Coal seam drilling and grouting water conservation mining method

Abstract

The present application provides a coal seam drilling grouting water conservation mining method, the coal seam drilling grouting water conservation mining method comprises the following steps: surveying the hydrogeological conditions of coal mine area, determining the position of reconstructed water-resisting layer, according to the survey results, setting the reconstructed water-resisting layer at the top of the fissure zone before the working face mining, setting the reconstructed water-resisting layer in the middle of the fissure zone after the working face mining, designing the water conservation scheme of the reconstructed water-resisting layer after the working face mining, the water conservation scheme includes drilling arrangement and grouting parameters, the drilling arrangement includes at least one of surface drilling and underground drilling, constructing grouting drilling, preparing grouting material, carrying out grouting operation, after grouting is completed, effect test and evaluation are carried out, and the expected water conservation effect is ensured. The coal seam drilling grouting water conservation mining method can effectively solve the problem of coal mine water disaster, and ensure the safety of mine and the rational utilization of water resources.

Description

Technical Field

[0001] This invention relates to the field of coal seam mining technology, specifically to a method for coal seam drilling and grouting for water retention mining. Background Technology

[0002] In related technologies, grouting methods have been applied to the field of coal mine water hazard prevention and control. For example, the advanced treatment technology for water hazards in the coal seam floor uses grouting modification through directional drilling along the seam to solve the problems of limited construction location, short drilling sections when encountering water-bearing layers, and large grouting blind zones that exist in conventional downhole straight hole grouting methods.

[0003] Although grouting technology has been applied in coal mine water hazard prevention, its systematic application in water-conserving mining, especially in designing differentiated grouting schemes for different geological conditions, still faces many technical bottlenecks. In particular, coal seams are relatively shallow, rock fissures are well-developed, and the strata generally lack stable aquitards. Even if the mining-induced fracture zone does not directly affect the shallow aquifer, water within the aquifer will still leak downwards through primary and mining-induced fractures. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the technical problems in the related art.

[0005] Therefore, embodiments of the present invention propose a coal seam drilling and grouting method for water-retaining mining, which can effectively solve the problem of water hazards in coal mines and ensure mine safety and the rational utilization of water resources.

[0006] The coal seam drilling and grouting water-retaining mining method of this invention includes the following steps:

[0007] Investigate the hydrogeological conditions of the coal mining area, determine the distribution of soil layers above the top of the mined working face, and determine the location of the reconstructed aquitard.

[0008] Based on the exploration results, a reconstructed water-proof layer was set at the top of the fracture zone before the working face was mined, and a reconstructed water-proof layer was set in the middle of the fracture zone after the working face was mined.

[0009] After the working face is mined, a water-retaining scheme for reconstructing the aquitard is designed. The water-retaining scheme includes borehole layout and grouting parameters. The borehole layout includes at least one of surface boreholes and underground boreholes.

[0010] Construction grouting drilling, ensuring the drilling reaches the target grouting layer;

[0011] Prepare grouting materials, carry out grouting operations, and ensure that the grout is evenly diffused and fully filled in the target layer by controlling the grouting pressure and flow rate;

[0012] After grouting is completed, the effect is inspected and evaluated to ensure that the expected water retention effect is achieved.

[0013] The coal seam drilling and grouting water-retaining mining method of this invention can determine the location of the reconstructed aquitard based on the mining conditions of the working face. Furthermore, it can perform surface drilling and grouting as well as underground drilling and grouting for the reconstructed aquitard, thereby further strengthening waterproofing, preventing further leakage of groundwater, extending the mine's lifespan, and reducing drainage costs.

[0014] In some embodiments, the top soil layer of the mined working face includes, from bottom to top, a first water-retaining layer, a sandstone aquifer, a loess water-retaining layer, and a loose sand water-retaining layer. The location of the reconstructed water-retaining layer is determined according to the distribution of the fracture zone at the top of the mined working face.

[0015] In some embodiments, determining the location of the reconstructed waterproofing layer includes the following steps:

[0016] When the fracture zone develops after coal seam mining but does not penetrate the loess aquitard, a new aquitard is set at the bottom of the loose aquifer.

[0017] When the fracture zone develops to a height that extends to the bottom of the loose aquifer after coal seam mining, and the loess aquifer fails, a new aquifer is set at the bottom of the loose aquifer.

[0018] When the fracture zone develops to the surface after coal seam mining, or when there is no loose aquifer available to reconstruct a water-resistant layer, a reconstructed water-resistant layer is set in the middle of the fracture zone and grouting is used for repair and modification.

