A method for horizontal hole advanced grouting transformation of water-bearing strata in the roof and floor of coal seams

Abstract

The invention discloses a method for horizontal hole advanced grouting transformation of water-bearing strata in the roof and floor of coal seams. Based on the idea of pre-cracking and grouting to reduce water in water-bearing strata of coal measures strata, horizontal directional drilling on the ground or underground is used to carry out borehole deflagration pre-cracking on the water-bearing strata of coal measures strata, so that the original fissures are interconnected into a network or the number of secondary fissures is increased, improving the injectability of the strata. Then, water-consuming slurry is used for splitting grouting, so that the slurry fills into the fissures, realizing the water reduction transformation of the water-bearing strata, thereby eliminating the threat of groundwater outburst (gushing) of the water-bearing strata during the coal seam mining process.

Description

Technical Field

[0001] The present invention relates to a method for pre-grouting and reforming water-bearing strata in the roof and floor of coal seams by horizontal holes. Background Art

[0002] Currently, the development of coal resources in China shows a trend of shifting to the west, and the original eastern mining areas are characterized by an increasing mining depth. The water in the roof sandstone in the western mining areas and the water in the floor limestone in the eastern mining areas seriously restrict the large-scale and safe development of coal resources in China.

[0003] In response to the above problems, the main measures in both the eastern and western mining areas are to grout and reform the aquifers. In the eastern mining areas, the floor limestone aquifer is targeted, and in the western mining areas, the thick roof sandstone aquifer is targeted. The eastern mining areas have carried out grouting and reform of the floor limestone aquifer earlier and achieved certain results, but water inrush still occurs continuously in the grouting working face. Some coal mines in the western mining areas have tentatively carried out roof sandstone grouting projects, but with little effect, the grouting pressure is very high and the grouting volume is very small. The main reason for the poor effect of grouting and reform of aquifers in the east and west is the poor connectivity of the original pore fractures in the aquifers. The boreholes cannot fully expose the original pore fractures in the aquifers, resulting in many grouting blind spots and insufficient void filling rate. Summary of the Invention

[0004] Aiming at the deficiencies in the prior art, the purpose of the present invention is to provide a method for pre-grouting and reforming water-bearing strata in the roof and floor of coal seams by horizontal holes. This method is based on the process of deflagration pre-cracking - water-consuming slurry - splitting grouting, and can carry out pre-grouting and reform of water-bearing strata in the coal measure strata before coal mining, eliminating the threat of water inrush (gushing) from the water-bearing strata.

[0005] In order to solve the above technical problems, the present invention is implemented by adopting the following technical solutions:

[0006] A method for pre-grouting and reforming water-bearing strata in the roof and floor of coal seams by horizontal holes, the method comprising the following steps:

[0007] Step 1, analyze the distribution characteristics of water-bearing and water-resisting strata in the roof and floor and their spatial relationship with the coal seam, and determine the height of the water-conducting fracture zone in the mining roof and the depth of the floor failure zone;

[0008] Step 2, determine the water reduction reform layer position and thickness of the roof and floor aquifers according to the height of the water-conducting fracture zone in the roof and the depth of the floor failure zone obtained in Step 1;

[0009] Step 3, determine the water reduction reform area of the roof and floor aquifers according to the scope affected by the water-conducting fracture zone in the roof and the floor failure zone;

[0010] Step 4: Analyze the response characteristics of the number and length of the deflagration cracks in the boreholes in the water reduction and transformation areas of the roof and floor aquifers and the deflagration parameters, determine the powder charge volume, mass, and structural parameters for deflagration pre-splitting, and conduct deflagration pre-splitting;

[0011] Step 5: Determine the water-consuming materials and applicable ratios in the water reduction and transformation areas of the roof and floor aquifers through laboratory tests, and obtain applicable water-consuming slurries;

[0012] Step 6: Based on laboratory tests and numerical calculations, analyze the relationship between the initiation of high-pressure splitting grouting cracks in the water reduction and transformation areas of the roof and floor aquifers and different in-situ stress levels and borehole parameters. Combining the in-situ stress distribution characteristics and the construction technology of bedding holes, determine the spatial layout parameters of the grouting holes and the final pressure of high-pressure splitting grouting. The spatial layout parameters of the grouting holes include the spatial spacing, length, and azimuth of the bedding holes.

[0013] The present invention further includes the following technical features:

[0014] Specifically, Step 1 includes: calculating the height of the water-conducting fissure zone in the roof based on a statistical empirical formula, calculating the depth of the floor failure zone based on a theoretical calculation formula, and calculating the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone based on numerical simulation; comprehensively comparing the above three calculation results, and determining the maximum values of the height of the water-conducting fissure zone in the mined roof and the depth of the floor failure zone as the height of the water-conducting fissure zone in the mined roof and the depth of the floor failure zone.

