Method for constructing tailing pond in coal mining subsidence area and performing ecological reclamation

Abstract

The invention discloses a method for constructing a tailing pond in a coal mining subsidence area and carrying out ecological reclamation, which comprises the following steps: acquiring the height of a water flowing fissure zone of the coal mining subsidence area, and judging the hydraulic communication condition between the water flowing fissure zone and the tailing pond according to the height of the water flowing fissure zone; if no hydraulic communication exists, riprapping and silt squeezing are conducted in the water accumulation area of the coal mining subsidence area, and a stable dam foundation is formed; on the stable dam foundation, an initial dam is constructed through coal gangue, and reinforcement treatment is conducted on the initial dam through high-strength geotechnical cloth; obtaining surface subsidence prediction data of the coal mining subsidence area, and dynamically adjusting the height of the initial dam, the ore drawing position and the position of a flood drainage pipe according to the surface subsidence prediction data; during the operation period of the tailings pond, dust suppression measures are adopted for green and environment-friendly operation; and after the tailing pond is closed, ecological restoration is conducted on the beach face of the pond area. According to the method, benign transformation of the subsidence area, the tailing pond and the reclamation land is achieved, and the ecological and economic value of the land is improved.

Description

Technical Field

[0001] This invention belongs to the field of tailings dam engineering in metallurgical mines and ecological reclamation technology in coal mining subsidence areas, and particularly relates to a method for constructing tailings dams and carrying out ecological reclamation in coal mining subsidence areas. Background Technology

[0002] Currently, in the field of tailings disposal in metallurgical mines, traditional tailings dam construction mainly relies on natural valley terrain to build valley-type tailings dams, or on plains to form flat-ground tailings dams by building dams around the perimeter. The latter often requires a large amount of land resources. Meanwhile, for surface subsidence areas formed by coal mining activities, existing remediation methods mainly include converting them into fishponds, draining and dewatering, or backfilling with solid waste such as coal gangue. In addition, some research focuses on the resource utilization of tailings themselves, such as using them to produce building materials. Regarding tailings dam site selection, existing technologies have attempted to construct tailings dams directly above unfilled goaf areas. The core method involves detailed geological surveys, numerical simulation analysis of overburden stability, and site selection to assess feasibility and complete dam construction, aiming to solve the problem of safe tailings storage.

[0003] However, the aforementioned existing technical solutions still have significant limitations: First, this method is essentially a static preliminary assessment and one-time construction, lacking a dynamic control mechanism for dam height, ore discharge, and flood discharge facility locations during the long-term operation of the tailings dam, taking into account continuous geological subsidence (such as the continuous activity in coal mining subsidence areas). This results in insufficient safety risk management during operation. Second, the construction process fails to organically integrate with the co-disposal of regional solid waste (such as large stockpiles of coal gangue), failing to address the dual problems of dam material sourcing and solid waste accumulation. Third, for dam construction on particularly soft foundations (such as waterlogged subsidence areas), traditional initial dam technologies have limited adaptability, posing challenges to dam strength and long-term stability. Fourth, the solutions do not systematically address environmental protection measures such as dust control during tailings dam operation. Fifth, they do not consider land reuse and ecological value enhancement after tailings dam closure, failing to achieve the ultimate ecological and economic goal of "turning waste into treasure." Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method for constructing tailings dams and carrying out ecological restoration in coal mining subsidence areas, comprising: The height of the water-conducting fracture zone in the coal mining subsidence area is obtained, and the hydraulic connectivity between the water-conducting fracture zone and the tailings dam is determined based on the height of the water-conducting fracture zone. If there is no hydraulic connection, rocks are dumped and silt is squeezed out in the waterlogged areas of the coal mining subsidence zone to form a stable dam foundation; On the stable dam foundation, an initial dam is constructed using coal gangue, and the initial dam is reinforced with high-strength geotextile. Obtain surface subsidence prediction data of the coal mining subsidence area, and dynamically adjust the height of the initial dam, the ore discharge location, and the location of the flood discharge pipe based on the surface subsidence prediction data; During the operation of the tailings dam, dust suppression measures are adopted to ensure green and environmentally friendly operation. After the tailings dam is closed, ecological restoration will be carried out on the beach area of ​​the dam.

[0005] Preferably, the process of obtaining the height of the water-conducting fracture zone in the coal mining subsidence area includes: Calculate the height of the coal seam collapse zone and the height of the water-conducting fracture zone in the coal mining subsidence area, and determine whether the height of the water-conducting fracture zone is less than the thickness of the overlying bedrock, so as to ensure that the water-conducting fracture zone does not connect to the Quaternary topsoil layer.

[0006] Preferably, the stone-throwing and silt-draining process includes: By throwing stones into the waterlogged area, the silt is squeezed out of the dam foundation area, forming a stable foundation with the required bearing capacity.

