A method for determining a flat-cut coal body fracture range

Abstract

The invention provides a method for determining the rupture range of a flat-cut coal body. The method uses a combination of research analysis, numerical simulation and physical experiments to study the jet disturbance stage and the slot rheological stage, and introduces a feature selection method based on clustering to accurately determine the main control factors of coal body rupture under jet disturbance and after cutting, and then improves the stress distribution constitutive model of the coal body, thereby achieving accurate judgment of the rupture range of the flat-cut coal body. The method is of great significance to maintaining the stability of the slot and improving the pressure relief effect, avoiding the blockage of the gas migration channel, thereby improving the gas extraction effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of coal mining, in particular to a method for determining the rupture range of a flat-cut coal body. BACKGROUND

[0002] With the gradual extension of coal mining in China to the deep part, the geological conditions tend to be complex. The characteristics of high stress, high temperature and high gas pressure in deep coal seams result in their common features of micro-porosity, low permeability and strong adsorption, making gas extraction extremely difficult, which seriously restricts the prevention and control of mine disasters and the utilization of gas resources. By external disturbance, artificial induction of coal body crack initiation, expansion and penetration to create gas flow channels is the main idea to increase the permeability of coal seams and improve the effect of gas extraction. Hydraulic slotting can redistribute the stress field in the coal seam, increase the number, length, opening degree and connectivity area of coal seam cracks, and significantly improve the permeability. The disturbance caused by high-pressure jet cutting and the damage and rupture of coal body are closely related. However, there are many influencing factors of jet disturbance and slot rheology, and the main controlling factors are difficult to determine, resulting in unclear rupture range of flat-cut coal body under the action of different influencing factors.

[0003] Therefore, it is urgent to develop a method for determining the rupture range of flat-cut coal body. SUMMARY

[0004] The purpose of the present application is to provide a method for determining the rupture range of flat-cut coal body to solve the problems in the prior art.

[0005] The technical solution adopted to achieve the purpose of the present application is as follows: a method for determining the rupture range of flat-cut coal body, comprising the following steps, wherein steps 1) and 2) are performed simultaneously or in no particular order:

[0006] 1) Construct a flat-cut coal body damage influencing factor set R.

[0007] 2) Extract the flat-cut disturbed coal body damage characterization parameters.

[0008] 3) Use a clustering-based feature selection method to determine the main controlling factors of slot damage under flat-cut disturbance.

[0009] 4) Obtain the basic physical and mechanical parameters of the coal seam in the field mine, and construct a similar simulation physical model.

[0010] 5) Carry out a high-pressure jet flat-cut coal body similar experiment, arrange a strain detector in the similar model, and obtain the coal body stress in real time. According to the change of jet pressure during the cutting process, a coal body stress distribution constitutive model in the jet disturbance stage is constructed.

[0011] 6) According to the change of slot spacing and slot width after cutting, determine the long-term evolution law of slot-containing coal body deformation, and construct a coal body stress distribution model in the slot rheology stage.

[0012] 7) According to the coal body parameters in the jet disturbance stage, including the elastic modulus, cohesion, and internal friction angle, a coal body damage constitutive model is constructed to obtain the coal body failure critical stress σ1 in the cutting process, and the damage behavior of the coal body under the water jet impact is described.

[0013] 8) According to the coal body parameters in the slot rheological stage, including the cumulative strain and rheological rate, a damage coal body rheological model is constructed to obtain the coal body failure critical stress σ2 after cutting, and the damage behavior of the coal body under the rheological effect is described.

[0014] 9) The coal body stress obtained in steps 7) and 8) is compared with the coal body failure critical stress according to the slot damage critical condition to determine whether the coal body has been damaged. If the coal body stress in the jet disturbance stage is greater than σ1, the coal body has been damaged in the cutting process. If the coal body stress in the slot rheological stage is greater than σ2, the coal body has been damaged after cutting.

