Porous scatter point type filling subsequent fully-mechanized mining method for shallow-buried room-pillar goaf

Abstract

The invention relates to a shallow-buried room-pillar goaf porous scatter point type filling subsequent fully-mechanized mining method, which comprises the following steps: S1, a filling method feasibility evaluation detailed process based on coal pillar and filling body stress analysis: S1.1, determining basic parameters: geological parameters: mining depth H (m), overlying rock volume weight gamma (kN / m3) and coal seam thickness h (m), coal pillar parameters: coal pillar width w (m), the uniaxial compressive strength sigma c (MPa) of the coal pillar; the filling rate is high, paste filling openings can be evenly distributed to all positions of an underground free space through the scattered-point type paste filling method, and the laminar flow and turbulent flow characteristics of paste can be better exerted in the small free space; porous scattered point type filling is adopted, on one hand, the position of a stress concentration area is determined, filling is carried out by determining the optimal position of a drill hole, the stability of a coal pillar-filling body is ensured, on the other hand, filling is not carried out on a stable area, unnecessary waste is avoided, and cost is saved.

Description

Technical Field

[0001] The invention relates to the technical field of coal mining, in particular to a method for fully mechanized mining of a shallow-buried room-and-pillar goaf with porous scattered filling. Background Art

[0002] After room-and-pillar mining, a large number of residual coal pillars are left in the goaf. These coal pillars will remain stable for a certain period of time. However, as the coal pillars are exposed to the outside for a longer time, they will weather and be accompanied by rheological phenomena, which will reduce the strength of the coal pillars. These low-strength coal pillars will cause sudden destruction of the coal pillars in front due to the impact of mining during the working face mining process. The destruction of the coal pillars will cause a chain reaction. Without the support of the coal pillars, the roof will sink and fracture rapidly, causing large-scale collapse. The sudden collapse will act on the working face of the lower coal seam, accompanied by mine earthquakes and hurricane disasters, which will have a great impact on the mining of the lower coal seam and easily cause casualties and safety accidents. Therefore, it is very necessary to study the mine pressure law of coal seam mining under the action of residual coal pillars in room-and-pillar goaf. The stress distribution state of the coal pillars mainly depends on the support pressure influence distance caused by coal room mining and the width of the coal pillars. Since it is a room-and-pillar goaf, the width of the coal pillars is fixed, and only the stress condition of the residual coal pillars needs to be considered. Summary of the Invention

[0003] The problem solved by the present invention is to provide a method for multi-porous scattered-point filling and subsequent comprehensive mining in shallow room-and-pillar goafs, which has a high filling rate. The scattered-point paste injection method can evenly distribute the paste injection ports to each position of the underground free space, and the paste can better exert its laminar and turbulent flow characteristics in such a small free space. The multi-porous scattered-point filling is used to determine the position of the stress concentration area on the one hand, and the filling is carried out by determining the optimal position of the drill hole, thereby ensuring the stability of the coal pillar-filling body. On the other hand, the relatively stable area does not need to be filled, thereby avoiding unnecessary waste and saving costs. The cost is low, and fly ash is used as the main filling material, so that coal-based solid waste can be reused, which can reduce costs.

[0004] In order to achieve the above object, the present invention adopts the following technical solution: a method for shallow buried room-and-pillar goaf with porous scattered filling and subsequent fully mechanized mining, comprising the following steps:

[0005] S1. Detailed process of feasibility assessment of filling methods based on stress analysis of coal pillars and filling bodies:

[0006] S1.1. Determine basic parameters

[0007] Geological parameters: Mining depth H (m)

[0008] Overburden density γ(kN / m 3 )

[0009] Coal seam thickness h(m)

[0010] Coal pillar parameters: Coal pillar width w (m)

[0011] Uniaxial compressive strength of coal pillar σ c (MPa)

[0012] Elastic modulus of coal pillar E C (GPa)

[0013] Backfill parameters Elastic modulus of backfill E f (GPa)

[0014] Compressive strength of backfill σ f (MPa)

[0015] m c is a rock material constant;

[0016] S1.2. Calculation of stress concentration factor of coal pillar:

[0017] 1. Based on the theory of elasticity, assuming the coal pillar is a homogeneous elastic body and ignoring geological defects such as joints and fissures; when the width-to-height ratio is met, the stress concentration factor K approaches 1.5, which is in line with the physical properties of the remaining coal pillar;

[0018] Stress concentration factor:

[0019] 2. Stress concentration factor criterion

[0020] If K > 1.5, the risk of coal pillar overload needs to be alerted;

