Close-distance coal seam working face staggered arrangement and partial filling cooperative alternate mining method

Abstract

The invention discloses a close-distance coal seam working face staggered arrangement and partial filling collaborative alternate mining method, and belongs to the field of coal mining. The method aims to solve the problems of stress superposition, difficult settlement control, low resource recovery rate and low mining efficiency in simultaneous mining of close-range coal seam groups, and comprises the following steps: designing relative spatial positions of working surfaces of upper and lower coal seams to be staggered, and during mining, pausing after the working surface of the upper coal seam is advanced by a set staggered distance L, and starting the mining of the lower coal seam; and then the parallel operation of bottom mining and top filling-top mining and bottom filling is alternately and circularly carried out between the upper working face and the lower working face. According to the method, the overlying strata is uniformly and effectively supported by the filling body, the reserved width of the section coal pillar is compressed to 0-10 m, the overlying strata is promoted to uniformly settle, the ground surface settlement gradient is reduced to below 0.05%, parallel operation of different steps is simultaneously executed through the two sections of working faces, the mining efficiency is remarkably improved, and the mining cost is reduced. And the comprehensive operating rate of the equipment is improved from below 65% to above 85%.

Description

Technical Field

[0001] This invention relates to a method for safe and efficient mining and strata control of closely spaced coal seams, specifically a method for alternating mining of closely spaced coal seam working faces with partial backfilling, belonging to the field of coal mining. Background Technology

[0002] Coal mining in close proximity is one of the important methods of coal mining today. However, the superposition of mining stress between the upper and lower coal seams makes the working face layout and strata control technically challenging. Currently, engineering practice mainly employs three working face layout methods: internal staggered, external staggered, and overlapping. While the internal staggered layout can reduce the stress superposition effect, it results in an excessively high coal pillar retention rate in certain sections. The external staggered layout can improve the coal pillar recovery rate, but the mining of the lower coal seam will be located within a high-stress superposition zone generated by the coal pillar of the upper coal seam, with a stress concentration factor reaching 2.0-2.5, which can easily trigger dynamic disasters such as rockbursts. In the overlapping layout, the strong superposition of mining disturbances between the upper and lower seams can easily lead to shear slip instability in key strata, forming step-like subsidence cracks that penetrate the surface, severely damaging the surface ecology and rendering the upper coal seam resources unminable.

[0003] In addition, the traditional fully mechanized mining paste filling technology used to achieve settlement control usually adopts a mode of sequential operation of "coal mining" and "filling" on the same working face. This mode has a fundamental contradiction between filling operation and mining operation in terms of time and space. The filling efficiency and the solidification and curing time of the filling body seriously restrict the continuous advancement of the coal mining machine, resulting in the equipment uptime usually being less than 65% and the mining efficiency being low.

[0004] In summary, there is an urgent need for a new collaborative mining method that can balance safe mining, surface subsidence control, resource recovery rate, and mining efficiency. Summary of the Invention

[0005] To address the problems of stress superposition, easy instability of overburden structure, difficulty in settlement control, and low resource recovery rate and mining efficiency in the simultaneous mining of closely spaced coal seams, this invention provides a method for simultaneous mining of closely spaced coal seams based on staggered working face arrangement and partial backfilling coordination, in order to achieve safe mining, improve resource recovery rate and control settlement, belonging to the field of coal mining.

[0006] The core concept of this invention is as follows: First, the spatial relative positions of the upper and lower coal seam working faces are designed to be staggered, that is, in the vertical projection direction, the center line of the upper coal seam working face coincides with the center line of the coal pillar of the lower coal seam section, thus dispersing the mining disturbance in space; by designing a time-sequential alternating operation mode of "upper mining and lower filling - lower mining and upper filling", the filling operation is carried out synchronously with the mining operation; finally, by using part of the filling body to form uniform and effective support for the overlying strata, the simultaneous mining of the upper and lower coal seams of close proximity is realized, achieving the goals of safe mining, controlling subsidence, improving resource recovery rate and mining efficiency.