[0007] Preferably, the process of constructing the initial dam using coal gangue and reinforcing the initial dam with high-strength geotextile includes: The initial dam body is constructed by layering and compacting coal gangue, and high-strength geotextile is laid in layers within the dam body. Among them, continuous reinforcement is arranged within the bottom 1 / 3 height range and the top 2 meters of the dam body, and structural reinforcement with a length of not less than 4 meters is arranged in the remaining parts, and the ends of the reinforcement are wrapped.

[0008] Preferably, the process of constructing the initial dam using coal gangue includes: Drainage ditches and collection wells are installed at the outer slope toe of the initial dam to collect and drain seepage water from the dam body; The high-strength geotextile is folded back at the slope of the initial dam, and the folding length is determined based on the geotextile's tensile strength, friction coefficient, and slope gradient.

[0009] Preferably, the process of dynamically adjusting the initial dam height based on the surface subsidence prediction data includes: Based on the predicted surface subsidence data, the width is reserved in the dam design of the subsidence area, and the dam structure is designed in sections according to different subsidence amounts, so that the dam body can maintain the predetermined cross-sectional shape after the subsidence stabilizes.

[0010] Preferably, the process of dynamically adjusting the ore dumping location based on the surface subsidence prediction data includes: Based on the latest surface subsidence prediction map, the location of ore dumping and the orientation of the beach will be adjusted before the flood season to ensure the reserved length of safe dry beach and flood control capacity.

[0011] Preferably, the process of dynamically adjusting the location of the drainage pipe based on the surface subsidence prediction data includes: The flood drainage system in the settlement area is constructed in phases, and the construction time of the flood drainage facilities is determined according to the reservoir elevation and settlement prediction.

[0012] Preferably, the dust suppression measures include: During the non-flood season, dry beach areas are covered to suppress dust. During the flood season, multiple points are used to release ore in rotation to keep the beach moist. The pond field method is used to build dams. Embankments are built in front of the dams and filled with tailings slurry, which is then naturally deposited to form sub-dams.

[0013] Preferably, the ecological restoration includes: The reservoir surface was leveled after closure, covered with soil, and planted with shrubs and weeds. Watering was then carried out to restore vegetation in the reservoir area.

[0014] Compared with the prior art, the present invention has the following advantages and technical effects: This invention employs a combined coal gangue and high-strength geotextile dam construction technology, which not only effectively disposes of coal mine solid waste but also significantly enhances the strength and stability of the initial dam on soft foundations, expanding the applicable geographical area of ​​the technology. Through a dynamic adjustment mechanism based on subsidence prediction, real-time safety control of the dam body, ore discharge, and flood discharge facilities is achieved, ensuring the safe operation of the tailings dam throughout its entire lifecycle. Green operation modes such as phased dust suppression and pond-based dam construction effectively control environmental pollution. Finally, through systematic ecological reclamation after dam closure, a positive transformation is achieved from subsidence area to tailings dam to reclaimed land, enhancing the ecological and economic value of the land and forming a comprehensive system solution integrating safe construction, environmentally friendly operation, and ecological restoration. Attached Figure Description

[0015] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings: Figure 1 This is a simplified diagram of seepage calculation for a homogeneous dam with a permeable foundation and no drainage facilities, according to an embodiment of the present invention. Figure 2 This is a schematic diagram of the sliding surface features corresponding to the unreinforced condition in an embodiment of the present invention; Figure 3 This is a schematic diagram of the reinforcement method according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the calculation model and the most dangerous sliding surface features in an embodiment of the present invention; Figure 5 This is a schematic diagram showing the calculation results of the foldback length in an embodiment of the present invention; Figure 6 This is a schematic diagram of the surface subsidence contour line results according to an embodiment of the present invention. Detailed Implementation

[0016] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0017] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0018] This embodiment provides a method for constructing tailings ponds and carrying out ecological restoration in coal mining subsidence areas, including: Obtain the height of the water-conducting fracture zone in the coal mining subsidence area, and determine the hydraulic connectivity between the water-conducting fracture zone and the tailings dam based on the height of the water-conducting fracture zone. If there is no hydraulic connection, rocks are dumped and silt is squeezed out in the waterlogged areas of the coal mining subsidence zone to form a stable dam foundation; On the stable dam foundation, the initial dam is constructed using coal gangue, and high-strength geotextile is used to reinforce the initial dam. Obtain surface subsidence prediction data for coal mining subsidence areas, and dynamically adjust the initial dam height, ore discharge location, and flood discharge pipe location based on the surface subsidence prediction data; During the operation of the tailings dam, dust suppression measures are adopted to ensure green and environmentally friendly operation. After the tailings dam is closed, ecological restoration will be carried out on the beach area of ​​the dam.

[0019] This embodiment uses coal gangue to construct the initial dam and reinforces the dam body with high-strength geotextile to improve its strength. Based on surface subsidence predictions, the dam body is heightened and the locations of ore discharge and flood discharge pipes are dynamically adjusted. During non-flood seasons, a covering method is used; during flood seasons, a multi-point rotating ore discharge method is employed, and the tailings pond method is used for dam construction to control dust pollution during operation, ensuring the tailings dam operates in a green and environmentally friendly manner. After the tailings dam is closed, ecological restoration is achieved using relevant ecological reclamation technologies.

