True triaxial rock strength criterion and parameter determination method
By introducing a hyperbolic Lode angle shape function and true triaxial experimental data fitting into the Mohr-Coulomb strength criterion, the prediction error of existing rock strength criteria under three-dimensional stress is solved, and high-precision rock strength prediction is achieved.
Patent Information
- Application Number
- CN202310628975.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2023-05-30
- Publication Date
- 2025-11-25
- Estimated Expiration
- 2043-05-30
AI Technical Summary
Existing rock strength criteria, such as the Mohr-Coulomb, Drucker-Prager, and Hoek-Brown criteria, fail to effectively account for rock failure under three-dimensional stress, resulting in inconvenience and errors in numerical calculations, especially inaccurate predictions under triaxial tension and compression.
A hyperbolic Lode angle shape function was used to replace the Mohr-Coulomb strength criterion to construct a true triaxial rock strength criterion. The undetermined parameters were fitted using experimental data of true and pseudo triaxial rock strength. The cohesion and internal friction angle were determined by combining the least squares method, and a high-precision rock strength prediction model was established.
It achieves high-precision prediction of rock strength under three-dimensional stress, solves the problems of smoothness and convexity of existing criteria on the π plane, and can efficiently complete the test in most rock mechanics laboratories.
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Figure CN119066732B_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of oil and gas field drilling development, and particularly relates to a true triaxial rock strength criterion and a parameter determination method. BACKGROUND
[0002] A rock strength criterion is a theory for judging whether rock will yield or break under different rock stress states, and is commonly used to predict the ultimate strength of rock under different stress states. The most commonly used and most far-reaching criterion is the Mohr-Coulomb (MC) criterion, but the MC criterion does not consider the influence of the intermediate principal stress, and only describes the ultimate strength of rock under triaxial compression stress states, and there are six singular points on the π plane, which is extremely inconvenient in numerical calculation applications. In view of the fact that the failure of rock is mainly controlled by the deviatoric stress, Drucker and Prager improved the von-Mises criterion and proposed the Drucker-Prager (DP) criterion, which is a conical surface in the principal stress space, and the limit trace on the π plane is a circle, so the DP criterion cannot describe the difference in strength of rock on different meridians. The DP criterion considers the influence of hydrostatic pressure and is more suitable for rock and soil materials than the von Mises criterion, but the strength of materials obtained by using different forms of the DP criterion differs by 3-4 times, and the inscribed circle underestimates the rock strength, while the circumscribed circle overestimates the rock strength, which is very dangerous in engineering, so it is generally believed that the DP criterion overestimates the strengthening effect of the intermediate principal stress on rock strength, and should be used with caution in rock and soil materials. In view of the defects of the MC criterion and the DP criterion, Lade and Duncan proposed the Lade-Duncan criterion in 1975 and 1977, but it is only suitable for weakly cohesive sandy soil materials. In 1977-1979, Lade modified the Lade-Duncan criterion, which is the famous modified Lade criterion. The modified Lade criterion considers the influence of the intermediate principal stress, and is a smooth curve on the π plane, overcoming the shortcomings of the classical MC criterion, and has broad application prospects. The only defect is that the limit trace on the π plane only connects with the MC criterion in the triaxial compression state, and overestimates the rock strength in the triaxial tension state. Strength criteria based on two parameters of cohesion and internal friction angle can be classified into MC type strength criteria, such as the DP criterion, the ML criterion, the Mogi-Coulomb (MGC) criterion, and the modified Wiebol-Cook (MWC) criterion. Another classical strength criterion is the rock failure empirical criterion proposed by Hoek and Brown in 1980, i.e. the Hoek-Brown criterion. Like the MC criterion, the HB criterion can distinguish the difference between triaxial tension and compression strengths, and the HB criterion has nonlinear characteristics on the meridian plane, and can reflect the failure characteristics of rock better than the MC criterion in the tension stress zone and high confining pressure stress state, but the criterion still does not consider the influence of the intermediate principal stress.