[0015] Specifically, the statistical empirical formula adopts the calculation formula for the predicted height of the water-conducting fissure zone in the "Code for the Reserving of Coal Pillars for Buildings, Water Bodies, Railways and Main Roadways and Coal Mining under Pressure" and the "Handbook for the Prevention and Control of Coal Mine Water";

[0016] The theoretical calculation formulas include the calculation formula for the maximum failure depth of the floor at the edge of the stope rock mass based on elastic theory, the calculation formula for the floor failure depth of the longwall working face based on elastic theory, and the calculation formula for the floor failure depth based on plastic theory; the maximum value of the floor failure zone depth obtained from the three theoretical calculation formulas is used as the floor failure zone depth obtained from the theoretical calculation formula;

[0017] The numerical simulation calculation is to calculate the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone based on FLAC3D numerical simulation, including constructing a numerical calculation model consistent with the geological, hydrogeological, stratigraphic structure, and coal seam mining process parameters, and conducting numerical simulation calculations on the mining process of coal seams with different advance distances, obtaining the height of the water-conducting fissure zone in the mined roof and the depth of the floor failure zone under different mining advance distances, analyzing and judging the fully mined nodes, and obtaining the maximum values of the height of the water-conducting fissure zone in the mined roof and the depth of the floor failure zone as the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone obtained from the numerical simulation calculation.

[0018] Specifically, Step 2 includes:

[0019] Step 2.1: According to the relationship between the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone obtained in Step 1 and the roof aquifer and the floor aquifer, determine the water reduction and transformation horizons for the roof aquifer and the floor aquifer respectively. The water reduction and transformation horizon is located in the aquifer with the best water-richness among the aquifers affected by the water-conducting fissure zone in the roof and the floor failure zone.

[0020] Step 2.2: Determine the water reduction and transformation thickness according to the aquifer with the best water-richness within the range of the height of the water-conducting fissure zone and the depth of the floor failure zone obtained in Step 1. When the thickness of the aquifer with the best water-richness is relatively large and the water-conducting fissure zone and the floor failure zone only affect its lower part and do not cover the entire aquifer, the water reduction and transformation thickness should be greater than the thickness of the part of the aquifer affected by the water-conducting fissure zone and the floor failure zone. When the thickness of the aquifer with the best water-richness is relatively small and it is within the range of the water-conducting fissure zone and the floor failure zone, the water reduction and transformation thickness should not be less than the thickness of the aquifer.

[0021] Specifically, in Step 3: When the water-conducting fissure zone in the mined roof and the floor failure zone in the mining area are within the same hydrogeological boundary range and fault boundary range, the area affected by the water-conducting fissure zone in the mined roof and the floor failure zone in the mining area is taken as the area of the aquifer water reduction and transformation region. When the areas affected by the water-conducting fissure zone in the mined roof and the floor failure zone in the mining area are within different hydrogeological boundary ranges and fault boundary ranges, the area of the aquifer water reduction and transformation region is obtained by combining the areas affected by the water-conducting fissure zone in the mined roof and the floor failure zone in the mining area with the hydrogeological boundary range and the fault boundary range.

[0022] Specifically, in Step 4, through carrying out physical model tests of similar materials in a deflagration chamber with different powder charge volumes, masses and structures, obtain the deflagration characteristics of the powder under different conditions, analyze the relationship between the powder charge volume, mass and structure and the deflagration pressure, the number and length of fissures, so as to determine the parameters of the powder charge volume, mass and structure for deflagration pre-splitting.

[0023] Specifically, Step 5 includes:

[0024] Collect and investigate the particle size, toxicity, water reduction effect, price characteristic information of existing water-consuming materials. Use indoor tests to study the physical properties such as viscosity distribution, specific gravity, stone formation rate and setting time of cement-based slurry after adding water-consuming materials under different ratios, and the mechanical properties such as compressive strength and flexural strength of the stone body. Compare and analyze the influence law of water-consuming materials on the water reduction performance of cement-based slurry. Based on means such as hydrographic observation, water pressure test, borehole peephole and indoor micro-CT scanning, obtain quantitative information on the water pressure and void characteristics of the roof and floor aquifers. By comparing the physical and mechanical properties of water-consuming materials with the water pressure and void characteristics of the roof and floor aquifers, comprehensively determine the water-consuming materials and applicable ratios that meet the requirements of the water pressure and void characteristics of the roof and floor aquifers.

[0025] Specifically, step 6 includes:

[0026] Using split grouting indoor similar material model tests and split grouting PFC numerical simulations respectively to calibrate the physical and mechanical properties parameters of typical roof and floor aquifers, and determine the similar model test materials, mix ratios and numerical calculation parameters of roof and floor aquifers; Based on the above parameters, as well as the in-situ stress conditions, boundary conditions and fracture conditions, use the PFC numerical calculation software to simulate the fracture initiation, extension and penetration processes in split grouting of the water reduction layer, study the stress field, strain field and displacement field of the fractured body, and analyze the fracture initiation laws of split grouting of the roof and floor water reduction layers under different fracture conditions; Based on the true triaxial fracturing test platform, considering the in-situ stress level, grouting pressure and fracture parameter conditions, use water reduction slurries with different performances to fracture the test blocks, and according to the changes in grouting pressure and flow rate, combined with the test data monitored and collected by acoustic emission and wave velocity meter equipment, analyze and obtain the fracture pressure and extension characteristics of split grouting of the water reduction layer under different in-situ stress levels, fracture parameters and different water reduction slurry performance conditions;

[0027] According to the development laws of deflagration fractures in the water-bearing rock layers of the coal seam roof and floor, the fracture initiation laws and ranges of split grouting, the in-situ stress distribution characteristics, the reformed area and the construction technology of bedding holes, determine the bedding hole layout azimuth, branch hole spacing and length parameters of the aquifer reform position;

[0028] Using split grouting PFC numerical simulation and split grouting indoor similar material model test to analyze and obtain the fracture initiation pressure and extension characteristics of split grouting of the target water reduction layers of the roof and floor under different fracture parameters, in-situ stress levels and water reduction slurry performance conditions. Obtain the fracture initiation pressure according to the linear offset point of the grouting pressure and the acoustic emission information, and determine the split grouting termination pressure value according to the fracture extension length and the borehole spacing parameter.