[0019] In some embodiments, in a plane orthogonal to the height direction of the fracture zone, the projected area of ​​the reconstructed waterproof layer at the bottom of the loose aquifer is larger than the projected area of ​​the fracture zone.

[0020] In some embodiments, the surface borehole includes a connected surface bend and a surface horizontal section, and the downhole borehole includes a downhole bend and a downhole horizontal section, at least a portion of the surface horizontal section and the downhole horizontal section are located within the reconstructed waterproof layer, and the surface horizontal section is located above the downhole horizontal section.

[0021] In some embodiments, the orifice of the surface borehole is located on the ground, the orifice of the downhole borehole is located in the working face roadway, and the distance between the orifice of the surface borehole and the fracture zone is greater than the distance between the orifice of the downhole borehole and the fracture zone.

[0022] In some embodiments, the downhole horizontal section is arranged adjacent to the bottom plate of the reconstructed aquitard.

[0023] In some embodiments, the preparation of the grouting material includes a fast-setting grouting material and a slow-setting grouting material. The slow-setting grouting material is used for grouting into the surface borehole, and the fast-setting grouting material is used for grouting into the downhole borehole.

[0024] In some embodiments, the grouting operation includes the following steps:

[0025] Grouting is performed into the downhole borehole, and after the grouting material in the downhole borehole has completely solidified, grouting is then performed into the surface borehole.

[0026] In some embodiments, the ratio of the amount of grouting material injected into the surface borehole to the amount of grouting material injected into the downhole borehole is not less than 8:2. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the reconstructed water-retaining layer and borehole arrangement in the coal seam drilling and grouting water-retaining mining method of this invention.

[0028] Figure 2 This is a schematic diagram of the arrangement of the reconstructed water-retaining layer in the coal seam drilling and grouting water-retaining mining method according to another embodiment of the present invention.

[0029] Figure 3 This is a schematic diagram of the arrangement of the reconstructed water-retaining layer in the coal seam drilling and grouting water-retaining mining method according to another embodiment of the present invention.

[0030] Figure label:

[0031] 100. First impermeable layer; 200. Sandstone aquifer; 300. Loess impermeable layer; 400. Loose sand impermeable layer; 500. Working face roadway; 600. Fissure zone.

[0032] 1. Reconstruct the waterproof layer.

[0033] 2. Ground drilling; 21. Ground bend section; 22. Ground horizontal section.

[0034] 3. Downhole drilling; 31. Downhole bend section; 32. Downhole horizontal section. Detailed Implementation

[0035] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0036] like Figures 1-3 As shown, the coal seam drilling and grouting water-retaining mining method of this embodiment includes the following steps:

[0037] The investigation of the hydrogeological conditions of the coal mining area aims to determine the distribution of soil layers above the top of the mined working face and identify the location of the reconstructed aquitard 1. Understandably, the investigation of the hydrogeological conditions of the coal mining area can be conducted through geological exploration, core drilling, and other methods to thoroughly investigate the distribution of aquifers and aquitards, the recharge, runoff, and discharge conditions of groundwater, and hydrogeological parameters (such as permeability and hydraulic conductivity). Testing the physical properties of the aquifer, such as particle size, apparent density, and porosity, provides a basis for the selection of grouting materials.

[0038] Optionally, experiments can be conducted indoors to test the diffusion range of the grouting material and to study the effects of grouting pressure and material properties on grout diffusion. Field tests can then be used to further validate the model test results and optimize subsequent grouting processes.

[0039] This provides a scientific basis for grouting scheme design, ensuring the rationality and effectiveness of grouting locations. It avoids blind construction, reduces resource waste and construction risks, and lays the foundation for subsequent selection of grouting materials and optimization of construction techniques.

[0040] Based on the exploration results, a reconstructed water-proof layer 1 was set at the top of the fracture zone 600 before the working face was mined, and a reconstructed water-proof layer 1 was set in the middle of the fracture zone 600 after the working face was mined.

[0041] It is understandable that before mining, the fracture zone 600 inside the coal mine is not developed, or during mining, a reservoir exists above the top of the fracture zone 600. In such cases, it is necessary to install a reconstructed aquitard 1 or to conduct drilling to drain water in order to protect the safety of the working face. If the reservoir is located in a water-scarce area, it is preferable to select a reconstructed aquitard 1 to avoid water loss.

