Coal pillar crack plugging material, preparation method and application

Abstract

The invention discloses a coal pillar crack plugging material as well as a preparation method and application thereof. The coal pillar crack plugging material is prepared by mixing composite powder, yellow mud and microcapsules, the composite powder comprises the following components in parts by mass: 5-8 parts of a surfactant, 3-6 parts of an antioxidant and 9-18 parts of a low-temperature co-fluxing agent; the yellow mud is prepared from the following components in parts by mass: 100 to 150 parts of loess and 850 to 900 parts of water; the mass part of the microcapsule is 10-15 parts. When the plugging material is used, the plugging material is sprayed on the surface of the coal pillar, so that cracks on the surface of the coal pillar can be plugged, and the plugging material can partially permeate into the cracks; when the coal pillar is pressed to enable the crack to expand and develop, the coal pillar crack plugging material is pressed to deform, so that the capsule wall of the microcapsule is broken, the capsule core absorbs water and expands to expand and plug the expanded and developed crack, the continuous air leakage prevention effect on the crack is achieved, and the possibility of coal spontaneous combustion of the coal pillar is effectively reduced.

Description

Technical Field

[0001] The present invention relates to a coal pillar crack sealing material, a preparation method and an application, and belongs to the technical field of coal mine fire prevention and extinguishing. Background Art

[0002] In order to reduce the waste of coal resources and improve the coal recovery rate in existing western mines, the technology of leaving coal pillars for mining is often adopted. However, during the coal mining process of the two-side working faces, the internal stress balance state of the coal pillar is broken, and stress concentration gradually appears near the coal pillar. The coal body undergoes fatigue damage under the repeated disturbance of stress transition, internal cracks are generated, and continuous development occurs, resulting in air leakage, which may lead to spontaneous coal combustion in local small coal pillars and affect the safe underground coal mining.

[0003] In response to this, the current industry uses sealing materials to seal the internal cracks of coal pillars to reduce the possibility of coal spontaneous combustion by preventing air leakage. Currently, there are many crack sealing materials and devices applied to coal mines at home and abroad. Among them, the Chinese invention patent with the publication number CN115849839A can reduce the friction between the foam and cement particles by adding waste engine oil, maintain the foam stability and promote the fluidity of the foam material, so as to penetrate deeper into the air leakage cracks in the gob for sealing. However, during the working face advancement process, the stress at the high position of the coal pillar is large, and the cracks expand and develop rapidly. And this material has strong fluidity. When the material is injected into the cracks from the high position, it will flow down rapidly under the action of gravity and cannot bond and seal the cracks at the high position of the coal pillar; the invention patent with the publication number CN113683348A uses cement and fly ash as the main materials, adds a quick-setting agent and a foaming liquid, and plugs the cracks by foaming the material to isolate the coal body from oxygen contact. However, the consolidation speed of this material is fast. After being injected into the cracks and solidifying, due to its lack of the ability of elastic deformation (that is, the volume will not shrink and deform), when the cracks in the coal pillar develop and expand for the second time, cracking and falling off are likely to occur, ultimately resulting in the failure of sealing; the invention patent with the publication number CN116716115A mainly absorbs a large amount of water by the hydrophilic groups in the physical inhibitor gel, covers the coal surface in the form of gel, seals the gaps in the coal, and isolates oxygen. However, the compressive strength of this material is weak, and when the internal stress field of the coal pillar changes due to subsequent coal seam mining, crushing is likely to occur, which will also lead to the failure of sealing.

[0004] To sum up, the existing various different sealing materials can achieve a certain sealing effect in the initial stage of coal pillar crack sealing. However, when the internal stress of the coal pillar changes due to subsequent coal seam mining, due to the expansion and development of the cracks under the stress change, the existing sealing materials cannot fill and seal the newly derived cracks, and the above existing materials lack certain adhesive wall-hanging characteristics during injection, resulting in the easy failure of sealing of the cracks at the high position, leading to continuous air leakage, and ultimately unable to effectively achieve the effect of preventing and extinguishing coal spontaneous combustion. Summary of the Invention

