Method for determining rock yield stress parameter

Abstract

The present application relates to a kind of rock yield stress parameter determination method, obtains the hoop stress strain curve of rock and axial stress strain curve, to obtain the hoop stress strain curvature and stress level relationship curve of rock, axial stress strain curvature and stress level relationship curve, fitting is carried out to test data, on each fitting curve, the extension line of two straight line segments is crossed in first point, the vertical bisector of two straight line segments is crossed in second point, connect first point and second point, and the abscissa of third point is yield stress parameter, the average of yield stress determined by stress strain curvature and stress level relationship curve is taken as the yield stress parameter of rock, to reduce the purpose of data error, the hoop stress strain curvature and stress relationship curve, axial stress strain curvature and stress level relationship curve are considered comprehensively, the shortcoming of undefined inflection point definition of traditional method is improved, the error of value is reduced, and data accuracy is improved.

Description

Technical Field

[0001] This invention relates to the field of engineering materials mechanics, specifically a method for determining the yield stress parameter of rock. Background Technology

[0002] The yield stress of rock refers to the stress threshold at which rock begins to undergo plastic deformation under stress. After experiencing a certain level of stress, rock undergoes reversible plastic deformation; this stage is called the yielding stage. During compression, when the stress reaches a certain value, a slight increase in stress followed by a rapid increase in rock stress occurs; the stress point at this point is called the yield stress. Yield stress is a crucial parameter in rock mechanics and engineering, with wide-ranging applications and significant importance. It is one of the key indicators for evaluating rock performance. Understanding the yield stress helps scientists and engineers predict rock behavior under specific stresses, such as performance under different temperatures or environmental conditions, thus guiding practical engineering applications. In design and engineering practice, understanding the yield stress helps assess the reliability and safety of rock engineering projects during long-term use. Predicting potential plastic deformation and failure of rock under loads exceeding the yield stress helps in developing preventative maintenance measures to ensure the safe operation of engineering structures. Understanding and determining the yield stress of rock is essential for engineering design, quality control, and reliability assessment, thus playing a vital role in the fields of rock mechanics and engineering. The yield stress of rock is closely related to the safety and long-term stable operation of rock engineering, but there has never been a specific and reliable analytical method to determine its value.

[0003] Existing techniques include the 0.2% yield strength method, which takes the slope of the initial portion of the stress-strain curve, shifts it by 0.2% of the strain, and then draws a parallel line along this slope. The intersection of this line with the stress-strain curve defines the stress value. However, this method is not straightforward for unconventional or nonlinear materials where a clear linear region may not exist. Furthermore, choosing different shifts (0.1% or 0.2% of strain) can lead to different yield stress results, introducing subjectivity and selectivity. Another method is the slope variation method, which uses the point where the slope of the stress-strain curve changes as the yield stress. In some cases, the stress-strain curve may not be clear or smooth, and the slope change may not be significant enough, making it difficult to accurately determine the yield point. Overall, these methods are susceptible to various factors when determining the yield stress, such as material inhomogeneity, specimen size, and the choice of test conditions. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for determining the yield stress parameter of rock, which can ensure that the yield stress parameter of rock samples is more clearly calibrated, improve the accuracy of yield stress parameter determination, and reduce data errors.

[0005] To achieve the above and other related objectives, this invention proposes a method for determining the yield stress parameter of rock, comprising the following steps:

[0006] Prepare a sample so that it has a cylindrical shape;

[0007] Obtain the triaxial test results of the specimen under the set confining pressure;

[0008] Based on the results of the triaxial test of the specimen under the set confining pressure, the curves showing the relationship between the circumferential stress-strain curvature and the stress level before the peak, as well as the curves showing the relationship between the axial stress-strain curvature and the stress level before the peak, were plotted.

[0009] Extend the upper and lower straight line segments of the curve relating axial stress-strain curvature to stress level and the curve relating circumferential stress-strain curvature to stress level to intersect at the first point;

[0010] Draw perpendicular bisectors for the upper and lower line segments respectively, and extend them to intersect at the second point;

[0011] Connect the first point and the second point at the third point, intersecting the axial stress-strain curvature versus stress level curve or the circumferential stress-strain curvature versus stress level curve.

[0012] The abscissa of the third point is determined as the yield stress parameter, and the average yield stress determined by the curves of the relationship between circumferential stress-strain curvature and stress level and the curves of the relationship between axial stress-strain curvature and stress level is the final yield stress parameter value.

