Shallow deep coal seam short wall interval lag filling coal mining method

Abstract

The invention discloses a shallow deep coal seam short wall interval lag filling coal mining method, and belongs to the technical field of coal mine filling mining. The method comprises the following steps: determining the width of a short-wall coal face according to the initial pressure fracture distance of a key layer, and arranging a plurality of short-wall coal faces; adopting an interval jump mining mode, firstly mining a first sequence of short-wall working faces, and reserving a second sequence of working faces which are not mined between adjacent working faces as interval coal pillars; directional main holes and branch holes are constructed under the interval coal pillars, and under-pressure grouting filling is conducted on the mined-out area, so that a filling body is formed; and after the filling body reaches the designed supporting strength, the interval coal pillars are stoped, and the steps are repeated. Complete separation of coal mining and filling procedures is realized, procedure interference is avoided, the production efficiency is improved, the mining cost is reduced, the solid waste utilization rate reaches 80% or above, top plate sinking and ground surface subsidence are effectively controlled, and the method is particularly suitable for mining of three-under-pressure covering resources of a shallow-buried deep coal seam under the condition of a hard top plate.

Description

Technical Field

[0001] This invention relates to the field of coal mine backfilling mining, and in particular to a method for short-walled delayed backfilling mining of shallow-buried deep coal seams. Background Technology

[0002] With the continuous exploitation of coal resources, many coal mines face the dual dilemma of resource depletion and the difficulty of mining resources under "three-under" conditions (buildings, railways, and water bodies). Mining shallow-buried deep coal seams under these conditions requires achieving efficient resource recovery while ensuring the safety of surface facilities and the ecological environment. In response to the characteristics of shallow-buried deep coal seams—small overburden thickness, rapid surface subsidence response, and high control difficulty—various technical systems have been developed, among which continuous mining and backfilling technology and post-support paste backfilling technology are widely used. The basic principle of continuous mining and backfilling technology is to divide the working face into multiple parallel branch roadways and adopt a skip-step retreat mining sequence: first, the odd-numbered branch roadways (e.g., 1, 3, 5…) are mined, and immediately after completion, the goaf is backfilled with gangue, paste, or high-water materials; after the backfill material stabilizes and reaches a certain strength, the even-numbered branch roadways (e.g., 2, 4, 6…) are then mined again. This technology, through the "mining-backfilling alternation" method, achieves a certain degree of coordinated operation between coal mining and backfilling.

[0003] However, the continuous mining and filling process has the following problems in practical application: 1) Due to the alternation of mining and filling operations, the output of a single working face is limited, making it difficult to meet the production needs of high-yield and high-efficiency mines; 2) Coal mining and filling operations are carried out alternately in the same working face or adjacent working faces, resulting in serious process overlap and low production efficiency; 3) Due to the constraints of the mining and filling cycle and the deployment of the face, the efficiency of coal resource recovery is difficult to further improve.

[0004] The basic principle of the backfilling technology is to utilize the space behind the hydraulic supports of the fully mechanized mining face to inject paste materials with specific rheological properties into the goaf in a timely manner after coal mining progresses. This technology adopts a synchronous "mining-movement-filling" operation mode: after the coal mining machine completes coal cutting and the hydraulic supports move forward, the paste material is immediately transported to the goaf behind the supports through a filling system installed on the support shield beam.

[0005] However, the post-support paste filling process has the following problems in practical application: 1) High investment: It requires special modification of the hydraulic support and the addition of equipment such as filling sleeves and pipe dragging systems, which greatly increases the one-time investment; 2) Low efficiency: Coal mining and filling operations are carried out simultaneously, and the filling speed is limited by the coal mining speed. Moreover, the equipment maintenance is complicated and the overall efficiency is not high; 3) Complex process: The preparation, transportation and filling of paste materials need to be precisely controlled, which places high demands on equipment and management.

[0006] In summary, although continuous mining and filling technology and post-staple paste filling technology each have their own characteristics, they share the following common problems: 1) Severe interference between mining and backfilling processes: Neither process can completely separate coal mining and backfilling operations, and the overlap of processes leads to low production efficiency; 2) High investment costs: The continuous mining and filling process results in a high equipment idle rate due to the alternation of mining and filling, and the post-frame paste filling process requires modification of the hydraulic support, resulting in a large one-time investment; 3) Limited roof control effect: Existing technology is not capable of controlling the hard roof of shallow-buried coal seams. The filling material is not in close contact with the roof, and the surface settlement control effect is limited.

