A method for constructing a mesoscopic joint constitutive model of high-temperature rocks

Abstract

The present invention provides a method for constructing a mesoscopic joint constitutive model of high-temperature rock, which relates to the technical field of numerical simulation of rock mechanics. The method first establishes a preliminary mathematical expression of the mesoscopic joint constitutive relationship of rock considering crack slip and temperature effects, and obtains the macroscopic physical and mechanical properties of the rock; then establishes a numerical geometric model of the rock sample, and assigns the thermodynamic parameters and preliminary constitutive relationship of the target rock to the unit body and the contact surface of the unit body of the numerical model; replicates the laboratory test conditions and conducts parallel numerical simulation tests; finally, compares the numerical simulation results with the laboratory test results, and uses the back analysis method to obtain the coefficient equation required for the mesoscopic joint constitutive relationship of the corresponding rock specimen, thus completing the construction of the mesoscopic joint constitutive model of high-temperature rock. This method simultaneously considers the crack slip effect and the temperature effect. The mesoscopic joint constitutive model of high-temperature rock constructed by using the back analysis method has a high degree of coincidence with the test results and can be applied to the numerical simulation of rock mechanics.

Description

Technical Field

[0001] The present invention relates to the technical field of numerical simulation of rock mechanics, and particularly to a method for constructing a mesoscopic joint constitutive model of high-temperature rock. Background Art

[0002] With the increasing depletion of shallow resources on the earth, the demand for the exploitation of deep resources and the development and utilization of deep underground space is constantly increasing. Deep rock masses have physical properties and mechanical behaviors different from those of shallow rock masses under high temperature and high pressure conditions, which bring many challenges to engineering applications such as enhanced geothermal systems and high-level radioactive waste disposal. As one of the most common engineering materials in engineering applications, understanding its mechanical constitutive behavior under thermo-mechanical coupling conditions is a key issue in our continuous exploration of the deep earth.

[0003] However, so far, the research on the thermo-mechanical coupling behavior of high-temperature rock is still insufficient, mainly because the experimental technical means for conducting mechanical tests on rock at actual high temperatures are very lacking. Therefore, using numerical simulation as an alternative technology to reproduce the real-time process of the thermo-mechanical coupling behavior of rock has become a feasible approach. As one of the numerical simulation methods, discontinuous methods such as the discrete element method complete the nucleation and propagation of microcracks in a discrete manner. And such microcracks are affected by both slip effect and temperature effect, and a mesoscopic joint constitutive model of rock that simultaneously considers the crack slip effect and temperature effect is needed to describe its thermodynamic behavior in order to more accurately reproduce the thermo-mechanical coupling behavior of the entire rock model in discrete element software. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for constructing a mesoscopic joint constitutive model of high-temperature rock to realize the construction of the mesoscopic joint constitutive model of high-temperature rock in view of the above-mentioned deficiencies of the prior art.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: A method for constructing a mesoscopic joint constitutive model of high-temperature rock, comprising the following steps:

[0006] Step 1, establish a preliminary mathematical expression of the mesoscopic joint constitutive relationship of rock considering crack slip effect and temperature effect;

[0007] Step 1.1, considering the slip effect of thermal stress cracks under thermo-mechanical coupling, modify the residual cohesive force and residual internal friction angle of the Coulomb friction sliding criterion to slip displacement dependence;

[0008] The expression for the influence of the shear parameters of thermal stress cracks by slip deformation is:

[0009]

[0010]

[0011] Among them, and are the residual cohesive force and residual internal friction angle affected by the crack slip distance, and are the slip weakening or strengthening coefficient equations of the corresponding residual cohesive force and residual internal friction angle, c0 and are the initial cohesive force and internal friction angle of the mesoscopic joints of the rock without temperature influence;

[0012] Step 1.2: Considering the temperature effect under the thermo-mechanical coupling, modify the cohesive force, internal friction angle, and tensile strength of the Coulomb friction sliding criterion to temperature dependence;

[0013] Considering the temperature effect, modify the cohesive force c0, internal friction angle tensile strength σ

[0014] , c , , t0 , , temp-t , , temp , , temp-t , , temp , , temp-max ,

[0013] , temp-c ,

[0016] , c , , , max ,

[0019] , , temp-t , , temp-t ,

[0021] , temp-t , , max , ,

[0015] , temp-c , , temp-t ,

[0017] , t0 ,

[0012] , t0 , , temp-max ,

[0020] ,

[0018] to temperature dependence, and the expression is:

[0014] c temp = f temp-c c0 (3)

[0015]

[0016] σ temp-t = f temp-t σ t0 (5)

[0017] Among them, c temp , σ temp-t are the cohesive force, internal friction angle, and tensile strength affected by the temperature effect respectively; f temp-c , f temp-t are the temperature dependence coefficient equations of the cohesive force, internal friction angle, and tensile strength respectively;

[0018] Under the action of high temperature, modify the maximum tensile strength T max and the maximum shear strength S max of the mesoscopic joints of the rock in the Coulomb friction sliding criterion to temperature dependence, as shown in the following formula:

[0019] T temp-max = -σ temp-t A c = f temp-t σ t0 A c (6)

[0020]

[0021] Among them, T temp-maxis the maximum tensile strength of the joint dependent on temperature, S temp-max is the maximum shear strength of the joint dependent on temperature, A c is the joint area, F n is the normal force of the joint;

[0022] Step 1.3: Establish a preliminary mathematical expression for the mesoscopic joint constitutive relation of rock considering both crack slip effect and temperature effect;

[0023] For tensile cracks, the residual tensile strength is set to 0; for shear cracks, their mechanical behavior is affected by both temperature and crack slip deformation. Therefore, the mechanical relation of the corresponding residual shear parameters of shear cracks becomes the following formula:

[0024]

[0025]

[0026]

[0027] where and are the residual cohesion and residual internal friction angle considering both joint slip effect and temperature effect, is the maximum residual shear strength considering both crack slip effect and temperature effect;

[0028] Step 2: Prepare multiple rock specimens, measure and analyze the rock specimens respectively, and conduct high-temperature rock mechanics tests to obtain the macroscopic physical and mechanical properties of the rock;

[0029] Step 2.1: Measure the mineral composition of the target rock specimen;

[0030] Measure the mineral composition of the target rock specimen to determine the mineral crystal composition and proportion of the rock specimen;

[0031] Step 2.2: Collect and organize the thermodynamic properties of all mineral crystals of the rock specimen;

[0032] Collect and organize the thermodynamic properties of all mineral crystals of the rock specimen. Among them, the thermal parameters include the linear thermal expansion coefficient α t , the thermal conductivity k, and the specific heat capacity C p ; the mechanical parameters include: density ρ m , Poisson's ratio ν m , Young's modulus E m , cohesion c m , internal friction angle tensile strength σ tm ; the mechanical properties of the contact surface between mineral crystals are taken as the average of the mechanical parameters of adjacent mineral crystals;

[0033] Step 2.3: Conduct a variety of high-temperature rock mechanics tests on the rock specimens to obtain the stress-strain curves and tensile strengths of the rock specimens;

[0034] Based on the stress-strain relationship and tensile strength of the unheated rock specimens, determine the initial mechanical parameters of the numerical geometric model of the rock specimens, including density ρ, Poisson's ratio ν, Young's modulus E, cohesion c, internal friction angle and tensile strength σ t ;

[0035] According to the stress-strain curve, back-calculate the temperature-dependent coefficient equations of cohesion f temp-c , the temperature-dependent coefficient equation of internal friction angle the temperature-dependent coefficient equation of tensile strength f temp-t , the crack slip weakening or strengthening coefficient equation of residual cohesion the crack slip weakening / strengthening coefficient equation of residual internal friction angle

[0036] When conducting a variety of high-temperature rock mechanics tests on the rock specimens, it is necessary to pre-treat the rock specimens by heating and cooling first;

[0037] Step 3: Establish a numerical geometric model of the rock specimens in the discrete element numerical simulation software, and input the thermodynamic parameters and preliminary constitutive relations of the target rock into the unit bodies and the contact surfaces between unit bodies of the numerical geometric model;

[0038] Step 3.1: Generate a 1:1 numerical geometric model in the discrete element numerical simulation software according to the size of the laboratory rock specimens to be modeled;

[0039] Step 3.2: Traverse the numerical unit bodies in the numerical geometric model according to the proportion of different mineral components in the polycrystalline rock specimens, randomly group the units according to the true mineral proportion measured in Step 2.1, and define them as corresponding mineral crystals;

[0040] Step 3.3: Identify the mineral crystals and the contact surfaces within and between crystals in the numerical geometric model, and assign the thermodynamic parameters and constitutive relations to the crystal units and the contact surfaces between crystals;

