Accurate fidelity testing method for three-resistance strength parameters of coal rock before heat injection and anti-reflection

Abstract

The invention belongs to the field of coal seam coal rock mechanical property testing, and particularly relates to an accurate fidelity testing method for three-resistance strength parameters of coal rock before heat injection and permeability increase. Comprising the following steps: S1, sample preparation; s2, testing equipment configuration; s3, environment control; testing in the testing cover, setting the temperature and humidity in the testing cover to be consistent with the original sample environment, setting the temperature fluctuation range to be less than or equal to + / -1 DEG C, and maintaining parameter stability through an automatic adjusting system; s4, testing compressive strength; loading at a constant speed of 0.5 MPa / s, recording a failure load and calculating compressive strength c = Fc / A; s5, tensile strength testing; stretching at the speed of 1MPa / s, recording the fracture load and calculating the tensile strength r = 2Fr / piDt; s6, testing the shear strength; loading shear force at a constant speed, recording a failure load and calculating shear strength; S7, analyzing data; and after abnormal values are removed, generating a strength parameter curve, and comparing mechanical property data in different stress states. The accurate fidelity testing method for the three-resistance strength parameters of the coal rock before coal seam heat injection and permeability increase has the advantages of being easy and convenient to operate, rapid in testing, accurate in data and the like.

Description

Technical Field

[0001] The invention belongs to the field of coal seam coal rock mechanical property testing, and specifically is a method for accurately and faithfully testing the three-resistance strength parameters of coal rock before heat injection and permeability enhancement. Background Art

[0002] In modern mining, with the increase of mining depth and the development of technology, coal mining faces more and more complex geological environment and rock mechanical conditions. Especially for coal seam heat injection permeability enhancement technology, its successful implementation is closely related to the accurate determination of coal rock mechanical parameters. As the main carrier in the mining process, the mechanical properties of coal rock are directly related to the safety, production efficiency and economic benefits of coal mines. Therefore, the determination and research of coal rock mechanical parameters have important practical significance and theoretical value.

[0003] Coal rock is a complex multiphase material, mainly composed of organic and inorganic matter, and its internal structure has significant heterogeneity and anisotropy. The physical and mechanical properties of coal rock are affected by many factors, including the origin of coal, sedimentary environment, geological history and moisture content. Heat injection can heat the coal seam to increase its temperature, thereby reducing the stress and cohesion of the coal seam, promoting the formation or expansion of microcracks in the coal seam, and enhancing the permeability of the coal seam, which will help to release coalbed methane faster and improve mining efficiency. There are also certain risks in the coal seam heat injection permeability enhancement operation, such as gas outburst and coal rock collapse. By measuring the mechanical parameters of coal rock, these risks can be evaluated and controlled to ensure the safety of the operation. Therefore, before implementing heat injection permeability enhancement, the impact on the surrounding environment must be considered. Accurate mechanical parameters can help predict and evaluate the impact of heat injection measures on coal seams, so as to take corresponding protective measures.

[0004] The determination of coal rock mechanical parameters is mainly to obtain the mechanical properties of coal seams and surrounding rocks during the process of heat injection and permeability enhancement. These parameters include compressive strength, tensile strength, and shear strength. By determining these parameters, a scientific basis can be provided for the design, implementation, and safety assessment of heat injection and permeability enhancement in coal seams.

[0005] At present, the determination of mechanical parameters of coal and rock mainly relies on traditional testing methods. These methods usually require destructive testing of coal and rock samples to obtain data, which has some obvious limitations: Insufficient test accuracy: Due to the heterogeneity of coal and rock materials, a single test method is often difficult to fully reflect their mechanical properties. Each test is conducted on a different device. Over time, the physical properties of coal and rock will change, and the parameters cannot be maintained as the monitoring environment changes.

[0006] Complex operation: The operation steps of traditional testing methods are cumbersome, with high requirements for the professional skills of testers, which are prone to human errors. For example, if the preparation and installation process of the test specimen is not rigorous, it may affect the test results.

[0007] Long time consumption: Each test needs to be carried out independently, and the overall test cycle is long, which affects the accuracy of test data.

[0008] Therefore, there is an urgent need for a new testing method that can not only improve the testing accuracy, but also effectively shorten the testing time and improve work efficiency. Summary of the Invention

[0009] The purpose of the present invention is to integrate multiple testing technologies, aiming to improve the accuracy and efficiency of testing, reduce human errors, and provide a scientific basis for coal mine safety management and resource development, and provide a precise and faithful testing method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement.

