Preparation and experimental method of fractured rock samples filled with water to reflect water migration and water content conditions

Abstract

The present invention discloses a preparation and experimental method for a filled fracture rock sample reflecting water migration and water-containing conditions, which relates to the technical field of rock mechanics experiments and includes: processing sandstone blocks into cuboids larger than standard cylindrical specimens; placing rectangular plates on the drilling machine workbench, marking the positions of the drill holes according to the required specimen positions, and using a core drill to extract specimens; using a high-pressure water jet device to cut a through fracture in the middle of the specimen, and the fracture characteristics include the dip angle β and the length 2 a , and the fracture widths are the same, forming a control group of different rock specimens; cutting and polishing with a grinding machine to make standard cylindrical and disc specimens; air-drying and crushing the clay retrieved from the sampling site, and preparing clay-filled fracture specimens according to the natural water content of the on-site clay; the present invention can provide a basis for understanding the mechanism of water-rock interaction and revealing the mechanism of water-induced related rock mass engineering disasters.

Description

Technical Field

[0001] The present invention relates to the technical field of rock mass mechanics experiments, in particular to a preparation method and an experimental method for a filled fissure rock sample reflecting the water migration and water-containing conditions. Background Art

[0002] Large-scale rock mass engineering construction is often in a geomechanical environment such as "high stress, high temperature, high water pressure and disturbance", and water is one of the most important environmental influencing factors. When there are water-sensitive rocks (such as sandstone, mudstone, limestone, etc.) or filling media between structural planes (such as clay, montmorillonite, etc.) in engineering rock masses, complex physical, chemical and mechanical interactions (i.e., water-rock interaction) will occur when water contacts the rock mass, thus frequently triggering engineering geological disasters such as landslides of reservoir banks / open-pit slopes, large deformations of deep-buried caverns and floor heave of roadways.

[0003] The primary prerequisite for revealing the water-rock interaction mechanism is to clarify the water occurrence characteristics in the rock mass (rock). At present, most of the research on water-rock interaction focuses on the "content" of water in the rock, and mostly uses water content or saturation to characterize the water-containing state of the rock, and mostly assumes that the water in the rock is evenly distributed. In recent years, scholars have gradually realized that the migration process of water / moisture in the rock and the resulting non-uniform distribution of water will also significantly affect the mechanical properties and failure modes of the rock. However, the water occurrence characteristics in actual engineering rock masses are very complex. Under the influence of factors such as reservoir water level rise and fall, groundwater seepage and underground space humidity diffusion, water migrates back and forth in the rock mass, causing continuous changes in the water content, spatial distribution and wet-dry cycle of the water in the rock mass. Therefore, most of the current relevant research can only reflect some aspects of the water-containing conditions of the rock mass caused by water migration.

[0004] Filled fissure rock masses are very common in actual engineering. In many engineering disaster cases induced by water, water-sensitive rocks are usually present in the rock mass, and the fissures are filled with clay (or muddy) media. Such rock masses can be called clay-filled fissure rock masses. In this case, the water-rock interaction caused by water migration is bound to be affected by the rock mass fissures and the clay media filling them. However, most of the current research on fissure rock masses related to water focuses on their seepage characteristics, ignoring the influence of water migration on the mechanical property degradation and failure mechanism of clay-filled fissure rock masses.

[0005] It can be seen that under the combined action of moisture migration and loads (such as excavation of engineering rock masses), the mechanical properties of clay-filled fractured rock masses will deteriorate, and rupture and instability may occur, thus triggering major rock mass engineering disasters. To reveal the mechanical properties and rupture mechanism of filled fractured rock masses under the influence of moisture migration, and thus deeply understand the water-rock interaction and reveal the mechanism of water-induced related rock mass engineering disasters, there is an urgent need for methods and techniques to prepare filled fracture specimens that can reflect the moisture migration and water-containing conditions, visualize the process of moisture migration in filled fractured rock masses, and conduct physical experiments on the deterioration and rupture of the mechanical properties of filled fractured rock masses under the combined action of moisture migration and loads. However, there is currently a lack of relevant specimen preparation methods, observation methods for the moisture migration process in filled fractured rock masses and theoretical models, and relevant experimental data have not been obtained. Summary of the Invention

[0006] To solve the problems existing in the prior art, the object of the present invention is to provide a preparation and experimental method for filled fracture rock samples that can reflect the moisture migration and water-containing conditions, and the present invention can provide a basis for understanding the mechanism of water-rock interaction and revealing the mechanism of water-induced related rock mass engineering disasters.

[0007] To achieve the above object, the technical solution adopted by the present invention is: a preparation method for filled fracture rock samples that can reflect the moisture migration and water-containing conditions, comprising the following steps:

[0008] Step 1: Process the sandstone block into a cuboid larger than the standard cylindrical specimen.

[0009] Step 2: Place the rectangular plate on the drilling machine workbench, mark the positions of the drill holes according to the required specimen positions, and use a core drill to extract the specimens.

[0010] Step 3: Use a high-pressure water jet equipment to cut a through fracture in the middle of the specimen, and the fracture characteristics include the dip angle β and the length 2 a , and the fracture width is the same, forming a control group of different rock specimens.

[0011] Step 4: Cut and polish with a grinding machine to make standard cylindrical and disc specimens.

