Method for determining engineering scale of coal mine working face based on overlying strata damage degree

Abstract

The invention provides a method for determining the engineering scale of a coal mine working face based on the damage degree of overlying strata, and relates to the technical field of coal mining. According to the method for determining the engineering scale of the coal mine working face based on the overlying strata damage degree, a rock core is drilled on the basis of an engineering site to manufacture a standard sample, basic mechanical parameters of each layer of rock are obtained based on an indoor test, and the position of a key layer of the overlying strata on the working face is determined according to a test result; then, determining an acoustic emission evolution law of the rock of the key layer through an indoor test, constructing a segmented constitutive model of the rock of the key layer, and importing the obtained segmented constitutive model into FLAC 3D numerical simulation software through a fish language to carry out engineering scale numerical simulation; the proper advancing speed of the working face is determined by simulating the damage and damage characteristics of the overlying strata on the working face under different working face engineering scales (advancing speeds).

Description

Technical Field

[0001] The invention relates to the technical field of coal mining, and in particular to a method for determining the engineering scale of a coal mine working face based on the degree of overburden damage. Background Art

[0002] In recent years, with the continuous improvement of science and technology, the safety situation of coal mine production has continued to improve steadily, but the safety situation is still severe. Among them, the engineering scale of coal mine working face (working face width, height, length and advancement speed) has a significant impact on coal mine safety and production efficiency. Reasonable working face engineering scale can significantly improve the safety and production efficiency of coal mine production.

[0003] At present, the engineering scale of coal mine working faces is determined according to the stability and support conditions of the surrounding rock. However, the overlying rock strata on the working face are in complex geological conditions and have complex mechanical properties. The above traditional methods rarely consider these complex factors, which will reduce coal mining efficiency and safety in operations to a certain extent. Summary of the invention

[0004] The present invention provides a method for determining the engineering scale of a coal mine working face based on the damage degree of overlying rock, and determines the reasonable engineering scale of the working face according to the damage degree of the overlying rock strata, so as to take into account both safety and production efficiency.

[0005] In order to achieve the above-mentioned purpose, the technical solution adopted by the present invention is as follows: a method for determining the engineering scale of a coal mine working face based on the degree of overburden damage, the method comprising the following steps: Step 1, obtaining the geological parameters of each rock layer in the mining area and sampling the rocks in each rock layer through a coring drill.

[0006] Step 2: Obtain the compressive strength, elastic modulus, Poisson's ratio, internal friction angle and tensile strength of each rock layer through indoor tests.

[0007] Step 3: Determine the key layer of the overlying rock formation on the working face through theoretical analysis and calculation.

[0008] Step 4: Obtain the tensile strength and acoustic emission energy evolution law of the key layer through cyclic loading and unloading tests.

[0009] Step 5: Construct a segmented constitutive model of the key layer rock through theoretical analysis and calculation.

[0010] Step 6: Embed the segmented constitutive model of the key layer rock into the numerical simulation software for secondary development.

[0011] Step 7: According to the geological parameters of each rock layer and the indoor test parameters, a numerical simulation model is established in the numerical simulation software to simulate the damage characteristics of the overlying rock layer under different working face engineering scales.

[0012] Step 8. The damage degree of the overburden stratum is characterized by the overburden stratum damage coefficient. The overburden stratum damage coefficients corresponding to different working face engineering scales are fitted to obtain the evolution law of the overburden stratum damage coefficients under different working face engineering scales, and then the working face engineering scale corresponding to the position with the smallest change in the overburden stratum damage coefficient is selected as the reasonable engineering scale of the working face.

[0013] Furthermore, the specific steps of step 2 are as follows: Step 21, processing rocks in each rock layer into rock samples.

[0014] Step 22: Place the rock sample on a uniaxial compression testing machine to perform a uniaxial compression test.

[0015] Step 23: Place the rock sample on a uniaxial compression testing machine and conduct a Brazilian splitting test.

[0016] Step 24: Obtain stress-strain curves of uniaxial compression test and Brazilian splitting test by using a uniaxial compression testing machine, and obtain compressive strength, elastic modulus, Poisson's ratio, internal friction angle and tensile strength of various rock samples.

[0017] Furthermore, the specific steps of step 3 are as follows: Step 31, calculate the load on the rock layer of the top plate of the working face according to formula (1).

[0018] Formula (1).

