An in-situ water conservation coal mining method based on structure and seepage stability of floor aquifer

Abstract

The application discloses an in-situ water conservation mining method of floor aquifer based on structure and seepage stability. The method comprises the following steps: firstly, obtaining the geological, hydrogeological and mining technical parameters of a target working face, determining the mining floor damage depth, the pressure water guide lifting zone height, the mining floor equivalent permeability, the critical thickness corresponding to the structure stability of the aquiclude and the critical equivalent permeability corresponding to the in-situ protection of the floor aquifer; then, determining whether the structure stability condition and the seepage stability condition are met; when either or both of the conditions are not met, selecting the strength sensitive rock stratum and / or the permeability sensitive rock stratum to implement grouting modification according to the determination result, determining the modified horizon and thickness, and re-checking after modification; if the conditions are still not met, adjusting the working face length and / or the advancing distance and repeating the determination. The application realizes quantitative discrimination and parameter optimization of water conservation mining under the in-situ protection condition of the floor aquifer, and takes into account the mine safety mining, the aquifer recharge capacity and the production water demand.

Description

Technical Field

[0001] This invention relates to the field of water-conserving mining technology, and in particular to an in-situ water-conserving coal mining method based on a bottom aquifer with stable structure and seepage. Background Technology

[0002] In coal mining, especially in deep, highly confined aquifers, the problems of floor water inrush and groundwater loss are becoming increasingly prominent. Mining-induced stress redistribution and rock mass damage can easily lead to instability of aquifer structures and the development of water-conducting channels, threatening mine safety and damaging the regional aquatic ecosystem. Therefore, achieving in-situ protection of the floor aquifer while ensuring coal mining efficiency has become a key technical issue in water-conserving coal mining.

[0003] To address water hazard prevention in the floor slab, existing technologies have proposed various methods, including floor grouting reinforcement, drainage and pressure reduction, the installation of waterproof coal pillars, strip mining, and optimization of mining parameters. While these methods can improve the floor slab's water-blocking capacity or reduce the risk of water inrush under certain conditions, they still have significant shortcomings.

[0004] First, most methods focus on a single aspect of the stability of the impermeable structure or the control of seepage channels, lacking a method for coordinating the dual constraints of structural stability and seepage stability. For example, a Chinese invention patent application (CN121701201A) discloses an in-situ water-retaining mining method for a high-salt, high-pressure aquifer base, which only uses the base failure depth, the height of the pressure rise, and the minimum safe impermeable thickness for strength constraint determination, but does not consider the potential energy attenuation effect of the pressure rise and the influence of the mining area. Furthermore, using compressive strength may lead to an underestimation of the safe impermeable thickness. Another Chinese invention patent application (CN119227426A) discloses a water-retaining mining discrimination method for in-situ protection of the base with pressure water, which compares the permeability corresponding to the allowable water loss and safe inflow with the permeability of the mining base, but does not fully reflect the synergistic constraints of structural stability and seepage stability, and does not adequately consider the coordination between production water demand and aquifer recharge capacity.

[0005] Second, existing technologies do not adequately consider the coordination between aquifer recharge capacity, safe mining conditions, and the water demand for production at the working face. When the aquifer recharge is sufficient, the level of mine intensification can be improved by using production water consumption as a constraint while ensuring safe production. However, existing methods mostly use safe water inflow as the criterion, ignoring the water demand for production, which can easily lead to the loss of the aquifer's water supply function.

[0006] Third, the thickness of grouting modification is mostly determined by experience, which is not specific enough to address the differences in water-blocking performance of different rock strata. For example, a Chinese invention patent application (publication number CN121273275A) discloses a method for treating a well-drilled high-pressure aquifer area, which modifies the aquifer itself to isolate water, but it is difficult to meet the requirements of in-situ protection, and the grouting thickness lacks quantitative basis.

[0007] In summary, existing technologies lack an in-situ water-retaining coal mining method for bottom aquifers that can simultaneously meet the dual constraints of structural stability and seepage stability, and comprehensively consider aquifer recharge, safe mining, and production water requirements. Summary of the Invention

[0008] To address the aforementioned technical shortcomings, the present invention aims to provide an in-situ water-retaining coal mining method based on structurally and seepage-stable bottom aquifers. This method fully considers the differences in mining space and formation water-blocking performance, takes structural stability and seepage stability as common constraints, and proposes methods for determining the grouting modification thickness and stratum location. While ensuring the in-situ protection effect of the bottom aquifer, it also takes into account the safe mining and water demand of the working face. The determination method is simple, highly operable, and has strong field applicability.

