A method for grouting reinforcement of a caving and breaking area of a coal mine working face

Abstract

The application discloses a kind of coal mine working face collapse broken area grouting reinforcement method, comprising the following steps: S1, field investigation, master end face leakage, from the quantitative analysis of its collapse broken reason in two aspects of geological factors and engineering factors;S2, by theoretical calculation, physical experiment, numerical simulation determines grouting opportunity, grouting position, grouting material and grouting parameter;S3, using the "deep and shallow hole" grouting mode is carried out grouting reinforcement to coal mine working face collapse broken area.The application according to various factors of coal mine working face collapse, pertinence proposes the grouting mode of "deep and shallow hole" combination, shallow hole uses low pressure slow injection, for closing working face superficial range coal body fissure, forms "curtain", prevents slurry to run leakage, uses flower pipe grouting, increases slurry diffusion path, guarantees slurry effective diffusion;Then deep hole grouting is carried out again, and the coal body with relatively low deep fissure development degree is modified by grouting;To improve the integrity and strength of working face advanced coal body, improve the slice condition, form better support to top coal and roof, and then control top coal leakage.

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] Coal wall spalling and roof collapse in a coal mining face can seriously impact safe and efficient production. During coal mining, the impact of mining stresses causes primary fractures in the coal wall and roof to develop and connect, forming new fractures. Furthermore, geological conditions such as deep burial depth, steep inclination, and fault structures contribute to coal wall spalling and roof collapse in the working face. Therefore, to reduce the impact of face collapse on mining operations and increase the speed of working face advancement, measures are needed to manage the fractured areas of the working face.

[0003] The formation of collapsing and crushing areas in working faces is influenced by a variety of factors. For working faces with deep, soft coal and steep inclinations, there is currently a lack of lightweight supports with high initial support force. Replacing these heavy supports can lead to problems such as tilting due to their high inertia. Therefore, given the inability to change support performance or the length of the working face, a reinforcement method for managing collapsing and crushing areas in working faces 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 areas of a coal mine working face.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] The present invention provides a grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face, comprising the following steps:

[0007] S1. Conduct on-site investigations to understand the end face leakage situation and quantitatively analyze the causes of collapse and breakage from both geological and engineering factors;

[0008] S2. Comprehensively determine the grouting timing, grouting location, grouting materials and grouting parameters through theoretical calculations, physical experiments, numerical simulations and other methods;

[0009] S3. Use the "deep and shallow hole" grouting method to grout and reinforce the collapsed and broken areas of the coal mine working face.

[0010] Preferably, the geological factors include burial depth, coal seam properties, inclination, and fault structure; and the engineering factors include mining stress and support performance.

[0011] Preferably, step S2 includes:

[0012] S2.1, calculate the abutment pressure zone distribution in front of the working face, determine the grouting time and position of the broken area in front of the working face, that is, simulate the abutment pressure distribution of the working face in front of the working face under the influence of mining and the corresponding plastic zone distribution by means of numerical simulation software, and verify the simulation results with the theoretical calculation results, analyze the fracture development position in front of the working face through the calculation results, and determine the grouting time and position of the working face;

[0013] S2.2, study the mechanical properties of the grouted coal mass after grouting, that is, the mechanical properties of the coal slurry fusion body, that is, perform uniaxial compression tests on coal slurry fusion body samples of different grouting materials, compare and analyze the performance of different grouting materials according to the test results, and determine the best grouting material;

[0014] S2.3, establish a three-dimensional grouting numerical model of the working face, simulate the influence of changes in grouting pressure, grouting time, borehole length and borehole spacing on grouting effect, and determine the optimal grouting pressure, grouting time, borehole length and borehole spacing.

[0015] Preferably, step S3 comprises:

[0016] S3.1, determine the grouting position: select the area where spalling has occurred or has signs of spalling as the grouting position;

[0017] S3.2, grouting hole arrangement: according to the borehole length and borehole spacing determined in step S2.3, drill deep grouting holes and shallow grouting holes at the grouting site, wherein the deep grouting holes and shallow grouting holes are arranged in a staggered manner in the horizontal direction; the shallow grouting holes are directly perpendicular to the coal wall, and the deep grouting holes are inclined at an angle of 15-30° according to the specific engineering conditions;

[0018] S3.3, hole sealing: use a woven bag combined with the grout itself to seal the hole, after the hole is formed, tightly wrap the woven bag around the end of the grouting pipe, insert it into the grouting hole, and start grouting until the grout starts to leak at the hole, then stop grouting, wait for 30 s-60 s, and then start grouting the fractured coal body.

[0019] Preferably, the shallow grouting holes use low-pressure slow grouting, with a grouting pressure of 2-3 MPa; the deep grouting holes use high-pressure grouting, with a grouting pressure of 3-5 MPa; if the coal wall leaks during grouting, stop grouting immediately, wait for 30 s-60 s for solidification, and then continue grouting. The shallow holes use low-pressure slow grouting to seal the coal body fractures in the shallow range of the working face, form a "curtain" to prevent the grout from leaking, use a flower pipe for grouting to increase the grout diffusion path and ensure effective grout diffusion; then perform deep hole grouting to modify the coal body with relatively low fracture development degree in the deep part; thereby improving the integrity and strength of the working face, improving the spalling condition, providing better support for the top coal and roof, and further controlling the top coal leakage.