[0019] in, is the load of the kth rock layer on the top plate of the working face.

[0020] , and are the bulk density, thickness and elastic modulus of the i-th rock layer, i=1, 2,…, k.

[0021] and are the elastic modulus and thickness of the top plate, respectively.

[0022] Step 32: When the k+1th rock layer is a hard rock layer, the rock layers below the k+1th layer no longer need to bear the load brought by the upper rock layer, so there is formula (2):

[0023] Formula (2).

[0024] in, is the load of the k+1th rock layer on the top plate of the working face.

[0025] Substituting equation (1) into equation (2), we get equation (3):

[0026] Formula (3).

[0027] in, and are the elastic modulus and thickness of the k+1th rock layer respectively.

[0028] , and are the elastic modulus, bulk density and thickness of the i-th rock layer respectively.

[0029] is the bulk density of the i+1th rock layer.

[0030] Step 33: Use formula (3) to determine the hard rock layer.

[0031] Calculate layer by layer from the top of the working face upwards. When the calculation result of the k+1th rock layer satisfies formula (3), that is, the load of the kth rock layer on the top of the working face is greater than the load of the k+1th rock layer on the top of the working face, then the k+1th rock layer is a hard rock layer.

[0032] Step 34: Calculate the breaking distance of each hard rock layer using formula (4).

[0033] Formula (4).

[0034] in, is the breaking distance of the i-th hard rock layer.

[0035] is the tensile strength of the i-th hard rock layer.

[0036] is the load of the i-th rock layer on the top plate of the working face.

[0037] Step 35: compare the breaking distances of the hard rock layers, and the hard rock layer with the smallest breaking distance is the key layer.

[0038] Furthermore, the specific implementation process of step 4 is as follows: take the key layer core to make a rock sample, symmetrically stick the acoustic emission probe on both sides of the rock sample, and then place the rock sample in a uniaxial compression testing machine for a cyclic loading and unloading test to obtain the tensile strength of the key layer rock sample and the acoustic emission energy evolution law.

[0039] Furthermore, the specific steps of step 5 are as follows: Step 51, obtain the Felicity ratio according to formula (5).

[0040] Formula (5).

[0041] Among them, FR i is the Felicity ratio in the i-th cycle.

[0042] P i+1 is the stress level when the acoustic emission during the i+1th loading process is equal to the i-th acoustic emission reaching its maximum value.

[0043] P imax is the highest stress level in the i-th loading.

[0044] Step 52, according to the deformation and failure characteristics of the rock sample in the cyclic loading and unloading test, the loading process is divided into three stages, namely, the fracture compaction stage, the elastic deformation stage and the plastic failure stage; wherein, when the Felicity ratio is greater than 1, it is the fracture compaction stage, when the Felicity ratio is equal to 1, it is the elastic deformation stage, and when the Felicity ratio is less than 1, it is the plastic failure stage.

[0045] Step 53, the evolution law of acoustic emission energy obtained by the cyclic loading and unloading test is used to define the crack compaction and plastic failure process of the rock sample; the compaction coefficient is determined by formula (6), and the compaction coefficient is used to reflect the compaction degree of the rock sample in the crack compaction stage; the damage coefficient is determined by formula (7), and the damage coefficient is used to reflect the damage degree of the rock sample in the plastic failure stage.

[0046] Formula (6).

[0047] Formula (7).

[0048] Where C is the compaction coefficient of the rock sample.

[0049] is the cumulative energy of acoustic emission in the mth cycle during the fracture pressure stage.

[0050] It is the accumulated energy of acoustic emission at the end of the fracture compaction stage.

[0051] D is the damage coefficient of the rock sample.

[0052] is the accumulated energy of acoustic emission in the nth cycle during the plastic failure stage.

[0053] It is the accumulated energy of acoustic emission at the end of the plastic failure stage.

[0054] Step 54: According to equations (8), (9) and (10), the constitutive models of the rock specimen at the stages of crack compaction, elastic deformation and plastic failure are constructed respectively.

[0055] Formula (8).

[0056] Formula (9).

[0057] Formula (10).

[0058] in, is the stress at the fracture compaction stage.

[0059] is the tangent modulus of the rock sample at the fracture compaction stage.

[0060] C is the compaction coefficient of the rock sample.

[0061] For strain.

[0062] is the stress in the elastic deformation stage.

[0063] is the axial stress at the end of the fracture compaction stage.