[0015] Further, in step 1), through literature research and field data analysis of high-pressure jet cutting coal, a set of factors affecting the damage of flat-cut coal is constructed. The set of factors includes jet disturbance factors and slot rheological factors. The jet disturbance factors include impact pressure, impact time, and impact flow. The slot rheological factors include slot width, slot spacing, coal strength, and coal moisture content.

[0016] Further, the dynamics software is used to numerically simulate the high-pressure jet cutting coal, the jet disturbance factors and the slot rheological factors are changed, and the damage characterization parameters of the flat-cut disturbed coal are extracted based on the numerical simulation results. The characterization parameters include the damage characterization parameters in the jet disturbance stage and the damage characterization parameters in the slot rheological stage. The damage characterization parameters in the jet disturbance stage include peak stress and plastic energy ratio. The damage characterization parameters in the slot rheological stage include cumulative strain and rheological rate.

[0017] Further, after step 2), there is also a step of carrying out high-pressure jet cutting coal sample mechanical experiments, randomly selecting and changing some of the factors, and verifying the numerical simulation results according to the characteristic parameter changes.

[0018] Further, step 3) specifically includes the following sub-steps:

[0019] 3.1) Use clustering algorithm to cluster the factors in set R to obtain clustering result R i ={R1, R2, …, R k}. Wherein, the clustering condition is that the change of each set R i can cause the corresponding change of the coal body damage characterization parameters.

[0020] 3.2) Calculate the discrimination r of each set R i to other arbitrary set R i′ . i .

[0021] The calculation formula is shown in formula (1).

[0022]

[0023] In the formula, |r i | is the size of set R i , is the difference between set R1 and R2 in the characteristic parameter.

[0024] 3.3) Calculate the total discrimination average Mean i of each set R i according to all discriminations, and the average discrimination maximum Max i and the average discrimination minimum Min i for each characteristic parameter.

[0025] 3.4) Calculate the discrimination parameter f i . The calculation formula is shown in formula (2).

[0026]

[0027] 3.5) Arrange the set R i in descending order according to the discrimination parameter f i , and get Find the point or inflection point i0 of sharp change in the broken line graph of , which is the main damage controlling factor selected from the influencing factor set R.

[0028] Further, in step 5), on the basis of introducing strain rate and damage factor, the equivalent stress of the material is quantitatively characterized by formula (3):

[0029]

[0030] When the damage factor D of the coal body is 1, the coal body completely fails, and the equivalent stress is shown in formula (4):

[0031]

[0032] In the formula, σ I is the actual rupture strength of the coal body, H EL is the Hugoniot elastic limit. P * is the normalized hydrostatic pressure, P* = P a / P HEL , P a is actual pressure. P HEL is the pressure of coal body in Hugoniot elastic limit. is actual equivalent strain rate of coal body, is 10s-1 reference strain rate. K n is damage variable under the influence of nth master factor, n is strain under the influence of nth master factor, and epsilon 0 is strain in undamaged state. C is coal body constant. B and M are coal body residual strength constants.

[0033] Further, in step 6), a coal body stress distribution model in a slot rheological stage is constructed based on the improved Nishihara model. The coal body stress distribution model in the slot rheological stage is composed of a Hookean body, a Kelvin body and an ideal viscoplastic body in series. The one-dimensional rheological equation expression of the improved Nishihara model considering the damage of coal body around the slot is shown as formula (5):

[0034] When sigma < sigma s , the rheological equation is expressed as:

[0035]

[0036] When sigma f > sigma >= sigma s , the rheological equation expression is shown as formula (6):

[0037]

[0038] When sigma >= sigma f , the rheological equation expression is shown as formula (7):

[0039]

[0040] Wherein, H is the damage variable under the influence of master factors and shown as formula (8):

[0041]

[0042] In the formula, H n is the damage variable under the influence of nth master factor, and E n is the elastic modulus under the influence of nth master factor. E0 is the elastic modulus in undamaged state.

