A method for constructing a rock damage constitutive model based on micro-crack propagation evolution

Abstract

The application discloses a kind of rock damage constitutive model construction methods based on micro crack propagation evolution, comprising the following steps: based on static equilibrium relationship, geometry damage theory constructs initial rock damage constitutive model;Based on crack length, obtain rock crack propagation damage variable;Based on fracture mechanics, obtain the strength of crack propagation damage microelement;Based on the initial rock damage constitutive model, rock crack propagation damage variable, the strength of crack propagation damage microelement, constructs target rock damage constitutive model.The application utilizes biological retardation growth model to characterize crack propagation length evolution, defines rock damage based on geometry damage theory with crack propagation length, establishes rock damage constitutive model, which can better reflect the mechanical behavior of rock crack propagation, and provides a new idea for quantitative study of rock crack propagation damage evolution.

Description

Technical Field

[0001] This invention belongs to the field of rock damage, and in particular relates to a method for constructing a rock damage constitutive model based on the evolution of microcrack propagation. Background Technology

[0002] Due to geological tectonic activity, rocks contain numerous micro-cracks and pores, among other microscopic defects. During rock deformation and failure, the initiation, propagation, and interconnection of these microscopic defects make the rock's mechanical properties highly complex. The stress-strain curves of defective rock materials generally exhibit nonlinear characteristics, displaying strain hardening, stiffness degradation, strain softening, and shear dilatation properties.

[0003] To accurately describe the complex mechanical behavior of rocks, many scholars, based on the Lemaitre equivalent strain hypothesis and the concept of effective stress, have constructed rock constitutive models by introducing damage variables, thus creating damage constitutive models that can accurately characterize the nonlinear mechanical behavior of rocks. Previously, many scholars defined damage variables using macroscopic mechanical property parameters such as rock elastic modulus, strain, CT number, resistivity, and acoustic characteristics; however, this method struggles to consider the influence of crack development characteristics on constitutive relations. Statistical damage theory posits that the macroscopic nonlinear mechanical behavior of rocks is the result of the heterogeneous evolution of their microscopic defects. It proposes using probability distribution functions to characterize the heterogeneity of rock element strength, establishing damage variables from a microscopic perspective, which can better reflect the dynamic damage evolution process of rock failure. Although traditional statistical damage mechanics models use functions such as Weibull distribution, geometric distribution, and normal distribution to characterize rock damage states and can perform rigorous theoretical calculations of rock damage, quantitative research on the relationship between crack propagation length, angle, number, and damage evolution remains insufficient.

[0004] Facts and experiments have proven that the nonlinear mechanical behavior of rocks is closely related to the propagation and evolution of internal cracks. The damage accumulation and dynamic evolution process of rock deformation and failure is essentially an external manifestation of the initiation, propagation, and connection of microscopic cracks. However, existing research has rarely established a quantitative relationship between crack propagation and evolution and rock damage. Furthermore, previous damage constitutive models based on the Lemaitre strain equivalence hypothesis rarely consider the strength of rock micro-elements after damage and failure, making it difficult to accurately describe the nonlinear characteristics of rock strain softening and residual deformation stages. Although some scholars have determined the strength of damaged micro-elements using the Mohr-Coulomb yield criterion, nonlinear flow law, and energy dissipation principle, most of these methods are based on traditional materials mechanics, with fewer utilizing fracture mechanics methods to solve for the fracture failure strength of rock damaged micro-elements.

[0005] Therefore, a method for constructing rock damage needs to be proposed to accurately describe the mechanical properties of the deformation and failure process of damaged rocks. Summary of the Invention

[0006] The purpose of this invention is to provide a method for constructing a rock damage constitutive model based on the evolution of microscopic crack propagation. This method utilizes a biologically inhibited growth model to characterize crack propagation length and establishes a quantitative relationship between crack propagation length and rock damage. Furthermore, it employs fracture mechanics to solve for the fracture failure strength of the rock damage micro-element. Based on damage theory and fracture mechanics, a damage constitutive model for the propagation of microscopic cracks in rock is established to accurately describe the mechanical properties of the deformation and failure process of damaged rock, thus solving the problems existing in the prior art.

