Coal rock mass creep disturbance test method

Abstract

The invention discloses a coal rock mass creep disturbance test method, which belongs to the technical field of rock mechanics and engineering, and comprises the following steps: S1, carrying out a conventional compression test, and determining creep and disturbance test parameters; s2, carrying out a graded loading creep test; s3, carrying out a creep disturbance test; applying a disturbance load to the test piece according to creep and disturbance test parameters, and monitoring stress, strain, damage evolution and instability failure characteristics of the test piece under the action of dynamic load disturbance; judging the next test process according to the deformation evolution rule of the test piece after each disturbance; and S4, determining a strength limit neighborhood of the test piece under the action of creep and disturbance according to a test result. According to the method, key information such as the deformation rule, the instability failure characteristic and the strength limit of the coal rock mass can be disclosed, then the damage evolution rule, the strength limit and the instability mechanism of the coal rock mass under the creep action and the dynamic load disturbance action are researched, and scientific basis and technical support are provided for stability prediction and control of engineering rock mass in engineering practice.

Description

Technical Field

[0001] The invention relates to the field of rock mechanics and engineering technology, and in particular to a coal rock mass creep disturbance test method. Background Art

[0002] With the continuous development of modern underground rock mass engineering technology and the continuous expansion of engineering scale, especially the development and utilization of deep rock mass resources, the stress environment faced by engineering rock mass is becoming increasingly complex and changeable. In this context, relatively stable rock mass is extremely sensitive to various external disturbances. Even a small stress change may cause significant deformation effects, thereby threatening the overall stability of the engineering rock mass. This phenomenon is particularly prominent in the field of coal mining, especially in the stability analysis of residual coal pillars.

[0003] Research has shown that when the coal-rock mass is in the critical state of the "strength limit neighborhood", its stability becomes extremely fragile, and even a small stress disturbance may become the "last straw" that triggers the failure and instability of the coal-rock mass. For the residual coal pillars that have undergone creep damage, although they have formed a relatively stable equilibrium structure with the overlying rock strata, the internal stress state has often approached or reached the strength limit. In this case, once the residual coal pillars are subjected to stress disturbances during the re-mining process, it is very easy to cause rapid deformation and destruction of the coal pillars, thereby threatening the stability of the entire coal pillar group and even the entire mining field.

[0004] In order to deeply explore this complex mechanical phenomenon and provide effective theoretical guidance and technical support for engineering practice, it is particularly important to carry out creep perturbation tests on anthracite samples. By simulating the creep behavior under different perturbation parameters, key information such as deformation law, instability failure characteristics and strength limit of creep coal samples under external perturbation can be revealed. This information is of vital engineering significance for predicting and controlling the stability of residual coal pillars under re-mining disturbance.

[0005] It is worth noting that the creep perturbation effect, as an important phenomenon in the field of rock mechanics, is directly affected by the stress state of the coal rock mass. Only when the stress state of the coal rock mass is in the strength limit neighborhood can external perturbations induce significant rheological strain increments. Therefore, accurately determining the strength limit neighborhood of the coal rock mass and its threshold stress is not only the basis for studying the creep perturbation effect, but also the key to evaluating the stability of the coal rock mass under perturbation.

[0006] In summary, how to reveal key information such as the deformation law, instability failure characteristics and strength limit of coal and rock masses through creep disturbance tests, and provide scientific basis and technical support for the prediction and control of residual coal pillar stability in engineering practice, is a technical problem that needs to be solved. Summary of the invention

[0007] The purpose of the present invention is to provide a coal rock creep disturbance test method to solve the problems existing in the above-mentioned prior art. Through the creep disturbance test, key information such as the deformation law, instability failure characteristics and strength limit of the coal rock mass is revealed, and then the damage evolution law, strength limit and instability mechanism of the coal rock mass under creep and dynamic load disturbance are studied, so as to provide a scientific basis and technical support for the stability prediction and control of engineering rock masses such as residual coal pillars in engineering practice.

[0008] To achieve the above object, the present invention provides the following solutions:

[0009] The present invention provides a coal rock creep disturbance test method, comprising the following steps:

[0010] S1. Carry out conventional compression tests and determine creep and disturbance test parameters;

[0011] S2. Carry out graded loading creep test;

[0012] The specimen is preloaded. After the preloading is completed, the axial load is applied to the target creep stress level by using a graded creep loading method and kept constant. The specimen enters the stable creep stage and is ready to carry out the next stage of disturbance test.

[0013] S3. Conduct creep disturbance test;

[0014] After the specimen enters the stable creep stage, a disturbance load is applied to the specimen according to the creep and disturbance test parameters to monitor the stress, strain, damage evolution and instability failure characteristics of the specimen under dynamic load disturbance.

[0015] The next test process is determined according to the deformation evolution law of the specimen after each disturbance:

[0016] 1) The deformation of the specimen in the creep stage after the disturbance continues to grow, and the specimen undergoes accelerated creep until the specimen is destroyed;

[0017] 2) The deformation of the specimen in the creep stage after disturbance is kept stable, the disturbance intensity or the number of disturbances is changed, the disturbance action is repeated and the deformation of the specimen after disturbance is monitored until accelerated creep failure occurs to the specimen;

[0018] S4. Determine the strength limit neighborhood of the specimen under creep and disturbance based on the test results.

[0019] In one embodiment, in step S1, according to the uniaxial / triaxial compression test of the specimen, the stress-strain curve of the specimen is drawn, and its compressive strength peak value is obtained; according to the stress-strain curve of the specimen under the uniaxial / triaxial compression test conditions, 3 to 5 marking points are selected, and the stress at the marking points is used as the creep stress level of the disturbance load, and the stress value of each creep stress level can be determined in turn. The creep time of the specimen at each creep stress level is greater than 24 hours, and the confining pressure and test temperature are kept constant during the creep test.

[0020] In one embodiment, in step S1, the specimen creep disturbance test parameters include:

[0021] 1) Disturbance rate: According to the range of dynamic load disturbance strain rate in coal mines and the strain characteristics of the specimen, the loading rate range of the disturbance test is determined to be 0.01 mm / s to 0.1 mm / s;

[0022] 2) Disturbance intensity: According to the characteristics of engineering load, the strength of the specimen and the elastic modulus of the specimen, the disturbance intensity is determined to be 3MPa~10MPa;

[0023] 3) Disturbance timing: At each level of creep stress, after the specimen enters the stable creep stage, a disturbance is applied to the specimen. Multiple disturbances can be applied cyclically according to the test plan;

[0024] 4) Disturbance frequency / interval:

[0025] ① Single disturbance: After the disturbance is over and the specimen is stable in creep, the disturbance parameters are changed to apply the next disturbance;

[0026] ② Repeat disturbance: After the disturbance ends, wait for the set time to repeat the same disturbance parameters.

[0027] In one embodiment, in step S2, the specimen is installed in the triaxial pressure chamber of the testing machine, and a preloading process is performed to gradually apply confining pressure and axial pressure to the specimen so that the specimen is in a static horizontal stress state, at which time the confining pressure = pore water pressure. The test process ensures that the temperature in the triaxial pressure chamber is constant; after the preparation work is completed, the creep time of the specimen at each stress level is greater than 24h or the strain rate is less than 10 -8 ·s -1 The specimen is considered to have entered the stable creep stage and is ready to carry out the next stage of disturbance test.

