Rock uniaxial compression damage model considering microcrack mechanical behavior

Abstract

The invention discloses a rock uniaxial compression damage model considering microcrack mechanical behaviors. The model reflects that rock damage is caused by slippage and extension of microcracks. According to a microcrack slippage model and an energy balance principle, a rock uniaxial compression stress-strain relationship is established, and it is considered that microcracks obey a Weibull distribution model. And further taking a strain energy density criterion as a microfracture propagation criterion, solving the wing crack propagation length of the composite fracture by adopting an iteration method, and obtaining a rock damage variable evolution equation represented by the wing crack propagation length. Therefore, a rock uniaxial compression damage model is provided, and the rationality of the rock uniaxial compression damage model is verified. Parameter sensitivity analysis is adopted to research the influence of the microcrack length, the friction coefficient and the rock fracture toughness on the mechanical properties of the rock. Research results show that macroscopic mechanical properties of the rock are macroscopic reflection of microscopic mechanical parameters of the rock, so that the rock damage constitutive model established from the microscopic perspective can better reveal the deformation and failure mechanism of the rock, and the rock damage constitutive model has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of rock mechanics analysis, and in particular relates to a rock uniaxial compression damage model taking into account the mechanical behavior of microcracks. Background Art

[0002] The initiation and expansion of microcracks under external loads is the fundamental mechanical mechanism that causes progressive damage to rocks until they are destroyed. Although macroscopic damage mechanics based on continuum mechanics has made significant progress in the study of rock damage models, it is mainly based on the thermodynamic framework, by introducing associated and non-associated plastic flow laws to establish the corresponding macroscopic phenomenological damage constitutive equation. Therefore, it fails to well reflect the mesoscopic phenomena of the influence of mechanical behaviors such as microcrack closure, friction slip, expansion and interaction on rock deformation and failure characteristics, and it is difficult to reveal the intrinsic mechanical mechanism of rock failure.

[0003] The emergence, development and application of mesomechanics, which takes mesoscopic primitives (such as microcracks, micropores, etc.) as research objects, has provided a powerful tool for the study of rock damage theory and has developed a variety of rock mesoscopic damage models. Zhou et al. assumed that microcracks obey random distribution and proposed a corresponding uniaxial compression damage model for rock based on the initiation and extension criteria of microcracks under compression loads; however, they did not consider the contribution of displacement caused by microcrack initiation, extension and friction sliding under compression loads to the total deformation of rock.

[0004] In summary, from the current research status at home and abroad, it can be seen that predecessors have carried out in-depth research on the rock damage constitutive model from the perspective of mesomechanics, but they have failed to consider the interaction between microcracks in the loading process of rock, especially the influence of mutual inhibition on its mechanical properties, resulting in incorrect calculation of the number of activated microcracks in loaded rocks, resulting in certain errors between the calculated results of the theoretical model and the measured results. Summary of the invention

[0005] In order to solve the above problems, the present invention proposes a rock uniaxial compression damage model considering the mechanical behavior of microcracks.

[0006] The rock uniaxial compression damage model considering the mechanical behavior of microcracks of the present invention is:

[0007] σ=E(1-D)ε (27)

[0008] Where D is the rock damage variable, σ is the stress, ε is the strain, and E is the elastic modulus of the rock.

[0009] The calculation formula of the rock damage variable is:

[0010]

[0011] Where N is the density of microcracks in the rock, l is the tensile wing crack, and l * =0.27a,l ** =0.083a, 4bh represents the unit area, θ is the microcrack inclination angle, f is the friction coefficient, and a represents the crack half-length.

[0012] The stress intensity factor at the tip of the microcrack is

[0013]

[0014] In the formula, τ * is the effective shear stress, θ is the microcrack inclination angle, l * =0.27a,l ** =0.083a, a represents the half length of the crack, K I represents the mode I stress intensity factor, K II represents the type II stress intensity factor.

[0015] The extension length of the microcrack is calculated using the strain energy density criterion, that is, when the strain energy density S of the wing crack is greater than the minimum strain energy density S c When , the microcracks begin to propagate, and the strain energy density S of the wing crack can be solved by the following formula:

[0016]

[0017] In the formula,

[0018] K I represents the mode I stress intensity factor, K II represents the mode II stress intensity factor, θ is the microcrack inclination, E is the elastic modulus of rock, and v is the Poisson's ratio of rock.

