Calibration method for finite-discrete element input parameters of water-containing rock

Abstract

The invention discloses a method for calibrating finite-discrete element input parameters of a water-containing rock, which comprises the following steps of: respectively carrying out a uniaxial tensile test, a uniaxial compression test and a triaxial compression test on a dry rock sample and rock samples with different water contents; obtaining an evolution equation of the tensile strength along with the moisture content, an evolution equation of the elastic modulus and the uniaxial compressive strength along with the moisture content, and an evolution equation of the cohesive force and the internal friction angle along with the moisture content; carrying out a lateral constraint water absorption swelling test on the dry rock to obtain a vertical expansion evolution curve; on the basis of the obtained results, the fracture energy, the humidity expansion coefficient and the humidity diffusion coefficient in the finite-discrete element method are calibrated; on the basis of the calibration parameters, finite-discrete element uniaxial and triaxial compression numerical simulation of the rock samples with different water contents is carried out, and simulation results are obtained; and when the error between the test result and the simulation result is within a preset threshold value, obtaining a final parameter calibration result. The invention provides a simple, accurate and efficient parameter calibration means for water-rock interaction mechanism research.

Description

Technical Field

[0001] The invention belongs to the technical fields of rock mechanics, geotechnical engineering and numerical simulation, and in particular relates to a calibration method for finite-discrete element input parameters of water-bearing rock. Background Art

[0002] Water-rock interaction has long been a hot topic in rock mechanics and geotechnical engineering. Water absorption by rocks causes numerous natural and engineering disasters, including rainfall-induced landslides, rainfall-induced rock slope instability, landslides induced by reservoir water level fluctuations, sudden water inrush in tunnels, and large deformation and damage caused by water absorption in soft rock tunnels. Therefore, research on the mechanisms of water-rock interaction is urgently needed.

[0003] Currently, existing technologies for studying water-rock interactions are primarily divided into two categories: laboratory experiments and numerical simulations. Laboratory experiments encompass testing the mechanical properties of water-bearing rocks, such as Brazilian splitting, uniaxial tension, uniaxial compression, and triaxial compression, as well as microstructural observations. These experiments utilize methods such as scanning electron microscopy, environmental scanning microscopy, X-ray diffraction, computed tomography, energy dispersive spectroscopy, and mercury intrusion porosimetry. These experiments aim to reveal the evolution of mechanical properties and micro- and macrostructural changes in rocks before and after water absorption, thereby exploring the mechanisms by which water causes rock degradation. However, laboratory experiments suffer from limitations such as high cost, long lead times, and low reproducibility of results, limiting their widespread application.

[0004] In numerical simulation, continuum-based finite element methods, finite difference methods, extended finite element methods, and real-world fracture process analysis methods, as well as discontinuum-based discrete element methods, block discrete element methods, particle discrete element methods, and discontinuous deformation methods, have been used to study rock mechanics. However, continuum methods require the introduction of cohesive elements when simulating rock cracking, making it difficult to accurately capture crack initiation and imposing significant constraints. Discontinuum methods, on the other hand, face challenges such as complex parameter calibration, difficulty in aligning macroscopic and microscopic parameters, and non-intuitive crack morphology, resulting in significant deficiencies in rock cracking simulation and parameter calibration.

[0005] The finite-discrete element method (FDEM) can model and analyze the deformation and failure of water-bearing rocks and is a powerful tool for studying the mechanisms of water-rock interaction. Parameter calibration is an essential step before conducting numerical simulations. However, there is currently no reasonable method for calibrating the input parameters involved in simulating the mechanical properties of water-bearing rocks using the FDEM.

[0006] In view of the above problems in the existing technology, it is urgent to propose a calibration method for the finite-discrete element input parameters of water-bearing rocks. Summary of the Invention

[0007] To solve the above technical problems, the present invention provides a calibration method for the finite-discrete element input parameters of water-bearing rock. The input parameters calibrated by this method can be directly used as the parameters required for the numerical simulation calculation of water-bearing rock, and can further accurately simulate the mechanical properties and expansion behavior of water-bearing rock, which is suitable for the study of the mechanism of water-rock interaction.

