Filling fractured rock sample preparation and experiment method for reflecting moisture migration water-containing conditions

Abstract

The invention discloses a preparation and experiment method of a filled fractured rock sample reflecting moisture migration water-containing conditions, and relates to the technical field of rock mass mechanics experiments, and the preparation and experiment method comprises the following steps: processing a sandstone block material into a cuboid larger than a standard cylindrical sample; the rectangular plate is placed on a drilling machine workbench, the drilling position is marked according to the needed sample position, and a rock core drilling machine is used for preparing a sample; high-pressure water jet equipment is used for cutting a penetrating crack in the middle of the sample, the crack characteristics comprise the inclination angle beta and the length 2a, the crack widths are the same, and control groups of different rock samples are formed; cutting and grinding by using a stone grinding machine to prepare standard cylinder and disc samples; the method comprises the following steps: air-drying and grinding clay taken back from a sampling site, preparing a clay filler according to the natural moisture content of the clay on site, and preparing a clay filling crack sample; the method can provide a basis for understanding a water-rock interaction mechanism and revealing a water-induced related rock mass engineering disaster mechanism.

Description

Technical Field

[0001] The present invention relates to the technical field of rock mass mechanics experiments, and particularly to a preparation method and an experimental method for a filled fissure rock sample reflecting 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 pressure and disturbance", and water is one of the most important environmental influencing factors. When highly water-sensitive rocks (such as sandstone, mudstone, limestone, etc.) or filling media between structural planes (such as clay, montmorillonite, etc.) exist 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 reservoir bank / open-pit slope landslides, large deformations of deep-buried caverns and roadway floor heaves.

[0003] The primary prerequisite for revealing the water-rock interaction mechanism is to clarify the occurrence characteristics of water in rock masses (rocks). At present, most of the relevant studies on water-rock interaction focus on the "content" of water in rocks, mostly using water content or saturation to characterize the water-containing state of rocks, and mostly assuming that the water in rocks is evenly distributed. In recent years, scholars have gradually realized that the migration process of water / moisture in rocks and the resulting non-uniform distribution of water will also significantly affect the mechanical properties and failure modes of rocks. However, the occurrence characteristics of water 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 water in the rock mass. Therefore, most of the current relevant studies can only reflect some aspects of the water-containing conditions of rock masses caused by water migration.

[0004] Filled fissure rock masses are very common in actual engineering. In many engineering disaster cases induced by water, highly water-sensitive rocks usually exist in the rock mass, and the fissures are filled with clay (or argillaceous) 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 studies on fissure rock masses related to water focus on their seepage characteristics, ignoring the influence of water migration on the mechanical property deterioration and fracture mechanism of clay-filled fissure rock masses.

[0005] It can be seen that under the combined action of water 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 water 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 technologies that can prepare filled fractured specimens reflecting the water-containing conditions of water migration, visualize the process of water 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 water migration and loads. However, there is currently a lack of relevant specimen preparation methods, observation methods for the water 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 purpose of the present invention is to provide a preparation and experimental method for filled fractured rock samples reflecting the water-containing conditions of water migration, which 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 purpose, the technical solution adopted by the present invention is: a preparation method for filled fractured rock samples reflecting the water-containing conditions of water migration, comprising the following steps: Step 1: Process sandstone blocks into cuboids larger than standard cylindrical specimens. 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 obtain specimens. Step 3: Use a high-pressure water jet device to cut a through crack in the middle of the specimen. The crack characteristics include the dip angle β and length 2 a , and the crack widths are 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 according to the natural water content of the on-site clay.

[0008] The present invention also provides an experimental method for filled fractured rock samples reflecting the water-containing conditions of water migration as described above, comprising the following steps: Step A: Carry out water absorption and 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 water immersion and air-drying time nodes. Step B: Conduct nuclear magnetic resonance observation experiments on the water migration process and laws in 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.