[0028] In one embodiment, a disturbance test with different disturbance intensities is performed, including the following contents:

[0029] ① Initial creep: first apply axial force to the specimen to the initial creep stress level and keep it constant, and wait for the creep deformation of the specimen to stabilize;

[0030] ② The first disturbance: According to the test plan, the first disturbance is applied, and the axial force is loaded to the first target value at the set loading rate. After the axial force reaches the first target value, it is immediately unloaded to the initial value at the same rate. The first disturbance ends and the strain of the specimen during the disturbance process is recorded;

[0031] ③ Post-disturbance creep: After the disturbance, the specimen creeps under the initial creep conditions until the specimen undergoes stable creep. The strain of the specimen in the creep stage is recorded, and the creep rate in the stable creep stage is calculated accordingly.

[0032] ④ If the specimen undergoes stable creep, a second disturbance is performed to increase the disturbance intensity, and the axial force is loaded to the second target value at the set loading rate. After the axial force reaches the second target value, it is immediately unloaded to the initial value at the same rate, and the second disturbance ends;

[0033] ⑤ Repeat operations ③ and ④, gradually increasing the disturbance intensity until the specimen exhibits accelerated creep or unstable failure.

[0034] In one embodiment, a repeated perturbation test is performed, including the following:

[0035] ① Initial creep: first apply axial force to the specimen to the initial creep stress level and keep it constant, and wait for the creep deformation of the specimen to stabilize;

[0036] ② The first disturbance: According to the test plan, the first disturbance is applied, and the axial force is loaded to the first target value at the set loading rate. After the axial force reaches the first target value, it is immediately unloaded to the initial value at the same rate. The first disturbance ends and the strain of the specimen during the disturbance process is recorded;

[0037] ③ Post-disturbance creep: After the disturbance, the specimen creeps under the initial creep conditions until the specimen undergoes stable creep. The strain of the specimen in the creep stage is recorded, and the creep rate in the stable creep stage is calculated accordingly.

[0038] ④ If the specimen undergoes stable creep, a second disturbance is performed with the same disturbance parameters as in step ②;

[0039] ⑤ Repeat operations ③ and ④ until the specimen experiences the target number of disturbances, and observe whether the specimen is damaged during the target number of disturbances;

[0040] ⑥ If the specimen is damaged during the target number of disturbances, the test is terminated; if the specimen is not damaged during the target number of disturbances, the creep stress level is increased step by step and the specimen enters the steady-state creep stage, and operations ② to ⑤ are repeated until the specimen exhibits accelerated creep or unstable damage.

[0041] In one embodiment, creep perturbation test data processing and analysis includes the following:

[0042] The stress, axial and radial deformation of the specimen are collected by the data acquisition system of the testing machine. The data acquisition system of the testing machine records the stress and deformation data of the whole process of graded loading creep and dynamic load disturbance test. After the test, the strain data during each disturbance is sorted and extracted, and combined with the axial stress value, the strain of the specimen before the disturbance, the strain peak during the disturbance and the strain data after the disturbance are recorded respectively;

[0043] The disturbance effect of the specimen is characterized from the following two aspects:

[0044] 1) Disturbance instantaneous strain

[0045] When a disturbance is applied to a specimen in a stable creep state, the instantaneous strain of the specimen increases suddenly. The instantaneous increment of the specimen strain during the disturbance is defined as the disturbance instantaneous strain, which is the difference between the peak disturbance strain and the strain before the disturbance.

[0046] 2) Disturbance residual strain

[0047] When a disturbance is applied to a specimen in a stable creep state, the instantaneous strain of the specimen increases suddenly. As the disturbance stops, the strain of the specimen recovers to a certain extent. The strain difference of the specimen before and after the disturbance is defined as the disturbance residual strain, which is the difference between the strain after the disturbance and the strain before the disturbance.

[0048] By arranging the above data, the instantaneous strain and residual strain of the specimen during each disturbance are plotted as a function of the disturbance intensity / number of disturbances, and the strain and damage characteristics of the specimen under different disturbance parameter conditions are further analyzed.

[0049] In one embodiment,

[0050] 1) Disturbance tests with different disturbance intensities

[0051] According to the disturbance effect of the specimen, the critical disturbance intensity of the specimen under different creep stress conditions is determined. When the disturbance intensity is lower than the critical intensity, the specimen is insensitive to the disturbance, and the specimen is mainly elastically deformed during the disturbance loading stage, and the elastic deformation can be largely recovered during the disturbance unloading process. When the disturbance intensity is higher than the critical intensity, the specimen is more sensitive to the disturbance, and the specimen produces more irreversible plastic deformation during the disturbance loading process. The damage effect of the specimen is significant during the disturbance process, and with the increase of the disturbance intensity, the disturbance residual strain of the specimen increases.

[0052] 2) Repeated perturbation test

[0053] According to the disturbance effect of the specimen, the creep stress threshold at which the specimen undergoes instability failure under repeated disturbance, that is, the destructive creep stress level, is determined. When the creep stress level is lower than the stress threshold, the cumulative damage of the specimen under repeated disturbance increases and tends to stabilize, and the specimen remains stable; when the creep stress level exceeds the stress threshold, the cumulative damage of the specimen under repeated disturbance develops rapidly, leading to instability failure of the specimen.

[0054] In one embodiment, the method for determining the strength limit neighborhood of a specimen includes the following contents:

[0055] The sources of stress on the specimen during the test include: creep stress level and stress applied by disturbance action;

[0056] Depending on whether the specimen is disturbed or not, the relationship between the stress state of the specimen during the test and its stability can be expressed as:

[0057] (1) The specimen is unstable and damaged during the disturbance process. The stress state of the specimen is within the strength limit neighborhood of the specimen, and its stress state satisfies: specimen stress > strength limit neighborhood threshold stress > disturbance damage strength;

[0058] (2) If the specimen does not fail after being disturbed, and the stress state of the specimen is outside the strength limit neighborhood of the specimen, then its stress state satisfies: specimen stress < strength limit neighborhood threshold stress < disturbance failure strength.

[0059] In one embodiment,

[0060] 1) Disturbance tests with different disturbance intensities

[0061] Under the condition of single disturbance test, the disturbance residual strain of the specimen under different creep stress levels and disturbance parameters is mainly analyzed, and the sum of the critical disturbance strength and the creep stress level is taken as the strength limit neighborhood threshold stress of the coal sample under the creep stress level and disturbance action;

[0062] 2) Repeated perturbation test

[0063] Under the repeated disturbance test conditions, the specimen will only fail when it reaches the creep stress level and is subjected to repeated disturbance. The strength limit neighborhood threshold stress of the coal sample under repeated disturbance is determined based on the creep stress level threshold of the specimen.

