Active mountainous area coal mining ground fracture loss reduction method based on isolation ditch

Abstract

The invention discloses an active mountainous area coal mining ground fracture loss reduction method based on an isolation ditch, and the method comprises the steps: firstly building an initial numerical model, obtaining an initial surface subsidence curve, and determining a ground fracture intense development position; establishing a numerical model in the presence of the ground fracture, obtaining a surface subsidence curve in the presence of the ground fracture, and researching the influence of the ground fracture on the initial surface subsidence curve; establishing a numerical model in the presence of a plurality of isolation ditches, and researching the influence of the isolation ditches with different parameters on the surface subsidence curve in the presence of the ground fissures to obtain parameters for achieving a satisfactory isolation effect of the isolation ditches; and finally, carrying out site construction according to the parameters for achieving the satisfactory isolation effect of the isolation ditch. According to the method, the strong development position of the ground fracture is pre-judged in advance through numerical calculation, the isolation ditch is actively arranged in advance, and a ground surface deformation damage transmission path caused by underground coal seam mining is blocked in advance.

Description

Technical Field

[0001] The invention belongs to the field of mine mining damage and ecological restoration, and specifically is an active mountain coal mining ground fissure damage reduction method based on isolation trenches. Background Art

[0002] Ground fissure disasters, as a typical form of ecological damage in the process of coal mining, bring about many ecological and environmental problems such as soil degradation, vegetation destruction, water and sand bursting, and destroy surface buildings such as houses, farmland, roads, bridges, and water conservancy facilities. The prevention and control of ground fissure disasters has become an important issue that needs to be urgently addressed in the field of mining subsidence and ecological restoration. The existing methods for controlling ground fissures in coal mining are mainly passive and avoidance prevention methods.

[0003] Passive prevention and control methods are methods of treatment after the development of ground fissures. The basic principle is to classify ground fissures into tensile, step, opening, graben, collapse, etc. through on-site surveys. According to the development characteristics of different types of ground fissures, they are treated according to the process of "filling cracks → leveling the site → vegetation restoration". For surface buildings, mining subsidence is generally predicted, and coal pillars of larger width are left under villages, rivers, and buildings; or resource mining is directly abandoned in this area and left underground; or filling mining, strip mining and other methods are adopted in this area, but the resource recovery rate is significantly reduced and the economic benefits are not good. For surface buildings, structural damage caused by ground fissures is generally resisted by strengthening the building structure and foundation, but it will inevitably increase the design and construction costs. The document with application number 202010327316.7 published a method for treating surface collapse cracks in shallow buried thick coal seam mining based on Gufang Group. According to the development characteristics of wide cracks, local terrain transformation is carried out in the crack development area to form artificial channels, and ecological restoration is carried out in combination with biological measures. The document with application number 201911162933.X published a method for controlling coal mining subsidence in the western aeolian sand area. Based on the distribution law of mining subsidence in the aeolian sand area, it combines crack filling with desertification prevention and control, soil and water conservation, and vegetation restoration.

[0004] The avoidance prevention method refers to keeping buildings away from serious surface subsidence areas by setting a certain safety distance to avoid damage from ground fissures. For example, according to the complexity of the geological environment of the mining area and the degree of mining subsidence, it is divided into simple, medium and complex categories. The degree of mining subsidence is assessed according to the impact range, geological hazards, aquifers, topography, land resources, etc., and the minimum avoidance distance of buildings and structures is clarified. The document with application number 201811204373.5 published a method for predicting the degree of ground subsidence in coal mining in flat terrain areas covered by loose layers. The maximum development width and maximum displacement height of ground fissures are used as prediction indicators of the degree of surface subsidence to evaluate the degree of surface subsidence. The document with application number 201810869987.9 published a method for evaluating the degree of ground subsidence in coal mining areas, and obtained a classification standard for the degree of surface subsidence based on the evaluation indicators. However, this method requires buildings to avoid ground fissures by a certain distance, which is bound to reduce the utilization rate of land resources. Summary of the invention

[0005] In view of the deficiencies in the prior art, the technical problem that the present invention intends to solve is to provide an active method for reducing ground fissures in mountainous area coal mining based on isolation trenches.