[0009] Step C: Use the MTS rock mechanics experimental system to conduct Brazilian splitting experiments on filled fractured disk 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; 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 characteristic fractures; 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; 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 in the rock sample caused by water migration, and use the inclination angle β and length 2 a to characterize the fracture; calculate the mechanical property indexes of the filled fractured rock samples under different loading conditions, and obtain the degradation law of the mechanical properties of fractured rocks under the influence of water migration according to the changes of the mechanical property indexes with the water content and fracture characteristic characterization indexes.

[0010] As a further improvement of the present invention, in Step A, the water absorption and water loss experiment is specifically as follows: Place the filled or unfilled fractured specimens after dry-wet cycling treatment in an oven for drying, and place the dried specimens in a drying dish for storage; subsequently, conduct saturation experiments and air-drying experiments after saturation on the dried specimens after different numbers of dry-wet 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.

[0011] As a further improvement of the present invention, the saturation scheme of the saturation experiment includes: (1) Simulate the water migration from the central 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.

[0012] As a further improvement of the present invention, 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 discs and cylindrical specimens 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 durations to obtain fractured specimens with different water contents; then, nuclear magnetic resonance (NMR) observation experiments are conducted on the specimens with different water contents.

[0013] As a further improvement of the present invention, in the NMR experiment, the gray values of the NMR images correspond one-to-one with the water contents at different positions. When establishing the quantitative correspondence relationship, the image is first calibrated. Taking the NMR image of a fractured disc 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 specimen image is extracted. Thus, the volumetric water content at different positions of the rock sample after immersion or air-drying for different durations is obtained through conversion from the gray value, 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.

[0014] As a further improvement of the present invention, 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 based on the water migration law in the clay-filled fractured rock mass. When the temperature is constant, the water 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; the Boltzmann transformation parameter is introduced, p is a position function, represented in two-dimensional coordinates, i.e., , then the water migration control equation is transformed into: According to the initial and boundary conditions of water migration, the relationship between the water content and or time t is obtained through experiments, and then the diffusion coefficient can be determined, thereby determining the specific expression of the water migration equation; among them, the initial and boundary conditions of water migration are: .

[0015] As a further improvement of the present invention, the water migration law is expressed by an empirical formula containing the relationship parameters between the water content and the Boltzmann transformation parameter : ; In the formula, the parameters and Measured by nuclear magnetic resonance observation experiments on rock samples with different soaking or air-drying times, and thus according to the experimental data, the parameters are fitted to obtain a 、 b and c ; Combining the relational expressions: and , an expression for the diffusion coefficient with 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.

[0016] 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 in the uniaxial compression test, and the strength σ UCS , the compressive strength σ TCS in the triaxial compression test: ; ; where is the confining pressure; taking 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 fractured rock mechanics parameter set, an expression for the variation law of the mechanical property indexes with the water migration water content characterization indexes and 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.

[0017] As a further improvement of the present invention, it further includes: According to the stress-strain data of the fractured rock samples filled with water under water migration and 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 filled with water under water migration and different loading conditions.

[0018] The present invention prepares rock sample fractures by means of high-pressure water jets, 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 actual fractured rock masses 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 fractured rock masses filled with clay, as well as the degradation law and fracture mechanism of the mechanical properties of fractured rock masses 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.

[0019] The beneficial effects of the present invention are as follows: 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 fractured rock masses filled with clay before and after water-rock interaction. This provides reliable microscopic data support for the degradation mechanism of rock masses and reveals the mesoscopic damage process of the internal structure of rock masses by water. By using mercury intrusion testing and SEM image processing technology, the changes in the internal pore structure of rock masses can be quantitatively analyzed. This quantitative evaluation method can accurately reveal the influence of water migration on the porosity and structural strength of rock masses, and provide a reference for the change of the physical properties of fractured rock masses.

[0020] 2. The present invention uses sandstone as the fracture wall and clay as the filling medium, and conducts micro and mesoscopic test experiments on the sandstone and clay fillers before and after water-rock interaction respectively, analyzes the mineral composition and micro and mesoscopic structures of the sandstone and clay fillers, provides a method for studying the micro and mesoscopic mechanisms, and also provides experimental data for the mechanism analysis of the degradation of the mechanical properties of water-induced clay-filled fractured rock masses.

[0021] 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 fractured rock masses in actual engineering. It enriches the understanding of water migration in fractured rock masses 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.

