Method for constructing rock dynamic damage constitutive relation under freeze thawing-load action

Abstract

The invention discloses a method for constructing a rock dynamic damage constitutive relation under the freeze-thaw-load effect, and belongs to the technical field of rock damage, and the method comprises the following steps: determining a dynamic damage evolution equation based on evolution characteristics of a rock dynamic damage rate under the freeze-thaw-load effect and a macromechanical parameter change rule; the method comprises the following steps: abstracting a rock under the action of freeze-thaw-load into four parts, namely freeze-thaw damage, load-bearing damage, coupling damage and non-damage, bearing effective stress by the non-damage part, bearing residual stress by the damage part, and establishing a rock constitutive model based on a dynamic damage rate; freeze-thaw cycle and conventional triaxial compression tests of the red sandstone are carried out, and the rationality of the model is verified through test results. According to the method, the model is established in a mode of combining theoretical derivation and test verification, the goodness of fit between the obtained theoretical curve and the test curve is high, the mechanical behavior of rock freeze-thaw load damage can be well reflected, and theoretical guidance can be provided for design and construction of cold region engineering.

Description

Technical Field

[0001] The invention relates to the field of rock damage technology, and in particular to a method for constructing a dynamic damage constitutive relationship of rock under freeze-thaw-load action. Background Art

[0002] my country's cold regions are widely distributed and contain rich resources such as minerals, forests and land. Rock weathering caused by freeze-thaw cycles is one of the main geological disasters. With the intensification of resource development in the western cold regions, the construction and operation of civil engineering projects such as railways, highways and tunnels in the cold regions are increasingly touching rocks under low temperatures and temperature alternation. Rocks in cold region engineering structures are always in a certain stress field and are subjected to freeze-thaw cycles of seasons and day and night. Such an environment has an important influence on the mechanical properties of rocks, and their deformation and failure mechanisms show different characteristics compared with normal temperature. Since rocks are aggregates of various mineral particles formed under geological action and are natural damaged materials, they are affected by the environment, and internal microscopic defects expand and aggregate, and materials are continuously damaged, which deteriorates the rock's mechanical properties and leads to destruction. The study of the mechanical properties of frozen-thawed rocks has become a key scientific issue that needs to be urgently solved in the prevention and control of freeze-thaw disasters.

[0003] At present, the research on the mechanical properties of frozen-thawed rocks at home and abroad is mostly concentrated on the experimental level, and the establishment of theoretical damage constitutive models is mostly based on the damage evolution law to determine the damage variables under load, introduce constitutive models, and reflect the deformation and failure process of frozen-thawed rocks under load. The research results have a good description of the brittle-ductile damage process of frozen-thawed rocks, but there are few studies on the damage rate of frozen-thawed rocks under load. There is a lack of constitutive relationships based on the idea of ​​"dynamic damage evolution rate → dynamic damage variables → constitutive model" to study the damage, deformation and failure characteristics of rocks under freeze-thaw-load. The presence or absence of confining pressure has a great influence on the crack propagation path, and different confining pressures also have significant differences in the inhibitory effect on the internal defects of different rocks. The deformation and failure of rocks under conventional uniaxial and triaxial compression is an important basic research to understand and reveal rock engineering disasters under complex stress environments. Most of the current models are limited to uniaxial stress states and lack consideration of the influence of complex stress environments on the evolution law of rock deformation and failure. Although some achievements have been made in the study of rock damage mechanical properties under low temperature and freeze-thaw cycle conditions in terms of microstructure evolution and macromechanical properties, there is a lack of quantitative damage identification combining microstructure and macromechanical properties. At the same time, the model parameters obtained mainly by fitting experimental data lack clear physical meanings, and cannot reflect the internal mechanism of freeze-thaw damage and the general law of change of the selected physical quantities, and are not universal. Summary of the invention

