Carbonate shear degradation model construction method under hydrochemistry-three-dimensional stress disturbance

Abstract

The invention relates to a carbonate rock shear degradation model construction method under hydrochemistry-three-dimensional stress disturbance. The method comprises the following steps: performing fitting calculation according to water chemical environment-wave velocity data to obtain an initial damage variable; shear stress loading damage is calculated according to the shear direction process damage corresponding to different shear stress loading stages; calculating to obtain a shear crack initiation stress yield function and a shear critical stress yield function according to a shear strength criterion under hydrochemistry-three-dimensional stress disturbance coupling; according to the shear crack initiation stress yield function and the shear critical stress yield function, carbonate rock shear degradation deformation stages under different stress states are divided, a model element is constructed according to the initial damage variable and the shear stress loading damage, and a carbonate rock shear degradation model under hydrochemistry-three-dimensional stress disturbance is obtained. By adopting the method, carbonate rock shear degradation evolution conditions under different water chemical environments and different stress disturbances can be fitted.

Description

Technical Field

[0001] This invention belongs to the field of deep mining and underground engineering research, and in particular relates to a method for constructing a shear degradation model of carbonate rocks under hydrochemical-three-dimensional stress disturbance. Background Technology

[0002] With the development of technology in the fields of deep mineral resource mining and underground engineering construction, deep rock mass mechanical property assessment technology has emerged. Based on carbonatite rock mechanical tests, it analyzes the strength, deformation and damage patterns of rock masses in complex geological environments, providing a stability design basis for underground tunnel excavation and safe mining of mineral resources.

[0003] In traditional techniques, the chemical immersion method with room temperature water is used to qualitatively determine the deterioration effect of the hydrochemical environment on carbonate rocks by comparing the strength changes of the rock mass before and after immersion. Combined with conventional triaxial shear tests in the laboratory to obtain strength parameters such as cohesion and internal friction angle of the carbonate rocks, the shear strength formula of the rock mass is derived based on the Mohr-Coulomb shear strength criterion to construct a model of shear deterioration of carbonate rocks, which is used to determine whether the rock mass has undergone shear failure.

[0004] However, the aforementioned methods, relying on the Mohr-Coulomb criterion, only consider the effects of normal and shear stresses, neglecting the influence of lateral stress on the shear strength of carbonate rocks. In deep engineering, carbonate rocks are actually in a true triaxial state under the combined effects of normal, lateral, and shear stresses, leading to a significant deviation between the calculated rock mass shear strength and the actual engineering conditions, thus failing to accurately guide deep engineering design. The consideration of the hydrochemical environment remains at a qualitative comparison level, preventing the model from truly reflecting the differentiated patterns of carbonate rock shear degradation under different hydrochemical conditions. Furthermore, the influence of engineering disturbance stresses is ignored or simplified, making it impossible to obtain dynamic damage evolution data of carbonate rocks under low-frequency, low-amplitude disturbance stresses generated by common engineering practices such as mechanical excavation and blasting. This results in the constructed model only describing shear behavior under static conditions and failing to accurately predict the risk of rock mass instability caused by disturbances in actual engineering projects. Summary of the Invention

[0005] Therefore, it is necessary to provide a hydrochemical-three-dimensional stress perturbation model for constructing a model of shear degradation of carbonate rocks under different hydrochemical environments that can reflect the true triaxial shear mechanical properties of carbonate rocks under different hydrochemical conditions.

[0006] Firstly, this application provides a method for constructing a hydrochemical-three-dimensional stress perturbation model of carbonatite shear degradation, including:

[0007] S1. Obtain hydrochemical environment-wave velocity data corresponding to the hydrochemical environment carbonate rock wave velocity test; the hydrochemical environment carbonate rock wave velocity test corresponds to the measurement of wave velocity in fractured carbonate rocks under different temperature variables, pH variables, and blank control.

[0008] S2. Initial damage variables are calculated by fitting water chemistry environment-wave velocity data;

[0009] S3. Obtain stress response data from true triaxial perturbation shear tests on fractured carbonate rocks under different hydrochemical environments; the preset three-dimensional stress simulation parameters corresponding to the true triaxial perturbation shear tests include geostress simulation parameters, mechanical perturbation simulation parameters, and shear loading parameters; geostress simulation parameters include normal stress and lateral stress; mechanical perturbation simulation parameters include perturbation amplitude, perturbation frequency, and perturbation cycle number; shear stress loading parameters include multi-level average shear stress loading values ​​starting from the initial shear stress loading value; stress response data include shear strength index and shear strain; shear strength index includes crack initiation stress, critical stress, and failure stress; shear strain includes reversible strain and irreversible strain;

[0010] S4. The irreversible strain during the shear stress loading process characterizes the damage in the shear direction. Based on the damage in the shear direction corresponding to different shear stress loading stages in the true triaxial perturbation shear test, and combined with the mechanical perturbation simulation parameters and the influence of different hydrochemical environments on the mechanical properties of carbonate rocks, the damage features are extracted to obtain the shear stress loading damage.

[0011] S5. Based on the initial damage variables and lateral response forces, the Mohr-Coulomb shear strength criterion is modified to obtain the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling. Based on the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling, the shear initiation stress yield function and the shear critical stress yield function are calculated.

[0012] S6. Based on the shear initiation stress yield function and the shear critical stress yield function, the carbonatite shear deterioration deformation stages under different stress states are divided. Model elements are constructed according to the initial damage variables and shear stress loading damage to obtain the carbonatite shear deterioration model under hydrochemical-three-dimensional stress disturbance.

[0013] In one embodiment, initial damage variables are calculated based on water chemistry environment-wave velocity data fitting, including:

[0014] S21. The relationship between the wave velocity variation in the hydrochemical environment is obtained by fitting the hydrochemical environment-wave velocity data.

[0015] The relationship between wave velocity changes in the water chemical environment can be obtained using the following formula:

[0016] v(C,pH)=(v0-aC)·eb·pH

[0017] Where v(C,pH) is the wave velocity under the combined effects of temperature and pH; C is temperature; pH is pH; v0 is the theoretical wave velocity reference value corresponding to the initial state C=0 and pH=0; a is the wave velocity sensitivity to temperature; b is the wave velocity sensitivity to pH.

[0018] S22. Using the undamaged wave velocity of carbonate rocks corresponding to the blank control as a reference, the relationship of wave velocity change in the hydrochemical environment is transformed to obtain a dimensionless initial damage variable.

[0019] The initial damage variable is obtained using the following formula:

[0020]

[0021] Where D0 is the initial damage variable; v ref The wave velocity of carbonate rocks under undamaged conditions.

[0022] In one embodiment, irreversible strain during shear stress loading is used to characterize the damage in the shear direction. Based on the damage in the shear direction corresponding to different shear stress loading stages in the true triaxial perturbation shear test, and combined with the mechanical perturbation simulation parameters and the influence of different hydrochemical environments on the mechanical properties of carbonate rocks, damage features are extracted to obtain the shear stress loading damage, including:

[0023] The damage under shear stress loading can be obtained using the following formula:

[0024]

[0025] Where D1 represents shear stress loading damage; A represents disturbance amplitude; f represents disturbance frequency; n represents hardening exponent; t represents the duration of each level of average shear stress loading value; α, β, and c represent characteristic parameters of carbonate rock materials; and p represents the hardening exponent of the carbonate rock microdynamic disturbance elastoplastic strain as a function of disturbance frequency.

[0026] In one embodiment, the Mohr-Coulomb shear strength criterion is modified based on the initial damage variable and lateral response force to obtain the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling. The shear initiation stress yield function and the shear critical stress yield function are then calculated based on the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling, including:

[0027] S51. Based on the change of critical stress under different lateral stresses in the true triaxial perturbation shear test, the Mohr-Coulomb shear strength criterion is modified to obtain a shear strength criterion that takes into account lateral stress; the shear strength criterion corresponds to the shear strength criterion expression constructed by coordinating the internal friction angle and lateral stress with the cohesion parameter.

[0028] S52. Based on the influence of the hydrochemical environment on the critical stress and failure stress, the cohesion parameters of the internal friction angle and lateral stress coordination are corrected according to the initial damage variables to obtain the shear strength criterion under the coupling of hydrochemistry and three-dimensional stress disturbance.

[0029] S53. Based on the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling, the damage effect yield function of hydrochemical-three-dimensional stress shear direction process is obtained;

[0030] The yield function of the damage effect in the hydrochemical-three-dimensional stress-shear direction process is obtained using the following formula:

[0031]

[0032] c * =c(1-D0)

[0033] Where τ is the shear stress; σ n Normal stress; σ p Lateral stress; σ is the internal friction angle; c is the cohesive force parameter for lateral stress coordination; σ ρ denoted as lateral stress corresponding to the maximum shear stress in carbonate rocks; K is the equivalent lateral stress when the strength and lateral stress are both zero; d is the stress parameter related to cohesion influenced by mineral composition and other factors. The internal friction angle after degradation correction; c * D0 represents the cohesive force parameter for lateral stress coordination after degradation correction; D0 represents the initial damage variable.