[0005] In response to the problems existing in the above-mentioned prior art, the present invention provides a coal pillar fissure plugging material, a preparation method and an application thereof, which has certain adhesion and wall-hanging properties, can seal cracks at different positions during spraying, and can adaptively fill and seal newly derived cracks when the cracks expand and develop under pressure in the later stage, thereby achieving the effect of preventing and extinguishing coal spontaneous combustion.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is: a coal pillar fissure plugging material, which is composed of a mixture of composite powder, yellow mud slurry and microcapsules;

[0007] The composite powder comprises, by weight: 5 to 8 parts of a surfactant, 3 to 6 parts of an antioxidant, and 9 to 18 parts of a low-temperature eutectic agent;

[0008] The yellow mud slurry comprises, by weight: 100-150 parts of loess and 850-900 parts of water;

[0009] The microcapsules are present in an amount of 10 to 15 parts by mass.

[0010] Furthermore, the microcapsule consists of two parts: a capsule wall and a capsule core particle. The capsule wall is wrapped around the outer surface of the capsule core. The material of the capsule wall includes the following components in terms of mass percentage: 10% to 12% ethyl cellulose, 15% to 18% anhydrous ethanol and 70% to 75% xylene; the material of the capsule core particle is a water-swellable rubber material.

[0011] Furthermore, the surfactant is sodium alginate.

[0012] Furthermore, the antioxidant is apigenin.

[0013] Furthermore, the low-temperature eutectic agent is a mixture of choline chloride and anhydrous citric acid, and the mass ratio of the two is 1:2.

[0014] Furthermore, the mass ratio of loess to water in the yellow mud slurry is 6:1 to 9:1.

[0015] The preparation method of the above-mentioned coal pillar fissure plugging material comprises the following specific steps:

[0016] A. Preparation of yellow mud slurry: Add loess into a container containing aqueous solution, stir at a speed of 1500-1800 r / min for 3-5 minutes to mix evenly to form yellow mud slurry;

[0017] B. Preparation of composite powder: crushing the seaweed and mixing it with an alkaline solution to release sodium alginate from the cells, then filtering, washing and drying to extract the sodium alginate; then mixing apigenin, choline chloride, anhydrous citric acid and sodium alginate according to the required mass fractions and stirring for 2 to 3 minutes to form a composite powder;

[0018] C. Preparation of microcapsules: Ethyl cellulose, absolute ethanol and xylene are added into a container according to mass percentages, and stirred at a speed of 1500 - 1800 r / min for 5 - 6 min to form a uniform wall coating solution; natural rubber and sodium polyacrylate are mixed and vulcanized to make a water-absorbing and swelling rubber material, and then the core particles are manufactured by extrusion and spheronization, air-dried and screened through a sieve; finally, the wall coating solution is sprayed on the outer surface of each core particle, and after air-blowing drying, microcapsules are obtained;

[0019] D. Preparation of coal pillar crack sealing material: The prepared composite powder and microcapsules are poured into yellow mud and continuously stirred at a speed of 1500 - 1800 r / min for 2 - 4 min to prepare a coal pillar crack sealing material after uniform mixing.

[0020] Furthermore, the stirring time in step B is 3 min, the stirring time in step C is 6 min, and the stirring time in step D is 2 min.

[0021] The usage method of the above coal pillar crack sealing material has the following specific application steps:

[0022] ① After the working face cut-through forms a coal pillar, before cracks occur in the coal pillar, a layer of steel fiber asbestos mesh is hung on the two side surfaces of the coal pillar along the working face strike;

[0023] ② After the steel fiber asbestos mesh is hung, a layer of the prepared coal pillar crack sealing material is evenly sprayed and brushed on the surface of the coal pillar through a mining spraying device to seal the cracks on the surface of the coal pillar, and the spraying thickness of the coal pillar crack sealing material is 4 - 5 mm;

[0024] ③ As the working face advances, the stress of each section of the coal pillar rises, and the cracks in some sections of the coal pillar expand and develop under pressure. At this time, the coal pillar crack sealing material deforms under pressure, causing the wall of the microcapsule to rupture, and the core absorbs water and swells to expand and seal the expanded and developed cracks, realizing the continuous air leakage prevention effect on the cracks.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. The interaction between sodium alginate and loess after dissolution in the present invention forms a three-dimensional network structure, enabling the material to stably adhere to the surface of the coal body, having strong adhesiveness, so that the material can effectively seal the high-level cracks of the coal pillar; adding apigenin can enhance the adhesiveness of the solution. The material can stably maintain its shape without external force, and will undergo plastic deformation under stress for subsequent deformation and rupture of the microcapsule. Moreover, this three-dimensional network structure has good water retention performance, providing the required water volume for subsequent water absorption and swelling of the core.

