A sample preparation and testing method for studying self-closing characteristics of rock mass fractures

Abstract

This invention relates to the field of rock material performance testing, and in particular to a sample preparation and testing method for studying the self-closing characteristics of rock fractures. Addressing the limitations of existing technologies in achieving simultaneous acquisition and fusion of multi-source information, and in the refined observation and quantitative characterization of fracture surface self-closing behavior, the following solution is proposed, comprising sample preparation, fracture surface monitoring, sample sealing, external monitoring, and experimental testing steps. A matching rock specimen with an intermediate fracture surface is fabricated. Fixed fiber optic sensors are deployed on the fracture surface. After multiple sealing operations, fiber optics or traditional deformation sensors are selectively deployed on the outer surface of the specimen. A triaxial testing system is then used to conduct fracture self-closing performance testing under temperature-stress-seepage-chemical multi-field coupling conditions to obtain key characterization parameters. This invention achieves refined observation and quantitative characterization of fracture surface self-closing behavior under temperature-stress-seepage-chemical multi-field coupling conditions.

Description

Technical Field

[0001] This invention relates to the field of rock material performance testing, and in particular to a sample preparation and testing method for studying the self-closing characteristics of rock fractures. Background Technology

[0002] As my country's energy strategy expands into deeper geological environments and major underground engineering projects extend into complex geological conditions, the high stress, high osmotic pressure, and multi-field coupling environment of deep rock masses cause their mechanical behavior to differ significantly from that of shallow rock masses. The self-closing characteristic of rock mass fissures is a key factor controlling the long-term stability of the surrounding rock and the effectiveness of groundwater storage. Under the coupling effect of stress and seepage, natural fissure surfaces will gradually close, exhibiting a "self-closing" behavior. This process not only directly changes the seepage channels and seepage paths of the rock mass but also affects the deformation coordination and long-term strength of the surrounding rock through stress redistribution, thus having a profound impact on the sealing performance of energy reservoirs, the stability of deep tunnels, and the barrier performance of high-level radioactive waste geological disposal sites.

[0003] In-depth research on the self-closing characteristics of rock fractures requires sample preparation and testing methods that can realistically simulate natural rough fractures and accurately characterize their responses under high temperature, seepage, stress, and chemical coupling. However, existing testing methods for the self-closing characteristics of rock fractures mostly only obtain macroscopic mechanical parameters of the rock mass, failing to achieve in-situ, dynamic, and quantitative characterization of local closure displacement, contact evolution, and seepage path changes at the fracture surface. This makes it difficult to meet the technical requirements for studying the multi-field coupling mechanism of deep rock masses, predicting long-term engineering safety, and disaster prevention and control. Furthermore, it cannot provide accurate experimental data support for the design and safety assessment of major projects such as deep-earth resource development, carbon dioxide geological storage, and nuclear waste disposal. Therefore, this proposal suggests a sample preparation and testing method for studying the self-closing characteristics of rock fractures. Summary of the Invention

[0004] This invention proposes a sample preparation and testing method for studying the self-closing characteristics of rock mass fractures, which solves the problems in the prior art of being unable to achieve simultaneous acquisition and fusion of multi-source information, as well as the problem of fine observation and quantitative characterization of fracture surface self-closing behavior.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A sample preparation and testing method for studying the self-closing characteristics of rock mass fractures includes the following steps:

[0007] S1. Sample preparation: Two matching rock blocks with intermediate fracture surfaces are processed. The matching rock blocks can be composed of the same type of rock or two different types of rock. The processing methods of the target blocks with fracture surfaces include forming natural fracture surfaces in a single rock block using the Brazilian splitting method, forming natural fracture surfaces at the interface of two naturally cemented rocks using the Brazilian splitting method, or artificially prefabricating fracture surfaces with different roughness and undulation to meet the research needs of different fracture types.

[0008] S2. Fracture Surface Monitoring: Fiber optic sensors are installed on the fracture surface and fixed with epoxy resin. The fiber optic sensors can be installed in single or multiple lines along the axial direction of the rock sample, or in a grid pattern, to achieve accurate monitoring of the local structural evolution of the fracture surface.