[0021] S1.3. Strength check of coal pillar without backfill

[0022] 1. According to the Hoek - Brown strength criterion:

[0023] σ1 is the maximum principal stress at coal pillar failure, σ3 is the minimum principal stress at coal pillar failure

[0024] s represents the rock joint state parameter, 0 ≤ s ≤ 1

[0025] m c is a rock material constant, reflecting the hardness of the rock, with a value range of 0 - 25;

[0026] S1.3. Strength check of coal pillar without backfill

[0027] Fs represents the safety factor of the coal pillar;

[0028] When the maximum principal stress σ1 at coal pillar failure satisfies it indicates that the coal pillar strength is sufficient and will not become unstable under the current stress state; if Then the coal pillar may be damaged due to overload and needs to be backfilled;

[0029] The calculated results of the K stress concentration coefficient and the Fs safety factor are used as the criteria for the necessity of backfilling:

[0030] If K > 1.5 and Fs < 1.5 → Backfilling must be implemented;

[0031] If K ≤ 1.5 or Fs ≥ 1.5 → Natural support can be considered;

[0032] S1.4. Obtain the position of the borehole according to the position of the coal pillar and the position of the backfilling surface. The calculation formula for the distance between the position of the borehole and the coal pillar is as follows: [[ID=1,4]]

[0033] When the stress concentration coefficient and the safety factor satisfy K > 1.5 and Fs < 1.5, backfilling must be implemented; The required backfilling position can be effectively backfilled by the multi - hole scattered paste backfilling method; The paste backfilling direction is continuous or regular filling along the horizontal direction;

[0034] Calculation formula for the distance between the optimal borehole position and the center of the coal pillar:

[0035] R n = [B·n + L·(n + 1) + B·(1 - v%)] ÷ 2

[0036] In the formula: R n is the distance between the optimal borehole position and the center of the coal pillar, n is the number between the borehole and the left and right coal pillars; B is the distance between the coal pillars; L is the length of the coal pillar; v is the filling rate of the backfilling surface;

[0037] The ultimate strength theory holds that the stability of the backfill mainly depends on the stress and strength of the backfill; The safety factor of the backfill is used to quantitatively evaluate its stability and the safety factor of the backfill should be F sf greater than 1.2;

[0038]

[0039] In the formula: F sf is the safety factor of the backfill; P[[ID=,43]] u is the load that the backfill can bear; P Z is the actual load borne by the backfill;

[0040]

[0041] γ0 is the average density of the backfill; H f is the height of the backfill; B is the distance between the coal pillars; L is the length of the coal pillar; W is the width of the coal pillar;

[0042]

[0043] σ m is the ultimate compressive strength of the filling body; A, C, a, and b are all empirical constants, and at the same time, it is necessary to satisfy A + C = 1;

[0044] When F sf > 1.2, the spacing between the optimal hole position of the drill hole and the center of the coal pillar can be determined;

[0045] S1.3 Stress analysis of the coal pillar - filling body after filling

[0046] 1. If the deformation of the filling body and the coal pillar is coordinated and the stress is distributed according to the elastic modulus, the stress sharing ratio of the coal pillar is:

[0047]

[0048] At this time, the stress of the coal pillar:

[0049]

[0050] If the deformation of the filling body and the coal pillar is coordinated and the stress is distributed according to the elastic modulus, the stress sharing ratio of the filling body is:

[0051]

[0052] At this time, the stress of the filling body: [[ID=3�]]

[0053]

[0054] Stability criterion:

[0055] Safety criterion for coal pillar: That is, when the actual stress σ of the coal pillar cp is less than or equal to the compressive strength σ of the coal pillar c divided by the safety factor F s , it indicates that the coal pillar meets the safety and stability requirements under the current stress state and will not be damaged due to excessive stress.

[0056] Safety criterion for filling body: That is, when the actual stress σ of the filling body ft is less than or equal to the compressive strength σ of the filling body f divided by the safety factor F sf , it shows that the filling body is within the safe stress range during operation and will not fail due to excessive stress, ensuring its reliable support for the coal pillar or roof;

[0057] S2. Specific process of filling:

[0058] S2.1 Build a storage bin for storing fly ash and cement, and transport the fly ash and cement to the metering hopper through a screw conveyor;

[0059] S2.2. Build a reservoir for storing water, and pump the water to another metering hopper.

[0060] S2.3. Convey the fly ash, cement, and water in the metering hopper to a double-horizontal-shaft compulsory mixer in a certain proportion, and convey the mixed paste to a paste buffer pool.

