An active mountainous coal mining ground fissure reduction method based on isolation ditch

Abstract

The application discloses an active mountainous coal mining ground fissure reduction method based on isolation trenches, and comprises the following steps: firstly, an initial numerical model is established, an initial ground subsidence curve is obtained, and a ground fissure intensive development position is determined; then, a numerical model under the condition of the ground fissure is established, a ground subsidence curve under the condition of the ground fissure is obtained, and the influence of the ground fissure on the initial ground subsidence curve is studied; then, a plurality of numerical models under the condition of the isolation trenches are established, the influence of the isolation trenches with different parameters on the ground subsidence curve under the condition of the ground fissure is studied, and parameters of the isolation trenches achieving a satisfactory isolation effect are obtained; finally, field construction is carried out according to the parameters of the isolation trenches achieving the satisfactory isolation effect. The application can predict the ground fissure intensive development position in advance through numerical calculation, and the isolation trench is actively set in advance to block the transmission path of the surface deformation and damage caused by the underground coal seam mining in advance.

Description

Technical Field

[0001] This invention belongs to the field of mining damage and ecological restoration, specifically a proactive method for reducing fissures in mountainous coal mining areas based on isolation ditches. Background Technology

[0002] Ground fissures, a typical form of ecological damage during coal mining, cause numerous ecological and environmental problems such as soil degradation, vegetation destruction, and water and sand runoff, while also damaging surface structures such as buildings, farmland, roads, bridges, and water conservancy facilities. The prevention and control of ground fissures has become a crucial issue urgently needing to be addressed in the field of mining subsidence and ecological restoration. Existing methods for treating ground fissures in coal seams are mainly passive and avoidance-based.

[0003] Passive prevention and control methods are methods for treating ground fissures after their development. The basic principle is to classify ground fissures into tensile, step-type, open-type, graben-type, and subsidence-type based on on-site surveys, and then treat them according to the development characteristics of different types, following a process of "filling the fissures → leveling the site → vegetation restoration." For surface structures, subsidence is generally predicted through mining, and a relatively wide coal pillar is left under villages, rivers, or buildings; or resource mining in this area is directly abandoned, leaving it underground; or methods such as filling mining or strip mining are used, but these significantly reduce resource recovery rates and have poor economic benefits. For surface structures, structural damage caused by ground fissures is generally resisted by reinforcing the building structure and foundation, but this inevitably increases design and construction costs. A document with application number 202010327316.7 discloses a method for treating surface subsidence fissures in shallow-buried thick coal seam mining based on the Gufang Group. Based on the development characteristics of wide fissures, local topographical modification is carried out in the fissure development area to form artificial channels, combined with biological measures for ecological restoration. The document with application number 201911162933.X discloses a method for treating coal mining subsidence in the western aeolian sandy area. Based on the distribution pattern of mining subsidence in the aeolian sandy area, it combines crack filling with desertification prevention, soil and water conservation and vegetation restoration.

[0004] Avoidance-based prevention methods refer to maintaining a safe distance between buildings and severely subsided areas to prevent damage from ground fissures. For example, mining areas are categorized into simple, moderate, and complex types based on the complexity of their geological environment and the degree of subsidence. The degree of mining subsidence is assessed based on factors such as the impact area, geological hazards, aquifers, topography, and land resources, determining the minimum avoidance distance for buildings and structures. Application No. 201811204373.5 discloses a method for predicting the degree of surface subsidence damage in flat areas under loose strata, using the maximum width and maximum fault height of ground fissures as predictive indicators to evaluate the degree of surface subsidence damage. Application No. 201810869987.9 discloses a method for evaluating the degree of surface subsidence damage in coal mining areas, obtaining a grading standard for the degree of surface subsidence based on evaluation indicators. However, this method requires buildings to avoid ground fissures at a certain distance, inevitably reducing land resource utilization. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the technical problem this invention aims to solve is to provide an active method for reducing ground fissures in mountainous coal mining areas based on isolation trenches.

[0006] The technical solution of this invention to solve the aforementioned technical problem is to provide an active method for reducing ground fissures in mountainous coal mining areas based on isolation trenches, characterized in that the method includes the following steps:

[0007] Step 1: Establish an initial numerical model, obtain the initial surface subsidence curve, and determine the location of strong ground fissure development;

[0008] Step 2: Establish a numerical model for the presence of ground fissures, obtain the surface subsidence curve for the presence of ground fissures, and study the influence of ground fissures on the initial surface subsidence curve in Step 1.