[0022] 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 moisture on clay fillings. This has 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 moisture migration on the deterioration of fractured rock mass. Especially in different cases such as fracture width and filling degree, the action modes of moisture on clay are different. Through microstructural testing and nuclear magnetic resonance technology, the migration path of moisture in clay and its erosion and weakening effects on fractures are analyzed, and further discussion is carried out on how the swelling effect of clay leads to the structural deterioration and mechanical property decline of fractured rock mass.

[0023] 5. By controlling the water content of rock samples and the moisture migration path, the moisture migration behavior under different water content conditions is simulated. This process can reproduce the migration of moisture from the inside to the outside or from the outside to the inside in fractured rock samples, and truly reflect the water-containing characteristics of fractured rock mass in actual engineering. The present invention verifies the deterioration law of rock samples during the process of moisture migration from fractures to the outside or from the outside to fractures by designing two water absorption and water loss experimental schemes. This innovative experimental design enables the research to not only focus on the influence of static water content on mechanical properties, but also cover the comprehensive action effect of moisture on fractured rock samples during the dynamic migration process.

[0024] 6. By designing two different soaking schemes, the present invention not only simulates the moisture migration from fractures to the surroundings (from the inside to the outside), but also simulates the situation of moisture migration from the outside to fractures (from the outside to the inside). This two-way moisture migration mode can more truly reproduce the actual moisture migration process in engineering and provide more diverse experimental data.

[0025] 7. Through nuclear magnetic resonance gray-scale image analysis, the present invention establishes the migration control equation of moisture under different water-containing states, and then determines the moisture diffusion coefficient. This not only provides a theoretical basis for the moisture migration law in rock mass, but also quantitatively characterizes the diffusion and distribution of moisture in fractured rock mass through a mathematical model, laying a foundation for the mechanical research of rock mass 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 mass. This quantitative analysis method helps to reveal the specific influence of the change in volumetric water content during the moisture migration process on the mechanical properties of rock mass (such as elastic modulus, compressive strength, etc.).

[0026] 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 the 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 clay under different moisture migration boundary conditions accordingly.

[0027] 9. Through in-depth research on the rock mass fracture process 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 caused by moisture (such as slope landslides and cavern instability).

[0028] 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 fractured rock mass degradation, researchers can better predict the impact of moisture migration on engineering rock masses and improve the stability assessment ability of geotechnical engineering.

[0029] 11. Through experiments under different loading conditions (such as Brazilian splitting test, uniaxial compression, and triaxial compression tests), 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.

[0030] 12. Through 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 process of crack formation, propagation, and fracture 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.

[0031] 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. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 is a flow chart of the experimental method in the embodiment of the present invention; Figure 2Line drawing of the equipment for preparing and detecting fractures in the embodiments of the present invention; Figure 3 Schematic diagram of the clay-filled fractured rock sample in the embodiments of the present invention; Figure 4 Schematic diagram of the migration of moisture from the periphery of the rock sample towards the fracture (from the outside to the inside) in the embodiments of the present invention; Figure 5 Schematic diagram of the migration of moisture from the central fracture towards the periphery of the rock sample (from the inside to the outside) in the embodiments of the present invention Figure 6 Schematic diagram of the gray-scale correction of nuclear magnetic resonance images in the embodiments of the present invention; Figure 7 Schematic diagram of the migration process of moisture in rock in the embodiments of the present invention; Figure 8 Schematic diagram of rock fracture under the influence of water in the embodiments of the present invention. Detailed implementation manners

[0033] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0034] Embodiment

[0035] As Figure 1 shown, a method for preparing a fractured rock sample filled with moisture to reflect moisture migration conditions includes: 1. To improve the success rate of sample preparation, first process the sandstone block into a cuboid slightly larger than the standard cylindrical (50 mm in diameter × 100 mm in height) sample.