[0064] It is the tangent modulus of the cyclic loading and unloading envelope in the elastic deformation stage.

[0065] is the axial strain at the end of the fracture compaction stage.

[0066] is the stress in the plastic failure stage.

[0067] is the axial stress at the end of the elastic deformation stage.

[0068] It is the tangent modulus of the cyclic loading and unloading envelope in the plastic failure stage.

[0069] is the axial strain at the end of the elastic deformation stage.

[0070] Furthermore, the specific implementation process of step 6 is as follows: the segmented constitutive model of the key layer rock is embedded into the FLAC 3D numerical simulation software through the FISH language to achieve secondary development.

[0071] Furthermore, in step 7, the non-critical layer rock adopts the Mohr-Coulumb failure criterion, and the critical layer rock adopts the segmented constitutive model of the critical layer rock embedded in the secondary development as the failure criterion.

[0072] Furthermore, in step 7, the geological parameters of each rock layer and the indoor test parameters include the thickness of each rock layer, rock type, density, compressive strength of each type of rock, Poisson's ratio and internal friction angle parameters.

[0073] Furthermore, in step 8, the damage degree of the overburden strata corresponding to the engineering scales of different working faces is fitted by Origin software.

[0074] Furthermore, in step 8, the overburden damage coefficient expression is:

[0075] Formula (11).

[0076] in, is the damage coefficient of the overlying rock.

[0077] is the volume of a plastic unit.

[0078] is the volume of the observed space.

[0079] The beneficial technical effect of the present invention is as follows: the method of the present invention for determining the engineering scale of a coal mine working face based on the degree of overburden damage is based on producing standard samples based on core drilling at the engineering site, obtaining basic mechanical parameters of each layer of rock based on indoor tests, determining the position of a key layer of the overburden on the working face according to the test results, and then determining the acoustic emission evolution law of the key layer of rock through indoor tests, and constructing a segmented constitutive model of the key layer of rock, and then importing the obtained segmented constitutive model into FLAC 3D numerical simulation software through fish language for engineering scale numerical simulation, and determining a suitable working face advancement speed by simulating the damage and destruction characteristics of the overburden on the working face under different working face engineering scales (advancement speeds).

[0080] Compared with the traditional method of selecting the working face advancement speed only by experience or design requirements, the method of determining the engineering scale of the coal mine working face based on the overburden damage degree of the present invention effectively improves the accuracy of the selection of the working face advancement speed by combining field investigation, indoor experiments and numerical simulation, takes into account both safety and production efficiency, and has important engineering guiding significance for the safety and efficiency of coal mining. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 It is a flow chart of a method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to an embodiment of the present invention.

[0082] Figure 2 Schematic diagram of a uniaxially compressed standard rock sample according to an embodiment of the present invention.

[0083] Figure 3 Schematic diagram of Brazilian splitting standard rock sample according to an embodiment of the present invention.

[0084] Figure 4 Schematic diagram of the Brazilian splitting test according to an embodiment of the present invention.

[0085] Figure 5 It is a schematic diagram of uniaxial compression and cyclic loading and unloading tests according to an embodiment of the present invention.

[0086] Figure 6 Schematic diagram of acoustic emission monitoring according to an embodiment of the present invention.

[0087] Figure 7 Schematic diagram of cyclic loading and unloading stress path of an embodiment of the present invention.

[0088] Figure 8 Schematic diagram of the evolution law of Felicity ratio in an embodiment of the present invention.

[0089] Fig. 9 It is a schematic diagram of stress-strain of cyclic loading and unloading of a standard rock sample in a key layer of an embodiment of the present invention.

[0090] Fig.10 It is a schematic diagram for comparing the segmented constitutive model of the key layer rock and the test data in an embodiment of the present invention.

[0091] Fig.11 This is a distribution diagram of the plastic zone of the overlying strata when the working face advances 2 meters per day in an embodiment of the present invention.

[0092] Fig.12 This is a distribution diagram of the plastic zone of the overlying strata when the working face advances at a speed of 4 meters per day in an embodiment of the present invention.

[0093] Fig.13 This is a distribution diagram of the plastic zone of the overlying strata when the working face advances 6 meters per day in an embodiment of the present invention.

[0094] Fig.14 This is a distribution diagram of the plastic zone of the overlying strata when the working face advances at a speed of 8 meters per day in an embodiment of the present invention.

