Multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring

Abstract

The present invention provides a method for identifying the type of multi-coal seam mining based on numerical simulation and surface settlement monitoring, and relates to the technical field of coal mine safety monitoring in mining engineering. The method does not require the deployment of an expensive underground microseismic monitoring system to monitor the rupture of the main key layers between layers, nor does it require the deployment of complex surface monitoring points. It only requires the use of stress gauge equipment on the existing hydraulic supports in the mine and a simple surface settlement monitoring point layout. The multi-coal seam mining type formed by the target mining area and the coal seam above it can be determined by comparing the time when the step changes between the two occur and analyzing the maximum curvature change characteristics of the surface rock formations. The method of comprehensively analyzing the type of multi-coal seam mining based on numerical simulation and surface settlement monitoring is more convincing than theoretical analysis, and can provide a reference for mines with similar geological conditions. The multi-coal seam mining type identification effect is good, and the identification process is simple.

Description

Technical Field

[0001] The present invention belongs to the technical field of coal mine safety monitoring in mining engineering, and specifically relates to a multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring, and especially relates to an initial mining site of a lower coal seam in a coal seam group. Background Art

[0002] As the shallow coal seams in major coal mining areas in my country have been mined out, most mining companies have entered the stage of developing medium and deep coal resources. Scientific issues such as the stability of the overburden caused by the downward mining of coal seam groups have become increasingly prominent. The movement of rock layers caused by coal seam mining is the main cause of many disasters such as surface collapse in mining areas, surface water loss caused by mining, and water inrush from the roof of coal mines. During the downward mining of coal seam groups, the breaking of the main key layers between coal seams will cause the vertical "three zones" (caving zone, fracture zone and curved sinking zone) of the upper and lower adjacent goafs to interpenetrate and even overlap, which will greatly increase the possibility of the above-mentioned disasters.

[0003] In some mining areas, due to different coal seam occurrence conditions and the inability to mine individual coal seams, mining conditions with multiple coal seam spacings will be formed, that is, underground coal seams often exist in a multi-coal seam occurrence state, and the coal seam spacings are not the same. The difference in spacing between the upper and lower coal seams will lead to different degrees of interconnection between the vertical "three belts" of the upper and lower adjacent goafs formed by the downward mining of the coal seam group, and the geological disasters caused will also be different. At present, scholars such as Ren Gang and Yu Bin have carried out a lot of research on the mutual disturbance influence mechanism of close-range multi-coal seam mining, but the research objects are single, and no comparative study has been carried out on medium-distance multi-coal seam mining and long-distance multi-coal seam mining at the same time; Cheng et al. obtained the depth of the bottom plate damage zone formed by the upper coal seam and the depth of the roof damage zone formed by the lower coal seam through the empirical formula recorded in the "Specifications for Coal Pillar Retention and Compression Coal Mining in Buildings, Water Bodies, Railways and Main Shafts and Lanes", and divided the multi-coal seam mining activities into three types: close-range multi-coal seam mining, medium-distance multi-coal seam mining and long-distance multi-coal seam mining, but only carried out field measurements and theoretical research on medium-distance multi-coal seam mining, and no research on the identification of multi-coal seam mining types was found. Moreover, although the results calculated by the empirical formula have a certain guiding role, the results calculated by the empirical formula are often greatly deviated from the actual situation on site.

[0004] Some scholars have proposed a method to judge the type of multi-coal seam mining by the spatial relationship of the damage zones formed by the upper and lower coal seams, but this method has two disadvantages. First, it is difficult to accurately capture the spatial shape of the three vertical zones of the lower coal seam and the spatial shape of the damage zone of the upper coal seam floor. Although methods such as digital panoramic borehole imaging and surface borehole flushing fluid observation are usually used to measure the height of the vertical "three zones", they cannot accurately capture the spatial shape of the vertical "three zones". Microseismic monitoring, downhole water injection test and ultrasonic imaging and other technologies can measure the damage depth of the coal seam floor, but cannot accurately measure the spatial shape of the floor damage zone. Therefore, the caving zone or fracture zone of the lower coal seam may intersect with the floor damage zone formed by the mining of the upper coal seam locally, rather than intersecting as a whole, resulting in an erroneous judgment. Secondly, when the caving zone or fracture zone of the lower coal seam does not intersect with the floor damage zone of the upper coal seam, because the rock layer between the above-mentioned damage zones is too thin, the rock layer between the two coal seams may not have its original strength under the action of mining stress, resulting in an erroneous judgment. Summary of the invention

[0005] In response to the above-mentioned existing technical problems, the present invention establishes a method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence characteristics during multi-coal seam downward mining, aiming to provide a convenient and reliable method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence characteristics, so as to guide coal mining enterprises to carry out corresponding disaster prevention and control.

