A design method of key parameters of a target grouting filling mound column water conservation coal mining

Abstract

The present application belongs to the technical field of coal mining, and particularly relates to a key parameter design method for target grouting filling mound column water conservation coal mining. The method comprises: collecting mine hydrogeological and mining geological data, obtaining coal rock stratum burial depth, thickness, physical and mechanical parameters and gangue fragmentation expansion coefficient; using discrete element numerical simulation to determine the caving zone height under the non-sufficient mining critical advance length; calculating the grouting drilling depth and caving zone porosity; preparing and testing the mechanical strength and diffusion accumulation angle of the grouting material in the laboratory; combining the non-sufficient mining critical coefficient, applying the rock stratum subsidence probability integral method, scientifically designing the filling mound column spacing, radius and grouting amount; finally forming a cemented mound column in the caving zone through ground drilling grouting, stably supporting the overburden rock stratum and controlling the aquifer structure deformation. The method parameter design is simple and accurate, and avoids the time and space interference of the traditional filling process.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, specifically relating to a key parameter design method for targeted grouting and filling of pier columns for water-retaining coal mining. Background Technology

[0002] With the development of coal resources, underground mining activities inevitably disturb the overlying strata, leading to the development of water-conducting fracture zones, which in turn damages the aquifer structure and causes a series of ecological and environmental problems such as groundwater level drop, surface vegetation death, and soil erosion. In traditional water-conserving coal mining techniques, backfilling mining methods, which utilize backfill bodies to control strata movement, are one of the effective ways to protect aquifers. However, existing technologies such as backfilling behind supports and continuous mining with backfilling have significant limitations: these methods often interfere with the coal mining process in time and space, and backfilling operations must be carried out during coal mining intervals, reducing the efficiency of the working face and making it difficult to adapt to the demands of high-intensity, continuous mining. Furthermore, the parameter design of traditional backfilling methods relies heavily on empirical estimations and lacks scientific quantitative basis, resulting in unstable support effects and poor economic efficiency. Summary of the Invention

[0003] To address the technical problems mentioned in the background, this invention provides a key parameter design method for targeted grouting and filling abutment columns in water-retaining coal mining. This method involves intermittent grouting and filling the caving zone behind the working face, allowing the grout to bond with the gangue in the caving zone to form filling abutment columns. This stabilizes and supports the overlying strata, controls strata subsidence, and maintains the structural stability of aquifers with water supply and ecological value, thereby achieving water-retaining coal mining. The method includes the following steps:

[0004] Step 1: Collect hydrogeological and mining geological data of the mine, and obtain the burial depth H1, thickness M, physical and mechanical parameters of the coal and rock strata, working face dimensions, and the fragmentation coefficient K of the gangue in the goaf caving zone. p ;

[0005] Step 2: Based on the data obtained in Step 1, establish a goaf caving zone model using the discrete element numerical simulation software UDEC to simulate the rock strata caving behavior of the working face under the condition of insufficient mining critical advance length, and determine the working face at the insufficient mining critical advance length L. t The height H of the collapse zone under the given conditions d The non-fully-exploited critical advance length L t The critical state of the working face when it advances to the point of rock collapse stability is determined by simulating the rock collapse process.

[0006] Step 3: Based on the height H of the landslide zone d Calculate the drilling depth H of the grouting borehole. ks， Where H ks Used to ensure that the borehole penetrates the collapse zone while leaving a safety margin;

[0007] Step 4: Based on the fragmentation coefficient K of the gangue in the goaf caving zone p The porosity of the caving zone was calculated. The porosity Characterizes the proportion of voids in the collapse zone that can be filled by grouting;

[0008] Step 5: Prepare grouting materials with different mechanical strengths and flow properties, and test the mechanical strength F and grout diffusion-packing angle of the grouting materials in the laboratory. And select grouting materials that meet the support requirements based on the test results;

[0009] Step 6: Based on the critical coefficient of inadequate extraction Determine the spacing D of the filling piers. The spacing D is used to ensure that the piers support the overlying rock layer at intervals and to control the subsidence of the rock layer.