[0020] Preferably, when grouting, the lower hole is grouted first, and then the upper hole is grouted, one hole is grouted after one grouting hole is constructed, until all the drilling holes are constructed and grouted.

[0021] The present application has the beneficial effect that according to various factors of coal mine working face caving, the present application proposes a grouting mode of combination of deep and shallow holes, the shallow hole uses low pressure slow injection for closing the coal body fissure in the surface range of the working face, forming a curtain, preventing the slurry from leaking, using flower tube grouting, increasing the slurry diffusion path, and ensuring the effective diffusion of the slurry; then deep hole grouting is carried out, and the coal body with relatively low deep fissure development degree is grouted and modified; thereby improving the integrity and strength of the working face advanced coal body, improving the spalling condition, forming a better support for the top coal and roof, and further controlling the top coal leakage. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained without creative labor on the basis of these drawings.

[0023] Figure 1 The working face and roadway layout provided for the embodiments of the present application;

[0024] Figure 2 The FLAC3D numerical model diagram provided for the embodiments of the present application;

[0025] Figure 3 The advanced stress distribution diagram of working face advancing 100m provided for the embodiments of the present application;

[0026] Figure 4 The compressive strength distribution diagram of three different samples in the embodiments of the present application;

[0027] Figure 5 The deformation modulus distribution diagram of three different samples in the embodiments of the present application;

[0028] Figure 6 The real-time photo of failure mode of three different samples in the embodiments of the present application;

[0029] Figure 7 The three-dimensional coal seam grouting numerical simulation model diagram established in the embodiments of the present application;

[0030] Figure 8 The slurry diffusion curve diagram under different grouting time in the embodiments of the present application;

[0031] Figure 9 Figure of slurry diffusion curve under different grouting pressure in the embodiment of the present application;

[0032] Figure 10 Cloud picture of slurry diffusion simulation under different borehole length in the embodiment of the present application;

[0033] Figure 11 Grouting hole layout scheme in the embodiment of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative work fall within the protection scope of the present application.

[0035] EMBODIMENT

[0036] The coal wall spalling and roof falling in a coal mine working face have seriously affected the safe and efficient production of the working face. In the process of coal mining, due to the influence of mining stress, the original fissures of the coal wall and roof are developed and connected, new fissures are formed, and the combined action of the geological conditions such as large burial depth, large inclination and fault structure, thus leading to the coal wall spalling and roof falling in the working face. The geological conditions of the working face are as follows:

[0037] (1) The working face is the first mining working face of the lower mining area of II (3), the working face is 184 m long, the strike length is about 1410 m, the mining area is 272886 m 2 . The working face elevation is -754.4~ -864.1, corresponding to the ground elevation +30.4~ +33.7, the average burial depth is about 777.2 m, the inclination of the 7# coal seam is 12.0°-26.5°, the average is 22.6°, and the coal seam thickness is 4.65 m. The working face and roadway layout are shown in Figure 1 . The working face is a fully mechanized top coal caving mining, the mining height is 2.5 m, the ratio of caving to mining height is 1:0.86, and the full caving method is used to manage the roof.

[0038] (2) In the process of mining, the west side of the working face is adjacent to the downhill area of the lower mining area of II (3), the south side is connected with the south boundary of the lower mining area of II (3), the east side is the boundary of the minefield, and the north side is the area which has not been mined. Therefore, considering the specific geological conditions around the working face, the mining process is less affected by the surrounding stress distribution.

[0039] (3) Coal seam and roof and floor conditions

[0040] The coal of No. 7 is soft and brittle, and cracks are very developed after being loaded, so that a complete sample cannot be taken for mechanical property test, and the coal is poor in viscosity and is in the form of sand. The coal seam is 2.90-7.50m in thickness at two poles and 4.65m in average thickness. The immediate roof of the working face is sandy mudstone, 0-4.80m in thickness and 3.6m in average thickness. The main roof is medium sandstone, 9.26-15.16m in thickness and 11.70m in average thickness.

[0041] In order to reduce the influence of the caving and falling of the working face on the mining of the working face and improve the advancing speed of the working face, the broken area of the coal mine working face is treated according to the method of the application, and the specific steps are as follows:

[0042] S1.1, analyze the geological factors:

[0043] After measurement, it is determined that the average buried depth of the working face is about 777.2 m, the inclination angles of the east and west parts are 12° and 25.7° respectively, the coal seam structure is relatively complex, there is a 0.5m thick carbonaceous mudstone parting on the east and west sides of the chute, and the parting thickness is 0.5m. The coal seam thickness is 2.90-7.50m, and the average thickness is 4.65m. The thinnest place is at the L13 point of the chute, and the thickest place is at the C25 point on the east side of the material way. It is found through mine investigation that the coal seam is hard and brittle, cracks are developed after being loaded, the viscosity is poor, the broken coal is in the form of sand, and it is easy to break under pressure. Its bearing capacity is low. Under the combined action of tectonic stress, ground stress and mining stress, the working face coal body loses stability and is damaged due to the difficulty in bearing the roof pressure, so the coal body is broken; the working face exposes many faults, including 15 faults in the chute, 11 faults in the material way and 5 faults in the cut; the influence of the faults on the working face is firstly mainly reflected in the change of stress distribution in the area near the faults; secondly, the mechanical properties of the working face coal body and the roof and floor rock mass are affected by the fault structure, so that the mechanical properties are poor and the integrity is poor, which leads to the fact that the coal and rock mass is broken particularly prominent during the working face passing through the fault, and then spalling and leakage and falling occur.

