Triaxial direct tensile mechanical behavior test method of rock under in-situ multi-field coupling environment

Abstract

This invention relates to a method for testing the triaxial direct tensile mechanical behavior of rocks under in-situ multi-field coupling conditions. It is based on a true three-dimensional stress-flow coupling testing system and a tensile testing component. The true three-dimensional stress-flow coupling testing system provides an in-situ multi-field environment coupled with fluid pressure and confining pressure, and applies axial pressure. The tensile testing component converts the axial pressure into axial tension on the rock sample through a pressure-to-tension conversion structure. It also integrates a temperature control module for temperature control and a multi-parameter sensing module for simultaneous acquisition of stress, deformation, acoustic emission, and ultrasonic waves. This method is based on a modification of a conventional multifunctional true triaxial fluid-structure interaction testing system, requiring no large-scale modifications to the core equipment. It is adaptable to different types of rock samples (granite, shale, sandstone, coal, etc.) and allows for flexible adjustment of test parameters such as confining pressure, temperature, and fluid pressure, making it suitable for rock mechanics testing needs in various deep engineering fields.

Description

Technical Field

[0001] This invention relates to the field of rock mechanics testing technology, and in particular to a method for testing the triaxial direct tensile mechanical behavior of rocks under in-situ multi-field coupling conditions. Background Technology

[0002] Currently, rock tensile strength testing mainly employs the direct tensile method and the Brazilian splitting method. Conventional testing methods can only be conducted in simple environments with uniaxial compressive strength, no confining pressure, and no seepage at room temperature, and the test parameters are limited. Existing triaxial testing methods primarily rely on rock compression tests, which can simulate confining pressure, temperature, or seepage environments, but lack a suitable direct tensile loading method and cannot achieve fully coupled simulation of temperature, fluid pressure, and confining pressure. Furthermore, the synchronization and accuracy of multi-parameter monitoring are insufficient, making it difficult to systematically acquire the mechanical, acoustic, and seepage response data during the rock tensile process. The main problems are as follows: (1) Unable to simulate in-situ multi-field coupling environment: Conventional tensile tests are only carried out in a single field environment without lateral constraints, normal temperature and no seepage. They cannot reproduce the in-situ environment of the combined effects of underground stratum temperature, fluid pressure and confining pressure. The test results deviate greatly from the actual mechanical properties of the rock mass and are difficult to reflect the influence of multi-field coupling on the tensile strength and failure mode of rock.

[0003] (2) Single test parameters and lack of multi-dimensional linkage analysis: Existing methods can only obtain basic mechanical parameters such as rock tensile strength and elastic modulus, but cannot simultaneously monitor key indicators such as rock acoustic emission signals, ultrasonic wave velocity / amplitude changes, and seepage parameter evolution during the tensile process. It is difficult to deeply analyze the damage evolution law of rocks from microcrack initiation to macroscopic fracture.

[0004] (3) Poor compatibility between tensile loading and multi-field simulation: Although the existing triaxial testing device can realize multi-field environment simulation, it lacks a dedicated pressure-tension conversion mechanism, and cannot carry out direct tensile tests on rocks in multi-field coupling environment. In addition, some methods use indirect tensile methods, which cannot reflect the true direct tensile characteristics of rocks.

[0005] (4) Insufficient standardization and precision of test operation: The specimen clamping and sealing methods of conventional direct tensile test are not perfect, which can easily lead to problems such as seepage and leakage, and loss of sound energy transmission. In addition, the synchronization control of multi-parameter monitoring is poor, resulting in insufficient reliability and comparability of test data. Summary of the Invention

[0006] This invention aims to provide a method for testing the triaxial direct tensile mechanical behavior of rocks under in-situ multi-field coupling conditions. It can realize direct tensile loading of rocks under in-situ multi-field conditions with full coupling of temperature, fluid pressure, and confining pressure. At the same time, it can simultaneously and accurately test multi-dimensional parameters such as stress, axial / radial deformation, acoustic emission, and ultrasonic waves during the rock tensile process. This solves the problems of conventional testing methods being unable to simulate in-situ multi-field environments and having limited test parameters. It enables the linkage analysis of multiple parameters of rock tensile mechanical properties and damage evolution, providing a scientific and reliable experimental testing method for the study of deep rock mass mechanical properties.

[0007] This invention is achieved through the following technical solution: This application presents a method for testing the triaxial direct tensile mechanical behavior of rocks under in-situ multi-field coupling conditions. This method is based on a true three-dimensional stress-flow coupling testing system and a tensile testing assembly. The true three-dimensional stress-flow coupling testing system provides an in-situ multi-field environment coupled with fluid pressure and confining pressure, and applies axial pressure. The tensile testing assembly converts the axial pressure into axial tension of the rock sample through a pressure-tension conversion structure. It also integrates a temperature control module for temperature control and a multi-parameter sensing module for simultaneous acquisition of stress, deformation, acoustic emission, and ultrasonic waves. Specifically, the true three-dimensional stress-flow coupling testing system includes a vertical frame, a triaxial loading system, and a pressure chamber. The triaxial loading system includes six hydraulic cylinders; the output of the upper cylinder is connected to an upper pressure head, and the output of the lower cylinder is connected to a lower pressure head. The pressure chamber is operably installed in the hollow portion of the vertical frame. The pressure chamber has a connection port in each of the six directions, allowing the telescopic rods of the six cylinders to extend into the pressure chamber from one of these ports. The pressure chamber has a fluid injection channel and a fluid outflow channel. The tensile testing assembly includes an external load-bearing frame, a specimen clamping device, auxiliary measuring components, and a seepage pad. The external load-bearing frame includes an upper tensile frame for docking with the upper indenter of the triaxial loading system and converting the upper pressure into a lower tensile force, and a lower tensile base for docking with the lower indenter of the triaxial loading system and converting the lower pressure into an upper tensile force. The specimen clamping device includes an upper tensile head for connecting to the lower tensile base and clamping the upper end of the specimen, and a lower tensile head for connecting to the upper tensile frame and clamping the lower end of the specimen. The auxiliary measuring components include a displacement sensing module for measuring the axial tensile deformation and radial deformation of the specimen, and a temperature control module for providing a temperature field to the specimen. The permeation pad has a fluid channel. There is a permeation pad between the upper tensile head and the upper end of the sample, and there is a permeation pad between the lower tensile head and the lower end of the sample. An acoustic sensing component is provided at the end of the permeation pad that is in contact with the sample. The sample and the permeation pad are wrapped with a thermoplastic film. The tensile test assembly is placed in a pressure chamber. The upper tensile frame is connected to the upper pressure head of the triaxial loading system, and the lower tensile base is connected to the lower pressure head of the triaxial loading system.