[0041] Among them, the crystal units are set as elastic constitutive models, and the constitutive relation of the contact surfaces between crystals is set as the preliminary mathematical expression of the mesoscopic joint constitutive relation of rocks considering crack slip effect and temperature effect obtained in Step 1;

[0042] Step 4: Copy the laboratory test conditions and conduct parallel numerical simulation tests in the discrete element numerical simulation software;

[0043] Replicate the laboratory test conditions and conduct parallel heating and loading numerical simulation tests on the models established in the discrete element numerical simulation software;

[0044] Step 5: Compare the numerical simulation results with the laboratory test results, and use the back analysis method to obtain the coefficient equations required for the mesoscopic joint constitutive relationship of the corresponding rock specimens, and complete the construction of the mesoscopic joint constitutive model of high-temperature rocks;

[0045] Step 5.1: According to the heating and loading numerical simulation tests carried out in Step 4, compare the stress-strain relationship and tensile strength of the numerical geometric model and the specimen under the action of load after the same heating-cooling pretreatment. Based on the differences between the simulation results and the test results, modify the initial mechanical parameters of the numerical geometric model, conduct parallel heating and loading numerical simulation tests again, and compare the test results again. Repeat this process until the numerical simulation results are consistent with the test results or within the set error range, so as to determine the quantitative relationship between the mechanical parameters at different temperatures and the initial mechanical parameters;

[0046] Step 5.2: Based on the obtained quantitative relationships at different temperatures, establish the coefficient equation f of the temperature dependence of the cohesion of the rock specimen at different temperatures temp-c , the coefficient equation of the temperature dependence of the internal friction angle , the coefficient equation f of the temperature dependence of the tensile strength temp-t , the crack slip weakening / reinforcement coefficient equation of the residual cohesion , the crack slip weakening / reinforcement coefficient equation of the residual internal friction angle

[0047] Step 5.3: Substitute the obtained coefficient equation f of the temperature dependence of the cohesion temp-c , the coefficient equation of the temperature dependence of the internal friction angle , the coefficient equation f of the temperature dependence of the tensile strength temp-t , the crack slip weakening / reinforcement coefficient equation of the residual cohesion , the crack slip weakening / reinforcement coefficient equation of the residual internal friction angle into the mechanical relationship of the corresponding residual shear parameters of the shear crack to complete the construction of the mesoscopic joint constitutive model of high-temperature rocks.

[0048] The beneficial effects of adopting the above technical solution are as follows: A method for constructing a mesoscopic joint constitutive model of high-temperature rock provided by the present invention combines high-temperature rock mechanics tests, uses discrete element numerical simulation software, and constructs a mesoscopic joint constitutive model of high-temperature rock by means of the inverse analysis method. It can simultaneously consider the influence of crack slip effect and temperature effect on the mesoscopic joints of rock, and can further restore the nucleation and expansion mechanism of mesoscopic joints of rock after being subjected to high temperature in the discrete element software. The constitutive model constructed by this method is verified by numerical simulation tests, and the obtained results have a high degree of coincidence with the laboratory test results, and can be applied to the field of rock mechanics numerical simulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 It is a flowchart of a method for constructing a mesoscopic joint constitutive model of high-temperature rock provided by an embodiment of the present invention;

[0050] Figure 2 It is a stress-strain curve diagram obtained by performing a uniaxial compression test on a rock specimen provided by an embodiment of the present invention after different temperature treatments;

[0051] Figure 3 It is a temperature-dependent relationship diagram of cohesion, internal friction angle, and tensile strength obtained by laboratory tests provided by an embodiment of the present invention, where (a) is the dependence relationship between cohesion and internal friction angle and temperature, and (b) is the dependence relationship between tensile strength and temperature;

[0052] Figure 4 It is a slip weakening or strengthening coefficient equation of residual cohesion and residual internal friction angle obtained by laboratory tests provided by an embodiment of the present invention;

[0053] Figure 5 It is a numerical geometric model of a rock specimen established by UDEC provided by an embodiment of the present invention, where (a) is the numerical geometric model of a cylindrical specimen, and (b) is the numerical geometric model of a disk specimen;

[0054] Figure 6 It is a schematic diagram of heating-cooling treatment of a numerical geometric model provided by an embodiment of the present invention;

[0055] Figure 7 It is a schematic diagram of a loading simulation test on a numerical geometric model in an embodiment of the present invention, where (a) is a cylindrical model for performing a uniaxial compression test, and (b) is a disk model for performing a Brazilian split;