[0020] Furthermore, the process of obtaining the height of the water-conducting fracture zone in the coal mining subsidence area includes: Calculate the height of the coal seam collapse zone and the height of the water-conducting fracture zone in the coal mining subsidence area, and determine whether the height of the water-conducting fracture zone is less than the thickness of the overlying bedrock, in order to ensure that the water-conducting fracture zone does not conduct to the Quaternary topsoil layer.

[0021] Furthermore, rock dumping and silt removal includes: By throwing stones into the waterlogged area, the silt is squeezed out of the dam foundation area, forming a stable foundation with the required bearing capacity.

[0022] Furthermore, the process of constructing the initial dam using coal gangue and reinforcing it with high-strength geotextile includes: The initial dam body is constructed by layering and compacting coal gangue, and high-strength geotextile is laid in layers within the dam body. Among them, continuous reinforcement is arranged within the bottom 1 / 3 height range and the top 2 meters of the dam body, and structural reinforcement with a length of not less than 4 meters is arranged in the remaining parts, and the ends of the reinforcement are wrapped.

[0023] Furthermore, this embodiment utilizes a method of combining coal gangue and high-strength geotextile for dam construction, achieving the goal of using solid waste generated during coal mine production as the building material for the initial dam and greatly enhancing its stability. This solves the problems of limited applicability of existing technologies and the accumulation of some solid waste from coal mines.

[0024] Furthermore, the process of constructing the initial dam using coal gangue includes: Drainage ditches and collection wells are set at the outer slope toe of the initial dam to collect and drain seepage water from the dam body; High-strength geotextile is folded back at the slope of the initial dam. The folding length is determined based on the geotextile's tensile strength, friction coefficient, and slope gradient.

[0025] Furthermore, the process of dynamically adjusting the initial dam height based on surface subsidence prediction data includes: Based on the predicted data of surface subsidence, the width is reserved in the design of the dam body in the subsidence area, and the dam body structure is designed in sections according to different amounts of subsidence, so that the dam body can maintain the predetermined cross-sectional shape after the subsidence stabilizes.

[0026] Furthermore, the process of dynamically adjusting the ore dumping location based on surface subsidence prediction data includes: Based on the latest surface subsidence prediction map, the location of ore dumping and the orientation of the beach will be adjusted before the flood season to ensure the reserved length of safe dry beach and flood control capacity.

[0027] Furthermore, the process of dynamically adjusting the location of the flood discharge pipe based on surface subsidence prediction data includes: The flood drainage system in the settlement area is constructed in phases, and the construction time of the flood drainage facilities is determined according to the reservoir elevation and settlement prediction.

[0028] Furthermore, this embodiment utilizes a method of dynamically adjusting the dam height and the positions of the ore discharge and flood discharge pipes to achieve the goal of ensuring the operational safety of the tailings dam. This solves the problem that existing technologies only provide a one-time safe tailings dam construction solution, but cannot guarantee the safety of the tailings dam during operation.

[0029] Furthermore, dust suppression measures include: During the non-flood season, dry beach areas are covered to suppress dust. During the flood season, multiple points are used to release ore in rotation to keep the beach moist. The pond field method is used to build dams. Embankments are built in front of the dams and filled with tailings slurry, which is then naturally deposited to form sub-dams.

[0030] Furthermore, this embodiment utilizes a green and environmentally friendly operating mode to achieve the goal of green and environmentally friendly operation of tailings ponds, solving the problem that existing technologies have not provided a method for green and environmentally friendly operation of tailings ponds.

[0031] Furthermore, ecological restoration includes: The reservoir surface was leveled after closure, covered with soil, and planted with shrubs and weeds. Watering was then carried out to restore vegetation in the reservoir area.

[0032] This embodiment utilizes the method of ecological restoration after tailings closure to "turn waste into treasure" and solves the problem that existing technologies do not fully utilize the value created by tailings closure.

[0033] As a preferred implementation method, taking the construction of the Sijiaying Iron Mine tailings dam in the Fanggezhuang Coal Mine subsidence area of ​​Tangshan City, Hebei Province as an example, this embodiment introduces a method for constructing a tailings dam and carrying out ecological restoration in a coal mining subsidence area, including the following steps performed sequentially: S1. Calculate the height of the water-conducting fracture zone in the overlying strata of the coal mining subsidence area and confirm that the water-conducting fracture zone is not hydraulically connected to the tailings dam.

[0034] S2. In the waterlogged areas of the coal mining subsidence zone, rocks are dumped to squeeze out silt and form a stable dam foundation.

[0035] S3. After constructing the initial dam using coal gangue, reinforce the dam body with high-strength geotextile to improve the strength of the initial dam.

[0036] S4. Based on the prediction of surface subsidence, the dam body is heightened and the location of the ore discharge and flood discharge pipes is dynamically adjusted.