[0008] Furthermore, the acoustic sensing assembly includes two acoustic emission receiving probes and one ultrasonic emission probe; optionally, the ceramic sensing surfaces of the acoustic emission receiving probes and the ultrasonic emission probe are pre-coated with ultrasonic coupling agent.

[0009] Optionally, the seepage pad is used to groove the contact surface that contacts the sample to install the acoustic sensing components. The acoustic emission receiving probe and the ultrasonic emission probe are respectively embedded in the mounting groove of the seepage pad, and a buffer spring is provided at the bottom of the mounting groove.

[0010] The method for testing the triaxial direct tensile mechanical behavior of rocks under in-situ multi-field coupling includes the following steps: Preloading: Axial pressure is applied to the upper and lower cylinders to perform preloading; Slowly fill the pressure chamber with hydraulic oil until it is completely filled. Start the high-pressure oil pump to slowly pressurize the pressure chamber and raise the confining pressure to the set value; Turn on the temperature control device to raise the temperature of the pressure chamber and the sample to the test set value; The seepage fluid is injected into the sample through the upper seepage pad until the fluid flowing out of the fluid outlet is free of bubbles and the flow rate is stable, thus realizing the venting of the seepage channel; then the fluid pressure is applied to the set value to ensure that the confining pressure of the pressure chamber is always greater than the fluid pressure of the sample. After the confining pressure, temperature, and fluid pressure have all reached their set values ​​and stabilized for a period of time, the in-situ multi-field coupling environment is constructed, and the initial values ​​of all parameters are recorded at this time.

[0011] Axial loading is applied by the upper and lower hydraulic cylinders, and the tensile test assembly converts the axial pressure into axial tension acting on both ends of the specimen, realizing the direct tensile testing of the rock specimen; during the loading process, mechanical parameters, acoustic parameters, and seepage parameters are collected in real time. The loading process continues until the rock sample fails under tensile stress. The peak tensile stress, failure strain, and abrupt changes in each parameter at the moment of failure are recorded before loading is stopped. This method achieves simultaneous multi-parameter testing of direct tensile rock under in-situ multi-field conditions through standardized procedures for sample preparation, apparatus assembly, multi-field environment construction, tensile loading, and multi-parameter monitoring. The testing process is standardized, the data is accurate, and the repeatability is high.

[0012] Specifically, before preloading, the data acquisition system is activated to simultaneously acquire and store stress, deformation, acoustic emission, and ultrasonic parameters; optionally, the acquisition frequency can be set to ≥100Hz. This enables precise matching of the time series of each parameter, providing a foundation for multi-parameter linkage analysis.

[0013] Preferably, the mechanical parameters include tensile force, axial deformation, and radial deformation, and the axial strain, radial strain, elastic modulus, and Poisson's ratio are calculated in real time.

[0014] Preferably, the acoustic parameters include acoustic emission signal, ultrasonic longitudinal / transverse wave velocity, amplitude, and waveform distortion characteristics.

[0015] Preferably, the seepage parameters include seepage flow rate and inlet / outlet fluid pressure difference.

[0016] Optionally, the test method for the triaxial direct tensile mechanical behavior of rocks under in-situ multi-field coupling environment also includes the following steps: observing and recording the tensile failure morphology, crack propagation path, and macroscopic fracture surface characteristics of the specimen, and taking pictures, scanning, and measuring the crack size of the specimen.

[0017] Furthermore, the upper tension frame includes support columns, an upper cylinder connecting plate, and a lower tension plate. The upper cylinder connecting plate and the lower tension plate are connected together by multiple support columns. The upper cylinder connecting plate has an upper mounting recess at its center that matches the upper pressure head of the triaxial loading system. The lower tension head is connected to the lower tension plate. The lower tension base includes a ball spline, a lower cylinder connecting plate, and an upper tension plate. The upper tension plate and the lower cylinder connecting plate are connected together by a ball spline. The upper tension head is connected to the upper tension plate.

[0018] Furthermore, spline guide seats are fixedly installed on both sides of the lower tension plate, and two ball splines are respectively vertically installed in one of the spline guide seats and are clearance-fitted with it.

[0019] Furthermore, the temperature control device includes a magnetic base, a heater bracket, and a ring heating device. The ring heating device is a ring structure arranged coaxially with the sample. The ring heating device is mounted on the heater bracket, which is fixed on the magnetic base. The ring heating device is connected to an external temperature control system.

[0020] Compared with the prior art, this application has at least the following beneficial effects: 1. This application can simultaneously construct an in-situ multi-field underground environment coupled with temperature, fluid pressure, and confining pressure, reproduce the real stress and environmental characteristics of deep rock masses, solve the problem of the disconnect between the test conditions of conventional testing methods and engineering practice, and the test results can better reflect the tensile mechanical properties of rocks in in-situ environment.

[0021] 2. This application integrates multi-dimensional sensing modules such as stress, deformation, acoustic emission, and ultrasound. Through the data acquisition system, it realizes real-time and accurate acquisition and time series matching of various parameters, and realizes the linkage monitoring of mechanical and acoustic parameters during rock tensile process, which is conducive to providing complete data support for in-depth analysis of the rock tensile damage evolution mechanism.

[0022] 3. This application can realize direct tensile loading of rocks in a multi-field coupling environment through the pressure-tension conversion structure of the tensile test component, avoiding the problem of uneven stress distribution in indirect tensile methods such as the Brazilian splitting method, and can accurately obtain the true direct tensile strength and tensile failure mode of the rock.