[0013] In one embodiment of the present invention, the steps of plotting the relationship curves between the circumferential stress-strain curvature and the stress level before the peak, and the relationship curves between the axial stress-strain curvature and the stress level before the peak, include:

[0014] The stress values ​​from the triaxial test results of the specimen under a set confining pressure were used as the abscissa, and the circumferential stress-strain curvature and axial stress-strain curvature were used as the ordinate, respectively, and plotted in a Cartesian coordinate system. The data were fitted using a power function to obtain the relationship curves between the circumferential stress-strain curvature and the stress level, and the relationship curves between the axial stress-strain curvature and the stress level.

[0015] In one embodiment of the present invention, the step of drawing perpendicular bisectors for the upper and lower line segments includes:

[0016] Determine the starting point for calculation, wherein the calculation formula for the starting point satisfies:

[0017]

[0018] In the formula, x1 is the point corresponding to the opening angle between the straight line segment and the fitted curve is 1 / 10000°, where 1 / 10000° makes the angle between the fitted curve and the straight line segment small enough to meet the accuracy requirements for the calculation of the starting point. x0 is the point of coincidence between the fitted straight line and the function. F1(x) is the stress-strain curvature fitting function, and F2(x) is the linear fitting function of the straight line segment.

[0019] In one embodiment of the present invention, the calculation formulas for the pre-peak circumferential stress-strain curvature and the pre-peak axial stress-strain curvature satisfy the following:

[0020]

[0021] In the formula, ε i-1 ε i ε i+1 These are the strain abscissa values ​​of points adjacent to point i; σ i-1 , σ i , σ i+1 These are the corresponding stress ordinate values; R is the radius of curvature; K i Let be the stress-strain curvature corresponding to point i.

[0022] In one embodiment of the present invention, the step of preparing the sample includes:

[0023] A complete rock block was selected, core samples were drilled, and the core samples were processed to prepare standard cylindrical rock specimens.

[0024] In one embodiment of the present invention, the triaxial test results of the specimen under a set confining pressure include the circumferential and axial stress-strain curves of the rock under the set conditions.

[0025] In one embodiment of the present invention, the results of the triaxial test of the specimen under a set confining pressure also include circumferential strain and axial strain;

[0026] The circumferential strain is measured by a circumferential chain strain gauge, and the axial strain is measured by an axial LVDT sensor.

[0027] In one embodiment of the present invention, the peak corresponds to the stress-strain curve of the sample before it reaches the peak strength;

[0028] In one embodiment of the present invention, in the step of fitting the data with a power function, the threshold of the function correlation coefficient is greater than 0.9.

[0029] By adopting the above technical solution, the technical effect of the present invention is as follows: The present invention first obtains the circumferential and axial stress-strain curves of the rock from the triaxial test results. Based on this, the circumferential stress-strain curvature and stress level relationship curves and the axial stress-strain curvature and stress level relationship curves of the rock are calculated respectively. The test data are fitted to obtain the fitted curves. The upper and lower straight line segments of each fitted curve are extended to intersect at the first point. The upper and lower straight line segments are perpendicularly bisectors to intersect at the second point. The first point and the second point are connected to intersect the fitted curve at the third point. The abscissa of this point is determined as the yield stress parameter. The average yield stress determined by the circumferential stress-strain curvature and stress level relationship curves and the axial stress-strain curvature and stress level relationship curves is taken to comprehensively determine the yield stress parameter of the rock, thereby reducing data error. The present invention comprehensively considers the circumferential stress-strain curvature and stress relationship curves and the axial stress-strain curvature and stress level relationship curves, which can significantly improve the accuracy of the results, reduce the error, effectively improve the shortcomings of the traditional method in the unclear definition of the inflection point, reduce the error of the value, and achieve good results. Attached Figure Description

[0030] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 This is a schematic diagram of stress-strain curvature calculation used in one embodiment of the present invention;

[0032] Figure 2 This is a schematic diagram illustrating the calculation of the starting point of the perpendicular bisector in one embodiment of the present invention;

[0033] Figure 3 This is a hardening stress-strain curve diagram used in one embodiment of the present invention;

[0034] Figure 4 This is a softening stress-strain curve diagram used in one embodiment of the present invention;

[0035] Figure 5 This is a schematic diagram illustrating the determination of the rock yield stress point using the circumferential stress-strain curve in one embodiment of the present invention.

[0036] Figure 6 This is a schematic diagram illustrating the determination of the rock yield stress point using the axial stress-strain curve in one embodiment of the present invention.