[0008] The present invention proposes a method for calibrating input parameters of a finite-discrete element method for water-bearing rock, comprising the following steps:

[0009] The rock samples were dried and treated with water to obtain dry rock samples and rock samples with different water contents;

[0010] Uniaxial tensile tests, uniaxial compression tests, and triaxial compression tests were carried out on dry rock samples and rock samples with different moisture contents. The corresponding evolution equations of tensile strength with moisture content, elastic modulus and uniaxial compressive strength with moisture content, and cohesion and internal friction angle with moisture content were obtained.

[0011] Laterally restrained water absorption swelling tests were carried out on dry rocks to obtain vertical expansion evolution curves;

[0012] Based on the evolution equations of tensile strength with moisture content, elastic modulus and uniaxial compressive strength with moisture content, cohesion and internal friction angle with moisture content, and vertical expansion evolution curve, the input parameters in the finite-discrete element method, including fracture energy, moisture expansion coefficient, and moisture diffusion coefficient, are calibrated;

[0013] Based on the calibrated input parameters, finite-discrete element uniaxial and triaxial compression numerical simulations of rock samples with different water contents were carried out to obtain simulation results;

[0014] When the error between the test result and the simulation result is within the preset threshold, the final parameter calibration result is obtained.

[0015] Optionally, the process of obtaining the evolution equation of tensile strength with moisture content includes:

[0016] Uniaxial tensile tests were carried out on dry rock samples and rock samples with different water contents to obtain the uniaxial tensile strength and tensile stress-strain curves of dry rocks and rocks with different water contents. The evolution equation of tensile strength with water content was obtained by fitting the experimental data.

[0017] Optionally, the process of obtaining the evolution equations of elastic modulus and uniaxial compressive strength with moisture content includes:

[0018] Uniaxial compression tests were carried out on dry rock samples and rock samples with different water contents to obtain the elastic modulus, uniaxial compressive strength and uniaxial compressive stress-strain curves of dry rocks and rocks with different water contents. The evolution equations of the elastic modulus and uniaxial compressive strength with water content were obtained by fitting the experimental data.

[0019] Optionally, the process of obtaining the evolution equations of cohesion and internal friction angle with water content includes:

[0020] Triaxial compression tests were carried out on dry rock samples and rock samples with different water contents. The cohesion, internal friction angle, triaxial compressive strength of dry rocks and rocks with different water contents, as well as triaxial compression stress-strain curves under different confining pressures were obtained. The evolution equations of cohesion and internal friction angle with water content were obtained by fitting the experimental data.

[0021] Optionally, the process of calibrating the fracture energy in the finite-discrete element method includes:

[0022] A specimen model with the same size as that used in the mechanical test was established, and the penalty parameter was taken as 100 times the elastic modulus. The mechanical parameters input into the finite-discrete element method were all based on experimental data. Normal loading was performed on the upper and lower ends of the specimen model at a loading rate consistent with the test. The trial-and-error method was used to continuously adjust the first fracture energy and the second fracture energy so that the simulation results of the uniaxial compressive strength, triaxial compressive strength and stress-strain curve were close to the experimental results. When the relative error between the simulation results and the test results was less than the preset threshold, the calibration was successful, and the first fracture energy and the second fracture energy at this time were the calibration results.

[0023] Optionally, the process of calibrating the humidity expansion coefficient and the humidity diffusion coefficient includes:

[0024] A specimen model identical to that used in the lateral restraint water absorption and swelling test was established, with the normal displacements of the four sides and bottom of the specimen model fixed, the penalty parameter taken as 100 times the elastic modulus, and the input mechanical parameters all based on experimental data. A saturated moisture content was applied to the surface of the specimen model, and the humidity expansion coefficient and humidity diffusion coefficient were continuously adjusted using a trial-and-error method, so that the simulation results of the maximum vertical expansion deformation and the expansion deformation-time curve were close to the experimental results. When the relative error between the simulation results and the experimental results was less than the preset threshold, the calibration was successful, and the humidity expansion coefficient and humidity diffusion coefficient at this time were the calibration results.

[0025] Optionally, the standard size rock specimen for mechanical testing is 50 mm in diameter and 100 mm in height;

[0026] The standard size cylindrical rock sample used for the lateral restraint water swelling test is 50 mm in diameter and 20 mm in height.

[0027] Optionally, the water contents of the rock samples with different water contents include 1%, 2%, 3%, 4%, 5% and 6%.

[0028] Optionally, the confining pressure of the triaxial compression test includes 2 MPa, 4 MPa, 6 MPa and 8 MPa.