[0009] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention provides an in-situ water-retaining coal mining method based on structurally and seepage-stabilized aquifers, comprising the following steps: S1. Obtain the geological, hydrogeological, and mining technical parameters of the target working face, including the working face length, advance distance, coal seam thickness, thickness, pressure and recharge rate of the confined aquifer, distance between the coal seam and the confined aquifer, and thickness, strength and porosity of each rock layer between the coal seam and the confined aquifer. S2. Based on the above parameters, determine the depth of the mining-induced floor failure and the height of the confined water rise zone, obtain the mining permeability of each rock layer between the mining-induced floor failure zone and the confined water rise zone, and calculate the equivalent permeability of the mining-induced floor for each rock layer; determine the critical thickness corresponding to the stability of the aquifer structure and the critical equivalent permeability corresponding to the stability of the floor aquifer and normal mining. S3. Determine whether the structural stability conditions are met based on the distance between the coal seam and the aquifer on the floor, the depth of the mining-induced floor failure, and the height of the confined water conduction zone. Determine whether the seepage stability conditions are met based on the equivalent permeability and critical equivalent permeability of the mining-induced floor. S4. When one or both of the structural stability conditions and seepage stability conditions are not met, select strength-sensitive rock layers and / or permeability-sensitive rock layers for grouting modification according to the judgment result, and determine the grouting modification layer position and grouting modification thickness. After grouting modification, repeat the judgment in step S3. If the structural stability and seepage stability conditions cannot be met by grouting modification alone, then after adjusting the working face length and / or the advancing distance, repeat steps S2 to S4 to make a judgment until the structural stability and seepage stability conditions are met.

[0010] Preferably, in step S2, the formula for calculating the equivalent permeability of the mining base plate is: ; In the formula, The distance between the coal seam and the confined aquifer is in meters (m). The depth of the mining-induced floor failure is measured in meters (m). The height of the pressurized water riser is in meters (m). The thickness of each rock layer between the mining-induced floor failure zone and the confined water uplift zone is measured in meters (m). The mining permeability of each rock stratum between the mining-induced floor failure zone and the confined water uplift zone is given by m. 2 .

[0011] Preferably, in step S2, the formula for calculating the critical thickness corresponding to the stability of the waterproof layer structure is as follows: ; In the formula, The length of the working surface is in meters (m). The distance the working face advances, in meters (m). The pressure of the pressurized water is MPa. The height of the pressurized water riser is in meters (m). The pressure attenuation coefficient is expressed in MPa / m. The bending moment coefficient, ; The equivalent tensile strength (MPa) of each rock stratum between the mining-induced floor failure zone and the confined water uplift zone. The calculation formula is: ; In the formula, The distance between the coal seam and the confined aquifer is in meters (m). The depth of the mining-induced floor failure is measured in meters (m). The height of the pressurized water riser is in meters (m). The thickness of each rock layer between the mining-induced floor failure zone and the confined water uplift zone is measured in meters (m). The tensile strength of each rock layer between the mining-induced floor failure zone and the confined water conduction zone. .

[0012] Preferably, in step S2, the critical equivalent permeability corresponding to the in-situ protection of the bottom aquifer is the minimum value among the following three: the equivalent permeability corresponding to the aquifer recharge, the equivalent permeability corresponding to the maximum water inflow when the working face is safely mined, and the equivalent permeability corresponding to the working face water consumption. Among them, the equivalent permeability corresponding to the aquifer recharge is The calculation formula is: ; In the formula, The length of the working surface is in meters (m). The distance the working face advances, in meters (m). The pressure of the pressurized water is MPa. The recharge rate of the confined aquifer is expressed in m / s. The thickness of the confined aquifer is in meters (m). The viscosity coefficient is the hydrodynamic viscosity, in Pa·s; The distance between the coal seam and the confined aquifer is in meters (m). The depth of the mining-induced floor failure is measured in meters (m). The height of the pressurized water riser is in meters (m). The equivalent permeability corresponding to the maximum water inflow during safe mining of the working face The calculation formula is: ; In the formula, The maximum water inflow rate corresponding to safe mining of the working face, m 3 / s; The equivalent permeability corresponding to the water consumption at the working face The calculation formula is: ; In the formula, The water consumption required for normal mining operations at the working face, m 3 / s.

