Method and device for testing uniaxial compression relaxation stress threshold value of rock-like material

Abstract

The invention relates to a rock material mechanical property testing technology, in particular to a rock-like material uniaxial compression relaxation stress threshold value testing method and device, which adopts a multi-stage stress loading and single sample continuous testing mode, and adopts fixed short-time observation in combination with an objectively determined stress relaxation rate threshold value criterion to test the rock-like material uniaxial compression relaxation stress threshold value. The rock-like material uniaxial compression relaxation stress threshold value is rapidly and accurately measured, the test period of a traditional complete relaxation curve measuring method is remarkably shortened, and meanwhile the reliability and repeatability of a test result are kept.

Description

Technical Field

[0001] This invention relates to rock material mechanical property testing technology, and more particularly to a method and apparatus for testing the uniaxial compression relaxation stress threshold of rock-like materials. Background Technology

[0002] Stress relaxation is the phenomenon that the internal stress of a material gradually decreases over time while maintaining a constant total strain. This phenomenon has significant engineering implications in rock engineering, directly affecting the long-term stability assessment of engineering structures. Accurately determining the relaxation stress threshold of rock-like materials is crucial for applications such as support structures, long-term stable underground caverns, and underground energy storage in rock engineering.

[0003] This threshold represents the critical stress level at which a material does not undergo significant stress relaxation under long-term loading, and is a parameter for assessing the long-term stability of an engineering project. In tunnel support engineering, if the stress borne by the support structure exceeds the relaxation stress threshold of the rock material, the support effect will gradually decrease over time, potentially leading to structural instability. In underground energy storage facilities, the stress relaxation characteristics of the surrounding rock are directly related to the long-term sealing and safety of the storage chamber.

[0004] Currently, the relaxation performance of rock-like materials is mostly tested using a complete relaxation curve determination method, which involves long-term testing under different constant strains to obtain a complete stress-time curve. However, this existing method has the following drawbacks: (1) The test cycle is extremely long, and the test cycle for a single sample may last for months or even years, which seriously affects the progress of the project; (2) It is inefficient and time-consuming, which cannot meet the needs of rapid evaluation and is difficult to adapt to the fast-paced requirements of modern engineering construction; (3) It is costly, occupying expensive test equipment for a long time, resulting in high operating costs and increasing project investment; (4) It has poor engineering applicability, making it difficult to meet the needs of rapid material screening and evaluation in engineering design and scientific research, thus limiting its widespread application in practical engineering.

[0005] In summary, the existing technology suffers from the lack of a rapid, accurate, and cost-effective method for testing the uniaxial compressive relaxation stress threshold of rock-like materials. Summary of the Invention

[0006] This invention provides a method for testing the uniaxial compressive relaxation stress threshold of rock-like materials, which can quickly and accurately determine the uniaxial compressive relaxation stress threshold of rock-like materials, significantly shorten the testing cycle, reduce testing costs, and solve the technical problems of long test cycles, low efficiency, and high costs in the prior art.

[0007] Firstly, this invention provides a method for testing the uniaxial compressive relaxation stress threshold of rock-like materials. Based on the principles of multi-level stress loading and continuous testing of a single specimen, the method establishes a test starting point through setting an initial nominal stress and conducting a relaxation test. The initial nominal stress is set to 0.5-0.6 times the uniaxial compressive strength of the rock-like material. An axial strain control mode is used to load at a specific strain rate and maintain constant strain for a preset time during the relaxation test. The stress level is adjusted downwards through high-stress relaxation judgment and load reduction / sample replacement. When the measured stress relaxation rate exceeds a set threshold, significant relaxation is determined, the nominal stress is reduced, and a new specimen is used for retesting. Similarly, the stress level is adjusted upwards through low-stress relaxation judgment and load increase. When the stress relaxation rate does not exceed the threshold, the nominal stress is gradually increased on the same specimen until significant relaxation occurs. The final nominal stress that meets the conditions is determined as the material's relaxation stress threshold. As described above, this invention achieves rapid approximation and accurate determination of the relaxation stress threshold of rock-like materials by innovatively adjusting the stress upward and changing the stress downward, combined with fixed short-term observation and stress relaxation rate threshold criterion. Compared with the traditional complete relaxation curve method, it shortens the test cycle from several months / years to tens of hours, while maintaining high accuracy and high reliability.

