Grouting reinforcement method for caving and breaking area of coal mine working face

Abstract

The invention discloses a grouting reinforcement method for a coal mine working face collapse and burst broken area, which comprises the following steps: S1, on-site investigation and survey are carried out, end face leakage and burst conditions are mastered, and collapse and burst broken reasons are quantitatively analyzed from two aspects of geological factors and engineering factors; s2, the grouting opportunity, the grouting position, the grouting material and the grouting parameters are determined through theoretical calculation, physical experiments and numerical simulation; and S3, a deep and shallow hole grouting mode is adopted for conducting grouting reinforcement on the caving and breaking area of the coal mine working face. According to various factors of coal mine working face collapse, a grouting mode combining deep and shallow holes is provided in a targeted mode, low-pressure slow grouting is adopted for the shallow holes, the shallow holes are used for sealing coal cracks in the working face superficial range, forming a curtain and preventing grout from leaking, floral tube grouting is adopted, the grout diffusion path is increased, and effective diffusion of grout is guaranteed; then deep hole grouting is carried out, and grouting modification is carried out on the coal body with the relatively low deep fracture development degree; therefore, the completeness and strength of the advanced coal body of the working face are improved, the caving condition is improved, top coal and a top plate are better supported, and then top coal leakage is controlled.

Description

Technical Field

[0001] The invention relates to the technical field of coal mining, in particular to a grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face. Background Art

[0002] When the coal wall and roof fall in the coal mining face, it will seriously affect the safe and efficient production of the working face. During the coal mining process, due to the influence of mining stress, the original cracks in the coal wall and roof of the mining area develop and penetrate, forming new cracks. At the same time, the combined effect of geological conditions such as deep burial depth, large inclination and fault structure leads to the coal wall and roof falling in the working face. Therefore, in order to reduce the impact of the collapse of the working face on the mining of the working face and increase the advancement speed of the working face, measures need to be taken to control the broken area of ​​the working face.

[0003] The formation of the collapsed and broken area of ​​the working face is affected by many factors. For the working face with deep soft coal and large inclination, it is currently impossible to provide a support with large initial support force and lighter weight. Replacing a large-mass support will cause the support to tilt due to large inertia. Therefore, in the case where the performance of the support and the length of the working face cannot be changed, a reinforcement method for managing the collapsed and broken area of ​​the working face is urgently needed. Summary of the invention

[0004] In view of the above-mentioned technical deficiencies, the purpose of the present invention is to provide a grouting reinforcement method for the collapsed and broken area of ​​a coal mine working face.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions: The present invention provides a grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face, comprising the following steps: S1. Conduct on-site investigation to understand the leakage of the end face and quantitatively analyze the causes of collapse and breakage from the perspectives of geological and engineering factors; S2. Comprehensively determine the grouting timing, grouting location, grouting materials and grouting parameters through theoretical calculation, physical experiment, numerical simulation and other methods; S3. Use the "deep and shallow hole" grouting method to grout and reinforce the collapsed and broken areas of the coal mine working face.

[0006] Preferably, the geological factors include burial depth, coal seam properties, inclination, and fault structure; the engineering factors include mining stress and support performance.

[0007] Preferably, step S2 comprises: S2.1. Calculate the distribution of the supporting pressure zone in front of the working face and determine the timing and location of grouting in the collapsed and broken area of ​​the working face, that is, use numerical simulation software to simulate the distribution of the supporting pressure of the advanced working face under the influence of the working face mining and the corresponding plastic zone distribution, and verify them with the theoretical calculation results. Through the calculation results, analyze the location of the crack development in front of the working face and determine the timing and location of the advanced grouting of the working face; S2.2. Study the mechanical properties of the broken coal body after grouting reinforcement at the working face, that is, the mechanical properties of the coal slurry fusion body, that is, conduct uniaxial compression tests on coal slurry fusion body samples with different grouting materials, compare and analyze the performance of different grouting materials based on the test results, and determine the best grouting material; S2.3. Establish a three-dimensional grouting numerical model of the working face, simulate the influence of changes in several parameters such as grouting pressure, grouting time, drilling length and drilling spacing on the grouting effect, and determine the optimal grouting pressure, grouting time, drilling length and drilling spacing.

[0008] Preferably, step S3 comprises: S3.1. Determine the grouting location: select the area where spalling has occurred or has signs of spalling as the grouting location; S3.2, grouting hole arrangement: according to the borehole length and borehole spacing determined in step S2.3, deep grouting holes and shallow grouting holes are drilled at the grouting site, wherein the deep grouting holes and shallow grouting holes are arranged alternately in the horizontal direction; the shallow grouting holes are drilled directly perpendicular to the coal wall, while the deep grouting holes are drilled at an elevation angle of 15-30° according to the specific engineering conditions; S3.3. Sealing the hole: Use a woven bag combined with the slurry to seal the hole. After the hole is formed, wrap the woven bag tightly around the end of the grouting pipe and insert it into the grouting hole. Start grouting when leakage just begins to appear at the hole mouth, stop grouting, wait for 30 s to 60 s to solidify, and then start grouting into the fractured coal body.

[0009] Preferably, the shallow grouting holes are grouted at low pressure and slow pressure, with a grouting pressure of 2-3 MPa; the deep grouting holes are grouted at a higher pressure of 3-5 MPa; if leakage occurs in the coal wall during the grouting process, the grouting is stopped immediately, and the grouting is continued after waiting for 30 s to 60 s for solidification. The shallow holes are grouted at low pressure and slow pressure to close the coal body cracks in the shallow range of the working face, forming a "curtain" to prevent the slurry from leaking, and the flower tube is used for grouting to increase the slurry diffusion path and ensure the effective diffusion of the slurry; then the deep hole grouting is carried out to grout the coal body with relatively low development degree of deep cracks; thereby improving the integrity and strength of the leading coal body in the working face, improving the spalling condition, forming better support for the top coal and the roof, and then controlling the leakage of the top coal.

