Method for determining fracture range of horizontally cut coal body

Abstract

The invention provides a method for determining the fracture range of a horizontally cut coal body. According to the method, aiming at the problem that the fracture range of the flat cut coal body is difficult to determine, a method of combining research analysis, numerical simulation and physical experiments is adopted, researches are respectively carried out from a jet disturbance stage and a slot rheological stage, and a clustering-based feature selection method is introduced, so that main control factors of coal body fracture under jet disturbance and after seam cutting are accurately determined, and the fracture range of the flat cut coal body is determined. Further, the coal stress distribution constitutive model is improved, and the fracture range of the flat cut coal body is accurately judged. The method has important significance on maintaining the stability of the seam and the groove and improving the pressure relief effect, and the gas migration channel is prevented from being blocked, so that the gas extraction effect is improved.

Description

Technical Field

[0001] The invention relates to the technical field of coal mining, and in particular to a method for determining a fracture range of a flat-cut coal body. Background Art

[0002] As my country's coal mining gradually extends to deeper areas, geological conditions tend to become more complex. The characteristics of high geostress, high geotemperature and high gas pressure in deep coal seams lead to the common characteristics of micropores, low permeability and strong adsorption, which makes gas extraction extremely difficult, seriously restricting mine disaster prevention and gas resource utilization. Through external disturbance, artificially inducing the initiation, expansion and penetration of coal body cracks and creating gas flow channels are the main ideas to increase the permeability of coal seams and improve the effect of gas extraction. Hydraulic cutting can redistribute the stress field in the coal seam, increase the number, length, opening and connection area of ​​coal seam cracks, and significantly improve the permeability. The disturbance caused by high-pressure jet cutting is closely related to coal body damage and fracture. However, there are many factors affecting jet disturbance and seam rheology, among which the main controlling factors are difficult to determine, resulting in the unclear range of coal body fracture under different influencing factors.

[0003] Therefore, it is urgent to develop a method to determine the fracture range of flat-cut coal. Summary of the invention

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

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

[0006] 1) Construct a set of influencing factors R of flat-cut coal body destruction.

[0007] 2) Extract the damage characterization parameters of the horizontal shear disturbance coal body.

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

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

[0010] 5) Carry out similar experiments on high-pressure jet cutting of coal, arrange strain detectors in similar models, and obtain coal stress in real time. According to the change of jet pressure during the cutting process, construct a constitutive model of coal stress distribution in the jet disturbance stage.

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

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

[0013] 8) According to the coal body parameters 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 failure after slot cutting, and to describe the destructive behavior of coal body under rheological effect.

[0014] 9) The coal body stress obtained in step 7) and step 8) is compared with the critical stress of coal body destruction according to the critical conditions of seam groove destruction to determine whether the coal body is destroyed. If the coal body stress in the jet disturbance stage is greater than σ1, the coal body is destroyed during the seam cutting process. If the coal body stress in the seam groove rheology stage is greater than σ2, the coal body is destroyed after seam cutting.

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

[0016] Furthermore, dynamic software is used to perform numerical simulation on high-pressure jet cutting of coal body, and the influencing factors of jet disturbance and slot rheology are changed. The damage characterization parameters of the flat-cut disturbed coal body are extracted based on the changes in numerical simulation results. The characterization parameters include the damage characterization parameters of the jet disturbance stage and the damage characterization parameters of the slot rheology stage. The damage characterization parameters of the jet disturbance stage include peak stress and plastic performance ratio. The damage characterization parameters of the slot rheology stage include cumulative strain and rheological rate.

[0017] Furthermore, after step 2), there is also a step of conducting a mechanical experiment of high-pressure jet cutting of coal samples, randomly selecting and changing some influencing factors, and verifying the numerical simulation results according to the changes in characteristic parameters.

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

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

[0020] 3.2) Calculate each set R i To any other set R i′ The discrimination r i .