[0009] S3. Sample sealing: The assembled sample is sealed with multiple layers of sealing, including primary and secondary sealing, to ensure the stability of the sample under complex environments such as high pressure seepage and high temperature. The primary sealing involves placing the sample between the upper and lower rigid pressure heads and wrapping it with a high-temperature and corrosion-resistant sealing sleeve. The secondary sealing involves setting a sealing ring and a retainer at the upper and lower rigid pressure heads after the primary sealing to improve the sealing effect.

[0010] S4. External monitoring: A conventional triaxial specimen deformation monitoring sensor is installed on the outer surface of the rock specimen, and / or an optical fiber is fixed with epoxy resin for deformation measurement. Both methods can also be used in combination. The optical fibers on the surface of the rock specimen can be arranged vertically, horizontally, spirally or in a dense grid pattern, and the arrangement density can be adjusted according to the monitoring requirements to achieve multi-mode monitoring of the overall deformation of the specimen.

[0011] S5. Experimental Testing: The sealed sample with the monitoring device installed is placed in a triaxial chamber, and the self-closing effect of the crack is tested under complex conditions. Test data reflecting the evolution of the rock block and the crack surface structure are obtained, and structural parameters characterizing the overall sample and the self-closing effect of the crack are extracted based on the test data.

[0012] The above technical solution enables multi-dimensional monitoring of the crack interior and the sample surface, allowing simultaneous acquisition of structural evolution data of the crack surface and the overall sample. This provides a comprehensive data foundation for subsequent quantitative characterization of crack self-closing behavior. At the same time, multiple sealing processes ensure the smooth conduct of the experiment under complex conditions.

[0013] As a further improvement to the above scheme, in S5, the complex conditions are to apply confining pressure, temperature and water pressure to the rock specimen to make it reach a consolidation state, with permeable stones set at the upper and lower ends of the specimen, and the specimen can be pre-saturated by applying back pressure; in the saturation or crack self-closure test process, fluids with different chemical properties can be used to simulate the crack self-closure behavior under different chemical environments.

[0014] The above technical solutions can realistically reproduce the multi-field coupled geological environment of deep rock masses, realize the simulation study of fracture self-closure behavior under different hydrological and chemical conditions, and make the experimental results more consistent with engineering practice.

[0015] As a further improvement to the above scheme, the consolidated rock specimens are loaded using displacement control or stress control methods. The mechanical loading methods can be cyclic loading and unloading, graded loading, or long-term creep test under a fixed load, or long-term relaxation test under a fixed shear displacement, to meet the research needs of different mechanical loading conditions.

[0016] The above technical solutions can simulate the stress state of deep rock masses under different stress conditions, enabling a systematic study of the self-closing characteristics of fractures under various mechanical conditions, thus enriching the research dimensions and applicable scenarios of the experiment.

[0017] As a further improvement to the above scheme, the crack self-closure experiment can be carried out under different confining pressure, temperature, water pressure and chemical environments, and set according to different stress paths. The experiment can be carried out under single field, two field, three field or four field coupling conditions to realize the crack self-closure characteristic test under temperature-stress-seepage-chemical multi-field coupling conditions. For experiments involving high temperature, temperature compensation optical fiber should be set to correct the influence of temperature on optical fiber signal and improve the accuracy of monitoring data.

[0018] The above technical solution breaks through the limitation of traditional testing methods that can only carry out single-field or simple two-field coupling experiments, and realizes accurate testing of the self-closing characteristics of cracks under multi-field coupling conditions. At the same time, the setting of temperature-compensated optical fiber effectively eliminates the interference of temperature on optical fiber sensing signal and ensures the reliability of monitoring data.

[0019] As a further improvement to the above scheme, the permeability coefficient test of the self-closing characteristic of the fracture during the seepage process can be carried out by steady-state method, transient method or periodic oscillation method, and the appropriate test method can be selected according to the experimental requirements.