[0009] Step 3: Establish numerical models with several isolation trenches in existence, study the influence of isolation trenches with different parameters on the surface subsidence curve with ground fissures obtained in Step 2, and obtain the parameters for the isolation trenches to achieve satisfactory isolation effect.

[0010] Step 4: Based on the parameters obtained in Step 3 for achieving satisfactory isolation effect of the isolation trench, carry out on-site construction.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0012] (1) Based on the re-clarification of the effectiveness, applicability and economy of passive and avoidance prevention and control methods, this invention proposes an active method for reducing ground fissures in mountainous coal mining based on isolation trenches. By numerical calculation, the location of strong ground fissure development is predicted in advance, and isolation trenches are set up in advance to block the transmission path of surface deformation and damage caused by underground coal seam mining.

[0013] (2) Based on the characteristics of surface subsidence in mountainous areas and guided by the theory of mining subsidence and ecological restoration, this invention predicts surface subsidence and sets up isolation ditches in advance on the surface, thus realizing the proactive protection of the target before mining. This changes the previous situation where ground fissures had already developed and the surface had already subsided after mining, and the ground fissures were passively treated.

[0014] (3) This invention achieves proactive prevention and control of ground fissure disasters, reduces surface subsidence and deformation caused by ground fissure development, and reduces the avoidance distance of surface infrastructure. It truly realizes the transfer, guidance and reduction of the damage to the surface caused by ground fissure development. The principle is scientific, the construction is simple, convenient and quick, and safe and effective.

[0015] (4) This invention combines ground fissure treatment with surface environmental protection, which is of great practical significance for promoting the ecological restoration of coal mining subsidence areas in mountainous areas, protecting the ecological environment and building green mines. It can not only achieve proactive prevention and control of ground fissure disasters, but also achieve the unity of social, ecological and economic benefits.

[0016] (5) This invention uses an isolation trench to transfer and reduce the damage of ground fissures to the surface. On the one hand, the isolation trench reduces the damage range of ground fissures to the surface, blocks the propagation path of the stress field to a certain extent, and prevents the expansion of the surface damage range; on the other hand, the isolation trench separates the target protected object from the moving rock mass, and the isolation trench is filled with loose filling material. When the rock strata continue to move, it squeezes the loose filling material, so that the force cannot be transmitted to the target protected object, and blocks the force propagation path to a certain extent. At the same time, because the loose filling material has a certain pressure relief and stress-relieving effect, it also weakens the degree of force. Attached Figure Description

[0017] Figure 1 This is an overall flowchart of the present invention;

[0018] Figure 2 This is a numerical simulation result of the horizontal movement curve of the ground surface on the working surface in Embodiment 1 of the present invention;

[0019] Figure 3 This is a numerical simulation result diagram of the horizontal deformation curve of the surface covering the working surface in Embodiment 1 of the present invention;

[0020] Figure 4This is a schematic diagram showing the location of strongly developed ground fissures on the working surface of Embodiment 1 of the present invention;

[0021] Figure 5 This is a surface subsidence curve diagram under the presence of ground fissures in Embodiment 1 of the present invention;

[0022] Figure 6 This is a surface subsidence curve diagram under the presence of the isolation ditch in Embodiment 1 of the present invention.

[0023] Figure 7 This is a schematic diagram of the on-site construction of Embodiment 1 of the present invention.

[0024] In the diagram, 1 is the ground surface, 2 is the target protection object, 3 is the ground fissure, 4 is the isolation ditch, 5 is the filling material, and 6 is the topsoil. Detailed Implementation

[0025] Specific embodiments of the present invention are given below. These specific embodiments are only used to further illustrate the present invention in detail and do not limit the scope of protection of the claims of the present invention.

