Three-dimensional numerical modeling method for transverse isotropic rock containing initial microcracks

Abstract

The invention provides a three-dimensional numerical modeling method for a transverse isotropic rock containing an initial microcrack, which comprises the following steps: constructing a transverse isotropic rock model containing the initial microcrack, and introducing an initial gap to simulate the initial microcrack existing in the rock; initial estimation is conducted on the initial microcrack parameters, and meanwhile homogenization treatment is conducted on the modulus of the flexible rock matrix and the modulus of the weak surface, so that deformation parameters of the flexible rock matrix and deformation parameters of the weak surface are consistent; and calibrating the initial microcrack parameters, the deformation parameters and the strength parameters, and establishing a transverse isotropic rock three-dimensional numerical model containing the initial microcracks based on the calibrated parameters. According to the method, the initial sub-linear compaction stage under the uniaxial compression condition can be embodied, meanwhile, the effects of a rigid layer, a flexible layer and a soft surface on rock mechanical characteristics can be better embodied, and the reliability and accuracy of three-dimensional numerical modeling and simulation are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geotechnical engineering, and particularly relates to a three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks. BACKGROUND

[0002] Transverse isotropy (TI) is a special type of anisotropy that describes the mechanical properties of rock. Specifically, the mechanical properties of rock in a certain plane (referred to as the isotropic plane) are the same, but in the direction perpendicular to the plane, the mechanical properties (such as elastic modulus, strength, wave velocity, etc.) are significantly different. Three-dimensional numerical modeling method is an extremely common and necessary technical means in analyzing transversely isotropic rock. Considering the strong direction dependence of the mechanical behavior of this kind of rock, traditional analytical methods are difficult to handle complex boundary conditions or engineering disturbances, while three-dimensional numerical modeling method can accurately quantify the anisotropic response.

[0003] At present, in the three-dimensional discrete element model of transversely isotropic rock, the initial microcracks are not considered, which leads to the fact that the existing model cannot reflect the initial compaction stage under uniaxial compression, the stress-strain curve under uniaxial compression is not perfect, and the bimodality of rock cannot be reflected. In addition, some models still do not comprehensively consider the initial microcracks in the interior of transversely isotropic rock when simulating the rock, which leads to the deviation between the simulation results and the actual mechanical behavior of the rock. SUMMARY

[0004] The present application aims to provide a three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks, which can truly reflect the mechanical properties and interaction relationship of different components (rigid rock matrix, flexible rock matrix and weak plane) in the interior of the rock.

[0005] In order to achieve the above-mentioned purpose, the present application provides a three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks, which comprises the following steps:

[0006] S1, constructing a transversely isotropic rock model containing initial microcracks, including rigid rock matrix, flexible rock matrix and weak plane, introducing initial gap to simulate the initial microcracks existing in the rock, and the angle between the weak plane and the model axial direction is β;

[0007] S2, preliminarily estimating the initial microcrack parameters, and homogenizing the modulus of the flexible rock matrix and the weak plane to make the deformation parameters of the flexible rock matrix and the weak plane consistent;

[0008] S3, calibrating the initial microcrack parameters, deformation parameters, and strength parameters, and establishing a three-dimensional numerical model of transversely isotropic rock containing initial microcracks based on the calibrated parameters.

[0009] Furthermore, S1 adopts a plane joint contact model as the contact model between particles in the rigid rock matrix and the flexible rock matrix in the rock model. The parameter setting follows the isotropy assumption. The rigid rock matrix and the flexible rock matrix have elastic isotropy characteristics, and different Young's moduli are set, while the strength parameters are the same. The weak surface is installed between the rigid rock matrix and the flexible rock matrix, and a smooth joint contact model is adopted. The Young's modulus at the weak surface is set to be the same as that of the flexible rock matrix. An initial gap is introduced in the plane joint contact model of the rock matrix part to simulate the initial microcracks in the rock.