[0013] Preferably, in step S3, structural stability is the primary condition for water-retaining mining. The structural stability condition for water-retaining mining is: the distance between the coal seam and the confined aquifer - the depth of the mining-induced floor failure - the height of the confined water conduction zone > the critical thickness corresponding to the structural stability of the aquifer. The seepage stability condition for water-retaining mining is: the equivalent permeability of the mining-induced floor is less than or equal to the critical equivalent permeability of the floor corresponding to the stability of the aquifer and normal mining.

[0014] Preferably, in step S4, strength-sensitive rock layers and / or permeability-sensitive rock layers are selected for grouting modification based on the determination results, and the grouting modification layer location and grouting modification thickness are determined, specifically including: If the structural stability condition is met but the seepage stability condition is not met, then grouting of the permeability-sensitive rock layer is selected, and the minimum grouting thickness is determined in combination with the seepage stability condition. If the structural stability condition is not met but the seepage stability condition is met, then grouting of strength-sensitive rock strata should be selected, and the minimum grouting thickness should be determined in combination with the structural stability condition. If neither the structural stability condition nor the seepage stability condition is met, then grouting is selected for strength-sensitive rock layers and permeability-sensitive rock layers. The grouting reinforcement layer positions and thicknesses are determined according to the structural stability condition and the seepage stability condition, respectively, and the scheme with the smallest total reinforcement thickness is taken as the final scheme.

[0015] Preferably, in step S4, the method for determining the strength-sensitive rock layer and the permeability-sensitive rock layer is as follows: from the rock layers between the mining-induced floor failure zone and the confined water conduction zone, select rock layers other than mudstone and sandy mudstone with a porosity greater than the critical value for grouting reinforcement testing; determine the strength sensitivity based on the difference in tensile strength of the rock layers before and after grouting modification; and determine the permeability sensitivity based on the difference in the reciprocal of the permeability of the rock layers before and after grouting modification. Intensity sensitivity The calculation method is as follows: ; In the formula, The tensile strength (MPa) of each rock stratum between the mining-induced floor failure zone and the confined water uplift zone; The tensile strength of each rock layer after grouting modification is expressed in MPa. The method for calculating permeability sensitivity is as follows: ; The permeability of each rock layer between the mining-induced floor failure zone and the confined water uplift zone is given by m. 2 ; The permeability of each rock stratum after grouting modification is expressed in m. 2 .

[0016] Preferably, in step S4, the grouting modification area is the area enclosed by the intersection of an extended line drawn along the boundary of the goaf according to the bottom plate movement angle and the grouting modification layer.

[0017] Preferably, the depth of the mining-induced bottom plate failure and the height of the pressurized water guide zone in step S2 are obtained through field testing or numerical simulation.

[0018] Beneficial effects: 1. This invention incorporates the structural stability of the aquifer and the seepage stability of the floor as dual constraints into the water-conserving coal mining discrimination system, overcoming the shortcomings of existing technologies that rely on a single criterion. By determining whether the "remaining thickness after subtracting the failure depth and lift height from the distance between the coal seam and the aquifer" is greater than the critical thickness for structural stability, and whether the "equivalent permeability of the mining-induced floor" is less than or equal to the critical equivalent permeability for seepage stability, the water-conserving capacity of the floor and the risk of water loss under mining conditions can be comprehensively and scientifically assessed, providing a more reliable technical basis for water-conserving coal mining.

[0019] 2. This invention, in determining the critical equivalent permeability for seepage stability, simultaneously considers three constraints: "aquifer recharge," "maximum safe water inflow at the working face," and "working face production water consumption," using the minimum of these three as the control standard. This ensures that no water inrush accidents occur underground, avoids excessive drainage of the aquifer which could damage its water supply function, and simultaneously meets the normal production water needs of the working face, achieving a balance between safety, environmental protection, and economic benefits.

[0020] 3. For situations where structural stability or seepage stability is not met, this invention selects either strength-sensitive or permeability-sensitive rock strata for grouting modification, and determines the minimum required grouting thickness through inversion calculations, avoiding the blind reliance on experience to determine grouting parameters. When neither condition is met, the optimal solution can be selected by comparing the total reinforcement thickness of different grouting schemes, thus improving the project's economic efficiency.