[0042] After the working face is mined, the fracture zone 600 will redevelop. Therefore, it is necessary to set up a reconstructed water-proof layer 1 in the middle of the fracture zone 600 to facilitate subsequent grouting operations inside the reconstructed water-proof layer 1.

[0043] After the working face is mined, a water-retaining scheme for reconstructing the aquitard 1 is designed. The water-retaining scheme includes the borehole layout and grouting parameters. The borehole layout includes at least one of the surface borehole 2 and the downhole borehole 3.

[0044] Understandably, the location, spacing, depth, and structure of boreholes are designed based on geological conditions and grouting requirements. Boreholes can be drilled using surface directional drilling or downhole directional drilling, with the optimal solution selected based on actual conditions. Preferably, grouting is performed using both surface boreholes 2 and downhole boreholes 3 in the reconstructed aquitard 1 located in the middle of the fracture.

[0045] Construction grouting drilling is carried out to reach the target grouting layer. It is understood that ground drilling 2 can adopt the casing drilling process. After the hole is formed, the valve-type grouting pipe is sent to the bottom of the hole. A single packer is used in the directional drilling to fill the gap between the grouting pipe and the hole with grouting material.

[0046] Downhole, a directional drilling rig is used to drill at an angle to the horizontal section after opening a hole in the top plate. After directional drilling to the horizontal section, the casing is installed. The directional drilling of the horizontal section proceeds normally, and the entire section is grouted after the hole is formed.

[0047] It should be noted that the grouting drilling process also requires the study of parameters such as grouting pressure, flow rate, final borehole pressure, and final borehole grout volume to determine the optimal grouting parameters and ensure that the grout diffuses evenly and fills the target layer.

[0048] Specifically, regarding downhole grouting, grouting and sealing drilling sites are arranged at corresponding locations in the working face transport roadway or conveyor belt roadway, depending on the location of the reconstructed aquitard. Optionally, the grouting drilling sites are spaced 60 m apart, with 3 to 5 boreholes arranged in each grouting station. The borehole inclination angle can be adjusted as needed within the range of -40° to -55°, and grouting is carried out into the area of ​​the reconstructed aquitard.

[0049] For borehole structures, two-diameter casing structures are used for boreholes constructed in solid coal areas, while three-diameter casing structures are used for boreholes around goaf areas, Ordovician limestone boreholes, and boreholes passing through roadways. The structural parameters are as follows:

[0050] One open Drill 11 m, go down The protective pipe is 10 m long.

[0051] Second phase Drilled 36 m, went down The orifice pipe is 35 m long.

[0052] Three openings Drilled 61 m, went down The orifice pipe is 60 m long.

[0053] The following uses The drill bit has reached the final borehole level. Furthermore, due to the combined damage to the floor slab from mine pressure and water pressure within the goaf of the working face, the depth of damage may increase. Therefore, during construction, the borehole structure must be adjusted reasonably according to the actual situation to ensure the smooth progress of drilling and grouting.

[0054] After the pipe is installed, grouting and pipe reinforcement are performed on the borehole. To avoid fracturing the base plate, the grouting pressure should be gradually increased. The initial grouting pressure is the measured water pressure plus 1 MPa, and then the pressure is increased by 1 MPa for each subsequent grouting session until the three grouting sessions are completed (equivalent to pipe reinforcement). If a connection is found between the borehole and the water outlet in the goaf during grouting, measures such as increasing the grout concentration, adding aggregates, early-strength agents (accelerators), and intermittent grouting are taken to block the water outlet. If no connection is found, grouting is performed according to the normal grouting process.

[0055] In addition, grouting processes can also employ sequential grouting, single-hole grouting, continuous multi-hole grouting, and intermittent grouting. That is to say, based on the characteristics of each of these grouting methods, continuous multi-hole grouting can be used to improve grouting and sealing efficiency when reconstructing the aquitard. When encountering large karst fissures, if the grouting volume is excessive, measures such as adding aggregates can be taken to control the grout diffusion range.

[0056] For ground drilling grouting, the ground grouting station needs to be equipped with two sets of clay slurry preparation systems, two high-speed vortex slurry mixers, and six grouting pumps, capable of producing clay slurry, cement slurry, and clay-cement slurry with different proportions. The design grouting capacity for a single pump and a single grouting pipeline is 15 m. 3 / h, up to 3 grouting pumps can be used simultaneously for grouting, with a maximum grouting capacity of 45 m³ / h. 3 / h. If the amount of grout required to recreate the waterproof layer is particularly large during construction, multiple pumps can be used for simultaneous grouting, or a high-flow-rate grouting pump (pump capacity not less than 50 m³ / h) can be added. 3 / h) to speed up the grouting project.

