A method for determining the critical index value for monitoring coal body stress and warning rock burst

Abstract

The present invention provides a method for determining the critical index value for monitoring coal body stress to pre-warn rock bursts, which relates to the technical field of monitoring coal body stress to pre-warn rock bursts. First, determine the critical ground stress at which roadway rock bursts occur; and convert the critical ground stress at which roadway rock bursts occur into the critical mining peak stress at which roadway rock bursts occur; then clarify the characteristic curve representing the mutual feedback balance of the loaded deformation between the stress gauge borehole and the stress gauge; finally, take the critical mining peak stress as the "most dangerous stress" state around the borehole where the stress gauge is installed, and by plotting the characteristic curve representing the mutual feedback balance of the loaded deformation between the borehole where the stress gauge is located and the stress gauge under the action of the critical mining peak stress, further determine the critical warning index value for the stress gauge to pre-warn the risk of roadway rock bursts. This method fully considers the degree of coupling correlation between the warning initial value and factors such as the coal body burst proneness, the stiffness of the stress gauge, and the borehole size.

Description

Technical Field

[0001] The present invention relates to the technical field of monitoring coal body stress for early warning of rock bursts, and particularly relates to a method for determining the critical index value for monitoring coal body stress and early warning of rock bursts. Background Art

[0002] Coal mine rock bursts are phenomena in which coal and rock masses suddenly become unstable and release impact energy under high stress, and they are recognized as world-class problems in the international mining and rock mechanics fields. As coal mining in China continues to develop deeper, the frequency and intensity of rock bursts are increasing. More than 95% of the rock bursts in China occur in roadways. Accurately monitoring and early warning of impact hazards (the possibility of rock bursts) is an important basis for the scientific prevention and control of rock bursts. The essential driving cause of rock bursts is the loading of high stress on the coal body. Therefore, directly monitoring the stress of the coal body using a coal body borehole stress sensor (stress gauge) to characterize the stress magnitude of the coal body is a commonly used monitoring and early warning technology for predicting rock bursts.

[0003] Generally speaking, the current methods for determining the critical index value for early warning of impact hazards based on coal body stress monitoring are insufficient, mainly reflected in the following aspects: (1) There is a lack of a quantitative characterization equation for the mutual feedback stress between the roadway surrounding rock borehole and the hydraulic pressure stress gauge, and it is impossible to establish a mapping relationship between the hydraulic pressure reading of the borehole stress gauge and the critical stress for the occurrence of rock bursts; (2) The existing determination methods all use laboratory tests, numerical simulations, and engineering experience for determination, lacking consideration of the cross-scale effect between small specimens and engineering structures, and the coupling correlation degree between the early warning initial value and factors such as the impact tendency of the coal body, the stiffness of the stress gauge, and the borehole size cannot be fully considered when determining the critical index value. (3) Whether it is soft coal or hard coal in engineering, the installation depth of the stress gauge is 8m, 12m, or 14m. This approach is mechanical and one-sided, unable to accurately reflect the stress change law of the surrounding rock in the elastic zone, and the installation depth of the stress gauge in the coal body needs to be determined. Therefore, the technical factors considered in the existing methods for determining the critical index value for monitoring coal body stress and early warning of rock bursts are not comprehensive, resulting in no effective method for determining the critical index value for monitoring coal body stress and early warning of rock bursts, and leading to low accuracy of rock burst monitoring and early warning. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for determining the critical index value for monitoring coal body stress and early warning of rock bursts in view of the above-mentioned deficiencies of the prior art. By analyzing the mutual feedback balance relationship between the roadway borehole surrounding rock and the stress gauge, a quantitative mapping function between the critical stress of the roadway rock burst and the monitoring reading of the stress gauge is established, and then a method for determining the critical index value for early warning of impact hazards that can comprehensively consider factors such as the impact physical properties of the coal body, the stiffness of the stress gauge, and the borehole size is given, making the monitoring and early warning of impact hazards more targeted and the early warning results more reliable.

[0005] To solve the above technical problems, the technical solution adopted by the present invention is: a method for determining the critical index value for monitoring coal body stress and warning rock burst,

[0006] Determine the critical ground stress at which rock burst occurs in the roadway;

[0007] Considering the effect of the redistribution of mining-induced stress caused by roadway excavation, convert the critical ground stress at which rock burst occurs in the roadway into the critical mining peak stress at which rock burst occurs in the roadway;

[0008] Clarify the characteristic curve of the mutual feedback balance of the loaded deformation between the stress gauge borehole and the stress gauge;

[0009] Take the critical mining peak stress at which rock burst occurs as the "most dangerous stress" state around the borehole where the stress gauge is installed. By plotting the characteristic curve of the mutual feedback balance of the loaded deformation between the borehole where the stress gauge is located and the stress gauge under the action of the critical mining peak stress, further determine the warning critical index value for the stress gauge to warn of the danger of rock burst in the roadway.