[0021] 4. This invention re-verifies the dual conditions after grouting modification. If the conditions are still not met, the mining parameters such as the working face length and advancing distance are further adjusted and the judgment is repeated, forming a closed-loop optimization process. This mechanism can adapt to different geological conditions, ensuring that the final mining scheme simultaneously meets the requirements of structural stability and seepage stability, significantly improving the field applicability and reliability of the method.

[0022] 5. The parameters involved in this invention (such as the depth of floor failure caused by mining, the height of the confined water uplift zone, the thickness and strength of each rock layer, etc.) can all be obtained through conventional geological exploration, field testing, or numerical simulation. The calculation formulas are clear, and the judgment logic is straightforward. The technical solution is easy for engineering technicians to master and implement, and is suitable for promotion and application in mines with the threat of confined water in the floor. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 A flowchart of an in-situ water-retaining coal mining method for a bottom aquifer based on structural and seepage stability is provided for this invention. Figure 2 This is a schematic diagram of grouting modification of strength-sensitive rock strata that does not meet the requirements of structural stability but meets the requirements of seepage stability, provided in Embodiment 1 of the present invention. Figure 3 This is a schematic diagram of grouting modification of permeability-sensitive rock formations that meets the requirements of structural stability but not seepage stability, as provided in Embodiment 2 of the present invention. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] See Figure 1 The flowchart illustrates an in-situ water-retaining coal mining method based on structurally and seepage-stable aquifers. Taking a high-pressure aquifer in North China as an example, the method determines whether the existing mining conditions meet the requirements for water-retaining mining, and if not, the grouting reinforcement layer and thickness to be implemented. The specific steps include: S1. Review the geological and hydrogeological survey reports, mine development plan, and mechanical test reports of the target working face to obtain the geological parameters and mining technical parameters of the target working face. The working face length is 100m, the advance distance is 600m, the coal seam thickness is 3m, the thickness of the confined aquifer is 100m, the pressure of the confined aquifer is 6MPa, and the recharge rate is 9.26×10⁻⁶. -7 The coal seam speed is m / s and the distance between the coal seam and the confined aquifer is 80m. The lithology, thickness, strength, porosity and permeability of each rock layer between the coal seam and the confined aquifer are shown in Table 1.

[0027] Table 1: S2. Using traditional segmented water pressure testing and resistivity monitoring, the depth of the target working face’s mining floor failure was determined to be 15m, the height of the confined water riser zone was 20m, and the mining permeability and tensile strength of each rock layer between the mining floor failure zone and the confined water riser zone are shown in Table 2. Substitute into the formula and The equivalent permeability coefficient of the mining base plate is 7.75×10⁻⁶. - 14 m 2 The equivalent tensile strength of each rock layer between the mining-induced bottom plate failure zone and the confined water conduction zone is 3.02 MPa.

[0028] Table 2: Water pressure attenuation coefficient The bending moment coefficient is equal to 0.01 MPa / m, determined based on the ratio of the working face advance distance to the working face length. The value is 0.00452. Substituting the working face parameters, guide belt height, equivalent tensile strength, water pressure attenuation coefficient, and bending moment coefficient into the equation... It can be seen that the thickness of the waterproof layer that maintains structural stability is 55.9m.

[0029] Based on the geological conditions of the target working face and on-site mining data, the aquifer recharge rate within the target working face area is: =0.009259m 3 / s=800m 3 / d, to meet the maximum water inflow of 1000m³ during safe mining at the working face. 3 / d, the water consumption for production at the working face is 600m³ 3 / d ， Therefore, the equivalent permeability corresponding to meeting the water demand at the working face is taken as the critical equivalent permeability of the bottom plate for the aquifer to remain stable and for normal mining, and substituted into the formula. =12×10 -14 m 2 .

[0030] S3. Determine whether the target working face meets the structural stability and seepage stability conditions for water-conserving mining. Among them, structural stability is the primary condition for water-conserving mining. The structural stability condition for water-conserving mining is that the distance between the coal seam and the confined aquifer - the depth of the mining-induced floor failure - the height of the confined water conduction zone > the thickness corresponding to the structural stability of the aquifer. The seepage stability condition for water-conserving mining is that the equivalent permeability of the mining-induced floor is less than or equal to the critical equivalent permeability of the floor corresponding to the stability of the aquifer and normal mining.

[0031] Substituting the parameters into the above criteria, it can be seen that the structural stability requirement is not met, but the seepage stability requirement is met.