[0007] To achieve the above objectives, this invention provides a method for constructing a rock damage constitutive model based on the evolution of microcrack propagation, comprising the following steps:

[0008] An initial constitutive model of rock damage is constructed based on static equilibrium relations and geometric damage theory;

[0009] Based on crack length, obtain the rock crack propagation damage variable;

[0010] Based on fracture mechanics, the strength of a crack-propagating damaged micro-element is obtained;

[0011] Based on the initial rock damage constitutive model, rock crack propagation damage variables, and the strength of the crack propagation damage micro-element, a target rock damage constitutive model is constructed.

[0012] Preferably, based on phenomenological theory, the microstructure of rocks is divided into intact rock micro-elements, rock crack propagation damage micro-elements, and rock pores.

[0013] Preferably, an initial rock damage constitutive model is constructed based on the principal stresses of the rock in different directions and the linear elastic relationship between intact rock micro-elements in different directions.

[0014] Preferably, the process of obtaining the principal stress of the rock includes: obtaining rock pore damage and rock crack propagation damage based on geometric damage theory; constructing a functional relationship between the nominal stress of the rock, the equivalent stress of the intact rock micro-element, and the equivalent stress of the crack propagation damage micro-element based on static equilibrium; and obtaining the principal stress of the rock based on the geometric relationship between the functional relationship, rock pore damage, rock crack propagation damage, and the stress area of ​​the micro-element.

[0015] Preferably, the process of obtaining the rock crack propagation damage includes: obtaining the rock stress surface occupied by the crack throughout the entire airfoil crack based on the ultimate length of crack propagation; and obtaining the rock crack propagation damage based on the ratio of the crack propagation surface to the rock stress surface occupied by the crack throughout the entire airfoil crack.

[0016] Preferably, the process of obtaining the strength of the crack propagation damage micro-element includes: obtaining the first equivalent stress of the crack propagation damage micro-element based on the ASHBY model; obtaining the second equivalent stress of the crack propagation damage micro-element based on the Mohr-Coulomb yield criterion; and obtaining the strength of the crack propagation damage micro-element based on the quantitative relationship between the first equivalent stress and the second equivalent stress.

[0017] Preferably, the process of constructing the target rock damage constitutive model includes obtaining the target rock damage constitutive model based on the effective stress of the intact rock micro-element, the strength of the crack propagation damage micro-element, the rock crack propagation damage, the crack propagation length, and the initial rock damage constitutive model.

[0018] Preferably, the target rock damage constitutive model is modified based on the soft rock compaction strain to obtain a soft rock damage constitutive model. When the soft rock compaction strain is zero, the soft rock damage constitutive model is the target rock damage constitutive model.

[0019] Preferably, the process of determining the strength parameters in the target rock damage constitutive model includes: obtaining the rock cohesion and friction angle parameters based on the relationship between the rock peak strength and the confining pressure; obtaining the rock fracture toughness based on the rock three-bend point experiment; obtaining the crack propagation rate based on the subcritical crack propagation experiment; and obtaining the soft rock compaction strain based on the intercept of the elastic stage tangent of the stress-strain curve and the strain axis.

[0020] The technical effects of this invention are as follows:

[0021] (1) This invention uses a biological inhibited growth model to characterize the evolution of crack propagation length. Based on geometric damage theory, rock damage is defined by crack propagation length, and a rock damage constitutive model is established. This model can better reflect the mechanical behavior of rock crack propagation and provides a new idea for the quantitative study of rock crack propagation damage evolution.

[0022] (2) This invention proposes a method for solving the strength of rock damage micro-elements based on fracture mechanics. Compared with traditional material mechanics methods, this method can better characterize the strength of rock crack propagation damage micro-elements. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments and descriptions of this application are used to explain this application and do not constitute an undue limitation of this application. In the drawings:

[0024] Figure 1 This is a schematic diagram of a generalized rock stress model in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the airfoil crack structure in an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram illustrating the verification of the theoretical model in an embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram illustrating the effect of initial damage on the stress-strain curve in an embodiment of the present invention.

[0028] Figure 5 This is a schematic diagram illustrating the effect of elastic modulus on stress-strain curves in an embodiment of the present invention.

[0029] Figure 6 This is a schematic diagram illustrating the effect of cohesion on the stress-strain curve in an embodiment of the present invention;

[0030] Figure 7 This is a schematic diagram illustrating the effect of the friction angle on the stress-strain curve in an embodiment of the present invention;

[0031] Figure 8 This is a schematic diagram illustrating the effect of crack initiation toughness on the stress-strain curve in an embodiment of the present invention.

[0032] Figure 9 This is a schematic diagram illustrating the effect of the crack interface friction factor on the stress-strain curve in an embodiment of the present invention.