[0019] The minimum strain energy density S c The calculation formula is

[0020]

[0021] In the formula, K Ιc is the static fracture toughness of rock; S c Also known as the fracture threshold, E is the elastic modulus of the rock, and v is the Poisson's ratio of the rock.

[0022] The length of the microcrack at a certain moment is calculated by the following formula

[0023]

[0024] In the formula, l tis the wing crack length at a certain time t, S is the wing crack strain energy density, S c is the fracture threshold.

[0025] The number of microcracks activated when the rock is damaged is

[0026] N=(1-D n )N0=(1-D n )kε m (26)

[0027] Where N is the number of microcracks, D n is the rock damage at a certain time step n, N0 is the number of microcracks activated per unit volume under a given strain ε, N0 = kε m , k and m are parameters that describe the material failure characteristics.

[0028] The beneficial effects of the present invention are:

[0029] The present invention discloses a rock uniaxial compression damage model considering the mechanical behavior of microcracks, which reflects that rock damage is caused by the slip and extension of microcracks. According to the microcrack slip model and the energy balance principle, the uniaxial compression stress-strain relationship of rock is established, and it is considered that the microcracks obey the Weibull distribution model. Then, the strain energy density criterion is used as the criterion for microcrack extension, and the wing crack extension length of the composite fracture is solved by the iterative method, and the rock damage variable evolution equation expressed by the wing crack extension length is obtained. Thus, a rock uniaxial compression damage model is proposed, and its rationality is verified. Parameter sensitivity analysis is used to study the influence of microcrack length, friction coefficient and rock fracture toughness on the mechanical properties of rock. The research results show that the macroscopic mechanical properties of rock are the macroscopic manifestation of its microscopic mechanical parameters. Therefore, the rock damage constitutive model established from a microscopic perspective can better reveal its deformation and failure mechanism, and has a good application prospect. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a rock specimen with microcracks under uniaxial compression and a microcrack slip model.

[0031] Figure 2 It is a comparison chart of the test and calculation curves of sandstone under uniaxial compression load.

[0032] Figure 3 It is the axial stress, damage and axial strain curve under uniaxial compression.

[0033] Figure 4 It is the mechanical properties of the specimen at different microcrack lengths.

[0034] Figure 5 It is the mechanical property of the specimen at different microcrack friction coefficients.

[0035] Figure 6 It is the mechanical property of the specimen at different rock fracture toughness. DETAILED DESCRIPTION

[0036] Embodiments of the present invention are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to be used to explain the present invention, but should not be understood as limiting the present invention.

[0037] Firstly, based on the microcrack slip model and energy balance principle, the uniaxial compression stress-strain relationship of rock was established.

[0038] Figure 1 (a) is a rock unit containing a microcrack. The mechanical behavior of the microcrack initiation and propagation under compression load is shown in Figure 1 (b) As shown. Under the compressive load, the microcrack surface is first closed, and then shear stress is generated on its upper and lower surfaces, and a sliding tendency appears on the microcrack surface. Since the microcrack surface is closed, the friction force acting on it will prevent the rock block from sliding. When the shear stress component on the microcrack surface exceeds its friction force, the specimen will undergo frictional sliding along the microcrack surface, and then stress concentration will be generated at the microcrack tip. As the compressive load continues to increase, when the stress intensity factor at the microcrack tip P, P' meets the microcrack initiation and propagation criterion, tensile wing cracks Q, Q' will be generated at the microcrack tip, as shown in Figure 1 As shown in (b), with the continuous expansion of microcracks, the tensile wing cracks will gradually expand in the direction of the compressive load and eventually lead to axial splitting failure of the rock specimen.

[0039] Under uniaxial compression, the normal stress σ on the microcrack surface is θ and shear stress τ θ They are:

[0040] σ θ =σcos 2 θ (1)

[0041] τ θ =σsinθcosθ (2)

[0042] Where: θ is the microcrack inclination angle.

[0043] Assume the microcrack surface friction angle is The corresponding friction coefficient Under uniaxial compression, the shear stress on the microcrack surface will cause the microcrack to slip, and the corresponding normal stress acting on the microcrack surface will produce friction to prevent the microcrack from slipping. It can be seen that when the specimen slides along the microcrack surface, the corresponding effective shear stress τ on the microcrack surface *It should be greater than 0. Therefore, according to equations (1) and (2), the sliding driving force on the microcrack surface can be obtained as:

[0044]

[0045] Under uniaxial compression load, Figure 1 The stress intensity factor at the microcrack tip is shown as:

[0046]

[0047] In the formula, τ * is the effective shear stress, θ is the microcrack inclination angle, l * =0.27a,l ** =0.083a, a represents the half length of the crack, K I represents the mode I stress intensity factor, K II represents the type II stress intensity factor.