[0034] S54. The shear initiation stress yield function and the shear critical stress yield function are calculated based on the shear critical stress function.

[0035] The shear initiation stress yield function can be obtained using the following formula:

[0036]

[0037] Where F1 is the shear initiation stress yield function;

[0038] The shear critical stress yield function can be obtained using the following formula:

[0039]

[0040] Where F2 is the shear critical stress yield function.

[0041] In one embodiment, the shear degradation deformation stages of carbonate rocks under different stress states are divided based on the shear initiation stress yield function and the shear critical stress yield function. Model elements are constructed according to the initial damage variables and shear stress loading damage to obtain a hydrochemical-three-dimensional stress perturbation-based carbonate rock shear degradation model, including:

[0042] S61. Based on the initial damage variables and shear stress loading damage, damage elastic elements, damage fractional-order viscoelastic-plastic elements, and nonlinear viscoelastic elements are used as model elements.

[0043] S62. When the stress state is less than the shear initiation stress yield function condition, the shear deterioration deformation stage of carbonate rock is the undeteriorated deformation stage, and the shear deterioration model of carbonate rock under hydrochemical-three-dimensional stress disturbance is an elastic model characterized by damaged elastic elements.

[0044] S63. When the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state is less than the shear critical stress yield condition, the shear deterioration deformation stage of carbonate rock is the initial stage of deterioration deformation. The shear deterioration model of carbonate rock under hydrochemical-three-dimensional stress disturbance is a damage fractional viscoelastic-plastic model characterized by damage fractional viscoelastic-plastic elements.

[0045] S64. When the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state reaches and exceeds the shear critical stress yield condition, the shear deterioration deformation stage of carbonate rock is the unstable expansion stage of deterioration deformation. The hydrochemical-three-dimensional stress perturbation model of carbonate rock shear deterioration is a nonlinear viscoplastic model with nonlinear viscoplastic elements.

[0046] In one embodiment, based on the initial damage variable and shear stress-loaded damage, damage elastic elements, damage fractional-order viscoelastic elements, and nonlinear viscoelastic elements are used as model elements, including:

[0047] S611. Calculate the damaged elastic element based on the initial damage variables;

[0048] The expression for the damaged elastic element can be obtained through the following formula:

[0049]

[0050] Where G is the elastic shear modulus; τ is the shear stress on the carbonate rock; and D0 is the initial damage variable.

[0051] S612. Construct constitutive equations for viscoelastic-plastic elements of carbonate rocks based on shear stress loading damage, and obtain damage fractional-order viscoelastic-plastic elements by performing Laplace transform and inverse transform on the constitutive equations for viscoelastic-plastic elements of carbonate rocks.

[0052] The expression for the damage fractional-order viscoelastic-plastic element can be obtained using the following formula:

[0053]

[0054] in, Fractional viscosity coefficient; α is the fractional order; D1 is the damage under shear stress loading; τ ci For crack initiation stress;

[0055] S613. Starting from the unsteady propagation of shear plastic deformation in carbonate rocks, a nonlinear viscoplastic element constitutive equation is constructed based on the shear stress loading damage, and the nonlinear viscoplastic element is obtained by combining the deterioration integral of the viscosity coefficient loss due to high shear stress.

[0056] The expression for the nonlinear viscoplastic element can be obtained through the following formula:

[0057]

[0058] Where, τ cd The critical stress; is the fractional viscosity coefficient; t is time.

[0059] In one embodiment, the hydrochemical-three-dimensional stress perturbation model for carbonatite shear degradation is as follows:

[0060] The following formula is used to obtain the shear degradation model of carbonate rocks under hydrochemical-three-dimensional stress perturbation:

[0061]

[0062] Wherein, F1<0 means the stress state is less than the shear initiation stress yield function condition; F1≥0∩F2<0 means the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state is less than the shear critical stress yield condition; F1≥0∩F2≥0 means the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state reaches and exceeds the shear critical stress yield condition.

[0063] In one embodiment, the method further includes:

[0064] S71. Obtain the shear strain fitting curves of the carbonate rock shear degradation model under different hydrochemical environments and shear stresses under different hydrochemical environments and shear stresses.

[0065] S72. Compare the fitted curve of shear strain with the measured shear strain of fractured carbonate rocks under different hydrochemical conditions using true triaxial perturbation shear tests to obtain the error.

[0066] S73. Analyze the error and update the model parameters of the hydrochemical-three-dimensional stress disturbance carbonate rock shear degradation model based on the error analysis results.

[0067] The aforementioned method for constructing a hydrochemical-three-dimensional stress disturbance model of carbonate rock shear degradation covers low-temperature to high-temperature and strongly acidic to neutral hydrochemical environments that may be encountered in deep engineering through hydrochemical environment simulation, avoiding the limitations of single-parameter tests. In stress condition simulation, it breaks through the limitations of traditional shear tests that only consider normal and shear stress, introducing lateral stress as a geostress simulation parameter. Simultaneously, through mechanical disturbance simulation parameters, it recreates the low-frequency, low-amplitude disturbances generated by mechanical excavation and blasting, ensuring that the test conditions are highly consistent with the actual scenarios of hydrochemical corrosion, three-dimensional geostress, and construction disturbances in deep engineering. By constructing a dual damage characterization system of initial damage variables and shear stress loading damage, a full-stage quantitative description of the damage process in carbonate rocks is achieved. The initial damage variable transforms the initial degradation degree of carbonate rocks under hydrochemical conditions into an intuitive dimensionless parameter, avoiding the subjectivity of traditional damage assessment. Shear stress loading damage uses irreversible strain during the shear process as the core characterization index. Combined with the damage characteristics of multi-stage shear stress loading, quantitative dynamic damage parameters are obtained through integral calculation, accurately capturing the damage evolution law under the coupling of shear loading and hydrochemical environment. The two types of damage parameters complement each other, forming a complete quantitative damage chain from the initial state to loading failure. The shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling ensures compatibility with conventional working conditions and can also classify stress states through the shear initiation stress yield function and the shear critical stress yield function, enabling the finally constructed shear degradation model to adapt to the mechanical behavior of carbonate rocks under different hydrochemical environments and stress states. Attached Figure Description

[0068] To more clearly illustrate the technical solutions in the embodiments or related technologies of this application, the accompanying drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0069] Figure 1 This is a schematic diagram of the process for constructing a hydrochemical-three-dimensional stress disturbance model of carbonate rock shear degradation according to the present invention.

[0070] Figure 2 This is a graph showing the change in wave velocity after corrosion of fractured carbonate rocks as a function of water chemical environment temperature and pH.

[0071] Figure 3 This is a structural diagram of the hydrochemical-three-dimensional stress perturbation model of carbonate rock shear degradation of the present invention.

[0072] Figure 4 This invention provides true triaxial perturbation shear test data and model fitting for homogeneous carbonate rocks under different hydrochemical environmental temperatures.

[0073] Figure 5 This invention relates to true triaxial perturbation shear test data and model fitting for homogeneous limestone under different hydrochemical environments and pH conditions. Detailed Implementation

[0074] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0075] In one embodiment, such as Figure 1 As shown, a method for constructing a shear degradation model of carbonate rocks under hydrochemical-three-dimensional stress perturbation is provided. This embodiment illustrates the application of this method to a terminal. It is understood that this method can also be applied to a server, and to a system including both a terminal and a server, and can be implemented through interaction between the terminal and the server. In this embodiment, the method includes the following steps:

[0076] S1. Obtain hydrochemical environment-wave velocity data corresponding to the hydrochemical environment carbonate rock wave velocity test; the hydrochemical environment carbonate rock wave velocity test corresponds to the measurement of wave velocity in fractured carbonate rocks under different temperature variables, pH variables, and blank control conditions.

[0077] The illustrative hydrochemical environment carbonate rock wave velocity test refers to an experiment that measures the sound wave propagation velocity of fractured carbonate rock under different hydrochemical environmental conditions by controlling two key variables: temperature and pH value, and setting up a blank control (original fractured carbonate rock that has not undergone hydrochemical corrosion treatment). This is based on acoustic emission technology. The test utilizes the correlation between wave velocity and the integrity of the internal structure of the carbonate rock; that is, the dissolution of cement and the increase in pores and fractures within the carbonate rock will obstruct sound wave propagation and reduce wave velocity. The changes in wave velocity indirectly reflect the degree of degradation of the initial structure of the carbonate rock by the hydrochemical environment.