[0061] S2.4. Drill holes evenly distributed on the ground leading to the goaf, and use a piston-type paste pump to inject the paste from the paste buffer pool into the underground room-and-pillar goaf through the paste delivery pipe.

[0062] S2.5. After the paste solidifies smoothly, orderly arrange the return airway and the haulage airway in the corresponding area, and at the same time build a longwall fully mechanized mining face; then, fully utilize the fully mechanized mining technology to carry out operations.

[0063] Preferably, in S2.1, the filling material is mainly fly ash, cement, and water as the filling material.

[0064] Preferably, in S2.4, to effectively fill the room-and-pillar goaf, it is necessary to determine the positions of the drill holes so that they can effectively fill the goaf and avoid waste caused by too small drill hole spacing.

[0065] Preferably, in S2.4, the designed depth of the drill hole is 1.5 m below the roof of the goaf from the ground, and the drill holes are arranged in a scatter pattern within the goaf range.

[0066] Preferably, in S2.4, drill holes according to the planned filling point positions; the diameter of the drill holes should meet the installation requirements of the filling pipeline, generally between 100 - 200 mm; during the drilling process, pay attention to ensuring that the verticality and depth of the drill holes meet the design requirements, with the verticality deviation not exceeding 1%, and the depth error controlled within ±0.5 m.

[0067] Preferably, in S2.5, after longwall comprehensive mining, the remaining coal pillars and filling bodies are mined out.

[0068] Preferably, in S2, the filling structure includes a fly ash storage bin, a cement storage bin, a screw conveyor, a double horizontal shaft forced mixer, a reservoir, a paste conveying pipe, a piston-type paste pump, a paste buffer pool, a casing, a rock mass, a coal pillar, a coal seam, and a room and pillar goaf. Coal pillars are distributed on the outer wall at the bottom of the rock mass, coal seams are distributed on the outer wall at the bottom of the rock mass, room and pillar goafs are arranged between the coal pillars, a casing is embedded and installed in the rock mass, a paste conveying pipe is installed in the casing, a piston-type paste pump is installed at the top of the rock mass, and the output end of the piston-type paste pump is connected to the outer wall of the paste conveying pipe in a penetrating manner. A paste buffer pool is opened at the top of the rock mass, a reservoir is opened at the top of the rock mass, a double horizontal shaft forced mixer is installed between the paste buffer pool and the reservoir, a screw conveyor is installed on one side of the reservoir, and one end of the screw conveyor is installed on the outer wall of the double horizontal shaft forced mixer. A cement storage bin is installed at the top of the rock mass, a fly ash storage bin is installed at the top of the rock mass, and one end of the screw conveyor is installed in the inner walls of the fly ash storage bin and the cement storage bin in a penetrating manner.

[0069] The beneficial effects of the present invention are as follows: the filling rate is high, and the dispersed paste perfusion method can evenly distribute the paste perfusion ports to each position of the underground free space. The paste can better exert its laminar flow and turbulent flow characteristics in this small free space.

[0070] On the one hand, the use of porous dispersed filling determines the location of the stress concentration area. By determining the optimal position of the drilling hole, filling is carried out to ensure the stability of the coal pillar - filling body. On the other hand, for relatively stable areas, filling can be avoided, thus avoiding unnecessary waste and saving costs.

[0071] The cost is low. Using fly ash as the main filling material can recycle coal-based solid waste and reduce costs. Description of the Drawings

[0072] Figure 1 is the process flow chart of the present invention;

[0073] Figure 2 is the schematic diagram of the dispersed paste perfusion of the present invention.

[0074] Legend Explanation:

[0075] 1. Fly ash storage bin; 2. Cement storage bin; 3. Screw conveyor; 4. Double horizontal shaft forced mixer; 5. Reservoir; 6. Paste conveying pipe; 7. Piston-type paste pump; 8. Paste buffer pool; 9. Casing; 10. Rock mass; 11. Coal pillar; 12. Coal seam; 13. Room and pillar goaf. Detailed Embodiment

[0076] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0077] Specific embodiments are given below.