[0003] Rock is a complex natural material, for understanding and mastering the bearing capacity of rock, domestic and foreign scholars have carried out a large number of research. Rock in nature is destroyed under the action of three-dimensional stress, the shape characteristics of the established three-dimensional rock strength criterion in the principal stress space and π plane, defects and its fitting effect on true triaxial rock strength experimental data need to carry out more comprehensive research, at the same time, the application of the three-dimensional MC type strength criterion and three-dimensional HB type strength must carry out true triaxial rock strength experiment, at present, most of the rock mechanics laboratories at home and abroad still can not meet this requirement. SUMMARY
[0004] To solve the problem of existing rock strength experiment, the application provides a true triaxial rock strength criterion and parameter determination method, so as to consider the influence of three-dimensional stress on rock failure, and the undetermined parameters contained in the criterion can be conveniently measured.
[0005] In one aspect, a true triaxial rock strength criterion and parameter determination method are provided, the method comprising:
[0006] S1, rock strength criterion conversion;
[0007] S2, replacement of Lode angle shape function and construction of true triaxial rock strength criterion;
[0008] S3, fitting of undetermined parameters of modified strength criterion based on true triaxial rock strength experimental data, and determination of prediction error;
[0009] S4, fitting of undetermined parameters of Mohr-Coulomb strength criterion based on pseudo triaxial rock strength experimental data;
[0010] S5, using the modified rock strength criterion based on the undetermined parameters determined in step S4, predicting true triaxial rock strength experimental data, and determining the fitting error;
[0011] S6, comparison of the undetermined parameters determined in steps S3 and S4 and analysis of the true triaxial rock strength prediction error determined in steps S3 and S5;
[0012] S7, preparing standard core samples and carrying out pseudo triaxial strength experiments of rock under different confining pressures;
[0013] S8, fitting of undetermined parameters based on pseudo triaxial rock strength experimental data.
[0014] In some embodiments, the S1 comprises:
[0015] The Mohr-Coulomb strength criterion expressed by principal stress is converted into a form expressed by hydrostatic pressure, second stress deviator invariant and Lode angle three variables.
[0016] In some embodiments, the S2 comprises:
[0017] The Lode angle shape function in the Mohr-Coulomb strength criterion is replaced by a hyperbolic Lode angle shape function to obtain a modified Mohr-Coulomb strength criterion.
[0018] In some embodiments, the S3 comprises:
[0019] Obtaining true triaxial rock strength experimental data;
[0020] Based on the least squares method and the true triaxial rock strength criterion, fitting the true triaxial rock strength experimental data, the strength parameters in the true triaxial rock strength criterion are calculated; the strength parameters include cohesion and internal friction angle.
[0021] In some embodiments, the S4 comprises:
[0022] Obtaining pseudo-triaxial rock strength experimental data;
[0023] Based on the least squares method and the true triaxial rock strength criterion, fitting the pseudo-triaxial rock strength experimental data, the strength parameters in the pseudo-triaxial rock strength criterion are calculated; the strength parameters include cohesion and internal friction angle.
[0024] In some embodiments, the S4 further comprises:
[0025] Based on the strength parameters in the pseudo-triaxial strength criterion, predicting true triaxial rock strength, calculating fitting error.
[0026] In some embodiments, the S5 comprises:
[0027] Substituting the strength parameters in the pseudo-triaxial rock strength criterion into the true triaxial strength criterion, fitting the true triaxial rock strength experimental data, calculating prediction error.
[0028] In some embodiments, the S6 comprises:
[0029] Based on the strength parameters in the true triaxial rock strength criterion, the strength parameters in the pseudo-triaxial rock strength criterion, and the prediction error, judging the feasibility of calculating cohesion and internal friction angle based on pseudo-triaxial rock strength data to predict true triaxial rock strength.
[0030] In some embodiments, the S7 comprises:
[0031] Based on the first preset number of standard core samples, performing rock pseudo-triaxial strength experiments under a second preset number of confining pressures to obtain rock strength data of each standard core sample under different confining pressures;
[0032] The first preset number is greater than or equal to 5, and the second preset number is greater than or equal to 5.
[0033] In some embodiments, the S8 comprises:
[0034] Based on the least square method, the rock strength data is fitted using the modified Mohr-Coulomb strength criterion to obtain the rock cohesion and internal friction angle.