[0078] For example, during the experiment, fractured carbonate rock was selected as a typical carbonate rock sample, and multiple sets of experimental conditions were designed around two variables: temperature and pH. The temperature variable covered six gradients: 5℃, 23℃, 41℃, 59℃, 77℃, and 95℃. The pH variable covered six gradients: 1.5, 2.5, 3.5, 4.5, 5.5, and 7.0. Fractured carbonate rock untouched by any hydrochemical corrosion served as a blank control. During the experiment, each group of samples was pretreated in a hydrochemical environment with the corresponding temperature and pH value, such as soaking for 10 days at 59℃. After pretreatment, the wave velocity of each group of samples was measured using an acoustic wave testing device. The hydrochemical environment-wave velocity data were collected for different temperatures, pH values, and the blank control. For example, at a temperature of 59°C, the wave velocity of the sample with pH=1.5 was 5.52 km / s, the wave velocity of the sample with pH=7.0 was 5.95 km / s, and the wave velocity of the blank control sample was 6.02 km / s.

[0079] S2. The initial damage variables are calculated by fitting the hydrochemical environment-wave velocity data.

[0080] The initial damage variable D0 is a dimensionless parameter used to quantitatively characterize the degree of initial structural deterioration of fractured carbonate rocks under hydrochemical conditions before shear loading, caused by mineral dissolution and the development of pores and fractures. It transforms the indirect physical quantity of wave velocity into an intuitive indicator of the degree of damage.

[0081] like Figure 2As shown, when the hydrochemical environment temperature is constant (59℃), changes in pH value also significantly affect the wave velocity of carbonate rocks. Under strongly acidic conditions (pH=1.5), the wave velocity of carbonate rocks decreases significantly to 5.52 km / s; however, as the hydrochemical environment gradually becomes neutral (pH=7), the wave velocity increases significantly to 5.95 km / s. This exponential increase indicates that under strongly acidic conditions, the microstructure of carbonate rocks experiences more severe chemical erosion, leading to the dissolution of cementing materials and an increase in pores and fissures, thus significantly reducing the wave velocity. Furthermore, when the pH value of the hydrochemical environment remains at 3 (moderately acidic environment) and does not change over time, the wave velocity of the carbonate rock sample is highest at a lower temperature (5℃), reaching 6.35 km / s; as the ambient temperature gradually increases to 95℃, the wave velocity of the carbonate rock sample decreases significantly to 5.21 km / s. This indicates that high-temperature environments significantly exacerbate the damage and deterioration of the internal microstructure of carbonate rocks, potentially leading to the initiation and propagation of microcracks, reduced mineral cementation strength, and increased pore volume expansion, thereby decreasing the propagation speed of ultrasound waves within the carbonate rocks. Comparing the wave velocity of carbonate rocks under the aforementioned corrosion-deteriorated conditions with that of untreated raw carbonate rock samples (wave velocity 6.02 km / s), it was found that both increased ambient temperature and increased acidity significantly reduced the internal structural integrity of the carbonate rocks. Notably, the wave velocity of untreated carbonate rocks falls at an intermediate level compared to the wave velocities under the aforementioned conditions, further validating the significant impact of hydrochemical environmental conditions on the microstructural deterioration of carbonate rocks. For example, an expression for the coupling relationship between wave velocity and temperature and pH value was constructed. Furthermore, a reference wave velocity under undamaged conditions was introduced, using the wave velocity of the blank control sample as a calibration benchmark. Specifically, an initial damage variable was defined. To ensure the damage variable is physically reasonable, the wave velocity corresponding to the undamaged state is typically set as the reference value; that is, when the material is undamaged, the wave velocity is approximately equal to the reference wave velocity.

[0082] S3. Obtain stress response data from true triaxial perturbation shear tests on fractured carbonate rocks under different hydrochemical environments; the preset three-dimensional stress simulation parameters corresponding to the true triaxial perturbation shear tests include geostress simulation parameters, mechanical perturbation simulation parameters, and shear loading parameters; geostress simulation parameters include normal stress and lateral stress; mechanical perturbation simulation parameters include perturbation amplitude, perturbation frequency, and perturbation cycle number; shear stress loading parameters include multi-level average shear stress loading values ​​starting from the initial shear stress loading value; stress response data include shear strength index and shear strain; shear strength index includes crack initiation stress, critical stress, and failure stress; shear strain includes reversible strain and irreversible strain.

[0083] True triaxial disturbance shear test of fractured carbonate rock under different hydrochemical environments refers to applying shear loads to fractured carbonate rock samples pretreated with different hydrochemical environments in a test environment simulating deep-earth three-dimensional stress state and mechanical excavation disturbance. The test monitors the stress and strain response of the samples during loading, recreating the complex working conditions of carbonate rock simultaneously subjected to in-situ stress, construction disturbance, and hydrochemical corrosion in deep engineering, and obtaining key data reflecting the mechanical behavior and damage evolution of the samples. Among these, the in-situ stress simulation parameters are used to simulate the three-dimensional stress on the rock mass in the deep-earth environment, including the normal stress σ. n and lateral stress σ p The normal stress corresponds to the radial pressure on the rock mass underground, and the lateral stress corresponds to the tangential pressure on the rock mass. Based on the stress distribution characteristics of the free face in engineering where the lateral stress is greater than the normal stress, for example, the normal stress is set to 10 MPa and the lateral stress is set to 15 MPa in the test, or the normal stress is set to 7 MPa and the lateral stress is set to 9 MPa. These values ​​are roughly matched with the actual ground stress level in deep ground. The uniform loading rate is 1 MPa / s, loading from 1 MPa to the set value to ensure that the stress application process is consistent with the stress change law of the engineering project.

[0084] The mechanical disturbance simulation parameters are used to simulate low-frequency, low-amplitude disturbances generated during construction processes such as mechanical excavation and blasting. These parameters include disturbance amplitude A, disturbance frequency f, and the number of disturbance cycles N. The disturbance amplitude refers to the maximum fluctuation range of the disturbance stress, and is set to 0.8 MPa, referencing the intensity of shock waves after blasting attenuation or the disturbance generated by mining equipment in engineering. The disturbance frequency corresponds to the vibration frequency of the construction disturbance, and is set to 2 Hz, taking into account the low-frequency vibration characteristics of mechanical excavation. The number of disturbance cycles refers to the total number of disturbances; to ensure that the disturbance is sufficient to cause cumulative damage within the rock mass, it is set to 3600 cycles, covering the typical disturbance duration of a single excavation operation.

[0085] Shear loading parameters are used to simulate the gradual accumulation of shear stress in the rock mass during excavation, using multi-stage average shear stress loading values ​​starting from an initial shear stress loading value. The initial shear stress loading value is set to 0.4τ. p The stress at which the specimen breaks down is τ, and the loading rate is 1 MPa / s, meaning it is loaded at a rate of 1 MPa / s up to 0.4τ. p Subsequent multi-stage average shear stress loading value τ avr The stress level gradient is set to 0.6τ. p 0.7τ p 0.8τ p 0.9τ p τ p Each loading rate is maintained at 1 MPa / s to simulate the entire process of rock mass shear stress gradually increasing from the initial state to the failure state as the excavation depth or range expands in engineering.

[0086] During the true triaxial perturbation shear test, stress response data, including shear strength parameters and shear strain, were collected in real time using the stress sensors and strain monitoring system of the testing equipment. Among these, the shear strength parameters are key parameters reflecting the specimen's resistance to shear failure, including the initiation stress τ. ci Critical stress τ cd and destructive stress τ p Initiation stress refers to the shear stress at which microcracks begin to form inside the specimen; critical stress refers to the shear stress at which the specimen begins to deteriorate rapidly; and failure stress refers to the maximum shear stress at which the specimen undergoes macroscopic failure.

[0087] Shear strain is a parameter reflecting the degree of deformation of a specimen under shear stress. Based on whether it can be recovered after unloading, it is divided into reversible strain and irreversible strain. Reversible strain refers to strain that can be fully recovered after unloading, corresponding to the elastic deformation stage of the specimen, at which point no new damage is generated inside the rock mass. Irreversible strain refers to strain that cannot be recovered after unloading, originating from the initiation, propagation, and penetration of microcracks within the rock mass. For example, in the low-stress loading stage, such as 0.4τ... p The specimen exhibits predominantly reversible strain with relatively small irreversible strain, but this becomes more pronounced during high-stress loading stages, such as at 0.9τ. p To τ p The irreversible strain increases significantly, and with increasing acidity or temperature, the irreversible strain under the same stress level is even greater.

[0088] S4. The irreversible strain during shear stress loading is used to characterize the damage in the shear direction. Based on the damage in the shear direction corresponding to different shear stress loading stages in the true triaxial perturbation shear test, and combined with the mechanical perturbation simulation parameters and the influence of different hydrochemical environments on the mechanical properties of carbonate rocks, the damage features are extracted to obtain the shear stress loading damage.

