Filling and subsidence reducing method for goaf end bottom plate

Abstract

The invention relates to the technical field of coal filling mining, in particular to a goaf end bottom plate filling subsidence reduction method which comprises the steps that the range of a bottom plate failure zone below a coal seam is determined, and a rock stratum with a certain thickness is selected below the bottom plate failure zone to serve as a bottom plate pressure-bearing protection layer; a goaf bottom plate area corresponding to the position under the separation layer area in the masonry beam structure serves as a goaf end range used for grouting; the bottom interface of the pressure-bearing protection layer of the bottom plate serves as a grouting layer, and grouting drill holes are constructed to communicate with the grouting layer; working face stoping is carried out, and when grouting filling can be carried out on the bottom plate pressure-bearing protection layer from a certain grouting drill hole, paste-like filling materials are injected into the grouting layer position from the grouting drill hole. According to the method, paste-like filling is performed on the end part of the goaf bottom plate to form a basin bottom type goaf structure, so that overlying strata in a separation layer area in masonry beam structures at the end parts of the two sides of the mining boundary can be effectively supported, and the development degree of cracks in the separation layer area and surface cracks is controlled. The method can reduce surface subsidence and save filling cost.

Description

Technical Field

[0001] The invention relates to the technical field of coal filling mining, in particular to a method for reducing the subsidence of a bottom plate at the end of a goaf. Background Art

[0002] The mining of coal resources is usually accompanied by the formation of goafs. The mining of coal seams causes the removal of the coal body that originally supported the overlying rock strata. The overlying rock strata gradually lose support under the action of gravity, and then delamination, fracture and sinking occur. This series of processes will inevitably lead to surface subsidence problems, which are manifested as the appearance of surface cracks, changes in terrain undulations, and local ground collapse. This surface subsidence not only damages the natural environment, but may also pose a serious threat to surface buildings, transportation infrastructure, farmland and water systems. Within the mining range, the expansion of the overlying rock fracture field and the nonlinear deformation of the rock strata further aggravate the degree and scope of subsidence, leading to the degradation of the ecosystem and the loss of water resources.

[0003] In view of the stratum damage and surface subsidence caused by coal mining, underground backfill mining technology is widely regarded as one of the important means to solve this problem. This technology forms an effective support structure by backfilling a certain amount of backfilling materials in the goaf, thereby slowing down the delamination, fracture and sinking process of the overlying strata, and reducing the surface subsidence and crack expansion caused by mining. Underground backfill mining technology can not only significantly improve the mechanical environment of the goaf, but also optimize the resource utilization efficiency of coal mining to a certain extent, and promote coal mining to develop in a more green and sustainable direction. However, if the goaf is filled directly, the crushing and expansion characteristics of rock collapse cannot be utilized, and a large amount of backfilling materials will be consumed, resulting in high filling costs and low filling and coal mining efficiency. Summary of the invention

[0004] In view of the above technical problems, the present invention proposes a method of partially filling the floor plate only at the end of the goaf. By filling the floor plate in the end area, an expansion effect is generated and the overburden is supported, thereby effectively alleviating the problem of large opening of the overburden longitudinal cracks during the mining process at the boundary of the goaf, and reducing the risk of longitudinal cracks between adjacent rock layers. The specific method is as follows:

[0005] A method for reducing subsidence by filling the bottom plate at the end of a goaf, comprising the following steps:

[0006] S1: Determine the scope of the floor damage zone below the coal seam, select a rock layer of a certain thickness below the floor damage zone as the floor pressure-bearing protective layer, the floor pressure-bearing protective layer arches up under the grouting pressure, but does not generate cracks that connect to the upper floor damage zone, or the generated cracks are not connected to the cracks in the floor damage zone;

[0007] S2: The goaf floor area corresponding to the delamination zone in the masonry beam structure is used as the end range of the goaf for grouting;

[0008] S3: The bottom interface of the bottom plate pressure protection layer is used as the grouting layer, and the grouting drilling holes are constructed to connect the grouting layers;

[0009] S4: Carry out mining on the working face. When a grouting borehole is capable of grouting into the bottom plate pressure protection layer, a paste-like filling material is injected into the grouting layer from the grouting borehole.

[0010] Preferably, in step S1, the rock layer at the bottom of the bottom plate pressure-bearing protective layer has a low elastic modulus and good water-proof properties.

[0011] Preferably, in step S3, the working face is advanced to the mining position, and grouting holes are constructed in the horizontal tunnels on both sides of the working face toward the coal seam floor grouting layer within the end range of the goaf area used for grouting, and the grouting holes are inclined toward the cutting direction on the plane; the grouting holes are constructed in pairs in the horizontal tunnels on both sides of the working face at a certain distance from the cutting direction along the advancing direction of the working face.

[0012] Preferably, in step S3, along the advancing direction of the working face, grouting drilling holes are constructed in sequence at a certain distance from the leading basic top breaking position in the direction of the cutting eye.

