A top cutting and filling mining method with high recovery rate of large roadway protective coal pillar

Abstract

The application discloses a top-cutting and filling mining method with high recovery rate of a large-roadway protective coal pillar and belongs to the field of coal mine filling mining. The filling mining process is adopted to mine to the original stop-mining line, the width of the protective coal pillar is reduced to determine the optimized stop-mining line position and a top-cutting roadway is excavated, and the protective coal pillar is reserved between the top-cutting roadway and the large roadway; a plurality of top-cutting holes are constructed in the top-cutting roadway, the top-cutting holes are connected to form a top-cutting surface by directional blasting or hydraulic fracturing, and the stress transmission between the overburden above the top-cutting roadway and the overburden above the large roadway is disconnected; after the top-cutting roadway is filled, the protective coal pillar between the top-cutting roadway and the filling mining working face is filled and recovered. The stress transmission path is blocked by the top-cutting surface, the overburden is supported in cooperation with the filling body, the recovery rate of the large-roadway protective coal pillar is greatly improved, and the long-term stability of the large-roadway surrounding rock is ensured.

Description

Technical Field

[0001] This invention belongs to the field of coal mine backfilling mining technology, specifically relating to a roof cutting and backfilling mining method with high recovery rate of main roadway protective coal pillars. Background Technology

[0002] In underground coal mining, main roadways (such as main haulage roadways and return air roadways) are long-term engineering projects serving the entire mine or the entire mining level. To ensure that the main roadways are not damaged by mining during their service life, regardless of whether traditional caving mining or backfilling mining methods are used, a certain width of protective coal pillar must be left when the working face advances to the vicinity of the main roadway. The amount of coal pressed down by this protective coal pillar is often quite large, accounting for 5% to 15% of the mine's recoverable reserves in some mines; as the burial depth increases and the mining intensity increases, the size of the protective coal pillar tends to increase, resulting in a large amount of high-quality coal resources being accumulated for a long time or even eventually abandoned, causing serious resource waste.

[0003] Even though some mines use backfilling mining technology to control overburden movement, the rock strata above the backfill may still slowly flex and stress transfer due to factors such as the compression deformation of the backfill material after being stressed, untimely or incomplete filling, etc. This means that a large protective coal pillar still needs to be retained between the main roadway and the backfilling mining face, which cannot fundamentally solve the contradiction between coal pillar retention and resource recovery.

[0004] The fundamental purpose of leaving protective coal pillars in the main roadway is to isolate the impact of violent overburden movement and stress transfer in the goaf on the main roadway, and to prevent the surrounding rock of the main roadway from being in a high-stress state. As the fully mechanized or backfilling face gradually advances towards the main roadway, the damage range of the overburden above the goaf and the peak value of the lateral support pressure continuously shift towards the main roadway, and the stress level of the overburden above the main roadway increases significantly. When the width of the protective coal pillar is insufficient or the stress control effect is poor, the excessively high concentrated stress above the main roadway will directly cause severe deformation and instability of the surrounding rock of the roadway, typically manifested as severe roof subsidence, floor heave, large deformation of the sidewalls, and even impact failure. The existing support system cannot withstand it, and the roadway is forced to undergo multiple repairs or even be scrapped.

[0005] In the prior art, for example, Chinese patent application CN108518222A discloses a method for re-mining coal pillars along the stop-mining line of extra-thick coal seams using paste filling combined with roof pre-splitting. This method involves performing deep-hole pre-splitting blasting on the roof of the extra-thick coal seam to destroy the pressure arch structure above the goaf and the stop-mining line coal pillar, and then using paste filling to fill the stop-mining line coal pillar. However, this method destroys the pressure arch structure at the original stop-mining line location through pre-splitting blasting, without involving the technical concept of excavating a dedicated roof-cutting roadway and forming a roof-cutting face at the optimized stop-mining line location. The purpose of the pre-splitting blasting is to reduce the exposed area of ​​the roof and the pressure intensity, rather than to block the stress transmission path between the overburden above the main roadway and the overburden above the filling working face.

[0006] For example, Chinese patent CN106930763B discloses a method for filling the protective coal pillars in the residual mining area of ​​extra-thick coal seams. This method involves filling a closed area with paste at the rear of the goaf when the working face advances to the protective coal pillar. This method does not involve the technical means of excavating a roof-cutting roadway within the protective coal pillar and cutting off the stress transmission path through the roof-cutting face.

[0007] Therefore, there is an urgent need for a mining method that can significantly improve the recovery rate of the protective coal pillars in the main roadway and ensure the long-term safety of the main roadway through the pressure relief mechanism. Summary of the Invention

[0008] To overcome the shortcomings of existing technologies, this invention provides a method for roof cutting and backfilling mining with high recovery rate of protective coal pillars in main roadways.