[0006] The technical solution of the present invention is:

[0007] A multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring comprises the following steps:

[0008] Step 1: Select a target mining area from a coal mine with multiple coal seams, determine the position of the main key layer between coal seams according to the corresponding geological drilling columnar table and the characteristics that the main key layer needs to meet; arrange settlement monitoring points on the surface overlying the target mining area to obtain surface settlement data during the mining process of the target mining area;

[0009] Step 2: Establish a numerical model of the target mining area based on the corresponding geological drilling columnar table and the mining geological instructions compiled by the mine production department, arrange settlement monitoring points for the main key layers and surface rock layers in the numerical model, simulate the mining process of the target mining area through numerical simulation software, and obtain the settlement data of the settlement monitoring points of each mining step in the numerical model of the target mining area;

[0010] Step 3: Preliminarily calculate the floor damage depth formed by mining the upper coal seam in the target mining area and the height of the collapse zone and the height of the water-conducting fracture zone formed by mining the coal seam where the target mining area is located according to the empirical formula, and then preliminarily infer the multi-coal seam mining type composed of the target mining area and its upper coal seam based on the safe mining ratio of multi-coal seam mining;

[0011] Step 4: By comparing the measured data of the surface settlement monitoring points in the target mining area with the surface rock settlement monitoring point data obtained in the numerical simulation, the numerical model grid size of the target mining area is continuously corrected until the settlement characteristics obtained by the numerical simulation and the measured settlement characteristics reach the best match, and the optimal parameters of the numerical model are obtained;

[0012] Step 5: Based on the height of overburden fractures caused by mining of the coal seam where the target mining area is located in the numerical model, further verify the multi-coal seam mining type formed by the target mining area and its upper coal seam;

[0013] Step 6: Select other mining areas from the multi-coal seam coal mine as new target mining areas, use the optimal parameters of the numerical model obtained in step 4, establish the numerical model of the mining area according to the methods of steps 2 to 3, and preliminarily infer the multi-coal seam mining type formed by the mining area and its upper coal seam;

[0014] Step 7: Repeat step 6 until three different multi-coal seam mining types are inferred;

[0015] Step 8: Through the numerical simulation process, the data of the settlement monitoring points in the numerical model of the target mining area corresponding to the three different multi-coal seam mining types preliminarily inferred are analyzed to obtain the maximum settlement value increment change characteristics and the maximum curvature change characteristics of the surface rock layer corresponding to each target mining area;

[0016] Step 9: Based on the corresponding maximum settlement increment change characteristics and the maximum curvature change characteristics of the surface rock strata obtained from the numerical simulation process of the three types of multi-coal seam mining, the distinction criteria for multi-coal seam mining types are summarized for the identification of multi-coal seam mining types.

[0017] Furthermore, according to the multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring, the characteristics that the main key layer needs to meet include: ① geometric characteristics: the main key layer has a large thickness; ② lithological characteristics: compared with other rock layers, the main key layer has high strength and a large elastic modulus; ③ deformation characteristics: when the main key layer sinks and deforms, the sinking and deformation of all or part of the overlying rock layers are synchronized with it; ④ fracture characteristics: the fracture of the main key layer causes the fracture of all or part of the overlying rock layers, causing rock layer movement and deformation over a large range.

[0018] Furthermore, according to the multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring, the manner of arranging subsidence monitoring points on the surface overlying the target mining area is as follows: a surface subsidence monitoring line is arranged parallel to the direction of the coal seam, and the surface subsidence monitoring line is composed of equally spaced surface subsidence monitoring points.

[0019] Furthermore, according to the multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring, the step 2 further includes the following steps:

[0020] Step 2.1: Based on the stratum distribution and stratum thickness information recorded in the geological drilling columnar table, a geological model of the target mining area is established through modeling software;

[0021] Step 2.2: Import the geological model of the target mining area into the numerical simulation software to establish the numerical model of the target mining area, and arrange settlement monitoring points on the main key layers and the surface rock layers in the numerical model of the target mining area;

[0022] Step 2.3: Assign the rock mechanical parameters of each stratum in the mining geological specification to the corresponding stratum in the numerical model, select the rock constitutive relationship and failure criterion, and establish the boundary conditions and deadweight conditions;

[0023] Step 2.4: Determine the initial mining position, stop mining position, strike length, dip length and mining step length of the target mining area in the numerical simulation according to the mining geological instructions;

[0024] Step 2.5: Use numerical simulation software to simulate the coal mining process and obtain the settlement data of the settlement monitoring points in each mining step in the numerical model.

[0025] Furthermore, according to the multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring, the safe mining ratio of multi-coal seam mining refers to the ratio of the coal seam spacing to the sum of the heights of the upper and lower coal seam damage zones.