[0008] Preferably, the specific implementation process of the initial nominal stress setting and relaxation test steps includes obtaining the uniaxial compressive strength of the rock-like material through a uniaxial compression test according to GB / T 50266 standard, mounting the specimen on a rock uniaxial compression stress relaxation testing machine, applying the strain to the initial nominal stress at a specified strain rate using an axial strain control mode, maintaining the specimen strain constant, and ensuring that the allowable strain deviation is ±2% of the applied strain value. In summary, by performing specimen preparation and strength testing according to national standards, this invention ensures the accuracy and reliability of the basic data, and the use of the axial strain control mode ensures precise control of the loading process.

[0009] Preferably, the stress relaxation measurement process establishes a complete data acquisition and processing system. By recording the initial axial stress value and the remaining axial stress value after relaxation stabilization within a preset time period, the difference between the two is calculated to obtain the stress relaxation amount. Then, the stress relaxation rate is calculated and compared with a threshold for judgment. In summary, this invention, by establishing a standardized data measurement and calculation process, ensures the accuracy and consistency of relaxation measurement, providing a data foundation for comparison between different samples and different materials.

[0010] Preferably, the preset time T is set to be no less than 6 hours. This time parameter is determined based on the statistical analysis of a large amount of rock material relaxation test data and the summary of engineering practice experience. As described above, by setting a fixed and relatively short observation time, this invention significantly shortens the single test cycle while ensuring the relaxation phenomenon is fully manifested. Compared with the traditional method's observation period of at least several months, this invention significantly improves testing efficiency.

[0011] Preferably, the stress relaxation rate threshold K is determined through a preparatory relaxation test, and the K value is calculated by using 0.3R... c 0.5R c 0.7R c Stress relaxation rates η1, η2, and η3 were obtained by conducting 3-hour preparatory relaxation tests at three stress levels. Based on statistical analysis of a large amount of experimental data, for most types of rock materials, a short-term observation of 3 hours is sufficient to effectively reflect their relaxation trend at that stress level. The η1, η2, and η3 were calculated using the formula K = max(η1, η2, η3) + 0.2%. This 0.2% safety margin is an empirical value set based on a large amount of comparative experimental data to balance the safety and accuracy of the test. In summary, this invention solves the problem of objectivity and repeatability in threshold determination by establishing a K-value calculation method based on quantifiable indicators, ensuring that different technicians can obtain consistent K values ​​for the same material.

[0012] Preferably, the method includes an approximate threshold determination mechanism. When the stress level increases to 0.8-0.9 times the uniaxial compressive strength but still does not reach the stress relaxation rate threshold, the test is stopped and the nominal stress at that time is recorded as the approximate threshold. In summary, this invention, by setting a reasonable upper limit for testing and an approximate threshold mechanism, avoids sample damage caused by overloading, while providing an effective threshold determination scheme for high-strength materials.

[0013] Preferably, the rock-like material sample adopts standardized geometric specifications, specifically a φ50×100 cylindrical standard sample. Controlled geometric tolerances include allowable deviations of height and diameter of ±3mm, allowable deviations of unevenness at both end faces of ±0.05mm, and allowable deviations of end face perpendicularity of ±0.25°. In summary, by establishing standardized sample geometry, this invention eliminates the influence of sample geometry on test results, improving the reproducibility and comparability of the test results.