[0029] Optionally, the loading rate used in the uniaxial tension, uniaxial compression and triaxial compression tests of rock is 0.001 mm / s;

[0030] The loading rate used in the finite-discrete element uniaxial and triaxial compression numerical simulations is 0.01 m / s.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] The calibration method for water-bearing rock proposed in the present invention realizes the input parameter values ​​of the finite-discrete element method in simulating the mechanical properties and deformation behavior of water-bearing rock, including two fracture energies and the humidity expansion coefficient and the humidity diffusion coefficient, and proposes a verification method for the correctness of the parameter calibration results, thereby realizing accurate simulation of the mechanical properties and expansion behavior of water-bearing rock, effectively solving the problem of difficulty in parameter calibration of the finite-discrete element method in simulating the mechanical properties of water-bearing rock in the existing technology, providing a simple, accurate and efficient parameter calibration method for the study of water-rock interaction mechanism, and improving the reliability and practicality of numerical simulation in the fields of rock mechanics and geotechnical engineering.

[0033] Compared to traditional discrete element method calibration procedures, the parameter calibration method proposed in this paper is significantly simpler and more convenient. With a penalty parameter set at 100 times the elastic modulus, the basic rock mechanical parameters input into the finite-discrete element method can be directly derived from experimental data. Only parameters related to fracture energy and humidity need to be calibrated. This creates a one-to-one correspondence between macroscopic and microscopic parameters, resulting in clear physical meaning. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of this application. The exemplary embodiments and descriptions of this application are intended to explain this application and do not constitute an improper limitation on this application. In the accompanying drawings:

[0035] Figure 1 Schematic diagram of a method flow in an embodiment of the present invention;

[0036] Figure 2 Schematic diagrams of uniaxial tensile tests of embodiments of the present invention, wherein (a) is a schematic diagram of a uniaxial tensile test of dry rock; (b) is a schematic diagram of a uniaxial tensile test of water-containing rock;

[0037] Figure 3 Schematic diagrams of uniaxial compression tests of embodiments of the present invention, wherein (a) is a schematic diagram of a uniaxial compression test of dry rock; (b) is a schematic diagram of a uniaxial compression test of water-bearing rock;

[0038] Figure 4 Schematic diagrams of triaxial compression tests of embodiments of the present invention, wherein (a) is a schematic diagram of a triaxial compression test of dry rock; (b) is a schematic diagram of a triaxial compression test of water-bearing rock;

[0039] Figure 5 This is a schematic diagram of a dry rock lateral restraint water absorption swelling test according to an embodiment of the present invention;

[0040] Figure 6 Schematic diagrams of uniaxial compression numerical models of embodiments of the present invention, wherein (a) is a schematic diagram of a uniaxial compression numerical model of dry rock; (b) is a schematic diagram of a triaxial compression numerical model of dry rock;

[0041] Figure 7 Schematic diagram of a numerical model of lateral confinement and water swelling of dry rock according to an embodiment of the present invention;

[0042] Figure 8 Schematic diagram of calibration result verification of an embodiment of the present invention; wherein, (a) is a schematic diagram of calibration result verification of uniaxial compression parameters of water-bearing rock; (b) is a schematic diagram of calibration result verification of triaxial compression parameters of water-bearing rock. DETAILED DESCRIPTION

[0043] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments in this application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0044] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer-executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0045] Example 1

[0046] This embodiment provides a method for calibrating input parameters of a finite-discrete element method for water-bearing rock, comprising the following steps:

[0047] The rock samples were dried and treated with water to obtain dry rock samples and rock samples with different water contents;

[0048] Uniaxial tensile tests, uniaxial compression tests, and triaxial compression tests were carried out on dry rock samples and rock samples with different moisture contents. The corresponding evolution equations of tensile strength with moisture content, elastic modulus and uniaxial compressive strength with moisture content, and cohesion and internal friction angle with moisture content were obtained.

[0049] Laterally restrained water absorption swelling tests were carried out on dry rocks to obtain vertical expansion evolution curves;

[0050] Based on the evolution equations of tensile strength with moisture content, elastic modulus and uniaxial compressive strength with moisture content, cohesion and internal friction angle with moisture content, and vertical expansion evolution curve, the input parameters in the finite-discrete element method, including fracture energy, moisture expansion coefficient, and moisture diffusion coefficient, are calibrated;

[0051] Based on the calibrated input parameters, finite-discrete element uniaxial and triaxial compression numerical simulations of rock samples with different water contents were carried out to obtain simulation results;

[0052] When the error between the test result and the simulation result is within the preset threshold, the final parameter calibration result is obtained.

