A fluidized filling mining method for side-wall coal compression in open-pit coal mines

Abstract

The invention discloses a fluidized filling mining method for end wall compressed coal in an open-pit coal mine. When the working wall is advanced normally, fluidized filling mining equipment such as a fluidized coal mining drill and a filling pump are arranged at the end wall platform at the bottom of the pit where the spoil yard and the working wall intersect in the open-pit coal mine. The coal body is crushed by a high-pressure water jet, and the crushed coal-water mixture is collected, separated and transported. At the same time, a slag-based paste is used to fill the coal mining cavity in situ. The end wall compressed coal can be mined while the stability of the slope is controlled. On the one hand, the problem of waste of end wall compressed coal resources can be solved and the resource recovery rate can be improved. On the other hand, solid waste such as gangue in the mining process can be fully utilized to reduce the pollution to the environment caused by slag in the open-pit spoil yard. The stability of the end wall can be greatly improved under the premise of realizing safe and efficient mining of the end wall compressed coal. The invention is particularly suitable for mining the end wall compressed coal in open-pit coal mines with relatively poor geological conditions and soft coal seams.

Description

Technical Field

[0001] The invention relates to a method for mining compressed coal at the end wall of an open-pit coal mine, in particular to a method for mining compressed coal at the end wall of an open-pit coal mine by fluidized filling, and belongs to the technical field of coal mining. Background Art

[0002] Open-pit coal mining refers to the direct open-pit mining of coal deposited on the surface or shallow coal layers due to geographical changes. Since open-pit coal mines can utilize more ore layers, the open-pit coal mining method can obtain a larger proportion of coal mines than the underground coal mining method. About 40% of the world's coal production uses open-pit mining, and the coal output of open-pit coal mines in my country accounts for 20% of the total coal output. Open-pit coal mining has become the first choice for regional coal resource mining with its advantages of high resource recovery rate, low production cost, simple process and high safety factor. However, due to the characteristics of open-pit mining, the slope stops operating after advancing to the boundary defined by the economically reasonable stripping ratio. A large amount of coal resources that cannot be exposed will be covered as an important part of the end slope or the boundary working slope slope, which not only causes a waste of resources, but also the remaining coal is easily spontaneously combusted after being exposed to oxygen for a long time. Therefore, it is necessary to mine the end slope pressure coal in the open-pit coal mine.

[0003] At present, the main coal mining methods for end-slope coal compression include steep slope mining method, end-slope coal mining machine mining method, underground horizontal tunnel mining method and open-pit-underground coordinated mining method. The steep slope mining method requires effective control of the slope angle before mining to ensure that the slope has good stability. Then, on this basis, the width of the flat plate of the coal-bearing step on the lower side of the slope is shortened to increase the slope angle, thereby realizing the mining of the end-slope compressed coal in the open-pit coal mine. Although the steep slope mining method can utilize advanced coal mining equipment and help reduce investment costs, it is only suitable for geological environments with stable slopes and high rock strength, and the equipment needs to be adjusted many times during use, which has a certain impact on production efficiency. At the same time, the amount of auxiliary engineering is large, and highly coordinated management is required on site; the end-slope coal mining machine mining method is to use an end-slope coal mining machine similar to the room-and-pillar coal mining machine in a mine to mine the end-slope compressed coal in an open-pit coal mine. Although the end-slope coal mining machine mining method is simple and convenient, does not require underground support, does not require a large amount of mine construction, and can be used in complex geological environments, it requires a large amount of capital investment in the early stage of open-pit coal mine construction and has high costs; the underground horizontal tunnel mining method is to expose the coal seam at the end of the slope The transport tunnel and return air tunnel are excavated first, and the working face is constructed. The end-wall pressure coal is mined by underground mining. Although the underground horizontal tunnel mining method has a simple process, flexible layout and easy management, it is only suitable for open-pit coal mines with simple hydrogeological conditions, good slope stability and gently inclined or horizontal coal seams. In addition, the underground horizontal tunnel mining method has poor production continuity and adaptability, high requirements for tunnel support, poor safety of the end-wall working face, and slope stability cannot be guaranteed; the open-pit-underground coordinated mining method is a mining method in which open-pit mining and underground horizontal tunnel mining are carried out simultaneously. The key to this mining method is to clarify the safe distance and time sequence of open-pit and underground mining in spatial position, ensure the slope stability during mining, and ensure that mining can be carried out safely. The open-pit-underground coordinated mining method is only suitable for coal mines with strong rock slopes, thick coal seams, high stability and large coal volume, and in the case of poor spatial distribution, the two mining operations are prone to interfere with each other.

