A method for mitigating mining subsidence by injecting water into the bottom strata to expand the anti-arch structure.

Abstract

This invention relates to the field of coal mining and subsidence control, specifically to a method for mitigating mining subsidence by injecting water into the floor strata to induce arching and reduce subsidence. The method includes determining the extent of the floor failure zone below the coal seam, selecting a certain thickness of strata below the failure zone as an isolation and protection zone, and establishing a water-injection expansion zone below the isolation and protection zone. The adjacent strata are non-swellable when exposed to water. Directional boreholes are drilled in the working face roadway, with the horizontal section of the borehole located within the water-injection expansion zone. After the working face passes a certain horizontal section of the directional borehole but before reaching its opening, high-pressure water is injected into the borehole. The injection pressure is then reduced, and the injection volume is controlled to reach the water absorption limit of the expansion zone. This invention causes the floor strata to expand by injecting water, thereby lifting the floor strata to support the goaf, reducing the subsidence of the overlying strata, and controlling surface subsidence. This invention achieves subsidence reduction solely through water injection expansion, resulting in low cost and environmental friendliness.

Description

Technical Field

[0001] This invention relates to the field of coal mining and subsidence control, specifically to a method for mitigating mining subsidence by injecting water into the bottom rock strata to expand and reverse arch. Background Technology

[0002] Coal mining has created large-scale goaf areas, causing the overlying strata to gradually collapse under gravity, leading to surface subsidence. This surface deformation can cause cracks, tilting, and even collapse of buildings and infrastructure (such as houses, roads, bridges, and railway tunnels), posing a serious threat to the lives and property of residents. Surface subsidence also damages land resources, causing vegetation degradation, disrupting surface drainage systems, leading to river flow interruptions, lake drying up, and a drop in groundwater levels, affecting the sustainable use of regional water resources. Simultaneously, the subsidence process destroys habitats, affecting the balance and stability of the mining area's ecosystem. Surface subsidence caused by coal mining has profound negative impacts on the environment, economy, and society, urgently requiring effective prevention and control measures to reduce its harm.

[0003] Currently, some mining areas typically employ backfilling mining methods to address issues such as environmental damage, surface subsidence, and coal resource waste. By filling the mined space with solid, paste, or high-water-content backfill materials during the mining process, a backfill body is formed to support and control the overlying strata, thereby significantly reducing the adverse environmental impact of coal mining. However, commonly used partial backfilling mining techniques require the construction of a separate backfilling pipeline system at the stope or surface, increasing coal mining costs and causing backfilling interference problems that hinder efficient coal mining. Summary of the Invention

[0004] To address the high cost and low efficiency of existing subsidence control methods, this invention proposes a method for mitigating mining subsidence by injecting water into the bottom rock strata to expand and reverse arch, applicable to situations where the coal seam floor contains easily absorbing and expanding rock strata; the method includes the following steps:

[0005] S1: Determine the extent of the floor failure zone below the coal seam. Select a rock stratum of a certain thickness below the floor failure zone as an isolation protection zone. The isolation protection zone arches upward after the water-injected expansion zone expands, but does not generate fissures that connect to the upper floor failure zone, or the generated fissures do not connect with the fissures in the floor failure zone. The lower part of the isolation protection zone is the water-injected expansion zone. The rock strata in the water-injected expansion zone have the characteristic of swelling when exposed to water. The rock strata adjacent to the isolation protection zone and the water-injected expansion zone are selected to be rock strata that do not swell when exposed to water.

[0006] S2: Construct directional boreholes in the roadways on one or both sides of the working face. The horizontal section of the directional borehole is constructed in the water-injection expansion zone. The directional borehole is constructed in the direction of the opposite roadway in the width direction of the working face, and in the direction of the cut-out in the working face advancement direction.

[0007] S3: Install packers at the borehole opening of the directional borehole to seal the rock strata corresponding to the bottom plate failure zone and the isolation protection zone;

[0008] S4: After the working face has passed a certain horizontal section of a directional borehole and before reaching the borehole opening, high-pressure water is injected into the directional borehole to form cracks in the water-injected expansion zone. Then, the water injection pressure is reduced and the water injection volume is controlled to reach the water absorption limit of the water-injected expansion zone.

[0009] Preferably, in step S1, the water-injection expansion zone is selected from rock strata rich in clay minerals.