[0026] Further, according to the multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring, the method for preliminarily estimating the multi-coal seam mining type consisting of the target mining area and its upper coal seam according to the safe mining ratio of multi-coal seam mining is:

[0027] When the coal seam spacing D is not greater than the destruction depth H of the upper coal seam floor fl The height H of the lower coal seam collapse zone C When the sum is D≤H C +H fl , with r 1 represents the safe mining ratio of multi-coal seam mining at this time. According to formula (1), r 1 ≤1, the multi-coal seam mining type is preliminarily inferred to be close-distance multi-coal seam mining; when the coal seam spacing D is greater than the destruction depth H of the upper coal seam floor fl The height H of the lower coal seam collapse zone C The sum of the above mentioned depths should not be greater than the damage depth H of the upper coal seam floor. fl The height H of the water-conducting fracture zone with the lower coal seam fr The sum is HC +H fl <D≤H fr +H fl , with r 2 represents the safe mining ratio of multi-coal seam mining at this time. According to formula (2), r 2 ≤1, the multi-coal seam mining type is preliminarily inferred to be medium-distance multi-coal seam mining; when the coal seam spacing is greater than the destruction depth H of the upper coal seam floor fl The height H of the water-conducting fracture zone with the lower coal seam fr When the sum is D>H fr +H fl According to formula (2), we can know that r 2 >1, the multi-coal seam mining type is preliminarily inferred to be long-distance multi-coal seam mining;

[0028]

[0029]

[0030] Further, according to the multi-coal seam mining type identification method based on numerical simulation and surface settlement monitoring, the multi-coal seam mining type distinction standard is: compare the working face roof pressure step moment with the surface maximum settlement value increment step moment; if the surface maximum settlement value increment step moment is later than the working face roof pressure step moment, and the difference between the maximum settlement value increment at the step point and the inflection point accounts for 50% or more of the maximum settlement value increment peak value, then it can be judged that the rock formation movement caused by coal seam mining has entered the full mining stage; after the rock formation movement enters the full mining stage, it is obtained through the settlement monitoring line data arranged on the surface of the target mining area: if the surface rock formation maximum curvature change curve shows a stable trend, it can be classified as long-distance multi-coal seam mining; if the surface rock formation maximum curvature change curve shows a downward trend, it can be classified as medium-distance multi-coal seam mining; if the surface rock formation maximum curvature change curve shows an upward trend, it can be classified as close-distance multi-coal seam mining.

[0031] Compared with the prior art, the beneficial effects of adopting the above technical scheme are as follows: the method of the present invention does not require the deployment of expensive underground microseismic monitoring systems to monitor the fracture conditions of the main key layers between layers, nor does it require the deployment of complex surface monitoring points. Moreover, the method of the present invention for comprehensively analyzing the types of multi-coal seam mining based on numerical simulation and surface subsidence monitoring is more convincing than theoretical analysis, and can provide a reference for mines with similar geological conditions. The multi-coal seam mining type identification effect is good, and the identification process is simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a flow chart of a method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring in this embodiment;

[0033] Figure 2A schematic diagram of the numerical model of the A stope provided in the embodiment;

[0034] Figure 3 (a) is a trend diagram of the maximum settlement value increment of the settlement monitoring point in the numerical model of the target mining area, which is preliminarily estimated to correspond to the medium-distance multi-coal seam mining type in the embodiment; (b) is a trend diagram of the maximum curvature of the surface rock layer of the settlement monitoring point in the numerical model of the target mining area, which is preliminarily estimated to correspond to the medium-distance multi-coal seam mining type in the embodiment;

[0035] Figure 4 (a) is a trend diagram of the maximum settlement value increment of the settlement monitoring point in the numerical model of the target mining area, which is preliminarily estimated to correspond to the close-range multi-coal seam mining type in the embodiment; (b) is a trend diagram of the maximum curvature of the surface rock layer of the settlement monitoring point in the numerical model of the target mining area, which is preliminarily estimated to correspond to the close-range multi-coal seam mining type in the embodiment;

[0036] Figure 5 (a) is a trend diagram of the maximum settlement value increment of the settlement monitoring point in the numerical model of the target mining area, which is preliminarily speculated to correspond to the long-distance multi-coal seam mining type according to the embodiment; (b) is a trend diagram of the maximum curvature of the surface rock strata at the settlement monitoring point in the numerical model of the target mining area, which is preliminarily speculated to correspond to the long-distance multi-coal seam mining type according to the embodiment. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The specific embodiments described here are only used to explain the present invention and are not used to limit the present invention.

[0038] This embodiment selects a coal mine with multiple coal seams in Shanxi Province. The mine mainly has four mined coal seams, namely No. 2+3 coal seams, No. 4 coal seam, No. 8 coal seam and No. 9 coal seam. These four coal seams are nearly horizontal coal seams with simple structures. Among them, No. 2+3 coal seam is buried at a depth of about 187.67m and an average thickness of 5.0m; No. 4 coal seam is buried at a depth of about 196.11m and an average thickness of 3.0m; No. 8 coal seam is buried at a depth of about 249.69m and an average thickness of 4.0m; No. 9 coal seam is not mined at this stage.