[0004] Although the above-mentioned coal mining operation method for end-wall coal compression has made some progress and practical application, there are still problems such as large engineering workload, poor working face stability, low end-wall resource recovery rate, and difficult to control slope stability. Summary of the invention

[0005] In view of the problems existing in the above-mentioned prior art, the present invention provides a fluidized filling mining method for the end wall compressed coal in an open-pit coal mine, which can greatly improve the stability of the end wall while realizing safe and efficient mining of the end wall compressed coal. It is particularly suitable for mining the end wall compressed coal in open-pit coal mines with relatively poor geological conditions and soft coal seams.

[0006] To achieve the above purpose, the open-pit coal mine end-wall pressure coal fluidized filling mining method specifically includes the following steps:

[0007] Step 1: According to the length and thickness of the end wall coal seam to be mined in the open-pit coal mine, a fluidized filling mining scheme for end wall coal pressure is calculated and planned, including coal mining channels and reserved coal pillars between the coal mining channels. The fluidized filling mining scheme for end wall coal pressure adopts a high-pressure sealed drill rod retreat mining method, and the coal mining channels and reserved coal pillars are arranged in sequence from outside to inside along the end wall direction;

[0008] Step 2, the first coal mining channel is constructed by the end wall pressure coal fluidized filling mining scheme, and a layer drill hole of a set depth is drilled on the end wall vertical wall along the end wall direction by using a high-pressure sealed drill rod equipped with a coal-breaking drill bit, and the outer diameter of the coal-breaking drill bit is larger than the outer diameter of the high-pressure sealed drill rod. After the high-pressure sealed drill rod and the coal-breaking drill bit are withdrawn, the coal-breaking drill bit is replaced with a hydraulic cutting nozzle, and then the high-pressure sealed drill rod equipped with a hydraulic cutting nozzle is re-inserted into the borehole, and high-pressure water is sent into the high-pressure sealed drill rod by a high-pressure water pump, and a high-pressure water jet is formed through the hydraulic cutting nozzle to impact and crush the coal body. The crushed coal is mixed with water to form a coal-water mixture, and the coal-water mixture is discharged from the annular channel between the high-pressure sealed drill rod and the borehole to the outside of the borehole, and the rotation and retreat movement of the high-pressure sealed drill rod are controlled. After the high-pressure water jet breaks the coal, a hydraulic coal-breaking cavity is formed in the coal mining channel;

[0009] Step 3, the coal-water mixture is led to the vibrating screen through a pipeline for separation, the large coal particles separated by the vibrating screen are transported to the coal bunker, the coal-water mixture containing fine coal particles separated by the vibrating screen enters the heavy medium suspension device for separation, the coal-water mixture separated by the heavy medium suspension device enters the filter press for filtration, the filter cake separated by filtration is sent to the coal bunker, and the water separated by filtration enters the water tank connected to the high-pressure water pump for recycling;

[0010] Step 4, after the first hydraulically broken coal cavity is mined, the next coal mining channel is mined after the reserved width of the reserved coal pillar, and the hydraulically broken coal cavity is filled with filling materials at the same time;

[0011] Step 5, and so on, repeat Step 1 to Step 4 to complete the end wall coal compression mining and filling of hydraulic coal breaking cavities under the condition of reserved coal pillar support. After the mining of the coal mining channel located on the innermost side of the end wall is completed, the hydraulic coal breaking cavities located on the innermost side of the end wall are filled with filling materials. At the same time, the mining of coal mining channels is carried out on the reserved coal pillars between the filled and dried hydraulic coal breaking cavities until all the reserved coal pillars are mined and filled.

[0012] As a further improvement of the present invention, the calculation process of the reserved width of the reserved coal pillar in the Step 1 end support coal fluidized filling mining scheme is as follows:

[0013] The end-wall coal body was sampled on site, and the stress-strain curve of the coal body shearing process was obtained through rock direct shear test. According to the Mohr-Coulomb criterion, the relationship between the cohesion and internal friction angle of the end-wall coal body sample was obtained as follows:

[0014]

[0015] Where: f is the normal stress perpendicular to the shear plane; τ is the shear strength; c is the cohesion of the coal body; is the friction angle within the coal body;

[0016] In the width direction of the reserved coal pillar, the actual load borne by the reserved coal pillar is:

[0017]

[0018] Where: a is the width of the reserved coal pillar; b is the width of the coal mining channel; γ is the average bulk density of the overlying strata; H is the average thickness of the overlying strata;