[0010] Step 7: Using the probability integral method for predicting rock strata subsidence, calculate the maximum subsidence value W of the target protected aquifer under different filling pier base radii R. Through iterative calculation, ensure that W is less than the subsidence threshold W of the aquifer in water-retaining coal mining. max This allows for the determination of the pier radius R and grouting volume Q.

[0011] Step 8: Based on the key parameters obtained in the above steps, grouting is carried out in the caving zone using ground drilling to form filling columns, so as to achieve water-retaining coal mining. The grouting process ensures that the grout and the gangue in the caving zone are bonded together to form a stable support structure.

[0012] In an optional embodiment, the physical and mechanical parameters in step 1 include at least one of the following: coal density, compressive strength, elastic modulus, and Poisson's ratio; the working face dimensions include the working face dip length and strike length; and the fragmentation coefficient K... p Obtained through on-site measurements or laboratory compaction tests.

[0013] In an optional embodiment, the discrete element numerical simulation method described in step 2 is implemented using UDEC software. The simulation process includes establishing a numerical model of the coal and rock strata, setting boundary conditions, applying mining loads, and determining the caving zone height H through iterative calculations. d The non-fully-exploited critical advance length L t Related to the coal seam burial depth H1, L t Through formula L t = H1× Preliminary estimate, This is the critical coefficient for incomplete extraction.

[0014] In an optional embodiment, the drilling depth H of the grouting borehole described in step 3 is... ksThe calculation formula is:

[0015] ;

[0016] Where H1 is the burial depth of the coal and rock strata, in meters; H d The height of the collapse zone is in meters; K1 is the set borehole depth margin coefficient, with a value ranging from 0.8 to 0.95.

[0017] In an optional embodiment, the porosity of the caving zone described in step 4... The calculation formula is:

[0018] ;

[0019] Among them, K p K represents the coefficient of rock fragmentation in the goaf caving zone. p The value range is 1.2 to 1.8, and the porosity is... Used to quantify the available space for grouting and filling.

[0020] In an optional embodiment, the grouting material in step 5 is prepared from ordinary silicate cement, gangue, fly ash, and water. The mechanical strength F and flow characteristics of the grouting solidified body are controlled by adjusting the water-cement ratio, the amount of aggregate added, and the proportion of water-reducing agent and accelerator. The mechanical strength F of the grouting solidified body must meet the following conditions:

[0021] ;

[0022] Where H1 is the burial depth of the coal and rock strata in meters; K2 is the safety factor, with a value ranging from 1.1 to 1.5.

[0023] In an optional embodiment, the formula for calculating the spacing D of the filling piers in step 6 is:

[0024] ;

[0025] Among them, L t H1 represents the critical advance length for non-fully mined conditions, in meters; H1 represents the burial depth of the coal and rock strata, in meters. This is the critical coefficient for incomplete extraction. The value range is 1 / 3 to 1 / 2.

[0026] In an optional embodiment, the filling pier in step 7 is approximately frustum-shaped, and the pier height is based on the caving zone height H. d The formula for calculating the grouting volume Q of a single pier column is as follows:

[0027] ;

[0028] Where R is the radius of the bottom surface of the filling pier column, in meters; K1 is the borehole depth allowance coefficient, with a value ranging from 0.8 to 0.95; The angle of slurry diffusion and accumulation, in degrees; This refers to the porosity of the collapse zone.

[0029] In an optional embodiment, the probability integral method based on rock subsidence prediction in step 7 includes the following algorithmic steps:

[0030] a) Set multiple candidate values ​​for the radius R of the bottom surface of the filling pier column;

[0031] b) For each candidate value of R, the maximum subsidence value W of the target protected aquifer is obtained through rock strata movement prediction analysis;

[0032] c) Plot the relationship curve between the maximum settlement value W and the radius R of the bottom surface of the infilled pier column;

[0033] d) The aquifer subsidence threshold W based on the requirements for water-conserving coal mining. max Determine from the relationship curve that W≤W max The critical value of the radius R of the bottom surface of the filling pier column is used to determine the R value adopted in the design;

[0034] e) Substitute the determined critical value of R into the calculation formula for the grouting volume Q of the pier column to calculate the grouting volume Q.