[0010] Preferably, during grouting, the lower low-position holes are grouted first, and then the upper high-position holes are grouted. Grouting is performed for each grouting hole constructed until all the boreholes are constructed and grouted.

[0011] The beneficial effects of the present invention are as follows: according to various factors of coal mine working face collapse, the present invention specifically proposes a grouting mode combining "deep and shallow holes", and low-pressure slow injection is adopted in shallow holes to close the coal body cracks in the shallow range of the working face, forming a "curtain" to prevent slurry leakage, and flower pipe grouting is used to increase the slurry diffusion path to ensure effective diffusion of slurry; then deep hole grouting is carried out to modify the coal body with relatively low degree of deep crack development by grouting; thereby improving the integrity and strength of the leading coal body of the working face, improving the spalling condition, forming better support for the top coal and roof, and thus controlling the leakage of top coal. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0013] Figure 1 A working face and tunnel layout diagram provided for an embodiment of the present invention; Figure 2 A FLAC3D numerical model diagram provided by an embodiment of the present invention; Figure 3 The advance stress distribution diagram of the working face advanced 100m provided in the embodiment of the present invention; Figure 4 The compressive strength distribution diagram of three different samples in the embodiment of the present invention; Figure 5 The deformation modulus distribution diagram of three different samples of the embodiment of the present invention; Figure 6 These are real-time photos of the failure morphologies of three different samples of the embodiments of the present invention; Figure 7 A three-dimensional coal seam grouting numerical simulation model diagram established in an embodiment of the present invention; Figure 8 It is a slurry diffusion curve diagram at different grouting times in the embodiment of the present invention; Fig. 9 It is a slurry diffusion curve diagram under different grouting pressures in the embodiment of the present invention; Fig.10 It is a simulated cloud diagram of slurry diffusion under different drilling length conditions in the embodiment of the present invention; Fig.11This is a diagram of the layout of grouting holes in an embodiment of the present invention. DETAILED DESCRIPTION

[0014] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0015] Example The coal wall spalling and roof collapse in a coal mine working face have seriously affected the safe and efficient production of the working face. Due to the influence of mining stress during coal mining, the original cracks in the coal wall and roof of the mining area develop and penetrate, forming new cracks. At the same time, the combined effect of geological conditions such as deep burial depth, large inclination angle and fault structure has led to coal wall spalling and roof collapse in the working face. The geological overview of the working face is as follows: (1) The working face is the first mining face of the lower mining area of ​​II (3), with a working face length of 184 m, a strike length of about 1410 m, and a mining face slope area of ​​272,886 m 2 The working face elevation is -754.4~-864.1, corresponding to the ground elevation of +30.4~+33.7, with an average burial depth of about 777.2 m. The inclination of the 7# coal seam is 12.0°-26.5°, with an average of 22.6°, and the coal seam thickness is 4.65 m. The working face and tunnel layout are as follows: Figure 1 The working face is a comprehensive mechanized top coal caving mining, with a mining height of 2.5m, a caving to mining ratio of 1:0.86, and a full caving method to manage the roof.

[0016] (2) During the mining process, the working face is adjacent to the downhill area of ​​the Ⅱ(3) lower mining area on the west, connected to the southern boundary of the Ⅱ(3) lower mining area on the south, the boundary of the well field on the east, and the unmined area on the north. Therefore, given the specific geological conditions around the working face, its mining process is relatively less affected by the surrounding stress distribution.

[0017] (3) Coal seam and its roof and floor conditions No. 7 coal is soft and brittle. After being loaded, the cracks are very developed and it is impossible to remove complete samples for mechanical property testing. The viscosity is poor and the broken coal is like quicksand. The thickness of the coal seam at both ends is 2.90-7.50m, with an average thickness of 4.65m. The direct roof of the working face is sandy mudstone, with a thickness of 0~4.80m and an average thickness of 3.6m. The basic roof is medium sandstone, with a thickness of 9.26~15.16m and an average thickness of 11.70m.

[0018] In order to reduce the impact of working face collapse on working face recovery and increase the working face advancement speed, the broken area of ​​the coal mine working face is treated according to the method of the present invention. The specific steps are as follows: S1.1. Analysis of geological factors: After measurement, it was determined that the average burial depth of the working face was about 777.2 m, and the dip angles in the east and west were 12° and 25.7° respectively; the coal seam structure was relatively complex, with a 0.5m thick layer of carbonaceous mudstone intercalated with gangue on the east and west sides of the chute, and the thickness of the intercalated gangue was 0.5m. The thickness of the coal seam was 2.90-7.50m, with an average of 4.65m. The thinnest part was at point L13 of the chute, and the thickest part was at point C25 on the east side of the material road. The mine investigation found that the coal seams are very hard and brittle, cracks develop after being loaded, and the viscosity is poor. The broken coal is in the form of quicksand and is easy to break after being compressed. Its bearing capacity is low. Under the combined action of tectonic stress, ground stress, and mining stress, the coal body at the working face is unstable and damaged because it cannot withstand the pressure of the roof, so the coal body is broken; the working face exposes multiple faults, including 15 faults in the chute, 11 faults in the material channel, and 5 faults in the cutting eye; the impact of faults on the working face is first mainly manifested in the change of stress distribution in the area near the fault; secondly, the fault structure will affect the mechanical properties of the coal body and the roof and floor rock mass of the working face, causing their mechanical properties and integrity to deteriorate, which leads to the particularly prominent coal and rock mass crushing phenomenon during the working face crossing the fault, and then the occurrence of spalling and leakage.