[0009] The technical solution adopted by this invention to solve its technical problem is:

[0010] A method for high-recovery-rate roof-cutting and backfilling mining with protective coal pillars in main roadways includes the following steps:

[0011] S1. Backfill mining is carried out on coal resources outside the stop line of the main roadway protection coal pillar until the backfill mining face advances to the original stop line and the backfilling work of the last backfill branch roadway is completed.

[0012] S2. Reduce the width of the main roadway protective coal pillar to determine the optimized stop line position, and excavate the top-cutting roadway at the optimized stop line position. The optimized stop line position is located between the original stop line and the main roadway. The protective coal pillar is retained between the top-cutting roadway and the main roadway.

[0013] S3. In the top-cutting tunnel, multiple top-cutting holes are constructed from the top plate of the top-cutting tunnel to the overburden layer. The top-cutting holes are arranged at intervals along the dip direction of the top-cutting tunnel. The top-cutting holes are treated by directional blasting or hydraulic fracturing to make the top-cutting holes interconnected to form a top-cutting surface. The top-cutting surface disconnects the overburden layer above the top-cutting tunnel from the overburden layer above the main tunnel.

[0014] S4. Fill the cut-off tunnel;

[0015] S5. The protective coal pillar between the top cutting roadway and the original stop mining line is backfilled and recovered.

[0016] Preferably, in steps S1 and S5, the backfilling mining process is a fully mechanized unit compaction backfilling process, including: dividing the coal resources to be recovered into several standard blocks, and sequentially carrying out tunneling branch roadway operations, isolation branch roadway operations, and backfilling branch roadway operations for each standard block; in the backfilling branch roadway operations, the paste backfill material is prepared by adding cementitious material, fine powder, additives, and water, with coal gangue as aggregate, the mass concentration of the paste backfill material being 70.0%~80.0%, the coal gangue content being 1000kg / m3~1300kg / m3, the maximum particle size being 8mm~15mm, and the content of coal gangue with a particle size less than 0.08mm being greater than or equal to 15%.

[0017] Preferably, in step S2, the optimized stop line location is determined comprehensively based on the mine geological conditions, the surrounding rock conditions of the main roadway, and the conditions of the backfilling mining face, and the protective coal pillar retained between the top-cutting roadway and the main roadway can form a cooperative bearing with the subsequent backfill body; the width of the protective coal pillar retained between the top-cutting roadway and the main roadway is smaller than the original width of the main roadway protective coal pillar, specifically 15~50m; the cross-sectional width of the top-cutting roadway is 3~6m, the cross-sectional height is the same as the coal seam thickness, and the length of the top-cutting roadway is the same as the dip length of the backfilling mining face.

[0018] Preferably, in step S3, the depth of the top-cutting holes is determined according to the situation of the direct top and the basic top. The top-cutting holes penetrate the direct top and have a depth of 6.0m to 15.0m. When using directional blasting, the spacing between the top-cutting holes is 0.3m to 1.5m, and the diameter of the top-cutting holes is 42mm to 50mm. When using hydraulic fracturing, the spacing between the top-cutting holes is 6m to 12m, and the diameter of the top-cutting holes is 80mm to 150mm. The arrangement direction of the top-cutting holes is vertically upward or at an angle of 5° to 30° with the vertical direction.

[0019] Preferably, in step S3, the directional blasting process includes: filling each of the top-cutting holes with explosives, using double detonators and double detonating cords for detonation, and setting transverse guide holes in the top-cutting holes along the direction of the top-cutting tunnel to guide the blasting connection between each top-cutting hole through the transverse guide holes.

[0020] Preferably, in step S3, the hydraulic fracturing process includes: injecting high-pressure water into each of the top-cutting holes, setting transverse guide holes in each of the top-cutting holes along the direction of the top-cutting tunnel, and guiding the hydraulic fractures between the top-cutting holes to connect through the transverse guide holes.

[0021] Preferably, in step S4, before filling the top-cutting tunnel, isolation walls are constructed at both ends of the top-cutting tunnel to form a closed space. Then, filling material is pumped into the closed space for filling. The isolation walls are constructed using masonry blocks and cement mortar, or modular isolation devices are used.

[0022] Preferably, in step S5, after the protective coal pillar between the top-cutting roadway and the original stop-mining line is backfilled and recovered using the backfilling mining process, a backfill body is formed in the goaf. The backfill body and the backfill body of the top-cutting roadway in step S4 jointly support the overburden strata.

[0023] Preferably, in step S2, the excavation of the top-cutting tunnel is carried out simultaneously with the filling work of the last filling branch tunnel in step S1, or after step S1 is completed.

[0024] Preferably, the top-cutting surface formed in step S3 is a continuous fracture surface extending along the direction of the top-cutting lane.