[0026] This invention provides an active method for reducing ground fissures in mountainous coal mining areas based on isolation trenches (hereinafter referred to as the method), characterized by the following steps:

[0027] Step 1: Establish an initial numerical model, obtain the initial surface subsidence curve, and determine the location of strong ground fissure development;

[0028] First, the physical and mechanical parameters of the coal and rock strata and the topsoil in the predicted area of ​​surface subsidence over the coal mining face are obtained. Then, based on the physical and mechanical parameters of the coal and rock strata and the topsoil, an initial numerical model is established. The initial numerical model is then calculated using numerical analysis methods to simulate the surface subsidence process after coal mining and obtain the initial surface subsidence curve. Finally, based on the initial surface subsidence curve, areas with strong ground fissure development are delineated, and the locations of strong ground fissure development are delineated within these areas to provide a basis for determining the location of isolation ditch 4.

[0029] Preferably, in step 1, the physical and mechanical parameters of the coal and rock strata include tensile strength, shear modulus, bulk modulus, cohesion, internal friction angle, density, thickness, and a composite columnar section.

[0030] Preferably, in step 1, the physical and mechanical parameters of the topsoil layer include the topsoil layer type, soil structure, soil layer thickness, soil elastic modulus, cohesion, unit weight, and internal friction angle.

[0031] Preferably, in step 1, the initial surface subsidence curve includes the horizontal movement curve and the horizontal deformation curve of the initial surface subsidence.

[0032] Preferably, in step 1, the initial numerical model is established from bottom to top using FLAC3D finite element software, based on the thickness and properties of each rock layer and the comprehensive columnar section.

[0033] Preferably, in step 1, the lateral boundary of the initial numerical model is set with horizontal constraints, the bottom boundary is set with vertical constraints, and the top is subjected to a load according to the coal seam burial depth.

[0034] Step 2: Establish a numerical model for the presence of ground fissures, obtain the surface subsidence curve for the presence of ground fissures, and study the influence of ground fissures on the initial surface subsidence curve in Step 1.

[0035] First, obtain the basic parameters and intensity parameters of the ground fissures. Then, based on the basic parameters and intensity parameters of the ground fissures, set a ground fissure simulation unit at a certain location in the initial numerical model obtained in step 1 where there is no boundary effect, and establish a numerical model with the presence of ground fissures. Then, perform simulation calculations on the numerical model with the presence of ground fissures to obtain the surface subsidence curve with the presence of ground fissures. Compare it with the initial surface subsidence curve obtained in step 1 to obtain the influence of ground fissures on the initial surface subsidence curve in step 1.

[0036] Preferably, in step 2, the basic parameters of the ground fissure include the fissure dip angle, displacement, and underground extension depth. These parameters are obtained through on-site surveys and statistical analysis. Generally, the fissure dip angle is 60-80°, the displacement is 10-100cm, and the underground extension depth can reach up to 100 meters. For ease of numerical calculation, the underground extension depth is taken as 50m.

[0037] Preferably, in step 2, the ground fissure strength parameters include cohesion, internal friction angle, normal stiffness modulus, and shear stiffness modulus.

[0038] Preferably, in step 2, a certain location is more than 80m away from the boundary of the initial numerical model.

[0039] Preferably, in step 2, the ground fissure simulation unit is achieved by establishing a contact surface, including the upper plate and the lower plate of the ground fissure; the surface subsidence of the upper plate and the lower plate of the ground fissure is achieved by setting different ground fissure displacement amounts.

[0040] Step 3: Establish numerical models with several isolation trenches 4 in existence, study the influence of isolation trenches 4 with different parameters on the surface subsidence curve with the ground fissures obtained in Step 2, and obtain the parameters for isolation trenches 4 to achieve satisfactory isolation effect.

[0041] S3.1 Determine the location of isolation trench 4: Based on the location of the strong development of ground fissures determined in step 1, set up isolation trench 4 at the ground fissure 3 located at the location of the strong development of ground fissures; the safe distance between isolation trench 4 and the target protected object 2 shall be set according to the needs of the target protected object 2.

[0042] Preferably, in step S3.1, the safe distance between the isolation ditch 4 and the target protected object 2 is greater than 20m.

[0043] S3.2. Based on the location of the isolation trench 4 obtained in step S3.1, obtain the parameters of the isolation trench 4 and the parameters of the filling material 5 in the isolation trench 4;

[0044] Preferably, in step S3.2, the parameters of the isolation trench 4 include the shape and size of the isolation trench 4;

[0045] The isolation trench 4 has a rectangular cross-sectional shape; its dimensions include the length, width, and depth of the isolation trench 4. In this embodiment, the length of the isolation trench 4 is approximately equal to (i.e., very similar to) or the same as the extension length of the ground fissure, the width is 0.5~1m, and the depth is 10~15m.

