Method for predicting rock macroscopic failure mechanism based on mesoscopic tension shear damage model

Abstract

The invention relates to a method for predicting a rock macroscopic failure mechanism based on a mesoscopic tension shear damage model, and belongs to the field of rock mass engineering. The problems that an existing rock model is insufficient in reliability and accuracy when predicting the macroscopic failure evolution law and / or strength in the quasi-static state, and it is difficult to reveal at least one of damage and failure micromechanics mechanisms in the quasi-static state are solved. The method comprises the following steps: S1, obtaining experimental data through single-axis, three-axis and CCNBD experiments; s2, constructing a tension damage model; s3, constructing a shear damage model; s4, obtaining a sigma < 1-L > curve according to the tension damage model; obtaining a sigma < 1 >-D1 curve according to the shear damage model; and S5, combining the two models to predict the damage strength and / or law during quasi-static loading. According to the method, by combining the tension damage model and the shear damage model, the accuracy and reliability of the rock model in predicting the evolution law and strength of the macroscopic damage in the quasi-static state are improved, and a mesomechanics mechanism of the damage in the quasi-static state is disclosed.

Description

Technical Field

[0001] The invention relates to the technical field of rock mass engineering, and in particular to a method for predicting a macroscopic failure mechanism of rock based on a microscopic tension shear damage model. Background Art

[0002] In underground rock engineering, such as mining, nuclear waste storage construction, shale gas mining, etc., the rock is actually in a triaxial geostress state before disturbance. Understanding the damage and fracture properties of rock under triaxial stress state is of great significance for the development of such projects. When conducting indoor rock mechanics experiments, the influence of geostress can be studied by studying the damage and fracture properties of rock under different confining pressure conditions. Many scholars use conventional triaxial compression tests to study the basic mechanical properties of rocks, analyze the influence of confining pressure on rock deformation and strength, and use strength criteria to estimate rock strength. Although there are many existing rock damage models, they are often difficult to reflect reality. For example, there is a lack of accuracy in predicting the macroscopic failure law and strength of rocks under quasi-static conditions. Summary of the invention

[0003] In view of the above analysis, the present invention aims to provide a method for predicting the macroscopic failure mechanism of rock based on a microscopic tensile shear damage model, so as to solve at least one of the following problems existing in the existing rock damage model: (1) insufficient reliability and accuracy in predicting the evolution law of macroscopic damage and destruction of rock under quasi-static conditions; (2) insufficient reliability and accuracy in predicting the strength of rock under quasi-static conditions; (3) difficulty in revealing the microscopic mechanical mechanism of rock damage and destruction under quasi-static conditions.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] The present invention provides a method for predicting the macroscopic failure mechanism of rock based on a mesoscopic tensile shear damage model, comprising the following steps:

[0006] S1. Through uniaxial and triaxial tests and CCNBD experiments, experimental data of rock samples are obtained, including stress-strain curves under different confining pressures, characteristic stresses during loading, material property parameters, and quasi-static fracture toughness K IC ;

[0007] S2. Based on the experimental data of S1, the tension model parameters are determined; based on the interaction between multiple cracks and the superposition principle, the wing crack extension model under quasi-static loading is obtained, and combined with the determined tension model parameters, a rock mesoscopic tension damage model is constructed;

[0008] The method for determining the value of the crack length correction parameter λ includes: calculating based on the crack initiation stress of the wing crack growth model in uniaxial compression being equal to the crack initialization stress; the method for determining the value of the crack spacing w includes: calculating based on the strength of the wing crack growth model in uniaxial compression being equal to the experimental uniaxial compressive strength;

[0009] S3. Based on the experimental data of S1, the shear model parameters are determined; based on the Mohr-Coulomb criterion and Weibull statistical distribution, combined with the determined shear model parameters, a rock mesoscopic shear damage model is constructed;

[0010] The method for determining the values ​​of the rock homogeneity coefficient m and the material constant a includes: obtaining the strength fitting intercept of the rock under pure shear failure under medium and high confining pressure conditions according to the stress-strain curve, and determining it in combination with the expression of the mesoscopic shear damage model;

[0011] S4. According to the rock mesoscopic tensile damage model constructed in S2, the σ1-L relationship curve between the axial stress σ1 and the wing crack extension length L under different confining pressures is obtained; according to the rock mesoscopic shear damage model constructed in S3, the σ1-D1 relationship curve between the axial stress σ1 and the shear damage D1 under different confining pressures is obtained;

[0012] S5. According to the σ1-L relationship curve and the σ1-D1 relationship curve, the peak strength of rock under different confining pressures predicted by the tension damage model and the peak strength of rock under different confining pressures predicted by the shear damage model are obtained respectively; combining the peak strength of rock predicted by the two models, the damage and failure law and / or strength of rock under low confining pressure and / or medium and high confining pressure during quasi-static loading are predicted.

[0013] Further, in step S2, the method for determining the value of the crack length correction parameter λ specifically includes the following steps: according to the wing crack extension model, the crack initiation stress is equal to the crack initialization stress during uniaxial compression, and formula (1) is derived;

[0014]

[0015] In formula (1), σ ci-I is the crack initialization stress obtained from the uniaxial test, μ is the friction coefficient of the rock sample, b is the initial oblique crack length of the rock sample, and θ0 is the inclination angle of the initial oblique crack of the rock sample; other parameters μ, b, θ0, K determined based on the experimental data in S1 are IC Substitute into formula (1) and calculate the value of λ.

[0016] Further, in step S2, the method for determining the value of the crack spacing w specifically includes the following steps:

[0017] S211, according to the wing crack growth model under uniaxial compression, the formula (2) is derived, based on the determined λ and other parameters μ, b, θ0, K IC , draw the curve of L changing with σ1 for different w values, and obtain the axial stress peak σ in each σ1-L change curve p,t That is, the theoretical uniaxial compressive strength value, based on the σ corresponding to different w values p,t , we get p,t -w fitting graph;

[0018]

[0019] S212. Based on the stress-strain curve of the rock sample under uniaxial compression in S1, the experimental uniaxial compressive strength value σ of the rock sample is obtained. p,exp ; From the σ p,t -w In the fitting graph, find σ p,t =σ p,exp The corresponding horizontal coordinate point value is the crack spacing w.