[0037] Figure 7This is a schematic diagram illustrating the determination of the rock yield stress point using the circumferential stress-strain curve in one embodiment of the present invention;

[0038] Figure 8 This is a schematic diagram illustrating the determination of the rock yield stress point using the axial stress-strain curve in one embodiment of the present invention;

[0039] Figure 9 A schematic diagram of determining the yield stress of the hardening stress-strain curve in Example 3 using the conventional method (1);

[0040] Figure 10 A schematic diagram of determining the yield stress of the hardening stress-strain curve in Example 4 using the conventional method (2);

[0041] Figure 11 A schematic diagram of determining the yield stress of the softening stress-strain curve in Example 5 using the conventional method (1);

[0042] Figure 12 A schematic diagram of determining the yield stress of the softening stress-strain curve in Example 6 using the conventional method (2). Detailed Implementation

[0043] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0044] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0045] This invention can be applied to determine the yield parameters of rock materials with different textures, including softening and hardening rock materials. When determining the yield parameters of rock materials, it is necessary to obtain the circumferential stress-strain curvature versus stress curve and the axial stress-strain curvature versus stress level curve of the rock sample. Specifically, this can be done according to the following embodiment:

[0046] Example 1:

[0047] A method for determining the yield stress parameter of rock, wherein the rock material used in this method is a hardening rock material, includes the following steps:

[0048] S101: Sample preparation; Select a complete rock sample, drill a core, process the core, and prepare a standard cylindrical rock sample of 50mm×100mm (diameter×height) according to the "Standard for Test Methods of Engineering Rock Mass" (GB / T50266—2013);

[0049] S102: Triaxial Compression Test; A triaxial compression test is performed on a standard rock sample under a set confining pressure to obtain the triaxial test results of the rock under the set confining pressure, such as... Figure 3 As shown, this corresponds to the hardening stress-strain curve.

[0050] S103: Plot the relationship between the circumferential stress-strain curvature and the stress level in front of the peak and the axial stress-strain curvature and the stress level in front of the peak, respectively, based on the rock stress-strain curves.

[0051] The stress value is used as the abscissa, and the circumferential stress-strain curvature and axial stress-strain curvature are used as the ordinate, plotted in a Cartesian coordinate system; the data are fitted with a power function to obtain the curves of the relationship between circumferential stress-strain curvature and stress level, and the curves of the relationship between axial stress-strain curvature and stress level; among them, the peak corresponds to the part of the stress-strain curve before the sample reaches the peak strength; the formula for calculating the stress-strain curvature is shown in formula (1):

[0052]

[0053] In the formula, ε i-1 ε i ε i+1 These are the strain abscissa values ​​of points adjacent to point i; σ i-1 , σ i , σ i+1 These are the corresponding stress ordinate values; R is the radius of curvature; K i Let be the stress-strain curvature corresponding to point i.

[0054] In one embodiment, the calculated relationship between circumferential stress-strain curvature and stress level, and the relationship between axial stress-strain curvature and stress level are illustrated in the diagram below. Figure 1 As shown, the implementation results are as follows: Figure 5 and Figure 6 The scattered points are shown in the figure; among them, the curves showing the relationship between circumferential stress-strain curvature and stress level, the curves showing the relationship between axial stress-strain curvature and stress level, and their power function fitting curves of the rock block samples are shown in the figure. Figure 5 and Figure 6 As shown in the solid line portion, in one embodiment, the fitting correlation coefficient of the power function should be greater than 0.9.

[0055] S104: Determine the yield stress using the circumferential stress-strain curvature versus stress level curve and the axial stress-strain curvature versus stress level curve. Based on step S103, extend the upper and lower straight segments of the axial stress-strain curvature versus stress level curve and the circumferential stress-strain curvature versus stress level curve to form lines B1 and B2, intersecting at the first point A. Then, draw perpendicular bisectors for the upper and lower straight segments. The step of drawing perpendicular bisectors for the upper and lower straight segments includes:

[0056] Determine the starting point for calculation, wherein the calculation formula for the starting point satisfies:

[0057]

[0058] In the formula, x1 is the point corresponding to the opening angle between the straight line segment and the fitted curve is 1 / 10000°, where 1 / 10000° makes the angle between the fitted curve and the straight line segment small enough to meet the accuracy requirements for the calculation of the starting point. x0 is the point of coincidence between the fitted straight line and the function. F1(x) is the stress-strain curvature fitting function, and F2(x) is the linear fitting function of the straight line segment.