[0046] Preferably, in step S3.2, the filling material 5 in the isolation trench 4 is a mixture of coal gangue, sawdust, and soil (preferably loess); the mass ratio of coal gangue, sawdust, and soil is 1:0.5~0.7:0.5~0.7; the coal gangue, sawdust, and soil are dry-mixed in a mixer to form the filling material 5. The coal gangue is obtained through tunnel excavation, and the coal gangue used is coal gangue powder with a particle size of less than 100mm; the sawdust is obtained from a wood processing plant; and the soil is sourced locally.

[0047] S3.3. Set different parameters for isolation trench 4, and excavate isolation trench 4 on the numerical model with the existence of ground fissures obtained in step 2 to establish several numerical models with the existence of isolation trench 4.

[0048] S3.4. Simulate and calculate the numerical models for all isolation trenches 4 to obtain the surface subsidence curves for each isolation trench 4. Then compare them with the surface subsidence curves for each isolation trench 4 obtained in step 2 to obtain the influence of isolation trench 4 with different parameters on the surface subsidence curves for the existence of ground fissures. Finally, obtain the parameters for isolation trench 4 to achieve satisfactory isolation effect.

[0049] Preferably, in step S3.4, the standard for the isolation trench 4 to achieve a satisfactory isolation effect is that the horizontal deformation of the ground surface of the target protected object 2 is less than 2 mm / m.

[0050] Step 4: Based on the parameters obtained in Step 3 for achieving satisfactory isolation effect in isolation trench 4, carry out on-site construction.

[0051] Preferably, in step 4, the on-site construction method for the isolation trench 4 is as follows: a top-down stripping method is adopted. Based on the location of the isolation trench 4 obtained in step 3 and the parameters for achieving a satisfactory isolation effect, a small dose of emulsion explosive is used for cyclic blasting from top to bottom, and the blasted rock fragments are transported to the ground via a hoisting winch; then, the filling material 5 is laid layer by layer in the isolation trench 4 until it reaches 0.5~1.0m from the ground surface; then, topsoil 6 is covered until it is 0.1~0.3m above the ground surface; finally, it is compacted to prevent surface water and rainwater from seeping into the isolation trench 4.

[0052] Example 1:

[0053] The mine is located on the eastern wing of the Daqing syncline in the Baoding mining area of ​​Panzhihua City, Sichuan Province. The minefield is dominated by fold structures, with 50 major faults, primarily trending NNE and NE. There are currently six mineable coal seams within the minefield, belonging to a close-range coal seam group mining operation. The 43158 working face is located in the third mining area. To the east of the working face are the already mined 43154 and 43156 working faces; to the west is the 1400-meter track incline; to the south is the area damaged by excessive mining in small mines; and to the north is the area yet to be mined. The working face has a strike length of 908m and a dip length of 185m. The working face mines coal seam No. 15, with an average thickness of 1.5m. The maximum burial depth of the coal seam is 113m. The surface topography is low to medium mountain terrain and complex slopes, with crisscrossing valleys. The topsoil is reddish-brown clay, approximately 3m thick.

[0054] Step 1: Establish an initial numerical model, obtain the initial surface subsidence curve, and determine the location of strong ground fissure development;

[0055] (1) Obtaining the physical and mechanical parameters of the coal and rock strata: Through field investigation, production geological data of working face 43158 were collected and analyzed, and a comprehensive columnar section of coal seam No. 15 was obtained. The pseudo-roof is 0.17m of silty mudstone, the immediate roof is 2.29m of silty mudstone, the basic roof is nearly 4m of siltstone, and the floor is 1.82m of siltstone. The physical and mechanical parameters of the coal and rock strata are shown in Table 1.

[0056]

[0057] Physical and mechanical parameters of the topsoil were obtained: Based on field surveys and experimental results, the topsoil had a high water content, ranging from 50% to 70%. The soil samples had a void ratio greater than 1.3, indicating a state of stiff plasticity and plasticity. The internal friction angle was relatively small, mostly less than 20°, and the cohesion was relatively large, mostly greater than 33 kPa. The physical and mechanical parameters of the topsoil are shown in Table 2.