[0064] Compared with the prior art, the present invention has achieved the following technical effects:

[0065] After the specimen enters the stable creep stage, the present invention applies a disturbance load to the specimen according to the creep and disturbance test parameters, monitors the stress, strain, damage evolution and instability failure characteristics of the specimen under the dynamic load disturbance, and determines the next test process according to the deformation evolution law of the specimen after each disturbance. Through the above-mentioned creep disturbance test, key information such as the deformation law, instability failure characteristics and strength limit of the coal rock mass can be revealed, and then the damage evolution law, strength limit and instability mechanism of the coal rock mass under creep and dynamic load disturbance can be studied, providing a scientific basis and technical support for the stability prediction and control of engineering rock masses such as residual coal pillars in engineering practice.

[0066] Other technical solutions included in the present invention can also achieve the following technical effects:

[0067] 1. The disturbance test of the present invention can adjust the axial loading rate by servo loading, thereby realizing the disturbance effect of different disturbance parameters, with precise control and a large variable range, and realizing more test schemes.

[0068] 2. The creep effect and disturbance effect of the present invention are uniformly realized by a servo testing machine, which makes the operation more convenient and the control more precise.

[0069] 3. Based on the experimental methods and principles, the present invention redefines the parameters that characterize the creep disturbance effect and the strength limit neighborhood of coal rock mass, and uses this to determine the strength limit neighborhood of coal rock samples under creep disturbance, providing methodological guidance for the prediction and control of the stability system of coal rock mass under dynamic load disturbance. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0071] Figure 1 It is a schematic diagram of the overall structure of the test device involved in the present invention and the connection of each system;

[0072] Figure 2 is a cross-sectional view of the arrangement of the radial displacement sensor in an embodiment of the present invention;

[0073] Figure 3 This is a diagram showing the internal structure of a triaxial pressure chamber in an embodiment of the present invention;

[0074] Figure 4 This is a schematic diagram of the structure of a self-balancing pressure chamber in an embodiment of the present invention;

[0075] Figure 5Schematic diagram of the coal rock creep disturbance test process and loading path in an embodiment of the present invention;

[0076] Figure 6a Schematic diagram of axial loading mode of creep disturbance test (different disturbance intensities) in an embodiment of the present invention;

[0077] Figure 6b Schematic diagram of axial loading method of creep disturbance test (repeated disturbance) in an embodiment of the present invention;

[0078] Figure 7 Schematic diagram of strain evolution of coal rock mass under creep and disturbance in an embodiment of the present invention;

[0079] Among them, Ⅰ, axial servo loading system; Ⅱ, triaxial pressure chamber and main test system; Ⅲ, confining pressure tracking system; Ⅳ, temperature control system; Ⅴ, acoustic emission monitoring system; Ⅵ, data acquisition and control system.

[0080] 1. Loading cylinder; 2. Axial loading piston; 3. Axial displacement sensor; 4. Servo oil source system; 5. Electro-hydraulic servo valve; 6. Press; 7. Axial force sensor; 8. Plug on the kettle body; 81. Axial balance piston; 82. Plug cover on the kettle body; 83. Axial pressure balance channel; 9. Triaxial pressure chamber; 10. High and low temperature constant temperature water bath; 11. Radial displacement sensor; 12. Plug on the core; 13. Test piece; 14. Sensor probe; 15. Push-pull cylinder; 16. Confining pressure tracking pump; 17. Constant temperature water bath heating and cooling system; 18. Controller; 19. Control computer; 20. Acoustic emission sensor; 21. Acoustic emission monitor. DETAILED DESCRIPTION

[0081] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] The purpose of the present invention is to provide a coal rock creep disturbance test method to solve the problems existing in the prior art. Through the creep disturbance test, key information such as the deformation law, instability failure characteristics and strength limit of the coal rock mass is revealed, and then the damage evolution law, strength limit and instability mechanism of the coal rock mass under creep and dynamic load disturbance are studied, so as to provide a scientific basis and technical support for the stability prediction and control of engineering rock masses such as residual coal pillars in engineering practice.

[0083] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0084] When conducting the test of the present invention, the Before the test, all coal samples were saturated with water and their basic physical parameters such as size and density were measured.

[0085] The main equipment used in the creep disturbance test is an electro-hydraulic servo triaxial creep testing machine, which can realize axial constant displacement loading through axial displacement sensor, axial force sensor and high-precision servo valve. The loading rate is 0-3 mm / s. Taking the standard cylindrical coal sample of Ф50×100 mm as an example, the strain rate of the coal sample corresponding to the displacement loading is 0-3×10 -2 ·s -1 , dynamic loads of different amplitudes and intensities can be applied to the specimen by controlling the axial loading rate, realizing dynamic loading of different strain rates and its disturbance effect. The testing machine can automatically record the test axial pressure, confining pressure, axial and radial deformation, temperature and other data and draw curves, with the characteristics of stable measurement and control system, high measurement accuracy and good pressure stabilization effect.

[0086] The test device (electro-hydraulic servo triaxial creep testing machine) used in the present invention is as follows:

[0087] like Figure 1 As shown in the figure, the test device consists of an axial servo loading system I, a triaxial pressure chamber and a main test system II, a confining pressure tracking system III, a temperature control system IV, an acoustic emission detection system V, and a data acquisition and control system VI. The axial servo loading system I adopts servo loading control, and the confining pressure tracking system III adopts a high-precision confining pressure tracking pump 16 to control the confining pressure in the triaxial pressure chamber 9 and keep it constant. The temperature control system IV is controlled by a constant temperature water bath heating and cooling system 17, and the radial deformation measurement system adopts eight evenly distributed radial displacement sensors 11 for measurement. The damage of the specimen is monitored by the acoustic emission monitor 21 of the acoustic emission monitoring system V. The acoustic emission detection system V uses an acoustic emission probe that is close to the surface of the specimen 13 to monitor through the channel at the bottom of the pressure chamber. The acoustic emission probe adopts a waterproof and pressure-resistant structure and can work normally in a water pressure environment of 0 to 5 MPa.

[0088] The axial servo loading system I is composed of a loading cylinder 1, a servo oil source system 4, an axial force sensor 7, an electro-hydraulic servo valve 5, and a controller 18. The controller 18 controls the axial loading rate and amplitude after receiving the feedback signals of each sensor, and can adopt various loading methods such as constant displacement, constant force, and constant displacement target force to realize dynamic and static combined loading. The axial loading system I is a loading cylinder 1 and its servo oil source system 4 arranged above the press 6. An axial displacement sensor 3 is arranged on the top of the loading cylinder 1, and the axial displacement sensor 3 is connected to the controller 18; the axial loading piston 2 of the loading cylinder 1 is connected to the axial force sensor 7 and the electro-hydraulic servo valve 5, and the electro-hydraulic servo valve 5 is connected to the servo oil source system 4 and the controller 18. The controller 18 controls the axial loading rate and amplitude after receiving the feedback signals of each sensor, and adopts various loading methods such as constant displacement, constant force, and constant displacement target force to realize dynamic and static combined loading.

