A method for upward mining and gas control of coal seam strip cemented backfilling in extremely close proximity

Abstract

This invention discloses a method for mining and controlling gas in extremely close-proximity coal seams using strip cemented backfilling. First, based on interlayer spacing and lithology, the width of the lower initial coal seam to be mined and the width of the retaining strip are determined, and the mining and support work of the retaining strip is completed. Grouting is then performed on the surface through grouting boreholes to seal disturbing fractures. Hydraulic fracturing and gas extraction are carried out in the upper high-outburst coal seam until the outburst risk is eliminated. Then, a mixture of crushed gangue and cementing slurry is filled into the strip roadway. Subsequently, under the cover of the gangue cemented strip, the retaining strip gangue cemented backfilling mining is completed. Finally, once the strength of each lower gangue cemented strip reaches the required level, the upper high-outburst coal seam gangue cemented backfilling mining is completed. This invention, through strip cemented backfilling of the lower coal seam for roof control, releases extremely close-proximity coal seam resources containing high-outburst adjacent layers, effectively controlling strata movement and surface subsidence.

Description

Technical Field

[0001] This invention relates to the field of coal mining technology, specifically to a method for upward mining and gas control of coal seams with extremely close spacing and cemented backfilling. Background Technology

[0002] In coal mining, the use of gangue cemented backfilling not only effectively controls surface subsidence but also enables the full utilization of solid waste such as coal mine waste gangue and fly ash. When the upper coal seam of a very closely spaced coal seam is a high-gas outburst coal seam, an upward mining method should be adopted. However, due to the small distance between coal seams, mining the lower coal seam easily disrupts the mining conditions of the upper coal seam. Furthermore, as coal mining extends deeper, deep coal seams face a situation of "high ground stress - strong mining disturbance." The disturbance stress from mining the lower very closely spaced coal seam causes the upper high-outburst coal seam to become softer and more fragmented, increasing the risk of outbursts. To address these issues, there is an urgent need to find an upward mining and gas control method for very closely spaced coal seams with upper high-outburst risk, to ensure and improve the mining conditions of the upper high-outburst coal seam, and to unlock the resources of closely spaced coal seams in the "three underground" areas (underground, underground, and underground). Summary of the Invention

[0003] The purpose of this invention is to provide a method for mining and controlling gas in extremely close-range coal seams with strip cemented backfilling. This method can effectively solve the problems of mining conditions being damaged and the risk of outbursts increasing in the upper high-outburst coal seams caused by disturbance from mining of the lower coal seams, thus ensuring safe mining conditions for the upper high-outburst coal seams.

[0004] To achieve the above objectives, the present invention provides a method for upward mining and gas control of extremely close-range coal seam strip cemented backfilling, comprising the following steps:

[0005] S1. First, based on the spacing and lithology of closely spaced coal seam interlayers, divide the width of the mining strip and the reserved strip in the lower first mining coal seam, and complete the mining and support work of the mining strip.

[0006] S2. Drill grouting holes for the retained coal pillar from the ground into the retained strip, and grout through the holes to seal the disturbing cracks in the retained coal pillar and improve the support strength of the retained strip;

[0007] S3. Drill a row of pressure relief boreholes from the mining strip roadway upwards to the upper high-gas coal seam; in the upper high-gas coal seam, pressure is relieved by hydraulic cutting, inducing some stress to transfer to the remaining coal pillars on both sides. The pressure relief boreholes are arranged at intervals D along the length of the mining strip; multiple radial nozzles are arranged on the high-pressure water pipe, and each radial nozzle has multiple nozzles arranged in a ring. High-pressure water forms a circumferential pressure relief groove at each nozzle. N pressure relief grooves are cut at different heights in the high-gas coal seam for pressure relief; after the hydraulic cutting is completed, gas in the upper high-gas coal seam is extracted through the pressure relief boreholes until the outburst risk is eliminated;

[0008] S4. Repeat steps S2-S3 until all mining strips are mined. Fill each mining strip roadway and goaf with a mixture of crushed gangue and cementing slurry, providing protection and support through the retained strips, until the gangue cemented strips reach the required strength. Complete the gangue cemented backfilling mining of each retained strip under the protection and support of the gangue cemented strips.