[0037] S5. During non-flood seasons, the tailings dam should be covered, while during flood season, a multi-point rotating ore discharge method should be used, and the tailings pond method should be adopted to construct dams to control dust pollution during operation.

[0038] S6. After the tailings dam is closed, ecological restoration is achieved using relevant ecological reclamation technologies.

[0039] Specifically, S1, distribution of overlying fracture characteristics; By analyzing the overlying strata failure characteristics of the coal mining subsidence area and calculating the height of the water-conducting fracture zone, the geological feasibility of the construction can be demonstrated to ensure that the water-conducting fracture zone will not be hydraulically connected to the tailings dam.

[0040] The height of the collapse zone is calculated using equation (1), and the height of the water-conducting fracture zone is calculated using equation (2) or equation (3). The larger value of the two equations is taken as the final result.

[0041] (1) (2) (3) In the formula: H m H represents the height of the landslide zone, in meters (m). li M represents the height of the water-conducting fracture zone, in meters; M represents the mining thickness of the coal seam, in meters.

[0042] The engineering geological conditions of Fanggezhuang Coal Mine are classified as moderately complex, while the hydrogeological conditions are classified as complex. No karst collapse columns were found in the tailings pond areas No. 1 and No. 2. As shown in Table 1, the average mining thicknesses of coal seams 5, 7, 8, 9, 11, 12, and 12.5 are 1.20m, 3.80m, 2.20m, 2.40m, 1.10m, 5.00m, and 2.20m, respectively, with average interlayer spacings of 33.41m, 9.81m, 13.57m, 15.96m, 18.38m, and 6.95m, respectively. The average thickness of the Quaternary topsoil layer is 123.96m, and the thickness of the bedrock overlying coal seam 5 is 239.95m.

[0043] The calculated heights of the caving zone and water-conducting fracture zone for each coal seam are shown in Table 1. The comprehensive value of the water-conducting fracture zone height for coal seam 12.5 is 130 m, which is less than the thickness of the overlying bedrock. Therefore, the water-conducting fracture zone will not connect to the Quaternary topsoil layer and has no hydraulic connection with the deeper water-conducting fracture zone. The overlying rock fracture analysis results verify the feasibility of constructing a tailings dam in the coal mining subsidence area of ​​Fanggezhuang Coal Mine.

[0044] Table 1 S2, shoveling to displace silt; In this embodiment, considering that the initial tailings dam is built on a waterlogged subsidence area, the method of dumping rocks to squeeze out silt is used to ensure the stability of the foundation. That is, when the roadbed outside the dam and the foundation of the initial dam are located in a pond, large stones are used for backfilling to squeeze the silt in the pond out of the foundation area.

[0045] S3, Initial dam constructed using a combination of coal gangue and high-strength geotextile; S3.1 Use coal gangue to construct the initial dam; This embodiment uses industrial waste coal gangue to construct the initial dam. The Guye area has numerous coal mines, resulting in a huge stockpile of coal gangue, but lacks a means of consumption, making its long-term storage an environmental burden. This embodiment, through relevant compaction tests, strength tests, permeability tests, and chemical mineral tests, proves that coal gangue can be used as a dam construction material. While ensuring the stability and safety of the dam body, it broadens the uses of coal gangue and reduces the land occupied by stockpiling. One dam alone consumed 714,000 m³ of coal gangue. 3 .

[0046] S3.2. Based on the characteristics of coal gangue, add anti-seepage devices; This embodiment calculates the seepage situation based on the non-uniformity coefficient of coal gangue.

[0047] The seepage of a coal gangue dam body under the condition that there are no drainage facilities inside or outside the dam body is calculated using a formula method for steady flow. A simplified calculation diagram is shown below. Figure 1 .

[0048] The downstream escape height h0 is calculated using the following formula, with two cases: when k > k0: When k≤k0: (5) Then solve for the wetting line equation using the following formula: (6) The expression for the unit width flow rate q is: (7) In the formula: k is the permeability coefficient of the dam body, in m / d; k0 is the permeability coefficient of the dam foundation, taken as 1.0 m / d; H1 is the upstream water level, taken as 6.5 m; H2 is the downstream water level, considered as no water; h0 is the height of the downstream outlet point, in m; m1 is the upstream slope ratio, taken as 1:1.75; m2 is the downstream slope ratio, taken as 1:2; b is the width of the top of the dam body, taken as 5.0 m; H is the height of the dam body, taken as 8.0 m; T is the thickness of the permeable foundation, taken as 7.0 m.

[0049] For the case where there is no water downstream, the slope along the seepage section AB is: (8) The slope along the foundation section BC is: (9) This embodiment considers the non-uniformity and variation range of the dam's permeability coefficient, with permeability coefficients of 20 m / d, 10 m / d, 5 m / d, 1 m / d, 0.5 m / d, and 0.1 m / d respectively. The permeability coefficient of the permeable foundation is 1.0 m / d. Corresponding to the above conditions, the height of the seepage outlet point on the slope and other relevant parameters are calculated using the Lizheng software. The initial dam seepage calculation results are shown in Table 2. At the seepage outlet point on the phreatic line, when the slope seepage streamline inclination angle is tangent to the slope angle θ, it represents the most dangerous situation of seepage failure. Calculating the critical seepage gradient under the most dangerous condition plays a crucial role in analyzing the dam's safety.