[0012] Step 5: Air-dry and crush the clay retrieved from the sampling site, and prepare the clay-filled fracture specimens according to the natural moisture content of the on-site clay.

[0013] The present invention also provides an experimental method for filled fracture rock samples that can reflect the moisture migration and water-containing conditions as described above, comprising the following steps:

[0014] Step A: Carry out water absorption - water loss experiments on filled or unfilled fractured rock samples after different numbers of wet - dry cycles, measure the water absorption and water loss curves of the fractured specimens, and provide a reference for the selection of immersion and air - drying time nodes;

[0015] Step B: Conduct nuclear magnetic resonance observation experiments on the water migration process and law of filled or unfilled fractured rock samples, and observe the water migration process and spatial distribution during the immersion and air - drying processes of the fractured specimens.

[0016] Step C: Use the MTS rock mechanics experimental system to conduct Brazilian splitting experiments on filled - fractured disc specimens with different water contents and different fracture characteristics, monitor the basic mechanical information of load - displacement and stress - strain, and use an acoustic emission system to monitor acoustic emission signals, and use a high - speed camera and a high - speed microscopic monitoring system for rock fracture processes to observe and record the crack propagation process;

[0017] Step D: Use a multi - field and multi - phase rock triaxial test system to conduct uniaxial compression experiments and triaxial compression experiments on cylindrical specimens with different water contents and different fracture characteristics; during the experiment, monitor the basic mechanical information of load - displacement and stress - strain, and use an acoustic emission system to monitor acoustic emission signals and record the crack propagation process;

[0018] Step E: Take the immersion time and the air - drying time after saturation after multiple immersion - air - drying cycle operations as variables to characterize the changes in the water content and spatial distribution of water in the rock sample caused by water migration, and use the dip angle β and length 2 a to characterize the fracture; calculate the mechanical property indexes of filled - fractured rock samples under different loading conditions, and obtain the deterioration law of the mechanical properties of fractured rocks affected by water migration according to the changes of the mechanical property indexes with the water content and fracture characteristic characterization indexes.

[0019] As a further improvement of the present invention, in Step A, the water absorption - water loss experiment is specifically as follows:

[0020] Place the filled or unfilled fractured specimens after wet - dry cycle treatment in an oven for drying, and store the dried specimens in a desiccator; then, conduct a saturation experiment and an air - drying experiment after saturation on the dried specimens after different numbers of wet - dry cycles; among them, in the saturation experiment, the states experienced by the specimens are successively dry, unsaturated, saturated, and long - term saturated; in the air - drying experiment after saturation, the states experienced by the specimens are successively saturated, unsaturated, and dry.

[0021] As a further improvement of the present invention, the saturation scheme of the saturation experiment includes:

[0022] (1) Simulate the water migration from the central fracture to the surrounding of the rock sample;

[0023] (2) Simulate the migration of moisture from the periphery of the rock sample towards the fracture direction; and in the experimental process, use a water-repellent agent and paraffin to treat the fracture and its adjacent areas.

[0024] As a further improvement of the present invention, in step B, the nuclear magnetic resonance observation experiment is specifically as follows:

[0025] In the process of preparing the fractured rock samples with different water contents, select some fractured disk and cylindrical specimens, select multiple time nodes during the water absorption and air-drying processes. First, perform different-time immersion and air-drying treatments on the fractured rock samples after different numbers of wet-dry cycles to obtain fractured specimens with different water contents; then, conduct nuclear magnetic resonance observation experiments on the specimens with different water contents.

[0026] As a further improvement of the present invention, in the nuclear magnetic resonance experiment, the gray value of the nuclear magnetic resonance image corresponds one-to-one with the water content at different positions. When establishing its quantitative correspondence relationship, first calibrate the image, use the nuclear magnetic resonance image of the fractured disk or cylindrical rock sample that is saturated with water and has a uniform water distribution as the calibration standard, extract the maximum gray value of the calibrated specimen image, and thus convert the gray value to obtain the volumetric water content at different positions of the rock sample at different immersion or air-drying times, which is used to determine the diffusion coefficient during the moisture migration process in the fractured rock mass and establish the moisture migration equation; then, determine the theoretical model of moisture migration in the fractured rock mass filled with clay.

[0027] As a further improvement of the present invention, the specific method for determining the theoretical model of moisture migration in the fractured rock mass filled with clay is as follows:

[0028] Determine the moisture migration control equation through the moisture migration law in the clay-filled fractured rock mass. When the temperature is constant, the moisture migration control equation is: In the formula, is the volumetric water content, is the diffusion coefficient, which is a function of the water content or time t , is the gradient operator; introduce the Boltzmann transformation parameter , p is a position function, represented in two-dimensional coordinates, that is , then the moisture migration control equation is transformed into: According to the initial and boundary conditions of moisture migration, obtain the relationship between the water content and or time t through experiments, and then the diffusion coefficient can be determined, thereby determining the specific expression of the moisture migration equation; among them, the initial and boundary conditions of moisture migration are: .

[0029] As a further improvement of the present invention, an empirical formula including the relationship parameters between the water content and the Boltzmann transformation parameter is used to describe the water migration law: ; In the formula, the parameters and are measured by nuclear magnetic resonance observation experiments on rock samples with different soaking or air-drying times. Thus, according to the experimental data, the parameters a , b and c are obtained by fitting; combined with the relational expressions: and , an expression of the diffusion coefficient with the water content as the independent variable is established: Thus, the diffusion coefficient of water migration in the fractured rock mass filled with water and the specific expression of the migration control equation are determined.