[0029] Specifically, in step 6, the bedding hole layout azimuth should be kept as parallel as possible to the maximum principal stress direction of the in-situ stress, and the angle with the maximum principal stress direction should be reduced as much as possible; The branch hole spacing is comprehensively determined according to the fracture extension distance, grouting pressure and the rated working capacity of the grouting pump set; The branch hole length is determined according to the reformed area.

[0030] Compared with the prior art, the present invention has the following technical effects:

[0031] Based on the idea of pre - splitting and creating fractures - grouting to reduce water in the water - bearing rock strata of coal measures, this invention uses surface or underground horizontal directional drilling to conduct borehole explosion - combustion pre - splitting on the water - bearing rock strata of coal measures, making the original fractures connect with each other to form a network or increasing the number of secondary fractures, improving the injectability of the rock strata. Then, it uses water - consuming slurry for splitting grouting, enabling the slurry to fill into the fractures, realizing the water - reducing transformation of the water - bearing rock strata, and thus eliminating the threat of groundwater outburst (gushing) from the water - bearing rock strata during coal seam mining. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is the technical route diagram of the method of the present invention;

[0033] Figure 2 is the schematic diagram of numerical simulation calculation of the failure ranges of the mining - disturbed roof and floor;

[0034] Figure 3 is the schematic diagram of the layout of the transformation parameters of the target aquifers in the roof and floor and the parameters of the branch holes;

[0035] Figure 4 is (a) the orifice grouting pressure curve; (b) the crack initiation morphology of circular - hole splitting grouting, where the white line segments represent tensile micro - cracks and the dark - gray particles represent rock specimens;

[0036] Figure 5 is the crack morphology of splitting grouting with slurries of different water - cement ratios: (a) water - cement ratio of 1.0, (b) water - cement ratio of 2.0, (c) water - cement ratio of 3.0;

[0037] Figure 6 is the slurry propagation path (green particles) of splitting grouting under different in - situ stress levels (maximum principal stress - minimum principal stress): (a) 25 - 10 MPa, (b) 25 - 13 MPa, (c) 25 - 16 MPa;

[0038] Figure 7 is the crack propagation morphology of splitting grouting along weak planes with different dips: (a) 30°, (b) 60°, (c) 90°

[0039] Figure 8 is the propagation path of splitting grouting and the crack propagation morphology under different crack width conditions: (a) 3 mm, (b) 8 mm, (c) 15 mm;

[0040] MEANINGS OF THE REFERENCE NUMERALS: 1 is the damage range of the mining - disturbed roof, 2 is the mining space of the coal seam, 3 is the damage range of the mining - disturbed floor, 4 is the height of the target aquifer transformation, 5 is the width of the target aquifer transformation, 6 is the horizontal spacing of the bedding - parallel branch boreholes, 7 is the vertical spacing of the bedding - parallel branch holes, 8 is the length of the target aquifer transformation. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0041] The present invention provides a method for advanced grouting transformation of water-bearing rock formations in the roof (floor) of coal seams based on deflagration pre-splitting - water-consuming slurry - splitting grouting. This method first analyzes the distribution characteristics of water-bearing and water-resisting strata in the roof and floor and their spatial relationship with the coal seam, and determines the target strata for transformation in the advanced areas of the roof and floor respectively according to the size of the damaged range of surrounding rocks during mining. Secondly, it analyzes the direction of the groundwater flow field, boundary characteristics, etc. of the target aquifer and the occurrence state such as the magnitude and direction of in-situ stress, so as to determine the size of the transformation plane range in the advanced area, the layout direction of horizontal directional drilling, etc. Then, it uses surface or underground horizontal directional drilling to construct bedding holes in the target roof or floor aquifer, and then realizes deflagration pre-splitting of the water-bearing rock formation by loading gunpowder or propellant in the bedding holes, so as to generate secondary fractures in the aquifer rock formation to penetrate the primary fractures or to extend and cross the primary fractures. Finally, it uses water-consuming slurry to carry out high-pressure splitting grouting in the bedding boreholes to achieve full coverage of the slurry in the water-bearing rock formation, improve the filling rate of the water-bearing rock formation, and achieve the purpose of water reduction transformation.

[0042] Specifically, it includes the following steps:

[0043] Step 1: Analyze the distribution characteristics of water-bearing and water-resisting strata in the roof and floor and their spatial relationship with the coal seam, and determine the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone.

[0044] According to geological and hydrogeological data, combined with borehole columns, analyze the distribution characteristics of water-bearing and water-resisting strata in the roof and floor and their spatial relationship with the coal seam. Based on the coal mining technology and occurrence characteristics of the coal seam, comprehensively determine the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone by using empirical formulas, theoretical calculation formulas and numerical simulation calculations. Among them, the theoretical calculation formula for the height of the water-conducting fissure zone in the roof is a statistical empirical formula; the theoretical calculation formulas for the depth of the floor failure zone include the calculation formulas for the depth of the edge of the stope rock mass and the floor failure depth of the longwall working face based on elastic theory and the calculation formula for the floor failure depth based on plastic theory.