[0048] According to the energy balance principle, the work W1 done by the load on the elastic body is equal to the elastic strain energy U released by the crack expansion. e and the energy W dissipated due to frictional sliding between crack surfaces f The sum is:

[0049] W1=U e +W f (5)

[0050] like Figure 1 As shown in (a), assuming that the strain generated by the microcrack under the compressive stress is Δε1, then due to the Poisson's ratio effect, the microcrack will also have a small strain value perpendicular to the compressive stress direction, assuming it is Δε2, then the work done by σ is:

[0051] W1=4bhσΔε1 (6)

[0052] Among them: 4bh represents the unit area.

[0053] The linear relationship between Δε1, Δε2 and applied stress within the elastic range can be written as:

[0054]

[0055] Where: [S ij ](i,j=1,2) is the flexibility tensor caused by a single microcrack. According to the symmetry, S ij =S ji , from formula (6) and (7), we can get:

[0056] W1=4bhS 11 σ 2 (8)

[0057] According to fracture mechanics, the elastic strain energy released due to microcrack growth is (for plane stress problems):

[0058]

[0059] Substituting formula (4) into formula (9) yields:

[0060]

[0061] Under the action of shear stress, if the specimen slides along the microcrack surface for a distance of δ, the energy consumed by frictional sliding is:

[0062] W f =2aδ·fσ θ (11)

[0063] Assuming that the microcrack spacing is not considered, the sliding distance δ is:

[0064]

[0065] Where: l ** =0.083a.

[0066] Substituting formula (12) into formula (11), we get:

[0067]

[0068] From (5), (10), and (13), by comparing the coefficients, we can obtain the flexibility tensor component caused by a single crack: in:

[0069] B i is the parameter related to the tensile wing crack l,

[0070] If the density of microcracks in the rock is assumed to be N, and all microcracks are of equal size, parallel and uniformly distributed, and their interactions are ignored, the strain caused by the extension of microcracks is:

[0071]

[0072] Assuming that the rock mass strain is a small strain, the total strain ε should be the elastic strain ε e (before crack extension) and the strain ε caused by microcrack extension d The sum is:

[0073] ε=ε e +ε d (15)

[0074] According to Hooke's law, stress σ and elastic strain ε e Should meet:

[0075] ε e =D:σ (16)

[0076] Where: D is the flexibility tensor. For plane stress problems, Using equations (14) to (16), the total strain is:

[0077]

[0078] Where: E and v are the elastic modulus and Poisson's ratio of the rock respectively.

[0079] Formula (17) is based on the plane stress problem. For the plane strain problem, we only need to replace E with E / (1-v 2 ), v is replaced by v / (1-v 2 )

[0080] Then under uniaxial compression load, combined with Figure 1 (b), assuming that the stress and strain in the direction of the compressive load are σ and ε respectively, then the corresponding stress-strain relationship can be obtained from formula (17):

[0081] ε=σ / E+NS 11 σ (18)

[0082] Put S 11 Substituting into formula (18) and transforming it, we can get:

[0083]

[0084] The rock damage variable D is introduced to describe the weakening of rock elastic modulus due to the increase of microcrack density and microcrack extension, that is:

[0085]

[0086] Where:

[0087]

[0088] Secondly, the strain energy density criterion is used as the criterion for microcrack extension, and the wing crack extension length of the composite fracture is solved by an iterative method, and the rock damage variable evolution equation expressed by the wing crack extension length is obtained. Thus, a new uniaxial compression damage model of rock is proposed and its rationality is verified.

[0089] The strain energy density criterion is used to calculate the wing crack extension length, that is, when the wing crack strain energy density S is greater than the minimum strain energy density S c When the cracks begin to propagate.

[0090] The wing crack strain energy density S can be solved by the following formula:

[0091]

[0092] in: When θ3 = 0, S is the strain energy density in the direction of the wing crack.

[0093] Minimum strain energy density S c The calculation formula is:

[0094]

[0095] Where: K Ιc is the static fracture toughness of rock; S c Also called fracture threshold.

