Triaxial test device and rock-soil mechanical property test method

Abstract

The invention discloses a triaxial test device, and relates to the technical field of rock-soil mechanical property testing, the triaxial test device comprises a fixed frame, a loading device, a temperature control box, a side constraint assembly and a test rod, the loading device is fixedly arranged on the fixed frame, the temperature control box is fixedly arranged in the fixed frame, and a first opening at the top of the temperature control box is used for the input of the output end of the loading device; the side restraining assembly comprises a first restraining plate, a second restraining plate, a third restraining plate and a fourth restraining plate which are distributed in the circumferential direction, the restraining plates which are oppositely arranged are connected through pull rods, a to-be-tested piece is placed in an enclosed space of the restraining plates, and a testing rod is fixedly connected outside each restraining plate; one end, far away from the constraint plate, of each test rod can extend out of a second opening in the side part of the temperature control box, and a first displacement sensor is arranged on the fixed frame. The invention further discloses a rock-soil mechanical property testing method which is implemented by adopting the triaxial testing device. According to the invention, high test precision can be ensured, and the test reliability is high.

Description

Technical Field

[0001] This invention relates to the field of geotechnical mechanical property testing technology, and in particular to a triaxial testing device and a geotechnical mechanical property testing method. Background Technology

[0002] Concrete possesses excellent compressive strength and good durability, resisting environmental effects such as weathering, corrosion, and high temperatures. It also exhibits good plasticity and workability, making it suitable for casting and forming various complex structures. However, under extreme high-temperature conditions such as tunnel fires, industrial furnace explosions, nuclear power plant accidents, and high-rise building fires, concrete structures must possess good heat resistance and mechanical stability under high temperature and complex stress conditions to ensure structural safety and service reliability. High temperatures lead to a series of degradation phenomena in concrete, such as moisture evaporation, decomposition of chemically bound water, propagation of interfacial microcracks, and internal stress concentration caused by the mismatch of thermal expansion between aggregates and the matrix. These changes significantly weaken its material properties. Furthermore, the strength and deformation behavior of concrete are greatly affected by the stress state, and the concrete in the aforementioned engineering structures is subjected to complex stress conditions during service. Therefore, in-depth research on the mechanical behavior of concrete under high temperature and complex stress conditions is particularly crucial. Currently, there are many technical challenges in conducting high-temperature triaxial tests, including: First, when the experiment is conducted directly in a high-temperature environment, precision sensors such as strain gauges and displacement gauges used for monitoring are prone to inaccuracy or even burnout, severely affecting the accuracy of data acquisition. Second, high-temperature triaxial loading often involves high-temperature cooling before triaxial testing, which involves a proportional conversion process and fails to achieve true thermo-compression coupling, making it impossible to account for strength degradation and plastic deformation caused by temperature changes. Third, current high-temperature heating methods mostly use external electric heating mantles or radiation heating, making it difficult to ensure uniform temperature distribution inside the sample, reducing the reliability and representativeness of the test results. Fourth, mechanical loads in high-temperature environments are usually uniaxial conditions, making it impossible to achieve triaxial stress loading under high-temperature conditions or temperature loading under triaxial stress conditions. Due to these problems, the current experimental setup cannot guarantee good testing accuracy, and the measurement results also have certain deviations. Therefore, there is an urgent need for a triaxial testing device and a method for testing the mechanical properties of soil and rock to solve these technical problems. Summary of the Invention

[0003] The purpose of this invention is to provide a triaxial testing device and a method for testing the mechanical properties of soil and rock, so as to solve the problems existing in the prior art, and to ensure high testing accuracy and high testing reliability.