[0007] To address the above issues, existing literature (such as CN121184128A, CN120402158A, etc.) has proposed some improvement schemes, but these have not fundamentally solved the problems of separating the mining and filling processes and controlling costs.

[0008] Therefore, there is an urgent need to develop a backfilling mining method for shallow-buried deep coal seams that can achieve full separation of mining operations, reduce investment costs, improve production efficiency, and effectively control roof subsidence. This method involves forming strip-shaped goafs through short-wall interval skip mining, followed by delayed backfilling under the protection of inter-coal pillars. This achieves full separation of mining operations, reduces costs, and increases output, thereby effectively releasing coal resources under the "three underground" conditions and ensuring the sustainable development of the mine. Summary of the Invention

[0009] The purpose of this invention is to provide a short-walled, delayed backfilling method for mining shallow-buried deep coal seams, in order to solve the problems of mutual interference between mining and backfilling processes, high investment costs, difficulty in roof control, and low solid waste utilization rate in the existing technology.

[0010] To achieve the above objectives, this invention provides a method for short-walled, spaced-backfill mining of shallow coal seams, applicable to shallow coal seams with a burial depth of less than 200 meters, comprising the following steps: S1. Working face layout: The width of the shortwall working face is determined based on the initial pressure breaking distance of the key layer of the coal seam roof, and multiple shortwall mining working faces are arranged. S2, Interval Jump Mining: The interval jump mining mode is adopted, which divides multiple shortwall working faces into a first sequence and a second sequence. The first sequence of shortwall working faces is mined first, and the unmined second sequence working faces are reserved between adjacent first sequence working faces as interval coal pillars. The interval coal pillars are used to support the roof and protect the backfilling operation of the mined shortwall working faces. S3. Delayed backfilling: After the first sequence of shortwall working faces is mined, grouting boreholes are drilled under the inter-coal pillars to grout and backfill the goaf of the mined shortwall working faces to form a backfill body. S4. Coal pillar recovery: After the filling body reaches the designed support strength, the intermittent coal pillars are mined back, and steps S2 to S3 are repeated until all coal pillars are recovered.

[0011] Preferably, in S1, the width of the short wall working face is determined based on the initial crushing distance of the main roof, secondary main roof, or direct roof, and is 20 to 50 meters.

[0012] Preferably, in S2, the width of the spacer coal pillar is 1 to 2 times the width of the short-wall working face.

[0013] Preferably, in step S2, the coal mining and backfilling processes are independent of each other, and the coal mining and backfilling operations are carried out on different working faces to avoid process interference.

[0014] Preferably, in S3, the construction method of the grouting borehole is as follows: under the spacer coal pillar, a directional main borehole is drilled parallel to the coal seam along the working face advance direction, and branch holes are arranged at intervals along the main borehole to form a grouting network.

[0015] Preferably, the directional main borehole is located in the middle and lower part of the main roof, secondary main roof, or direct roof, 2 to 4 meters away from the underlying weak rock layer; the interval between the branch holes is 40 to 60 meters.

[0016] Preferably, in step S3, the grouting and filling adopts a pressurized grouting method, and the grout fills the cavity of the goaf until it is densely filled along the interface of the old roof, the secondary old roof, or the direct roof.

[0017] Preferably, in step S3, the grout is a solid waste polymer grout made primarily of coal gangue and fly ash, with a grout mass concentration of 60% to 70% and a uniaxial compressive strength of not less than 3.5 MPa after 28 days of curing.

[0018] Preferably, in step S3, the solidification time of the filling material is 24 to 96 hours.

[0019] Preferably, in step S3, the goaf forms a long, arched structure, which is used to store the filling slurry and together with the filling slurry forms a supporting entity.

[0020] Preferably, in step S4, the design support strength is such that the filling material meets the strength requirement of being able to independently support the top plate.

[0021] Preferably, four adjacent shortwall working faces are divided into a group, and a "1-mining, 3-reserving" skip mining mode is adopted within the group, with interval skip mining and delayed filling carried out in four stages.

[0022] The technical principle of this invention is based on the mechanical balance of the roof and the optimization of the mining and filling process: 1) Roof mechanical balance principle: The spacer coal pillars and the backfill body jointly bear the roof pressure, forming a stable support system. The spacer coal pillars play a key supporting role in the initial stage, protecting the backfilling operation. After the backfill body solidifies, it shares the roof load with the spacer coal pillars to prevent roof failure and surface subsidence.