[0044] S1.2, analyze the engineering factors:

[0045] (1) According to the simulation research during the mining of the working face, the peak value of the working face advance stress reaches 41.2MPa, so that the coal wall in front of the working face is damaged, mining cracks are developed, and the coal seam and its roof are broken; (2) the working face currently uses ZFH6200 / 16 / 28 hydraulic support, the working resistance of the support is only 6200kN, but the support itself is heavy (38t), due to the large inclination angle of the working face, the heavy support slides and falls downward under the action of inertia; at the same time, the vertical stress and the advance stress are borne by the hydraulic support and the coal wall, when the working resistance of the hydraulic support is limited, the stress on the coal wall relatively increases, and thus the coal wall breaking and spalling are aggravated;

[0046] S2.1, with the help of FLAC3D numerical simulation software, the support pressure distribution of the advanced working face under the influence of working face mining and the corresponding plastic zone distribution are simulated and studied, and the theoretical calculation results are verified with each other, through the calculation results, the fracture development position in front of the working face is analyzed, the working face advance grouting opportunity and position are determined, which includes the following steps:

[0047] S2.1.1, according to the site situation of the coal mine, a FLAC3D numerical model with length 320m, width 5m and height 80m is built; for the strata that cannot be reflected on the upper part of the model, a load of 20.15 MPa is applied in the vertical direction based on the weight of rock mass, different working conditions are set according to different advancing distances of the working face, that is, the working face is excavated for 20m, 40m, 60m, 80m, 100m and 120m. The model is stress boundary on the upper boundary, and the rest is displacement boundary. The established model is shown in Figure 2

[0048] Before and after the working face is excavated, stress concentration will occur in the coal wall of the working face end surface, with the increase of the advancing distance of the working face, the vertical stress borne by the surrounding rock of the working face increases, but the increment 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 basically tends to be stable. The stress simulation results in front of the working face are extracted, the results show that when the advancing distance of the working face is 20m, 40m, 60m, 80m, 100m and 120m, the support pressure reaches the peak value at 6.2m in front of the working face, which is 33.4MPa, 33.6MPa, 41.2MPa, 41.6MPa, 42.1 MPa and 41.5MPa respectively. With the increase of the distance from the working face, 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, the curve gradually decreases after reaching the support pressure peak value at 6.2m, a secondary peak appears at 25m from the working face, and then the stress gradually decreases until it decreases to the original rock stress at about 70m from the working face.

[0049] S2.1.2, working face grouting opportunity and position determination

[0050] ​From the above, the influence range of the abutment pressure in front of the working face is about 70 m, and the most intense influence area is about 30 m in front of the working face. The peak value of the abutment pressure is about 6.2-8.3 m in front of the working face. The stress and broken zone of the coal in front of the working face will change significantly, and the stress of the coal in front of the working face can be divided into four different zones, and the development of the coal cracks in each zone is different, as shown in FIG. 1. In order to determine the reasonable grouting time and position, the following analysis is made in different zones: Figure 3

[0051] ① Stable pressure zone, that is, the zone outside 70 m in front of the working face, the stress level of the coal is close to the original stress, the coal is relatively complete, and mainly exists tectonic fissures and primary fissures. Due to the small fissure opening, the grouting operation in this zone is difficult, and therefore, it is not recommended to grout in this zone;

[0052] ② Slowly increasing pressure zone, that is, the zone of 30-70 m in front of the working face, which is the front end of the abutment pressure influence zone, and the abutment pressure gradually increases in this zone. Under the influence of the mining stress, the tectonic fissures are developed again, and new fissures are generated. However, the fissures do not develop a lot, and therefore, the zone is not suitable for grouting;

[0053] ③ Intense pressure zone, that is, the zone of 6.2-30 m in front of the working face, in which the stress value rapidly rises to the peak value, and the influence on the coal is extremely significant. Under the action of the high stress, the coal fissures significantly increase, and considering the groutability, this stage is favorable for the injection and propagation of the grout;

[0054] ④ Pressure relief zone, that is, the zone of 0-6.2 m in front of the working face, which is the most serious broken zone of the coal in front of the working face. The internal fissures of the coal are highly developed, and even the coal spalling and falling off may occur. In this zone, the end face grouting operation is adopted, and the fast-setting grouting material is used to seal the coal fissures in the shallow range of the working face, so as to form a "curtain" and avoid the problems of the failure to timely solidify and the grout loss.