[0057] Three 2-inch grouting pipelines need to be laid from the surface grouting station to the well site. For low-speed grouting, one pipeline is in operation and two are on standby. For high-speed grouting, two pipelines are in operation and one is on standby. Considering the local climate, winter temperatures are low, so winter freeze protection must be considered in advance when laying the pipelines. It is required that there be no low-lying points in the pipelines between the surface grouting station and the well site. After each grouting operation and flushing of the pipelines, both ends of the pipelines must be opened to drain water, and no residual water should remain in the pipelines.

[0058] Grouting methods are divided into two types: continuous grouting and intermittent grouting.

[0059] Continuous grouting: Grouting is carried out continuously from start to finish, with only adjustments made to the pump flow rate, pump pressure, and grout mix ratio. Advantages of continuous grouting: Fewer auxiliary grouting steps, higher efficiency; less grout waste, higher utilization rate; longer grout diffusion distance, resulting in better filling of fissures and cavities.

[0060] Intermittent grouting involves multiple, intermittent, and repeated grouting sessions. The interval between sessions for pure cement grout is typically 2–4 hours, while for clay-cement grout it is typically 4–8 hours. Before stopping grouting, a suitable amount of clean water must be injected into the hole to ensure unobstructed grouting channels. The water volume should generally be no less than twice the total volume of the grouting pipeline and the grouting hole. Intermittent grouting is often used to reduce the amount of grout injected and to mitigate the occurrence of secondary disasters. The intermittent grouting method is as follows:

[0061] Quantitative intermittent method. When encountering water-rich areas such as karst caves and runoff zones, where the grouting volume is large, in order to save grouting materials, the predetermined amount of grout is injected and then paused for a period of time. This process is repeated multiple times until the grouting is completed.

[0062] Intermittent grouting with varying quantities. If grout leakage occurs at the working face, grouting should be stopped immediately, paused for a period of time, the cause analyzed, and measures taken before grouting resumes.

[0063] Continuous grouting is often used during grouting. When encountering large karst fissures, the principle is to grout as much as possible. If the amount of grout is too large, measures such as adding aggregate can be taken to control the grout diffusion range.

[0064] The grouting pressure directly affects the grout's diffusion distance and effective filling range. To ensure proper grout diffusion, the pressure should not be set too low, causing incomplete filling, nor too high, leading to excessive grout diffusion and potentially enlarging existing fracture channels, creating new breaches. The total grouting pressure consists of the weight of the grout column within the borehole and the pressure generated by the grouting pump. Based on past grouting experience, the final grouting pressure should be no less than 1.5 times the maximum hydrostatic pressure of the aquifer being grouted.

[0065] Furthermore, considering that the modified area is above a goaf and has a water outlet channel, to prevent excessive pressure from having a counterproductive effect, enlarging the existing fracture channels, and thus increasing the water inflow at the working face, the grouting pressure should be gradually increased when entering the goaf area to avoid reaching the design final pressure all at once. High-pressure grouting can only be carried out after the water outlet channel has been sufficiently reinforced. The specific grouting pressure should be scientifically and rationally adjusted during actual construction based on the measured water level in the borehole and the grouting situation.

[0066] A water pressure test is conducted before grouting, and this test must be performed before each grouting operation. The main purpose is to determine the water absorption rate per unit grouting layer and to clear any blockages in the grouting pipeline and rock fissures within the borehole. The water pressure test results are expressed as the water absorption rate q.

[0067]

[0068] In the formula: q is the water absorption rate;

[0069] Q represents the input flow rate;

[0070] P is the total pressure acting within the test section;

[0071] L represents the length of the injected layer.

[0072] Based on the results of the water pressure test, the initial grout mix ratio is determined. Generally, a test injection with diluted grout is necessary to understand the grout intake of the hole, and the grout concentration is then adjusted according to the grouting results.

[0073] Start grouting: Once the initial grouting concentration is determined, the command is issued to the grouting station, which then begins to prepare the grout according to the required ratio. After the grouting is prepared, the grouting pump is turned on to pump the grout into the grouting pipe and grouting hole. The grouting pump speed should also be gradually increased from low to high.