[0053] As a specific implementation method, the following steps are included:

[0054] Step 1: Process the rocks obtained from the drilling into standard size cylindrical rock samples for indoor rock mechanics testing. The dry rock samples are treated with water absorption to obtain rock samples with different moisture contents. Uniaxial tensile tests are carried out on dry and water-containing rocks to obtain the uniaxial tensile strength (ft) of dry and water-containing rocks. d and ft w ) and tensile stress-strain curves, and fitting the test data to obtain the evolution equation of tensile strength with moisture content;

[0055] ft w (w)=ae bw +c,

[0056] Where w represents the moisture content of the sample, ft w (w) represents the tensile strength when the moisture content is w, and a, b, and c are the constant coefficients of the fitting equation.

[0057] Furthermore, the standard size rock sample used for the indoor rock mechanics test in step 1 has a diameter of 50 mm and a height of 100 mm.

[0058] Step 2: Conduct uniaxial compression tests on dry and water-containing rocks to obtain the elastic modulus and uniaxial compressive strength (E d 、UCS d and E w 、UCS w ) and uniaxial compression stress-strain curves, and fitting the test data to obtain the evolution equations of elastic modulus and uniaxial compressive strength with moisture content;

[0059] E w (w)=de fw +g,

[0060] UCS w (w)=he iw +j,

[0061] Among them, E w (w) and UCS w (w) are the elastic modulus and uniaxial compressive strength when the moisture content is w, d, f, g, h, i, and j are the constant coefficients of the fitting equation.

[0062] Step 3: Carry out triaxial compression tests on dry and water-containing rocks under different confining pressures to obtain the cohesion, internal friction angle, triaxial compressive strength (c d 、φ d 、TCS d and c w 、φ w 、TCS w ) and triaxial compression stress-strain curves under different confining pressures, and fitting the test data to obtain the evolution equations of cohesion and internal friction angle with water content;

[0063] c w (w)=ke lw +m,

[0064]

[0065] Among them, c w (w) and φ w (w) are the cohesion and internal friction angle when the moisture content is w, respectively; k, l, m, n, p, and q are the constant coefficients of the fitting equation.

[0066] Step 4: Process the rock obtained from the drilling into a standard-sized cylindrical rock sample for swelling test. Conduct a lateral restrained water absorption swelling test on the dry rock to obtain the vertical expansion evolution curve of the rock sample.

[0067] Step 5: Based on the data obtained from the indoor tests in steps 1 to 3, as the input of mechanical parameters in the finite-discrete element method, numerical tests of dry rock finite-discrete element uniaxial compression and triaxial compression under different confining pressures are carried out respectively, and the two fracture energies are calibrated (the first fracture energy Gf I and the second fracture energy Gf II ); The calibration process is to first establish a specimen model with the same dimensions as the test specimen, i.e., a cylindrical specimen with a diameter of 50 mm and a height of 100 mm. The penalty parameter is set to 100 times the elastic modulus. The input mechanical parameters such as elastic modulus, tensile strength, cohesion, and internal friction angle are all based on experimental data. Then, normal loading is applied to the upper and lower ends of the specimen at a loading rate consistent with the test, and Gf is continuously adjusted using a trial-and-error method. I and Gf II, so that the simulated uniaxial compressive strength, triaxial compressive strength and stress-strain curve are close to the experimental results. Finally, when the relative error between the numerical results and the simulation results is less than 5%, the calibration is successful. At this time, Gf I and Gf II This is the result of calibration;

[0068] Step 6: Based on the rock vertical expansion evolution curve obtained in step 4, a finite-discrete element numerical test of lateral constraint water absorption and swelling of dry rock is carried out to calibrate the humidity expansion coefficient (β) and humidity diffusion coefficient (k). The calibration process is as follows: first, establish the same specimen model as that used in the test, that is, a cylindrical specimen with a diameter of 50 mm and a height of 20 mm. The normal displacement of the four sides and the bottom of the specimen is fixed. The penalty parameter is taken as 100 times the elastic modulus. The input mechanical parameters such as elastic modulus, tensile strength, cohesion and internal friction angle are all based on experimental data. Then, a saturated moisture content is applied to the surface of the specimen. Due to the moisture gradient difference inside the specimen, moisture is continuously conducted downward. The "trial and error method" is used to continuously adjust β and k so that the maximum vertical expansion deformation and expansion deformation-time curve obtained by simulation are close to the experimental results. Finally, when the relative error between the numerical results and the simulation results is less than 5%, the calibration is successful, and k and m at this time are the calibration results;