[0023] 2) Arch-shaped structure reinforcement principle: After the short-wall mining is completed, the old roof (or the second old roof) forms a long, arch-shaped goaf. This arch-shaped structure has good self-stabilizing characteristics. On the one hand, it can store a large amount of solid waste, and on the other hand, it can form a solidified entity through grouting, which enhances the stability of the filling body.

[0024] 3) Complete Separation of Mining and Backfilling: Through the intermittent skip-mining mode, coal mining and backfilling operations are allocated to different working faces, achieving complete separation of the processes. Coal mining and backfilling operations are carried out simultaneously on different working faces without interference, significantly improving production efficiency.

[0025] 4) Key layer control principle: The width of the short-wall working face is determined based on the initial crushing distance of the key layer, ensuring that the roof remains stable during mining and providing a safe working environment for backfilling operations.

[0026] Therefore, the short-walled spaced delayed backfilling method for mining shallow-buried deep coal seams of the present invention has the following beneficial effects: (1) The present invention uses an intermittent skip mining mode to allocate coal mining and backfilling operations to different working faces. Coal mining and backfilling operations are carried out simultaneously on different working faces without interfering with each other. This process separation design avoids the problem of process cross-interference in traditional continuous mining and backfilling or backfilling after the support frame.

[0027] (2) This invention does not require modification of hydraulic supports and can be implemented using conventional integrated mechanized coal mining equipment, significantly reducing initial investment. Compared with traditional methods such as paste filling and gangue filling, the initial investment is reduced. At the same time, the all-solid waste polymer slurry uses industrial solid waste such as coal gangue and fly ash as the main raw materials, resulting in low material costs and reduced overall mining costs, thus exhibiting good economic efficiency.

[0028] (3) Based on the principle of key layer control, the width of the short-wall working face is precisely determined according to the initial pressure breaking distance of the key layer, ensuring that the roof remains stable during mining. The spacer coal pillar and the backfill body jointly bear the roof pressure, forming a stable support system, effectively controlling roof subsidence and surface settlement, and protecting surface buildings and the ecological environment.

[0029] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the process flow of the shallow-buried deep coal seam short-walled interval delayed filling coal mining method of the present invention; Figure 2 This is a schematic diagram of the first stage in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram of the second stage in Embodiment 1 of the present invention; Figure 4This is a schematic diagram of the third stage in Embodiment 1 of the present invention; Figure 5 This is a schematic diagram of the fourth stage in Embodiment 1 of the present invention. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0032] 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 some embodiments of the present invention, but not all embodiments.

[0033] Example 1 This embodiment takes a short-walled spaced delayed backfilling mining project as an example, and uses the short-walled spaced delayed backfilling coal mining method of the present invention for backfilling mining.

[0034] The mine is located in the Caojiashan Village area, southwest of Fangshan County, Lüliang City, Shanxi Province, 18 km from the county seat (218° azimuth). It is administratively under the jurisdiction of Yukou Town, Fangshan County. Its area is 5.9695 km². 2 The geographical coordinates are: 111°07′48″~111°09′09″ east longitude and 37°47′25″~37°48′04″ north latitude. The 110214 coal face of Huaqiang Coal Mine has existing buildings and the coal seam is only about 160 meters deep. By adopting short-wall interval delayed backfilling mining technology, the protective coal pillars under the buildings and structures within the Huaqiang Coal Mine's mining area can be released, thereby increasing the mine's service life.

[0035] like Figure 1 As shown, the specific steps are as follows: Based on the key layer location information shown in Table 1, the fracture distance is calculated: For a single critical layer, the formula for calculating the failure moment of a fixed-support beam is as follows: ; In the formula: The critical layer fracture distance; For critical layer thickness; For the tensile strength of the key layer; It bears the load for the critical layer.

[0036] The working face width corresponding to the critical layer limit span calculated by substituting relevant data is shown in Table 1 below, and the fracture angle is... Calculate based on 72° for now.

[0037] Table 1: Key Layer Location Information

[0038] Since there is a goaf of No. 9 coal seam in the upper part of the 110214 working face, the No. 9 coal seam has a mining height of 1.6m and its roof is K2 limestone, which is only 15m away from K3 limestone. Considering that the fracture zone has extended to K3 limestone after the No. 9 coal seam is mined out, K4 limestone, which is 37.55m away from No. 11 (10+11) coal seam, is selected as the key layer. Its corresponding mining width is 42m. Considering a certain surplus coefficient, the mining width of the 110214 working face is selected as 34m.