[0074] Grouting parameter adjustment: During the grouting process, if the pressure does not rise for a long time, the following measures can be taken: increase the pump flow rate, or even use two pumps to grout simultaneously; increase the grout concentration, or change the grout type; add early strength agent or aggregate.

[0075] End of grouting: As the borehole pressure gradually increases, if clay-cement mixture grout or clay grout is being injected, it should be immediately replaced with pure cement grout. When the borehole pressure reaches the grouting end pressure, it indicates that grouting is about to end. At this point, the pump speed should be gradually reduced until the grouting pump flow rate also meets the grouting end standard. Maintain this for 30 minutes, then end the grouting. Before ending the grouting, take a cement grout sample to observe the setting time.

[0076] After grouting, pressurize with water: Once the grouting standard is met, press water into the hole. The water volume should be slightly greater than the sum of the volumes of the pipe and the casing inside the hole. If water cannot be pressed in after grouting, this step can be omitted. Clean the hole promptly according to the cement grout setting time.

[0077] Detailed records of the construction process: The water pressure test and grouting process should be recorded in detail; the specific gravity, pump volume, pump pressure, and orifice pressure of each grout should be measured and recorded in accordance with the format of the grouting shift report; the grouting volume data and the water pressure test data before and after grouting should be summarized in a timely manner, and the grouting effect should be analyzed to provide a basis for the next step of construction.

[0078] Prepare grouting materials, carry out grouting operations, and ensure that the grout is evenly diffused and fully filled in the target layer by controlling the grouting pressure and flow rate.

[0079] Understandably, grouting materials are prepared according to geological conditions and grouting requirements to ensure the fluidity, permeability, and sealing properties of the grout. The grout is then injected into the target layer using grouting equipment, with grouting pressure and flow rate controlled to ensure uniform diffusion and full filling. Real-time monitoring of parameters such as grouting pressure and flow rate ensures the smooth progress of the grouting process and allows for timely detection and handling of any abnormalities.

[0080] In other words, it ensures that the grout diffuses evenly and fills the target layer to form a stable waterproof layer. This improves the grouting effect and enhances water retention capacity. Monitoring the grouting process ensures the safety and smooth progress of the grouting operation.

[0081] After grouting is completed, the effect is inspected and evaluated to ensure that the expected water retention effect is achieved.

[0082] Understandably, methods such as core drilling and water injection tests are used to examine the sealing and permeability of the grouting layer and evaluate the grouting effect. Based on the test results, the grouting effect is evaluated to determine whether the expected water retention effect has been achieved. If the expected effect has not been achieved, supplementary grouting or other remedial measures are required. All parameters and test results during the grouting process are recorded, and data analysis is conducted to provide a reference for subsequent grouting operations.

[0083] In other words, ensuring the effectiveness of grouting guarantees the safety and efficiency of water-retaining mining. It provides a reference for subsequent grouting operations, optimizing grouting plans. Through data recording and analysis, it improves the scientific rigor and reliability of grouting technology.

[0084] Therefore, the coal seam drilling grouting water-retaining mining method of the present invention can determine the location of the reconstructed water-retaining layer 1 according to the mining conditions of the working face, and can also perform grouting of the surface borehole 2 and the underground borehole 3 for the reconstructed water-retaining layer 1, thereby further strengthening waterproofing, preventing groundwater from continuing to seep out, extending the mine life and reducing drainage costs.

[0085] In some embodiments, the top soil layer of the mined working face includes, from bottom to top, a first water-retaining layer 100, a sandstone aquifer 200, a loess water-retaining layer 300, and a loose sand water-retaining layer 400. The location of the reconstructed water-retaining layer 1 is determined based on the distribution of the fracture zone 600 at the top of the mined working face.

[0086] Understandably, if the fracture zone 600 does not penetrate the first aquitard 100, the flow of groundwater will be effectively blocked, resulting in good drainage. However, if the fracture zone 600 penetrates the first aquitard 100, groundwater will directly enter the coal seam through the fracture, leading to an increased risk of water hazards.

[0087] The sandstone aquifer 200 itself has high permeability. If the fracture zone 600 develops to this layer, groundwater will flow downward through the fractures and natural fissures in the sandstone, increasing the possibility of water damage.

[0088] Due to the loose nature of loess, even if the fissure zone 600 does not completely penetrate the layer, groundwater may still flow downwards through the fissures and pores of the loess, affecting the drainage effect.

[0089] The high permeability of loose sand layers makes it easy for groundwater to pass through, especially when fissures are developed, resulting in poor drainage.