[0036] 2. Then place the rectangular plate on the drilling machine workbench to ensure that it does not move during the drilling process. Use a core drill with a diamond drill bit, select a drill bit with a diameter of 50 mm, mark the drilling position according to the required sample position, and prepare the sample. Start the drill, and the drill bit slowly presses down and starts drilling. Use a coolant (such as water or oil) to cool the drill bit to prevent overheating, and at the same time reduce cracks and debris in the sandstone. After drilling is completed, extract the cylindrical core, which is the required sample. During the drilling process, maintain the stability of the drill bit and a consistent downward pressure to avoid cracks or irregularities on the surface of the sample.

[0037] 3. Use a high-pressure water jet equipment to cut a through fracture in the middle of the sample. As Figure 2 shown, the fracture characteristics include the dip angle β (taking 15°, 30°, 45°, 60° and 90°) and the length 2a (taking 6, 8, 10 and 12 mm), and the fracture width is the same (about 2 mm), forming a control group of different rock samples.

[0038] 4. Then use a grinder to cut and grind to make cylindrical and disc specimens with heights of 100 mm and 25 mm respectively.

[0039] 5. The clay collected from the sampling site was air-dried, crushed, and passed through a 0.5 mm sieve. Clay filling was prepared according to the natural moisture content of the clay on site. The filling degree of each sample was uniformly considered as 100%, and clay-filled crack samples were prepared, such as Figure 3 In order to study the influence of clay filling medium, some non-filled fracture samples were retained for comparative tests. At this point, the preparation of rock samples was completed.

[0040] This embodiment also provides an experimental method for filling fractured rock samples to reflect water migration and water-containing conditions as described above, specifically comprising: The water absorption and water loss experiments were carried out on the fractured rock samples after different times of dry-wet cycles. First, the fractured samples (filled or unfilled) after dry-wet cycles were placed in an oven for drying, and the dried samples were stored in a drying dish; then, the dried samples after different times of dry-wet cycles were subjected to saturated water (the samples were from dry to unsaturated to saturated to long-term saturation) and saturated and then air-dried (the samples were from saturated to unsaturated to dry) experiments, and the water absorption and water loss curves of the fractured samples were determined to provide a reference for the selection of immersion and air-drying time nodes.

[0041] In order to consider the directionality of water migration in actual rock mass engineering, the experiment of this embodiment designs two saturation schemes. Among them, scheme 1 simulates the migration of water from the middle crack to the surrounding of the rock sample (from inside to outside). Figure 5 As shown in Figure 2, Scheme 2 simulates the migration of water from the surrounding areas of the rock sample to the cracks (from outside to inside). Figure 4 As shown in the figure, during the experiment, the cracks and the surrounding areas must be treated with hydrophobic agents and paraffin.

[0042] Next, we will conduct nuclear magnetic resonance observation experiments on the water migration process and laws of fractured rock samples (filled or unfilled). In the process of preparing fractured rock samples with different water contents, some typical fractured disks and cylinders were selected (without considering the influence of fracture characteristics on water migration laws). The experiment will select multiple time points in the water absorption and air drying process. First, the fractured rock samples after different times of dry-wet cycles are immersed in water and air-dried for different times to obtain fractured samples with different water contents. Then, nuclear magnetic resonance experiments are conducted on these samples with different water contents to observe the migration process and spatial distribution of water during the immersion and air-drying of fractured samples.

[0043] The gray value of the NMR image corresponds to the moisture content at different locations. To quantitatively establish this correspondence, the image needs to be calibrated first, such as Figure 6As shown, the nuclear magnetic resonance images of the saturated and uniformly water-distributed filled-fracture disc or cylindrical rock samples are used as the calibration standard (the water content of the calibration rock samples can be easily measured by experiments). The maximum gray value of the calibration sample image is extracted, and thus the volumetric water content at different positions of the rock samples at different immersion or air-drying times can be obtained by converting the gray value. These observed data will provide an experimental basis for determining the diffusion coefficient during the water migration process in fractured rock masses and establishing the water migration equation. The water migration process in rocks is as shown in Figure 7 shown.