[0089] Shear stress loading damage D1 refers to the dynamic damage degree parameter of fractured carbonate rocks under the coupled action of initial damage variable D0 and true triaxial perturbation shear loading, which varies with shear time and shear stress level. It is also a dimensionless parameter. Specifically, the greater the irreversible strain during shear stress loading, the more severe the deterioration of the internal structure of the rock mass and the higher the degree of damage. This accurately captures the dynamic damage evolution law under the coupled action of shear loading and hydrochemical environment.

[0090] Schematic, a calculation expression for the damage D1 in the shear direction is defined, introducing the strain integral under multi-stage stress loading, and defining D1 as... in, This represents the initial shear strain value corresponding to the i-th stress level. This represents the final shear strain value corresponding to the i-th stress level. Let N be the real-time strain value at a certain moment during the shearing process, N be the number of the multi-level average shear stress loading values ​​corresponding to the total shear stress levels, and T be the duration of each level of shear stress loading. Furthermore, under different hydrochemical environmental conditions of temperature and pH, the shear-direction damage of both unanchored and anchored carbonate rocks exhibits characteristics of evolution with time and shear stress level. For example... Figure 4 As shown, based on the irreversible strain characteristics of different shear stress loading stages in true triaxial perturbation shear tests—namely, the deceleration stage, the constant-rate stage, and the acceleration stage—when the shear stress level is low, the damage in the shear direction initially increases rapidly and then remains essentially constant, similar to the evolution characteristics of shear strain at low stress levels, exhibiting characteristics of the deceleration stage. As the shear stress level increases, the loaded damage increases significantly, and with increasing loading time, the rate of damage growth gradually stabilizes, exhibiting characteristics of the constant-rate stage. When the shear stress reaches the critical shear stress, the damage in the shear direction increases rapidly. After exceeding the critical stress, the rate of damage deterioration accelerates, finally accelerating suddenly and reaching its maximum value, leading to the failure of the carbonate rock. The characteristics of damage evolution in this stage are similar to those of the acceleration stage of shear strain. In a schematic manner, damage characteristics are extracted by combining mechanical disturbance simulation parameters and the influence of the hydrochemical environment. Specifically, the disturbance amplitude A and disturbance frequency f from the mechanical disturbance simulation parameters are incorporated into the damage calculation. Since the larger the disturbance amplitude and the higher the frequency, the more intense the propagation of microcracks inside the rock mass and the faster the irreversible strain grows, the correlation between A, f and the damage growth rate needs to be determined by fitting experimental data when calculating D1. For example, the deformation of carbonate rock under microdynamic disturbance can be characterized as elastoplastic deformation resisting microdynamic disturbance. Among them, G k Let n represent the modulus of carbonate rock affected by microdynamic disturbance, and n represent the hardening exponent under shear stress loading. Then, in the unit increment expression, the increment of elastoplastic shear strain due to microdynamic disturbance can be expressed as: Microscopic structural damage to carbonate rocks caused by microdynamic disturbances mainly manifests as rearrangement, fracture, and slippage of particles and crystals within the carbonate rock. This microscopic damage reduces the strength and stiffness of the carbonate rock, typically leading to a decrease in its modulus G. k The decrease in modulus is directly proportional to the decrease in D1, and the modulus after damage is... G k During the micro-dynamic disturbance process, its functional relationship G is related to A and the loading time t. k =A α ·t β Among them, α and β carbonate rock material parameters, therefore, the unit increment of disturbance damage can be characterized by the elastoplastic deformation induced by microdynamic disturbance. Right now The integration was obtained, In the shear direction, the perturbed elasto-plastic strain decreases nonlinearly with increasing amplitude. According to the Manson-Coffin empirical formula, the fatigue life of carbonate rocks is positively correlated with frequency. Therefore, a function relating the microdynamic perturbed elasto-plastic strain to the amplitude of the microdynamic perturbed is constructed as γ = cf. p Where c represents the material parameters of the carbonate rock, and p represents the hardening exponent of the carbonate rock's microdynamic perturbation elastoplastic strain as a function of the perturbation, thus yielding... Where A≠0, f≠0, β≠n+1. Since A and f are independent of the loading time and there is no necessary relationship between them, when A=0 and f=0, the unit increment of the elastoplastic deformation of the carbonate rock is time-dependent and grows as a power function. Therefore, this is attributed to the new parameter K to obtain the shear stress loading damage.

[0091] When f≠0,

[0092] S5. Based on the initial damage variables and lateral response forces, the Mohr-Coulomb shear strength criterion is modified to obtain the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling. Based on the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling, the shear initiation stress yield function and the shear critical stress yield function are calculated.

[0093] The traditional Mohr-Coulomb shear strength criterion is only applicable to conditions where lateral stress is zero, considering only the influence of normal stress and shear stress on the strength of carbonate rocks. However, in deep engineering, the rock mass is under true triaxial stress, and lateral stress has a significant impact on shear strength. Specifically, the shear strength of carbonate rocks initially increases and then decreases with increasing lateral stress. Furthermore, the hydrochemical environment degrades the internal friction angle and cohesion of carbonate rocks through the initial damage variable D0, factors not covered by the traditional criterion. Therefore, the Mohr-Coulomb shear strength criterion needs to be modified by incorporating the initial damage variable D0 and lateral stress to construct a shear strength criterion applicable to the coupled hydrochemical-three-dimensional stress perturbation condition. Based on the modified shear strength criterion and combined with the experimentally observed crack initiation stress and critical stress characteristics, shear crack initiation stress yield functions and shear critical stress yield functions are constructed, respectively.

[0094] S6. Based on the shear initiation stress yield function and the shear critical stress yield function, the carbonatite shear deterioration deformation stages under different stress states are divided. Model elements are constructed according to the initial damage variables and shear stress loading damage to obtain the carbonatite shear deterioration model under hydrochemical-three-dimensional stress disturbance.

[0095] The shear degradation deformation stage of carbonate rocks refers to a stage with significant differences in mechanical behavior, defined based on the stress state, strain characteristics, and damage evolution of carbonate rocks during shear loading. This stage is based on the aforementioned shear initiation stress-yield function and shear critical stress-yield function. The differences in mechanical behavior across different stages are mainly reflected in strain rate, damage growth rate, and deformation reversibility. Illustratively, under low stress, carbonate rocks exhibit primarily elastic deformation with slow damage growth. Once the stress reaches the initiation threshold, the carbonate rock enters a viscoelastic-plastic deformation stage, where damage grows steadily. Finally, once the stress reaches the critical threshold, the carbonate rock enters a nonlinear viscoelastic deformation stage, where damage deteriorates rapidly until failure occurs. For example, in specific divisions, the range of values ​​for the shear initiation stress yield function and the shear critical stress yield function are used as stage boundaries. When the shear initiation stress yield function F1 < 0, the stress state of the carbonate rock has not reached the initiation threshold. At this time, the carbonate rock only undergoes reversible elastic deformation, and no new microcracks are generated inside. D1 remains basically unchanged. This stage is defined as the elastic deformation stage. When F1 ≥ 0 and F2 < 0, the stress state of the carbonate rock reaches the initiation threshold but has not reached the critical threshold. At this time, the carbonate rock begins to undergo irreversible viscoelastic-plastic deformation, microcracks slowly expand, and D1 grows at a stable rate. This stage is defined as the viscoelastic-plastic deformation stage. When F1 ≥ 0 and F2 ≥ 0, the stress state of the carbonate rock reaches the critical threshold. At this time, the carbonate rock undergoes nonlinear viscoelastic deformation, microcracks rapidly penetrate to form a macroscopic failure surface, and D1 grows sharply to its peak value. This stage is defined as the nonlinear viscoelastic failure stage.

[0096] Furthermore, the model components are constructed with damage coupling as the core. Combining the initial damage variable D0 and the shear stress loading damage D1, three types of core components are designed to correspond to the mechanical behavior at different deformation stages. The damage elastic component characterizes the mechanical behavior at the elastic deformation stage, reflecting the degradation of the elastic properties of carbonate rocks by the hydrochemical environment. A larger D0 corresponds to a smaller elastic modulus and a larger elastic strain under the same stress, consistent with the experimental law of reduced elastic properties of carbonate rocks under strong acid and high temperature environments. The damage fractional-order viscoelastic-plastic component characterizes the mechanical behavior at the viscoelastic-plastic deformation stage, accurately describing the time dependence and damage coupling effect of viscoelastic-plastic deformation. A larger D1 corresponds to a smaller viscosity coefficient and a faster increase in viscoelastic-plastic strain, matching the deformation law under different hydrochemical environments. The nonlinear viscoplastic component characterizes the mechanical behavior at the nonlinear viscoplastic failure stage, introducing the superposition effect of D0 and D1 to reflect the synergistic degradation effect of hydrochemical damage and shear damage near failure, leading to a sharp increase in viscoplastic strain and ultimately causing carbonate rock failure. The three types of model elements are combined according to the stress state at different deformation stages to form a hydrochemical-three-dimensional stress disturbance model of carbonate rock shear degradation.