[0007] This invention provides a method for the coordinated and alternating mining of closely spaced coal seam working faces with partial backfilling, comprising the following steps: A. The spatial relative positions of the upper and lower coal seam working faces are arranged in an alternating manner. The upper and lower coal seam working faces are respectively arranged with a machine rail roadway and a return air roadway. In the area between the machine rail roadway of the working face and the center line of the working face, along the dip length of the working face for a length of M (M is 1 / 2 of the length of the working face), hydraulic supports are arranged and filled. B. First, the upper coal seam working face is mined and filled immediately. After the advance distance reaches the set offset L, its mining and filling operations are suspended, and the mining operations of the lower coal seam working face are started immediately. C. The lower coal seam working face carries out mining work in one work cycle unit, with a total advance distance of S; within this work cycle unit, the mined and unfilled areas of the upper coal seam working face are simultaneously filled with paste. D. The upper coal seam working face carries out mining work in one work cycle unit, with a total advance distance of S; within this work cycle unit, the mined and unfilled areas of the lower coal seam working face are simultaneously filled with paste. E. Repeat steps C and D to form a cyclical operation pattern in which mining and filling alternate between the upper and lower coal seam working faces until the entire coal seam is mined.

[0008] Further, in step A, the staggered arrangement means that, in the vertical projection direction, the centerline of the upper coal seam working face coincides with the centerline of the lower coal seam section coal pillar; correspondingly, the centerline of the lower coal seam working face also coincides with the centerline of the upper coal seam section coal pillar. The width of the reserved section coal pillar is 0-10m. The reserved section coal pillar width of 0m is a coal pillar-free roadway reuse arrangement, that is, within the same coal seam, the machine rail roadway of the current working face is retained and used as the return air roadway of the next adjacent working face, and the section coal pillars between adjacent working faces within the same coal seam are eliminated.

[0009] Furthermore, in step B, the offset L should satisfy any of the following conditions: ① When the length of the fully decompression zone formed by mining the upper coal seam is L2 > L1 + S, then the offset L should satisfy: L1 + S < L <L2; ② When affected by geological or mining conditions, such as the small mining height or low extraction rate of the upper coal seam, the weak roof lithology, or the influence of geological structures, etc., when the length L2 of the fully pressure-relieved area formed by the mining of the upper coal seam < L1 + S, the stagger distance L should satisfy: L > L1 + S; Among them, L1 is the length of the significantly affected area of the advanced abutment pressure in front of the working face of the lower coal seam; S is the total advancing distance of one operation cycle unit; L2 is the length of the fully pressure-relieved area formed behind the goaf after the mining of the upper coal seam; the L1 and L2 are determined by on-site measurement, engineering analogy or numerical simulation calculation.

[0010] Furthermore, in steps C and D, the duration of the operation cycle unit corresponds to an integer multiple of the mine production shift system, ensuring that the filling paste reaches a safety strength not lower than 1 MPa at the end of the cycle unit. Preferably, the duration of the operation cycle unit is 16 hours, 12 hours or 8 hours, corresponding to two consecutive shifts of the three-shift work system, two consecutive shifts of the four-six work system or one full shift of the three-shift work system respectively.

[0011] Furthermore, in steps C and D, the calculation method of the total advancing distance S is S = n × h; where n is the number of times the coal cutter completes coal cutting along the full length of the working face within one operation cycle unit, and the value range is 3 - 8 cuts; h is the cutting depth of the coal cutter, and the value range is 0.6 - 0.8 m; the value range of the total advancing distance S is 1.8 - 6.4 m.

[0012] Furthermore, in steps C and D, the mined area to be filled is a rectangular area located behind the backfill hydraulic support of the support, with a dip length of M along the working face and a width of the total advancing distance S within one operation cycle unit along the advancing direction.

