Method for calculating goaf overburden strata settlement based on overburden internal failure characteristics

Abstract

The application provides a goaf overburden strata settlement calculation method based on internal damage characteristics of overburden, and the method comprises the following steps: obtaining a detection image; determining a fractal description of a damage variable by using a digital image processing technology and a fractal box covering method according to the detection image; calculating a crack area distribution weight of overburden at different depths, and determining an optimal fractal box size according to a relationship between an information space dimension and a box covering fractal dimension; determining a fractal damage constitutive model by determining an overburden body damage factor according to the fractal description of the damage variable and the optimal fractal box size; calculating additional stress of overburden at different depths according to a stress balance principle, and calculating the settlement of overburden at different depths by using a layer summation method. By using the fractal damage constitutive relationship, the application constructs a goaf overburden strata settlement calculation model, so that the settlement of overburden at different depths is calculated, the calculation precision is improved, and the purpose of calculating the goaf overburden settlement by using the fractal theory is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of goaf overburden settlement calculation, and particularly relates to a goaf overburden settlement calculation method and device based on overburden internal damage characteristics. BACKGROUND

[0002] After underground mineral resources are mined, the original stress balance state is broken, and the entire goaf overburden system reaches a new stress balance through deformation and damage under the action of unbalanced force. Macroscopically, the goaf overburden damage process is a spatial three-dimensional evolution process starting from the roof and ending at the ground; microscopically, the essence of overburden deformation and damage is a dynamic development process of “initiation-expansion-penetration-healing” of overburden internal cracks under the influence of mining. Therefore, the mining overburden damage mechanism is ultimately a dynamic development problem of mining cracks.

[0003] In recent years, domestic and foreign scholars have made a large number of research results on the stress field distribution and evolution law of surrounding rock in the process of coal mining, and have proposed natural balance arch, pressure arch and continuous beam hypotheses, and successively established masonry beam, transmission rock beam and “three-zone” theories. The mining subsidence theory has achieved fruitful results through years of research by numerous experts and scholars. The deformation and damage of internal rock layers of overburden are limited by the difficulty of obtaining field data, and there are fewer achievements. SUMMARY

[0004] The present application aims to at least solve one of the technical problems in the related art.

[0005] To this end, a first purpose of the present application is to propose a goaf overburden settlement calculation method based on overburden internal damage characteristics, which solves the technical problem that the deformation and damage of internal rock layers of overburden cannot be determined due to the difficulty of obtaining internal overburden data in the existing method. By using the stress balance principle, the influence of coal mining on overburden stress is determined, and by using the fractal damage constitutive relation, a goaf overburden settlement calculation model is constructed, so as to realize the calculation of the additional stress increase of internal overburden rock layers of different depths and the settlement of overburden layers of different depths caused by mining, improve the calculation accuracy, and achieve the purpose of calculating the goaf overburden settlement by using the fractal theory.

[0006] A second purpose of the present application is to propose a goaf overburden settlement calculation device based on overburden internal damage characteristics.

[0007] A third purpose of the present application is to propose a computer device.

[0008] A fourth purpose of the present application is to propose a non-transitory computer readable storage medium.

[0009] To achieve the above object, the first aspect of the present application proposes a goaf overburden strata settlement calculation method based on internal damage characteristics of overburden, comprising: obtaining a detection image; determining a fractal description of a damage variable by using a digital image processing technology and a fractal box covering method according to the detection image; calculating a crack area distribution weight of overburden at different depths, and determining an optimal fractal box size according to a relationship between an information space dimension and a box covering fractal dimension; establishing a fractal damage constitutive model by determining an overburden body damage factor according to the fractal description of the damage variable and the optimal fractal box size; calculating an additional stress of overburden strata at different depths according to a stress balance principle, and obtaining a settlement of overburden strata at different depths by using a layer summation method.

[0010] Optionally, in an embodiment of the present application, the fractal description of the damage variable of the crack unit is determined by using the digital image processing technology and the fractal box covering method according to the detection image, comprising:

[0011] The detection image is binarized to obtain a binarized image under an optimal threshold value;

[0012] The binarized image is processed to obtain a damage area;

[0013] The fractal description of the damage variable is determined by using the fractal box covering method.

[0014] Optionally, in an embodiment of the present application, the crack area distribution weight of overburden at different depths is calculated, and the optimal fractal box size is determined according to the relationship between the information space dimension and the box covering fractal dimension, comprising:

[0015] The crack areas are arranged in an order from small to large, and data total intervals are divided into a preset number of subintervals to obtain an information amount of crack area distribution. The interval size is changed constantly to obtain a crack information space dimension;

[0016] The optimal fractal box size is determined according to the relationship between the information space dimension and the box covering fractal dimension;

[0017] The relationship between the information space dimension and the box covering fractal dimension is expressed as:

[0018] D≤D I <2

[0019] D1 is the information space dimension, and D is the box covering fractal dimension;

[0020] The optimal fractal box size is expressed as:

[0021]

[0022] r is the optimal fractal box size, n0 is the initial porosity, and D1 is the information space dimension.

[0023] Optionally, in an embodiment of the present application, according to the fractal description of the damage variable and the optimal fractal box size, the fractal damage constitutive model is established by determining the overburden damage factor, comprising:

[0024] The fractal description of the damage variable is brought into the damage constitutive relationship to obtain the fractal damage constitutive model.

[0025] The fractal damage constitutive model is expressed as:

[0026]

[0027] Wherein, ε is the strain of the overburden rock, σ1 is the minor principal stress, ν is the Poisson's ratio of the overburden rock, σ2 is the intermediate principal stress, σ3 is the major principal stress, E is the initial elastic modulus, A is the post-mining crack area, a is the D-dimensional length of the crack, r is the optimal fractal box size, D is the box covering fractal dimension, F is the strength of the overburden rock element, and F0 is the Weibull statistical parameter.

