Creep and fatigue equivalent test and analysis method for reconstructed fracture shear seepage

Abstract

A creep and fatigue equivalent test and analysis method for reconstructing fracture shear seepage, comprising the following steps: (1) preparing a master sample of a fractured rock specimen, and performing fracture morphology scanning and internal CT scanning to extract geometric feature data; (2) preparing multiple sub-samples based on the geometric feature data by using fracture surface carving and 3D printing technology; (3) performing direct shear tests on the master sample and some sub-samples, comparing the degree of agreement between stress-strain test curves, and verifying the preparation method of the sub-samples; (4) performing a shear seepage test on the sub-samples, and analyzing the shear stress-shear displacement-time curve; (5) performing a shear seepage creep test on the sub-samples, and analyzing the shear stress-shear displacement-time curve; (6) performing a shear seepage fatigue test on the sub-samples, and analyzing the shear stress-shear displacement-time curve; (7) comparing and analyzing the results of the creep test and the fatigue test, equivalent damage variables are obtained, a method for replacing the creep test with the fatigue test is obtained, and the fatigue long-term strength is calculated.

Description

Technical Field

[0001] The present invention belongs to the field of geotechnical engineering, and in particular relates to a creep and fatigue equivalent test and analysis method for reconstructing fracture shear seepage. Background Art

[0002] Creep is a key mechanical property of rock, often contributing to large deformations and even instability in underground engineering, structure foundations, and slopes. While stress and time are key factors influencing rock creep, the effects of seepage and temperature on creep are also gaining increasing attention. As geotechnical engineering continues to expand into underground spaces, it is crucial to consider the rheological properties of deep rock masses under the influence of both seepage and temperature.

[0003] At present, the research on rock creep at home and abroad is mostly focused on the study of rock creep characteristics under triaxial compression conditions. There is relatively little research on the long-term shear creep mechanism of rock joint stress-seepage coupling. In order to ensure the sealing of the seepage shear box, the maximum seepage water pressure that can be achieved during the test is not high. There are few results involving high seepage water pressure in previous studies.

[0004] In terms of sample preparation, the traditional method is to reconstruct the cracks by water jet cutting or engraving machine cutting on the same material sample. This does not take into account the impact of non-experimental factors on the test caused by the inclination and length of the reconstructed cracks not being completely consistent and the inability to well control the size and length of non-through cracks.

[0005] Creep test loading takes a long time, and there is a lack of high-stiffness and high-stability rock rheology testing equipment, which limits the research on creep characteristics.

[0006] To this end, this invention improves shear tests involving seepage, applying confining pressure during the seepage test to ensure that the rubber sleeve wraps around the specimen and prevents seepage. This ensures the shear box operates normally and stably under high seepage pressure (up to 2 MPa). It also provides a method for creating reconstructed fractured rock specimens by combining fracture surface engraving and 3D printing technology. Furthermore, it uses damage variables to perform equivalent creep and fatigue tests, and uses fatigue test results to estimate the long-term strength of the specimen.

[0007] The current status of relevant rock creep property tests in China is as follows:

[0008] 1. The article "Experimental Study on Dynamic Mechanical Failure Characteristics of Marble Containing Prefabricated Fractures Using SHPB" describes a dynamic compression test on marble specimens containing prefabricated fractures using an SHPB device (see "Chinese Journal of Rock Mechanics and Engineering," Issue 12, 2017, by Li Diyuan and Han Zhenyu). In this article, a split-Hopkinson pressure bar (SHPB) test platform was used to conduct dynamic compression tests on marble from Leiyang City, Hunan Province. The traditional method of cutting prefabricated fractures in natural rock was used, but the problem of prefabricated fractures not being able to be completely consistent in inclination and length within the same specimen was overlooked.

[0009] 2. The paper "Study on a Constitutive Model of Granite Creep Process Considering Temperature Effects" conducted experimental studies on creep characteristics of Beishan granite under different temperature conditions. Combining the damage evolution laws during rock creep failure, a new high-temperature damage rheological element was proposed. However, this experiment did not consider seepage effects, which is significantly different from actual deep rock conditions.

[0010] 3. The article "Development of a rock joint shear-seepage coupling test system" studied the development and research of a rock joint shear-seepage coupling test system (see "Chinese Journal of Rock Mechanics and Engineering", Issue 6, 2008, author: Xia Caichu, et al.), and introduced the composition and functions of the test system in detail. However, its permeability pressure only reached 0.5 MPa, which is difficult to promote in deep rock research with high permeability water pressure. Summary of the Invention

[0011] In order to overcome the deficiencies of the prior art, the present invention provides a creep and fatigue equivalent test and analysis method for reconstructing fracture shear seepage.