[0006] The technical solution of the present invention to solve the technical problem is to provide an active type mountainous area coal mining ground fissure reduction method based on isolation trench, characterized in that the method comprises the following steps: Step 1: Establish an initial numerical model, obtain an initial surface subsidence curve and determine the location where ground fissures are strongly developed; Step 2: Establish a numerical model under the existence of ground fissures, obtain a surface subsidence curve under the existence of ground fissures, and study the influence of ground fissures on the initial surface subsidence curve of step 1; Step 3, establishing a numerical model with the presence of several isolation trenches, studying the influence of isolation trenches with different parameters on the surface subsidence curve under the presence of ground fissures obtained in step 2, and obtaining the parameters of the isolation trenches to achieve satisfactory isolation effect; Step 4: Carry out on-site construction according to the parameters of the isolation trench obtained in step 3 to achieve satisfactory isolation effect.

[0007] Compared with the prior art, the present invention has the following beneficial effects: (1) Based on the re-clarification of the effectiveness, applicability and economy of passive and avoidance prevention methods, the present invention proposes an active method for reducing ground fissures in mountainous areas based on isolation trenches. Through numerical calculations, the locations where ground fissures are strongly developed are predicted in advance, isolation trenches are actively set in advance, and the transmission path of surface deformation and damage caused by underground coal mining is blocked in advance.

[0008] (2) The present invention is based on the characteristics of surface subsidence in mountainous areas and guided by the theory of mining subsidence and ecological restoration. Through surface subsidence prediction, isolation ditches are set up on the surface in advance, thereby achieving the goal of proactively protecting objects before mining on the working face. This changes the previous situation in which ground fissures have developed and the surface has subsided after mining on the working face, and the ground fissures have been passively managed.

[0009] (3) The present invention realizes active prevention and control of ground fissure disasters, reduces surface settlement and deformation caused by the development of ground fissures, shortens the avoidance distance of surface infrastructure, and truly realizes the transfer, guidance, and reduction of the degree of damage to the surface caused by the development of ground fissures. The principle is scientific, the construction is simple, convenient, fast, safe and effective.

[0010] (4) The present invention combines ground fissure management with surface environmental protection, which has important practical significance for promoting ecological restoration of coal mining subsidence areas in mountainous areas, protecting the ecological environment, and building green mines. It can not only achieve active prevention and control of ground fissure disasters, but also achieve the unity of social benefits, ecological benefits and economic benefits.

[0011] (5) The present invention sets up an isolation ditch to transfer and reduce the damage of the ground fissures to the ground surface. On the one hand, the isolation ditch reduces the damage range of the ground fissures to the ground surface, blocks the propagation path of the stress field to a certain extent, and prevents the expansion of the damage range of the ground surface; on the other hand, the isolation ditch isolates the target protection object from the moving rock mass, and the isolation ditch is filled with loose filling materials. When the rock layer continues to move, the loose filling materials are squeezed, so that the force cannot be transmitted to the target protection object, and the force propagation path is blocked to a certain extent. At the same time, because the loose filling material has a certain pressure release and pressure relief effect, it also weakens the degree of force. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is the overall flow chart of the present invention; Figure 2 This is a numerical simulation result diagram of the horizontal movement curve of the overlying surface of the working face in Example 1 of the present invention; Figure 3 This is a numerical simulation result diagram of the horizontal deformation curve of the overlying surface of the working face of Example 1 of the present invention; Figure 4 This is a schematic diagram of the location where ground fissures are strongly developed on the surface overlying the working face of Example 1 of the present invention; Figure 5 A surface subsidence curve diagram in the presence of ground fissures according to Example 1 of the present invention; Figure 6 The surface subsidence curve diagram of the isolation trench in Example 1 of the present invention is shown in FIG. Figure 7 This is a schematic diagram of on-site construction of Example 1 of the present invention.

[0013] In the figure, ground surface 1, target protection object 2, ground fissure 3, isolation ditch 4, filling material 5, and topsoil 6. DETAILED DESCRIPTION

[0014] The specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the claims of the present invention.