[0056] Figure 8 It is a stress-strain curve diagram obtained by performing a uniaxial compression test on a numerical geometric model in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0057] The following describes in detail the specific implementation manners of the present invention in conjunction with the accompanying drawings and embodiments. The following embodiments are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0058] In this embodiment, a method for constructing a mesoscopic joint constitutive model of high-temperature rock is as Figure 1 shown, and it includes the following steps:

[0059] Step 1: Establish a preliminary mathematical expression for the constitutive relationship of mesoscopic joints in rock considering crack slip effect and temperature effect;

[0060] Step 1.1: Considering the slip effect of thermal stress cracks under thermo-mechanical coupling, modify the residual cohesive force and residual internal friction angle of the Coulomb friction sliding criterion (Coulomb Friction Criteria) to be dependent on slip displacement;

[0061] The expression for the shear parameters of thermal stress cracks affected by slip deformation is:

[0062]

[0063]

[0064] Among them, and are the residual cohesive force and residual internal friction angle affected by the crack slip distance, and are the slip weakening or strengthening coefficient equations of the corresponding residual cohesive force and residual internal friction angle, c0 and are the initial cohesive force and internal friction angle of the mesoscopic joints in rock without being affected by temperature;

[0065] Step 1.2: Considering the temperature effect under thermo-mechanical coupling, modify the cohesive force, internal friction angle, and tensile strength of the Coulomb friction sliding criterion to be temperature-dependent;

[0066] Considering the temperature effect, modify the cohesive force c0, internal friction angle tensile strength σ t0 of the joints of the Coulomb friction sliding criterion to be temperature-dependent, and the expression is:

[0067] c temp = f temp-c c0 (3)

[0068]

[0069] σ temp-t = f temp-t σ t0 (5)

[0070] Among them, ctemp , σ temp-t are the cohesion, internal friction angle, and tensile strength affected by the temperature effect, respectively; f temp-c , f temp-t are the temperature-dependent coefficient equations of cohesion, internal friction angle, and tensile strength, respectively;

[0071] Under high-temperature action, the maximum tensile strength T max and the maximum shear strength S max of the mesoscopic joints of rock in the Coulomb friction sliding criterion are modified to temperature dependence as shown in the following formula:

[0072] T temp-max =-σ temp-t A c =f temp-t σ t0 A c (6)

[0073]

[0074] where T temp-max is the temperature-dependent maximum tensile strength of the joint, S temp-max is the temperature-dependent maximum shear strength of the joint, A c is the joint area, and F n is the normal force of the joint;

[0075] Step 1.3: Establish a preliminary mathematical expression for the constitutive relationship of the mesoscopic joints of rock considering both crack slip effect and temperature effect;

[0076] For tensile cracks, it can be considered that there is no resistance in the direction perpendicular to the crack surface, so the residual tensile strength is set to 0; for shear cracks, their mechanical behavior is affected by both temperature and crack slip deformation. Therefore, the mechanical relationship of the corresponding residual shear parameters of shear cracks becomes as shown in the following formula:

[0077]

[0078]

[0079]

[0080] where and are the residual cohesion and residual internal friction angle considering both joint slip effect and temperature effect, is the maximum residual shear strength considering both crack slip effect and temperature effect;

[0081] The mechanical relationship of the residual shear parameters corresponding to the shear crack is the preliminary mathematical expression of the mesoscopic joint constitutive relation of rock, and the coefficient equations in this expression are all to be determined.

[0082] Step 2: Prepare multiple rock specimens, measure and analyze the rock specimens respectively, and conduct various high-temperature rock mechanics tests to obtain the macroscopic physical and mechanical properties of the rock.

[0083] Step 2.1: Measure the mineral composition of the target rock specimen.

[0084] Measure the mineral composition of the target rock specimen to determine the mineral crystal composition and proportion of the rock specimen.

[0085] Step 2.2: Collect and organize the thermodynamic properties of all mineral crystals of the rock specimen.

[0086] Collect and organize the thermodynamic properties of all mineral crystals of the rock specimen. Among them, the thermal parameters include the linear thermal expansion coefficient α t , the thermal conductivity coefficient k, and the specific heat capacity C p ; the mechanical parameters include: density ρ m , Poisson's ratio ν m , Young's modulus E m , cohesion c m , internal friction angle tensile strength σ tm ; the mechanical properties of the contact surface between mineral crystals are taken as the average value of the mechanical parameters of adjacent mineral crystals.