[0004] In order to solve the above technical problems, the present invention discloses a method for constructing a dynamic damage constitutive relationship of rock under freeze-thaw-load. The method is based on the evolution characteristics of the dynamic damage rate of rock, and takes into account the influence of freeze-thaw, confining pressure and axial stress on cold region projects. The established rock damage constitutive model uses the peak point method to derive the theoretical relationship between the model parameters and the characteristic parameters of rock deformation and failure, and verifies the rationality of the model through experiments. It can better describe the mechanical behavior of rock under various confining pressures and freeze-thaw times.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] The method for constructing the dynamic damage constitutive relation of rock under freeze-thaw-load action specifically includes the following steps:

[0007] Step 1: Based on the dynamic damage rate evolution characteristics and the variation law of macroscopic mechanical parameters, the dynamic damage evolution equation of rock under freeze-thaw-load is determined;

[0008] Step 2: Abstract the rock into damaged parts and undamaged parts, with the undamaged part bearing effective stress and the damaged part bearing residual stress, and establish a rock constitutive model based on dynamic damage rate under freeze-thaw-load;

[0009] Step 3: Determine the model parameter expression according to the geometric conditions of the peak point of the rock stress-strain curve;

[0010] Step 4: Conduct freeze-thaw cycle and conventional triaxial compression tests on red sandstone;

[0011] Step 5: Compare and verify the experimental results with the theoretical model.

[0012] Furthermore, in step 1, it is assumed that under freeze-thaw-load, the ratio of the rock damage rate after freeze-thaw to the difference between the undamaged state before loading and the damage generated during loading is closely related to the strain, and the ratio and strain involved satisfy a power function relationship. A differential equation is established to describe the dynamic damage and destruction process of freeze-thaw rock under loading:

[0013]

[0014] In ε 1 = 0, D(ε 1 )=0,R=1-D F-T , the dynamic damage evolution equation of rock under freeze-thaw-load is obtained:

[0015]

[0016] Among them, D(ε 1 ) is the load damage variable of freeze-thaw rock; ε 1 is the axial strain; (1-DF-T ) is the value of the undamaged rock before freezing and thawing load, D F-T is the freeze-thaw damage variable; m is the model strain influencing parameter; t is the model parameter; R is the integral constant.

[0017] Furthermore, the following variables are defined respectively:

[0018] Freeze-thaw damage variables:

[0019] Load damage variable: Total damage variable: Therefore, the total damage variable of rock under freeze-thaw-load is proposed: D T =D F-T +(1-D F-T )D(ε 1 );

[0020] The freeze-thaw damage variables are defined by combining the mesostructure and macroscopic mechanical parameters cohesion:

[0021] The dynamic damage evolution equation of rock under freeze-thaw-load is obtained as follows:

[0022]

[0023] The first-order derivative and second-order derivative of strain are calculated for the dynamic damage evolution equation, and the dynamic damage evolution rate and dynamic damage acceleration of rock under freeze-thaw-load are obtained respectively:

[0024]

[0025] Among them, D F-T is the freeze-thaw damage variable; D T is the total damage variable; C 0 , C F-T is the cohesion of unfrozen and thawed rocks; ρ 0 , F-T is the porosity of unfrozen and thawed rocks; V, V F-T 、V(ε 1 ), V S They are the total rock volume, freeze-thaw damage volume, load damage volume and coupled damage volume; is the dynamic damage evolution rate; a T (ε 1 ) is the dynamic damage acceleration.

[0026] Furthermore, in step 2, assuming that the undamaged part bears the effective stress and the damaged part bears the residual stress, then: 1 V=σ 1 ′[VVF-T -V(ε 1 )+V S ]+σ r [V F-T +V(ε 1 )-V S ];

[0027] Assuming that the constitutive relation of the undamaged part follows the generalized Hooke's law, according to the coordination relationship between the damage of rock microelement and the deformation of the undamaged part, without considering the lateral damage, the constitutive model expression of rock based on dynamic damage rate under freeze-thaw-load is determined:

[0028]

[0029] In the formula, σ 1 , σ 1 ′、σ r are the axial nominal stress, effective stress and residual stress respectively; μ is Poisson's ratio; E F-T is the elastic modulus of freeze-thaw rock.