[0020] Furthermore, in step S3, the method for obtaining the value of the homogeneity coefficient m and the material constant a specifically includes the following steps:

[0021] S311, selecting the maximum confining pressure σ among the different confining pressures described in step S1 3-max As the basis for calculating m and a, according to the confining pressure σ 3-max The peak stress σ is determined by the stress-strain curve under 1-max and σ 1-max The corresponding axial strain ε 1-max The measured value of

[0022] S312, according to the stress-strain curve described in S1, obtain the axial stress peak value, i.e., the strength σ under different confining pressures σ3 p , according to the medium and high confining pressure σ p -σ3 linear fitting intercept d1, and combined with the intercept expression of the shear damage model described in S3 when σ3 = 0, we get formula (3):

[0023]

[0024] In formula (3), is the internal friction angle of the rock sample;

[0025] S313. Since the reasonable value range of shear damage D1 is 0-1 and the reasonable value range of homogeneity coefficient m is m≥1, the value of D1 is set to a series of point values ​​between 0 and 1 in the numerical calculation software, and the value of m is set to a series of point values ​​greater than or equal to 1. Based on formula (3), the corresponding values ​​of different m values ​​are determined without considering a. D at the maximum value 1-max Theoretical calculated value, based on D 1-max Theoretical calculation value combined with rock damage theory to determine the axial strain ε under different m values 1-max Theoretical calculated value of

[0026] S314, Comparison ε 1-max The theoretical calculated value and the measured value are adjusted by adjusting the value of m until the two are consistent or meet the expected difference range, so as to determine the optimal solution of m value. Substitute the optimal solution of m value into formula (3) and use the D corresponding to the optimal solution of m value 1-max The theoretical calculated value replaces D1 in formula (3) to obtain the optimal solution of the value of a.

[0027] Furthermore, the axial strain ε 1-max The specific method for determining the theoretical calculation value of includes: Since the rock damage under medium and high confining pressure conditions is shear damage, combined with rock damage theory, formula (4) is obtained:

[0028]

[0029] In formula (4), α is Poisson’s ratio, and E0 is the elastic modulus of the rock sample in the initial undamaged state.

[0030] Furthermore, step S5 specifically includes the following steps: when the confining pressure is constant, the peak strength values ​​predicted by the two models are compared, and the model with lower peak strength is used as a benchmark to predict the type and / or intensity of rock macroscopic failure and / or the quantitative change law of damage failure.

[0031] Furthermore, the rock sample is yellow sandstone, the low confining pressure is σ3≤10Mpa, and the medium and high confining pressure is σ3≥15Mpa.

[0032] Further, in step S2, the rock mesoscopic tensile damage model includes model I and model II;

[0033] The expression of model I is formula (5):

[0034]

[0035] The expression of model II is formula (6):

[0036]

[0037] In formula (5) and formula (6), K Iis the stress intensity factor of the wing crack tip under quasi-static conditions, σ1 is the axial stress, σ3 is the confining pressure, L is the wing crack extension length; λ is the crack length correction parameter, w is the crack spacing; μ is the friction coefficient of the rock sample, b is the initial oblique crack length of the rock sample, and θ0 is the inclination angle of the initial oblique crack of the rock sample;

[0038] Step S4 specifically includes: according to equations (5) and (6), when K I =K IC When the confining pressure σ3 is a constant, the σ1-L relationship curve under the confining pressure is obtained.

[0039] Further, in step S3, the rock mesoscopic shear damage model is expressed as formula (7):

[0040]

[0041] In formula (7), D1 is the shear damage of rock, σ1 is the axial stress, σ3 is the confining pressure, is the internal friction angle of the rock sample, m is the homogeneity coefficient, and a is the material constant.

[0042] The present invention also provides a method for constructing a rock tension damage model under dynamic load, which mainly includes: by introducing correction coefficients related to the crack growth rate v, the damage variable β, and the crack closure coefficient η, the rock mesoscopic tension damage model under quasi-static loading obtained by the method described above is corrected to obtain the rock tension damage model under dynamic load.

[0043] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0044] (1) The present invention effectively solves the limitations of existing rock constitutive models in predicting rock strength by innovatively combining the tension damage model with the shear damage model. These limitations include: focusing only on a single failure mode of rock (tension or shear), and ignoring the interaction between tension and shear forces in the analysis of rock failure. In addition, the present invention also proposes an innovative parameter determination method for key parameters (such as λ, w, m, a) in the tension damage model and the shear damage model, so that the method for predicting the macroscopic failure mechanism of rock established by combining the two models can more accurately reflect the physical properties and behavior of the rock, thereby enhancing the accuracy and reliability of predicting the strength of rock under quasi-static conditions based on the rock constitutive model.

[0045] (2) The present invention significantly improves the accuracy and reliability of the rock constitutive model in predicting the evolution law of rock macroscopic damage under quasi-static conditions by combining the tension damage model and the shear damage model and combining the above-mentioned key model parameter determination method.

[0046] (3) Based on the combination of the two models and the key parameter determination method provided by the present invention, the accuracy and reliability of the macroscopic damage evolution law and strength prediction of rocks under quasi-static conditions have been significantly improved, which can better reveal the microscopic mechanical mechanism of rock damage under quasi-static conditions.

[0047] (4) Furthermore, conventional loading experiments and acoustic emission analysis methods were used to verify the accuracy and reliability of the combined two models provided by the present invention in predicting the macroscopic failure law and strength of rocks under quasi-static conditions. By comparing the theoretical predictions with the experimental data results, it was found that the prediction results of the combined two microscopic damage models (i.e., tension and shear models) provided by the present invention were highly consistent with the results of conventional loading experiments and acoustic emission analysis methods. This shows that the method provided by the present invention is accurate, reliable and stable in predicting the macroscopic failure mechanism of rocks under quasi-static conditions, and has important significance and application value for the development of rock engineering.

[0048] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents particularly pointed out in the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like components throughout the drawings.

[0050] Figure 1 A photo of the appearance of a yellow sandstone sample used in the method provided in an embodiment of the present invention;

[0051] Figure 2 The morphology of the yellow sandstone sample after the sandstone is destroyed under conventional loading conditions used in the method provided in the embodiment of the present invention;

[0052] Figure 3 A stress-strain curve diagram of a yellow sandstone sample under different confining pressures in the method provided in an embodiment of the present invention;

[0053] Figure 4 A stress-strain diagram including characteristic stress, a volume strain curve diagram and a crack volume strain curve diagram of a yellow sandstone sample under a confining pressure of 0 in the method provided in an embodiment of the present invention;

[0054] Figure 5 A stress-strain diagram including characteristic stress, a volume strain curve diagram, and a crack volume strain curve diagram of a yellow sandstone sample under a confining pressure of 20 MPa in the method provided in an embodiment of the present invention;

[0055] Figure 6 A curve showing the relationship between the peak stress and the confining pressure of a yellow sandstone sample under different confining pressures in the method provided in an embodiment of the present invention;

[0056] Figure 7 A curve showing the relationship between crack initialization stress and confining pressure of a yellow sandstone sample under different confining pressures in the method provided in an embodiment of the present invention;

[0057] Figure 8 A comparison chart of the theoretical crack initialization stress and the experimental measured value when λ is 0.05 in the method provided in an embodiment of the present invention;

[0058] Fig. 9 In the method provided in the embodiment of the present invention, the crack spacing w is equal to 2.4×10 -3 The curve of L changing with σ1 at m;

[0059] Fig.10 The theoretical uniaxial compressive strength value σ in the method provided in the embodiment of the present invention p,t Fitting diagram with crack spacing w;