[0033] Figure 10 This is a schematic diagram illustrating the effect of crack propagation rate on stress-strain curves in an embodiment of the present invention.

[0034] Figure 11 This is a schematic diagram illustrating the effect of the initial crack propagation length parameter on the stress-strain curve in an embodiment of the present invention.

[0035] Figure 12 This is a flowchart of the construction method in an embodiment of the present invention. Detailed Implementation

[0036] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0037] It should be noted that the steps shown in the flowchart in the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and although a logical order is shown in the flowchart, in some cases the steps shown or described may be executed in a different order than that shown here.

[0038] Example 1

[0039] like Figure 1-12 As shown, this embodiment provides a method for constructing a rock damage constitutive model based on the evolution of microcrack propagation, including:

[0040] According to phenomenological theory, the microstructure of damaged rocks can be generalized into three parts: intact rock micro-elements, crack propagation damage micro-elements, and pores. The stress model at the microscale is shown below. Figure 1 .

[0041] In the figure, σ is the nominal stress of the rock, σ′ is the equivalent stress of the intact rock element, and σ″ is the equivalent stress of the crack-propagated damaged element; A0 is the stress-bearing area of ​​the rock, A1 is the stress-bearing area of ​​the intact rock element, A2 is the stress-bearing area of ​​the crack-propagated damaged rock element, and A3 is the stress-bearing area of ​​the rock pores.

[0042] Assuming the rock pores cannot withstand the load, according to the static equilibrium relationship, we have:

[0043] σA0=σ′A1+σ″A2 (1)

[0044] Depend on Figure 1 The geometric relationships of the force-bearing areas of a meso-micro element are as follows:

[0045] A0=A1+A2+A3 (2)

[0046] According to geometric damage theory:

[0047]

[0048]

[0049] In the formula, D0 represents rock pore damage, i.e., initial rock damage; D1 represents rock crack propagation damage.

[0050] Substituting equations (2) to (4) into equation (1), we get:

[0051] σ=σ′(1-D0-D1)+σ″D1 (5)

[0052] According to equation (5), the principal stress of the rock can be expressed as:

[0053] σ1=σ1′(1-D0-D1)+σ″1D1 (6)

[0054] σ3=σ3′(1-D0-D1)+σ″3D1 (7)

[0055] σ1′ is the equivalent maximum principal stress of the intact rock micro-element, and σ″1 is the equivalent maximum principal stress of the crack propagation damage micro-element;

[0056] σ3′ is the equivalent minimum principal stress of the intact rock element, and σ″3 is the equivalent minimum principal stress of the crack propagation damage element.

[0057] If a complete rock micro-element can be considered as an ideal elastic material, and its stress-strain follows a linear elastic relationship, then:

[0058] σ1′=Eε1+2νσ3′ (8)

[0059] In the formula, E and ν are the elastic modulus and Poisson's ratio of the intact rock micro-element, and ε1 is the axial strain of the rock.

[0060] From equations (6), (7), and (8), the damage constitutive model of the rock can be obtained as follows:

[0061] σ1=(1-D0-D1)Eε1+2νσ3+D1(σ″1-2νσ″3) (9)

[0062] Assuming the rock crack propagation damage element exhibits wing-shaped crack propagation, such as Figure 2 As shown.

[0063] When rock is under compression and the stress exceeds the fracture toughness of an airfoil crack, according to the Ashby model:

[0064]

[0065]

[0066]

[0067]

[0068]

[0069] In the formula, a is the radius of the initial crack in the rock, l is the propagation length of the wing-shaped crack, α is the crack initiation angle, and K... Ic Rock fracture toughness, μ is the friction factor at the crack interface, and β is the correction factor.

[0070] Assuming the rock crack propagation damage element obeys the Mohr-Coulomb yield criterion, then:

[0071]

[0072] From equations (10) and (15), we can obtain:

[0073]

[0074]

[0075]

[0076]

[0077] In the formula, c and These are rock cohesion and friction angle, respectively.

[0078] After a rock fractures, crack propagation reduces the effective stress-bearing area, leading to cumulative damage. Therefore, the effective area after crack propagation can be defined as rock crack propagation damage.