[0019] According to the Mohr-Coulomb yield criterion, the vertical stress σ1 borne by the reserved coal pillar is:

[0020]

[0021] Where: σ1 is the vertical stress borne by the reserved coal pillar; σ3 is the lateral stress;

[0022] Based on the symmetry of the stress distribution of the reserved coal pillar, when the lateral stress σ3 at the edge of the reserved coal pillar is 0, the lateral stress σ3 in the yield zone gradually increases from the outside to the inside and reaches the maximum at the junction with the core area. Once the internal stress of the core area reaches the peak stress, the elastic state of the core area gradually disappears and the reserved coal pillar becomes unstable. At this time, σ3 = λγH, and the corresponding maximum vertical stress σ 1,max for

[0023]

[0024] Where: λ is the lateral pressure coefficient of the coal seam;

[0025] When the reserved coal pillar is critically unstable, the maximum vertical stress on the reserved coal pillar is equal to the ultimate strength σ zl , then the critical conditions for sudden instability of the reserved coal pillar are as follows:

[0026]

[0027] The width of the plastic yield zone on one side of the reserved coal pillar is:

[0028]

[0029] Where: h is the thickness of the coal seam;

[0030] Combining the above equations ① to ⑥, we can obtain the reserved width of the reserved coal pillar.

[0031] As a further improvement of the present invention, the calculation process of the width of the coal mining channel in the Step 1 end-support coal fluidized filling mining scheme is as follows:

[0032] According to the continuity equation between two points of a fluid:

[0033] ρS a v a =ρS b v b ⑦

[0034] Where: ρ is the fluid density; S a , S b are the inner and outer cross-sectional areas of the nozzle respectively; v a , v b are the jet velocities inside and outside the nozzle, respectively;

[0035] According to Bernoulli's equation:

[0036]

[0037] Where: P a , P b are the static pressure inside and outside the nozzle respectively; h a ,h b v is the height difference between the inside and outside of the nozzle; a , v b are the jet velocities inside and outside the nozzle, respectively;

[0038] Combining ⑦ and ⑧, we can get the jet flow rate Q t as follows:

[0039]

[0040] Where: Q t is the jet flow rate; P is the jet pressure; d is the nozzle diameter;

[0041] The total energy of water jet coal breaking is E t The calculation formula is as follows:

[0042] E t =Q t P ⑩

[0043] Where: E t is the total energy of water jet breaking coal;

[0044] Specific energy SE is defined as the energy consumed by crushing a unit volume of coal. The calculation formula of specific energy SE is as follows:

[0045]

[0046] Where: V is the volume of broken coal;

[0047] According to the high pressure water pump motor efficiency:

[0048]

[0049] Where: P I is the motor input power; P E is the motor output power; η is the motor efficiency;

[0050] Then the specific energy SE is:

[0051]

[0052] Where: T is the time required to crush a unit volume of coal;

[0053] The coal breaking volume V is:

[0054]

[0055] Where: R is the radius of the hydraulic coal breaking cavity; L is the depth of the hydraulic coal breaking cavity;

[0056] Combining the above formula ⑨ to Obtain the radius of the hydraulic coal breaking cavity, and determine the width of the coal mining channel based on the radius of the hydraulic coal breaking cavity.

[0057] As a further improvement of the present invention, in Step 2, after the drilling of the layer is completed, the coal-breaking drill bit is first replaced with a reaming drill bit to expand the hole mouth of the borehole, and then the hole mouth sealing unit is lowered and fixedly installed at the expanded hole position. The hole mouth sealing unit is a tubular structure with an inner diameter larger than the outer diameter of the high-pressure sealing drill pipe. The rear pipe section of the hole mouth sealing unit is coaxially and tightly connected with the high-pressure sealing drill pipe through a supporting sealing ring. The hole mouth sealing unit is provided with a water-coal discharge outlet on the pipe section in front of the supporting sealing ring. An annular water-coal circulation channel is formed between the inner wall of the pipe section in front of the water-coal discharge outlet of the hole mouth sealing unit and the high-pressure sealing drill pipe. After the hole mouth sealing unit is fixedly installed, the high-pressure sealing drill pipe equipped with a hydraulic cutting nozzle is re-inserted into the borehole for hydraulic mining.

[0058] As a further improvement of the present invention, when drilling the bedding holes on the end wall in Step 2, the bedding holes are drilled obliquely upward.

[0059] As a further improvement of the present invention, when filling the hydraulically broken coal cavities in Step 4, permanent coal mining cavities which are not to be filled are reserved between a number of filled hydraulically broken coal cavities.

