A method for pre-reinforcing surrounding rock of lower coal seam roadway in ultra-short distance coal seam mining

Abstract

The application discloses a kind of lower coal seam roadway surrounding rock pre-reinforcement methods of ultra-close distance coal seam mining, comprising: step 1, field investigation, obtain the basic profile of upper coal seam mining face and coal rock occurrence characteristics, then determine the position of lower coal seam face return airway and lower coal seam face haulage roadway, then analyze the influence of floor failure depth of upper coal seam mining face on the stability of surrounding rock of lower coal seam face return airway and lower coal seam face haulage roadway during mining;Step 2, based on the analysis result of step 1, formulate the pre-grouting reinforcement scheme of lower coal seam face return airway and lower coal seam face haulage roadway;Step 3, according to the pre-grouting reinforcement scheme formulated in step 2, after grouting, monitor the deformation of roadway surrounding rock during the use of lower coal seam face return airway and lower coal seam face haulage roadway, and then test the grouting effect according to the monitoring result.

Description

Technical Field

[0001] This invention belongs to the field of coal mining technology, specifically a method for pre-reinforcing the surrounding rock of lower coal seam roadways in very close-range coal seam mining. Background Technology

[0002] In the mining of closely spaced coal seams, the close proximity of the seams causes damage to the surrounding rock of the lower coal seam roadways, making tunneling and support difficult. Existing methods for controlling the surrounding rock of lower coal seam roadways mainly include adjusting the roadway layout, grouting reinforcement, and active and passive support.

[0003] Adjusting the roadway layout involves arranging the relative positions of roadways between upper and lower coal seams. By using coal pillars of a certain width, the roadways can be arranged in various configurations, such as internal staggered, external staggered, or parallel staggered, thereby ensuring the stability of the surrounding rock in the lower coal seam. This method effectively ensures the safe mining of closely spaced coal seams, but requires the retention of coal pillars of a certain width, reducing the resource recovery rate. Application No. 202110470097.2 discloses a method for co-directional internal staggered roadway layout in extremely close-range coal seam mining. It analyzes the impact of different working face lengths on floor damage, the diffusion range of coal pillars of different widths on the floor, and three different roadway layout schemes, and selects appropriate roadway layout parameters. Application No. 202211041018.7 discloses a coordinated mining method for closely spaced coal seams. By designing different mining directions for upper and lower coal seams in conjunction with roadway layout, it achieves shorter excavation lengths for the upper coal seam, fewer openings, and mining without reserved coal pillars in both upper and lower coal seams.

[0004] Grouting reinforcement is a method to improve the integrity of the surrounding rock in lower coal seam roadways by injecting grout. This method reduces the impact of upper coal seam mining on lower coal seam roadways, but the grouting range is difficult to control when injecting grout into the upper rock strata, leading to poor grouting effect. Application No. 202411049153.5 discloses a roadway layout and support method for downward mining of very close coal seam groups. This method supports the upper coal seam roadway, improving the recovery rate of upper coal seam coal. Simultaneously, coal pillars are set below the upper coal seam goaf in the lower coal seam, providing support to the intermediate rock strata. Grouting reinforcement improves the strength of the rock strata and reduces the impact of upper coal seam mining on lower coal seam mining. Application No. 202311247785.8 discloses a method to improve the quality of soft rock roadway formation in downward mining of close coal seam groups by injecting grout into the soft rock roof of the lower coal seam, creating a strength difference between the grouted and ungrouted roof. During the mining of the lower coal seam, the roof naturally falls, improving the strength and integrity of the roof in the goaf-side roadway.

[0005] Active and passive support is a method combining active and passive support, used to strengthen the surrounding rock of the roadway in a timely manner and ensure stability. This method guarantees the safe mining of the lower coal seam, but due to the impact of the upper coal seam mining, it requires increased support density and strength, leading to increased support costs. Application No. 202110733894.5 discloses a method for mining very close-range coal seams, where the mining face is located in the lower coal seam, using anchor-mesh-cable active support to achieve normal mining while effectively solving the stability problem of the roof below the goaf. Application No. 202510032662.5 discloses a design method for self-forming roadways by cutting the roof of close-range coal seams, designing support in different areas, introducing constrained concrete columns and unit hydraulic supports alternately to achieve coordinated active and passive support and improve roadway stability.