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

[0022]

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

[0024] 3.3) Calculate each set R based on all discriminations i The average value of the total discrimination i , and the average maximum value of discrimination Max for each representation parameter i and the minimum value of average discrimination Min i .

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

[0026]

[0027] 3.5) 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 the destruction selected from the influencing factor set R.

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

[0029]

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

[0031]

[0032] In the formula, σ I is the actual fracture strength of the coal body, H EL is the Hugoniot elastic limit. * To normalize the 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, C is the coal body constant, B and M are the coal body residual strength constants.

[0033] Further, 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 in series. The one-dimensional rheological equation expression of the improved Nishihara model considering the damage of the coal body around the slot is shown in formula (5):

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

[0035]

[0036] When σ f >σ≥σ s When , the rheological equation is expressed as shown in formula (6):

[0037]

[0038] When σ≥σ f When , the rheological equation is expressed as shown in formula (7):

[0039]

[0040] Among them, H is the damage variable under the influence of the main control factors, as shown in formula (8):

[0041]

[0042] In the formula, 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.

[0043] The technical effects of the present invention are unquestionable:

[0044] A. Using a combination of research and analysis, numerical simulation, and physical experiments, we conducted research from the jet disturbance stage and the slot rheology stage, and introduced a clustering-based feature selection method to accurately determine the main controlling factors affecting coal fracture;

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

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

[0047] D. The invention is of great significance to maintaining the stability of the seam and improving the pressure relief effect, avoiding the blockage of the gas migration channel, thereby improving the gas extraction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 A flow chart of a method for determining the fracture range of a flat-cut coal body;

[0049] Figure 2 Schematic diagram of the improved Nishihara model considering the damage of coal around the seam. DETAILED DESCRIPTION

[0050] The present invention is further described below in conjunction with the embodiments, but it should not be understood that the above subject matter of the present invention is limited to the following embodiments. Without departing from the above technical ideas of the present invention, various substitutions and changes are made according to the common technical knowledge and customary means in the art, which should all be included in the protection scope of the present invention.

[0051] Embodiment 1:

[0052] This embodiment aims to solve the problem that it is difficult to determine the critical condition of slot failure under flat shear disturbance. Figure 1 In order to determine the main controlling factors under jet disturbance and after coal body cutting, and then obtain the coal body fracture range under different influencing factors, this embodiment provides a method for determining the fracture range of flat-cut coal body, including the following steps, wherein step 1) and step 2) are performed simultaneously or in no particular order:

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

[0054] 2) Extract the damage characterization parameters of the flat-cut disturbed coal body. Use dynamic software to perform numerical simulation on high-pressure jet cutting of coal body, change the influencing factors of jet disturbance and the influencing factors of slot rheology, and extract the damage characterization parameters of the flat-cut disturbed coal body based on the changes in numerical simulation results. The characterization parameters include the damage characterization parameters of the jet disturbance stage and the damage characterization parameters of the slot rheology stage. The damage characterization parameters of the jet disturbance stage include peak stress and plastic performance ratio. The damage characterization parameters of the slot rheology stage include cumulative strain and rheological rate.

[0055] 3) Carry out mechanical experiments on high-pressure jet cutting of coal samples, randomly select and change some influencing factors, and verify the steps of numerical simulation results according to the changes in characteristic parameters.

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

[0057] 4.1) Use the clustering algorithm to cluster the factors in the set R and obtain the clustering result R i = {R1, R2, ..., R k}. Among them, the clustering condition is each set R i Any change in the coal body damage characterization parameters can cause corresponding changes.

[0058] 4.2) Calculate each set R i To any other set R i′ The discrimination r i .

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

[0060]

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

[0062] 4.3) Calculate each set R based on all discriminations i The average value of the total discrimination i , and the average maximum value of discrimination Max for each representation parameter i and the minimum value of average discrimination Min i .

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

[0064]

[0065] 4.5) 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 the destruction selected from the influencing factor set R.