[0020] The above technical solutions allow for flexible selection of permeability coefficient testing methods based on different experimental conditions, fracture types, and research precision requirements, ensuring the accuracy and adaptability of permeability coefficient data and providing reliable indicators for analyzing the impact of fracture self-closure on rock mass seepage characteristics.

[0021] As a further improvement to the above scheme, it also includes the steps of conducting microstructure tests on rock specimens or fracture surfaces before and after the experiment to obtain data reflecting the evolution of the internal structure of the specimens. Microstructure tests include, but are not limited to, scanning electron microscopy (SEM), nuclear magnetic resonance (NMR), mercury intrusion porosimetry (MIP), gas adsorption analysis, as well as CT scanning or digital image correlation (DIC) three-dimensional reconstruction of the fracture surface. Through comparative analysis of the microstructure before and after the experiment, the intrinsic mechanism of fracture self-closure can be revealed more deeply.

[0022] The above technical solutions enable multi-scale research from macroscopic mechanical response and microscopic crack evolution to microscopic structural changes. By combining dynamic monitoring data during the experiment with microscopic structural comparisons before and after the experiment, the evolutionary mechanism of crack self-closure can be revealed in essence, making the research conclusions more scientific and in-depth.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] 1. This invention combines customized fracture rock sample preparation process with distributed optical fiber sensing technology. Based on the traditional triaxial test system, it realizes refined observation and quantitative characterization of the self-closing behavior of fracture surfaces under multi-field coupling conditions of temperature-stress-seepage-chemistry, breaking through the limitation of traditional methods that can only obtain macroscopic mechanical parameters of rock mass.

[0025] 2. This invention realizes the synchronous acquisition and fusion of multi-source information from "fiber optic monitoring inside the crack - multi-mode sensing on the sample surface - macroscopic loading of the triaxial system". It can not only obtain the stress-strain response of the whole sample, but also realize the in-situ, dynamic and quantitative characterization of local closure displacement, contact evolution and seepage path change of the crack surface based on distributed fiber optic sensing for the first time. The monitoring dimensions are more comprehensive and the data is more accurate.

[0026] 3. The sample preparation process of this invention is flexible and can prepare matching rock blocks with different rock types and different fracture surface forms (natural splitting surface, artificial prefabricated rough surface). The experimental test can be set with a variety of complex conditions and loading methods, which is suitable for the study of the self-closing characteristics of rock fractures in different research scenarios and has wide applicability.

[0027] 4. This invention employs a multi-seal process, utilizing a combination of sealing sleeves, sealing rings, and ferrules to ensure the testing stability of rock specimens under complex conditions such as high pressure, high temperature, and seepage. Simultaneously, temperature-compensated optical fibers correct signal errors, enhancing the reliability and accuracy of experimental data. Furthermore, by combining microstructural testing before and after the experiment, the evolutionary mechanism of crack self-closure can be revealed from a macroscopic and microscopic perspective.

[0028] 5. The key parameters of fracture self-closing behavior obtained by this invention can effectively reveal the self-closing effect of fractures under different mechanical and seepage paths, providing reliable experimental basis and methodological support for the study of rock mass mechanical damage evolution, fluid transport law and multi-field coupling mechanism in deep underground engineering, and also providing key technical support for the design and safety evaluation of major projects such as deep earth resource development, carbon dioxide geological storage and nuclear waste disposal. Attached Figure Description

[0029] Figure 1 This is a flowchart of the testing method according to an embodiment of the present invention;

[0030] Figure 2 A schematic diagram of the optical fiber layout for the sample in an embodiment of the present invention.

[0031] Explanation of key symbols:

[0032] 1. Rigid indenter; 2. Compression sleeve; 3. Sealing ring; 4. Permeable stone; 5. Sealing sleeve; 6. Rock specimen; 7. Fracture surface; 8. Optical fiber. Detailed Implementation

[0033] The present invention will now be further described in conjunction with the accompanying drawings and specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0034] Example 1:

[0035] Please combine Figure 1 - Figure 2 This embodiment describes a sample preparation and testing method for studying the self-closing characteristics of rock mass fractures. Specifically, it focuses on the study of the natural fracture self-closing characteristics of a single granite rock mass. The specific steps are as follows:

[0036] 1. Sample preparation: Select a complete granite block, process it into a standard cylindrical block, and use the Brazilian splitting method to split the cylindrical block into two semi-circular solids of similar size, which serve as matching rock blocks 6 with a natural fracture surface 7 in the middle.