[0004] To achieve the above objectives, the present invention provides the following solution: This invention provides a triaxial testing apparatus, comprising a fixed frame, a loading device, a temperature control chamber, a side constraint assembly, and a test rod. The loading device is fixedly mounted on the fixed frame, and its output end can pass through the fixed frame. The temperature control chamber is fixedly mounted inside the fixed frame, and a first opening is provided on the top of the temperature control chamber for the output end of the loading device to enter. The side constraint assembly includes a first constraint plate, a second constraint plate, a third constraint plate, and a fourth constraint plate distributed circumferentially. Adjacent constraint plates are perpendicular to each other, and the first constraint plate and the third constraint plate are opposite to each other and connected by a first tie rod. The second constraint plate and the fourth constraint plate are opposite to each other and connected by a second tie rod. The test piece is placed within the enclosed space of the constraint plates and can fit against the inner wall of each constraint plate. A test rod is fixedly connected to the outer wall of each constraint plate. The side of the temperature control chamber has four second openings, and the end of each test rod away from the constraint plate can extend out of the second opening. A first displacement sensor is provided on the fixed frame, which can monitor the movement displacement of the test rod.

[0005] In some embodiments, the test rod is a rod made of a low thermal conductivity material, wherein the thermal conductivity of the low thermal conductivity material is no greater than 3 W / (m·K).

[0006] In some embodiments, multiple support frames are also included. The fixed frame includes a top plate, a bottom plate, and columns. The top plate and the bottom plate are parallel to each other. The columns include at least four columns, which are respectively vertically fixed at the four corners of the bottom plate and the top plate. The support frame is vertically fixed on the bottom plate, and the test rod can pass through the top of the support frame and slide relative to it.

[0007] In some embodiments, a support base is also included. A third opening is provided on the top plate, a fourth opening is provided on the bottom plate opposite to the third opening, and a fifth opening is provided at the bottom of the temperature control box. The fifth opening is directly opposite to the first opening. The third opening is used for the support base to extend out and enter the fifth opening to fit against the test piece. The output end of the loading device can extend out of the third opening and enter the first opening to fit against the test piece.

[0008] In some embodiments, the temperature control box includes a switch door and a box body, the side of the switch door is rotatably connected to the box body, and the switch door is provided with an observation window, which is sealed with double-layer high-temperature resistant glass.

[0009] In some embodiments, the loading device includes an electro-hydraulic servo cylinder and a magnetostrictive displacement sensor, wherein the magnetostrictive displacement sensor is disposed inside the electro-hydraulic servo cylinder and is used to monitor the displacement of the piston rod of the electro-hydraulic servo cylinder.

[0010] In some embodiments, a rigid pad is provided between the constraint plate and the test piece.

[0011] In some embodiments, the test rod is a zirconium oxide rod.

[0012] In some embodiments, an upper connecting assembly is also included, comprising an upper connecting seat, a first force transmission rod, and a pressure pad that are fixedly connected in sequence. The upper connecting seat is used to be fixedly connected to the output end of the loading device, and the pressure pad is used to fit against the upper surface of the test piece. The support base comprises a lower connecting seat, a second force transmission rod, and a placement platform that are fixedly connected in sequence. The lower connecting seat is used to be fixedly mounted on the base plate, and the placement platform is used to fit against the lower surface of the test piece. Both the pressure pad and the placement platform are made of zirconium oxide and their ends are circumferentially filled with aluminum silicate insulation cotton.

[0013] The present invention also provides a method for testing the mechanical properties of soil and rock, which is implemented using the triaxial testing apparatus described above, and includes the following steps. S1: Place the test piece into the side constraint assembly inside the temperature control chamber, set the temperature control parameters, and start the heating system to heat up to the target temperature; S2: Install the first displacement sensor to monitor the displacement of the test bar; S3: Select an optical observation system to acquire surface images according to requirements; S4: Start the loading device to apply axial load according to the test target path; S5: Output the corresponding stress-strain curve.