[0097] In the aforementioned method for constructing a hydrochemical-three-dimensional stress-induced shear degradation model of carbonate rocks, different temperature and pH variables, along with a blank control, were set up. Wave velocity in fractured carbonate rocks was measured to obtain hydrochemical environment-wave velocity data, ensuring the accuracy and comprehensiveness of the initial damage variable calculation. Through multivariate experiments, the independent effects of temperature and pH on carbonate rock wave velocity were clearly identified, accurately reflecting the initial degradation degree of carbonate rocks under different hydrochemical environments. This avoids damage assessment bias caused by single-variable experiments, ensuring the model can accurately capture the initial influence of the hydrochemical environment on the mechanical behavior of carbonate rocks. The setting of geostress parameters recreates the actual stress distribution where lateral stress near the free face is greater than normal stress. Mechanical disturbance parameters simulate the true intensity and duration of construction disturbances, while multi-stage shear loading covers the entire process from elastic deformation to failure of the rock mass. By combining initial damage variables and the shear stress-loaded damage-corrected Mohr-Coulomb criterion and constructing a yield function, a deep integration of damage effects and strength criteria is achieved, significantly improving the model's prediction accuracy. The deformation stages are divided based on the shear initiation stress yield function and the shear critical stress yield function. Damage elastic, damage fractional-order viscoelastic-plastic, and nonlinear viscoelastic elements are constructed by combining the initial damage variable and the shear stress loading damage. This allows for flexible adaptation to the mechanical response under different stress states, enabling an accurate description of the entire shear degradation process. The staged element combination method avoids the shortcomings of traditional models that use single elements and cannot adapt to multi-stage behavior, allowing the model to accurately reproduce the shear strain evolution law of carbonate rocks under different hydrochemical environments and stress states.

[0098] In one embodiment, initial damage variables are calculated based on water chemistry environment-wave velocity data fitting, including:

[0099] S21. The relationship between the changes in water chemical environment wave velocity is obtained by fitting the water chemical environment-wave velocity data.

[0100] The relationship between wave velocity changes in the water chemical environment can be obtained using the following formula:

[0101] v(C,pH)=(v0-aC)·e b·pH

[0102] Where v(C,pH) is the wave velocity under the combined effects of temperature and pH; C is temperature; pH is pH; v0 is the theoretical wave velocity reference value corresponding to the initial state C=0 and pH=0; a is the wave velocity sensitivity to temperature; b is the wave velocity sensitivity to pH.

[0103] S22. Using the undamaged wave velocity of carbonate rocks corresponding to the blank control as a reference, the relationship of wave velocity change in the hydrochemical environment is transformed to obtain a dimensionless initial damage variable.

[0104] The initial damage variable is obtained using the following formula:

[0105]

[0106] Where D0 is the initial damage variable; v ref The wave velocity of carbonate rocks under undamaged conditions.

[0107] Indicatively, the closer the measured wave velocity is to the reference wave velocity, the lower the degree of damage, and the initial damage variable tends to zero; when the measured wave velocity is significantly lower than the reference value, the degree of damage gradually increases, and the initial damage variable tends to 1, effectively reflecting the comprehensive influence of temperature and pH environmental factors on the damage state of carbonate rocks. For example, the 1stOpt software is used to fit the acquired hydrochemical environment-wave velocity data, and the parameters a, b, and v0 of the coupling relationship expression between wave velocity and temperature / pH value are determined through optimization algorithms such as the least squares method.

[0108] In one embodiment, irreversible strain during shear stress loading is used to characterize the damage in the shear direction. Based on the damage in the shear direction corresponding to different shear stress loading stages in the true triaxial perturbation shear test, and combined with the mechanical perturbation simulation parameters and the influence of different hydrochemical environments on the mechanical properties of carbonate rocks, damage features are extracted to obtain the shear stress loading damage, including:

[0109] The damage under shear stress loading can be obtained using the following formula:

[0110]

[0111] Where D1 represents shear stress loading damage; A represents disturbance amplitude; f represents disturbance frequency; n represents hardening exponent; t represents the duration of each level of average shear stress loading value; α, β, and c represent characteristic parameters of carbonate rock materials; and p represents the hardening exponent of the carbonate rock microdynamic disturbance elastoplastic strain as a function of disturbance frequency.

[0112] The specific value of D1 was determined by fitting experimental data. Indicatively, for experimental data under different hydrochemical environments and shear stages, 1stOpt software was used for fitting to determine the parameters in the D1 expression, such as the hardening exponent n and material parameter K, ultimately obtaining the shear stress loading damage D1 under different working conditions. For example, in the deceleration stage at 5℃, pH=3.5, and without anchoring, the D1 fitting parameters n=0.28 and K=1.60, corresponding to a D1 value that first rapidly increases with time and then tends to stabilize, with a peak value of approximately 0.08; while in the acceleration stage, D1 increases sharply to a peak value of approximately 0.16, reflecting the rapid deterioration of damage near failure.

[0113] In one embodiment, the Mohr-Coulomb shear strength criterion is modified based on the initial damage variable and lateral response force to obtain the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling. The shear initiation stress yield function and the shear critical stress yield function are then calculated based on the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling, including:

[0114] S51. Based on the variation of critical stress under different lateral stresses in the true triaxial perturbation shear test, the Mohr-Coulomb shear strength criterion is modified to obtain a shear strength criterion that considers lateral stress; the shear strength criterion corresponds to the shear strength criterion expression constructed by coordinating the internal friction angle and lateral stress cohesion parameters.

[0115] Schematic illustration of the basic form of a shear strength criterion that considers lateral stress effects. in, Let σ be the internal friction angle, c be the cohesive force parameter for lateral stress coordination, and σ be the internal friction angle. ρ Let K be the lateral stress corresponding to the maximum shear stress in carbonate rocks, K be the equivalent lateral stress with the same strength as when the lateral stress is zero, and d be a stress parameter related to mineral composition. This is achieved by introducing the lateral stress σ. p The quadratic term is used to reflect the law that the shear strength first increases and then decreases with the lateral stress, and when σ p When = 0, the formula degenerates into the traditional Mohr-Coulomb criterion. Where ρ is the cohesive force, ensuring compatibility with conventional operating conditions.

[0116] Table 1. Critical shear stress of three types of rocks under true three-dimensional stress under different lateral stresses.

[0117]

[0118] For example, as shown in Table 1, the critical shear stress function is obtained based on the true triaxial shear test, and then fitted to obtain...

[0119] S52. Based on the influence of the hydrochemical environment on the critical stress and failure stress, the cohesion parameters of the internal friction angle and lateral stress coordination are modified according to the initial damage variables to obtain the shear strength criterion under the coupling of hydrochemistry and three-dimensional stress disturbance.

[0120] Hydrochemical environments alter the internal structure of carbonate rocks through dissolution, thereby deteriorating their mechanical parameters. Experimental studies show that as the temperature of the hydrochemical environment increases, the critical stress and failure stress of carbonate rocks initially increase and then decrease. Simultaneously, as the pH value of the hydrochemical environment decreases, the critical stress and failure stress of carbonate rocks continuously decrease. Illustratively, an initial damage variable D0 is introduced to correct for the degradation of the criterion parameters. Since the initial damage D0 caused by the hydrochemical environment reduces the internal friction angle and cohesion of carbonate rocks, therefore... And c is modified to be a function related to D0. c * =c(1-D0). Substituting the corrected parameters into the basic form, we obtain the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling.

[0121] S53. Based on the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling, the damage effect yield function of hydrochemical-three-dimensional stress shear direction process is obtained.

[0122] The yield function of the damage effect in the hydrochemical-three-dimensional stress-shear direction process is obtained using the following formula:

[0123]

[0124] c * =c(1-D0)

[0125] Where τ is the shear stress; σ n Normal stress; σ p Lateral stress; σ is the internal friction angle; c is the cohesive force parameter for lateral stress coordination; σ ρ denoted as lateral stress corresponding to the maximum shear stress in carbonate rocks; K is the equivalent lateral stress when the strength and lateral stress are both zero; d is the stress parameter related to cohesion influenced by mineral composition and other factors. The internal friction angle after degradation correction; c * D0 represents the cohesive force parameter for lateral stress coordination after degradation correction; D0 represents the initial damage variable.

[0126] S54. The shear initiation stress yield function and the shear critical stress yield function are calculated based on the shear critical stress function.

[0127] The shear initiation stress yield function can be obtained using the following formula:

[0128]

[0129] Where F1 is the shear initiation stress yield function;

[0130] The shear critical stress yield function can be obtained using the following formula:

[0131]

[0132] Where F2 is the shear critical stress yield function.