[0027] 2. The microcapsules of the present invention use ethyl cellulose, absolute ethanol, and xylene as the wall materials, so that the wall of the microcapsules can isolate water from the core at the initial stage to prevent it from swelling, ensuring that the material can smoothly enter the interior of the fissures. When the stress of the coal pillar increases and the fissures develop secondarily, causing the wall of the microcapsule to be stressed and rupture, and at the same time, the material will experience a certain degree of water loss under low-temperature conditions. At this time, when the water-absorbing swelling rubber in the core contacts water, water molecules will enter the water-absorbing swelling rubber through physical actions such as diffusion, capillary action, and surface adsorption, causing continuous swelling, further sealing the coal pillar fissures secondarily, reducing the internal porosity of the coal pillar, and at the same time, the water content of the material decreases after absorbing water, increasing the viscosity of the material. When the anti-deformation force and osmotic pressure difference of the water-absorbing swelling rubber reach equilibrium, it remains relatively stable, ultimately achieving the effect of elastic water stop and effectively realizing the continuous sealing effect on the fissures.

[0028] 3. When the plugging material prepared by the present invention is used, spraying the plugging material on the surface of the coal pillar can achieve the plugging of the fissures on the surface of the coal pillar, and the plugging material can partially penetrate into the interior of the fissures. At the same time, using a steel fiber asbestos mesh to lay a net on the surface of the coal pillar can prevent the crushed coal from protruding due to stress concentration and crushing in some areas of the coal pillar, and monitor the fissure development areas inside the coal pillar in each section through the phenomenon of net breakage, and further drill and inject the plugging material into the net breakage area of the coal pillar to achieve precise plugging of the internal fissures of the coal pillar. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is the process flow chart of the preparation of the coal pillar fissure plugging material of the present invention;

[0030] Figure 2 is the rheological property diagram of the coal pillar fissure plugging material of the present invention;

[0031] Among them, (a) is the relationship diagram between shear stress and shear rate; (b) is the relationship diagram between viscosity and shear rate;

[0032] Figure 3 is the schematic diagram of the principle of the microcapsule expanding and plugging the fissure after being compressed and ruptured in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention will be further described below.

[0034] Example 1: The coal pillar fissure plugging material of this example is composed of a composite powder, yellow mud, and microcapsules; the composite powder includes, by mass: 8 parts of sodium alginate, 6 parts of apigenin, and 18 parts of a deep eutectic solvent; the deep eutectic solvent is composed of choline chloride and anhydrous citric acid, and the mass ratio of the two is 1:2; the yellow mud includes, by mass: 100 parts of loess and 900 parts of water; the microcapsules are 10 parts by mass.

[0035] Such asFigure 1 As shown in the figure, the preparation process of this embodiment is as follows:

[0036] A. Prepare yellow mud slurry: Add 100 parts of loess by mass to a container containing 900 parts of aqueous solution, and stir at a speed of 1800 r / min for 3 min at 40 °C to form a uniform yellow mud slurry after mixing;

[0037] B. Prepare composite powder: Crush seaweed and mix it with an alkaline solution to release sodium alginate from cells, then filter, wash and dry to extract sodium alginate; Then, mix 6 parts of apigenin, 6 parts of choline chloride, 12 parts of anhydrous citric acid and 8 parts of sodium alginate by mass and stir evenly for 3 min to form a composite powder;

[0038] C. Prepare microcapsules: Add 10% of ethyl cellulose, 18% of anhydrous ethanol and 72% of xylene by mass percentage to a container, and stir at a speed of 1800 r / min for 6 min to form a wall coating solution for the capsule; Mix natural rubber and sodium polyacrylate and vulcanize to make a water-absorbing and swelling rubber material, then manufacture core particles by extrusion and rolling, air-dry and screen through a mesh; Finally, spray the wall coating solution on the outer surface of each core particle, and obtain microcapsules after drying by blowing air, and weigh 10 parts of microcapsules;

[0039] D. Prepare a coal pillar crack sealing material: Pour the above-prepared composite powder and microcapsules into the yellow mud slurry and continuously stir at a speed of 1800 r / min for 4 min, and prepare the coal pillar crack sealing material of Example 1 after uniform mixing.