[0069] Step 7: Based on the fitted equations from Step 3, consider the softening effect of water on rock mechanical parameters using the finite element method (FEM). Based on the parameters calibrated in Steps 5 and 6, conduct FEM uniaxial and triaxial compression numerical tests on rock samples with varying water contents. Compare the simulation results with the experimental results to verify the accuracy of the parameter calibration.

[0070] Furthermore, the method for absorbing water from the dry rock sample in step 1 is to first dry the rock sample, then add water to the top of the rock sample to a predetermined moisture content, let it stand for a period of time to allow the water to be evenly distributed in the sample and completely absorbed by the sample, ensuring that there is no free water in the sample, and at the same time wrap the water-containing rock sample with plastic wrap and aluminum foil to prevent water loss and cause changes in moisture content, and finally place it in the laboratory awaiting subsequent experimental arrangements.

[0071] Furthermore, the rock samples with different moisture contents in steps 1 to 3 include 1%, 2%, 3%, 4%, 5% and 6%.

[0072] Furthermore, the confining pressures of the triaxial compression test in step 3 include 2 MPa, 4 MPa, 6 MPa and 8 MPa.

[0073] Furthermore, the loading rate used in the rock uniaxial tension, uniaxial compression and triaxial compression indoor tests in steps 1 to 3 is 0.001 mm / s.

[0074] Furthermore, the diameter of the standard-sized cylindrical rock sample used for the lateral restraint water swelling test in step 4 is 50 mm and the height is 20 mm.

[0075] Furthermore, the lateral restraint water absorption and swelling test method in step 4 is to impose a moisture content boundary on the top of the dry rock sample. Due to the existence of the humidity gradient, water continuously diffuses from the upper surface of the rock sample to the inside, and eventually reaches the saturated moisture content;

[0076] Furthermore, the model size used in the finite-discrete element uniaxial and triaxial compression numerical simulations in step 5 is 50 mm×100 mm.

[0077] Furthermore, the loading rate used in the uniaxial and triaxial compression numerical simulations in step 5 is 0.01 m / s.

[0078] Furthermore, the premise for calibrating the fracture energy using the dry rock uniaxial and triaxial compression numerical tests in step 5 is that when the moisture content changes slightly, the influence of water on the fracture energy is negligible and can be considered as a constant.

[0079] Furthermore, the premise assumption for calibrating the fracture energy using the dry rock uniaxial and triaxial compression numerical tests in step 5 is that when the moisture content changes slightly, the influence of water on the fracture energy is negligible.

[0080] Furthermore, the model size used in the finite-discrete element lateral constraint swelling simulation in step 6 is 50 mm×100 mm.

[0081] This embodiment proposes a new finite-discrete element input parameter calibration method for water-bearing rocks. For the first time, the softening effect of water on rocks is considered in the finite-discrete element method. The evolution equations of the mechanical parameters of rocks with different water contents with water content are obtained through fitting experiments. The fitting equations are introduced into the finite-discrete element method through secondary development, so that the finite-discrete element method automatically softens the rock mechanical parameters to the corresponding water content when calculating the water absorption of rocks. Secondly, it demonstrates how to calibrate the two fracture energies of the joint unit, and also uses the lateral constraint swelling numerical experiment to calibrate the moisture expansion coefficient and conductivity coefficient of the triangular unit. The other mechanical parameters are directly taken from the parameters obtained in the experiment. In this way, the calibration of the input parameters in the finite-discrete element simulation of water-bearing rocks is completed, so that the finite-discrete element can more realistically simulate the mechanical behavior of rock water absorption.