[0055] S2.2, the mechanical properties of the coal slurry fusion body after the grouting reinforcement of the broken coal in front of the working face are studied, that is, the uniaxial compression test of the coal slurry fusion body sample of different grouting materials is carried out, the performance of the different grouting materials is compared and analyzed according to the test results, and the best grouting material is determined. The specific steps are as follows:

[0056] S2.2.1, sample coal slurry fusion body preparation: the grouting reinforcement materials that can be selected include three materials, namely, Jiumo Na inorganic grouting single material, micro-nano modified coal-friendly grouting double material (No. 1) and solid special silicate modified polyurethane material, which are hereinafter referred to as "Jiumo Na", "No. 1" and "solid special" respectively. ​

[0057] Jiumina material is based on ordinary Portland cement, adding retarder and early strength agent, etc. Its initial setting time is very long, with great fluidity within 2 hours, and final setting after 10 hours in general. Its water-cement ratio range is very small, and solid-liquid separation is easy to occur when water-cement ratio is large. Its market price is 4500-5500 yuan / ton;

[0058] No. 1 solid-resistant material is mixed with sulphoaluminate clinker and components A and B such as lime, gypsum, etc. After mixing with water, it has good early setting and early strength performance, and strong coal bonding. Its particle size can reach 1300 mesh, which can enter into small cracks. Its water-cement ratio range is large, and the purpose of controlling the fluidity and viscosity of the slurry can be achieved by changing the water-cement ratio and temperature of the slurry material. Its market price is 11000-12000 yuan / ton.

[0059] Guan Te uses Portland modified polyurethane material A and B components mixed uniformly at a volume ratio of 1:1 to rapidly polymerize into insoluble high molecular material. This material has certain compressive strength, bonding strength, flame resistance, 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 sealing and reinforcement with the deformation of the coal seam. However, during the use of the material, there have been cases of heat, material pouring, high-pressure pipeline burst, polymer material splashing onto the skin causing burns, and poisoning or physiological discomfort after inhalation. The current market price of the material is 20000-21000 yuan / ton.

[0060] In the field of concrete, cubic sample molds are often used to mix various grouting materials with crushed coal, pour and process them into 100mm x 100mm x 100mm samples. The main equipment for sample pouring and preparation includes: hand-operated high-speed slurry mixer, fractal sieve, automatic vibration machine, measuring cylinder, sample mold, release agent, etc.

[0061] (1) No. 1 solid-resistant coal slurry fusion sample

[0062] No. 1 solid-resistant grouting material is made into samples according to different slurry water-cement ratios, different coal mixing amounts and different curing times. The double-liquid rapid-setting grouting material sample has a fast setting speed and certain expansion performance after setting, accompanied by heat release. Therefore, in order to successfully demold, the sample should be demolded 20-30 minutes after pouring the slurry into the mold, otherwise the sample will expand and be difficult to demold from the mold due to heat release. Since No. 1 solid-resistant material contains ettringite after pouring, it may react with carbon dioxide in the air, so it is sealed and stored with plastic wrap until the required age.

[0063] (2) Jiumina coal slurry fusion sample

[0064] The water-cement ratio of 0.4:1 is mixed to make the Kumenah single liquid inorganic grouting material sample, the sample has long initial setting time, the sample is solidified and formed after 2d, and the sample can be smoothly demolded after 2d, which has the conditions for testing.

[0065] (3) solidant coal slurry fusion sample

[0066] Solidant chemical material A and B components are mixed at a ratio of 1:1 without adding water. The material is combined tightly with the plastic mold. A layer of preservative film must be added between the slurry and the mold during pouring, otherwise the sample cannot be smoothly demolded from the mold. After the slurry is stirred uniformly, the sample is mixed for 1-3 min initial setting. The sample is expanded during the setting process. In order to smoothly demold, the sample is demolded after 15-30 min after the slurry is poured into the mold.

[0067] S2.2.2, uniaxial compression test

[0068] In this test, the loading system selects the C64.106 type electro-hydraulic servo universal testing machine of the mining science center of China University of Mining Industry, and the maximum load of the equipment is 1000kN. The test adopts displacement control mode, and the loading rate is 0.5mm / min, and the data sampling is 10 data per second.

[0069] The test is divided into pre-test and formal test. In order to avoid material waste caused by poor design, 4 samples are used for pre-test, and through pre-test, irrelevant variables can be accurately controlled.

[0070] In the formal test part, No. 1, Kumenah and solidant different material samples are made, which are respectively recorded as sample 1, sample 2 and sample 3. There are a total of 17 groups of samples of No. 1 material with different slurry water-cement ratios (0.4, 0.5, 0.6, 0.8), different coal contents (400g, 500g, 600g) and different curing times (2h, 4h, 6h, 12h, 1d, 3d, 7d), and 3 samples are tested for each group. In order to ensure the normal progress of the test, one extra sample is prepared for each factor during pouring. The sample preparation scheme is shown in Table 1, and a total of 72 coal slurry fusion samples are prepared for uniaxial compression test.

[0071]

[0072] According to the basic performance of different materials in the previous section, in order to master the mechanical properties of different materials and coal fusion, this section uses the control variable method to conduct uniaxial compression test on the coal slurry fusion body made by pouring broken coal sample and No. 1, Kumenah and solidant grouting material. The different comparison results of each sample compressive strength, peak stress value, strength average value, forming time, etc. are shown in Table 2.

[0073]

[0074] (1) Analyze the stress-strain curve, from Figure 4 It can be seen that at the same age, the peak strength of the Naigu I coal slurry fusion sample is 14.87MPa, the peak strength of the Jiumina coal slurry fusion sample is 26.38MPa, and the peak strength of the Guante coal slurry fusion sample is 15.20MPa. Among them, the Jiumina material has the highest strength, but its initial setting time and curing time are longer, making it unsuitable for end-face grouting. The Guante two-liquid chemical slurry material sample has the best plasticity, but it is expensive, about four times that of the Jiumina material and twice that of the Naigu I material, and its strength is only comparable to that of the Naigu I material. Therefore, from an economic perspective, the Naigu I material has a greater advantage, and from a technical perspective, the Naigu I material also meets the requirements.