[0050] Table 2 The critical seepage gradient under the most dangerous condition is: (10) In the formula, The effective unit weight of coal gangue is taken as 10 kN / m³. 3 ; The specific weight of water is taken as 10 kN / m³. 3 ; Let be the internal friction angle of the coal gangue, taken as 39°; The downstream slope of the dam is taken as 26.565°. (11) Then J cr =0.277. With a safety factor of 2.0, the allowable hydraulic gradient is 0.138, which is less than the hydraulic gradient of 0.20 for horizontal seepage, so quicksand may occur.

[0051] Due to the high non-uniformity coefficient of coal gangue and the presence of some degree of particle size deficiency, piping failure may occur under seepage conditions. The critical hydraulic gradient for piping failure is: (12) The specific gravity of coal gangue is taken as 2.55, corresponding to a porosity of 30%, and its critical hydraulic gradient for piping failure is 1.435. A safety factor of 2.0 is used, and the allowable hydraulic gradient is 0.717. Since the hydraulic gradient of the phreatic line of the dam body is around 0.20, which is less than the critical hydraulic gradient, piping failure will not occur in the dam body.

[0052] The above calculations show that, in this embodiment without seepage control measures, the phreatic line of the dam body emerges on the downstream slope. To ensure the safety of the dam body, this embodiment adopts necessary dewatering and drainage facilities to minimize the height of the phreatic line and control the hydraulic gradient at the groundwater outflow point. Simultaneously, necessary reverse filtration measures are implemented on the upstream and downstream slopes of the dam body.

[0053] Therefore, this embodiment, based on the characteristics of coal gangue, incorporates drainage facilities to prevent and reduce the seepage hazards of tailings dams. A drainage ditch is installed at the outer foot of the initial dam to concentrate seepage water from the tailings pond into a collection well within the ditch, from which it is then pumped into the pond by submersible pumps or used for dust suppression spraying.

[0054] S3.3. High-strength geotextile is used to reinforce the initial dam; This embodiment takes into account that the reservoir area is located above a continuously developing subsidence pit. To improve the stability of the dam, high-strength geotextile is used to reinforce the dam body. Taking one reservoir as an example, a total of 924,000 m³ of specially made high-strength reinforced geotextile is used. 2 263,000 m² of ordinary 500g / m² geotextile 2Safety measures taken in response to hazardous factors.

[0055] (1) Calculate the parameters; The calculation covers six materials, with the allowable tensile strength of geotextile taken as 10 kN / m. The laying spacing is taken as 0.4 m, 0.6 m, 0.8 m, and 1.0 m, respectively. Calculation parameters for coal gangue and dam foundation silt are shown in Table 3.

[0056] Table 3 (2) Reinforcement process; 1) Calculate the stability parameters before reinforcement; To analyze the overall stability of the dam body under unreinforced conditions, this embodiment uses the calculation formula recommended in the design code for roller-compacted earth-rock dams to analyze the dam's stability. The potential sliding surface location falls into two categories: one is a circular path running through the initial dam's toe; the other is an overall circle cut out from the bottom of the initial dam, starting from the upstream tailings deposit. Comparatively, the former has a smaller safety factor.

[0057] Figure 2 The sliding surface is the toe circle that cuts through the top of the dam and slides out from the dam toe. The coordinates of the center point of the sliding arc are X=5.0, Y=12.0m, R=12m. The static safety factor is 1.333, and the safety factor under the 8-degree earthquake condition is 1.169, which meets the requirements of the specification. The labels ① to ⑤ correspond to the materials in Table 3.

[0058] Although the overall settlement of the foundation is relatively large, the axial elongation deformation of the geotextile is required to be limited and comparable to the horizontal tensile deformation value of the foundation. Under the condition of a tensile modulus of 60 MPa (equivalent to 300 kN / m), the tensile force of the geotextile should be less than 10 kN / m; under the condition of a tensile modulus not greater than 200 MPa, the tensile force of the geotextile should not be greater than 30 kN / m.

[0059] Due to the influence of geotextile strain, the stress field variation characteristics of the dam body under different reinforcement spacing are not obvious. Generally, continuous reinforcement should be arranged within the bottom 1 / 3 of the dam height; an appropriate amount of continuous reinforcement should also be arranged within the top 2.0m of the dam. The vertical spacing of the reinforcement can be 0.4m to 0.6m. In other locations, "structural" reinforcement to maintain the integrity of the dam body can be arranged. The length of the reinforcement should not be less than 4.0m, and the vertical spacing of the reinforcement can be 0.6m to 1.0m. Wrapping measures should be taken at the ends of the reinforcement, such as... Figure 3 As shown.