[0087] Step 2.3: Conduct various high-temperature rock mechanics tests on the rock specimen to obtain the stress-strain curve and tensile strength of the rock specimen.

[0088] Meanwhile, according to the stress-strain relationship and tensile strength of the rock specimen without heat treatment, determine the initial mechanical parameters of the numerical geometric model of the rock specimen, including density ρ, Poisson's ratio ν, Young's modulus E, cohesion c, internal friction angle and tensile strength σ t ;

[0089] Back-calculate the temperature-dependent coefficient equations f temp-c of cohesion, the temperature-dependent coefficient equation of internal friction angle and the temperature-dependent coefficient equation f of tensile strength temp-t based on the stress-strain curve and the laboratory test results, as well as the crack slip weakening / reinforcement coefficient equations of residual cohesion and the crack slip weakening / reinforcement coefficient equations of residual internal friction angle

[0090] Before conducting various high-temperature rock mechanics tests on rock specimens, it is necessary to perform heating-cooling pretreatment on the rock specimens. The treatment method is as follows:

[0091] Using an electric furnace, slowly heat the rock specimen at a heating rate not exceeding 10 °C / min. After reaching the target temperature, continue to hold for 1 - 3 hours, and then slowly cool to room temperature in the heating furnace;

[0092] In this embodiment, all the rock specimens used are prepared according to the recommended test standards of the International Society for Rock Mechanics, namely 3 cylindrical specimens with a diameter of 50 mm and a length of 110 mm for uniaxial compression tests and 3 disk specimens with a diameter of 50 mm and a thickness of 25 mm for Brazilian splitting tests. Both types of specimens are Abenstok granite.

[0093] In this embodiment, first measure the mineral composition of the target rock specimen. It is measured that the feldspar composition accounts for 50%, the quartz composition accounts for 44%, and the mica composition accounts for 6%.

[0094] Then collect and organize the thermodynamic property parameters of all mineral crystals in the rock specimen. The mechanical parameters include: density ρ m , Poisson's ratio ν m , Young's modulus E m , cohesion c m , internal friction angle tensile strength σ tm , as shown in Table 1.

[0095] Table 1 Mechanical parameter values of all mineral crystals in the rock specimen

[0096]

[0097]

[0098] The mechanical parameters of the contact surface between mineral crystals are taken as the average of the mechanical properties of adjacent crystals, as shown in Table 2.

[0099] Table 2 Mechanical parameter values of the contact surface between mineral crystals

[0100]

[0101] The thermal parameters include: linear thermal expansion coefficient α t , thermal conductivity k and specific heat capacity C p , as shown in Table 3.

[0102]

[0103] After collecting all the parameters, it is necessary to perform heating-cooling pretreatment on the rock specimen. Taking the cylindrical specimen for uniaxial compression test as an example in this embodiment:

[0104] First, use an electric furnace to slowly heat the rock specimens at a heating rate not exceeding 10 °C / min, and then slowly cool them to room temperature in the heating furnace. Three specimens are heated to 25 °C, 400 °C, and 600 °C respectively. The specimens heated to 400 °C and 600 °C need to be kept at the target temperature for 36 hours. The heating treatment method for the disk specimens used in the Brazilian splitting test is the same.

[0105] After the specimens are cooled to room temperature, uniaxial compression tests are carried out on the cylindrical specimens, and Brazilian splitting tests are carried out on the disk specimens. The loading rates are 0.1 mm / min and 0.05 mm / min respectively. Record the Brazilian splitting strength and uniaxial compression stress-strain curves of the specimens after different temperature treatments, as Figure 2 shown.

[0106] Finally, inversely calculate the cohesion temperature-dependent coefficient equation f temp-c and the internal friction angle temperature-dependent coefficient equation and the tensile strength temperature-dependent coefficient equation f temp-t , as Figure 3 shown; the crack slip weakening or strengthening coefficient equation of the residual cohesion and the crack slip weakening / strengthening coefficient equation of the residual internal friction angle as Figure 4 shown.