[0040] Example 2: The coal pillar crack sealing material of this embodiment is composed of a composite powder, yellow mud slurry and microcapsules; The composite powder includes by mass: 7 parts of sodium alginate, 5 parts of apigenin, and 15 parts of deep eutectic solvent; The deep eutectic solvent is composed of choline chloride and anhydrous citric acid, and the mass ratio of the two is 1:2; The yellow mud slurry includes by mass: 150 parts of loess and 900 parts of water; The microcapsules are 15 parts by mass.

[0041] As Figure 1 shown, the preparation process of this embodiment is as follows:

[0042] A. Prepare yellow mud slurry: Add 150 parts of loess by mass to a container containing 900 parts of aqueous solution, and stir at a speed of 1600 r / min for 5 min at 40 °C to form a uniform yellow mud slurry after mixing;

[0043] B. Preparation of composite powder: Crush seaweed and mix it with an alkaline solution to release sodium alginate from the cells. Then, filter, wash, and dry it to extract sodium alginate. Next, mix 5 parts of apigenin, 5 parts of choline chloride, 10 parts of anhydrous citric acid, and 7 parts of sodium alginate by mass and stir evenly for 2 minutes to form a composite powder.

[0044] C. Preparation of microcapsules: Add 10% ethyl cellulose, 15% anhydrous ethanol, and 75% xylene to a container by mass percentage, and stir at a speed of 1600 r / min for 5 minutes to mix evenly to form a wall coating solution for the capsule. Mix natural rubber and sodium polyacrylate and vulcanize them to make a water-absorbing and swelling rubber material. Then, use the extrusion and spheronization method to manufacture core particles for the capsule, air-dry them, and screen them through a mesh. Finally, spray the wall coating solution on the outer surface of each core particle, and obtain microcapsules after drying by blowing air, and weigh 15 parts of microcapsules.

[0045] D. Preparation of coal pillar crack plugging material: Pour the above-prepared composite powder and microcapsules into yellow mud slurry and continuously stir at a speed of 1600 r / min for 3 minutes to prepare the coal pillar crack plugging material of Example 2 after uniform mixing.

[0046] Example 3: The coal pillar crack plugging material of this example is composed of a composite powder, yellow mud slurry, and microcapsules. The composite powder includes, by mass: 6 parts of sodium alginate, 4 parts of apigenin, and 12 parts of a deep eutectic solvent. The deep eutectic solvent is composed of a mixture of choline chloride and anhydrous citric acid, and the mass ratio of the two is 1:2. The yellow mud slurry includes, by mass: 100 parts of loess and 800 parts of water. The microcapsules are 12 parts by mass.

[0047] As Figure 1 shown, the preparation process of this example is as follows:

[0048] A. Preparation of yellow mud slurry: Add 100 parts of loess to a container containing 800 parts of an aqueous solution, and stir at a speed of 1500 r / min for 3 minutes at 40 °C to mix evenly to form yellow mud slurry.

[0049] B. Preparation of composite powder: Crush seaweed and mix it with an alkaline solution to release sodium alginate from the cells. Then, filter, wash, and dry it to extract sodium alginate. Next, mix 4 parts of apigenin, 4 parts of choline chloride, 8 parts of anhydrous citric acid, and 6 parts of sodium alginate by mass and stir evenly for 3 minutes to form a composite powder.

[0050] C. Preparation of microcapsules: Add 12% ethyl cellulose, 18% absolute ethanol, and 70% xylene into a container by mass percentage, and stir at a speed of 1500 r / min for 5 min to form a uniform wall coating solution; Mix natural rubber and sodium polyacrylate and vulcanize them to make a water-absorbing and swelling rubber material, then use the extrusion and spheronization method to manufacture core particles, air-dry them and screen them through a mesh; Finally, spray the wall coating solution on the outer surface of each core particle, and obtain microcapsules after drying by blowing air, and weigh 12 parts of microcapsules;

[0051] D. Preparation of coal pillar crack sealing material: Pour the above-prepared composite powder and microcapsules into yellow mud and continuously stir at a speed of 1700 r / min for 2 min to prepare the coal pillar crack sealing material of Example 3 after uniform mixing.