[0044] Then, determine the theoretical model of water migration in the filled-fractured rock mass. When the fractured rock samples are immersed or saturated and then air-dried for different times ( or ), water migrates in the rock samples, resulting in different water-containing states at different positions inside the rock samples, that is, the spatio-temporal state of water in the filled-fractured rock mass is constantly changing. Through the water migration law in the clay-filled fractured rock mass and determine the specific expression of the water migration equation: When the temperature is constant, the control equation of water migration (humidity diffusion) can be expressed as: In the formula, is the volumetric water content (the ratio of water to rock volume), 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 position function, and in plane problems, it is represented by two-dimensional coordinates, that is , then the control equation of water migration can be expressed as: Further consider the initial and boundary conditions of water migration: It can be seen that by obtaining the relationship between the water content and (or time t) through experiments, the diffusion coefficient can be determined, and thus the specific expression of the water migration equation can be determined. In this embodiment, the filled-fractured rock mass is taken as the research object, and the immersion and air-drying with different cycle numbers are considered, that is, the time t in the above formula is or .

[0045] Through nuclear magnetic resonance experiments and resonance gray image processing technology, determine the diffusion coefficient and the specific expression of the water migration equation, and use an empirical formula containing three parameters to express the water migration law (that is, the relationship between the volumetric water content and the Boltzmann transformation parameter ): .

[0046] In this formula, the parameters and They can all be measured by nuclear magnetic resonance observation experiments on rock samples with different soaking or air-drying times. Thus, based on the experimental data, parameters a, b, and c can be obtained by fitting. Combining the relational expression: An expression for the diffusion coefficient with volumetric water content as the independent variable can be established: According to the above research idea, the diffusion coefficient of water migration in fractured rock masses filled with clay and the specific expression of the migration control equation can be determined.

[0047] To study the influence of clay-filled media, mechanical experiments will be carried out on fractured rock samples under three basic loading conditions (indirect tension, uniaxial compression, and triaxial compression) in this test. During the Brazilian splitting experiment on fractured disk specimens with different water contents and different fracture characteristics using the MTS 816 rock mechanics test system, in addition to monitoring basic mechanical information such as load-displacement and stress-strain, acoustic emission (AE) signals will also be monitored using an AE system, and a high-speed camera and a high-speed microscopic monitoring system for rock fracture processes will be used to observe and record the crack propagation process.

[0048] Subsequently, a multi-field and multi-phase rock triaxial test system will be used to carry out uniaxial and triaxial experiments on cylindrical specimens with different water contents and different fracture characteristics. During the experiment, in addition to monitoring basic mechanical information such as load-displacement and stress-strain, acoustic emission (AE) signals will also be monitored using an AE system to record the crack propagation process. Since the specimen is wrapped in a rubber sleeve and placed in a pressure chamber during the triaxial compression experiment, the AE probe needs to be arranged on the outer walls of the upper and lower platens and the loading cylinder to monitor the AE signals during the rock fracture process. During the triaxial compression experiment, the confining pressure σ3 is to be 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.

[0049] Taking the soaking time and the air-drying time after saturation after n soaking-air-drying cycle operations as variables (during the soaking and air-drying processes, the water content of the specimen may be the same but the water distribution is different, and the soaking and air-drying times are distinguished by “+” and “-”), characterizing the changes in the water content and spatial distribution in the rock mass caused by water migration, and using the dip angle β and length 2a to characterize the fracture. Organize the experimental data and calculate the macroscopic mechanical property indexes of the fractured rock samples under different loading conditions, including the tensile strength T in the Brazilian splitting experiment, the elastic modulus E and strength σ UCS in the uniaxial compression experiment, and the compressive strength σ TCS in the triaxial compression experiment. Study the variation of the above mechanical property indexes with the water content state and fracture characteristic characterization indexes, and clarify the degradation law of the mechanical properties of fractured rocks under the influence of water migration, that is: For the Brazilian splitting experiment condition, For the uniaxial compression experiment condition, For the triaxial compression experiment condition, where 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 φ calculated from the triaxial compression test data are taken as the mechanical parameter set of fractured rock. A program is compiled by MATLAB to fit the experimental data, and an expression for the variation law of the above mechanical parameters with the water migration water content characterization index and fracture characteristics is established, that is: Analyze the mathematical function form of the deterioration law expression of different mechanical parameters, study the physical meaning of the parameters it contains, and its relationship with the experimental conditions (loading conditions, water content state, fracture characteristics), so as to establish a deterioration model of the mechanical parameters of the filled fractured rock mass under the influence of water migration.