[0075] (2) Deformation modulus

[0076] 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 is shown in Figure 2. Figure 5 As can be seen from the data, at the same age, the Kumina single-material grouting material sample had the highest deformation modulus, at 0.88 GPa; the Naigu I double-material sample was second, at 0.46 GPa; and the Guante double-liquid chemical slurry sample had the lowest deformation modulus, at 0.15 GPa. This indicates that the Kumina single-material grouting material sample had a weak ability to resist deformation, the Naigu I double-material sample performed better, and the Guante double-liquid chemical slurry sample was the best. For coal-slurry amalgamations, the deformation modulus curves showed a consistent trend with the compressive strength. This indicates that as the slurry gradually solidifies, the compressive strength and deformation modulus of the fractured coal mass after grouting reinforcement increase simultaneously.

[0077] (3) Failure morphology of coal slurry fusion bodies with different slurry materials

[0078] The failure morphology of coal slurry fusion is as follows Figure 6As shown, in the post-casting sample, the slurry filled the pores and cracks between the broken coal bodies, achieving different levels of filling. This process formed a certain buffer effect between the rock bodies, expanded the original point and line contact between the rock bodies into a more extensive surface contact, thereby improving the stability and conduction efficiency of the overall structure; observing the internal failure pattern of the sample, it was found that the cracking position would initially directly penetrate the low-strength coal body, because the coal body strength was lower than the slurry stone body. At the same time, the sample was prone to splitting and shearing, which eventually led to the overall structural damage of the coal slurry fusion body. In rare cases, the damage site may also occur at the interface between the coal body and the slurry cementation surface, but overall, the damage is mainly from the coal body.

[0079] Through further observation of the damaged sample, the failure patterns of different materials are different. The No. 1 Durability material sample shows good plasticity. During the bearing stress process, the slurry layer initially showed good deformation and bearing capacity, but the thick slurry layer wrapped the coal body. After the initial cracking in the weak part of the coal body inside the sample, the originally well-bearing slurry layer was dislocated and pulled, and under the continuous action of the load, the coal body crack continuously expanded, and the slurry layer was broken. The crack eventually penetrated and affected the entire sample. The single material sample of Kumenah had high brittleness, and after the initial cracking in the coal body position, the sample mainly occurred splitting failure, and the number of intuitive damage cracks was less than that of the No. 1 Durability double material sample. The solid Ant double liquid chemical material sample had higher plasticity, and the sample mainly occurred tensile failure. The coal body inside the sample became powder after the sample was damaged, indicating that the solid Ant double liquid chemical material had better adhesion.

[0080] In summary, the initial setting time and sample curing time of No. 1 Durability material are relatively short, and it can be cured within 20 minutes, reaching 90% of the peak strength after 2 hours, i.e. 9.05 MPa. It can well meet the early strength and rapid setting requirements of the end face grouting, and its consolidation strength to the coal body is equivalent to that of the organic high polymer material solid Ant used by the mine, and the price of this material is more economical, only about 50% of that of the solid Ant material. Therefore, considering the technical and economic applicability, No. 1 Durability material is selected instead of solid Ant material for use in the working face.

[0081] S2.3.1, Grouting numerical model establishment

[0082] Through the study of the fusion sample of coal and grouting material in the working face, it is determined that the No. 1 grouting material with solid resistance is 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 is taken as 20 m x 20 m x 4.6 m, and a three-dimensional coal seam grouting numerical simulation model is constructed. Through the model, the influence of the changes of key parameters such as grouting pressure, grouting time, borehole length and borehole spacing on the grouting effect is simulated. According to the actual working conditions, the diameter of the grouting hole in the model is set to 0.05 m, and the hole depth is 6 m, as shown in FIG. 1. Figure 7 The bottom of the model is set as a fixed boundary, and the four sides are set as sliding boundaries. Considering the gravity of the overburden rock, the upper part of the model adopts a free boundary to simulate the free flow of grouting liquid on the boundary.

[0083] S2.3.2, parameter setting

[0084] In order to accurately reveal the grouting diffusion law of the caving and broken area of the working face, the model parameters are set in detail. According to the theory of rock and soil seepage field, this paper selects the Darcy's law module in porous medium and underground water flow as the simulation basis

[86] . In the seepage field, the inner boundary of the model is subjected to the action of grouting pressure, and the initial pore pressure is set on the outer boundary. The viscosity of No. 1 solid-resistant material will change with time during the grouting process

[87] . In order to be closer to the actual situation, the viscosity of No. 1 solid-resistant material is measured by a viscometer before simulation. Through fitting, the viscosity change with time is obtained, and it is applied to the simulation to ensure the accuracy of the diffusion law. The specific data of material properties in the selected module are shown in Table 3:

[0085]

[0086] After setting the basic property parameters of the material, the grouting parameters can be set. In order to explore the grouting diffusion law under the conditions of no grouting pressure, grouting time, borehole length and borehole spacing, the parameters need to be set, as shown in Table 4:

[0087]