[0059] Formula (2) determines point C, and the starting point of the lower straight line is determined by formula (2) as point B. The two perpendicular bisectors are 1 and 2, respectively, which are extended to intersect at the second point D. Points A and D are connected to intersect the circumferential stress-strain curvature and stress level relationship curve at the third point E. The abscissa of the third point E is determined as the yield stress parameter determined by the circumferential strain data, which is 72.36 MPa. The same method is used to process the axial stress-strain curvature and stress relationship curve, and the yield stress parameter determined by the axial strain data is 72.53 MPa. The difference between the two is small. The yield stress obtained by combining the circumferential stress-strain curvature and stress level relationship curve and the axial stress-strain curvature and stress level relationship curve is taken as the average value of 72.45 MPa, which is determined as the final yield stress parameter. The corresponding results are as follows. Figure 5 and Figure 6 As shown; where the calculation formula for the starting point of the perpendicular bisector is shown in formula (2), and the calculation diagram is shown in... Figure 2 As shown.

[0060] In one embodiment, since the circumferential stress-strain curve is more sensitive to stress deformation, circumferential stress deformation occurs earlier than axial stress deformation; the deformation before the peak is more continuous and smooth, and the data after the peak is not continuous under different test environments and conditions, thus making it difficult to determine the yield stress; the present invention uses the stress-strain curve before the peak to determine the yield stress parameter of rock materials, and the relationship curve between circumferential stress-strain curvature and stress level is more accurate in determining the yield stress of rocks than the relationship curve between axial stress-strain curvature and stress level.

[0061] Example 2:

[0062] A method for determining the yield stress parameter of rock, wherein the rock material used in this method is a softening rock material, includes the following steps:

[0063] S201: Sample preparation; Select an intact rock sample, drill a core, process the core, and prepare a standard cylindrical rock sample of 50mm×100mm (diameter×height) according to the "Standard for Test Methods of Engineering Rock Mass" (GB / T50266—2013);

[0064] S202: Triaxial Compression Test; A triaxial compression test is performed on a standard rock specimen under a set confining pressure to obtain the triaxial test results of the rock under the set confining pressure, such as... Figure 4 As shown, this corresponds to the softening type stress-strain curve.

[0065] S203: Plot the relationship between the circumferential stress-strain curve and the stress level in front of the peak and the relationship between the axial stress-strain curvature and the stress level in front of the peak, respectively, based on the rock stress-strain curve.

[0066] The stress value is used as the abscissa, and the circumferential stress-strain curvature and axial stress-strain curvature are used as the ordinate, plotted in a Cartesian coordinate system; the data are fitted with a power function to obtain the curves of the relationship between circumferential stress-strain curvature and stress level, and the curves of the relationship between axial stress-strain curvature and stress level; among them, the peak corresponds to the part of the stress-strain curve before the sample reaches the peak strength; the formula for calculating the stress-strain curvature is shown in formula (1):

[0067]

[0068] In the formula, ε i-1 ε i ε i+1 These are the strain abscissa values ​​of points adjacent to point i; σ i-1 , σ i , σ i+1 These are the corresponding stress ordinate values; R is the radius of curvature; K i Let be the stress-strain curvature corresponding to point i.

[0069] In one embodiment, the calculated relationship between circumferential stress-strain curvature and stress level, and the relationship between axial stress-strain curvature and stress level are illustrated in the diagram below. Figure 1 As shown, the implementation results are as follows: Figure 7 and Figure 8 The scattered points are shown in the figure; among them, the curves showing the relationship between circumferential stress-strain curvature and stress level, the curves showing the relationship between axial stress-strain curvature and stress level, and their power function fitting curves of the rock block samples are shown in the figure. Figure 7 and Figure 8As shown in the solid line portion, in one embodiment, the fitting correlation coefficient of the power function should be greater than 0.9.

[0070] S204: Determine the yield stress using the circumferential stress-strain curvature versus stress level curve and the axial stress-strain curvature versus stress level curve. Based on step S103, extend the upper and lower straight segments of the axial stress-strain curvature versus stress level curve and the circumferential stress-strain curvature versus stress level curve to form lines B1 and B2, intersecting at the first point A. Then, draw perpendicular bisectors for the upper and lower straight segments. The step of drawing perpendicular bisectors for the upper and lower straight segments includes:

[0071] Determine the starting point for calculation, wherein the calculation formula for the starting point satisfies:

[0072]

[0073] In the formula, x1 is the point corresponding to the opening angle between the straight line segment and the fitted curve is 1 / 10000°, x0 is the point of coincidence between the fitted straight line and the function, F1(x) is the stress-strain curvature fitting function, and F2(x) is the linear fitting function of the straight line segment.