[0006] The above methods ensure safe mining of nearby coal seams and improve resource recovery rates. However, with the retention of coal pillars, roadway preparation time is long, tunneling and support processes are complex, and corresponding tunneling and support costs are high. Therefore, there is an urgent need to develop a method for controlling the surrounding rock of lower coal seam roadways to solve the above problems. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to provide a method for pre-reinforcing the surrounding rock of lower coal seam roadways in very close-range coal seam mining.

[0008] The technical solution of this invention to solve the aforementioned technical problem is to provide a method for pre-reinforcing the surrounding rock of a lower coal seam roadway in close-range coal seam mining, characterized in that the method includes the following steps:

[0009] Step 1: Conduct on-site investigation to obtain the basic overview and coal-rock strata occurrence characteristics of the upper coal seam mining face; then, based on the basic overview and coal-rock strata occurrence characteristics of the upper coal seam mining face, determine the locations of the return airway and transport roadway of the lower coal seam mining face; then, based on the locations of the return airway and transport roadway of the lower coal seam mining face, analyze the impact of the floor failure depth h during the mining of the upper coal seam mining face on the surrounding rock stability of the return airway and transport roadway of the lower coal seam mining face.

[0010] Step 2: Based on the analysis results of Step 1, formulate a pre-grouting reinforcement scheme for the return airway and transport roadway of the lower coal seam working face.

[0011] Step 3: After grouting according to the pre-grouting reinforcement plan formulated in Step 2, monitor the deformation of the surrounding rock in the return airway and transport roadway of the lower coal seam working face during use, and then verify the grouting effect based on the monitoring results.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] (1) In the process of mining the upper coal seam, the present invention performs pre-grouting reinforcement of the surrounding rock of the lower coal seam roadway, which improves the integrity of the surrounding rock of the lower coal seam roadway. Compared with the traditional method, it saves the process of grouting the roadway before excavation. The active reinforcement of the surrounding rock avoids the instability phenomena such as roof leakage and roof collapse that occur during the roadway excavation under the condition of very close coal seam, and significantly improves the safety of the lower coal seam roadway excavation.

[0014] (2) Based on the depth of damage to the floor of the upper coal seam and the characteristics of mining impact during the mining process of the upper coal seam mining face, this invention divides the damage range of the floor of the upper coal seam mining face into plastic crack damage zone and disturbance impact zone, and clarifies the impact range of the mining of the upper coal seam mining face on the floor damage, thus pointing the way for the advanced grouting reinforcement of the surrounding rock of the lower coal seam roadway.

[0015] (3) This invention performs zoned precise grouting of the surrounding rock of the lower coal seam roadway in the upper coal seam mining face. Targeting the plastic crack failure zone and the disturbance-affected zone, precise grouting is achieved by adjusting grouting parameters such as the grouting hole angle, grouting hole arrangement, grouting pressure, and grouting radius. This achieves the dual goals of saving grouting materials and improving the stability of the roadway surrounding rock. During the mining of the lower coal seam, there is no need to leave coal pillars, reducing the waste of coal pillar resources used to maintain the stability of the lower coal seam roadway, increasing the coal recovery rate, and increasing economic benefits.

[0016] (4) The present invention divides the damage range of the roadway floor by the damage depth of the upper coal seam floor and realizes precise grouting of the surrounding rock of the lower coal seam roadway, which provides a favorable surrounding rock environment for the excavation of the lower coal seam roadway. The advanced pre-grouting reinforcement of the surrounding rock of the lower coal seam roadway increases the roadway excavation speed, accelerates the mine succession from the overall perspective, and realizes safe and efficient production. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the overall technical process of the present invention.

[0018] Figure 2 This is a schematic diagram of the longitudinal section of the pre-grouting reinforcement of the upper coal seam mining face roadway to the lower coal seam roadway according to the present invention;

[0019] Figure 3 This is a top view of the cross-section of the pre-grouting reinforcement of the upper coal seam mining face roadway to the lower coal seam roadway according to the present invention;

[0020] Figure 4 This is a diagram showing the surrounding rock displacement curve during the excavation of the transport roadway in the first mining face of the lower coal seam according to Embodiment 1 of the present invention.

[0021] Figure 5 This is a diagram showing the displacement curve of the surrounding rock during the mining of the transport roadway in the first mining face of the lower coal seam in Embodiment 1 of the present invention.