[0060] Fig.11 In the method provided in the embodiment of the present invention, w=1.6×10 -3 m, the curve of L changing with σ1 when the confining pressure is less than or equal to 10MPa;

[0061] Fig.12 In the method provided in the embodiment of the present invention, w=1.6×10 -3 Comparison chart of theoretical strength and experimental measured values ​​under different confining pressures at m;

[0062] Fig.13 A σ1-L relationship curve between the axial stress σ1 and the wing crack extension length L under different confining pressures in the method provided in an embodiment of the present invention;

[0063] Fig.14 A σ1-D1 relationship curve between the axial stress σ1 and the shear damage D1 under different confining pressures in the method provided in an embodiment of the present invention;

[0064] Fig.15 A comparison diagram of the peak strength and actual strength of sandstone obtained by the tension and shear mesoscopic models in the method provided in an embodiment of the present invention;

[0065] Fig.16 The diagram is a diagram showing the evolution of damage variables D1 and D2 with differential stress generated during loading under different confining pressures in the method provided in an embodiment of the present invention, where (a) is the confining pressure σ3=0 MPa, and (b) is the confining pressure σ3=20 MPa;

[0066] Fig.17A diagram showing the evolution of the cumulative damage value of sandstone at peak stress under different confining pressures as a function of the confining pressure in the method provided in an embodiment of the present invention;

[0067] Fig.18 This is a graph showing how the ratio of the cumulative energy of tension-type acoustic emission to shear-type acoustic emission changes with confining pressure in the verification example of the present invention. DETAILED DESCRIPTION

[0068] The preferred embodiments of the present invention are described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0069] Based on in-depth research, the inventors of the present invention found that the existing rock constitutive models and strength criteria have some limitations, either using a single tension and shear model to study rock strength, or ignoring the tension and shear properties of rock failure. This biased methodology, coupled with the irrationality of determining some model parameters, has led to the existing rock models being inaccurate in predicting rock strength, damage evolution laws, and micromechanical mechanisms under quasi-static conditions, and difficult to reveal the quantitative change laws. Therefore, an innovative method is needed to overcome the above limitations of the existing rock models to improve the model's predictive ability and explanatory power for rock failure damage under quasi-static conditions.

[0070] Based on this, the present invention provides a method for predicting the macroscopic failure mechanism of rock based on a mesoscopic tensile shear damage model, comprising the following steps:

[0071] S1. Through uniaxial and triaxial tests and CCNBD experiments, experimental data of rock samples are obtained, including stress-strain curves under different confining pressures, characteristic stresses during loading, material property parameters, and quasi-static fracture toughness K IC ;

[0072] S2. Based on the experimental data of S1, the tension model parameters are determined; based on the interaction between multiple cracks and the superposition principle, the wing crack extension model under quasi-static loading is obtained, and combined with the determined tension model parameters, a rock mesoscopic tension damage model is constructed;

[0073] The method for determining the value of the crack length correction parameter λ includes: calculating based on the crack initiation stress of the wing crack growth model in uniaxial compression being equal to the crack initialization stress; the method for determining the value of the crack spacing w includes: calculating based on the strength of the wing crack growth model in uniaxial compression being equal to the experimental uniaxial compressive strength;

[0074] S3. Based on the experimental data of S1, the shear model parameters are determined; based on the Mohr-Coulomb criterion and Weibull statistical distribution, combined with the determined shear model parameters, a rock mesoscopic shear damage model is constructed;

[0075] The method for determining the values ​​of the rock homogeneity coefficient m and the material constant a includes: obtaining the strength fitting intercept of the rock under pure shear failure under medium and high confining pressure conditions according to the stress-strain curve, and determining it in combination with the expression of the mesoscopic shear damage model;

[0076] S4. According to the rock mesoscopic tensile damage model constructed in S2, the σ1-L relationship curve between the axial stress σ1 and the wing crack extension length L under different confining pressures is obtained; according to the rock mesoscopic shear damage model constructed in S3, the σ1-D1 relationship curve between the axial stress σ1 and the shear damage D1 under different confining pressures is obtained;

[0077] S5. According to the σ1-L relationship curve and the σ1-D1 relationship curve, the peak strength of rock under different confining pressures predicted by the tension damage model and the peak strength of rock under different confining pressures predicted by the shear damage model are obtained respectively; combining the peak strength of rock predicted by the two models, the damage and failure law and / or strength of rock under low confining pressure and / or medium and high confining pressure during quasi-static loading are predicted.

[0078] Compared with the prior art, the present invention innovatively combines the tension damage model with the shear damage model, effectively solving the limitations of the existing rock constitutive model in predicting rock strength, which include: focusing only on a single failure mode of rock (tension or shear), and ignoring the interaction between tension and shear forces in the analysis of rock failure. In addition, the present invention also proposes an innovative parameter determination method for key parameters (such as λ, w, m, a) in the tension damage model and the shear damage model, so that the method for predicting the macroscopic failure mechanism of rock established by combining the two models can more accurately reflect the physical properties and behavior of the rock, thereby enhancing the accuracy and reliability of predicting the strength of rock under quasi-static conditions based on the rock constitutive model.

[0079] The present invention significantly improves the accuracy and reliability of the rock constitutive model in predicting the evolution law of rock macroscopic damage and destruction under quasi-static conditions by combining the tension damage model and the shear damage model and combining the above-mentioned key model parameter determination method.

[0080] Based on the combination of the two models and the key parameter determination method provided by the present invention, the accuracy and reliability of the macroscopic damage and destruction evolution law and strength prediction of rocks under quasi-static conditions are significantly improved, which can better reveal the microscopic mechanical mechanism of rock damage and destruction under quasi-static conditions.

[0081] Specifically, in step S2, the method for determining the value of the crack length correction parameter λ (i.e., step S20) specifically includes the following steps: according to the wing crack extension model, the crack initiation stress is equal to the crack initialization stress during uniaxial compression, and formula (1) is derived:

[0082]

[0083] In formula (1), σ ci-I is the crack initialization stress obtained from the uniaxial test, μ is the friction coefficient of the rock sample, b is the initial oblique crack length of the rock sample, θ0 is the inclination angle of the initial oblique crack of the rock sample, and other parameters μ, b, θ0, K determined based on the experimental data in S1 are IC Substitute into formula (1) and calculate the value of λ.

[0084] Further, in step S2, the method for determining the crack spacing w (i.e., step S21) specifically includes the following steps:

[0085] S211, according to the wing crack growth model under uniaxial compression, the formula (2) is derived, based on the determined λ and other parameters μ, b, θ0, K IC , draw the curve of L changing with σ1 for different w values, and obtain the axial stress peak σ in each σ1-L change curve p,t That is, the theoretical uniaxial compressive strength value, based on the σ corresponding to different w values p,t , we get p,t -w fitting graph;

[0086]

[0087] S212. Based on the stress-strain curve of the rock sample under uniaxial compression in S1, the experimental uniaxial compressive strength value σ of the rock sample is obtained. p,exp ; From the σ p,t -w In the fitting graph, find σ p,t =σ p,exp The corresponding horizontal coordinate point value is the crack spacing w.