[0019] S1.2. Analyze engineering factors: (1) According to the simulation study during the mining period of the working face, the peak value of the leading stress of the working face reached 41.2MPa, which damaged the coal wall in front of the working face, developed mining cracks, and caused the coal seam and its roof to break. (2) The hydraulic support currently used in the working face is ZFH6200 / 16 / 28. The working resistance of this support is only 6200kN, but its mass is relatively heavy (38t). Due to the large inclination of the working face, the heavy support slides downward and falls due to inertia. At the same time, because the vertical stress and leading stress are shared by the hydraulic support and the coal wall, when the working resistance of the hydraulic support is limited, the force on the coal wall is relatively increased, which in turn aggravates the breakage and spalling of the coal wall. S2.1. The distribution of support pressure and corresponding plastic zone of the advanced working face under the influence of mining is simulated by FLAC3D numerical simulation software, and verified with the theoretical calculation results. The location of crack development in front of the working face is analyzed through the calculation results, and the timing and location of advanced grouting of the working face are determined. The specific steps include: S2.1.1. According to the on-site conditions of the coal mine, a FLAC3D numerical model with a length of 320m, a width of 5m and a height of 80m was built. For the strata that cannot be reflected in the upper part of the model, a load of 20.15 MPa was applied in the vertical direction based on the deadweight of the rock mass. Different working conditions were set according to the different advancement distances of the working face, that is, the working face was excavated at 20m, 40m, 60m, 80m, 100m and 120m. Except for the upper boundary of the model which is a stress edge, the rest are displacement edges. The established model is as follows Figure 2 shown.

[0020] Before and after the excavation of the working face, stress concentration will occur in the coal wall at the end of the working face. As the working face advances, the vertical stress on the surrounding rock of the working face increases, but the increase gradually decreases. When the advancing distance is 20m, 40m, 60m, 80m, 100m and 120m, the vertical stress is 30.65 MPa, 37.06 MPa, 39.29 MPa, 41.09 MPa, 42.14 MPa and 42.76 MPa. When the advancing distance reaches 100m, the vertical stress is basically stable. The stress simulation results in front of the working face are extracted. The results show that when the working face advances at 20m, 40m, 60m, 80m, 100m and 120m, the support pressure reaches a peak at 6.2m in front of the working face, which are 33.4MPa, 33.6MPa, 41.2MPa, 41.6MPa, 42.1MPa and 41.5MPa, respectively. As the distance from the working face increases, the advance support pressure curve generally increases first and then decreases, and then a secondary peak appears, and finally decreases to the original rock stress. In the range of 0-4m from the working face, the support pressure increases sharply, and the curve reaches the support pressure peak at 6.2m and then gradually decreases. After a secondary peak appears at 25m from the working face, the stress gradually decreases until it decreases to the original rock stress at about 70m from the working face.

[0021] S2.1.2. Determination of the timing and location of grouting at the working face As can be seen from the previous text, the influence range of the advanced support pressure of the working face is about 70m in front of the working face. Within this range, the most violently affected area is about 30m in front of the working face, and the peak of the advanced support pressure is about 6.2~8.3m in front of the working face. The stress and crushing area of ​​the coal body in front of the working face will change significantly due to mining. The stress of the coal body in front of the working face is divided into four different areas, and the development of coal body cracks in each area is also different, such as Figure 3 In order to determine the appropriate grouting time and location, the following analysis is performed in different zones: ① The pressure stabilization area, that is, the area 70m in front of the working face, has a coal body stress level close to the original ground stress. The coal body here is relatively complete, and mainly structural fractures and primary fractures exist. Due to the small fracture opening, grouting in this area is more difficult, so grouting in this area is not recommended; ② Slowly pressurized area, that is, the area 30~70m in front of the working face. This is the front end of the advance support pressure influence area. The advance support pressure gradually increases in this area. Under the influence of mining stress, structural cracks are redeveloped and new cracks are generated. However, the cracks have not developed in large quantities, so this area is not suitable for grouting; ③ The intense pressure increase zone, that is, the area 6.2~30m in front of the working face, where the stress value rises rapidly to the peak value, and the impact on the coal body is extremely significant. Under the action of high stress, the number of coal body cracks increases significantly. Considering the injectability, this stage is conducive to the injection and propagation of slurry; ④ Decompression zone, i.e. the area 0~6.2m in front of the working face, is the area where the coal body is most severely broken in front of the working face. The internal cracks of the coal body are highly developed, and even coal body spalling and falling off may occur. In this area, end face grouting is adopted, and fast-setting grouting materials are used to seal the coal body cracks in the shallow range of the working face to form a "curtain" to avoid the problem of failure to solidify in time and slurry leakage.

[0022] S2.2. Study the mechanical properties of the broken coal body after grouting reinforcement at the working face, that is, the mechanical properties of the coal slurry fusion body, that is, conduct uniaxial compression tests on coal slurry fusion body samples with different grouting materials, compare and analyze the performance of different grouting materials based on the test results, and determine the best grouting material. The specific steps are as follows: S2.2.1. Preparation of sample coal slurry fusion body: The grouting reinforcement materials available include three materials: Jiumina inorganic grouting single material, micro-nano modified coal-friendly grouting double material (Naigu No. 1) and Guante silicate modified polyurethane material, hereinafter referred to as "Jiumina", "Naigu No. 1" and "Guante" respectively; Jiumina material is based on ordinary Portland cement, with retarders and early strength agents added. It has a long initial setting time, has great fluidity within 2 hours, and generally has final setting after 10 hours. Its applicable water-cement ratio range is very small, and solid-liquid separation is prone to occur when the water-cement ratio is large. Its market unit price is 4500-5500 yuan / ton; Naigu No. 1 material is made of sulphoaluminate clinker and A and B components such as lime and gypsum. After mixing with water, it has good early setting and early strength properties, and is also very adhesive to coal. Its particle size can reach 1300 meshes, and it can enter small cracks. At the same time, the water-cement ratio has a wide range of applications. The fluidity and viscosity of the slurry can be controlled by changing the water-cement ratio and temperature of the slurry material. Its market unit price is 11,000~12,000 yuan / ton; Guant uses silicate modified polyurethane material A and B components to mix evenly in a volume ratio of 1:1 and then quickly polymerize into an insoluble polymer material. This material has certain compressive strength, adhesion, flame retardancy, solvent corrosion resistance, toughness and other properties. It is insoluble in water and can maintain good strength even in the presence of water. It can maintain the function of plugging and reinforcement as the coal seam deforms; however, during the use of this material, there have been cases of overheating, material pouring, high-pressure pipeline bursting, polymer material splashing onto the skin causing burns, and poisoning or physiological discomfort caused by inhalation by personnel. The current market price of this material is 20,000-21,000 yuan / ton.

