Ground large-diameter borehole high-efficiency danger-resolving method for sealing goaf water

Abstract

The application provides a ground large-diameter drilling high-efficiency danger relieving method for closed goaf water, and relates to the technical field of coal mining. The ground large-diameter drilling high-efficiency danger relieving method for closed goaf water comprises the following steps: determining the overburden damage height D, and determining the static water quantity Q of the goaf and the dynamic recharge quantity Q of the aquifer based on the overburden damage height D; determining the drilling point position for large-diameter pumping, and determining the drilling depth based on the drilling point position; determining the parameters of the water pump and the equipped number of the water pump; setting the large-diameter drilling at the drilling point position; and monitoring the water change in the goaf. Through the analysis on the goaf water inrush intensity and the mining geological conditions, the ground large-diameter drilling point position is accurately arranged and constructed, the water change in the goaf is intelligently monitored, and the long-time stable operation effectively relieves the goaf water disaster threat of the closed goaf under the condition of abundant recharge source, and realizes the high-efficiency danger relieving.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, and in particular to an efficient method for resolving water accumulation in sealed goaf areas using large-diameter surface boreholes. Background Technology

[0002] During coal mine production, after coal mining is completed, large areas of goaf are formed in the finished mining areas. Due to mining activities, the roof strata of the coal seam collapse and fracture, causing damage to aquifers (or impermeable layers) in a large area of ​​the strata above the roof, creating water-conducting fractures. Water is released from these aquifers, forming goaf water accumulation. Over time, the area and volume of water accumulation in the goaf gradually increase, especially in closed goafs with abundant recharge sources. The large amount of accumulated water and its high pressure pose a serious threat to coal mine safety. Because old goaf water in closed spaces generally has characteristics such as large volume, high water head, and good concealment, it can suddenly surge into the mine without effective mitigation measures, causing sudden old goaf water inrush accidents. Currently, the following two methods are commonly used to deal with water accumulation in closed goafs under complex conditions:

[0003] One method is the protective coal pillar method. For closed old workings with abundant water supply, large water volume, high water head, strong concealment, high treatment difficulty, and high treatment cost, coal mines often directly designate them as old workings prohibited mining areas according to the "three zones" management method for old workings. Based on the mine pressure theory, the width of the water-proof coal pillar is calculated and water-proof coal (rock) pillars are left. This method leaves water-proof coal pillars from a standardized and scientific perspective to effectively resist the pressure of old workings and avoid water hazard threats. It is simple and easy to implement, eliminating the treatment process and cost of old workings. However, this method is too simplistic and crude. It occupies mineable coal resources, reduces the recovery rate of coal resources, and wastes resources. It has a negative impact on the mining efficiency and production benefits of coal mining enterprises and is not in line with the rational development and utilization of coal resources.

[0004] Another method is direct water release via underground drainage boreholes, which is the most traditional and conventional method for treating old goaf water in coal mines. However, achieving good treatment results with this method is often limited by the characteristics of the old goaf water itself and the capacity of the mine's underground drainage system. When the old goaf water is statically stored and the water head pressure is not high, using underground drainage boreholes to eliminate the threat of old goaf water hazards has a certain degree of safety and effectiveness. However, when facing closed goaf areas with large water accumulation and abundant dynamic replenishment, using conventional drainage boreholes to eliminate the threat of old goaf water hazards becomes less effective. However, the treatment effect is often unsatisfactory and faces many bottlenecks. First, the drainage system equipped in the mine may not be able to effectively meet the drainage needs of large amounts of old working water. Second, closed goaf areas often require the construction of special drainage roadways to ensure drainage effect. In this case, conventional underground water drainage technology methods require the addition of corresponding roadway engineering, additional drainage equipment, or even systemic drainage transformation, which greatly increases the engineering investment and time cost of old working water hazard treatment, making it difficult to control in terms of economic benefits and ease of implementation.