[0010] Furthermore, when estimating the microcrack density and microcrack width based on the bimodality and compaction deformation in S2, the microcrack density and microcrack width are estimated using experimental data, and the microcrack density p is equal to the tensile modulus E of the model. t and compression modulus E c Ratio E t / E c According to the model height H, the average number of particles n in the height direction, the microcrack density p and the initial nonlinear compression deformation ε g To calculate the microcrack width g0, the formula is:

[0011]

[0012] Furthermore, in S2, the microcrack closure stress is determined by combining the initial nonlinear compression deformation obtained from the actual test. A straight line with a slope of elastic modulus is constructed at this stress point, and the distance from the intersection with the horizontal axis to the origin is the initial nonlinear compression deformation ε g , and then calculate the microcrack width using the g0 calculation formula.

[0013] Furthermore, when the moduli of the flexible rock matrix and the weak surface in S2 are homogenized, the deformation parameters of the plane joint contact in the flexible rock matrix are converted to Deformation parameter k for contact with smooth joints in weak surfaces n ,k s To unify, is the contact normal stiffness of the flexible rock matrix, is the contact tangential stiffness of the flexible rock matrix, k n is the normal stiffness of the weak surface, k s is the tangential stiffness of the weak surface.

[0014] Furthermore, the deformation parameters of planar joint contacts in flexible rock matrices are Contact effective modulus through a flexible rock matrix To determine the proportional coefficient α of the contact normal stiffness and the contact tangential stiffness of the flexible rock matrix, The final result is obtained by autonomous calculation by the software. By comparing and adjusting the elastic modulus of two or more models, uniaxial compression tests are performed on specimens under the same β, the elastic modulus of the two models is calculated, and the contact effective modulus and deformation parameters of the models are changed to make the elastic modulus of the two models the same.

[0015] Furthermore, when the moduli of the flexible rock matrix and the weak surface in S2 are homogenized, there is an equivalent coefficient K e , so that the elastic modulus of the two models is the same, based on the equivalent coefficient K e , the deformation parameters of the flexible rock matrix and the weak surface are converted by the following formula:

[0016]

[0017] Furthermore, when calibrating the initial microcrack parameters in S3, the microcrack density and microcrack width obtained in S2 are used as the initial microcrack parameters of the plane joint contact of the matrix layer, and a uniaxial compression simulation test is performed on the model. The gap density of the plane joint contact in the matrix is ​​adjusted by adjusting the rigidity. and width g 0,stiff Initial nonlinear compression deformation ε when matching β is 0° g0 Then, by adjusting the gap density of the plane joint contact of the soft rock matrix and width g 0,soft Initial nonlinear compression deformation ε when matching β is 90° g90 , and at the same time adjust the gap width of the rigid rock matrix to meet the changing trend of the initial nonlinear compression deformation under different β.

[0018] Furthermore, when calibrating the deformation parameters in S3, the deformation parameters E of the contact between the particles and the plane joints in the rigid rock matrix are adjusted. c 、k n 、k s 、 To match the elastic modulus E0 of the model under uniaxial compression when β is 0°; adjust the deformation parameters of the plane joint contact in the flexible rock matrix and the smooth joint contact in the weak surface k n 、k s To match the elastic modulus E of the model under uniaxial compression when β is 90° 90 Among them, E c is the effective stiffness of the particle, k n ,k s are the normal stiffness and tangential stiffness of the particle, Effective normal and tangential contact moduli of the rigid rock matrix, respectively, are the normal and tangential contact stiffness of the rigid rock matrix.

[0019] Further, when calibrating the strength parameters in S3, the average tensile strength of the contact between the planar joint in the flexible rock matrix and the rigid rock matrix is adjusted to match the direct tensile strength DTS0 of the model when β is 0°; the tensile strength parameter σ b of the smooth joint contact of the weak plane is adjusted to match the direct tensile strength DTS 90 of the model when β is 90°; the cohesion strength parameter of the contact between the planar joint in the flexible rock matrix and the rigid rock matrix is adjusted to match the uniaxial compressive strength UCS 90 of the model when β is 90°; the cohesion strength parameter c b of the smooth joint contact of the weak plane is adjusted to match the uniaxial compressive strength UCS 30 of the model when β is 30°; and the strength parameters of the matrix and the weak plane are adjusted to meet the uniaxial compressive strength variation trend at different β.