[0013] The beneficial effects of the present invention: (1) Through the collaborative design of staggered layout and partial filling of the working face, the present invention optimizes the stope mechanical environment. The set advancing stagger distance L plays a key role: on the one hand, using the supporting effect of the filling body in the lower coal seam, the significantly affected area L1 of the advanced abutment pressure in front of the working face of the lower coal seam is greatly reduced, avoiding the risk of stress superposition; on the other hand, it ensures that the filling operation of the lower coal seam can be carried out in the pressure-relieved area of the goaf of the upper coal seam, providing favorable conditions for the formation of the early strength of the filling body; (2) The present invention uses the staggered filling method to achieve uniform and effective support for the overlying strata. On the one hand, the width of the section coal pillar left in the traditional layout method is compressed from more than 20 m to 0 - 10 m, significantly reducing the loss of coal resources and increasing the extraction rate by more than 15%; on the other hand, this support mode realizes uniform support for the overlying strata, enabling the overall coordinated settlement of the overlying strata, reducing the surface settlement gradient to less than 0.5‰, and avoiding the damage to the surface ecology caused by stepped settlement; (3) The “upper mining and lower filling - lower mining and upper filling” cyclical alternating operation mode is adopted, so that the filling operation is parallel to the mining operation in time and distributed in different working faces in space. This successfully realizes the parallel operation of different steps in two working faces at the same time. The division of labor is clear and there is no interference between them, which ensures that effective coal mining production can be carried out in three shifts a day, and increases the overall equipment uptime from below 65% to above 85%. Attached Figure Description

[0014] Figure 1 This is a three-dimensional schematic diagram of the overall arrangement of closely spaced coal seams according to the present invention; Figure 2 This is a schematic diagram of the staggered arrangement of the upper and lower coal seam working faces according to the present invention; Figure 3 This is a schematic diagram illustrating the staggered arrangement of the upper and lower coal seam working faces during filling according to the present invention; Figure 4 For along Figure 3 Sectional view of section I-I; Figure 5 For along Figure 3 Sectional view of section II-II; Figure 6 For along Figure 3 Sectional view of section III-III; Figure 7 This is a schematic diagram of rock strata collapse and overlying settlement after the application of the present invention; Figure 8 This is a diagram illustrating the alternating cyclical operation of the upper and lower coal seam working faces during the application of this invention; Figure 9 This is a Gantt chart illustrating the alternating cyclical operation of the upper and lower coal seam working faces during the application of this invention; In the diagram: 1. Upper coal seam, 2. Lower coal seam, 3. Upper coal seam working face, 4. Lower coal seam working face, 5. Area to be filled, 6. Area to be mined, 7. Upper coal seam section coal pillar, 8. Lower coal seam section coal pillar, 9. Upper coal seam working face track roadway, 10. Upper coal seam working face return airway, 11. Lower coal seam working face track roadway, 12. Lower coal seam working face return airway, 13. Filling body, 14. Collapsed gangue, 15. Boundary coal pillar. Detailed Implementation

[0015] The present invention will be further illustrated by the following embodiments, but is not limited to the following embodiments. Example 1

[0016] A coal mine contains two closely spaced coal seams with stable occurrence and gentle dip angles. The upper coal seam has an average thickness of 2.3m, the lower coal seam has an average thickness of 3.5m, and the average distance between the two seams is 2.4m. The mining method of this invention is employed, and the specific steps are as follows: A. The spatial relative positions of the upper and lower coal seam working faces are designed to be staggered, such as... Figure 1 and Figure 2 As shown, in the vertical projection direction, the centerline of the upper coal seam working face 3 coincides with the centerline of the lower coal seam section coal pillar 8 of the lower coal seam working face 4; correspondingly, the centerline of the lower coal seam working face 4 also coincides with the centerline of the upper coal seam section coal pillar 7 of the upper coal seam working face 3.