[0013] Preferably, in step S4, the paste-like filling material is a composite material containing cement, bentonite and polymer components.

[0014] The inventive points and beneficial effects of the present invention are as follows: 1. The present invention proposes a filling and expansion method that focuses on the bottom plate at the end of the goaf, which forms a basin-type goaf structure by performing paste-like filling at the end of the goaf bottom plate. It can effectively support the overlying rock strata corresponding to the delamination zone in the masonry beam structure at the ends of the mining boundary, and control the development degree of cracks in the delamination zone (located at the boundary of the goaf) and surface cracks.

[0015] 2. The present invention can reduce the equivalent mining height of the coal seam within the end range of the goaf, thereby reducing the settlement of the overlying rock strata and reducing surface subsidence.

[0016] 3. The present invention avoids the high cost problem of full filling and significantly improves the efficiency of the filling operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram (inclination) of overburden fracture and surface subsidence under normal mining;

[0018] Figure 2 It is a schematic diagram of the principle of the method for reducing subsidence by filling the bottom plate at the end of the goaf area of ​​the present invention (inclination);

[0019] Figure 3It is a plan view of the drilling arrangement of the method for filling and reducing the subsidence of the bottom plate at the end of the goaf area of ​​the present invention;

[0020] In the figure: bottom plate pressure protection layer-1, bottom plate uniform rupture zone-2, bottom plate crushing and expansion zone-3, delamination zone-4, directional grouting drilling hole-5, end bottom plate filling area-6, basic top fracture position-7, horizontal tunnel-8. DETAILED DESCRIPTION

[0021] In order to better understand the technical content of the present invention, specific embodiments are given and described as follows in conjunction with the accompanying drawings.

[0022] like Figure 2-3 As shown, in order to solve the problems of high cost, low efficiency and environmental burden in the existing subsidence control methods, the present invention proposes a method for reducing subsidence by filling the bottom plate at the end of the goaf, which provides an innovative technical path for green coal mining and ecological restoration. The specific steps include:

[0023] S1: Determine the scope of the floor damage zone below the coal seam, the floor damage zone includes a floor crushing and expansion zone 3 and a floor uniform fracture zone 2. In the floor crushing and expansion zone 3, the floor rock strata are broken in an irregular network, and have certain expansion characteristics due to the gaps between the broken blocks; in the floor uniform fracture zone 2, the floor rock strata are broken in regular vertical and horizontal cracks, the floor damage zone can form a water-conducting channel, and the floor uniform fracture zone is obvious after the floor grouting; a certain thickness of rock strata (usually including multiple rock strata) is selected below the floor damage zone as the floor pressure-bearing protective layer 1, the floor pressure-bearing protective layer 1 is arched under the action of grouting, but no cracks are generated to connect to the upper floor damage zone, or the generated cracks are not connected to the cracks in the floor damage zone; the rock strata at the bottom of the floor pressure-bearing protective layer 1 preferably have a low elastic modulus and good water-insulating properties, such as mudstone.

[0024] S2: Determine the end range of the goaf for grouting, such as Figure 1-2 As shown, after the working face is mined, the overlying rock strata form a masonry beam structure, and the goaf floor area corresponding to the separation zone 4 in the three horizontal zones in the masonry beam structure is used as the end range of the goaf for grouting; the masonry beam structure and the division of the three horizontal zones are common knowledge in this field, and you can refer to "Mine Pressure and Rock Strata Control", pages 77-78, Qian Minggao, China University of Mining and Technology Press Co., Ltd., 3rd edition in January 2021. The separation zone 4 in the three horizontal zones of the masonry beam refers to the rock strata detachment phenomenon caused by coal seam mining. The top plate rock strata load directly above the separation zone 4 is not transmitted to the goaf floor directly below the separation zone 4. The load on the goaf floor directly below the separation zone 4 is relatively small, which is conducive to the grouting filling of the floor;

[0025] S3: The bottom interface of the bottom plate pressure-bearing protective layer 1 is used as the grouting layer, and a grouting borehole 5 is constructed to connect the grouting layer;

[0026] like Figure 2-3 As shown, the arrangement of the grouting boreholes 5 is as follows: the working face adopts a single-lane arrangement, that is, the return air lane and the transport lane are arranged on both sides of the working face respectively. The single-lane arrangement is a well-known arrangement in the art and will not be described in detail here; the working face mining position is advanced, and grouting boreholes 5 are constructed in the lanes 8 on both sides of the working face toward the coal seam floor grouting layer within the end range of the goaf area for grouting, and the grouting boreholes 5 are inclined in the plane toward the eye-cutting direction; the grouting boreholes 5 are constructed in pairs in the lanes 8 on both sides of the working face along the advancing direction of the working face from the eye-cutting start at a certain distance, and the vertical depth and angle of each pair of grouting boreholes 5 as well as the plane inclination angle are the same, and the terminal hole of the grouting borehole 5 is constructed to the grouting layer;