[0095] Fig.15 This is a distribution diagram of the plastic zone of the overlying strata when the working face advances at a speed of 10 meters per day in an embodiment of the present invention.

[0096] Fig.16 This is a distribution diagram of the plastic zone of the overlying strata when the working face advances at a speed of 12 meters per day in an embodiment of the present invention.

[0097] Fig.17 This is a distribution diagram of the plastic zone of the overlying strata when the working face advances at a speed of 14 meters per day in an embodiment of the present invention.

[0098] In the figure, 1-uniaxial compression standard specimen, 2-Brazilian splitting standard specimen, 3-Brazilian splitting fixture, 4-uniaxial compression testing machine, 5-testing machine control system, 6-acoustic emission probe, 7-acoustic emission detection system. DETAILED DESCRIPTION

[0099] In order to make the purpose, technical scheme and beneficial effects of the present invention more clearly understood, the present invention is further described in detail below in combination with specific embodiments and with reference to the accompanying drawings. Certain embodiments of the present invention will be described more comprehensively with reference to the accompanying drawings, in which some but not all embodiments will be shown. In fact, the various embodiments of the present invention can be implemented in many different forms and should not be construed as being limited to the embodiments described herein; rather, these embodiments are provided so that the present invention meets applicable legal requirements.

[0100] In the description of the present invention, it should be noted that the terms "inside", "outside", "upper", "lower", "front", "back" and the like indicate directions or positional relationships based on directions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance.

[0101] This example is based on the actual situation of the Buertai Coal Mine in Shendong Mining Area. Figures 1 to 17 As shown, a method for determining the engineering scale of a coal mine working face based on the degree of overburden damage is provided, comprising the following steps.

[0102] Step 1: Use a coring drill to obtain the geological parameters of each rock layer in the mining area and take samples of the rocks in each rock layer.

[0103] Step 2: Obtain the compressive strength, elastic modulus, Poisson's ratio, internal friction angle and tensile strength of each rock layer through indoor tests.

[0104] The specific steps of step 2 are as follows: Step 21, processing the rocks in each rock layer into rock samples, wherein the uniaxial compression test rock sample 1 is 50mm×100mm standard cylindrical specimen, Brazilian splitting test rock specimen 2 The standard cylindrical specimen of 25mm×50mm makes the rock specimen conform to the ISRM standard.

[0105] Step 22, placing the uniaxial compression test rock sample 1 on the uniaxial compression test machine 4, and conducting a uniaxial compression test. The test is controlled by the test machine control system 5, using a displacement control method, and the loading and unloading rate is set to 0.25mm / min until the uniaxial compression test rock sample 1 is destroyed.

[0106] Step 23, place the Brazilian splitting test rock sample 2 into the Brazilian splitting fixture 3, and then place it on the uniaxial compression testing machine 4 to perform the Brazilian splitting test. The test is controlled by the testing machine control system 5, using a displacement control method, and the loading and unloading rate is set to 0.25 mm / min until the Brazilian splitting test rock sample 2 is destroyed.

[0107] Step 24, obtain the stress-strain curves of the uniaxial compression test and the Brazilian splitting test through the uniaxial compression testing machine 4, and obtain the compressive strength, elastic modulus, Poisson's ratio, internal friction angle and tensile strength of various rock samples.

[0108] Step 3: Determine the key layer of the overlying rock formation on the working face through theoretical analysis and calculation.

[0109] The specific steps of step 3 are as follows: Step 31. Calculate the load on the rock layer of the top plate of the working face according to formula (1).

[0110] Formula (1).

[0111] in, is the load of the kth rock layer on the top plate of the working face.

[0112] , and are the bulk density, thickness and elastic modulus of the i-th rock layer, i=1, 2,…, k.

[0113] and are the elastic modulus and thickness of the top plate, respectively.

[0114] Step 32: When the k+1th rock layer is a hard rock layer, the rock layers below the k+1th layer no longer need to bear the load brought by the upper rock layer, so there is formula (2):

[0115] Formula (2).

[0116] in, is the load of the k+1th rock layer on the top plate of the working face.

[0117] Substituting equation (1) into equation (2), we get equation (3):

[0118] Formula (3).

[0119] in, and are the elastic modulus and thickness of the k+1th rock layer respectively.

[0120] , and are the elastic modulus, bulk density and thickness of the i-th rock layer respectively.