[0043] The technical effect of the present application is self-evident:

[0044] ​A. Adopting the method of combining investigation and analysis, numerical simulation and physical experiment, research is carried out from the jet disturbance stage and the slot flow deformation stage respectively, and the feature selection method based on clustering is introduced, so as to accurately determine the main control factors affecting the coal body fracture;

[0045] B. Through theoretical research, the coal body stress distribution constitutive model is optimized, and the accurate judgment of the flat-cut coal body fracture condition is realized;

[0046] C. Based on the functional relationship between the main control factors and the coal body stress, the fracture range of the flat-cut coal body in space and time scales under different main control factors is determined through numerical simulation;

[0047] D. The application is of great significance to maintain the stability of the slot and improve the pressure relief effect, avoids the blockage of the gas migration channel, and thus improves the gas extraction effect. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 It is a flat-cut coal body fracture range determination method flow chart;

[0049] Figure 2 It is an improved Nishihara model considering the damage of coal body around the slot. DETAILED DESCRIPTION

[0050] The application will be further described below in conjunction with the embodiments, but should not be understood as limiting the above-mentioned subject matter of the application only to the following embodiments. According to ordinary technical knowledge and conventional means in the art, various substitutions and changes can be made without departing from the technical idea of the application, which should be included in the protection scope of the application.

[0051] Example 1:

[0052] This embodiment aims at the problem that the critical condition of slot damage under flat-cut disturbance is difficult to determine. Referring to Figure 1 In order to determine the main control factors under jet disturbance and after cutting the slot of coal body, and then obtain the coal body fracture range under the action of different influence factors, this embodiment provides a flat-cut coal body fracture range determination method, which comprises the following steps, wherein steps 1) and 2) are carried out simultaneously or in no particular order:

[0053] 1) Construct the flat-cut coal body damage influence factor set R. Through literature research and field data analysis of high-pressure jet cutting coal body, the flat-cut coal body damage influence factor set is constructed. The influence factor set includes jet disturbance influence factors and slot flow deformation influence factors. The influence factors in the jet disturbance stage include impact pressure, impact time and impact flow. The influence factors in the slot flow deformation stage include slot width, slot spacing, coal body strength and coal body moisture content.

[0054] 2) Extracting the failure characterization parameters of the flat-cut disturbed coal body. Numerical simulation of the high-pressure jet cutting coal body is performed using dynamic software. The jet disturbance influencing factors and the slot rheological influencing factors are changed, and the failure characterization parameters of the flat-cut disturbed coal body are extracted based on the numerical simulation results. The characterization parameters include the failure characterization parameters in the jet disturbance stage and the failure characterization parameters in the slot rheological stage. The failure characterization parameters in the jet disturbance stage include the peak stress and the plastic energy ratio. The failure characterization parameters in the slot rheological stage include the cumulative strain and the rheological rate.

[0055] 3) Carrying out the high-pressure jet cutting coal sample mechanical experiment, randomly extracting and changing part of the influencing factors, and verifying the numerical simulation results according to the characteristic parameter changes.

[0056] 4) Using the clustering-based feature selection method to determine the main control factors of the slot failure under flat-cut disturbance. Step 4) specifically includes the following sub-steps:

[0057] 4.1) Using a clustering algorithm to cluster the factors in set R to obtain clustering results R i ={R1, R2, …, R k}. Wherein, the clustering condition is that the change of each set R i can cause the corresponding change of the coal body failure characterization parameters.

[0058] 4.2) Calculating the discrimination r i of each set R i′ to any other set R i .

[0059] The calculation formula is shown in formula (1).

[0060]

[0061] In the formula, |r i | is the size of set R i , is the difference between set R1 and R2 in the characteristic parameters.

[0062] 4.3) Calculating the total discrimination average Mean i of each set R i , and the maximum average discrimination Max i and the minimum average discrimination Min i for each characterization parameter according to all the discriminations.

[0063] 4.4) Calculating the discrimination parameter f i . The calculation formula is shown in formula (2).