[0039] Figure 1 FIG. 1 is a flow chart of a method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring in this embodiment. Figure 1 As shown, the multi-coal seam mining type identification method based on numerical simulation and surface subsidence monitoring includes the following steps:

[0040] Step 1: Select a target mining area from a coal mine with multiple coal seams, and determine the position of the main key layer between coal seams according to the corresponding geological drill hole columnar table and the characteristics that the main key layer needs to meet; arrange settlement monitoring points on the overlying surface of the target mining area to obtain surface settlement data during the mining process of the target mining area;

[0041] Step 1.1: Select a target mining area from a coal mine with multiple coal seams, and determine the position of the main key layer between coal seams according to the characteristics that the main key layer needs to meet based on the geological drill hole columnar table;

[0042] Compared with other rock layers, the main key layer needs to meet the following characteristics: ① Geometric characteristics: the main key layer is thicker; ② Rock properties: compared with other rock layers, the main key layer has high strength and large elastic modulus; ③ Deformation characteristics: when the main key layer sinks and deforms, the sinking and deformation of all or part of the overlying rock layers are synchronized with it; ④ Fracture characteristics: The fracture of the main key layer leads to the fracture of all or part of the overlying rock layers, causing rock layer movement and deformation over a large range.

[0043] In this embodiment, the A mining area is selected as the target mining area from the coal mine with multiple coal seams. The A mining area belongs to the No. 8 coal seam, and its upper coal seam has been mined. According to the geological drilling columnar table shown in Table 1 and the characteristics that the main key layer needs to meet, it is determined that the main key layer in the downward mining of multiple coal seams is located in the Taiyuan Formation C 3t The rock type is siltstone.

[0044] Table 1 Geological drilling columnar table

[0045]

[0046]

[0047]

[0048] Step 1.2: Arrange settlement monitoring points on the surface overlying the target mining area to obtain surface settlement data during the mining process of the target mining area;

[0049] In this embodiment, settlement monitoring points are arranged on the overlying surface of the A mining field to obtain surface settlement data during the mining of the lower No. 8 coal seam;

[0050] The arrangement of surface subsidence monitoring points is as follows: the surface subsidence monitoring line is arranged parallel to the direction of the coal seam, and the surface subsidence monitoring line is composed of surface subsidence monitoring points at equal intervals.

[0051] The strike length of the A mining field in this embodiment is 300m. 51 settlement monitoring points are arranged on the overlying surface of the A mining field along the strike direction of the coal seam, with one settlement monitoring point arranged every 10m.

[0052] Step 2: Establish a numerical model of the target mining area based on the corresponding geological drilling columnar table and the mining geological instructions compiled by the mine production department, arrange settlement monitoring points for the main key layers and surface rock layers in the numerical model, simulate the mining process of the target mining area through numerical simulation software, and obtain the settlement data of the settlement monitoring points of each mining step in the numerical model of the target mining area;

[0053] Step 2.1: Based on the stratum distribution and stratum thickness information recorded in the geological drilling columnar table, a geological model of the target mining area is established through modeling software such as CAD;

[0054] Step 2.2: Import the geological model of the target mining area into the numerical simulation software to establish the numerical model of the target mining area, and arrange settlement monitoring points on the main key layers and the surface rock layers in the numerical model of the target mining area;

[0055] Figure 2 This is a schematic diagram of the numerical model of the A stope in this embodiment. The numerical model block adopts the Mohr-Coulomb model, and the joint model adopts the joint surface contact Coulomb slip model. In the numerical model of the A stope, a settlement monitoring point is arranged every 10m along the x-axis direction, and a total of 51 settlement monitoring points are arranged.

[0056] Step 2.3: Assign the rock mechanical parameters of each stratum in the mining geological specification to the corresponding stratum in the numerical model, select the rock constitutive relationship and failure criterion, and establish the boundary conditions and deadweight conditions;

[0057] In this embodiment, the left and right sides and the bottom of the numerical model of the A stope are all subject to normal displacement constraints, that is, the left and right boundaries limit horizontal displacement and allow node displacement in the vertical direction; the bottom boundary limits vertical displacement and allows horizontal displacement.

[0058] Step 2.4: Determine the initial mining position, stop mining position, strike length, dip length and mining step length of the target mining area in the numerical simulation according to the mining geological instructions;

[0059] Step 2.5: Use numerical simulation software to simulate the coal mining process and obtain the settlement data of the settlement monitoring points in each mining step in the numerical model.

[0060] This implementation method uses numerical simulation software to simulate the mining process of No. 8 coal seam, such as Figure 2 As shown, the mining length of No. 8 coal seam along the x-axis direction is 300m, the step distance of each mining step is 10m, and there are 30 mining steps in total. The settlement data of the settlement monitoring point in the numerical model in each mining step are obtained.