[0079]

[0080] Crack propagation area A l =πl 2 The crack propagated to its maximum length l lim At that time, the crack occupies the entire rock stress surface A between the airfoil cracks. S Then we have:

[0081]

[0082] Assuming there are N units of rock A The number of cracks can be obtained from equations (20) and (21) to derive the rock crack propagation damage model:

[0083]

[0084] Rock deformation and failure are essentially an evolutionary process of crack initiation, propagation, and connection. There is an intrinsic relationship between rock deformation and crack propagation length. Studies have found that in the early stages of crack propagation, crack length increases rapidly. However, as the crack length increases, the strain energy dissipation at the crack tip increases, hindering crack length development and causing a decrease in the crack length growth rate. This is similar to the growth retardation of biological populations in nature due to environmental influences. Therefore, we can assume that the crack propagation length in the rock deformation and failure process follows a biological population growth retardation model. For a small deformation dε in the rock and a crack growth dl, we have:

[0085]

[0086] In the formula, the crack propagation length l > 0, l lim Let be the crack propagation limit length, and k be the crack propagation rate. From equation (23), we can obtain:

[0087]

[0088] q is the initial length parameter for rock crack propagation.

[0089] Substituting equations (15), (16), (22), and (24) into equation (9), we can obtain the constitutive model of rock microstructure damage:

[0090]

[0091] Treating the nonlinear compaction stage of soft rock as a rock damage recovery process, and introducing the soft rock compaction strain ε0 to modify equation (25), we have the soft rock damage constitutive model:

[0092]

[0093] For brittle rocks, the compaction stage is very short, and the compaction strain ε0=0, so equation (26) degenerates into equation (25).

[0094] Methods for determining model parameters

[0095] Strength parameters

[0096] In the model, the parameters E and ν can be determined by the triaxial compression stage and the linear elastic stage; c and The parameters can be determined based on the relationship between peak rock strength and confining pressure; K Ic It can be obtained from the three-bend point test of rock; k can be obtained from the subcritical crack propagation test. ε0 is the intercept of the tangent to the elastic stage of the stress-strain curve with the strain axis.

[0097] initial damage

[0098] According to geometric damage theory:

[0099]

[0100] In the formula, n represents the initial porosity of the rock, which can be non-destructively measured by nuclear magnetic resonance experiments.

[0101] Detailed crack parameters

[0102] Based on the homogenization of rock cracks using micromechanics, the equivalent crack propagation angle α can be assumed to be 45°. When the stress intensity at the crack tip exceeds the fracture toughness of an airfoil crack, the crack begins to propagate in an airfoil manner as follows:

[0103]

[0104] By determining the functional relationship between triaxial compressive initiation stress and confining pressure, and substituting it into equation (28), the interface factor μ of the rock crack section and the initial equivalent radius a of the rock homogenization crack can be determined.

[0105] Assuming the initial damage to the rock is also crack propagation damage, according to equation (22), we have:

[0106]

[0107] When l = 0, then D1 = D0, and the crack propagation limit length can be obtained:

[0108]

[0109] The initial crack propagation length parameter q can be obtained from equation (25) when ε = 0; when ε = 0, the crack propagation length l0 is not 0, but is the original population length of crack propagation. Taking the initial crack characterization length l0 = 0.001, the initial crack propagation length parameter can be obtained from equation (25):

[0110]

[0111] Comparison and verification

[0112] To verify the rationality of the damage constitutive model in this embodiment, the stress-strain curve of carbonaceous mudstone with a confining pressure of 4 MPa was introduced for comparison and verification. Figure 3 The parameters of the micromechanical damage model for carbonaceous mudstone determined using the above methods are summarized in Table 1.

[0113] Table 1

[0114]

[0115] from Figure 3 As can be seen, the damage constitutive model proposed in this embodiment has a higher degree of agreement with the experimental results, especially in reflecting the strain softening and post-peak deformation stages after crack propagation in carbonaceous mudstone, thus verifying the rationality of the model. The statistical damage theory is used to determine the strength influencing factor of the rock damage micro-element; traditional materials mechanics methods use the frictional force after rock yielding failure as the strength of the damage micro-element, which has a certain degree of subjectivity; while this embodiment uses fracture mechanics methods to directly solve the fracture failure strength of the rock damage micro-element, which can better characterize the strength of the damaged rock micro-element and has rigorous physical significance.

[0116] Influence of model parameters on rock mechanical properties

[0117] The constitutive model parameters in this embodiment mainly include Figure 1 Mechanical parameters of intact rock micro-elements E and ν, and crack propagation damaged micro-elements c. K Ic The parameters are μ, D0 (initial damage state parameter of rock), q and k (efficiency parameters for transforming intact rock micro-element into crack-propagating damaged micro-element); changes in each parameter of the model directly affect the stress performance of intact rock micro-element and crack-propagating damaged micro-element, and change the contribution of each micro-element to the overall stress of the rock, thus showing the difference in stress-strain curves.