[0022] In the diagram, 1 is the upper coal seam, 2 is the rock strata between the upper and lower coal seams, 3 is the lower coal seam, 4 is the rock strata on the floor of the lower coal seam, 5 is the return airway of the upper coal seam working face, 6 is the transport airway of the upper coal seam working face, 7 is the return airway of the lower coal seam working face, 8 is the transport airway of the lower coal seam working face, 9 is the grouting hole, 10 is the upper coal seam mining face, 11 is the plastic cracking failure zone, 12 is the disturbance influence zone, 13 is the roadway centerline, 14 is the working face advance direction, and 15 is the influence range of the advance support pressure. Detailed Implementation

[0023] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the present invention.

[0024] This invention provides a method for pre-reinforcing the surrounding rock of the lower coal seam roadway in ultra-close coal seam mining (hereinafter referred to as the method), applicable to ultra-close coal seams with a layer spacing of less than 5m (i.e., the thickness of the rock stratum 2 between the upper and lower coal seams is less than 5m), characterized in that the method includes the following steps:

[0025] Step 1: Conduct in-depth field research to obtain the basic overview and coal and rock strata occurrence characteristics of the upper coal seam mining face 10; then, based on the basic overview and coal and rock strata occurrence characteristics of the upper coal seam mining face 10, determine the locations of the return airway 7 and the transport airway 8 of the lower coal seam mining face; then, based on the locations of the return airway 7 and the transport airway 8 of the lower coal seam mining face, analyze the impact of the floor failure depth h during the mining of the upper coal seam mining face 10 on the surrounding rock stability of the return airway 7 and the transport airway 8 of the lower coal seam mining face.

[0026] Preferably, in step 1, the basic overview of the upper coal seam mining face 10 includes the mining method, mining sequence, mining and tunneling succession, tunneling technology and production system.

[0027] Preferably, in step 1, the coal and rock strata occurrence characteristics include coal and rock thickness, dip angle, interbedded rock, interlayer spacing, lithology, and physical and mechanical parameters of the coal and rock strata.

[0028] Step 2: Based on the analysis results of Step 1, formulate a pre-grouting reinforcement scheme for the return airway 7 and the transport roadway 8 of the lower coal seam working face.

[0029] Preferably, in step 2, the pre-grouting reinforcement scheme includes, in sequence, calculating the depth of floor damage h of the upper coal seam mining face 10 during mining, dividing the floor damage zones of the upper coal seam mining face 10 during mining, designing the arrangement of grouting holes 9 in each floor damage zone, determining grouting technical indicators and selecting grouting process, determining the distance between the grouting and the upper coal seam mining face 10, and formulating an on-site construction plan.

[0030] Preferably, in step 2, the specific steps of the pre-grouting reinforcement scheme are as follows:

[0031] S21. Calculate the floor failure depth h of the upper coal seam mining face after 10 mining cycles:

[0032] The floor failure depth h of a longwall face in the upper coal seam is determined by referring to the empirical formula for the floor failure depth of the longwall face. (m), H represents mining depth (m), a represents coal seam dip angle (°), and L represents working face dip length (m);

[0033] S22. Divide the floor failure zones of the upper coal seam mining face 10: Based on the basic overview of the upper coal seam mining face 10 obtained in step 1 and the locations of the return airway 7 and the transport airway 8 of the lower coal seam working face, according to the floor failure depth h in step S21, divide the rock strata 2, lower coal seam 3, and lower coal seam floor rock strata 4 below the return airway 5 and the transport airway 6 of the upper coal seam working face into a plastic crack failure zone 11 and a disturbance influence zone 12 (e.g., ...). Figure 2 As shown, Figure 2 In the diagram, the cross-section is perpendicular to the roadway, representing a longitudinal section. Inclined straight lines indicate the inclination of the grouting holes 9. Dashed lines represent the extent of the plastic crack failure zone 11 and the disturbance influence zone 12. The plastic crack failure zone 11 is directly below the upper coal seam mining face 10, with a large failure range, hence the large number of grouting holes 9 and their relatively large inclination angles. The disturbance influence zone 12 is on both sides of the upper coal seam mining face 10, with a small failure range, hence the fewer grouting holes 9 and their relatively small inclination angles. The plastic crack failure zone 11 is directly below the upper coal seam mining face 10, while the disturbance influence zone 12 is on both sides of the upper coal seam mining face 10, providing a reliable basis for achieving precise zoning.

[0034] S23. Determine the arrangement of the grouting holes 9 in each damaged zone of the base plate in step S22 to achieve precise grouting in each zone (e.g., Figure 3 As shown, Figure 3 In the middle, the cross-section is parallel to the return airway 5 of the upper coal seam working face, which is a cross-sectional view. The white arrow indicates the direction of working face advancement 14).