[0030] Furthermore, in step 3, the geometric condition of the peak point of the rock stress-strain curve is:

[0031] (a)ε 1 =ε p , σ 1 =σ p ;

[0032] (b)

[0033] From conditions (a) and (b), we get two model parameter expressions:

[0034]

[0035]

[0036] in, σ p and ε p represent the peak stress and peak strain of the stress-strain curve, respectively.

[0037] The beneficial effects of the present invention are:

[0038] 1. Based on the evolution characteristics of dynamic damage rate, the dynamic damage evolution equation of rock under freeze-thaw-load is determined; the total area of ​​rock microelement is simplified into four parts: freeze-thaw damage, load damage, coupled damage and undamaged, and the undamaged part bears effective stress and the damaged part bears residual stress. A rock constitutive model based on dynamic damage rate under freeze-thaw-load is established, and freeze-thaw cycle and conventional triaxial compression tests of red sandstone are carried out. The rationality of the model is verified by the test results;

[0039] 2. The constitutive model is established by combining theoretical deduction with experimental verification. The obtained theoretical curve has a high degree of agreement with the experimental curve, which can well reflect the mutual influence between rock damage evolution and axial stress, freeze-thaw cycle and stress state under various confining pressures and freeze-thaw cycles, and can provide theoretical guidance for the design and construction of cold region projects.

[0040] 3. The method of the present invention is simple and practical to operate. The constitutive relationship established can take into account both the low-temperature environmental effect of rock materials and their mechanical properties, and reveals the relationship between the microscopic damage state and the macroscopic mechanical response, and derives the theoretical relationship between the model parameters and the characteristic parameters of rock deformation and failure, thereby enhancing the applicability of the model. Whether it is theoretical analysis or numerical simulation, the constitutive relationship established by the present invention can be used as a reference, especially for geotechnical engineering construction in a wide range of cold regions, which has certain reference significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the process of the present invention;

[0042] Figure 2 The theoretical curve and experimental curve of the rock constitutive model based on the dynamic damage rate under freeze-thaw-load in the embodiment;

[0043] Figure 2 a is the theoretical curve and experimental curve of the model under different confining pressures of 0 freeze-thaw cycles in the embodiment;

[0044] Figure 2 b is the theoretical curve and experimental curve of the model under 5 freeze-thaw cycles with different confining pressures in the embodiment;

[0045] Figure 2 c is the theoretical curve and experimental curve of the model under different confining pressures of 10 freeze-thaw cycles in the embodiment;

[0046] Figure 2 d is the theoretical curve and experimental curve of the model under 20 freeze-thaw cycles with different confining pressures in the embodiment;

[0047] Figure 2 e is the theoretical curve and experimental curve of the model under 30 freeze-thaw cycles with different confining pressures in the embodiment;

[0048] Figure 2f is the theoretical curve and experimental curve of the model under 40 freeze-thaw cycles with different confining pressures in the embodiment.

[0049] Figure 3 The dynamic damage evolution characteristic curve of red sandstone under different freeze-thaw times and confining pressure in the embodiment;

[0050] Figure 3 a is the dynamic damage evolution characteristic curve of red sandstone under different confining pressures after 0 freeze-thaw cycles in the embodiment;

[0051] Figure 3 b is the dynamic damage evolution characteristic curve of red sandstone under different confining pressures after 5 freeze-thaw cycles in the embodiment;

[0052] Figure 3 c is the dynamic damage evolution characteristic curve of red sandstone under different confining pressures after 10 freeze-thaw cycles in the embodiment;

[0053] Figure 3 d is the dynamic damage evolution characteristic curve of red sandstone under different confining pressures after 20 freeze-thaw cycles in the embodiment.