[0012] To achieve the above object, the present invention adopts the following technical solutions:

[0013] The creep and fatigue equivalent test and analysis method for reconstructing fracture shear seepage is as follows:

[0014] (1) Prepare a fractured rock sample as a master sample, perform CT scanning of the fracture surface morphology and the internal pore and fracture structure, and extract the geometric characteristic data of the fractured rock sample;

[0015] (2) Based on the geometric feature data, multiple reconstructed fractured rock specimens are processed and manufactured as sub-samples using fracture surface carving and 3D printing technology, so that the reconstructed fractures replicate the fracture geometric features of the parent sample;

[0016] (3) Conduct direct shear tests on the parent sample and some sub-samples of the fractured rock specimen, compare the degree of agreement between the stress-strain test curves of the sub-samples and the parent sample stress-strain test curves, and verify the preparation method of the reconstructed fractures of the sub-samples that can reflect the mechanical properties of the parent sample;

[0017] (4) Using reconstructed fractured rock specimens, conduct shear seepage tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions;

[0018] (5) Using reconstructed fractured rock specimens, conduct shear seepage creep tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions;

[0019] (6) Using reconstructed fractured rock specimens, conduct shear seepage fatigue tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions;

[0020] (7) Comparative analysis of the test results of the reconstructed fracture shear seepage creep test and the reconstructed fracture shear seepage fatigue test was conducted. Through equivalent damage variables, a method of replacing the reconstructed fracture shear seepage creep test with the reconstructed fracture shear seepage fatigue test was obtained, and the fatigue long-term strength was calculated based on the fatigue test data.

[0021] (8) Draw the fatigue limit trajectory and creep limit trajectory through long-term fatigue strength. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Flowchart of creep and fatigue equivalent test and analysis methods for reconstructing fracture shear seepage;

[0023] Figure 2 This is the principle diagram of the rock stress-seepage coupled shear rheology test system;

[0024] Figure 3 is the isochronous stress-strain curve;

[0025] Figure 4 Schematic diagram of the variables for reconstructing the damage variable calculation formula for fracture shear seepage fatigue test;

[0026] Figure 5 Schematic diagram of the calculation formula for damage variables in the reconstruction of fracture shear seepage creep test;

[0027] Figure 6 This is the strain diagram for reconstructing the fracture shear seepage fatigue test;

[0028] Figure 7 is the fatigue limit locus line diagram;

[0029] Figure 8 is the creep limit locus line diagram;

[0030] Figure 9 A simplified flow chart of the creep and fatigue equivalent test and analysis method for reconstructing fracture shear seepage; DETAILED DESCRIPTION

[0031] like Figure 1 As shown in Figure 2, the creep and fatigue equivalent test and analysis method for reconstructing fracture shear seepage is as follows:

[0032] 1. Prepare a fractured rock sample as a master sample, perform a CT scan of the fracture surface morphology and the internal pore and fracture structure, and extract the geometric characteristic data of the fractured rock sample. The specific method is as follows:

[0033] A regular cylindrical rock sample with a diameter of 25 mm and a height of 50 mm was prepared as a parent sample. Using the Brazilian splitting test, the parent sample was split into two parts containing rough fracture surfaces, designated as parent sample fracture surface 1 and parent sample fracture surface 2. CT scanning technology was used to obtain the geometric shape, size, spatial distribution, and interconnectedness of the parent sample's pores through incident X-rays. A non-contact laser topography scanner was used to obtain geometric characteristic data of the parent sample's rough fracture surface morphology parameters, such as roughness, average aperture, and joint roughness coefficient (JRC).

[0034] 2. Based on the geometric feature data, fracture surface engraving and 3D printing technology are used to process and produce multiple reconstructed fracture rock specimens as sub-samples, so that the reconstructed fractures replicate the fracture geometric features of the parent sample. The specific method is as follows:

[0035] The rock sample to be reconstructed with fractures is cut into two uniform pieces along the longitudinal axis using a cutting machine to form smooth cross sections, which are recorded as section 1 to be processed and section 2 to be processed.

[0036] Based on the geometric feature data of the rough crack surface morphology parameters of the mother sample obtained by a non-contact laser topography scanner, a high-precision mechanical engraving machine is used to perform three-dimensional engraving on the surface of the to-be-processed section 1 and the to-be-processed section 2, and the crack morphologies of the mother sample crack surface 1 and the mother sample crack surface 2 are reconstructed as sub-samples; the crack morphologies of the engraved sub-sample crack surface 1 and the sub-sample crack surface 2 are laser scanned to obtain the geometric feature data of their crack surface morphology parameters, and the degree of completeness of the reconstructed sub-sample crack surface in replicating the geometric features of the mother sample crack surface is checked;