[0133] Schematic representation of shear initiation stress τ ci It is the shear stress at which microcracks begin to initiate within carbonate rocks, and it represents the critical threshold for carbonate rocks to transition from elastic deformation to viscoelastic-plastic deformation. True triaxial perturbation shear tests revealed that τ... ci Also affected by the hydrochemical environment and three-dimensional stress, i.e., as D0 increases, τ ci Decrease; with lateral stress σ p Increase, τ ci The temperature first rises and then falls, and its changing pattern is similar to the critical stress τ. cd Consistent, it can be based on the shear strength criterion under the coupling of hydrochemistry and three-dimensional stress perturbation, and τ ci Substitute the values ​​to construct the shear initiation stress yield function.

[0134] Shear critical stress τ cd This is the critical threshold at which damage in carbonate rocks transitions from steady-state growth to accelerated growth, corresponding to the turning point where carbonate rocks shift from viscoelastic-plastic deformation to nonlinear viscoelastic failure. (This is related to τ...) ci Similarly, τ cd The variation law also conforms to the shear strength criterion under the coupling of water chemistry and three-dimensional stress perturbation. Therefore, using a similar logic to constructing F1, τ cd Substitute the criteria to construct the shear critical stress yield function F2.

[0135] In one embodiment, the shear degradation deformation stages of carbonate rocks under different stress states are divided based on the shear initiation stress yield function and the shear critical stress yield function. Model elements are constructed according to the initial damage variables and shear stress loading damage to obtain a hydrochemical-three-dimensional stress perturbation-based carbonate rock shear degradation model, including:

[0136] S61. Based on the initial damage variables and shear stress loading damage, damage elastic elements, damage fractional-order viscoelastic-plastic elements, and nonlinear viscoelastic elements are used as model elements.

[0137] like Figure 4 As shown, in the construction of the hydrochemical-three-dimensional stress perturbation model of carbonate rock shear degradation, the selection of model components must be closely combined with the influence of the initial damage variable D0 and the shear stress loading damage D1 to ensure that the mechanical behavior of carbonate rock under different stress states can be accurately characterized.

[0138] Damaged elastic elements are primarily used to characterize the elastic deformation behavior of carbonate rocks under low stress conditions. Their core feature is incorporating the initial damage variable D0 into the calculation of the elastic modulus. Because the dissolving effect of a hydrochemical environment increases the porosity and fissures within carbonate rocks, reducing their elastic bearing capacity, the elastic shear modulus of this element needs to be corrected to G(1-D0), where G is the elastic shear modulus of the carbonate rock under undamaged conditions, thus reflecting the deteriorating effect of D0 on the elastic properties of the carbonate rock. When the carbonate rock is subjected to only a small shear stress, the deformation is mainly reversible elastic deformation, and the damaged elastic element can accurately capture the mechanical response at this stage.

[0139] The damage fractional-order viscoelastic-plastic element is designed for the viscoelastic-plastic behavior of carbonate rocks after they enter the deterioration deformation stage. Its core principle is to combine fractional-order theory with damage mechanics, while simultaneously considering the coupling effect of D0 and D1. The introduction of fractional-order theory aims to more accurately describe the time dependence of viscoelastic-plastic deformation in carbonate rocks. During shear loading, the growth of viscoelastic-plastic strain in carbonate rocks does not follow the linear law of traditional integer-order calculus, but rather exhibits a complex nonlinear time dependence. The introduction of fractional-order theory can flexibly adapt to this characteristic. Furthermore, the viscosity coefficient of this element needs to be modified to... in The fractional viscosity coefficient under undamaged conditions is represented by D1, which reflects the exacerbating effect of damage on viscoelastic-plastic deformation during shear loading. Meanwhile, D0 indirectly changes the initiation threshold and growth rate of viscoelastic-plastic deformation by affecting the initial structural integrity of carbonate rocks, ensuring that the element can characterize the viscoelastic-plastic behavior under hydrochemical-shear loading coupling.

[0140] The nonlinear viscoplastic element corresponds to the nonlinear degradation stage of carbonate rocks nearing failure. At this stage, microcracks rapidly propagate within the carbonate rock, damage increases dramatically, and deformation exhibits significant nonlinear characteristics. The design of this element focuses on the superimposed degradation effect of D0 and D1. As shear stress increases to a critical value, the accumulated damage within the carbonate rock reaches a certain level. The initial porosity caused by D0 and the newly formed cracks induced by D1 interpenetrate, causing the viscosity coefficient to decrease rapidly over time, with a reduction far exceeding the effect of a single damage. Therefore, the viscosity coefficient of this element is defined as a time-dependent function, incorporating dual corrections for D0 and D1 to accurately capture the nonlinear characteristics of the rapidly increasing deformation before carbonate rock failure.

[0141] S62. When the stress state is less than the shear initiation stress yield function condition, the shear degradation deformation stage of carbonate rock is the undegraded deformation stage, and the shear degradation model of carbonate rock under hydrochemical-three-dimensional stress disturbance is an elastic model characterized by damaged elastic elements.

[0142] The criterion for determining the undeteriorated deformation stage is the shear initiation stress yield function F1. When the stress state satisfies F1 < 0, it indicates that the shear stress borne by the carbonate rock has not yet reached the threshold for the initial initiation of microcracks. At this time, the deformation of the carbonate rock is mainly reversible elastic deformation, without generating new damage. Therefore, this stage is defined as the undeteriorated deformation stage. The shear strain increases linearly with the shear stress, and the strain can be completely recovered after unloading. No new deterioration occurs in the internal structure of the carbonate rock, and D1 remains basically unchanged. In this stage, the carbonate rock shear deterioration model under hydrochemical-three-dimensional stress perturbation uses the damaged elastic element as the sole characterizer and is constructed as an elastic model. When the shear stress is low, the microcracks inside the carbonate rock are in a closed state. Even if there are initial pores caused by D0, they do not expand or form. Therefore, the deformation is only caused by the elastic deformation of the carbonate rock, and there is no need to introduce viscoelastic-plastic or nonlinear elements.

[0143] S63. When the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state is less than the shear critical stress yield condition, the shear deterioration deformation stage of carbonate rock is the initial stage of deterioration deformation. The shear deterioration model of carbonate rock under hydrochemical-three-dimensional stress disturbance is a damage fractional-order viscoelastic-plastic model characterized by damage fractional-order viscoelastic-plastic elements.

[0144] The determination of the initial stage of deterioration deformation requires that the stress state simultaneously reaches and exceeds the shear initiation stress yield condition F1≥0, indicating that the shear stress has triggered the initial initiation of microcracks inside the carbonate rock, and the stress state is still less than the shear critical stress yield condition F2<0, meaning that although microcracks have been generated, they have not yet entered the rapid propagation stage, and the damage growth is relatively stable. Therefore, this stage is defined as the initial stage of deterioration deformation, that is, the deformation is composed of elastic deformation and viscoelastic-plastic deformation, among which viscoelastic-plastic deformation is irreversible deformation. As the loading time increases, D1 increases slowly, and the growth rate of shear strain gradually accelerates, but the overall growth is still within a controllable and stable range.

[0145] Based on the mechanical behavior characteristics of this stage, the hydrochemical-three-dimensional stress perturbation model of carbonate rock shear degradation uses a damage fractional-order viscoelastic-plastic element. When carbonate rock enters the initial stage of degradation deformation, the simple elastic model can no longer capture the irreversible viscoelastic-plastic deformation, while the traditional integer-order viscoelastic-plastic model is difficult to accurately describe the nonlinear time correlation of deformation. The damage fractional-order viscoelastic-plastic element, through the flexibility of fractional-order theory and the coupling of damage correction, can simultaneously adapt to the time-dependent characteristics of viscoelastic-plastic deformation and the coupled damage effect of hydrochemical-shear loading.

[0146] S64. When the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state reaches and exceeds the shear critical stress yield condition, the shear deterioration deformation stage of carbonate rock is the unstable expansion stage of deterioration deformation. The hydrochemical-three-dimensional stress perturbation model of carbonate rock shear deterioration is a nonlinear viscoplastic model with nonlinear viscoplastic elements.

[0147] The criteria for determining the unstable propagation stage of deterioration deformation are that the stress state simultaneously satisfies F1≥0 and F2≥0. At this point, the shear stress has exceeded the critical stress threshold of the carbonate rock, and the microcracks inside the carbonate rock enter the rapid penetration stage. The damage grows at an exponential rate, and the deformation exhibits significant nonlinear characteristics. Macroscopic failure may occur at any time. Therefore, this stage is defined as the unstable propagation stage of deterioration deformation, that is, viscoelastic-plastic deformation dominates, and the deformation rate increases sharply. After unloading, only a very small part of the elastic deformation can be recovered, and most of the deformation is irreversible plastic deformation. D1 rapidly approaches 1, and the bearing capacity of the carbonate rock decreases sharply.