[0054] Figure 4 The dynamic damage evolution rate curve of red sandstone under different freeze-thaw times and confining pressure in the embodiment;

[0055] Figure 4 a is the dynamic damage rate evolution curve of red sandstone under different confining pressures after 0 freeze-thaw cycles in the embodiment;

[0056] Figure 4 b is the dynamic damage rate evolution curve of red sandstone under different confining pressures after 5 freeze-thaw cycles in the embodiment;

[0057] Figure 4 c is the dynamic damage evolution characteristic curve of red sandstone under different confining pressures after 10 freeze-thaw cycles in the embodiment;

[0058] Figure 4 d is the dynamic damage rate evolution curve of red sandstone under different confining pressures after 20 freeze-thaw cycles in the embodiment. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0060] For the study of rock mass stability in cold regions, the influence of factors such as freeze-thaw cycles and load effects must be considered first. The embodiment of the present invention discloses a method for constructing a dynamic damage constitutive relationship of rock under freeze-thaw-load effects. The flow chart is shown in FIG. Figure 1 Considering the combined effect of freeze-thaw cycles and loads, this method combines theoretical deduction with experimental verification. The theoretical curve of the damage constitutive model established is in good agreement with the experimental data, which can well reflect the mutual influence between rock damage evolution and axial stress, freeze-thaw cycles and stress state under various confining pressures and freeze-thaw cycles, and can provide theoretical guidance for the design and construction of cold region projects.

[0061] Example

[0062] A method for constructing a dynamic damage constitutive relation of rock under freeze-thaw-load, comprising:

[0063] 1. Based on the evolution characteristics of dynamic damage rate and the variation law of macroscopic mechanical parameters, the dynamic damage evolution equation of rock under freeze-thaw-load is determined.

[0064] Considering that the damage evolution of rock under freeze-thaw-load is approximately an "S" curve, the corresponding damage rate is approximately a normal distribution curve. Assuming that under freeze-thaw-load, the ratio of the rock damage rate after freeze-thaw to the difference between the undamaged rock before loading and the damage generated during loading is closely related to the strain, and the ratio and strain involved satisfy the power function relationship, a differential equation is established to describe the dynamic damage and destruction process of freeze-thaw rock under loading:

[0065]

[0066] In ε 1 = 0, D(ε 1 )=0,R=1-D F-T , the dynamic damage evolution equation of rock under freeze-thaw-load is obtained:

[0067]

[0068] Among them, D(ε 1 ) is the load damage variable of freeze-thaw rock; ε 1 is the axial strain; (1-D F-T ) is the value of the undamaged rock before freezing and thawing. F-T is the freeze-thaw damage variable; m is the model strain influencing parameter; t is the model parameter; R is the integral constant.

[0069] Define the following variables, freeze-thaw damage variables: Load damage variable: Total damage variable:

[0070] Therefore, the total damage variable of rock under freeze-thaw-load is proposed: D T =D F-T +(1-D F-T )D(ε 1 ).

[0071] The freeze-thaw damage variables are defined by combining the mesostructure and macroscopic mechanical parameters cohesion:

[0072] The dynamic damage evolution equation of rock under freeze-thaw-load is obtained as follows:

[0073]

[0074] The first-order derivative and second-order derivative of strain are calculated for the dynamic damage evolution equation, and the dynamic damage evolution rate and dynamic damage acceleration of rock under freeze-thaw-load are obtained respectively:

[0075]

[0076] Among them, D F-T is the freeze-thaw damage variable; D T is the total damage variable; C 0 , C F-T is the cohesion of unfrozen and thawed rocks; ρ 0 , F-T is the porosity of unfrozen and thawed rocks; V, V F-T 、V(ε 1 ), V S They are the total rock volume, freeze-thaw damage volume, load damage volume and coupled damage volume; is the dynamic damage evolution rate; a T (ε 1 ) is the dynamic damage acceleration.

[0077] 2. The rock is abstracted into damaged part and undamaged part, and the undamaged part bears effective stress and the damaged part bears residual stress. A rock constitutive model based on dynamic damage rate under freeze-thaw-load is established.

[0078] Assuming that the undamaged part bears the effective stress and the damaged part bears the residual stress, then: 1 V=σ 1 ′[VV F-T -V(ε 1 )+V S ]+σ r [V F-T +V(ε 1 )-V S ].