[0015] The present invention provides an active type mountainous area coal mining ground fissure loss reduction method based on isolation trench (hereinafter referred to as method), characterized in that the method comprises the following steps: Step 1: Establish an initial numerical model, obtain an initial surface subsidence curve and determine the location where ground fissures are strongly developed; First, the physical and mechanical parameters of the coal-rock layer and the physical and mechanical parameters of the topsoil layer in the surface subsidence prediction area overlying the coal mining working face are obtained; then, based on the physical and mechanical parameters of the coal-rock layer and the physical and mechanical parameters of the topsoil layer, an initial numerical model is established; then, the initial numerical model is calculated by a numerical analysis method to simulate the surface subsidence process after coal seam mining, and an initial surface subsidence curve is obtained; finally, according to the initial surface subsidence curve, a strongly developed area of ​​ground fissures is divided, and then the strongly developed position of ground fissures is circled in the strongly developed area of ​​ground fissures, providing a basis for determining the position of the isolation ditch 4; Preferably, in step 1, the physical and mechanical parameters of the coal formation include tensile strength, shear modulus, bulk modulus, cohesion, internal friction angle, density, thickness and comprehensive bar graph.

[0016] Preferably, in step 1, the physical and mechanical parameters of the topsoil layer include topsoil type, soil layer structure, soil layer thickness, elastic modulus, cohesion, bulk density and internal friction angle of the soil.

[0017] Preferably, in step 1, the initial surface subsidence curve includes a horizontal movement curve and a horizontal deformation curve of the initial surface subsidence.

[0018] Preferably, in step 1, the initial numerical model is established from bottom to top using FLAC3D finite element software according to the thickness, properties and comprehensive column chart of each rock layer.

[0019] Preferably, in step 1, horizontal constraints are set on the lateral boundaries of the initial numerical model, vertical constraints are set on the bottom boundary, and loads are applied to the top according to the buried depth of the coal seam.

[0020] Step 2: Establish a numerical model under the existence of ground fissures, obtain a surface subsidence curve under the existence of ground fissures, and study the influence of ground fissures on the initial surface subsidence curve of step 1; First, basic parameters of ground fissures and ground fissure intensity parameters are obtained; then, according to the basic parameters of ground fissures and ground fissure intensity parameters, a ground fissure simulation unit is set at a position where there is no boundary effect in the initial numerical model obtained in step 1, and a numerical model under the existence of ground fissures is established; then, a simulation calculation is performed on the numerical model under the existence of ground fissures to obtain a surface subsidence curve under the existence of ground fissures, and the curve is compared 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; Preferably, in step 2, the basic parameters of the ground fissures include the ground fissure inclination, displacement and underground extension depth. The basic parameters of the ground fissures are obtained through field survey and statistical analysis. Generally, the ground fissure inclination is 60-80°, the displacement is 10-100 cm; the underground extension depth can reach up to 100 meters. For the convenience of numerical calculation, the underground extension depth is taken as 50m.

[0021] Preferably, in step 2, the ground fissure strength parameters include cohesion, internal friction angle, normal stiffness modulus and shear stiffness modulus.

[0022] Preferably, in step 2, a certain location is greater than 80 m from the boundary of the initial numerical model.

[0023] Preferably, in step 2, the ground fissure simulation unit is realized by establishing a contact surface, including an upper plate of the ground fissure and a lower plate of the ground fissure; and the surface settlement of the upper plate of the ground fissure and the lower plate of the ground fissure is realized by setting different ground fissure displacement amounts.

[0024] Step 3, establishing a numerical model with the presence of several isolation trenches 4, studying the influence of isolation trenches 4 with different parameters on the surface subsidence curve under the presence of ground fissures obtained in step 2, and obtaining the parameters of the isolation trenches 4 to achieve a satisfactory isolation effect; S3.1. Determine the position of the isolation trench 4: according to the position where the ground fissures are strongly developed determined in step 1, set the isolation trench 4 at the ground fissure 3 where the ground fissures are strongly developed; the safety distance between the isolation trench 4 and the target protected object 2 is set according to the needs of the target protected object 2; Preferably, in step S3.1, the safety distance between the isolation trench 4 and the target protection object 2 is greater than 20m.