[0027] Preferably, Figure 3 As shown, along the advancing direction of the working face, grouting boreholes 8 are constructed in the direction of the eye cutting at a certain distance (such as 4-6m) from the leading basic top breaking position 7, that is, this position is the orifice position of the grouting borehole 5;

[0028] S4: Performing mining on the working face. When a grouting borehole 5 is capable of grouting into the bottom plate pressure-bearing protective layer 1, a paste-like filling material is injected from the grouting borehole 5 into the grouting layer. At this time, the basic top of the grouting borehole 5 is not broken, and the formation pressure on the bottom plate of the grouting area of ​​the grouting borehole 5 is relatively small, which is conducive to grouting. The paste-like filling material can be a composite material containing cement, bentonite, polymer and other components, which has good adhesion, expansion and low permeability. Of course, those skilled in the art can also select other paste-like filling materials known in the art as needed;

[0029] The present invention only performs grouting filling at the end of the goaf, so a paste-like filling material is selected. Compared with the fly ash slurry material, the paste-like filling material has poor fluidity. This characteristic enables it to be accurately filled within the end range of the goaf for grouting, avoiding the filling material from flowing too large, which is not conducive to control within the end range of the goaf for grouting.

[0030] The injected paste-like filling material gradually lifts the bottom plate pressure protection layer 1 and the bottom plate uniform fracture zone 2 and the bottom plate crushing and expansion zone 3 on the top within the end range of the goaf area used for grouting; the bottom plate uniform fracture zone 2 and the bottom plate crushing and expansion zone 3 will increase the damage range under the action of grouting, and the looseness of the irregular rock blocks in the bottom plate crushing and expansion zone 3, that is, the degree of crushing and expansion, will also increase, further enriching the goaf space and compressing the delamination in the delamination zone 4 in the masonry beam structure at the ends of the mining boundary (or reducing the amount of delamination in the delamination zone 4), and together with the paste-like filling material, offsetting the space formed by part of the coal seam mining, thereby reducing the equivalent mining height of the coal seam within the end range of the goaf area used for grouting, thereby reducing the settlement of the overlying rock strata, controlling the development degree of the cracks at the boundary of the goaf and the cracks on the surface, and reducing surface subsidence.

[0031] The present invention performs grouting filling at the end of the goaf. After filling, the end bottom plate of the goaf presents an expanded and bulging shape, gradually changing from the original "cliff-like" structure to a "basin-like" structure. Compared with the traditional goaf structure, the basin-like structure formed by the expansion back-arch effect can effectively support the overlying rock strata corresponding to the delamination zone 4 in the masonry beam structure at the ends of both sides of the mining boundary, avoiding the fracture or delamination of the overlying rock strata in the delamination zone 4 due to the loss of coal body bearing.

Claims

1. A method for reducing subsidence by filling the bottom plate at the end of a goaf, characterized in that: The steps include: S1: Determine the scope of the floor damage zone below the coal seam, select a rock layer of a certain thickness below the floor damage zone as the floor pressure-bearing protective layer, the floor pressure-bearing protective layer arches up under the grouting pressure, but does not generate cracks that connect to the upper floor damage zone, or the generated cracks are not connected to the cracks in the floor damage zone; S2: The goaf floor area corresponding to the delamination zone in the masonry beam structure is used as the end range of the goaf for grouting; S3: The bottom interface of the bottom plate pressure protection layer is used as the grouting layer, and the grouting drilling holes are constructed to connect the grouting layers; S4: Carry out mining on the working face. When a grouting borehole is capable of grouting into the bottom plate pressure protection layer, a paste-like filling material is injected into the grouting layer from the grouting borehole.

2. The method for reducing subsidence by filling the bottom plate at the end of the goaf according to claim 1 is characterized in that: In step S1, the rock layer at the bottom of the bottom plate pressure-bearing protective layer has a low elastic modulus and good water-proof properties.

3. The method for reducing subsidence by filling the bottom plate at the end of the goaf according to claim 1, characterized in that: In step S3, the mining position of the advanced working face is advanced, and grouting holes are constructed in the horizontal tunnels on both sides of the working face toward the grouting layer of the coal seam floor within the end range of the goaf area used for grouting, and the grouting holes are inclined toward the cutting direction on the plane; the grouting holes are constructed in pairs in the horizontal tunnels on both sides of the working face at a certain distance from the cutting direction along the advancing direction of the working face.

4. The method for reducing subsidence by filling the bottom plate at the end of the goaf according to claim 3 is characterized in that: In step S3, along the advancing direction of the working face, grouting drilling holes are constructed in sequence at a certain distance from the leading basic top breaking position in the direction of the cutting eye.

5. The method for reducing subsidence by filling the bottom plate at the end of a goaf according to any one of claims 1 to 4, characterized in that: In step S4, the paste-like filling material is a composite material containing cement, bentonite and polymer components.

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