[0005] Among existing technologies for treating water accumulation in old goaf areas, especially when facing water accumulation in closed goaf areas with abundant recharge sources, there is no highly efficient, stable, safe, and reliable technology that can simultaneously achieve both high efficiency and economic benefits without increasing the burden on underground systems or wasting coal resources. Summary of the Invention

[0006] This invention provides an efficient method for resolving water accumulation in sealed goaf areas using large-diameter boreholes, addressing the problems of existing technologies that require additional burden on downhole systems and waste coal resources.

[0007] This invention provides an efficient method for mitigating water accumulation in sealed goaf areas using large-diameter surface boreholes, comprising:

[0008] Determine the overburden failure height D, and based on the overburden failure height D, determine the static water accumulation Q in the goaf. 积 and dynamic recharge of aquifer Q 动补 ;

[0009] Determine the drilling locations for large-diameter drainage, and determine the drilling depth based on the drilling locations;

[0010] Determine the parameters of the water pump and the number of water pumps required;

[0011] A large-diameter borehole is drilled at the specified drilling location;

[0012] Monitor changes in water accumulation within the goaf.

[0013] According to the present invention, a highly efficient method for resolving water accumulation in a sealed goaf through large-diameter surface boreholes includes the step of determining the overburden failure height D, wherein:

[0014] The fracture-mining ratio C is obtained by dividing the measured height of the overlying strata failure in the goaf by the mining height under the same coal seam, geological mining conditions, and mining parameters in the same mine.

[0015] Based on the fracture-to-mining ratio C obtained from the analysis of measured data, the overburden failure height D is determined by analogy method according to the actual mining thickness M of the goaf to be drained.

[0016] According to the present invention, a highly efficient method for resolving water accumulation in a sealed goaf through large-diameter surface boreholes is provided, wherein the static water accumulation Q in the goaf is determined based on the overburden failure height D. 积 and dynamic recharge of aquifer Q 动补 The steps include:

[0017] The static water accumulation Q in the goaf is determined based on the water inflow volume, water level, water filling coefficient, mining height, and coal seam dip angle. 积 ;

[0018] The dynamic recharge Q of the aquifer was determined using analytical methods and hydrogeological analogy. 动补 .

[0019] According to the present invention, a highly efficient method for resolving water accumulation in a sealed goaf through large-diameter ground boreholes includes the step of determining the location of the large-diameter drainage borehole, comprising:

[0020] Based on the elevation of the working face roadway and the bottom plate of the goaf, the water accumulation parameters are determined, and the relatively low water collection point is determined as the borehole point based on the water accumulation parameters; wherein, the water accumulation parameters include the distribution range, water depth and dynamic replenishment of water in the goaf.

[0021] According to the present invention, a highly efficient method for resolving water accumulation in a sealed goaf through large-diameter ground boreholes includes determining the borehole depth based on the borehole location, wherein:

[0022] Measure the ground elevation of the borehole point;

[0023] The borehole depth is obtained based on the difference between the ground elevation and the floor elevation of the goaf.

[0024] According to the present invention, a highly efficient method for relieving water accumulation in a sealed goaf through large-diameter ground boreholes includes the step of setting up large-diameter boreholes at the borehole locations, comprising:

[0025] A primary casing is installed in the loose sand or topsoil layer at the borehole point, with the lower end of the primary casing positioned below the top interface of the bedrock.

[0026] The primary casing is secured with cement grout.

[0027] A secondary casing is installed inside the large-diameter borehole, with the lower end of the secondary casing positioned below the bottom plate of the goaf.

[0028] According to the present invention, a method for efficiently relieving water accumulation in a sealed goaf through a large-diameter ground borehole is provided, wherein the lower end of the primary casing is located 5-10m below the top interface of the bedrock.

[0029] According to the present invention, a method for efficiently relieving water accumulation in a sealed goaf by large-diameter ground borehole is provided, wherein the lower end of the secondary casing is set 5-10m below the bottom plate of the goaf, and the inner diameter of the secondary casing is at least 150mm larger than the outer diameter of the water pump.