[0023] Various grouting materials are mixed with crushed coal and cast using the cubic sample mold commonly used in the concrete field, and then processed into 100mm×100mm×100mm samples. The main equipment for sample casting and preparation includes: manual slurry high-speed mixer, fractal screen, automatic vibrator, measuring cylinder, sample mold, release agent, etc.

[0024] (1) Naigu I coal slurry fusion sample The Naigu No. Ⅰ grouting material was made into samples according to different slurry water-cement ratios, different coal content and different curing times. Since the double-liquid quick-setting grouting material sample initially solidifies in 3~5 minutes, the solidification speed is fast, and there will be certain expansion performance after solidification, accompanied by heat release. Therefore, in order to smoothly demould, the sample must be demoulded 20min~30min after the slurry is molded, otherwise it will be difficult to fall off the mold due to heat release. Since the Naigu No. Ⅰ material contains calcium aluminate after pouring, it may react with carbon dioxide in the air, so it is sealed with plastic wrap and cured to the required age.

[0025] (2) Kumina coal slurry fusion sample A water-cement ratio of 0.4:1 was adopted to make the Kumina single-liquid inorganic grouting reinforcement material sample. The sample had a long initial setting time and was solidified after 2 days. It could be demoulded smoothly after 2 days and met the conditions for testing.

[0026] (3) Guante coal slurry fusion sample Guant chemical material A and B components are mixed in a ratio of 1:1. No water is needed. The material is tightly combined with the plastic mold. When pouring, a layer of plastic wrap must be added between the slurry and the mold, otherwise the sample cannot be smoothly removed from the mold! After the material is stirred evenly, the slurry and the sample are mixed for 1~3 minutes for initial coagulation. The sample releases heat and expands during the molding process. For smooth demolding, demolding is performed 15min~30min after the slurry is filled into the mold.

[0027] S2.2.2. Uniaxial compression test In this test, the loading system used was the C64.106 electro-hydraulic servo universal testing machine from the Mining Science Center of China University of Mining and Technology, which has a maximum load of 1000kN. The test used displacement control, with a loading rate of 0.5mm / min and data sampling of 10 data per second.

[0028] The test is divided into preliminary test and formal test. In order to avoid waste of materials due to inadequate design, four samples are used for preliminary test. The preliminary test can accurately control irrelevant variables.

[0029] In the formal experiment, a group of samples of different materials, Naigu I, Jiumina and Guant, were made, which were recorded as sample 1, sample 2 and sample 3 respectively. There were 17 groups of samples with different slurry water-cement ratios (0.4, 0.5, 0.6, 0.8) of Naigu I material, different coal content (400g, 500g, 600g) and different curing time (2h, 4h, 6h, 12h, 1d, 3d, 7d). Three samples were tested in each group, and the arithmetic mean was taken as the uniaxial compressive strength value of the group. In order to ensure the normal progress of the test, one more sample was prepared under each factor during pouring for backup. The sample preparation plan is shown in Table 1. A total of 72 coal slurry fusion samples were made for uniaxial compression test.

[0030]

[0031] According to the previous understanding of the basic properties of different materials, in order to master the mechanical properties of different materials after fusion with coal, this section uses the control variable method to conduct uniaxial compression tests on the coal slurry fusion body cast by crushed coal samples and Naigu No. Ⅰ, Jiumina, and Guant grouting materials. The different comparison results of the compressive strength, peak stress value, strength mean, and forming time of each sample are shown in Table 2.

[0032]

[0033] (1) Analyze the stress-strain curve, from Figure 4 It can be seen that at the same age, the peak strength of the coal slurry fusion sample of Naigu I is 14.87MPa, the peak strength of the coal slurry fusion sample of Jiumina is 26.38MPa, and the peak strength of the coal slurry fusion sample of Guante is 15.20MPa. Among them, Jiumina has the highest strength, but its initial setting time and solidification time are long, which is not suitable for end face grouting. The plasticity of the Guante two-liquid chemical slurry material sample is the best, but its price is expensive, about 4 times that of Jiumina material and 2 times that of Naigu I material, and its strength is only equivalent to Naigu I. Therefore, from an economic point of view, Naigu I material has a greater advantage, and from a technical point of view, Naigu I material also meets the requirements.

[0034] (2) Deformation modulus The deformation modulus can better reflect the deformation characteristics of coal slurry fusion body. In this paper, the deformation modulus of coal slurry fusion body is defined as the ratio of peak stress to strain. Figure 5 The deformation modulus change curve of coal slurry fusion bodies of different materials. Figure 5 It can be seen that at the same age, the deformation modulus of the Jiumina single-material grouting material sample is the largest, which is 0.88GPa; the second is the Naigu I double-material sample, which is 0.46GPa; the deformation modulus of the Guant double-liquid chemical slurry material sample is the smallest, which is 0.15GPa. This shows that the Jiumina single-material grouting material sample has a weak ability to resist deformation, the Naigu I double-material sample is better, and the Guant double-liquid chemical slurry material sample is the best; for the coal slurry fusion, its deformation modulus change curve and compressive strength show a consistent trend. This shows that as the slurry gradually solidifies, the compressive strength and deformation modulus of the broken coal body after grouting reinforcement increase synchronously.