[0121] is the bulk density of the i+1th rock layer.

[0122] Step 33: Use formula (3) to determine the hard rock layer.

[0123] Calculate layer by layer from the top of the working face upwards. When the calculation result of the k+1th rock layer satisfies formula (3), that is, the load of the kth rock layer on the top of the working face is greater than the load of the k+1th rock layer on the top of the working face, then the k+1th rock layer is a hard rock layer.

[0124] Now we calculate the geological data of the 22207 working face of the Buertai Coal Mine in Shendong Mining Area, and the calculation results are shown in Table 1: Table 1 Calculation results of hard rock formations in the 22207 working face of the Buertai Coal Mine in Shendong Mining Area

[0125]

[0126] After calculation, it was found that layers 12, 13 and 21 are hard rock layers.

[0127] Step 34: Calculate the breaking distance of each hard rock layer using formula (4).

[0128] Formula (4).

[0129] in, is the breaking distance of the i-th hard rock layer.

[0130] is the tensile strength of the i-th hard rock layer.

[0131] is the load of the i-th rock layer on the top plate of the working face.

[0132] Step 35, compare the breaking distances of each hard rock layer, and the hard rock layer with the smallest breaking distance is the key layer. After calculation, it is found that the breaking distances of the 12th, 13th, and 21st hard rock layers are 1.84cm, 8.49cm, and 7.98cm respectively. After comparison, it can be known that the key layer of the overlying rock layer on the working face is the 12th rock layer.

[0133] Step 4: Obtain the tensile strength and acoustic emission energy evolution law of the key layer through cyclic loading and unloading tests.

[0134] The specific implementation process of step 4 is as follows: Take the core of the key layer to make a rock sample, specifically A standard cylindrical sample of 50mm×100mm is used to make the rock sample meet the ISRM standard. The acoustic emission probe 6 is symmetrically pasted on both sides of the rock sample, and then the rock sample is placed in a uniaxial compression tester for cyclic loading and unloading tests. The acoustic emission detection system 7 adopts displacement control, the loading and unloading rate is set to 0.25mm / min, the loading gradient is set to 3kN, and the load increases step by step from 0→3kN→0kN→6kN→0kN→9kN→0kN... until the sample is completely destroyed, and the tensile strength and acoustic emission energy evolution law of the key layer rock sample are obtained.

[0135] Step 5: Construct a segmented constitutive model of the key layer rock through theoretical analysis and calculation.

[0136] The specific steps of step 5 are as follows: Step 51. Obtain the Felicity ratio according to formula (5).

[0137] Formula (5).

[0138] Among them, FR i is the Felicity ratio in the i-th cycle.

[0139] P i+1 is the stress level when the acoustic emission during the i+1th loading process is equal to the i-th acoustic emission reaching its maximum value.

[0140] P imax is the highest stress level in the i-th loading.

[0141] Step 52, according to the deformation and failure characteristics of the rock sample in the cyclic loading and unloading test, the loading process is divided into three stages, namely, the fracture compaction stage, the elastic deformation stage and the plastic failure stage; wherein, when the Felicity ratio is greater than 1, it is the fracture compaction stage, when the Felicity ratio is equal to 1, it is the elastic deformation stage, and when the Felicity ratio is less than 1, it is the plastic failure stage.

[0142] Step 53, the evolution law of acoustic emission energy obtained by the cyclic loading and unloading test is used to define the crack compaction and plastic failure process of the rock sample; the compaction coefficient is determined by formula (6), and the compaction coefficient is used to reflect the compaction degree of the rock sample in the crack compaction stage; the damage coefficient is determined by formula (7), and the damage coefficient is used to reflect the damage degree of the rock sample in the plastic failure stage.

[0143] Formula (6).

[0144] Formula (7).

[0145] Where C is the compaction coefficient of the rock sample.

[0146] is the cumulative energy of acoustic emission in the mth cycle during the fracture pressure stage.

[0147] It is the accumulated energy of acoustic emission at the end of the fracture compaction stage.

[0148] D is the damage coefficient of the rock sample.

[0149] is the accumulated energy of acoustic emission in the nth cycle during the plastic failure stage.

[0150] It is the accumulated energy of acoustic emission at the end of the plastic failure stage.

[0151] The detailed calculation results are as follows:

[0152] .

[0153] .