[0079] Assuming that the constitutive relation of the undamaged part follows the generalized Hooke's law, according to the coordination relationship between the damage of rock micro-element and the deformation of the undamaged part, without considering the lateral damage, the constitutive model expression of rock based on dynamic damage rate under freeze-thaw-load is determined:

[0080]

[0081] In the formula, σ 1 , σ 1 ′、σ r are the axial nominal stress, effective stress and residual stress respectively; μ is Poisson's ratio; E F-T is the elastic modulus of freeze-thaw rock.

[0082] 3. Determine the model parameter expression based on the geometric conditions of the peak point of the rock stress-strain curve.

[0083] The geometric conditions of the peak point of the rock stress-strain curve are: (a) ε 1 =ε p , σ 1 =σ p (b)

[0084] From conditions (a) and (b), we get two model parameter expressions:

[0085]

[0086]

[0087] in, σ p and ε p represent the peak stress and peak strain of the stress-strain curve respectively.

[0088] Through the above theoretical derivation, the dynamic damage evolution equation and constitutive model of rock under freeze-thaw-load are established.

[0089] 4. Design and implementation of experimental plan.

[0090] The rationality of the model was verified experimentally. The RSM-SY5 intelligent sonic wave detector was used to measure the longitudinal wave velocity of each specimen, and specimens with similar wave velocities were selected as test rock samples. The XMT605 American rapid freeze-thaw testing machine was used to conduct freeze-thaw cycle tests on standard red sandstone samples, and the physical parameters of the red sandstone under a specific number of freeze-thaw cycles were recorded. The MTS815 rock mechanics testing system was used to conduct triaxial compression tests under different confining pressures on rocks that had undergone a specific number of freeze-thaw cycles, and the mechanical parameter-strain relationship curves of the rocks under different numbers of freeze-thaw cycles and confining pressures were recorded. Using the experimental data, the total damage variable-strain relationship curves under different numbers of freeze-thaw cycles and confining pressures were calculated based on the total damage evolution equation and constitutive relationship of the rock, and compared with the experimental results to prove the correctness and practicality of the theory. For specific calculation results, see Figure 2-4 .

[0091] The results show that Figure 2 The theoretical curves of the damage constitutive model of red sandstone under different freeze-thaw cycles and confining pressures were calculated and compared with the experimental curves. The two curves are close under the same freeze-thaw cycle and confining pressure, which proves the universality of the constitutive model. Figure 3 , 4 It can be seen that the dynamic damage evolution goes through four stages: unchanged damage, accelerated damage expansion, slow damage increase and complete damage, which correspond to the compaction-elastic deformation, plastic deformation, post-peak softening and residual deformation stages of the theoretical curve, indicating the consistency between the mesomechanical response of the rock and the deformation and failure process of the stress-strain test curve.

[0092] 5. Compare and verify the experimental results with the theoretical model.

[0093] The specific process is as follows:

[0094] a) Select fresh and complete large pieces of red sandstone from the project site and process them into cylindrical standard specimens with a height to diameter ratio of 2:1 using the water drilling method;

[0095] b) Select specimens with intact appearance, and use RSM-SY5 intelligent acoustic wave detector to measure the longitudinal wave velocity of the specimens. Perform freeze-thaw cycle and triaxial compression tests on 72 specimens with similar wave velocities;

[0096] c) Place the selected rock sample in a constant temperature and humidity test chamber and dry it at 105°C for 48 hours until constant weight is reached, i.e. the mass change of the sample does not exceed 0.1% within 24 hours; then take the dried rock sample out of the oven and cool it naturally in a drying dish;

[0097] d) The dried specimens were forced to be saturated with water using the vacuum pumping method. The vacuum pressure value was set to -0.1 MPa. After continuously extracting the air in the container for 2 hours, a certain amount of distilled water was added to the container. Then, the air in the container was continuously extracted for 4 hours until no bubbles appeared in the water. The vacuum pump was turned off and the rock sample was immersed in water for more than 24 hours.