[0025] S3.2, according to the position 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; Preferably, in step S3.2, the parameters of the isolation trench 4 include the shape and size of the isolation trench 4; The cross-sectional shape of the isolation trench 4 is rectangular; the dimensions include the length, width and depth of the isolation trench 4. In this embodiment, the length of the isolation trench 4 is equivalent to (i.e., very close to) or the same as the extension length of the ground fissure, the width is 0.5-1 m, and the depth is 10-15 m.

[0026] Preferably, in step S3.2, the filling material 5 in the isolation trench 4 is a mixture of gangue, sawdust and soil (preferably loess); the mass ratio of gangue, sawdust and soil is 1:0.5~0.7:0.5~0.7; the gangue, sawdust and soil are dry-mixed in a mixer to form the filling material 5. The gangue is obtained by tunneling, and the gangue is a gangue powder with a particle size of less than 100 mm; the sawdust is obtained in a wood processing plant; and the soil is obtained locally.

[0027] S3.3, setting different parameters of the isolation trench 4, excavating the isolation trench 4 on the numerical model with the ground fissure obtained in step 2, and establishing several numerical models with the isolation trench 4; S3.4. Simulate and calculate the numerical models of all isolation ditches 4 to obtain the surface subsidence curves of the respective isolation ditches 4, and then compare them with the surface subsidence curves of the respective ground fissures obtained in step 2 to obtain the influence of isolation ditches 4 with different parameters on the surface subsidence curves in the presence of ground fissures, and obtain the parameters of the isolation ditches 4 to achieve a satisfactory isolation effect.

[0028] 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 surface of the target protection object 2 is less than 2 mm / m.

[0029] Step 4: Perform on-site construction according to the parameters of the isolation trench 4 obtained in step 3 to achieve satisfactory isolation effect.

[0030] Preferably, in step 4, the on-site construction method of the isolation ditch 4 is: adopting a top-down stripping method. According to the position of the isolation ditch 4 obtained in step 3 and the parameters for achieving a satisfactory isolation effect of the isolation ditch 4, a small dose of emulsion explosive is used to perform cyclic blasting from top to bottom, and the blasted rocks are transported to the ground by a lifting winch; then the filling material 5 is laid layer by layer in the isolation ditch 4 until it is 0.5~1.0m from the ground surface; then the topsoil 6 is covered until it is 0.1~0.3m above the ground surface; finally, compaction is performed to prevent surface water and rainwater from infiltrating into the isolation ditch 4.

[0031] Embodiment 1: The mine is located in the eastern wing of the Daqing syncline in the Baoding mining area of ​​Panzhihua City, Sichuan Province. The mine field is dominated by fold structures, with a total of 50 large faults, and the fault strikes are mainly NNE and NE. There are currently 6 coal seams available for mining in the mine field, which belongs to the mining of close-range coal seams. The 43158 working face is located in the third mining area. To the east of the working face are the 43154 and 43156 working faces that have been mined, to the west is the 1400 track uphill, to the south is destroyed by small kilns that have been over-mined, and to the north has not been mined yet. The strike length of the working face is 908m and the inclination length is 185m. The working face mined the No. 15 coal seam with an average thickness of 1.5m. The maximum burial depth of the coal seam is 113m. The surface is a medium and low mountain landform and a composite slope with interlaced gullies. The topsoil layer is reddish-brown clay, about 3m thick.

[0032] Step 1: Establish an initial numerical model, obtain an initial surface subsidence curve and determine the location where ground fissures are strongly developed; (1) Obtaining the physical and mechanical parameters of coal strata: Through field investigation, the production geological data of the 43158 working face were collected and analyzed, and the comprehensive columnar diagram of the No. 15 coal seam was obtained. The pseudo-top was 0.17 m of muddy siltstone, the direct top was 2.29 m of muddy siltstone, the basic top was nearly 4 m of siltstone, and the bottom was 1.82 m of siltstone. The physical and mechanical parameters of the coal strata are shown in Table 1.

[0033]

[0034] Obtaining physical and mechanical parameters of the topsoil layer: Through field investigation and experimental results, the moisture content of the topsoil layer is relatively high, between 50% and 70%. The porosity ratio of the soil sample is greater than 1.3, and it is in a hard plastic and plastic state. The internal friction angle is small, mostly less than 20°, and the cohesion is large, mostly greater than 33kPa. The physical and mechanical parameters of the topsoil layer are shown in Table 2.