[0020] The above scheme of the present application has the following beneficial effects:

[0021] The three-dimensional numerical modeling method of the transversely isotropic rock containing initial microcracks provided by the present application can reflect the initial nonlinear compaction stage under uniaxial compression conditions, and the crack initiation stress is lower and the brittleness is higher, compared with the transversely isotropic rock model without initial microcracks. Compared with the traditional model, the crack initiation stress is reduced by 26.03%, and the brittleness index is increased by 2.52%. In addition, compared with the isotropic rock model containing initial microcracks, the brittleness index of the model proposed by the present application increases first and then decreases with the increase of β, which can better reflect the effect of rigid layer, flexible layer and weak plane on rock mechanical properties. Therefore, the reliability and accuracy of three-dimensional numerical modeling and simulation are improved.

[0022] Other beneficial effects of the present application will be described in detail in the following specific embodiment part. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 It is the overall step flow chart of the present application.

[0024] Figure 2 A three-dimensional discrete element model diagram of transversely isotropic rock considering initial micro-cracks of the present application;

[0025] Figure 3 A curve diagram of initial micro-crack closure deformation of shale samples of the present application under uniaxial compression when β is 90°;

[0026] Figure 4 A comparison diagram of elastic modulus of two models of the present application, wherein (a) is a structural comparison diagram, (b) is a result diagram when β is 0°, (c) is a result diagram when β is 45°, and (d) is a result diagram when β is 90°;

[0027] Figure 5 A parameter calibration flowchart of the present application;

[0028] Figure 6 A crack initiation stress comparison curve diagram of the present application;

[0029] Figure 7 A brittleness index comparison curve diagram of the present application;

[0030] Figure 8 A comparison diagram of test and simulation results of the present application, wherein (a) is UCS, (b) is elastic modulus, (c) is compaction deformation, and (d) is model uniaxial compressive strength reliability. DETAILED DESCRIPTION

[0031] The embodiments of the present application will be described in detail with specific reference felt to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, but not all the embodiments. The present application can be implemented or applied in other different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of the present application.

[0032] ​​​It is noted that various aspects of the embodiments within the scope of the appended claims are described below. It should be apparent that the aspects described herein can be implemented in a wide variety of forms and that any particular structure and / or function described herein is merely illustrative. Based on the teachings herein one skilled in the art should appreciate that an aspect described herein can be implemented independently of any other aspects and that an aspect described herein can be implemented both as any number of software and / or hardware structures and as any number of processes and / or operations. For example, an apparatus can be implemented as any number of structural and / or functional combinations of the aspects described herein. Additionally, any aspect described herein can be implemented alone or in combination with any other aspect described herein.

[0033] It is also noted that the illustrative figures can show components of the present disclosure in schematic form and that the drawings are not necessarily drawn to scale. In addition, in the following description, numerous specific details are provided, such as particular structures, components, and processes, in order to provide a thorough understanding of examples. However, it will be apparent to one skilled in the art that the aspects described herein can be practiced without these specific details.

[0034] As shown in Figure 1 , the embodiments of the present application provide a three-dimensional numerical modeling method for transversely isotropic rock with initial micro-cracks. The corresponding transversely isotropic rock refers to the mechanical properties of the rock in a certain specific plane (referred to as the isotropic plane) are the same, but in the direction perpendicular to the plane, its mechanical properties (such as elastic modulus, strength, wave speed, etc.) are significantly different. Therefore, the three-dimensional numerical modeling method needs to first establish a transversely isotropic rock model with initial micro-cracks, that is:

[0035] S1, constructing a transversely isotropic rock model with initial micro-cracks.

[0036] The established model includes three parts: rigid rock matrix, flexible rock matrix and weak plane. For details, please refer to Figure 2, the Flat-joint contact model is used as the contact model between particles in the rigid rock matrix (FJC1) and the flexible rock matrix (FJC2) in the rock model, and the parameter setting follows the isotropic assumption. The rigid rock matrix and the flexible rock matrix have the elastic isotropic property, that is, different Young's moduli are set, and the strength parameters are the same. The smooth joint contact model is used for the soft weak plane (SJC) installed between the rigid rock matrix and the flexible rock matrix. The Young's modulus at the soft weak plane is set the same as that of the flexible rock matrix, and the angle between the soft weak plane and the model (uniaxial compression) axis is denoted as β. The initial gap is introduced in the flat-joint contact model of the rock matrix part to simulate the initial microcracks existing in the rock.