[0030] According to the present invention, a method for efficiently resolving water accumulation in a sealed goaf through a large-diameter ground borehole is provided, wherein the secondary casing extending 5m above the top boundary of the water-conducting fracture zone to the borehole opening is a solid pipe, and the secondary casing extending 5m above the top boundary of the water-conducting fracture zone to the bottom of the borehole is a screen pipe.

[0031] According to the present invention, a highly efficient method for mitigating water accumulation in a sealed goaf through large-diameter ground boreholes includes the step of monitoring changes in water accumulation within the goaf, comprising:

[0032] Based on the obtained water level in the borehole and the flow rate in the drainage pipe, determine the flow rate versus time curve, the water level versus time curve, and the flow rate versus water level curve.

[0033] The changes in water accumulation within the goaf are obtained based on the flow rate versus time curve, the water level versus time curve, and the flow rate versus water level curve.

[0034] The efficient method for mitigating water accumulation in sealed goaf areas using large-diameter surface boreholes provided by this invention has the following advantages:

[0035] 1. The present invention provides an efficient method for mitigating water accumulation in closed goaf areas through large-diameter ground boreholes. By analyzing the water inflow intensity and mining geological conditions in the goaf area, the method precisely arranges and constructs large-diameter ground boreholes. Through intelligent monitoring of water accumulation changes in the goaf area, the method operates stably for a long time, effectively eliminating the threat of water hazards from old goaf water in closed goaf areas under conditions of abundant water supply, thus achieving efficient mitigation.

[0036] 2. The efficient method for relieving water accumulation in closed goaf areas by large-diameter surface drilling of the present invention is independent of the mine production system, avoids increasing the burden on the mine drainage system and the investment in complex underground treatment projects, and does not affect the normal operation of the mine system. It is significantly superior to the traditional method of draining old goaf water underground.

[0037] 3. The efficient method for relieving water accumulation in closed goaf areas by large-diameter ground drilling of the present invention can customize and optimize the large-diameter ground drainage scheme according to the old goaf water treatment target, taking into account both effectiveness and cost control.

[0038] 4. The efficient method of large-diameter ground borehole drilling for water accumulation in closed goaf areas, as described in this invention, reduces the amount of water accumulation and water head in the closed goaf areas after implementation, ensuring safe production in mines and improving the utilization rate of coal resources. Attached Figure Description

[0039] To more clearly illustrate the technical solutions in this 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 some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0040] Figure 1 This is a schematic diagram of the spatial location of overlying rock damage and water-bearing (impermeable) rock strata provided by the present invention.

[0041] Figure 2 This is a schematic diagram of the installation of a submersible pump in a borehole, provided by the present invention.

[0042] Figure 3 This is a schematic diagram of the structure of the large-diameter borehole provided by the present invention.

[0043] Figure 4 This invention relates to an efficient method for resolving water accumulation in sealed goaf areas using large-diameter surface boreholes. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0045] In the description of the embodiments of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not 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 the embodiments of the present invention. In addition, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0046] In the description of the embodiments of the present invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the embodiments of the present invention based on the specific circumstances.

[0047] In embodiments of the present 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," "on top of," and "over" 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.

[0048] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of the present 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.

[0049] The following is combined with Figures 1-3 This invention describes a specific implementation method for efficiently resolving water accumulation in enclosed goaf areas using large-diameter ground boreholes.

[0050] like Figure 1 As shown, the efficient method for resolving water accumulation in sealed goaf areas using large-diameter surface boreholes includes:

[0051] Step S100: Determine the overburden failure height D, and determine the static water accumulation Q in the goaf based on the overburden failure height D. 积 and dynamic recharge of aquifer Q 动补 ;

[0052] Step S200: Determine the drilling points for large-diameter drainage and determine the drilling depth based on the drilling points;

[0053] Step S300: Determine the parameters of the water pump and the number of water pumps required;

[0054] Step S400: Set a large-diameter borehole at the drilling point;

[0055] Step S500: Monitor changes in water accumulation within the goaf.