[0010] Specifically, it includes the following steps:

[0011] Step 1: Obtain the rock mechanics parameters of the coal body in the surrounding rock of the roadway to be monitored and warned;

[0012] Step 2: Calculate the critical ground stress P at which rock burst occurs in the roadway to be monitored and warned cr ;

[0013] Step 2.1: Obtain the support stress p of the roadway to be warned s ;

[0014] Step 2.2: Calculate the critical fracture zone radius ρ fcr and the critical softening zone radius ρ cr of the rock burst occurring in the roadway to be monitored and warned, which are shown in the following formulas respectively:

[0015]

[0016]

[0017] Calculate the critical ground stress P cr at which rock burst occurs in the roadway to be monitored and warned

[0018]

[0019] where ρ0 is the radius of the roadway after equivalent the roadway to be monitored as a homogeneous, continuous and isotropic circular roadway; m is an intermediate variable, is the internal friction angle of the coal and rock medium in the plastic softening zone, p fcrThe acting stress of the surrounding rock fragmentation zone on the plastic softening zone during the roadway impact initiation is as shown in the following formula:

[0020]

[0021] Among them, is the internal friction angle of the coal and rock medium in the fragmentation zone,

[0022] Step 3: Adopt the method of laboratory testing to determine the correction function curve of the critical stress value for the occurrence of roadway rockburst, draw the function graph, and determine the unequal pressure correction coefficient η mod-lateral of the critical in-situ stress for the occurrence of roadway rockburst and the cross-section form correction coefficient η mod-sec ;

[0023] Step 3.1: Fabricate roadway specimens;

[0024] Take raw coal specimens according to the rib of the roadway to be monitored and warned in the coal mine, and process them into standard specimens; drill through holes at the center position of the specimens as simulated roadways;

[0025] Step 3.2: Determine the unequal pressure correction coefficient η mod-lateral of the critical in-situ stress for the occurrence of roadway rockburst and the cross-section form correction coefficient η mod-sec according to the cross-section shape of the roadway to be monitored and warned;

[0026] Case 1: If the cross-section of the roadway to be monitored and warned is circular:

[0027] Step 1: Sample and prepare n specimens on-site. Use a biaxial loading testing machine to conduct biaxial equal-pressure loading on 3 specimens with circular through holes. The loading paths are the same for the lateral and vertical pressure rates until the specimens undergo rockburst failure. Record the critical stress index values P ex-cr1 、P ex-cr2 、P ex-cr3 obtained by the testing machine during the loading. Take the average of the three as the critical stress index value P ex-cr =P ex-cr1 +P ex-cr2 +P ex-cr3 under equal-pressure conditions for the circular simulated roadway during the occurrence of rockburst; Set the horizontal lateral pressure loading loads P horizontal of the n - 3 specimens to be 95%P ex-cr 、90%P ex-cr 、85%P ex-cr 、80%P ex-cr 、75%P ex-cr 、70%P ex-cr 、65%P ex-cr, 60% P ex-cr , 55% P ex-cr , 50% P ex-cr , 45% P ex-cr , 40% P ex-cr , 35% P ex-cr , 30% P ex-cr , 25% P ex-cr , 20% P ex-cr , load the vertical stress until the simulated roadway undergoes rock burst, and record the critical stress values P of the roadway rock burst occurrence under different lateral loading loads respectively ex-cr-95％ , P ex-cr-90％ , P ex-cr-85％ , P ex-cr-80％ , P ex-cr-75％ , P ex-cr-70％ , P ex-cr-65％ , P ex-cr-60％ , P ex-cr-55％ , P ex-cr-50％ , P ex-cr-45％ , P ex-cr-40％ , P ex-cr-35％ , P ex-cr-30％ , P ex-cr-25％ , P ex-cr-20％ , plot the data of each group on a plan, draw a fitted correction curve, and form a determination diagram of the correction coefficient of the critical ground stress value of the roadway rock burst occurrence under different lateral pressure loading conditions of the circular roadway;

[0028] Step 2: Determine the correction coefficient η of the unequal pressure loading condition of the critical ground stress value of the circular roadway rock burst occurrence mod-lateral ;

[0029] ① Use the in-situ stress testing technology to determine the horizontal in-situ stress component P ground-h and the vertical in-situ stress component P ground-v ;

[0030] ② Let P min = min{P ground-h , P ground-v}, and obtain the lateral pressure coefficient λ lateral = P min / P cr ;

[0031] ③ Let the lateral loading load P horizontal of the specimen in the laboratory = λ lateral P ex-cr ; Check the critical ground stress value P horizontal corresponding to the current value of the lateral loading load P ex-cr from the critical ground stress value correction diagram, and calculate and determine the correction coefficient η mod-lateralAs shown in the following formula:

[0032] η mod-lateral =P ex-cr / P ex-cr-100％ (5)

[0033] Wherein, P ex-cr-100％ =100%P ex-cr is the loading result when the lateral pressure coefficient is equal to 1, that is, the loading result of the equal-pressure boundary loading;