[0060] As a further improvement of the present invention, when the hydraulically broken coal cavities are filled with filling materials in Step 4, the filling materials include slag from the spoil dump in the open-pit coal mine and by-products such as gangue and coal slime produced in high-pressure water jet mining. The filling materials are crushed into different particle sizes and then mixed with a set amount of cement, fly ash and other cementitious materials to form slag-coal slime water-based cementitious filling materials.

[0061] Compared with the prior art, the present open-pit coal mine end wall pressure coal fluidized filling mining method arranges fluidized coal mining drills, filling pumps and other fluidized filling mining equipment at the end wall platform at the intersection of the spoil dump and the working wall in the open-pit coal mine while the working wall is advancing normally. The coal body is crushed by high-pressure water jets, and the crushed coal-water mixture is collected, separated and transported. At the same time, slag-based paste is used to fill the coal mining holes in situ, and the end wall pressure coal can be recovered while controlling the stability of the slope. On the one hand, it can solve the problem of waste of end wall pressure coal resources, expand the mining range of open-pit coal mines, and improve the resource recovery rate; on the other hand, it can make full use of solid waste such as gangue in the mining process, reduce the pollution of the environment caused by slag in the open-pit spoil dump, and can greatly improve the stability of the end wall under the premise of realizing safe and efficient mining of the end wall pressure coal. It is particularly suitable for mining the end wall pressure coal in open-pit coal mines with relatively poor geological conditions and soft coal seams. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 3D schematic diagram of backfill mining of the present invention, wherein: (a) is a schematic diagram of the first coal mining channel mining, (b) is a schematic diagram of the second coal mining channel mining and the first hydraulic coal breaking cavity backfilling;

[0063] Figure 2 Schematic diagram of the end section of the backfill mining of the present invention, wherein: (a) is a schematic diagram of the first coal mining channel when the mining is completed, (b) is a schematic diagram of the second coal mining channel when the mining is completed and the first hydraulic coal breaking cavity is filled, (c) is a schematic diagram of the third coal mining channel when the mining is completed and the first and second hydraulic coal breaking cavities are filled;

[0064] Figure 3 It is a schematic diagram of the three-dimensional structure in the hydraulic mining process of the present invention;

[0065] Figure 4 It is a schematic diagram for calculating the reserved width of the reserved coal pillar of the present invention.

[0066] In the figure: 1. drilling rig, 2. high-pressure sealed drill pipe, 3. hydraulic cutting nozzle, 4. coal-water mixture, 5. orifice sealing unit, 6. vibrating screen, 7. heavy medium cyclone, 8. filter press, 9. water tank, 10. high-pressure water pump, 11. coal bunker. DETAILED DESCRIPTION

[0067] The present invention is further described below with reference to the accompanying drawings (hereinafter described with the drilling direction of the high-pressure sealed drill rod as the front, the direction of the inner spoil field relative to the end wall as the outer direction, and the direction of the working wall relative to the end wall as the inner direction).

[0068] This open-pit coal mine end wall pressure coal fluidized filling mining method arranges fluidized coal mining drills, filling pumps and other fluidized filling mining equipment at the end wall platform at the intersection of the spoil field and the working wall in the open-pit coal mine while the working wall is advancing normally. It uses high-pressure water jets to crush the coal body, collect, separate and transport the crushed coal-water mixture, and uses slag-based paste to fill the coal mining cavity in situ, controlling the stability of the slope while recovering the end wall pressure coal. It specifically includes the following steps:

[0069] Step 1. According to the length and thickness of the end-wall coal seam to be mined in the open-pit coal mine, calculate and plan the end-wall coal fluidized filling mining plan including the coal mining channel and the reserved coal pillars located between the coal mining channels. The end-wall coal fluidized filling mining plan adopts a high-pressure sealed drill rod retreat mining method. The coal mining channels and reserved coal pillars are arranged in sequence from the outside to the inside along the end wall.

[0070] The calculation process of the reserved width of the reserved coal pillar in the left and right directions in the end-wall pressure coal fluidized filling mining plan is as follows:

[0071] The end-wall coal body was sampled on site, and the stress-strain curve of the coal body shearing process was obtained through the rock direct shear test. According to the Mohr-Coulomb criterion, the relationship between the cohesion and the internal friction angle of the end-wall coal body sample was obtained as follows:

[0072]

[0073] Where: f is the normal stress perpendicular to the shear plane; τ is the shear strength; c is the cohesion of the coal body; is the friction angle within the coal body.