[0014] Preferably, the test equipment configuration reflects the technical characteristics of system integration, including a rock uniaxial compressive stress relaxation testing machine, a deformation measurement device, and a data acquisition system. The testing accuracy of the equipment meets the requirements of GB / T 50266 standard. In summary, this invention ensures the accuracy and reliability of the testing process by establishing complete equipment technical specifications.

[0015] Secondly, the present invention provides a uniaxial compression relaxation stress threshold testing device for rock-like materials, including a rock uniaxial compression stress relaxation testing machine, a deformation measuring device, a data acquisition system, a control module, and a calculation module.

[0016] The above-mentioned beneficial effects of the present invention are as follows: through innovative multi-level stress loading and continuous testing of a single specimen, the testing efficiency is improved, shortening the testing cycle of traditional methods from several months / years to tens of hours; By applying stress upwards and changing the sample branch loading downwards, the sample consumption is minimized while ensuring test accuracy, thus reducing test costs. By combining fixed short-term observations with stress relaxation rate threshold criteria, a standardized judgment system was established, which improved the comparability and engineering applicability of test results between different materials.

[0017] The core inventive aspect of this invention lies in its breakthrough overcoming the technical bottleneck of traditional relaxation tests requiring complete time history curves. It proposes a rapid approximation method based on a stress relaxation rate threshold, achieving a shift from trading time for accuracy to trading intelligence for efficiency. The upward adjustment of the same sample and the downward adjustment of the same sample effectively solve the problem of the influence of historical stress on the specimen, ensuring the reliability of the test results. Based on a quantifiable K-value determination method, it solves the problems of objectivity and repeatability of core judgment parameters, achieving complete standardization of the test method and demonstrating high engineering applicability. Attached Figure Description

[0018] Figure 1 A schematic flowchart of the uniaxial compression relaxation stress threshold test method for rock-like materials provided by the present invention.

[0019] Figure 2 An experimental diagram showing the change of relaxation stress over time, provided by this invention.

[0020] Figure 3 This is a schematic diagram of the framework of the testing device system provided by the present invention. Detailed Implementation

[0021] The following description and accompanying drawings fully illustrate specific embodiments of the invention to enable those skilled in the art to practice them. The embodiments represent only possible variations. Individual components and functions are optional unless explicitly required, and the order of operation may vary. Parts and features of some embodiments may be included in or replace parts and features of other embodiments. The scope of embodiments of the invention encompasses the entire scope of the claims and all available equivalents thereof. Throughout this document, each embodiment may be referred to individually or collectively with the term "invention," which is merely for convenience and, if more than one invention is disclosed, is not intended to automatically limit the scope of application to any single invention or inventive concept. Relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, without requiring or implying any actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed. The various embodiments in this document are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the structures, products, etc., disclosed in the embodiments, since they correspond to the disclosed parts, the descriptions are relatively simple; relevant details can be found in the method section.

[0022] Terminology Explanation Before describing the technical solution in detail, the terminology used in this invention will be explained first: Stress relaxation refers to the phenomenon that the internal stress of a material gradually decreases over time under the condition that the total strain remains constant. It is an important rheological property of rock materials and directly affects the long-term stability and safety of engineering structures.

[0023] Relaxation stress threshold: refers to the critical stress level at which a material does not experience significant stress relaxation under long-term loading. It is a parameter for assessing the long-term stability of rock engineering. When the working stress is below this threshold, the structure can maintain long-term stability.

[0024] Stress relaxation rate: refers to the ratio of the stress relaxation amount of a material to the initial stress within a fixed observation period, expressed as a percentage. It is a standard indicator for quantitatively evaluating the degree of relaxation and provides a scientific basis for establishing the judgment criteria in this invention.

[0025] Stress relaxation rate threshold K: refers to the critical stress relaxation rate value for judging whether a material has undergone significant relaxation. It is the core judgment parameter of the test method of this invention. It is objectively determined through preliminary experiments and calculation formulas to ensure the repeatability and reliability of the test results.