[0034] Case 2: If the cross-section of the in-situ roadway is non-circular:

[0035] Step S1: Determine the cross-section form correction coefficient η of the critical ground stress for roadway rockburst occurrence mod-sec ;

[0036] At the site, m specimens are prepared. Using a biaxial loading testing machine, three specimens with circular through-holes are subjected to biaxial equal-pressure loading. The loading paths are such that the lateral and vertical pressure rates are the same until the specimens undergo rockburst failure. Record the critical ground stress index values P ex-cr1 、P ex-cr2 、P ex-cr3 obtained by the testing machine loading. Take the average of the three as the critical ground stress index value P ex-cr =P ex-cr1 +P ex-cr2 +P ex-cr3 under equal-pressure conditions for simulating roadway rockburst occurrence; Subject three specimens with non-circular through-holes to biaxial equal-pressure loading. The loading paths are such that the lateral and vertical pressure rates are the same until the specimens undergo rockburst failure. Record the critical ground stress index values Pˊ ex-cr1 、Pˊ ex-cr2 、Pˊ ex-cr3 obtained by the testing machine loading. Take the average of the three as the critical ground stress index value Pˊ ex-cr =Pˊ ex-cr1 +Pˊ ex-cr2 +Pˊ ex-cr3 under equal-pressure conditions for non-circular simulated roadway rockburst occurrence; Then calculate the cross-section form correction coefficient η of the critical ground stress for roadway rockburst occurrence mod-sec As shown in the following formula:

[0037]

[0038] Step S2: The same as Steps 1 and 2 in Case 1, determine the unequal-pressure loading condition correction coefficient η of the critical ground stress value for non-circular roadway rockburst occurrence mod-lateral ;

[0039] Step 4: Determine the unequal pressure and cross-section form correction value P of the critical ground stress for roadway rockburst occurrence cr-mod ;

[0040] The unequal pressure and cross-section form correction value P of the critical ground stress for roadway rockburst occurrence cr-mod is shown in the following formula:

[0041] P cr-mod = η mod-sec η mod-lateral P cr (7)

[0042] In the formula, when the roadway cross-section form is circular, η mod-sec takes the value of 1;

[0043] Step 5: Calculate the critical mining peak stress P for rockburst occurrence in the stress concentration area of the surrounding rock of the roadway to be monitored and warned mcr , as shown in the following formula:

[0044]

[0045] Step 6: Determine the depth range of the multi-point stress gauge monitoring points in the stress concentration area of the surrounding rock of the roadway to be monitored and warned;

[0046] According to the critical softening zone radius ρ cr and critical fracture zone radius ρ fcr calculated in Step 2, determine the depth range of the multi-point stress gauge monitoring points as [ρ fcr - ρ0, ρ cr - ρ0];

[0047] Step 7: Calculate the reduction value P of the critical mining peak stress for rockburst occurrence used to determine the stress monitoring and warning critical index value mcr-monitor , as shown in the following formula:

[0048] P mcr-monitor = η c P mcr (9)

[0049] where η c is the reduction coefficient of the critical mining peak stress value for rockburst occurrence;

[0050] Step 8: Test and obtain the load-displacement response curve of the borehole stress gauge to be designed, that is, test and obtain the load-deformation response characteristic curve of the stress gauge, and obtain the deformation stiffness of the borehole stress gauge to be designed;

[0051] Step 9: Based on Formulas (10), (11), and (12), and let P = P mcr-monitor , plot the reduction value P of the critical mining peak stress for rockburst occurrencemcr-monitor Borehole convergence curve under control

[0052]

[0053] where u a is the shrinkage displacement of the borehole surrounding rock; ρ d is the radius of the broken zone of the borehole surrounding rock; λ1 is the softening modulus reduction of coal and rock.

[0054]

[0055] where P is the mining-induced stress in the elastic zone of the roadway surrounding rock where the monitoring borehole is located; ρ p is the radius of the plastic softening zone of the monitoring borehole surrounding rock, p d-p is the acting stress of the broken zone of the monitoring borehole surrounding rock on the boundary of the softening zone, as shown in the following formula:

[0056]

[0057] where p monitor is the oil pressure reading of the stress gauge in the monitoring borehole.

[0058] Step 10: Plot the load-displacement response curve of the stress gauge obtained in Step 8 into the borehole convergence curve under the control of the critical mining peak stress reduction value for rock burst occurrence, and obtain the "borehole-stress gauge" mutual feedback balance curve of the rock burst roadway. Determine the critical index value a1 for monitoring the coal body stress to warn of rock burst through the intersection point of the two curves.