[0017] The distance between the upper coal seam working face machine track roadway 9 and the upper coal seam working face return air roadway 10, and the distance between the lower coal seam working face machine track roadway 11 and the lower coal seam working face return air roadway 12, i.e., the working face length is 200m; For example Figure 3 As shown, hydraulic supports with backfilling are installed within a 100m diagonal length along the working face, between the upper coal seam working face track roadway 9 and the lower coal seam working face track roadway 11 and the centerline of the working face. Matching paste backfilling systems are also installed in the upper coal seam working face track roadway 9 and the lower coal seam working face track roadway 11. The width of the upper coal seam section coal pillar 7 and the lower coal seam section coal pillar 8 is 10m. Figure 4-6 The diagram shows the state of bottom sampling and top filling during filling.

[0018] B, such as Figure 8 and Figure 9 As shown, in this embodiment, the mine adopts a three-eight work system, and the work cycle unit is set to 16 hours (i.e., two consecutive production shifts). The coal cutting depth of the coal mining machine is 0.8m. Within one cycle unit, the coal is cut 8 times along the entire length of the working face. Therefore, the total advancing distance S = 8 × 0.8m = 6.4m.

[0019] Based on field measurements and numerical simulations, the length L1 of the zone significantly affected by the advance support pressure in front of the lower coal seam working face 4 is approximately 28m, and the length L2 of the zone with sufficient pressure relief behind the goaf of the upper coal seam is approximately 40m. Therefore, the set advance offset L must satisfy: L1 + S = 28 + 6.4 = 34.4m < L < L2 = 40m. In this example, L = 37m is taken.

[0020] First, the upper coal seam working face 3 is mined, adopting the "mining and filling at the same time" mode. Paste is filled behind the hydraulic support behind the frame. After the advance distance reaches 37m, the mining and filling operations are suspended, and the mining operation of the lower coal seam working face 4 is started immediately.

[0021] C. For example Figure 4 , Figure 5 , Figure 8 , Figure 9As shown, the lower coal seam working face 4 underwent a 16-hour mining operation, advancing a total of 6.4m. During these 16 hours, using the filling system located in the upper coal seam, paste was used to fill the mined area to be filled behind the hydraulic support behind the upper coal seam working face, with a length of M=100m and a width of S=6.4m. Figure 6 As shown, at the end of this 16-hour period, the filled paste, after solidification, achieved a compressive strength of 1 MPa, meeting the strength and safety requirements for subsequent mining operations in adjacent areas. The filling operation and the mining operation of the lower coal seam were spatially separate but temporally parallel.

[0022] D. A 16-hour mining operation was conducted at the upper coal seam working face 3, advancing a total of 6.4 meters. During this 16-hour period, the backfilling system located in the lower coal seam was used to backfill the mined area behind the hydraulic support at the lower coal seam working face, with a length of M=100m and a width of S=6.4m. At the end of the 16 hours, the backfilled paste, after solidification, achieved a compressive strength of 1MPa, meeting the strength and safety requirements for subsequent mining operations in adjacent areas. The backfilling operation was spatially separate from the upper coal seam mining operation but ran concurrently in time.

[0023] E. Repeat steps C and D to form an alternating cyclical operation mode of "downward mining and upward charging - upward mining and downward charging". Continue to operate in this mode until the entire coal seam is mined.

[0024] Due to the adoption of the aforementioned method of staggered working face arrangement and partial filling, the overlying strata, under the uniform and effective support of the filling body, produced the following: Figure 7 The resulting gentle and uniform settlement has a settlement gradient controlled below 0.5‰; whereas the traditional method of total collapse leads to step-like settlement. This invention effectively protects the surface ecology.