[0035] The outer ends of the upper coal seam 1 are taken as coal pillars. Based on the central axis 13 of the roadway, the return air roadway 5 and the transport roadway 6 of the upper coal seam working face are divided. The side closer to the upper coal seam mining working face 10 is the mining side, and the side closer to the coal pillar is the coal pillar side. Then, the arrangement of the grouting holes 9 is designed according to different roadway areas.

[0036] Preferably, in step S23, for the plastic crack failure zone 11, the arrangement of the grouting holes 9 on the mining side is as follows: the hole arrangement is in a quincunx pattern, with 2 to 3 holes arranged in each row, and the number of holes in adjacent rows is different; the distance between holes in the same row, i.e., the hole spacing, is 0.6 to 1 m, and the distance between adjacent rows, i.e., the row spacing, is 2.5 to 3.5 m; the grouting holes 9 face the mining side and the angle with the vertical direction is 30 to 60°, and the final hole depth exceeds the bottom plate failure depth h.

[0037] Preferably, in step S23, for the disturbance-affected zone 12, the arrangement of the grouting holes 9 on the coal pillar side is as follows: the hole pattern is three-hole, arranged in two rows, the distance between adjacent rows (row spacing) is 1.5~2m, and the distance between holes in the same row (hole spacing) is 2.5~3.5m; the grouting holes 9 face the coal pillar side and the angle with the vertical direction is 20~50°, and the final hole depth exceeds the bottom plate failure depth h.

[0038] S24. After determining the arrangement of grouting holes 9 in each base plate failure zone, the grouting technical indicators for the plastic crack failure zone 11 and the disturbance influence zone 12 are determined by establishing the relationship between grouting pressure P, grouting radius R and grouting volume Q. The grouting technical indicators for the plastic crack failure zone 11 and the disturbance influence zone 12 are different. The grouting technical indicators are then combined with the grouting process to improve the grouting effect.

[0039] Preferably, in step S24, the grouting pressure P includes pipeline loss pressure P1, pipeline loss pressure inside the grouting hole P2, and grout outlet pressure P3.

[0040] (kPa), f1 represents the friction coefficient of the grouting pipe, L g1 Indicates the total length of the grouting pipeline (m);

[0041] (Pa), μ represents the dynamic viscosity of the grout (Pa•s), L represents the length of the grouting hole (m), r represents the radius of the grouting pipe (m), and ν represents the grout flow velocity (m / s).

[0042] (kPa), γ represents the slurry bulk density (kN / m³). 3 ), Δh represents the grouting height difference (m);

[0043] (MPa), S t This represents the tensile strength of the rock strata (MPa).

[0044] Preferably, in step S24, the grouting radius... (m), k is the rock permeability coefficient (m / s), P is the grouting pressure (kPa), t is the grouting time (s), r is the grouting pipe radius (m), n is the porosity (%), and μ is the dynamic viscosity of the grout (Pa•s).

[0045] Preferably, in step S24, the grouting volume (m) 3 N is the number of grouting holes (units), R is the grouting radius (m), and a 岩 The maximum fracture width (reference value) of the grouting rock layer (m).

[0046] Preferably, in step S24, the grouting technical indicators include specific pressure value, diffusion range, and grouting volume.

[0047] Preferably, in step S24, the grouting technical indicators for the plastic crack failure zone 11 are as follows: in the plastic crack failure zone 11, the grouting pressure P is appropriately increased by 0.3~0.5MPa to ensure that the grouting reinforcement range is increased by 0.2~0.4m, so as to achieve mutual coverage between the grouting holes 9 and improve the integrity of the surrounding rock of the return airway 7 and the transport roadway 8 of the lower coal seam working face;

[0048] The specific grouting technical indicators for the disturbance-affected zone 12 are as follows: if the grouting radius of a certain grouting hole 9 is smaller than its calculated value, the grouting pressure of the surrounding grouting holes 9 in the disturbance-affected zone 12 will be increased by 0.5~1MPa and the grouting radius will be expanded by 0.4~0.8m, so that the reinforcement range of the surrounding grouting holes 9 covers the area not reinforced by the grouting hole 9.

[0049] Preferably, in step S24, a one-time grouting process with orifice sealing and grout stopping is adopted, and the grouting material is ultrafine cement slurry.