[0089] like Figure 3 and Figure 4 As shown, the triaxial pressure chamber 9 adopts a self-balancing structure, and the self-balancing pressure chamber is arranged in the upper plug of the pressure chamber to balance the influence of the confining pressure in the triaxial pressure chamber 9 on the axial pressure. The self-balancing pressure chamber is composed of a kettle upper plug 8, an axial balancing piston 81, a kettle upper plug pressure cover 82, and an axial pressure balancing channel 83; the kettle upper plug 8 is sealed at the top opening of the triaxial pressure chamber 9, the axial pressure balancing channel 83 is arranged in the kettle upper plug 8, and the axial balancing piston 81 is arranged in the axial pressure balancing channel 83 and penetrates into the triaxial pressure chamber 9, which can balance the influence of the confining pressure on the axial pressure; one end of the axial balancing piston 81 is connected to the axial force sensor 7, and the other end is in contact with the core upper plug 12, and both ends adopt spherical contact to eliminate the horizontal force caused by the uneven cross section; the triaxial pressure chamber 9 is placed in the guide rail of the base of the press 6, and the triaxial pressure chamber 9 can be pushed and pulled forward and backward by the push-pull cylinder 15, which is convenient for installing and disassembling the test piece.

[0090] like Figure 2 and Figure 3As shown, the triaxial pressure chamber 9 has 8 radial displacement sensors 11 evenly arranged along the circumference in the middle thereof. The sensor probe 14 can adjust the length to adapt to the test pieces 13 of different sizes, and all adopt a waterproof structure. The angle between two adjacent radial displacement sensors 11 is 45°. The outer shell of the radial displacement sensor 11 is welded and fixed to the outer wall of the triaxial pressure chamber 9. The internal retractable sensor probe 14 contacts the surface of the test piece 13. The sensor probe 14 can control its length by screw thread or by replacing the probe, and is used to measure the radial deformation of the test pieces 13 of different diameters. During the test, the axial deformation of the test piece 13 is measured by the axial displacement sensor 3 in the loading cylinder 1, and the radial deformation is measured by the evenly distributed 8 radial displacement sensors 11. The axial and radial strains during the test are calculated in combination with the diameter, height and other parameters of the test piece 13. The radial displacement sensor 11 has a measurement range of 0 to 20 mm, a measurement accuracy of <±0.1% FS, and a measurement resolution of 0.001 mm.

[0091] A high and low temperature constant temperature water bath 10 is arranged outside the triaxial pressure chamber 9 and is connected to the triaxial pressure chamber 9 as a whole to keep the temperature inside the triaxial pressure chamber 9 constant. A temperature sensor is arranged inside the triaxial pressure chamber 9 and connected to the temperature control system IV; the temperature control system IV receives the temperature feedback from the temperature sensor and controls the temperature.

[0092] Four optional channels are reserved at the bottom of the triaxial pressure chamber 9, and acoustic emission can be used to monitor the damage of the test piece 13 during the test, and strain gauges can also be used to measure the deformation of different positions of the test piece 13.

[0093] The acoustic emission detection system V is provided with an acoustic emission monitor 21 and four acoustic emission sensors 20. The acoustic emission sensors 20 are arranged on the surface of the test piece 13 and connected to the acoustic emission monitor 21 through the acoustic emission detection channel. The acoustic emission sensor 20 is arranged in the triaxial pressure chamber 9, close to the surface of the test piece 13, and is used to monitor the damage and destruction of the test piece 13 during the test. It is connected to the acoustic emission monitor 21 through a dedicated channel at the bottom of the triaxial pressure chamber 9. The acoustic emission sensor 20 is specially treated and can work normally under a water pressure environment of 0 to 5 MPa. Among them, the constant displacement loading rate of the axial servo loading system I is 0 to 3 mm / s, the constant force loading rate is 0 to 20 kN / s, the range of the axial displacement sensor 3 is 0 to 150 mm, the measurement accuracy is <±0.1% FS, and the measurement resolution is 0.001 mm. The loading amplitude of the loading cylinder 1 is 0-150 mm, and the corresponding axial displacement sensor 3 has a measuring range of 0-150 mm, a measuring accuracy of <±0.1% FS, and a measuring resolution of 0.001 mm; the servo oil source system 4 cooperates with the electro-hydraulic servo valve 5 and the controller 18 to realize high-precision axial loading control and axial loading at different loading rates; by adjusting the axial displacement loading rate, dynamic loads of different levels and amplitudes can be achieved, wherein the relationship between the height (l) of the specimen 13, the axial strain rate (ε), and the axial loading rate (v) is: v=ε×l, thereby the axial loading rate required for the test can be calculated based on the strain rate and the height of the specimen 13.

[0094] The data acquisition and control system VI adopts the existing control program and is specifically provided with a control cabinet, a control computer 19 and a controller 18. The controller 18 receives data such as the axial displacement sensor 3, the radial displacement sensor 11 and the axial force sensor 7, temperature and confining pressure, and simultaneously collects data such as the axial and radial deformation, axial force, confining pressure, temperature, etc. during the test, and can receive feedback of the axial force and axial displacement, realize various loading modes such as axial constant force, constant displacement, constant displacement target force and axial force maintenance, and realize axial force loading in different modes, different rates and different levels.

[0095] The cavity size of the triaxial pressure chamber 9 is Ф200×400mm, and loading tests of three sizes of specimens of Ф100×200mm, Ф50×100mm, and Ф25×50mm can be carried out by replacing the plug 12 on the core; the plug on the kettle body is provided with a self-balancing cavity, and the stroke of the axial balancing piston 81 is 0~40mm.

[0096] The high-precision confining pressure tracking pump 16 has a pressure range of 0 to 20 MPa, an accuracy of <±0.05 MPa, and a measurement resolution of 0.001 MPa.

[0097] The temperature control system IV adopts a combination system of high and low temperature constant temperature bath, circulation pump, etc. to achieve constant temperature control of the triaxial pressure chamber 9, with refrigeration, heating, water circulation and temperature self-constant functions, the temperature control range is 5 ~ 80 ℃, and the temperature control accuracy is ≤ ± 0.2 ℃.

[0098] During the test, the axial deformation of the specimen 13 is measured by the axial displacement sensor 3 in the loading cylinder 1, and the radial deformation is measured by 8 evenly distributed radial displacement sensors 11. The axial and radial strains during the test are calculated in combination with parameters such as the diameter and height of the specimen 13.

[0099] Combination Figure 1 to Figure 7 As shown, the present invention provides a coal rock creep disturbance test method. The creep disturbance test is divided into two stages: first, a creep test is carried out, and then a dynamic load disturbance test is carried out on the basis of the creep test. Among them, the creep test adopts a graded loading creep test method, and the dynamic load disturbance effect is mainly achieved by loading and unloading at different axial rates (different strain rates). Each completion of "loading-unloading" is a disturbance cycle. During the test, different loading and unloading rates and loading and unloading amplitudes are controlled to achieve disturbance effects of different disturbance rates and different disturbance intensities. See the loading path of the creep and disturbance test for details. Figure 5 , the specific test method includes the following steps:

[0100] S1. Carry out conventional compression tests and determine creep and disturbance test parameters;

[0101] S2. Carry out graded loading creep test;

[0102] The specimen (such as coal sample, the same below) is subjected to a preloading process. After the preloading is completed, the axial load is applied to the target creep stress level by means of graded loading creep and kept constant. The specimen enters the stable creep stage and is ready to carry out the next stage of disturbance test;

[0103] S3. Conduct creep disturbance test;

[0104] After the specimen enters the stable creep stage, a disturbance load is applied to the specimen according to the creep and disturbance test parameters to monitor the stress, strain, damage evolution and instability failure characteristics of the specimen under dynamic load disturbance. Specifically, after completing a disturbance, the deformation of the specimen before and after the disturbance is recorded. After the disturbance ends, the specimen enters the creep stage and the next disturbance cycle is performed after an interval of 2 hours.