[0030] As a further improvement of the present invention, in step E, the mechanical property indexes include: the tensile strength T in the Brazilian splitting test, the elastic modulus E and the strength σ UCS in the uniaxial compression test, and the compressive strength σ TCS in the triaxial compression test: ; ; where is the confining pressure; the tensile strength T measured by the Brazilian splitting test, the elastic modulus E measured by the uniaxial compression test, and the cohesion c and the friction angle φ calculated from the triaxial compression test data are taken as the fractured rock mechanics parameter set, and an expression of the variation law of the mechanical property indexes with the water migration water content characterization indexes and the fracture characteristics is established, that is: Analyze the mathematical function form of the degradation law expressions of different mechanical parameters, study the physical meanings of the parameters included therein, and their relationships with the experimental conditions, so as to establish a degradation model of the mechanical parameters of the fractured rock mass filled with water under the influence of water migration.

[0031] As a further improvement of the present invention, it further includes:

[0032] According to the stress-strain data of the fractured rock samples filled with water under water migration and different loading conditions obtained from experiments, study the influence laws of the water content state, fracture characteristics, and loading conditions on the form of the stress-strain curve, and establish a constitutive model of the fractured rock mass filled with water under water migration and different loading conditions.

[0033] The present invention prepares rock sample fractures by the high-pressure water jet method, fills clay medium into the fractures to prepare fractured rock samples filled with clay, and then designs different water immersion methods to simulate the migration conditions of water in the actual fractured rock mass filled with clay. Based on this, fractured rock samples filled with clay that can reflect the water content conditions at different time nodes of water migration can be prepared. Indoor mechanical experiments are carried out using these rock samples, so as to study the migration law of water in the fractured rock mass filled with clay, as well as the degradation law and fracture mechanism of the mechanical properties of the fractured rock mass filled with clay under the influence of water migration. The research results can provide a basis for understanding the mechanism of water-rock interaction and revealing the mechanism of water-induced related rock mass engineering disasters.

[0034] The beneficial effects of the present invention are as follows:

[0035] 1. Through mineral composition analysis (such as XRD diffraction analysis, EDS energy dispersive spectrometer analysis) and microscopic morphology analysis (such as SEM images), the present invention can quantitatively analyze the microscopic changes of mineral particles in the fractured rock mass filled with clay before and after water-rock interaction. This provides reliable microscopic data support for the degradation mechanism of the rock mass and reveals the mesoscopic damage process of the internal structure of the rock mass by water. Using mercury intrusion testing and SEM image processing technology, the changes in the pore structure inside the rock mass can be quantitatively analyzed. This quantitative evaluation method can accurately reveal the influence of water migration on the porosity and structural strength of the rock mass, and provide a reference for the change of the physical properties of the fractured rock mass.

[0036] 2. The present invention uses sandstone as the fracture wall and clay as the filling medium, and conducts micro-meso tests on the sandstone and clay fillers before and after water-rock interaction respectively, analyzes the mineral composition and micro-meso structure of the sandstone and clay fillers, provides a method for studying the micro-meso mechanism, and also provides experimental data for the mechanism analysis of the degradation of the mechanical properties of the water-induced clay-filled fractured rock mass.

[0037] 3. By controlling the dip angle, length and width of the fractures in the experiment, the present invention studies the influence of these fracture geometric characteristics on the water migration path and speed, and simulates the complexity of water migration in the fractured rock mass in actual engineering. It enriches the understanding of water migration in the fractured rock mass and also provides an experimental basis for the in-depth study of the coupling effect between fracture geometric parameters and water degradation in the future.

[0038] 4. Through the experiment of clay-filled fractured rock mass under simulated actual engineering conditions, the present invention reveals the softening and swelling effects of water on clay fillings. This is of guiding significance for problems such as water-induced landslides and instability of underground spaces involved in geotechnical engineering. The research results show that the presence of clay fillings significantly affects the influence of water migration on the deterioration of fractured rock masses. Especially under different conditions such as fracture width and filling degree, the action modes of water on clay are different. Through microscopic testing and nuclear magnetic resonance technology, the migration path of water in clay and its erosion and weakening effects on fractures are analyzed, and further exploration is carried out on how the swelling effect of clay leads to the structural deterioration and mechanical property degradation of fractured rock masses.

[0039] 5. By controlling the water content of rock samples and the water migration path, the water migration behavior under different water content conditions is simulated. This process can reproduce the migration of water in fractured rock samples from the inside out or from the outside in, and truly reflect the water-containing characteristics of fractured rock masses in actual engineering. The present invention verifies the deterioration law of rock samples during the process of water migrating from fractures outward or from the outside to fractures by designing two water absorption and water loss experimental schemes. This innovative experimental design enables the research not only to be limited to the influence of static water content on mechanical properties, but also to cover the comprehensive action effect of water on fractured rock samples during the dynamic migration process.

[0040] 6. By designing two different immersion schemes, the present invention not only simulates the water migration from fractures to the surroundings (from the inside out), but also simulates the situation of water migrating from the outside to fractures (from the outside in). This two-way water migration mode can more truly reproduce the actual water migration process in engineering and provide more diverse experimental data.

