present invention, which is determined by the attached claims.

Claims

1. A method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers, characterized in that: The specific steps include: S1, obtain the hydrogeological characteristics and parameters of the engineering geology before and after grouting of the loose aquifer in the coal mine roof, and evaluate the effect of grouting transformation; S2, based on the geological prototype of the working face and the hydrogeological characteristics and parameters before and after grouting in step S1, construct a hydrogeological engineering geological model of the study area after grouting, and conduct physical and numerical simulation tests; S3, based on the results of the physical simulation and numerical simulation tests in step S2, determine the source of the water inrush, and construct the thematic map of the water inrush source criteria, the thematic map of the mining impact criteria, and the thematic map of the water inrush channel criteria in combination with the hydrogeological characteristics and parameters before and after the grouting in step S1; S4, obtain the hazard contour map of the study area and divide the area into regions.

2. The method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers according to claim 1 is characterized in that: Step S1 specifically includes the following steps: S1-1, obtain samples of loose aquifers in the coal mine roof before and after grouting by drilling and coring, analyze the particle grading characteristics of the water-bearing sand layer before grouting, the diffusion and occurrence of slurry after grouting, and conduct uniaxial compression tests on the core samples to test their compressive strength; S1-2, obtain the hydrogeological parameters before and after grouting based on the pumping test and water pressure test. The hydrogeological parameters before and after grouting include: water permeability, unit water yield, and permeability coefficient. Then determine the water richness, permeability grade, thickness and water level of the ungrouted area and the grouting area of ​​the loose aquifer, and then analyze the grouting effect; S1-3, collect water samples from each aquifer after grouting, analyze the water quality difference between the grouting area and the non-grouting area through conventional ion comparison of water samples, and comprehensively evaluate the slurry diffusion effect; S1-4, determine the level of water mining in the study area; According to the hydrogeological characteristics and parameters of engineering geology before and after grouting, the grouting transformation effect of the loose aquifer after grouting was evaluated in terms of water richness and permeability level, slurry diffusion effect, and water body mining level.

3. The method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers according to claim 1 is characterized in that: In step S2, in the physical simulation test, the mining process of the model is tracked and photographed, and computer image processing technology is used to perform instantaneous feature image processing on the process of overburden movement and change and the overburden damage state during the mining process, so as to obtain the development morphology and spatial characteristics of the collapse zone and the water-conducting fracture zone in the physical model test; On the basis of physical simulation, numerical simulation software was used to establish an engineering geological model to simulate the collapse and failure law of overburden rock during the working face mining process after grouting, obtain the stress field, displacement field change curves and overburden rock crack development process at different stages, and measure the development height of the collapse zone and water-conducting fracture zone after the working face mining is completed.

4. The method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers according to claim 3 is characterized in that: In step S2, based on the geological prototype of the working face and the drilling exploration data of the mining area, the coal seam burial depth and coal seam thickness data are obtained; Based on physical and numerical simulation tests, the development height of the collapse zone and the water-conducting fracture zone is obtained, and the contour map of the overburden failure height is obtained by combining the different mining heights of the un-grouting area and the grouting area; Based on the statistical data of underground exploration boreholes, the contour map of the proportion of overlying mudstone is obtained.

5. The method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers according to claim 4 is characterized in that: In step S3, Considering the water-richness, permeability, thickness and water level of the ungrouted and grouted areas of the loose aquifer, and taking them as sub-criteria of the water source of water inrush, the weighted information entropy and criterion weight of the water source criterion evaluation process are calculated, and the thematic map of the water source criterion of water inrush is constructed. Taking the thickness and burial depth of coal seams as sub-criteria of mining impact criteria, the weight information entropy and criterion weight of the mining impact criteria evaluation process are calculated, and the mining impact criteria thematic map is constructed. Taking the overburden failure height and the overburden mudstone ratio as the sub-criteria of the water inrush channel criterion, the overburden failure height and the overburden mudstone ratio are obtained according to the different mining heights in the grouting area and the non-grouting area, and the thematic map of the water inrush channel criterion is constructed.

6. The method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers according to claim 5 is characterized in that: In step S4, First, the thematic map of water inrush source criteria, the thematic map of mining impact criteria, and the thematic map of water inrush channel criteria are normalized, and the weights of water inrush source criteria, mining impact criteria, water inrush channel criteria and corresponding sub-criteria are calculated, and then the cumulative sum is performed to obtain the hazard contour map in the study area.

7. A method for evaluating the risk of water inrush and sand burst caused by mining after grouting transformation of loose aquifers according to any one of claims 1 to 6, characterized in that: In step S4, the area division includes Class I danger zone: There is no area where RC ≥ 0.65; Category II more dangerous area: the area where 0.50≤RC<0.65; Category III relatively safe area: the area where 0.40≤RC<0.50; Category IV safety zone: area where RC < 0.40; Among them, RC is the hazard coefficient, which can be obtained from the hazard contour map.

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