[0078] See Figures 1 to 2 , a post-mining gob multi-hole scattered-point filling subsequent fully-mechanized mining method for shallowly-buried room-and-pillar mining areas, including the following steps:

[0079] S1. Detailed process for evaluating the feasibility of the filling method based on the stress analysis of coal pillars and filling bodies:

[0080] S1.1. Determine the basic parameters

[0081] Geological parameters: Mining depth H (m)

[0082] Unit weight of overlying strata γ (kN / m 3 )

[0083] Coal seam thickness h (m)

[0084] Coal pillar parameters: Coal pillar width w (m)

[0085] Uniaxial compressive strength of coal pillar σ c (MPa)

[0086] Elastic modulus of coal pillar E C (GPa)

[0087] Filling body parameters Elastic modulus of filling body E f (GPa)

[0088] Compressive strength of filling body σ f (MPa)

[0089] m c is a rock material constant;

[0090] S1.2. Calculate the stress concentration coefficient of the coal pillar:

[0091] 1. Based on the theory of elasticity, assume that the coal pillar is a homogeneous elastic body, ignoring geological defects such as joints and fissures; when the width-to-height ratio is the case, the stress concentration coefficient K approaches 1.5, which is in line with the physical properties of the remaining coal pillars;

[0092] Stress concentration coefficient:

[0093] 2. Stress concentration coefficient criterion

[0094] If K > 1.5, the risk of overloading of the coal pillar needs to be alerted.

[0095] S1.3. Strength check of the coal pillar without filling

[0096] 1. According to the Hoek - Brown strength criterion:

[0097] σ1 is the maximum principal stress at the failure of the coal pillar, and σ3 is the minimum principal stress at the failure of the coal pillar

[0098] s represents the rock joint state parameter, 0 ≤ s ≤ 1

[0099] m c is a rock material constant, reflecting the hardness of the rock, with a value range of 0 - 25;

[0100] 2. Stability criterion

[0101] Fs represents the safety factor of the coal pillar;

[0102] When the maximum principal stress σ1 at the failure of the coal pillar satisfies it indicates that the strength of the coal pillar is sufficient and it will not become unstable under the current stress state; if then the coal pillar may be damaged due to overloading and needs to be filled;

[0103] The calculation results of K (stress concentration coefficient) and Fs (safety factor) are used as the criteria for the necessity of filling:

[0104] If K > 1.5 and Fs < 1.5 → filling must be implemented;

[0105] If K ≤ 1.5 or Fs ≥ 1.5 → natural support can be considered;

[0106] S1.4. Obtain the position of the borehole according to the position of the coal pillar and the position of the filling surface. The calculation formula for the spacing between the position of the borehole and the coal pillar is as follows:

[0107] When the stress concentration coefficient and the safety factor satisfy K > 1.5 and Fs < 1.5, filling must be implemented; the required filling position can be effectively filled by the multi - hole scattered paste filling method; the paste filling direction is to fill continuously or regularly along the horizontal direction;

[0108] Calculation formula for the spacing of the optimal borehole position from the center of the coal pillar:

[0109] R n = [B·n + L·(n + 1) + B·(1 - v%)] ÷ 2

[0110] In the formula: R nis the distance between the optimal hole position for drilling and the center of the coal pillar, n is the number between the drill hole and the left and right coal pillars; B is the distance between coal pillars; L is the length of the coal pillar; v is the filling rate of the filling surface;

[0111] The ultimate strength theory holds that the stability of the filling body mainly depends on the stress and strength of the filling body; the safety factor of the filling body is used to quantitatively evaluate its stability and the safety factor of the filling body should be F sf greater than 1.2;

[0112]

[0113] In the formula: F sf is the safety factor of the filling body; P u is the load that the filling body can bear; P Z is the actual load borne by the filling body;

[0114]

[0115] γ0 is the average density of the filling body; H f is the height of the filling body; B is the distance between coal pillars; L is the length of the coal pillar; W is the width of the coal pillar;

[0116]

[0117] σ m is the ultimate compressive strength of the filling body; A, C, a, and b are all empirical constants, and at the same time, it is necessary to satisfy A + C = 1;

[0118] When F sf > 1.2, the distance between the optimal hole position for drilling and the center of the coal pillar can be determined;

[0119] S1.3. Stress analysis of the coal pillar - filling body after filling

[0120] 1. If the deformation of the filling body and the coal pillar is coordinated and the stress is distributed according to the elastic modulus, the stress sharing ratio of the coal pillar is:

[0121]

[0122] At this time, the stress of the coal pillar:

[0123]

[0124] If the deformation of the filling body and the coal pillar is coordinated and the stress is distributed according to the elastic modulus, the stress sharing ratio of the filling body is:

[0125]

[0126] At this time, the stress of the filling body:

[0127]

[0128] Stability criterion:

[0129] Safety criterion for coal pillar: That is, when the actual stress σ of the coal pillar cp is less than or equal to the compressive strength σ of the coal pillar c divided by the safety factor F s , it indicates that the coal pillar meets the safety and stability requirements under the current stress state and will not be damaged due to excessive stress;