[0009] S5. The lower first coal seam has been fully mined, and the strength of each gangue cemented strip (6) has reached the standard. The upper high-outburst coal seam (2) gangue cemented backfilling mining has been completed.

[0010] Furthermore, the distance between the first coal seam mined in the lower part and the upper high-outburst coal seam shall not be less than 3m.

[0011] Furthermore, the width ratio of the recovered strip to the retained strip is 1:1.

[0012] Furthermore, in step S3, to avoid inducing concentrated stress and causing significant instability and failure in the retained coal pillar, the radius R of the stress relief groove, the borehole spacing D, and the coal seam firmness coefficient f are... c interlayer strength coefficient f r The following relationship should be satisfied:

[0013] (1) When 0 <f r ≤3 and 0 <f c When R ≤ 1, R and D satisfy the following conditions: R ≥ 1.6m, D ≤ 9m;

[0014] (2) When 0 <f r ≤3 and f c When R > 1, R and D satisfy the following conditions: R ≥ 1m, D ≤ 10m;

[0015] (3) When f r >3 and 0 <f c When R ≤ 1, R and D satisfy the following conditions: R ≥ 2m, D ≤ 9m;

[0016] (4) When f r >3 and f c When R > 1, R and D satisfy the following conditions: R ≥ 1m, D ≤ 9m.

[0017] Furthermore, in step S3, the pressure relief grooves in a single pressure relief borehole are N = 1, 2, or 3.

[0018] Furthermore, in step S4, the average particle size of the crushed gangue is 15–30 mm.

[0019] The beneficial effects of this invention are:

[0020] (1) By constructing hydraulic slots in the upper high-outburst coal seam through the mining strip of the lower coal seam at very close distance, some stress is induced to transfer to both sides, and gas is extracted and depressurized until the outburst risk is eliminated, so as to provide sufficient guarantee for the mechanical strength of the gangue cement body to meet the standard and the safe mining of the upper high-outburst coal seam.

[0021] (2) After the lower coal seam is divided into strips, the coal pillar and gangue cemented strips are alternately supported and controlled by staggered mining to complete the gangue cemented backfilling mining of the lower coal seam, providing complete floor conditions for the mining of the upper coal seam. Attached Figure Description

[0022] Figure 1 This is a construction schematic diagram of the method for upstream mining and gas control of coal seam strip cementation and backfilling at extremely close distances according to the present invention;

[0023] Figure 2 This is a schematic diagram showing the relative positions of the hydraulically cut pressure relief grooves in adjacent layers within the strip according to the present invention. In the diagram: 1-lower first-mined coal seam, 2-upper high-outburst coal seam, 3-mining strip, 4-grouting borehole for retaining coal pillar.

[0024] 5-Relief drilling, 6-Gange cemented strip, 7-Retained strip, 8-Interlayer. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0026] This invention addresses the situation where two coal seams are very close together, with the upper seam being a high-gas outburst seam. It employs an upward mining method, first mining the bottom seam, then the upper seam. After mining a portion of the lower seam, the upper high-gas outburst seam needs to be treated by first enhancing permeability with hydraulic pressure and then extracting gas. This eliminates the high gas hazard and ensures low stress on the roof and floor of the upper seam, meeting the conditions for coal seam mining. Figure 1 As shown, a method for upward mining and gas control of coal seams with extremely close proximity through strip cemented backfilling includes the following steps:

[0027] S1. First, based on the spacing and lithology of closely spaced coal seams, the widths of the mining strip 3 and the retention strip 7 in the lower first-mining coal seam 1 are determined, and the mining and support work of mining strip 3 is completed. The support adopts the bolt and cable method, meaning support is provided simultaneously with mining to ensure the safety of the goaf, working face, and both roadways. The widths of mining strip 3 and retention strip 7 are designed at a 1:1 ratio.