[0010] Preferably, in step S2, the directional drilling is parallel to the width direction of the working face.

[0011] The inventive point and beneficial effects of this invention: Based on the characteristic of water-absorbing and swelling rock layers existing outside the foundation failure zone, this invention designs these layers as water-absorbing and swelling zones. Then, directional drilling is used to fracturing these zones, creating conductive fractures. Water is then injected to cause the rock layers within the water-absorbing and swelling zones to expand, forming an anti-arch effect between the water-absorbing and swelling zones and the overlying foundation rock layers. This supports the overlying rock layers and mitigates subsidence. Compared to traditional methods, this method does not require large amounts of filling material; the expansion effect is achieved solely through water injection. This water injection expansion does not cause secondary pollution to the environment, and the anti-arch structure significantly enhances the bearing capacity of the foundation, reducing the surface subsidence rate, which aligns with modern green mining principles. Attached Figure Description

[0012] Figure 1 This is a schematic diagram illustrating the mechanism of water injection expansion and anti-arching of the bottom rock strata to mitigate mining subsidence in this invention;

[0013] Figure 2 This is a schematic diagram of the directional drilling construction plan in the bottom rock stratum water injection expansion anti-arch to mitigate mining subsidence according to the present invention;

[0014] In the diagram: Water-injection expansion zone-1, isolation protection zone-2, uniform fracture zone of the base plate-3, fracture expansion zone of the base plate-4, fissure zone-5, collapse zone-6, directional drilling-7, fissure-8, borehole packer-9. Detailed Implementation

[0015] To better understand the technical content of this invention, specific embodiments are described below in conjunction with the accompanying drawings. Various aspects of this invention are described with reference to the accompanying drawings, which illustrate numerous illustrative embodiments. The embodiments of this invention are not limited to those shown in the drawings. It should be understood that this invention is implemented through any of the various concepts and embodiments described above, as well as the concepts and embodiments described in detail below, because the concepts and embodiments disclosed in this invention are not limited to any particular implementation. Furthermore, some aspects of this invention can be used alone or in any suitable combination with other aspects disclosed in this invention.

[0016] like Figure 1-2 To address the high cost and low efficiency issues of existing subsidence control methods, this invention proposes a method for mitigating mining subsidence by injecting water into the bottom rock strata to expand and reverse arch, applicable to situations where the coal seam floor contains easily absorbing and expanding rock strata; the specific steps include:

[0017] S1: Based on the lithology and thickness of the floor strata, the extent of the floor failure zone below the coal seam is determined. This failure zone includes a floor fracture and expansion zone 4 and a floor uniform fracture zone 3. In the floor fracture and expansion zone 4, the floor strata are fractured in an irregular network pattern, with relatively small fragments. Due to the gaps between the fragments, they exhibit expansion characteristics. In the floor uniform fracture zone 3, the floor strata have regularly distributed longitudinal and transverse fractures, forming relatively large, regular fragments. This failure zone can form water-conducting channels. A certain thickness of rock is selected below the floor failure zone. A layer (usually containing multiple rock layers) serves as an isolation and protection zone 2. After the water-injected expansion zone 1 expands, the isolation and protection zone 2 arches upwards, but does not generate fissures that connect to the upper bottom plate failure zone, or the generated fissures do not connect with the fissures in the bottom plate failure zone. The lower part of the isolation and protection zone 2 is the water-injected expansion zone 1. The rock layers in the water-injected expansion zone 1 are capable of swelling when exposed to water. The rock layers adjacent to the isolation and protection zone 2 and the water-injected expansion zone are selected as rock layers that do not swell when exposed to water. The water-injected expansion zone 1 is generally selected as rock layers rich in clay minerals (montmorillonite, illite, etc.).

[0018] S2: Construct directional boreholes 7 in the roadways on one or both sides of the working face. The horizontal section of the directional boreholes 7 is constructed in the water-injection expansion zone 1. The directional boreholes 7 are constructed in the direction of the opposite roadway in the width direction of the working face. Preferably, the directional boreholes 7 are parallel to the width direction of the working face. The directional boreholes 7 are constructed in the direction of the cutting eye in the working face advancing direction (i.e., the length direction of the working face).