[0026] Nominal stress: refers to the preset stress level applied to the specimen during the test. It is a benchmark parameter for controlling the test process and judging the degree of relaxation. The threshold can be accurately approximated by adjusting the nominal stress step by step.

[0027] Axial strain control mode: refers to the method of indirectly controlling the stress loading by precisely controlling the axial deformation of the specimen, which can achieve constant strain and is a technical means to realize stress relaxation test.

[0028] Multi-stage stress loading: refers to a loading strategy that applies different stress levels to the same specimen step by step according to a preset step size. It is one of the innovative points of this invention to improve testing efficiency.

[0029] Preliminary relaxation test: refers to a short-term relaxation test conducted before the formal test. It is used to determine the objective value of the stress relaxation rate threshold K and is a technical step to ensure the standardization and repeatability of the test method.

[0030] The core innovation of this invention lies in establishing an objective and operable method for determining the stress relaxation rate threshold K, which solves the problem of inconsistent test results caused by subjective judgment in traditional methods. Specifically, it includes: The relaxation characteristic parameters of the material were obtained through preliminary relaxation tests. Short-time relaxation tests were conducted at three representative stress levels: 0.3R... c 0.5R c 0.7R c At each stress level, strain was kept constant for 3 hours, and the corresponding stress relaxation rates η1, η2, and η3 were measured. The 3-hour observation period was based on statistical analysis of extensive experimental data. For most types of rock materials, a short observation period of 3 hours is sufficient to effectively reflect the relaxation trend at that stress level, ensuring the full manifestation of the relaxation phenomenon while significantly shortening the experimental cycle. The threshold K was calculated using the formula K=max(η1,η2,η3)+0.2%. This formula physically means that the maximum stress relaxation rate of the material at different stress levels is used as a benchmark, with a safety margin of 0.2% added as the judgment threshold. This 0.2% safety margin is an empirical value set based on extensive comparative experimental data, through statistical analysis of the variability in relaxation behavior of different types of rock materials, to balance the safety and accuracy of the test, ensuring both the scientific validity of the threshold and the safety of the test. This method allows different technicians to obtain completely consistent K values ​​for the same material, solving the problem of subjectivity in parameter determination.

[0031] This invention provides a method for testing the uniaxial compressive relaxation stress threshold of rock-like materials. For example... Figure 1 As shown, Figure 1This is a flowchart illustrating the uniaxial compression relaxation stress threshold test method for rock-like materials provided by the present invention. The method provided by the present invention can be executed by a rock material testing device, which can be implemented through software and / or hardware. The method includes the following steps: Step 101: Initial Nominal Stress Setting and Relaxation Test This step is used to establish a benchmark reference point. First, the uniaxial compressive strength R of the rock-like material is obtained through a uniaxial compression test according to the current national standard "Standard for Testing Methods of Engineering Rock Mass" GB / T 50266. c A preliminary relaxation test was conducted according to the aforementioned method to determine the stress relaxation rate threshold K. The prepared rock-like material specimen was then mounted on a uniaxial compression stress relaxation testing machine, ensuring good contact and alignment between the specimen and the loading system.

[0032] The initial nominal stress σ1 is set to the uniaxial compressive strength R. c The initial stress is 0.5-0.6 times that of the standard strain. This ratio is based on a large amount of experimental statistical data. It can avoid the problem of insufficient relaxation due to excessively low initial stress, while also preventing premature failure of the specimen due to excessively high initial stress. An axial strain control mode is adopted, with a strain of (1-5)×10⁻⁶. -5 A strain rate of / s is precisely applied to the initial nominal stress σ1. This strain rate ensures the stability and controllability of the loading process. Immediately after loading, the specimen strain is kept constant, with the allowable strain deviation controlled within ±2% of the applied strain value. A relaxation test is performed for a preset time T, during which stress changes are continuously monitored, and complete stress-time data are recorded. The technical advantage of this step is that it establishes a standardized testing starting point, providing basic data for subsequent judgment and adjustment.