[0023] 4. The test process of this application is standardized and highly repeatable: Through standardized sample preparation, device assembly, multi-field environment construction, and loading monitoring process, key aspects such as sample processing accuracy, device installation and calibration, and loading / unloading rate have been strictly regulated, which effectively improves the repeatability of the test and the comparability and reliability of the test data.

[0024] 5. This application has strong adaptability and wide application range: This method is based on the modification of a conventional multifunctional true triaxial fluid-structure interaction test system. It does not require large-scale modification of the core equipment and can be adapted to different types of rock samples (granite, shale, sandstone, coal, etc.). The test parameters of confining pressure, temperature and fluid pressure can be flexibly adjusted, and it is suitable for rock mechanics testing needs in a variety of deep engineering fields.

[0025] 6. Precise coupling and control of multiple environments in this application: By applying and stabilizing confining pressure, temperature and fluid pressure in stages, the precise construction of in-situ multiple environments is achieved, ensuring that the confining pressure is slightly higher than the fluid pressure, and avoiding interference of hydraulic fracturing on the tensile test.

[0026] 7. High-efficiency acoustic energy transmission in acoustic sensing: By using a buffer spring at the bottom of the probe and applying coupling agent to the ceramic surface, the probe and the sample are kept in close contact, reducing the reflection and loss of acoustic energy at the interface and improving the accuracy of acoustic signal acquisition. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a half-section view of the tensile test component placed in the true three-dimensional stress-flow coupling test system in the embodiment. Figure 2 This is a three-dimensional view of the true three-dimensional stress-flow coupling test system in the embodiment; Figure 3 This is a top view of the true three-dimensional stress-flow coupling test system in the embodiment; Figure 4 This is a schematic diagram of the structure of the thermal insulation outer shell covering the outside of the tensile test component in the embodiment; Figure 5 This is a perspective view of the tensile test components in the embodiment; Figure 6 This is a cross-sectional view of the tensile test component in the embodiment; Figure 7 This is a perspective view of the external support frame in the embodiment; Figure 8 This is a cross-sectional view of the external support frame in the embodiment; Figure 9 This is a perspective view of the specimen clamping device and the specimen in the embodiment; Figure 10 This is a cross-sectional view of the specimen clamping device and the specimen in the embodiment; Figure 11 This is a perspective view of the pad block in the embodiment; Figure 12 This is a cross-sectional view of the pad block in the embodiment; Figure 13 This is a schematic diagram of the specimen clamping device, auxiliary measurement components, and specimen in the embodiment; Figure 14 This is a schematic diagram of the thermal insulation shell in the embodiment. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this invention can be combined with each other. It should also be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0031] In the description of this invention, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use, or the orientation or positional relationship commonly understood by those skilled in the art. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0032] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0033] like Figure 1 As shown in this embodiment, the in-situ multi-field coupled environment rock triaxial direct tensile mechanical behavior testing method is implemented based on a true three-dimensional stress-flow coupling testing system 100 and a tensile test assembly 200. The true three-dimensional stress-flow coupling testing system 100 provides an in-situ multi-field environment coupled with fluid pressure and confining pressure, and can apply axial pressure. The tensile test assembly 200 converts the axial pressure provided by the true three-dimensional stress-flow coupling testing system 100 into axial tension of the rock sample. It also integrates a temperature control module for temperature control and a multi-parameter sensing module for simultaneous acquisition of stress, deformation, acoustic emission, and ultrasonic waves. This method achieves multi-parameter synchronous testing of direct rock tensile forces in an in-situ multi-field environment through standardized sample preparation, device assembly, multi-field environment construction, tensile loading, and multi-parameter monitoring procedures. The testing process is standardized, the data is accurate, and the repeatability is high.

[0034] like Figure 2 , Figure 3 As shown, the true three-dimensional stress-seepage coupling test system 100 includes a vertical frame 101, a pressure chamber 102, a hydraulic cylinder 103, a front sliding platform 104, a rear sliding platform 105, an equipment base 106, and supporting temperature control, seepage control, and hydraulic control systems.

[0035] The vertical frame 101 is a vertical frame structure, and the pressure chamber 102 is operably placed in the center of the vertical frame. The pressure chamber 102 is used to contain high-pressure liquid and to place the tensile test assembly 200. Six hydraulic cylinders 103 are located in the upper, lower, left, right, front, and rear directions of the triaxial pressure chamber 102, respectively. The pressure chamber 102 has loading ports adapted to the hydraulic cylinders 103. The telescopic rods of the six hydraulic cylinders 103 can extend into the pressure chamber 102 through the loading ports. The telescopic rods of the six hydraulic cylinders 103 are respectively connected to pressure heads. The pressure head of the upper hydraulic cylinder 103 is the upper pressure head, and the pressure head of the lower hydraulic cylinder 103 is the lower pressure head.

[0036] In an exemplary embodiment, hydraulic cylinders 103 in the Y-axis and Z-axis directions are mounted on a vertical frame 101, and their telescopic rods can be connected to the interior of pressure chamber 102 through corresponding interfaces. Pressure chamber 102 has multiple threaded holes on the edges of the two interfaces in the X-axis direction, which can be tightly connected to the cylinder bodies of the two hydraulic cylinders 103 in the X-axis direction, ultimately forming a sealed space inside pressure chamber 102. Circular high-strength, pressure-resistant, and wear-resistant rubber strips are spaced at intervals along the inner edges of the six interfaces in pressure chamber 102, enabling dynamic sealing to ensure the high-pressure hydraulic oil seal within pressure chamber 102, while allowing the telescopic rods of the hydraulic cylinders 103 to move freely.

[0037] The two hydraulic cylinders 103 in the X-axis direction are connected to the front sliding platform 104 and the rear sliding platform 105 respectively, facilitating the movement of the two hydraulic cylinders 103 in the X-axis direction. In use, the two open hydraulic cylinders 103 in the X-axis direction can be separated from the pressure chamber 102 first, and the tensile test assembly 200 can be placed into the pressure chamber 102 through the loading port in the X-axis direction. Then, the cylinder bodies of the two hydraulic cylinders 103 in the X-axis direction are connected to the pressure chamber 102 and the fixing screws are tightened to form a sealed space in the pressure chamber 102.