[0010] The present invention adopts the following technical solutions: A precise and faithful testing method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement, including: S1: Sample preparation Select coal and rock samples from the coal seam. The drilling of the samples meets the requirements of diameter D≥50mm, total length t≥50cm for each layer, and single-section length of broken samples≥100mm; clean and smooth the surface of the samples; S2: Configuration of testing equipment Adopt a multifunctional rock mechanics testing instrument integrating tensile, compressive, and shear testing devices, equipped with high-precision sensors, high-speed cameras, and an automated control system, and operate inside a transparent testing cover; S3: Environmental control Conduct tests inside the testing cover, set the temperature and humidity inside the testing cover to be the same as the original environment of the sample, with a temperature fluctuation range≤±1°C, and maintain the parameters stable through an automatic adjustment system; S4: Compressive strength test Load at a constant speed of 0.5MPa / s, record the failure load and calculate the compressive strength c = Fc / A; Among them, c is the compressive strength, MPa; F c is the failure load, N; A is the cross-sectional area of the sample, mm 2 ; S5: Tensile strength test Stretch at a rate of 1MPa / s, record the fracture load and calculate the tensile strength r = 2Fr / πDt; Among them, r is the tensile strength, MPa; F r is the fracture load, N; D is the diameter of the test piece, mm; t is the height of the test piece, mm; S6: Shear strength test Apply a constant shear force at a constant speed, record the failure load, and calculate the shear strength: Where: τ is the shear stress, MPa; σ is the normal stress, MPa; F p is the failure load of the specimen, N; A is the shear cross-sectional area of the specimen, mm 2 ; f is the friction coefficient of the balls under the lower plate of the testing machine, which can be determined by the friction correction test; α is the angle between the shear plane and the horizontal plane, °; S7: Data analysis Generate the strength parameter curve after removing the outliers, and compare the mechanical property data under different stress states.

[0011] In some embodiments, when preparing the sample in S1, it is necessary to ensure that the cutting size is adapted to the testing device, and mechanical grinding is used for surface treatment to eliminate the stress concentration area.

[0012] In some embodiments, the spatial arrangement order of the testing device in S2 is: tensile testing device → compressive testing device → shear testing device, and a high-speed camera is arranged outside the testing cover to monitor the crack propagation.

[0013] In some embodiments, the temperature and humidity control accuracy in S3 is: temperature deviation ±0.5°C, humidity deviation ±3%RH.

[0014] In some embodiments, when calculating each strength in S4 - S6, the measurement of the shear plane angle α is corrected in real time by a laser angle gauge, and the friction coefficient f is determined through a pre-experiment friction correction test.

[0015] In some embodiments, the Grubbs criterion is used to remove outliers in S7, and the significance level is set to 0.05.

[0016] In some embodiments, after mechanical grinding, surface roughness detection needs to be carried out, and the Ra value is controlled within the range of 0.8 - 1.6 μm.

[0017] In some embodiments, the frame rate of the high-speed camera is not less than 1000 fps, and it is used in conjunction with the DIC digital image correlation system for full-field strain analysis.

[0018] Compared with the prior art, the present invention has the following beneficial effects: Improve the test accuracy: The multifunctional testing equipment can reduce the errors between different testing methods and improve the reliability of the overall test. Through precise environmental control and real-time monitoring, the accuracy of the test data is improved.

[0019] Shorten the test time: Adopt a standardized test process to make the test results more comparable. Completing the tests of three strength parameters at one time greatly shortens the time of traditional test methods and improves work efficiency.

[0020] Reduce human error: Automatic control and data recording reduce the influence of human operation and ensure the accuracy of test data. Combining statistical analysis methods ensures the reliability of coal and rock mechanical property parameters.

[0021] The accurate and faithful test method for three anti-strength parameters of coal and rock before heat injection and permeability enhancement provided by the present invention has the advantages of simple operation, rapid testing, accurate data, etc., and is applicable to the mechanical property testing of coal mines and related research institutions, providing important technical support for coal mine safety production. With the improvement of the requirements for safety and efficiency in the coal industry, this method has broad application prospects and market value. Brief Description of the Drawings

[0022] Figure 1 It is a schematic diagram of the sample structure; Figure 2 It is a schematic diagram of the test device structure; Figure 3 It is a schematic diagram of the structure after the test cover is installed; In the figure, 1 - sample, 2 - tensile test device, 3 - compressive test device, 4 - shear test device, 5 - sensor, 6 - high-speed camera, 7 - data acquisition system, 8 - test cover, 9 - temperature and humidity sensor, 10 - temperature and humidity regulator. Detailed Embodiments

[0023] To make the purposes, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention; based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] S1: Sample Preparation The selection and preparation of Sample 1 are important factors affecting the test results. In this step, the following standards are followed for operation: Sample source: Select representative coal and rock samples from the coal seam to ensure that the samples can reflect the actual situation within the range of heat injection and permeability enhancement. Samples should be collected from different positions and depths to obtain more comprehensive mechanical properties.