[0035] (3) Failure morphology of coal slurry fusion bodies with different slurry materials The failure morphology of coal slurry fusion is as follows Figure 6 As shown in the figure, in the poured specimens, the slurry filled the pores and cracks between the broken coal bodies, achieving different levels of enrichment. This process formed a certain buffering effect between the rock masses, and at the same time expanded the inter-rock conduction mode that was originally limited to point contact and line contact, and transformed it into a more extensive surface contact conduction, thereby improving the stability and conduction efficiency of the overall structure; observing the internal failure morphology of the specimens, it was found that the cracking position would initially directly penetrate the low-strength coal body part, because the strength of the coal body is lower than that of the slurry stone body. At the same time, the specimens are prone to splitting, breaking, and shear slippage, which ultimately leads to damage to the overall structure of the coal slurry fusion body. In rare cases, the damaged part may also appear at the interface between the coal body and the slurry cementation surface, but in general, the damage mainly comes from the coal body.

[0036] Through further observation of the samples after destruction, it is found that the failure forms of different materials are different. The double-material sample of Naigu I shows good plasticity. In the process of bearing stress, the slurry layer initially shows good deformation and bearing capacity, but the thicker slurry layer wraps the coal body. After cracking occurs at the weaker part of the coal body inside the sample, the slurry layer with good bearing capacity is displaced and pulled. Under the continued action of the load, the cracks in the coal body continue to expand, and the slurry layer breaks together. The cracks eventually penetrate and affect the entire sample. The single-material sample of Kumina has high brittleness. After cracking occurs at the coal body, the sample mainly undergoes splitting failure, and the number of visual failure cracks is less than that of the double-material sample of Naigu I; the sample of Guante double-liquid chemical material has higher plasticity, and the sample mainly undergoes tensile failure. After the internal failure of the sample, the coal body becomes powdery, indicating that the adhesion of Guante double-liquid chemical material is better.

[0037] In summary, the initial setting time and sample solidification time of Naigu No. 1 material are short, and it can be solidified within 20 minutes, and reach 90% of the peak strength, i.e. 9.05MPa, after 2 hours. It can well meet the early strength and rapid setting requirements of end face grouting. At the same time, its consolidation strength on the coal body is equivalent to that of the organic polymer material Guante used by the mine. The price of this material is also more economical, only about 50% of Guante material. Therefore, this paper selects Naigu No. 1 material instead of Guante material for use in this working face from the perspective of technology and economic applicability.

[0038] S2.3.1. Establishment of grouting numerical model Through the study of the fusion sample of coal and grouting materials in the working face, it was determined that the Naigu No. Ⅰ grouting material was used as the shallow hole grouting material for the working face advancement. Based on the geological background of Xuzhuang Coal Mine, for the convenience of calculation, the simulation area was set to 20 m×20 m×4.6 m, and a three-dimensional coal seam grouting numerical simulation model was constructed. The model simulates the influence of changes in key parameters such as grouting pressure, grouting time, borehole length and borehole spacing on the grouting effect. According to the actual working conditions, the diameter of the grouting hole in the model is set to 0.05m, and the hole depth is 6m. Figure 7 The bottom of the model is set as a fixed boundary, and the surrounding areas are set as sliding boundaries. Considering the gravity of the overburden, a free boundary is used in the upper part of the model to simulate the free flow of the grouting fluid on the boundary.

[0039] S2.3.2 Parameter setting In order to accurately reveal the grouting diffusion law in the collapsed and broken area of ​​the working face, the model parameters were carefully set. Based on the theory of geotechnical seepage, this paper selected the Darcy's law module in porous media and groundwater flow as the simulation basis

[86] . In the seepage field, the inner boundary of the model is affected by the grouting pressure, while the initial pore pressure is set on the outer boundary. During the grouting process of the Naigu No. 1 material, its viscosity will change over time

[87] . In order to be closer to the actual situation, this paper measured the viscosity of the Naigu No. 1 slurry with a viscometer before simulation. Through fitting, the change of viscosity over time was obtained and applied to the simulation to ensure the accuracy of the diffusion law. The specific data of the material properties in the selected module are shown in Table 3:

[0040] After setting the basic material property parameters, the grouting parameters can be set. In order to explore the slurry diffusion law under grouting pressure, grouting time, drilling length and drilling spacing, the parameters that need to be set are shown in Table 4:

[0041] S2.3.3. Slurry diffusion law at different grouting times In order to study the diffusion law of slurry in coal body at different times, this section uses the control variable method to limit the grouting pressure to 2MPa for shallow holes and 5MPa for deep holes, the length of shallow holes is 2m, the length of deep holes is 6m, and the spacing of holes is 3m for shallow holes and 6m for deep holes. The grouting hole diameter adopts the 0.05m grouting hole size selected in actual construction. The transient calculation method is used to set the total grouting time to 30min. The slurry diffusion range is recorded every 1min. The conclusion is that the slurry diffuses after flowing out of the grouting pipe radially, and the diffusion area is approximately cylindrical. The cement slurry concentration is higher near the grouting pipe. As time goes by, the diffusion range of the slurry in the coal seam gradually expands, but the growth rate of its diffusion speed gradually slows down, especially after 10min, the change of the slurry diffusion range tends to be stable. The analysis is that, on the one hand, due to the effect of grouting pressure, the slurry can flow into the pores of the coal body and effectively fill the cracks in the coal seam, which promotes the expansion of the diffusion range. As the grouting time increases, the diffusion of the slurry in the coal seam gradually tends to saturation, resulting in a gradual slowdown in the diffusion rate and leakage of the slurry from the grouting port; on the other hand, due to the short solidification time of the slurry, it can be seen from the test in Chapter 3 that the solidification time of the micro-nano modified coal-friendly and solid-resistant No. Ⅰ grouting material is about 20 minutes, so the grouting time is extended, and the grouting range no longer changes, that is, the slurry reaches the final diffusion range. Comparing the diffusion of the slurry at different times in the three-dimensional model, it can be seen that the slurry diffuses faster within 8 minutes, but fails to reach the effective diffusion radius, and the "curtain" cannot be effectively formed between the shallow holes. When deep high-pressure grouting is performed, slurry leakage is likely to occur. After 10 minutes, the slurry diffusion range growth rate is not obvious, and the slurry between the shallow holes is effectively communicated. Therefore, the on-site grouting time is considered to be no less than 10 minutes.

[0042] Combination Figure 8 From the slurry diffusion curve, we can derive the specific diffusion radius of the slurry at different time points: when the grouting time reaches 2 minutes, the maximum diffusion radius of the slurry is measured to be 2.06 m; as the grouting time is extended to 4 minutes, the maximum diffusion radius increases to 2.65 m, an increase of 31.55% compared with 2 minutes. Further extending the grouting time to 6 minutes, the maximum diffusion radius of the slurry reaches 2.82 m, an increase of 6.41% compared with 4 minutes. When the grouting time is extended to 8 minutes, the maximum diffusion radius is 2.95 m, an increase of 4.60% compared with 6 minutes. Finally, when the grouting time reaches 10 minutes, the maximum diffusion radius of the slurry is 3.03 m, an increase of 2.71% compared with 8 minutes. The maximum diffusion radius shows the characteristics of first increasing rapidly and then slowing down until it is basically unchanged. Therefore, it can be considered that extending the grouting time to a certain extent can alleviate the attenuation of the grouting pressure during the penetration and diffusion process, thereby increasing the diffusion range of the grouting slurry on the working face.

[0043] S2.3.4. Grout diffusion law under different grouting pressures In order to study the diffusion of slurry in coal under different grouting pressure conditions, this section sets up four numerical calculation schemes. According to the grouting mode combining "shallow hole-deep hole", low-pressure slow injection and deep hole high-pressure grouting are adopted. The grouting pressure is set to P0=0.5MPa, 1MPa, 2MPa, 3MPa for shallow holes, and P1=3MPa, 4MPa, 5MPa, 6MPa for deep holes. The diffusion law of Naigu No. Ⅰ micro-nano modified coal-friendly grouting material under different grouting pressures is analyzed. At the same time, the drilling length is controlled to be 2m for shallow holes and 6m for deep holes, and the drilling spacing is 3m for shallow holes and 6m for deep holes. Through section drawing and cropping, the pressure decay is set to 0.1MPa pressure as the baseline, and the grouting time node of 10min is analyzed to obtain the slurry diffusion range under different grouting pressures; The simulation analysis results show that the grouting pressure has a significant effect on the diffusion effect of slurry in the coal body. With the increase of grouting pressure, the driving force of the slurry is also enhanced, thereby effectively supplementing the tip of the crack. In particular, when the shallow hole grouting pressure is set to 0.5MPa and 1MPa, and the deep hole pressure is 3MPa and 4MPa, the boreholes are not effectively connected, and a "curtain" structure is formed. Under this pressure condition, the slurry is prone to leakage during deep high-pressure grouting. However, when the shallow hole grouting pressure exceeds 2MPa, the shallow grouting holes are fully filled with slurry, indicating that the broken coal body is effectively filled with slurry under this grouting pressure. After the slurry solidifies, it can not only reinforce the surface surrounding rock, but also form a curtain structure, effectively preventing the loss of slurry during deep hole grouting.

[0044] Fig. 9The curves of slurry diffusion under different grouting pressures are shown in Figure 1. The experimental results show that there is an obvious positive correlation between grouting pressure and slurry diffusion distance. The diffusion range under different grouting pressures when the grouting time is 8 minutes is selected for analysis. When the deep hole grouting pressure is 3MPa, the slurry diffusion distance in the coal seam is measured to be 1.73m; when the grouting pressure is increased to 4MPa, the slurry diffusion distance increases to 2.21m; further increasing the grouting pressure to 5MPa, the slurry diffusion distance is significantly expanded to 2.95m; and when the grouting pressure reaches 6MPa, the slurry diffusion distance further increases to 3.17m, with an increase of 27.75%, 33.49% and 7.46% respectively. It can be seen from the curve that at the same time, with the increase of grouting pressure, the grouting diffusion range increases accordingly, but the increment gradually decreases. The analysis shows that the degree of fragmentation in the broken area of ​​the working face is large, so that the slurry permeability in the area is mainly controlled by the degree of fragmentation of the coal body, which shows that the grouting pressure has a relatively small effect on the permeability of the slurry. Therefore, during the actual grouting process on site, the grouting pressure should be determined based on the specific engineering conditions on site, but the minimum grouting pressure for shallow holes should be above 2.0MPa to ensure sufficient driving force. For deep hole grouting, the grouting pressure can be increased to a certain extent to increase the penetration and diffusion range of the slurry, but high-pressure grouting should not be used for shallow holes, as the shallow parts are relatively broken, and high-pressure grouting will cause leakage and slurry running.