[0098] e) Take out 12 saturated specimens, 3 pieces in each group, and conduct triaxial compression tests at confining pressures of 0MPa, 2MPa, 4MPa and 6MPa respectively;

[0099] f) The remaining 60 saturated specimens were placed in a rapid freeze-thaw testing machine for freeze-thaw cycle tests in an open saturated state. When they had undergone 5, 10, 20, 30 and 40 freeze-thaw cycles respectively, 60 specimens were taken out for triaxial compression tests with confining pressures of 0 MPa, 2 MPa, 4 MPa and 6 MPa.

[0100] The experiment was based on the SL264-2001 rock test procedure. The freeze-thaw cycle temperature change cycle was set to +20℃→-20℃→+20℃, and a thermistor temperature sensor was placed in the center of a standard rock sample to ensure that the temperature inside the sample reached the set value. The cycle time was controlled according to the temperature, and one freeze-thaw cycle was about 6h. During the triaxial compression test, a 1000kN force sensor was used in the vertical direction to test the axial load, and an axial extensometer and a chain-type circumferential displacement extensometer were used to test the axial and lateral deformation of the rock sample.

[0101] The stress-strain test curve obtained through freeze-thaw cycle and mechanical property test of red sandstone is compared with the theoretical curve under different freeze-thaw times and confining pressures obtained by the damage constitutive model. When the freeze-thaw times and confining pressures are the same, the two curves have a good fit, which proves the correctness and practicality of the method of the present invention. Figure 3-4 It can be seen from the curve shape that under the action of freeze-thaw-load, the dynamic damage evolution curve of red sandstone is approximately an "S" curve, the dynamic damage rate is approximately a normal distribution curve, and the acceleration is approximately an asymmetric wavy line function curve, which is consistent with the actual situation. Therefore, the established damage evolution equation can be used to describe the dynamic damage process of rock, and better reflect the rock damage unchanged stage, accelerated damage expansion stage, slow damage increase stage, and complete damage stage, which correspond to the compaction-elastic deformation, plastic deformation, post-peak softening and residual deformation stages of the model theoretical curve, respectively, indicating the consistency of the deformation and failure process of the rock mesomechanical response and the stress-strain test curve.

[0102] This method determines the dynamic damage evolution equation based on the evolution characteristics of the dynamic damage rate of rock under freeze-thaw-load and the change law of macroscopic mechanical parameters; the rock under freeze-thaw-load is abstracted into four parts: freeze-thaw damage, load damage, coupled damage and undamaged, and the undamaged part bears the effective stress and the damaged part bears the residual stress, and a rock damage constitutive model is established; freeze-thaw cycle and conventional triaxial compression tests on red sandstone are carried out, and the rationality of the model is verified by the experimental results.

[0103] This method is a combination of theoretical deduction and experimental verification. The theoretical curve obtained by the established model has a high degree of consistency with the experimental curve. It can well reflect the mutual influence between rock damage evolution and axial stress, freeze-thaw cycles and stress state under various confining pressures and freeze-thaw times, and can provide theoretical guidance for the design and construction of cold region projects.

[0104] This method can well reflect the mechanical behavior of rocks under various confining pressures and freeze-thaw times, and better describe the stress-strain relationship of rock freeze-thaw loads. The results are more in line with the characteristics of rock materials in cold regions.

[0105] The method of the present invention is simple and practical to operate. The established rock constitutive model based on dynamic damage rate can take into account both the low temperature environmental effect of rock materials and their mechanical properties, and reveals the relationship between the microscopic damage state and the macroscopic mechanical response, and derives the theoretical relationship between the model parameters and the characteristic parameters of rock deformation and failure, thereby enhancing the applicability of the model. Whether it is theoretical analysis or numerical simulation, the constitutive relationship established by the present invention can be used for reference, especially for the construction of geotechnical engineering in a wide range of cold regions, and has certain reference significance.