[0096] The wing crack length l at a certain time t t Calculated by the following formula:

[0097]

[0098] Grady et al. proposed a microcrack evolution model when studying the oil shale blasting problem. They used the Weibull distribution model to describe the number of activated microcracks, namely:

[0099] N0=kε m (25)

[0100] Where: N0 is the number of microcracks activated per unit volume under a given strain ε; k and m are parameters that describe the failure characteristics of the material.

[0101] At a certain time step n, let the rock damage be D n , then the number of activated microcracks N when considering damage can be expressed as:

[0102] N=(1-D n )N0=(1-D n )kε m (26)

[0103] According to the Lemaitre equivalent principle, the uniaxial compression damage model of rock can be expressed as:

[0104] σ=E(1-D)ε (27)

[0105] Where: D is the rock damage variable, calculated by formula (21).

[0106] The model calculation process is:

[0107] ①First, the initial stress is taken as zero, then a stress increment Δσ is given, and the stress intensity factor at the microcrack tip is calculated by equation (4). Then, according to equations (21) to (24), it is determined whether the microcrack is extended. If the microcrack extension condition is not met, then N = 0 and l = 0. Then, the corresponding strain increment Δε under the stress increment Δσ is calculated by equation (27). Then the stress gradually increases until the microcrack begins to extend. Let this moment be t n At this time, the stress and strain are σ n and ε n This stage corresponds to the linear elastic stage before the microcracks in the rock expand.

[0108] ②Let t n+1 The strain increment at the moment is Δε n+1 , and the number of activated microcracks N is calculated by formula (26): n (At this time, take D n =0) and take the microcrack extension length l n = 0, and then substitute into formula (21) to calculate the corresponding damage increment ΔD n+1 , and the corresponding stress increment Δσ is calculated by formula (27) n+1 .

[0109] ③ Put t n+1 The damage increment ΔD at the time n+1 Substitute into formula (26) to calculate the increment of activated microcrack number ΔN n+1 , substituting into formula (21) to obtain the damage increment ΔD n+1 The corresponding microcrack extension length increment Δl n+1 .

[0110] By iteratively solving ② and ③, the stress-strain curve of the rock in the damage stage can be obtained, and then combined with the stress-strain curve of the elastic stage obtained by ①, the complete rock compression stress-strain curve can be obtained.

[0111] The following experimental results of Zhou et al. are used to verify the model. The rock used in the experiment is sandstone taken from the construction site of Xiangjiaba Hydropower Station in Sichuan Province. The rock parameters are: elastic modulus E = 34 GPa, Poisson's ratio υ = 0.3, fracture toughness K IC =1.1MPa·m 1 / 2 、Density 2600kg / m 3 The specimen is a standard cylindrical specimen with a height of 100 mm and a diameter of 50 mm. The uniaxial compression test curve is as follows: Figure 2 The test results are used to verify the rock uniaxial compression damage model proposed in this paper, and the relevant parameters are: k = 5e22m -3, m = 7.1, microcrack size 2a = 2e-4m, friction coefficient f = 0.26, microcrack inclination angle θ = 45°. The theoretical calculation curve is as follows Figure 2 , we can see that:

[0112] (1) The theoretical curve is very consistent with the test results, especially in the linear elastic stage. There is a certain error between the two near the peak stage. The theoretical and experimental peak strengths are 131.03MPa and 137.68MPa, respectively, and the latter is about 95.17% of the former, that is, the error is very small. After the peak strength, the shapes of the two curves are basically the same.

[0113] (2) According to the constitutive model proposed in this paper, the elastic limit strength of rock is 79.3 MPa, that is, when the compressive strength is greater than this, the specimen begins to be damaged; its peak compressive strength is 131.03 MPa, that is, the former is about 60.5% of the latter. Many scholars believe through research that the elastic limit strength of the specimen is about 30% to 70% of its peak strength, which is consistent with the research results of predecessors.

[0114] Finally, parameter sensitivity analysis was used to study the effects of microcrack length, friction coefficient and rock fracture toughness on the mechanical properties of rock.