[0154] Step 54: According to equations (8), (9) and (10), the constitutive models of the rock specimen at the stages of crack compaction, elastic deformation and plastic failure are constructed respectively.

[0155] Formula (8).

[0156] Formula (9).

[0157] Formula (10).

[0158] in, is the stress at the fracture compaction stage.

[0159] is the tangent modulus of the rock sample at the fracture compaction stage.

[0160] C is the compaction coefficient of the rock sample.

[0161] For strain.

[0162] is the stress in the elastic deformation stage.

[0163] is the axial stress at the end of the fracture compaction stage.

[0164] It is the tangent modulus of the cyclic loading and unloading envelope in the elastic deformation stage.

[0165] is the axial strain at the end of the fracture compaction stage.

[0166] is the stress in the plastic failure stage.

[0167] is the axial stress at the end of the elastic deformation stage.

[0168] It is the tangent modulus of the cyclic loading and unloading envelope in the plastic failure stage.

[0169] is the axial strain at the end of the elastic deformation stage.

[0170] After calculation, the segmented constitutive model expression of the key layer rock is as follows:

[0171] .

[0172] Step 6: Embed the segmented constitutive model of the key layer rock into the numerical simulation software for secondary development.

[0173] The specific implementation process of step 6 is as follows: the segmented constitutive model of the key layer rock is embedded into the FLAC 3D numerical simulation software through the FISH language to achieve secondary development.

[0174] Step 7: According to the geological parameters of each rock layer and the indoor test parameters, a numerical simulation model is established in the numerical simulation software to simulate the damage characteristics of the overlying rock layer under different working face engineering scales.

[0175] Among them, the geological parameters of each rock layer and the indoor test parameters include the thickness of each rock layer, rock type, density, compressive strength of each type of rock, Poisson's ratio and internal friction angle parameters.

[0176] The Mohr-Coulumb failure criterion is used for non-critical layer rocks, while the segmented constitutive model of critical layer rocks embedded in the secondary development is used as the failure criterion for critical layer rocks.

[0177] The specific steps of step 7 are as follows: Step 71: The geological parameters of each rock layer and the indoor test parameters are used to construct different rock layers in the FLAC 3D numerical simulation software.

[0178] Step 72: Select a constitutive model for the key layer, that is, the segmented constitutive model of the key layer rock obtained in step 5.

[0179] Step 73: Set the engineering scale of the working face. In this embodiment, the working face width is set to 100m, the working face height is set to 4m, and the working face length is set to 100m. The overburden damage characteristics of the working face at advancement speeds of 2m / d, 4m / d, 6m / d, 8m / d, 10m / d, 12m / d and 14m / d are simulated respectively.

[0180] Step 8: The overburden stratum damage degree reflects the degree of overburden stratum damage during the FLAC 3D numerical simulation. The overburden stratum damage degree is characterized by the overburden stratum damage coefficient. The larger the overburden stratum damage coefficient, the more unstable the overburden stratum:

[0181] Formula (11).

[0182] in, is the damage coefficient of the overlying rock.

[0183] is the volume of a plastic unit.

[0184] is the volume of the observed space.

[0185] The overburden damage coefficient corresponding to different working face engineering scales was fitted by Origin software to obtain the evolution law of the overburden damage coefficient under different working face engineering scales. Then, the working face engineering scale corresponding to the position with the smallest change in the overburden damage coefficient was selected as the reasonable engineering scale of the working face.

[0186] The evolution law of the damage coefficient of the overburden strata under different working face engineering scales in this embodiment is as follows:

[0187] .

[0188] The fitting curve is a monotonically decreasing function with an inflection point of (7.01, 29.19), that is, when the width, height and length of the working face remain unchanged and the advancement speed is 7.01 m / d, the damage degree of the overburden strata decreases fastest, and after the inflection point, the change in the damage degree of the overburden strata is the smallest. The reasonable advancement speed of the working face should not be less than 7.01 m / d.

[0189] According to the operating procedures of the 22207 working face of the Buertai Coal Mine, the coal miner cuts coal for 17 hours a day, the average operating speed of the coal miner is 7 m / min, and the cutting depth of the coal miner is 0.865 m. After calculation, the maximum advancement speed of the working face under ideal conditions is 20.53 m / d. Therefore, the reasonable advancement speed of the working face is further determined to be 7.01-20.53 m / d.