[0074] Formula (2) determines point C, and the starting point of the lower straight line is determined by formula (2) as point B. The two perpendicular bisectors are 1 and 2, respectively, which are extended to intersect at the second point D. Points A and D are connected to intersect the circumferential stress-strain curvature and stress level relationship curve at the third point E. The abscissa of the third point E is determined as the yield stress determined by the circumferential strain data, which is 106.25 MPa. The yield stress determined by the axial stress-strain curvature and stress level relationship curve is 106.58 MPa, and the difference between the two is also small. The yield stress obtained by combining the circumferential stress-strain curvature-stress level relationship curve and the axial stress-strain curvature-stress level relationship curve is taken as the average value of 106.42 MPa, which is determined as the final yield stress parameter. The yield stress obtained by combining the circumferential stress-strain curvature and stress level relationship curve and the axial stress-strain curvature and stress level relationship curve is taken as the average value of 72.45 MPa, which is determined as the final yield stress parameter. The corresponding results are as follows. Figure 7 and Figure 8 As shown; where the calculation formula for the starting point of the perpendicular bisector is shown in formula (2), and the calculation diagram is shown in... Figure 2 As shown.

[0075] In contrast, the following explanation uses existing methods for determining rock yield stress parameters:

[0076] Example 3:

[0077] The yield stress parameters of the rock material were obtained using the traditional 0.2% yield strength method. Specifically, the same hardening stress-strain curve as in Example 1 was obtained, as shown below. Figure 2 As shown. The difference lies in the way the curve is processed compared to Example 1, and in obtaining different yield stress parameters for rock materials.

[0078] In Example 3, the yield stress of the rock material was obtained by processing the hardening stress-strain curve, such as... Figure 9 As shown. Specifically, the slope of the initial portion of the stress-strain curve is taken, then offset by 0.2% of the strain, and a parallel line is drawn along this slope. The intersection of this line and the stress-strain curve is defined as the yield stress of the rock material. The stress level corresponding to its vertical axis is 71.48 MPa, which is taken as the yield stress.

[0079] Example 4:

[0080] The yield stress parameters of the rock material were obtained using the traditional slope variation method. Specifically, the same hardening stress-strain curve as in Example 1 was obtained, such as... Figure 2 As shown. The difference lies in the way the curve is processed compared to Example 1, and in obtaining different yield stress parameters for rock materials.

[0081] In Example 4, the yield stress of the rock material was obtained by processing the hardening stress-strain curve, such as... Figure 10 As shown. The intersection of two straight lines with different slopes is determined as the yield stress of the rock material, and the stress level corresponding to its ordinate is 73.01 MPa, which is taken as the yield stress.

[0082] Example 5:

[0083] The yield stress parameters of the rock material were obtained using the traditional 0.2% yield strength method (1). Specifically, the same softening stress-strain curve as in Example 2 was obtained, such as... Figure 3 As shown. The difference lies in the way the curve is processed compared to Example 2, and in obtaining different yield stress parameters for the rock material.

[0084] In Example 5, the yield stress of the rock material was obtained by processing the softening stress-strain curve, such as... Figure 11 As shown in the diagram. Specifically, the slope of the initial portion of the stress-strain curve is taken, then offset by 0.2% of the strain. A parallel line is then drawn along this slope, and the intersection of this line and the stress-strain curve is defined as the yield stress of the rock material. The stress level corresponding to its ordinate is 104.44 MPa, which is taken as the yield stress.

[0085] Example 6:

[0086] The yield stress parameters of the rock material were obtained using the traditional slope variation method (2). Specifically, the softening stress-strain curve, identical to that in Example 2, was obtained. Figure 3 As shown. The difference lies in the processing method of the curve compared to Example 2, and the different yield stress parameters of the rock material obtained. In Example 6, the yield stress of the rock material is obtained by processing the softening stress-strain curve, as shown... Figure 12 As shown. The intersection of two straight lines with different slopes is determined as the yield stress of the rock material, and the stress level corresponding to its ordinate is 100.79 MPa, which is taken as the yield stress.