[0039] The 110214 longwall longwall face was divided into 5 shortwall longwall faces, each 34 meters long (including two roadways with a width of 9 meters). An odd-numbered sequence interval mining pattern was adopted, dividing the multiple shortwall faces into a first sequence (1, 3, 5) and a second sequence (2, 4). Specifically, shortwall faces 1, 3, and 5 were mined first, forming interval coal pillars (2, 4). The width of the interval coal pillars was the same as the width of the shortwall face, used to support the roof and protect the backfilling operations of the mined shortwall faces. The specific implementation steps are as follows: Phase 1: As Figure 2 As shown, the first sequence (1, 3, 5) short-wall working faces are first skipped.

[0040] Phase Two: Delayed Filling like Figure 3 As shown, after the mining of shortwall faces 1, 3, and 5 is completed, boreholes are arranged at appropriate locations underground. A directional main borehole is drilled approximately 3 meters below the K4 rock stratum interface of the working face. Another directional main borehole is drilled parallel to the coal seam along the direction of the working face advance. Branch boreholes are then drilled at intervals of approximately 50 meters to form a grouting network. Pressurized grouting is used to fill the mined shortwall faces 1, 3, and 5.

[0041] The grouting slurry uses a solid waste polymer slurry, with coal gangue and fly ash as the main raw materials. The slurry concentration is 65%, and the uniaxial compressive strength after 28 days of curing is not less than 4.0 MPa. The solidification time of the filling body is approximately 36 hours.

[0042] Phase Three: As Figure 4 As shown, the second sequence (2, 4) short-wall working faces are skipped.

[0043] Phase Four: such as Figure 5 As shown, grouting was performed on the short wall working faces 2 and 4.

[0044] The following results were achieved after adopting this method: The coal mining and backfilling processes are completely separated and do not interfere with each other, increasing production efficiency by about 25%; no need to modify hydraulic supports, reducing one-time investment by about 40%; the cost of all-solid-waste polymer slurry is low, reducing overall mining costs by about 20%; solid waste utilization rate reaches over 85%; roof control is good, and surface subsidence is within the allowable range; resources under the buildings are successfully released, increasing coal production by about 80% and extending the mine's service life.

[0045] Example 2 This embodiment takes the Shanxi Fangshan Jinhui Ruilong Coal Industry Co., Ltd.'s Gongguang Coal Paste Backfilling Mining Project as an example. To recover coal pillars and release coal pressure from underground, under-mining, and under-mining areas, the short-wall interval delayed backfilling mining method of this invention is adopted. This design arranges backfilling mining faces within the coal pillar area of ​​the industrial site. The backfilling mining area is selected from the block covered by the coal pillar area on the east side of the bottom of the mine. Based on the experience of similar mines in China, a "grouping and rotation" method is adopted, dividing the four adjacent strips (A, B, C, D) of the working face into one group. The four strips within the group are mined in four stages, i.e., the mining and backfilling cycle is carried out in four phases. Each stage of mining follows a "mining 1, leaving 3" skip-mining pattern.

[0046] Phase 1: Mining strip A, while reserving B, C, and D as interstitial coal pillars; Second stage: Delayed filling of strip A, and mining of strip B after the filling material solidifies; Third stage: Delayed filling of strip B, and mining of strip C after the filling material solidifies; Fourth stage: Delayed filling of strip C, mining strip D after the filling material solidifies, and finally filling strip D.

[0047] Each working face is divided into 4 groups per round, with each round consisting of advancing 76.8 meters (16 branch tunnels). A retreating method is used for mining and backfilling one tunnel at a time. After each round of mining is completed, the backfilling strength is allowed to reach the designed support strength before the next group of tunnels is started, and so on, to complete the tunneling and backfilling operations of the entire working face.

[0048] After adopting the method of this invention, pillarless mining of the entire working face is realized, and the resource recovery rate is greatly improved; the coal mining and backfilling processes are independent of each other, and the production efficiency is increased by about 28%; the solid waste utilization rate reaches more than 82%; the roof is well controlled and the surface subsidence is effectively controlled; the industrial site covering resources is successfully released, and the service life of the mine is extended by about 5 years.