[0130] Safety criterion for filling body: That is, when the actual stress σ of the filling body ft is less than or equal to the compressive strength σ of the filling body f divided by the safety factor F sf , it shows that the filling body is within the safe stress range during operation and will not fail due to excessive stress, ensuring its reliable supporting effect on the coal pillar or roof;

[0131] S2. Specific filling process:

[0132] S2.1. Build a storage bin 1 for storing fly ash and a storage bin 2 for cement, and convey the fly ash and cement to the metering hopper through a screw conveyor 3; in S2.1, the filling material is fly ash, and the main filling materials are cement and water;

[0133] S2.2. Build a reservoir 4 for storing water, and convey the water to another metering hopper through a water pump;

[0134] S2.3. Convey the fly ash, cement and water in the metering hopper to a double-shaft forced mixer 4 in a certain proportion, and convey the mixed paste to the paste buffer tank 8;

[0135] S2.4. Drill holes evenly distributed on the ground leading to the goaf, and use a piston paste pump 7 to inject the paste from the paste buffer tank 8 into the underground room-and-pillar goaf 13 through the paste conveying pipe 6; in S2.4, to effectively fill the room-and-pillar goaf 13, it is necessary to determine the position of the drill holes so that they can effectively fill the goaf and avoid waste caused by too small drill hole spacing; in S2.4, the designed depth of the drill holes is 1.5 m below the roof of the goaf from the ground, and the drill holes are arranged in a scattered manner within the goaf; in S2.4, drill holes are made according to the planned filling point positions; the diameter of the drill holes should meet the installation requirements of the filling pipeline, generally between 100 - 200 mm; during the drilling process, attention should be paid to ensuring that the verticality and depth of the drill holes meet the design requirements, with the verticality deviation not exceeding 1%, and the depth error controlled within ±0.5 m;

[0136] S2.5. After the paste has solidified smoothly, arrange the return airway and the haulage roadway in an orderly manner in the corresponding area, and at the same time set up a longwall fully mechanized mining face; then, fully utilize the fully mechanized mining technology to carry out operations; in S2.5, after longwall comprehensive mining, the remaining coal pillars 11 and the filling body are mined out;

[0137] In S2, the filling structure includes a fly ash storage bin 1, a cement storage bin 2, a screw conveyor 3, a double-horizontal-shaft forced mixer 4, a water storage tank 5, a paste delivery pipe 6, a piston-type paste pump 7, a paste buffer tank 8, a casing 9, a rock mass 10, coal pillars 11, a coal seam 12, and a room-and-pillar goaf 13. Coal pillars 11 are distributed and arranged on the outer wall at the bottom end of the rock mass 10, the coal seam 12 is distributed and arranged on the outer wall at the bottom end of the rock mass 10, room-and-pillar goafs 13 are distributed and arranged between the coal pillars 11 and the coal seam 12. The casing 9 is distributed and embedded in the rock mass 10, the paste delivery pipe 6 is installed in the casing 9, the piston-type paste pump 7 is installed at the top end of the rock mass 10, and the output end of the piston-type paste pump 7 is connected through and to the outer wall of the paste delivery pipe 6. A paste buffer tank 8 is opened at the top end of the rock mass 10, a water storage tank 5 is opened at the top end of the rock mass 10. A double-horizontal-shaft forced mixer 4 is installed between the paste buffer tank 8 and the water storage tank 5. A screw conveyor 3 is installed on one side of the water storage tank 5, and one end of the screw conveyor 3 is installed on the outer wall of the double-horizontal-shaft forced mixer 4. The cement storage bin 2 is installed at the top end of the rock mass 10, the fly ash storage bin 1 is installed at the top end of the rock mass 10, and one end of the screw conveyor 3 is connected through and installed on the inner walls of the fly ash storage bin 1 and the cement storage bin 2.