[0058]

[0059] (2) Based on the physical and mechanical parameters of the coal and rock strata and the topsoil, an initial numerical model is established, and then the initial surface subsidence curve is obtained (e.g., Figure 2 and Figure 3 (as shown)

[0060] The model dimensions are 1060m × (100~240m), with 80m coal pillars on each side boundary and a working face advance length of 900m. The excavation step distance is determined to be 20m based on the basic top cycle. The constitutive equations follow the Mohr-Coulomb yield criterion. Horizontal stress is applied along the vertical direction of the model, and the lateral pressure coefficient is set to 1.2. The displacement and velocity at the bottom and side boundaries of the model are limited to 0. The numerical calculation process is as follows: initial stress equilibrium → distributed excavation of coal seam No. 15. Monitoring points are set every 10m along the model slope, for a total of 100 monitoring points along the working face direction, to monitor surface subsidence changes during the mining of coal seam No. 15.

[0061] (3) Delineate the locations of strong ground fissures (e.g.) Figure 4 (as shown)

[0062] Along the strike of the working face (30-180m): Numerical simulation results show that the horizontal surface movement is 167-323mm and the horizontal deformation is -14.4-4.3mm / m. The negative horizontal deformation value indicates that the surface covered by the working face (30-180m) is in a compressed state, which is unfavorable for the development of ground fissures.

[0063] Along the working face strike of 180–390 m: The horizontal displacement of the covered surface continuously increases, reaching a maximum of 781 mm. Meanwhile, the horizontal deformation of the surface changes from negative to positive, with an average value of 7.18 mm / m, indicating that the covered surface has transitioned from a compressive to a tensile state. The surface in this area is a steep slope with a maximum gradient of 54.7°. Due to the combined effects of mining subsidence and steep slope slippage, the surface is conducive to the development of ground fissures.

[0064] Along the working face strike of 390-540m: Field investigation revealed that the surface covered by this area is a valley with a gentle slope and underdeveloped gullies. The maximum horizontal surface movement was 487mm, and the minimum was 178mm. The horizontal deformation changed from positive to negative, ranging from -5.89 to -12.78 mm / m. This indicates that the valley is generally under compression, which is not conducive to the development of ground fissures.

[0065] Along the working face strike of 540–810 m: The slope of the surface covered by the working face continuously increases from 540 m to 810 m. Specifically, the surface slope between monitoring points 570 m and 600 m increases from 6° to 26.1°, with horizontal deformation values ​​ranging from 0.33 to 5.47 mm / m, indicating that the covered surface is generally under tension. The horizontal displacement values ​​at monitoring points 570 m, 780 m, and 810 m are positive, while the horizontal displacement values ​​at other points are negative, indicating that the surface near these three points is conducive to the development of ground fissures.

[0066] Along the strike of the working face 810~900m: The maximum horizontal movement of the surface covered by the working face 810~900m is 57mm and the maximum horizontal deformation is 1.82mm / m. It can be seen that the coal seam mining has little impact on the subsidence of the surface at this location.

[0067] In summary, along the strike of the working face, the locations with strong ground fissures are 180-390m, 570m, 780m, and 810m above the surface from the opening to the stopping line.

[0068] Step 2: Establish a numerical model for the presence of ground fissures, obtain the surface subsidence curve for the presence of ground fissures, and study the influence of ground fissures on the initial surface subsidence curve in Step 1.

[0069] (1) Obtaining basic parameters of ground fissures: Based on the field survey results of ground fissures already developed in the mining area and the development characteristics of common ground fissures, the dip angle of the ground fissures was determined to be 70°. The underground extension depth of ground fissures varies, with some reaching hundreds of meters. Based on existing geological survey results, the underground extension depth of the ground fissures was determined to be 50m. The displacement of ground fissures varies depending on the development type of the ground fissures. Taking the tensile ground fissure as an example, the maximum displacement of the ground fissure can reach 1m. In this embodiment, based on existing field survey results, the displacement is set at 50cm.

[0070] The ground fissure strength parameters were obtained by searching existing literature, as shown in Table 3.