[0035] The technical scheme provided by the present application has at least the following beneficial effects: the embodiment of the present application provides a true triaxial rock strength criterion and parameter determination method, which comprises rock strength criterion conversion; replacement of Lode angle shape function and construction of true triaxial rock strength criterion; fitting of undetermined parameters of the modified strength criterion based on true triaxial rock strength experimental data and determination of prediction error; fitting of undetermined parameters of the Mohr-Coulomb strength criterion based on pseudo-triaxial rock strength experimental data; prediction of true triaxial rock strength experimental data using the modified rock strength criterion based on the undetermined parameters determined in step S4, and determination of fitting error; comparison of the undetermined parameters determined in steps S3 and S4 and analysis of the true triaxial rock strength prediction error determined in steps S3 and S5; preparation of standard core samples and carrying out rock pseudo-triaxial strength experiments under different confining pressures; fitting of undetermined parameters based on pseudo-triaxial rock strength experimental data. The method provided by the embodiment of the present application replaces the Lode angle shape function of the MC strength criterion with a hyperbolic Lode angle shape function to establish a true triaxial rock strength criterion, which solves the problem that the existing three-dimensional rock strength criterion cannot simultaneously satisfy the requirements of smooth and convex yield surface, and at the same time, the modified MC strength criterion can simultaneously intersect with the triaxial tensile and triaxial compression stress points on the π plane. The undetermined parameters of the criterion can be obtained by pseudo-triaxial strength experiments. The method saves time and effort, can be completed in most rock mechanics laboratories, and has very high prediction accuracy for true triaxial rock strength experimental data. BRIEF DESCRIPTION OF DRAWINGS
[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.
[0037] Figure 1 An implementation flowchart of a true triaxial rock strength criterion and parameter determination method provided by an exemplary embodiment of the present application is shown;
[0038] Figure 2A technical roadmap of a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown.
[0039] Figure 3 A schematic diagram showing the stress state on the principal stress space and deviatoric plane or π plane in a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown.
[0040] Figure 4 A comparison diagram of MC criterion Lode angle shape function and hyperbolic Lode angle shape function in a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown.
[0041] Figure 5 A comparison diagram of the minimum absolute deviation of true triaxial strength criterion fitting and the prediction results of existing strength criterion in a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown.
[0042] Figure 6 A comparison diagram of the cohesion fitted based on true triaxial experimental data and pseudo triaxial experimental data in a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown.
[0043] Figure 7 A comparison diagram of the internal friction angle fitted based on true triaxial experimental data and pseudo triaxial experimental data in a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown.
[0044] Figure 8 A radar chart of the average minimum absolute deviation of MCYL criterion fitting based on pseudo triaxial experimental data and true triaxial experimental data in a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown.
[0045] Figure 9 Rock strength and MC criterion fitting curve under different confining pressures in a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown. DETAILED DESCRIPTION
[0046] In order to make the purpose, technical scheme and advantages of the present application more clear, the implementation of the present application will be described in further detail below with reference to the drawings.
[0047] Example one,
[0048] Figure 1 An implementation flowchart of a true triaxial rock strength criterion and parameter determination method provided by the embodiment of the present application is shown.
[0049] Figure 2A technical roadmap of a true triaxial rock strength criterion and parameter determination method provided by one example embodiment of the present application is shown.
[0050] Referring to Figure 1 The true triaxial rock strength criterion and parameter determination method provided by the embodiment of the present application can include steps S1 to S8.
[0051] S1, rock strength criterion conversion.
[0052] In some embodiments, the S1 includes:
[0053] The Mohr-Coulomb strength criterion expressed by principal stresses is converted into a form expressed by three variables of hydrostatic pressure, second stress deviator invariant and Lode angle.
[0054] Figure 3 A representation schematic diagram of stress states on a principal stress space and a deviatoric plane or a pi plane is shown.
[0055] Specifically, the MC strength criterion expressed by principal stresses is shown in formula (1),
[0056]
[0057] In formula (1), σ1 is the first principal stress, unit: MPa; σ3 is the third principal stress, unit: MPa; c o is the cohesion, unit: MPa; is the internal friction angle, unit: °.