[0061] Step 3: Preliminarily calculate the floor damage depth formed by mining the upper coal seam in the target mining area and the height of the collapse zone and water-conducting fracture zone formed by mining the coal seam where the target mining area is located by using the empirical formula in the "Specifications for Coal Pillar Retention and Coal Compressing Mining in Buildings, Water Bodies, Railways and Main Wells and Lanes", and preliminarily infer the multi-coal seam mining type consisting of the target mining area and its upper coal seam based on these empirical values ​​and the safe mining ratio of multi-coal seam mining;

[0062] In the present invention, the ratio of the coal seam spacing D to the sum of the heights of the upper and lower coal seam damage zones is defined as the safe mining ratio r of multi-coal seam mining. The damage depth H of the upper coal seam floor fl The height of the damaged zone of the lower coal seam roof (including the height of the collapsed zone H C Or the height of the water-conducting fracture zone H fr ) are calculated by the empirical formula in the "Specifications for the Establishment of Coal Pillars and Compressed Coal Mining in Buildings, Water Bodies, Railways and Main Wells and Lanes". When the coal seam spacing D is not greater than the destruction depth H of the upper coal seam floor fl The height H of the lower coal seam collapse zone C When the sum is D≤H C +H fl , with r 1 represents the safe mining ratio of multi-coal seam mining at this time. According to formula (1), r 1 ≤1, the multi-coal seam mining type is preliminarily inferred to be close-distance multi-coal seam mining; when the coal seam spacing D is greater than the destruction depth H of the upper coal seam floor fl The height H of the lower coal seam collapse zone C The sum of the above mentioned depths should not be greater than the damage depth H of the upper coal seam floor. fl The height H of the water-conducting fracture zone with the lower coal seam fr The sum is H C +H fl <D≤H fr +H fl , with r 2 represents the safe mining ratio of multi-coal seam mining at this time. According to formula (2), r 2 ≤1, the multi-coal seam mining type is preliminarily inferred to be medium-distance multi-coal seam mining; when the coal seam spacing is greater than the destruction depth H of the upper coal seam floor fl The height H of the water-conducting fracture zone with the lower coal seam fr When the sum is D>H fr +H fl， According to formula (2), we can know that r 2 >1, the multi-coal seam mining type is preliminarily inferred to be long-distance multi-coal seam mining.

[0063]

[0064]

[0065] In this example, the thickness of the No. 2+3 coal seam in the upper part of the A mining area is 5m, and the working face length of the upper coal seam is L=110m. The floor failure depth H of the upper coal seam is calculated by the empirical formula (3) in the "Specifications for the Establishment of Coal Pillars and Compressed Coal Mining in Buildings, Water Bodies, Railways and Main Wells and Lanes" of China: fl =12.64m; the thickness M of the lower coal seam where the A mining area is located, namely the No. 8 coal seam, is 4m. The rock property of the No. 8 coal seam roof is hard. The collapse zone H of the No. 8 coal seam is calculated by empirical formulas (4) and (5): C =18.89m, height of water-conducting fracture zone H fl =70m, the distance between the upper and lower coal seams is 58m, and the safe mining ratio r of multi-coal seam mining is calculated by formula (2) 2 ≤1, it is preliminarily judged that the A mining area and its upper coal seam constitute a medium-distance multi-coal seam mining type.

[0066] Hfl=0.7007+0.1079L (3)

[0067]

[0068]

[0069] Step 4: By comparing the measured data of the surface settlement monitoring points in the target mining area with the surface rock settlement monitoring point data obtained in the numerical simulation, the numerical model grid size is continuously corrected until the settlement characteristics obtained by the numerical simulation and the measured settlement characteristics reach the best match, and the optimal parameters of the numerical model are obtained;

[0070] Step 5: Based on the height of overburden fractures caused by mining of the coal seam where the target mining area is located in the numerical model, further verify the multi-coal seam mining type formed by the target mining area and its upper coal seam;

[0071] By comparing the measured surface settlement monitoring point data with the surface rock settlement monitoring point data obtained in the numerical simulation, the numerical model grid size is continuously corrected until the settlement characteristics obtained by the numerical simulation match the measured settlement characteristics to the best degree. Based on the existing research and understanding of the movement and destruction of overburden rocks caused by coal seam mining, the height of the overburden rock fissure development caused by the mining of the lower coal seam obtained by numerical simulation is analyzed to further verify that the A mining area and its upper coal seam constitute a medium-distance multi-coal seam mining type.

[0072] Step 6: Select other mining areas from the coal mine with multiple coal seams as new target mining areas, use the optimal parameters of the numerical model obtained in step 4, establish the numerical model of the mining area according to the methods of steps 2 to 3, and preliminarily infer the multi-coal seam mining type formed by the mining area and the coal seam above it;

[0073] Through the above steps, this embodiment has determined that mining area A is a medium-distance multi-coal seam mining type. Next, this embodiment continues to select other mining areas from a coal mine with multiple coal seams in Shanxi Province as new target mining areas, and establishes a numerical model of the mining area according to the methods of steps 2 to 3, and preliminarily infers the multi-coal seam mining type constituted by the mining area and its upper coal seam.

[0074] Step 7: Repeat step 6 until three different multi-coal seam mining types are inferred;

[0075] By repeatedly executing step 6, this embodiment preliminarily infers the multi-coal seam mining types formed by the other two mining areas outside the A mining area finally selected from the multi-coal seam coal mine in Shanxi Province and their respective upper coal seams as long-distance multi-coal seam mining type and short-distance multi-coal seam mining type. In this way, this embodiment preliminarily infers three different multi-coal seam mining types in this step.