[0037] S2, the initial microcrack parameters are estimated, and the modulus of the flexible rock matrix and the soft weak plane is homogenized. This step specifically includes the following sub-steps:

[0038] S21, the microcrack density and width are estimated according to the bimodality and the compaction deformation. In this embodiment, the test data when β is 90° are used to estimate the microcrack density and width. The microcrack density p is approximately equal to the ratio of the tensile modulus E t to the compression modulus E c , that is, E t / E c . The microcrack width (initial gap width) g0 is calculated according to the model height H, the average number of particles in the height direction n, the microcrack density p, and the initial nonlinear compaction deformation ε g , and the formula is as follows:

[0039]

[0040] Referring to Figure 3 , in this embodiment, the microcrack closure stress is determined according to the model size, the number of particles, and the initial nonlinear compaction deformation obtained from the real test. The distance from the intersection point of the straight line with the elastic modulus to the origin is the initial nonlinear compaction deformation ε g , so that the microcrack width is calculated by formula (1).

[0041] S22, the modulus of the flexible rock matrix and the soft weak plane is homogenized. In this embodiment, the deformation parameters of the flat-joint contact in the flexible rock matrix k and the deformation parameters of the smooth-joint contact in the soft weak plane k n , k s are homogenized. Wherein, is the contact normal stiffness of the flexible rock matrix, is the contact tangential stiffness of the flexible rock matrix, and kn is the normal stiffness of the weak surface, k s is the tangential stiffness of the weak surface. Through this sub-step, the flexible rock matrix and the weak surface in the model can be considered as an integrated form.

[0042] In this example, the deformation parameters of the plane joint contact in the flexible rock matrix are Contact effective modulus through a flexible rock matrix and the proportional coefficient α of the contact normal stiffness and contact tangential stiffness of the flexible rock matrix, The final result is calculated by the software. Figure 4 In this embodiment, two transversely isotropic rock models with different weak surfaces are used to homogenize the modulus of the weak surface and the flexible rock matrix, which needs to be verified by continuously setting and adjusting the deformation parameters and the effective contact modulus.

[0043] Specifically, during the verification process, the elastic moduli of the two different models mentioned above were compared. These two different models are: i. A planar joint contact model is used for the weak plane contact, whose microscopic parameters are consistent with those of the contact in the flexible rock matrix; ii. A smooth joint contact model is used for the weak plane contact, where only the weak plane changes, while all other parameters remain the same. Uniaxial compression tests were performed on specimens with the same β value, and the elastic moduli of the two models were calculated. The contact effective modulus and deformation parameters of the models were then varied to achieve the same elastic modulus under the two models.

[0044] After continuous adjustment, there is an equivalent coefficient K e , so that the elastic modulus of the two models is the same. Based on the equivalent coefficient K e , the deformation parameters of the flexible rock matrix and weak surface are converted according to the following formula:

[0045]

[0046] Among them, α is the proportional coefficient of the normal stiffness and tangential stiffness corresponding to the flexible rock matrix and the weak surface. It should be noted that in these formulas and k n Unit conversion is required.

[0047] S3, calibrate the initial microcrack parameters, deformation parameters, and strength parameters, and establish a three-dimensional numerical model of transversely isotropic rock containing initial microcracks based on the calibrated parameters. Please also refer to Figure 5 , this step specifically includes the following sub-steps:

[0048] S31, calibrate the initial microcrack parameters: use the microcrack density and width obtained in S21 as the initial assignment of microcrack parameters of the planar joint contact of the matrix layer, and perform a uniaxial compression simulation test on the model to simultaneously match the conditions when β is 0° and 90°.