[0037] For the areas where the fracture morphology of sub-sample fracture surface 1 and sub-sample fracture surface 2 is partially incomplete due to the carving accuracy and fails to perfectly replicate the geometric features of the parent sample fracture surface, 3D printing technology is used to fill in the partially incomplete areas; based on the geometric feature data of the parent sample extracted by non-contact laser morphology scanning and CT scanning, a triangular mesh model (STL) is constructed, and the STL file of the core skeleton is constructed using Avizo software. It is imported into the 3D printer, and the information discretization of the model is completed by setting the printing parameters to start the printing work; the appropriate 3D printing raw materials are determined through ratio tests, and the strength parameters of the raw materials are close to those of the parent rock, with an error of no more than 5%; phenolic resin-coated quartz sand beads (coated silica) are selected. Beads (CBS) were used as the printing matrix material, and selective laser sintering (SLS) technology was used. Phenolic resin was used as the binder to prepare the 3D printing material. The excellent high-temperature resistance of phenolic resin was utilized to obtain the repaired sub-sample crack surface 3 and sub-sample crack surface 4 produced by 3D printing. The samples were water-saturated: the processed samples were placed in 25°C water and soaked for 60 hours to fully saturate the samples. Subsequently, the samples were stored in a constant temperature and humidity chamber.

[0038] 3. Conduct direct shear tests on the parent sample and some sub-samples of the fractured rock specimen, compare the degree of agreement between the stress-strain test curves of the sub-samples and the parent sample, and verify the preparation method of the fracture reconstruction of the sub-samples that can reflect the mechanical properties of the parent sample. The specific method is as follows:

[0039] The parent sample and sub-sample of the saturated reconstructed fractured rock specimen were placed on a rock shear rheology tester for direct shear tests. The shear box was positioned, and then the specimens were preloaded with normal stress and shear stress. The normal stress was first applied to 4 MPa at a loading rate of 0.05 MPa / s. Then, the normal stress was kept constant and shear stress was applied to the specimen at a shear rate of 0.1 mm / min until shear failure. By comparing the degree of agreement between the stress-strain test curves of the sub-sample and the parent sample, the mechanical properties of the reconstructed fractured rock specimens produced by fracture surface carving and 3D printing technology were checked, and the sub-sample peak strength was obtained as the loading basis for subsequent rheological and fatigue tests.

[0040] 4. Using the reconstructed fractured rock specimens, conduct shear seepage tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions. The specific methods are as follows:

[0041] The rock fracture surface shear seepage test device was used to conduct reconstructed fracture shear seepage tests under different working conditions. The principle of the test system is shown in Figure 2The test was carried out in five groups at 0℃, 50℃, 100℃, 150℃ and 200℃, using graded loading. The specific grading method was as follows: the shear stress τ was selected as 20%, 40%, 60%, 80% and 100% of the peak strength in step 3 respectively. The specific loading target value was adjusted according to the situation during the test; the sub-sample was placed on a rock shear rheology tester for shear seepage test. The sub-sample was sealed with a special high-temperature resistant rubber sleeve. Under the action of confining pressure, the sub-sample was wrapped around to achieve anti-seepage. The shear box was positioned, and then the sub-sample was pre-loaded vertically and tangentially. The confining pressure of 2MPa was first applied at a loading speed of 0.05MPa / s, and then the confining pressure was kept unchanged and the normal stress was applied at a rate of 0.05MPa / s to 4MPa, after the load is stable, start the constant pressure and constant speed pump, maintain the seepage water pressure of 2.0MPa at the water inlet and the atmospheric pressure at the water outlet, and turn on the temperature control switch to keep the triaxial chamber at a constant temperature after the seepage water volume is stable; conduct a shear test on the sub-sample, load the shear stress τ to the first-level stress value at a loading speed of 0.05MPa / s, and load it to the next-level stress value at a rate of 0.05MPa / s after the seepage water volume is stable; according to the test results of the shear seepage test, apply the Boltzmann principle for superposition, and use temperature as a parameter to draw the shear characteristic curves of shear stress τ-shear strain γ and shear strain γ-time t at different temperatures to determine the instantaneous shear strength under different temperatures and shear stresses;

[0042] Special high temperature resistant rubber sleeve is applicable to temperature of 0-400℃, can withstand confining pressure of 0-200MPa, is resistant to acid and alkali corrosion, and has ultra-low permeability;

[0043] 5. Using the reconstructed fractured rock specimens, conduct shear seepage creep tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions. The specific methods are as follows:

[0044] The test was carried out in five groups at 0℃, 50℃, 100℃, 150℃ and 200℃, using graded loading. The specific grading method was as follows: the shear stress was selected as 20%, 40%, 60%, 80% and 100% of the peak strength in step 3 respectively. The specific loading target value was adjusted according to the situation during the test; the sub-sample was placed on a rock shear rheology tester for shear seepage test, and the sub-sample was sealed with a special high-temperature resistant rubber sleeve. Under the action of confining pressure, the sub-sample was wrapped to achieve waterproofing. The shear box was positioned, and then the sample was pre-loaded vertically and tangentially. First, a confining pressure of 2MPa was applied at a loading speed of 0.05MPa / s, and then the confining pressure was kept constant. The normal stress was applied to 4MPa at a rate of 0.05MPa / s. After the loading was stable, the constant pressure and constant speed pump was started, and the water inlet was kept at The seepage water pressure is 2.0MPa, and the atmospheric pressure at the outlet is kept constant. When the seepage volume is stable, turn on the temperature control switch to keep the triaxial chamber at a constant temperature. The sub-sample is subjected to a shear seepage creep test, and the sample is subjected to the first-level active shear loading. The shear stress τ is 20% of the peak strength and is maintained for about 24 hours. When the creep deformation value of the sub-sample is less than 0.001mm / 2h, it is considered that the creep deformation has reached stability, and the next level of loading is carried out at a rate of 0.05MPa / s. According to the test results of the shear seepage creep test, the Boltzmann principle is applied for superposition, and the shear characteristic curves of shear stress τ-shear strain γ and shear strain γ-time t are drawn with temperature as a parameter. Then, according to the step creep results, the shear strain value at the same time after each level of loading is selected, and the following is obtained: Figure 3 , isochronous stress-strain curve;

[0045] 6. Using the reconstructed fractured rock specimens, conduct shear seepage fatigue tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions. The specific methods are as follows:

[0046] The test was carried out in five groups at 0℃, 50℃, 100℃, 150℃ and 200℃, using constant lower limit graded fatigue loading. The specific grading method was: the shear stress was selected as 20%, 40%, 60%, 80% and 100% of the peak strength in step 3 respectively. The specific loading target value was adjusted according to the situation during the test; the sub-sample was placed on a rock shear rheology tester for shear seepage test, and the sub-sample was sealed with a special high-temperature resistant rubber sleeve. Under the action of confining pressure, the sub-sample was wrapped to achieve anti-seepage, the shear box was positioned, and then the sub-sample was pre-loaded vertically and tangentially. The confining pressure was first applied to 2MPa at a loading speed of 0.05MPa / s, and then the confining pressure was kept constant, and the normal stress was applied to 4MPa at a rate of 0.05MPa / s. After the loading was stable, the constant pressure and constant speed pump was started, the water inlet maintained a seepage water pressure of 2.0MPa, and the water outlet maintained atmospheric pressure. After the seepage volume stabilized, the temperature control switch was turned on to keep the triaxial chamber constant. Temperature; a shear seepage fatigue test was conducted on the sub-sample. In this experiment, only one loading waveform and frequency were used to study the effects of different upper limit stresses on the fatigue failure process. The upper limit stress of the cyclic load was the shear stress value of that level. The cyclic load frequency was set to 0.1 Hz, the loading waveform was a sine wave, and the loading path was a constant lower limit loading, that is, each time the shear stress was loaded to the target value, it was unloaded to 10% of the peak strength. When the tangential strain rate of the sub-sample was less than 0.001 mm / 2 h, the deformation was considered to have reached stability, and then an axial pressure was applied at a rate of 0.05 MPa / s to the lower stress value. Based on the test results of the shear seepage fatigue test, the Boltzmann principle was applied for superposition, and the shear characteristic curves of shear stress τ-shear strain γ and shear strain γ-time t were plotted with temperature as a parameter. The strain value corresponding to the upper limit stress of the cyclic load was extracted, and the shear strain γ-time t curve corresponding to the upper limit stress was plotted.

[0047] 7. Comparative analysis of the test results of the reconstructed fracture shear seepage creep test and the reconstructed fracture shear seepage fatigue test was conducted. By using equivalent damage variables, a method for replacing the reconstructed fracture shear seepage creep test with the reconstructed fracture shear seepage fatigue test was obtained. The long-term fatigue strength was calculated based on the fatigue test data. The specific method is as follows:

[0048] Creep loading mode, that is, the sample is loaded with a fixed stress level for a long time, and the stress amplitude of the fixed stress is 0. In this case, the creep test is equivalent to a fatigue loading test with an infinite number of cycles and the stress amplitude approaches 0. Compared with the perturbation stress level, the frequency and waveform of the perturbation load have a secondary effect on fatigue.