[0035] In an optional embodiment, the ground drilling and grouting method in step 8 includes drilling using casing drilling technology, with grouting boreholes spaced at intervals along the working face advancement direction, the interval being the spacing D between the filling piers; during the grouting process, grout is injected into the collapse zone through the boreholes, and the grout diffuses and cements with the gangue using its own weight to form grouting filling piers, which support the overlying rock strata to control the structural stability of the aquifer.

[0036] The advantages of this application compared to existing technologies are:

[0037] This invention provides a key parameter design method for targeted grouting and filling piers in water-conserving coal mining, which has significant advantages compared with existing technologies. First, this invention scientifically quantifies key parameters (such as pier spacing, radius, and grouting volume) through discrete element numerical simulation and probabilistic integral methods, avoiding the blindness of traditional experience-based design and improving parameter accuracy and support reliability. Second, this method uses ground drilling grouting to form filling piers at intervals in the caving zone of the goaf, without interfering with the coal mining process, achieving spatiotemporal separation of high-intensity mining and water conservation measures, making it particularly suitable for efficient production in large-scale mines in western China. Third, the grouting material ratio is optimized and tested in the laboratory to ensure that the mechanical strength meets the requirements of deep support, while the grout diffusion characteristics are adapted to the void structure of the caving zone, improving the stability and economy of the piers. Furthermore, this invention is highly innovative, organically combining strata control and hydrological protection, and effectively maintaining the stability of the aquifer structure and reducing ecological disturbance through a simple and systematic parameter design process. Attached Figure Description

[0038] Figure 1 To determine the critical advance length L for insufficient mining at the working face, the UDEC discrete element numerical simulation method is used in this invention. t The height H of the caving zone under certain conditions d A schematic diagram of the principle;

[0039] Figure 2 This invention employs a probability integral method for predicting rock strata subsidence to calculate aquifer subsidence curves under different filling pier radii.

[0040] Figure 3 Fitting curves for aquifer settlement under different infilled pier base radii;

[0041] Figure 4 This is a schematic diagram illustrating the method for calculating the grouting volume of the truncated cone-shaped grouting filling pier column according to the present invention;

[0042] Figure 5 This is a front view illustrating the principle of a targeted grouting and filling method for water-retaining coal mining piers according to the present invention.

[0043] Figure 6 This is a top view illustrating the principle of a targeted grouting and filling method for water-retaining coal mining piers according to the present invention.

[0044] In the diagram: 1-Grouting borehole; 2-Key aquifer; 3-Collapse zone; 4-Grouting filling pillar; 5-Coal seam; 6-Grouting material; 7-Borehole terminal; 8-Vegetation root system; 9-Working face return airway; 10-Working face transport roadway; 11-Protective coal pillar; 12-Working face advance direction; 13-Stop mining line. Detailed Implementation

[0045] Example 1: Application Case of Key Parameter Design for Targeted Grouting and Filling Pier Columns in Water-Conserving Coal Mining in a Western Mine

[0046] A western coal mine has a designed production capacity of 800 Mt / a. Currently, the main coal seam being mined is seam 2-2, with a burial depth of approximately 300 m and an average thickness of 5 m. It contains the Salawusu Formation aquifer, a key aquifer with significant water supply and ecological value. Based on surface vegetation type and water resource protection needs, the subsidence threshold for water-conserving mining is estimated at 0.5 m. Traditional caving mining methods pose a risk of damaging the Salawusu Formation aquifer. The proposed 20116 working face has a dip length of approximately 160 m and a strike length of 1220 m. Compaction characteristic tests on the gangue in the goaf of the adjacent 20114 working face yielded a gangue fragmentation coefficient of 1.7.