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

[0067] 6) Carry out similar experiments on high-pressure jet cutting of coal, arrange strain detectors in similar models, and obtain coal stress in real time. According to the change of jet pressure during the cutting process, a constitutive model of coal stress distribution in the jet disturbance stage is constructed. Based on the introduction of strain rate and damage factor, the equivalent stress of the material is quantified by formula (3):

[0068]

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

[0070]

[0071] In the formula, σ I is the actual fracture strength of the coal body, H EL is the Hugoniot elastic limit. * To normalize the 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 body constants. B and M are coal body residual strength constants.

[0072] 7) According to the changes in the slot spacing and slot width after slot cutting, the long-term evolution law of the deformation of the coal body with slots is determined, and the stress distribution model of the coal body in the slot rheological stage is constructed. Figure 2, a stress distribution model of coal in the slot rheological stage is constructed based on the improved Nishihara model. The stress distribution model of coal in the slot rheological stage is composed of a Hooke body, a Kelvin body and an ideal viscoplastic body in series. The model reflects the mechanical characteristics of the coal in the deceleration rheological stage, the stable rheological stage and the acceleration rheological stage. E1 and E2 are the elastic moduli of the sample, η1, η2, η3 are the viscosity coefficients, σs and σf are the constant load strength and the failure strength of the sample, Ⅰ describes the deformation process of the coal rock material when loaded, Ⅱ describes the process of the coal rock material entering the deceleration rheological stage, Ⅲ describes the process of the coal rock material entering the stable rheological stage, and Ⅳ describes the process of the coal rock material entering the accelerated rheological stage. The one-dimensional rheological equation expression of the improved Nishihara model considering the damage of the coal around the slot is shown in formula (5):

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

[0074]

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

[0076]

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

[0078]

[0079] Among them, H is the damage variable under the influence of the main control factors, as shown in formula (8):

[0080]

[0081] In the formula, 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.

[0082] 8) According to the coal body parameters in the jet disturbance stage, including elastic modulus, cohesion, and internal friction angle, a coal body damage constitutive model is constructed to obtain the critical stress σ1 of coal body failure during the cutting process, which describes the destructive behavior of the coal body under the impact of water jet.

[0083] 9) According to the coal body parameters 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 after cutting, and to describe the destructive behavior of coal body under the rheological effect.

[0084] 10) The coal body stress obtained in step 8) and step 9) is compared with the critical stress of coal body destruction according to the critical conditions of seam failure to determine whether the coal body is damaged. If the stress of the coal body in the jet disturbance stage is greater than σ1, the coal body is damaged during the seam cutting process. If the stress of the coal body in the seam rheology stage is greater than σ2, the coal body is damaged after seam cutting.

[0085] This embodiment considers the failure process of the slot under the flat shear disturbance from two aspects, namely the jet disturbance stage and the slot rheology stage, and can more accurately determine the influencing factors, characterization parameters and critical failure stress, which is innovative in research ideas. This embodiment uses a clustering-based feature selection method to determine the main controlling factors of slot failure under the flat shear disturbance, and optimizes the constitutive model of coal body stress distribution in the jet disturbance stage and the slot rheology stage based on the main controlling factors, which is innovative in research methods.

[0086] Embodiment 2:

[0087] This embodiment provides a method for determining the fracture range of a flat-cut coal body, comprising the following steps, wherein step 1) and step 2) are performed simultaneously or in no particular order:

[0088] 1) Construct a set of influencing factors R of flat-cut coal body destruction.

[0089] 2) Extract the damage characterization parameters of the horizontal shear disturbance coal body.

[0090] 3) Use clustering-based feature selection method to determine the main controlling factors of slot damage under flat shear disturbance.

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

[0092] 5) Carry out similar experiments on high-pressure jet cutting of coal, arrange strain detectors in similar models, and obtain coal stress in real time. According to the change of jet pressure during the cutting process, construct a constitutive model of coal stress distribution in the jet disturbance stage.