[0052] The application methods of the above Examples 1 to 3 are the same, and are specifically as follows:

[0053] ① After the working face cutting-through forms a coal pillar, before cracks are generated in the coal pillar, hang a layer of steel fiber asbestos mesh on the surfaces of both sides of the coal pillar along the working face strike;

[0054] ② After hanging the steel fiber asbestos mesh, evenly spray and brush a layer of the prepared coal pillar crack sealing material on the surface of the coal pillar to seal the cracks on the surface of the coal pillar, and the spraying thickness of the coal pillar crack sealing material is 4 - 5 mm;

[0055] ③ As the working face advances, the stress of each section of the coal pillar rises, and the cracks in some sections of the coal pillar expand and develop under pressure. At this time, the coal pillar crack sealing material deforms under pressure, causing the wall of the microcapsule to rupture, and the core absorbs water and swells to expand and seal the expanding cracks, realizing the continuous air leakage prevention effect on the cracks; In addition, if the coal pillar deforms severely under pressure and the steel fiber asbestos mesh breaks, then according to the breakage situation of the asbestos mesh on the surface of the coal pillar, cut off the asbestos mesh at the breakage position, drill holes at the breakage position using a mining drill, and use a grouting pump to inject any one of the sealing materials of Examples 1 to 3 into the coal pillar at the drilling position to seal the internal cracks of the coal pillar and prevent air leakage from causing low-temperature spontaneous combustion inside the coal pillar.

[0056] Experimental verification:

[0057] (1) Material water retention performance test:

[0058] By heating the sealing materials prepared in Examples 1 to 3 under constant temperature in a 70°C channel condition, and then using an analytical balance to weigh the mass change of the slurry before and after heating to calculate the water retention rate;

[0059]

[0060] As can be seen from the above table, all three embodiments have good water retention performance, which can ensure that after the material is injected into the coal pillar fissures, while plugging the fissures, it slows down the evaporation of the free water on the coal surface, thereby effectively delaying the temperature of the coal-oxygen reaction, and this water retention performance also helps the core of the microcapsule to absorb water and expand after the subsequent rupture of the microcapsule.

[0061] (2) Rheological property test of materials:

[0062] The rheological properties of the material will affect its flowing form. By using the steady shear rate mode of the rheometer, the fluidity, thixotropy and viscosity of the material are tested.

[0063] According to Figure 2 It is obtained that the shear stress of each material in Embodiments 1 to 3 increases with the increase of the shear rate, and the viscosity decreases with the increase of the shear rate, showing an obvious "shear thinning" effect, indicating that the plugging materials in each embodiment of the present invention have obvious pseudoplasticity and good material rheological properties; and at the same shear rate, the plugging material prepared in Embodiment 3 has the largest shear stress and viscosity.

[0064] (3) Microcapsule swelling rate test:

[0065] By using coal blocks to apply pressure to the plugging materials prepared in Embodiments 1 to 3 to damage the outer capsule wall of the microcapsules, so that the water-absorbing and swelling rubber is immersed in the plugging materials, and left standing for 2 - 3 h under the condition of constant temperature of 40°C, the swelling time, swelling rate and tensile strength are analyzed, and the XL-250 type tensile machine is used to measure the tensile strength of the specimen:

[0066] Implementation item Expansion time Expansion rate Tensile strength Example 1 Expansion for 3 h 42％ 5.47 MPa Example 2 Expansion for 2.4 h 34％ 7.16 MPa Example 3 Expansion for 2.7 h 39％ 6.24 MPa

[0067] As can be seen from the above table, the plugging materials prepared in Embodiments 1 to 3 all have a high water-absorbing and swelling effect, and the swelling time and swelling rate of the water-absorbing and swelling rubber in Embodiment 1 are the highest. From this, it can be known that the swelling time and swelling rate of the water-absorbing and swelling rubber are proportional to the water-soil mass ratio of the prepared plugging materials. However, due to the absorption of water molecules, the inhomogeneity of the vulcanized network of the rubber matrix will be aggravated, so the tensile strength decreases with the increase of the swelling rate; through comprehensive analysis, the microcapsules of the three embodiments can all ensure that after being immersed in the coal pillar fissures and being pressured, they will undergo micro-expansion to perform secondary filling and plugging of the expanded fissures, as Figure 3 shown.