[0028] S2. Grouting borehole 4 is constructed from the ground into the retained coal pillar within the retained strip 7. Grouting is performed through the borehole to seal the disturbing fractures within the retained coal pillar and improve the support strength of the retained strip 7. The grouting borehole 4 extends to the bottom of the retained strip 7, and an appropriate grouting pressure is selected to ensure the grouting quality of the disturbing fractures.

[0029] S3. Drill a row of pressure relief boreholes 5 from the upper high-gas coal seam 2 within the mining strip 3. That is, after a single mining strip 3 is partially mined, forming a goaf, the pressure relief boreholes 5 can be drilled. Pressure is relieved by hydraulic cutting within the upper high-gas coal seam 2, inducing some stress to transfer to the remaining coal pillars on both sides. The pressure relief boreholes 5 are arranged at intervals D along the direction of the mining strip 3. Multiple radial nozzles are arranged on the high-pressure water pipes, each with multiple nozzles arranged in a ring. High-pressure water forms a circumferential pressure relief groove at each nozzle. N pressure relief grooves are cut at different heights in the high-gas coal seam 2 for pressure relief. After the hydraulic cutting is completed, gas from the upper high-gas coal seam 2 is extracted through the pressure relief boreholes 5 until the outburst risk is eliminated. Above a single mining strip 3, gas is extracted from the high-outburst coal seam 2. Due to hydraulic depressurization, the stress in this part of the coal seam is transferred to the retaining coal pillars of the mining strips 7 on both sides, thereby reducing the pressure on the roof above mining strip 3 and minimizing the occurrence of roof falls and leaks. In this step, to avoid inducing concentrated stress that could act on the retaining coal pillars and cause significant instability, the spacing of the depressurization boreholes and the radius of the depressurization slots are selected based on the following conditions during construction, thus ensuring the stability of the construction and the coal seam. (Reference) Figure 2 The specific conditions are as follows: the radius R of the pressure relief groove, the borehole spacing D, and the coal seam firmness coefficient f. c interlayer strength coefficient f r The following relationship should be satisfied:

[0030] (1) When 0 <f r ≤3 and 0 <f c When R ≤ 1, R and D satisfy the following conditions: R ≥ 1.6m, D ≤ 9m;

[0031] (2) When 0 <f r ≤3 and f c When R > 1, R and D satisfy the following conditions: R ≥ 1m, D ≤ 10m;

[0032] (3) When f r >3 and 0 <f c When R ≤ 1, R and D satisfy the following conditions: R ≥ 2m, D ≤ 9m;

[0033] (4) When f r >3 and f c When R > 1, R and D satisfy the following conditions: R ≥ 1m, D ≤ 9m.

[0034] The radius R of the groove needs to be achieved with the pressure of high-pressure water. The pressure relief grooves N in a single pressure relief borehole can be 1, 2, or 3.

[0035] S4. Repeat steps S2-S3 until all mining strips 3 are mined. Fill each mining strip 3 roadway and goaf with a mixture of crushed gangue and cementing slurry, providing shielding support through the retained strips 7, until the gangue cemented strips 6 reach the required strength. The average particle size of the crushed gangue is 15-30mm. Complete the backfilling mining of each retained strip 7 under the shielding support of the gangue cemented strips 6. In this step, once the gangue cemented strips 6 reach the required strength, they will form a supporting force, thereby reducing the supporting force on the retained strips 7, which is beneficial for the mining of the retained strips 7. After the mining of strip 7 is completed, a row of pressure relief boreholes needs to be drilled above it to perform pressure relief treatment and extract gas from the high-outburst coal seam 2 in the manner described in step 3. At this point, the gas in the entire high-outburst coal seam 2 has been treated and its gas hazard has been eliminated. At the same time, the pressure resistance of the bottom plate of the high-outburst coal seam 2 has also been strengthened, thus providing safe mining conditions for the high-outburst coal seam.