[0050] In addition, based on the stress-strain data of the filled fractured rock samples obtained from the test under water migration and different loading conditions, study the influence law 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 filled fractured rock mass under water migration and different loading conditions.

[0051] In this embodiment, a water valve is used to control the water migration mode in the clay-filled fractured rock mass, and two immersion schemes are also adopted: Scheme 1 simulates the water migration from the middle fracture to the periphery of the rock sample (from the inside to the outside), and Scheme 2 simulates the water migration from the periphery of the rock sample to the fracture direction (from the outside to the inside). During the experiment, a water repellent and paraffin are used to treat the fracture and its adjacent area.

[0052] 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.

[0053] In this embodiment, a drilling machine is used to take samples, and then a grinding machine is used to cut and polish them to make standard cylindrical and disc samples with heights of 100 mm and 25 mm respectively. Furthermore, a high-pressure water jet equipment 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, in order to simulate the special object of the actual project to simulate the filled fractured rock mass.

[0054] This embodiment comprehensively considers the complex water content conditions caused by water migration and its interaction with the clay-filled fractured rock mass, proposes a method for characterizing the water content state of water migration, and prepares clay-filled fractured rock mass samples under different water content states.

[0055] In this embodiment, microscopic tests and analyses are carried out. 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 sample; microscopic morphology analysis (video microscopic images, SEM images, and polarized light microscopic image analysis) to qualitatively and quantitatively analyze the change degree of the microscopic morphology of the sample mineral particles before and after the water-rock interaction; pore structure analysis (SEM images and mercury intrusion tests) to quantitatively analyze the damage degree of the internal micropore structure of the sample before and after the water-rock interaction through image processing technology. These methods are used to determine the changes in the mineral components and microscopic structural characteristics of the fracture wall and filling material before and after the water-rock interaction, and to reveal the microscopic mechanism of the water-rock interaction in the clay-filled fractured rock mass.

[0056] In this embodiment, nuclear magnetic resonance observation experiments are carried out to analyze the nuclear magnetic resonance gray-scale image characteristics of the water migration process, in order to study the water migration process in the clay-filled fractured rock mass, clarify the evolution law of the water spatial distribution and the law of the diffusion coefficient changing with time during the water migration process, establish the water migration control equation, and construct the theoretical model of the water migration process in the clay-filled fractured rock mass.

[0057] In this embodiment, a method for characterizing the water content state caused by water migration is proposed. Clay-filled fractured rock samples with different water content states and different fracture characteristics are prepared, and indirect tensile, uniaxial, and triaxial compression failure experiments are carried out on them; the relationships between the deformation (elastic modulus) and strength (tensile, uniaxial, and triaxial compression) characteristics of the rock samples and the water content state characterization indexes and fracture characteristics (length and dip angle) are studied to clarify 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 mass engineering disasters.

[0058] In this embodiment, a method for characterizing the complex water content state caused by water migration is proposed. The deterioration law of the mechanical properties of the clay-filled fractured rock mass induced by water migration is clarified from the perspective of the 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 the engineering rock mass considering the effects of water migration and mechanical parameter deterioration is constructed. It is to reveal the fracture mechanism of the clay-filled fractured rock mass under the combined action of water migration and external load, and to explore its preliminary engineering applications.

[0059] Based on the above experiments and studies, according to the moisture migration boundary conditions and moisture migration control equations of actual projects, study the moisture migration law and water occurrence characteristics in engineering rock masses. According to the mechanical parameter degradation 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 moisture migration and explore engineering applications.

[0060] The above-described embodiments only represent the specific implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent 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 deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A preparation method of a fractured rock sample filled with water that reflects water migration and water content conditions, characterized in that, It includes the following steps: Step 1: Process the sandstone block into a cuboid larger than the standard cylindrical specimen. Step 2: Place the rectangular plate 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 device to cut a through crack in the middle of the specimen. The crack characteristics include dip angle β and length 2 a , and the crack widths are 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 a clay-filled fracture specimen by configuring a clay filler according to the natural water content of the on-site clay.