[0082] Example 2

[0083] The method for calibrating the input parameters of the finite-discrete element of water-bearing rock described in this embodiment is as follows: Figure 1 As shown:

[0084] Step 1: Process the rock obtained by drilling into a cylindrical rock sample with a diameter of 50mm and a height of 100mm. Dry the natural rock sample to obtain a dry rock sample. Then add water to the top of the dry rock sample to a predetermined moisture content (1%, 2%, 3%, 4%, 5% and 6%). Let it stand for a period of time to allow the water to be evenly distributed in the sample and completely absorbed by the sample to ensure that there is no free water in the sample. At the same time, wrap the water-containing rock sample with plastic wrap and aluminum foil to prevent water loss and change in moisture content. Carry out uniaxial tensile tests on dry and different moisture content rock samples with a loading rate of 0.001mm / s. Figure 2 As shown. The uniaxial tensile strength and tensile stress-strain curves of dry and water-containing rocks were obtained, and the evolution equation of uniaxial tensile strength with water content was obtained by fitting the test data.

[0085] Step 2: Uniaxial compression tests were carried out on cylindrical dry rock samples with a diameter of 50 mm and a height of 100 mm and rock samples with different moisture contents (1%, 2%, 3%, 4%, 5% and 6%) at a loading rate of 0.001 mm / s. Figure 3 As shown, the elastic modulus, uniaxial compressive strength and uniaxial compressive stress-strain curves of dry and water-containing rocks are obtained, and the evolution equations of elastic modulus and uniaxial compressive strength with water content are obtained;

[0086] Step 3: Triaxial compression tests were carried out on cylindrical dry rock samples with a diameter of 50 mm and a height of 100 mm and rock samples with different moisture contents (1%, 2%, 3%, 4%, 5% and 6%). The confining pressures were set to 2 MPa, 4 MPa, 6 MPa and 8 MPa, respectively, and the loading rate was 0.001 mm / s. Figure 4 As shown, the cohesion, internal friction angle, triaxial compressive strength and triaxial compression stress-strain curves of dry and water-containing rocks are obtained, and the evolution equations of cohesion and internal friction angle with water content are obtained;

[0087] Step 4: First, place a 50mm diameter, 20mm high disc sample into a metal ring with an inner diameter of 20mm, and place filter paper and a permeable plate on the top and bottom of the sample respectively; then place a fixed metal load block on the top and install a dial indicator. The metal load block can generate a constant pressure of 5kPa on the mudstone sample; finally, add water until it covers the permeable plate, and start recording the dial indicator reading. During the first two hours of the test, take a reading every 10 minutes, and then take a reading every 30 minutes. Carry out the dry rock lateral restraint water absorption and swelling test to obtain the vertical expansion evolution curve of the rock, such as Figure 5 As shown;

[0088] Step 5: Finite-discrete element uniaxial compression and triaxial compression numerical tests were carried out on dry rock samples with a width of 50 mm and a height of 100 mm. The confining pressures were set to 2 MPa, 4 MPa, 6 MPa, and 8 MPa, respectively, and the loading rate was 0.01 m / s. Although this loading rate is much higher than that used in the experiment, the mechanical time step in the simulation is 1×10 -8 s / step, that is, each step only loads 1×10 -10 m, this value is small enough to ensure that the system is quasi-static and the entire simulation process can be completed in a short time, such as Figure 6 As shown, two fracture energies are calibrated;

[0089] Step 6: Conduct a finite-discrete element numerical test of the lateral constraint water absorption and swelling of the dry rock sample. First, a moisture content boundary is applied to the top of the 50 mm × 20 mm dry rock sample. Due to the existence of the humidity gradient, water continuously diffuses from the upper surface of the rock sample to the inside, and eventually reaches the saturated moisture content, such as Figure 7 As shown, the humidity expansion coefficient and humidity diffusion coefficient are calibrated;

[0090] Step 7: Based on the fitting equations of rock mechanical parameters varying with water content obtained from the experiments in steps 1 to 3, the softening effect of water on rock mechanical parameters is considered in the finite-discrete element method. Finite-discrete element uniaxial and triaxial compression numerical tests are carried out on rock samples with different water contents (1%, 2%, 3%, 4%, 5% and 6%), with the confining pressures set to 2MPa, 4MPa, 6MPa and 8MPa, respectively. Figure 8 As shown in Figure 3, the simulation results are compared with the test results to verify the correctness of the parameter calibration.