[0056] The present invention provides an efficient method for mitigating water accumulation in closed goaf areas through large-diameter ground boreholes. By analyzing the water inflow intensity and mining geological conditions in the goaf area, the method precisely arranges and constructs large-diameter ground boreholes. Through intelligent monitoring of water accumulation changes in the goaf area, the method operates stably for a long time, effectively eliminating the threat of water hazards from old goaf water in closed goaf areas under conditions of abundant water supply, thus achieving efficient mitigation.

[0057] The present invention provides an efficient method for resolving water accumulation in closed goaf areas through large-diameter surface boreholes. This method is independent of the mine production system, avoids increasing the burden on the mine drainage system and the investment in complex underground treatment projects, and does not affect the normal operation of the mine system. It is significantly superior to traditional methods for draining old goaf water underground.

[0058] The present invention provides an efficient method for resolving water accumulation in closed goaf areas through large-diameter ground drilling. It allows for customized and optimized large-diameter ground drainage schemes based on the goals of old goaf water treatment, balancing effectiveness and cost control.

[0059] The present invention provides an efficient method for mitigating water accumulation in closed goaf areas through large-diameter surface boreholes. After implementation, this method reduces the amount of water accumulation and the water head height in the closed goaf areas, ensuring safe production in mines and improving the utilization rate of coal resources.

[0060] In one embodiment of the present invention, the step of determining the overburden failure height D includes:

[0061] Step S110: Divide the measured results of the overburden failure height of the goaf under the same coal seam, the same geological mining conditions, and the same mining parameters of the mine by the mining height to obtain the fracture-mining ratio C and obtain the measured data of the goaf.

[0062] Step S120: Based on the fracture-to-mining ratio C obtained from the analysis of measured data, the overburden failure height D is determined by analogy method according to the actual mining thickness M of the goaf to be drained.

[0063] like Figure 1 As shown, assuming the regional fracturing ratio is C and the coal seam thickness is M under these mining conditions, the overburden destruction height D = M * C during coal seam mining.

[0064] In one embodiment of the present invention, the static water accumulation Q in the goaf is determined based on the overburden failure height D. 积 and dynamic recharge of aquifer Q 动补 The steps include:

[0065] Step S130: Determine the static water accumulation Q in the goaf based on the water inflow volume, water level, water filling coefficient, mining height, and coal seam dip angle. 积 ;

[0066] like Figure 1 As shown, the fracture zone contains aquifers H1 and H2. The static water accumulation Q in the goaf is determined. 积 and dynamic recharge of aquifer Q 动补 It is necessary to analyze the recharge intensity of the aquifers (aquifers H1 and H2) within the mining impact range. The main analysis parameters are: aquifer thickness M, permeability coefficient K, aquifer water level H, and water inflow Q at the mining face during production. 正 ;

[0067] Step S140: Determine the dynamic recharge Q of the aquifer using analytical methods and hydrogeological analogy methods. 动补 .

[0068] In one embodiment of the present invention, the step of determining the drilling location for large-diameter extraction includes:

[0069] Step S210: Determine the water accumulation parameters based on the floor elevation of the working face roadway and the goaf space in the goaf area, and determine the relatively low water collection point as the borehole point based on the water accumulation parameters; wherein, the water accumulation parameters include the distribution range of water accumulation in the goaf area, water accumulation depth and dynamic replenishment volume.

[0070] The location of large-diameter drainage boreholes is crucial as it directly affects the efficiency of water drainage. When determining the location of the boreholes, the topography and the impact on the surrounding environment should also be considered. Under the same conditions, choosing flat and well-drained locations for the layout of large-diameter boreholes can better ensure drainage efficiency and reduce the impact on the surrounding environment.

[0071] In one embodiment of the present invention, determining the drilling depth based on the drilling point includes:

[0072] Step S220: Measure the ground elevation of the borehole point;

[0073] Step S230: Obtain the borehole depth based on the difference between the ground elevation and the floor elevation of the goaf.

[0074] It should be noted here that after determining the location of the large-diameter borehole, an RTK instrument is used to measure the ground elevation H of the borehole location. 地面 Analyze the corresponding floor elevation H of the goaf. 底板 Calculate the borehole depth L=H 地面 -H 底板 The drilling depth is calculated in order to calculate the pump head.