[0041] 7. Through nuclear magnetic resonance gray-scale image analysis, the present invention establishes the migration control equation of water under different water-containing states, and then determines the water diffusion coefficient. This not only provides a theoretical basis for the water migration law in rock masses, but also quantitatively characterizes the diffusion and distribution of water in fractured rock masses through a mathematical model, laying a foundation for the mechanical research of rock masses under water-containing conditions. The present invention proposes the volumetric water content as an independent variable to study the deterioration law of the mechanical properties of fractured rock masses. This quantitative analysis method helps to reveal the specific influence of the change in volumetric water content during the water migration process on the mechanical properties of rock masses (such as elastic modulus, compressive strength, etc.).

[0042] 8. The present invention quantitatively observes the migration process of moisture under different water content states through nuclear magnetic resonance technology. This quantitative and visual research can more precisely reveal the influence of moisture on the mechanical properties of rock masses, establish the corresponding relationship between volumetric water content and image gray value, then establish a theoretical framework for moisture migration based on unsaturated diffusion theory, determine the diffusion coefficient according to the nuclear magnetic resonance results, and thus determine the specific expression of the moisture migration control equation with volumetric water content as the independent variable, and analyze the migration law in the fractured rock mass filled with cracks under different moisture migration boundary conditions.

[0043] 9. Through in-depth research on the fracture process of rock masses under moisture migration, the present invention reveals the mechanical degradation and fracture mechanism of clay-filled fractured rock masses under different moisture conditions and loading conditions. This research provides a key theoretical basis and technical support for understanding and predicting engineering disasters (such as slope landslides and cavern instability) caused by moisture.

[0044] 10. The present invention provides experimental data on moisture migration, mechanical degradation, and water-rock interaction, which can be used as the basis for numerical simulation. By establishing a numerical model of moisture migration and the degradation of fractured rock masses, researchers can better predict the impact of moisture migration on engineering rock masses and improve the stability assessment ability of geotechnical engineering.

[0045] 11. Through experiments under different loading conditions (such as Brazilian splitting experiment, uniaxial compression, and triaxial compression experiments), the present invention establishes a mechanical parameter degradation model of fractured rock masses under the influence of moisture migration. This model can provide the mechanical response law of fractured rock masses under moisture migration, especially the key parameters such as elastic modulus, tensile strength, and friction angle during the water-induced degradation process.

[0046] 12. Through the real-time acoustic emission (AE) system for real-time monitoring of acoustic emission signals and combined monitoring with a high-resolution camera, the experiment can accurately capture the fracture formation, propagation, and the fracture process caused by moisture migration. This dynamic monitoring method provides valuable real-time data for in-depth study of the fracture mechanism in fractured rock masses and can also warn of the mechanical failure process of fractured rock masses under different water content conditions.

[0047] 13. The research results of the present invention are not limited to the stability assessment of slopes, tunnels, and underground caverns in geotechnical engineering, but can also be applied to the prevention and control of disasters such as reservoir bank landslides in water conservancy and hydropower projects and slope instability in mining engineering, providing theoretical support and technical guidance for preventing fracture and instability problems caused by moisture migration in rock mass engineering. Description of the Drawings

[0048] Figure 1 is the flow chart of the experimental method in the embodiment of the present invention;

[0049] Figure 2Line drawing of the equipment for preparing and detecting fissures in the embodiments of the present invention;

[0050] Figure 3 Schematic diagram of the fissured rock sample filled with clay in the embodiments of the present invention;

[0051] Figure 4 Schematic diagram of the migration of moisture from the periphery of the rock sample towards the fissure direction (from outside to inside) in the embodiments of the present invention;

[0052] Figure 5 Schematic diagram of the migration of moisture from the middle fissure towards the periphery of the rock sample (from inside to outside) in the embodiments of the present invention

[0053] Figure 6 Schematic diagram of the gray correction of the nuclear magnetic resonance image in the embodiments of the present invention;

[0054] Figure 7 Schematic diagram of the migration process of moisture in the rock in the embodiments of the present invention;

[0055] Figure 8 Schematic diagram of the rock fracture under the influence of water in the embodiments of the present invention. Detailed implementation manners

[0056] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0057] Embodiment

[0058] As Figure 1 shown, a method for preparing a fissured rock sample filled with water reflecting the moisture migration condition includes:

[0059] 1. To improve the sample preparation success rate, first process the sandstone block into a cuboid slightly larger than the standard cylindrical (50 mm in diameter × 100 mm in height) sample.

[0060] 2. Then place the rectangular plate on the drill press workbench to ensure that it does not move during the drilling process. Use a core drill with a diamond bit, select a bit with a diameter of 50 mm, mark the drilling position according to the required sample position, and prepare the sample. Start the drill press, and the bit slowly presses down and starts drilling. Use a coolant (such as water or oil) to cool the bit to prevent overheating, and at the same time reduce the cracks and debris of the sandstone. After drilling is completed, extract the cylindrical core, which is the required sample. During the drilling process, maintain the stability of the bit and a consistent downward pressure to avoid cracks or irregularities on the sample surface.

[0061] 3. Use a high-pressure water jet equipment to cut a through fissure in the middle of the sample, as Figure 2As shown, the fracture characteristics include dip angle β (taking 15°, 30°, 45°, 60° and 90°) and length 2a (taking 6, 8, 10 and 12 mm), and the fracture widths are the same (about 2 mm), forming a control group of different rock specimens.