[0045] Step 1.1: Calculation of the water-conducting fissure zone in the roof based on the statistical empirical formula

[0046] According to the coal mining method of the working face, the coal mining thickness of the coal seam, the lithological characteristics of the overlying strata, etc., use the calculation formula for the predicted height of the water-conducting fissure zone (Table 1) in the "Code for Reserving Coal Pillars and Coal Mining under Buildings, Water Bodies, Railways and Main Roadways" (2017 version) and the "Handbook of Coal Mine Water Control" (published by China Coal Industry Publishing House in 2013) to calculate the development height of the water-conducting fissure zone, and compare to obtain the maximum development height of the water-conducting fissure zone.

[0047] Table 1 Predicted formulas for the height of the water-conducting fissure zone in the roof

[0048]

[0049] Note: 1. ∑M is the cumulative mining thickness.

[0050] 2. Application range of the formula: single-layer mining thickness is 1 - 3 m, and the cumulative mining thickness does not exceed 15 m.

[0051] 3. The ± term in the calculation formula is the mean square error.

[0052] Step 1.2, calculation of the floor failure zone depth based on the theoretical calculation formula:

[0053] Step 1.2.1, calculation of the maximum floor failure depth at the edge of the stope rock mass based on elastic theory:

[0054] From the principal stress formula of elastic mechanics theory, the principal stress equation at the edge of the stope is obtained. According to the Mohr-Coulomb criterion, the length of the horizontal failure zone at the edge of the stope is obtained. Thus, the shape of the failure zone caused by stress concentration at the edge of the stope can be obtained, and based on geometric relationships, the maximum floor failure depth at the edge of the stope rock mass is:

[0055]

[0056] In the formula: γ is the unit weight; H is the buried depth; L x is the advancing length of the working face; σ c is the uniaxial compressive strength of the rock mass.

[0057] Step 1.2.2, calculation of the floor failure depth of the longwall working face based on elastic theory:

[0058] From elastic mechanics, the stress equation of a concentrated force acting on an isotropic and homogeneous infinite plane can be obtained at any point on the plane. Using the superposition principle, it can be extended and applied to the case of a uniformly loaded free boundary, and the stress distribution pattern of the floor can be drawn. Through stress analysis and finding the extreme value, the floor failure depth of the longwall working face is:

[0059]

[0060] In the formula: n is the maximum stress concentration coefficient; σ c is the uniaxial compressive strength of the rock mass; H is the mining depth; γ is the unit weight of the rock mass;

[0061] φ0 is the weighted average internal friction angle of the floor rock mass.

[0062] Step 1.2.3, calculation of the floor failure depth based on plastic theory:

[0063] For the floor failure depth caused by mining, generally, the calculation method of foundation mechanics in soil mechanics is used. According to plastic theory, the ultimate equilibrium zone in the foundation is divided into three zones. Due to the influence of the abutment pressure formed by mining, the failure depth can be obtained. Therefore, the floor failure depth caused by mining is:

[0064]

[0065] Where: L x is the advancing length of the working face, is the weighted average internal friction angle of the floor rock mass, and θ is the angle between the failure slip line and the failure depth of the floor.

[0066] Based on the floor failure depth obtained under the three working conditions and the calculation formula, determine the maximum value of the floor failure depth as the floor failure depth.

[0067] Step 1.3, Based on the FLAC3D numerical simulation, calculate the height of the water-conducting fractured zone in the roof and the depth of the floor failure zone during coal mining:

[0068] Construct a numerical calculation model consistent with parameters such as geology, hydrogeology, stratigraphic structure, and coal seam mining technology, and conduct numerical simulation calculations on the coal mining process of coal seams with different advance distances. Obtain the height of the water-conducting fractured zone in the roof and the depth of the floor failure zone under different mining advance distances, analyze and judge the fully mined nodes, and obtain the maximum values of the height of the water-conducting fractured zone in the roof and the depth of the floor failure zone after mining ( Figure 2 , where 1 is the damaged range of the roof during coal mining, 2 is the coal mining space, and 3 is the damaged range of the floor during coal mining).

[0069] In summary, based on the statistical empirical formula in Step 1.1, the theoretical calculation formula in Step 1.2, and the numerical simulation calculation in Step 1.3, compare and determine the maximum values of the height of the water-conducting fractured zone in the roof and the depth of the floor failure zone as the height of the water-conducting fractured zone in the roof and the depth of the floor failure zone.

[0070] Step 2, Determine the water reduction transformation horizons and thicknesses of the roof and floor aquifers according to the height of the water-conducting fractured zone in the roof and the depth of the floor failure zone obtained in Step 1:

[0071] Step 2.1: Based on the relationship between the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone obtained in Step 1 and the roof aquifer and the floor aquifer, determine the water reduction and transformation horizons for the roof aquifer and the floor aquifer respectively. The water reduction and transformation horizon is located in the aquifer with the best water-richness affected by the water-conducting fissure zone in the roof and the floor failure zone. (The purpose of constructing the water reduction layer is to carry out advanced water reduction and transformation on the roof and floor aquifers to achieve the safe extraction of coal resources. Therefore, the construction horizon of the water reduction layer should be based on the relationship between the damage range of the surrounding rock affected by mining and the aquifer.) The height of the water-conducting fissure zone and the depth of the floor failure referred to here are the maximum values of the water-conducting fissure zone in the roof and the depth of the floor failure obtained by comprehensively statistically analyzing the empirical formula, theoretical calculation formula, and numerical simulation calculation in Step 1. Therefore, to achieve the maximum water reduction in the aquifer without increasing the height of the water-conducting fissure zone and the depth of the floor failure, the water reduction and transformation horizon should be located in the aquifer with the best water-richness affected by the predicted water-conducting fissure zone and the depth of the floor failure.