[0033] Step 102: High Stress Relaxation Judgment and Load Reduction Sample Replacement This step identifies and handles significant relaxation conditions. After a preset time T, the system automatically calculates the stress relaxation amount Δσ, which is the difference between the initial axial stress value at this strain level and the remaining axial stress value after relaxation stabilization. The stress relaxation rate Δσ / σ1 is calculated and compared with the stress relaxation rate threshold K determined through preliminary tests. When Δσ / σ1 > K, the system determines that the material has undergone significant relaxation at this stress level, indicating that the current stress level exceeds the material's relaxation stress threshold. At this point, a stress reduction strategy is implemented, reducing the nominal stress by 0.05-0.1 times the uniaxial compressive strength R. c The choice of this reduction range is based on the principles of materials mechanics and engineering practice experience. It can ensure effective stress adjustment while avoiding excessive adjustment range that would reduce the approximation efficiency.

[0034] A sample replacement procedure is performed, using a new sample that has not experienced a high stress history to avoid the influence of stress history on the test results. Based on the reduced nominal stress, a relaxation test is repeated for a preset time T. This judgment process is repeated until a stress level where no significant relaxation occurs is found. The innovation of this step lies in effectively eliminating the interference of stress history effects by replacing the sample under reduced stress, thus ensuring the accuracy of the test results.

[0035] Step 103, Low stress relaxation judgment is the same as with load increase. This step handles cases where relaxation is not significant, achieving an accurate approximation of the threshold.

[0036] When the stress relaxation rate Δσ / σ1 ≤ K, the system determines that the material does not relax significantly at this stress level, indicating that the current stress level is still below the material's relaxation stress threshold, and conditions are available to further increase the stress. A stress increase strategy is then implemented, increasing the nominal stress on the same specimen by an increment to the next level, with the increment being equal to the uniaxial compressive strength R. c 0.01-0.05 times. Continue to perform relaxation tests of the same duration T on the same sample to make full use of sample resources and improve testing efficiency.

[0037] The process is repeated cyclically, gradually increasing the stress level. After each increase, a complete relaxation observation and assessment are performed until the stress relaxation rate measured in a certain test exceeds an objectively determined threshold K, at which point the test is stopped. The innovation of this step lies in the fact that, similarly, by applying multiple levels of loading to the same specimen, specimen consumption is significantly reduced, and testing efficiency is improved.

[0038] Step 104: Threshold Determination This step ensures the precise determination of the final threshold. The nominal stress corresponding to the last time the stress relaxation rate condition (Δσ / σ1 ≤ K) is met before the test is stopped is taken as the uniaxial compressive relaxation stress threshold for this type of rock material. This determination method ensures that the obtained threshold does not undergo significant relaxation and is as close as possible to the material's true threshold. If the stress level has increased to 0.8-0.9 times the uniaxial compressive strength R during the test, this step is not recommended. c If the stopping condition Δσ / σ1>K is not met, the test is stopped and the nominal stress at this time is recorded as an approximate threshold to avoid specimen failure due to overloading.

[0039] Finally, the system automatically generates a complete test report, including threshold results, test process data, and test condition records.

[0040] Example: like Figure 2 As shown below, the technical solution of the present invention will be described in detail through a specific embodiment, focusing on the process of determining the stress relaxation rate threshold K.

[0041] A sandstone engineering project needs to assess the long-term stability of the surrounding rock, and the relaxation stress threshold test is performed using the method of this invention.

[0042] First, basic parameters were determined. The test material was sandstone samples taken from the engineering site, prepared into φ50×100 cylindrical standard specimens according to GB / T 50266 standard, with geometric tolerances controlled within the specified range. The test was conducted in a constant temperature and humidity laboratory, with the temperature controlled at 20±2℃ and the relative humidity at 60±5%. The uniaxial compressive strength R of the sandstone was measured through a uniaxial compression test. c =80MPa.