[0074] In the width direction of the reserved coal pillar, according to the effective area theory, such as Figure 4 As shown in the figure, the load borne by the reserved coal pillar under end-wall mining is the sum of the load of the overlying strata within the width of the reserved coal pillar and half the width of the adjacent coal mining channel. The actual load borne by the reserved coal pillar is:

[0075]

[0076] Where: a is the width of the reserved coal pillar; b is the width of the coal mining channel; γ is the average bulk density of the overlying strata; H is the average thickness of the overlying strata.

[0077] According to the Mohr-Coulomb yield criterion, the vertical stress σ1 borne by the reserved coal pillar is:

[0078]

[0079] Where: σ1 is the vertical stress of the reserved coal pillar; σ3 is the lateral stress; c is the cohesion of the coal body; is the friction angle within the coal body.

[0080] According to the two-zone constraint theory, the reserved coal pillar produces a "saddle-shaped" stress distribution with large sides and small middle under the action of the overburden load. Based on the symmetry of the reserved coal pillar stress distribution, the lateral stress σ3=0 at the edge of the reserved coal pillar, and the lateral stress σ3 in the yield zone gradually increases from the outside to the inside to the junction with the core zone, which is the maximum. Once the internal stress of the core zone reaches the peak stress, the elastic state of the core zone gradually disappears, and the reserved coal pillar becomes unstable. At this time, σ3=λγH, and the corresponding maximum vertical stress σ 1,max for

[0081]

[0082] Where: λ is the lateral pressure coefficient of the coal seam.

[0083] According to the cusp mutation theory, when the reserved coal pillar is critically unstable, the maximum vertical stress on the reserved coal pillar is equal to the ultimate strength σ zl , then the critical conditions for sudden instability of the reserved coal pillar are as follows:

[0084]

[0085] The width of the plastic yield zone on one side of the reserved coal pillar is:

[0086]

[0087] Where: h is the thickness of the coal seam;

[0088] Combining the above equations ① to ⑥, we can obtain the reserved width of the reserved coal pillar.

[0089] The calculation process of the width of the coal mining channel in the left and right directions in the end-wall coal pressure fluidized filling mining scheme is as follows:

[0090] According to the continuity equation between two points of a fluid:

[0091] ρS a v a =ρS b v b ⑦

[0092] Where: ρ is the fluid density; S a , S b are the inner and outer cross-sectional areas of the nozzle respectively; v a , v b are the jet velocities inside and outside the nozzle, respectively.

[0093] According to Bernoulli's equation:

[0094]

[0095] Where: P a , P b are the static pressure inside and outside the nozzle respectively; h a ,h b v is the height difference between the inside and outside of the nozzle; a , v b are the jet velocities inside and outside the nozzle, respectively.

[0096] Combining ⑦ and ⑧, we can get the jet flow rate Q t as follows:

[0097]

[0098] Where: Q t is the jet flow rate; P is the jet pressure; d is the nozzle diameter.

[0099] The total energy of water jet coal breaking is E t The calculation formula is as follows:

[0100] E t =Q t P ⑩

[0101] Where: E t It is the total energy of water jet breaking coal.

[0102] In order to calculate the volume of coal broken by water jet, the specific energy SE is defined as the energy consumed by breaking a unit volume of coal. The specific energy SE calculation formula is as follows:

[0103]

[0104] Where: V is the volume of broken coal.

[0105] According to the high pressure water pump motor efficiency:

[0106]

[0107] Where: P I is the motor input power; P E is the motor output power; η is the motor efficiency.

[0108] Then the specific energy SE is:

[0109]

[0110] Where: T is the time required to crush unit volume of coal.

[0111] Since the coal mining cavity is approximately cylindrical, the coal breaking volume V is:

[0112]

[0113] Where: R is the radius of the hydraulic coal breaking cavity; L is the depth of the hydraulic coal breaking cavity.

[0114] Combining the above formula ⑨ to Obtain the radius of the hydraulic coal breaking cavity, and determine the width of the coal mining channel based on the radius of the hydraulic coal breaking cavity.