[0050] S25. To ensure that the grouting work will not affect the mining of the upper coal seam face 10, the grouting work is arranged in front of the upper coal seam face 10 along the face advance direction 14; the distance of the grouting ahead of the upper coal seam face 10 is determined according to the influence range 15 of the advance support pressure of the upper coal seam face 10.

[0051] S26. Develop an on-site construction plan based on actual site conditions:

[0052] To prevent grout leakage through cracks, parallel operations were implemented to improve efficiency. Each construction section was defined as 10-15m long, and construction was carried out in concentrated sections. When grouting of the previous section began, preparations were made for drilling the next section.

[0053] Step 3: After grouting according to the pre-grouting reinforcement plan formulated in Step 2, monitor the deformation of the surrounding rock in the return airway 7 and transport roadway 8 of the lower coal seam working face during their use, and then verify the grouting effect based on the monitoring results.

[0054] Preferably, in step 3, the monitoring parameters are: the roof subsidence, left flank approach, and right flank approach within 60 days.

[0055] Preferably, in step 3, if the monitoring results are: the roof subsidence of the roadway within 60 days does not exceed 400mm, and the left and right side migration within 60 days does not exceed 300mm, the grouting effect is judged to be good and meets the standard; otherwise, it does not meet the standard.

[0056] Preferably, in step 3, when the standard is not met, a single hydraulic prop combined with a metal articulated top beam is used to reinforce the roadway within a 20m range before and after the surrounding rock deformation monitoring point.

[0057] Preferably, in step 3, the specific implementation of the reinforced support is as follows: the metal articulated roof beam is parallel to the central axis 13 of the roadway and closely attached to the roof of the return airway 7 and the transport roadway 8 of the lower coal seam working face, with a distance of 1.5~2.0m between adjacent rows; the single hydraulic prop is closely attached to the metal articulated roof beam, and the distance between adjacent single hydraulic props in the same row, i.e., the column spacing, is 0.8~1.0m.

[0058] Example 1:

[0059] The main coal-bearing strata of the mine are the Lower Permian Shanxi Formation and the Upper Carboniferous Taiyuan Formation. The terrain is mainly composed of loess platforms, mounds, ridges, and loess gullies, with severe erosion and complex topography. The mine field is generally a broad and gently symmetrical syncline structure trending northeast, with gentle dips of 3°-12° on both flanks. Fault structures are relatively well-developed within the mine field. During exploration and production, a total of 8 faults were exposed, which can be divided into two groups: one group of compressive faults parallel to the fold axis and the other group of extensional faults perpendicular to the fold axis, both exposed in the tunnels. The Taiyuan Formation in the mining area contains five coal seams: No. 6, 7, 8, 10, and 11. The average total thickness of the coal seams is 9.03m. Among them, No. 8 and No. 10 are minable coal seams with an average total thickness of 8.03m, belonging to a closely spaced coal seam group. The upper coal seam of No. 8 has a thickness of 4.46m; the lower coal seam of No. 10 has a thickness of 3.57m; the intermediate strata are sandy mudstone with a thickness of 3.96m; and the floor of the No. 10 coal seam is medium-coarse sandstone with a thickness of 3.4m.

[0060] In step 1:

[0061] (1) Basic overview of the upper coal seam working face: The No. 8 coal seam 8108 working face adopts the strike longwall fully mechanized coal mining method, the downward mining sequence, the fully mechanized tunneling technology, the working face is 160m long, the strike length is 680m, the working face roof is supported by hydraulic supports, the return airway and transport roadway are supported by anchor net cable, the U-shaped ventilation method is adopted, the roof is managed by the caving method, the three-shift working method is adopted, the mining-to-tunneling ratio is 1:2, the average burial depth of the No. 8 coal seam is 267m, and the average burial depth of the No. 10 coal seam is 276m.

[0062] (2) Characteristics of coal and rock strata occurrence: Based on field surveys and experimental results, coal seam No. 8 is 4.46m thick and dips at 8°; coal seam No. 10 is 3.57m thick and dips at 8°; the intermediate strata are mudstone, 3.72m thick, and brittle; the bottom of coal seam No. 10 is medium-coarse sandstone, 3.4m thick. The physical and mechanical parameters of the coal and rock strata are shown in Table 1.

[0063] Table 1

[0064]

[0065] The return airway and transport roadway of the No. 10 coal seam working face are located below the return airway and transport roadway of the 8108 working face. Due to the impact of the mining of the 8108 working face, the surrounding rock of the return airway and transport roadway of the No. 10 coal seam working face is significantly affected.