[0025] Beneficial effects:

[0026] 1. This invention involves excavating a dedicated top-cutting roadway at the optimized stop line of the main roadway's protective coal pillar, and forming a top-cutting surface through directional blasting or hydraulic fracturing, completely separating the overburden layer directly above the top-cutting roadway from the overburden layer above the main roadway. This mechanism fundamentally cuts off the path of high stress transmission from the overburden layer on the backfilling mining face to the main roadway, effectively preventing the main roadway from being in a high-stress state for a long time and fundamentally ensuring the stability of the surrounding rock of the main roadway. Existing pre-splitting blasting mainly aims to reduce the exposed roof area, but does not fundamentally cut off the stress transmission path. This invention, by forming a continuous fracture surface extending along the dip direction of the top-cutting roadway, fundamentally cuts off stress transmission, achieving a more thorough stress-blocking effect.

[0027] 2. This invention significantly improves the recovery rate of the main roadway protection pillar: Due to the stress-blocking effect of the roof cutting face, the overlying strata above the main roadway are no longer affected by the mining stress of the backfilling mining face, thus significantly reducing the width of the main roadway protection pillar. The optimized width of the main roadway protection pillar (the pillar between the roof cutting roadway and the main roadway) can be greatly reduced, while the main roadway protection pillar between the roof cutting roadway and the original stop line can be fully recovered through backfilling mining.

[0028] 3. The backfill material in the cut-off roadway and the backfill material formed after the recovery of the protective coal pillar, together constitute a support system for the overburden. During the initial slow subsidence of the roof, the backfill material can effectively support it and prevent large-scale rotation and subsidence of the roof. The cut-off surface continuously plays a stress-isolation role. The two work together to ensure the long-term safety of the main roadway.

[0029] 4. This invention does not require the addition of large-scale mining equipment. Existing roadway excavation can be carried out using the mine's main tunneling machine, conventional rock drilling equipment can be used for roof cutting, and existing mine filling systems can be used for backfilling. The entire method has clear process steps, is easy to operate, has low input costs, and significant economic benefits. Attached Figure Description

[0030] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0031] Figure 1 A schematic diagram of the rock strata structure relative to the original stop line and the main roadway during coal mine backfilling mining;

[0032] Figure 2 This is a forward schematic diagram of the rock strata structure relative to the top cut roadway layout and the main roadway protective coal pillar in an embodiment of the present invention;

[0033] Figure 3 This is a lateral schematic diagram of the rock strata structure relative to the top cut roadway layout and the main roadway protective coal pillar in an embodiment of the present invention;

[0034] Figure 4 This is a diagram showing the rock strata structure and stress distribution after the main roadway protective coal pillar is recovered using the top-cutting and backfilling mining method of this invention.

[0035] The meanings of the markings in the diagram are as follows:

[0036] 1. Top-cutting roadway; 2. Existing permanent protection main roadway in the coal mine; 3. Main roadway protection coal pillar; 4. Top-cutting face; 5. Backfill body; 6. Overburden layer; 7. Original stop line; 8. Top-cutting hole; 9. Isolation wall of integrated mechanized unit compacted backfilling process; I. Stress change zone in front of the working face; II. Initial roof control zone of the backfilling working face; III. Compacted zone of the backfilling working face; A. Original rock stress zone; B. Stress influence zone of the main roadway; C. Stress growth zone; D. Stress stability zone. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0038] Example 1:

[0039] like Figures 1-4 As shown in the figure, this embodiment provides a method for roof cutting and backfilling mining with high recovery rate of main roadway protective coal pillars.

[0040] The coal mine employs a fully mechanized unit compaction filling process for mining, and the permanent main roadway 2 (including the main haulage roadway and return air roadway) needs to remain stable over a long period. In the original mining design of this embodiment, due to the large burial depth of the coal seam, high ground stress, and the large impact range of the fully mechanized mining process, the original stop line 7 was 180m away from main roadway 2, resulting in a huge amount of coal pressure on the protective coal pillar.

[0041] The method described in this embodiment is used to recover the protective coal pillar in the main roadway. The specific implementation is as follows:

[0042] Step 1: Fill in and mine the coal resources outside the original cessation of mining.

[0043] The backfilling mining process in this embodiment is a fully mechanized unit compaction backfilling process well known to those skilled in the art, including: dividing the coal resources to be recovered into several standard blocks, and performing tunneling branch roadway operations, isolation branch roadway operations, and backfilling branch roadway operations in each standard block in sequence; in the backfilling branch roadway operation, the backfilling material is an existing material well known to those skilled in the art, which is made by adding cementitious material and water to coal gangue as aggregate.

[0044] The coal resources outside the original cessation line 7 were mined using a fully mechanized unit compaction backfilling process. The fully mechanized unit compaction backfilling mining unit was arranged in a "U" shape, and the coal resources to be recovered were divided into several standard blocks according to the design dimensions.