[0059] The beneficial effects of adopting the above technical solutions are as follows: The method for determining the critical index value for monitoring the coal body stress to warn of rock burst provided by the present invention takes into account the mutual feedback stress effect between the borehole in the roadway surrounding rock and the oil pressure stress gauge and its quantitative characterization equation, and establishes a mapping relationship between the oil pressure reading of the borehole stress gauge and the critical stress for rock burst occurrence; the present invention takes into account the cross-scale effect between the small specimen and the engineering structure, and adopts the method of determining the correction coefficient in the laboratory to improve the applicability of the theoretical method to guide the engineering site; the method for determining the critical index value of the present invention fully considers the coupling correlation degree between the early warning initial value and factors such as the coal body rock burst tendency, the stiffness of the stress gauge, and the borehole size. Description of the Drawings

[0060] Figure 1 is the flow chart of the method for determining the critical index value for monitoring the coal body stress to warn of rock burst provided in this embodiment;

[0061] Figure 2 is the diagram for determining the correction coefficient of the critical stress value for rock burst occurrence in a circular roadway under different lateral pressure loadings provided in this embodiment;

[0062] Figure 3The loading path diagram of the specimen boundary under biaxial loading provided in this embodiment;

[0063] Figure 4 The mutual feedback balance curve diagram of "drilling - stress gauge" for the roadway with rock burst in this embodiment. Detailed implementation manners

[0064] The following combines the drawings and embodiments to further describe in detail the detailed implementation manners of the present invention. The following embodiments are used to illustrate the present invention, but are not used to limit the scope of the present invention.

[0065] A method for determining the critical index value for monitoring coal body stress and warning of rock burst

[0066] Determine the critical in - situ stress for the occurrence of roadway rock burst;

[0067] Considering the effect of the redistribution of mining - induced stress caused by roadway excavation, convert the critical in - situ stress for the occurrence of roadway rock burst into the critical peak mining - induced stress for the occurrence of roadway rock burst;

[0068] Define the characterization curve of the mutual feedback balance characteristics of the load - induced deformation between the stress gauge borehole and the stress gauge;

[0069] Take the critical peak mining - induced stress for the occurrence of rock burst as the "most dangerous stress" state (i.e., the maximum allowable safety stress before the occurrence of rock burst) around the borehole where the stress gauge is installed. By plotting the characterization curve of the mutual feedback balance characteristics of the load - induced deformation between the borehole where the stress gauge is located and the stress gauge under the action of the critical peak mining - induced stress, further determine the warning critical index value for the stress gauge to warn of the danger of roadway rock burst.

[0070] As Figure 1 shown, it specifically includes the following steps:

[0071] Step 1: Obtain the rock mechanics parameters of the coal body in the surrounding rock of the roadway to be monitored and warned; the rock mechanics parameters include the uniaxial compressive strength σ c , elastic modulus E, impact modulus index K = λ1 / E, residual degradation modulus λ2, residual strength coefficient ξ; where λ1 is the post - peak softening modulus;

[0072] Step 2: Calculate the critical in - situ stress for the occurrence of rock burst in the roadway to be monitored and warned;

[0073] Step 2.1: Obtain the support stress p s of the roadway to be warned;

[0074] Step 2.2: Calculate the critical fracture zone radius ρ fcr , critical softening zone radius ρ cr , respectively as shown in the following formulas:

[0075]

[0076]

[0077] Calculate the critical ground stress P for the occurrence of rock burst in the roadway to be monitored and warned cr It is:

[0078]

[0079] Among them, ρ0 is the roadway radius after equivalent the roadway to be monitored as a homogeneous, continuous and isotropic circular roadway; m is an intermediate variable, is the internal friction angle of the coal and rock medium in the plastic softening zone, p fcr is the acting stress of the surrounding rock broken zone on the plastic softening zone when the roadway rock burst starts, as shown in the following formula:

[0080]

[0081] Among them, is the internal friction angle of the coal and rock medium in the broken zone,

[0082] Step 3: Adopt the method of laboratory test to determine the correction function curve of the critical stress value for the occurrence of roadway rock burst, draw the function graph, and determine the non-uniform pressure correction coefficient η of the critical ground stress for the occurrence of roadway rock burst mod-lateral and the section form correction coefficient η mod-sec ;

[0083] Step 3.1: Make roadway specimens;

[0084] According to the roadway rib of the roadway to be monitored and warned in the coal mine, take the raw coal specimen and process it into a standard specimen with a size of 300mm×300mm×300mm; at the center position of the specimen, drill a through hole with a diameter of 45mm as the simulated roadway. According to the actual section shape of the on-site roadway, the drilled through hole can be circular, rectangular, trapezoidal, semi-circular arch, etc.;

[0085] Step 3.2: Determine the non-uniform pressure correction coefficient η of the critical ground stress for the occurrence of roadway rock burst according to the section shape of the roadway to be monitored and warned mod-lateral and the section form correction coefficient η mod-sec ;

[0086] Case 1: If the section of the roadway to be monitored and warned is circular:

[0087] Step 1: Prepare n specimens. Using a 5000 kN biaxial loading testing machine, subject 3 specimens with circular through-holes to biaxial equal-pressure loading. The loading path is such that the lateral and vertical pressure rates are the same until the specimens undergo rock burst failure. Record the critical ground stress index value P of rock burst occurrence obtained from the loading of the testing machine. ex-cr1 、P ex-cr2 、P ex-cr3 . Take the average of the three as the critical ground stress index value P of rock burst occurrence in the circular simulated roadway under equal-pressure conditions. ex-cr =P ex-cr1 +P ex-cr2 +P ex-cr3 ; For the n - 3 specimens, sequentially set the horizontal lateral pressure loading loads P horizontal to be 95%P ex-cr 、90%P ex-cr 、85%P ex-cr 、80%P ex-cr 、75%P ex-cr 、70%P ex-cr 、65%P ex-cr 、60%P ex-cr 、55%P ex-cr 、50%P ex-cr 、45%P ex-cr 、40%P ex-cr 、35%P ex-cr 、30%P ex-cr 、25%P ex-cr 、20%P ex-cr . Load the vertical stress until the simulated roadway undergoes rock burst, and respectively record the critical ground stress values P ex-cr-95％ 、P ex-cr-90％ 、P ex-cr-85％ 、P ex-cr-80％ 、P ex-cr-75％ 、P ex-cr-70％ 、P ex-cr-65％ 、P ex-cr-60％ 、P ex-cr-55％ 、P ex-cr-50％ 、P ex-cr-45％ 、P ex-cr-40％ 、P ex-cr-35％ 、P ex-cr-30％ 、P ex-cr-25％ 、P ex-cr-20％ . Plot each group of data on a plan view, draw a fitted correction curve, and form a diagram for determining the correction coefficient of the critical ground stress value of rock burst occurrence in the circular roadway under different lateral pressure loading conditions, as shown in Figure 2 . The loading stress path of the specimens is as shown in Figure 3 .

[0088] Step 2: Determine the correction coefficient η of the unequal pressure loading condition for the critical ground stress value at which rock burst occurs in circular roadways mod-lateral ;

[0089] ① Use the commonly used ground stress measurement technology in the industry to determine the horizontal ground stress component P ground-h and the vertical ground stress component P ground-v in the cross-section of the roadway to be monitored and pre-warned;

[0090] ② Let P min = min{P ground-h , P ground-v}, and obtain the lateral pressure coefficient λ lateral = P min / P cr ;

[0091] ③ Let the lateral loading load P horizontal of the specimen in the laboratory = λ lateral P ex-cr ; Check the critical ground stress value correction diagram to obtain the critical ground stress value P horizontal corresponding to the current value of the lateral loading load, and calculate and determine the correction coefficient η ex-cr of the unequal pressure loading condition as shown in the following formula: mod-lateral η

[0092] = P mod-lateral / P ex-cr / P ex-cr-100％ (5)

[0093] where P ex-cr-100％ = 100%P ex-cr is the loading result when the lateral pressure coefficient is equal to 1, that is, the loading result of the equal pressure boundary loading;

[0094] Case 2: If the cross-section of the on-site roadway is non-circular (rectangular, trapezoidal, semi-circular arch, etc.):

[0095] Step S1: Determine the cross-section form correction coefficient η of the critical ground stress at which rock burst occurs in the roadway mod-sec ;

[0096] Prepare m specimens, use a 5000 kN biaxial loading testing machine, subject 3 specimens with circular through-holes to biaxial equal pressure loading, and the loading paths are the same for both the lateral and vertical pressure rates until the specimens undergo rock burst failure, record the critical ground stress index values P ex-cr1 , P ex-cr2 , P ex-cr3 obtained by the testing machine loading, and take the average of the three as the critical ground stress index value P ex-cr = P ex-cr1 + Pex-cr2 +P ex-cr3 ; Three specimens with non-circular through-holes are subjected to biaxial equal-pressure loading, and the loading paths are such that the lateral and vertical pressure rates are the same until the specimens undergo rock burst failure. Record the critical ground stress index value Pˊ of the rock burst occurring in the non-circular roadway obtained by the loading of the testing machine. ex-cr1 、Pˊ ex-cr2 、Pˊ ex-cr3 Take the average of the three as the critical ground stress index value Pˊ of the rock burst occurring in the non-circular simulated roadway under equal-pressure conditions. ex-cr =Pˊ ex-cr1 +Pˊ ex-cr2 +Pˊ ex-cr3 ; Then calculate the section form correction coefficient η of the critical ground stress for the occurrence of roadway rock burst. mod-sec As shown in the following formula:

[0097]

[0098] Step S2: The same as Steps 1 and 2 in Case 1, determine the unequal-pressure loading condition correction coefficient η of the critical ground stress for the occurrence of rock burst in the non-circular roadway. mod-lateral ;

[0099] Step 4: Determine the unequal-pressure and section form correction value P of the critical ground stress for the occurrence of roadway rock burst. cr-mod ;

[0100] The unequal-pressure and section form correction value P of the critical ground stress for the occurrence of roadway rock burst. cr-mod As shown in the following formula:

[0101] P cr-mod =η mod-sec η mod-lateral P cr (7)

[0102] In the formula, when the roadway section form is circular, η mod-sec takes the value of 1;

[0103] Step 5: Calculate the critical mining peak stress P for the occurrence of rock burst in the stress concentration area of the surrounding rock of the roadway to be monitored and pre-warned. mcr , as shown in the following formula:

[0104]

[0105] Step 6: Determine the depth range of the monitoring points of the multi-point stress gauges in the stress concentration area of the surrounding rock of the roadway to be monitored and pre-warned;

[0106] According to the critical softening zone radius ρ calculated in Step 2 for the occurrence of roadway rock burst cr , the critical fracture zone radius ρfcr , it is determined that the depth range of the monitoring points of the multi-point stress gauge is [ρ fcr -ρ0, ρ cr -ρ0];

[0107] Step 7: Calculate the temporary mining-induced stress value P of the surrounding rock in the elastic zone of the roadway for determining the critical warning index value of stress monitoring mcr-monitor , as shown in the following formula:

[0108] P mcr-monitor = η c P mcr (9)

[0109] Among them, η c is the reduction coefficient of the critical mining-induced peak stress value during rock burst occurrence, generally taking 75% - 85%.

[0110] Step 8: Through experimental testing, obtain the load-displacement response curve of the drill hole stress gauge to be designed, that is, test and obtain the load-deformation response characteristic curve of the stress gauge, and obtain the deformation stiffness of the drill hole stress gauge to be designed;

[0111] Step 9: Based on Formulas (10), (11), and (12), and let P = P mcr-monitor , draw the drill hole convergence curve under the control of the reduction value P of the critical mining-induced peak stress during rock burst occurrence; mcr-monitor

[0112]

[0113] Among them, u a is the shrinkage displacement of the drill hole surrounding rock, m; ρ d is the radius of the broken zone of the drill hole surrounding rock, m; λ1 is the softening modulus reduction of coal and rock, MPa.

[0114]

[0115] Among them, P is the mining-induced stress in the elastic zone of the surrounding rock of the roadway where the monitoring drill hole is located, MPa; ρ p is the radius of the plastic softening zone of the monitoring drill hole surrounding rock, m; p d-p is the acting stress of the broken zone of the monitoring drill hole surrounding rock on the boundary of the softening zone, MPa, as shown in the following formula:

[0116]

[0117] Among them, p monitor is the oil pressure indication of the stress gauge in the monitoring drill hole, MPa.

[0118] Step 10: And plot the load-displacement response curve of the stress gauge obtained in Step 8 into the drill hole convergence curve under the control of the reduction value of the critical mining-induced peak stress during rock burst occurrence, to obtain as​Figure 4 The mutual feedback balance curve diagram of the roadway with rock burst "drilling - stress gauge" as shown determines the critical index value a1 for monitoring the stress of the coal body to pre - warn rock burst through the intersection point of the two curves (this critical index value is the ordinate of the intersection point of the two curves).

[0119] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope defined by the claims of the present invention.

Claims

1. A method for determining the critical index value for monitoring coal mass stress and warning rock burst, characterized in that: Determine the critical ground stress for the occurrence of roadway rock burst; Considering the effect of the redistribution of mining-induced stress caused by roadway excavation, convert the critical ground stress for the occurrence of roadway rock burst into the critical mining peak stress for the occurrence of roadway rock burst; Clarify the characteristic curve representing the mutual feedback balance of the loading and deformation between the stress gauge borehole and the stress gauge; Take the critical mining peak stress for the occurrence of rock burst as the "most dangerous stress" state around the borehole where the stress gauge is installed. By plotting the characteristic curve representing the mutual feedback balance of the loading and deformation between the borehole where the stress gauge is located and the stress gauge under the action of the critical mining peak stress, further determine the warning critical index value for the stress gauge to warn of the danger of roadway rock burst; It includes the following steps: Step 1: Obtain the rock mechanics parameters of the coal mass in the surrounding rock of the roadway to be monitored and warned; Step 2: Calculate the critical ground stress P for the occurrence of rock burst in the roadway to be monitored and pre-warned cr ; Step 3: By using the method of laboratory tests, determine the correction function curve of the critical stress value for roadway rockburst occurrence, draw the function graph, and determine the unequal pressure correction coefficient η of the critical in-situ stress for roadway rockburst occurrence mod-lateral and the section form correction coefficient η mod-sec ; Step 4: Determine the unequal pressure and cross-section form correction value P of the critical ground stress for roadway rockburst cr-mod ; The unequal pressure and cross-section form correction value P of the critical ground stress for roadway rockburst cr-mod is shown in the following formula: P cr-mod = η mod-sec η mod-lateral P cr (1) In the formula, when the roadway section shape is circular, η mod-sec takes the value of 1; Step 5: Calculate the critical mining peak stress P at which rock burst occurs in the stress concentration area of the surrounding rock of the roadway to be monitored and warned mcr ; Step 6: Determine the depth range of the monitoring points of the multi-point stress gauges in the stress concentration area of the surrounding rock of the roadway to be monitored and warned; The critical softening zone radius ρ of roadway rock burst occurrence calculated according to Step 2 cr , the critical fracture zone radius ρ fcr , determine that the monitoring point depth range of the multi-point stress gauge is [ρ fcr - ρ0, ρ cr - ρ0], where ρ0 is the roadway radius after equivalent the roadway to be monitored as a homogeneous, continuous and isotropic circular roadway; Step 7: Calculate the reduction value P of the critical mining peak stress at the occurrence of rock burst for determining the critical index value of stress monitoring and early warning, as shown in the following formula: mcr-monitor , as shown in the following formula: P mcr-monitor = η c P mcr (2) Among them, η c is the reduction coefficient of the critical mining peak stress value for rock burst occurrence; Step 8: Through experimental tests, obtain the load-displacement response curve of the borehole stress gauge to be designed, that is, obtain the response characteristic curve of the loading and deformation of the stress gauge, and obtain the deformation stiffness of the borehole stress gauge to be designed; Step 9: Let the mining-induced stress P in the elastic zone of the roadway surrounding rock where the monitoring borehole is located be P mcr-monitor , and plot the borehole convergence curve under the control of the critical mining-induced peak stress reduction value P mcr-monitor ; Step 10: Plot the load-displacement response curve of the stress gauge obtained in Step 8 into the borehole convergence curve controlled by the reduction value of the critical mining peak stress for the occurrence of rock burst, obtain the "borehole-stress gauge" mutual feedback balance curve of the rock burst roadway, and determine the critical index value a1 for monitoring coal mass stress and warning rock burst through the intersection point of the two curves.