[0115] Step 2, such as Figure 3 As shown, the first coal mining channel is constructed by the end wall compressed coal fluidized filling mining scheme, and a drill rig 1 and a high-pressure sealed drill rod 2 equipped with a coal-breaking drill bit are used to drill a layer-coordinated borehole of a set depth on the end wall vertical wall along the direction of the end wall, and the outer diameter of the coal-breaking drill bit is larger than the outer diameter of the high-pressure sealed drill rod 2. After the high-pressure sealed drill rod 2 and the coal-breaking drill bit are withdrawn, the coal-breaking drill bit is replaced with a hydraulic cutting nozzle 3, and then the high-pressure sealed drill rod 2 equipped with the hydraulic cutting nozzle 3 is re-inserted into the borehole, and high-pressure water is delivered into the high-pressure sealed drill rod 2 by a high-pressure water pump 10, and a high-pressure water jet is formed through the hydraulic cutting nozzle 3 to impact and crush the coal body, and the crushed coal is mixed with water to form a coal-water mixture 4, which is discharged from the annular channel between the high-pressure sealed drill rod 2 and the borehole to the outside of the borehole, and the rotation and retreat movement of the high-pressure sealed drill rod 2 are controlled. After the high-pressure water jet breaks the coal, a hydraulic coal-breaking cavity is formed in the coal mining channel.

[0116] Step 3, the coal-water mixture 4 is led to the vibrating screen 6 through a pipeline for separation. After the coal-water mixture is roughly separated by screens of different apertures, the separated large particles of coal are transported to the coal bunker 11, and the coal-water mixture containing fine particles of coal enters the heavy medium suspender 7 for separation. The high-ash fine mud carried in the coal-water mixture is screened out by a cyclone to reduce the ash content of the clean coal. The coal-water mixture separated by the heavy medium suspender enters the filter press 8 for filtration, and the filter cake separated by filtration is sent to the coal bunker. The water separated by filtration enters the water tank 9 connected to the high-pressure water pump for recycling.

[0117] Step 4, such as Figure 1 , Figure 2 As shown, after the first hydraulically broken coal cavity is mined, the mining work of the next coal mining channel is carried out after the reserved width of the reserved coal pillar is left, and the hydraulically broken coal cavity is filled with filling materials at the same time.

[0118] Step 5, and so on, repeat Step 1 to Step 4 to complete the end wall coal compression mining and filling of hydraulic coal breaking cavities under the condition of reserved coal pillar support. After the mining of the coal mining channel located on the innermost side of the end wall is completed, the hydraulic coal breaking cavities located on the innermost side of the end wall are filled with filling materials. At the same time, the mining of coal mining channels is carried out on the reserved coal pillars between the filled and dried hydraulic coal breaking cavities until all the reserved coal pillars are mined and filled.

[0119] During the mining process of the coal mining channel, in order to effectively collect the coal-water mixture discharged out of the borehole, as a further improvement scheme of the present invention, in Step 2, after the drilling of the layer-by-layer hole is completed, the coal-breaking drill bit is first replaced with a hole-reaming drill bit to expand the borehole, and then the borehole mouth position is expanded, and then the borehole sealing unit 5 is lowered and fixedly installed at the expanded hole position. The borehole sealing unit 5 is a tubular structure with an inner diameter larger than the outer diameter of the high-pressure sealing drill pipe. The rear pipe section of the borehole sealing unit 5 is coaxially and tightly connected with the high-pressure sealing drill pipe 2 through a supporting sealing ring. The pipe section of the borehole sealing unit 5 located in front of the supporting sealing ring is provided with a water-coal discharge outlet. An annular water-coal flow channel is formed between the inner wall of the pipe section of the borehole sealing unit 5 located in front of the water-coal discharge outlet and the high-pressure sealing drill pipe 2. After the orifice sealing unit 5 is fixedly installed, the high-pressure sealing drill pipe 2 equipped with a hydraulic cutting nozzle 3 is re-inserted into the borehole for hydraulic mining. During the mining process, the coal-water mixture 4 can be discharged through the water-coal discharge outlet of the orifice sealing unit 5.

[0120] To facilitate the smooth discharge of the coal-water mixture, as a further improvement of the present invention, when drilling a bedding hole on the end wall in Step 2, the bedding hole is drilled obliquely upward. With this arrangement, the coal-water mixture can be discharged smoothly along the annular channel between the high-pressure sealed drill rod and the borehole under the action of its own gravity.

[0121] Since the strength of the filling material is better than that of the end coal body, intermittent filling can be carried out. That is, in order to further reduce costs, as a further improvement scheme of the present invention, when filling the hydraulically broken coal holes in Step 4, permanent coal mining holes that are not filled can be retained between several filled hydraulically broken coal holes based on the support strength calculation.

[0122] In order to obtain local materials and reduce filling costs, as a further improvement scheme of the present invention, when the hydraulically broken coal cavities are filled with filling materials in Step 4, the filling materials include slag from the spoil dump in the open-pit coal mine and by-products such as gangue and coal slime produced in high-pressure water jet mining. The filling materials are crushed into different particle sizes and then mixed with a set amount of cement, fly ash and other cementitious materials to form slag-coal slime water-based cementitious filling materials.