[0064]

[0065] 4.5) on the set R i According to the degree of differentiation parameter f i In descending order, get In The sharp change point or inflection point i0 is found in the broken line graph, That is, the damage master factor selected from the impact factor set R.

[0066] 5) Obtain the basic physical and mechanical parameters of the coal seam in the field mine, and construct a similar simulation physical model.

[0067] 6) Carry out high-pressure jet flow flat cutting coal body similar experiment, arrange strain detector in similar model, get coal body stress in real time. According to the change of jet flow pressure in cutting seam process, construct coal body stress distribution constitutive model in jet flow disturbance stage. On the basis of introducing strain rate and damage factor, the equivalent stress of material is quantitatively characterized by formula (3):

[0068]

[0069] When the damage factor D of coal body is 1, the coal body completely fails, and the equivalent stress is shown in formula (4):

[0070]

[0071] In the formula, σ I is the actual fracture strength of coal body, H EL is the Hugoniot elastic limit. P * is the normalized hydrostatic pressure, P * = P a / P HEL , P a is the actual pressure. P HEL is the pressure when the coal body is in the Hugoniot elastic limit. is the actual equivalent strain rate of coal body, is the reference strain rate of 10 s-1. K n is the damage variable under the influence of the nth master factor, ε n is the strain under the influence of the nth master factor, and ε0 is the strain in the undamaged state. A, N and C are coal body constants. B and M are coal body residual strength constants.

[0072] 7) According to the change of seam slot spacing and seam slot width after cutting seam, determine the long-term evolution law of seam slot coal body deformation, and construct the seam slot rheological stage coal body stress distribution model. See Figure 2, a stress distribution model of coal mass in the slotting rheological stage is constructed based on the improved Nishihara model. The stress distribution model of coal mass in the slotting rheological stage is composed of a Hookean body, a Kelvin body and an ideal viscoplastic body in series. The model reflects the mechanical characteristics of the deceleration rheological stage, the stable rheological stage and the acceleration rheological stage of coal mass. E1 and E2 are the elastic modulus of the sample, η1, η2 and η3 are the viscosity coefficients, σs and σf are the constant load strength and the failure strength of the sample respectively, I is to describe the deformation process of the coal and rock material under loading, II is to describe the process of the coal and rock material entering the deceleration rheological stage, III is to describe the process of the coal and rock material entering the stable rheological stage, and IV is to describe the process of the coal and rock material entering the acceleration rheological stage. The one-dimensional rheological equation expression of the improved Nishihara model considering the damage of coal mass around the slot is shown as formula (5):

[0073] When σ < σ s , the rheological equation is expressed as:

[0074]

[0075] When σ f > σ ≥ σ s , the rheological equation is expressed as formula (6):

[0076]

[0077] When σ ≥ σ f , the rheological equation is expressed as formula (7):

[0078]

[0079] Wherein, H is the damage variable considering the influence of the main control factors and is shown as formula (8):

[0080]

[0081] In the formula, H n is the damage variable considering the influence of the nth main control factor, E n is the elastic modulus considering the influence of the nth main control factor. E0 is the elastic modulus in the undamaged state.

[0082] 8) According to the parameters of coal mass in the jet disturbance stage, including the elastic modulus, the cohesive force and the internal friction angle, a coal mass damage constitutive model is constructed to obtain the coal mass failure critical stress σ1 in the slotting process, and the damage behavior of coal mass under the impact of water jet is described.

[0083] 9) According to the parameters of coal mass in the slotting rheological stage, including the cumulative strain and the rheological rate, a damage coal mass rheological model is constructed to obtain the coal mass failure critical stress σ2 after slotting, and the damage behavior of coal mass under the rheological effect is described.

[0084] 10) The coal body stress obtained in steps 8) and 9) is compared with the coal body damage critical stress according to the slot damage critical condition, to determine whether the coal body is damaged. If the jet flow disturbance stage coal body stress is greater than σ1, the coal body is damaged during the slotting process. If the slot rheological stage coal body stress is greater than σ2, the coal body is damaged after slotting.