[0049] Therefore, this invention provides a short-walled, spaced-backfill mining method for shallow-buried deep coal seams, completely separating mining and backfilling processes. These processes can be carried out simultaneously on different working faces without interference, increasing production efficiency by 20%–30%. It eliminates the need for modifications to hydraulic supports, reducing initial investment and overall mining costs. During mining, it creates large-scale strip-shaped goaf areas, providing backfilling space and achieving a solid waste utilization rate of over 80%. Furthermore, by having the spaced coal pillars and backfilling bodies jointly bear the roof pressure, it controls roof subsidence and surface settlement, successfully freeing up resources under industrial sites, buildings, and roads. Coal production increases by 50%–100%, extending the mine's service life. This method can be widely applied to the mining of shallow-buried deep coal seams and resources under "three-under" (underground, underground, and road) structures, and is particularly suitable for shallow-buried, deep, hard gray-rock coal seams with hard roofs (old or secondary roofs) or where the immediate roof is not broken, demonstrating broad application prospects.

[0050] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for short-walled, spaced-backfilling mining of shallow-buried deep coal seams, characterized in that, Includes the following steps: S1. Working face layout: The width of the shortwall working face is determined based on the initial pressure breaking distance of the key layer of the coal seam roof, and multiple shortwall mining working faces are arranged. S2, Interval Jump Mining: The interval jump mining mode is adopted, which divides multiple shortwall working faces into a first sequence and a second sequence. The first sequence of shortwall working faces is mined first, and the unmined second sequence working faces are reserved between adjacent first sequence working faces as interval coal pillars. The interval coal pillars are used to support the roof and protect the backfilling operation of the mined shortwall working faces. S3. Delayed backfilling: After the first sequence of shortwall working faces is mined, grouting boreholes are drilled under the inter-coal pillars to grout and backfill the goaf of the mined shortwall working faces to form a backfill body. S4. Coal pillar recovery: After the filling body reaches the designed support strength, the intermittent coal pillars are mined back, and steps S2 to S3 are repeated until all coal pillars are recovered.

2. The method for short-walled, spaced-lag backfilling mining of shallow-buried deep coal seams according to claim 1, characterized in that: In S1, the width of the short wall working face is determined based on the initial crushing distance of the main roof, secondary main roof, or direct roof, and is 20 to 50 meters.

3. The method for short-walled, spaced-backfill mining of shallow-buried deep coal seams according to claim 2, characterized in that: In S2, the width of the spacer coal pillar is 1 to 2 times the width of the short-wall working face.

4. The method for short-walled, spaced-lag backfilling mining of shallow-buried deep coal seams according to claim 3, characterized in that: In S3, the construction method of grouting boreholes is as follows: under the spacer coal pillar, directional main boreholes are drilled parallel to the coal seam along the working face advance direction, and branch holes are arranged at intervals along the main boreholes to form a grouting network.

5. The method for short-walled, spaced-lag backfilling mining of shallow-buried deep coal seams according to claim 4, characterized in that: The directional main borehole is located in the middle and lower part of the main roof, secondary main roof, or direct roof, 2 to 4 meters away from the weak rock layer below; the interval between the branch holes is 40 to 60 meters.

6. The method for short-walled, spaced-lag backfilling mining of shallow-buried deep coal seams according to claim 5, characterized in that: In S3, the grouting and filling adopts the pressurized grouting method, and the grout fills the cavity of the goaf until it is densely filled along the old roof, the secondary old roof or the direct roof interface.

7. The method for short-walled, spaced-lag backfilling mining of shallow-buried deep coal seams according to claim 6, characterized in that: In S3, the grout is a solid waste polymer grout with coal gangue and fly ash as the main raw materials, with a grout mass concentration of 60%~70% and a uniaxial compressive strength of not less than 3.5MPa after 28 days of curing.

8. The method for short-walled, spaced-lag backfilling mining of shallow-buried deep coal seams according to claim 7, characterized in that: In S3, the solidification time of the filling material is 24 to 96 hours.

9. A method for short-walled, spaced-backfill mining of shallow-buried deep coal seams according to claim 8, characterized in that: In S3, the goaf forms a long, arched structure, which is used to store the filling slurry and together with the filling slurry forms a supporting entity.

10. A method for short-walled, spaced-lag backfilling mining of shallow-buried deep coal seams according to claim 9, characterized in that: The four adjacent shortwall working faces are divided into a group, and the "1 mined, 3 left" skip mining mode is adopted within the group. The interval skip mining and delayed filling are carried out in four stages.

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