[0105] The next test process is determined according to the deformation evolution law of the specimen after each disturbance:

[0106] 1) If the deformation of the specimen continues to grow in the creep stage after the disturbance, it means that the dynamic load disturbance has destroyed the stable creep state of the specimen, causing the specimen to accelerate creep until the specimen is destroyed;

[0107] 2) If the deformation of the specimen in the creep stage after disturbance can be maintained stable, it means that the specimen is insensitive to the dynamic load disturbance of the existing parameters, and the creep coal sample is still in a stable state. At this time, it is necessary to change the disturbance intensity or the number of disturbances, repeat the disturbance action and monitor the deformation of the specimen after disturbance until the specimen undergoes accelerated creep failure;

[0108] S4. Determine the strength limit neighborhood of the specimen under creep and disturbance based on the test results.

[0109] After the specimen enters the stable creep stage, the present invention applies a disturbance load to the specimen according to the creep and disturbance test parameters, monitors the stress, strain, damage evolution and instability failure characteristics of the specimen under the dynamic load disturbance, and determines the next test process according to the deformation evolution law of the specimen after each disturbance. Through the above-mentioned creep disturbance test, key information such as the deformation law, instability failure characteristics and strength limit of the coal rock mass can be revealed, and then the damage evolution law, strength limit and instability mechanism of the coal rock mass under creep and dynamic load disturbance can be studied, providing a scientific basis and technical support for the stability prediction and control of engineering rock masses such as residual coal pillars in engineering practice.

[0110] In one embodiment, in step S1, according to the uniaxial / triaxial compression test of the specimen, the stress-strain curve of the specimen is drawn, and its compressive strength peak value is obtained; according to the stress-strain curve of the specimen under the uniaxial / triaxial compression test conditions, 3 to 5 marking points are selected, and the stress at the marking points is used as the creep stress level for applying the disturbance load. Generally, the initial creep stress level is determined to be 30% to 40% Rc (Rc represents the yield strength of the material, the same below), and the graded loading gradient is 10% Rc. The stress value of each level of creep stress level can be determined in turn. The creep time of the specimen at each level of creep stress level is greater than 24 hours, and the confining pressure and test temperature are kept constant during the creep test.

[0111] In one embodiment, in combination Figure 5 As shown in Table 1, in step S1, the specimen creep disturbance test parameters include:

[0112] 1) Disturbance rate: According to the range of dynamic load disturbance strain rate of coal mine and the strain characteristics of the specimen, the loading rate range of the disturbance test is determined to be 0.01mm / s~0.1mm / s (corresponding to the strain rate of the specimen is 10 -4 ~10 -3 ·s -1 ), which can be specifically divided into four disturbance rates: 0.01mm / s, 0.02mm / s, 0.05mm / s, and 0.1mm / s;

[0113] 2) Disturbance intensity (σ d): According to the characteristics of engineering load, the strength of the specimen and the elastic modulus of the specimen, the disturbance intensity is determined to be 3MPa~10MPa;

[0114] 3) Disturbance timing: At each level of creep stress, after the specimen enters the stable creep stage, a disturbance is applied to the specimen. Multiple disturbances can be applied cyclically according to the test plan;

[0115] 4) Disturbance frequency / interval:

[0116] ① Single disturbance: After the disturbance is over and the coal sample is creeping stably, the disturbance parameters are changed to apply the next disturbance. The creep interval between two disturbance cycles is 2h;

[0117] ② Repeat disturbance: After the disturbance is completed, wait for 10 minutes and repeat the same disturbance parameters. The number of repeated disturbances is preliminarily determined to be 5 times.

[0118] The disturbance parameters of the creep disturbance test of coal samples are shown in Table 1. The selected values ​​of parameters such as creep stress level, disturbance / loading rate, disturbance intensity and number of disturbance cycles can be seen from Table 1. Subsequent loading tests are carried out according to the parameter values ​​in Table 1.

[0119] Table 1 Coal sample creep disturbance test disturbance parameters

[0120]

[0121] In one embodiment, in step S2, the specimen is installed in the triaxial pressure chamber of the testing machine, and a preloading process is performed to gradually apply confining pressure and axial pressure to put the specimen in a static horizontal stress state. At this time, the confining pressure = pore water pressure. The test process ensures that the temperature in the triaxial pressure chamber is constant. After the preparation work is completed, the axial load is applied to the target creep stress level by using a graded loading creep method and kept constant. The creep time of the specimen at each stress level is greater than 24 hours or the deformation is stable (strain rate <10 -8 ·s -1 ) is considered as the specimen entering the stable creep stage and preparing for the next stage of disturbance test.

[0122] In one embodiment, a disturbance test with different disturbance intensities is performed, including the following contents:

[0123] Taking the initial creep stress level of 3.6MPa, disturbance rate of 0.01mm / s, disturbance intensity of 3MPa, and disturbance once as an example, the creep coal sample disturbance failure test process is introduced as follows:

[0124] ① Initial creep: The specimen is first loaded to 3.6MPa (axial force 7kN). After 24h of creep, the creep deformation of the specimen tends to be stable.

[0125] ② The first disturbance: According to the test plan, the first disturbance was applied, and the axial force was loaded to 13kN at a loading rate of 0.01mm / s. After the axial force reached the target value, it was immediately unloaded to 7kN at the same rate. The first disturbance was ended, and the strain of the specimen during the disturbance process was recorded;

[0126] ③ Post-disturbance creep: After the disturbance, the specimen creeps for 2 h under an axial stress of 3.6 MPa until the specimen undergoes stable creep. The strain of the specimen in the creep stage is recorded, and the creep rate in the stable creep stage is calculated accordingly.

[0127] ④ If the specimen undergoes stable creep, a second disturbance is performed, the disturbance intensity is increased to 4MPa, and the axial force is loaded to 15kN at a loading rate of 0.01mm / s. After the axial force reaches the target value, it is immediately unloaded to 7kN at the same rate, and the second disturbance ends;

[0128] ⑤ Repeat operations ③ and ④, gradually increasing the disturbance intensity until the specimen exhibits accelerated creep or unstable failure.

[0129] In one embodiment, a repeated perturbation test is performed, including the following:

[0130] Taking the initial creep stress level of 3.6MPa (graded loading gradient of 1.5MPa), disturbance rate of 0.01mm / s, disturbance intensity of 3MPa, and repeated disturbance for 5 times as an example, the creep coal sample disturbance failure test process is introduced as follows:

[0131] ① Initial creep: The specimen is first loaded to 3.6MPa (axial force 7kN). After 24h of creep, the creep deformation of the specimen tends to be stable.