[0118] Stress-strain curves of rocks with different initial damage are shown below. Figure 4 As shown in the figure, initial damage affects the entire stress-strain process of the rock, especially the peak stress and residual stress. Initial rock damage mainly reflects... Figure 1In the rock stress model, the effective stress area decreases as the initial damage to the rock increases, and the peak stress during the deformation and failure process decreases. The greater the initial damage to the rock, the more fully the internal defects of the rock develop, resulting in increased residual stress and enhanced ductility.

[0119] Stress-strain curves of rocks with different elastic moduli are shown below. Figure 5 As shown in the figure, the higher the elastic modulus of the rock, the greater the peak stress, the steeper the stress-strain curve, and the more pronounced the brittle characteristics. This is because the elastic modulus reflects... Figure 1 The mechanical properties of intact rock micro-elements are as follows: the greater the elastic modulus of the rock, the higher the bearing capacity and the smaller the deformation of the intact rock micro-elements; after the peak stress, as the strain increases, a large number of intact rock micro-elements fracture and break down into damaged micro-elements; compared with intact rock micro-elements, crack-propagated damaged micro-elements have much lower strength, so they exhibit a rapid decrease in stress.

[0120] Stress-strain curves of rocks with different cohesion and friction angles are shown below. Figure 6 and Figure 7 As shown in the figure, cohesion and friction angle primarily affect the stress-strain curve after crack propagation in the rock. With increasing cohesion and friction angle, both the peak stress and residual strength of the rock increase. Cohesion and friction angle mainly reflect... Figure 1 The yield strength of the crack propagation damaged micro-element is as follows: the greater the cohesion and friction angle, the higher the strength of the crack propagation damaged micro-element, and the greater its contribution to the overall stress of the rock. The stress-strain curve of the rock is more significantly affected by the mechanical properties of the crack propagation damaged micro-element, showing larger peak stress and residual stress, and enhanced ductility.

[0121] Stress-strain curves of rocks with different fracture toughness and crack interface friction factors are shown in the figure. Figure 8 and Figure 9 As shown in the figure, fracture toughness and crack interface friction factor have a significant impact on the mechanical properties after crack propagation. With increasing fracture toughness and crack interface friction factor, the bearing capacity of the rock increases after crack propagation. Fracture toughness and crack interface friction factor reflect... Figure 1 The ability of a crack-propagated damaged micro-element to resist fracture failure is related to the fracture toughness and the friction factor at the crack interface. The greater the fracture toughness and the greater the friction factor at the crack interface, the slower the crack propagation damage develops in the rock, and the higher the strength of the crack-propagated damaged micro-element. Therefore, it exhibits an increase in bearing capacity after crack propagation.

[0122] Stress-strain curves for different crack propagation rates and initial crack length parameters are shown in the figure. Figure 10 and Figure 11As shown in the figure, the peak stress and strain of the rock decrease with increasing crack propagation rate, while increasing with increasing initial crack propagation length. The crack propagation rate and initial crack propagation length primarily reflect the efficiency of transforming intact rock elements into crack-damaged elements. A decrease in crack propagation rate or an increase in the initial crack propagation length (i.e., a decrease in the original population size of the crack propagation length) results in lower efficiency of transforming intact rock elements into crack-damaged elements. Therefore, the rock damage is smaller, the mechanical properties are better, and both peak stress and strain increase.

[0123] This embodiment utilizes a biologically inhibited growth model to characterize the evolution of crack propagation length. Based on geometric damage theory, it proposes defining rock damage by crack propagation length and establishes a damage evolution model for microscopic crack propagation, providing a new approach for quantitative research on rock crack propagation damage evolution. A method for solving the strength of rock damage micro-elements based on fracture mechanics is proposed, which better characterizes the strength of rock crack propagation damage micro-elements compared to traditional materials mechanics methods. Based on damage theory and fracture mechanics, this embodiment establishes a rock damage constitutive model based on microscopic crack propagation. This model can well reflect the mechanical behavior of rock crack propagation, and the physical meaning of the model parameters is clear. In the constitutive model, increasing the strength parameter of the micro-element increases the rock's bearing capacity and makes its brittle characteristics more pronounced; while increasing the initial damage state parameter and the damage micro-element efficiency parameter decreases the rock's peak stress, increases its residual strength, and enhances its ductility; revealing the stress mechanism of damaged rock from a microscopic perspective.