[0088] Specifically, in step S3, the method for obtaining the value of the homogeneity coefficient m and the material constant a (i.e., step S31) specifically includes the following steps:

[0089] S311, selecting the maximum confining pressure σ among the different confining pressures described in step S1 3-max As the basis for calculating m and a, according to the confining pressure σ 3-max The peak stress σ is determined by the stress-strain curve under 1-max and σ 1-max The corresponding axial strain ε 1-max The measured value of

[0090] S312, according to the stress-strain curve described in S1, obtain the axial stress peak value, i.e., the strength σ under different confining pressures σ3 p , according to the medium and high confining pressure σ p -σ3 linear fitting intercept d1, and combined with the intercept expression of the shear damage model described in S3 when σ3 = 0, we get formula (3):

[0091]

[0092] In formula (3), is the internal friction angle of the rock sample;

[0093] S313. Since the reasonable value range of shear damage D1 is 0-1 and the reasonable value range of homogeneity coefficient m is m≥1, the value of D1 is set to a series of point values ​​between 0 and 1 in the numerical calculation software, and the value of m is set to a series of point values ​​greater than or equal to 1. Based on formula (3), the corresponding values ​​of different m values ​​are determined without considering a. D at the maximum value 1-max Theoretical calculated value, based on D 1-max Theoretical calculation value combined with rock damage theory to determine the axial strain ε under different m values 1-max Theoretical calculated value of

[0094] Preferably, the axial strain ε 1-max The specific method for determining the theoretical calculation value of includes: Since the rock damage under medium and high confining pressure conditions is shear damage, combined with rock damage theory, formula (4) is obtained:

[0095]

[0096] In formula (4), α is Poisson’s ratio, and E0 is the elastic modulus of the rock sample in the initial undamaged state.

[0097] S314, Comparison ε 1-max The theoretical calculated value and the measured value are adjusted by adjusting the value of m until the two are consistent or meet the expected difference range, so as to determine the optimal solution of m value. Substitute the optimal solution of m value into formula (3) and use the D corresponding to the optimal solution of m value 1-max The theoretical calculated value replaces D1 in formula (3) to obtain the optimal solution of the value of a.

[0098] In some preferred embodiments, step S5 specifically includes the following steps: when the confining pressure is constant, compare the peak strength values ​​predicted by the two models, use the model with lower peak strength as a benchmark, and predict the type and / or intensity of rock macroscopic failure and / or the quantitative change law of damage and failure.

[0099] It should be noted that in step S1, the material characteristic parameters include: material mechanical characteristic parameters and material geometric characteristic parameters of the rock sample. The material mechanical characteristic parameters specifically include: elastic modulus E and Poisson's ratio α, internal friction angle Friction coefficient μ; the material geometric characteristic parameters specifically include: initial oblique crack length b, initial oblique crack inclination angle θ0.

[0100] In some preferred embodiments, step S1 specifically includes the following steps:

[0101] S11. Through uniaxial loading and conventional triaxial loading tests, experimental data of rock samples are obtained, including stress-strain curves under different confining pressures σ3, elastic modulus E and Poisson's ratio α included in material characteristic parameters, and characteristic stress during loading;

[0102] The characteristic stresses include: crack initiation stress σ ci , peak stress σ p , crack closure stress σ cc , crack damage stress σ cd .

[0103] S12, according to the medium and high confining pressure σ p -σ3 linear fitting curve slope, CCNBD splitting experiment, σ ci -σ3 The slope and intercept of the linear fitting graph are used to determine the material characteristic parameters including the internal friction angle and friction coefficient μ, quasi-static fracture toughness K IC , initial oblique crack length b and initial oblique crack inclination angle θ0; S12 specifically includes the following steps:

[0104] S121, according to σ under medium and high confining pressure p -σ3 linear fit graph slope k1 and combined Determining the internal friction angle of a rock specimen according to Determine the friction coefficient μ of the rock specimen;

[0105] S122. Determine the peak load P according to the load-displacement curve of the CCNBD specimen under compression load. max , and through K IC =f(P max ) Calculate K IC ;

[0106] S123, according to σ ci -The slope k2 and intercept d2 of the linear fit graph of σ3, combined with and The initial oblique crack length b and the initial oblique crack inclination angle θ0 of the rock sample are calculated and determined.

[0107] It can be understood that the CCNBD cleavage test refers to a Cracked Chevron Notched Brazilian Disc cleavage test.

[0108] In some preferred embodiments, in steps S1-S5, the rock sample is yellow sandstone, the low confining pressure is σ3≤10 MPa, and the medium-high confining pressure is σ3≥15 MPa.

[0109] Specifically, in step S2, the rock microscopic tensile damage model includes model I and model II; the expression of model I is formula (5):

[0110]

[0111] The expression of model II is formula (6):

[0112]

[0113] In formula (5) and formula (6), K I is the stress intensity factor of the wing crack tip under quasi-static conditions, σ1 is the axial stress, σ3 is the confining pressure, L is the wing crack extension length; λ is the crack length correction parameter, w is the crack spacing; μ is the friction coefficient of the rock specimen, b is the initial oblique crack length of the rock specimen, and θ0 is the inclination angle of the initial oblique crack of the rock specimen.

[0114] Further, the step S4 of “obtaining the σ1-L relationship curve between the axial stress σ1 and the wing crack extension length L under different confining pressures according to the tensile damage model constructed in S2” specifically includes: according to equations (5) and (6), when K I =K IC When the confining pressure σ3 is a constant, the σ1-L relationship curve under the confining pressure is obtained.

[0115] Specifically, in step S3, the rock mesoscopic shear damage model is expressed as formula (7):

[0116]

[0117] In formula (7), D1 is the shear damage of rock, σ1 is the axial stress, σ3 is the confining pressure, is the internal friction angle of the rock sample, m is the homogeneity coefficient, and a is the material constant.