[0049] The specific equivalent methods are as follows:

[0050] Damage variable D under fatigue loading Fatigue :

[0051]

[0052] Where: E——initial elastic modulus of the sample;

[0053] E'——specimen fatigue unloading elastic modulus;

[0054] γ——shear strain;

[0055] γ'——fatigue unloading residual strain;

[0056] The specific meanings of the variables in the damage variable formula of the reconstructed fracture shear seepage fatigue test are shown in Figure 4 ;

[0057] Damage variable D under creep loading Creep :

[0058]

[0059] Where: E——initial elastic modulus of the sample;

[0060] E t ——creep elastic modulus at any moment;

[0061] The specific meanings of the variables in the damage variable formula of the reconstructed fracture shear seepage creep test are given in Figure 5 ;

[0062] According to the above two equations, the damage variables in each cycle and the damage variables at any moment in the creep process are calculated respectively. According to the equivalent relationship of damage variables D Creep =D Fatigue , the strain value corresponding to the upper limit stress of the reconstructed fracture shear seepage fatigue test is equivalent to the strain value corresponding to the fixed stress in the reconstructed fracture shear seepage creep test, and a typical creep process curve is obtained;

[0063] The long-term fatigue strength of the specimen is calculated using the results of the reconstructed fracture shear seepage fatigue test. The long-term fatigue strength of the specimen is the stress level when the viscoplastic strain rate approaches 0. The long-term fatigue strength of the specimen is derived by establishing a functional relationship between the stress level and the viscoplastic strain rate.

[0064] γ vp =γ-γ ep -γ ve

[0065] Where: γ vp ——viscoplastic strain;

[0066] γ——total shear strain;

[0067] γ ep ——instantaneous strain;

[0068] γ ve——Viscoelastic strain;

[0069] where γ and γ ep It is directly measured by the reconstructed fracture shear seepage fatigue test, using constant lower limit graded fatigue loading. When unloading to the lower limit stress, γ ve It is the sum of the viscoelastic strain measured at a lower stress level and the viscoelastic strain recovered after unloading. The specific meaning of the variable is shown in Figure 6 ;

[0070] The viscoplastic strain rate is expressed as

[0071]

[0072] Where: η2——Plastic viscosity coefficient

[0073] ——Long-term shear strength

[0074] When shear stress hour

[0075]

[0076] When shear stress hour

[0077]

[0078] Further expressed as

[0079]

[0080] The viscoplastic strain rate obtained from the reconstructed fracture shear seepage fatigue test Plotted against the corresponding shear stress τ in the coordinate system, multiple sets of viscoplastic strain rate and corresponding shear stress data points are obtained through graded loading fatigue tests, and a straight line is obtained by fitting. The intercept of the straight line is the long-term fatigue strength of the sample.

[0081] 8. Draw the fatigue limit trajectory and creep limit trajectory through long-term fatigue strength. The specific method is as follows:

[0082] When the shear stress level is lower than the fatigue long-term strength When , due to its low shear stress level, the fatigue process curve obtained by reconstructing the strain value corresponding to the upper limit stress of the fracture shear seepage fatigue test will not have a non-steady-state fatigue stage. At this time, the sub-sample will not be damaged, and its final shear strain can be found in the fatigue limit trajectory.

[0083] Using the same idea, the stress values of each level of graded loading are extracted, and the reconstructed fracture shear seepage fatigue test is carried out by loading separately to obtain the ultimate strain values corresponding to different upper limit stress conditions, and connect the ultimate strain values corresponding to different loads and the fatigue initiation stress. and fatigue long-term strength Obtain fatigue limit trajectory, such as Figure 7 ; The fatigue limit locus is equivalently represented to reconstruct the creep limit locus of the fracture shear seepage creep test and obtain the creep initiation stress and creep long-term strength like Figure 8 .