[0107] Step 3: Establish a numerical geometric model of the rock specimens in the discrete element numerical simulation software, and input the thermodynamic parameters and preliminary constitutive relations of the target rock into the unit body and the contact surface between unit bodies of the numerical geometric model;

[0108] Step 3.1: Generate a 1:1 numerical geometric model of the rock specimens in the discrete element numerical simulation software according to the size of the laboratory rock specimens to be modeled;

[0109] Step 3.2: Traverse the numerical unit bodies in the numerical geometric model according to the proportion of different mineral components in the polycrystalline rock specimens, randomly group the units according to the true mineral proportion measured in Step 2.1, and define them as corresponding mineral crystals;

[0110] Step 3.3: Identify the mineral crystals and the contacts within and between crystals in the numerical geometric model, and assign the thermodynamic parameters and constitutive relations to the crystal units and the contacts between crystals;

[0111] Among them, the crystal units are set as elastic constitutive models, and the constitutive relation of the contacts between crystals is set as the preliminary mathematical expression of the mesoscopic joint constitutive relation of the rock considering the crack slip effect and the temperature effect obtained in Step 1. The coefficient equations in the preliminary mathematical expression are as Figure 3 andFigure 4 as shown

[0112] In this embodiment, a 1:1 numerical geometric model of a rock specimen is established in the discrete element numerical simulation software UDEC, that is, a cylindrical model with a diameter of 0.05 and a length of 0.11, and a disc model with a diameter of 0.05 and a thickness of 0.025;

[0113] Traverse the numerical unit cells in the geometric model, randomly group the unit cells according to the ratio of quartz 44%, feldspar 50%, and mica 6%, and define the unit cells as corresponding mineral crystals, as Figure 5 shown

[0114] Step 4: Copy the laboratory test conditions and conduct parallel numerical simulation tests in the discrete element numerical simulation software;

[0115] Including heating-cooling pretreatment simulation, and conducting uniaxial / triaxial loading and Brazilian splitting test simulation on the pretreated model;

[0116] In this embodiment, copy the laboratory test conditions and conduct parallel heating loading numerical simulation tests on the model established in the discrete element numerical simulation software. Conduct heating-cooling pretreatment on the numerical geometric model, apply an initial temperature of 25°C on the outer surface of the model, and a temperature boundary condition that increases at a rate of 10°C / min. Save the model when the boundary temperature condition reaches 400°C and 600°C respectively; reconstruct the saved model and keep the temperature at 400°C and 600°C until the temperature distribution in the model is uniform; then reduce the boundary temperature condition at a rate of -10°C / min until 25°C, and keep the temperature boundary condition of 25°C until the model temperature completely drops to 25°C. The whole process is as Figure 6 shown

[0117] Conduct uniaxial compression and Brazilian splitting simulation tests on the numerical geometric model, as Figure 7 shown. Apply a loading rate of 2.1×10-2 m / s on the top and bottom boundaries of the cylindrical model, and a loading rate of 2.2×10-3 m / s on the disc model.

[0118] Step 5: Compare the numerical simulation results and the laboratory test results, and use the back analysis method to obtain the coefficient equation required for the mesoscopic joint constitutive relationship of the corresponding rock specimen, and complete the construction of the mesoscopic joint constitutive model of high-temperature rocks;

[0119] Step 5.1: According to the heating and loading numerical simulation test carried out in Step 4, compare the stress-strain relationship and tensile strength of the numerical geometric model and the specimen under load after the same heating-cooling pretreatment. Based on the differences between the simulation results and the test results, modify the initial mechanical parameters of the numerical geometric model, conduct the heating and loading parallel numerical simulation test again, and compare the test results again. Repeat this process until the numerical simulation results are consistent with the test results or within the set error range (less than 10%). Thus, determine the quantitative relationship between the mechanical parameters (cohesion, internal friction angle, tensile strength, residual cohesion, residual internal friction angle, etc.) at different temperatures and the initial mechanical parameters. In this embodiment, the stress-strain curve obtained from the uniaxial compression test of the numerical geometric model is as Figure 8 shown. Comparing Figure 8 with Figure 2 shows that the numerical simulation results are in good agreement with the test results.

[0120] Step 5.2: Based on the obtained quantitative relationships at different temperatures, establish the temperature-dependent coefficient equations for the cohesion of rock specimens at different temperatures, f temp-c , the temperature-dependent coefficient equation for the internal friction angle , the temperature-dependent coefficient equation for the tensile strength, f temp-t , the crack slip weakening / strengthening coefficient equation for the residual cohesion , and the crack slip weakening / strengthening coefficient equation for the residual internal friction angle [[ID=*]]

[0121] Step 5.3: Substitute the obtained temperature-dependent coefficient equations for the cohesion, f temp-c , the temperature-dependent coefficient equation for the internal friction angle , the temperature-dependent coefficient equation for the tensile strength, f temp-t , the crack slip weakening / strengthening coefficient equation for the residual cohesion , and the crack slip weakening / strengthening coefficient equation for the residual internal friction angle into the mechanical relationships (8), (9), and (10) of the corresponding residual shear parameters of the shear crack to complete the construction of the mesoscopic joint constitutive model of high-temperature rock.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features. And these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope defined by the claims of the present invention.