[0014] The present invention achieves the following technical effects compared to the prior art: The triaxial testing device provided by this invention adopts a temperature-controlled chamber for overall heating and insulation, ensuring that the temperature difference between the inside and outside of the test piece is controlled within a reasonable range, avoiding large temperature gradients between different parts of the test piece. The test piece is constrained by a side constraint assembly, and then loaded by a loading device. During the compression process, the test piece displaces circumferentially, causing the constraint plate to move outward, which in turn stretches the tie rod. The displacement of the constraint plate pushes the test rod to move, with the outer end of the test rod in a normal temperature range. A first displacement sensor is installed in this environment, ensuring its accuracy is not affected by high temperatures, thus enabling precise quantitative observation of confining pressure under high-temperature triaxial conditions. The lateral displacement and stress measurement of the sample are decoupled from the high-temperature environment. A test rod with a low thermal conductivity is used to draw the deformation from the high-temperature zone to the normal temperature zone for measurement, fundamentally avoiding damage to precision sensors such as strain gauges and linear displacement sensors (LVDTs) caused by high temperatures, thus improving measurement stability and data reliability. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the triaxial testing device in some embodiments of the present invention; Figure 2 This is a schematic diagram of the fixed frame structure in some embodiments of the present invention; Figure 3 This is a schematic diagram of the temperature control box in some embodiments of the present invention; Figure 4 This is a schematic diagram of the side constraint assembly in some embodiments of the present invention; Figure 5 This is a schematic diagram of the structure of the side constraint assembly connecting the test bar in some embodiments of the present invention; Figure 6 This is a schematic diagram showing the connection of the side constraint assembly, test bar, and support frame in some embodiments of the present invention; Figure 7 This is a schematic diagram of the triaxial testing apparatus without a loading device and a fixed frame in some embodiments of the present invention; Figure 8 This is a schematic diagram of the loading device in some embodiments of the present invention; Figure 9 This is a schematic diagram of the structure of the upper connection component in some embodiments of the present invention; Figure 10This is a schematic diagram of the support base in some embodiments of the present invention.

[0017] In the diagram: 101-Test piece; 1-Loading device; 11-Electro-hydraulic servo cylinder; 12-Load sensor; 2-Fixed frame; 21-Top plate; 211-Third opening; 22-Bottom plate; 221-Fourth opening; 23-Column; 3-Temperature control box; 31-Box body; 32-Door switch; 33-First opening; 34-Second opening; 35-Observation window; 4-Test rod; 5-Support frame; 6-Side constraint assembly; 61-First constraint plate; 62-Second constraint plate; 63-Third constraint plate; 64-Fourth constraint plate; 65-Pull rod; 66-Nut; 67-Rigid pad; 7-Upper connecting assembly; 71-Upper connecting seat; 72-First force transmission rod; 73-Pressure pad; 8-Support seat; 81-Lower connecting seat; 82-Second force transmission rod; 83-Placement platform. Detailed Implementation

[0018] 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. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0019] The purpose of this invention is to provide a triaxial testing device and a method for testing the mechanical properties of soil and rock, so as to solve the problems existing in the prior art, and to ensure high testing accuracy and high testing reliability.

[0020] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1 like Figures 1-10As shown, the present invention provides a triaxial testing device, including a fixed frame 2, a loading device 1, a temperature control chamber 3, a side constraint assembly 6, and a test bar 4. The temperature control chamber 3 has a resistance heating function. The loading device 1 is fixedly mounted on the fixed frame 2, and the output end of the loading device 1 can pass through the fixed frame 2. The temperature control chamber 3 is fixedly mounted inside the fixed frame 2, and the top of the temperature control chamber 3 is provided with a first opening 33 for the output end of the loading device 1 to enter. The side constraint assembly 6 includes a first constraint plate 61, a second constraint plate 62, a third constraint plate 63, and a fourth constraint plate 64 distributed circumferentially. Adjacent constraint plates are perpendicular to each other, and the first constraint plate 61 and the third constraint plate 64 are perpendicular to each other. Plate 63 is arranged opposite each other and connected by a first tie rod. The second constraint plate 62 and the fourth constraint plate 64 are arranged opposite each other and connected by a second tie rod. The test piece 101 is placed in the enclosed space of the constraint plate and can fit against the inner wall of each constraint plate. A test rod 4 is fixedly connected to the outer wall of each constraint plate. The side of the temperature control box 3 is provided with four second openings 34. The diameter of the second opening 34 is smaller than the diameter of the first opening 33, and the diameter of the second opening 34 matches the outer circumference of the test rod 4. The end of each test rod 4 away from the constraint plate can extend out of the second opening 34. A first displacement sensor is provided on the fixed frame 2. The first displacement sensor can monitor the movement displacement of the test rod 4. The temperature control chamber 3 employs an overall heating and insulation design to keep the temperature difference between the inside and outside of the test piece 101 within a reasonable range, avoiding large temperature gradients between different parts of the test piece 101. The test piece 101 is constrained by the side constraint assembly 6, and then the test piece 101 is loaded within the side constraint assembly 6 by the loading device 1. During the compression process, the test piece 101 is displaced circumferentially, causing the constraint plate to move outward, which in turn stretches the tie rod 65. The displacement of the constraint plate pushes the test rod 4 to move. The outer end of the test rod 4 is in the room temperature zone. The first displacement sensor is set in this environment, and the accuracy of the first displacement sensor is not affected by the high temperature, thus enabling quantitative and accurate observation of confining pressure under high temperature triaxial conditions. The lateral displacement and stress measurement links of the sample are decoupled from the high temperature environment. The deformation is taken out from the high temperature zone to the room temperature zone for measurement by using the test rod 4 with a low thermal conductivity coefficient, which fundamentally avoids the damage of high temperature to precision sensors such as strain gauges and linear displacement sensors (LVDT), improving measurement stability and data reliability.