[0038] Of course, the pressure chamber 102 has multiple fluid channels, some of which serve as injection channels to allow different fluids to be injected, while the remaining channels serve as outflow channels to allow fluids to flow out. During the experiment, high-temperature and high-pressure liquids can be injected into the pressure chamber 102.

[0039] In some embodiments, the true three-dimensional stress-flow coupling test system 100 can provide a coupling environment of 0~60MPa confining pressure and 0~60MPa fluid pressure. Axial pressure is applied by the hydraulic cylinder 103, and the tensile test component 200 is accurately positioned and installed by the front sliding platform 105 and the rear sliding platform 106.

[0040] The tensile testing assembly 200 is the core component for realizing pressure-to-tensile force conversion and multi-parameter monitoring. Please refer to [link / reference]. Figures 4-8 The tensile test assembly 200 includes an external load-bearing frame 1, a specimen clamping device 2, an auxiliary measuring component 3, and a thermal insulation shell.

[0041] The core function of the external load-bearing frame 1 is to efficiently and accurately convert the axial pressure applied by the true three-dimensional stress-flow coupling testing system 100 into axial tensile forces acting on both ends of the rock sample, ensuring the alignment of the tensile loading and avoiding lateral force interference. For example... Figure 4 , Figure 5As shown, the external load-bearing frame 1 includes an upper tension frame 11 and a lower tension base 12. The upper tension frame 11 includes high-strength support columns 111, an upper hydraulic cylinder connecting plate 112, and a lower tension plate 113. The upper hydraulic cylinder connecting plate 112 and the lower tension plate 113 are connected together by multiple support columns 111. Figure 4 In the exemplary embodiment shown, the upper ends of the four support columns 111 are respectively fixedly connected to the four corners of the upper hydraulic cylinder connecting plate 112, and the lower ends of the four support columns 111 are respectively fixedly connected to the four corners of the lower tension plate 113 to ensure the overall rigidity of the frame.

[0042] The upper cylinder connecting plate 112 has clearance grooves 1121 on both sides to reserve axial movement space for the ball spline 121. The four corners of the upper cylinder connecting plate 112 are chamfered to fit the internal space of the pressure chamber 102; the upper cylinder connecting plate 112 has a circular upper mounting recess 1122 at its center, and the inner diameter of the upper mounting recess 1122 is precisely matched with the outer diameter of the upper pressure head of the true three-dimensional stress seepage coupling test system 100, so as to achieve a rigid connection with the upper pressure head.

[0043] The lower tension base 12 includes a ball spline 121, a lower cylinder connecting plate 123, and an upper tension plate 122. The upper tension plate 122 and the lower cylinder connecting plate 123 are connected together by the ball spline 121. A circular lower mounting recess 1231 is formed at the center of the lower cylinder connecting plate 123. The lower mounting recess 1231 precisely matches the outer diameter of the lower pressure head of the true three-dimensional stress-flow coupling test system 100, and cooperates with the upper tension frame 11 to achieve fixation of the device and transmission of loading force in the triaxial pressure chamber 1021011. Figure 4 In the exemplary embodiment, the upper ends of the two high-precision ball splines 121 are rigidly connected to the upper tension plate 122 by fastening nuts, and the lower ends of the two high-precision ball splines 121 are connected to the lower cylinder connecting plate 123. Each end of the ball spline 121 is fixed by two fastening nuts to achieve precise transmission and guidance of axial force.

[0044] Optionally, spline guide seats 13 are fixed on both sides of the lower tension plate 113, and two ball splines 121 are respectively vertically installed in one of the spline guide seats 13 and fitted with a clearance, so as to realize the linkage guidance between the upper tension frame 11 and the lower tension base 12, ensure the straightness of the entire device during axial loading, and avoid test errors caused by lateral forces.

[0045] The specimen clamping device 2 is the core module for core fixation, seepage realization, and acoustic signal acquisition. Figure 9 , Figure 10As shown, the specimen clamping device 2 includes an upper stretching head 21 and a lower stretching head 22. The upper stretching head 21 has an upper clamping groove 23 for accommodating the upper end head 51 of the specimen 5, and the lower stretching head 22 has a lower clamping groove 24 for accommodating the lower end head 52 of the specimen 5. The upper clamping groove 23 has an upper clearance opening 25 for the upper end head 51 to be inserted laterally, and the lower clamping groove 24 has a lower clearance opening 26 for the lower end head 52 to be inserted laterally. The upper end head 51 is configured to be inserted laterally into the upper clamping groove 23 through the upper clearance opening 25, and the lower end head 52 is configured to be inserted laterally into the lower clamping groove 24 through the lower clearance opening 26.

[0046] In an exemplary embodiment, the specimen 5 is an anisotropic specimen, which includes an upper end 51, a lower end 52 and a middle section 52. The diameters of the upper end 51 and the lower end 52 are larger than the diameter of the middle section 52. The two ends of the middle section 52 are connected to the upper end 51 and the lower end 52 respectively and transition smoothly.

[0047] The upper clearance opening 25 and lower clearance opening 26 on the side of the specimen clamping device 2 are T-shaped structures, which allow the upper end head 51 and the lower end head 52 to be inserted radially, while preventing the upper end head 51 from moving axially away from the upper tension head 21 and the lower end head 52 from moving axially away from the lower tension head 22. The two ends of the specimen 5 are fixed to the specimen clamping device 2 by snap-fit, which not only facilitates the installation of the specimen 5, but also ensures the uniformity of the force on the specimen.

[0048] The upper tension head 21 is connected to the upper tension plate 122 of the external bearing frame 1 via the upper fixed support 14, and the lower tension head 22 is connected to the lower tension plate 113 of the external bearing frame 1 via the lower fixed support 15. In an exemplary embodiment, a positioning hole 27 is provided at the center of the upper end of the upper tension head 21 to connect with the upper fixed support 14, and a positioning hole 27 is provided at the center of the lower end of the lower tension head 22 to connect with the lower fixed support 15. Optionally, the upper tension head 21 is fixed to the upper fixed support 14 by screws, the upper fixed support 14 is fixed to the upper tension plate 122 by screws, the lower tension head 22 is fixed to the lower fixed support 15 by screws, and the lower fixed support 15 is fixed to the lower tension plate 113 by screws. The pressure applied by the upper and lower pressure heads of the true three-dimensional stress-flow coupling test system 100 is converted into tension force on the upper tension head 21 and the lower tension head 22, thereby achieving axial tension force on the sample 5.