Claims

1. A method for constructing a mesoscopic joint constitutive model of high-temperature rock, characterized in that: It includes the following steps: Step 1: Establish a preliminary mathematical expression for the mesoscopic joint constitutive relation of rock considering crack slip effect and temperature effect; Step 2: Prepare multiple rock specimens, conduct measurement analysis and high-temperature rock mechanics tests on the rock specimens respectively, and obtain the macroscopic physical and mechanical properties of the rock; Step 3: Establish a numerical geometric model of the rock specimen in the discrete element numerical simulation software, and input the thermodynamic parameters and preliminary constitutive relation of the target rock into the element body and the contact surface between element bodies of the numerical geometric model; Step 4: Replicate the laboratory test conditions and conduct parallel numerical simulation tests in the discrete element numerical simulation software; Step 5: Compare the numerical simulation results and the laboratory test results, and use the inverse analysis method to obtain the coefficient equation required for the mesoscopic joint constitutive relation of the corresponding rock specimen, and complete the construction of the high-temperature rock mesoscopic joint constitutive model.

2. The method for constructing a mesoscopic joint constitutive model of high-temperature rock according to claim 1, wherein: The specific method of Step 1 is as follows: Step 1.1: Considering the slip effect of thermal stress cracks under thermo-mechanical coupling, modify the residual cohesion and residual internal friction angle of the Coulomb friction sliding criterion to slip displacement dependence; Step 1.2: Considering the temperature effect under thermo-mechanical coupling, modify the cohesion, internal friction angle, and tensile strength of the Coulomb friction sliding criterion to temperature dependence; Step 1.3: Establish a preliminary mathematical expression for the mesoscopic joint constitutive relation of rock considering crack slip effect and temperature effect.

3. A method for constructing a mesoscopic joint constitutive model of high-temperature rock according to claim 2, characterized in that: In Step 1.1, the expression for the shear parameters of thermal stress cracks affected by slip deformation is: Among them, and are the residual cohesive force and residual internal friction angle affected by the crack slip distance, and are the slip weakening or strengthening coefficient equations of the corresponding residual cohesive force and residual internal friction angle, c0 and are the initial cohesive force and internal friction angle of the rock mesoscopic joint not affected by temperature.

4. A method for constructing a mesoscopic joint constitutive model of high-temperature rock according to claim 3, characterized in that: In step 1.2, considering the temperature effect, the cohesion c0 and the internal friction angle tensile strength σ t0 of the Coulomb friction sliding criterion joint are modified to be temperature-dependent, and the expression is: c temp = f temp-c c0 (3) σ temp-t = f temp-t σ t0 (5) Among them, c temp , σ temp-t are the cohesion, internal friction angle, and tensile strength affected by the temperature effect, respectively; f temp-c , f temp-t are the temperature dependence coefficient equations of cohesion, internal friction angle, and tensile strength, respectively; Under high temperature, the maximum tensile strength T max and the maximum shear strength S max of the mesoscopic joints of rock under the Coulomb friction sliding criterion are modified to temperature dependence as shown in the following formula: T temp-max = -σ temp-t A c = f temp-t σ t0 A c (6) Among them, T temp-max is the maximum tensile strength of the joint with temperature dependence, S temp-max is the maximum shear strength of the joint with temperature dependence, A c is the joint area, F n is the joint normal force.

5. A method for constructing a mesoscopic joint constitutive model of high-temperature rock according to claim 4, characterized in that: In Step 1.3, for tensile cracks, the residual tensile strength is set to 0; for shear cracks, its mechanical behavior is affected by both temperature and crack slip deformation. Therefore, the mechanical relation of the corresponding residual shear parameters of shear cracks becomes the following formula: Among them, and are the residual cohesive force and residual friction angle that simultaneously consider the joint slip effect and temperature effect, is the maximum residual shear strength that simultaneously considers the crack slip effect and temperature effect.