[0035]

[0036] (2) According to the physical and mechanical parameters of the coal-rock layer and the topsoil layer, an initial numerical model is established to obtain the initial surface subsidence curve (such as Figure 2 and Figure 3 shown); The model size is 1060m×(100~240m), the boundary coal pillars on both sides are 80m each, the working face advancement length is 900m, and the excavation step is determined to be 20m per step according to the basic top cycle. The constitutive equation complies with 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 of the bottom and side boundaries of the model are limited to 0. The numerical calculation process is: initial stress balance → distributed excavation of the No. 15 coal seam. A monitoring point is set at an interval of 10m along the model slope, and a total of 100 monitoring points are set along the working face to monitor the surface subsidence changes during the mining of the No. 15 coal seam.

[0037] (3) Identify locations where ground fissures are most developed (e.g. Figure 4 shown); 30~180m along the working face: Numerical simulation results show that the horizontal movement of the ground surface is 167~323mm and the horizontal deformation is -14.4~-4.3mm / m. The horizontal deformation value is negative, indicating that the ground surface covered by 30~180m along the working face is in a compressed state as a whole, which is not conducive to the development of ground fissures.

[0038] 180~390m along the working face: The horizontal movement value of the surface covered by the working face 180~390m continues to increase, with a maximum value of 781mm. The horizontal deformation of the surface changes from negative to positive, with an average value of 7.18mm / m, indicating that the surface as a whole has evolved from a compression state to a tension state. The surface in this area is a steep slope with a maximum slope of 54.7°. The surface is affected by the combined effects of mining subsidence and steep slope sliding, which is conducive to the development of ground fissures.

[0039] 390~540m along the working face: Through on-site investigation, the surface covered by the working face at 390~540m is a valley with a small slope and no gullies. The maximum horizontal movement of the surface is 487mm and the minimum is 178mm. The horizontal deformation value changes from positive to negative, ranging from -5.89 to -12.78mm / m. This shows that the valley is in a compressed state as a whole, which is not conducive to the development of ground fissures.

[0040] Along the working face strike 540~810m: The slope of the surface covered along the working face strike 540~810m continues to increase. The surface slope between the monitoring points 570m and 600m increased from 6° to 26.1°, and the horizontal deformation value was 0.33~5.47mm / m, indicating that the covered surface was in a state of tension as a whole. The horizontal displacement values ​​at the monitoring points 570m, 780m and 810m were positive, and the horizontal displacement values ​​at other points were negative, indicating that the surface near the three points was conducive to the development of ground fissures.

[0041] 810~900m along the working face: The maximum horizontal movement of the surface covered by the working face at 810~900m is 57mm, and the maximum horizontal deformation is 1.82mm / m. It can be seen that coal seam mining has little impact on the subsidence of the surface at this location.

[0042] In summary, along the direction of the working face, the ground fissures are strongly developed at 180~390m, 570m, 780m and 810m from the surface of the cutting eye to the stop mining line.

[0043] Step 2: Establish a numerical model under the existence of ground fissures, obtain a surface subsidence curve under the existence of ground fissures, and study the influence of ground fissures on the initial surface subsidence curve of step 1; (1) Obtaining basic parameters of ground fissures: According to the field survey results of ground fissures that have developed in the well field and the characteristics of common ground fissure development, the ground fissure inclination is determined to be 70°. The extension depth of ground fissures underground varies, and some can reach hundreds of meters. Combined with the existing geological survey results, the underground extension depth of ground fissures is determined to be 50m. The displacement of ground fissures varies depending on the type of ground fissure development. Taking the tensile ground fissure as an example, the maximum displacement of ground fissures can reach 1m. In this embodiment, the displacement is determined to be 50cm based on the existing field survey results.

[0044] Obtain ground fissure strength parameters: The ground fissure strength parameters were obtained by searching existing literature, see Table 3.

[0045]

[0046] (2) According to the basic parameters of the ground fissures and the ground fissure intensity parameters, a ground fissure simulation unit is set at a position where there is no boundary effect in the initial numerical model obtained in step 1, and a numerical model with the presence of ground fissures is established; (3) Simulate the numerical model under the existence of ground fissures and obtain the surface subsidence curve under the existence of ground fissures (such as Figure 5 As shown in the figure, the initial surface subsidence curve is compared with the initial surface subsidence curve obtained in step 1 to obtain the influence of the ground fissure on the initial surface subsidence curve in step 1.