[0045] The main operating procedures include: First, using a roadheader to recover coal resources from each branch roadway (excavating branch roadway); after the coal resources are recovered, immediately using a fully mechanized unit compaction filling process well-known to those skilled in the art to seal the outlets at both ends of the branch roadway with an isolation wall 9, to facilitate filling and seal air leakage (isolation branch roadway); after isolation is completed and the corresponding conditions are met, filling material is pumped into its interior for compaction filling (filling branch roadway). The filling material is an existing material well-known to those skilled in the art, and is made in an existing manner. The filling material is mainly composed of coal gangue (approximately 60%~70% by mass), with the addition of appropriate amounts of fly ash (approximately 8%~15% by mass), binder (cement, approximately 10%~15% by mass), admixtures (approximately 0.5%~1.5% by mass), and water (approximately 20%~25% by mass). After mixing and proportioning above ground and transportation via underground pipelines, the filling material is pumped to the filling branch roadway through the above-ground and underground pipelines. After solidification, the filling material has a certain strength (uniaxial compressive strength ≥3MPa) and can effectively support the roof.

[0046] In this embodiment, the admixture is a water-reducing agent, and the specific proportions of the paste filling material are: 1200 kg / m³ of coal gangue, 1200 kg / m³ of fly ash, 200 kg / m³ of cement, 10 kg / m³ of water-reducing agent, and 420 kg / m³ of water, with a mass concentration of 79%. Under this proportion, the 28-day uniaxial compressive strength of the filling body can meet the requirements of the roof support.

[0047] The backfilling mining face continued to advance until it reached the original stop line 7 and the backfilling work of the last branch roadway was completed.

[0048] like Figure 1 and Figure 4 As shown, the original main roadway protective coal pillar is retained on one side of main roadway 2, and the original stop-mining line 7 is located at a certain distance outside main roadway 2. The backfilling mining face adopts a fully mechanized unit compaction backfilling process, advancing from the side away from main roadway 2 towards the original stop-mining line 7. The structure of the overburden stratum 6 is also shown in the figure, including the immediate roof, the main roof, and other strata. The area outside the original stop-mining line 7 is the area that has been mined and backfilled, while the area inside the original stop-mining line 7 is the main roadway protective coal pillar area, which was not mined in the original design. From the stress distribution perspective, as the backfilling mining face gradually advances to the original stop-mining line 7, a stress change zone I is formed in front of the working face, and the stress state of the overburden above main roadway 2 has not yet been significantly affected. The area outside the original stop line 7 is the area that has been mined and filled. The end closest to the working face is the initial control zone II of the filling working face, where the filling material has not yet fully borne the load. The area far from the working face is the compaction zone III of the filling working face, where the filling material has been compacted by the overlying strata and has fully played its load-bearing role.

[0049] Step 2: Reduce the width of the main roadway protective coal pillar to determine the optimized stop line position, and excavate the top cutting roadway 1 at this position. The optimized stop line position is located between the original stop line and the main roadway, and the protective coal pillar is retained between the top cutting roadway and the main roadway.

[0050] The optimized stop line location is determined comprehensively based on the mine's geological conditions, the surrounding rock conditions of the main roadway, and the conditions of the backfilling mining face. This ensures that the protective coal pillar retained between the top-cutting roadway and the main roadway can form a co-supporting structure with the subsequent backfill. The width of the protective coal pillar retained between the top-cutting roadway and the main roadway is smaller than the original main roadway protective coal pillar width, specifically 15m to 50m. The cross-sectional width of the top-cutting roadway is 3m to 6m, the cross-sectional height is the same as the coal seam thickness, and the length of the top-cutting roadway is the same as the dip length of the backfilling mining face.

[0051] The phrase "able to form a synergistic bearing capacity with the subsequent backfill" refers to the following: when determining the optimized stop-mining line location, a synergistic bearing capacity model of "backfill-coal pillar-overburden" is established through numerical simulation (such as using FLACD or similar geotechnical engineering numerical analysis software). The stress distribution and deformation characteristics of the coal pillar and backfill under different protective coal pillar widths are calculated so that the selected protective coal pillar width can meet the following conditions: after backfilling mining is completed, the protective coal pillar and backfill undergo coordinated deformation under the load of the overburden strata, and the stress levels of both are within their respective long-term bearing capacity ranges, avoiding the premature instability of either structure due to the mismatch of their bearing capacities.