[0076] Step 8: Through the numerical simulation process, the data of the settlement monitoring points in the numerical model of the target mining area corresponding to the three different multi-coal seam mining types preliminarily inferred are analyzed to obtain the maximum settlement value increment change characteristics and the maximum curvature change characteristics of the surface rock strata of the settlement monitoring points in the numerical model of the target mining area corresponding to each multi-coal seam mining type;

[0077] The solution method for the maximum settlement value increment change characteristics of the settlement monitoring point is: select the maximum settlement value of all monitoring points at the two time points at the beginning and end of a certain time period, and make a difference between the two maximum settlement values, that is, to obtain the maximum settlement value increment of the time period; take each time period of the entire mining cycle as the x-axis, and the maximum settlement value increment of the entire mining cycle of the lower coal seam where the target mining area is located as the y-axis, so as to obtain the maximum settlement value increment change trend of the entire mining cycle of the lower coal seam; similarly, take the mining step in the numerical simulation as the x-axis, and the y-axis is still the maximum settlement value increment, so as to obtain the maximum settlement value increment change characteristics of the surface rock stratum and the main key layer of the lower coal seam where the target mining area is located under the numerical simulation conditions. Figure 3 (a) is a preliminary guess of the present embodiment, which is a maximum settlement increment trend diagram of the settlement monitoring point in the numerical model of the target mining area corresponding to the medium-distance multi-coal seam mining type. Figure 4 The preliminary speculation of this embodiment shown in (a) is the maximum settlement value increment trend diagram of the settlement monitoring point in the numerical model of the target mining area corresponding to the close-range multi-coal seam mining type and Figure 5 (a) is a trend diagram of the maximum settlement value increment of the settlement monitoring point in the numerical model of the target mining area corresponding to the long-distance multi-coal seam mining type according to the preliminary speculation of the embodiment.

[0078] The solution method for the maximum curvature change characteristics of the surface rock formation at the settlement monitoring point is: take each time period of the entire mining cycle as the x-axis, select the maximum curvature of the surface rock formation settlement monitoring point of the lower coal seam where the target mining area is located in the entire mining cycle as the y-axis, and you can get the maximum curvature change trend of the surface of the lower coal seam in the entire mining cycle. Similarly, take the mining step in the numerical simulation as the x-axis, and the y-axis is still the maximum curvature of the surface monitoring point, and you can get the maximum curvature change characteristics of the surface rock formation in the entire mining cycle of the lower coal seam under the numerical simulation conditions. Figure 3 (b) is a preliminary guess of the embodiment shown as the maximum curvature trend diagram of the surface rock layer at the settlement monitoring point in the numerical model of the target mining area corresponding to the medium-distance multi-coal seam mining type, Figure 4 (b) is a preliminary guess of the embodiment shown in FIG. 1 for the maximum curvature trend diagram of the surface rock layer at the settlement monitoring point in the numerical model of the target mining area corresponding to the close-range multi-coal seam mining type and Figure 5 The preliminary speculation of this embodiment shown in (b) is a trend diagram of the maximum curvature of the surface rock layer at the settlement monitoring point in the numerical model of the target mining area corresponding to the long-distance multi-coal seam mining type.

[0079] Step 9: Based on the maximum settlement increment change characteristics and the maximum curvature change characteristics of the surface rock strata obtained from the numerical simulation process of the three types of multi-coal seam mining, the distinction criteria of the multi-coal seam mining types are summarized;

[0080] For the numerical simulation process of three types of multi-coal seam mining, the maximum surface settlement increments when the step point and peak point appear in the maximum settlement increment change curves of the surface rock layer and the main key layer are defined as S mu and S max , and obtain the difference S of the maximum surface settlement increment at two moments Δ =S max -S mu , define the ratio n = S Δ / S max In order to judge the multi-coal seam mining factor when the rock formation movement enters the full mining stage, based on a large amount of monitoring data, this embodiment sets 50% as the early warning indicator. If the multi-coal seam mining factor n ≥ 50% during the surface settlement monitoring process, and the maximum settlement value increment step moment of the surface rock formation is later than the maximum settlement value increment step moment of the main key layer, it can be judged that the rock formation movement enters the full mining stage from the non-full mining stage. Furthermore, by comparing the maximum curvature change characteristics of the surface obtained by numerical simulation of three types of multi-coal seam mining, the standard that can distinguish the three types of multi-coal seam mining is extracted.

[0081] In the multi-coal seam mining type of medium-distance multi-coal seam mining corresponding to the A mining field in this embodiment, the multi-coal seam mining factor n=51.0%≥50%, that is, the rock formation movement enters the full mining stage from the non-full mining stage, and the maximum curvature change curve of the surface shows a downward trend after entering the full mining stage, such as Figure 3 (b) as shown.