[0148] To address the mechanical behavior at this stage, the hydrochemical-three-dimensional stress perturbation model of carbonate rock shear degradation is constructed using a nonlinear viscoplastic element as the core characterization. At this point, the deformation of carbonate rock no longer satisfies the relatively stable growth law of the viscoelastic-plastic stage. Instead, due to the superimposed degradation effect of D0 and D1, a nonlinear phenomenon occurs where the viscosity coefficient decreases rapidly over time and the deformation increases sharply. Traditional viscoelastic-plastic elements cannot capture this drastic nonlinear change, while nonlinear viscoplastic elements, through the design of time-related viscosity coefficients, can accurately adapt to this characteristic.

[0149] In one embodiment, based on the initial damage variable and shear stress-loaded damage, damage elastic elements, damage fractional-order viscoelastic elements, and nonlinear viscoelastic elements are used as model elements, including:

[0150] S611. Calculate the damaged elastic element based on the initial damage variables.

[0151] The expression for the damaged elastic element can be obtained through the following formula:

[0152]

[0153] Where G is the elastic shear modulus; τ is the shear stress on the carbonate rock; and D0 is the initial damage variable.

[0154] The core of constructing a damaged elastic element is to incorporate the initial damage variable D0 into the characterization of elastic mechanical properties to reflect the deteriorating effect of the hydrochemical environment on the initial structural integrity of carbonate rocks. The initial damage variable D0 is a dimensionless parameter obtained by fitting the wave velocity test data of carbonate rocks in a hydrochemical environment. Its value ranges from 0 to 1, representing the degree of development of porosity and fractures inside the carbonate rock caused by the hydrochemical environment. In other words, the larger the D0, the more fragmented the initial structure of the carbonate rock and the weaker its elastic bearing capacity.

[0155] Under the influence of hydrochemical conditions, initial damage D0 reduces the elastic shear modulus of carbonate rocks because the dissolution pores and fissures within the carbonate rocks reduce the effective bearing area, leading to increased strain under the same stress. Based on the experimentally observed linear negative correlation between the elastic modulus and the initial damage, the elastic shear modulus is corrected to G(1-D0).

[0156] S612. Construct constitutive equations for viscoelastic-plastic elements of carbonate rocks based on shear stress loading damage. Perform Laplace transform and inverse transform on the constitutive equations for viscoelastic-plastic elements of carbonate rocks to obtain damage fractional-order viscoelastic-plastic elements.

[0157] The expression for the damage fractional-order viscoelastic-plastic element can be obtained using the following formula:

[0158]

[0159] in, Fractional viscosity coefficient; α is the fractional order; D1 is the damage under shear stress loading; τ ci This is the initiation stress.

[0160] After carbonate rocks enter the deterioration deformation stage under shear loading, the core characteristic of viscoelastic-plastic deformation is that the deformation accumulates over time and is irreversible. This behavior is directly related to the shear stress loading damage D1. The larger D1 is, the more developed the microcracks are inside the carbonate rock, and the faster the growth rate of viscoelastic-plastic deformation. Based on the experimentally observed law that the viscoelastic-plastic strain rate is negatively correlated with (1-D1) and positively correlated with shear stress, and considering that the time dependence of the viscoelastic-plastic deformation of carbonate rocks does not follow the linear law of traditional integer-order calculus, fractional-order theory is introduced to flexibly adapt to this nonlinear time correlation, and constitutive equations for viscoelastic-plastic elements are constructed. in,

[0161] S613. Starting with the unsteady propagation of shear plastic deformation in carbonate rocks, a nonlinear viscoplastic element constitutive equation is constructed based on the damage caused by shear stress loading. The nonlinear viscoplastic element is obtained by combining the integral of the loss and degradation of the viscosity coefficient due to high shear stress.

[0162] The expression for the nonlinear viscoplastic element can be obtained through the following formula:

[0163]

[0164] Where, τ cd The critical stress; is the fractional viscosity coefficient; t is time.

[0165] The constitutive equation of a nonlinear viscoplastic element is The damage and degradation of carbonate rocks are not only affected by the duration of disturbance, but also by the damage and degradation of the viscosity coefficient due to high shear stress. Therefore, it is defined that after entering this stage, the viscosity coefficient becomes a time-dependent function.

[0166] The construction of nonlinear viscoplastic elements starts with the unstable propagation of shear plastic deformation in carbonate rocks. It focuses on capturing the nonlinear characteristics of the rapid increase in deformation caused by the superposition of high shear stress and damage when carbonate rocks are close to failure, and considers the damage and deterioration effect of high shear stress on the viscosity coefficient.

[0167] Optionally, when the stress state reaches and exceeds the initiation stress yield condition, the carbonate rock begins to deteriorate and deform. The viscoelastic-plastic strain rate is calculated using Perzyna's overstress theory. Where F0 is the initial value of the yield function, which is 1. The Perzyna overstress theory represents this as follows: When the stress state reaches and exceeds the shear critical stress yield condition, the rock undergoes nonlinear viscoplastic deformation. The viscoplastic strain rate is calculated using Perzyna overstress theory. The Perzyna overstress theory is expressed as follows:

[0168] In one embodiment, the hydrochemical-three-dimensional stress perturbation model for carbonatite shear degradation is as follows:

[0169] The following formula is used to obtain the shear degradation model of carbonate rocks under hydrochemical-three-dimensional stress perturbation:

[0170]

[0171] Wherein, F1<0 means the stress state is less than the shear initiation stress yield function condition; F1≥0∩F2<0 means the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state is less than the shear critical stress yield condition; F1≥0∩F2≥0 means the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state reaches and exceeds the shear critical stress yield condition.

[0172] Schematic representation of the shear initiation stress yield function F1, when the actual shear stress τ reaches the initiation stress τ. ciWhen τ > τ, the function value is 0; when τ > τ ci When the function value is greater than 0, it indicates that the carbonate rock has entered the deterioration and deformation stage; when τ < τ ci When F2 = 0, the function value is less than 0, indicating that the carbonate rock is in the elastic deformation stage. When F2 = 0, it indicates that the shear stress of the carbonate rock reaches τ. cd When F2>0, the carbonate rock is in the nonlinear viscoplastic failure stage, and the damage grows rapidly until failure. When F2<0, the carbonate rock is in the elastic or viscoelastic-plastic deformation stage.

[0173] In one embodiment, the method further includes:

[0174] S71. Obtain the shear strain fitting curves of the carbonate rock shear degradation model under different hydrochemical environments and shear stresses under hydrochemical-three-dimensional stress perturbation.

[0175] Indicatively, based on the test results of shear rock damage mechanics under different temperature and pH hydrochemical environments, the shear degradation model of carbonate rock under hydrochemical-three-dimensional stress perturbation at different temperatures and pH was verified, and the shear strain fitting curves under different hydrochemical environments and shear stresses were obtained.

[0176] S72. Compare the fitted shear strain curve with the actual shear strain measured by true triaxial perturbation shear test on fractured carbonate rocks under different hydrochemical conditions to obtain the error.

[0177] Furthermore, the calculated values ​​of the shear strain fitting curves under various working conditions are compared with the measured shear strain values ​​from true triaxial perturbation shear tests. The fitting accuracy of the model is evaluated using quantitative error indices, such as... Figure 4 and Figure 5 As shown, for example, considering the volatility of experimental data and the engineering application requirements of the model, relative error is selected as the core evaluation index. Relative error can eliminate the influence of differences in data magnitude and more intuitively reflect the fitting accuracy.

[0178] S73. Analyze the error and update the model parameters of the hydrochemical-three-dimensional stress disturbance carbonate rock shear degradation model based on the error analysis results.

[0179] By analyzing the causes of errors, the model parameters are adjusted in a targeted manner to reduce fitting errors, improve the model's adaptability to complex working conditions, and ensure that the model can accurately characterize the shear degradation behavior of carbonate rocks under the coupling of hydrochemistry and three-dimensional stress disturbance.

[0180] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0181] The above-described embodiments are merely illustrative of several implementation methods of the embodiments of this application, and their descriptions are relatively specific and detailed. However, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the embodiments of this application, and these modifications and improvements all fall within the protection scope of the embodiments of this application.