[0088] S2.3.3, grouting diffusion law under different grouting time

[0089] To study the diffusion behavior of slurry in coal bodies at different times, this section uses the control variable method to limit the grouting pressure to 2 MPa for shallow holes and 5 MPa for deep holes. The shallow hole length is 2 m, the deep hole length is 6 m, and the drilling spacing is 3 m for shallow holes and 6 m for deep holes. The grouting hole diameter adopts the 0.05 m grouting hole size selected in actual construction. Using the transient calculation method, the total grouting time is set to 30 minutes. The slurry diffusion range is recorded every 1 minute. The conclusion is that the slurry diffuses radially after flowing out of the grouting pipe. The diffusion area is approximately cylindrical. The cement slurry concentration is higher near the grouting pipe. Over time, the diffusion range of the slurry in the coal seam gradually expands, but the growth rate of its diffusion rate gradually slows down. In particular, after 10 minutes, the change in the slurry diffusion range tends to stabilize. This analysis suggests that, on the one hand, the grouting pressure allows the slurry to flow into the pores of the coal body and effectively fill the cracks in the coal seam, expanding the diffusion range. As the grouting time increases, the slurry gradually reaches saturation in the coal seam, causing the diffusion rate to gradually slow and the slurry to leak from the grouting port. On the other hand, due to the short slurry setting time (as shown in the experiments in Chapter 3), the micro-nano modified coal-friendly and solid-resistant No. 1 grouting material sets in approximately 20 minutes), so extending the grouting time results in no change in the grouting range, indicating that the slurry has reached its final diffusion range. Comparing the slurry diffusion at different times in the three-dimensional model shows that within 8 minutes, the slurry diffuses rapidly, but fails to reach an effective diffusion radius, and an effective "curtain" is not formed between shallow holes. This makes slurry leakage more likely during deep high-pressure grouting. However, after 10 minutes, the slurry diffusion range slows down significantly, allowing for effective communication between shallow holes. Therefore, a minimum on-site grouting time of 10 minutes is recommended.

[0090] Combine Figure 8 The slurry diffusion curves shown in the figure reveal 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 increases to 4 minutes, the maximum diffusion radius increases to 2.65 m, a 31.55% increase compared to the 2-minute time. Further extending the grouting time to 6 minutes, the maximum diffusion radius reaches 2.82 m, a 6.41% increase compared to the 4-minute time. When the grouting time is extended to 8 minutes, the maximum diffusion radius reaches 2.95 m, a 4.60% increase compared to the 6-minute time. Finally, when the grouting time reaches 10 minutes, the maximum diffusion radius of the slurry reaches 3.03 m, a 2.71% increase compared to the 8-minute time. The maximum diffusion radius shows a pattern of initially increasing rapidly and then slowing down until it remains essentially constant. Therefore, it can be concluded 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 in the working face.

[0091] S2.3.4, slurry diffusion law under different grouting pressure

[0092] In order to study the diffusion of slurry in coal under different grouting pressure, four numerical calculation schemes were set up in this section. According to the "shallow hole-deep hole" combined grouting mode, low pressure slow injection and deep hole high pressure grouting were adopted. The grouting pressure was set as shallow hole P0=0.5MPa, 1MPa, 2MPa, 3MPa, deep hole P1=3MPa, 4MPa, 5MPa, 6MPa. The diffusion law of No. 1 micro-nano modified coal-friendly grouting material under different grouting pressure was analyzed. At the same time, the length of the drill hole was controlled as shallow hole 2m deep hole 6m, and the drill hole spacing was shallow hole 3m deep hole 6m. Through section drawing and cutting processing, the pressure attenuation was taken as the reference line of 0.1MPa pressure, and the diffusion range of slurry under different grouting pressure was obtained by analyzing the 10min node of grouting time.

[0093] The simulation results show that the grouting pressure has a significant effect on the diffusion of slurry in coal. With the increase of grouting pressure, the driving force of slurry also increases, which effectively supplements the tip of the fracture. Especially when the shallow hole grouting pressure is set as 0.5MPa and 1MPa, and the deep hole pressure is 3MPa and 4MPa, the drill holes are not effectively connected, forming a curtain-like structure. Under this pressure condition, slurry is prone to leakage when 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 is effectively filled with slurry under this grouting pressure. After the slurry solidifies, not only can it reinforce the surface surrounding rock, but also can form a curtain structure to effectively prevent slurry leakage during deep hole grouting.

[0094] Figure 9The experimental results show that there is a positive correlation between the grouting pressure and the slurry diffusion distance. The diffusion range under different grouting pressures at 8 min is analyzed. When the deep hole grouting pressure is 3 MPa, the slurry diffusion distance in the coal seam is 1.73 m; when the grouting pressure increases to 4 MPa, the slurry diffusion distance increases to 2.21 m; further increasing the grouting pressure to 5 MPa, the slurry diffusion distance significantly expands to 2.95 m; and when the grouting pressure reaches 6 MPa, the slurry diffusion distance further increases to 3.17 m, with a growth rate of 27.75%, 33.49%, and 7.46%, respectively. From the curve, it can be seen that at the same time, with the increase of grouting pressure, the grouting diffusion range increases accordingly, but the increment gradually decreases. Analysis shows that the broken area of the working face has a large degree of fragmentation, which makes the slurry permeability in the area mainly controlled by the degree of fragmentation of the coal body, and thus the influence of grouting pressure on the permeability of the slurry is relatively small. Therefore, in the actual grouting process, the grouting pressure should be determined based on the specific engineering conditions on site, but the minimum grouting pressure of the shallow hole should be above 2.0 MPa to ensure sufficient driving force. For deep hole grouting, the grouting pressure can be increased to some extent to increase the permeation and diffusion range of the slurry, but high pressure grouting should not be used for shallow holes. The shallow part is more broken, and high pressure grouting can cause slurry leakage and running.