[0118] The present invention also provides a method for constructing a rock tensile damage model under dynamic load, which mainly includes: by introducing correction coefficients related to the crack growth rate v, the damage variable β, and the crack closure coefficient η, the rock mesoscopic tensile damage model under quasi-static loading obtained by the above method is corrected to obtain the rock tensile damage model under dynamic load. Specifically, the following steps are included:

[0119] (1) Introducing the first correction factor related to the crack growth rate v and the second correction factor Modify Model I and Model II to obtain equations (5-1) and (6-1) respectively;

[0120]

[0121] (2) Based on formula (6-1), when When σ3 = 0, a tensile damage model under one-dimensional direct dynamic load is constructed; and / or when When σ3 is a constant, a tension damage model under three-dimensional direct dynamic load is constructed;

[0122]

[0123] (4) When σ as =σ cc Or as =σ ci When, based on formula (5-2) and set σ3=0 and β=0, and the one-dimensional dynamic and static combined loading and σ as =σ cc Or as =σ ci Tensile damage model when ; and / or,

[0124] When σ as >σ ci When, based on formula (5-2) and set When σ3=0, the one-dimensional dynamic and static combined loading and σ as >σ ci Tensile damage model when ; and / or,

[0125] When σ as =σ cc Or as =σ ci When, based on formula (5-2) and set When β=0 and σ3 is a constant, the three-dimensional dynamic and static combined loading and σ as =σ cc Or as =σ ciTensile damage model when ; and / or,

[0126] When σ as >σ ci When, based on formula (5-2) and set When σ3 is a constant, the three-dimensional dynamic and static combined loading and σ as >σ ci Tensile damage model.

[0127] It should be noted that in formulas (5-1), (5-2) and (6-1), v r is the Rayleigh wave velocity, v is the crack growth rate, v is set to a constant value and is calculated as the average crack growth rate Replace; K Id is the stress intensity factor value of the wing crack tip under dynamic load; the damage variable β is the ratio of the crack body strain after crack initialization to the crack body strain at the peak strength of the rock. is the dynamic fracture toughness of rock.

[0128] The average crack growth rate and The method for obtaining the value of includes the following steps:

[0129] 1) Average crack growth rate It is obtained by calculating the ratio of crack extension length to crack extension time, wherein the crack extension length is the wing crack extension length L corresponding to the maximum value of the axial stress σ1 obtained based on the tension damage model expression under the one-dimensional direct dynamic load or the one-dimensional dynamic-static combined load and through data fitting, and the crack extension time is the time corresponding to the peak strength of the rock in the one-dimensional direct impact test or the one-dimensional dynamic-static combined impact test.

[0130] 2) Carry out one-dimensional direct impact test to obtain the stress-strain curve of rock samples at different strain rates, so as to obtain the peak strength σ at different strain rates. p That is, the measured strength; according to the measured strength and combined with the tensile damage model expression under the one-dimensional direct dynamic load and k(v) = 1, the dynamic fracture toughness of the rock is calculated in the numerical calculation software The value of is set to a series of point values, and different At different strain rates The variation curve of σ1-L is obtained from the theoretical strength, and the theoretical strength is close to the measured strength under different strain rates. The value of is fitted. relationship;

[0131] The method for determining the value of the damage variable β specifically includes the following steps:

[0132] 1) According to formula (8) and in combination with the stress-strain curve in step S11, as well as the elastic modulus E and the Poisson's ratio α, a curve of the relationship between the crack body strain and the axial strain under different confining pressures σ3 is obtained;

[0133]

[0134] In formula (8), ε axial is the axial strain, ε lateral is the hoop strain, ε V is the body strain, is the elastic body strain, is the inelastic body strain, i.e. the crack body strain, E is the elastic modulus of the rock sample, and α is the Poisson’s ratio of the rock sample;

[0135] 2) According to the pre-applied axial static load σ in the dynamic and static combined loading as and confining pressure σ bs , and accordingly, the value of the damage variable β is obtained from the relationship curve between the crack body strain and the axial strain under different confining pressures σ3.

[0136] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments.

[0137] Example 1-1

[0138] This embodiment provides a method for predicting the macroscopic failure mechanism of rock based on a microscopic tensile shear damage model, comprising the following steps:

[0139] S1. Experimental data of rock samples are obtained through uniaxial and triaxial tests and CCNBD experiments, including stress-strain curves under different confining pressures, characteristic stresses during loading, material property parameters, and quasi-static fracture toughness K IC ; Specifically including the following steps:

[0140] S11. Using the TAW-2000 rock mechanics testing system independently developed by the Institute of Geology and Geophysics, Chinese Academy of Sciences, uniaxial loading and conventional triaxial loading tests were carried out at room temperature. Specifically, the axial strain-controlled loading method was adopted with a loading rate of 0.02 mm per minute. The axial strain and circumferential strain were measured by the axial strain gauge and the circumferential strain gauge, respectively. During uniaxial loading, the specimen was placed in a suitable position and loaded until macroscopic fractures occurred in the rock specimen. During conventional triaxial loading, the axial stress and confining pressure were first loaded to the target hydrostatic stress state at a loading rate of 1 MPa / min, and then loaded at an axial strain rate of 0.02 / min until a macroscopic fracture surface was produced in the rock specimen, and the acoustic emission signal in this process was simultaneously collected.

[0141] The rock samples used in this test are yellow sandstone samples, such as Figure 1 The yellow sandstone sample is mainly composed of quartz mineral particles, with a content percentage of 70%; the content percentages of plagioclase, microcline, chlorite, dolomite, ankerite, calcite, and muscovite are 11%, 8%, 3%, 2%, 2%, 2%, 2%, and 2% respectively, and the mineral crystallinity is 89%. The basic physical parameters and loading confining pressure of the yellow sandstone sample are shown in Table 1;

[0142] Table 1 Basic physical parameters, loading and confining pressure settings, and macroscopic failure types of yellow sandstone specimens

[0143]

[0144] Through the above uniaxial loading and conventional triaxial loading tests, the experimental data of the yellow sandstone specimens were obtained, including the stress-strain curves under different confining pressures σ3 (such as Figure 3 ), elastic modulus E and Poisson's ratio α (as shown in Table 2 below) included in the material characteristic parameters, characteristic stress during loading; the characteristic stress includes: crack initialization stress σ ci , peak stress σ p , and the crack closure stress σ cc , crack damage stress σ cd The morphology of the yellow sandstone sample after sandstone failure under conventional loading conditions is as follows: Figure 2 As shown;

[0145] Table 2 Elastic modulus and Poisson's ratio of yellow sandstone samples under different confining pressures

[0146]

[0147] Where, the peak stress σ p The size of can be directly obtained through the stress-strain curve, and the other characteristic stresses need to be obtained indirectly by calculating the volume strain and the crack volume strain. For brittle rocks, the volume strain reflects the ratio of the total volume change in the rock to the total volume. The crack volume strain is equal to the inelastic volume strain of the rock during loading, and its size is equal to the volume strain of the rock minus the elastic volume strain. The calculation formula is (8);

[0148] According to the method of determining rock volume strain and crack volume strain according to formula (8) and combining Figure 3 The stress-strain data of the sandstone specimen in Table 1 are taken as an example. The specimen is subjected to uniaxial loading (i.e., specimen S1 in Table 1) and confining pressure is 20 MPa (i.e., specimen S6 in Table 1). The calculation results are shown in Table 1. Figure 4 and Figure 5 As shown; the characteristic stresses of the remaining six specimens (i.e., S2-S5 and S7-S8) can be obtained using a similar method.