[0123] The fluidized filling mining method for the end wall pressure coal of an open-pit coal mine can greatly improve the stability of the end wall under the premise of realizing safe and efficient mining of the end wall pressure coal, and is particularly suitable for mining the end wall pressure coal of an open-pit coal mine with relatively poor geological conditions and soft coal seams.

Claims

1. A method for fluidized filling mining of open-pit coal mine end wall pressure coal, characterized in that: The specific steps include: Step 1: According to the length and thickness of the end wall coal seam to be mined in the open-pit coal mine, a fluidized filling mining scheme for end wall coal pressure is calculated and planned, including coal mining channels and reserved coal pillars between the coal mining channels. The fluidized filling mining scheme for end wall coal pressure adopts a high-pressure sealed drill rod retreat mining method, and the coal mining channels and reserved coal pillars are arranged in sequence from outside to inside along the end wall direction; Step 2, the first coal mining channel is constructed by the end wall pressure coal fluidized filling mining scheme, and a layer drill hole of a set depth is drilled on the end wall vertical wall along the end wall direction by using a high-pressure sealed drill rod equipped with a coal-breaking drill bit, and the outer diameter of the coal-breaking drill bit is larger than the outer diameter of the high-pressure sealed drill rod. After the high-pressure sealed drill rod and the coal-breaking drill bit are withdrawn, the coal-breaking drill bit is replaced with a hydraulic cutting nozzle, and then the high-pressure sealed drill rod equipped with a hydraulic cutting nozzle is re-inserted into the borehole, and high-pressure water is sent into the high-pressure sealed drill rod by a high-pressure water pump, and a high-pressure water jet is formed through the hydraulic cutting nozzle to impact and crush the coal body. The crushed coal is mixed with water to form a coal-water mixture, and the coal-water mixture is discharged from the annular channel between the high-pressure sealed drill rod and the borehole to the outside of the borehole, and the rotation and retreat movement of the high-pressure sealed drill rod are controlled. After the high-pressure water jet breaks the coal, a hydraulic coal-breaking cavity is formed in the coal mining channel; Step 3, the coal-water mixture is led to the vibrating screen through a pipeline for separation, the large coal particles separated by the vibrating screen are transported to the coal bunker, the coal-water mixture containing fine coal particles separated by the vibrating screen enters the heavy medium suspension device for separation, the coal-water mixture separated by the heavy medium suspension device enters the filter press for filtration, the filter cake separated by filtration is sent to the coal bunker, and the water separated by filtration enters the water tank connected to the high-pressure water pump for recycling; Step 4, after the first hydraulically broken coal cavity is mined, the next coal mining channel is mined after the reserved width of the reserved coal pillar, and the hydraulically broken coal cavity is filled with filling materials; Step 5, and so on, repeat Step 1 to Step 4 to complete the end wall coal compression mining and filling of hydraulic coal breaking cavities under the condition of reserved coal pillar support. After the mining of the coal mining channel located on the innermost side of the end wall is completed, the hydraulic coal breaking cavities located on the innermost side of the end wall are filled with filling materials. At the same time, the mining of coal mining channels is carried out on the reserved coal pillars between the filled and dried hydraulic coal breaking cavities until all the reserved coal pillars are mined and filled.

2. The open-pit coal mine end-wall pressure coal fluidized filling mining method according to claim 1 is characterized in that: Step 1 The calculation process of the reserved width of the reserved coal pillar in the end-wall pressure coal fluidized filling mining plan is as follows: The end-wall coal body was sampled on site, and the stress-strain curve of the coal body shearing process was obtained through rock direct shear test. According to the Mohr-Coulomb criterion, the relationship between the cohesion and internal friction angle of the end-wall coal body sample was obtained as follows: Where: f is the normal stress perpendicular to the shear plane; τ is the shear strength; c is the cohesion of the coal body; is the friction angle within the coal body; In the width direction of the reserved coal pillar, the actual load borne by the reserved coal pillar is: Where: a is the width of the reserved coal pillar; b is the width of the coal mining channel; γ is the average bulk density of the overlying strata; H is the average thickness of the overlying strata; According to the Mohr-Coulomb yield criterion, the vertical stress σ1 borne by the reserved coal pillar is: Where: σ1 is the vertical stress borne by the reserved coal pillar; σ3 is the lateral stress; Based on the symmetry of the stress distribution of the reserved coal pillar, when the lateral stress σ3 at the edge of the reserved coal pillar is 0, the lateral stress σ3 in the yield zone gradually increases from the outside to the inside and reaches the maximum at the junction with the core area. Once the internal stress of the core area reaches the peak stress, the elastic state of the core area gradually disappears and the reserved coal pillar becomes unstable. At this time, σ3 = λγH, and the corresponding maximum vertical stress σ 1,max for Where: λ is the lateral pressure coefficient of the coal seam; When the reserved coal pillar is critically unstable, the maximum vertical stress on the reserved coal pillar is equal to the ultimate strength σ zl , then the critical conditions for sudden instability of the reserved coal pillar are as follows: The width of the plastic yield zone on one side of the reserved coal pillar is: Where: h is the thickness of the coal seam; Combining the above equations ① to ⑥, we can obtain the reserved width of the reserved coal pillar.