[0047] Step 3, establishing a numerical model with the presence of several isolation trenches, studying the influence of isolation trenches with different parameters on the surface subsidence curve under the presence of ground fissures obtained in step 2, and obtaining the parameters of the isolation trenches to achieve satisfactory isolation effect; S3.1. Determine the location of the isolation trench: According to the location where the ground fissures are strongly developed (such as Figure 4 ), an isolation ditch is set near the location where the ground fissures are strongly developed (in this embodiment: an isolation ditch 4 is set 10m away from the location where the ground fissures are strongly developed); the safety distance between the isolation ditch and the target protection object is set according to the needs of the target protection object; on the premise that the ground fissures have not developed, by setting the isolation ditch 4 in advance, the greater the degree of weakening of the horizontal movement and deformation of the surface, the smaller the possibility of causing the development of ground fissures in this area.

[0048] S3.2. According to the position 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 1.0 m and a depth of 10 m.

[0049] S3.3, setting different isolation trench parameters, excavating isolation trenches on the numerical model with the ground fissures obtained in step 2, and establishing several numerical models with the isolation trenches; S3.4. Simulate and calculate the numerical models under the existence of all isolation ditches to obtain the surface subsidence curves under the existence of the respective isolation ditches, and then compare them with the surface subsidence curves under the existence of ground fissures obtained in step 2 to obtain the influence of isolation ditches with different parameters on the surface subsidence curve under the existence of ground fissures, and obtain the parameters for the isolation ditches to achieve satisfactory isolation effect and the surface subsidence curves under the existence of the isolation ditches with the parameters (such as Figure 6 as shown).

[0050] Step 4: Based on the parameters of the isolation trench obtained in step 3 to achieve satisfactory isolation effect, on-site construction is carried out, such as Figure 7 shown.

[0051] Any matters not described in the present invention are applicable to the prior art.

Claims

1. An active method for reducing ground fissure damage in mountainous area coal mining based on isolation trenches, characterized in that: The method comprises the following steps: Step 1: Establish an initial numerical model, obtain an initial surface subsidence curve and determine the location where ground fissures are strongly developed; Step 2: Establish a numerical model under the existence of ground fissures, obtain a surface subsidence curve under the existence of ground fissures, and study the influence of ground fissures on the initial surface subsidence curve of step 1; Step 3, establishing a numerical model with the presence of several isolation trenches, studying the influence of isolation trenches with different parameters on the surface subsidence curve under the presence of ground fissures obtained in step 2, and obtaining the parameters of the isolation trenches to achieve satisfactory isolation effect; Step 4: Carry out on-site construction according to the parameters of the isolation trench obtained in step 3 to achieve satisfactory isolation effect.

2. The active type mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 1 is characterized in that: Step 1 is specifically as follows: first, obtain the physical and mechanical parameters of the coal-rock layer and the physical and mechanical parameters of the topsoil layer in the surface subsidence prediction area overlying the coal mining working face; then, establish an initial numerical model based on the physical and mechanical parameters of the coal-rock layer and the physical and mechanical parameters of the topsoil layer; then, calculate the initial numerical model to simulate the surface subsidence process after coal seam mining, and obtain the initial surface subsidence curve; finally, divide the area with intense development of ground fissures according to the initial surface subsidence curve, and then circle the location with intense development of ground fissures in the area with intense development of ground fissures, so as to provide a basis for determining the location of the isolation ditch.

3. The active mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 2 is characterized in that: In step 1, the physical and mechanical parameters of the coal rock formation include tensile strength, shear modulus, bulk modulus, cohesion, internal friction angle, density, thickness and comprehensive histogram; In step 1, the physical and mechanical parameters of the topsoil layer include the topsoil type, soil layer structure, soil layer thickness, elastic modulus, cohesion, bulk density and internal friction angle of the soil; In step 1, the initial surface subsidence curve includes a horizontal movement curve and a horizontal deformation curve of the initial surface subsidence; In step 1, the initial numerical model was established from bottom to top using FLAC3D finite element software according to the thickness, properties and comprehensive histogram of each rock layer; In step 1, horizontal constraints are set on the lateral boundaries of the initial numerical model, vertical constraints are set on the bottom boundary, and loads are applied on the top according to the buried depth of the coal seam.