[0149] S12, according to the medium and high confining pressure σ p -σ3 linear fitting curve slope, CCNBD splitting experiment, σ ci -σ3 The slope and intercept of the linear fitting graph are used to determine the material characteristic parameters including the internal friction angle and friction coefficient μ, quasi-static fracture toughness K IC , initial oblique crack length b and initial oblique crack inclination angle θ0; S12 specifically includes the following steps:

[0150] S121, according to the peak stress σ under different confining pressures obtained in S11 p , we can get the following through data fitting: Figure 6 The σ shown p -σ3 relationship curve, from Figure 6 It can be seen that the linear fit is better when the confining pressure is 15MPa, 20MPa, 25MPa and 30MPa. According to the σ under medium and high confining pressure (i.e., confining pressure σ3 ≥ 15MPa), p -σ3 linear fitting graph slope k1 = 3.22 and combined Determining the internal friction angle of sandstone specimens according to The friction coefficient of the sandstone sample was determined to be μ = 0.62;

[0151] S122. Determine the peak load P according to the load-displacement curve of the CCNBD specimen under compression load. max , and through K IC =f(P max ) Calculate K IC =0.38MPa·m 1 / 2 ; K IC =f(P max The specific calculation formula of ) is formula (9):

[0152]

[0153] In formula (9), P max is the peak load of the CCNBD specimen, B is the thickness of the Brazilian disc specimen, R is the radius of the Brazilian disc specimen, and according to the method recommended by the International Society of Rock Mechanics (ISRM), four dimensionless constants are defined to characterize the geometric dimensions of the rock, namely a0, a1, a2, a3, a4, a5, a6, a7, a8, a9, a10, a11, a12, a13, a14, a15, a16, a17, a18, a20, a21, a19, a22, a23, a24, a35, a19, a25, a26, a36, a40, a27, a37, a40, a19, a28, a38, a40, a39, a41, a50, a60, a71 B 、a s ; u and ω in formula (9) can be obtained by using a0 and a B The numerical value is obtained by linear interpolation calculation

[0154]

[0155] S123, based on the crack initialization stress σ under different confining pressures obtained in S11 ci , we can get the following through data fitting: Figure 7 As shown ci -σ3 relationship curve and its slope k2=3.2113 and intercept d2=39.799, combined with and The initial oblique crack length of the sandstone sample is calculated to be b = 3.3 × 10 -4 m and the initial oblique crack inclination angle θ0 = 65.36°.

[0156] S2. Based on the experimental data of S1, the tension model parameters are determined, and based on the interaction between multiple cracks and the superposition principle, the wing crack extension model under quasi-static loading is obtained. Combined with the determined tension model parameters, a rock mesoscopic tension damage model is constructed; S2 specifically includes the following steps:

[0157] S20, method for determining the value of crack length correction parameter λ:

[0158] S201, the crack initialization stress under confining pressure = 0 included in the S1 experimental data, that is, σ under uniaxial compression ci-I =39MPa(from Figure 4 It can be obtained that μ = 0.62, b = 3.3 × 10 -4 Substituting m and θ0=65.36° into equation (1), we obtain λ=0.05.

[0159]

[0160] S202, further verifying the accuracy and stability of the method for determining the λ value based on the calculation that the crack initiation stress of the wing crack growth model under uniaxial compression is equal to the crack initialization stress;

[0161] Specifically, according to formula (5), when the tension wing crack extension length L = 0, it is the crack initialization stress under the respective confining pressure, that is, formula (5) is simplified to formula (11):

[0162]

[0163] According to formula (11), when λ = 0.05, the crack initiation stress under different confining pressure conditions can be obtained, which is Figure 7 The measured values ​​are compared, such as Figure 8 shown.

[0164] from Figure 8It can be seen that the λ value determined by the method provided by the present invention is basically consistent with the theoretical crack initialization stress value and the measured value at different confining pressures, which shows that the method for determining the λ value provided by the present invention has high accuracy and stability, and can establish a closer connection with the actual fracture process of the rock. In fact, although λ is an empirical parameter, its value plays a key role in the analysis of rock tension crack propagation. Compared with the λ value method proposed in the prior art, the new method provided by the present invention shows higher accuracy and reliability in determining the λ value. This improvement lays a solid foundation for accurately predicting the strength of rock, the law of damage evolution, and revealing its micromechanical mechanism.

[0165] S21. Method for determining the value of crack spacing w:

[0166] S211, according to formula (2), based on the determined λ=0.05 and other parameters μ=0.62, b=3.3×10 -4 m and θ0=65.36°, K IC =0.38MPa·m 1 / 2 , plot the curve of L changing with σ1 for different w values. For example, when w = 2.4×10 -3 When m, the curve of L changing with σ1 is as follows Fig. 9 As shown, from Fig. 9 We get w = 2.4 × 10 -3 The peak axial stress σ at m p,t =90MPa; σ corresponding to different w values p,t , we get p,t -w fitting graph, see Fig.10 ;

[0167] S212, based on the stress-strain curve of the sandstone sample in S1 under uniaxial compression (i.e. Figure 4 ), and the experimental uniaxial compressive strength value σ of the sandstone sample is obtained p,exp =68MPa; Fig.10 The σ shown p,t -w fitting graph, find σ p,t =σ p,exp =68MPa, the corresponding abscissa value is the crack spacing w=1.6×10 -3 m.

[0168] S213. Further verify the accuracy and stability of the method for determining the value of w based on the calculation that the strength of the wing crack growth model under uniaxial compression is equal to the experimental uniaxial compressive strength;

[0169] Specifically, according to the obtained w = 1.6 × 10 -3Substituting m into formula (5), we can obtain the evolution law of the crack extension length of the tension wing with the axial stress under different confining pressures. From the uniaxial and triaxial test results in Table 1, it can be seen that specimens S1, S2, S3, and S4 suffered from tensile failure. Therefore, the compressive strength of these four specimens is used to test whether the selection of w value is stable, as shown in Fig.11 As shown; further, according to Figure 3 The actual strength of the sandstone sample obtained when the confining pressure is less than or equal to 10MPa is Fig.11 The strength of the sandstone in the Fig.12 As shown. Fig.12 It can be seen that the w value determined by the compressive strength under uniaxial compression conditions is basically consistent with the theoretical strength value and the measured value when the sandstone is tensilely damaged under different confining pressure conditions, which shows that the accuracy and stability of the w value determined by this method are relatively high. The w value plays a key role in the analysis of rock tensile crack propagation. Compared with the w value method proposed in the prior art, the new method provided by the present invention shows higher accuracy, stability and reliability in determining the w value, and is more closely related to the actual response characteristics of the rock. This improvement has laid a solid foundation for accurately predicting the strength of the rock, the law of damage evolution, and revealing its micromechanical mechanism.