[0045] S2.3.5 Effect of drilling length on slurry diffusion law In order to study the diffusion law of slurry in coal body under different drilling length conditions, this section uses the control variable method to limit the grouting pressure to 2MPa, the drilling spacing to 3m for shallow holes and 6m for deep holes, and the grouting hole diameter uses the 0.05m grouting hole size selected in actual construction. Since the shallow hole is to form a "curtain", it is easy to leak slurry if it is too shallow, and it will enter the undeveloped part of the cracks if it is too deep, and the slurry diffusion effect is poor, making it difficult to form a "curtain". Therefore, a shallow hole drilling depth of 2m is selected to simulate the slurry diffusion law under the conditions of shallow holes of 2m and deep holes of 4m, 6m and 8m. The nodes at the grouting time of 5min and 25min are analyzed, and the simulated cloud map is as follows Fig.10 As shown, from Fig.10It can be seen that the diffusion area of ​​the slurry after flowing out of the grouting pipe is approximately cylindrical. At the same time, the length of the borehole has a significant effect on the diffusion range of the slurry, which is mainly manifested in that the diffusion range of the slurry gradually decreases with the increase of the distance from the working surface, which means that the grouting pressure shows a trend of attenuation during the penetration and diffusion process. Similarly, the grouting time of 8min is selected for analysis. When the deep hole position is 2m, the slurry diffusion range is 2.05m; when the deep grouting hole position is 4m, the slurry diffusion range is 1.41m, which is 31.22% lower than the deep grouting hole position of 2m; when the deep grouting hole position is 6m, the slurry diffusion range is 1.22m, which is 13.47% lower than the deep grouting hole position of 4m; when the deep grouting hole position is 8m, the slurry diffusion range is 1.01m, which is 17.21% lower than the deep grouting hole position of 6m. When the borehole length increases from 2m to 4m, the slurry diffusion range attenuates significantly. The reason is that shallow boreholes are arranged at the 2m position of the shallow hole, which increases the grouting density. Therefore, the slurry diffusion range is larger, so that the attenuation ratio is larger at a depth of 4m.

[0046] Through the calculation and simulation results of the advance support pressure of the working face in the previous article, the peak value of the advance stress concentration of the working face is 6~8m. Therefore, in order to ensure effective grouting reinforcement of the areas with the most severe coal body crushing and the highest degree of crack development in the stress reduction zone, the drilling length should be no less than 6m.

[0047] S2.3.6 Study on slurry diffusion law under different drilling hole spacing In order to study the diffusion law of slurry in coal body under different borehole spacing conditions, this section uses the control variable method to limit the grouting pressure to 2MPa for shallow holes and 2m for borehole length, 5MPa for deep holes and 6m for borehole length. The grouting hole diameter uses the 0.05m grouting hole size selected in actual construction, and simulates the slurry diffusion law under different hole spacing conditions of the same grouting pressure and borehole depth, shallow hole 2m and deep hole 4m, shallow hole 3m and deep hole 6m, shallow hole 4m and deep hole 8m. Using the transient calculation method, the total grouting time is set to 30min, and the slurry diffusion range is recorded every 1min. Through three-dimensional slicing processing, the position of 5~10m height is intercepted for analysis. The slurry diffusion law of different hole spacings is as follows: when the shallow hole spacing is 2m and the deep hole spacing is 4m, the slurry diffusion radius can reach 2m within 2min, which may cause leakage in the shallow area. In addition, as the number of holes drilled increases, the workload and working hours of workers will increase, resulting in a reduction in effective production time, which in turn has an adverse impact on the production efficiency of the mine. Under the conditions of a shallow hole spacing of 3m and a deep hole spacing of 6m, the diffusion radius of the slurry can reach 3m after 10 minutes of grouting, and the diffusion radius of the deep part can also reach 1.2m. In this way, while ensuring that the deep coal body is effectively reinforced, excessive waste of slurry is also avoided. However, when the shallow hole spacing is expanded to 4m and the deep hole spacing is 8m, it is difficult for the slurry to reach the expected diffusion radius of 4m within 12 minutes. Although attempts can be made to expand the penetration and diffusion range of the slurry by increasing the grouting time or grouting pressure, the effect of this approach is limited. At the same time, it should be noted that since the grouting material uses a double-material quick-setting material, too long a grouting time may cause the previously injected slurry to solidify, which is not conducive to the smooth injection of subsequent slurry. Therefore, in actual operations, it is necessary to comprehensively consider various factors to ensure the optimization of grouting effects and mine production benefits; S3.1. Determination of grouting location: mainly determined based on on-site observation, grouting is carried out in areas where spalling or signs of spalling occur; S3.2, grouting hole arrangement parameters: determined according to the numerical simulation results and the actual situation on site. The actual mining height on site is generally controlled at 2.7-3.0 m. To facilitate construction, the grouting hole opening position is determined within 1 m below the top plate of the working face. The shallow hole opening is 2.2 m from the bottom plate, and the deep hole opening is 2.4 m from the bottom plate; the horizontal spacing of the shallow grouting holes is set to 3 m, that is, one arrangement is made every two brackets, and the horizontal spacing of the deep grouting holes is 6 m, that is, one arrangement is made every four brackets. The two rows of grouting holes are arranged in a staggered manner in the horizontal direction to ensure the uniformity and effectiveness of the grouting effect; the shallow hole is 2-3 m deep, and the deep hole is 6-8 m deep. The specific depth can be adjusted appropriately according to the fault gangue and coal body thickness on site while keeping the final hole layer unchanged; the shallow grouting holes are directly perpendicular to the coal wall, while the deep grouting holes are drilled at an elevation angle of 15 to 30 degrees according to the specific engineering conditions. When the degree of spalling is more serious, the elevation angle should be smaller; and when the degree of roof leakage is larger, the elevation angle should be larger; the drilling operation uses ZQS-80 / 2.8 handheld pneumatic drill or mining pneumatic coal drill as the main equipment, and is used in conjunction with a 44mm special drill bit and a 42mm diameter, 1000mm long twist drill rod. Because the coal body is affected by the advance support pressure, the degree of crushing is high, which is easy to cause the hole to collapse. In this case, the segmented hole-making process can be used for drilling construction to ensure the smooth progress of the construction process and reduce the occurrence of hole collapse; S3.3. Sealing the hole: Use a woven bag combined with the slurry itself to seal the hole. After the hole is formed, tightly wrap the woven bag around the end of the grouting pipe (hole end), insert it into the grouting hole, start grouting until leakage begins at the hole mouth, stop grouting, wait for 30 s to 60 s, and then start grouting the fractured coal body; low-pressure slow injection is used for shallow holes, and the grouting pressure is 2-3 MPa; high-pressure grouting is used for deep holes, 3-5 MPa. If leakage occurs in the coal wall during the grouting process, stop grouting immediately, wait for 30 s to 60 s for solidification, and then continue grouting; Furthermore, when grouting, the lower low-level holes are grouted first, and then the upper high-level holes. Grouting is carried out for each grouting hole constructed, and production can only be carried out after all the holes are constructed and grouting. The working face is carried out in the order of "grouting-recovery-grouting". The grouting hole layout plan is as follows: Fig.11 shown.