[0049] Specifically, the interstitial density of the rigid joints along the plane of the matrix is ​​adjusted. and width g 0,stiff Initial nonlinear compression deformation ε when matching β is 0° g0 Then, by adjusting the gap density of the plane joint contact of the soft rock matrix and width g 0,soft Initial nonlinear compression deformation ε when matching β is 90° g90 , and at the same time, the gap width of the rigid rock matrix is ​​fine-tuned to meet the changing trend of the initial nonlinear compaction deformation under different β.

[0050] S32, calibrate the deformation parameters: by adjusting the deformation parameter E of the contact between the particles and the plane joints in the rigid rock matrix c 、k n 、k s 、 To match the elastic modulus E0 of the model under uniaxial compression when β is 0°; adjust the deformation parameters of the plane joint contact in the flexible rock matrix and the smooth joint contact in the weak surface k n 、k s To match the elastic modulus E of the model under uniaxial compression when β is 90° 90 .

[0051] S33, calibrate the strength parameters by adjusting the average tensile strength of the contact between the plane joints in the flexible rock matrix and the rigid rock matrix To match the direct tensile strength DTS0 of the model when β is 0°; by adjusting the tensile strength parameter σ of the smooth joint contact of the weak surface b To match the direct tensile strength DTS of the model when β is 90° 90 By adjusting the cohesive strength parameters of the plane joints in the flexible rock matrix and the rigid rock matrix To match the uniaxial compressive strength UCS of the model when β is 90° 90 ; By adjusting the cohesive strength parameter c of the smooth joint contact of the weak surface b To match the uniaxial compressive strength UCS of the model when β is 30° 30 ; At the same time, the strength parameters of the matrix and weak surface are fine-tuned to meet the uniaxial compressive strength change trend at different β.

[0052] Therefore, the initial microcrack parameters, deformation parameters and strength parameters are calibrated by S3, and when they are applied to the model, the initial linear compaction stage of the model under uniaxial compression conditions can be reflected, and the crack initiation stress is lower (see Figure 6 ), and the brittleness is higher (see Figure 7 ). Taking the model with β as 0° as an example, compared with the traditional model, the crack initiation stress is reduced by 26.03%, and the brittleness index is increased by 2.52%. At the same time, compared with the isotropic rock model containing initial microcracks, the brittleness index of the model obtained by the method increases first and then decreases with the increase of β, which can better reflect the effect of rigid rock matrix, flexible rock matrix and weak plane on the mechanical properties of rock.

[0053] The effect of the method is further illustrated by specific cases, and the real test data refers to the direct tensile test and uniaxial compression test of shale. In the case, a cuboid rock sample model with a size of 20mm×12mm×12mm and a particle number of about 15000 is constructed, and a sheet rock sample model with a size of 40mm×8mm×2mm and a particle number of about 3400 is constructed, which are respectively used to simulate uniaxial compression test and direct tensile test. At the same time, five different β values are set, 0°, 30°, 45°, 60° and 90°.

[0054] The real test data of Jin et al. is analyzed, and the compression elastic modulus E c , tensile elastic modulus E t , uniaxial compressive strength UCS, direct tensile strength DTS and nonlinear compaction deformation ε g are calculated under different β. Taking E t / E c of β as 90° as the estimate of microcrack density p, p is obtained as 0.73. According to the uniaxial compression standard sample height H, the average particle number n in the height direction, the microcrack density p and the nonlinear compaction deformation ε g of β as 90°, the estimate of microcrack width g0 is calculated as 0.0034mm.

[0055] Two different transversely isotropic rock models with soft weak plane and flexible layer matrix are used to modulize the modulus of soft weak plane and flexible layer matrix. The contact of soft weak plane of one of them is a flat joint contact model, and the micro parameters are consistent with the contact micro parameters in flexible rock medium; the contact of soft weak plane of the other is a smooth joint contact model, and only the soft weak plane changes, the rest are consistent. The uniaxial compression test is carried out on the samples with the same β, the elastic modulus of the two models is calculated, and the deformation parameters, contact effective modulus, etc. of the two models are changed so that the elastic modulus of the two models is the same, and there is an equivalent coefficient K eAmong them, the comparison results of the elastic modulus of the model under different deformation parameters are as follows: Figure 4 As shown, Figure 4 (b) Figure 4 (c) Figure 4 (d)