[0066] In step 2:

[0067] S21, H is 267m; a is 8°; L is 160m;

[0068]

[0069] S22. Based on the basic overview of the 8108 working face and the location of the transport roadway and return airway of the first mining working face of No. 10 coal seam, according to the depth of floor damage, the sandy mudstone, No. 10 coal seam, and medium-coarse sandstone below the 8108 transport roadway and 8108 return airway are divided into plastic cracking failure zone and disturbance influence zone.

[0070] S23. The outer sides of the 8108 transport roadway and the 8108 return air roadway are taken as coal pillars. Based on the roadway centerline 13, the 8108 transport roadway and the 8108 return air roadway are divided. The side closer to the 8108 working face is the mining side, and the side closer to the coal pillar is the coal pillar side. Then, the arrangement of grouting holes is designed according to different roadway areas.

[0071] (1) For the plastic crack failure zone 11, the arrangement of the grouting holes 9 on the mining side is as follows: the hole arrangement is in a plum blossom shape, with 2 to 3 holes arranged in each row, the hole spacing is 0.8m, and the row spacing is 2.5m; the grouting holes 9 face the mining side, with an angle of 40° with the vertical direction, and the final hole depth exceeds the bottom plate failure depth by 16.5m.

[0072] (2) For the disturbance-affected zone 12, the arrangement of the grouting holes 9 on the coal pillar side is as follows: the hole pattern is three-hole, arranged in two rows with a row spacing of 1.5m and a hole spacing of 3m; the grouting holes 9 face the coal pillar side, with an angle of 30° with the vertical direction, and the final hole depth exceeds the bottom plate failure depth by 16.5m.

[0073] S24. Grouting technical specifications;

[0074] (1) f1 is set to 0.25, L g1 Take 10m;

[0075] μ is 0.15 Pa∙s, L is 20 m, r is 0.025 m, and ν is 1 m / s;

[0076] γ is taken as 15KN / m 3 Δh is taken as 16.5m;

[0077] (MPa); S t Take 5.957 MPa.

[0078]

[0079] (2) Grouting radius (m), k is taken as 1.51×10 -9 m / s, t is 900s, n is 12%.

[0080]

[0081] (3) Grouting volume (m) 3 ), N is 1814; a 岩 Take 0.009m (reference value).

[0082]

[0083] (4) The specific technical indicators for grouting in the plastic crack failure zone 11 are: the grouting pressure P is increased by 0.3 MPa to ensure that the grouting reinforcement range is increased by 0.3 m;

[0084] The specific grouting technical specifications for the disturbance-affected zone 12 are as follows: If the grouting radius of a certain grouting hole 9 is smaller than its calculated value, then the grouting pressure of the surrounding grouting holes 9 in the disturbance-affected zone 12 will be increased by 0.5 MPa and the grouting radius will be expanded by 0.4 m, so that the reinforcement range of the surrounding grouting holes 9 covers the area not reinforced by the grouting hole 9.

[0085] (5) The orifice-sealed grouting process is adopted for one-time grouting, and the grouting material is ultrafine cement slurry;

[0086] S25. According to the actual measurement of the influence range of the advance support pressure of the 8108 coal mining face, which is 18m, in order to avoid the influence range of the advance support pressure of 15, the distance of grouting ahead of the 8108 coal mining face is determined to be 20m.

[0087] S26. To prevent grout leakage through cracks, parallel operations are implemented to improve efficiency. Each 10m section is designated as a construction segment, and construction is carried out in concentrated segments. When grouting begins in one segment, preparations are made for drilling the next segment.

[0088] In step 3:

[0089] Roadway Surrounding Rock Deformation Monitoring: The "cross observation method" was used to monitor the deformation of the surrounding rock during the first mining face of the No. 10 coal seam. According to the monitoring results, during the excavation process, the roof subsidence of the transport roadway reached 270mm, the left flank approach reached 237mm, and the right flank approach reached 203mm (e.g., ...). Figure 4 As shown); during the mining process, the roof subsidence of the transport roadway reached 307mm, the left flank approach reached 260mm, and the right flank approach reached 224mm (as shown). Figure 5 As shown in the figure, all of these are subsidence amounts within a normal longwall face, indicating that the grouting effect is good.