4. The active mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 1 is characterized in that: Step 2 specifically includes: firstly obtaining basic parameters and strength parameters of ground fissures; then, according to the basic parameters and strength parameters of ground fissures, setting a ground fissure simulation unit at a certain position where there is no boundary effect in the initial numerical model obtained in step 1, and establishing a numerical model under the existence of ground fissures; then, simulating and calculating the numerical model under the existence of ground fissures, obtaining a surface subsidence curve under the existence of ground fissures, and comparing the curve with the initial surface subsidence curve obtained in step 1, and obtaining the influence of ground fissures on the initial surface subsidence curve of step 1.

5. The active mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 4 is characterized in that: In step 2, the basic parameters of the ground fissure include the ground fissure inclination, 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 greater than 80 m from the boundary of the initial numerical model; In step 2, the ground fissure simulation unit is realized by establishing a contact surface, including the upper plate of the ground fissure and the lower plate of the ground fissure; the surface settlement of the upper plate of the ground fissure and the lower plate of the ground fissure is realized by setting different ground fissure displacements.

6. The active mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 5 is characterized in that: The inclination of the ground fissure is 60~80°, the displacement is 10~100cm, and the underground extension depth is 50m.

7. The active mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 1 is characterized in that: Step 3 specifically is: S3.

1. Determine the location of the isolation trench: according to the location where the ground fissures are strongly developed determined in step 1, set an isolation trench at the location where the ground fissures are strongly developed; The safety distance between the isolation ditch and the target protection object is set according to the needs of the target protection object; S3.2, according to the position of the isolation trench obtained in step S3.1, obtaining the parameters of the isolation trench and the parameters of the filling material in the isolation trench; S3.3, setting different isolation trench parameters, excavating isolation trenches on the numerical model with the ground fissures obtained in step 2, and establishing several numerical models with the isolation trenches; S3.

4. Simulate and calculate the numerical models under the existence of all isolation ditches to obtain the surface subsidence curves under the existence of respective isolation ditches, and then compare them with the surface subsidence curves under the existence of ground fissures obtained in step 2, respectively, to obtain the influence of isolation ditches with different parameters on the surface subsidence curve under the existence of ground fissures, and obtain the parameters of the isolation ditch to achieve satisfactory isolation effect.

8. The active mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 7 is characterized in that: In step S3.1, the safety distance between the isolation ditch and the target protection 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 a rectangle; the size includes the length, width and depth of the isolation trench; In step S3.2, the filling material in the isolation ditch is a mixture of gangue, sawdust and soil; the mass ratio of gangue, sawdust and soil is 1:0.5~0.7:0.5~0.7; the gangue, sawdust and soil are dry-mixed in a mixer to form the filling material; In step S3.4, the standard for the isolation ditch to achieve a satisfactory isolation effect is that the horizontal deformation of the surface of the target protected object is less than 2 mm / m.

9. The active mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 8, characterized in that: In step S3.2, the length of the isolation trench is equivalent to the extension length of the ground fissure, with a width of 0.5-1 m and a depth of 10-15 m; The coal gangue is obtained through tunnel excavation, and the coal gangue adopts coal gangue powder with a particle size less than 100mm; the sawdust is obtained from the wood processing plant; and the soil is obtained locally.

10. The active mountainous area coal mining ground fissure damage reduction method based on isolation trench according to claim 1, characterized in that: In step 4, the on-site construction method of the isolation ditch is: according to the position of the isolation ditch obtained in step 3 and the parameters for achieving satisfactory isolation effect of the isolation ditch, use emulsion explosives to carry out cyclic blasting from top to bottom, and transport the blasted rocks to the ground; then lay the filling materials layer by layer in the isolation ditch until they are 0.5~1.0m from the ground surface; then cover with topsoil until they are 0.1~0.3m above the ground surface; finally, compaction is carried out to prevent surface water and rainwater from seeping into the isolation ditch.

Images