[0085] The embodiment considers the slot damage process under flat cutting disturbance from two aspects of the jet flow disturbance stage and the slot rheological stage, can more accurately determine the influencing factors, characterization parameters and critical damage stress, and has innovation in research ideas. The embodiment uses a feature selection method based on clustering to determine the main control factors of slot damage under flat cutting disturbance, and optimizes the coal body stress distribution constitutive model of the jet flow disturbance stage and the slot rheological stage based on the main control factors, which has innovation in research method.

[0086] Embodiment 2:

[0087] The embodiment provides a flat cutting coal body fracture range determination method, which comprises the following steps, wherein steps 1) and 2) are performed simultaneously or in no particular order:

[0088] 1) Construct a flat cutting coal body damage influencing factor set R.

[0089] 2) Extract the flat cutting disturbance coal body damage characterization parameters.

[0090] 3) Use a feature selection method based on clustering to determine the main control factors of slot damage under flat cutting disturbance.

[0091] 4) Obtain the basic physical and mechanical parameters of the coal seam in the field mine, and construct a similar simulation physical model.

[0092] 5) Carry out a high-pressure jet flat cutting coal body similar experiment, arrange a strain detector in the similar model, and obtain the coal body stress in real time. According to the change of jet flow pressure in the slotting process, a coal body stress distribution constitutive model in the jet flow disturbance stage is constructed.

[0093] 6) According to the change of slot interval and slot width after slotting, the long-term evolution law of the slot-containing coal body deformation is determined, and a coal body stress distribution model in the slot rheological stage is constructed.

[0094] 7) According to the coal body parameters in the jet flow disturbance stage, including the elastic modulus, the cohesion, and the internal friction angle, a coal body damage constitutive model is constructed, the coal body damage critical stress σ1 in the slotting process is obtained, and the damage behavior of the coal body under the water jet impact is described.

[0095] 8) According to the coal body parameters in the slot rheological stage, including the cumulative strain and the rheological rate, a rheological model of the damaged coal body is constructed, the coal body damage critical stress σ2 after slotting is obtained, and the damage behavior of the coal body under the rheological effect is described.

[0096] 9) The coal body stress obtained in steps 7) and 8) is compared with the coal body damage critical stress according to the slot damage critical condition, to determine whether the coal body is damaged. If the jet disturbance stage coal body stress is greater than σ1, the coal body is damaged during the slotting process. If the slot rheology stage coal body stress is greater than σ2, the coal body is damaged after slotting.

[0097] Example 3:

[0098] The main content of this example is the same as that of example 2, wherein in step 1), the set of factors affecting the damage of the flat-cut coal body is constructed through literature research and field data analysis of high-pressure jet cutting of coal bodies. The set of factors includes jet disturbance factors and slot rheology factors. The jet disturbance factors include impact pressure, impact time and impact flow. The slot rheology factors include slot width, slot spacing, coal body strength and coal body moisture content.

[0099] Example 4:

[0100] The main content of this example is the same as that of example 2 or 3, wherein the high-pressure jet cutting of coal bodies is numerically simulated using dynamic software, the jet disturbance factors and the slot rheology factors are changed, and the damage characterization parameters of the flat-cut disturbed coal body are extracted based on the numerical simulation results. The characterization parameters include damage characterization parameters in the jet disturbance stage and damage characterization parameters in the slot rheology stage. The damage characterization parameters in the jet disturbance stage include peak stress and plastic energy ratio. The damage characterization parameters in the slot rheology stage include cumulative strain and rheological rate.

[0101] Example 5:

[0102] The main content of this example is the same as that of any one of examples 2-4, wherein after step 2), there is also a step of carrying out a high-pressure jet cutting of coal sample mechanical experiment, randomly selecting and changing part of the factors, and verifying the numerical simulation results according to the characteristic parameter changes.