[0047] This embodiment involves intermittent grouting and filling the caving zone behind the working face. The grout binds with the gangue in the caving zone to form filling pillars that stably support the overlying strata, effectively controlling strata subsidence, maintaining the stability of the aquifer structure, and thus achieving the goal of water-conserving coal mining. The specific implementation process of this method is as follows:

[0048] Step 1: Collection and Analysis of Mine Geological and Mining Data

[0049] First, comprehensive hydrogeological and mining geological data of the mine were collected, obtaining information such as coal seam depth H1=300 m, average thickness of coal seam 5 M=5 m, and dip length L of working face 20116. q =160 m, Path length L z =1220 m, through systematic testing of the gangue in the goaf, the crushing expansion coefficient K of the gangue in the goaf was obtained. p =1.7. These fundamental data provide an important basis for subsequent parameter design. Physical and mechanical parameters include coal and rock density, compressive strength, elastic modulus, and Poisson's ratio. These parameters were obtained through field sampling and laboratory testing to ensure the accuracy and reliability of the data. The determination of the working face size considered the requirements of mining efficiency and strata control. The coefficient of fragmentation was obtained using a combination of field measurements and laboratory compaction tests to ensure the scientific validity of the data.

[0050] Step 2: Determine the height of the landslide zone using discrete element numerical simulation.

[0051] Based on the coal and rock strata thickness, mechanical parameters, and burial depth data obtained in step 1, a UDEC discrete element numerical model of the 20116 working face was established. The discrete element numerical simulation method can accurately simulate the deformation and failure process of rock mass under mining influence, and is particularly suitable for analyzing the development characteristics of caving zones. During the simulation, a coal and rock strata numerical model conforming to actual geological conditions was established, reasonable boundary conditions and mining loads were set, and the development height of the caving zone was determined through iterative calculations.

[0052] like Figure 1 As shown, through UDEC discrete element numerical simulation, the movement and collapse patterns of the overlying strata during the working face advancement can be clearly observed. t Related to the coal seam burial depth H1, L t Through formula L t = H1× Preliminary estimate, This represents the critical coefficient for incomplete mining. This step provides crucial information on rock strata movement for subsequent grouting parameter design.

[0053] Step 3: Calculation of grouting borehole drilling depth

[0054] Based on the caving zone height H determined in step 2 d Calculate the drilling depth H of the grouting borehole ks Determining the drilling depth requires considering the borehole's penetration into the collapse zone while allowing for an appropriate safety margin to ensure effective grouting. The calculation formula is as follows:

[0055] ;

[0056] In the formula, H1 is the coal seam burial depth, taken as 300 m; H d The height of the collapse zone 3 is taken as 25 m. K1 is the set borehole depth margin coefficient, taken as 0.9. This coefficient is selected to take into account the heterogeneity of the rock strata and construction errors, ensuring that the borehole can effectively reach the predetermined position. The calculated drilling depth H of the grouting borehole is then obtained. ks =277.5 m.

[0057] Among them, the drilling depth H of the grouting borehole ks It is the core control parameter for ground drilling construction. Its physical meaning is the vertical depth that must be measured from the ground surface, penetrate the entire collapse zone and extend into the stable rock layer below it. This depth must be greater than the bottom boundary depth of the collapse zone, otherwise the grout will not be able to be effectively injected into the target area, resulting in ineffective grouting. "Safety margin" is a redundant depth reserved to cope with geological uncertainties (such as local rock layer undulations, simulation errors, drilling deviation) to ensure the robustness of project implementation.

[0058] Step 4: Calculation of porosity in the caving zone

[0059] Based on the coal gangue fragmentation coefficient K in the goaf caving zone p =1.7, calculate the porosity of the caving zone. Porosity characterizes the proportion of voids in the collapse zone that can be filled by grouting, and is a key parameter for determining the amount of grout to be injected.