[0052] Those skilled in the art can determine whether a protective coal pillar can form a cooperative load-bearing structure with the backfill body through the following methods:

[0053] (1) Numerical simulation method: A three-dimensional numerical model of “filling body-coal pillar-overburden” is established using methods familiar to those skilled in the art. The elastic modulus of the filling body (usually 1 GPa ~ 5 GPa), Poisson's ratio (usually 0.2 ~ 0.3) and the mechanical parameters of the coal pillar are set. By simulating the stress-strain response of the two under different coal pillar widths, when the timing and location of the stress peaks of the two meet the conditions for coordinated deformation, it can be considered that coordinated bearing can be formed.

[0054] (2) Empirical formula method: Calculate the bearing capacity of coal pillars of different widths according to the coal pillar strength formula (such as the Bieniawski formula), and determine the bearing capacity of the filling body according to the filling body strength test known to those skilled in the art. When the ratio of the bearing capacity of the two is in a reasonable range (usually 0.8~1.2), it can be considered that a synergistic bearing can be formed.

[0055] Based on the mine's geological conditions (the immediate roof is siltstone, with a thickness of 8m to 12m and a uniaxial compressive strength of 45 MPa to 60 MPa), the surrounding rock conditions of the main roadway, and the conditions of the backfilling mining face, the optimized location of the main roadway protection coal pillar stop line was determined.

[0056] Based on comprehensive analysis, the optimized stop line location was determined to be 50m away from main roadway 2, meaning the width of the protective coal pillar 3 in the main roadway between top cutting roadway 1 and main roadway 2 is 50m. The distance between top cutting roadway 1 and the original stop line 7 is 130m.

[0057] A tunneling machine was used to excavate the top-cutting roadway 1 at the optimized stop-mining line location. The cross-sectional width of the top-cutting roadway 1 is 4.5m, the cross-sectional height is the same as the coal seam thickness (in this embodiment, the coal seam thickness is 5m), and the length of the top-cutting roadway 1 is the same as the dip length of the backfilling mining face (in this embodiment, it is 150m).

[0058] The excavation of the top cutting tunnel 1 is carried out simultaneously with the filling work of the last filling branch tunnel in step one, so as to improve the overall mining efficiency.

[0059] like Figures 2-3As shown, a top-cutting roadway 1 is excavated at the optimized stop-mining line location determined after reducing the width of the main roadway's protective coal pillar. Top-cutting roadway 1 is located between the original stop-mining line 7 and the main roadway 2. Between top-cutting roadway 1 and the main roadway 2 is the optimized retained protective coal pillar 3, whose width is smaller than the original main roadway's protective coal pillar. Within top-cutting roadway 1, multiple top-cutting holes 8 are constructed from the roof of top-cutting roadway 1 towards the overburden stratum 6. The top-cutting holes 8 are spaced apart along the dip direction of top-cutting roadway 1, and their arrangement direction is either vertically upward or at a certain angle to the vertical direction. After processing each top-cutting hole 8 using directional blasting or hydraulic fracturing techniques, the top-cutting holes 8 are interconnected to form a top-cutting surface 4. The top-cutting surface 4 disconnects the overburden stratum above top-cutting roadway 1 from the overburden stratum above main roadway 2, thereby blocking the stress transfer path between the two. The figure also shows the location of the isolation wall 9 for the compacted filling process of the integrated mechanized unit. The isolation wall 9 is set at both ends of the top cutting lane 1 to close the top cutting lane 1 and form a closed space for filling.

[0060] Step 3: Construct the top-cutting hole 8 in the top-cutting tunnel 1 and form the top-cutting surface 4.

[0061] Within the top-cutting tunnel 1, top-cutting holes 8 are constructed from the roof of the tunnel 1 directly upwards into the overlying strata. The top-cutting holes 8 are evenly spaced along the dip direction of the tunnel 1, with a spacing of 0.6m. The depth of the top-cutting holes 8 is 12.5m (in this embodiment, the direct roof thickness is approximately 10m, the mining height is 5m, and the coefficient of fragmentation is taken as 1.4). The diameter of the top-cutting holes 8 is 50mm. The arrangement direction of the top-cutting holes 8 is vertically upwards.

[0062] A total of 250 top-cutting holes (150m ÷ 0.6m = 250 holes) were constructed. Directional fracture blasting was used to treat each top-cutting hole 8. Explosives were loaded into each top-cutting hole 8, with a charge coefficient of 0.7 and a stemming coefficient of 0.3. Double detonators and double detonating cords were used for detonation. Two detonating cords extended to the bottom of the top-cutting hole 8, with each detonating cord using one detonator, and the two detonators connected in parallel. Lateral guide holes were installed in each top-cutting hole 8 along the dip direction of the top-cutting tunnel 1 to guide the blasting connection between the top-cutting holes 8.

[0063] The transverse guide hole in this embodiment is a commonly used guide structure in the art. It cooperates with the top-cutting hole 8 to form a directional fracturing system. During blasting, the transverse guide hole can utilize the stress concentration effect of its hole wall to guide the blasting cracks to preferentially expand along the dip direction of the top-cutting tunnel 1, thereby ensuring effective communication between each top-cutting hole 8 along the dip direction.