[0093] 6) According to the changes in the slot spacing and slot width after slot cutting, the long-term evolution law of the deformation of the coal body containing slots is determined, and a stress distribution model of the coal body in the slot rheology stage is constructed.

[0094] 7) According to the coal body parameters in the jet disturbance stage, including elastic modulus, cohesion, and internal friction angle, a coal body damage constitutive model is constructed to obtain the critical stress σ1 of coal body failure during the cutting process, which describes the destructive behavior of the coal body under the impact of water jet.

[0095] 8) According to the coal body parameters 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 failure after slot cutting, and to describe the destructive behavior of coal body under rheological effect.

[0096] 9) The coal body stress obtained in step 7) and step 8) is compared with the critical stress of coal body destruction according to the critical conditions of seam groove destruction to determine whether the coal body is destroyed. If the coal body stress in the jet disturbance stage is greater than σ1, the coal body is destroyed during the seam cutting process. If the coal body stress in the seam groove rheology stage is greater than σ2, the coal body is destroyed after seam cutting.

[0097] Embodiment 3:

[0098] The main contents of this embodiment are the same as those of embodiment 2, wherein, in step 1), a set of influencing factors of flat-cut coal body destruction is constructed through literature research and field data analysis on high-pressure jet cutting of coal bodies. The set of influencing factors includes jet disturbance influencing factors and slot rheological influencing factors. The influencing factors of the jet disturbance stage include impact pressure, impact time and impact flow rate. The influencing factors of the slot rheological stage include slot width, slot spacing, coal body strength and coal body moisture content.

[0099] Embodiment 4:

[0100] The main content of this embodiment is the same as that of Embodiment 2 or 3, wherein a dynamic software is used to perform numerical simulation on high-pressure jet cutting of coal body, the jet disturbance influencing factors and the slot rheology influencing factors are changed, and the damage characterization parameters of the flat-cut disturbed coal body are extracted based on the changes in the numerical simulation results. The characterization parameters include the damage characterization parameters of the jet disturbance stage and the damage characterization parameters of the slot rheology stage. The damage characterization parameters of the jet disturbance stage include peak stress and plastic performance ratio. The damage characterization parameters of the slot rheology stage include cumulative strain and rheological rate.

[0101] Embodiment 5:

[0102] The main contents of this embodiment are the same as any one of embodiments 2 to 4, wherein after step 2), there is also a step of conducting a mechanical experiment of high-pressure jet cutting of coal samples, randomly extracting and changing some influencing factors, and verifying the numerical simulation results according to the changes in characteristic parameters.

[0103] Embodiment 6:

[0104] The main contents of this embodiment are the same as any one of Embodiments 2 to 5, wherein step 3) specifically includes the following sub-steps:

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

[0106] 3.2) Calculate each set R i’ To any other set R i’ The discrimination r i .

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

[0108]

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

[0110] 3.3) Calculate each set R based on all discriminations i’ The average value of the total discrimination i , and the average maximum value of discrimination Max for each representation parameter i and the minimum value of average discrimination Min i .

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

[0112]

[0113] 3.5) 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 the destruction selected from the influencing factor set R.

[0114] Embodiment 7:

[0115] The main contents of this embodiment are the same as any one of Embodiments 2 to 6, wherein in step 5), based on the introduction of strain rate and damage factor, the equivalent stress of the material is quantitatively characterized by formula (3):

[0116]

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

[0118]

[0119] In the formula, σ I is the actual fracture strength of the coal body, H ELis the Hugoniot elastic limit. * To normalize the 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 body constants. B and M are coal body residual strength constants.