[0028] Optionally, in an embodiment of the present application, the additional stress of the overburden rock layer at different depths is calculated according to the stress balance principle, and the settlement of the overburden rock layer at different depths is calculated using the layering summation method, comprising:

[0029] According to the stress balance relationship, the normal stress of the overburden rock layer at different depths is calculated, and the total stress of the overburden rock layer at different depths before mining is calculated.

[0030] According to the normal stress of the overburden rock layer at different depths and the total stress of the overburden rock layer at different depths before mining, the additional stress of the overburden rock layer at different depths is calculated.

[0031] Each depth of the overburden rock layer is divided into a preset number of sub-layers, the settlement is calculated, and the layering settlement is obtained.

[0032] According to the layering settlement, the settlement of the overburden rock layer at different depths is calculated by summation.

[0033] Optionally, in an embodiment of the present application, each depth of the overburden rock layer is divided into a preset number of sub-layers, the settlement is calculated, and the layering settlement is obtained, comprising:

[0034] The additional stress is brought into the fractal damage constitutive model to obtain the layering settlement.

[0035] To achieve the above purpose, the second aspect embodiment of the present application proposes a goaf overburden layer settlement calculation device based on the internal damage characteristics of the overburden rock, comprising:

[0036] The acquisition module is configured to acquire the detection image.

[0037] The processing module is configured to determine the fractal description of the damage variable by using the digital image processing technology and the fractal box covering method according to the detection image.

[0038] a size determining module configured to calculate a crack area distribution weight of overburden rock at different depths, and determine an optimal fractal box size according to a relationship between a dimension of an information space and a fractal dimension of a box cover;

[0039] a construction module configured to establish a fractal damage constitutive model by determining an overburden rock damage factor according to the fractal description of the damage variable and the optimal fractal box size;

[0040] a calculation module configured to calculate an additional stress of overburden rock at different depths according to a stress balance principle, and calculate a settlement of overburden rock at different depths by using a stratified summation method.

[0041] Optionally, in an embodiment of the present application, the processing module is specifically configured to:

[0042] perform binaryzation processing on the detection image to obtain a binaryzation image under an optimal threshold value;

[0043] perform processing on the binaryzation image to obtain an area of the damage region;

[0044] use a fractal box cover method to determine the fractal description of the damage variable.

[0045] To achieve the above object, a third aspect of the present application provides a computer device, comprising a memory, a processor and a computer program stored in the memory and executable on the processor, and when the processor executes the computer program, the computer program implements the overburden rock strata settlement calculation method based on internal damage characteristics of overburden rock of a goaf area as described above.

[0046] To achieve the above object, a fourth aspect of the present application provides a non-transitory computer readable storage medium, when instructions in the storage medium are executed by a processor, the instructions enable a kind of overburden rock strata settlement calculation method based on internal damage characteristics of overburden rock of a goaf area.

[0047] The overburden rock strata settlement calculation method based on internal damage characteristics of overburden rock of a goaf area, the device, the computer device and the non-transitory computer readable storage medium of the present application, solve the technical problem that the deformation and damage of the internal rock strata of the overburden rock cannot be determined due to the difficulty in obtaining the internal data of the overburden rock in the prior art, by using the stress balance principle, the influence of the coal mining process on the stress of the overburden rock is determined, and by using the fractal damage constitutive relationship, the overburden rock strata settlement calculation model of the goaf area is constructed, so as to realize the calculation of the additional stress increase of the internal rock strata at different depths of the overburden rock caused by mining and the settlement of the overburden rock at different depths, improve the calculation precision, and achieve the purpose of calculating the overburden rock settlement of the goaf area by using the fractal theory.

[0048] Additional aspects and advantages of the application will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following and the attached drawings. BRIEF DESCRIPTION OF DRAWINGS

[0049] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings.

[0050] Figure 1 A flow chart of a goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock provided by an embodiment of the present application;

[0051] Figure 2 A fracture area partial wing distribution and normal distribution schematic diagram of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0052] Figure 3 A fractal box number and fractal size double logarithm relationship schematic diagram of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0053] Figure 4 A drilling space detection position layout diagram of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0054] Figure 5 A different depth overburden rock drilling detection image diagram of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0055] Figure 6 A different threshold binary image of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0056] Figure 7 A 7m-8m different statistical interval width overburden rock fracture distribution diagram of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0057] Figure 8 A goaf filling settlement calculation model schematic diagram of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0058] Figure 9 A goaf additional stress settlement calculation model schematic diagram of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0059] Figure 10 An overburden rock settlement calculation principle diagram of the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden rock of the embodiment of the present application;

[0060] Figure 11 An additional stress distribution diagram for the goaf overburden strata settlement calculation method based on the internal damage characteristics of overburden strata of the embodiments of the present application;

[0061] Figure 12 A comparison diagram of the theoretical value and the measured value of the goaf overburden strata settlement calculation method based on the internal damage characteristics of overburden strata of the embodiments of the present application;

[0062] Figure 13 The structure diagram of a goaf overburden strata settlement calculation device based on the internal damage characteristics of overburden strata provided in Embodiment Two of the present application. DETAILED DESCRIPTION

[0063] The embodiments of the present application are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present application, and cannot be understood as a limitation of the present application.

[0064] At present, the theoretical achievements of the surface deformation calculation of the goaf are fruitful, but the research achievements of the deformation of different strata in the internal overburden are less due to the monitoring means and cost limitations. In order to study the settlement mechanism of the overburden at different depths of the goaf, the drilling peep instrument detection data of the first layer of coal mining working face in the mining area are assumed to be based on the assumption that the occurrence of the overburden settlement conforms to the response mechanism from the top to the surface from bottom to top, and the overburden settlement mechanism is divided into two parts of overburden crushing and expansion and upper additional stress compaction.