[0072] Step 2.2: Determine the water reduction and transformation thickness according to the aquifer with the best water-richness within the range of the height of the water-conducting fissure zone and the depth of the floor failure obtained in Step 1. When the thickness of the aquifer with the best water-richness is relatively large and the water-conducting fissure zone and the floor failure zone only affect its lower part without covering the entire aquifer, the water reduction and transformation thickness should be greater than the thickness of the part of the aquifer affected by the water-conducting fissure zone and the floor failure zone. When the thickness of the aquifer with the best water-richness is relatively small and it is within the range of the water-conducting fissure zone and the floor failure zone, the water reduction and transformation thickness should not be less than the thickness of the aquifer.

[0073] Step 3: Determine the area of the water reduction and transformation area for the roof and floor aquifers:

[0074] Analyze the flow field and boundary characteristics of the target aquifers in the roof and floor, determine the hydrogeological boundary conditions of the aquifers, fault boundaries, and the corresponding boundaries of the mining damage range in the mining area, etc. Through comparing the boundary ranges, comprehensively determine the water reduction area range. Determination principle: When the water-conducting fissure zone in the roof and the floor failure zone in the mining area are within the same hydrogeological boundary range and fault boundary range, the affected range of the water-conducting fissure zone in the roof and the floor failure zone in the mining area is used as the area of the water reduction and transformation area for the aquifer; when the affected range of the water-conducting fissure zone in the roof and the floor failure zone in the mining area is within different hydrogeological boundary ranges and fault boundary ranges, the affected range of the water-conducting fissure zone in the roof and the floor failure zone in the mining area combined with the hydrogeological boundary range and the fault boundary range is used as the area of the water reduction and transformation area for the aquifer. Among them, for the roof boundary of the affected range of the water-conducting fissure zone in the roof and the floor failure zone in the mining area, according to the movement angle of the overlying rock strata in the roof and the coal seam mining area, determine the plane area of the roof damage caused by coal seam mining; for the floor boundary of the affected range of the water-conducting fissure zone in the roof and the floor failure zone in the mining area, according to the advanced plastic failure range of the floor and the coal seam mining area, determine the floor damage area.

[0075] Step 4: Analyze the response characteristics of the number and length of the deflagration fissures in the boreholes in the water reduction and transformation areas of the roof and floor aquifers and the deflagration parameters, determine the parameters such as the volume, mass, and structure of the gunpowder charge for deflagration pre-splitting, and conduct deflagration pre-splitting.

[0076] By conducting indoor physical model tests of similar materials with different gunpowder charge volumes, masses, and structures, obtain the deflagration characteristics of gunpowder under different conditions, and analyze the relationships between the gunpowder charge volume, mass, and structure and the deflagration pressure, the number and length of the fissures; among them, for the indoor physical model tests of similar materials, standard rock mechanics test samples are made of different grades of cement for physical and mechanical property tests to obtain test samples with physical and mechanical properties similar to those of the roof and floor water-bearing rock strata, so as to determine the cement grade and proportion of the similar model material tests.

[0077] Step 5: Based on the injectability and flow field characteristics of the water reduction and transformation areas of the roof and floor aquifers, determine the water-consuming materials and their applicable proportions that meet the requirements of the water reduction and transformation areas of the roof and floor aquifers through indoor tests, and obtain applicable water-consuming slurries:

[0078] Collect and investigate the characteristic information of existing water-consuming materials (silica fume, hydroxypropyl methyl cellulose ether) such as particle size, toxicity, water reduction effect, price, etc., and use indoor tests to study the physical properties such as viscosity distribution, specific gravity, stone formation rate, and setting time of cement-based slurries (cement slurries or clay-cement slurries) after adding water-consuming materials under different proportions, as well as the mechanical properties such as the compressive strength and flexural strength of the stone bodies, and compare and analyze the influence law of water-consuming materials on the water reduction performance of cement-based slurries;

[0079] Based on means such as hydrographic observation, water pressure test, borehole peephole, and indoor micro-CT scanning, obtain quantitative information on the water pressure and void characteristics of the roof and floor aquifers;

[0080] By comparing the physical and mechanical properties of the water-consuming materials with the water pressure and void characteristics of the roof and floor aquifers, comprehensively determine the water-consuming materials and their applicable proportions that meet the requirements such as the water pressure and void characteristics of the roof and floor aquifers.

[0081] Step 6: Based on indoor tests and numerical calculations, analyze the relationship between the crack initiation of high-pressure split grouting in the water reduction and transformation areas of the roof and floor aquifers and different in-situ stress levels, borehole parameters, and combinations, and combine the in-situ stress distribution characteristics and the construction technology of bedding holes, etc., to determine the spatial layout parameters of the grouting holes (spatial spacing, length, azimuth, etc.) and the final pressure of high-pressure split grouting:

[0082] Indoor tests and the particle flow code (PFC) software are used to calibrate the physical and mechanical property parameters of the aquifers in the roof and floor. Through comprehensive research, the similar model test materials, proportions, and numerical calculation parameters of the aquifers in the roof and floor are determined. Based on the above parameters, indoor model tests and the PFC numerical calculation software are used to study the crack initiation, propagation and evolution laws, and grouting pressure in split grouting, reveal the crack initiation law of split grouting in typical roof aquifers, and comprehensively determine the quantitative relationships between factors such as the crack propagation length, grouting pressure, and water-consuming slurry proportion.