[0048] Furthermore, during the construction process, the final grouting pressure is adjusted in real time to ensure that the actual diffusion radius is not less than 2m. The grouting effect is deeply affected by the coal and rock conditions on site. Therefore, each grouting operation must record the grouting pressure, time, hole parameters and other data in detail. By evaluating the improvement of the integrity of the coal wall and top coal, the rationality of the grouting process and parameters is fed back to optimize the grouting scheme. During grouting, leakage, grouting pressure and grouting volume are used as the three key indicators to jointly determine the timing of grouting termination. Once leakage occurs, the grouting pressure reaches the preset final pressure or the grouting volume reaches the design value, the grouting should be suspended. If the grouting volume is far lower than the design value, grouting will occur. Although grouting should be suspended, re-injection should be considered. According to the actual situation on site, the final grouting pressure of shallow holes can be set to 3MPa, and the grouting volume is designed to be 3 tons. For deep boreholes, the grouting pressure can be considered to be less important based on reaching the design value of the grouting volume or leakage. The grouting volume is designed to be 5 tons, and the final grouting pressure is not set for the time being.

[0049] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A grouting reinforcement method for the collapsed and broken area of ​​a coal mine working face, characterized in that: The following steps are involved: S1. Conduct on-site investigation to understand the leakage of the end face and quantitatively analyze the causes of collapse and breakage from the perspectives of geological and engineering factors; S2. Determine the grouting timing, grouting location, grouting materials and grouting parameters through theoretical calculation, physical experiments and numerical simulation; S3. Use the "deep and shallow hole" grouting method to grout and reinforce the collapsed and broken areas of the coal mine working face.

2. A grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face as claimed in claim 1, characterized in that: The geological factors include burial depth, coal seam properties, inclination, and fault structure; the engineering factors include mining stress and support performance.

3. A grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face as claimed in claim 1, characterized in that: Step S2 includes: S2.

1. Calculate the distribution of the supporting pressure zone in front of the working face and determine the timing and location of grouting in the collapsed and broken area of ​​the working face, that is, use the FLAC3D numerical simulation software to simulate the distribution of the supporting pressure of the advanced working face under the influence of the working face mining and the corresponding plastic zone distribution, and verify it with the theoretical calculation results. Through the calculation results, analyze the location of the crack development in front of the working face and determine the timing and location of the advanced grouting of the working face; S2.

2. Study the mechanical properties of the broken coal body after grouting reinforcement at the working face, that is, the mechanical properties of the coal slurry fusion body, that is, conduct uniaxial compression tests on coal slurry fusion body samples with different grouting materials, compare and analyze the performance of different grouting materials based on the test results, and determine the best grouting material; S2.

3. Establish a three-dimensional grouting numerical model of the working face, simulate the influence of changes in several parameters such as grouting pressure, grouting time, drilling length and drilling spacing on the grouting effect, and determine the optimal grouting pressure, grouting time, drilling length and drilling spacing.

4. A grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face as claimed in claim 1, characterized in that: Step S3 includes: S3.

1. Determine the grouting location: select the area where spalling has occurred or has signs of spalling as the grouting location; S3.2, grouting hole arrangement: according to the borehole length and borehole spacing determined in step S2.3, deep grouting holes and shallow grouting holes are drilled at the grouting site, wherein the deep grouting holes and shallow grouting holes are arranged alternately in the horizontal direction; the shallow grouting holes are drilled directly perpendicular to the coal wall, while the deep grouting holes are drilled at an elevation angle of 15-30 degrees according to the specific engineering conditions; S3.

3. Sealing the hole: Use a woven bag combined with the slurry to seal the hole. After the hole is formed, wrap the woven bag tightly around the end of the grouting pipe and insert it into the grouting hole. Start grouting when leakage just begins to appear at the hole mouth, stop grouting, wait for 30 s to 60 s to solidify, and then start grouting into the fractured coal body.

5. A grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face as claimed in claim 4, characterized in that: The shallow grouting holes adopt low-pressure slow grouting, with a grouting pressure of 2-3 MPa; the deep grouting holes adopt higher pressure grouting, 3-5 MPa; if leakage occurs in the coal wall during the grouting process, the grouting is stopped immediately, and the grouting is continued after waiting for 30 s to 60 s for solidification.

6. A grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face as claimed in claim 4, characterized in that: When grouting, grout the lower low-position holes first, then the upper high-position holes. Grout one hole at a time as one grouting hole is constructed until all the holes are constructed and grouting is completed.

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