[0049] The specimen clamping device 2 has an clearance opening on its side to accommodate the installation and clamping of the specimen 5 and the arrangement of sensors. A seepage pad 6 is installed between the upper tension head 21 and the upper end 51 of the specimen 5, and between the lower tension head 22 and the lower end 52 of the specimen 5. The seepage pad 6 has a seepage interface on its end face, which is used to connect to an external seepage control system. Before the specimen 5 is placed into the specimen clamping device 2, it needs to be wrapped with a thermoplastic film 7. The thermoplastic film 7 can achieve a joint seal between the specimen 5 and the seepage pad 6 to prevent fluid leakage.

[0050] like Figure 11 , Figure 12 As shown, a fluid channel 61 is opened on the side of the seepage pad 6. Fluid can be injected through the fluid channel 61 of the upper seepage pad 6, and then flow out through the fluid channel 61 of the lower seepage pad 6 after passing through the sample 5. Preferably, the seepage pad 6 is made of a high-rigidity material to ensure the stability of seepage and the effective transmission of force.

[0051] An acoustic sensing component is provided at the end of the seepage pad 6 that is in contact with the sample 5. In some embodiments, the acoustic sensing component includes three high-precision probes evenly arranged, two of which are acoustic emission receiving probes 62 and the other is an ultrasonic emission probe 63.

[0052] The seepage pad 6 is used to groove the contact surface with the sample 5 to install the acoustic sensing components. Three high-precision probes are embedded in the mounting groove of the seepage pad. A buffer spring is set at the bottom of the mounting groove to effectively prevent the probes from being damaged by rigid contact during loading and to ensure the service life of the sensing elements. The wires of the acoustic emission receiving probe and the ultrasonic emission probe are led out through the wiring hole 28 of the specimen clamping device 2 and connected to the external data acquisition system to realize the synchronous acquisition of acoustic signals of the generation and expansion of microcracks inside the sample 5 during the tensile process.

[0053] like Figure 13 As shown, the auxiliary measurement component 3 includes a displacement sensing module and a temperature control module, enabling precise measurement of axial / radial deformation and simulation of the in-situ temperature field during sample tensile testing. All measuring elements are modularly designed, facilitating easy assembly and disassembly and simple calibration. Specifically, the displacement sensing module includes an axial displacement sensor LVDT31 and a radial displacement sensor 32, with the radial displacement sensor 32 being a radial extensometer. One end of the axial displacement sensor LVDT31 is connected to the side of the upper fixed support 14 via a bracket, and the other end is connected to the side of the lower fixed support 15 via a bracket, allowing direct measurement of the axial tensile deformation of the sample 5 with micron-level accuracy.

[0054] Before the sample 5 is installed, the radial displacement sensor 32 is fixed in the middle of the sample 5 in advance to measure the radial deformation of the sample 5 in real time during the tensile process, which can provide data for the calculation of mechanical parameters such as elastic modulus and Poisson's ratio.

[0055] The temperature control device 33 includes a magnetic base 331, a heater bracket 332, and a ring-shaped heating device 333. The ring-shaped heating device 333 has a ring structure and is arranged coaxially with the sample 5. The ring-shaped heating device 333 is mounted on the heater bracket 332, which is fixed on the magnetic base 331. The magnetic base 331 is placed on the lower tension base 12, and the device can be quickly fixed and disassembled by magnetic attraction, adapting to rock core specimens of different diameters. The ring-shaped heating device 333 is connected to an external temperature control system, which can achieve precise temperature control that can be extended from room temperature to 150℃, with a temperature control accuracy of ±2℃, providing a uniform temperature field for the rock core and simulating the geothermal environment of deep strata.

[0056] The thermal insulation shell 300 is made of high-strength thermal insulation material and is fitted over the tensile test assembly 200 to reduce heat loss, ensure the uniformity and stability of the sample temperature field, and prevent debris from flying and damaging the sensing components when the sample breaks. Figure 14 In the exemplary embodiment shown, the top and bottom of the thermal insulation shell 300 are open to avoid obstructing the upper and lower pressure heads of the true three-dimensional stress-flow coupling test system 100. U-shaped notches 301 are formed on the bottom of the left and right sides of the thermal insulation shell 300. These notches 301 are adapted to the support guide columns 111 and ball splines 121 of the external load-bearing frame 1 to avoid structural interference. A small notch 302 is formed on the right side of the bottom front, serving as a channel for the pipelines, flow lines, and sensor wires of the auxiliary measurement component 3, ensuring the regularity of the pipeline arrangement. Raised handles 303 are installed on both sides of the top of the thermal insulation shell 300 for easy quick assembly and disassembly of the device.

[0057] This embodiment conducts in-situ direct tensile tests on standard cylindrical rock specimens under coupled conditions of multiple fields of temperature, fluid pressure, and confining pressure. Simultaneously, multiple parameters including stress, axial deformation, radial deformation, acoustic emission, and ultrasonic waves are measured. Specific test steps include: Step 1, Sample preparation and pretreatment.

[0058] The rock is processed into a cylindrical standard specimen with expanded diameters at both ends. The working section 52 of the middle section of specimen 5 has a diameter of 50 mm and a length of 100 mm. The diameter of the expanded sections at both ends of specimen 5 is slightly smaller than the inner diameter of the clamping groove of the tensile head. The flatness error of the end face and the expanded diameter of specimen 5 is ≤0.02 mm, and the perpendicularity error is ≤0.01 mm. There are no obvious cracks or defects on the surface of specimen 5. Specimen 5 is dried and polished to remove surface impurities and ensure the fit between specimen 5 and specimen clamping device 2 and sensor probe.

[0059] Step 2, sensor probe installation and debugging.