[0062] 4. Then use a grinding machine to cut and polish to make cylindrical and disc specimens with heights of 100 mm and 25 mm respectively.

[0063] 5. Air-dry the clay retrieved from the sampling site, crush it, and sieve it through a 0.5 mm sieve. Prepare clay-filled fracture specimens according to the natural water content of the on-site clay, and the filling degree of each specimen is uniformly considered as 100%. As Figure 3 shown. To study the influence of the clay-filled medium, some unfilled fracture specimens are reserved for comparative tests. So far, the preparation of rock specimens is completed.

[0064] This embodiment also provides an experimental method for a filled fracture rock sample reflecting the water migration and water-bearing conditions as described above, specifically including:

[0065] Carry out water absorption and water loss experiments on the fractured rock samples after different numbers of wet-dry cycles. First, place the fractured specimens (filled or unfilled) after wet-dry cycle treatment in an oven for drying, and store the dried specimens in a drying dish; subsequently, conduct experiments on the dried specimens after different numbers of wet-dry cycles for water saturation (the specimens change from dry → unsaturated → saturated → long-term saturated) and air-drying after saturation (the specimens change from saturated → unsaturated → dry), and measure the water absorption and water loss curves of the fractured specimens to provide a reference for the selection of water immersion and air-drying time nodes.

[0066] To consider the directionality of water migration in actual rock mass engineering, two water saturation schemes are designed in this embodiment. Among them, Scheme 1 simulates the water migration from the middle fracture to the surrounding of the rock sample (from the inside to the outside), as Figure 5 shown, and Scheme 2 simulates the water migration from the surrounding of the rock sample to the fracture direction (from the outside to the inside), as Figure 4 shown. During the experiment, a water repellent and paraffin wax must be used to treat the fracture and its nearby areas.

[0067] Next, nuclear magnetic resonance observation experiments will be carried out on the moisture migration process and law in fractured rock samples (filled or unfilled). During the preparation of fractured rock samples with different water contents, some typical filled fractured disc and cylindrical specimens are selected (without considering the influence of fracture characteristics changes on the moisture migration law). The experiment will select multiple time nodes during the water absorption and air-drying processes. First, the fractured rock samples after different numbers of wet-dry cycles will be immersed in water and air-dried for different times to obtain fractured specimens with different water contents. Then, for these specimens with different water contents, nuclear magnetic resonance experiments will be carried out to observe the migration process and spatial distribution of moisture during the immersion and air-drying processes of the fractured specimens.

[0068] The gray value of the nuclear magnetic resonance image corresponds one-to-one with the water content at different positions. To quantitatively establish this correspondence, the image needs to be calibrated first, such as Figure 6 shown. Taking the nuclear magnetic resonance image of a filled fractured disc or cylindrical rock sample that is saturated with water and has a uniform moisture distribution as the calibration standard (the water content of the calibration rock sample can be easily measured by experiments), the maximum gray value of the calibration specimen image is extracted. Thus, the volumetric water content at different positions of the rock sample at different times of immersion or air-drying can be obtained by converting the gray value. These observation data will provide an experimental basis for determining the diffusion coefficient during the moisture migration process in fractured rock masses and establishing the moisture migration equation. The moisture migration process in rocks is as Figure 7 shown.

[0069] Then, determine the theoretical model of moisture migration in filled fractured rock masses. When the fractured rock sample is immersed in water or saturated and then air-dried for different times ( or ), moisture migrates in the rock sample, resulting in different water content states at different positions inside the rock sample, that is, the spatio-temporal state of moisture in the filled fractured rock mass is constantly changing. Through the moisture migration law in clay-filled fractured rock masses, and determine the specific expression of the moisture migration equation:

[0070] When the temperature is constant, the control equation of moisture migration (humidity diffusion) can be expressed as: In the formula, is the volumetric water content (the ratio of water to the volume of rock), is the diffusion coefficient (which is a function of the water content or time t), is the gradient (del) operator. Introduce the Boltzmann transformation parameter , p is a function of position. In plane problems, it is represented by two-dimensional coordinates, that is , then the moisture migration control equation can be expressed as: Further consider the initial and boundary conditions of moisture migration: It can be seen that by obtaining the water content and The relationship between (or time t) can be used to determine the diffusion coefficient , thereby determining the specific expression of the water migration equation. In this embodiment, the filled fractured rock mass is taken as the research object, and the immersion and air drying of different cycle numbers are considered. That is, the time t in the above formula is or .

[0071] By using nuclear magnetic resonance experiments and resonance gray image processing technology to determine the diffusion coefficient and the specific expression of the water migration equation, the water migration law is expressed by an empirical formula containing three parameters (i.e., the volumetric water content and the Boltzmann transformation parameter relationship): .

[0072] In this formula, the parameters and can both be measured by nuclear magnetic resonance observation experiments on rock samples with different immersion or air drying times. Thus, according to the experimental data, the parameters a, b, and c can be obtained by fitting. Combining the relationship: The diffusion coefficient expression with the volumetric water content as the independent variable can be established: According to the above research idea, the diffusion coefficient of water migration in the filled fractured rock mass and the specific expression of the migration control equation can be determined.