[0060] 3) Calculate the stability parameters after reinforcement; Stability calculations for reinforced coal gangue dams show that the location of the most dangerous sliding surface is similar to that in the unreinforced case. (See details...) Figure 4The materials labeled ① to ⑤ correspond to those in Table 3.

[0061] The static and dynamic stability of the dam body before and after reinforcement both meet the specifications. Overall, the seismic action reduces the dam's safety factor by approximately 12%. When the seismic intensity is 9 degrees, corresponding to 0.6m of vertical reinforcement, the dam's safety factor decreases by more than 10%. The calculation results of the dam's safety factor are shown in Table 4.

[0062] Table 4 This embodiment considers the possible reduction of the shear strength parameter of coal gangue under the influence of factors such as construction and groundwater. It simulates and calculates the dam safety factor under four working conditions when the internal friction angle increases from 30° to 38° under the condition of vertical laying spacing of 0.6m. See Table 5 for details.

[0063] According to the calculation results, the safety factor of the dam body against sliding increases with the increase of the internal friction angle of the dam body. Even under the condition of an internal friction angle of 30°, the static and dynamic stability of the dam body is guaranteed.

[0064] This analysis shows that reinforcement is very effective in enhancing the seismic performance of dams, and reinforcement of dams can lead to the wider application of this technology.

[0065] Table 5 4) Determining the fold length of geotextile; According to specifications, when the vertical spacing of geotextiles is greater than 0.4m, to improve the reinforcement effect and prevent damage to the masonry slope due to slippage, the geotextiles need to be folded back on the slope surface. Figure 5 As shown.

[0066] The tensile strength of the geotextile is: (13) The frictional resistance corresponding to the foldback length is: (14) Then the foldback length for: (15) Since the tension of the bottom layer of fabric on the dam slope is the greatest, and for a 1:2 slope with an internal friction angle of 35° for the coal gangue and a structural condition of 8m height, the calculated foldback length is 3.08m.

[0067] S4. Dynamically adjust the dam height, ore discharge location, and flood discharge pipe location; S4.1 Surface subsidence patterns; To obtain the displacement angle values ​​of the bedrock and topsoil layers, this embodiment deploys subsidence observation stations on the surface of the Fanggezhuang Coal Mine. Two observation lines are arranged along the strike of the coal seam, and three observation lines are arranged along the dip of the coal seam. Simultaneously, two observation roadways are excavated in the bedrock above the first longwall face of Coal Mine No. 7. Through analysis of the observation station data, the displacement angle of the bedrock between the incline and strike of the Fanggezhuang Coal Mine is preliminarily determined to be 72°, the displacement angle of the topsoil layer is 35°, and the initial mining subsidence coefficient is 0.80 ~ 0.93.

[0068] The surface movement and deformation pattern of the Fanggezhuang coal mine conforms to the probability integral method model. The maximum deformation value on the main cross-section of the moving basin is calculated as follows: (16) Among them W max i represents the maximum surface subsidence, in mm. max K represents the maximum inclination of the earth's surface, in mm / m. max U represents the maximum curvature of the Earth's surface, in units of 10⁻³ / m. max 1 is the maximum horizontal movement on the surface, in mm; m is the normal mining thickness of the coal seam, in m; q is the subsidence coefficient; α is the dip angle of the coal seam; b is the horizontal movement coefficient; r is the main influence radius, in m.

[0069] This embodiment uses the direction parallel to the strike and within the downhill calculation boundary of the inclined main section passing through the goaf as the abscissa, and the direction parallel to the dip direction and within the left calculation boundary of the strike main section passing through the goaf as the ordinate, to obtain the deformation calculation formula for any point (x, y) on any cross-section forming an angle φ with the coal seam strike. The calculation formula for surface subsidence is as follows: (17) The formula for calculating the tilt of the earth's surface is as follows: (18) The formula for calculating the curvature of the Earth's surface is as follows: (19) The formula for calculating horizontal deformation of the Earth's surface is as follows: (20) The parameters predicted using the probability integral method selected in this calculation are shown in Table 6. Due to the unavailability of mining data for the working face before 2012, the calculated cumulative surface subsidence contour lines within the delineated area of ​​tailings ponds No. 1 and No. 2 from 2012 to 2024 are shown in Table 6. Figure 6 As shown on the left, the newly added subsidence contour lines of the 65 working faces after 2024 are as follows: Figure 6 As shown on the right.

[0070] Table 6 S4.2 Dynamically adjust the dam height; Taking the second reservoir as an example, this embodiment has made reservations for the settlement area by predicting settlement. The initial width of the dam crest of the largest settlement area on the west side is 27.8m, and it is expected that after the final settlement stabilizes, it will be consistent with the non-settlement area at 5m.