[0083] Step 6.1, (1) Split grouting PFC numerical simulation analysis: Core samples of the target aquiferous rock strata in the typical roof and floor are taken, and indoor physical and mechanical tests on the rock are carried out to obtain parameters such as the modulus, strength, fracture toughness coefficient, density, Poisson's ratio, cohesion, internal friction angle, and permeability coefficient of the grouted formation, as well as the failure characteristics of the rock samples in uniaxial and triaxial tests; the parameter calibration of the Ordovician limestone top strata under different crack density conditions is carried out using the particle element numerical simulation software (PFC), that is, the numerical simulations of uniaxial and triaxial tests are carried out using the PFC software. By adjusting the meso-mechanical parameters of the particles and aggregates, the uniaxial and triaxial failure characteristics of the rock samples obtained from the numerical simulation are basically consistent with those of the rock samples in the indoor uniaxial and triaxial rock tests, so as to determine the reasonable meso-mechanical parameters of the grouted medium particle units and their aggregates; based on the in-situ stress conditions, boundary conditions, crack conditions, etc. of the water-reducing layers in the roof and floor, the PFC numerical calculation software is used to simulate the crack initiation, propagation, and penetration processes in the split grouting of the water-reducing layers, study the stress field, strain field, and displacement field of the cracked body, and analyze the crack initiation law of split grouting in the water-reducing layers of the roof and floor under different crack conditions.

[0084] (2) Indoor similar material model test for split grouting: Cement slurry stone specimens with the same physical and mechanical properties as those of the typical roof and floor water-reducing layers are prepared, and cracks are prefabricated in the specimens; based on the true triaxial fracturing test platform, considering conditions such as the in-situ stress level, grouting pressure, and crack parameters, specimens are fractured using water-reducing slurries with different properties. According to the changes in grouting pressure and flow rate, combined with the test data monitored and collected by equipment such as acoustic emission and wave velocity meters, the crack pressure and propagation characteristics of split grouting in the water-reducing layer under different in-situ stress levels, crack parameters, and different water-reducing slurry properties are analyzed.

[0085] Step 6.2: According to the development law of deflagration fissures in the water-bearing rock formations of the coal seam roof and floor, the initiation law and scope of splitting grouting fissures, the characteristics of in-situ stress distribution, the area of the transformation scope, and the construction technology of bedding holes, etc., determine the bedding hole layout azimuth angle (relationship with the in-situ stress distribution), branch hole spacing (vertical and horizontal), length and other parameters at the aquifer transformation position (Figure 3); among them, the bedding hole layout azimuth should be kept as parallel as possible to the direction of the maximum principal stress of the in-situ stress, and the angle with the direction of the maximum principal stress should be reduced as much as possible; the branch hole spacing is comprehensively determined based on the fissure extension distance, grouting pressure, and the rated working capacity of the grouting pump unit; the branch hole length is determined according to the area of the transformation scope.

[0086] Step 6.3: In summary, based on numerical simulation calculations and model tests, comprehensively obtain the splitting grouting fissure initiation pressure and extension characteristics of the target water-reducing layers of the roof and floor under different fissure parameters, in-situ stress levels, water-reducing slurry properties, etc. The fissure initiation pressure is obtained based on the linear offset point of the grouting pressure and the acoustic emission information, and the splitting grouting termination pressure value is determined according to the fissure extension length and the borehole spacing parameters.

[0087] Example:

[0088] 1) Splitting grouting numerical simulation calculation scheme

[0089] For different in-situ stress level conditions, it is realized by fixing the maximum principal stress and changing the minimum principal stress. According to the in-situ stress test results of the floor rock mass of a certain mine in the Handan-Xingtai mining area, the average maximum principal stress of the strata is 25 MPa, and the average minimum principal stress is 13 MPa; for different slurry water-cement ratio conditions, according to the common slurry water-cement ratio range in the grouting project in the advanced area at the top of the Ordovician limestone in the field, the water-cement ratio range is set to 1:1 - 3:1; for different fissure aperture and length conditions, according to the mesoscopic characteristics of the Ordovician limestone roof rock mass obtained by micro-CT scanning, three calculated apertures of 3 mm, 8 mm, and 15 mm are set according to the fissure aperture classification. In summary, a numerical calculation scheme is obtained by the control variable method (Table 2).

[0090] Table 2 Numerical simulation scheme

[0091]

[0092] 2) Calibration of numerical simulation calculation parameters

[0093] Parameters such as slurry viscosity, slurry bulk modulus, and macroscopic permeability used in the simulation calculation process are shown in Table 3, where the maximum principal stress and the minimum principal stress are 25 MPa and 16 MPa respectively. The splitting grouting pressure change curve of the intact limestone is obtained through simulation calculation ( Figure 4) The fracture initiation pressure of the split grouting is the maximum value of the pressure curve, that is, the fracture initiation pressure is 27.09 MPa. Assuming that the formation is in a saturated state and the grout does not flow into the formation before the borehole wall ruptures, that is, the pore pressure in the formation is not affected by the stress state of the borehole wall. According to Terzaghi's effective stress theory, the theoretical fracture initiation pressure can be obtained as follows:

[0094] p c -p0 = 3(σ3 - p0) - (σ1 - p0) + R m In Equation (4), σ3

[0095] and σ1 are the minimum principal stress and the maximum principal stress respectively, R m is the tensile strength of the rock formation, p0 is the pore pressure, and p c is the fracture initiation pressure of the rock.