[0043] Next, a preliminary relaxation test is performed to determine the K value. At 0.3R... c A 3-hour relaxation test was conducted under a stress level of 24 MPa, and the stress relaxation rate η1 was measured to be 0.3%; at a stress level of 0.5R... c A 3-hour relaxation test was conducted under a stress level of 40 MPa, and the stress relaxation rate η2 was measured to be 0.6%; at a stress level of 0.7R... c A 3-hour relaxation test was conducted under a stress level of 56 MPa, and the stress relaxation rate η3 was measured to be 0.8%.

[0044] According to the formula K=max(η1,η2,η3)+0.2%=0.8%+0.2%=1.0%, the stress relaxation rate threshold K=1.0% is determined, where the safety margin of 0.2% is determined based on comparative test data.

[0045] Then, a relaxation stress threshold test was performed. The preset observation time was set to T = 6 hours. The initial nominal stress was set to σ1 = 0.55R. c =44MPa, using axial strain control mode with 2×10 -5 A strain rate of 44 MPa was applied, and then the strain was kept constant for 6 hours for relaxation observation. The test results showed that the stress relaxation amount Δσ = 0.35 MPa, and the stress relaxation rate was 0.8% < 1.0%, indicating that the relaxation was not significant.

[0046] On the same specimen, the nominal stress was increased to 45.6 MPa, and observations were continued for 6 hours, yielding a stress relaxation rate of 0.92% < 1.0%. This process was repeated, and when the stress was increased to 52.0 MPa, the measured stress relaxation rate was 1.31% > 1.0%, meeting the stopping condition. Therefore, the uniaxial compressive relaxation stress threshold for this sandstone was determined to be 50.4 MPa (the stress level that last met the condition before stopping). The entire testing process took only 36 hours.

[0047] like Figure 3As shown, the present invention also provides a device for testing the uniaxial compression relaxation stress threshold of rock-like materials, the device comprising: The uniaxial compression stress relaxation testing machine for rocks adopts a precision servo control system, which can realize the precise control of axial strain and real-time monitoring of stress. The equipment accuracy meets the requirements of GB / T 50266 standard, the maximum loading capacity is not less than 2000kN, and the strain control accuracy reaches ±0.1%, providing a hardware foundation for testing. The deformation measurement device, which uses a measurement system composed of a high-precision displacement sensor and a strain gauge, can monitor the axial and radial deformation of the sample in real time during loading and relaxation processes. The measurement accuracy reaches the micrometer level, providing accurate feedback signals for strain control. The data acquisition system is a comprehensive data processing platform composed of high-speed data acquisition cards and professional software. It can simultaneously record parameters such as stress, strain, and time, with a sampling frequency of up to 1000Hz, ensuring the integrity and accuracy of the data. The control module integrates intelligent control algorithms and expert systems, and has a built-in K-value calculation formula (including a 3-hour preparatory test duration setting and a 0.2% safety margin parameter). It can automatically control the loading strain rate, nominal stress adjustment and test time according to the preset program, and automatically determine whether the stress level needs to be adjusted or the sample needs to be replaced based on the objectively determined stress relaxation rate threshold K, thus realizing the automation and intelligence of the testing process. The calculation module, with its built-in professional data processing algorithms and analysis models, can automatically perform preparatory relaxation tests, calculate the stress relaxation rate threshold K, calculate the stress relaxation amount Δσ and stress relaxation rate Δσ / σ in real time, and automatically determine the uniaxial compression relaxation stress threshold of rock-like materials according to the judgment criteria, while generating detailed test reports and data charts.

[0048] The specific functions and implementation methods of each module correspond to the corresponding steps in the aforementioned method embodiments. Through modular design, the device achieves high integration and standardization.