[0060] porosity It is a dimensionless parameter describing the percentage of pore volume within the loose medium of the caving zone, directly determining the effective space capacity that can be occupied by slurry in a unit volume of gangue pile; its value is affected by K. p Dominant, K p The larger the value, the more severely the gangue is broken and the more loosely it is packed. The higher the corresponding value, the better; this parameter is connected to geological measurements (K). p This is a crucial bridge between grouting and engineering grouting (grouting volume Q), enabling grouting design to move beyond the crude "guessing" approach; its calculation formula is:

[0061] ;

[0062] In the formula, K p The coefficient of rock fragmentation in the caving zone is taken as 1.7, and the porosity of the caving zone is calculated. =41.2%. Coefficient of disintegration K p The value ranges from 1.2 to 1.8, reflecting the volume change characteristics of gangue under different compaction states. Accurate calculation of the porosity provides a scientific basis for subsequent grouting volume design.

[0063] Step 5: Preparation and performance testing of grouting materials

[0064] Grouting materials with different mechanical strengths and flow properties were prepared, and the mechanical strength F and grout diffusion-packing angle of the grouting materials were tested in the laboratory. And select grouting materials that meet the support requirements based on the test results;

[0065] Among them, "mechanical strength F" refers to the maximum stress that the grouting solidified body can withstand under uniaxial compression conditions, characterizing its ability to support the overlying rock strata over a long period of time; "grout diffusion and accumulation angle" "" refers to the angle between the natural slope and the horizontal plane of freshly mixed grout in an unconstrained, free-stabilized state. It reflects the grout's fluidity, permeability, and self-stabilizing accumulation capacity within the voids of the gangue, directly affecting the final shape and density of the filled pier. These two aspects constitute two sides of the same coin in the performance of grouting materials.

[0066] F determines whether the pier can "hold up". It determines whether the slurry can "flow in and be piled up stably".

[0067] In an alternative implementation, grouting materials with different mechanical strengths and flow properties are prepared by adjusting the water-cement ratio, aggregate addition, water-reducing agent, and accelerator. The grouting materials are mainly composed of ordinary Portland cement, gangue, fly ash, and water. Laboratory tests are conducted on the mechanical strength F and grout diffusion and packing angle of the grout solidified body at a porosity of 41.2% as measured in step 5. The mix proportions and corresponding physical and mechanical parameters of the prepared grouting solidified body are shown in Table 1. The required condition is that the mechanical strength F of the grouting solidified body must meet the following conditions:

[0068] ;

[0069] In the formula, H1 is the coal seam burial depth, taken as 300 m, and K2 is the set safety factor, taken as 1.1; the calculated F = 8.25 MPa was obtained. The performance of various grouting materials with different proportions was tested in the laboratory, and the results are shown in Table 1.

[0070] Table 1. Mix proportions and corresponding physical and mechanical parameters of the grouting solidified body

[0071]

[0072] Comparative analysis revealed that grouting material #5 has a mechanical strength of 8.3 MPa, meeting the requirement of F > 8.25 MPa, and a diffusion-packing angle of 45°, exhibiting good flow characteristics. Considering both economic and performance requirements, grouting material #5 was ultimately selected as the grouting material. The optimized mix proportions of the grouting material ensured the supporting performance and construction feasibility of the filled pier columns.

[0073] Step 6: Design of pier spacing for filling

[0074] Based on the insufficient critical extraction coefficient The spacing D between the filling piers is determined. The design of the pier spacing must ensure that the piers can intermittently support the overlying rock strata and effectively control rock strata subsidence. Among these factors, the "critical coefficient for incomplete mining" is... It is the length L of the working face advance under the condition of insufficient mining. t The dimensionless parameter relating the quantitative relationship with the coal seam burial depth H1 is, in essence, a spatial response scale of the overlying strata structure stability to mining disturbance. A smaller value indicates that the rock strata at the same burial depth stabilize earlier, allowing for a larger spacing between piers; conversely, a larger value necessitates denser pier spacing. This coefficient directly links macroscopic geological conditions with microscopic support requirements, serving as a key factor in achieving universal applicability of parameter design. Its calculation formula is:

[0075] ;

[0076] In the formula, L tH1 represents the critical advance length for non-fully mined coal seams; H1 is the coal seam depth, taken as 300 m. The critical coefficient for incomplete mining is taken as 1 / 2; the calculated spacing between the filling piers is D = 150 m. (Critical coefficient for incomplete mining) The value ranges from 1 / 3 to 1 / 2, which ensures effective control of rock strata movement. The rational design of the pier spacing is a key aspect of achieving water-conserving coal mining.

[0077] Step 7: Determining the radius of the filling pier and the grouting volume

[0078] Using the probabilistic integral method for predicting rock strata subsidence, the maximum subsidence value W of the target protected aquifer is calculated under different infilled pier base radii R. Iterative calculations are then used to ensure that W is less than the subsidence threshold W for water-retaining coal mining aquifers. max This allows for the determination of the pier radius R and grouting volume Q.

[0079] Among them, the "probability integral method" is a classic theoretical model widely used in predicting coal mine strata movement. It treats the subsidence at any point on the surface or within the strata caused by mining as the result of the superposition of multiple independent random events. The entire subsidence basin morphology can be characterized by a finite number of parameters (such as the subsidence coefficient, the tangent of the main influence angle, and the inflection point offset). Extending this method to discrete pier support systems requires treating each pier as a local "reverse mining source," and its support effect is manifested by suppressing the bending and subsidence of surrounding strata. The "maximum subsidence value W" refers to the maximum vertical displacement of the target aquifer floor or key stratum calculated by the probability integral model under a given R; it is a direct quantitative indicator for measuring water retention effectiveness. max It is a rigid control standard set based on the hydrogeological functions of the aquifer (such as the threshold for maintaining spring flow and the allowable range of groundwater level fluctuations);

[0080] In one alternative implementation, the specific algorithm steps include:

[0081] a) Set multiple candidate values ​​for the radius R of the bottom surface of the filling pier: 10m, 20m, 30m, 40m, 50m;

[0082] b) For each candidate value of R, the maximum subsidence value W of the target protected aquifer is obtained through rock strata movement prediction analysis;

[0083] like Figure 2 As shown, the aquifer settlement curves corresponding to different bottom radii of the filled piers clearly reflect the influence of pier size on the rock strata control effect.

[0084] c) Plot the curve showing the relationship between the maximum settlement value W and the radius R of the bottom surface of the filled pier column;

[0085] like Figure 3As shown in the figure, the fitted curve indicates that the aquifer subsidence value gradually decreases as the radius of the pier base increases. When the radius of the pier base R > 30.33 m, the maximum subsidence value W of the target protected aquifer is < 0.5 m, which meets the requirements for water-conserving mining.

[0086] d) The aquifer subsidence threshold W based on the requirements for water-conserving coal mining. max =0.5 m, and from the relationship curve, we can determine that W≤W max The critical value of the radius R of the bottom surface of the filling pier is 30.33 m;

[0087] e) Substitute the determined critical value of R into the formula for calculating the grouting volume Q of the pier column to obtain the grouting volume Q.

[0088] The probability integral method for predicting rock strata subsidence was used to calculate the subsidence curves of the target protected aquifer when the radius R of the bottom surface of the infilled pier column was 10 m, 20 m, 30 m, 40 m, and 50 m. For example... Figure 2 As shown, the fitted curve of aquifer settlement as a function of the pier base radius is obtained as follows: Figure 3 As shown, when the radius R of the bottom surface of the filling pier is greater than 30.33 m, the maximum subsidence W of the target protected aquifer is less than 0.5 m, which meets the subsidence threshold W for the aquifer in the water-conserving mining of this mine. max <0.5 m requirement.