[0056] Then, the microcrack parameters, deformation parameters, and strength parameters are calibrated based on the calibration process. The specific calibration results are shown in Table 1, Table 2, and Table 3:

[0057] Table 1 Calibration of microscopic parameters of plane joint contact (FJC1) in rigid rock matrix

[0058]

[0059] Table 2 Calibration of microscopic parameters of flexible layer matrix plane joint contact (FJC2)

[0060]

[0061] Table 3 Calibration table of microscopic parameters of weak surface smooth joint contact (SJC)

[0062]

[0063]

[0064] The results of the comparison between the final parameter calibration and the actual test data are as follows: Figure 8 As shown, these include UCS, elastic modulus, and compaction deformation. As can be seen above, the numerical simulation results in this case are in good agreement with the experimental results of Jin et al. Although the trend of compaction deformation as a function of β differs somewhat from the experimental results in the numerical simulation, this trend is consistent with theoretical predictions, which show that crack-induced strain should increase with increasing β. The deviations primarily occur at β values ​​of 45° and 60°, which may be attributed to the differences in the properties of the shale specimens and the wavy structural characteristics of the bedding planes.

[0065] Since the reliability of the particle model may become an uncertain factor affecting the credibility of the results without control indicators such as the coefficient of variation, 10 groups of samples were generated for each β by changing the seed of the random number generator to verify the reliability of this method. Figure 8(d) shows the variation of the peak strength (UCS) of the 10 groups of samples under uniaxial compression test. The results show that the coefficient of variation of UCS is less than 5%, and the maximum value appears at β = 30°, which is 4.02%. This result is generally sufficient to meet the requirements of rock engineering applications. Therefore, it is proved that the transversely isotropic rock model obtained by the method has been well calibrated, and can accurately describe the mechanical behavior of transversely isotropic shale containing initial microcracks under uniaxial compression, especially in the nonlinear crack closure stage.

[0066] It is worth mentioning that the case in the embodiment is based on PFC3D, including modeling, parameter calibration, numerical simulation, etc. For other similar function software, the method provided in the embodiment can also be used for three-dimensional numerical modeling and simulation.

[0067] The technical features of the above embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered as the scope of the present application.

[0068] The above embodiments only express several implementation manners of the present application, and the description is specific and detailed, but it should not be understood as a limitation on the scope of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are all within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks, characterized in that: The steps include: S1, construct a transversely isotropic rock model with initial microcracks, including a rigid rock matrix, a flexible rock matrix, and a weak plane. An initial gap is introduced to simulate the initial microcracks in the rock. The angle between the weak plane and the model axis is β; S2, preliminarily estimate the initial microcrack parameters and homogenize the moduli of the flexible rock matrix and the weak surface to make the deformation parameters of the flexible rock matrix consistent with the deformation parameters of the weak surface; S3, calibrating the initial microcrack parameters, deformation parameters, and strength parameters, and establishing a three-dimensional numerical model of transversely isotropic rock containing initial microcracks based on the calibrated parameters.

2. The three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 1, characterized in that: In S1, a plane joint contact model is used as the contact model between particles in the rigid rock matrix and the flexible rock matrix in the rock model. The parameter setting follows the isotropy assumption. The rigid rock matrix and the flexible rock matrix have elastic isotropy characteristics, and different Young's moduli are set, while the strength parameters are the same. The weak surface is installed between the rigid rock matrix and the flexible rock matrix, and a smooth joint contact model is adopted. The Young's modulus at the weak surface is set to be the same as that of the flexible rock matrix. An initial gap is introduced in the plane joint contact model of the rock matrix part to simulate the initial microcracks in the rock.

3. The three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 1, characterized in that: In S2, when estimating the microcrack density and microcrack width based on the bimodality and compaction deformation, the test data are used to estimate the microcrack density and microcrack width. The microcrack density p is equal to the tensile modulus E of the model. t and compression modulus E c Ratio E t / E c According to the model height H, the average number of particles n in the height direction, the microcrack density p and the initial nonlinear compression deformation ε g To calculate the microcrack width g0, the formula is:

4. The three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 3, characterized in that: In S2, the microcrack closure stress is determined by combining the initial nonlinear compression deformation obtained from the actual test. A straight line with a slope of elastic modulus is constructed at this stress point, and the distance from the intersection with the horizontal axis to the origin is the initial nonlinear compression deformation ε g , and then calculate the microcrack width using the g0 calculation formula.