[0075] like Figure 2 As shown, the selection and configuration of drainage pumps are equally crucial, directly affecting the drainage efficiency and treatment effect of water accumulation in the goaf. After determining the borehole locations and pump head, the hourly drainage capacity of the pumps is determined based on the old goaf water treatment objectives. Based on the hourly drainage capacity and pump head, the corresponding pump parameters and quantity are designed. When selecting the pump type, the actual efficiency and head loss of the pump should be considered. The selected pump head should be greater than the sum of the expected head loss and the required head. A deep-well vertical centrifugal pump with stable performance, high efficiency, and low maintenance costs should be selected.

[0076] In one embodiment of the present invention, the step of setting a large-diameter borehole at the borehole location includes:

[0077] Step S410: Install a primary casing in the loose sand or topsoil layer at the borehole point, with the lower end of the primary casing positioned below the top interface of the bedrock.

[0078] After determining the pump parameters and the required number of pumps, the parameters for large-diameter boreholes need to be designed. These parameters include the borehole diameter and borehole structure. Based on the selected pump model and the predicted overburden failure height at the working face, combined with the characteristics of the overburden, the parameters for large-diameter boreholes on the ground are determined. In areas with loose sand or topsoil layers on the surface, a two-stage borehole is generally used. A primary casing is installed to prevent borehole collapse in the loose sand or topsoil layers. The lower end of the primary casing is positioned 5-10m below the top interface of the bedrock.

[0079] Step S420: Secure the primary casing with cement grout;

[0080] Step S430: Install a secondary casing into the large-diameter borehole, with the lower end of the secondary casing positioned below the bottom plate of the goaf.

[0081] like Figure 3 As shown, cement grout is used to solidify the primary casing, which improves its stability. The diameter of the primary casing should be larger than that of the secondary casing by two levels. The lower end of the secondary casing is set 5-10m below the bottom plate of the goaf. The inner diameter of the secondary casing is at least 150mm larger than the outer diameter of the water pump to facilitate the raising and lowering of the water pump. The primary casing is a solid pipe, while the secondary casing combines a solid pipe and a screen pipe. The secondary casing from 5m above the top boundary of the water-conducting fracture zone to the borehole opening is a solid pipe, while the secondary casing from 5m above the top boundary of the water-conducting fracture zone to the bottom of the borehole is a screen pipe.

[0082] For large-diameter drilling, directional drilling rigs are the first choice. For holes less than 150m deep, non-directional drilling rigs can be used for step-by-step directional drilling to consider economic costs. For holes deeper than 150m, directional drilling rigs are used to ensure the verticality of the borehole and facilitate the installation and pumping of drainage equipment such as water pumps.

[0083] In one embodiment of the present invention, the step of monitoring changes in water accumulation within a goaf area includes:

[0084] Step S510: Based on the obtained water level in the borehole and the flow rate of the drainage pipe, determine the flow rate versus time curve, the water level versus time curve, and the flow rate versus water level curve.

[0085] Step S520: Based on the flow rate versus time curve, the water level versus time curve, and the flow rate versus water level curve, the changes in water accumulation in the goaf are obtained.