[0190] So far, the present embodiment has been described in detail in conjunction with the accompanying drawings. Based on the above description, those skilled in the art should have a clear understanding of the method for determining the engineering scale of a coal mine working face based on the degree of overburden damage of the present invention. The method for determining the engineering scale of a coal mine working face based on the degree of overburden damage of the present invention is based on the production of standard samples by drilling cores on site, and the basic mechanical parameters of each layer of rock are obtained based on indoor tests. The position of the key layer of the overburden on the working face is determined based on the test results, and then the acoustic emission evolution law of the key layer of rock is determined through indoor tests, and a segmented constitutive model of the key layer of rock is constructed. The obtained segmented constitutive model is then imported into the FLAC 3D numerical simulation software through the fish language for engineering scale numerical simulation, and the appropriate working face advancement speed is determined by simulating the damage and destruction characteristics of the overburden on the working face under different working face engineering scales (advancement speeds). Compared with the traditional method of selecting the working face advancement speed only by experience or design requirements, the method of determining the engineering scale of the coal mine working face based on the overburden damage degree of the present invention effectively improves the accuracy of the selection of the working face advancement speed by combining field investigation, indoor experiments and numerical simulation, takes into account both safety and production efficiency, and has important engineering guiding significance for the safety and efficiency of coal mining.

[0191] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the engineering scale of a coal mine working face based on the degree of overburden damage, characterized in that: The method comprises the following steps: Step 1: obtain geological parameters of each rock layer in the mining area and sample rocks in each rock layer through a coring drill; Step 2, obtaining the compressive strength, elastic modulus, Poisson's ratio, internal friction angle and tensile strength of each rock layer through indoor tests; Step 3: Determine the key layer of the overlying rock formation on the working face through theoretical analysis and calculation; Step 4: Obtain the tensile strength and acoustic emission energy evolution law of the key layer through cyclic loading and unloading tests; Step 5: Construct a segmented constitutive model of the key layer rock through theoretical analysis and calculation; Step 6: embed the segmented constitutive model of the key layer rock into the numerical simulation software for secondary development; Step 7: According to the geological parameters of each rock layer and the indoor test parameters, a numerical simulation model is established in the numerical simulation software to simulate the damage characteristics of the overlying rock layer under different working face engineering scales; Step 8. The damage degree of the overburden stratum is characterized by the overburden stratum damage coefficient. The overburden stratum damage coefficients corresponding to different working face engineering scales are fitted to obtain the evolution law of the overburden stratum damage coefficients under different working face engineering scales, and then the working face engineering scale corresponding to the position with the smallest change in the overburden stratum damage coefficient is selected as the reasonable engineering scale of the working face.

2. A method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 1, characterized in that: The specific steps of step 2 are as follows: Step 21, processing rocks in each rock layer into rock samples; Step 22, placing the rock sample on a uniaxial compression testing machine to perform a uniaxial compression test; Step 23, placing the rock sample on a uniaxial compression testing machine to perform a Brazilian splitting test; Step 24: Obtain stress-strain curves of uniaxial compression test and Brazilian splitting test by using a uniaxial compression testing machine, and obtain compressive strength, elastic modulus, Poisson's ratio, internal friction angle and tensile strength of various rock samples.

3. A method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 2, characterized in that: The specific steps of step 3 are as follows: Step 31, calculate the load on the rock layer of the top plate of the working face according to formula (1); ; Formula (1) in, is the load of the kth rock layer on the top plate of the working face; , and are the bulk density, thickness and elastic modulus of the i-th rock layer, i=1, 2, …, k; and are the elastic modulus and thickness of the top plate, respectively; Step 32: When the k+1th rock layer is a hard rock layer, the rock layers below the k+1th layer no longer need to bear the load brought by the upper rock layer, so there is formula (2): ; Formula (2) in, is the load of the k+1th rock layer on the top plate of the working face; Substituting equation (1) into equation (2), we get equation (3): ; Formula (3) in, and are the elastic modulus and thickness of the k+1th rock layer respectively; , and are the elastic modulus, bulk density and thickness of the i-th rock layer respectively; is the bulk density of the i+1th rock layer; Step 33, using formula (3) to determine the hard rock layer; Calculate layer by layer from the top of the working face upwards. When the calculation result of the k+1th layer satisfies formula (3), that is, the load of the kth layer on the top of the working face is greater than the load of the k+1th layer on the top of the working face, then the k+1th layer is a hard rock layer. Step 34, using formula (4) to calculate the breaking distance of each hard rock layer; ; Formula (4) in, is the breaking distance of the i-th hard rock layer; is the tensile strength of the i-th hard rock layer; is the load of the i-th rock layer on the top plate of the working face; Step 35: compare the breaking distances of the hard rock layers, and the hard rock layer with the smallest breaking distance is the key layer.