[0103] Example 6:

[0104] The main content of this example is the same as that of any one of examples 2-5, wherein step 3) specifically includes the following sub-steps:

[0105] 3.1) Use clustering algorithm to cluster the factors in set R, and obtain clustering result R i’ ={R1, R2, …, R k}. Wherein, the clustering condition is that the change of each set R i’ can cause the corresponding change of the coal body damage characterization parameters.

[0106] 3.2) Calculate each set R i’ to other arbitrary one set R i’ r i .

[0107] The formula is shown in equation (1).

[0108]

[0109] In the formula, |r i | is the size of set R i’ , is the difference between set R1 and R2 in the characteristic parameter.

[0110] 3.3) Calculate the total discrimination average Mean i’ of each set R i , and the average discrimination maximum Max i and the average discrimination minimum Min i for each characteristic parameter according to all the discrimination degrees.

[0111] 3.4) Calculate the discrimination parameter f i . The formula is shown in equation (2).

[0112]

[0113] 3.5) Sort the set R i’ in descending order according to the discrimination parameter f i , and get Find the point of sharp change or inflection i0 in the broken line graph, which is the main controlling factor selected from the impact factor set R.

[0114] Example 7:

[0115] The main content of this embodiment is the same as any one of examples 2-6, wherein in step 5), on the basis of introducing the strain rate and damage factor, the equivalent stress of the material is quantitatively characterized by equation (3):

[0116]

[0117] When the damage factor D of the coal body is 1, the coal body completely fails, and the equivalent stress is shown in equation (4):

[0118]

[0119] In the formula, σ I is the actual rupture strength of the coal body, H ELis the Hugoniot elastic limit. * is the normalized hydrostatic pressure, P * =P a / P HEL , P a is the actual pressure. HEL It is the pressure when the coal body is at the Hugoniot elastic limit. is the actual equivalent strain rate of coal mass, is the reference strain rate of 10s-1. K n is the damage variable under the influence of the nth main control factor, ε n is the strain under the influence of the nth main controlling factor, ε0 is the strain under the non-destructive state. A, N and C are coal constants. B and M are coal residual strength constants.

[0120] Example 8:

[0121] The main content of this embodiment is the same as any one of Embodiments 2 to 7, wherein, in step 6), a stress distribution model of the coal body in the slot rheology stage is constructed based on the improved Nishihara model. The stress distribution model of the coal body in the slot rheology stage is composed of a Hooke body, a Kelvin body, and an ideal viscoplastic body connected in series. The one-dimensional rheological equation of the improved Nishihara model considering the damage of the coal body around the slot is expressed as shown in formula (5):

[0122] When σ<σ s When , the rheological equation is expressed as:

[0123]

[0124] When σ f >σ≥σ s When , the rheological equation is expressed as shown in formula (6):

[0125]

[0126] When σ≥σ f When , the rheological equation is expressed as shown in formula (7):

[0127]

[0128] Among them, H is the damage variable under the influence of the main control factors, as shown in formula (8):

[0129]

[0130] Where H n To consider the damage variable under the influence of the nth main control factor, E n is the elastic modulus under the influence of the nth main controlling factor. E0 is the elastic modulus in the lossless state.