Claims

1. A creep and fatigue equivalent test and analysis method for reconstructing fracture shear seepage, characterized in that: The specific steps are as follows: (1) Prepare a fractured rock sample as a master sample, perform CT scanning of the fracture surface morphology and the internal pore and fracture structure, and extract the geometric characteristic data of the fractured rock sample; (2) Based on the geometric feature data, multiple reconstructed fractured rock specimens are processed and manufactured as sub-samples using fracture surface carving and 3D printing technology, so that the reconstructed fractures replicate the fracture geometric features of the parent sample; The specific method is as follows: The rock sample to be reconstructed with fractures is cut into two uniform pieces along the longitudinal axis using a cutting machine to form smooth cross sections, which are recorded as section 1 to be processed and section 2 to be processed. Based on the geometric feature data of the rough crack surface morphology parameters of the mother sample obtained by a non-contact laser topography scanner, a high-precision mechanical engraving machine is used to perform three-dimensional engraving on the surface of the to-be-processed section 1 and the to-be-processed section 2, and the crack morphologies of the mother sample crack surface 1 and the mother sample crack surface 2 are reconstructed as sub-samples; the crack morphologies of the engraved sub-sample crack surface 1 and the sub-sample crack surface 2 are laser scanned to obtain the geometric feature data of their crack surface morphology parameters, and the degree of completeness of the reconstructed sub-sample crack surface in replicating the geometric features of the mother sample crack surface is checked; For areas of the fracture morphology of sub-sample fracture surface 1 and sub-sample fracture surface 2 where local defects caused by carving accuracy failed to perfectly replicate the geometric features of the parent sample fracture surface, 3D printing technology was used to complete the local defective areas. A triangular mesh model was constructed based on the parent sample geometric feature data extracted by non-contact laser morphology scanning and CT scanning. A triangular mesh model file of the core skeleton was constructed using Avizo software and imported into the 3D printer. The information of the model was discretized by setting the printing parameters and printing began. Suitable 3D printing raw materials were determined through ratio testing. The strength parameters of the raw materials were similar to those of the parent rock, with an error of no more than 5%. Phenolic resin-coated quartz sand beads were selected as the printing matrix material. Selective laser sintering technology was used to prepare the 3D printing material with phenolic resin as the binder. Taking advantage of the excellent high-temperature resistance of phenolic resin, the repaired sub-sample fracture surface 3 and sub-sample fracture surface 4 were obtained by 3D printing. The samples were water-saturated: the processed samples were placed in 25°C water and soaked for 60 hours to fully saturate the samples. Subsequently, the samples were stored in a constant temperature and humidity chamber. (3) Conduct direct shear tests on the parent sample and some sub-samples of the fractured rock specimen, compare the degree of agreement between the stress-strain test curves of the sub-samples and the parent sample, and verify the preparation method of the reconstructed fractures of the sub-samples that can reflect the mechanical properties of the parent sample; The specific method is as follows: The parent sample and sub-sample of the saturated reconstructed fractured rock specimen were placed on a rock shear rheology tester for direct shear tests. The shear box was positioned, and then the specimens were preloaded with normal stress and shear stress. The normal stress was first applied to 4 MPa at a loading rate of 0.05 MPa / s. Then, the normal stress was kept constant and shear stress was applied to the specimen at a shear rate of 0.1 mm / min until shear failure. By comparing the degree of agreement between the stress-strain test curves of the sub-sample and the parent sample, the mechanical properties of the reconstructed fractured rock specimens produced by fracture surface carving and 3D printing technology were checked, and the sub-sample peak strength was obtained as the loading basis for subsequent rheological and fatigue tests. (4) Using reconstructed fractured rock specimens, conduct shear seepage tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions; (5) Using reconstructed fractured rock specimens, conduct shear seepage creep tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions; (6) Using reconstructed fractured rock specimens, conduct shear seepage fatigue tests at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions; (7) Comparative analysis of the test results of the reconstructed fracture shear seepage creep test and the reconstructed fracture shear seepage fatigue test was conducted. Through equivalent damage variables, a method of replacing the reconstructed fracture shear seepage creep test with the reconstructed fracture shear seepage fatigue test was obtained, and the fatigue long-term strength was calculated based on the fatigue test data. (8) Draw the fatigue limit trajectory and creep limit trajectory through long-term fatigue strength.

2. The creep and fatigue equivalent test and analysis method for reconstructed fracture shear seepage according to claim 1 is characterized in that: Prepare a fractured rock sample as a master sample, perform a fracture surface morphology scan and a CT scan of the internal pore and fracture structure, and extract the geometric characteristic data of the fractured rock sample. The method is as follows: A cylindrical rock sample with a diameter of 25 mm and a height of 50 mm was made as a mother sample. The mother sample was split into two parts containing rough fracture surfaces through the Brazilian splitting test, which were recorded as mother sample fracture surface 1 and mother sample fracture surface 2. CT scanning technology was used to obtain the geometric shape, size, spatial distribution and interconnectedness of the mother sample pores through incident X-rays. The geometric characteristic data of the morphological parameters of the rough fracture surface of the mother sample, including roughness, average opening and joint surface roughness coefficient, were obtained through a non-contact laser topography scanner.