[0090] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A method for pre-reinforcing the surrounding rock of a lower coal seam roadway in close-range coal seam mining, characterized in that, The method includes the following steps: Step 1: Conduct on-site investigation to obtain the basic overview and coal and rock strata occurrence characteristics of the upper coal seam mining face (10); then, based on the basic overview and coal and rock strata occurrence characteristics of the upper coal seam mining face (10), determine the location of the return airway (7) and the transport airway (8) of the lower coal seam mining face; then, based on the location of the return airway (7) and the transport airway (8) of the lower coal seam mining face, analyze the influence of the floor damage depth h during the mining of the upper coal seam mining face (10) on the surrounding rock stability of the return airway (7) and the transport airway (8) of the lower coal seam mining face; Step 2: Based on the analysis results of Step 1, formulate a pre-grouting reinforcement scheme for the return airway (7) and the transport roadway (8) of the lower coal seam working face. The pre-grouting reinforcement scheme includes calculating the floor damage depth h of the upper coal seam mining face (10) in sequence, dividing the floor damage zones of the upper coal seam mining face (10) in the mining, designing the arrangement of grouting holes (9) in each floor damage zone, determining the grouting technical indicators and selecting the grouting process, determining the distance of grouting ahead of the upper coal seam mining face (10), and formulating the on-site construction plan. The specific steps of the pre-grouting reinforcement scheme are as follows: S21. Calculate the depth of floor failure h of the upper coal seam mining face (10) during mining: The depth of floor failure h in the upper coal seam mining face (10) is determined by referring to the empirical formula for the depth of floor failure in the working face. H represents the mining depth, a represents the coal seam dip angle, and L represents the working face dip length; S22. Divide the floor damage zone of the upper coal seam mining face (10): Based on the basic overview of the upper coal seam mining face (10) obtained in step 1 and the positions of the return airway (7) and the transport airway (8) of the lower coal seam mining face, according to the floor damage depth h in step S21, divide the rock strata (2), lower coal seam (3) and lower coal seam floor rock strata (4) between the upper and lower coal seams below the return airway (5) and the transport airway (6) of the upper coal seam mining face into a plastic cracking damage zone (11) and a disturbance influence zone (12). The plastic cracking damage zone (11) is directly below the upper coal seam mining face (10), and the disturbance influence zone (12) is on both sides of the upper coal seam mining face (10). S23. Determine the arrangement of the grouting holes (9) in each damaged section of the base plate in step S22 to achieve precise grouting in each section: The outer ends of the upper coal seam (1) are taken as coal pillars. Based on the central axis (13) of the roadway, the return air roadway (5) and the transport roadway (6) of the upper coal seam working face are divided. The side closer to the upper coal seam mining face (10) is the mining side, and the side closer to the coal pillar is the coal pillar side. The arrangement of grouting holes (9) is designed according to different roadway areas. S24. After determining the arrangement of the grouting holes (9) in each base plate failure zone, the grouting technical indicators of the plastic crack failure zone (11) and the disturbance influence zone (12) are determined by establishing the relationship between the grouting pressure P, the grouting radius R and the grouting volume Q. Then, the grouting technical indicators are combined with the grouting process to improve the grouting effect. S25. To ensure that the grouting work will not affect the mining of the upper coal seam mining face (10), the grouting work is arranged in front of the upper coal seam mining face (10) along the working face advance direction (14); the distance of the grouting ahead of the upper coal seam mining face (10) is determined according to the influence range (15) of the advance support pressure of the upper coal seam mining face (10). S26. Based on the actual site conditions, formulate a site construction plan: In order to prevent grout leakage through cracks, implement parallel operations, determine 10~15m as a construction section, carry out concentrated construction in sections, and prepare for drilling the next section when the grouting of the previous section begins. Step 3: After grouting according to the pre-grouting reinforcement plan formulated in Step 2, during the use of the return airway (7) and the transport roadway (8) of the lower coal seam working face, the deformation of the surrounding rock of the roadway is monitored, and the grouting effect is tested according to the monitoring results.

2. The method for pre-reinforcing the surrounding rock of the lower coal seam roadway in ultra-close-distance coal seam mining according to claim 1, characterized in that, In step 1, the basic overview of the upper coal seam mining face (10) includes mining method, mining sequence, mining succession, tunneling technology and production system; In step 1, the occurrence characteristics of coal and rock strata include coal and rock thickness, dip angle, interbedded rock, interlayer spacing, lithology, and physical and mechanical parameters of coal and rock strata.