[0032] S4. Based on the determination results of step S3, select strength-sensitive rock strata for grouting, and determine the minimum grouting thickness in combination with structural stability requirements; select rock strata between the mining-induced floor failure zone and the confined water conduction zone that are excluding uninjectable rock strata such as mudstone and sandy mudstone and have a porosity greater than 5% of the critical value for grouting reinforcement test, and the reinforcement test results are shown in Table 3.

[0033] Table 3: The strength sensitivity ranking is limestone (6.4 MPa) > medium-grained sandstone (3.1 MPa) > fine-grained sandstone (3.0 MPa). Limestone is the preferred layer for grouting modification. Based on the remaining thickness corresponding to the distance between the coal seam and the confined aquifer - the depth of the mining-induced floor failure - the height of the confined water conduction zone, the required equivalent strength is calculated to be 4.67 MPa. Further calculation shows that the required modified thickness of the limestone is 11.59 m, which is less than the remaining limestone layer thickness of 15 m. Therefore, reinforcing only the limestone is sufficient to meet the requirements; that is, reinforcing the limestone to 11.59 m can achieve water-conserving mining. Figure 2 ).

[0034] Example 2, This embodiment takes a high-pressure bottom plate mine in North China as an example to determine whether the existing mining conditions meet the requirements for water-retaining mining, and if not, the grouting reinforcement layer and thickness that need to be taken.

[0035] This embodiment provides an in-situ water-retaining coal mining method based on structurally and seepage-stable aquifers, specifically as follows: S1. Review the geological and hydrogeological survey reports, mine development plan, and mechanical test reports of the target working face to obtain the geological parameters and mining technical parameters of the target working face. The working face length is 80m, the advance distance is 400m, the coal seam thickness is 2m, the thickness of the confined aquifer is 50m, the pressure of the confined aquifer is 5MPa, and the recharge rate is 1.1574×10 -5 The coal seam speed is m / s and the distance between the coal seam and the confined aquifer is 60m. The lithology, thickness, strength, porosity and permeability of each rock layer between the coal seam and the confined aquifer are shown in Table 4.

[0036] Table 4: S2. Using traditional segmented water pressure testing and resistivity monitoring, the depth of the mining-induced floor failure zone in the target working face was determined to be 7m, and the height of the confined water riser zone was 5m. The mining permeability and strength of each rock stratum between the mining-induced floor failure zone and the confined water riser zone are shown in Table 5. Substituting these values ​​into the formula... and The equivalent permeability of the mining base plate is 16×10⁻⁶. - 14 m 2 The equivalent tensile strength of each rock layer between the mining-induced bottom plate failure zone and the confined water conduction zone is 3.01 MPa.

[0037] Table 5: Water pressure attenuation coefficient The bending moment coefficient is equal to 0.01 MPa / m, determined based on the ratio of the working face advance distance to the working face length. The value is 0.00264. Substituting the working face parameters, guide belt height, equivalent tensile strength, water pressure attenuation coefficient, and bending moment coefficient into the equation... It can be seen that the thickness of the waterproof layer that maintains structural stability is 28.9m.

[0038] Based on the geological and hydrogeological conditions of the target working face and on-site mining data, the aquifer recharge rate within the target working face area is: =0.009259m 3 / s=400m 3 / d, to meet the maximum water inflow of 1000m³ during safe mining at the working face. 3 / d, the water consumption for production at the working face is 600m³ 3 / d ， Therefore, the equivalent permeability corresponding to the water inflow at the working face equaling the aquifer recharge is taken as the critical equivalent permeability of the floor plate for the aquifer to remain stable and for normal mining. Substituting this into the formula... =14×10 -14 m 2 .

[0039] S3. Determine whether the target working face meets the structural stability and seepage stability conditions for water-conserving mining. Structural stability is the primary condition for water-conserving mining. The structural stability condition for water-conserving mining is: the distance between the coal seam and the confined aquifer - the depth of the mining-induced floor failure - the height of the confined water conduction zone > the thickness corresponding to structural stability of the aquifer. The seepage stability condition for water-conserving mining is: the equivalent permeability of the mining-induced floor is less than or equal to the critical equivalent permeability of the floor corresponding to stable aquifer and normal mining. Substituting the parameters into the above determination requirements, it can be seen that the structural stability requirement is met, but the seepage stability requirement is not met.