[0025] This embodiment also includes a preparation stage for the filling station and working face: Constructing a ground paste preparation system: employing a three-stage crushing process (final aggregate particle size ≤15mm) and a twin-shaft forced mixer unit (system production capacity >300m³). 3 The paste preparation and delivery system consists of components such as a high-pressure plunger pump (outlet pressure ≥12MPa) and a high-pressure plunger pump (outlet pressure ≥12MPa). The filler aggregate and powder made from gangue are buffered in the finished gangue stockpile. Fly ash and cementing materials are stored in special silos. Sufficient water and admixtures are prepared. The power supply, water supply and air supply systems are checked to confirm that the equipment is running normally. The reliability of underground pipelines, control valves, material placing devices and filling bags is confirmed.

[0026] In this embodiment, the filling station and the formal filling stage of the working face include the following: Crushed gangue and cement, fly ash and other binders are fed into a twin-shaft forced mixer according to the proportion through a metering hopper and belt conveyor. At the same time, a certain amount of clean water and additives are added to make a paste. The paste is temporarily stored in a hopper and then pressurized by a concrete pump. It is then pumped to the working face for filling through a conveying system consisting of seamless steel pipes on the ground and composite pipes underground.

[0027] A telescopic template or flexible baffle is erected behind the hydraulic support, and filling pipes are arranged along the working face. The ends are connected to diversion valves and hoses to ensure that the filling area is covered. The ground filling station pumps the paste to the working face through the pipes and monitors the pump pressure in real time to avoid pipe blockage.

[0028] In this embodiment, after completing the paste filling in steps C and D, before proceeding to the next cycle, the safety of the conveying pipeline and the state of the slurry are checked to prevent residual paste from solidifying and clogging the pipeline.

[0029] In this embodiment, during the cyclical advancement process, the roof contact rate of the goaf is monitored and controlled to be ≥85%. The roof contact quality is dynamically optimized by adjusting the slump of the paste (180-220mm). Real-time linkage control between the mining progress and the backfilling ratio is achieved to ensure that the backfilling operation lags behind the mining progress by no more than one cycle step.

[0030] Conventional fully mechanized coal mining with paste backfilling follows a sequence of cutting coal, then enclosure, then backfilling, and waiting for solidification. In this embodiment, coal cutting and paste backfilling are carried out alternately and cyclically on the upper and lower coal seams, respectively, thereby achieving coordinated operation of backfilling and coal mining and improving the efficiency of coal mining production. Example 2

[0031] A coal mine contains two closely spaced coal seams with stable occurrence and gentle dip angles. The upper coal seam has an average thickness of 1.0 m, the lower coal seam has an average thickness of 2.5 m, and the average distance between the two seams is 3.8 m. The mining method of this invention is employed, and the specific steps are as follows: A. The spatial relative positions of the upper and lower coal seam working faces are designed to be staggered, such as... Figure 1 and Figure 2 As shown, in the vertical projection direction, the centerline of the upper coal seam working face 3 coincides with the centerline of the lower coal seam section coal pillar 8 of the lower coal seam working face 4; correspondingly, the centerline of the lower coal seam working face 4 also coincides with the centerline of the upper coal seam section coal pillar 7 of the upper coal seam working face 3.

[0032] The distance between the upper coal seam working face machine track roadway 9 and the upper coal seam working face return air roadway 10, and the distance between the lower coal seam working face machine track roadway 11 and the lower coal seam working face return air roadway 12, i.e., the working face length is 100m; For example Figure 3As shown, hydraulic supports are installed and filled in the area between the upper coal seam working face track roadway 9, the lower coal seam working face track roadway 11 and the center line of the working face, with a length of M=50m along the dip of the working face; and a matching paste filling system is installed in the upper coal seam working face track roadway 9 and the lower coal seam working face track roadway 11.

[0033] The design of coal pillar retention is a coal pillar-free roadway reuse layout. That is, within the same coal seam, after the current working face is mined, the machine rail roadway is retained and used as the return air roadway of the next adjacent working face, and the section coal pillar between adjacent working faces in the same coal seam is eliminated.

