A method for filling and reducing subsidence of the end floor of a goaf

Abstract

The present application relates to coal filling mining technical field, specifically to a kind of goaf end floor filling subsidence reduction method, including determining the range of floor failure zone below coal seam, select certain thickness of rock stratum as floor pressure protection layer below floor failure zone;The floor area of goaf directly below in the masonry beam structure is used as the goaf end range for grouting;The bottom interface of floor pressure protection layer is used as grouting horizon, grouting drilling hole is connected grouting horizon;Working face is mined, when grouting from certain grouting drilling hole can be filled into floor pressure protection layer, paste-like filling material is injected into grouting horizon from the grouting drilling hole.The present application forms basin bottom type goaf structure by paste-like filling in the end of goaf floor, can effectively support the overburden strata in the delamination zone of masonry beam structure in the two sides of mining boundary, control the development degree of delamination zone fracture and surface fissure.The present application can reduce surface subsidence, save filling cost.

Description

Technical Field

[0001] This invention relates to the field of coal backfilling mining technology, specifically to a method for reducing settlement by backfilling the bottom plate at the end of a goaf. Background Technology

[0002] Coal mining is typically accompanied by the formation of goaf areas. As coal seams are mined, the coal body that originally supported the overlying strata is removed. Under the influence of gravity, the overlying strata gradually lose their support, leading to delamination, fracturing, and subsidence. This series of processes inevitably triggers surface subsidence, manifesting as surface cracks, changes in topography, and localized ground collapse. This surface subsidence not only damages the natural environment but also poses a serious threat to surface buildings, transportation infrastructure, farmland, and water systems. Within the mining area, the expansion of the overlying strata's fracture field and the nonlinear deformation of the strata further exacerbate the degree and extent of subsidence, leading to ecosystem degradation and water resource loss.

[0003] Underground backfilling mining technology is widely considered a crucial solution to the geological damage and surface subsidence caused by coal mining. This technology involves backfilling the goaf with a certain amount of material to form an effective support structure, thereby mitigating the delamination, fracturing, and subsidence of the overlying strata and reducing surface subsidence and fracture propagation caused by mining. Underground backfilling mining technology not only significantly improves the mechanical environment of the goaf but also optimizes the resource utilization efficiency of coal mining to a certain extent, promoting a greener and more sustainable development of coal mining. However, directly backfilling the goaf fails to utilize the fragmentation characteristics of rock collapse, consumes a large amount of backfilling material, resulting in high backfilling costs and low backfilling and mining efficiency. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention proposes a method for partially filling the bottom plate at the end of the goaf. By filling the bottom plate in the end region, an expansion effect is generated, causing it to bulge and support the overlying strata. This effectively alleviates the problem of large opening of longitudinal fractures in the overlying strata during goaf boundary mining, while also reducing the risk of longitudinal fractures connecting adjacent strata. The specific method is as follows:

[0005] A method for reducing settlement by filling the end slab of a goaf includes the following steps:

[0006] S1: Determine the extent of the failure zone of the floor below the coal seam, and select a rock layer of a certain thickness below the failure zone as the pressure-bearing protective layer of the floor. The pressure-bearing protective layer of the floor arches upward under the grouting pressure, but does not generate cracks that connect to the upper failure zone of the floor, or the generated cracks are not connected to the cracks of the failure zone of the floor.

[0007] S2: The goaf floor area directly below the delamination zone in the masonry beam structure is taken as the goaf end range for grouting;

[0008] S3: The bottom interface of the pressure-bearing protective layer of the base plate is used as the grouting layer, and the grouting borehole is connected to the grouting layer.

[0009] S4: When the working face is being mined, and a certain grouting borehole is able to grout into the pressure protection layer of the bottom plate, a paste-like filling material is injected from the grouting borehole into the grouting layer.

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

[0011] Preferably, in step S3, at the advanced working face mining position, grouting boreholes are constructed in the horizontal roadways on both sides of the working face towards the coal seam floor grouting layer within the range of the end of the goaf for grouting. The grouting boreholes are inclined in the plane towards the cutting direction. The grouting boreholes are constructed in pairs at a certain distance from the cutting direction along the working face advancing direction in the horizontal roadways on both sides of the working face.

[0012] Preferably, in step S3, grouting boreholes are drilled sequentially at a certain distance from the pre-break position of the basic top along the working face advancing direction towards the cutting eye.

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

[0014] The inventive points and beneficial effects of this invention are as follows: 1. This invention proposes a filling and expansion method focusing on the bottom plate of the goaf end. By filling the bottom plate of the goaf with a paste-like substance to form a basin-shaped goaf structure, it can effectively support the overlying rock strata corresponding to the delamination zone in the masonry beam structure on both sides of the mining boundary, and control the development degree of fissures in the delamination zone (located at the goaf boundary) and surface fissures.