[0096] According to the mechanical parameters of the Ordovician top formation (σ3 = 16 MPa, σ1 = 25 MPa, R m = 3.96 MPa), the calculated theoretical fracture initiation pressure is 26.96 MPa, which is in good agreement with the numerical calculation results, indicating that the numerical simulation parameter settings are reasonable.

[0097] Table 3 Calculation parameters during split grouting

[0098]

[0099]

[0100] 3) Numerical calculation results of split grouting

[0101] Through the numerical simulation calculation of particle element (PFC), the diffusion shape and path of the grout during split grouting can be obtained (figure), and the fracture initiation pressure value of split grouting can be judged according to the grouting pressure change curve. Tables 4 - 7 are the fracture initiation pressure results of split grouting under different slurry water-cement ratios, in-situ stress levels, crack or weak plane dips, crack or weak plane openings, etc.

[0102] Table 4 Simulation calculation results of split grouting fracture initiation pressure under different slurry water-cement ratios

[0103]

[0104] Table 5 Simulation calculation results of split grouting fracture initiation pressure under different in-situ stress levels

[0105]

[0106] Table 6 Simulation calculation results of split grouting fracture initiation pressure under different dip angles

[0107]

[0108] Table 7 Simulation calculation results of the fracture initiation pressure of splitting grouting under different opening conditions

[0109]

[0110]

Claims

1. A method for horizontal hole advanced grouting transformation of water-bearing rock strata in the roof and floor of a coal seam, characterized in that, The method comprises the following steps: Step 1: Analyze the distribution characteristics of the water-bearing and water-resisting strata in the roof and floor and their spatial relationship with the coal seam, and determine the height of the water-conducting fissure zone in the mined roof and the depth of the floor failure zone; Step 2: Determine the water reduction and transformation horizons and thicknesses of the roof and floor aquifers according to the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone obtained in Step 1; Step 3: Determine the areas of the water reduction and transformation regions of the roof and floor aquifers according to the scopes affected by the water-conducting fissure zone in the roof and the floor failure zone; Step 4: Analyze the response characteristics of the number, length of the borehole deflagration fissures and deflagration parameters in the water reduction and transformation regions of the roof and floor aquifers, determine the powder charge volume, mass and structural parameters for deflagration pre-splitting, and conduct deflagration pre-splitting; Step 5: Determine the water-consuming materials and applicable ratios in the water reduction and transformation regions of the roof and floor aquifers through laboratory tests, and obtain applicable water-consuming slurries; Step 6: Based on laboratory tests and numerical calculations, analyze the relationship between the initiation of the high-pressure splitting grouting fissures and different in-situ stress levels and borehole parameters in the water reduction and transformation regions of the roof and floor aquifers, and combine the in-situ stress distribution characteristics and the construction technology of the bedding holes to determine the spatial layout parameters of the grouting holes and the final pressure of the high-pressure splitting grouting. The spatial layout parameters of the grouting holes include the spatial spacing, length and azimuth of the bedding holes; The said Step 2 includes: Step 2.1: According to the relationship between the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone obtained in Step 1 and the roof aquifer and the floor aquifer, respectively determine the water reduction and transformation horizons of the roof aquifer and the floor aquifer. The water reduction and transformation horizons are located in the aquifers with the best water-richness among the aquifers affected by the water-conducting fissure zone in the roof and the floor failure zone; Step 2.2: Determine the water reduction and transformation thickness according to the aquifer with the best water-richness within the range of the height of the water-conducting fissure zone and the depth of the floor failure zone obtained in Step 1; when the thickness of the aquifer with the best water-richness is relatively large and the water-conducting fissure zone and the floor failure zone only affect its lower part and do not cover the aquifer, the water reduction and transformation thickness should be greater than the thickness of the part of the aquifer affected by the water-conducting fissure zone and the floor failure zone; when the thickness of the aquifer with the best water-richness is relatively small and it is within the range of the water-conducting fissure zone and the floor failure zone, the water reduction and transformation thickness should not be less than the thickness of the aquifer; In the said Step 3: When the water-conducting fissure zone in the mined roof and the floor failure zone in the mining area are within the same hydrogeological boundary range and fault boundary range, the scope affected by the water-conducting fissure zone in the mined roof and the floor failure zone in the mining area is taken as the area of the water reduction and transformation region of the aquifer; when the scopes affected by the water-conducting fissure zone in the mined roof and the floor failure zone in the mining area are within different hydrogeological boundary ranges and fault boundary ranges, the area of the water reduction and transformation region of the aquifer is obtained by combining the scope affected by the water-conducting fissure zone in the mined roof and the floor failure zone in the mining area with the hydrogeological boundary range and the fault boundary range; The said Step 6 includes: The physical and mechanical properties of typical roof and floor aquifers are calibrated by using indoor similar material model tests of splitting grouting and PFC numerical simulation of splitting grouting respectively, and the similar model test materials, ratios and numerical calculation parameters of roof and floor aquifers are determined; based on the above parameters, as well as the in-situ stress conditions, boundary conditions and fracture conditions, the PFC numerical calculation software is used to simulate the fracture initiation, extension and penetration processes in the water-reducing layer splitting grouting, study the stress field, strain field and displacement field of the fractured rock mass, and analyze the fracture initiation law of the roof and floor water-reducing layer splitting grouting under different fracture conditions; based on the true triaxial fracturing test platform, considering the in-situ stress level, grouting pressure and fracture parameter conditions, the test blocks are fractured by using water-reducing slurries with different performances, and according to the changes in grouting pressure and flow rate, combined with the test data monitored and collected by acoustic emission and wave velocity instrument equipment, the fracture pressure and extension characteristics of the water-reducing layer splitting grouting under different in-situ stress levels, fracture parameters and different water-reducing slurry performances are analyzed and obtained. According to the explosion-induced fracture development law of the water-bearing rock layers in the coal seam roof and floor, the fracture initiation law and range of splitting grouting, the in-situ stress distribution characteristics, the reformed area and the construction technology of the bedding holes, the layout azimuth, branch hole spacing and length parameters of the bedding holes at the aquifer reformed position are determined. By using PFC numerical simulation of splitting grouting and indoor similar material model tests of splitting grouting, the fracture initiation pressure and extension characteristics of the splitting grouting of the target water-reducing layers in the roof and floor under different fracture parameters, in-situ stress levels and water-reducing slurry performances are analyzed and obtained. The fracture initiation pressure is obtained according to the linear offset point of the grouting pressure and the acoustic emission information, and the splitting grouting termination pressure value is determined according to the fracture extension length and the borehole spacing parameters.