[0036] S5. The lower first coal seam 1 has been fully mined, and the strength of each gangue cemented strip 6 has met the standard. The upper high-outburst coal seam 2 gangue cemented backfilling mining has been completed.

[0037] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes that can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention are all within the protection scope of the claims of the present invention.

Claims

1. A method for upward mining and gas control of coal seams with extremely close spacing and cemented backfilling, characterized in that, Includes the following steps: S1. First, based on the spacing and lithology of the interlayers of the closely spaced coal seams, divide the width of the mining strip (3) and the retention strip (7) in the lower first mining coal seam (1) and complete the mining and support work of the mining strip (3); S2. Grouting boreholes (4) are drilled from the ground into the reserved strip (7) to seal the disturbing cracks in the reserved coal pillar and improve the support strength of the reserved strip (7). S3. A row of pressure relief boreholes (5) is constructed from the mining strip (3) into the upper high-burst coal seam (2). Pressure is relieved by hydraulic cutting in the upper high-burst coal seam (2), inducing some stress to transfer to the coal pillars on both sides. The pressure relief boreholes (5) are arranged along the length of the mining strip (3) at a spacing of D. Multiple radial nozzles are arranged on the high-pressure water pipe. Each radial nozzle has multiple nozzles arranged in a ring. High-pressure water forms a circumferential pressure relief groove at each nozzle. N pressure relief grooves are cut at different heights in the upper high-burst coal seam (2) to relieve pressure. After the hydraulic cutting is completed, gas in the upper high-burst coal seam (2) is extracted through the pressure relief boreholes (5) until the outburst risk is eliminated. S4. Repeat steps S2-S3 until all mining strips (3) are mined. Fill the roadway and goaf of each mining strip (3) with a mixture of crushed gangue and cementing slurry. Provide shielding and support through the reserved strips (7) until the gangue cemented strips (6) reach the required strength. Complete the gangue cementing backfilling mining of each reserved strip (7) under the shielding and support of the gangue cemented strips (6). S5. The lower first coal seam (1) has been fully mined, and the strength of each gangue cemented strip (6) has reached the standard. The upper high-outburst coal seam (2) gangue cemented backfilling mining has been completed.

2. The method for upstream mining and gas control of extremely close-range coal seam strip cemented backfilling as described in claim 1 The method, characterized in that, The distance between the lower first coal seam (1) and the upper high-bursting coal seam (2) shall not be less than 3 m.

3. The method for upward mining and gas control of extremely close-range coal seam strip cemented backfilling according to claim 1, characterized in that, The width ratio of the mining strip (3) to the retention strip (7) is 1:

1.

4. The method for upward mining and gas control of extremely close-range coal seam strip cemented backfilling according to claim 1, characterized in that, In step S3, to avoid inducing concentrated stress and causing significant instability and failure in the retained coal pillar, the radius of the pressure relief groove is... R Spacing of pressure relief drilling holes D Coal seam firmness coefficient f c. Interlayer strength coefficient f r should satisfy the following relationship: (1) When 0 < f r≤3 and 0< f When c≤1, R and D satisfy the following condition: R≥ 1.6m D ≤9m; (2) When 0 < f r≤3 and f When c > 1, R and D satisfy the following condition: R≥ 1m, D ≤10m; (3) When f r > 3 and 0 < f When c≤1, R and D satisfy the following condition: R≥ 2m, D ≤9m; (4) When f r > 3 and f When c > 1, R and D satisfy the following condition: R≥ 1m, D ≤9m.

5. The method for upward mining and gas control of extremely close-range coal seam strip cemented backfilling according to claim 4, characterized in that, In step S3, the number of pressure relief grooves in a single pressure relief borehole is N = 1, 2, or 3.

6. The method for upward mining and gas control of extremely close-range coal seam strip cemented backfilling according to claim 1, characterized in that, In step S4, the average particle size of the crushed gangue is 15~30 mm.

Images