[0065] The present application uses the digital image processing technology and the fractal box covering method to determine the fractal characteristics of the crack unit collected by the drilling peep instrument, calculates the crack area distribution weight of the overburden at different depths, determines the optimal fractal box size according to the relationship between the information space dimension and the box covering fractal dimension, assumes that the internal unit strength of the rock conforms to the Weibull distribution, establishes the fractal damage constitutive model by determining the damage factor of the overburden, calculates the additional stress of the overburden layer at different depths according to the stress balance principle, calculates the strata settlement of the rock mass according to the stratified summation method, and compares and analyzes the calculation results with the field settlement monitoring data, thereby providing a theoretical method for the settlement calculation of the overburden of the goaf and the prevention and control of related disasters.

[0066] The goaf overburden strata settlement calculation method and device based on the internal damage characteristics of overburden strata of the embodiments of the present application are described below with reference to the accompanying drawings.

[0067] Figure 1 The flowchart of the goaf overburden strata settlement calculation method based on the internal damage characteristics of overburden strata provided in Embodiment One of the present application.

[0068] AsFigure 1 As shown, the goaf overburden strata settlement calculation method based on the internal damage characteristics of overburden strata includes the following steps:

[0069] Step 101, obtaining a detection image;

[0070] Step 102, determining the fractal description of the damage variable according to the detection image by using digital image processing technology and fractal box covering method;

[0071] Step 103, calculating the crack area distribution weight of overburden strata at different depths, and determining the optimal fractal box size according to the relationship between the information space dimension and the box covering fractal dimension;

[0072] Step 104, establishing a fractal damage constitutive model by determining the overburden strata damage factor according to the fractal description of the damage variable and the optimal fractal box size;

[0073] Step 105, calculating the additional stress of overburden strata at different depths according to the stress balance principle, and calculating the settlement of overburden strata at different depths by using the layer summation method.

[0074] The goaf overburden strata settlement calculation method based on the internal damage characteristics of overburden strata according to the embodiments of the present application obtains a detection image; determines the fractal description of the damage variable according to the detection image by using digital image processing technology and fractal box covering method; calculates the crack area distribution weight of overburden strata at different depths, and determines the optimal fractal box size according to the relationship between the information space dimension and the box covering fractal dimension; establishes a fractal damage constitutive model by determining the overburden strata damage factor according to the fractal description of the damage variable and the optimal fractal box size; calculates the additional stress of overburden strata at different depths according to the stress balance principle, and calculates the settlement of overburden strata at different depths by using the layer summation method. Thus, the technical problem that the deformation and damage of internal strata of overburden strata cannot be determined due to the difficulty in obtaining internal data of overburden strata in the prior art can be solved; the influence of coal mining process on overburden stress is determined by using the stress balance principle, and a goaf overburden strata settlement calculation model is constructed by using the fractal damage constitutive relationship, so as to realize the calculation of the additional stress increase of internal strata of overburden strata at different depths and the settlement of overburden strata at different depths caused by mining, improve the calculation accuracy, and achieve the purpose of calculating the goaf overburden settlement by using the fractal theory.

[0075] On the basis of goaf drilling detection, the present application establishes a damage constitutive relationship of overburden deformation by using digital image processing technology and fractal theory, and establishes a goaf overburden settlement model according to the stress balance principle and the layer summation method, considering the influence of overburden crack development on lithology weakening in the process of coal mining.

[0076] The application utilizes digital image gray scale recognition principle to automatically recognize overburden fissure and overburden broken block, obtains binary image under the best threshold, the best binary pixel threshold is 90, and the statistical distribution law of fissure area can be determined better; the damage variable evolution law is established by using box covering method, and the best fractal size is determined according to the information dimension method, wherein, with the increase of overburden depth, the fissure development degree of rock gradually intensifies, the complexity of fissure edge continuously improves, and the corresponding fractal dimension gradually increases. The application also establishes a vertical stress model of any point in overburden by using stress balance principle, determines the influence of coal mining process on overburden stress, so as to realize the calculation of overburden layer settlement at different depths; meanwhile, the overburden layer settlement calculation model of goaf established by using fractal damage constitutive relation can preferably calculate the additional stress increase of overburden at different depths and the settlement of each overburden layer caused by mining, and the calculation result is close to the field measured value.

[0077] Further, in the embodiment of the application, according to the detection image, the fractal description of the damage variable of the fissure unit is determined by using digital image processing technology and fractal box covering method, including:

[0078] The detection image is binarized to obtain a binary image under the best threshold;

[0079] The binary image is processed to obtain the area of the damage region;

[0080] The fractal description of the damage variable is determined by using the fractal box covering method.

[0081] If a square box with a size of r is used to cover a two-dimensional plane, the number of boxes N(r) required and r satisfy: N(r)∝r -2 ; if a small cube with a size of r is used to cover a three-dimensional body, the number of boxes N(r) required and r satisfy: N(r)∝r -3 According to the idea, a square with a size of r is used to cover the defect part of the damage observation area, and the number of boxes N(r) required and the size r of the box satisfy:

[0082] N(r)=a·r -D (1)

[0083] Wherein, N(r) is the number of boxes, r is the size of the box, D is the fractal dimension of the fissure region, and a is the fractal dimension length of the fissure.

[0084] If the logarithm of both sides of formula (1) is taken, formula (2) can be obtained:

[0085] logN(r)=-Dlogr+b (2)

[0086] Where N(r) is the number of boxes, r is the size of the box, D is the fractal dimension of the fissure region, and b is a constant.

[0087] The limit expression of the fractal dimension is:

[0088]

[0089] Where N(r) is the number of boxes, r is the size of the box, and D is the fractal dimension of the fissure region.

[0090] The distribution of the fissures on the structure surface of the overburden rock above the goaf is complex and has a high degree of anisotropy and random distribution. According to the weakest link principle, a statistical law is established for the random distribution of the strength of the material, and a random damage theory is established. The expression of the two-parameter Weibull distribution function is:

[0091]

[0092] Where x is the statistical quantity, and m and F0 are the Weibull statistical parameters.