[0058] As shown in Figure 3 , the three principal stresses can be expressed by the Lode angle, the hydrostatic pressure and the distance r of a certain point on the pi plane to the origin, and the conversion relationship is shown in formula (2),
[0059]
[0060] In formula (2), θ is the Lode angle, °; ξ is the hydrostatic pressure, MPa; r is the distance of a certain point on the pi plane to the origin, MPa.
[0061] The strength criterion expressed by principal stresses is expressed by three variables of the Lode angle, the hydrostatic pressure and r on the deviatoric stress plane, and then the MC strength criterion is converted into formula (3),
[0062]
[0063] Formula (3) can also be written in the form of the Lode angle shape function, as shown in formula (4),
[0064]
[0065] wherein g MC (θ) is a MC criterion Lode angle shape function, as shown in equation (5),
[0066]
[0067] S2, replacement of Lode angle shape function and construction of true triaxial rock strength criterion;
[0068] In some embodiments, the S2 includes:
[0069] The Lode angle shape function in the Mohr-Coulomb strength criterion is replaced by a hyperbolic Lode angle shape function to obtain a modified Mohr-Coulomb strength criterion.
[0070] Figure 4 A comparison chart of MC criterion Lode angle shape function and hyperbolic Lode angle shape function is shown.
[0071] Referring to Figure 4 Since the MC criterion Lode angle shape function does not meet the requirements of smoothness and convexity, and the influence of the intermediate principal stress is not considered, Yu and Liu proposed a hyperbolic Lode angle shape function as shown in equation (6). This model can obtain a hyperbolic approximation curve of any straight line. Due to the characteristics of the hyperbolic function, this model necessarily meets the requirements of convexity and smoothness. Equation (6) is used to replace the MC criterion Lode angle shape function g MC (θ), the MC criterion is modified, and a true triaxial rock strength criterion is constructed.
[0072]
[0073] S3, fitting of undetermined parameters of the modified strength criterion based on true triaxial rock strength experimental data and determination of prediction error.
[0074] In some embodiments, the S3 includes:
[0075] Obtaining true triaxial rock strength experimental data;
[0076] Fitting the true triaxial rock strength experimental data based on least squares method and the true triaxial rock strength criterion to calculate strength parameters in the true triaxial rock strength criterion; the strength parameters include cohesion and internal friction angle.
[0077] In some embodiments, in order to eliminate the influence of individual abnormal data points on the fitting result and ensure that the fitting curve is located in the region of the majority of normal data sets, the least squares method is selected, the sum of error absolute values is taken as the objective function (equation 7), and a set of true triaxial rock strength experimental data is fitted by the strength criterion constructed in step S2 to determine the undetermined parameters and the prediction error.
[0078]
[0079] in formula (7), are true triaxial rock strength test value and predicted value respectively, i represents the i-th group of data, and N represents the number of experiments.
[0080] S4, fitting of undetermined parameters of Mohr-Coulomb strength criterion based on pseudo-triaxial rock strength test data.
[0081] In some embodiments, the S4 comprises:
[0082] obtaining pseudo-triaxial rock strength test data;
[0083] fitting the pseudo-triaxial rock strength test data based on least square method and the true triaxial rock strength criterion, to calculate the strength parameters in the pseudo-triaxial rock strength criterion, including cohesion and internal friction angle.
[0084] In some embodiments, the same as formula (7), the MC strength criterion is used to fit the pseudo-triaxial strength test data in the true triaxial rock strength test data, to determine the undetermined parameters, namely cohesion and internal friction angle.
[0085] In some embodiments, the S4 further comprises:
[0086] predicting true triaxial rock strength based on the strength parameters in the pseudo-triaxial strength criterion, to calculate fitting error.
[0087] S5, based on the undetermined parameters determined in step S4, using the modified rock strength criterion to predict true triaxial rock strength test data, and determining fitting error.
[0088] In some embodiments, the S5 comprises:
[0089] substituting the strength parameters in the pseudo-triaxial rock strength criterion into the true triaxial strength criterion, to fit the true triaxial rock strength test data, and calculate prediction error.