Claims

1. A method for testing the uniaxial compressive relaxation stress threshold of rock-like materials, characterized in that, include: An initial nominal stress is set, and the strain is applied to the initial nominal stress using an axial strain control mode while maintaining a constant strain. A relaxation test is then conducted for a preset time. Measure the stress relaxation amount, calculate the stress relaxation rate, and compare it with the stress relaxation rate threshold K. When the stress relaxation rate exceeds the stress relaxation rate threshold K, the nominal stress is reduced and a new specimen is used for retesting. When the stress relaxation rate does not exceed the stress relaxation rate threshold K, the nominal stress is increased on the same specimen and the test continues until the stress relaxation rate exceeds the stress relaxation rate threshold K and the test is stopped. The nominal stress corresponding to the last time the stress relaxation rate did not exceed the stress relaxation rate threshold K before the test was stopped was taken as the uniaxial compressive relaxation stress threshold of the rock-like material.

2. The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials according to claim 1, characterized in that, The initial nominal stress is set to 0.5-0.6 times the uniaxial compressive strength of the rock-like material.

3. The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials according to claim 1, characterized in that, The loading process of the axial strain control mode includes: (1-5)×10 -5 A strain rate of / s is applied to the initial nominal stress; Keep the strain of the specimen constant, with the allowable deviation of strain being ±2% of the applied strain value.

4. The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials according to claim 1, characterized in that, The determination of the stress relaxation amount includes: Record the initial axial stress value at this strain level within the preset time period; Record the remaining axial stress value after relaxation and stabilization; The difference between the initial axial stress value and the remaining axial stress value is calculated as the stress relaxation amount.

5. The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials according to claim 1, characterized in that, The preset time T is set to be no less than 6 hours.

6. The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials according to claim 1, characterized in that, The stress relaxation rate threshold K is determined through a preparatory relaxation test, including: K value calculation, within 0.3R... c 0.5R c 0.7R c Stress relaxation rates η1, η2, and η3 were obtained by conducting 3-hour preparatory relaxation tests at three stress levels. The stress relaxation rate threshold K was determined by calculating K=max(η1,η2,η3)+0.2%.

7. The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials according to claim 1, characterized in that, The reduction in nominal stress is equal to the uniaxial compressive strength R. c 0.05-0.1 times; the increment of the nominal stress is the uniaxial compressive strength R. c 0.01-0.05 times.

8. The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials according to claim 1, characterized in that, The method further includes an approximate threshold determination step: if the stopping condition is not met even when the stress level has increased to 0.8-0.9 times the uniaxial compressive strength, the test is stopped and the nominal stress at this time is recorded as the approximate threshold.

9. The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials according to claim 1, characterized in that, The rock-like material specimen adopts standardized geometric specifications, including: a standard cylindrical specimen with a diameter of φ50×100 mm; allowable deviations for height and diameter of ±3 mm; allowable deviations for unevenness of both end faces of ±0.05 mm; and allowable deviations for perpendicularity of end faces of ±0.25°.

10. A device for testing the uniaxial compressive relaxation stress threshold of rock-like materials, characterized in that, The method for testing the uniaxial compressive relaxation stress threshold of rock-like materials as described in any one of claims 1-9 includes: A uniaxial compressive stress relaxation testing machine for rock materials is used to apply compressive loads in an axial strain control mode to the rock-like material specimens while maintaining constant strain. A deformation measurement device is used to monitor the strain changes of the rock-like material sample in real time during loading and relaxation processes; A data acquisition system is used to record and store stress, strain, and time data during the test process; The control module is used to control the loading strain rate, nominal stress adjustment and test time. It has a built-in K-value calculation formula and automatically determines whether the stress level needs to be adjusted or the specimen needs to be replaced based on the objectively determined stress relaxation rate threshold K. The calculation module is used to automatically perform a preparatory relaxation test, calculate the stress relaxation rate threshold K, calculate the stress relaxation amount Δσ and stress relaxation rate Δσ / σ in real time, and determine the uniaxial compressive relaxation stress threshold of the rock-like material.

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