[0034] B. In this embodiment, the mine adopts a three-eight work system, and the work cycle unit is set to 8 hours (i.e., one full shift). The coal mining machine cuts to a depth of 0.6m and cuts coal 3 times along the entire length of the working face within one cycle unit. Therefore, the total advancing distance S = 3 × 0.6m = 1.8m.

[0035] Based on field measurements and numerical simulations, the length L1 of the zone significantly affected by the advance support pressure in front of the lower coal seam working face 4 is approximately 25m, and the length L2 of the zone with sufficient pressure relief behind the goaf of the upper coal seam is approximately 35m. Therefore, the set advance offset L must satisfy: L1 + S = 25 + 1.8 = 26.8m < L < L2 = 35m. In this example, L = 30m is taken.

[0036] First, the upper coal seam working face 3 is mined, adopting the "mining and filling at the same time" mode. Paste is filled behind the hydraulic support behind the frame. After the advance distance reaches 30m, the mining and filling operations are suspended, and the mining operation of the lower coal seam working face 4 is started immediately.

[0037] C, such as Figure 4 , Figure 5 As shown, the lower coal seam working face 4 underwent an 8-hour mining operation, advancing a total of 1.6m. During these 8 hours, using the filling system located in the upper coal seam, paste was used to fill the mined area to be filled behind the hydraulic support behind the upper coal seam working face, with a length of M=50m and a width of S=1.6m. Figure 6 As shown, at the end of this 8-hour period, the filled paste, after solidification, has a compressive strength of 1 MPa, meeting the strength and safety requirements for subsequent mining operations in adjacent areas. The filling operation and the mining operation of the lower coal seam are spatially separate but temporally parallel.

[0038] D. An 8-hour mining operation will be conducted at the upper coal seam working face 3, advancing a total of 1.6m. During this 8-hour period, the backfilling system located in the lower coal seam will be used to backfill the mined area behind the hydraulic support at the lower coal seam working face, with a length of M=50m and a width of S=1.6m. At the end of the 8 hours, the backfilled paste, after solidification, will have a compressive strength of 1MPa, meeting the strength and safety requirements for subsequent mining operations in adjacent areas. The backfilling operation is spatially separate from the upper coal seam mining operation but runs concurrently in time.

[0039] E. Repeat steps C and D to form an alternating cyclical operation mode of "downward mining and upward charging - upward mining and downward charging". Continue to operate in this mode until the entire coal seam is mined.

[0040] This embodiment combines the collaborative mining method of the present invention with the pillarless roadway reuse technology, achieving significant comprehensive benefits: by setting a reasonable stagger distance of L=30m, the superposition of advance support pressure between upper and lower coal seams is avoided, ensuring that the lower coal seam working face is always mined within the pressure relief protection zone of the upper coal seam goaf, effectively avoiding the hazards of strong dynamic pressure, and providing favorable conditions for the early strength formation of the backfill body. By adopting a pillarless layout within the same coal seam, the section pillar is completely eliminated, increasing the coal extraction rate by more than 30% compared to traditional fully mechanized mining methods. Figure 7 As shown, the effective and uniform bearing capacity of the backfill ensures the slow and uniform settlement of the overlying strata, with the measured surface settlement gradient being less than 0.5‰, effectively protecting the surface ecological environment. The alternating parallel operation mode minimizes the impact of backfill curing time on mining, and the overall equipment uptime remains stable at over 85%, significantly improving mining efficiency.