[0064] After the blasting, the cutting holes 8 are interconnected along the dip direction, forming a continuous cutting surface 4. The cutting surface 4 completely separates the overburden layer 6 directly above the cutting tunnel 1 from the overburden layer 6 above the main tunnel 2.

[0065] After the top cutting is completed, those skilled in the art can use detection methods well known in the art to verify the penetration effect of the top cutting surface. For example, a borehole inspection instrument can be used to observe through a preset observation hole, or the formation effect of the top cutting surface can be indirectly judged by monitoring the water level changes and gas emission changes of the boreholes on both sides of the top cutting tunnel. When the penetration rate between each top cutting hole reaches more than 80%, the top cutting surface can be considered to have been effectively formed.

[0066] Step 4: Fill the top cut tunnel 1.

[0067] After the top cutting surface 4 is completed, integrated mechanized unit compaction filling process isolation walls 9 are constructed at both ends of the top cutting tunnel 1. The integrated mechanized unit compaction filling process isolation walls 9 are constructed using masonry blocks and cement mortar, with a thickness of not less than 0.6m. The integrated mechanized unit compaction filling process isolation walls 9 create a closed space in the top cutting tunnel 1.

[0068] After isolation is completed, filling material is pumped into the sealed space of the top cut roadway 1 for filling. The filling material is the same as in step one, made primarily of coal gangue, with the addition of binder and water. After the filling material solidifies, it forms filling body 5.

[0069] Step 5: Mining the protective coal pillar in the main roadway between the top cutting roadway 1 and the original stop line 7.

[0070] Using the same integrated mechanized unit compaction filling process as in step one, the protective coal pillar (130m wide) between the top-cutting roadway 1 and the original stop line 7 is mined. After the mining is completed, a filling body 5 is formed in the goaf of this area. This filling body 5, together with the filling body 5 of the top-cutting roadway 1 in step four, supports the overburden stratum 6.

[0071] like Figure 4 As shown, after all mining and backfilling work is completed, the top-cutting roadway 1 has been filled and compacted by the backfill body 5. The protective coal pillar between the top-cutting roadway 1 and the original stop line 7 has also been fully recovered through backfilling mining, forming the backfill body 5 in the goaf. The backfill body of the top-cutting roadway 1 and the backfill body in the protected coal pillar recovery area together constitute the support system for the overburden stratum 6. The top-cutting face 4 continuously plays a stress-isolating role, keeping the overburden stratum 6 above the main roadway 2 disconnected from the overburden stratum 6 inside the top-cutting roadway 1 (away from the main roadway). From the stress distribution perspective, the area above the main roadway 2 is in the original rock stress zone A, and there is only a small area of ​​main roadway stress influence zone B near the main roadway 2. The stress above the backfilling mining face is mainly concentrated in the stress growth zone C and the stress stability zone D, and cannot be transmitted to the area above the main roadway 2 through the top-cutting face 4. Due to the blocking effect of the top cutting surface 4 and the supporting effect of the filling body 5, the main roadway 2 is always in a low stress state, the surrounding rock remains stable for a long time, and the recovery rate of the main roadway protective coal pillar is greatly improved.

[0072] Figure 4 In this embodiment, γH represents the self-weight stress of the overlying strata, k is the lateral support stress concentration factor, and kγH is the peak concentrated stress at the edge of the coal pillar. This embodiment cuts off the stress transmission by continuously cutting the top surface 4, so that only the self-weight stress γH of the overlying strata exists around the main roadway 2, thus eliminating the damage of the peak concentrated stress kγH at the edge of the coal pillar to the surrounding rock of the main roadway.

[0073] Implementation results:

[0074] Using the method of this embodiment, in the original main roadway protection coal pillar (180m wide), only the 50m coal pillar between the top cutting roadway 1 and the main roadway 2 is retained as the optimized main roadway protection coal pillar 3, while the remaining 130m wide main roadway protection coal pillars are all recovered. The recovery rate of the main roadway protection coal pillars reaches 130m / 180m≈72.2%.

[0075] Due to the stress blocking effect of the top cutting surface 4, the stress of the overlying strata on the filling mining face cannot be transmitted to the top of the main roadway 2, and the surrounding rock of the main roadway 2 remains stable for a long time.

[0076] Example 2:

[0077] The difference between this embodiment and embodiment 1 is that in step three, the hydraulic fracturing process, which is well known to those skilled in the art, is used instead of the directional blasting process to form the top cut surface 4.

[0078] Cutting holes 8 are constructed within the cutting tunnel 1, with a spacing of 8m between them. The cutting depth is the same as the blasting cutting depth, and the diameter is 100mm. Transverse guide holes are installed within each cutting hole 8 along the dip direction of the cutting tunnel 1.