[0124] The above description is merely a preferred embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A method for constructing a rock damage constitutive model based on the evolution of micro-crack propagation, characterized in that, Includes the following steps: Based on phenomenological theory, the microstructure of rocks is divided into intact rock micro-elements, rock crack propagation damage micro-elements, and rock pores. An initial constitutive model of rock damage is constructed based on static equilibrium relations and geometric damage theory; Based on crack length, obtain the rock crack propagation damage variable; The crack length during the rock deformation and failure process follows a biological population growth retardation model, which is used to characterize the nonlinear evolution of crack length with rock strain. The rock crack propagation damage model is as follows: ； in, For rock crack propagation damage variables, For crack propagation length, This represents the maximum length of crack propagation. The crack length during the rock deformation and failure process follows a biological population growth retardation model, which characterizes the nonlinear evolution of crack length with rock strain and specifically satisfies the following differential equation: ； Wherein, the analytical solution is , For crack propagation length, The crack propagation limit length, This represents the crack propagation rate. The initial length parameter for rock crack propagation. The axial strain of the rock; Based on fracture mechanics, the strength of a crack-propagated damaged micro-element is obtained. The process of obtaining the strength of the crack-propagated damaged micro-element includes: obtaining the first equivalent stress of the crack-propagated damaged micro-element based on the ASHBY model; obtaining the second equivalent stress of the crack-propagated damaged micro-element based on the Mohr-Coulomb yield criterion; and obtaining the strength of the crack-propagated damaged micro-element based on the quantitative relationship between the first equivalent stress and the second equivalent stress. Based on the initial rock damage constitutive model, rock crack propagation damage variables, and the strength of the crack propagation damage micro-element, a target rock damage constitutive model is constructed.

2. The method for constructing a rock damage constitutive model based on microcrack propagation and evolution according to claim 1, characterized in that, An initial rock damage constitutive model is constructed based on the principal stresses of rocks in different directions and the linear elastic relationship between intact rock micro-elements in different directions.

3. The method for constructing a rock damage constitutive model based on microcrack propagation evolution according to claim 2, characterized in that, The process of obtaining the principal stress of the rock includes obtaining rock pore damage and rock crack propagation damage based on geometric damage theory; Based on the static equilibrium relationship, a functional relationship is constructed between the nominal stress of the rock, the equivalent stress of the intact rock micro-element, and the equivalent stress of the crack-propagated damaged micro-element. Based on the functional relationship, the geometric relationship between rock pore damage, rock crack propagation damage, and the stress area of ​​the micro-element, the principal stress of the rock is obtained.

4. The method for constructing a rock damage constitutive model based on microcrack propagation evolution according to claim 3, characterized in that, The process of obtaining the rock crack propagation damage includes: obtaining the rock stress surface occupied by the crack throughout the entire airfoil crack based on the ultimate length of crack propagation; and obtaining the rock crack propagation damage based on the ratio of the crack propagation surface to the rock stress surface occupied by the crack throughout the entire airfoil crack.

5. The method for constructing a rock damage constitutive model based on microcrack propagation evolution according to claim 1, characterized in that, The process of constructing the target rock damage constitutive model includes obtaining the target rock damage constitutive model based on the effective stress of the intact rock micro-element, the strength of the crack propagation damage micro-element, the rock crack propagation damage, the crack propagation length, and the initial rock damage constitutive model.

6. The method for constructing a rock damage constitutive model based on microcrack propagation evolution according to claim 1, characterized in that, The target rock damage constitutive model is modified based on the soft rock compaction strain to obtain the soft rock damage constitutive model. When the soft rock compaction strain is zero, the soft rock damage constitutive model is the target rock damage constitutive model.

7. The method for constructing a rock damage constitutive model based on microcrack propagation evolution according to claim 1, characterized in that, The process of determining the strength parameters in the target rock damage constitutive model includes obtaining the rock cohesion and friction angle parameters based on the relationship between the rock peak strength and the confining pressure. Rock fracture toughness was obtained based on the three-bend point test. Crack propagation rate was obtained based on subcritical crack propagation experiments; The compaction strain of soft rock is obtained based on the intercept of the tangent to the strain axis in the elastic stage of the stress-strain curve.

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