[0022] It should be noted that a high-temperature resistant optical observation system can also be installed inside the temperature control chamber 3 to observe the loading changes of the test specimen 101 in real time. Before the test, the test specimen 101 is prepared according to the standard. A high-temperature stable contrast coating can be sprayed on the surface of the test specimen 101, and image recognition marks can be set to assist in recording the deformation process of the specimen at high temperature, thereby improving the completeness and spatial resolution of deformation observation.

[0023] The temperature control system of temperature control chamber 3 adopts a PID closed-loop control algorithm, combined with multi-point thermocouple feedback signals for adjustment. The heating rate, target temperature, and isothermal time are set via a host computer control system to achieve uniform temperature distribution control. During the isothermal stage, the temperature difference between the inside and outside of the sample is controlled within ±1℃. Temperature control chamber 3 has a temperature control range of 25℃ to 900℃, with a heating rate of 1~15℃ / min. The interface area between temperature control chamber 3 and loading device 1 adopts a multi-layer high-temperature resistant, heat-insulating, and flexible sealing composite structure, balancing thermal stability and displacement adaptability, improving the overall system sealing, and preventing temperature fluctuations in the thermal field caused by heat leakage and gas convection.

[0024] In a preferred embodiment, the constraint plates are made of Inconel X-750 high-temperature resistant alloy, and each constraint unit in each direction consists of two constraint plates and four tie rods 65. By selecting tie rods 65 of different diameters, different levels of lateral constraint force can be adjusted. Nuts 66 are provided at both ends of the tie rods 65, which can be used to adjust and apply the initial lateral confinement prestress of the specimen.

[0025] In some embodiments, the test rod 4 is a rod made of a low thermal conductivity material, with a thermal conductivity not exceeding 3 W / (m·K), preferably a zirconia rod. If the thermal conductivity of the test rod 4 is too high, it can easily lead to the rapid dissipation of local heat from the constraint plate, causing a drop in temperature at the edge area where the test piece 101 contacts the constraint plate, disrupting the uniform temperature field formed by the overall heating and insulation of the temperature control chamber 3, and triggering temperature gradients inside and outside the test piece or in local areas. Low thermal conductivity materials such as zirconia can maintain a temperature that is basically consistent with the temperature of the constraint plate and the test piece, ensuring that the test piece remains in a uniform high-temperature environment throughout the entire loading test, making the test data more consistent with the material properties under real working conditions. Zirconia can maintain high rigidity and strength even under high-temperature conditions. When the test piece 101 is loaded and deformed, pushing the constraint plate to compress the test rod 4, the test rod 4 itself is not prone to bending, deformation, or breakage, avoiding additional displacement measurement errors introduced by the deformation of the test rod 4 itself.