[0071]

[0072] (2) Based on the basic parameters and intensity parameters of the ground fissure, set up a ground fissure simulation unit at a certain location in the initial numerical model obtained in step 1 where there is no boundary effect, and establish a numerical model under the presence of ground fissures.

[0073] (3) Perform numerical simulation calculations on the ground fissures to obtain the surface subsidence curves (e.g., ...) Figure 5 As shown in the figure, the influence of ground fissures on the initial surface subsidence curve obtained in step 1 is obtained by comparing it with the initial surface subsidence curve obtained in step 1.

[0074] Step 3: Establish numerical models with several isolation trenches in existence, study the influence of isolation trenches with different parameters on the surface subsidence curve with ground fissures obtained in Step 2, and obtain the parameters for the isolation trenches to achieve satisfactory isolation effect.

[0075] S3.1 Determine the location of the isolation trench: Based on the location of the strongly developed ground fissures determined in step 1 (e.g., Figure 4An isolation ditch is set up near the location where ground fissures are strongly developed (in this embodiment, the isolation ditch 4 is set up 10m away from the location where ground fissures are strongly developed); the safe distance between the isolation ditch and the target protected object is set according to the needs of the target protected object; under the premise that ground fissures have not developed, the stronger the reduction of horizontal surface deformation by setting up the isolation ditch 4 in advance, the less likely it is to cause ground fissures to develop in the area.

[0076] S3.2. Based on the location of the isolation trench obtained in step S3.1, obtain the parameters of the isolation trench and the parameters of the filling material in the isolation trench; the isolation trench 4 is rectangular, with a width of 1.0m and a depth of 10m.

[0077] S3.3 Set different parameters for the isolation trenches, and excavate the isolation trenches on the numerical model with the existence of ground fissures obtained in step 2 to establish several numerical models with the existence of isolation trenches.

[0078] S3.4. Simulate the numerical models for all isolation trenches to obtain their respective surface subsidence curves. Compare these curves with the surface subsidence curves for the ground fissures obtained in step 2 to determine the influence of different isolation trench parameters on the surface subsidence curves for the ground fissures. Obtain the parameters required for the isolation trenches to achieve satisfactory isolation effects and the surface subsidence curves for the isolation trenches with these parameters (e.g., ...). Figure 6 (As shown).

[0079] Step 4: Based on the parameters obtained in Step 3 for achieving satisfactory isolation effect of the isolation trench, carry out on-site construction, such as... Figure 7 As shown.

[0080] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A proactive method for reducing ground fissures in mountainous coal mining based on isolation trenches, characterized in that, The method includes the following steps: Step 1: First, obtain the physical and mechanical parameters of the coal and rock strata and the topsoil in the predicted area of ​​surface subsidence over the coal mining face; then, based on the physical and mechanical parameters of the coal and rock strata and the topsoil, establish an initial numerical model; then, calculate the initial numerical model to simulate the surface subsidence process after coal seam mining and obtain the initial surface subsidence curve; finally, based on the initial surface subsidence curve, delineate the area with strong ground fissure development, and then delineate the location of strong ground fissure development in the area with strong ground fissure development to provide a basis for determining the location of the isolation trench. The initial surface subsidence curve includes the horizontal movement curve and the horizontal deformation curve of the initial surface subsidence; Step 2: First, obtain the basic parameters and intensity parameters of the ground fissure; then, based on the basic parameters and intensity parameters of the ground fissure, set up a ground fissure simulation unit at a certain location in the initial numerical model obtained in Step 1 where there is no boundary effect, and establish a numerical model with the presence of the ground fissure; then, perform simulation calculations on the numerical model with the presence of the ground fissure to obtain the surface subsidence curve with the presence of the ground fissure, and compare it with the initial surface subsidence curve obtained in Step 1 to obtain the influence of the ground fissure on the initial surface subsidence curve of Step 1. Step 3: S3.1 Determine the location of the isolation trench: Based on the location of the strong ground fissures determined in step 1, set up an isolation trench at the ground fissures in the location of the strong ground fissures; the safe distance between the isolation trench and the target protected object shall be set according to the needs of the target protected object; S3.

2. Based on the location of the isolation trench obtained in step S3.1, obtain the parameters of the isolation trench and the parameters of the filling material in the isolation trench; S3.3 Set different parameters for the isolation trenches, and excavate the isolation trenches on the numerical model with the existence of ground fissures obtained in step 2 to establish several numerical models with the existence of isolation trenches. S3.