3. The creep and fatigue equivalent test and analysis method for reconstructed fracture shear seepage according to claim 1 is characterized in that: Using reconstructed fractured rock specimens, shear seepage tests were conducted at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions. The method is as follows: A rock fracture surface shear seepage test device was used to conduct reconstructed fracture shear seepage tests under different working conditions. The test was conducted in five groups at 0℃, 50℃, 100℃, 150℃ and 200℃. Graded loading was used. The specific graded method was as follows: the shear stress τ was selected as 20%, 40%, 60%, 80% and 100% of the peak strength respectively. The specific loading target value was adjusted according to the situation during the test. The sub-sample was placed on the rock shear rheology tester for shear seepage test. The sub-sample was sealed with a special high-temperature resistant rubber sleeve. Under the action of confining pressure, the sub-sample was wrapped around to achieve anti-seepage. The shear box was positioned, and then the sub-sample was vertically Preload in the longitudinal and tangential directions, first apply a confining pressure of 2MPa at a loading rate of 0.05MPa / s, then keep the confining pressure constant and apply normal stress to 4MPa at a rate of 0.05MPa / s. After the loading is stable, start the constant pressure and constant speed pump, maintain the seepage water pressure of 2.0MPa at the water inlet and the atmospheric pressure at the water outlet. After the seepage volume is stable, turn on the temperature control switch to keep the triaxial chamber at a constant temperature; carry out a shear test on the sub-sample, load the shear stress τ to the first-level stress value at a loading rate of 0.05MPa / s, and after the seepage water volume is stable, load it to the next-level stress value at a rate of 0.05MPa / s; According to the results of shear seepage test, Boltzmann principle is applied for superposition. With temperature as parameter, shear characteristic curves of shear stress τ-shear strain γ and shear strain γ-time t at different temperatures are drawn to determine the instantaneous shear strength under different temperatures and shear stresses. The specially made high temperature resistant rubber sleeve is suitable for temperatures of 0-400℃, can withstand a confining pressure of 0-200MPa, is resistant to acid and alkali corrosion, and has an ultra-low permeability.

4. The creep and fatigue equivalent test and analysis method for reconstructed fracture shear seepage according to claim 1 is characterized in that: Using reconstructed fractured rock specimens, shear seepage creep tests were conducted at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions. The method is as follows: The test was conducted at five groups of temperatures of 0°C, 50°C, 100°C, 150°C and 200°C, using graded loading. The specific grading method was as follows: the shear stress was selected as 20%, 40%, 60%, 80% and 100% of the peak strength respectively. The specific loading target value was adjusted according to the situation during the test. The sub-sample was placed on a rock shear rheology tester for a shear seepage test. The sub-sample was sealed with a special high-temperature resistant rubber sleeve. Under the action of confining pressure, the sub-sample was wrapped to achieve waterproofing. The shear box was positioned, and then the sample was pre-loaded vertically and tangentially. A confining pressure of 2MPa was first applied at a loading rate of 0.05MPa / s, and then the confining pressure was kept constant. The normal stress was applied to 4MPa at a rate of 0.05MPa / s. After the loading was stable, the constant pressure and constant speed pump was started, and the water inlet was maintained at 2.0MPa. The seepage water pressure is maintained at atmospheric pressure at the outlet. When the seepage volume stabilizes, the temperature control switch is turned on to keep the triaxial chamber at a constant temperature. A shear seepage creep test is carried out on the sub-sample, and the sample is subjected to the first-level active shear loading. The shear stress τ is 20% of the peak strength and is maintained for about 24 hours. When the creep deformation value of the sub-sample is less than 0.001mm / 2h, the creep deformation is considered to have reached stability, and the next level of loading is carried out at a rate of 0.05MPa / s. Based on the test results of the shear seepage creep test, the Boltzmann principle is applied for superposition, and the shear characteristic curves of shear stress τ-shear strain γ and shear strain γ-time t are plotted with temperature as the parameter. Then, based on the step creep results, the shear strain value at the same time after each level of loading is selected to obtain the isochronous stress-strain curve.

5. The creep and fatigue equivalent test and analysis method for reconstructed fracture shear seepage according to claim 1 is characterized in that: Using reconstructed fractured rock specimens, shear seepage fatigue tests were conducted at different temperatures to analyze the shear stress-shear displacement-time curves under different working conditions. The method is as follows: The test was carried out in five groups at 0℃, 50℃, 100℃, 150℃ and 200℃, using constant lower limit graded fatigue loading. The specific grading method was as follows: the shear stress was selected as 20%, 40%, 60%, 80% and 100% of the peak strength respectively. The specific loading target value was adjusted according to the situation during the test. The sub-sample was placed on a rock shear rheology tester for shear seepage test. The sub-sample was sealed with a special high-temperature resistant rubber sleeve. Under the action of confining pressure, the sub-sample was wrapped around to achieve waterproofing. The shear box was positioned, and then the sub-sample was pre-loaded vertically and tangentially. The confining pressure was first applied to 2MPa at a loading speed of 0.05MPa / s, and then the confining pressure was kept constant. The normal stress was applied to 4MPa at a rate of 0.05MPa / s. After the loading was stable, the constant A constant-speed pump was used to maintain a seepage water pressure of 2.0 MPa at the water inlet and atmospheric pressure at the water outlet. After the seepage volume stabilized, the temperature control switch was turned on to keep the triaxial chamber at a constant temperature. A shear seepage fatigue test was conducted on the sub-sample. In this experiment, only one loading waveform and frequency were used to study the effects of different upper limit stresses on the fatigue failure process. The upper limit stress of the cyclic load was the shear stress value of that level. The cyclic load frequency was set to 0.1 Hz, the loading waveform was a sine wave, and the loading path was a constant lower limit loading, that is, each time the shear stress was loaded to the target value, it was unloaded to 10% of the peak strength. When the tangential strain rate of the sub-sample was less than 0.001 mm / 2 h, the deformation was considered to have reached stability, and then an axial pressure was applied at a rate of 0.05 MPa / s to the lower stress value. According to the test results of shear seepage fatigue test, the Boltzmann principle was applied for superposition, and the shear characteristic curves of shear stress τ-shear strain γ and shear strain γ-time t were plotted with temperature as the parameter. The strain value corresponding to the upper limit stress of cyclic load was extracted, and the upper limit stress corresponding to shear strain γ-time t curve was plotted.