[0132] ② The first disturbance: According to the test plan, the first disturbance was applied, and the axial force was loaded to 13kN at a loading rate of 0.01mm / s. After the axial force reached the target value, it was immediately unloaded to 7kN at the same rate. The first disturbance was ended, and the strain of the specimen during the disturbance process was recorded;

[0133] ③ Post-disturbance creep: After the disturbance, the specimen creeps for 2 h under an axial stress of 3.6 MPa until the specimen undergoes stable creep. The strain of the specimen in the creep stage is recorded, and the creep rate in the stable creep stage is calculated accordingly.

[0134] ④ If the specimen undergoes stable creep, a second disturbance is performed with the same disturbance parameters as in step ②;

[0135] ⑤ Repeat the operations of ③ and ④ until the specimen experiences 5 disturbances, and observe whether the specimen is damaged during the 5 disturbances;

[0136] ⑥ If the specimen is damaged during the 5 disturbances, the test is terminated; if the specimen is not damaged during the 5 disturbances, the creep stress level is increased step by step and the specimen enters the steady-state creep stage, and operations ② to ⑤ are repeated until the specimen exhibits accelerated creep or unstable damage.

[0137] In one embodiment, creep perturbation test data processing and analysis includes the following:

[0138] The stress, axial and radial deformation of the specimens are collected by the data acquisition system of the testing machine. The data acquisition system of the testing machine records the stress and deformation data of the whole process of the graded loading creep and dynamic load disturbance test, and the data acquisition frequency is 10 times / s. After the test, the strain data during each disturbance are sorted and extracted, and combined with the axial stress value, the strain of the coal sample before the disturbance, the strain peak during the disturbance, and the strain data after the disturbance are recorded respectively.

[0139] in accordance with Figure 5 The strain evolution of coal and rock mass during creep and disturbance is shown in Figure 7 In order to quantitatively describe the damage caused by dynamic load disturbance to creep coal and rock specimens and further characterize the disturbance effect of creep specimens, combined with Figure 5 and Figure 7 , the disturbance effect of creep coal samples is characterized mainly from the following two aspects:

[0140] (1) Disturbance instantaneous strain (Δε i1 )

[0141] When a perturbation is applied to a specimen in a stable creep state, the instantaneous strain of the specimen increases suddenly. The instantaneous increment of the specimen strain during the perturbation is defined as the "perturbation instantaneous strain". According to a large number of research results and test data, under the same conditions, the degree of damage to the rock specimen is positively correlated with the peak strain of the specimen. Therefore, the peak strain of the specimen during the perturbation process can also characterize the damage of the specimen under different perturbations to a certain extent. Taking the i-th perturbation as an example, combined with Figure 7 , disturbance instantaneous strain (Δε i1 ) is the peak strain of disturbance (ε i1 ) and the strain before disturbance (ε i0 ), that is:

[0142] Δε i1 =ε i1 -ε i0 ;

[0143] (2) Disturbance residual strain (Δε i2 )

[0144] When a disturbance is applied to a specimen in a stable creep state, the instantaneous strain of the specimen increases suddenly. As the disturbance stops, the strain of the specimen recovers to a certain extent. The strain difference between the specimen before and after the disturbance is defined as the "disturbance residual strain". The deformation of the specimen under the disturbance is mainly elastic and plastic deformation. Elastic deformation is reversible and can be recovered with the end of the disturbance. Plastic deformation is irreversible, which is mainly manifested as the strain difference before and after the disturbance, that is, the disturbance residual strain. The disturbance residual strain can quantitatively characterize the irreversible damage of the specimen during the disturbance process. Taking the i-th disturbance as an example, combined with Figure 7 , the perturbation residual strain (Δε i2 ) is the strain after disturbance (ε i2 ) and the strain before disturbance (ε i0 ), that is:

[0145] Δε i2 =ε i2 -ε i0 ;

[0146] By arranging the above data, the instantaneous strain (Δε i1 ), disturbance residual strain (Δε i2 ) with the disturbance intensity (σ d ) / disturbance number change curve, and further analyze the strain and damage characteristics of the specimen under different disturbance parameter conditions.

[0147] In one embodiment,

[0148] (1) Disturbance tests with different disturbance intensities

[0149] Under different disturbance intensity test conditions, the disturbance instantaneous strain (Δε i1 ), disturbance residual strain (Δε i2 ) with the disturbance intensity (σ d ) has the following regular characteristics:

[0150] 1) At different creep stress levels (σ cl ), the disturbance instantaneous strain and disturbance intensity of the specimen both show an obvious linear increasing relationship;

[0151] 2) The disturbance residual strain shows a trend of first decreasing and then increasing with the increase of disturbance intensity. That is, with the increase of disturbance intensity, there is a critical value of disturbance intensity. When this critical value is exceeded, the residual strain of the specimen under disturbance increases rapidly with the disturbance intensity.

[0152] Thus, the critical perturbation strength (σ dc ). Further, the critical disturbance intensity (σdc ) is understood as: when the disturbance intensity is lower than the critical strength, the specimen is insensitive to the disturbance, and the specimen is mainly elastically deformed during the disturbance loading stage, and the elastic deformation can be recovered to a large extent during the disturbance unloading process; when the disturbance intensity is higher than the critical strength, the specimen is more sensitive to the disturbance, and the specimen produces more irreversible plastic deformation during the disturbance loading process. The damage effect of the specimen is significant during the disturbance process, and with the increase of the disturbance intensity, the disturbance residual strain of the specimen increases.

[0153] (2) Repeated perturbation test

[0154] Under repeated disturbance test conditions, the instantaneous strain (Δε i1 ), disturbance residual strain (Δε i2 ) with the change curve of the disturbance times has the following regular characteristics:

[0155] 1) When the creep stress level is small, the instantaneous strain (Δε i1 ) changes relatively slowly with the number of disturbances, and the strain of the specimen is relatively stable under repeated disturbances. With the increase of creep stress level, the instantaneous strain (Δε i1 ) shows an increasing trend with the increase of disturbance times, but the increase amplitude gradually decreases; at the failure creep stress level, the instantaneous strain (Δε i1 ) shows an obvious increasing trend with the increase of disturbance times, and the disturbance instantaneous strain curve has an obvious upward feature;

[0156] 2) Under the non-destructive creep stress level, the disturbed residual strain of the specimen shows a gradually decreasing trend with the number of disturbances. According to its decreasing trend, the curve can be divided into two stages: "rapid decrease" and "slow decrease (gentle)", that is, the disturbed residual strain of the specimen tends to be buffered at the critical disturbance number. When the disturbance number is less than this critical disturbance number, the specimen is highly sensitive to the disturbance, and plastic strain is generated under the disturbance, and it shows a decreasing trend with the number of disturbances. When the disturbance number exceeds this critical disturbance number, the specimen's sensitivity to the disturbance decreases, and the residual strain of the specimen gradually tends to 0 under the subsequent disturbance, the damage of the specimen tends to be stable, and the specimen is in a relatively stable state under the disturbance.