[0170] S22. Based on the interaction and superposition principle between multiple cracks, the wing crack growth model under quasi-static loading is obtained, combining the tension model parameters determined in S1, S20 and S21, including the friction coefficient μ = 0.62, the quasi-static fracture toughness K IC =0.38MPa·m 1 / 2 , initial oblique crack length b = 3.3 × 10 -4 m, initial oblique crack inclination angle θ0 = 65.36°, crack length correction parameter λ = 0.05 and crack spacing w = 1.6 × 10 -3 m, constructing a rock microscopic tensile damage model, which includes model I and model II;

[0171] Substituting the model parameters into equation (5), we get the expression of model I, namely equation (12):

[0172]

[0173] Substituting the model parameters into equation (6), we get the expression of model II, namely equation (13):

[0174]

[0175] S3. Based on the experimental data of S1, the shear model parameters are determined; based on the Mohr-Coulomb criterion and Weibull statistical distribution, combined with the determined shear model parameters, a rock mesoscopic shear damage model is constructed;

[0176] S31. The method for obtaining the values ​​of the homogeneity coefficient m and the material constant a included in the shear model parameters specifically comprises the following steps:

[0177] S311, selecting the maximum confining pressure σ among the different confining pressures described in step S1 3-max That is, the confining pressure of sample S8 corresponding to 30 MPa is used as the calculation basis of m and a. Figure 3 The stress-strain curve shown is under a confining pressure of 30 MPa. The peak stress σ is determined 1-max =205MPa and σ 1-max =205MPa corresponding axial strain ε 1-max =2.4%;

[0178] S312, according to Figure 6 The medium and high confining pressure shown is σ3≥15MPa p The linear fitting intercept of -σ3 is d1=109.8, and combined with formula (3), formula (14) is obtained:

[0179]

[0180] In formula (14), is the internal friction angle of the sandstone sample;

[0181] S313. Since the reasonable value range of shear damage D1 is 0-1, and the reasonable value range of homogeneity coefficient m is m≥1, in the matlab software, the value of D1 is set to a series of point values ​​between 0 and 1, and the value of m is set to 1, 2, 3, 5, and 10. Based on formula (14), the corresponding values ​​of different m values ​​are determined without considering a. D at the maximum value 1-max Theoretical calculation values, according to formula (14), can be obtained when m is 1, 2, 3, 5, and 10, and the corresponding a values ​​are: 83.2MPa, 71.4MPa, 61.6MPa, 51.7MPa, and 42.7MPa.

[0182] Based on D 1-max Theoretical calculation value combined with rock damage theory to determine the axial strain ε under different m values 1-max Theoretical calculated value of

[0183] S314, Comparison ε 1-max The theoretical calculated value and the measured value are used to determine the ε corresponding to m = 5 and a = 51.7 MPa. 1-max The theoretical calculated value is consistent with the measured value of 2.4%.

[0184] Compared with the method for determining parameters a and m in the prior art, the method of calculating the values ​​of a and m based on data under medium and high confining pressures is based on the pure shear failure of rock when the confining pressure is large, and has higher accuracy, reliability and stability.

[0185] S32, based on the Mohr-Coulomb criterion and Weibull statistical distribution, combined with the parameters m=5, a=51.7Mpa determined by S31 and the parameters determined by S121 The rock mesoscopic shear damage model is constructed, and its expression is formula (15);

[0186]

[0187] S4. According to the tensile damage model constructed in S2, namely, formula (12), the σ1-L relationship curve between the axial stress σ1 and the wing crack extension length L under different confining pressures is obtained, as shown in Fig.13 According to the shear damage model constructed by S3, namely, formula (15), the σ1-D1 relationship curve between the axial stress σ1 and the shear damage D1 under different confining pressures is obtained, as shown in Fig.14 ;

[0188] S5. According to Fig.13 The σ1-L relationship curve and Fig.14 The σ1-D1 relationship curve in the figure is used to obtain the peak strength of sandstone under different confining pressures predicted by the tension damage model and the peak strength of sandstone under different confining pressures predicted by the shear damage model. The peak strength of sandstone predicted by the two models is compared with the actual strength of sandstone samples under different confining pressures, as shown in Figure 2. Fig.15 shown.

[0189] from Fig.15 It can be seen that when the confining pressure is less than or equal to 10MPa, the actual strength of sandstone is consistent with the predicted value of the tensile damage model; when the confining pressure is greater than or equal to 15MPa, the actual strength of sandstone is consistent with the predicted value of the shear damage model. Therefore, when the sandstone undergoes macroscopic tensile failure when the confining pressure is less than or equal to 10MPa, the tensile damage model can be used alone to predict the actual strength of sandstone without considering the influence of shear damage; when the sandstone undergoes macroscopic shear failure when the confining pressure is greater than or equal to 15MPa, the shear damage model can be used alone to predict the actual strength of sandstone without considering the influence of tensile damage. Fig.15 The data in the figure show that the critical confining pressure for macroscopic tension and shear failure of the sandstone sample used in this example under conventional quasi-static loading is about 10 MPa, and slightly greater than 10 MPa.

[0190] Furthermore, the tensile damage variable D2 can be expressed as According to equations (12) and (15), the evolution law of shear damage D1 and tension damage D2 with differential stress (σ1-σ3) under different confining pressure conditions is obtained, as follows: Fig.16 As shown in Figure 2, the evolution of the cumulative shear damage D1 and the cumulative tension damage D2 with the confining pressure is shown in Figure 2. Fig.17 shown.

[0191] Verification Example 1-2:

[0192] This verification example uses the acoustic emission method to further verify the accuracy and reliability of the microscopic tension / shear damage model constructed in the method provided in Example 1-1.

[0193] According to the acoustic emission clustering method, Fig.18 The results shown in Table 3 and Table 4 are obtained according to the moment tensor inversion method. Fig.18 As can be seen from the results in Tables 3 and 4, the internal damage of sandstone is mainly tensile when the confining pressure is less than or equal to 10 MPa, and is mainly shear when the confining pressure is greater than or equal to 15 MPa. This conclusion is consistent with the prediction results of combining two mesoscopic damage models (i.e., tension and shear models) in Example 1-1, further reflecting the accuracy and reliability of the mesoscopic damage model in Example 1-1.