[0068] The above is only the preferred embodiment of the present invention. It should be noted that: for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and retouches can still be made, and these improvements and retouches should also be regarded as the protection scope of the present invention.

Claims

1. A coal pillar fissure plugging material, characterized in that: It is composed of a mixture of composite powder, yellow mud and microcapsules; The composite powder comprises, by weight: 5 to 8 parts of a surfactant, 3 to 6 parts of an antioxidant, and 9 to 18 parts of a low-temperature eutectic agent; The yellow mud slurry comprises, by weight: 100-150 parts of loess and 850-900 parts of water; The microcapsules are present in an amount of 10 to 15 parts by mass.

2. The coal pillar fissure plugging material according to claim 1, characterized in that: The microcapsule consists of a capsule wall and capsule core particles, and the capsule wall wraps the outer surface of the capsule core.

3. The coal pillar fissure plugging material according to claim 2, characterized in that: The material of the capsule wall comprises the following components in terms of mass percentage: 10% to 12% of ethyl cellulose, 15% to 18% of anhydrous ethanol and 70% to 75% of xylene; the material of the capsule core particles is water-swelling rubber material.

4. The coal pillar fissure plugging material according to claim 1, characterized in that: The surfactant is sodium alginate.

5. The coal pillar fissure plugging material according to claim 1, characterized in that: The antioxidant is apigenin.

6. The coal pillar fissure plugging material according to claim 1, characterized in that: The low-temperature eutectic agent is a mixture of choline chloride and anhydrous citric acid, and the mass ratio of the two is 1:

2.

7. The coal pillar fissure plugging material according to claim 1, characterized in that: The mass ratio of loess to water in the yellow mud slurry is 6:1 to 9:

1.

8. A method for preparing the coal pillar fissure plugging material according to any one of claims 1 to 7, characterized in that: The specific steps are: A. Preparation of yellow mud slurry: Add loess into a container containing aqueous solution, stir at a speed of 1500-1800 r / min for 3-5 minutes to mix evenly to form yellow mud slurry; B. Preparation of composite powder: crushing the seaweed and mixing it with an alkaline solution to release sodium alginate from the cells, then filtering, washing and drying to extract the sodium alginate; then mixing apigenin, choline chloride, anhydrous citric acid and sodium alginate according to the required mass fractions and stirring for 2 to 3 minutes to form a composite powder; C. Preparation of microcapsules: adding ethyl cellulose, anhydrous ethanol and xylene into a container according to mass percentage, stirring at a speed of 1500-1800 r / min for 5-6 minutes to mix evenly to form a capsule wall coating liquid; mixing natural rubber and sodium polyacrylate and vulcanizing them to form a water-swelling rubber material, then extruding and spheronizing to manufacture capsule core particles, air-drying and screening through a screen; finally, spraying the capsule wall coating liquid on the outer surface of each capsule core particle, and drying by air blast to obtain microcapsules; D. Preparation of coal pillar fissure plugging materials: Pour the prepared composite powder and microcapsules into yellow mud slurry and stir continuously at a speed of 1500-1800 r / min for 2-4 min. After uniform mixing, the coal pillar fissure plugging materials are prepared.

9. The preparation method according to claim 8, characterized in that: The stirring time in step B is 3 min, the stirring time in step C is 6 min, and the stirring time in step D is 2 min.

10. A method for using the coal pillar fissure plugging material according to any one of claims 1 to 7, characterized in that: The specific application steps are: ① After the working face is cut through, a coal pillar is formed. Before cracks appear in the coal pillar, a layer of steel fiber asbestos mesh is hung on the surface of both sides of the coal pillar along the direction of the working face; ② After the steel fiber asbestos mesh is hung, a layer of prepared coal pillar crack plugging material is evenly sprayed on the surface of the coal pillar through mining spraying equipment to plug the cracks on the surface of the coal pillar. The spraying thickness of the coal pillar crack plugging material is 4 to 5 mm; ③ As the working face advances, the stress of coal pillars in each section increases, and the coal pillars in some sections are compressed, causing the cracks to expand and develop. At this time, the compression and deformation of the coal pillar crack plugging material causes the capsule wall of the microcapsule to rupture, and the capsule core absorbs water and expands to seal the expanded and developed cracks, thereby achieving a continuous air leakage prevention effect on the cracks.

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