[0090] Specifically, the cohesion and internal friction angle determined in step S4 are substituted into the modified MC strength criterion, to predict true triaxial rock strength test data, and determine fitting error.
[0091] S6, comparison of undetermined parameters determined in steps S3 and S4, and analysis of true triaxial rock strength prediction error determined in steps S3 and S5.
[0092] In some embodiments, the S6 comprises:
[0093] Based on the strength parameter in the true triaxial rock strength criterion, the strength parameter in the pseudo triaxial rock strength criterion, and the prediction error, the feasibility of calculating the cohesion and the internal friction angle based on the pseudo triaxial rock strength data to predict the true triaxial rock strength is determined.
[0094] The cohesion and the internal friction angle determined by the two methods are very small in comparison with the undetermined parameters determined in steps S3 and S4, which preliminarily indicates that the method of determining the undetermined parameters of the modified MC criterion based on the pseudo triaxial strength experimental data is feasible; further, in comparison with the prediction errors of the true triaxial rock strength determined in steps S3 and S5, it can be found that the prediction errors of the two methods are basically the same, and the prediction accuracy of the cohesion and the internal friction angle based on the pseudo triaxial strength experimental data to the true triaxial rock strength experimental data is also very high, which confirms the feasibility of the present application.
[0095] S7, preparing standard core samples and carrying out pseudo triaxial strength experiments of the rock under different confining pressures.
[0096] In some embodiments, the S7 comprises:
[0097] Based on the first preset number of standard core samples, pseudo triaxial strength experiments of the rock under the second preset number of confining pressures are carried out to obtain the rock strength data of each standard core sample under different confining pressures;
[0098] The first preset number is greater than or equal to 5, and the second preset number is greater than or equal to 5.
[0099] Optionally, pseudo triaxial strength experiments of the rock under 0MPa, 20MPa, 40MPa, 60MPa, and 80MPa confining pressures are carried out to test the strength of the rock under different confining pressures.
[0100] In a specific example, five standard cores with a diameter of 25mm and a length of 5mm are prepared, and a triaxial compression experimental instrument is used to test the strength of the cores under 0MPa, 20MPa, 40MPa, 60MPa, and 80MPa confining pressures.
[0101] S8, fitting of the undetermined parameters based on the pseudo triaxial rock strength experimental data.
[0102] Figure 9 The rock strength and the MC criterion fitting curve under different confining pressures are shown.
[0103] In some embodiments, the S8 comprises:
[0104] Based on the least squares method, the rock strength data are fitted using the modified Mohr-Coulomb strength criterion to obtain the cohesion and the internal friction angle of the rock.
[0105] Specifically, the least square method is also adopted, the rock strength under different confining pressures obtained in S7 is fitted by taking formula (7) as a target function, and the cohesion and internal friction angle of the rock are obtained by using the MC strength criterion.
[0106] The true triaxial rock strength criterion and parameter determination method provided by the embodiment of the present application adopts a hyperbolic Lode angle shape function to replace the Lode angle shape function of the MC strength criterion, establishes the true triaxial rock strength criterion, solves the problem that the existing three-dimensional rock strength criterion cannot simultaneously meet the requirements of smooth and convex yield surface, and simultaneously, the modified MC strength criterion can simultaneously intersect with the triaxial tensile and triaxial compression stress points on the pi plane, the undetermined parameters of the criterion can be obtained by using the pseudo-triaxial strength experiment, the method saves time and effort, can complete the test in most rock mechanics laboratories, and has very high prediction accuracy for the true triaxial rock strength experimental data.
[0107] Embodiment two,
[0108] In order to prove the feasibility of using pseudo-triaxial experimental data to determine the undetermined parameters of the true triaxial strength criterion, a large amount of experimental data is required to prove the feasibility of the present application, and 32 groups of true triaxial rock strength experimental data are selected to illustrate the feasibility of the present application.
[0109] Table 1 is a true triaxial rock strength experimental data table.