[0025] According to the test requirements, a standardized tool is used to cut the samples to meet the specifications of different tests. The diameter D of the drilled coal and rock core is required to be not less than 50 mm, and the total length t of the coal and rock core drilled in each layer is not less than 50 cm (to facilitate the production of sufficient standard rock specimens). The coal and rock cores in each layer should be kept as continuous as possible without breakage. If breakage occurs, the length of each small section should be ensured to be not less than 100 mm. The surface of the sample is cleaned to remove dust and impurities.

[0026] Surface treatment: After the sample is cut, surface treatment is required to ensure that its surface is smooth and free of cracks. This step can be achieved through mechanical grinding or chemical treatment. The purpose is to eliminate the stress concentration areas on the sample surface and reduce the errors occurring during the test.

[0027] S2: Testing equipment The selected testing equipment directly affects the accuracy and efficiency of the test. This invention uses a multi-functional rock mechanics testing instrument, which has the following functions: Comprehensive testing function: Through a multi-functional test bench, the instrument has a tensile testing device 2, a compressive testing device 3, and a shear testing device 4 from left to right, and can simultaneously measure the compressive, tensile, and shear strengths, avoiding the errors and time losses caused by multiple devices.

[0028] High-precision sensors: Equipped with high-precision sensors 5, a high-speed camera 6, and a data acquisition system 7, it can record stress and deformation data in real time to ensure the accuracy of the data.

[0029] Automation control: It has an automation control function, can automatically adjust the loading rate according to the set test parameters, improve the stability and repeatability of the test; automatically control the temperature and humidity in the test hood 8 to ensure that the environmental parameters remain unchanged and reduce the errors caused by the test environment.

[0030] S3: Environmental control The test is carried out in a dedicated test hood 8 to ensure that environmental factors such as the experimental temperature and humidity are in a stable state. At the same time, all specimens are placed in the test hood to ensure their physical properties are consistent and avoid errors.

[0031] A temperature and humidity sensor 9 is used to monitor the test environment in real time, and the test environment is automatically adjusted through a temperature and humidity regulator 10 to ensure that the sample maintains its original physical state during the test (for example, the temperature of the raw coal and rock sample is 10 °C, and the temperature in the experimental hood is maintained at 9 - 11 °C).

[0032] S4: Compressive strength test The compressive strength test is an important part of the coal and rock strength test. The specific steps are as follows: Sample placement: Place the processed sample in the compressive testing machine to ensure good contact between the sample and the test device, and avoid errors caused by poor contact.

[0033] Loading process: Apply pressure gradually. It is recommended to use constant-speed loading, usually controlled at 0.5 MPa / s, to avoid sudden failure of the sample due to too fast loading rate.

[0034] Data recording: Record the deformation of the sample and the applied load in real time until the sample fails. The maximum load at failure is the compressive strength, which is calculated by the following formula: c = F c / A where c is the compressive strength, MPa; F c is the failure load, N; A is the cross-sectional area of the sample, mm 2 .

[0035] S5: Tensile strength test The test method for tensile strength is relatively complex, and the specific steps are as follows: Sample installation: Install the sample on the tensile testing machine to ensure that there is no lateral displacement of the sample during the loading process.

[0036] Loading rate: Set an appropriate loading rate, usually controlled at 1 MPa / s, and increase the tensile force gradually to ensure that the sample can be evenly stressed before failure.

[0037] Failure record: Record the load at which the sample breaks, and calculate the tensile strength using the following formula: r = 2F r / πDt where r is the tensile strength, MPa; F r is the fracture load, N; D is the diameter of the specimen, mm; t is the height of the specimen, mm.

[0038] S6: Shear strength test The implementation steps of the shear strength test are as follows: Sample installation: Place the sample in the shear testing machine to ensure that the upper and lower clamps of the sample are fixed well.

[0039] Apply shear force: Apply shear force gradually. Usually use constant-speed loading to ensure that the sample is evenly stressed and avoid local stress concentration.