[0071] The reservoir is divided into two types: a settlement zone and a non-settlement zone. In the non-settlement zone, the initial dam crest width is 5m, with an upstream slope ratio of 1:1.6 and a downstream slope ratio of 1:2. Reinforced riprap is used for the dam construction, with each layer ranging from 1 to 3.2m in height, wrapped with 600g / m² high-strength reinforced geotextile. The dam axis is approximately 5440m long, and a protective layer is applied to the surface of the filter layer. In the settlement zone, the initial dam is designed with a final crest width of 5m and the same slope ratio, but repair conditions are reserved based on the specific settlement amount. The dam width is adjusted according to location, with the main settlement areas located on the west side and localized areas on the north and south sides. The design divides the dam structure into one type for every 1.6m of settlement, with transition sections between adjacent types. For example, in the westernmost settlement area, the bottom section from 23 to 29m elevation is divided into layers every 1.6m, each layer wrapped with two layers of 600g / m² geotextile; the section from 29 to 35m elevation is divided into layers every 3.2m, each layer wrapped with one layer of the same specification geotextile, and a 90mm permeable brick protective layer is laid on the slope. The initial dam is constructed using reinforced riprap, requiring high-strength reinforced geotextile with the following specifications: 600g / m², tensile strength ≥27kN / m laterally and ≥50kN / m longitudinally, tensile elongation ≥20%, puncture strength ≥5.0kN, permeability coefficient K×10⁻¹~10⁻³cm / s, and equivalent pore size 0.07~0.2mm.

[0072] Due to the unique geological conditions of this tailings dam, the geotextile's elongation rate must reach 20%; otherwise, it is easily broken, affecting the dam's stability. The reinforced geotextile consists of a middle layer (high-strength mesh) and an outer layer of non-woven fabric, needle-punched together. The middle layer enhances tensile strength, while the outer non-woven fabric provides protection, preventing sharp stones from puncturing the middle mesh and ensuring the tensile strength is not compromised, thus guaranteeing dam stability. Adhesive bonding must not be used when splicing the geotextiles, as this will affect the permeability coefficient, interfere with water filtration, and ultimately compromise dam stability. The material used must be aging-resistant polyester fiber; the use of non-aging-resistant polypropylene fibers (such as those used in woven bags) is strictly prohibited.

[0073] S4.3 Dynamically adjust the ore discharge position; In this embodiment, the location of ore dumping and the orientation of the beach are adjusted quarterly before the flood season based on the latest settlement prediction map to ensure that sufficient safe dry beach length is always reserved to guarantee flood control capacity.

[0074] S4.4 Dynamically adjust the position of the flood discharge pipe; Taking the Second Reservoir as an example, the entire backwater wharf is located within a settlement zone, therefore a phased construction approach was adopted. Initially, the inlet elevation of the flood discharge pipe within the dam was 32.5m, the initial dam crest elevation was 35m, the initial reservoir capacity was approximately 22.45 million m³, and the initial service life was approximately 5 years. The flood discharge pipe will require at least 4 years of water intake. The initial flood control capacity of the dam is estimated to exceed 2 million m³, capable of accommodating five 500-year floods (396,000 m³) without external discharge. The flood discharge system section is located in the settlement zone, and it is predicted that this section will settle by 3.5m before it becomes operational. Even if this section of the flood discharge system is completed at this stage, it is expected to be damaged by subsequent settlement.

[0075] For the reasons mentioned above, the construction of the flood discharge steel pipes on the flood discharge and backwater wharf, as well as the external flood discharge system after exiting the dam (the external flood discharge system after exiting the dam refers to the flood discharge steel pipes, stilling basin, and external flood discharge channels erected on the dam body), can be temporarily postponed. Construction of this section of the flood discharge system will begin three years after the reservoir elevation reaches 30.0m and it is put into operation. This will ensure that the flood discharge system is completed within the third to fourth year after the reservoir elevation reaches 32.5m. The flood discharge steel pipes will be installed as the sub-dam is subsequently raised to avoid damage to the flood discharge facilities due to settlement.

[0076] S5, a green and environmentally friendly operating mode; S5.1. Implement dust suppression measures in stages; During the flood season, ore is discharged from multiple points in rotation to keep the beach surface moist and avoid dust generation. During the non-flood season, dry beach areas are directly covered to physically suppress dust.

[0077] S5.2 Change the traditional method of building dams; This embodiment modifies the "alluvial method" for dam construction, instead using mechanical sand-pushing to build a sub-dam on the beach surface 50m to 70m inward from the dam body. However, the beach surface needs to be dried beforehand to facilitate the entry of construction machinery. Disturbing the dry beach surface generates significant dust. The alternative method uses a pond-field approach, where a small embankment is built in front of the dam, filled with tailings slurry, and naturally deposited to form the sub-dam. During construction, both the tailings inside and outside the embankment are moistened, effectively eliminating dust.

[0078] S6. Ecological restoration will be carried out after the reservoir is closed; After the beach surface is leveled, to prevent wind erosion and stabilize sand, a 100mm layer of soil is placed on the surface, and the entire beach is then vegetated with shrubs such as cotton locust. When planting, planting pits should be designed, with pit dimensions of at least 30cm in length, width, and depth, and a row and plant spacing of 1m. To ensure tree survival, a 100mm layer of suitable topsoil is added inside the pits, and watering is done after planting. Planting is done in spring and autumn, with watering after planting. Two to three years after planting, depending on the growth, the trees are pruned in autumn. Well-developed root systems and weeds are interspersed among the shrubs. From the subsidence area to the construction of the tailings dam, ecological restoration is finally carried out.