Claims

1. A method for determining the fracture range of a horizontally cut coal body, characterized in that: The following steps are involved: 1) Construct the set of factors affecting the fracture of flat-cut coal body R; 2) Obtain the basic physical and mechanical parameters of the coal seam in the on-site mine and build a similar simulation physical model; 3) Conduct similar experiments on high-pressure jet shearing of coal bodies. During the layout of similar simulation physical models, strain bricks are buried. The monitored strain data is used to invert the coal body stress, thereby obtaining the stress evolution law of the coal body at different locations in real time. 4) Based on the results of similar simulation experiments, the fracture characterization parameters under the factors affecting the fracture of the coal body during and after the cutting process are obtained; 5) Use simulation software to numerically simulate the long-term rheological process of high-pressure jet cutting and seaming of coal bodies. By changing the factors affecting the fracture of flat-cut coal bodies, the fracture characterization parameters of each influencing factor at different levels are obtained; 6) According to the degree of influence of different influencing factors on the fracture characterization parameters, the main controlling factors of the horizontal coal fracture are determined using the clustering-based feature selection method; 7) Based on response surface analysis, a central composite experimental design was conducted to investigate the main controlling factors of coal fracture. The experiment was numerically simulated using simulation software to obtain the stress distribution characteristics at different locations of the coal body during and after the cutting process under the influence of different main controlling factors. 8) Based on the changes in impact pressure, impact time, and impact angle during the cutting process, a stress distribution model of the coal body during the jet disturbance stage is constructed; 9) Based on the changes in the seam geometry, coal strength, and moisture content after seam cutting, the long-term evolution law of the coal deformation with seams is determined, and a stress distribution model of the coal during the seam rheological stage is constructed; 10) Based on the key parameters of the coal body during the jet disturbance stage, including elastic modulus, cohesion, and internal friction angle, a coal damage constitutive model is constructed to obtain the critical stress σ1 of coal body fracture during the cutting process, describing the fracture behavior of the coal body under the impact of the water jet; 11) Based on the key parameters of the coal body in the slot rheological stage, including the accumulated strain and rheological rate, a rheological model of damaged coal body is constructed to obtain the critical stress σ2 of coal body fracture after cutting, and to describe the fracture behavior of coal body under rheological effect; 12) Comparing the coal body stress obtained in step 7) with the critical stress of coal body fracture to determine whether the coal body has fractured; wherein, if the coal body stress during the jet disturbance stage is greater than σ1, the coal body has fractured during the slitting process; if the coal body stress during the slot rheology stage is greater than σ2, the coal body has fractured after slitting; 13) According to the above fracture conditions and combined with the stress distribution characteristics of the coal body, the fracture range of the flat-cut coal body is determined.

2. The method for determining the fracture range of a flat-cut coal body according to claim 1, characterized in that: In step 1), a set of influencing factors of flat-cut coal fracture is constructed through literature research and field data analysis on high-pressure jet cutting of coal bodies; the set of influencing factors includes influencing factors of the jet disturbance stage and influencing factors of the slot rheology stage; the influencing factors of the jet disturbance stage include impact pressure, impact time and impact angle; the influencing factors of the slot rheology stage include slot width, slot spacing, coal body strength and coal body moisture content.

3. The method for determining the fracture range of a flat-cut coal body according to claim 1, characterized in that: In step 4), a level of factors affecting the fracture of the flat-cut coal body is selected, and the coal body fracture characterization parameters at this level are obtained by monitoring the coal body stress in similar simulation experiments. At the same time, a comparison is provided for the results of the numerical simulation to verify the reliability of the numerical simulation; the characterization parameters include the fracture characterization parameters of the jet disturbance stage and the fracture characterization parameters of the slot rheology stage; the fracture characterization parameters of the jet disturbance stage include peak stress and plastic energy ratio; the fracture characterization parameters of the slot rheology stage include cumulative strain and rheological rate.

4. The method for determining the fracture range of a flat-cut coal body according to claim 1, characterized in that: In step 5), simulation software is used to numerically simulate the long-term rheological processes of high-pressure jet cutting of coal and slotted coal, respectively, by changing the levels of the influencing factors in the jet disturbance stage and the influencing factors in the slot rheological stage, and obtaining the fracture characterization parameters of each influencing factor at different levels.

5. The method for determining the fracture range of a flat-cut coal body according to claim 1, characterized in that: Step 6) specifically includes the following sub-steps: 6.1) Use clustering algorithm to cluster the factors in set R and obtain clustering result R i ={R1, R2, ..., R k }; where the clustering condition is each set R i Any change in the coal fracture characterization parameters can cause corresponding changes; 6.2) Calculate each set R i The discrimination r to any other set i ; The calculation formula is shown in formula (1); In the formula, |r i | is the set R i The size of is the difference in characteristic parameters between sets R1 and R2; 6.3) Calculate each set R based on all discriminations i The average value of the total discrimination i , and the maximum value of the average discrimination for each representation parameter Max i and the minimum value of average discrimination Min i ; 6.4) Calculate the discrimination parameter f i ; The calculation formula is shown in formula (2); 6.5) For the set R i According to the discrimination parameter f i Arrange in descending order, and get exist Find the point of sharp change or inflection point i0 in the line graph of It is the main controlling factor of rupture selected from the influencing factor set R.