[0093] It is assumed that the strength F of the overburden rock unit obeys the two-parameter Weibull distribution. Under the condition of a fractal scale of r, the total number of units is A / r 2 (A is the total area). Considering the initial damage caused by the goaf fissures, the number of the remaining effective units is [N-N(r)], and the number of the units that are damaged in the loading stress interval (x, x+dx) is:

[0094]

[0095] Where N f is the number of the units that are damaged in the loading stress interval, [N-N(r)] is the number of the effective units, N is the number of the statistical samples, N(r) is the number of the required boxes, F is the strength of the overburden rock unit, f(x) is the two-parameter Weibull distribution function, x is the statistical quantity, S is the standard deviation, r is the size of the box, D is the fractal dimension of the fissure region, a is the fractal dimension length of the fissure, and m and F0 are the Weibull statistical parameters.

[0096] The total number of the defective damage units should be the sum of the initial defective units N(r) and N f According to the number of the damage units, the damage variable can be expressed as:

[0097]

[0098] Where D f is the damage variable, N(r) is the initial defective unit, and N fA / r 2 A is the total number of unit bodies (A is the total area).

[0099] The fractal expression of damage variable can be obtained by bringing formula (1) and formula (5) into formula (6):

[0100]

[0101] D f D is the damage variable, r is the size of the box, D is the fractal dimension of the crack area, a is the fractal dimension length of the crack, A / r 2 A is the total number of unit bodies, A is the total area, F is the unit body strength of overburden rock, m and F0 are Weibull statistical parameters.

[0102] Further, in the embodiments of the present application, the crack area distribution weight of different depth overburden rock is calculated, and the optimal fractal box size is determined according to the relationship between the information space dimension and the box covering fractal dimension, including:

[0103] The crack area is arranged in order from small to large, and the total interval of data is divided into a preset number of subintervals to obtain the information amount of crack area distribution. The interval size is changed constantly to obtain the crack information space dimension;

[0104] The optimal fractal box size is determined according to the relationship between the information space dimension and the box covering fractal dimension;

[0105] The relationship between the information space dimension and the box covering fractal dimension is represented as:

[0106] D≤D I <2

[0107] D1 is the information space dimension, and D is the box covering fractal dimension;

[0108] The optimal fractal box size is represented as:

[0109]

[0110] r is the optimal fractal box size, n0 is the initial porosity, and D1 is the information space dimension.

[0111] Since the development process of overburden rock cracks at the top of the goaf during coal mining is extremely complex, the crack distribution has extremely uneven characteristics, but the crack area size has a skewed normal distribution characteristic. In engineering, the skewness coefficient C S and the kurtosis coefficient C E can respectively reflect the asymmetry and concentration of statistical data, as shown in formula (7) and formula (8). Figure 2

[0112] ​

[0113]

[0114] where S represents standard deviation, μ n represents the n-order central moment of statistical variable x i , and the calculation formula is as follows:

[0115]

[0116] where N is the number of statistical samples. The skewness can only reflect the single-peak data characteristics and cannot reflect the multi-peak distribution law of fracture area in the mining process.

[0117] First, the drilling detected fracture areas are arranged in ascending order, the minimum value is x min , the maximum value is x max , and the total interval of data [x min , x max ] is divided into n sub-intervals, then the length of each sub-interval is δ = (x max -x min ) / n, the i-th sub-interval can be expressed as [x min +(i-1)δ / n, x min +iδn], and the frequency of the interval is P i , the interval can reflect the information amount I(n) of fracture area distribution, which is as follows:

[0118]

[0119] I(n) is the total information amount of the fracture system space detected by drilling data, which is the entropy value of the system. By continuously changing the interval size δ, the drilling fracture information space dimension D I can be obtained as follows:

[0120] I(n) = I0+D I logδ (12)

[0121] where I(n) is the information amount of fracture area distribution, I0is the initial information amount, δ is the interval size, and D I is the drilling fracture information space dimension.

[0122] D I is the slope of the fitting straight line of double logarithm [I(n)]-log n, which can reflect the completeness characteristics of the fracture system space.

[0123] If C S = 0, the normal distribution can be used to describe the distribution law of x; if C SThe distribution of x can be described using the Weibull distribution, where x ≠ 0. If the probability of falling into each subinterval is equal, then x follows a uniform distribution, i.e., P(x) = 0. i =1 / n, then I(n) satisfies:

[0124]

[0125] Where I(n) represents the information content of the fracture area distribution, and n represents the number of layers.

[0126] If we disregard the weights of each subinterval, then the dimension D of the information space is... I This is the fractal dimension D determined by the box covering method in equation (3). Since a uniform distribution of the crack area is a very special case, if the probability of each subinterval is not equal, then the dimension D of the information space is... I It must be greater than D, thus it can be seen that the information dimension is a generalization of the capacity dimension, and the two satisfy the following relationship:

[0127] D≤D I <2 (14)

[0128] Depend on Figure 3 It can be seen that as r decreases, the slope of the fitted line gradually increases, and the fractal dimension D increases. From equation (14), we know that the maximum value of D is D0. I In order for the box covering the fractal dimension to reflect all the information of the crack, the dimension r should be small enough, therefore the information space dimension D can be used. I Replace D in equation (4) to determine the fractal box size r. Assuming the initial porosity is n0, we can see from equation (1):

[0129]

[0130] Where n0 is the initial porosity, A is the total area, r is the fractal size, and D is the area of ​​the fractal. I Let be the dimension of the information space.

[0131] Therefore, the most reasonable fractal size r is:

[0132]

[0133] Where r is the fractal size, n0 is the initial porosity, and D I Let be the dimension of the information space.