[0110] Table 1
[0111]
[0112]
[0113] Based on the least square method, the true triaxial rock strength criterion constructed by the present application is used to fit the above 32 groups of true triaxial rock strength experimental data, and the cohesion, internal friction angle and fitting error are obtained; based on the same method, the fitting error of the 10 kinds of commonly used strength criteria, Mohr-Coulomb (MC), Mogi-Coulomb (MGC), Modified-Lade (ML), Modified-Wiebols-Cook (MWC), MC criterion three-dimensional approximation criterion (MCJP), Hoek-Brown (HB), Pan-Hudson (PH), Generalized Priest (GP), Zhang-Zhu (ZZ), Hoek-Brown criterion three-dimensional approximation criterion (HBWW) on the experimental data in Table 1 is obtained.
[0114] Figure 5 The true triaxial strength criterion fitting minimum absolute deviation and the existing strength criterion prediction result comparison diagram is shown.
[0115] Reference Figure 5The minimum value of the prediction error of the existing strength criterion is compared with the prediction error of the strength criterion constructed in the application, and it can be seen that the true triaxial rock strength criterion constructed in the application has high fitting accuracy for the experimental data, which is less than or close to the minimum value of the prediction error of the existing criterion.
[0116] In the 32 groups of experimental data in Table 1, except for the Yuubari shale and Sandstone-Zhang two groups of experimental data, the remaining 30 groups all contain the strength data of the rock under the triaxial compression stress state, the pseudo-triaxial strength experimental data points in the 30 groups of true triaxial rock strength experimental data are extracted, and based on the least square method, the Mohr-Coulomb criterion is used to fit the pseudo-triaxial strength experimental data points, and the cohesion and internal friction angle are obtained.
[0117] Figure 6 The comparison diagram of the cohesion fitted based on the true triaxial experimental data and the pseudo-triaxial experimental data is shown.
[0118] Figure 7 The comparison diagram of the internal friction angle fitted based on the true triaxial experimental data and the pseudo-triaxial experimental data is shown.
[0119] Referring to Figure 6 and Figure 7 Comparing the cohesion and internal friction angle fitted by the true triaxial rock strength criterion constructed in the application and the experimental data in Table 1, it can be seen that the cohesion and internal friction angle determined by the two methods are very close, which preliminarily proves the feasibility of determining the parameters to be determined of the three-dimensional rock strength criterion using the pseudo-triaxial experimental data.
[0120] In order to further verify the feasibility of determining the parameters to be determined of the modified MC strength criterion using the pseudo-triaxial experimental data in the modified MC strength criterion established in the application, the strength parameters of the modified MC strength criterion determined by the pseudo-triaxial experimental data are used to study the fitting error of the true triaxial rock strength experimental data.
[0121] Figure 8 The MCYL criterion fitting average minimum absolute deviation radar chart based on the pseudo-triaxial experimental data and the true triaxial experimental data is shown.
[0122] Referring to Figure 8 Comparing the average minimum absolute deviation obtained by fitting, it can be seen that the average minimum absolute deviation obtained by predicting the true triaxial rock strength experimental data using the strength parameters determined by the two methods is very small, which shows that the strength parameters determined by the pseudo-triaxial experimental data applied to the modified MC strength criterion constructed in the application also have high prediction accuracy for the true triaxial rock strength experimental data, the prediction error is within an acceptable range, and the method for determining the parameters to be determined saves time and effort, and it is possible to complete the test in most rock mechanics laboratories.
[0123] Further, 5 standard cores are drilled on the same volcanic rock mass, and pseudo-triaxial compression experiments are carried out under 0MPa, 20MPa, 40MPa, 60MPa and 80MPa.
[0124] Table 2 is a data table of rock strength experiment results measured under different confining pressures.
[0125] Table
[0126] Confining pressure / MPa 0 20 40 60 80 Rock strength / MPa 98 170 247 284 326
[0127] Figure 9 Rock strength under different confining pressures and MC criterion fitting curves are shown.
[0128] Referring to Figure 9 Based on the least square method, the cohesion is 33.5MPa and the internal friction angle is 28.7° by using the MC strength criterion to fit the data in Table 2, so the strength parameters of the rock, i.e., the cohesion is 33.5MPa and the internal friction angle is 28.7°, of the true triaxial rock strength criterion constructed by the application can be determined.