[0037] 2. Crack surface monitoring: Three fiber optic sensors 8 are evenly spaced along the axial direction on the crack surface 7 of the granite. Epoxy resin is used to firmly fix the fiber optic sensors 8 to the crack surface 7 to ensure that the fiber optics 8 and the crack surface 7 deform synchronously.

[0038] 3. Sample sealing: The assembled granite rock sample 6 is placed between the upper and lower rigid pressure heads 1. The sample is wrapped with a high-temperature and corrosion-resistant sealing sleeve 5 to complete the initial sealing. Then, rubber sealing rings 3 and metal ferrules 2 are installed at the upper and lower rigid pressure heads 1 to achieve a secondary sealing, thus achieving multiple sealing.

[0039] 4. External monitoring: Fiber optic sensors 8 are spirally arranged on the outer surface of rock block 6. The fiber optics 8 are fixed with epoxy resin. The arrangement density is one circle every 10 cm of axial length. At the same time, three traditional axial deformation sensors are symmetrically installed around the rock block 6 to realize multi-mode monitoring of the overall deformation of the sample.

[0040] 5. Pre-experiment treatment: The sealed sample with the monitoring device installed is placed in the triaxial chamber of the triaxial test system. The upper and lower ends of the sample are fitted with permeable stones 4. The sample is pre-saturated by applying back pressure. The saturation medium is deionized water.

[0041] 6. Experimental Testing: A confining pressure of 10 MPa, a temperature of 25℃, and a water pressure of 2 MPa were applied to rock specimen 6 to achieve a consolidation state. The consolidated rock specimen 6 was subjected to graded loading using a displacement control method at a loading rate of 0.01 mm / min. The self-closing effect of the fracture under the coupled stress-seepage two-field conditions was carried out. During the seepage process, the permeability coefficient of the fracture was tested using the steady-state method. Simultaneously, monitoring data from the optical fiber 8 inside the fracture and the sensor on the specimen surface were collected to obtain multi-source data on the overall deformation of the specimen and the local structural evolution of the fracture surface 7.

[0042] 7. Microscopic Testing and Data Analysis: Before the experiment, CT scans were used to reconstruct the three-dimensional structure of the granite fracture surface 7. After the experiment, scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR) tests were performed on the fracture surface 7. The multi-source data obtained during the experiment were comprehensively analyzed to extract key parameters characterizing the self-closing behavior of the fracture, such as fracture closure displacement, closure rate, and evolution law of permeability coefficient. Combined with the microscopic structural data before and after the experiment, the self-closing evolution mechanism of natural fractures in granite was analyzed.

[0043] Example 2:

[0044] Combination Figure 1 - Figure 2 This embodiment, based on Embodiment 1, further improves upon the following: a sample preparation and testing method for studying the self-closing characteristics of rock mass fractures, specifically targeting the study of the self-closing characteristics of granite-basalt interface fractures under the coupled conditions of high temperature, chemical reaction, stress, and seepage. The specific steps are as follows:

[0045] 1. Sample preparation: Select naturally cemented granite-basalt blocks, and use the Brazilian splitting method to form natural fracture surfaces 7 at the interface between the two rocks. Select corresponding granite and basalt entities as matching rock blocks 6.

[0046] 2. Crack surface monitoring: Fiber optic sensors 8 are arranged in a grid pattern on the interface crack surface 7 with a grid spacing of 5mm. The fiber optic sensors 8 are fixed with epoxy resin to achieve full monitoring of the crack surface 7.

[0047] 3. Sample sealing: The assembled rock sample 6 is placed between the upper and lower rigid pressure heads 1, and the initial seal is completed by wrapping it with a high-temperature resistant sealing sleeve 5. A high-temperature resistant sealing ring 3 and an alloy ferrule 2 are set at the upper and lower rigid pressure heads 1 for secondary sealing.