3. The method for pre-reinforcing the surrounding rock of the lower coal seam roadway in ultra-close-distance coal seam mining according to claim 1, characterized in that, In step S23, for the plastic crack failure zone (11), the arrangement of the grouting holes (9) on the mining side is as follows: the hole arrangement is in a quincunx pattern, with 2 to 3 holes arranged in each row, and the number of holes in adjacent rows is different; the distance between holes in the same row is 0.6 to 1 m, and the distance between adjacent rows is 2.5 to 3.5 m; the grouting holes (9) face the mining side and the angle with the vertical direction is 30 to 60°, and the final hole depth exceeds the bottom plate failure depth h; In step S23, for the disturbance-affected area (12), the arrangement of the grouting holes (9) on the coal pillar side is as follows: the hole arrangement is a three-hole pattern, arranged in two rows, the distance between adjacent rows is 1.5~2m, and the distance between the holes in the same row is 2.5~3.5m; the grouting holes (9) face the coal pillar side and the angle with the vertical direction is 20~50°, and the final hole depth exceeds the bottom plate failure depth h.

4. The method for pre-reinforcing the surrounding rock of the lower coal seam roadway in ultra-close-distance coal seam mining according to claim 1, characterized in that, In step S24, the grouting pressure P includes pipeline loss pressure P1, pipeline loss pressure inside the grouting hole P2, and grout outlet pressure P3. f1 represents the friction coefficient of the grouting pipe, L g1 Indicates the total length of the grouting pipeline; μ represents the dynamic viscosity of the grout, L represents the length of the grouting hole, r represents the radius of the grouting pipe, and ν represents the grout flow velocity. γ represents the grout density, and Δh represents the grouting height difference; S t Indicates the tensile strength of the rock strata; In step S24, the grouting radius k is the rock permeability coefficient, P is the grouting pressure, t is the grouting time, r is the grouting pipe radius, n is the porosity, and μ is the dynamic viscosity of the grout. In step S24, the grouting volume N is the number of grouting holes, R is the grouting radius, and a 岩 This represents the maximum fracture width of the grouting rock layer.

5. The method for pre-reinforcing the surrounding rock of the lower coal seam roadway in ultra-close-range coal seam mining according to claim 1, characterized in that, In step S24, the grouting technical indicators for the plastic crack failure zone (11) are as follows: In the plastic crack failure zone (11), the grouting pressure P is increased by 0.3~0.5MPa to ensure that the grouting reinforcement range is increased by 0.2~0.4m, so as to achieve mutual coverage between the grouting holes (9) and improve the integrity of the surrounding rock of the return airway (7) and the transport roadway (8) of the lower coal seam working face; The specific grouting technical indicators for the disturbance-affected zone (12) are as follows: if the grouting radius of a certain grouting hole (9) is smaller than its calculated value, the grouting pressure of the grouting holes (9) surrounding the grouting hole (9) in the disturbance-affected zone (12) is increased by 0.5~1MPa and the grouting radius is expanded by 0.4~0.8m, so that the reinforcement range of the surrounding grouting holes (9) covers the area not reinforced by the grouting hole (9).

6. The method for pre-reinforcing the surrounding rock of the lower coal seam roadway in ultra-close-range coal seam mining according to claim 1, characterized in that, In step S24, a one-time grouting process with orifice sealing and grout stopping is adopted, and the grouting material is ultrafine cement slurry.

7. The method for pre-reinforcing the surrounding rock of the lower coal seam roadway in ultra-close-distance coal seam mining according to claim 1, characterized in that, In step 3, the monitoring parameters are: roof subsidence, left flank approach, and right flank approach within 60 days.

8. The method for pre-reinforcing the surrounding rock of the lower coal seam roadway in ultra-close-distance coal seam mining according to claim 1 or 7, characterized in that, In step 3, if the monitoring results are: the roof subsidence of the roadway within 60 days does not exceed 400mm, and the left and right side migration within 60 days does not exceed 300mm, the grouting effect is judged to be good and meets the standard; otherwise, it does not meet the standard. In step 3, when the standard is not met, a single hydraulic prop is used in conjunction with a metal articulated roof beam to reinforce the roadway within a 20m range before and after the surrounding rock deformation monitoring point. In step 3, the specific implementation method of strengthening the support is: the metal articulated roof beam is parallel to the central axis of the roadway (13), closely attached to the roof of the return air roadway (7) and the transport roadway (8) of the lower coal seam working face, and the distance between two adjacent rows is 1.5~2.0m; The individual hydraulic props are closely attached to the metal hinged top beam, and the distance between adjacent individual hydraulic props in the same row is 0.8~1.0m.

Images