[0194] Table 3 Moment tensor inversion results of sandstone sample S1 at different crack extension stages

[0195]

[0196] Table 4 Moment tensor inversion results of sandstone sample S6 at different crack extension stages

[0197]

[0198] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for predicting the macroscopic failure mechanism of rock based on a microscopic tensile shear damage model, characterized in that: The following steps are involved: S1. Through uniaxial and triaxial tests and CCNBD experiments, experimental data of rock samples are obtained, including stress-strain curves under different confining pressures, characteristic stresses during loading, material property parameters, and quasi-static fracture toughness K IC ; S2. Based on the experimental data of S1, the tension model parameters are determined; based on the interaction between multiple cracks and the superposition principle, the wing crack extension model under quasi-static loading is obtained, and combined with the determined tension model parameters, a rock mesoscopic tension damage model is constructed; The method for determining the value of the crack length correction parameter λ includes: calculating based on the crack initiation stress of the wing crack growth model in uniaxial compression being equal to the crack initialization stress; the method for determining the value of the crack spacing w includes: calculating based on the strength of the wing crack growth model in uniaxial compression being equal to the experimental uniaxial compressive strength; S3. Based on the experimental data of S1, the shear model parameters are determined; based on the Mohr-Coulomb criterion and Weibull statistical distribution, combined with the determined shear model parameters, a rock mesoscopic shear damage model is constructed; The method for determining the values ​​of the rock homogeneity coefficient m and the material constant a includes: obtaining the strength fitting intercept of the rock under pure shear failure under medium and high confining pressure conditions according to the stress-strain curve, and determining it in combination with the expression of the mesoscopic shear damage model; S4. According to the rock mesoscopic tensile damage model constructed in S2, the σ1-L relationship curve between the axial stress σ1 and the wing crack extension length L under different confining pressures is obtained; according to the rock mesoscopic shear damage model constructed in S3, the σ1-D1 relationship curve between the axial stress σ1 and the shear damage D1 under different confining pressures is obtained; S5. According to the σ1-L relationship curve and the σ1-D1 relationship curve, the peak strength of rock under different confining pressures predicted by the tension damage model and the peak strength of rock under different confining pressures predicted by the shear damage model are obtained respectively; combining the peak strength of rock predicted by the two models, the damage and failure law and / or strength of rock under low confining pressure and / or medium and high confining pressure during quasi-static loading are predicted.

2. The method according to claim 1, characterized in that In step S2, the method for determining the value of the crack length correction parameter λ specifically includes the following steps: according to the wing crack extension model, the crack initiation stress is equal to the crack initialization stress during uniaxial compression, and formula (1) is derived; In formula (1), σ ci-I is the crack initialization stress obtained from the uniaxial test, μ is the friction coefficient of the rock sample, b is the initial oblique crack length of the rock sample, and θ0 is the inclination angle of the initial oblique crack of the rock sample; other parameters μ, b, θ0, K determined based on the experimental data in S1 are IC Substitute into formula (1) and calculate the value of λ.

3. The method according to claim 2, characterized in that In step S2, the method for determining the value of the crack spacing w specifically includes the following steps: S211, according to the wing crack growth model under uniaxial compression, the formula (2) is derived, based on the determined λ and other parameters μ, b, θ0, K IC , draw the curve of L changing with σ1 for different w values, and obtain the axial stress peak σ in each σ1-L change curve p,t That is, the theoretical uniaxial compressive strength value, based on the σ corresponding to different w values p,t , we get p,t -w fitting graph; S212. Based on the stress-strain curve of the rock sample under uniaxial compression in S1, the experimental uniaxial compressive strength value σ of the rock sample is obtained. p,exp ; From the σ p,t -w fitting graph, find σ p,t =σ p,exp The corresponding horizontal coordinate point value is the crack spacing w.

4. The method according to claim 1, characterized in that: In step S3, the method for obtaining the value of the homogeneity coefficient m and the material constant a specifically includes the following steps: S311, selecting the maximum confining pressure σ among the different confining pressures described in step S1 3-max As the basis for calculating m and a, according to the confining pressure σ 3-max The peak stress σ is determined by the stress-strain curve under 1-max and σ 1-max The corresponding axial strain ε 1-max The measured value of S312, according to the stress-strain curve described in S1, obtain the axial stress peak value, i.e., the strength σ under different confining pressures σ3 p , according to the medium and high confining pressure σ p -σ3 linear fitting intercept d1, and combined with the intercept expression of the shear damage model described in S3 when σ3 = 0, we get formula (3): In formula (3), is the internal friction angle of the rock sample; S313. Since the reasonable value range of shear damage D1 is 0-1 and the reasonable value range of homogeneity coefficient m is m≥1, the value of D1 is set to a series of point values ​​between 0 and 1 in the numerical calculation software, and the value of m is set to a series of point values ​​greater than or equal to 1. Based on formula (3), the corresponding values ​​of different m values ​​are determined without considering a. D at the maximum value 1-max Theoretical calculated value, based on D 1-max Theoretical calculation value combined with rock damage theory to determine the axial strain ε under different m values 1-max Theoretical calculated value of S314, Comparison ε 1-max The theoretical calculated value and the measured value are adjusted by adjusting the value of m until the two are consistent or meet the expected difference range, so as to determine the optimal solution of m value. Substitute the optimal solution of m value into formula (3) and use the D corresponding to the optimal solution of m value 1-max The theoretical calculated value replaces D1 in formula (3) to obtain the optimal solution of the value of a.

5. The method according to claim 4, characterized in that The axial strain ε 1-max The specific method for determining the theoretical calculation value of includes: Since the rock damage under medium and high confining pressure conditions is shear damage, combined with rock damage theory, formula (4) is obtained: In formula (4), α is Poisson’s ratio, and E0 is the elastic modulus of the rock sample in the initial undamaged state.

6. The method according to claim 1, characterized in that Step S5 specifically includes the following steps: when the confining pressure is constant, compare the peak strength values ​​predicted by the two models, take the model with lower peak strength as the benchmark, and predict the type and / or intensity of rock macroscopic failure and / or the quantitative change law of damage and failure.

7. The method according to any one of claims 1 to 6, characterized in that: The rock sample is yellow sandstone, the low confining pressure is σ3≤10Mpa, and the medium and high confining pressure is σ3≥15Mpa.

8. The method according to claim 3, characterized in that In step S2, the rock mesoscopic tensile damage model includes model I and model II; The expression of model I is formula (5): The expression of model II is formula (6): In formula (5) and formula (6), K I is the stress intensity factor of the wing crack tip under quasi-static conditions, σ1 is the axial stress, σ3 is the confining pressure, L is the wing crack extension length; λ is the crack length correction parameter, w is the crack spacing; μ is the friction coefficient of the rock sample, b is the initial oblique crack length of the rock sample, and θ0 is the inclination angle of the initial oblique crack of the rock sample; Step S4 specifically includes: according to equations (5) and (6), when K I =K IC When the confining pressure σ3 is a constant, the σ1-L relationship curve under the confining pressure is obtained.

9. The method according to claim 4, characterized in that In step S3, the rock microscopic shear damage model is expressed as formula (7): In formula (7), D1 is the shear damage of rock, σ1 is the axial stress, σ3 is the confining pressure, is the internal friction angle of the rock sample, m is the homogeneity coefficient, and a is the material constant.

10. A method for constructing a rock tension damage model under dynamic load, characterized in that: It mainly includes: by introducing correction coefficients related to the crack growth rate v, the damage variable β, and the crack closure coefficient η, the rock mesoscopic tensile damage model under quasi-static loading obtained by the method described in any one of claims 1 to 9 is corrected to obtain a rock tensile damage model under dynamic load.

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