[0048] 4. External monitoring: Fiber optic cables 8 are laid out on the outer surface of rock specimen 6 in a dense grid pattern of vertical and horizontal intersections. The fiber optic cable 8 is laid out at a density of 1 cable every 5 cm. At the same time, circumferential deformation sensors are installed. Traditional axial deformation sensors are not set up. The overall deformation monitoring of the specimen is achieved only through fiber optic cables 8.

[0049] 5. Pre-experiment treatment: The sample is placed in a triaxial chamber with permeable stones 4 at the top and bottom. Back pressure is applied to pre-saturate the sample. The saturation medium is a 5% NaCl solution to simulate the chemical environment.

[0050] 6. Experimental Testing: A confining pressure of 15 MPa, a temperature of 80℃, and a water pressure of 3 MPa were applied to rock specimen 6 to bring the specimen to a consolidation state. A temperature-compensating fiber optic cable 8 was set to correct the influence of temperature on the fiber optic cable signal. Cyclic loading and unloading were carried out using a stress-controlled method, with a loading stress range of 5-15 MPa and 10 cycles. The self-closing effect of fractures under the four-field coupling conditions of temperature, stress, seepage, and chemical was tested. During the seepage process, the fracture permeability coefficient was tested using the transient method, and multi-source monitoring data were collected simultaneously.

[0051] 7. Microscopic Testing and Data Analysis: Before the experiment, digital image correlation (DIC) 3D reconstruction and mercury intrusion porosimetry (MIP) were performed on the fracture surface 7. After the experiment, gas adsorption analysis and CT scanning were performed on the rock specimen 6. The monitoring data were analyzed to extract the key characterization parameters of fracture self-closure. Combined with the microstructure test results, the self-closure characteristics and evolution law of the granite-basalt interface fracture under four-field coupling conditions were revealed.

[0052] The method of this invention is applicable to the testing of material and structural properties in rock mechanics, underground engineering and related fields. The type of rock specimen 6, the form of fracture surface 7, the monitoring method, the experimental conditions and the loading method can be adjusted according to specific research needs, which has high flexibility and applicability.

[0053] Example 3:

[0054] Combination Figure 1 - Figure 2 This embodiment, based on Embodiments 1 and 2, further improves upon the following: This embodiment studies the self-closing characteristics of sandstone-mudstone interface fractures under the coupled conditions of high temperature, chemical reaction, stress, and seepage. Utilizing the differences in mechanical properties between the sandstone and mudstone interfaces, it simulates the self-closing behavior of fractures in contact zones of different lithologies within deep sedimentary strata. The specific steps are as follows:

[0055] 1. Sample preparation: Select intact sandstone-mudstone blocks with natural cementation, process them into standard cylindrical test blocks, and use the Brazilian splitting method to form natural fracture surfaces 7 at the natural interface between sandstone and mudstone. Use the split sandstone test blocks and mudstone test blocks as matching rock test blocks 6, and retain the natural roughness and contact characteristics of the interface fractures.

[0056] 2. Fissure surface monitoring: Considering the characteristic that mudstone is easily softened when exposed to water, fiber optic sensors 8 are arranged in an asymmetrical grid pattern on the fissure surface 7 at the sandstone-mudstone interface (grid spacing of 8mm on the sandstone side and grid spacing of 5mm on the mudstone side). Water-resistant epoxy resin is used to tightly fix the fiber optic sensors 8 to the fissure surface to ensure that the fiber optics and the fissure surface deform synchronously, while avoiding physical disturbance of the adhesive layer to the mudstone fissure surface.

[0057] 3. Sample sealing: The assembled sandstone-mudstone matching sample block 6 is placed between the upper and lower rigid pressure heads 1, and the sample is wrapped with a high-temperature resistant and chemically resistant polytetrafluoroethylene sealing sleeve 5 to complete the initial sealing. At the junction of the upper and lower rigid pressure heads 1 and the sealing sleeve, a water-swellable rubber sealing ring 3 and a stainless steel ferrule 2 are set for secondary sealing to improve the impermeability and stability of the sealing structure and prevent chemical solutions from seeping in and causing the mudstone to soften and disintegrate.