[0138] Filling process: Insert the paste delivery pipe 6 to the bottom of the borehole, and then start injecting the paste. During the paste injection process, control the paste injection pressure and flow rate well, and adjust the paste injection parameters in a timely manner according to the paste injection situation such as the change of the paste injection pressure, the paste injection volume, etc. When the paste injection pressure suddenly rises or the paste injection volume reaches the design requirements, the paste injection of this borehole can be stopped, and then the paste injection of other boreholes is carried out in turn. The paste filling direction is horizontal filling, that is, the paste is filled in the left and right directions of the coal pillar 11, so as to avoid interference between the paste injections of adjacent boreholes;

[0139] The pipeline material of the paste delivery pipe 6 should be able to withstand the pressure during the filling process. Generally, wear-resistant and corrosion-resistant steel pipes are used. The pipeline diameter is determined according to the filling flow rate and the rheological properties of the paste, usually between 100 - 200 mm. Install necessary monitoring and control devices such as pipeline valves, pressure gauges, and flow meters to control the filling speed and pressure during the filling process. At the same time, reasonably support and fix the paste delivery pipe 6 and the installation casing 9 to prevent pipeline deformation and damage. Then, when installing inside the goaf, if the goaf roof is relatively stable, the pipeline can be suspended using the bolts or cables of the roof. If the roof is unstable, special brackets or hangers need to be used to support the pipeline to ensure its stability during the filling process.

[0140] Moreover, during the process of transporting the paste raw materials to the mixer and preparing the paste filling material, it includes: the fly ash in the fly ash storage bin 1 and the cement in the cement storage bin 2 are transported to the metering hopper by the screw conveyor 3 to better control the amount of fly ash and cement; the water is transported to another metering hopper by the water pump; the fly ash, cement, and water (the mixing ratio of fly ash and cement is 7:3, and the water-cement ratio is 1:1.0) are fully stirred by the two parallel mixing shafts of the double-horizontal-shaft forced mixer 4 to prepare the paste filling material. Among them, the paste raw materials include fly ash, cement, water, and water reducer. The water reducer is a polycarboxylic acid superplasticizer, which is transported to the inlet of the paste buffer tank 8 according to the pre-determined mixing ratio of each component of the filling material, and a stirring device is equipped in the buffer tank to prevent the paste from precipitating or stratifying. The piston-type paste pump 7 transports the paste in the paste buffer tank 8 to the paste delivery pipe 6 through the discharge port by the reciprocating movement of the piston in the cylinder body, and the delivery pipe should be selected as a steel pipe. The designed depth of the borehole is 1.5 m below the ground to the goaf roof, and it is arranged in a scattered manner within the goaf area, and the borehole spacing is arranged as 10 m × 10 m. Insert the paste delivery pipe 6 to the bottom of the borehole, and then start injecting the paste. After the paste solidifies to the final strength, arrange the return airway and the transportation roadway of the fully mechanized coal mining face and the longwall fully mechanized coal mining face. Use fully mechanized mining operations to extract the remaining coal pillars 11. This process is relatively simple and convenient, ensuring the efficiency of paste preparation.

[0141] Conduct paste mix proportion tests according to the fly ash, cement, and water used during construction. Pour the paste into a cube triple mold of 40 mm × 40 mm × 40 mm and place it in a curing box for curing (curing temperature 20 ± 3 °C, humidity 90%). After the specimens reach the specified age of 28 days, demold them and conduct uniaxial compressive strength tests on a special testing machine. According to the formulated test plan, make specimens indoors and measure their uniaxial compressive strength values at the corresponding ages. The results of the filling mix proportion tests are shown in Table 1:

[0142]

[0143]

[0144] 1) Water: The water used in construction shall comply with the "Standard for Mixing Water of Concrete", and the pH is about 7.

[0145] 2) Cement: Portland cement with a strength not lower than 32.5 MPa that complies with the national standard "Common Portland Cement" (GB175—2007) is adopted.

[0146] 3) Fly ash: Fly ash from a nearby power plant can be selected. The total content of SiO2, Al2O3 and Fe2O3 is greater than 70.0%, and the content of SO3 is less than 3.0%.

[0147] 4) The water-reducing agent used in the test is a polycarboxylate superplasticizer.

[0148] Analysis of test results:

[0149] 1) Strength: The strength of the paste is affected by two factors: the water-cement ratio and the fly ash-cement ratio. The larger the water-cement ratio, the thinner the paste and the lower the paste strength. The smaller the fly ash-cement ratio, the lower the cement content and the lower the paste strength.

[0150] 2) Viscosity: The viscosity of the cement-fly ash paste is greatly affected by the water-cement ratio. The larger the water-cement ratio, the thinner the paste and the lower the paste viscosity. According to this test, when the water-cement ratio is 1:(0.8 - 1.0), the paste has good fluidity, is easy to pump, and is easy to spread in cracks. When the water-cement ratio reaches 1:1.2, the viscosity of the paste increases significantly and the fluidity decreases.

[0151] According to the test results, on the basis of meeting the strength requirements, to ensure that the paste has good fluidity and considering the comprehensive economic benefits, the main filling material is finally determined to be filling material 1 - 2.