[0073] To study the influence of clay-filled media, mechanical experiments will be carried out on the filled fractured rock samples under three basic loading conditions (indirect tension, uniaxial compression, and triaxial compression) in this test. When using the MTS 816 rock mechanics test system to carry out the Brazilian splitting test on the filled fractured disk specimens with different water contents and different fracture characteristics, in addition to monitoring basic mechanical information such as load-displacement and stress-strain, an acoustic emission (AE) system is also used to monitor acoustic emission signals, and a high-speed camera and a high-speed microscopic monitoring system for the rock fracture process are used to observe and record the crack propagation process.

[0074] Then, a multi-field and multi-phase rock triaxial test system is used to carry out uniaxial and triaxial experiments on cylindrical specimens with different water contents and different characteristic fractures. During the experiment, in addition to monitoring basic mechanical information such as load-displacement and stress-strain, an acoustic emission (AE) system is also used to monitor acoustic emission signals and record the crack propagation process. Since in the triaxial compression experiment, the specimen is wrapped with a rubber sleeve and placed in a pressure chamber, the acoustic emission probe needs to be arranged on the outer walls of the upper and lower loading heads and the loading cylinder to monitor the acoustic emission signals during the rock fracture process. In the triaxial compression experiment, the confining pressure σ3 is selected according to the in-situ stress of typical rock engineering. The schematic diagram of rock fracture under the influence of water is as Figure 8 shown.

[0075] Taking the immersion time Saturation and air-drying time is a variable (during the immersion and air-drying processes, the moisture content of the specimen may be the same but the moisture distribution is different, and the immersion and air-drying times are distinguished by "+" and "-"), which characterizes the changes in the water content and spatial distribution in the rock mass caused by moisture migration. The fracture is characterized by the dip angle β and the length 2a. Organize the experimental data and calculate the macroscopic mechanical property indexes of the fractured rock samples filled with clay under different loading conditions, including the tensile strength T in the Brazilian splitting test, the elastic modulus E and the strength σ in the uniaxial compression test UCS , and the compressive strength σ in the triaxial compression test TCS . Study the variation of the above mechanical property indexes with the water content state and the fracture characteristic characterization indexes, and clarify the degradation law of the mechanical properties of fractured rocks under the influence of moisture migration, that is:

[0076] In the case of the Brazilian splitting test In the case of the uniaxial compression test In the case of the triaxial compression test Among them is the confining pressure. Take the tensile strength T measured by the Brazilian splitting test, the elastic modulus E measured by the uniaxial compression test, and the cohesion c and friction angle φ calculated from the triaxial compression test data as the mechanical parameter set of the fractured rock. Compile a program through MATLAB to fit the experimental data and establish an expression for the variation law of the above mechanical parameters with the moisture migration water content state characterization index and the fracture characteristics, that is: Analyze the mathematical function form of the degradation law expressions of different mechanical parameters, study the physical meanings of the parameters included, and their relationships with the experimental conditions (loading conditions, water content state, fracture characteristics), so as to establish a degradation model of the mechanical parameters of the fractured rock mass under the influence of moisture migration

[0077] In addition, according to the stress-strain data of the fractured rock samples filled with clay obtained from the tests under moisture migration and different loading conditions, study the influence laws of the water content state, fracture characteristics, loading conditions, etc. on the form of the stress-strain curve, and establish a constitutive model of the fractured rock mass under moisture migration and different loading conditions

[0078] In this embodiment, a water valve is adopted to control the moisture migration mode in the clay-filled fractured rock mass, and two immersion schemes are also adopted: Scheme 1 simulates the moisture migration from the middle fracture to the surrounding of the rock sample (from the inside to the outside), and Scheme 2 simulates the moisture migration from the surrounding of the rock sample to the fracture direction (from the outside to the inside). During the experiment, a water repellent and paraffin must be used to treat the fracture and its nearby area

[0079] In this embodiment, aiming at the problem of the research object of the rock mass, sandstone with high water sensitivity is used as the fracture wall, and fractures with different characteristics are prefabricated and filled with clay medium to simulate the common clay-filled fractured rock mass in actual engineering

[0080] In this embodiment, a drill is used to obtain specimens, and then a grinding machine is used to cut and polish them to make standard cylindrical and disc specimens with heights of 100 mm and 25 mm respectively. Furthermore, a high-pressure water jet device is used to prepare fractures with different characteristics (dip angle and length), and the clay medium retrieved from the actual engineering site is filled into the fractures to simulate the special object of the actual project in order to simulate the fractured rock mass filled with clay.

[0081] This embodiment comprehensively considers the complex water-containing conditions caused by water migration and their interaction with the fractured rock mass filled with clay, proposes a method for characterizing the water-containing state of water migration, and prepares samples of the fractured rock mass filled with clay under different water-containing states.

[0082] This embodiment conducts micro and meso-scale test analysis. The test contents include: mineral composition analysis (XRD diffraction analysis and EDS energy dispersive spectrometer element distribution analysis) to quantitatively analyze the mineral composition of the samples; micro-morphology analysis (video microscopy images, SEM images, and polarized light microscopy image analysis) to qualitatively and quantitatively analyze the degree of change in the micro-morphology of mineral particles in the samples before and after the water-rock interaction; pore structure analysis (SEM images and mercury intrusion tests) to quantitatively analyze the degree of damage to the internal micro-pore structure of the samples before and after the water-rock interaction through image processing technology. These methods are used to determine the changes in the mineral components and micro and meso-scale structural characteristics of the fracture walls and fillers before and after the water-rock interaction, and to reveal the micro and meso-scale mechanism of the water-rock interaction in the fractured rock mass filled with clay.