[0040] S4. Based on the results of step 3, select permeability-sensitive rock strata for grouting, and determine the minimum grouting thickness in combination with the seepage stability requirements; select rock strata between the mining-induced floor failure zone and the confined water conduction zone that are excluding uninjectable rock strata such as mudstone and sandy mudstone and have a porosity greater than 5% of the critical value for grouting reinforcement test, and the reinforcement test results are shown in Table 6.

[0041] Table 6: Seepage stability ranking: Medium-grained sandstone (0.615×10⁻⁶) 14 m -2 > Limestone (0.025×10) 14 m -2 )> Fine-grained sandstone (0.0208×10 14 m -2 The medium-grained sandstone layer was selected for grouting modification. The equivalent permeability corresponding to the water inflow at the working face equaling the aquifer recharge was used as the critical floor equivalent permeability for maintaining aquifer stability and normal mining. When all the medium-grained sandstone was modified, the equivalent permeability coefficient was 14.33 × 10⁻⁶. -14 m 2 This indicates that further modification of the limestone is still necessary. Based on the complete modification of the medium-grained sandstone, and using the equivalent permeability corresponding to the working face water inflow equaling the aquifer recharge as the critical floor equivalent permeability for maintaining aquifer stability and normal mining, the modification thickness of the fine-grained sandstone is calculated to be 2.86m. Therefore, the grouting modification layers are medium-grained sandstone and limestone, with modification thicknesses of 5m and 2.86m respectively, which can achieve water-retaining mining. Figure 3 ).

[0042] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for in-situ water-retaining coal mining based on structurally and seepage-stabilized aquifers, characterized in that, Includes the following steps: S1. Obtain the geological, hydrogeological, and mining technical parameters of the target working face; This includes the working face length, advance distance, coal seam thickness, thickness of the confined aquifer, pressure and recharge rate, distance between the coal seam and the confined aquifer, and the thickness, strength and porosity of each rock layer between the coal seam and the confined aquifer; S2. Based on the above parameters, determine the depth of the mining-induced floor failure and the height of the confined water rise zone, obtain the mining permeability of each rock layer between the mining-induced floor failure zone and the confined water rise zone, and calculate the equivalent permeability of the mining-induced floor for each rock layer; determine the critical thickness corresponding to the stability of the aquifer structure and the critical equivalent permeability corresponding to the stability of the floor aquifer and normal mining. The critical equivalent permeability is the minimum of the following three values: the equivalent permeability corresponding to the water inflow equal to the aquifer recharge, the equivalent permeability corresponding to the maximum water inflow required for safe mining of the working face, and the equivalent permeability corresponding to the water consumption required for the working face. S3. Determine whether the structural stability conditions are met based on the distance between the coal seam and the aquifer on the floor, the depth of the mining-induced floor failure, and the height of the confined water conduction zone. Determine whether the seepage stability conditions are met based on the equivalent permeability and critical equivalent permeability of the mining-induced floor. S4. When one or both of the structural stability conditions and seepage stability conditions are not met, strength-sensitive rock layers and / or permeability-sensitive rock layers are selected for grouting modification based on the judgment result, and the grouting modification layer position and grouting modification thickness are determined, specifically including: If the structural stability condition is met but the seepage stability condition is not met, then grouting of the permeability-sensitive rock layer is selected, and the minimum grouting thickness is determined in combination with the seepage stability condition. If the structural stability condition is not met but the seepage stability condition is met, then grouting of strength-sensitive rock strata should be selected, and the minimum grouting thickness should be determined in combination with the structural stability condition. If neither the structural stability condition nor the seepage stability condition is met, then grouting is selected for strength-sensitive rock layers and permeability-sensitive rock layers. The grouting reinforcement layer positions and thicknesses are determined according to the structural stability condition and the seepage stability condition, respectively, and the scheme with the smallest total reinforcement thickness is the final scheme. After grouting modification, the judgment in step S3 is repeated; If the structural stability and seepage stability conditions cannot be met by grouting modification alone, then after adjusting the working face length and / or the advancing distance, repeat steps S2 to S4 to make a judgment until the structural stability and seepage stability conditions are met.

2. The in-situ water-retaining coal mining method based on structurally and seepage-stabilized aquifers according to claim 1, characterized in that, In step S2, the formula for calculating the equivalent permeability of the mining base plate is: ; In the formula, The distance between the coal seam and the confined aquifer is in meters (m). The depth of the mining-induced floor failure is measured in meters (m). The height of the pressurized water riser is in meters (m). The thickness of each rock layer between the mining-induced floor failure zone and the confined water uplift zone is measured in meters (m). The mining permeability of each rock stratum between the mining-induced floor failure zone and the confined water uplift zone is given by m. 2 .