[0129] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than limit them; although the present application has been described in detail with reference to the foregoing embodiments, those ordinarily skilled in the art should understand: the technical solutions recorded in the foregoing embodiments can still be modified, or some technical features can be replaced equivalently; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.
Claims
1. A true triaxial rock strength criterion and parameter determination method, characterized in that, The method comprises: S1, rock strength criterion conversion; S2, replacement of Lode angle shape function and construction of true triaxial rock strength criterion; S3, fitting of undetermined parameters of modified strength criterion based on true triaxial rock strength experimental data and determination of prediction error; S4, fitting of undetermined parameters of Mohr-Coulomb strength criterion based on pseudo-triaxial rock strength experimental data; S5, prediction of true triaxial rock strength experimental data by using the modified rock strength criterion based on the undetermined parameters determined in step S4, and determination of fitting error; S6, comparison of undetermined parameters determined in steps S3 and S4 and analysis of true triaxial rock strength prediction error determined in steps S3 and S5; S7, preparation of standard core samples and carrying out rock pseudo-triaxial strength experiments under different confining pressures; S8, fitting of undetermined parameters based on pseudo-triaxial rock strength experimental data; The S1 includes: adopting the principal stress Mohr-Coulomb strength criterion represented by Converts into a form represented by three variables of hydrostatic pressure, second stress deviator invariant and Lode angle ; The S2 comprises: replacing the Lode angle shape function in the Mohr-Coulomb strength criterion with a hyperbolic Lode angle shape function to obtain a modified Mohr-Coulomb strength criterion; The hyperbolic Lode angle shape function is as follows: ； The S3 comprises: obtaining true triaxial rock strength experimental data; fitting the true triaxial rock strength experimental data based on least squares method and the true triaxial rock strength criterion to calculate strength parameters in the true triaxial rock strength criterion; the strength parameters in the true triaxial rock strength criterion include cohesion and internal friction angle; The S4 comprises: obtaining pseudo-triaxial rock strength experimental data; fitting the pseudo-triaxial rock strength experimental data based on least squares method and the true triaxial rock strength criterion to calculate strength parameters in the Mohr-Coulomb strength criterion; the strength parameters in the Mohr-Coulomb strength criterion include cohesion and internal friction angle; In S3 and S4, the least squares method takes the sum of absolute values of errors as the objective function, and the objective function is as follows: ； , In S3 true triaxial rock strength test values and predicted values; , In S4 false triaxial rock strength test values and predicted values; i denotes the i-th data set, N denotes the number of experiments.
2. The true triaxial rock strength criterion and parameter determination method according to claim 1, characterized in that, The S4 further comprises: Predicting true triaxial rock strength based on the strength parameters in the Mohr-Coulomb strength criterion and calculating fitting error.
3. The true triaxial rock strength criterion and parameter determination method according to claim 2, characterized in that, The S5 comprises: Substituting the strength parameters in the Mohr-Coulomb strength criterion into the true triaxial rock strength criterion to fit the true triaxial rock strength experimental data and calculate prediction error.
4. The true triaxial rock strength criterion and parameter determination method according to claim 3, characterized in that, The S6 comprises: Based on the strength parameters in the true triaxial rock strength criterion, the strength parameters in the Mohr-Coulomb strength criterion and the prediction error, judging the feasibility of calculating cohesion and internal friction angle based on pseudo-triaxial rock strength data to predict true triaxial rock strength.
5. The true triaxial rock strength criterion and parameter determination method according to claim 4, characterized in that, The S7 comprises: Based on the first preset number of standard core samples, carrying out rock pseudo-triaxial strength experiments under a second preset number of confining pressures to obtain rock strength data of each standard core sample under different confining pressures; The first preset number is greater than or equal to 5, and the second preset number is greater than or equal to 5.
6. The true triaxial rock strength criterion and parameter determination method according to claim 5, characterized in that, The S8 comprises: Based on least square method, the rock strength data is fitted using the modified Mohr-Coulomb strength criterion to obtain the rock cohesion and internal friction angle.