[0087] A comprehensive comparative analysis of two traditional methods for determining yield stress and the method proposed in this invention is presented in Table 1:

[0088]

[0089] Table 1 compares different methods for determining yield stress parameters. By comparing three different analysis methods for two different types of stress-strain curves (hardening and softening) in Examples 1 to 6, the yield stress parameters were determined. The method for determining rock yield stress parameters based on the stress-strain curvature-stress level relationship curve provided by this invention can effectively utilize the circumferential and axial stress-strain data of rock materials. The comprehensively determined yield stress is moderate and reasonable. At the same time, it overcomes the shortcomings of traditional methods. Compared with traditional methods, it effectively improves the empirical, uncertain, and error-prone aspects of traditional methods. It can be applied to the stability analysis of rock engineering structures, providing a valid reference for the long-term stability of engineering structures.

[0090] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0091] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A method for determining the yield stress parameter of rock, characterized in that, Includes the following steps: Prepare a sample so that it has a cylindrical shape; Obtain the triaxial test results of the specimen under a set confining pressure; Based on the results of the triaxial test of the specimen under the set confining pressure, the curves showing the relationship between the circumferential stress-strain curvature and the stress level before the peak, as well as the curves showing the relationship between the axial stress-strain curvature and the stress level before the peak, were plotted. Extend the upper and lower straight line segments of the curve relating axial stress-strain curvature to stress level and the curve relating circumferential stress-strain curvature to stress level to intersect at the first point; Draw perpendicular bisectors for the upper and lower line segments respectively, and extend them to intersect at the second point; Connect the first point and the second point, and intersect the axial stress-strain curvature versus stress level curve or the circumferential stress-strain curvature versus stress level curve at the third point; The abscissa of the third point is determined as the yield stress parameter, and the average yield stress determined by the curves of circumferential stress-strain curvature and stress level and the curves of axial stress-strain curvature and stress level is taken as the final yield stress parameter value.

2. The method for determining the rock yield stress parameter according to claim 1, characterized in that, The steps for plotting the relationship curves between pre-peak circumferential stress-strain curvature and stress level, and between pre-peak axial stress-strain curvature and stress level, include: The stress values ​​from the triaxial test results of the specimen under a set confining pressure were used as the abscissa, and the circumferential stress-strain curvature and axial stress-strain curvature were used as the ordinate, respectively, and plotted in a Cartesian coordinate system. The data were fitted using a power function to obtain the relationship curves between the circumferential stress-strain curvature and the stress level, and the relationship curves between the axial stress-strain curvature and the stress level.

3. The method for determining the rock yield stress parameter according to claim 1, characterized in that, The steps of drawing perpendicular bisectors for the upper and lower straight line segments include: Determine the starting point for calculation, wherein the calculation formula for the starting point satisfies: In the formula, x1 is the point corresponding to the opening angle between the straight line segment and the fitted curve is 1 / 10000°, x0 is the point of coincidence between the fitted straight line and the function, F1(x) is the stress-strain curvature fitting function, and F2(x) is the linear fitting function of the straight line segment.

4. The method for determining the rock yield stress parameter according to claim 1, characterized in that, The calculation formulas for the pre-peak circumferential stress-strain curvature and the pre-peak axial stress-strain curvature satisfy the following: In the formula, ε i-1 ε i ε i+1 These are the strain abscissa values ​​of points adjacent to point i; σ i-1 , σ i , σ i+1 These are the corresponding stress ordinate values; R is the radius of curvature; K i Let be the stress-strain curvature corresponding to point i.

5. The method for determining the rock yield stress parameter according to claim 1, characterized in that, The steps for preparing the sample include: A complete rock block was selected, core samples were drilled, and the core samples were processed to prepare standard cylindrical rock specimens.

6. The method for determining the rock yield stress parameter according to claim 1, characterized in that, The results of the triaxial test of the specimen under the set confining pressure include the circumferential and axial stress-strain curves of the rock under the set conditions.

7. The method for determining the rock yield stress parameter according to claim 1, characterized in that, The results of the triaxial test of the specimen under the set confining pressure also include circumferential strain and axial strain; The circumferential strain is measured by a circumferential chain strain gauge, and the axial strain is measured by an axial LVDT sensor.

8. The method for determining the rock yield stress parameter according to claim 1, characterized in that, The peak corresponds to the stress-strain curve of the sample before it reaches its peak strength.

9. The method for determining the rock yield stress parameter according to claim 2, characterized in that, In the step of fitting the data using a power function, the threshold value of the correlation coefficient of the function is greater than 0.9.

Images