[0058] 4. External monitoring: Fiber optic cables 8 are arranged in a dense grid pattern of vertical and circumferential crosses on the outer surface of the rock specimen 6. In the sandstone section, one vertical fiber is arranged every 6 cm axially and one circumferential fiber is arranged every 90° circumferentially. In the mudstone section, one vertical fiber is arranged every 4 cm axially and one circumferential fiber is arranged every 60° circumferentially, which is adapted to the more significant deformation characteristics of mudstone. At the same time, four high-precision circumferential deformation sensors are symmetrically installed on the circumference of the specimen. Axial deformation is monitored only through fiber optics, so as to achieve differential and accurate monitoring of the overall deformation of the specimen.

[0059] 5. Pre-experiment treatment: The sealed sample is placed in the triaxial chamber of the triaxial test system. High porosity permeable stone 4 is set at the upper and lower ends of the sample. The sample is first vacuumed, and then pre-saturated by applying back pressure. The saturation medium is a 3% Na2SO4 solution (simulating the chemical environment of sulfate-type groundwater in deep formations). During the saturation process, the confining pressure is controlled at 5MPa and the temperature at 25℃ to prevent the mudstone from softening excessively during the saturation stage.

[0060] 6. Experimental Testing: A confining pressure of 12 MPa, a temperature of 70℃, and a water pressure of 2.5 MPa were applied to sandstone-mudstone specimen 6. The specimen was then consolidated at constant temperature and pressure for 24 hours to achieve a stable consolidation state. A temperature compensation fiber 8 was installed to correct the influence of high temperature on the sensing signal of the fiber 8. The compensation fiber was positioned parallel to the monitoring fiber and away from the fracture surface. Cyclic loading and unloading were carried out using a stress control method. The loading stress range was 4-12 MPa, the loading rate was 0.5 MPa / min, the unloading rate was 0.8 MPa / min, and the number of cycles was 15. The fracture self-closure effect under the four-field coupling conditions of temperature-stress-seepage-chemical was investigated. During the seepage process, the permeability coefficient of the fracture was tested using the transient method. Multi-source monitoring data from the fiber inside the fracture, the fiber on the sample surface, and the deformation sensor were collected simultaneously. The closing displacement of the fracture surface, the overall deformation of the specimen, and the dynamic evolution of the permeability coefficient were recorded at different stages of cyclic loading and unloading.

[0061] 7. Microscopic Testing and Data Analysis: Before the experiment, digital image correlation (DIC) 3D reconstruction and mercury intrusion porosimetry (MIP) were performed on the fracture surface 7 at the sandstone-mudstone interface to obtain the initial pore structure, roughness, and connectivity parameters of the fracture surface. After the experiment, CT scanning and scanning electron microscopy (SEM) were performed on the fracture surface. At the same time, nuclear magnetic resonance (NMR) and gas adsorption analysis were performed on the sandstone and mudstone specimens to compare and analyze the microstructural evolution characteristics of the fracture surface caused by lithological differences. The multi-source monitoring data obtained during the experiment were comprehensively interpreted to extract key characterization parameters such as fracture closure displacement, closure rate, contact area evolution, and permeability coefficient decay law. Combined with the microstructural data before and after the experiment, the self-closing characteristics, evolution mechanism, and influence law of lithological differences on self-closing behavior of the sandstone-mudstone interface fracture under four-field coupling conditions were revealed.

[0062] This embodiment addresses the lithological differences between sandstone and mudstone (mudstone softens when exposed to water, while sandstone exhibits strong mechanical stability). Through customized design including asymmetric fiber optic deployment, water-resistant fixing adhesive, water-swellable sealing structure, and differentiated saturation control, it solves the problems of easy softening, easy disintegration, and low monitoring accuracy in testing interface fractures of soft rocks. It achieves accurate testing of the multi-field coupling self-closing characteristics of fractures at interfaces of different lithologies in sedimentary rock strata.