3. The in-situ water-retaining coal mining method based on structurally and seepage-stabilized aquifers according to claim 1, characterized in that, In step S2, the formula for calculating the critical thickness corresponding to the stability of the waterproof layer structure is as follows: ; In the formula, The length of the working surface is in meters (m). The distance the working face advances, in meters (m). The pressure of the pressurized water is MPa. The height of the pressurized water riser is in meters (m). The pressure attenuation coefficient is expressed in MPa / m. The bending moment coefficient, ; The equivalent tensile strength (MPa) of each rock stratum between the mining-induced floor failure zone and the confined water uplift zone. The calculation formula is: ; In the formula, The distance between the coal seam and the confined aquifer is in meters (m). The depth of the mining-induced floor failure is measured in meters (m). The height of the pressurized water riser is in meters (m). The thickness of each rock layer between the mining-induced floor failure zone and the confined water uplift zone is measured in meters (m). This refers to the tensile strength of each rock layer between the mining-induced floor failure zone and the confined water uplift zone.

4. The in-situ water-retaining coal mining method based on structurally and seepage-stabilized aquifers according to claim 3, characterized in that, In step S2, the inflow rate is equal to the equivalent permeability corresponding to the aquifer recharge rate. The calculation formula is: ; In the formula, The length of the working surface is in meters (m). The distance the working face advances, in meters (m). The pressure of the pressurized water is MPa. The recharge rate of the confined aquifer is expressed in m / s. The thickness of the confined aquifer is in meters (m). The viscosity coefficient is the hydrodynamic viscosity, in Pa·s; The distance between the coal seam and the confined aquifer is in meters (m). The depth of the mining-induced floor failure is measured in meters (m). The height of the pressurized water riser is in meters (m). The equivalent permeability corresponding to the maximum water inflow during safe mining of the working face The calculation formula is: ； In the formula, The maximum water inflow rate corresponding to safe mining of the working face, m 3 / s; The equivalent permeability corresponding to the water consumption at the working face The calculation formula is: ； In the formula, The water consumption required for normal mining operations at the working face, m 3 / s.

5. The in-situ water-retaining coal mining method based on structurally and seepage-stabilized aquifers according to claim 1, characterized in that, In step S3, structural stability is the primary condition for water-retaining mining. The structural stability condition for water-retaining mining is: the distance between the coal seam and the confined aquifer - the depth of the mining-induced floor failure - the height of the confined water conduction zone > the critical thickness corresponding to the structural stability of the aquifer. The seepage stability condition for water-retaining mining is: the equivalent permeability of the mining-induced floor is less than or equal to the critical equivalent permeability of the floor corresponding to the stability of the aquifer and normal mining.

6. The in-situ water-retaining coal mining method based on structurally and seepage-stabilized aquifers according to claim 1, characterized in that, In step S4, the method for determining the strength-sensitive rock layer and the permeability-sensitive rock layer is as follows: from the rock layers between the mining-induced floor failure zone and the confined water conduction zone, select rock layers other than mudstone and sandy mudstone with a porosity greater than the critical value for grouting reinforcement testing; determine the strength sensitivity based on the difference in tensile strength of the rock layers before and after grouting modification; and determine the permeability sensitivity based on the difference in the reciprocal of the permeability of the rock layers before and after grouting modification. Intensity sensitivity The calculation method is as follows: ; In the formula, The tensile strength (MPa) of each rock stratum between the mining-induced floor failure zone and the confined water uplift zone; The tensile strength of each rock layer after grouting modification is expressed in MPa. The method for calculating permeability sensitivity is as follows: ; The permeability of each rock layer between the mining-induced floor failure zone and the confined water uplift zone is given by m. 2 ; The permeability of each rock stratum after grouting modification is expressed in m. 2 .

7. The in-situ water-retaining coal mining method based on structurally and seepage-stabilized aquifers according to claim 1, characterized in that, In step S4, the grouting modification area is the area enclosed by the extension line drawn along the boundary of the goaf according to the bottom plate movement angle and intersecting with the grouting modification layer.

8. The in-situ water-retaining coal mining method based on structurally and seepage-stabilized aquifers according to claim 1, characterized in that, The depth of the mining-induced bottom plate failure and the height of the confined water riser zone in step S2 are obtained through field testing or numerical simulation.

Images