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

[0016] 3. This invention avoids the high cost problem of full filling and significantly improves the efficiency of filling operations. Attached Figure Description

[0017] Figure 1 This is a schematic diagram (dip) of the underlying rock fracture and surface subsidence during normal mining.

[0018] Figure 2 This is a schematic diagram (inclination) illustrating the principle of the bottom plate filling and settlement reduction method for the goaf end of the present invention;

[0019] Figure 3This is a schematic diagram of the borehole layout for the method of filling and reducing settlement at the end of the goaf in this invention.

[0020] In the diagram: Bottom plate pressure protection layer-1, Bottom plate uniform fracture zone-2, Bottom plate fracture expansion zone-3, Delamination zone-4, Directional grouting borehole-5, End bottom plate filling zone-6, Basic roof fracture location-7, Horizontal tunnel-8. Detailed Implementation

[0021] To better understand the technical content of the present invention, specific embodiments are described below in conjunction with the accompanying drawings.

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

[0023] S1: Determine the extent of the floor failure zone below the coal seam. The floor failure zone includes a floor fracture expansion zone 3 and a floor uniform fracture zone 2. In the floor fracture expansion zone 3, the floor rock strata are fractured in an irregular network pattern. Due to the gaps between the fractured blocks, they have certain expansion characteristics. In the floor uniform fracture zone 2, the floor rock strata are fractured with regular longitudinal and transverse fractures. The floor failure zone can form water-conducting channels. After floor grouting, the floor uniform fracture zone becomes obvious. Below the floor failure zone, select a rock stratum of a certain thickness (usually containing multiple rock strata) as the floor pressure-bearing protective layer 1. The floor pressure-bearing protective layer 1 arches upward under the grouting action, but does not generate fractures that connect to the upper floor failure zone, or the generated fractures do not connect with the fractures in the floor failure zone. The lowest rock stratum of the floor pressure-bearing protective layer 1 is preferably a rock stratum with low elastic modulus and good water-impermeability, such as mudstone.

[0024] S2: Determine the extent of the goaf end area to be used for grouting, such as Figure 1-2 As shown, after the working face is mined, the overlying strata form a masonry beam structure. The area of ​​the goaf floor directly below the delamination zone 4 in the transverse three zones of the masonry beam structure is designated as the goaf end area for grouting. The masonry beam structure and the division of the transverse three zones are common knowledge in this field. For reference, see "Mine Pressure and Strata Control", pp. 77-78, Qian Minggao, China University of Mining and Technology Press Co., Ltd., 3rd edition, January 2021. The delamination zone 4 in the transverse three zones of the masonry beam refers to the strata separation phenomenon caused by coal seam mining. The load of the roof strata directly above the delamination zone 4 is not transferred to the goaf floor directly below the delamination zone 4. The goaf floor directly below the delamination zone 4 has a smaller load, which is conducive to grouting and filling of the floor.

[0025] S3: Take the bottom interface of the pressure-bearing protective layer 1 of the base plate as the grouting layer, and construct grouting borehole 5 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 layout, that is, a return airway and a transport airway are arranged on both sides of the working face respectively. The single-lane layout is a well-known layout in the art and will not be described in detail here; at the advance working face mining position, grouting boreholes 5 are constructed in the horizontal roadways 8 on both sides of the working face towards the coal seam floor grouting layer within the goaf end range for grouting. The grouting boreholes 5 are inclined in the plane towards the cutting direction; the grouting boreholes 5 are constructed in pairs along the working face advancing direction, starting from the cutting direction and spaced at a certain distance in the horizontal roadways 8 on both sides of the working face. The vertical depth, angle and plane inclination of each pair of grouting boreholes 5 are the same. The final hole of the grouting boreholes 5 is constructed to the grouting layer.

[0027] Preferred, such as Figure 3 As shown, along the working face advancing direction, grouting boreholes 8 are constructed sequentially at a certain distance (e.g., 4-6m) from the advanced basic top breakage position 7 towards the cutting direction, that is, this position is the opening position of the grouting borehole 5;

[0028] S4: When the working face is being mined, and a grouting borehole 5 is able to grout into the pressure-bearing protective layer 1 of the bottom plate, a paste-like filling material is injected from the grouting borehole 5 into the grouting layer. At this time, the basic top at the grouting borehole 5 is not broken, and the ground pressure on the bottom plate in 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] This invention only performs grouting and filling at the end of the goaf, so a paste-like filling material is selected. Compared with fly ash slurry material, the paste-like filling material has poor fluidity. This characteristic allows it to be accurately filled within the range of the goaf end used for grouting, avoiding the filling material from flowing too widely, which is not conducive to controlling it within the range of the goaf end used for grouting.