[0060] Place a buffer spring 64 in the probe mounting slot of the seepage pad 6, and then embed two ultrasonic transmitting probes 63 and four acoustic transmitting receiving probes 62 into the corresponding mounting slots of the two seepage pads 6 in sequence to ensure that the probes are in close contact with the buffer springs 64 and avoid rigid contact damage to the probes during loading. Apply ultrasonic coupling agent evenly to the ceramic sensing surface of the probe to ensure efficient transmission of acoustic energy and reduce interface reflection loss. Precisely attach the probe-mounted permeation pad 6 to both ends of the sample 5, and check the contact between the probe and the sample 5 surface to ensure there are no gaps or offsets. Vaseline can be used as the ultrasonic coupling agent.

[0061] Step 3: Seal and clamp the sample.

[0062] The sample 5, with the seepage pad 6 properly attached, is then completely fitted into the heat-shrinkable sleeve 7. The heat-shrinkable sleeve 7 covers the entire sample 5, with a certain distance between the heat-shrinkable sleeve 7 and the upper end of the seepage pad 6 and the lower end of the seepage pad 6. The transmission line of the acoustic sensing component is led out from the end of the seepage pad 6. The heat-shrinkable sleeve 7 is heated evenly from bottom to top using a hot air gun, causing the heat-shrinkable sleeve 7 to shrink tightly and adhere to the sample 5 and the seepage pad 6, ensuring that there are no cavities or air bubbles inside the heat-shrinkable sleeve 7, achieving a complete seal of the sample 5 and preventing leakage of seepage fluid. Place the sealed sample 5 and the seepage pad 6 into the clamping groove of the tensile head, and precisely adjust the position so that the seepage hole of the seepage pad 6 is aligned with the opening direction on the side of the clamping groove to ensure the continuity and leak-free seepage channel. The sample 5, the seepage pad 6 and the specimen clamping device 2 can be fixed by fastening bolts and bolt holes 27 to ensure no relative sliding during the tensile process.

[0063] Step 4: Installation and calibration of auxiliary measuring components.

[0064] The surface of rock sample 5 is gently tapped, and the working status of acoustic emission receiving probe 62 is detected by acoustic emission acquisition system. The signal transmission effect of ultrasonic probe 63 is detected by ultrasonic emission / reception system to ensure that the acoustic sensing module is working properly. Install the axial displacement sensor LVDT31 on the bracket of the upper fixed support 14, adjust the fit between the probe of the axial displacement sensor LVDT31 and the corresponding position of the sample 5, and clear the axial displacement reading to zero. Place the radial displacement sensor 32 on the middle section 52 of the sample 5, adjust the clamping force and position of the radial displacement sensor 32 to ensure that the radial displacement sensor 32 is in uniform contact with the surface of the sample 5, and clear the radial displacement reading to zero. The annular heating device 333 is installed on the heater bracket 332 around the sample 5. The coaxiality of the annular heating device 333 and the sample 5 is adjusted to ensure the uniformity of the sample temperature field and to test the heating and temperature control accuracy of the temperature control device 33.

[0065] Step 5: Assembly of the device and installation of pressure chamber 102 To fit the tensile test assembly 200 with the thermal insulation shell 300, the tensile test assembly 200 and the thermal insulation shell 300 are sent into the designated position in the pressure chamber 102 of the true three-dimensional stress-flow coupling test system 100 through the front sliding platform 105 and the rear sliding platform 106. The upper hydraulic cylinder connecting plate 112 and the lower hydraulic cylinder connecting plate 123 of the tensile test assembly 200 are precisely connected to the two hydraulic cylinders 103 respectively in the Z-axis direction to ensure loading alignment. Connect the inlet and outlet pipes of the pressure chamber 102 to the seepage holes of the upper tension head 21 and lower tension head 22 respectively through the joints. Connect all the sensor cables to the external data acquisition system, organize the pipelines and fix them to prevent the pipelines from being pulled or damaged during the loading process. Test the working status of all sensors, temperature control, seepage, and hydraulic systems. After confirming that there are no abnormalities, connect the cylinder bodies of the two hydraulic cylinders in the X-axis direction to the pressure chamber and tighten the fixing screws to form a sealed space inside the pressure chamber.

[0066] Step 6: Preload and fill pressure chamber 102 with oil.

[0067] Turn on all system power, start the data acquisition system, set the acquisition frequency (≥100Hz), and realize the acquisition and storage of stress, deformation, acoustic emission, and ultrasonic parameters. Acoustic emission and ultrasonic waves can be integrated for data acquisition. Stress can be monitored and acquired through a stress monitoring device on the internal surface of the hydraulic cylinder 103 rod. This is standard technology in this field and will not be elaborated further here.

[0068] Axial pressure is applied by two hydraulic cylinders 103 in the Z direction to load the axial stress to 2%~5% of the predetermined tensile load for preloading. The working status of the loading system, sensing system and sealing structure is checked. After confirming that there is no load drift, signal abnormality and fluid leakage, the preloading state is maintained for 5 minutes. Slowly fill the pressure chamber 102 with hydraulic oil until it is completely filled, expel the air inside, and close the oil outlet of the pressure chamber 102 to complete the filling of the pressure chamber 102.

[0069] Step 7: In-situ multi-field environment construction and stabilization.

[0070] Confining pressure application: Start the high-pressure oil pump and slowly pressurize the pressure chamber 102 to raise the confining pressure to the test set value. The pressurization rate should be ≤0.5MPa / min to avoid sudden increase in confining pressure from impacting the sample.

[0071] Temperature application: Turn on the temperature control device 33 to raise the temperature of the pressure chamber 102 and the sample 5 to the test set value. The temperature control accuracy is ±1℃. After reaching the set temperature, keep it at that temperature for 30~60 minutes to ensure that the internal temperature field of the sample is uniform and stable.

[0072] Fluid pressure application: Start the seepage pump, slowly open the inlet, and inject seepage fluid into the sample 5 until the fluid flowing out of the outlet is free of bubbles and the flow rate is stable, thus achieving air venting of the seepage channel; then adjust the seepage control system to raise the fluid pressure to the test set value, ensuring that the confining pressure of the pressure chamber 102 is always 2%~5% greater than the fluid pressure of the sample 5, to prevent excessive fluid pressure from causing the heat shrink sleeve 7 to rupture and the experiment to fail; After the confining pressure, temperature, and fluid pressure all reach the set values ​​and stabilize for 30 minutes, the in-situ multi-field coupling environment is constructed, and the initial values ​​of all parameters are recorded at this time.