[0063] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing and testing samples to study the self-closing characteristics of rock mass fractures, characterized in that, Includes the following steps: S1. Sample preparation: Two matching rock specimens (6) with intermediate fracture surfaces (7) are processed to form a sample. S2, Crack surface monitoring: Fiber optic sensors (8) are installed on the crack surface (7) and fixed with epoxy resin adhesive. S3. Sample sealing: The assembled sample is sealed with a sealing device for primary and secondary sealing. The sealing device includes a sealing sleeve (5), a sealing ring (3), and a ferrule (2). S4. External monitoring: Install deformation sensors and / or lay optical fibers (8) on the outer surface of the rock specimen (6). S5. Experimental test: The sealed sample with the monitoring device installed is placed in a triaxial chamber and the self-closing effect of the crack is carried out under complex conditions to obtain test data reflecting the structural evolution of the rock block (6) and the crack surface (7). Based on the test data, the structural parameters characterizing the overall sample and the self-closing effect of the crack are analyzed and extracted.

2. The sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 1, characterized in that, In S1, the matching rock test block (6) is composed of the same type of rock or two different types of rock; the processing method of the target test block with fracture surface (7) is to form a natural fracture surface (7) in a single rock test block (6) by using the Brazilian splitting method, or to form a natural fracture surface (7) at the interface of two naturally cemented rocks by using the Brazilian splitting method, or to artificially prefabricate fracture surfaces (7) with different roughness and undulation.

3. The sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 1, characterized in that, In S2, the fiber optic sensor (8) is arranged in one or more lines along the axial direction of the rock sample (6), or arranged in a grid pattern.

4. The sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 1, characterized in that, In S3, the initial sealing involves placing the sample between the upper and lower rigid pressure heads (1) and wrapping it with a high-temperature and corrosion-resistant sealing sleeve (5). The secondary sealing involves setting a sealing ring (3) and a ferrule (2) at the upper and lower rigid pressure heads (1) after the initial sealing.

5. The sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 1, characterized in that, In S4, the optical fibers (8) on the outer surface of the rock sample block (6) are arranged in a vertical, horizontal, spiral or dense grid manner, and the arrangement density of the optical fibers (8) is adjusted according to the monitoring requirements. The optical fibers (8) are fixed to the outer surface of the rock sample block (6) by epoxy resin glue.

6. The sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 1, characterized in that, In S5, the complex conditions are to apply confining pressure, temperature and water pressure to the rock specimen (6) to make it reach a solidified state, with permeable stones (4) set at the upper and lower ends of the specimen, and the specimen can be pre-saturated by applying back pressure; during the saturation or crack self-closure test, fluids with different chemical properties are used.

7. The sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 6, characterized in that, In S5, the consolidated rock specimen (6) is loaded using displacement control or stress control methods. The mechanical loading methods are cyclic loading and unloading, graded loading, long-term creep test under a fixed load, or long-term relaxation test under a fixed shear displacement.

8. A sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 6, characterized in that, In S5, the self-closing experiment of the crack is carried out under different confining pressure, temperature, water pressure and chemical environment, and is set up according to different stress paths. The experiment can be carried out under single field, two field, three field or four field coupling conditions. For experiments involving high temperature, a temperature compensation fiber (8) is set up to correct the influence of temperature on the fiber (8) signal.

9. A sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 1, characterized in that, In S5, the permeability coefficient of the self-closing characteristic of the fracture during the seepage process is tested using the steady-state method, transient method, or periodic oscillation method.

10. A sample preparation and testing method for studying the self-closing characteristics of rock mass fractures according to claim 1, characterized in that, The method also includes the steps of conducting microstructure tests on the rock specimen (6) or the fracture surface (7) before and after the experiment to obtain data reflecting the evolution of the internal structure of the specimen. The microstructure tests include scanning electron microscopy, nuclear magnetic resonance, mercury intrusion porosimetry, gas adsorption analysis, and CT scanning or digital image correlation three-dimensional reconstruction of the fracture surface (7).

Images