[0026] In some embodiments, the triaxial testing apparatus further includes multiple support frames 5. The fixed frame 2 includes a top plate 21, a bottom plate 22, and columns 23. The top plate 21 and the bottom plate 22 are parallel to each other. The columns 23 include at least four columns, which are vertically fixed at the four corners of the bottom plate 22 and the top plate 21, respectively. The support frames 5 are vertically fixed on the bottom plate 22, and the test rod can pass through the top of the support frame 5 and slide relative to it. The support frame 5 provides precise guidance for the test rod. When the test piece 101 is loaded and displaced, the test rod is pushed to move by the constraint plate. The support frame 5 can ensure that the test rod moves accurately along a specific direction, avoiding deviation or swaying of the test rod. This allows the first displacement sensor to more accurately monitor the movement displacement of the test rod, improving the accuracy and reliability of displacement measurement. Furthermore, the first displacement sensor is a linear displacement sensor (LVDT), and four of them are installed on the four support frames 5 respectively, for real-time monitoring of the deformation of the tie rod 65 during the loading process. By combining the mechanical parameters of the tie rod 65, the lateral constraint force on the specimen under high temperature conditions can be indirectly calculated based on its deformation, thereby achieving accurate measurement and control of the triaxial stress state.

[0027] It should be noted that the columns 23 consist of four high-strength steel columns arranged in a rectangle, vertically connected between the top plate 21 and the bottom plate 22, and fixed together with high-strength bolts to form an integrated structure. This structure possesses excellent bending, compressive, and torsional resistance. The rigid top plate is used to install the loading device 1. Furthermore, the entire fixed frame 2 structure can maintain high stability and geometrical alignment under extreme conditions such as high temperature and multi-axis loading, ensuring that the loading path does not deviate. It is a key load-bearing unit for achieving precise temperature-force coupled loading tests.

[0028] In some embodiments, the triaxial testing apparatus further includes a support base 8, a third opening 211 on the top plate 21, a fourth opening 221 on the bottom plate 22 opposite to the third opening 211, and a fifth opening at the bottom of the temperature control chamber 3, which is directly opposite to the first opening 33. The third opening 211 allows the support base 8 to extend out and into the fifth opening to fit against the test piece 101. The output end of the loading device 1 can extend out of the third opening 211 and into the first opening 33 to fit against the test piece 101. The support base 8 can accurately fit against the test piece 101 through the openings of the top plate 21 and the temperature control chamber 3, and the output end of the loading device 1 can also accurately extend into contact with the test piece 101, ensuring that the loading force can be applied vertically and stably to the test piece 101, avoiding force deviation or tilting during the loading process, thereby improving loading accuracy and ensuring the reliability of the test results. The support base 8 provides a clear installation position and support benchmark for the test piece 101, making it easier for staff to place the test piece 101 in the designated position and to quickly and accurately complete the positioning of the test piece, thus improving the efficiency of test preparation.

[0029] In some embodiments, the temperature control chamber 3 includes a door 32 and a chamber body 31. The side of the door 32 is rotatably connected to the chamber body 31. An observation window 35 is provided on the door 32. The observation window 35 is sealed with double-layered high-temperature resistant glass, and the size of the observation window 35 is preferably 300 mm × 150 mm. Test personnel can directly observe the real-time status of the test specimen 101 during the loading process through the double-layered high-temperature resistant glass without opening the temperature control chamber 3 (to avoid disrupting the temperature field). This includes observing whether cracks appear, whether the deformation is uniform, and whether the adhesion with the constraint plate is stable. An external camera can be used to record the specimen's status within the observation window 35 throughout the entire process, providing intuitive visual evidence for post-test data review and analysis of abnormal phenomena (such as the causes of sudden specimen fracture), thus improving the traceability of test data and the accuracy of result analysis. An air gap is formed between the double-layered glass, which further enhances the thermal insulation effect (in conjunction with the overall insulation design of the temperature control chamber 3). This reduces the loss of high temperature inside the chamber through the observation window 35, avoiding temperature fluctuations or local temperature gradients caused by heat dissipation in the observation window 35 area. This ensures that the specimen is always in a uniform high-temperature environment, reducing the impact of temperature interference on the test results. The high-temperature resistant glass (such as quartz glass, high borosilicate glass, etc.) can withstand the high test temperatures inside the temperature control chamber 3 (typically reaching several hundred degrees Celsius), preventing the glass from cracking due to high temperatures. Compared with single-layered glass, the double-layered structure also reduces the risk of instantaneous leakage of high-temperature gas due to accidental breakage (such as the propagation of micro-cracks), providing additional safety protection for test personnel.