[0134] In order to study the fracture development characteristics of overburden rock in mining area, the field drilling detection was carried out in the typical working face, the detection drilling position was designed, which was 40 m away from the tangent line and 30 m away from the old goaf side along the working face advancing direction. In order to detect whether the original fracture exists in the designed hole position area, compare the information of overburden rock before and after mining in detail, two adjacent drillings were designed in this position, which were pre-mining observation hole and post-mining observation hole, the distance between pre-mining hole and post-mining hole was 1 m, and the drilling position was designed as shown in Figure 4 . The post-mining hole was observed by using drilling detector 45 days after the working face pushed through the designed hole position, the fracture evolution process of overburden rock at different buried depths was observed by image, and the typical observation results were shown as Figure 5 . First of all, the observed image needs to be binarized, that is, the gray value of pixel point of drilling image data is set to 0 or 255, so that the fracture and skeleton of the whole image are separated by pixel recognition method. The image in Figure 5 was binarized by using im2bw(Imagehreshold) command in Matlab, and the key was to determine the threshold value of binarization. Figure 6 The binarized images with different threshold values were given.

[0135] As can be seen from Figure 6 , the binarized image with threshold value = 90 can more truly reflect the real distribution of fracture and skeleton, and the binarized image of Figure 5 was processed under the condition of threshold value = 90. Then the area of damaged region was calculated by using IPP image processing software through image segmentation, image enhancement and fracture area extraction technology. Figure 7 The fracture evolution at the depth of 7 m to 8 m was shown in (a) to (d), which were the fracture distribution at different interval widths (10 μm, 20 μm, 30 μm and 40 μm) respectively. The total information I(n) was calculated by using formula (12), and then the slope of the fitting straight line was taken as the dimension D I of information space according to formula (13).

[0136] Figure 5 The fracture evolution corresponding to the overburden rock at different depths was shown in (a) to (o), which was gradually complex and the fracture development degree was gradually improved, and the fracture information was gradually increased. The fracture area of the observation area was calculated by using IPP image query method, the initial porosity n0 was obtained, and then the most reasonable fractal size r was obtained, and the fractal dimension calculation results of drilling image data at different depths were shown in Table 1. The observation area of each drilling detection data was 0.3 m 2 .

[0137]

[0138] Table 1

[0139] Further, in the embodiments of the present application, according to the fractal description of the damage variable and the optimal fractal box size, the fractal damage constitutive model is established by determining the overburden damage factor, comprising:

[0140] The fractal description of the damage variable is brought into the damage constitutive relationship to obtain the fractal damage constitutive model;

[0141] The fractal damage constitutive model is expressed as:

[0142]

[0143] Wherein, ε is the strain of the overburden above the goaf, σ1 is the minor principal stress, ν is the Poisson's ratio of the overburden, σ2 is the intermediate principal stress, σ3 is the major principal stress, E is the initial elastic modulus, A is the post-mining crack area, a is the D-dimensional length of the crack, r is the optimal fractal box size, D is the box covering fractal dimension, F is the strength of the overburden element, and F0 is the Weibull statistical parameter.

[0144] The overburden settlement above the goaf includes two parts of the overburden caving and the settlement caused by the additional stress. The overburden settlement is caused by the subsidence of the goaf free surface, accompanied by the crack development and the dilatancy phenomenon. The settlement caused by the additional stress will lead to the compression of the loose crack rock mass.

[0145] The crack produced after the overburden caving will cause the dilatancy of the rock mass. At this time, the area hB of the rock mass is composed of the pre-mining intact rock mass area HB and the post-mining crack area A (as shown in Figure 8 The area hB of the rock mass can be expressed as:

[0146] hB=HB+A (17)

[0147] The area of the crack can be calculated according to the total fractal box covering area of the overburden above the goaf.

[0148]

[0149] Wherein, N(r) is the number of the required boxes, a is the D-dimensional length of the crack, D total is the total fractal dimension of the crack of the overburden above the goaf, and r is the optimal fractal size.

[0150] The formula (18) is brought into the formula (17), and the arrangement can obtain:

[0151]

[0152] Wherein, H is the depth of the rock mass before the overburden caving, B is the width of the caved rock mass, a is the D-dimensional length of the crack, D total is the total fractal dimension of the crack of the overburden above the goaf, and r is the optimal fractal size.

[0153] Then the settlement S0 caused by filling the goaf is: Figure 8

[0154]

[0155] where H is the depth of the rock mass before the overburden collapse, M is the thickness of the coal seam, h is the depth of the rock mass after the overburden collapse, B is the width of the collapsed rock mass, a is the "D-dimensional length" of the fissure, D total is the total fractal dimension of the fissure above the goaf, and r is the optimal fractal size.

[0156] It can be seen from equation (20) that the settlement S1 caused by filling the goaf with the broken rock mass above the goaf is independent of H.

[0157] For the overburden rock with initial fissures, the damage constitutive relation can be expressed as:

[0158] ε = [σ1-ν(σ2+σ3)] / E(1-D f ) (21)

[0159] where ε is the strain of the overburden rock above the goaf, σ1 is the minor principal stress, σ2 is the intermediate principal stress, σ3 is the major principal stress, D f is the damage variable, E is the initial elastic modulus, and v is the Poisson's ratio of the overburden rock.

[0160] It is assumed that F in equation (7) obeys the D-P strength criterion, i.e.:

[0161]

[0162] where F is the strength of the overburden rock element, I1 and J2 are the first principal stress and second deviatoric stress invariants, and parameters α and k are strength parameters related to c、 . α is a constant related to c、 , and k is a constant related to c、 .

[0163] I1 and J2 can be expressed as:

[0164] I1 = σ1 + σ2 + σ3 (23)

[0165]

[0166] where σ1 is the minor principal stress, σ2 is the intermediate principal stress, and σ3 is the major principal stress.

[0167] α and k can be expressed as:

[0168]

[0169] where c、​ Shear strength parameter.

[0170] Substitute formula (7) and formula (23) into formula (21), and the damage constitutive model can be obtained as follows:

[0171]

[0172] Wherein, ε is the strain of overburden rock in goaf, σ1 is the minor principal stress, σ2 is the intermediate principal stress, σ3 is the major principal stress, v is the Poisson's ratio of overburden rock, E is the initial elastic modulus, A is the post-mining crack area, a is the 'D-dimensional length' of the crack, r is the optimal fractal box size, D is the box covering fractal dimension, F is the strength of overburden rock unit, and m and F0 are Weibull statistical parameters.