[0082] In the close-range multi-coal seam mining type of this embodiment, n=62.5%≥50%, that is, the rock formation movement enters the full mining stage from the non-full mining stage, and the maximum curvature change curve of the surface rock formation shows an upward trend after entering the full mining stage, such as Figure 4 (b) as shown.

[0083] In the long-distance multi-coal seam mining type of this embodiment, n=69.3%≥50%, that is, the rock formation movement enters the full mining stage from the non-full mining stage, and the maximum curvature change curve of the surface shows a stable trend after entering the full mining stage, such as Figure 5 (b) as shown.

[0084] According to the criteria for distinguishing the types of multi-coal seam mining in a coal mine with multiple coal seams in this embodiment summarized in step 9, combined with the fact that most mining companies will monitor the pressure changes of the working face roof by arranging stress gauge equipment on the hydraulic support of the underground working face during coal seam mining. The present invention summarizes the actual criteria for distinguishing the types of multi-coal seam mining in a coal mine with multiple coal seams on site as follows:

[0085] Compare the step time of the working face roof pressure with the step time of the maximum surface settlement increment. If the step time of the maximum surface settlement increment is later than the step time of the working face roof pressure, and the difference between the maximum settlement increment at the step point and the inflection point accounts for 50% or more of the peak value of the maximum settlement increment, it can be judged that the rock movement caused by coal seam mining has entered the full mining stage. After the rock movement enters the full mining stage, the settlement monitoring line data arranged on the surface of the target mining area show that if the maximum curvature change curve of the surface rock formation shows a stable trend, it can be classified as long-distance multi-coal seam mining; if the maximum curvature change curve of the surface rock formation shows a downward trend, it can be classified as medium-distance multi-coal seam mining; if the maximum curvature change curve of the surface rock formation shows an upward trend, it can be classified as close-distance multi-coal seam mining.

[0086] The method of the present invention is based on the view that surface settlement is the final manifestation of deep rock mass rupture extending to the surface. It is based on a method of comprehensive analysis of numerical simulation and surface settlement monitoring. It does not require the deployment of expensive underground microseismic monitoring systems to monitor the rupture of interlayer main key layers, nor does it require the deployment of complex surface monitoring points. It only requires the use of stress gauge equipment on the existing hydraulic supports in the mine and a simple surface settlement monitoring point layout. By comparing the time when the two undergo step changes and analyzing the maximum curvature change characteristics of the surface rock formations, the multi-coal seam mining type formed by the target mining area and the coal seam above it can be determined. The method of comprehensive analysis of multi-coal seam mining types based on numerical simulation and surface settlement monitoring of the present invention is more convincing than theoretical analysis, and can provide a reference for mines with similar geological conditions. The multi-coal seam mining type identification effect is good, and the identification process is simple.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, it should be understood by those skilled in the art that the technical solutions described in the aforementioned embodiments can still be modified, or some or all of the technical features therein can be replaced by equivalents. Therefore, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring, characterized in that: The method comprises the following steps: Step 1: Select a target mining area from a coal mine with multiple coal seams, determine the position of the main key layer between coal seams according to the corresponding geological drilling columnar table and the characteristics that the main key layer needs to meet; arrange settlement monitoring points on the surface overlying the target mining area to obtain surface settlement data during the mining process of the target mining area; Step 2: Establish a numerical model of the target mining area based on the corresponding geological drilling columnar table and the mining geological instructions compiled by the mine production department, arrange settlement monitoring points for the main key layers and surface rock layers in the numerical model, simulate the mining process of the target mining area through numerical simulation software, and obtain the settlement data of the settlement monitoring points of each mining step in the numerical model of the target mining area; Step 3: Preliminarily calculate the floor damage depth formed by mining the upper coal seam in the target mining area and the height of the collapse zone and the height of the water-conducting fracture zone formed by mining the coal seam where the target mining area is located according to the empirical formula, and then preliminarily infer the multi-coal seam mining type composed of the target mining area and its upper coal seam based on the safe mining ratio of multi-coal seam mining; Step 4: By comparing the measured data of the surface settlement monitoring points in the target mining area with the surface rock settlement monitoring point data obtained in the numerical simulation, the numerical model grid size of the target mining area is continuously corrected until the settlement characteristics obtained by the numerical simulation and the measured settlement characteristics reach the best match, and the optimal parameters of the numerical model are obtained; Step 5: Based on the height of overburden fractures caused by mining of the coal seam where the target mining area is located in the numerical model, further verify the multi-coal seam mining type formed by the target mining area and its upper coal seam; Step 6: Select other mining areas from the multi-coal seam coal mine as new target mining areas, use the optimal parameters of the numerical model obtained in step 4, establish the numerical model of the mining area according to the methods of steps 2 to 3, and preliminarily infer the multi-coal seam mining type formed by the mining area and its upper coal seam; Step 7: Repeat step 6 until three different multi-coal seam mining types are inferred; Step 8: Through the numerical simulation process, the data of the settlement monitoring points in the numerical model of the target mining area corresponding to the three different multi-coal seam mining types preliminarily inferred are analyzed to obtain the maximum settlement value increment change characteristics and the maximum curvature change characteristics of the surface rock layer corresponding to each target mining area; Step 9: Based on the corresponding maximum settlement increment change characteristics and the maximum curvature change characteristics of the surface rock strata obtained from the numerical simulation process of the three types of multi-coal seam mining, the distinction criteria for multi-coal seam mining types are summarized for the identification of multi-coal seam mining types.