[0030] In some embodiments, the loading device 1 includes an electro-hydraulic servo cylinder 11 and a magnetostrictive displacement sensor. The magnetostrictive displacement sensor is disposed inside the electro-hydraulic servo cylinder 11 and is used to monitor the displacement of the piston rod of the electro-hydraulic servo cylinder 11. The electro-hydraulic servo cylinder 11 can provide precise force control and displacement control. Combined with the high-precision displacement measurement capability of the magnetostrictive displacement sensor, accurate monitoring and control of the piston rod displacement can be achieved. The magnetostrictive displacement sensor has a resolution of micrometers or even higher, enabling the triaxial testing device to accurately apply a predetermined load to the specimen and accurately measure the specimen's response, thereby improving the accuracy and reliability of the test results.

[0031] It should be noted that a spoke-type load sensor 12 is installed in the loading path of the electro-hydraulic servo cylinder 11 to measure the axial load on the sample during loading in real time. The electro-hydraulic servo cylinder 11 integrates a magnetostrictive displacement sensor, which can accurately monitor the displacement changes of the piston rod. Both types of sensors are connected to the computer control system via signal lines to collect stress and strain data and plot stress-strain curves in real time. To improve measurement accuracy and sensor stability, both the spoke-type load sensor 12 and the magnetostrictive displacement sensor are externally placed outside the heating area, effectively reducing the impact of the high-temperature environment on the measurement system and ensuring the reliability and data accuracy of long-term high-temperature loading tests.

[0032] In some embodiments, a rigid pad 67 is provided between the constraint plate and the test specimen 101. Some test specimens 101 (such as brittle materials like rock or concrete, or materials that soften easily at high temperatures) have low surface strength. When in direct contact with the constraint plate, if the constraint plate has burrs or sharp edges, it can easily scratch the specimen surface or cause edge damage, affecting the initial integrity of the specimen. The rigid pad 67 can prevent direct friction and collision between the specimen and the constraint plate, maintaining the specimen's original state before the test, making the stress on the test specimen 101 more uniform. When the size of the test specimen 101 is slightly smaller than the space enclosed by the constraint plate (e.g., the specimen diameter is slightly smaller, and the height is slightly lower), the gap between the specimen and the constraint plate can be filled by replacing the rigid pad 67 with one of matching thickness and size, achieving stable constraint on specimens of different specifications without reprocessing the constraint plate.

[0033] In some embodiments, the triaxial testing apparatus further includes an upper connecting assembly 7, which includes an upper connecting seat 71, a first force transmission rod 72, and a pressure pad 73, which are sequentially fixedly connected. The upper connecting seat 71 is fixedly connected to the output end of the loading device 1, and the pressure pad 73 is used to adhere to the upper surface of the test piece 101. The support base 8 includes a lower connecting seat 81, a second force transmission rod 82, and a placement platform 83, which are sequentially fixedly connected. The lower connecting seat 81 is fixedly mounted on the base plate 22, and the placement platform 83 is used to adhere to the lower surface of the test piece 101. Both the pressure pad 73 and the placement platform 83 are made of zirconium oxide and their ends are circumferentially filled with aluminum silicate insulation cotton to improve thermal insulation performance. It should be noted that the pressure pad 73 and the placement platform 83 can also be made of high-strength steel. The pressure pad 73 and the placement platform 83 have good high-temperature strength and thermal stability, high end face precision, and can avoid loading eccentricity and local stress concentration. The second force transmission rod 82 ensures stable transmission of reaction force during the loading process. It should be noted that the shapes of the pressure pad 73 and the placement platform 83 can be determined according to the shape of the loading cross section of the test specimen 101 to ensure that the load is uniformly transferred to the surface of the specimen. The loading device 1 also includes a load sensor 12, the bottom surface of which is fixedly mounted on the upper surface of the upper connecting seat 71, and the top surface of which is fixedly connected to the output end of the electro-hydraulic servo cylinder 11. The load sensor 12 is used to output the magnitude of the load output by the electro-hydraulic servo cylinder 11 to the test specimen 101.