Claims

1. A method for constructing a hydrochemical-three-dimensional stress perturbation model of carbonatite shear degradation, characterized in that, The method includes: S1. Obtain the hydrochemical environment-wave velocity data corresponding to the hydrochemical environment carbonate rock wave velocity test; the hydrochemical environment carbonate rock wave velocity test corresponds to the measurement of wave velocity in fractured carbonate rocks under different temperature variables, pH variables and blank control. S2. The initial damage variables are calculated by fitting the water chemistry environment-wave velocity data. S3. Obtain stress response data from true triaxial perturbation shear tests on fractured carbonate rocks under different hydrochemical environments; the preset three-dimensional stress simulation parameters corresponding to the true triaxial perturbation shear tests include geostress simulation parameters, mechanical perturbation simulation parameters, and shear loading parameters; the geostress simulation parameters include normal stress and lateral stress; the mechanical perturbation simulation parameters include perturbation amplitude, perturbation frequency, and perturbation period number; the shear stress loading parameters include multi-level average shear stress loading values ​​starting from the initial shear stress loading value; the stress response data includes shear strength index and shear strain; the shear strength index includes crack initiation stress, critical stress, and failure stress; the shear strain includes reversible strain and irreversible strain. S4. The irreversible strain during the shear stress loading process characterizes the damage in the shear direction. Based on the damage in the shear direction corresponding to different shear stress loading stages in the true triaxial perturbation shear test, and combined with the mechanical perturbation simulation parameters and the influence of different hydrochemical environments on the mechanical properties of carbonate rocks, damage features are extracted to obtain the shear stress loading damage. S5. The Mohr-Coulomb shear strength criterion is modified according to the initial damage variable and the lateral response force to obtain the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling, and the shear initiation stress yield function and the shear critical stress yield function are calculated according to the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling. S6. Based on the shear initiation stress yield function and the shear critical stress yield function, the carbonatite shear deterioration deformation stages under different stress states are divided. According to the initial damage variable and the shear stress loading damage, model elements are constructed to obtain the carbonatite shear deterioration model under hydrochemical-three-dimensional stress disturbance.

2. The method according to claim 1, characterized in that, The initial damage variables calculated based on the water chemistry environment-wave velocity data include: S21. The relationship between the water chemical environment and wave velocity changes is obtained by fitting the water chemical environment-wave velocity data. The relationship between the wave velocity changes in the water chemical environment can be obtained using the following formula: v(C,pH)=(v0-aC)·e b·pH Where v(C,pH) is the wave velocity under the combined effects of temperature and pH; C is temperature; pH is pH; v0 is the theoretical wave velocity reference value corresponding to the initial state C=0 and pH=0; a is the wave velocity sensitivity to temperature; b is the wave velocity sensitivity to pH. S22. Using the wave velocity of carbonate rocks in the undamaged state corresponding to the blank control as a reference, the wave velocity change relationship of the hydrochemical environment is transformed into a dimensionless initial damage variable. The initial damage variable is obtained using the following formula: Where D0 is the initial damage variable; v ref The wave velocity of carbonate rocks under undamaged conditions.

3. The method according to claim 1, characterized in that, The irreversible strain during shear stress loading characterizes the damage in the shear direction. Based on the damage in the shear direction corresponding to different shear stress loading stages in the true triaxial perturbation shear test, and combined with the mechanical perturbation simulation parameters and the influence of different hydrochemical environments on the mechanical properties of carbonate rocks, damage features are extracted to obtain shear stress loading damage, including: The shear stress loading damage is obtained using the following formula: Wherein, D1 represents the shear stress loading damage; A represents the disturbance amplitude; f represents the disturbance frequency; n represents the hardening exponent; t represents the duration of each level of average shear stress loading value; α, β, and c represent the characteristic parameters of carbonate rock materials; and p represents the hardening exponent of the carbonate rock microdynamic disturbance elastoplastic strain as a function of the disturbance frequency.

4. The method according to claim 1, characterized in that, The Mohr-Coulomb shear strength criterion is modified based on the initial damage variable and the lateral response force to obtain the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling. The shear initiation stress yield function and the shear critical stress yield function are calculated based on the shear strength criterion under hydrochemical-three-dimensional stress perturbation coupling, including: S51. Based on the change of the critical stress under different lateral stresses in the true triaxial perturbation shear test, the Mohr-Coulomb shear strength criterion is modified to obtain a shear strength criterion considering lateral stress; the shear strength criterion corresponds to the shear strength criterion expression constructed by coordinating the internal friction angle and lateral stress with the cohesion parameter. S52. Based on the influence of the hydrochemical environment on the critical stress and the failure stress, the cohesion parameters of the internal friction angle and the lateral stress coordination are corrected according to the initial damage variables to obtain the shear strength criterion under the coupling of hydrochemical-three-dimensional stress disturbance. S53. Based on the shear strength criterion under the coupling of hydrochemistry and three-dimensional stress perturbation, the damage effect yield function of the hydrochemistry-three-dimensional stress shear direction process is obtained. The yield function of the damage effect in the hydrochemical-three-dimensional stress-shear direction process is obtained using the following formula: Where τ is the shear stress; σ n Normal stress; σ p Lateral stress; σ is the internal friction angle; c is the cohesive force parameter for lateral stress coordination; σ ρ denoted as lateral stress corresponding to the maximum shear stress in carbonate rocks; K is the equivalent lateral stress when the strength and lateral stress are both zero; d is the stress parameter related to cohesion influenced by mineral composition and other factors. The internal friction angle after degradation correction; c * D0 represents the cohesive force parameter for lateral stress coordination after degradation correction; D0 represents the initial damage variable. S54. Calculate the shear initiation stress yield function and the shear critical stress yield function based on the shear critical stress function. The shear initiation stress yield function is obtained using the following formula: Wherein, F1 is the shear initiation stress yield function; The shear critical stress yield function is obtained using the following formula: Wherein, F2 is the shear critical stress yield function.

5. The method according to claim 1, characterized in that, The carbonatite shear degradation deformation stages under different stress states are divided based on the shear initiation stress yield function and the shear critical stress yield function. Model elements are constructed according to the initial damage variables and the shear stress loading damage to obtain the hydrochemical-three-dimensional stress perturbation carbonatite shear degradation model, including: S61. Based on the initial damage variables and the shear stress loading damage, damage elastic elements, damage fractional-order viscoelastic-plastic elements, and nonlinear viscoelastic elements are used as model elements. S62. When the stress state is less than the shear initiation stress yield function condition, the shear deterioration deformation stage of carbonate rock is the undeteriorated deformation stage, and the shear deterioration model of carbonate rock under hydrochemical-three-dimensional stress disturbance is an elastic model characterized by the damaged elastic element. S63. When the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state is less than the shear critical stress yield condition, the carbonatite shear deterioration deformation stage is the initial stage of deterioration deformation. The hydrochemical-three-dimensional stress disturbance carbonatite shear deterioration model is a damage fractional viscoelastic-plastic model characterized by the damage fractional viscoelastic-plastic element. S64. When the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state reaches and exceeds the shear critical stress yield condition, the carbonatite shear deterioration deformation stage is the unstable expansion stage of deterioration deformation. The hydrochemical-three-dimensional stress disturbance carbonatite shear deterioration model is a nonlinear viscoplastic model based on the nonlinear viscoplastic element.

6. The method according to claim 5, characterized in that, The damage model based on the initial damage variable and the shear stress loading damage uses damage elastic elements, damage fractional-order viscoelastic-plastic elements, and nonlinear viscoelastic elements as model elements, including: S611. Calculate the damaged elastic element based on the initial damage variable; The expression corresponding to the damaged elastic element can be obtained through the following formula: Where G is the elastic shear modulus; τ is the shear stress on the carbonate rock; and D0 is the initial damage variable. S612. Construct the constitutive equation of the carbonatite viscoelastic-plastic element based on the shear stress loading damage, and perform Laplace transform and inverse transform on the constitutive equation of the carbonatite viscoelastic-plastic element to obtain the damage fractional-order viscoelastic-plastic element. The expression corresponding to the damage fractional-order viscoelastic-plastic element can be obtained through the following formula: in, Fractional viscosity coefficient; α is the fractional order; D1 is the damage under shear stress loading; τ ci For crack initiation stress; S613. Starting from the unstable propagation of shear plastic deformation in carbonate rocks, a nonlinear viscoplastic element constitutive equation is constructed based on the shear stress loading damage, and the nonlinear viscoplastic element is obtained by combining the integral of the loss and deterioration of the viscosity coefficient due to high shear stress. The expression for the nonlinear viscoplastic element is obtained through the following formula: Where, τ cd The critical stress; is the fractional viscosity coefficient; t is time.

7. The method according to claim 6, characterized in that, The hydrochemical-three-dimensional stress perturbation model for shear degradation of carbonate rocks is as follows: The following formula is used to obtain the shear degradation model of carbonate rocks under hydrochemical-three-dimensional stress perturbation: Wherein, F1<0 means the stress state is less than the shear initiation stress yield function condition; F1≥0∩F2<0 means the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state is less than the shear critical stress yield condition; F1≥0∩F2≥0 means the stress state reaches and exceeds the shear initiation stress yield condition, and the stress state reaches and exceeds the shear critical stress yield condition.

8. The method according to any one of claims 1-7, characterized in that, The method further includes: S71. Obtain the shear strain fitting curves of the carbonate rock shear degradation model under different hydrochemical environments and shear stresses under different hydrochemical environments and shear stresses. S72. Compare the shear strain fitting curve with the shear strain measured by the true triaxial perturbation shear test of fractured carbonate rocks under different hydrochemical conditions to obtain the error; S73. Analyze the error and update the model parameters of the hydrochemical-three-dimensional stress disturbance carbonate rock shear degradation model based on the error analysis results.

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