[0040] Data recording: Record the shear force at failure, and the shear strength is calculated by the following formula: In the formula: τ is the shear stress, MPa; σ is the normal stress, MPa; F p is the failure load of the specimen, N;A is the shear cross-sectional area of the specimen, in mm 2 ; f is the friction coefficient of the balls under the lower plate of the testing machine, which can be determined by the friction correction test; α is the angle formed by the shear plane and the horizontal plane, in °.

[0041] S7: Data analysis Data analysis is a crucial part of the entire testing process, mainly including the following steps: Data processing: Use data processing software to analyze the test results, including removing outliers, calculating the mean and standard deviation, etc., to ensure the scientific nature of the test results.

[0042] Strength parameter curve plotting: Plot the test results into strength parameter curves to facilitate visual comparison of the mechanical properties of different coal and rock samples.

[0043] Result evaluation: Compare the test results under different conditions, analyze the performance of coal and rock under different stress states, and provide a theoretical basis for the design of subsequent coal seam heat injection and permeability enhancement measures.

[0044] 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 them; 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 described 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 of the technical solutions of the embodiments of the present invention.

Claims

1. A precise and faithful testing method for the three anti-strength parameters of coal and rock before heat injection for permeability enhancement, characterized in that, Including: S1: Sample Preparation Select coal seam coal and rock samples. The drilled samples should meet the requirements that the diameter D≥50mm, the total length t of each layer≥50cm, and the length of each broken sample≥100mm. Clean and smooth the surface of the samples; S2: Test Equipment Configuration Use a multifunctional rock mechanics tester integrated with tensile, compressive, and shear test devices, equipped with high-precision sensors, high-speed cameras, and an automated control system, and operate inside a transparent test chamber; S3: Environmental Control Conduct tests inside the test chamber. Set the temperature and humidity inside the test chamber to be the same as the original environment of the samples, with the temperature fluctuation range≤±1°C, and maintain the parameters stable through an automatic adjustment system; S4: Compressive Strength Test Load at a constant speed of 0.5MPa / s, record the failure load, and calculate the compressive strength c = Fc / A; Among them, c is the compressive strength, MPa; F c is the failure load, N; A is the cross-sectional area of the sample, mm 2 ; S5: Tensile Strength Test Stretch at a rate of 1MPa / s, record the fracture load, and calculate the tensile strength r = 2Fr / πDt; Among them, r is the tensile strength, MPa; F r is the fracture load, N; D is the specimen diameter, mm; t is the specimen height, mm; S6: Shear Strength Test Load the shear force at a constant speed, record the failure load, and calculate the shear strength: In the formula: τ is the shear stress, MPa; σ is the normal stress, MPa; F p is the failure load of the specimen, N; A is the shear cross-sectional area of the specimen, mm 2 ; f is the friction coefficient of the ball under the lower plate of the testing machine, which can be determined by the friction correction test; α is the angle formed by the shear plane and the horizontal plane, °; S7: Data Analysis Generate strength parameter curves after removing outliers, and compare the mechanical property data under different stress states.

2. The accurate and faithful testing method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement according to claim 1, characterized in that, During sample preparation in S1, it is necessary to ensure that the cutting size matches the test device, and mechanical grinding is used for surface treatment to eliminate stress concentration areas.

3. The accurate and faithful testing method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement according to claim 1, characterized in that In S2, the spatial arrangement order of the test device is: tensile test device→compressive test device→shear test device, and the high-speed camera is set outside the test chamber to monitor crack propagation.

4. The accurate and faithful testing method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement according to claim 1, characterized in that, In S3, the temperature and humidity control accuracy is: temperature deviation±0.5°C, humidity deviation±3%RH.

5. The accurate and faithful testing method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement according to claim 1, characterized in that When calculating each strength in S4 - S6, the measurement of the shear plane angle α is corrected in real time using a laser angle gauge, and the friction coefficient f is determined through a pre-experiment friction correction test.

6. The accurate and faithful test method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement according to claim 1, characterized in that, In S7, the Grubbs criterion is used to remove outliers, and the significance level is set to 0.

05.

7. The accurate and faithful test method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement according to claim 2, characterized in that After the mechanical grinding, surface roughness detection is required, and the Ra value is controlled within the range of 0.8 - 1.6μm.

8. The accurate and faithful testing method for the three anti-strength parameters of coal and rock before heat injection and permeability enhancement according to claim 1, characterized in that, The frame rate of the high-speed camera is not less than 1000fps, and it is used in conjunction with the DIC digital image correlation system for full-field strain analysis.

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