4. A method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 3, characterized in that: The specific implementation process of step 4 is as follows: The key layer core is taken to make a rock sample, and the acoustic emission probes are symmetrically pasted on both sides of the rock sample. The rock sample is then placed in a uniaxial compression testing machine for a cyclic loading and unloading test to obtain the tensile strength of the key layer rock sample and the evolution law of acoustic emission energy.

5. A method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 4, characterized in that: The specific steps of step 5 are as follows: Step 51, obtain the Felicity ratio according to formula (5); ; Formula (5) in, FR i is the Felicity ratio in the i-th cycle; P i+1 is the stress level when the acoustic emission during the i+1th loading process is equal to the maximum value of the i-th acoustic emission; P imax is the highest stress level in the i-th loading; Step 52, according to the deformation and failure characteristics of the rock sample in the cyclic loading and unloading test, the loading process is divided into three stages, namely, the crack compaction stage, the elastic deformation stage and the plastic failure stage; wherein, when the Felicity ratio is greater than 1, it is the crack compaction stage, when the Felicity ratio is equal to 1, it is the elastic deformation stage, and when the Felicity ratio is less than 1, it is the plastic failure stage; Step 53, defining the crack compaction and plastic failure process of the rock sample by the acoustic emission energy evolution law obtained by the cyclic loading and unloading test; the compaction coefficient is determined by formula (6), and the compaction coefficient is used to reflect the compaction degree of the rock sample in the crack compaction stage; the damage coefficient is determined by formula (7), and the damage coefficient is used to reflect the damage degree of the rock sample in the plastic failure stage; ; Formula (6) ; Formula (7) in, C is the compaction coefficient of the rock sample; is the cumulative energy of acoustic emission in the mth cycle in the fracture pressure stage; It is the accumulated energy of acoustic emission at the end of the fracture compaction stage; D is the damage coefficient of the rock sample; is the accumulated energy of acoustic emission in the nth cycle in the plastic failure stage; It is the accumulated energy of acoustic emission at the end of the plastic failure stage; Step 54: construct the constitutive models of the rock sample at the stages of crack compaction, elastic deformation and plastic failure respectively according to equations (8), (9) and (10); ; Formula (8) ; Formula (9) ; Formula (10) in, is the stress at the fracture compaction stage; is the tangent modulus of the rock sample at the fracture compaction stage; C is the compaction coefficient of the rock sample; For strain; is the stress in the elastic deformation stage; is the axial stress at the end of the fracture compaction stage; is the tangent modulus of the cyclic loading and unloading envelope in the elastic deformation stage; is the axial strain at the end of the fracture compaction stage; is the stress in the plastic failure stage; is the axial stress at the end of the elastic deformation stage; D is the damage coefficient of the rock sample; is the tangent modulus of the cyclic loading and unloading envelope in the plastic failure stage; is the axial strain at the end of the elastic deformation stage.

6. A method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 5, characterized in that: The specific implementation process of step 6 is as follows: The segmented constitutive model of the key layer rock is embedded into the FLAC 3D numerical simulation software through the FISH language to achieve secondary development.

7. A method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 6, characterized in that: In step 7, the Mohr-Coulumb failure criterion is used for the non-critical layer rock, and the segmented constitutive model of the critical layer rock embedded in the secondary development is used as the failure criterion for the critical layer rock.

8. The method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 7 is characterized in that: In step 7, the geological parameters of each rock layer and the indoor test parameters include the thickness of each rock layer, rock type, density, compressive strength of each type of rock, Poisson's ratio and internal friction angle parameters.

9. A method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 8, characterized in that: In step 8, the overburden damage degree corresponding to different working face engineering scales is fitted using Origin software.

10. The method for determining the engineering dimensions of a coal mine working face based on the degree of overburden damage according to claim 8, characterized in that: In step 8, the overburden damage coefficient expression is: ; Formula (11) in, is the damage coefficient of the overlying rock formation; is the volume of a plastic unit; is the volume of the observed space.

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