[0095] S2.3.5, Effect of Drilling Length on Slurry Diffusion Law

[0096] To study the slurry diffusion law under different drilling lengths, this section uses the control variable method to limit the grouting pressure to 2 MPa, the drilling spacing to 3 m for shallow holes and 6 m for deep holes, and the grouting hole diameter to 0.05 m, which is the size of the grouting hole used in actual construction. Since the shallow hole is too shallow to form a "curtain" and too deep to enter the area with poor development of fractures, the slurry diffusion effect is poor and it is difficult to form a "curtain", therefore, a drilling depth of 2 m is selected for the shallow hole, and the slurry diffusion law under the conditions of shallow hole 2 m, deep hole 4 m, 6 m and 8 m is simulated. The simulation cloud map is shown in Figure 10 Figure 10 ​It can be seen that the diffusion area of slurry is approximately cylindrical after the slurry flows out of the grouting pipe, and the length of the borehole has a significant effect on the diffusion range of the slurry at the same time. The main performance is 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 presents a decaying trend in the process of penetration and diffusion. When the grouting time is 8 min, the diffusion range of the slurry is 2.05 m when the deep borehole is located at 2 m, and the diffusion range of the slurry is 1.41 m when the deep borehole is located at 4 m, which is 31.22% lower than that when the deep borehole is located at 2 m. When the deep borehole is located at 6 m, the diffusion range of the slurry is 1.22 m, which is 13.47% lower than that when the deep borehole is located at 4 m. When the deep borehole is located at 8 m, the diffusion range of the slurry is 1.01 m, which is 17.21% lower than that when the deep borehole is located at 6 m. When the length of the borehole changes from 2 m to 4 m, the attenuation of the diffusion range of the slurry is larger, which is because the shallow borehole is arranged at the position of 2 m, which increases the grouting density, so the diffusion range of the slurry is larger, which leads to a larger attenuation ratio at the depth of 4 m.

[0097] Through the calculation and simulation of the advanced support pressure of the working face, the peak value of the advanced stress concentration of the working face is 6-8 m, so in order to ensure the effective grouting and reinforcement of the area where the coal body is broken most seriously and the crack development degree is highest, the length of the borehole should not be less than 6 m.

[0098] S2.3.6, Study on the Diffusion Law of Slurry under Different Borehole Spacings

[0099] To study the slurry diffusion law in coal under different drilling spacing conditions, this section adopts the control variable method to limit the grouting pressure to 2 MPa for shallow holes and 5 MPa for deep holes, with a drilling length of 2 m. The grouting hole diameter is 0.05 m, which is the size of the actual construction selected. The simulation obtained the slurry diffusion law under different hole spacing conditions, such as shallow 2 m and deep 4 m, shallow 3 m and deep 6 m, and shallow 4 m and deep 8 m. The transient calculation method was used, with the total grouting time set to 30 minutes, and the slurry diffusion range was recorded every 1 minute. Through three-dimensional slice processing, the height of 5-10 m was analyzed, and the slurry diffusion law under different hole spacing conditions was as follows: when the shallow hole spacing was 2 m and the deep hole spacing was 4 m, the slurry diffusion radius could reach 2 m within 2 minutes, which might lead to shallow leakage. In addition, with the increase of the number of drilling, the workload and working time of workers would be increased, leading to the decrease of effective production time, and thus adversely affecting the production efficiency of the mine. Under the condition of shallow hole spacing of 3 m and deep hole spacing of 6 m, the slurry diffusion radius could reach 3 m after 10 minutes of grouting, and the deep diffusion radius could also reach 1.2 m. In this way, the deep coal body was effectively reinforced while avoiding excessive waste of slurry. However, when the shallow hole spacing was expanded to 4 m and the deep hole spacing was 8 m, the slurry was difficult to reach the expected 4 m diffusion radius within 12 minutes. Although increasing the grouting time or grouting pressure could try to expand the slurry penetration and diffusion range, the effect was limited. At the same time, it should be noted that due to the use of double-speed setting material for grouting, too long grouting time might cause the previous injected slurry to solidify, which was not conducive to the smooth injection of subsequent slurry. Therefore, various factors needed to be considered comprehensively in actual operation to ensure the optimization of grouting effect and mine production benefit;

[0100] S3.1, determination of grouting site: mainly determined by human observation on site, and grouting was carried out in the area with rib spalling or rib spalling signs;