[0090] like Figure 2 and Figure 3 As shown, the reconstructed aquitard 1 should be placed at the top of the fracture zone 600, that is, at the top of the sandstone aquifer 200 or at the bottom of the loess aquitard 300, to block groundwater from flowing downward through the fracture.

[0091] like Figure 1 As shown, the reconstructed waterproof layer 1 is located in the middle of the fracture zone 600, which can effectively block the flow path of groundwater. Especially in the case of fracture development, it significantly improves the water-proof performance of each layer. Furthermore, through the selection of grouting materials and process optimization, the stability and sealing performance of the waterproof layer are ensured, reducing the risk of water damage.

[0092] In some embodiments, determining the location of the reconstructed aquifer 1 includes the following steps: when the fracture zone 600 develops after coal seam mining but does not penetrate the loess aquifer 300, the reconstructed aquifer 1 is set at the bottom of the loose aquifer.

[0093] like Figure 2 As shown, a reconstructed aquitard 1 is installed at the bottom of the loose aquifer. The fracture zone 600 does not reach the loess aquitard 300, and groundwater mainly flows through the loose aquifer. The reconstructed aquitard 1 can effectively block the downward flow of groundwater.

[0094] When the fracture zone 600 develops to a height that connects to the bottom of the loose aquifer after coal seam mining, and the loess aquifer 300 fails, a reconstructed aquifer 1 is set at the bottom of the loose aquifer.

[0095] like Figure 3 As shown, a reconstructed impermeable layer 1 is installed at the bottom of the loose aquifer. If the loess impermeable layer 300 fails, groundwater may flow downwards through fissures and the loess layer. The reconstructed impermeable layer 1 enhances its impermeability and prevents groundwater flow.

[0096] When the fracture zone 600 develops to the surface after coal seam mining, or when there is no available loose aquifer to rebuild the aquifer 1, a rebuild aquifer 1 is set in the middle of the fracture zone 600 and grouting is used for repair and modification.

[0097] like Figure 1 As shown, a reconstructed aquitard 1 is installed in the middle of the fracture zone 600. Since the fracture zone 600 has reached the surface, it is impossible to install an aquitard at the bottom of the loose aquifer. Installing an aquitard in the middle of the fracture zone 600 can effectively prevent groundwater from flowing downward through the fracture.

[0098] In some embodiments, in a plane orthogonal to the height direction of the fracture zone 600, the projected area of ​​the reconstructed waterproof layer 1 at the bottom of the loose aquifer is greater than the projected area of ​​the fracture zone 600.

[0099] It is understandable that, such as Figure 1 As shown, the development range of fracture zone 600 may have some uncertainty, especially under complex geological conditions, where the connectivity and extension of fractures may exceed initial predictions. Furthermore, fracture zone 600 may be more densely packed or extended in some areas, leading to more complex groundwater flow paths. Therefore, by setting a larger projected area, it is ensured that the reconstructed aquitard 1 can cover all potential fracture areas, preventing groundwater from entering the mine through unblocked fractures due to insufficient coverage.

[0100] In actual geological conditions, the development of fracture zone 600 may contain prediction errors. For example, fracture zone 600 may extend further in some areas or be more densely packed in others. This uncertainty may result in the original cover being insufficient to completely block the flow of groundwater.

[0101] In other words, by setting a larger projected area for the reconstructed aquitard 1, a greater safety margin can be provided, reducing the risk of water damage caused by prediction errors. Even if the actual development range of the fracture zone 600 exceeds expectations, the reconstructed aquitard 1 can still effectively block the flow of groundwater.

[0102] In some embodiments, the surface borehole 2 includes a connected surface bend section 21 and a surface horizontal section 22, and the downhole borehole 3 includes a downhole bend section 31 and a downhole horizontal section 32. At least a portion of the surface horizontal section 22 and the downhole horizontal section 32 are placed on the reconstructed waterproof layer 1, and the surface horizontal section 22 is located above the downhole horizontal section 32.

[0103] It is understandable that, such as Figure 1 As shown, layered grouting can be achieved by placing the surface horizontal section 22 and the downhole horizontal section 32 at different depths of the reconstructed aquitard 1. This design allows grouting operations to be carried out at different depths, ensuring that the grout is evenly diffused and fully filled in each layer, thereby improving the overall grouting efficiency and effect.