6. The method for determining the fracture range of a flat-cut coal body according to claim 1, characterized in that: Step 7) specifically includes the following sub-steps: 7.1) Based on the response surface analysis, a central composite experimental design was conducted on the main controlling factors of the flat-cut coal fracture, and numerical simulation was carried out using simulation software. When the coal coordinates were (0, 0, 1) and the experimental time was 1 s, a horizontal main controlling factor was selected to construct the main controlling factor x and coal stress σ. C The functional relationship of (x, y, z, t): σ C (0,0,1,1)=f(x1,x2,x3……x n ) (3) Where x n is the nth main controlling factor under the selected level; 7.2) Based on the coordinates (0,0,1) and the main controlling factors at this level, change the experimental time to obtain the function set with experimental time t: σ C (0,0,1,t)=f(x1,x2,x3……x n ) (4) 7.3) Change different coordinates of the coal body and different main control factors, repeat steps 7.1) and 7.2) to obtain the coal body stress σ under the influence of different main control factors during the experiment C ; σ C (x,y,z,t)=f(X1,X2,X3……X n ) (5) Where x, y, z are the three-dimensional coordinates of the coal body; t is the experimental time; X n is the nth main controlling factor at any level.

7. The method for determining the fracture range of a flat-cut coal body according to claim 1, characterized in that: In step 8), based on the introduction of strain rate and damage factor, the equivalent stress of the material is quantitatively characterized by formula (6): When the damage factor of the coal body is D=1, the coal body is completely failed, and the equivalent stress is shown in formula (7): Where, σ I is the actual fracture strength of the coal body, H EL is the Hugoniot elastic limit; P * is the normalized hydrostatic pressure, P * =P a / P HEL , P a is the actual pressure; P HEL is the pressure when the coal body is at the Hugoniot elastic limit; is the actual equivalent strain rate of coal mass, 10s -1 Reference strain rate; K n is the damage variable under the influence of the nth main control factor, ε n is the strain under the influence of the nth main controlling factor, ε0 is the strain under the non-destructive state; C is the coal body constant; B and M are the coal body residual strength constants; This is the critical stress σ1 of coal body fracture during the jet disturbance stage.

8. The method for determining the fracture range of a flat-cut coal body according to claim 1, characterized in that: In step 9), a stress distribution model of the coal body in the slot rheological stage is constructed based on the improved Nishihara model. The stress distribution model of the coal body in the slot rheological stage is composed of a Hooke body, a Kelvin body, an ideal viscoplastic body, and a viscoplastic model that can reflect the accelerated creep stage. The rheological equation of the improved Nishihara model considering the damage of the coal body around the slot is shown in formula (8): When σ<σ s When , the rheological equation is expressed as: When σ f >σ≥σ s When , the rheological equation is expressed as shown in formula (9): When σ≥σ f When , the rheological equation is expressed as shown in formula (10): Among them, H is the damage variable under the influence of the main control factors, as shown in formula (11): Where H n To consider the damage variable under the influence of the nth main control factor, E n is the elastic modulus under the influence of the nth main controlling factor; E0 is the elastic modulus under the lossless state; σ f This is the critical stress σ2 of coal body rupture in the slot rheology stage.

9. The method for determining the fracture range of a flat-cut coal body according to claim 1, characterized in that: In step 12), whether the coal body is broken is determined by the following formula: Where t0 is the time when the slit is completed, the period before t0 is the jet disturbance stage, and the period after t0 is the slot rheology stage.

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