[0157] 3) At the damage creep stress level, the specimen is sensitive to disturbance. The specimen produces different residual strains under multiple disturbances, which leads to the increasing damage of the specimen at the damage creep stress level, and then leads to the instability of the specimen.

[0158] The creep stress threshold (σ) at which the specimen undergoes instability failure under repeated disturbance can be determined. clp), that is, the failure creep stress level. Further, the creep stress level threshold (σ clp ) is understood as: when the creep stress level is lower than the stress threshold, the cumulative damage of the specimen under repeated disturbance increases and tends to stabilize, and the specimen can maintain stability; when the creep stress level exceeds the stress threshold, the cumulative damage of the specimen under repeated disturbance develops rapidly, resulting in instability and failure of the specimen.

[0159] In one embodiment, the method for determining the strength limit neighborhood of a specimen includes the following contents:

[0160] According to the definition of "strength limit neighborhood", the fundamental reason why coal rock in a stable creep state becomes unstable during disturbance is that its stress state is in the "strength limit neighborhood". For stable coal rock in the "strength limit neighborhood", even a very small stress disturbance may trigger the destruction and instability of the coal rock. Therefore, studying the strength limit neighborhood and threshold stress of creeping coal rock under disturbance is of key significance for the prediction and control of the stability system of coal rock under dynamic load disturbance.

[0161] In the creep disturbance test method of the present invention, the sources of stress (σ) of the coal and rock specimens during the test process include: creep stress level (σ cl ) and the stress imposed by the disturbance, where the stress imposed by the disturbance is expressed as the disturbance intensity (σ d ), the stress of the specimen during the disturbance process can be expressed as:

[0162] σ=σ cl +σ d ;

[0163] Depending on whether the specimen is disturbed or not, the relationship between the stress state of the creep coal sample during the test and its stability can be expressed as:

[0164] (1) The coal sample is unstable and damaged during the disturbance process. The stress state of the coal sample is within the “strength limit neighborhood” of the coal sample. Its stress state satisfies: Coal sample stress σ>strength limit neighborhood threshold stress σ d0 > Disturbance damage intensity σ dp ;

[0165] (2) The coal sample does not suffer from instability after being disturbed, and the stress state of the coal sample is outside the "strength limit neighborhood" of the coal sample. Then its stress state satisfies: Coal sample stress σ<strength limit neighborhood threshold stress σ d0 <Disturbance damage intensityσ dp .

[0166] In one embodiment,

[0167] 1) Disturbance tests with different disturbance intensities

[0168] Under the condition of single disturbance test, the main analysis is the test specimen under different creep stress levels (σ cl ) and disturbance parameters. Under the disturbance of different strengths, there is a disturbance intensity that causes the residual strain to increase rapidly, which is called the critical disturbance intensity (σ dc ), when the critical disturbance intensity is exceeded, the coal sample will be damaged rapidly and then destroyed under the disturbance. dc ) and creep stress level (σ cl ) is taken as the strength limit neighborhood threshold stress (σ d0 ),Right now:

[0169] σ d0 =σ dc +σ cl ;

[0170] In the formula, σ d0 is the threshold stress of the strength limit neighborhood, MPa; σ dc is the critical disturbance intensity, MPa; σ cl is the creep stress level, MPa.

[0171] 2) Repeated perturbation test

[0172] Under repeated disturbance test conditions, the specimen will only fail when the creep stress level is broken and the specimen is subjected to repeated disturbance. There is a creep stress level threshold for the failure of the creep specimen under repeated disturbance. Only when the creep stress exceeds the stress level threshold will the internal structure of the coal sample develop rapidly under disturbance, leading to the failure of the coal sample. Therefore, according to the creep stress level threshold (σ clp ) to determine the strength limit neighborhood threshold stress (σ d1 ),Right now:

[0173] σ d1 =σ clp ;

[0174] In the formula, σ d1 is the threshold stress of the strength limit neighborhood, MPa; σ clp is the creep stress level, MPa.

[0175] The present invention uses specific examples to illustrate the principles and implementation methods of the present invention. The above examples are only used to help understand the method and core ideas of the present invention. At the same time, for those skilled in the art, according to the ideas of the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A coal rock creep disturbance test method, characterized in that: The following steps are involved: S1. Carry out conventional compression tests and determine creep and disturbance test parameters; S2. Carry out graded loading creep test; The specimen is preloaded. After the preloading is completed, the axial load is applied to the target creep stress level by using a graded creep loading method and kept constant. The specimen enters the stable creep stage and is ready to carry out the next stage of disturbance test. S3. Conduct creep disturbance test; After the specimen enters the stable creep stage, a disturbance load is applied to the specimen according to the creep and disturbance test parameters to monitor the stress, strain, damage evolution and instability failure characteristics of the specimen under dynamic load disturbance. The next test process is determined according to the deformation evolution law of the specimen after each disturbance: 1) The deformation of the specimen in the creep stage after the disturbance continues to grow, and the specimen undergoes accelerated creep until the specimen is destroyed; 2) The deformation of the specimen in the creep stage after disturbance is kept stable, the disturbance intensity or the number of disturbances is changed, the disturbance action is repeated and the deformation of the specimen after disturbance is monitored until accelerated creep failure occurs to the specimen; S4. Determine the strength limit neighborhood of the specimen under creep and disturbance based on the test results.

2. The coal rock creep disturbance test method according to claim 1, characterized in that: In step S3, dynamic load disturbance is achieved by loading and unloading at different axial rates. Each completion of "loading-unloading" is a disturbance cycle. During the test, disturbances of different disturbance rates and different disturbance intensities are achieved by controlling different loading and unloading rates and loading and unloading amplitudes.

3. The coal rock creep disturbance test method according to claim 1, characterized in that: In step S1, according to the uniaxial / triaxial compression test of the specimen, the stress-strain curve of the specimen is drawn, and its compressive strength peak value is obtained; according to the stress-strain curve of the specimen under the uniaxial / triaxial compression test conditions, 3 to 5 marking points are selected, and the stress of the marking points is used as the creep stress level of the disturbance load, and the stress value of each creep stress level can be determined in turn. The creep time of the specimen at each creep stress level is greater than 24 hours, and the confining pressure and test temperature are kept constant during the creep test; The specimen creep disturbance test parameters include: 1) Disturbance rate: According to the range of dynamic load disturbance strain rate in coal mines and the strain characteristics of the specimen, the loading rate range of the disturbance test is determined to be 0.01 mm / s to 0.1 mm / s; 2) Disturbance intensity: According to the characteristics of engineering load, the strength of the specimen and the elastic modulus of the specimen, the disturbance intensity is determined to be 3MPa~10MPa; 3) Disturbance timing: At each level of creep stress, after the specimen enters the stable creep stage, a disturbance is applied to the specimen. Multiple disturbances can be applied cyclically according to the test plan; 4) Disturbance frequency / interval: ① Single disturbance: After the disturbance is over and the specimen is stable in creep, the disturbance parameters are changed to apply the next disturbance; ② Repeat disturbance: After the disturbance ends, wait for the set time to repeat the same disturbance parameters.