[0173] Further, in the embodiment of the present application, the additional stress of the overburden rock layer at different depths is calculated according to the stress balance principle, and the settlement of the overburden rock layer at different depths is calculated using the layering summation method, including:

[0174] According to the stress balance relationship, the normal stress of the overburden rock layer at different depths is calculated, and the total stress of the overburden rock layer at different depths before mining is calculated;

[0175] According to the normal stress of the overburden rock layer at different depths and the total stress of the overburden rock layer at different depths before mining, the additional stress of the overburden rock layer at different depths is calculated;

[0176] The overburden rock layer at each depth is divided into a preset number of sub-layers, the settlement is calculated, and the layering settlement is obtained;

[0177] According to the layering settlement, the settlement of the overburden rock layer at different depths is calculated by summation.

[0178] Further, in the embodiment of the present application, the overburden rock layer at each depth is divided into a preset number of sub-layers, the settlement is calculated, and the layering settlement is obtained, including:

[0179] The additional stress is brought into the fractal damage constitutive model to obtain the layering settlement.

[0180] After the coal seam is mined, the overburden rock layer sinks due to gravity W, and the wedge bodies ABM and CDN on both sides of the overburden rock mass will generate horizontal pressure P (as shown in Figure 9 Therefore, the AB and CD surfaces will be subjected to vertical friction force f generated by pressure P. The present unit length of the mined-out section is the research object, according to the stress balance relationship, the normal stress σ 1t of the aa' section at a depth of h from the ground surface can be expressed as:

[0181] Bσ 1t = W + p - 2f h (27)

[0182] where W, p and f h are the self-weight of the rock mass above the aa' cross section, the foundation load and the frictional force, respectively. The foundation load can be calculated by multiplying the average bulk density of the rock by the depth, W, f h and the vertical upward pressure q on the layer are expressed as:

[0183]

[0184] where γ i is the average unit weight of the i-th layer of rock; h i is the distance from the bottom of the i-th layer of overburden to the surface; R i is the horizontal pressure on the i-th layer of rock, which can be expressed as:

[0185]

[0186] where γ i is the average unit weight of the i-th layer of rock; h i is the distance from the bottom of the i-th layer of overburden to the surface; γ i-1 is the average unit weight of the i-1-th layer of rock; h i-1 is the distance from the bottom of the i-1-th layer of overburden to the surface, is the internal friction angle of the i-th layer.

[0187] From equations (27), (28) and (29), σ 1t can be expressed as:

[0188]

[0189] where σ 1t is the total stress on the aa' surface, B is the total length under the additional stress, n is the number of layers, γ i is the average unit weight of the i-th layer of rock; h i is the distance from the bottom of the i-th layer of overburden to the surface; γ i-1 is the average unit weight of the i-1-th layer of rock; h i -1 is the distance from the bottom of the i-1-th layer of overburden to the surface, is the internal friction angle of the i-th layer, F is the load of the upper structure, G is the self-weight of the foundation (including overburden), B0 is the short side length of the aa' surface, and lo is the long side length of the aa' surface.

[0190] Before mining, the total stress on the aa' surface is:

[0191]

[0192] where σ 10γ is the total stress before mining, F is the load of the superstructure, G is the self-weight of the foundation (including the overburden), B0 is the short side length of the aa′ surface, l0 is the long side length of the aa′ surface, γ is the self-weight of the foundation and overburden, h is the depth of the rock mass after the overburden collapses, and α is the total stress before mining. i Let be the additional stress coefficient of the i-th layer of foundation overburden, which can be determined according to the "Code for Design of Building Foundations" (GB50007-2011), B be the total length under additional stress, n be the number of layers, and γ be the stress coefficient. i h represents the average unit weight of the i-th rock layer. i γ represents the distance from the bottom surface of the i-th overburden layer to the Earth's surface. i-1 h represents the average unit weight of the rock in the (i-1)th layer. i-1 Let represent the distance from the bottom surface of the (i-1)th layer of overburden to the ground surface. Then, the additional stress caused by mining is:

[0193]

[0194] Where σ1 is the additional stress caused by mining, σ 10 The total stress before mining, σ 1t Let γ be the total stress on surface aa′, F be the load of the superstructure, G be the self-weight of the foundation (including the overburden), B0 be the short side length of surface aa′, l0 be the long side length of surface aa′, γ be the self-weight of the foundation and overburden, h be the depth of the rock mass after the overburden collapse, and α be the total stress on surface aa′. i Let γ be the additional stress coefficient of the i-th layer of foundation overburden, B be the total length under additional stress, n be the number of layers, and γ be the stress coefficient of the i-th layer of foundation overburden. i h represents the average unit weight of the i-th rock layer. i γ represents the distance from the bottom surface of the i-th overburden layer to the Earth's surface. i-1 h represents the average unit weight of the rock in the (i-1)th layer. i-1 This represents the distance from the bottom surface of the (i-1)th layer of overburden to the Earth's surface.

[0195] For any overburden layer layered according to natural lithology, assuming a layer thickness of d, calculate the settlement S by dividing it into n sublayers. i Furthermore, the strain between the upper and lower layers should not exceed 1%. The settlement S of each layer in this stratum. i for:

[0196]

[0197] Where, ε i Let n be the strain of each layer, d be the number of layers, and d be the layer thickness. These values ​​are determined by the damage constitutive relation in equation (26). The vertical additional stress σ1 from equation (28) is substituted into equation (26), and the confining pressure is calculated based on the natural overburden weight. Damage parameters m and F0 are determined using indoor loading test data. Therefore, the total settlement of this layer is:

[0198]

[0199] wherein S0 is the settlement caused by the goaf, n is the number of layers, S i is the settlement of each layer, d is the total thickness of the layer, ε i is the strain of each layer.

[0200] The present application calculates the surrounding stress of the overburden rock according to the layering summation method, brings σ1 in formula (32) into formula (22), and determines the fractal dimension and the optimal fractal size r according to Table 2. Since the load transmitted by the foundation is much smaller than the influence of the goaf on the overburden settlement, it can be ignored. The overburden settlement of different depths of the overburden rock in the goaf is calculated.