[0101] S3.2, grouting hole arrangement parameters: according to the numerical simulation results, combined with the actual situation on site. The actual mining height is generally controlled in the range of 2.7-3.0 m, for the convenience of construction, the opening position of the grouting hole is determined within the range of 1 m below the working face roof. The shallow hole opening distance is 2.2 m above the floor, and the deep hole opening distance is 2.4 m above the floor; the horizontal spacing of the shallow grouting hole is set to 3 m, that is, every two supports are arranged once, and the horizontal spacing of the deep grouting hole is 6 m, that is, every four supports are arranged. 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 depth of the shallow hole is 2-3 m, and the depth of the deep hole is 6-8 m. The specific depth can be adjusted according to the on-site fault gangue and coal thickness under the premise of keeping the final hole horizon unchanged; the shallow grouting hole is directly perpendicular to the coal wall, while the deep grouting hole is drilled at an angle of 15-30 degrees according to the specific engineering situation. When the rib spalling is more serious, the angle should be taken smaller, and when the roof leakage is larger, the angle should be taken larger; the drilling operation adopts ZQS-80 / 2.8 handheld pneumatic drill or mine pneumatic drill as the main equipment, and cooperates with the use of 44 mm special drill bit and 42 mm diameter, 1000 mm long twist drill rod. Due to the influence of the advanced support pressure on the coal body, the crushing degree is high, which is easy to cause hole collapse. In this case, the segmented hole forming process can be used for drilling construction to ensure the smooth progress of the construction process and reduce the occurrence of hole collapse;

[0102] S3.3, hole sealing: using woven bag combined with slurry sealing. After the hole is formed, the woven bag is tightly wound around the end of the grouting pipe (the hole mouth end), inserted into the grouting hole, and the grouting is stopped when the hole mouth starts to leak. After 30 s-60 s, the fractured coal body is grouted; the shallow hole adopts low-pressure slow grouting, and the grouting pressure is 2-3 MPa; the deep hole adopts higher pressure grouting, 3-5 MPa. If the coal wall leaks during grouting, stop grouting immediately, wait for 30 s-60 s after solidification, and continue grouting;

[0103] Further, during grouting, the lower hole is grouted first, and then the upper hole is grouted. Each grouting hole is grouted, and after all the drilling and grouting are completed, production can be carried out. The working face is carried out in the order of "grouting-mining-grouting". The grouting hole arrangement scheme is shown in Figure 11 .

[0104] Further, in the construction process, real-time adjustment of grouting final pressure and other ensure that the actual diffusion radius is not less than 2m. Grouting effect is deeply influenced by the coal and rock conditions, so each grouting operation must record the grouting pressure, time, hole parameters and other data. Through the evaluation of the coal wall and top coal integrity improvement, feedback the rationality of grouting process and parameters, and then optimize the grouting scheme. When grouting, leakage, grouting pressure and grouting quantity are three key indicators to determine the termination time of grouting. Once leakage, grouting pressure reaches the preset final pressure or grouting quantity reaches the design value, grouting should be suspended. If the grouting quantity is far lower than the design value, it appears that the grouting (leakage) is running, although the grouting should be suspended, but need to consider regrouting. According to the actual situation, the final pressure of shallow hole grouting can be set to 3MPa, and the grouting quantity is designed to be 3 tons. For deep drilling, the grouting pressure can not be considered, and the grouting quantity is designed to be 5 tons, and the grouting final pressure is not set.

[0105] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application belong to the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face, characterized in that: The following steps are involved: S1. Conduct on-site investigations to understand the end face leakage situation and quantitatively analyze the causes of collapse and breakage from both geological and engineering factors; S2. Determine the grouting timing, grouting location, grouting materials and grouting parameters through theoretical calculation, physical experiments and numerical simulation. The specific steps are as follows: S2.

1. Calculate the distribution of the bearing pressure zone ahead of the working face and determine the timing and location of grouting in the collapsing and fractured areas of the working face. Specifically, use FLAC3D numerical simulation software to simulate the distribution of the bearing pressure and the corresponding plastic zone of the leading working face under the influence of mining. Verify these results with theoretical calculations. Based on these calculations, analyze the location of crack development ahead of the working face and determine the timing and location of leading grouting in the working face. S2.

2. Study the mechanical properties of the broken coal mass after grouting reinforcement at the working face, i.e., the mechanical properties of the coal-slurry amalgam. Specifically, conduct uniaxial compression tests on coal-slurry amalgam specimens using different grouting materials, compare and analyze the performance of different grouting materials based on the test results, and determine the optimal grouting material. S2.

3. Establish a three-dimensional grouting numerical model for the working face to simulate the effects of changes in 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; 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 according to 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 according to claim 1, characterized in that: Step S3 includes: S3.

1. Determine the grouting location: Select the area where spalling has occurred or shows signs of spalling as the grouting location; S3.

2. Grouting Hole Arrangement: Based on the borehole length and borehole spacing determined in step S2.3, deep and shallow grouting holes are drilled at the grouting location. The deep and shallow grouting holes are arranged in a staggered horizontal arrangement. Shallow grouting holes are drilled perpendicular to the coal wall, while deep grouting holes are drilled at an elevation angle of 15-30 degrees, depending on the specific project conditions. S3.

3. Sealing the hole: Use a woven bag combined with the slurry itself 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 seconds to 60 seconds to solidify, and then start grouting into the fractured coal body.

4. A grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face according to claim 3, 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 30 seconds to 60 seconds of solidification.

5. A grouting reinforcement method for a collapsed and broken area of ​​a coal mine working face according to claim 3, characterized in that: When grouting, grout the lower low-position holes first, then the upper high-position holes. Grouting is carried out for each grouting hole constructed until all the holes are completed and grouting is completed.

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