[0104] In other words, by using surface borehole 2 and downhole borehole 3 for grouting, grouting parameters, such as grouting pressure and flow rate, can be flexibly adjusted according to the geological conditions and grouting requirements of different layers, ensuring effective diffusion of the grout in each layer. Through layered grouting, all areas of the reconstructed aquitard 1 can be more comprehensively covered, reducing grouting blind spots and improving the aquitard effect.

[0105] Furthermore, the structural design of both the surface and downhole boreholes 3 can adapt to complex geological conditions, such as the permeability and fracture development of different strata. By adjusting the depth and location of the boreholes, it is ensured that the grouting material can cover all potential fracture areas, thereby improving the grouting effect.

[0106] In some embodiments, the opening of the surface borehole 2 is located on the ground, and the opening of the downhole borehole 3 is located in the working face roadway 500. The distance between the opening of the surface borehole 2 and the fracture zone 600 is greater than the distance between the opening of the downhole borehole 3 and the fracture zone 600.

[0107] It is understandable that, such as Figure 1 As shown, the coverage area of ​​the fracture zone gradually increases from bottom to top, meaning the fractures extend upwards from the coal seam roof, forming a radial fracture network. The borehole of surface borehole 2 is located on the surface, and the distance between the borehole of surface borehole 2 and the top of the fracture zone 600 is greater than the distance between the borehole of underground borehole 3 and the bottom of the fracture zone 600. This ensures that the construction distance between surface borehole 2 and the fracture zone 600 can be maintained during construction, minimizing excessive disturbance to the fracture zone 600 during the surface borehole 2 process.

[0108] In some embodiments, the downhole horizontal section 32 is arranged adjacent to the bottom plate of the reconstructed watertight layer 1.

[0109] It is understandable that, such as Figure 1 As shown, the underground horizontal section 32 is located adjacent to the bottom plate, allowing the grout to form an initial interlayer at the bottom plate location more quickly during grouting. This rapidly formed interlayer provides a good foundation for subsequent surface grouting. In other words, by first forming an interlayer at the bottom plate location through underground grouting, the flow path of groundwater entering the mine through the fracture zone 600 can be effectively reduced, thus lowering the risk of water hazards.

[0110] In other words, during downhole grouting, the grout is closer to the bottom of the target formation, reducing the resistance encountered during diffusion and accelerating the diffusion rate, thus forming a barrier layer more quickly. By optimizing the grouting pressure and flow rate, the uniform diffusion and full filling of the target formation are ensured, improving the grouting effect.

[0111] In some embodiments, the preparation of grouting materials includes fast-setting grouting materials and slow-setting grouting materials. Slow-setting grouting materials are used for grouting into the surface borehole 2, while fast-setting grouting materials are used for grouting into the downhole borehole 3.

[0112] Understandably, quick-setting grouting materials can rapidly form a waterproof layer, reducing the possibility of grout flow and leakage. They are suitable for scenarios requiring rapid sealing of cracks, improving construction efficiency. Retarded grouting materials, on the other hand, have a longer working time and are suitable for scenarios requiring uniform diffusion over a larger area. They can more fully fill cracks and pores, improving the grouting effect.

[0113] It should be noted that quick-setting grouting materials include quick-setting epoxy resin grouting materials, quick-setting polyurethane grouting materials, etc., while slow-setting grouting materials include cement-based materials, etc. In other words, by using slow-setting grouting materials and quick-setting grouting materials in the surface borehole 2 and the downhole borehole 3 respectively, a water-resistant layer can be quickly formed at the bottom of the reconstructed water-resistant layer 1 to facilitate grouting in the surface borehole 2.

[0114] In some embodiments, the grouting operation includes the following steps: grouting into the downhole borehole 3, and after the grouting material in the downhole borehole 3 has completely solidified, grouting into the surface borehole 2.

[0115] Underground grouting can understandably form a water-tight layer quickly in the middle or bottom of the 600mm fracture zone, reducing the flow path of groundwater and lowering the risk of water damage. The water-tight layer formed by underground grouting can effectively reduce the pressure of groundwater on the mine, ensuring safe production. Surface grouting can further expand the grouting range and enhance the water-tightening effect based on the water-tight layer formed by underground grouting.

[0116] In other words, through layered grouting both underground and on the surface, multiple layers can be formed at different depths, enhancing the overall water-tightening effect. Based on geological conditions, parameters such as grouting pressure and flow rate are optimized to ensure uniform diffusion and full filling of the grout within the target layer. Furthermore, multi-layered grouting both underground and on the surface can create multiple layers at different depths, enhancing the overall water-tightening effect and effectively blocking groundwater flow. Surface grouting can further extend the grouting range based on the layers formed by underground grouting, ensuring complete coverage of the target layer and reducing grouting blind spots.