4. Simulate and calculate the numerical models under the presence of all isolation ditches to obtain the surface subsidence curves under the presence of each isolation ditches. Then compare them with the surface subsidence curves under the presence of ground fissures obtained in step 2 to obtain the influence of isolation ditches with different parameters on the surface subsidence curves under the presence of ground fissures, and obtain the parameters for the isolation ditches to achieve satisfactory isolation effect. Step 4: Based on the parameters obtained in Step 3 for achieving satisfactory isolation effect of the isolation trench, carry out on-site construction.

2. The active method for reducing ground fissures in mountainous coal mining based on isolation trenches according to claim 1, characterized in that, In step 1, the physical and mechanical parameters of the coal and rock strata include tensile strength, shear modulus, bulk modulus, cohesion, internal friction angle, density, thickness, and a comprehensive columnar section. In step 1, the physical and mechanical parameters of the topsoil layer include topsoil type, soil structure, soil thickness, soil elastic modulus, cohesion, unit weight, and internal friction angle. In step 1, the initial numerical model was established from bottom to top using FLAC3D finite element software, based on the thickness and properties of each rock layer and the comprehensive columnar section. In step 1, the lateral boundary of the initial numerical model is set with horizontal constraints, the bottom boundary is set with vertical constraints, and the top is loaded according to the coal seam burial depth.

3. The active method for reducing ground fissures in mountainous coal mining based on isolation trenches according to claim 1, characterized in that, In step 2, the basic parameters of the ground fissure include the ground fissure dip angle, displacement, and underground extension depth. In step 2, the ground fissure strength parameters include cohesion, internal friction angle, normal stiffness modulus, and shear stiffness modulus; In step 2, a certain location is more than 80m away from the boundary of the initial numerical model; In step 2, the ground fissure simulation unit is achieved by establishing a contact surface, including the hanging wall and the footwall of the ground fissure; the surface subsidence of the hanging wall and the footwall of the ground fissure is achieved by setting different ground fissure displacement amounts.

4. The active method for reducing ground fissures in mountainous coal mining based on isolation trenches according to claim 3, characterized in that, The dip angle of the ground fissure is 60-80°, and the displacement is 10-100cm; the underground extension depth is taken as 50m.

5. The active method for reducing ground fissures in mountainous coal mining based on isolation trenches according to claim 1, characterized in that, In step S3.1, the safe distance between the isolation ditch and the target protected object is greater than 20m; In step S3.2, the parameters of the isolation trench include the shape and size of the isolation trench; the cross-sectional shape of the isolation trench is rectangular; the dimensions include the length, width and depth of the isolation trench. In step S3.2, the filling material in the isolation trench is a mixture of coal gangue, sawdust and soil; the mass ratio of coal gangue, sawdust and soil is 1:0.5~0.7:0.5~0.7; the coal gangue, sawdust and soil are dry-mixed in a mixer to form the filling material. In step S3.4, the standard for the isolation trench to achieve a satisfactory isolation effect is that the horizontal deformation of the ground surface of the target protected object is less than 2 mm / m.

6. The active method for reducing ground fissures in mountainous coal mining based on isolation trenches according to claim 5, characterized in that, In step S3.2, the length of the isolation trench is approximately equal to the extension length of the ground fissure, the width is 0.5–1m, and the depth is 10–15m. Coal gangue is obtained through tunnel excavation, and the coal gangue is made of coal gangue powder with a particle size of less than 100mm; sawdust is obtained from wood processing plants; soil is sourced locally.

7. The active method for reducing ground fissures in mountainous coal mining based on isolation trenches according to claim 1, characterized in that, In step 4, the on-site construction method of the isolation ditch is as follows: based on the location of the isolation ditch obtained in step 3 and the parameters for achieving a satisfactory isolation effect, emulsion explosives are used to perform cyclic blasting from top to bottom, and the blasted rock fragments are transported to the ground; then, the filling material is laid layer by layer in the isolation ditch until it reaches 0.5 to 1.0m from the ground surface; then, topsoil is covered until it is 0.1 to 0.3m above the ground surface; finally, it is compacted to prevent surface water and rainwater from seeping into the isolation ditch.

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