[0030] The injected paste-like filling material gradually lifts the bottom bearing protective layer 1 and the uniform fracture zone 2 and fracture expansion zone 3 of the bottom plate within the goaf end range used for grouting. Under the action of grouting, the uniform fracture zone 2 and fracture expansion zone 3 of the bottom plate will increase the damage range, and the looseness of the irregular rock blocks in the fracture expansion zone 3, i.e., the degree of fragmentation, will also increase. This further fills the goaf space and compresses the delamination zone 4 in the masonry beam structure at both ends of the mining boundary (or reduces the amount of delamination generated in the delamination zone 4). Together with the paste-like filling material, it offsets part of the space formed by coal seam mining, thereby reducing the equivalent mining height of the coal seam within the goaf end range used for grouting, thereby reducing the settlement of the overlying strata, controlling the development degree of goaf boundary fissures and surface fissures, and reducing surface subsidence.

[0031] This invention involves grouting and filling the end of the goaf. After filling, the bottom plate of the goaf end exhibits an expanded and bulging shape, gradually transforming from the original "cliff-like" structure into a "basin-like" structure. Compared to traditional goaf structures, the basin-like structure formed by the expansion and anti-arching effect can effectively support the overlying strata corresponding to the delamination zone 4 in the masonry beam structure on both sides of the mining boundary, avoiding the fracture or delamination phenomenon of the overlying strata of the delamination zone 4 due to the loss of coal body support.

Claims

1. A method for reducing settlement by filling the bottom plate at the end of a goaf, characterized in that, Includes the following steps: S1: Determine the extent of the floor failure zone below the coal seam. The floor failure zone includes a floor fracture expansion zone and a floor uniform fracture zone. In the floor fracture expansion zone, the floor strata are fractured in an irregular network pattern, exhibiting expansion characteristics due to gaps between the fractured blocks. In the floor uniform fracture zone, the floor strata exhibit regular longitudinal and transverse fractures, forming water-conducting channels. A certain thickness of rock strata below the floor failure zone is selected as the floor pressure-bearing protective layer. Under grouting pressure, the floor pressure-bearing protective layer arches upwards but does not generate fractures that connect to the upper floor failure zone, or the generated fractures do not connect with the fractures in the floor failure zone. The lowest rock strata of the floor pressure-bearing protective layer have low elastic modulus and good water-tightness. S2: The goaf floor area directly below the delamination zone in the masonry beam structure is taken as the goaf end range for grouting; S3: The bottom interface of the pressure-bearing protective layer of the bottom plate is used as the grouting layer, and grouting boreholes are constructed to connect the grouting layer; at the advance working face mining position, grouting boreholes are constructed in the horizontal roadways on both sides of the working face towards the coal seam bottom plate grouting layer within the range of the end of the goaf for grouting, and the grouting boreholes are inclined in the plane towards the cutting direction; the grouting boreholes are constructed in pairs at a certain distance from the cutting direction along the working face advancing direction in the horizontal roadways on both sides of the working face; S4: During working face mining, when a grouting borehole can grout into the pressure-bearing protective layer of the floor, a paste-like filling material is injected into the grouting layer from the grouting borehole. The injected paste-like filling material gradually lifts the pressure-bearing protective layer of the floor and the uniform fracture zone and fracture expansion zone of the floor above it within the range of the goaf used for grouting. Under the action of grouting, the uniform fracture zone and fracture expansion zone of the floor will increase the damage range, and the looseness of the irregular rock blocks in the fracture expansion zone of the floor will also increase, further filling the goaf space and compressing the delamination zone in the delamination area of ​​the masonry beam structure on both sides of the mining boundary. Together with the paste-like filling material, it offsets part of the space formed by coal seam mining, thereby reducing the equivalent mining height of the coal seam within the range of the goaf used for grouting, thereby reducing the settlement of the overlying strata, controlling the development degree of goaf boundary fissures and surface fissures, and reducing surface subsidence.

2. The method for reducing settlement by filling the bottom plate at the end of a goaf according to claim 1, characterized in that, In step S3, along the working face advancing direction, grouting boreholes are drilled sequentially at a certain distance from the pre-break position of the basic top to the cutting direction.

3. The method for reducing settlement by filling the bottom plate at the end of the goaf according to claim 2, characterized in that, In step S4, the paste-like filling material is selected as a composite material containing cement, bentonite, and polymer components.

Images