[0117] In some embodiments, the ratio of the amount of grouting material injected into the surface borehole 2 to the amount of grouting material injected into the downhole borehole 3 is not less than 8:2.

[0118] Understandably, in coal mine grouting and water retention projects, a design where the ratio of grouting material injected into surface borehole 2 to that injected into underground borehole 3 is no less than 8:2, along with a grouting sequence of underground grouting followed by surface grouting, allows for faster formation of an initial interlayer at the bottom slab, providing a solid foundation for subsequent surface grouting. This not only reduces the flow path of groundwater and lowers the risk of water damage but also, through supplementation and reinforcement by surface grouting, comprehensively covers the target strata, improving the overall grouting effect.

[0119] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0120] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0121] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0122] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0123] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0124] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for water-retaining mining by drilling and grouting in coal seams, characterized in that, Includes the following steps: The hydrogeological conditions of the coal mining area were investigated to determine the distribution of soil layers above the top of the mined working face and to identify the location of the reconstructed aquitard. The upper layer of the mined working face, from bottom to top, includes the first aquitard, a sandstone aquifer, a loess aquitard, and a loose sand aquitard. The location of the reconstructed aquitard was determined based on the distribution of fracture zones at the top of the mined working face. The determination of the location of the reconstructed aquitard includes the following steps: when the fracture zone developed after coal seam mining but did not penetrate the loess aquitard, a reconstructed aquitard is set at the bottom of the loose sand aquitard; when the fracture zone developed to a height reaching the bottom of the loose sand aquitard after coal seam mining, and the loess aquitard has failed, a reconstructed aquitard is set at the bottom of the loose sand aquitard; when the fracture zone developed to the surface after coal seam mining, or there is no loose sand aquitard available for reconstructing aquitard, a reconstructed aquitard is set in the middle of the fracture zone and grouting is used for repair and modification. Based on the exploration results, a reconstructed water-proof layer was set at the top of the fracture zone before the working face was mined, and a reconstructed water-proof layer was set in the middle of the fracture zone after the working face was mined. After the working face is mined, a water-retaining scheme for reconstructing the aquitard is designed. The water-retaining scheme includes borehole layout and grouting parameters. The borehole layout includes surface boreholes and downhole boreholes. The surface borehole includes a connected surface bend section and a surface horizontal section, and the downhole borehole includes a downhole bend section and a downhole horizontal section. At least a portion of the surface horizontal section and the downhole horizontal section are placed in the reconstructed water-tight layer, and the surface horizontal section is located above the downhole horizontal section. The opening of the surface borehole is located on the surface, and the opening of the downhole borehole is located in the working face roadway. The distance between the opening of the surface borehole and the fracture zone is greater than the distance between the opening of the downhole borehole and the fracture zone. The construction of grouting boreholes involves drilling to reach the target grouting layer. The grouting operation includes the following steps: grouting into the downhole borehole, and after the grouting material in the downhole borehole has completely solidified, grouting into the surface borehole. Prepare grouting materials, carry out grouting operations, and ensure that the grout is evenly diffused and fully filled in the target layer by controlling the grouting pressure and flow rate; After grouting is completed, the effect is inspected and evaluated to ensure that the expected water retention effect is achieved.

2. The coal seam drilling and grouting water-retaining mining method according to claim 1, characterized in that, In a plane orthogonal to the height direction of the fracture zone, the projected area of ​​the reconstructed waterproof layer at the bottom of the loose sand waterproof layer is larger than the projected area of ​​the fracture zone.

3. The coal seam drilling and grouting water-retaining mining method according to claim 1, characterized in that, The bottom plate of the downhole horizontal section is located adjacent to the reconstructed water-tight layer.

4. The coal seam drilling and grouting water-retaining mining method according to claim 3, characterized in that, The grouting material preparation includes fast-setting grouting material and slow-setting grouting material. Slow-setting grouting material is used for grouting into the surface borehole, while fast-setting grouting material is used for grouting into the downhole borehole.

5. The coal seam drilling and grouting water-retaining mining method according to claim 1, characterized in that, The ratio of the amount of grouting material injected into the surface borehole to the amount of grouting material injected into the downhole borehole shall not be less than 8:2.

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