4. The coal rock creep disturbance test method according to claim 1, characterized in that: In step S2, the specimen is installed in the triaxial pressure chamber of the testing machine, and a preloading process is performed, and confining pressure and axial pressure are gradually applied to make the specimen in a static horizontal stress state. At this time, the confining pressure = pore water pressure. The temperature in the triaxial pressure chamber is ensured to be constant during the test process; After the preparation work is completed, the creep time of the specimen at each stress level is greater than 24h or the strain rate is less than 10 -8 ·s -1 The specimen is considered to have entered the stable creep stage and is ready to carry out the next stage of disturbance test.

5. The coal rock creep disturbance test method according to claim 1, characterized in that: Conduct disturbance tests with different disturbance intensities, including the following: ① Initial creep: first apply axial force to the specimen to the initial creep stress level and keep it constant, and wait for the creep deformation of the specimen to stabilize; ② The first disturbance: According to the test plan, the first disturbance is applied, and the axial force is loaded to the first target value at the set loading rate. After the axial force reaches the first target value, it is immediately unloaded to the initial value at the same rate. The first disturbance ends and the strain of the specimen during the disturbance process is recorded; ③ Post-disturbance creep: After the disturbance, the specimen creeps under the initial creep conditions until the specimen undergoes stable creep. The strain of the specimen in the creep stage is recorded, and the creep rate in the stable creep stage is calculated accordingly. ④ If the specimen undergoes stable creep, a second disturbance is performed to increase the disturbance intensity, and the axial force is loaded to the second target value at the set loading rate. After the axial force reaches the second target value, it is immediately unloaded to the initial value at the same rate, and the second disturbance ends; ⑤ Repeat operations ③ and ④, gradually increasing the disturbance intensity until the specimen exhibits accelerated creep or unstable failure.

6. The coal rock creep disturbance test method according to claim 1, characterized in that: Conduct repeated perturbation tests, including the following: ① Initial creep: first apply axial force to the specimen to the initial creep stress level and keep it constant, and wait for the creep deformation of the specimen to stabilize; ② The first disturbance: According to the test plan, the first disturbance is applied, and the axial force is loaded to the first target value at the set loading rate. After the axial force reaches the first target value, it is immediately unloaded to the initial value at the same rate. The first disturbance ends and the strain of the specimen during the disturbance process is recorded; ③ Post-disturbance creep: After the disturbance, the specimen creeps under the initial creep conditions until the specimen undergoes stable creep. The strain of the specimen in the creep stage is recorded, and the creep rate in the stable creep stage is calculated accordingly. ④ If the specimen undergoes stable creep, a second disturbance is performed with the same disturbance parameters as in step ②; ⑤ Repeat operations ③ and ④ until the specimen experiences the target number of disturbances, and observe whether the specimen is damaged during the target number of disturbances; ⑥ If the specimen is damaged during the target number of disturbances, the test is terminated; if the specimen is not damaged during the target number of disturbances, the creep stress level is increased step by step and the specimen enters the steady-state creep stage, and operations ② to ⑤ are repeated until the specimen exhibits accelerated creep or unstable damage.

7. The coal rock creep disturbance test method according to claim 1, characterized in that: Creep perturbation test data processing and analysis include the following: The stress, axial and radial deformation of the specimen are collected by the data acquisition system of the testing machine. The data acquisition system of the testing machine records the stress and deformation data of the whole process of graded loading creep and dynamic load disturbance test. After the test, the strain data during each disturbance is sorted and extracted, and combined with the axial stress value, the strain of the specimen before the disturbance, the strain peak during the disturbance and the strain data after the disturbance are recorded respectively; The disturbance effect of the specimen is characterized from the following two aspects: 1) Disturbance instantaneous strain When a disturbance is applied to a specimen in a stable creep state, the instantaneous strain of the specimen increases suddenly. The instantaneous increment of the specimen strain during the disturbance is defined as the disturbance instantaneous strain, which is the difference between the peak disturbance strain and the strain before the disturbance. 2) Disturbance residual strain When a disturbance is applied to a specimen in a stable creep state, the instantaneous strain of the specimen increases suddenly. As the disturbance stops, the strain of the specimen recovers to a certain extent. The strain difference of the specimen before and after the disturbance is defined as the disturbance residual strain, which is the difference between the strain after the disturbance and the strain before the disturbance. By arranging the above data, the instantaneous strain and residual strain of the specimen during each disturbance are plotted as a function of the disturbance intensity / number of disturbances, and the strain and damage characteristics of the specimen under different disturbance parameter conditions are further analyzed.

8. The coal rock creep disturbance test method according to claim 7, characterized in that: 1) Disturbance tests with different disturbance intensities According to the disturbance effect of the specimen, the critical disturbance intensity of the specimen under different creep stress conditions is determined. When the disturbance intensity is lower than the critical intensity, the specimen is insensitive to the disturbance, and the specimen is mainly elastically deformed during the disturbance loading stage, and the elastic deformation can be largely recovered during the disturbance unloading process. When the disturbance intensity is higher than the critical intensity, the specimen is more sensitive to the disturbance, and the specimen produces more irreversible plastic deformation during the disturbance loading process. The damage effect of the specimen is significant during the disturbance process, and with the increase of the disturbance intensity, the disturbance residual strain of the specimen increases. 2) Repeated perturbation test According to the disturbance effect of the specimen, the creep stress threshold at which the specimen undergoes instability failure under repeated disturbance, that is, the destructive creep stress level, is determined. When the creep stress level is lower than the stress threshold, the cumulative damage of the specimen under repeated disturbance increases and tends to stabilize, and the specimen remains stable; when the creep stress level exceeds the stress threshold, the cumulative damage of the specimen under repeated disturbance develops rapidly, leading to instability failure of the specimen.

9. The coal rock creep disturbance test method according to claim 1, characterized in that: The method for determining the specimen strength limit neighborhood includes the following: The sources of stress on the specimen during the test include: creep stress level and stress applied by disturbance action; Depending on whether the specimen is disturbed or not, the relationship between the stress state of the specimen during the test and its stability can be expressed as: (1) The specimen is unstable and damaged during the disturbance process. The stress state of the specimen is within the strength limit neighborhood of the specimen, and its stress state satisfies: specimen stress > strength limit neighborhood threshold stress > disturbance damage strength; (2) If the specimen does not suffer from instability failure after the disturbance, and the stress state of the specimen is outside the strength limit neighborhood of the specimen, then its stress state satisfies: specimen stress < strength limit neighborhood threshold stress < disturbance failure strength.

10. The coal rock creep disturbance test method according to claim 9, characterized in that: 1) Disturbance tests with different disturbance intensities Under the condition of a single disturbance test, the disturbance residual strain of the specimen under different creep stress levels and disturbance parameters is mainly analyzed, and the sum of the critical disturbance strength and the creep stress level is taken as the strength limit neighborhood threshold stress of the specimen under the creep stress level and disturbance action; 2) Repeated perturbation test Under repeated disturbance test conditions, the specimen will only fail when it reaches the creep stress level and is subjected to repeated disturbance. The threshold stress of the strength limit neighborhood of the specimen under repeated disturbance is determined based on the threshold of the creep stress level at which the specimen fails.

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