[0083] This embodiment conducts nuclear magnetic resonance observation experiments to analyze the nuclear magnetic resonance gray-scale image characteristics during the water migration process, in order to study the water migration process in the fractured rock mass filled with clay, clarify the evolution law of the spatial distribution of water and the variation law of the diffusion coefficient with time during the water migration process, establish a water migration control equation, and construct a theoretical model for the water migration process in the fractured rock mass filled with clay.

[0084] This embodiment proposes a method for characterizing the water-containing state caused by water migration, prepares clay-filled fractured rock samples with different water-containing states and different fracture characteristics, and conducts indirect tensile, uniaxial, and triaxial compression failure experiments on them; studies the relationship between the deformation (elastic modulus) and strength (tensile, uniaxial, and triaxial compression) characteristics of the rock samples and the water-containing state characterization index and fracture characteristics (length and dip angle), clarifies the deterioration law of the deformation and strength characteristics of the clay-filled fractured rock mass under the influence of water migration, in order to establish a deterioration model of the mechanical parameters of the fractured rock mass, improve the deterioration law of the mechanical properties of the clay-filled fractured rock mass under different loading conditions, reveal the fracture process and mechanism of the fractured rock mass under water migration and different loading conditions, and reveal the fracture process and mechanism of the clay-filled fractured rock mass under water migration and load action, providing a theoretical basis for the mechanism of water-induced rock engineering disasters.

[0085] This embodiment proposes a method for characterizing complex water-containing states caused by water migration, clarifying the law of deterioration of the mechanical properties of clay-filled fractured rock masses induced by water migration from the perspective of water-rock interaction. Thus, a coupling model of water migration and mechanical parameter deterioration is established, its constitutive model is established, and a numerical model of engineering rock masses considering the effects of water migration and mechanical parameter deterioration is constructed. It is to reveal the fracture mechanism of clay-filled fractured rock masses under the combined action of water migration and external loads and to explore its preliminary engineering applications.

[0086] Based on the above experiments and research, according to the water migration boundary conditions and water migration control equations of actual projects, study the water migration law and water occurrence characteristics in engineering rock masses. According to the mechanical parameter deterioration model, provide parameters for the theoretical analysis of engineering stability. According to the acoustic emission monitored in the experiments, study the fracture process and mechanism. Thus, conduct research on the fracture mechanism of clay-filled fractured rock masses under the influence of water migration and explore its engineering applications.

[0087] The above-described embodiments merely represent the specific implementation manners of the present invention, and the description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. An experimental method for a fractured rock sample filled with water that reflects water migration and water content conditions, characterized in that, The preparation method of the filled fracture rock sample reflecting the water migration and water content conditions includes the following steps: Step 1: Process the sandstone block into a cuboid larger than the standard cylindrical specimen. Step 2: Place the cuboid on the drilling machine workbench, mark the drilling positions according to the required specimen positions, and use a core drill to obtain specimens. Step 3: Use a high-pressure water jet equipment to cut a through fracture in the middle of the specimen. The fracture characteristics include different dip angles β and different lengths 2a, and the fracture width is the same, forming a control group of different rock specimens. Step 4: Cut and polish with a grinding machine to make standard cylindrical and disc specimens. Step 5: Air-dry and crush the clay retrieved from the sampling site, and prepare clay-filled fracture specimens by configuring clay fillers according to the natural water content of the on-site clay. The experimental method includes the following steps: Step A: Carry out water absorption and water loss experiments on the filled or unfilled fracture rock samples after different numbers of wet-dry cycles, measure the water absorption and water loss curves of the fracture specimens, and provide a reference for the selection of immersion and air-drying time nodes. Step B: Carry out nuclear magnetic resonance observation experiments on the water migration process and law of the filled or unfilled fracture rock samples, and observe the water migration process and spatial distribution during the immersion and air-drying of the fracture specimens. Step C: Use an MTS rock mechanics experimental system to carry out Brazilian splitting experiments on the filled fracture disc specimens with different water content states and different fracture characteristics, monitor the basic mechanical information of load-displacement and stress-strain, and use an acoustic emission system to monitor the acoustic emission signals, and use a high-speed camera and a high-speed microscopic monitoring system for rock fracture process to observe and record the crack propagation process. Step D: Use a multi-field and multi-phase rock triaxial test system to carry out uniaxial compression experiments and triaxial compression experiments on cylindrical specimens with different water content states and different characteristic fractures; during the experiment, monitor the basic mechanical information of load-displacement and stress-strain, and use an acoustic emission system to monitor the acoustic emission signals and record the crack propagation process. Step E: Using the immersion time after multiple immersion-air drying cycle operations and the air drying time after saturation as variables to characterize the changes in the water content and spatial distribution of water within the rock sample caused by water migration, and using the dip angle β and the length 2a to characterize the fissure; calculating the mechanical property indexes of the fissure-filled rock sample under different loading conditions, and obtaining the degradation law of the mechanical properties of fissured rock under the influence of water migration according to the variation of the mechanical property indexes with the water content state and the fissure characteristic characterization indexes.