6. The method for constructing a mesoscopic joint constitutive model of high-temperature rock according to claim 5, wherein: The specific method of Step 2 is as follows: Step 2.1: Conduct mineral composition measurement on the target rock specimen; Conduct mineral composition measurement on the target rock specimen to determine the mineral crystal composition and proportion of the rock specimen; Step 2.2: Collect and sort out the thermodynamic properties of all mineral crystals of the rock specimen; Step 2.3: Conduct various high-temperature rock mechanics tests on the rock specimens to obtain the stress-strain curves and tensile strengths of the rock specimens; determine the initial mechanical parameters of the numerical geometric model of the rock specimens according to the stress-strain relationship and tensile strength of the unheated rock specimens; back-calculate the temperature-dependent coefficient equation f of cohesion temp-c and the temperature-dependent coefficient equation of the internal friction angle and the temperature-dependent coefficient equation f of the tensile strength temp-t , the crack slip weakening or strengthening coefficient equation of the residual cohesion and the crack slip weakening / strengthening coefficient equation of the residual internal friction angle 7. A method for constructing a mesoscopic joint constitutive model of high-temperature rock, characterized in that: In step 2.2, the thermodynamic properties of all mineral crystals of the rock specimen are collected and sorted out, where the thermal parameters include the linear thermal expansion coefficient α t , the thermal conductivity k, and the specific heat capacity C p ; the mechanical parameters include: the density ρ m , the Poisson's ratio ν m , the Young's modulus E m , the cohesive force c m , the internal friction angle , and the tensile strength σ tm ; the mechanical properties of the contact surface between mineral crystals are taken as the average of the mechanical parameters of adjacent mineral crystals.

8. A method for constructing a mesoscopic joint constitutive model of high-temperature rock, according to claim 6, characterized in that: In Step 2.3, when conducting various high-temperature rock mechanics tests on the rock specimen, the rock specimen needs to be pre-treated by heating-cooling.

9. A method for constructing a mesoscopic joint constitutive model of high-temperature rock, characterized in that: The specific method of Step 3 is as follows: Step 3.1: Generate a 1:1 numerical geometric model in the discrete element numerical simulation software according to the size of the laboratory rock specimen to be modeled; Step 3.2: Traverse the numerical element bodies in the numerical geometric model according to the proportion of different mineral components in the polycrystalline rock specimen, randomly group the elements according to the true mineral proportion measured in Step 2.1, and define them as corresponding mineral crystals; Step 3.3: Identify the mineral crystals and the contacts within and between crystals in the numerical geometric model, and assign the thermodynamic parameters and constitutive relations to the crystal elements and the contacts between crystals; Among them, the crystal element is set to an elastic constitutive model, and the constitutive relation of the contact surface between crystals is set to the preliminary mathematical expression of the mesoscopic joint constitutive relation of rock considering crack slip effect and temperature effect obtained in Step 1.

10. A method for constructing a mesoscopic joint constitutive model of high-temperature rocks according to claim 9, characterized in that: The specific method of Step 5 is as follows: Step 5.1: According to the heating and loading numerical simulation test carried out in Step 4, compare the stress-strain relationship and tensile strength of the numerical geometric model and the specimen under the action of load after the same heating-cooling pretreatment. Based on the differences between the simulation results and the test results, modify the initial mechanical parameters of the numerical geometric model, conduct the heating and loading parallel numerical simulation test again, and compare the test results again. Repeat this process until the numerical simulation results are consistent with the test results or within the set error range, thereby determining the quantitative relationship between the mechanical parameters at different temperatures and the initial mechanical parameters; Step 5.

2. Based on the obtained quantitative relationships at different temperatures, establish the temperature-dependent coefficient equations for the cohesion of rock specimens at different temperatures, denoted as f temp-c , the temperature-dependent coefficient equation for the internal friction angle , the temperature-dependent coefficient equation for the tensile strength, denoted as f temp-t , the crack slip weakening / reinforcement coefficient equation for the residual cohesion , the crack slip weakening / reinforcement coefficient equation for the residual internal friction angle Step 5.3: Substitute the obtained cohesive force temperature-dependence coefficient equation \(f\) temp-c , the internal friction angle temperature-dependence coefficient equation , the tensile strength temperature-dependence coefficient equation \(f\) temp-t , the crack slip weakening / reinforcement coefficient equation of the residual cohesive force , the crack slip weakening / reinforcement coefficient equation of the residual internal friction angle into the mechanical relationship of the corresponding residual shear parameters of the shear crack to complete the construction of the mesoscopic joint constitutive model of high-temperature rock.

Images