[0089] Calculate the grouting volume for working face 20116 based on the relevant parameters obtained from the preceding steps. For example... Figure 4 As shown, the grouting-filled pier 4 is truncated cone in shape. The grouting volume Q for a single pier can be calculated using the following formula:

[0090] ;

[0091] In the formula: K1 is the set borehole depth allowance coefficient, which is taken as 0.9; H d The height of the collapse zone is taken as 25 m; R is the radius of the bottom surface of the filling pier column, taken as 30.33 m; The porosity of the caving zone is taken as 41.2%; Taking the grout diffusion and accumulation angle as 45°, the calculated grouting volume for a single collapse zone pier column in working face 20116 is approximately Q≈11824.6 m³. 3 .

[0092] Step 8: Ground drilling and grouting implementation

[0093] Based on the key parameters obtained from the above steps, a filling pier was constructed in the collapse zone of the 20116 working face using ground drilling and grouting. The specific implementation process included drilling, grouting operations, and quality control.

[0094] Based on the key grouting parameters obtained in the preceding steps, a filling pier was constructed in the caving zone of the 20116 working face using surface drilling grouting. Grouting borehole 1 was positioned above coal seam 5, spaced 150m apart along the working face advancement direction 12, and drilled to borehole terminal 7 (depth 277.5m). During grouting, grouting material 6 was injected into the caving zone 3, bonding with gangue to form grouting filling pier 4. The pier supports the overlying strata, protecting the key aquifer 2 and vegetation root system 8. The working face layout includes the working face return airway 9, the working face transport airway 10, protective coal pillars 11, and the stop line 13, the main view of which is attached. Figure 5 As shown, the top view is as follows Figure 6 As shown in the diagram. This arrangement ensures the orderly progress of the mining process and coordinates with the spacing between the piers, ultimately achieving the goal of water-conserving coal mining.

[0095] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for designing key parameters for targeted grouting and filling of pier columns in water-retaining coal mining, characterized in that, Includes the following steps: Step 1: Collect hydrogeological and mining geological data of the mine, and obtain the burial depth H1, thickness M, physical and mechanical parameters of the coal and rock strata, working face dimensions, and the fragmentation coefficient K of the gangue in the goaf caving zone. p The physical and mechanical parameters mentioned in step 1 include at least one of the following: coal density, compressive strength, elastic modulus, and Poisson's ratio; the working face dimensions include the dip length and strike length of the working face; and the fragmentation coefficient K... p Obtained through on-site measurements or laboratory compaction tests; Step 2: Based on the data obtained in Step 1, establish a goaf caving zone model using discrete element numerical simulation software to simulate the rock strata caving behavior of the working face under the condition of insufficient mining critical advance length, and determine the working face at the insufficient mining critical advance length L. t The height H of the collapse zone under the given conditions d The non-fully-exploited critical advance length L t The critical state of the working face when it advances to the point of rock collapse stability is determined by simulating the rock collapse process. Step 3: Based on the height H of the landslide zone d Calculate the drilling depth H of the grouting borehole. ks， Where H ks Used to ensure that the borehole penetrates the collapse zone while leaving a safety margin; Step 4: Based on the fragmentation coefficient K of the gangue in the goaf caving zone p The porosity of the caving zone was calculated. The porosity Characterizes the proportion of voids in the collapse zone that can be filled by grouting; Step 5: Prepare grouting materials with different mechanical strengths and flow properties, and test the mechanical strength F and grout diffusion-packing angle of the grouting materials in the laboratory. And select grouting materials that meet the support requirements based on the test results; Step 6: Based on the critical coefficient of inadequate extraction Determine the spacing D of the filling piers. The spacing D is used to ensure that the piers support the overlying rock layer at intervals and to control the subsidence of the rock layer. Step 7: Using the probability integral method for predicting rock strata subsidence, calculate the maximum subsidence value W of the target protected aquifer under different filling pier base radii R. Through iterative calculation, ensure that W is less than the subsidence threshold W of the aquifer in water-retaining coal mining. max This allows for the determination of the pier radius R and grouting volume Q. Step 8: Based on the key parameters obtained in the above steps, grouting is carried out in the caving zone using ground drilling to form filling columns, so as to achieve water-retaining coal mining. The grouting process ensures that the grout and the gangue in the caving zone are bonded together to form a stable support structure.