2. The method for determining the critical index value for monitoring coal body stress and warning rock burst according to claim 1, wherein: The specific method of the said Step 2 is: Step 2.1: Obtain the support stress p of the roadway to be warned s ; Step 2.2: Calculate the critical fracture zone radius ρ and the critical softening zone radius ρ of the roadway prone to rock burst for monitoring and early warning, which are shown as follows: fcr , the critical softening zone radius ρ cr , respectively, as shown in the following formulas: Calculate the critical ground stress P for the occurrence of rock burst in the roadway to be monitored and warned cr It is as follows: where ρ0 is the roadway radius after equivalent the roadway to be monitored as a homogeneous, continuous and isotropic circular roadway; m is an intermediate variable, is the internal friction angle of the coal and rock medium in the plastic softening zone, p fcr is the acting stress of the surrounding rock broken zone on the plastic softening zone when the roadway impact starts, as shown in the following formula: Among them, is the internal friction angle of the coal and rock medium in the crushing zone, E is the elastic modulus, λ1 is the softening modulus of the coal and rock, λ2 is the residual modulus, ξ is the residual strength coefficient, and σ c is the uniaxial compressive strength.

3. A method for determining the critical index value for monitoring coal mass stress and warning rock burst, according to claim 2, characterized in that: The specific method of the said Step 3 is: Step 3.1: Make a roadway specimen; According to the roadway rib of the roadway to be monitored and warned in the coal mine, take the raw coal specimen and process it into a standard specimen; at the center position of the specimen, drill a through hole as the simulated roadway; Step 3.2: Determine the unequal pressure correction coefficient η of the critical ground stress for the occurrence of roadway rock burst according to the cross-sectional shape of the roadway to be monitored and warned mod-lateral and the cross-section form correction coefficient η mod-sec .