[0201]

[0202] Table 2

[0203] In order to monitor the overburden settlement caused by coal mining, a vertical borehole A is drilled away from the old goaf on the side of the working face cut hole area before mining until the coal seam floor; after the coal seam is mined, a comparison hole B is mined beside the A hole, and the settlement of the same fracture or joint zone before and after mining of the A hole and the B hole is compared, and the distance between the two is taken as the vertical settlement, as shown in Figure 11 The model calculation parameters are shown in Table 2.

[0204] The change rule of the additional stress above the goaf is shown in Figure 11 The comparison relationship between the measured strain values and the calculated values of each point of the overburden rock layer is shown in Figure 12 It can be seen from Figure 12 that the theoretical calculation value is close to the field monitoring value, which shows that the damage constitutive model established in the present application is reasonable in calculating the settlement of the goaf foundation. The purpose of calculating the overburden settlement of the goaf by using the fractal theory is achieved.

[0205] Figure 13 It is a structure schematic diagram of an overburden rock layer settlement calculation device based on the internal damage characteristics of the goaf provided in Embodiment 2 of the present application.

[0206] As shown in Figure 13 , the overburden rock layer settlement calculation device based on the internal damage characteristics of the goaf comprises:

[0207] The acquisition module 10 is used for acquiring the detection image;

[0208] The processing module 20 is used for determining the fractal description of the damage variable by using the digital image processing technology and the fractal box covering method according to the detection image;

[0209] The size determination module 30 is used for calculating the crack area distribution weight of the overburden rock at different depths, and determining the optimal fractal box size according to the relationship between the information space dimension and the box covering fractal dimension.

[0210] The construction module 40 is configured to establish a fractal damage constitutive model by determining the damage factor of the overburden rock mass according to the fractal description of the damage variable and the optimal fractal box size.

[0211] The calculation module 50 is configured to calculate the additional stress of the overburden rock mass at different depths according to the stress balance principle and calculate the settlement of the overburden rock mass at different depths by using the layer summation method.

[0212] The overburden rock stratum settlement calculation device based on the internal damage characteristics of the overburden rock in the embodiment of the application comprises an acquisition module configured to acquire a detection image; a processing module configured to determine the fractal description of the damage variable by using a digital image processing technology and a fractal box covering method according to the detection image; a size determination module configured to calculate the fracture area distribution weight of the overburden rock at different depths and determine the optimal fractal box size according to the relationship between the information space dimension and the box covering fractal dimension; a construction module configured to establish a fractal damage constitutive model by determining the damage factor of the overburden rock mass according to the fractal description of the damage variable and the optimal fractal box size; and a calculation module configured to calculate the additional stress of the overburden rock mass at different depths according to the stress balance principle and calculate the settlement of the overburden rock mass at different depths by using the layer summation method. Thus, the technical problem that the deformation and damage of the internal rock stratum of the overburden rock cannot be determined due to the difficulty in obtaining the internal data of the overburden rock in the prior art can be solved. The influence of the coal mining process on the stress of the overburden rock is determined by using the stress balance principle, and the overburden rock stratum settlement calculation model of the goaf is constructed by using the fractal damage constitutive relationship, so that the calculation of the additional stress increase of the internal rock stratum at different depths of the overburden rock and the settlement of the overburden rock stratum at different depths caused by mining is realized, the calculation accuracy is improved, and the purpose of calculating the overburden rock settlement of the goaf by using the fractal theory is achieved.

[0213] Further, in the embodiment of the application, the processing module is specifically configured to:

[0214] perform binaryzation processing on the detection image to obtain a binaryzation image under the optimal threshold value;

[0215] perform processing on the binaryzation image to obtain the area of the damage region;

[0216] determine the fractal description of the damage variable by using the fractal box covering method.

[0217] In order to realize the above-mentioned embodiments, the application further provides a computer device comprising a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the computer program, the computer device realizes the overburden rock stratum settlement calculation method based on the internal damage characteristics of the overburden rock of the goaf.

[0218] In order to achieve the above-mentioned embodiments, the application further provides a non-transitory computer-readable storage medium, which stores a computer program, and the computer program is executed by a processor to implement the goaf overburden strata settlement calculation method based on internal damage characteristics of overburden strata of the above-mentioned embodiments.

[0219] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. In addition, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0220] In addition, the terms "first", "second" are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first", "second" can explicitly or implicitly include at least one of the features. In the description of the present application, the meaning of "a plurality of" is at least two, for example, two, three, etc., unless otherwise specifically limited.

[0221] Any process or method descriptions in flow charts or described elsewhere herein can be understood as representing code modules, segments, or portions of code that include one or more executable instructions for implementing the specified logic functions or processes, and the preferred embodiments of the present application also include additional implementation involving other processes or methods. It should be understood that the order of the steps in the process or method described in the flow charts or otherwise described herein is not mandatory and that the steps can be performed in any order unless otherwise specifically noted.

[0222] The logic and / or steps represented in the flowcharts and / or described herein, for example, can be considered as a sequence of instructions to implement logical functions, and can be embodied in any computer-readable medium for use by an instruction execution system, apparatus, or device, such as a computer-based system, processor- based system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For purposes of this specification, a "computer-readable medium" can be any apparatus that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. The computer-readable medium can be a computer- readable storage medium or a computer-readable signal medium. The computer- readable storage medium can be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer-readable storage medium include the following: an electrical connection having one or more wires (electrical connections), a portable computer diskette (a magnetic device), a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, and a portable compact disc read-only memory (CDROM). In addition, the computer-readable medium can even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, for example, via optical scanning of the paper or other medium, then compiled, interpreted, or otherwise processed in a suitable manner, if necessary, and then stored in a computer memory.