2. The key parameter design method for targeted grouting and filling of pier columns for water-retaining coal mining according to claim 1, characterized in that, The drilling depth H of the grouting borehole mentioned in step 3 ks The calculation formula is: ； Where H1 is the burial depth of the coal and rock strata, in meters; H d The height of the collapse zone is in meters; K1 is the set borehole depth margin coefficient, with a value ranging from 0.8 to 0.

95.

3. The key parameter design method for targeted grouting and filling of pier columns for water-retaining coal mining according to claim 2, characterized in that, Step 4 describes the porosity of the caving zone. The calculation formula is: ； Among them, K p K represents the coefficient of rock fragmentation in the goaf caving zone. p The value range is 1.2 to 1.8, and the porosity is... Used to quantify the available space for grouting and filling.

4. The key parameter design method for targeted grouting and filling of pier columns for water-retaining coal mining according to claim 1, characterized in that, The grouting material mentioned in step 5 is prepared from ordinary Portland cement, gangue, fly ash, and water. The mechanical strength F and flow characteristics of the grouting solidified body are controlled by adjusting the water-cement ratio, aggregate addition amount, and the proportions of water-reducing agent and accelerator. The mechanical strength F of the grouting solidified body must meet the following conditions: ； Where H1 is the burial depth of the coal and rock strata in meters; K2 is the safety factor, with a value ranging from 1.1 to 1.

5.

5. The key parameter design method for targeted grouting and filling of pier columns for water-retaining coal mining according to claim 1, characterized in that, The formula for calculating the spacing D of the filling piers in step 6 is as follows: ； Among them, L t H1 represents the critical advance length for non-fully mined conditions, in meters; H1 represents the burial depth of the coal and rock strata, in meters. This is the critical coefficient for incomplete extraction. The value range is 1 / 3 to 1 / 2.

6. The key parameter design method for targeted grouting and filling of pier columns for water-retaining coal mining according to claim 3, characterized in that, The shape of the filling pier in step 7 is approximately frustum-shaped, and the pier height is based on the caving zone height H. d The formula for calculating the grouting volume Q of a single pier column is as follows: ； Where R is the radius of the bottom surface of the filling pier column, in meters; K1 is the borehole depth allowance coefficient, with a value ranging from 0.8 to 0.95; The angle of slurry diffusion and accumulation, in degrees; This refers to the porosity of the collapse zone.

7. The key parameter design method for targeted grouting and filling of pier columns for water-retaining coal mining according to claim 6, characterized in that, Step 7, using the probability integral method predicted by rock strata subsidence, includes the following steps: a) Set multiple candidate values ​​for the radius R of the bottom surface of the filling pier column; b) For each candidate value of R, the maximum subsidence value W of the target protected aquifer is obtained through rock strata movement prediction analysis; c) Plot the relationship curve between the maximum settlement value W and the radius R of the bottom surface of the infilled pier column; d) The aquifer subsidence threshold W based on the requirements for water-conserving coal mining. max From the relationship curve, determine the condition that W ≤ W max The critical value of the radius R of the bottom surface of the filling pier column is used to determine the R value adopted in the design; e) Substitute the determined critical value of R into the calculation formula for the grouting volume Q of the pier column to calculate the grouting volume Q.

8. The key parameter design method for targeted grouting and filling of pier columns for water-retaining coal mining according to claim 1, characterized in that, The ground drilling and grouting method described in step 8 includes drilling using casing drilling technology. The grouting boreholes are arranged at intervals along the working face advancement direction, with the interval distance being the spacing D between the filling piers. During the grouting process, the grout is injected into the collapse zone through the boreholes. The grout diffuses and cements with the gangue using its own weight to form grouting filling piers, which are used to support the overlying rock strata to control the structural stability of the aquifer.

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