[0106] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for constructing a dynamic damage constitutive relation of rock under freeze-thaw-load, characterized in that: The specific steps include: Step 1: Based on the dynamic damage rate evolution characteristics and the variation law of macroscopic mechanical parameters, the dynamic damage evolution equation of rock under freeze-thaw-load is determined; Step 2: Abstract the rock into damaged parts and undamaged parts, with the undamaged part bearing effective stress and the damaged part bearing residual stress, and establish a rock constitutive model based on dynamic damage rate under freeze-thaw-load; Step 3: Determine the model parameter expression according to the geometric conditions of the peak point of the rock stress-strain curve; Step 4: Conduct freeze-thaw cycle and conventional triaxial compression tests on red sandstone; Step 5: Compare and verify the experimental results with the theoretical model.

2. The method for constructing the dynamic damage constitutive relationship of rock under freeze-thaw-load as claimed in claim 1, characterized in that: In step 1, it is assumed that under freeze-thaw-load, the ratio of the rock damage rate after freeze-thaw to the difference between the undamaged state before loading and the damage generated during loading is closely related to the strain, and the ratio and strain involved satisfy a power function relationship. A differential equation is established to describe the dynamic damage and destruction process of freeze-thaw rock under loading: When ε1=0, D(ε1)=0, R=1-D F-T , the dynamic damage evolution equation of rock under freeze-thaw-load is obtained: Where D(ε1) is the load damage variable of freeze-thaw rock; ε1 is the axial strain; (1-D F-T ) is the value of the undamaged rock before freezing and thawing. F-T is the freeze-thaw damage variable; m is the model strain influencing parameter; t is the model parameter; R is the integral constant.

3. The method for constructing the dynamic damage constitutive relation of rock under freeze-thaw-load as claimed in claim 2, characterized in that: Define the following variables respectively: Freeze-thaw damage variables: Load damage variable: Total damage variable: Therefore, the total damage variable of rock under freeze-thaw-load is proposed: D T =D F-T +(1-D F-T )D(ε1); The freeze-thaw damage variables are defined by combining the mesostructure and macroscopic mechanical parameters cohesion: The dynamic damage evolution equation of rock under freeze-thaw-load is obtained as follows: The first-order derivative and second-order derivative of strain are calculated for the dynamic damage evolution equation, and the dynamic damage evolution rate and dynamic damage acceleration of rock under freeze-thaw-load are obtained respectively: Among them, D F-T is the freeze-thaw damage variable; D T is the total damage variable; C0, C F-T is the cohesion of unfrozen and thawed rocks; ρ0, ρ F-T is the porosity of unfrozen and thawed rocks; V, V F-T , V(ε1), V S They are the total rock volume, freeze-thaw damage volume, load damage volume and coupled damage volume; is the dynamic damage evolution rate; a T (ε1) is the dynamic damage acceleration.

4. The method for constructing the dynamic damage constitutive relation of rock under freeze-thaw-load as claimed in claim 3, characterized in that: In step 2, assuming that the undamaged part bears the effective stress and the damaged part bears the residual stress, then: σ1V=σ′1[VV F-T -V(ε1)+V S ]+σ r [V F-T +V(ε1)-V S ]; Assuming that the constitutive relation of the undamaged part follows the generalized Hooke's law, according to the coordination relationship between the damage of rock microelement and the deformation of the undamaged part, without considering the lateral damage, the constitutive model expression of rock based on dynamic damage rate under freeze-thaw-load is determined: In the formula, σ1, σ′1, σ r are the axial nominal stress, effective stress and residual stress respectively; μ is Poisson's ratio; E F-T is the elastic modulus of freeze-thaw rock.

5. The method for constructing the dynamic damage constitutive relation of rock under freeze-thaw-load as claimed in claim 4, characterized in that: In step 3, the geometric condition of the peak point of the rock stress-strain curve is: (a)ε1=ε p ,σ1=σ p ; From conditions (a) and (b), we get two model parameter expressions: in, and ε p represent the peak stress and peak strain of the stress-strain curve, respectively.

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