[0152] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution and inventive concept of the present invention, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A method for subsequent fully-mechanized mining with porous scattered filling in a shallowly-buried room-and-pillar goaf, characterized in that, It includes the following steps, S1. Detailed process for evaluating the feasibility of the filling method based on the stress analysis of coal pillars and filling bodies: S1.

1. Determine the basic parameters Geological parameters: Mining depth H (m) Overlying rock unit weight γ (kN / m 3 ) Coal seam thickness h (m) Coal pillar parameters: Coal pillar width w (m) Uniaxial compressive strength of coal pillar σ c (MPa) Elastic modulus E of coal pillar C (GPa) Backfill parameters, backfill elastic modulus E f (GPa) Compressive strength σ of the filling f (MPa) m c is a constant of the rock material S1.

2. Calculate the stress concentration coefficient of the coal pillar:

1. Based on the theory of elasticity, assuming that the coal pillar is a homogeneous elastic body and ignoring geological defects such as joints and fissures; when the width-to-height ratio is such that the stress concentration factor K approaches 1.5, which is consistent with the physical properties of the remaining coal pillars; Stress concentration factor:

2. Stress concentration coefficient criterion If K > 1.5, be vigilant about the risk of coal pillar overload; S1.

3. Check the strength of the coal pillar before filling 1. According to the Hoek - Brown strength criterion: σ1 is the maximum principal stress when the coal pillar fails, and σ3 is the minimum principal stress when the coal pillar fails s represents the rock joint state parameter (0 ≤ s ≤ 1) m c is a constant of rock material, reflecting the hardness of the rock, with a value range of 0 to 25; 2. Stability criterion Fs represents the safety factor of the coal pillar; When the maximum principal stress σ1 at the time of coal pillar failure satisfies it indicates that the strength of the coal pillar is sufficient and it will not become unstable under the current stress state; if then the coal pillar may be damaged due to overload and needs to be backfilled; The calculated results K (stress concentration coefficient) and Fs (safety factor) are used as the criteria for the necessity of filling: If K > 1.5 and Fs < 1.5 → Filling must be implemented; If K ≤ 1.5 or Fs ≥ 1.5 → Natural support can be considered; S1.

4. Obtain the position of the borehole based on the position of the coal pillar and the position of the filling surface. The calculation formula for the distance between the position of the borehole and the coal pillar is as follows: When the stress concentration coefficient and the safety factor satisfy K > 1.5 and Fs < 1.5, filling must be implemented; The required filling positions can be effectively filled by the multi - hole scattered - point paste filling method; The paste filling direction is to fill continuously or regularly along the horizontal direction; Calculation formula for the distance between the optimal borehole position and the center of the coal pillar: R n = [B·n + L·(n + 1) + B·(1 - v%)] ÷ 2 Where: R n is the distance between the optimal drilling hole position and the center of the coal pillar, n is the number of holes between the drill hole and the left and right coal pillars; B is the distance between the coal pillars; L is the length of the coal pillar; v is the filling rate of the filling surface; The ultimate strength theory holds that the stability of the filling body mainly depends on the stress and strength of the filling body; the safety factor of the filling body is used to quantitatively evaluate its stability, and the safety factor of the filling body should be F sf greater than 1.2; Where: F sf is the safety factor of the filling body; P u P is the load that the filling body can bear; Z is the load actually borne by the filling body; γ0 is the average density of the filling body; H f is the height of the filling body; B is the coal pillar spacing; L is the length of the coal pillar; W is the width of the coal pillar; σ m is the ultimate compressive strength of the filling body; A, C, a, and b are all empirical constants, and at the same time, it is necessary to satisfy A + C = 1; When F sf > 1.2, the spacing of the optimal hole position of the borehole from the center of the coal pillar can be determined; S1.

3. Stress analysis of the coal pillar - filling body after filling 1. If the filling body and the coal pillar are deformation - coordinated, the stress is distributed according to the elastic modulus, and the stress sharing ratio of the coal pillar is: At this time, the stress of the coal pillar: If the filling body and the coal pillar are deformation - coordinated, the stress is distributed according to the elastic modulus, and the stress sharing ratio of the filling body is: At this time, the stress of the filling body: Stability criterion: Safety criterion for coal pillar: That is, when the actual stress σ of the coal pillar cp is less than or equal to the compressive strength σ of the coal pillar c divided by the safety factor F s , it indicates that the coal pillar meets the requirements of safety and stability under the current stress state and will not be damaged due to excessive stress. Safety criterion for backfill: That is, when the actual stress σ of the backfill ft is less than or equal to the compressive strength σ of the backfill f divided by the safety factor F sf it indicates that the backfill is under a safe stress during operation and will not fail due to excessive stress, ensuring its reliable support for coal pillars or roof; S2. Specific filling process: S2.