[0073] Step 8: Tensile loading and simultaneous monitoring of multiple parameters.

[0074] Axial tensile loading is performed using a displacement control method, with a loading rate of 0.001~0.01 mm / min, which can be adjusted according to the rock type and test requirements. The tensile test assembly 200 converts the axial pressure applied by the test system into axial tensile force acting on both ends of the specimen 5, thereby achieving direct tensile testing of the rock specimen 5. During the loading process, the following parameters are collected in real time through the data acquisition system: Mechanical parameters: tensile stress, axial deformation, radial deformation, and real-time calculation of axial strain, radial strain, elastic modulus, and Poisson's ratio.

[0075] Acoustic parameters: ring count, energy, amplitude, arrival time, longitudinal / transverse wave velocity, amplitude, and waveform distortion characteristics of the acoustic emission signal.

[0076] Seepage parameters: seepage flow rate, pressure difference between inlet and outlet fluids.

[0077] Continue loading until rock specimen 5 fails under tensile stress. Record the peak tensile stress, failure strain, and abrupt changes of each parameter at the moment of failure of specimen 5, and then stop loading.

[0078] Step 9, unloading and depressurizing pressure chamber 102 Axial load unloading: Slowly unload the axial tensile load to the stress level corresponding to the confining pressure, with an unloading rate ≤0.5MPa / min, to avoid secondary damage to specimen 5; Fluid pressure unloading: Close the seepage inlet valve, keep the fluid outlet valve open, and allow the fluid pressure inside sample 5 to be released slowly and naturally. After the fluid outlet pressure drops to a stable low value, close the fluid outlet valve. Confining pressure and temperature unloading: Gradually reduce the confining pressure of pressure chamber 102 at a rate ≤0.5MPa / min, and simultaneously turn off the temperature control device 33 to allow pressure chamber 102 and sample 5 to cool down naturally to room temperature; Once the confining pressure drops to 0 MPa and the temperature drops to room temperature, the entire unloading process is complete.

[0079] Step 10: Sample removal and data processing and analysis.

[0080] Open the door of pressure chamber 102, take out the tensile test assembly 200 and the rock failure sample 5, and remove the heat shrink sleeve 7, seepage pad 6 and sensing components. Observe and record the tensile failure mode, crack propagation path, and macroscopic fracture surface characteristics of specimen 5. Take pictures, scan, and measure the crack size of the specimen. Export the test data of the multi-parameter synchronous acquisition system, and perform data preprocessing to remove outliers, filter, and calibrate; Conduct comprehensive data analysis: plot stress-strain curves, calculate mechanical parameters of rocks such as tensile strength, elastic modulus, and Poisson's ratio; analyze the damage evolution of rocks from microcrack initiation, propagation, penetration to macroscopic rupture by combining acoustic emission and ultrasonic parameters; analyze the influence mechanism of temperature, fluid pressure, and confining pressure coupling on the tensile mechanical properties, acoustic response, and seepage characteristics of rocks; and establish a multi-parameter characterization model for rock tensile damage.

[0081] This invention provides a novel in-situ multi-field environment synchronous testing method for rock tensile multi-parameters in the field of rock mechanics. It can not only obtain the in-situ tensile mechanical parameters of rocks, but also reveal the multi-parameter evolution law of rock tensile damage under multi-field coupling. It provides important experimental testing methods and theoretical basis for scientific research and engineering practice in fields such as deep energy development, underground engineering construction, and geological disaster prevention and control.

[0082] This application is applicable to the study of rock mechanical properties in fields such as deep mining, shale gas / geothermal resource development, tunnel and underground cavern engineering, and geological disaster prevention and control. It can simulate in-situ multi-field environments in the laboratory, including underground stratum temperature, fluid pressure, and confining pressure coupling, to conduct direct tensile tests on rocks and simultaneously test multi-dimensional parameters such as stress, deformation, acoustic emission, and ultrasonic waves. Specific application methods are as follows: Deep energy development: Testing the tensile mechanical properties and acoustic and seepage responses of shale, coal, and geothermal reservoir rocks under in-situ temperature-pressure-permeability coupled environments, providing experimental data for reservoir fracturing scheme design, production capacity optimization, and development stability evaluation.

[0083] Underground engineering construction: Analyze the tensile failure law of rock masses in engineering projects such as tunnels and underground energy storage facilities under confining pressure, groundwater seepage, and geothermal coupling, and guide the design and construction safety management of engineering support structures.

[0084] Geological disaster prevention and control: For geological disasters such as landslides, rock bursts, and karst collapses, the tensile failure threshold and multi-parameter evolution characteristics of the disaster rock mass in in-situ under multiple field environments are tested to provide a theoretical basis for early disaster prediction and risk assessment.

[0085] Fundamental research in rock mechanics: Conduct fundamental research on the tensile deformation and failure mechanism of rocks under in-situ multi-field coupling, the evolution law of microcracks, and the force-acoustic-permeability linkage response, so as to improve the theoretical system of deep rock mechanics.

[0086] This application fills the technical gap in the synchronous testing of multiple parameters of rock tensile stress under in-situ multi-field environment, and can provide a reliable experimental testing method for scientific research and engineering practice in related fields, and has important theoretical research value and practical application value.