6. The creep and fatigue equivalent test and analysis method for reconstructed fracture shear seepage according to claim 1 is characterized in that: The test results of the reconstructed fracture shear seepage creep test and the reconstructed fracture shear seepage fatigue test were compared and analyzed. By using equivalent damage variables, a method for replacing the reconstructed fracture shear seepage creep test with the reconstructed fracture shear seepage fatigue test was obtained. The long-term fatigue strength was calculated based on the fatigue test data as follows: Creep loading mode, that is, the sample is loaded with a fixed stress level for a long time, and the stress amplitude of the fixed stress is 0. In this case, the creep test is equivalent to a fatigue loading test with an infinite number of cycles and the stress amplitude approaches 0. Compared with the perturbation stress level, the frequency and waveform of the perturbation load have a secondary effect on fatigue. The specific equivalent methods are as follows: Damage variable D under fatigue loading Fatigue : Where: E——initial elastic modulus of the sample; E'——specimen fatigue unloading elastic modulus; γ——shear strain; γ'——fatigue unloading residual strain; Damage variable D under creep loading Creep : Where: E——initial elastic modulus of the sample; E t ——creep elastic modulus at any moment; According to the above two equations, the damage variables in each cycle and the damage variables at any moment in the creep process are calculated respectively. According to the equivalent relationship of damage variables D Creep =D Fatigue , the strain value corresponding to the upper limit stress of the reconstructed fracture shear seepage fatigue test is equivalent to the strain value corresponding to the fixed stress in the reconstructed fracture shear seepage creep test, and a typical creep process curve is obtained; The long-term fatigue strength of the specimen is calculated using the results of the reconstructed fracture shear seepage fatigue test. The long-term fatigue strength of the specimen is the stress level when the viscoplastic strain rate approaches 0. The long-term fatigue strength of the specimen is derived by establishing a functional relationship between the stress level and the viscoplastic strain rate. c vp =γ-γ ep -c ve Where: γ vp ——viscoplastic strain; γ——total shear strain; γ ep ——instantaneous strain; γ ve ——Viscoelastic strain; where γ and γ ep It is directly measured by the reconstructed fracture shear seepage fatigue test, using constant lower limit graded fatigue loading. When unloading to the lower limit stress, γ ve It is the sum of the viscoelastic strain measured at a lower stress level and the viscoelastic strain recovered by unloading; The viscoplastic strain rate is expressed as Where: η2——Plastic viscosity coefficient ——Long-term shear strength When shear stress hour When shear stress hour Further expressed as The viscoplastic strain rate obtained from the reconstructed fracture shear seepage fatigue test Plotted against the corresponding shear stress τ in the coordinate system, multiple sets of viscoplastic strain rate and corresponding shear stress data points are obtained through graded loading fatigue tests, and a straight line is obtained by fitting. The intercept of the straight line is the long-term fatigue strength of the sample.

7. The creep and fatigue equivalent test and analysis method for reconstructed fracture shear seepage according to claim 1 is characterized in that: The fatigue limit locus and creep limit locus are drawn by long-term fatigue strength as follows: Shear stress levels are lower than fatigue long-term strength When , due to its low shear stress level, the fatigue process curve obtained by reconstructing the strain value corresponding to the upper limit stress of the fracture shear seepage fatigue test will not have a non-steady-state fatigue stage. At this time, the sub-sample will not be damaged, and its final shear strain can be found in the fatigue limit trajectory. Using the same idea, the stress values of each level of graded loading are extracted, and the reconstructed fracture shear seepage fatigue test is carried out by loading separately to obtain the ultimate strain values corresponding to different upper limit stress conditions, and connect the ultimate strain values corresponding to different loads and the fatigue initiation stress. and fatigue long-term strength Obtain the fatigue limit trajectory; equivalently represent the fatigue limit trajectory to reconstruct the creep limit trajectory of the fracture shear seepage creep test and obtain the creep initiation stress and creep long-term strength

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