[0091] The above are merely preferred embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A method for calibrating input parameters of finite-discrete element method for water-bearing rock, characterized in that: The following steps are involved: The rock samples were dried and treated with water to obtain dry rock samples and rock samples with different water contents; Uniaxial tensile tests, uniaxial compression tests, and triaxial compression tests were carried out on dry rock samples and rock samples with different moisture contents. The corresponding evolution equations of tensile strength with moisture content, elastic modulus and uniaxial compressive strength with moisture content, and cohesion and internal friction angle with moisture content were obtained. Laterally restrained water absorption swelling tests were carried out on dry rocks to obtain vertical expansion evolution curves; Based on the evolution equations of tensile strength with moisture content, elastic modulus and uniaxial compressive strength with moisture content, cohesion and internal friction angle with moisture content, and vertical expansion evolution curve, the input parameters in the finite-discrete element method, including fracture energy, moisture expansion coefficient, and moisture diffusion coefficient, are calibrated; Based on the calibrated input parameters, finite-discrete element uniaxial and triaxial compression numerical simulations of rock samples with different water contents were carried out to obtain simulation results; When the error between the test result and the simulation result is within the preset threshold, the final parameter calibration result is obtained.

2. The method according to claim 1, characterized in that The process of obtaining the evolution equation of tensile strength with moisture content includes: Uniaxial tensile tests were carried out on dry rock samples and rock samples with different water contents to obtain the uniaxial tensile strength and tensile stress-strain curves of dry rocks and rocks with different water contents. The evolution equation of tensile strength with water content was obtained by fitting the experimental data.

3. The method according to claim 1, characterized in that The process of obtaining the evolution equations of elastic modulus and uniaxial compressive strength with moisture content includes: Uniaxial compression tests were carried out on dry rock samples and rock samples with different water contents to obtain the elastic modulus, uniaxial compressive strength and uniaxial compressive stress-strain curves of dry rocks and rocks with different water contents. The evolution equations of the elastic modulus and uniaxial compressive strength with water content were obtained by fitting the experimental data.

4. The method according to claim 1, wherein The process of obtaining the evolution equations of cohesion and internal friction angle with water content includes: Triaxial compression tests were carried out on dry rock samples and rock samples with different water contents. The cohesion, internal friction angle, triaxial compressive strength of dry rocks and rocks with different water contents, as well as triaxial compression stress-strain curves under different confining pressures were obtained. The evolution equations of cohesion and internal friction angle with water content were obtained by fitting the experimental data.

5. The method according to claim 1, wherein The process of calibrating the fracture energy in the finite-discrete element method includes: A specimen model with the same size as that used in the mechanical test was established, and the penalty parameter was taken as 100 times the elastic modulus. The mechanical parameters input into the finite-discrete element method were all based on experimental data. Normal loading was performed on the upper and lower ends of the specimen model, and the loading rate was consistent with the test. The trial-and-error method was used to continuously adjust the first fracture energy and the second fracture energy so that the simulation results of the uniaxial compressive strength, triaxial compressive strength and stress-strain curve were close to the experimental results. When the relative error between the simulation results and the test results was less than the preset threshold, the calibration was successful, and the first fracture energy and the second fracture energy at this time were the calibration results.

6. The method according to claim 5, characterized in that The process of calibrating the humidity expansion coefficient and humidity diffusion coefficient includes: A specimen model identical to that used in the lateral restraint water absorption and swelling test was established, with the normal displacements of the four sides and bottom of the specimen model fixed, the penalty parameter taken as 100 times the elastic modulus, and the input mechanical parameters all based on experimental data. A saturated moisture content was applied to the surface of the specimen model, and the humidity expansion coefficient and humidity diffusion coefficient were continuously adjusted using a trial-and-error method, so that the simulation results of the maximum vertical expansion deformation and the expansion deformation-time curve were close to the experimental results. When the relative error between the simulation results and the experimental results was less than the preset threshold, the calibration was successful, and the humidity expansion coefficient and humidity diffusion coefficient at this time were the calibration results.

7. The method according to claim 1, characterized in that The standard size of rock specimens used in mechanical testing is 50 mm in diameter and 100 mm in height; The standard size cylindrical rock sample used for the lateral restraint water swelling test is 50 mm in diameter and 20 mm in height.

8. The method according to claim 1, characterized in that The water contents of rock samples with different water contents include 1%, 2%, 3%, 4%, 5% and 6%.

9. The method according to claim 1, characterized in that The confining pressures of the triaxial compression test include 2 MPa, 4 MPa, 6 MPa, and 8 MPa.

10. The method according to claim 1, characterized in that The loading rate used in the uniaxial tension, uniaxial compression, and triaxial compression tests of rock was 0.001 mm / s; The loading rate used in the finite-discrete element uniaxial and triaxial compression numerical simulations is 0.01 m / s.

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