[0223] It should be understood that aspects of the application can be implemented in hardware, software, firmware or combinations thereof. In the above embodiments, various steps or methods can be implemented in software or firmware that is stored in memory and executed by a suitable instruction execution system. As such, in some embodiments, specifically configured hardware can be used to implement at least some of the functionality described herein. For example, if implemented in hardware, the hardware can include any or a combination of the following: a discrete logic circuit having logic gates for implementing logic functions upon data signals, an application specific integrated circuit having appropriate combinational logic gates, a programmable gate array (PGA), a field programmable gate array (FPGA), etc.

[0224] Those of skill in the art would understand that information and signals can be represented using any of a variety of technologies and techniques. For example, data, instructions, commands, information, signals, bits, symbols, and chips that can be referenced throughout the above description can be represented by voltages, currents, electromagnetic waves, magnetic fields or particles, optical fields or particles, or any combination thereof.

[0225] In addition, each of the functional units in the various embodiments of the present application can be integrated in one processing module, or each of the units can be physically present separately, or two or more units can be integrated in one module. The integrated module can be implemented in the form of hardware or in the form of a software functional module. When the integrated module is implemented in the form of a software functional module and sold or used as an independent product, it can also be stored in a computer readable storage medium.

[0226] The storage medium mentioned above can be a read-only memory, a magnetic disk or an optical disk, etc. Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A method for calculating the settlement of overburden strata in goaf areas based on the internal failure characteristics of overburden, characterized in that, Includes the following features: Acquire detection images; Based on the detected images, digital image processing techniques and fractal box covering methods are used to determine the fractal description of the damage variables; Calculate the distribution weights of fracture areas at different overburden depths, and determine the optimal fractal box size based on the relationship between the information spatial dimension and the box cover fractal dimension; wherein, the optimal fractal box size is expressed as: Where r is the optimal fractal box size. The initial porosity, Let be the dimension of the information space. The relationship between the dimension of the information space and the fractal dimension of the box covering is expressed as follows: , The box-covered fractal dimension; Based on the fractal description of the damage variables and the optimal fractal box size, a fractal damage constitutive model is established by determining the overburden damage factor; The additional stress of overburden strata at different depths is calculated based on the stress balance principle, and the settlement of overburden strata at different depths is calculated using the layered summation method.

2. The method as described in claim 1, characterized in that, The step of determining the fractal description of the damage variables of the fracture element based on the detected image using digital image processing technology and fractal box overlay method includes: The detected image is binarized to obtain a binarized image under the optimal threshold. The binarized image is processed to obtain the area of ​​the damaged region; The fractal description of the damage variable is determined using the fractal box covering method.

3. The method as described in claim 1, characterized in that, The calculation of the weighting of the distribution of fracture area at different depths of overburden, and the determination of the optimal fractal box size based on the relationship between the information spatial dimension and the box cover fractal dimension, further includes: Arrange the crack areas in ascending order and divide the total data interval into a preset number of sub-intervals to obtain the information content of crack area distribution. Continuously change the interval size to obtain the spatial dimension of crack information.

4. The method as described in claim 1, characterized in that, The step of establishing a fractal damage constitutive model by determining the overburden damage factor based on the fractal description of the damage variable and the optimal fractal box size includes: Substituting the fractal description of the damage variables into the damage constitutive relation, we obtain a fractal damage constitutive model; The fractal damage constitutive model is expressed as follows: in, For the overburden strain in the goaf, For minor principal stress, Poisson's ratio for overlying rocks, For the middle principal stress, For major principal stresses, The initial elastic modulus, This represents the post-mining fracture area. For cracks Dimension length, For optimal fractal box size, For the box-covered fractal dimension, For the strength of the overburden unit, m, These are the statistical parameters for Weibull.

5. The method as described in claim 1, characterized in that, The calculation of additional stress in overburden strata at different depths based on the stress balance principle, and the calculation of settlement in overburden strata at different depths using the layered summation method, includes: Based on the stress balance relationship, the normal stress of the overburden strata at different depths is calculated, and the total stress of the overburden strata at different depths before mining is calculated. The additional stress of the overburden strata at different depths is calculated based on the normal stress of the overburden strata at different depths and the total stress of the overburden strata at different depths before mining. The overburden layer at each depth is divided into a predetermined number of sub-layers, and the settlement is calculated to obtain the stratified settlement. Based on the stratified settlement, the settlement of overburden layers at different depths is calculated by summing.

6. The method as described in claim 5, characterized in that, The process of dividing the overburden layer at each depth into a predetermined number of sublayers, calculating the settlement, and obtaining the stratified settlement includes: The additional stress is incorporated into the fractal damage constitutive model to obtain the settlement amount of each layer.

7. A device for calculating settlement of overburden strata in goaf areas based on internal failure characteristics of overburden, characterized in that, include: The acquisition module is used to acquire the probe image; The processing module is used to determine the fractal description of the damage variable based on the detected image using digital image processing technology and fractal box covering method; The size determination module is used to calculate the distribution weight of fracture area at different depths of overburden and determine the optimal fractal box size based on the relationship between the information spatial dimension and the box cover fractal dimension; wherein, the determination of the optimal fractal box size is expressed as: Where r is the optimal fractal box size. The initial porosity, Let be the dimension of the information space. The relationship between the dimension of the information space and the fractal dimension of the box covering is expressed as follows: , The box-covered fractal dimension; A construction module is used to establish a fractal damage constitutive model by determining the overburden damage factor based on the fractal description of the damage variable and the optimal fractal box size. The calculation module is used to calculate the additional stress of overburden strata at different depths based on the stress balance principle, and to calculate the settlement of overburden strata at different depths using the layered summation method.

8. The apparatus as claimed in claim 7, characterized in that, The processing module is specifically used for: The detected image is binarized to obtain a binarized image under the optimal threshold. The binarized image is processed to obtain the area of ​​the damaged region; The fractal description of the damage variable is determined using the fractal box covering method.

9. A computer device, characterized in that, It includes a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the computer program, it implements the method as described in any one of claims 1-6.

10. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-6.

Images