[0019] S3: Install packer 9 at the opening of directional borehole 7 to seal the rock strata corresponding to the bottom plate failure zone and the isolation protection zone 2, so as to prevent water from seeping into non-target strata through directional borehole 7 during injection;

[0020] S4: When the working face has passed the horizontal section of a certain directional borehole 7 and before reaching the opening of that directional borehole 7 (e.g. Figure 2 (Solid line position within the working face) Using a high-pressure pump, a suitable amount of water is first injected into the directional borehole 7 under high pressure, forming a fissure 8 in the water-injection expansion zone 1. Then, the water injection pressure is reduced and the water injection volume is controlled to reach the water absorption limit of the rock strata in the water-injection expansion zone 1. After water injection, the rock strata in the water-injection expansion zone 1 undergo a water absorption expansion effect, and the volume of the water-injection expansion zone 1 expands, lifting the isolation protection zone 2, the uniform fracture zone 3 of the floor, and the floor failure zone 4. Among them, the uniform fracture zone 3 of the floor and the fracture expansion zone 4 of the floor will increase the damage range under the volume expansion effect of the water-injection expansion zone 1, and the looseness of the irregular rock blocks in the fracture expansion zone 4, i.e., the degree of fragmentation, will also increase, further filling the goaf space. Together with the volume expansion of the water-injection expansion zone 1, it offsets part of the space formed by coal seam mining, thereby reducing the equivalent mining height of the coal seam, reducing the height of the caving zone 6 and the fissure zone 5, and controlling the subsidence of the overlying strata to a certain extent, thus reducing surface subsidence.

[0021] This invention is not limited to the preferred embodiments described above. Anyone can derive other methods in various forms under the guidance of this invention. Any technical solution that is the same as or similar to this application falls within the protection scope of this invention.

Claims

1. A method for mitigating mining subsidence by injecting water into the bottom rock strata to expand and create an arch-like inverted arch, 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, and the fractured blocks are relatively small. Due to the gaps between the fractured blocks, they have a certain expansion characteristic. In the floor uniform fracture zone, the floor strata have regularly distributed longitudinal and transverse fractures, forming relatively large, regular fractured blocks. The floor failure zone can form water-conducting channels. Below the floor failure zone, a certain thickness of rock strata is selected as an isolation and protection zone. After the water-injected expansion zone expands, the isolation and protection zone arches upward, 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 lower part of the isolation and protection zone is the water-injected expansion zone. The rock strata in the water-injected expansion zone have the characteristic of swelling when exposed to water. The rock strata adjacent to the isolation and protection zone and the water-injected expansion zone are selected as rock strata that do not expand when exposed to water. S2: Construct directional boreholes in the roadways on one or both sides of the working face. The horizontal section of the directional borehole is constructed in the water-injection expansion zone. The directional borehole is constructed in the direction of the opposite roadway in the width direction of the working face, and in the direction of the cut-out in the working face advancement direction. S3: Install packers at the borehole opening of the directional borehole to seal the rock strata corresponding to the bottom plate failure zone and the isolation protection zone; S4: After the working face pushes past a certain horizontal section of a directional borehole and before reaching the borehole opening, high-pressure water is injected into the directional borehole to form cracks in the water-injected expansion zone. Then, the water injection pressure is reduced and the water injection volume is controlled to reach the water absorption limit of the water-injected expansion zone. After water injection, the rock strata in the water-injected expansion zone undergo a water absorption and expansion effect, causing the volume of the water-injected expansion zone to expand and lift the isolation and protection zone, the uniform fracture zone of the floor, and the floor failure zone. Among them, the uniform fracture zone and the fractured expansion zone of the floor will increase their damage range under the volume expansion effect of the water-injected expansion zone, and the looseness of the irregular rock blocks in the fractured expansion zone of the floor will also increase, filling the entire goaf space. Together with the volume expansion of the water-injected expansion zone, it offsets part of the space formed by coal seam mining, thereby reducing the equivalent mining height of the coal seam, lowering the height of the caving zone and fracture zone, and controlling the subsidence of the overlying strata to a certain extent, thus reducing surface subsidence.

2. The method for mitigating mining subsidence by water injection and expansion of the bottom strata to reduce subsidence, as described in claim 1, is characterized in that... In step S1, the water-injection expansion zone is selected from rock strata rich in clay minerals.

3. The method for mitigating mining subsidence by injecting water into the bottom strata to expand and reverse arch, as described in claim 1, is characterized in that... In step S2, the directional drilling is parallel to the width direction of the working face.

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