[0115] The rock calculation parameters are: density 2500kg / m 3 , elastic modulus E = 40 GPa, Poisson's ratio v = 0.2, the calculation model is as follows Figure 1 (b) The shape and size of the specimen are the same as before, and the calculation is based on the plane stress problem. The microcrack parameters are: microcrack inclination angle θ = 45°, microcrack size 2a = 60μm, friction coefficient between microcracks f = 0.7, and Weibull function characteristic parameter k of microcracks = 4e23 / m 3 , m = 6.5, fracture toughness K IC =0.4MPa·m 1 / 2 Then the axial stress, damage and axial strain curves of rock under uniaxial compression are as follows: Figure 3 . It can be seen that when the external force is small, the microcracks will not expand. At this time, the stress-strain curve is linear, and the damage to the specimen is 0, that is, no new damage is generated. When the external force exceeds the elastic limit of the rock, the microcracks begin to expand and the specimen begins to produce new damage, but at this time the microcracks are stable. That is, if the microcracks continue to expand, external force still needs to be applied, and the stress-strain curve still shows an upward trend. When the specimen reaches the peak strength, the corresponding damage is about 0.2. When the stress peak is reached, the stress of the specimen begins to decrease, and the damage increases rapidly with strain. The microcracks will converge to form macro cracks, eventually leading to rock destruction, which is consistent with the corresponding test results.

[0116] Taking this model as an example, the following study examines the effects of microcrack length, friction coefficient, and rock fracture toughness on the uniaxial compression mechanical properties of rock.

[0117] (1) Influence of microcrack length

[0118] The microcrack lengths 2a are 60 μm, 80 μm, 100 μm and 120 μm respectively, the rock elastic modulus E = 34 GPa, Poisson's ratio υ = 0.3, and the fracture toughness K IC =1.1MPa·m 1 / 2 、Density 2600kg / m 3 The specimen is a standard cylindrical specimen with a height of 100 mm and a diameter of 50 mm. The material failure characteristic parameter is: k = 5e22m -3 , m = 7.1, friction coefficient f = 0.26, microcrack inclination angle θ = 45°. The uniaxial compression stress-strain curve of rock changes with the length of microcracks as shown in Figure 4 . In general, as the length of the microcrack increases, the peak uniaxial compressive strength of the specimen decreases approximately linearly, and the peak strain of the specimen also gradually decreases. This is because under the same external load, as the length of the microcrack increases, the stress intensity factor at the crack tip gradually increases, and under the condition of constant fracture toughness, the external force required for microcrack extension should be reduced. Therefore, the peak strength and damage variables of the specimen show a decreasing and increasing trend respectively as the length of the microcrack increases.

[0119] (2) Influence of microcrack friction coefficient

[0120] The microcrack friction coefficient f is taken as 0.5, 0.6, 0.7 and 0.8 respectively, the rock elastic modulus E = 34 GPa, Poisson's ratio υ = 0.3, and the fracture toughness K IC =1.1MPa·m 1 / 2 、Density 2600kg / m 3 The specimen is a standard cylindrical specimen with a height of 100 mm and a diameter of 50 mm. The material failure characteristic parameter is: k = 5e22m -3 , m = 7.1, microcrack size 2a = 2e-4m, microcrack inclination angle θ = 45°. Then the uniaxial compression stress-strain curve of rock with the change of microcrack friction coefficient is as follows Figure 5 . In general, as the microcrack friction coefficient increases, the uniaxial compressive peak strength of the specimen increases, but the increase is different. When the microcrack friction coefficient is 0.5-0.7, the peak strength of the specimen increases less, approximately linearly; and when the microcrack friction coefficient is 0.7-0.8, the peak strength of the specimen increases rapidly. This is because as the microcrack friction coefficient increases, the ability of the microcrack to resist slip increases, and then the ability of the specimen to resist damage also increases, and ultimately leads to an increase in the peak compressive strength of the specimen. At the same time, Figure 5(c) It can also be seen that as the friction coefficient of the microcrack increases, the corresponding strain when the damage begins to appear also increases significantly, which means that as the friction coefficient of the microcrack increases, the ability of the specimen to resist damage increases nonlinearly.