2. The method for horizontal hole advanced grouting transformation of water-bearing strata in the roof and floor of coal seams according to claim 1, characterized in that, Step 1 includes: calculating the height of the water-conducting fracture zone in the roof based on the statistical empirical formula, calculating the depth of the floor failure zone based on the theoretical calculation formula, and calculating the height of the water-conducting fracture zone in the roof and the depth of the floor failure zone based on numerical simulation; comprehensively comparing the above three calculation results, and determining the maximum values of the height of the water-conducting fracture zone in the mined roof and the depth of the floor failure zone as the height of the water-conducting fracture zone in the mined roof and the depth of the floor failure zone.

3. The method for horizontal hole advanced grouting transformation of water-bearing strata in the roof and floor of coal seams according to claim 2, characterized in that, The statistical empirical formula adopts the formula for predicting the height of the water-conducting fracture zone in the Code for the Reserving of Coal Pillars for Buildings, Water Bodies, Railways and Main Roadways and Coal Mining under Pressure and the Handbook of Coal Mine Water Control. The theoretical calculation formulas include the formula for calculating the maximum failure depth of the floor at the edge of the stope rock mass based on the elastic theory, the formula for calculating the floor failure depth of the longwall working face based on the elastic theory, and the formula for calculating the floor failure depth based on the plastic theory. The maximum value of the floor failure zone depth obtained by the three theoretical calculation formulas is used as the floor failure zone depth obtained by the theoretical calculation formula. The numerical simulation calculation is to calculate the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone based on the FLAC3D numerical simulation, including constructing a numerical calculation model consistent with the geology, hydrogeology, stratigraphic structure, and coal seam mining process parameters, and conducting numerical simulation calculations on the mining process of coal seams with different advance distances to obtain the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone under different mining advance distances, analyzing and judging the fully mined nodes, and obtaining the maximum values of the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone after mining as the height of the water-conducting fissure zone in the roof and the depth of the floor failure zone based on the numerical simulation calculation.

4. The method for horizontal hole advanced grouting reform of water-bearing strata in the roof and floor of coal seams as described in claim 1, characterized in that In step 4, by conducting physical model tests of similar materials in a deflagration chamber with different powder charge volumes, masses, and structures, the deflagration characteristics of the powder under different conditions are obtained, and the relationships between the powder charge volume, mass, and structure and the deflagration pressure, number and length of fissures are analyzed, so as to determine the powder charge volume, mass, and structure parameters for deflagration pre-splitting.

5. The method for horizontal hole advanced grouting transformation of water-bearing strata in the roof and floor of coal seams according to claim 1, characterized in that Step 5 includes: Collect and investigate the particle size, toxicity, water-reducing effect, and price characteristic information of existing water-consuming materials, conduct laboratory tests to study the physical properties such as viscosity distribution, specific gravity, stone formation rate, and setting time of cement-based slurry after adding water-consuming materials under different ratios, as well as the mechanical properties such as compressive strength and flexural strength of the stone body, and compare and analyze the influence law of water-consuming materials on the water-reducing performance of cement-based slurry; based on means such as hydrographic observation, water pressure test, borehole peephole, and indoor micro-CT scanning, obtain quantitative information on the water pressure and void characteristics of the aquifers in the roof and floor; by comparing the physical and mechanical properties of water-consuming materials with the water pressure and void characteristics of the aquifers in the roof and floor, comprehensively determine the water-consuming materials and applicable ratios that meet the requirements of the water pressure and void characteristics of the aquifers in the roof and floor.

6. The method for horizontal hole advanced grouting transformation of water-bearing strata in the roof and floor of coal seams according to claim 1, characterized in that In step 6, the layout azimuth of the bedding holes should be kept as parallel as possible to the direction of the maximum principal stress of the in-situ stress, and the angle with the direction of the maximum principal stress should be reduced as much as possible; the spacing of the branch holes is comprehensively determined based on the fissure extension distance, grouting pressure, and rated working capacity of the grouting pump set; the length of the branch holes is determined according to the area of the transformation range.

Images