[0079] This embodiment uses solid waste generated during coal mining to construct the initial dam of a tailings dam, simultaneously solving the problems of coal mine solid waste accumulation and the source of materials for the initial dam. This significantly improves the strength of the initial dam, allowing it to be applied to a wider range of areas.

[0080] This embodiment not only ensures safety during tailings dam construction but also dynamically adjusts the dam height and ore discharge location by predicting foundation settlement, guaranteeing safety during operation. During tailings dam operation, this embodiment implements a series of measures to achieve green and environmentally friendly operation. After closure, ecological restoration technologies are used to achieve ecological restoration goals. Through the integration of these technologies, a set of technical solutions is ultimately formed that can be used as a reference for cities facing similar problems.

[0081] The above are merely preferred embodiments of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for constructing tailings dams and carrying out ecological restoration in coal mining subsidence areas, characterized in that, include: The height of the water-conducting fracture zone in the coal mining subsidence area is obtained, and the hydraulic connectivity between the water-conducting fracture zone and the tailings dam is determined based on the height of the water-conducting fracture zone. If there is no hydraulic connection, rocks are dumped and silt is squeezed out in the waterlogged areas of the coal mining subsidence zone to form a stable dam foundation; On the stable dam foundation, an initial dam is constructed using coal gangue, and the initial dam is reinforced with high-strength geotextile. Obtain surface subsidence prediction data of the coal mining subsidence area, and dynamically adjust the height of the initial dam, the ore discharge location, and the location of the flood discharge pipe based on the surface subsidence prediction data; During the operation of the tailings dam, dust suppression measures are adopted to ensure green and environmentally friendly operation. After the tailings dam is closed, ecological restoration will be carried out on the beach area of ​​the dam.

2. The method according to claim 1, characterized in that, The process of obtaining the height of the water-conducting fracture zone in a coal mining subsidence area includes: Calculate the height of the coal seam collapse zone and the height of the water-conducting fracture zone in the coal mining subsidence area, and determine whether the height of the water-conducting fracture zone is less than the thickness of the overlying bedrock, so as to ensure that the water-conducting fracture zone does not connect to the Quaternary topsoil layer.

3. The method according to claim 1, characterized in that, The rock-throwing and silt-draining process includes: By throwing stones into the waterlogged area, the silt is squeezed out of the dam foundation area, forming a stable foundation with the required bearing capacity.

4. The method according to claim 1, characterized in that, The process of constructing an initial dam using coal gangue and reinforcing the initial dam with high-strength geotextile includes: The initial dam body is constructed by layering and compacting coal gangue, and high-strength geotextile is laid in layers within the dam body. Among them, continuous reinforcement is arranged within the bottom 1 / 3 height range and the top 2 meters of the dam body, and structural reinforcement with a length of not less than 4 meters is arranged in the remaining parts, and the ends of the reinforcement are wrapped.

5. The method according to claim 4, characterized in that, The process of constructing an initial dam using coal gangue includes: Drainage ditches and collection wells are installed at the outer slope toe of the initial dam to collect and drain seepage water from the dam body; The high-strength geotextile is folded back at the slope of the initial dam, and the folding length is determined based on the geotextile's tensile strength, friction coefficient, and slope gradient.

6. The method according to claim 1, characterized in that, The process of dynamically adjusting the initial dam height based on the surface subsidence prediction data includes: Based on the predicted surface subsidence data, the width is reserved in the dam design of the subsidence area, and the dam structure is designed in sections according to different subsidence amounts, so that the dam body can maintain the predetermined cross-sectional shape after the subsidence stabilizes.

7. The method according to claim 1, characterized in that, The process of dynamically adjusting the ore-laying location based on the surface subsidence prediction data includes: Based on the latest surface subsidence prediction map, the location of ore dumping and the orientation of the beach will be adjusted before the flood season to ensure the reserved length of safe dry beach and flood control capacity.

8. The method according to claim 1, characterized in that, The process of dynamically adjusting the location of the flood discharge pipe based on the aforementioned surface subsidence prediction data includes: The flood drainage system in the settlement area is constructed in phases, and the construction time of the flood drainage facilities is determined according to the reservoir elevation and settlement prediction.

9. The method according to claim 1, characterized in that, The dust suppression measures include: During the non-flood season, dry beach areas are covered to suppress dust. During the flood season, multiple points are used to release ore in rotation to keep the beach moist. The pond field method is used to build dams. Embankments are built in front of the dams and filled with tailings slurry, which is then naturally deposited to form sub-dams.

10. The method according to claim 1, characterized in that, The ecological restoration includes: The reservoir surface was leveled after closure, covered with soil, and planted with shrubs and weeds. Watering was then carried out to restore vegetation in the reservoir area.

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