[0086] A highly efficient method for sealing water accumulation in goaf areas using large-diameter surface boreholes is employed. Monitoring and analyzing drainage volume and borehole water level data are crucial for effectiveness evaluation. Water level monitoring sensors are installed within the drainage boreholes to measure the water level. Flow monitoring devices are installed on the drainage pipelines to measure the flow rate. Analytically, the collected data is processed using statistical analysis software to plot flow-time and water level-time curves, and to calculate the relationship between flow rate and water level decline (QS curve), allowing for real-time monitoring of water accumulation in the goaf and assessment of drainage effectiveness. Simultaneously, an electromagnetic automatic start / stop control device is installed on the drainage pump within the borehole to achieve remote real-time monitoring and automatic control, improving pumping efficiency. Regular field surveys and data verification, combined with actual site conditions, ensure the authenticity and reliability of the monitoring data.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A highly efficient method for mitigating water accumulation in sealed goaf areas using large-diameter surface boreholes, characterized in that: include: Determine the overburden failure height D, and based on the overburden failure height D, determine the static water accumulation Q in the goaf. 积 and dynamic recharge of aquifer Q 动补 ; Determine the drilling locations for large-diameter drainage, and determine the drilling depth based on the drilling locations; Determine the parameters of the water pump and the number of water pumps required; A large-diameter borehole is drilled at the specified drilling location; Monitor changes in water accumulation within the goaf; The steps for determining the overburden failure height D include: The fracture-mining ratio C is obtained by dividing the measured height of the overlying strata failure in the goaf area by the mining height under the same coal seam, geological and mining conditions and mining parameters in the same mine. Based on the fracture-to-mining ratio C obtained from the analysis of measured data, the overburden failure height D is determined by analogy method according to the actual mining thickness M of the goaf to be drained. The static water accumulation Q in the goaf is determined based on the overlying strata failure height D. 积 and dynamic recharge of aquifer Q 动补 The steps include: The static water accumulation Q in the goaf is determined based on the water inflow volume, water level, water filling coefficient, mining height, and coal seam dip angle. 积 ; The dynamic recharge Q of the aquifer was determined using analytical methods and hydrogeological analogy. 动补 .

2. The efficient method for resolving water accumulation in sealed goaf areas using large-diameter surface boreholes according to claim 1, characterized in that, The step of determining the drilling locations for large-diameter extraction includes: Based on the elevation of the working face roadway and the bottom plate of the goaf, the water accumulation parameters are determined, and the relatively low water collection point is determined as the borehole point based on the water accumulation parameters; wherein, the water accumulation parameters include the distribution range, water depth and dynamic replenishment of water in the goaf.

3. The efficient method for resolving water accumulation in sealed goaf areas using large-diameter surface boreholes according to claim 2, characterized in that, Determining the borehole depth based on the borehole location includes: Measure the ground elevation of the borehole location; The borehole depth is obtained based on the difference between the ground elevation and the floor elevation of the goaf.

4. The efficient method for resolving water accumulation in a sealed goaf through large-diameter surface boreholes according to any one of claims 1 to 3, characterized in that, The step of setting a large-diameter borehole at the borehole location includes: A primary casing is installed in the loose sand or topsoil layer at the borehole location, with the lower end of the primary casing positioned below the top interface of the bedrock. The primary casing is secured with cement grout. A secondary casing is installed inside the large-diameter borehole, with the lower end of the secondary casing positioned below the bottom plate of the goaf.

5. The efficient method for resolving water accumulation in sealed goaf areas using large-diameter surface boreholes according to claim 4, characterized in that, The lower end of the primary casing is located 5-10m below the top interface of the bedrock.

6. The efficient method for resolving water accumulation in sealed goaf areas using large-diameter surface boreholes according to claim 4, characterized in that, The lower end of the secondary casing is located 5-10m below the bottom plate of the goaf, and the inner diameter of the secondary casing is at least 150mm larger than the outer diameter of the water pump.

7. The efficient method for resolving water accumulation in sealed goaf areas using large-diameter surface boreholes according to claim 4, characterized in that, The secondary casing extending 5m above the top boundary of the water-conducting fracture zone to the borehole opening is a solid pipe, while the secondary casing extending 5m above the top boundary of the water-conducting fracture zone to the bottom of the borehole is a screen pipe.

8. The efficient method for resolving water accumulation in a sealed goaf through large-diameter surface boreholes according to any one of claims 1 to 3, characterized in that, The steps for monitoring changes in water accumulation within the goaf area include: Based on the obtained water level in the borehole and the flow rate in the drainage pipe, determine the flow rate versus time curve, the water level versus time curve, and the flow rate versus water level curve. The changes in water accumulation within the goaf are obtained based on the flow rate versus time curve, the water level versus time curve, and the flow rate versus water level curve.

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