4. A method for determining the critical index value for monitoring coal body stress and warning rock burst, according to claim 3, characterized in that: Step 3.2 determines the unequal pressure correction coefficient η of the critical ground stress for the occurrence of roadway rockburst in the following two cases according to the cross-sectional shape of the roadway to be monitored and warned mod-lateral and the cross-section form correction coefficient η mod-sec : Case 1: If the cross-section of the roadway to be monitored and warned is circular: Step 1: Prepare n specimens by on-site sampling. Use a biaxial loading testing machine to conduct biaxial equal-pressure loading on 3 specimens with circular through-holes. The loading paths are such that the lateral and vertical pressure rates are the same until the specimens undergo rock burst failure, and record the critical stress index value P of rock burst occurrence obtained from the loading of the testing machine. ex-cr1 、P ex-cr2 、P ex-cr3 Take the average of the three as the critical stress index value P of rock burst occurrence in the circular simulated roadway under equal-pressure conditions. ex-cr =P ex-cr1 +P ex-cr2 +P ex-cr3 ; For the n - 3 specimens, sequentially set the horizontal lateral pressure loading loads P horizontal to be 95%P ex-cr 、90%P ex-cr 、85%P ex-cr 、80%P ex-cr 、75%P ex-cr 、70%P ex-cr 、65%P ex-cr 、60%P ex-cr 、55%P ex-cr 、50%P ex-cr 、45%P ex-cr 、40%P ex-cr 、35%P ex-cr 、30%P ex-cr 、25%P ex-cr 、20%P ex-cr Load the vertical stress until the simulated roadway undergoes rock burst, and respectively record the critical stress values P ex-cr-95％ 、P ex-cr-90％ 、P ex-cr-85％ 、P ex-cr-80％ 、P ex-cr-75％ 、P ex-cr-70％ 、P ex-cr-65％ 、P ex-cr-60％ 、P ex-cr-55％ 、P ex-cr-50％ 、P ex-cr-45％ 、P ex-cr-40％ 、P ex-cr-35％ 、P ex-cr-30％ 、P ex-cr-25％ 、P ex-cr-20％ Plot each group of data on a plane graph, draw a fitted correction curve, and form a graph for determining the correction coefficient of the critical ground stress value of rock burst occurrence in the circular roadway under different lateral pressure loading conditions. Step 2: Determine the unequal pressure loading condition correction coefficient η of the critical ground stress value for the occurrence of rock burst in circular roadways mod-lateral ; ① Using in-situ stress testing technology, determine the horizontal in-situ stress component P ground-h and the vertical in-situ stress component P ground-v ; ② Let P min = min{P ground-h , P ground-v}, and obtain the lateral pressure coefficient λ lateral = P min / P cr ; ③Apply the lateral loading load P to the specimen in the laboratory horizontal = λ lateral P ex-cr ; Obtain the lateral loading load P by referring to the figure according to the critical in-situ stress value correction diagram horizontal The critical in-situ stress value P corresponding to the current value ex-cr , Calculate and determine the correction coefficient η for the unequal pressure loading condition mod-lateral As shown in the following formula: η mod-lateral = P ex-cr / P ex-cr-100％ (7) Among them, P ex-cr-100％ = 100%P ex-cr is the loading result when the lateral pressure coefficient is equal to 1, that is, the loading result of the equal-pressure boundary; Case 2: If the cross-section of the on-site roadway is non-circular: Step S1: Determine the section form correction coefficient η of the critical ground stress for roadway rockburst mod-sec ; At the site, m specimens were prepared. Using a biaxial loading testing machine, 3 specimens with circular through-holes were subjected to biaxial equal-pressure loading. The loading paths were such that the lateral and vertical pressure rates were the same until the specimens suffered rock burst failure. Record the critical ground stress index value P of rock burst occurrence obtained by the loading of the testing machine. ex-cr1 、P ex-cr2 、P ex-cr3 , and take the average of the three as the critical ground stress index value P ex-cr = P ex-cr1 + P ex-cr2 + P ex-cr3 ; Subject 3 specimens with non-circular through-holes to biaxial equal-pressure loading. The loading paths are such that the lateral and vertical pressure rates are the same until the specimens suffer rock burst failure. Record the critical ground stress index value Pˊ of non-circular roadway rock burst occurrence obtained by the loading of the testing machine. ex-cr1 、Pˊ ex-cr2 、Pˊ ex-cr3 , and take the average of the three as the critical ground stress index value Pˊ of non-circular simulated roadway rock burst occurrence under equal-pressure conditions. ex-cr = Pˊ ex-cr1 + Pˊ ex-cr2 + Pˊ ex-cr3 ; Then calculate the cross-section form correction coefficient η mod-sec of the critical ground stress for rock burst occurrence in the roadway as shown in the following formula: Step S2: The same as Steps 1 and 2 in Case 1, determine the unequal pressure loading condition correction coefficient η of the critical ground stress value for the occurrence of rock burst in non-circular roadways mod-lateral .

5. A method for determining the critical index value for monitoring coal body stress and warning rock bursts according to claim 4, characterized in that: The critical mining peak stress P of the surrounding rock stress concentration area where rock burst occurs in the roadway to be monitored and warned in step 5 mcr As shown in the following formula:

6. A method for determining the critical index value for monitoring coal mass stress and warning rock burst, according to claim 5, characterized in that: The peak stress reduction value P of the critical mining-induced rock burst described in step 9 mcr-monitor The borehole convergence curve under the control is plotted based on the following formulas (10), (11), and (12): Among them, u a is the shrinkage displacement of the surrounding rock of the borehole; ρ d is the radius of the broken zone of the surrounding rock of the borehole; λ1 is the softening modulus reduction of coal and rock; Among them, P is the mining-induced stress in the elastic zone of the roadway surrounding rock where the monitoring borehole is located; ρ p is the radius of the plastic softening zone of the surrounding rock of the monitoring borehole; m is an intermediate variable, is the internal friction angle of the coal and rock medium in the plastic softening zone, p d-p is the acting stress of the broken zone of the surrounding rock of the monitoring borehole on the boundary of the softening zone, as shown in the following formula: Among them, p monitor is the oil pressure reading of the stress gauge in the monitoring borehole.

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