[0087] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for testing triaxial direct tensile mechanical behavior of rock in a multi-field coupling environment in situ, characterized in that, A true three-dimensional stress-flow coupling test system (100) and a tensile test assembly (200) were used. The true three-dimensional stress-seepage coupling test system (100) includes a vertical frame (101), a triaxial loading system and a pressure chamber (102). The triaxial loading system includes six hydraulic cylinders (103). The output of the upper hydraulic cylinder (103) is connected to an upper pressure head, and the output of the lower hydraulic cylinder (103) is connected to a lower pressure head. The pressure chamber (102) is operably installed in the hollow part of the vertical frame (101). The pressure chamber (102) has a connection port in each of the six directions. The telescopic rods of the six cylinders (103) can extend into the interior of the pressure chamber (102) from one of the connection ports respectively. The pressure chamber (102) has a fluid injection channel and a fluid outflow channel. The tensile test assembly (200) includes an external bearing frame (1), a specimen clamping device (2), an auxiliary measuring component (3), and a seepage pad (6); the external bearing frame (1) includes an upper tensile frame (11) for docking with the upper pressure head of the triaxial loading system and converting the upper pressure into a lower tension force, and a lower tensile base (12) for docking with the lower pressure head of the triaxial loading system and converting the lower pressure into an upper tension force; the specimen clamping device (2) includes an upper tensile head (21) for connecting to the lower tensile base (12) and clamping the upper end of the specimen (5), and a lower tensile head (22) for connecting to the upper tensile frame (11) and clamping the lower end of the specimen (5); the auxiliary measuring component (3) includes a displacement sensing module for measuring the axial tensile deformation and radial deformation of the specimen (5), and a temperature control module for providing a temperature field to the specimen (5). The permeation pad (6) has a fluid channel. There is a permeation pad (6) between the upper tension head (21) and the upper end of the sample (5). There is a permeation pad (6) between the lower tension head (22) and the lower end of the sample (5). An acoustic sensing component is provided at the end of the permeation pad (6) that is in contact with the sample (5). The sample (5) and the permeation pad (6) are wrapped with a thermoplastic film (7). The tensile test assembly (200) is placed in the pressure chamber (102). The upper tension frame (11) is connected to the upper pressure head of the triaxial loading system. The lower tension base (12) is connected to the lower pressure head of the triaxial loading system.

2. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to claim 1, characterized in that, The acoustic sensing assembly includes two acoustic emission receiving probes and one ultrasonic emission probe; optionally, the ceramic sensing surfaces of the acoustic emission receiving probes and the ultrasonic emission probe are pre-coated with ultrasonic coupling agent.

3. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to claim 2, characterized in that, The seepage pad (6) is used to groove the contact surface that contacts the sample (5) to install the acoustic sensing component. The acoustic emission receiving probe and the ultrasonic emission probe are respectively embedded in the mounting groove of the seepage pad, and a buffer spring is provided at the bottom of the mounting groove.

4. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to any one of claims 1-3, characterized in that, Includes the following steps: Preloading: Axial pressure is applied to the upper and lower cylinders (103) to perform preloading; Slowly fill the pressure chamber (102) with hydraulic oil until the pressure chamber (102) is completely filled with hydraulic oil. Start the high-pressure oil pump and slowly pressurize the pressure chamber (102) to raise the confining pressure to the set value; Turn on the temperature control device (33) to raise the temperature of the pressure chamber (102) and the sample (5) to the test set value; Injecting seepage fluid into the sample (5) through the upper seepage pad (6) until the fluid flowing out of the fluid outlet is free of bubbles and the flow rate is stable, thus realizing the exhaust of the seepage channel; then applying fluid pressure to the set value to ensure that the confining pressure of the pressure chamber (102) is always greater than the fluid pressure of the sample (5); After the confining pressure, temperature, and fluid pressure have all reached the set values ​​and stabilized for a period of time, the in-situ multi-field coupling environment is constructed, and the initial values ​​of all parameters are recorded at this time. The upper and lower cylinders (103) apply axial load, and the tensile test assembly (200) converts the axial pressure into axial tension acting on both ends of the sample (5), realizing the direct tension of the rock sample (5); during the loading process, mechanical parameters, acoustic parameters and seepage parameters are collected in real time. Continue loading until the rock specimen (5) fails under tensile stress. Record the peak tensile stress, failure strain and abrupt change characteristics of each parameter at the moment of failure of specimen (5), and then stop loading.

5. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to claim 4, characterized in that, Before preloading, start the data acquisition system to collect and store stress, deformation, acoustic emission, and ultrasonic parameters; optionally, set the acquisition frequency to ≥100Hz.

6. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to claim 4, characterized in that, The mechanical parameters include tensile force, axial deformation, and radial deformation, with axial strain, radial strain, elastic modulus, and Poisson's ratio calculated in real time; optionally, the acoustic parameters include acoustic emission signal, ultrasonic longitudinal / transverse wave velocity, amplitude, and waveform distortion characteristics. Optionally, the seepage parameters include seepage flow rate and inlet / outlet fluid pressure difference.

7. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to claim 4, characterized in that, It also includes the following steps: Observe and record the tensile failure mode, crack propagation path and macroscopic fracture surface characteristics of the specimen (5), and take pictures, scan and measure the crack size of the specimen.

8. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to any one of claims 1-3 and 5-8, characterized in that, The upper tension frame (11) includes support columns (111), an upper hydraulic cylinder connecting plate (112), and a lower tension plate (113). The upper hydraulic cylinder connecting plate (112) and the lower tension plate (113) are connected together by multiple support columns (111). The upper hydraulic cylinder connecting plate (112) has an upper mounting recess (1122) at its center that matches the upper pressure head of the triaxial loading system. The lower tension head (22) is connected to the lower tension plate (113). The lower tension base (12) includes a ball spline (121), a lower cylinder connecting plate (123) and an upper tension plate (122). The upper tension plate (122) and the lower cylinder connecting plate (123) are connected together by the ball spline (121). The upper tension head (21) is connected to the upper tension plate (122).

9. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to claim 8, characterized in that, The lower tension plate (113) is fixedly equipped with spline guide seats (13) on both sides, and two ball splines (121) are respectively vertically installed in one of the spline guide seats (13) and are clearance-fitted with it.

10. The method for testing the triaxial direct tensile mechanical behavior of rock under in-situ multi-field coupling environment according to any one of claims 1-3 and 5-8, characterized in that, The temperature control device (33) includes a magnetic base (331), a heater bracket (332), and a ring heating device (333). The ring heating device (333) is a ring structure arranged coaxially with the sample (5). The ring heating device (333) is installed on the heater bracket (332), and the heater bracket (332) is fixed on the magnetic base (331). The ring heating device (333) is connected to an external temperature control system.

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