3. The open-pit coal mine end-wall pressure coal fluidized filling mining method according to claim 1, characterized in that: Step 1 The calculation process of the width of the coal mining channel in the end-support coal fluidized filling mining scheme is as follows: According to the continuity equation between two points of a fluid: ρS a v a =ρS b v b ⑦ Where: ρ is the fluid density; S a , S b are the inner and outer cross-sectional areas of the nozzle respectively; v a , v b are the jet velocities inside and outside the nozzle, respectively; According to Bernoulli's equation: Where: P a , P b are the static pressure inside and outside the nozzle respectively; h a ,h b v is the height difference between the inside and outside of the nozzle; a , v b are the jet velocities inside and outside the nozzle, respectively; Combining ⑦ and ⑧, we can get the jet flow rate Q t as follows: Where: Q t is the jet flow rate; P is the jet pressure; d is the nozzle diameter; The total energy of water jet coal breaking is E t The calculation formula is as follows: E t =Q t P ⑩ Where: E t is the total energy of water jet breaking coal; Specific energy SE is defined as the energy consumed by crushing a unit volume of coal. The calculation formula of specific energy SE is as follows: Where: V is the volume of broken coal; According to the high pressure water pump motor efficiency: P.S E JP I η Where: P I is the motor input power; P E is the motor output power; η is the motor efficiency; Then the specific energy SE is: SE=P E T Where: T is the time required to crush a unit volume of coal; The coal breaking volume V is: V=πR 2 L Where: R is the radius of the hydraulic coal breaking cavity; L is the depth of the hydraulic coal breaking cavity; Combining the above formula ⑨ to Obtain the radius of the hydraulic coal breaking cavity, and determine the width of the coal mining channel based on the radius of the hydraulic coal breaking cavity.

4. The open-pit coal mine end-wall pressure coal fluidized filling mining method according to claim 1, characterized in that: In Step 2, after the drilling of the layer hole is completed, the coal-breaking drill bit is first replaced with a reaming drill bit to expand the hole mouth of the borehole, and then the hole mouth sealing unit is lowered and fixedly installed at the expanded hole position. The hole mouth sealing unit is a tubular structure with an inner diameter larger than the outer diameter of the high-pressure sealing drill pipe. The rear pipe section of the hole mouth sealing unit is coaxially and tightly connected with the high-pressure sealing drill pipe through a supporting sealing ring. The hole mouth sealing unit is provided with a water-coal discharge outlet on the pipe section in front of the supporting sealing ring. An annular water-coal flow channel is formed between the inner wall of the pipe section in front of the water-coal discharge outlet of the hole mouth sealing unit and the high-pressure sealing drill pipe. After the hole mouth sealing unit is fixedly installed, the high-pressure sealing drill pipe equipped with a hydraulic cutting nozzle is re-inserted into the borehole for hydraulic mining.

5. The open-pit coal mine end-wall pressure coal fluidized filling mining method according to claim 1, characterized in that: When drilling a bedding hole on the end wall in Step 2, the bedding hole is drilled obliquely upward.

6. The open-pit coal mine end-wall pressure coal fluidized filling mining method according to claim 1, characterized in that: When filling the hydraulically broken coal cavities in Step 4, permanent coal mining cavities which are not to be filled are reserved between several filled hydraulically broken coal cavities.

7. The open-pit coal mine end-wall pressure coal fluidized filling mining method according to claim 1, characterized in that: In Step 4, when filling materials are used to fill the hydraulically broken coal cavities, the filling materials include slag from the spoil dump in the open-pit coal mine and gangue and coal slime by-products produced during high-pressure water jet mining. The filling materials are crushed into different particle sizes and then mixed with a set amount of cement and fly ash cementitious materials to form slag-coal slime water-based cementitious filling materials.

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