[0120] Embodiment 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 in series. The one-dimensional rheological equation expression of the improved Nishihara model considering the damage of the coal body around the slot is 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] In the formula, 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 flat-cut coal body, characterized in that: The following steps are involved: 1) Construct the influencing factor set R of flat-cut coal body fracture; 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) Carry out similar experiments on high-pressure jet cutting of coal bodies, bury strain bricks during the layout of similar models, use the monitored strain data to invert the stress of the coal body, and then obtain the stress evolution law of the coal body at different positions in real time; 4) Based on the results of similar simulation experiments, the fracture characterization parameters under the factors affecting the fracture of the flat-cut 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 of coal and slit coal, and obtain the fracture characterization parameters of each influencing factor at different levels by changing the factors affecting the fracture of flat-cut coal; 6) According to the influence of different influencing factors on the fracture characterization parameters, the main controlling factors of flat-cut coal fracture are determined using the clustering-based feature selection method; 7) Based on response surface analysis, a central composite experimental design was conducted on the main controlling factors of flat-cut coal body fracture, and the experiment was numerically simulated using simulation software to obtain the stress distribution characteristics at different positions of the flat-cut coal body during and after the cutting process under the influence of different main controlling factors; 8) According to the changes of impact pressure, impact time and impact angle during the cutting process, a stress distribution model of the coal body in the jet disturbance stage is constructed; 9) According to the changes in the geometric parameters of the seam groove, the strength of the coal body and the moisture content after the seam cutting, the long-term evolution law of the deformation of the coal body with seams is determined, and the stress distribution model of the coal body in the seam groove rheology stage is constructed; 10) According to the key parameters of the coal body in the jet disturbance stage, including elastic modulus, cohesion, and internal friction angle, a coal body damage constitutive model is constructed to obtain the critical stress σ1 of coal body rupture during the cutting process, and to describe the rupture behavior of the coal body under the impact of water jets; 11) According to 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 rupture after cutting, and to describe the rupture behavior of coal body under rheological effect; 12) Compare the coal body stress obtained in step 7) with the critical stress of coal body rupture to determine whether the coal body has ruptured; if the coal body stress in the jet disturbance stage is greater than σ1, the coal body has ruptured during the slitting process; if the coal body stress in the slot rheology stage is greater than σ2, the coal body has ruptured after slitting. 13) According to the above-mentioned 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. A 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; 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 strength and coal 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 horizontal factor affecting the fracture of the flat-cut coal body is selected, and the fracture characterization parameters of the coal body at this level are obtained by monitoring the stress of the coal body in similar simulation experiments, and 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 the peak stress and the proportion of plasticity; the fracture characterization parameters of the slot rheology stage include the accumulated strain and the rheological rate.

4. A 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 process of high-pressure jet cutting of coal and slit coal, respectively, by changing the different levels of 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 the clustering algorithm to cluster the factors in the set R and obtain the clustering result R i = {R1, R2, ..., R k }; where the clustering condition is each set R i Any change in the coal body fracture characterization parameters can cause corresponding changes; 6.2) Calculate each set R i To any other set R i′ The discrimination r 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 average maximum value of discrimination Max for each representation parameter 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 (i=1,2,…,m); Find the point of sharp change or inflection point i0 in the line graph of It is the main controlling factor of the rupture selected from the influencing factor set R.

6. A 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 flat-cut coal fracture, and numerical simulation was carried out using simulation software. Taking the coal coordinates as (0,0,1) and the experimental time as 1s as an example, by selecting a level of main controlling factors, the main controlling factor x and coal stress σ were constructed. C The functional relationship of (x, y, z, t) is: σ C (0,0,1,1)=f(x1,x2,x3……x n ) (3) In the formula, x n is the nth main controlling factor under the selected level. 7.2) Based on the coordinates (0,0,1) and the main control factors at this level, change the experimental time, and 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 and different main control factors of the coal body, repeat steps 7.1) and 7.2), and 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) In the formula, 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 quantified by formula (6): When the damage factor of the coal body is D=1, the coal body fails completely, and the equivalent stress is shown in formula (7): In the formula, 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 lossless state; C is the coal body constant; B and M are the coal body residual strength constants. That is the critical stress σ1 of coal body rupture in 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 in series; the rheological equation expression 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): In the formula, 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. σ f This is the critical stress σ2 for coal rupture in the slot rheology stage.

9. A 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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