2. An experimental method for a filled fracture rock sample reflecting the water content condition of water migration, characterized in that, The filled fracture rock sample is prepared by the method for preparing a filled fracture rock sample reflecting water migration and water-bearing conditions described in claim 1. 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 the soaking 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 soaking and air-drying processes 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 contents 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 contents 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 soaking time 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, using the dip angle β and the length 2 a to characterize the fissure; calculating the mechanical property indexes of the fissure-filled rock sample under different loading conditions, and obtaining the deterioration 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.

3. The experimental method of the filled fracture rock sample reflecting the water content condition of water migration according to claim 2, 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 treatment, and store the dried specimens in a drying dish; then, 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.

4. The experimental method for a filled fractured rock sample reflecting water migration and water content conditions according to claim 3, 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 in the experimental process, use a water repellent and paraffin to treat the fracture and its nearby areas.

5. The experimental method of the filled fracture rock sample reflecting the water content condition of water migration according to claim 2, characterized in that, In step B, the nuclear magnetic resonance observation experiment is specifically as follows: During the preparation of filled fracture rock samples with different water contents, select some filled fracture discs and cylindrical specimens, select multiple time nodes during the water absorption and air-drying processes, first carry out soaking and air-drying treatments on the fracture rock samples after different numbers of wet-dry cycles for different times to obtain fracture specimens with different water contents; then, carry out nuclear magnetic resonance observation experiments on the specimens with different water contents.

6. The experimental method for a filled fractured rock sample reflecting water migration and water content conditions according to claim 5, characterized in that, In the nuclear magnetic resonance experiment, the gray values of the nuclear magnetic resonance images correspond one-to-one with the water contents at different positions. When establishing their quantitative correspondence relationship, the image is first calibrated. Taking the nuclear magnetic resonance image of a saturated and uniformly water-distributed fractured disc or cylindrical rock sample immersed in water as the calibration standard, the maximum gray value of the calibrated sample image is extracted. Then, the volumetric water content at different positions of the rock sample immersed in water or air-dried for different times is obtained by converting the gray value, 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 water is determined.

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 specific method for determining the theoretical model of water migration in the fractured rock mass filled with water is as follows: The moisture migration control equation is determined by the law of moisture migration in fractured rock masses filled with clay. When the temperature is constant, the moisture migration control equation is as follows: 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; the Boltzmann transformation parameter is introduced, p is a position function, expressed 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, the relationship between the water content and or time t is obtained 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: .

8. The experimental method for a filled fractured rock sample reflecting water migration and water content conditions according to claim 7, characterized in that Express the moisture migration law with an empirical formula containing the relationship parameters between the moisture content and the Boltzmann transformation parameter : ; In the formula, the parameters and are measured by nuclear magnetic resonance observation experiments on rock samples soaked or air-dried for different times. Thus, according to the experimental data, the parameters a , b and c are obtained by fitting; combined with the relationship formula: and , establish an expression for the diffusion coefficient with the moisture content as the independent variable: Thus, determine the diffusion coefficient of moisture migration in the fractured rock mass filled with water and the specific expression of the migration control equation.

9. The experimental method for a filled fractured rock sample reflecting the water content condition of water migration according to claim 8, characterized in that, In step E, the mechanical property indexes include: the tensile strength in the Brazilian splitting test T , the elastic modulus in the uniaxial compression test E and strength σ UCS , the compressive strength in the triaxial compression test σ TCS : ; ; where is the confining pressure; taking the tensile strength determined by the Brazilian splitting test T , the elastic modulus determined by the uniaxial compression test E , and the cohesion c and friction angle φ calculated from the triaxial compression test data as the mechanical parameter set of fractured rock, and establishing an expression for the variation law of the mechanical property indexes with the water content characterization index of water migration and the fracture characteristics, that is: Analyze the mathematical function forms of the deterioration 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 deterioration model of the mechanical parameters of the fractured rock mass filled with cracks under the influence of water migration.

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

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