[0079] High-pressure water (35 MPa ~ 45 MPa) was injected into each cut-top hole 8 using hydraulic fracturing equipment. The hydraulic fractures between the cut-top holes 8 were guided through transverse guide holes. The fracturing time for each cut-top hole 8 was 20 minutes. After fracturing, a continuous cut-top surface 4 was formed between the cut-top holes 8.

[0080] Compared to directional blasting, hydraulic fracturing has the advantages of being flameless, vibration-free, and safer, making it particularly suitable for high-gas mines or vibration-sensitive areas.

[0081] The remaining steps are the same as in Example 1, and will not be repeated here.

[0082] Methods for determining the cutting parameters:

[0083] In practical applications, the spacing, depth, and angle of the top-cutting holes 8 need to be designed according to the specific roof conditions of the mine. The following provides the methods for determining each parameter:

[0084] (1) Determination of the cutting depth H;

[0085] The cutting depth H should penetrate the immediate roof. It should be noted that theoretical calculations are only one method for determining the cutting depth; the actual implementation effect needs to be determined through a combination of test blasts and endoscopic measurements at the downhole working face. The formula for calculating the cutting depth is as follows:

[0086] (1);

[0087] (2);

[0088] Among them, h m h1 is the mining height (m), h1 is the cutting height (m), which is the thickness of the direct roof rock layer to be cut, H is the cutting hole depth (m), K is the fragmentation coefficient, and α is the cutting hole angle, which is the angle between the cutting hole and the vertical direction.

[0089] (2) Determining the spacing of the top-cutting holes;

[0090] The spacing of the top-cutting holes should be determined according to the top-cutting process used. When using directional blasting, the spacing of the top-cutting holes is usually 0.3m to 1.5m, preferably 0.4m to 1.0m; when using hydraulic fracturing, the spacing of the top-cutting holes is usually 6m to 12m, preferably 8m to 10m.

[0091] The spacing between the top holes should also meet the following condition: S1 ≤ 2 × R;

[0092] Where S1 is the spacing between the top-cutting holes; R is the effective radius of a single top-cutting hole, which can be determined through field tests or numerical simulations.

[0093] (3) Determination of the top hole angle α;

[0094] The top-cutting hole 8 can be arranged vertically upward (α=0°) or at a certain angle to the vertical direction (α=5°~30°). When the top rock strata are horizontal or nearly horizontal, it is preferable to arrange it vertically upward; when the top rock strata have a significant dip angle, the top-cutting hole should be arranged perpendicular to the rock strata bedding plane to ensure that the top-cutting surface is orthogonal or nearly orthogonal to the rock strata bedding plane, so as to obtain the best top-cutting effect.

[0095] (4) Determination of the diameter d of the top hole;

[0096] The diameter d of the top-cutting hole should be determined according to the top-cutting process. When using directional blasting, d is usually 42mm~50mm, which needs to be determined according to the blasting top-cutting process and equipment; when using hydraulic fracturing, d is usually 80mm~150mm, preferably 100mm~120mm.

[0097] Regarding the cross-sectional dimensions of the top-cutting roadway 1, the present invention is not limited to the specific values ​​listed in the above embodiments. In practical applications, the cross-sectional width of the top-cutting roadway 1 should meet the space requirements for top-cutting operations, typically 3~6m; the cross-sectional height is the same as the coal seam thickness, and the height of the top-cutting roadway is adjusted accordingly when the coal seam thickness changes.

[0098] Regarding the backfill material, this invention is not limited to the specific proportions listed in the above embodiments. In practical applications, those skilled in the art can determine the proportions of the backfill material based on the specific conditions of the mine (such as the source of gangue, the type of binder, strength requirements, etc.). The general principle is to maximize the utilization rate of solid waste such as gangue and reduce costs while meeting strength requirements.

[0099] For the integrated mechanized unit compaction filling process isolation wall 9 at both ends of the cut-off tunnel, this invention is not limited to the method of construction using masonry blocks and cement mortar. In practical applications, modular isolation devices, concrete pouring, and other methods can also be used for isolation, as long as a sealed space can be formed.