5. The three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 1, characterized in that: When the modulus of the flexible rock matrix and the weak surface in S2 are homogenized, the deformation parameter of the plane joint contact in the flexible rock matrix is ​​converted to Deformation parameter k for contact with smooth joints in weak surfaces n ,k s To unify, is the contact normal stiffness of the flexible rock matrix, is the contact tangential stiffness of the flexible rock matrix, k n is the normal stiffness of the weak surface, k s is the tangential stiffness of the weak surface.

6. The three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 5, characterized in that: Deformation parameters of planar joint contacts in flexible rock matrices Contact effective modulus through a flexible rock matrix and the proportional coefficient α of the contact normal stiffness and contact tangential stiffness of the flexible rock matrix, The final result is obtained by autonomous calculation by the software. By comparing and adjusting the elastic modulus of two or more models, uniaxial compression tests are performed on specimens under the same β, the elastic modulus of the two models is calculated, and the contact effective modulus and deformation parameters of the models are changed to make the elastic modulus of the two models the same.

7. The three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 6, characterized in that: When the moduli of the flexible rock matrix and the weak surface in S2 are homogenized, there is an equivalent coefficient K e , so that the elastic modulus of the two models is the same, based on the equivalent coefficient K e , the deformation parameters of the flexible rock matrix and the weak surface are converted by the following formula:

8. The three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 5, characterized in that: When calibrating the initial microcrack parameters in S3, the microcrack density and microcrack width obtained in S2 are used as the initial microcrack parameters of the plane joint contact of the matrix layer. The model is subjected to a uniaxial compression simulation test. The gap density of the plane joint contact in the matrix is ​​adjusted by adjusting the rigidity. and width g 0,stiff Initial nonlinear compression deformation ε when matching β is 0° g0 Then, by adjusting the gap density of the plane joint contact of the soft rock matrix and width g 0,soft Initial nonlinear compression deformation ε when matching β is 90° g90 , and at the same time adjust the gap width of the rigid rock matrix to meet the changing trend of the initial nonlinear compression deformation under different β.

9. The three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 8, characterized in that: When calibrating the deformation parameters in S3, the deformation parameter E of the contact between the particles and the plane joints in the rigid rock matrix is ​​adjusted. c 、k n 、k s 、 To match the elastic modulus E0 of the model under uniaxial compression when β is 0°; adjust the deformation parameters of the plane joint contact in the flexible rock matrix and the smooth joint contact in the weak surface k n 、k s To match the elastic modulus E of the model under uniaxial compression when β is 90° 90 ; Among them, E c is the effective stiffness of the particle, k n ,k s are the normal stiffness and tangential stiffness of the particle, is the effective contact modulus of the rigid rock matrix, are the contact normal stiffness and contact tangential stiffness of the rigid rock matrix, respectively.

10. A three-dimensional numerical modeling method for transversely isotropic rock containing initial microcracks according to claim 9, characterized in that: When calibrating the strength parameters in S3, the average tensile strength of the contact between the plane joints in the flexible rock matrix and the rigid rock matrix is ​​adjusted. To match the direct tensile strength DTS0 of the model when β is 0°; by adjusting the tensile strength parameter σ of the smooth joint contact of the weak surface b To match the direct tensile strength DTS of the model when β is 90° 90 By adjusting the cohesive strength parameters of the plane joint contact between the flexible rock matrix and the rigid rock matrix To match the uniaxial compressive strength UCS of the model when β is 90° 90 ; By adjusting the cohesive strength parameter c of the smooth joint contact of the weak surface b To match the uniaxial compressive strength UCS of the model when β is 30° 30 ; At the same time, the strength parameters of the matrix and weak surface are adjusted to meet the change trend of uniaxial compressive strength at different β.

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