1. Set up a storage bin (1) for storing fly ash and a storage bin (2) for storing cement, and transport the fly ash and cement to the metering hopper through a screw conveyor (3); S2.

2. Set up a reservoir (4) for storing water, and transport the water to another metering hopper through a water pump; S2.

3. Transport the fly ash, cement, and water in the metering hopper to a double - shaft forced mixer (4) in a certain proportion, and transport the mixed paste to the paste buffer tank (8); S2.

4. Drill holes evenly distributed on the ground leading to the goaf, and use a piston - type paste pump 7 to inject the paste from the paste buffer tank (8) into the underground room - pillar goaf (13) through the paste delivery pipe (6); S2.

5. After the paste solidifies smoothly, arrange the return airway heading and the transport airway heading in an orderly manner in the corresponding area, and at the same time set up a long - wall fully - mechanized mining face; Subsequently, fully utilize the fully - mechanized mining technology to carry out operations.

2. A method for subsequent fully-mechanized mining with porous scattered filling in a shallowly-buried room-and-pillar goaf according to claim 1, characterized in that, In S2.1, the filling materials are mainly fly ash, cement, and water.

3. A method for subsequent fully-mechanized mining with porous scattered filling in a shallowly-buried room-and-pillar goaf according to claim 1, characterized in that In S2.4, to effectively fill the room - pillar goaf (13), it is necessary to determine the position of the borehole so that it can effectively fill the goaf and avoid waste caused by too small borehole spacing.

4. A post-mining comprehensive coal mining method with porous scattered filling in a shallowly buried room-and-pillar goaf according to claim 1, characterized in that, In S2.4, the designed depth of the borehole is 1.5 m below the roof of the goaf from the ground, and the boreholes are scattered - point arranged within the goaf range.

5. A post-mining comprehensive mining method with porous scattered filling in a shallowly buried room-and-pillar goaf according to claim 1, characterized in that, In the step S2.4, drilling is carried out according to the planned positions of the filling points; the diameter of the drill holes should meet the installation requirements of the filling pipelines, generally between 100 and 200 mm; during the drilling process, attention should be paid to ensuring that the verticality and depth of the drill holes meet the design requirements, with the verticality deviation not exceeding 1% and the depth error controlled within ±0.5 m.

6. The post-mining comprehensive mining method with porous scattered filling in a shallowly buried room-and-pillar goaf according to claim 1, characterized in that In the step S2.5, the remaining coal pillars (11) and filling bodies are mined out after longwall comprehensive mining.

7. The device used in the method for subsequent fully-mechanized mining with porous scattered point filling in a shallowly-buried room-and-pillar goaf according to claim 1, characterized in that, In the step S2, the filling structure includes a fly ash storage bin (1), a cement storage bin (2), a screw conveyor (3), a double-horizontal-shaft forced mixer (4), a water storage tank (5), a paste delivery pipe (6), a piston-type paste pump (7), a paste buffer tank (8), a casing (9), a rock mass (10), a coal pillar (11), a coal seam (12), and a room-and-pillar goaf (13). The coal pillars (11) are distributed on the outer wall at the bottom end of the rock mass (10), the coal seam (12) is distributed on the outer wall at the bottom end of the rock mass (10), room-and-pillar goafs (13) are distributed and formed between the coal pillars (11) in the coal seam (12), the casing (9) is distributed and embedded in the rock mass (10), the paste delivery pipe (6) is installed in the casing (9), the piston-type paste pump (7) is installed at the top end of the rock mass (10), and the output end of the piston-type paste pump (7) is connected to the outer wall of the paste delivery pipe (6) in a penetrating manner. The paste buffer tank (8) is formed at the top end of the rock mass (10), the water storage tank (5) is formed at the top end of the rock mass (10), the double-horizontal-shaft forced mixer (4) is installed between the paste buffer tank (8) and the water storage tank (5), the screw conveyor (3) is installed on one side of the water storage tank (5), and one end of the screw conveyor (3) is installed on the outer wall of the double-horizontal-shaft forced mixer (4). The cement storage bin (2) is installed at the top end of the rock mass (10), the fly ash storage bin (1) is installed at the top end of the rock mass (10), and one end of the screw conveyor (3) is installed in the inner walls of the fly ash storage bin (1) and the cement storage bin (2) in a penetrating manner.

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