[0041] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for alternating mining of closely spaced coal seam working faces with staggered arrangement and partial backfilling, characterized in that... It includes the following steps: A. Design the relative spatial position of the upper and lower coal seam working faces as a staggered layout. The machine-gangue roadway and return airway are respectively arranged in the upper and lower coal seam working faces. Within the range of M along the dip length of the working face between the machine-gangue roadway of the working face and the centerline of the working face, post-fill hydraulic supports are arranged; M is 1 / 2 of the working face length. B. First, the upper coal seam working face is mined and filled immediately. After the advancing distance reaches the set stagger distance L, its mining and filling operations are suspended, and then the mining operation of the lower coal seam working face is immediately started. C. The lower coal seam working face conducts the mining work of one operation cycle unit, and the total advancing distance is S; within this operation cycle unit, the paste filling of the mined and to-be-filled area of the upper coal seam working face is carried out synchronously. D. The upper coal seam working face conducts the mining work of one operation cycle unit, and the total advancing distance is S; within this operation cycle unit, the paste filling of the mined and to-be-filled area of the lower coal seam working face is carried out synchronously. E. Repeat steps C and D to form a cyclic operation mode in which mining and filling are alternately carried out between the upper and lower coal seam working faces until the entire coal seam is mined.

2. The method for alternating and partially backfilling mining of closely spaced coal seam working faces according to claim 1, characterized in that: In step A, the staggered layout means that in the vertical projection direction, the centerline of the upper coal seam working face coincides with the centerline of the lower coal seam sectional coal pillar; correspondingly, the centerline of the lower coal seam working face also coincides with the centerline of the upper coal seam sectional coal pillar; the width of the reserved sectional coal pillar is 0 - 10m, and when the width of the reserved sectional coal pillar is 0m, it is a non-coal pillar roadway reuse layout, that is, within the same coal seam, the machine-gangue roadway of the current working face is reserved and used as the return airway of the next adjacent working face, and the sectional coal pillar between adjacent working faces within the same coal seam is cancelled.

3. The method for alternating and partially backfilling mining of closely spaced coal seam working faces according to claim 1, characterized in that: In step B, the stagger distance L should meet any of the following conditions: ① When the length L2 of the fully depressurized area formed by the mining of the upper coal seam > L1 + S, the stagger distance L should meet: L1 + S < L < L2; ② When affected by geological or mining conditions, the mining height of the upper coal seam is small, the extraction rate is low, the roof lithology is weak, or there are geological structure influence conditions, and the length L2 of the fully depressurized area formed by the mining of the upper coal seam < L1 + S, the stagger distance L should meet: L > L1 + S; Among them, L1 is the length of the significantly affected area of the advanced abutment pressure in front of the lower coal seam working face; S is the total advancing distance of one operation cycle unit; L2 is the length of the fully depressurized area formed behind the goaf after the mining of the upper coal seam; the L1 and L2 are determined by on-site measurement, engineering analogy or numerical simulation calculation.

4. The method for alternating and partially backfilling mining of closely spaced coal seam working faces according to claim 1, characterized in that: In steps C and D, the duration of the operation cycle unit corresponds to an integer multiple of the mine production shift system, ensuring that the filling paste reaches a safety strength not lower than 1MPa at the end of the cycle unit.

5. The method for alternating and partially backfilling mining of closely spaced coal seam working faces according to claim 4, characterized in that: The duration of the operation cycle unit is 16 hours, 12 hours or 8 hours, corresponding to two consecutive shifts of the three-shift-eight-hour work system, two consecutive shifts of the four-shift-six-hour work system or one full shift of the three-shift-eight-hour work system respectively.

6. The method for alternating and partially backfilling mining of closely spaced coal seam working faces according to claim 1, characterized in that: In steps C and D, the total advancing distance S is calculated as follows: S = n × h; where n is the number of times the coal mining machine completes coal cutting along the entire length of the working face within one work cycle unit, ranging from 3 to 8 cuts; h is the cutting depth of the coal mining machine, ranging from 0.6 to 0.8 m; and the total advancing distance S ranges from 1.8 to 6.4 m.

7. The method for alternating and partially backfilling mining of closely spaced coal seam working faces according to claim 1, characterized in that: In steps C and D, the area to be filled is a rectangular area located behind the hydraulic support for filling the frame, with a length of M along the working surface and a width of S along the advancing direction.

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