2. The experimental method for a filled fractured rock sample reflecting the water-bearing condition of water migration according to claim 1, characterized in that, In Step A, the water absorption and water loss experiment is specifically as follows: Place the filled or unfilled fracture specimens after wet-dry cycle treatment in an oven for drying, and place the dried specimens in a drying dish for storage; subsequently, carry out a saturation experiment and an air-drying experiment after saturation on the dried specimens after different numbers of wet-dry cycles; among them, in the saturation experiment, the states experienced by the specimens are successively dry, unsaturated, saturated, and long-term saturated; in the air-drying experiment after saturation, the states experienced by the specimens are successively saturated, unsaturated, and dry.

3. The experimental method for a filled fracture rock sample reflecting the water-bearing condition of water migration according to claim 2, characterized in that, The saturation scheme of the saturation experiment includes: (1) Simulate the water migration from the middle fracture to the surrounding of the rock sample. (2) Simulate the water migration from the surrounding of the rock sample to the fracture direction; and during the experiment, use a water repellent and paraffin to treat the fracture and its nearby areas.

4. The experimental method of the filled fractured rock sample reflecting the water-bearing condition of water migration according to claim 1, characterized in that In Step B, the nuclear magnetic resonance observation experiment is specifically as follows: In the process of preparing fractured rock samples with different water contents, some fractured disk and cylindrical samples are selected, and multiple time nodes during the water absorption and air-drying processes are chosen. First, the fractured rock samples after different numbers of wet-dry cycles are subjected to immersion and air-drying treatments for different times to obtain fractured samples with different water contents; then, nuclear magnetic resonance (NMR) observation experiments are carried out on the samples with different water contents.

5. The experimental method of the filled fractured rock sample reflecting the water migration water content condition according to claim 4, characterized in that, In the said NMR experiment, the gray values of the NMR images correspond one by one to the water contents at different positions. When establishing their quantitative correspondence relationship, the images are first calibrated. Taking the NMR image of a fractured disk or cylindrical rock sample that is saturated with water and has a uniform water distribution as the calibration standard, the maximum gray value of the calibrated sample image is extracted. Thus, the volumetric water content at different positions of the rock samples after immersion or air-drying for different times is obtained by converting the gray values, which is used to determine the diffusion coefficient during the water migration process in the fractured rock mass and to establish the water migration equation; then, the theoretical model of water migration in the fractured rock mass filled with clay is determined.

6. The experimental method of the filled fractured rock sample reflecting the water-bearing condition of water migration according to claim 5, characterized in that, The specific method for determining the theoretical model of water migration in the fractured rock mass filled with clay is as follows: The water migration control equation is determined according to the water migration law in the clay-filled fractured rock mass. When the temperature is constant, the water migration control equation is: where θ is the volumetric water content, D θ is the diffusion coefficient, which is a function of the water content θ or time t, is the gradient operator; Introduce the Boltzmann transformation parameter If p is a position function represented by two-dimensional coordinates, i.e., p(x, y), then the water migration control equation is transformed into: According to the initial and boundary conditions of moisture migration, by obtaining the relationship between water content θ and λ or time t through experiments, the diffusion coefficient D can be determined, and thus the specific expression of the moisture migration equation can be determined; among them, the initial and boundary conditions of moisture migration are: θ , thereby determining the specific expression of the moisture migration equation; among them, the initial and boundary conditions of moisture migration are:

7. The experimental method for a filled fractured rock sample reflecting water migration and water content conditions according to claim 6, characterized in that The water migration law is expressed by an empirical formula containing the relationship parameters between the water content θ and the Boltzmann transformation parameter λ: θ(λ) = -[θ s + atan -1 (bλ + c)] In the formula, the parameters θ and λ are measured by nuclear magnetic resonance observation experiments on rock samples with different soaking or air-drying times. Then, according to the experimental data, the parameters a, b, and c are obtained by fitting. Combining with the relational expression: θ(λ) = -[θ s + atan -1 (bλ + c)] and An expression for the diffusion coefficient with the moisture content as the independent variable is established: Thus, the specific expressions of the diffusion coefficient of water migration in the fractured rock mass filled with clay and the water migration control equation are determined.

8. The experimental method for a filled fractured rock sample reflecting the water content condition of water migration according to claim 7, characterized in that, In step E, the mechanical property indexes include: the tensile strength T in the Brazilian splitting test, the elastic modulus E and the strength σ in the uniaxial compression test UCS , and the compressive strength σ in the triaxial compression test TCS : where σ3 is the confining pressure; the tensile strength T determined by the Brazilian splitting test, the elastic modulus E determined by the uniaxial compression test, and the cohesion c and friction angle calculated from the triaxial compression test data are taken as the mechanical parameter set of fractured rocks, and an expression for the variation law of mechanical property indexes with the water migration water content characterization index and fracture characteristics is established, that is: Analyze the mathematical function forms of the degradation law expressions of different mechanical parameters, study the physical meanings of the parameters they contain, and their relationships with the experimental conditions, so as to establish a degradation model of the mechanical parameters of the fractured rock mass filled with clay under the influence of water migration.

9. The experimental method for a filled fractured rock sample reflecting water migration and water content conditions according to claim 8, characterized in that It also includes: According to the water migration and stress-strain data of the fractured rock samples under different loading conditions obtained from the experiments, study the influence laws of the water content state, fracture characteristics, and loading conditions on the form of the stress-strain curve, and establish a constitutive model of the fractured rock mass under water migration and different loading conditions.

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