[0100] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications and equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for high-recovery-rate roof-cutting and backfilling mining of main roadway protective coal pillars, characterized in that, Includes the following steps: S1. Backfill mining is carried out on coal resources outside the stop line of the main roadway protection coal pillar until the backfill mining face advances to the original stop line and the backfilling work of the last backfill branch roadway is completed. S2. Reduce the width of the main roadway protective coal pillar to determine the optimized stop line position, and excavate the top-cutting roadway at the optimized stop line position. The optimized stop line position is located between the original stop line and the main roadway. The protective coal pillar is retained between the top-cutting roadway and the main roadway. S3. In the top-cutting tunnel, multiple top-cutting holes are constructed from the top plate of the top-cutting tunnel to the overburden layer. The top-cutting holes are arranged at intervals along the dip direction of the top-cutting tunnel. The top-cutting holes are treated by directional blasting or hydraulic fracturing to make the top-cutting holes interconnected to form a top-cutting surface. The top-cutting surface disconnects the overburden layer above the top-cutting tunnel from the overburden layer above the main tunnel. S4. Fill the cut-off tunnel; S5. The protective coal pillar between the cut-off roadway and the original stop-mining line is backfilled and mined back; In step S2, the optimized stop line location is determined comprehensively based on the mine geological conditions, the surrounding rock conditions of the main roadway, and the conditions of the backfilling mining face, and the protective coal pillar retained between the top-cutting roadway and the main roadway can form a cooperative bearing with the subsequent backfill body; the width of the protective coal pillar retained between the top-cutting roadway and the main roadway is smaller than the original width of the main roadway protective coal pillar, specifically 15~50m; the cross-sectional width of the top-cutting roadway is 3~6m, the cross-sectional height is the same as the coal seam thickness, and the length of the top-cutting roadway is the same as the dip length of the backfilling mining face.

2. The method for high recovery rate roof cutting and backfilling mining of main roadway protective coal pillars according to claim 1, characterized in that, In steps S1 and S5, the backfilling mining process is a fully mechanized unit compaction backfilling process, including: dividing the coal resources to be recovered into several standard blocks, and sequentially performing tunneling, isolation, and backfilling operations on each standard block; in the backfilling operation, the paste backfill material is prepared by adding cementitious materials, fine powder, additives, and water, with coal gangue as aggregate, and the paste backfill material mass concentration being 70.0%~80.0% and the coal gangue content being 1000 kg / m³. 3 ~1300kg / m 3 The maximum particle size is 8mm~15mm, and the content of coal gangue with a particle size of less than 0.08mm is greater than or equal to 15%.

3. The method for high recovery rate roof cutting and backfilling mining with protective coal pillars in the main roadway according to claim 1, characterized in that, In step S3, the depth of the top-cutting holes is determined according to the situation of the direct roof and the basic roof. The top-cutting holes penetrate the direct roof and have a depth of 6.0m to 15.0m. When using directional blasting, the spacing between the top-cutting holes is 0.3m to 1.5m and the diameter of the top-cutting holes is 42mm to 50mm. When using hydraulic fracturing, the spacing between the top-cutting holes is 6m to 12m and the diameter of the top-cutting holes is 80mm to 150mm. The arrangement direction of the top-cutting holes is vertically upward or at an angle of 5° to 30° with the vertical direction.

4. The method for high recovery rate roof cutting and backfilling mining of main roadway protective coal pillars according to claim 1, characterized in that, In step S3, the directional blasting process includes: filling each of the top-cutting holes with explosives, using double detonators and double detonating cords for detonation, setting transverse guide holes in the top-cutting holes along the dipping direction of the top-cutting tunnel, and guiding the blasting connection between each top-cutting hole through the transverse guide holes.

5. The method for high recovery rate roof cutting and backfilling mining of main roadway protective coal pillars according to claim 1, characterized in that, In step S3, the hydraulic fracturing process includes: injecting high-pressure water into each of the top-cutting holes, setting transverse guide holes in each top-cutting hole along the direction of the top-cutting tunnel, and guiding the hydraulic fractures between the top-cutting holes to connect through the transverse guide holes.

6. The method for high recovery rate roof cutting and backfilling mining of main roadway protective coal pillars according to claim 1, characterized in that, In step S4, before filling the top cut tunnel, isolation walls are constructed at both ends of the top cut tunnel to form a closed space. Then, filling material is pumped into the closed space for filling. The isolation walls are constructed using masonry blocks and cement mortar, or modular isolation devices are used.

7. The method for high recovery rate roof cutting and backfilling mining with protective coal pillars in the main roadway according to claim 1, characterized in that, In step S5, after the protective coal pillar between the top-cutting roadway and the original stop-mining line is backfilled and recovered using the backfilling mining process, a backfill body is formed in the goaf. The backfill body and the backfill body in the top-cutting roadway in step S4 together support the overburden strata.

8. The method for high recovery rate roof cutting and backfilling mining of main roadway protective coal pillars according to claim 1, characterized in that, In step S2, the excavation of the top-cutting tunnel is carried out simultaneously with the filling work of the last filling branch tunnel in step S1, or after step S1 is completed.

9. The method for high recovery rate roof cutting and backfilling mining of main roadway protective coal pillars according to claim 1, characterized in that, The cut-top surface formed in step S3 is a continuous fracture surface extending along the dip direction of the cut-top tunnel.

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