2. The method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring according to claim 1 is characterized in that: The characteristics that the main key layer needs to meet include: ① Geometric characteristics: the main key layer is thick; ② Rock properties: compared with other rock layers, the main key layer has high strength and large elastic modulus; ③ Deformation characteristics: when the main key layer sinks and deforms, the sinking and deformation of all or part of the overlying rock layers are synchronized with it; ④ Fracture characteristics: The fracture of the main key layer leads to the fracture of all or part of the overlying rock layers, causing rock layer movement and deformation over a large range.

3. The method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring according to claim 1 is characterized in that: The method of arranging the settlement monitoring points on the overlying surface of the target mining area is as follows: a surface settlement monitoring line is arranged parallel to the direction of the coal seam, and the surface settlement monitoring line is composed of surface settlement monitoring points at equal intervals.

4. The method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring according to claim 1 is characterized in that: The step 2 further comprises the following steps: Step 2.1: Based on the stratum distribution and stratum thickness information recorded in the geological drilling columnar table, a geological model of the target mining area is established through modeling software; Step 2.2: Import the geological model of the target mining area into the numerical simulation software to establish the numerical model of the target mining area, and arrange settlement monitoring points on the main key layers and the surface rock layers in the numerical model of the target mining area; Step 2.3: Assign the rock mechanical parameters of each stratum in the mining geological specification to the corresponding stratum in the numerical model, select the rock constitutive relationship and failure criterion, and establish boundary conditions and deadweight conditions; Step 2.4: Determine the initial mining position, stop mining position, strike length, dip length and mining step length of the target mining area in the numerical simulation according to the mining geological instructions; Step 2.5: Use numerical simulation software to simulate the coal seam mining process and obtain the settlement data of the settlement monitoring points in each mining step in the numerical model.

5. The method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring according to claim 1 is characterized in that: The safe mining ratio of multi-coal seam mining refers to the ratio of the distance between coal seams to the sum of the heights of the upper and lower coal seam damage zones.

6. The method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring according to claim 5 is characterized in that: The method for preliminarily estimating the type of multi-coal seam mining consisting of the target mining area and the coal seam above it based on the safe mining ratio of multi-coal seam mining is: When the coal seam spacing D is not greater than the destruction depth H of the upper coal seam floor fl The height H of the lower coal seam collapse zone C When the sum is D≤H C +H fl , r1 represents the safe mining ratio of multi-coal seam mining at this time. According to formula (1), r1≤1, and the multi-coal seam mining type is preliminarily inferred to be close-range multi-coal seam mining; when the coal seam spacing D is greater than the destruction depth H of the upper coal seam floor fl The height H of the lower coal seam collapse zone C The sum of the above mentioned depths should not be greater than the damage depth H of the upper coal seam floor. fl The height H of the water-conducting fracture zone with the lower coal seam fr The sum is H C +H fl <D≤H fr +H fl , r2 represents the safe mining ratio of multi-coal seam mining at this time. According to formula (2), r2≤1, and the multi-coal seam mining type is preliminarily inferred to be medium-distance multi-coal seam mining; when the coal seam spacing is greater than the destruction depth H of the upper coal seam floor fl The height H of the water-conducting fracture zone with the lower coal seam fr When the sum is D>H fr +H fl According to formula (2), r2>1, the multi-coal seam mining type is preliminarily inferred to be long-distance multi-coal seam mining:

7. The method for identifying multi-coal seam mining types based on numerical simulation and surface subsidence monitoring according to claim 1 is characterized in that: The distinguishing criterion for the multi-coal seam mining type is as follows: comparing the step moment of the working face roof pressure with the step moment of the maximum surface settlement value increment; if the step moment of the maximum surface settlement value increment is later than the step moment of the working face roof pressure, and the difference between the maximum settlement value increment at the step point and the inflection point accounts for 50% or more of the peak value of the maximum settlement value increment, then it can be judged that the rock stratum movement caused by the coal seam mining has entered the full mining stage; after the rock stratum movement enters the full mining stage, it is concluded through the data of the settlement monitoring line arranged on the surface of the target mining area: if the surface rock stratum maximum curvature change curve shows a stable trend, it can be classified as long-distance multi-coal seam mining; if the surface rock stratum maximum curvature change curve shows a downward trend, it can be classified as medium-distance multi-coal seam mining; if the surface rock stratum maximum curvature change curve shows an upward trend, it can be classified as close-distance multi-coal seam mining.

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