[0121] (3) Influence of rock fracture toughness

[0122] Take the micro rock fracture toughness K IC 0.3MPa·m 1 / 2 , 0.4MPa·m 1 / 2 , 0.5MPa·m 1 / 2 and 0.6MPa·m 1 / 2 , rock elastic modulus E = 34GPa, Poisson's ratio υ = 0.3, density 2600kg / m 3 The specimen is a standard cylindrical specimen with a height of 100 mm and a diameter of 50 mm. The material failure characteristic parameter is: k = 5e22m -3 , m = 7.1, friction coefficient f = 0.26, microcrack size 2a = 2e-4m, microcrack inclination angle θ = 45°. Then the uniaxial compression stress-strain curve of rock with the change of rock fracture toughness is as follows Figure 6 . In general, as the fracture toughness of rock increases, the uniaxial compressive peak strength of the specimen increases, but the increase is different. When the fracture toughness of rock is 0.3-0.5, the peak strength of the specimen increases less, approximately linearly; and when the microcrack friction coefficient is 0.6, the peak strength of the specimen increases rapidly. This is because as the fracture toughness of rock increases, the ability of microcracks to resist cracking increases, and then the compressive strength of the specimen also increases, and ultimately leads to an increase in the peak compressive strength of the specimen. At the same time, Figure 6 (c) It can also be seen that as the fracture toughness of the rock increases, the corresponding strain when damage begins to appear also increases significantly, which indicates that as the fracture toughness of the rock increases, the ability of the specimen to resist damage increases nonlinearly.

[0123] The results of parameter sensitivity analysis show that as the length of microcracks increases and the friction coefficient decreases, the uniaxial compressive strength and peak strain of rocks decrease. When the length of microcracks is 60-120 μm, the uniaxial compressive strength decreases approximately linearly; when the microcrack friction coefficient increases from 0.5 to 0.8 and the rock fracture toughness increases from 0.3 MPa·m 1 / 2 Increase to 0.6MPa·m 1 / 2 When , the uniaxial compressive peak strength of rock increases slowly at first and then increases rapidly, which indicates that the microcrack friction coefficient and rock fracture toughness have a great influence on the peak strength of the specimen, and the degree of influence shows a nonlinear characteristic.

[0124] Although the above embodiments have been shown and described, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. Changes, modifications, substitutions and variations of the above embodiments by those of ordinary skill in the art are all within the scope of protection of the present invention.

Claims

1. A uniaxial compression damage model of rock considering the mechanical behavior of microcracks, characterized in that: The rock uniaxial compression damage model is: σ=E(1-D)ε (27) Where D is the rock damage variable, σ is the stress, ε is the strain, and E is the elastic modulus of the rock.

2. The rock uniaxial compression damage model considering the mechanical behavior of microcracks according to claim 1 is characterized in that: The calculation formula of the rock damage variable is: Where N is the density of microcracks in the rock, l is the tensile wing crack, and l * =0.27a,l ** =0.083a, 4bh represents the unit area, θ is the microcrack inclination angle, f is the friction coefficient, and a represents the crack half-length.

3. The rock uniaxial compression damage model considering the mechanical behavior of microcracks according to claim 1 is characterized in that: The stress intensity factor at the tip of the microcrack is In the formula, τ * is the effective shear stress, θ is the microcrack inclination angle, l * =0.27a,l ** =0.083a, a represents the half length of the crack, K I represents the mode I stress intensity factor, K II represents the type II stress intensity factor.

4. The rock uniaxial compression damage model considering the mechanical behavior of microcracks according to claim 1 is characterized in that: The extension length of the microcrack is calculated using the strain energy density criterion, that is, when the strain energy density S of the wing crack is greater than the minimum strain energy density S c When , the microcracks begin to propagate, and the strain energy density S of the wing crack can be solved by the following formula: In the formula, K I represents the mode I stress intensity factor, K II represents the mode II stress intensity factor, θ is the microcrack inclination angle, E is the elastic modulus of rock, and v is the Poisson's ratio of rock.

5. The rock uniaxial compression damage model considering the mechanical behavior of microcracks according to claim 4 is characterized in that: The minimum strain energy density S c The calculation formula is In the formula, K Ιc is the static fracture toughness of rock; S c Also known as the fracture threshold, E is the elastic modulus of the rock, and v is the Poisson's ratio of the rock.

6. The rock uniaxial compression damage model considering the mechanical behavior of microcracks according to claim 4 is characterized in that: The length of the microcrack at a certain moment is calculated by the following formula In the formula, l t is the wing crack length at a certain time t, S is the wing crack strain energy density, S c is the fracture threshold.

7. The rock uniaxial compression damage model considering the mechanical behavior of microcracks according to claim 1 is characterized in that: The number of microcracks activated when the rock is damaged is N(1-D). n )N0(1-D n )kε m (26) Where N is the number of microcracks, D n is the rock damage at a certain time step n, N0 is the number of microcracks activated per unit volume under a given strain ε, N0 = kε m , k and m are parameters that describe the material failure characteristics.

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