[0034] In summary, it should be noted that the test specimen 101 can be a geotechnical material such as concrete, mortar, or rock, and its shape may include cylinders or cuboids. The cross-sectional shape of the test specimen 101 can be customized with pressure pads 73 and placement platforms of corresponding shapes to ensure uniform stress and centering accuracy during loading. The loading device 1 supports multiple control modes, including stress control, strain control, and combined stress-strain control, enabling constant rate, variable rate, or multi-segment mixed rate loading, suitable for loading tests of material properties under different working conditions.

[0035] Example 2 This embodiment also provides a method for testing the mechanical properties of soil and rock, which is implemented using the triaxial testing apparatus in Embodiment 1, and includes the following steps. S1: Place the test piece 101 into the side constraint assembly 6 inside the temperature control chamber 3, set the temperature control parameters, and start the heating system to heat up to the target temperature; S2: Install the first displacement sensor to monitor the displacement of test rod 4; S3: Select an optical observation system to acquire surface images according to requirements; S4: Start loading device 1 to apply axial load according to the test target path; S5: Output the corresponding stress-strain curve.

[0036] Step S3: The surface images of the specimen acquired through the optical system can complement the mechanical data. For example, during loading, the images can visually capture the initiation and propagation paths of microcracks in the soil and rock specimens. Combined with the inflection points of the stress-strain curves, key parameters such as the initiation stress and peak stress of the specimen can be accurately determined. For heterogeneous soil and rock materials (such as fractured rocks), the influence of local defects on the overall mechanical properties can also be analyzed, so that the test results not only include macroscopic mechanical indicators but also reflect the microscopic failure mechanism, significantly improving the reliability of the data. This method decouples the lateral displacement and stress measurement of the specimen from the high-temperature environment. A test rod 4 with a low thermal conductivity is used to guide the deformation from the high-temperature region to the room temperature region for measurement, fundamentally avoiding the damage of high temperature to precision sensors such as strain gauges and linear displacement sensors (LVDTs), thus improving the measurement stability and data reliability.

[0037] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A triaxial testing apparatus, characterized in that: The device includes a fixed frame, a loading device, a temperature control chamber, a side constraint assembly, and a test rod. The loading device is fixedly mounted on the fixed frame, and its output end can pass through the fixed frame. The temperature control chamber is fixedly mounted inside the fixed frame, and its top has a first opening for the output end of the loading device to enter. The side constraint assembly includes a first constraint plate, a second constraint plate, a third constraint plate, and a fourth constraint plate distributed circumferentially. Adjacent constraint plates are perpendicular to each other, and the first constraint plate and the third constraint plate are opposite each other and connected by a first tie rod. The second constraint plate and the fourth constraint plate are opposite each other and connected by a second tie rod. The test piece is placed within the enclosed space of the constraint plates and can fit against the inner wall of each constraint plate. A test rod is fixedly connected to the outer wall of each constraint plate. The side of the temperature control chamber has four second openings, and the end of each test rod away from the constraint plate can extend out of the second opening. A first displacement sensor is provided on the fixed frame to monitor the movement displacement of the test rod.

2. The triaxial testing apparatus according to claim 1, characterized in that: The test rod is a rod made of a low thermal conductivity material, and the thermal conductivity of the low thermal conductivity material is no greater than 3 W / (m·K).

3. The triaxial testing apparatus according to claim 1, characterized in that: It also includes multiple support frames. The fixed frame includes a top plate, a bottom plate, and columns. The top plate and the bottom plate are parallel to each other. The columns include at least four columns, which are respectively vertically fixed at the four corners of the bottom plate and the top plate. The support frame is vertically fixed on the bottom plate, and the test rod can pass through the top of the support frame and slide relative to it.

4. The triaxial testing apparatus according to claim 3, characterized in that: It also includes a support base, a third opening on the top plate, a fourth opening on the bottom plate opposite to the third opening, a fifth opening on the bottom of the temperature control box opposite to the first opening, the third opening for the support base to extend and enter the fifth opening to fit against the test piece, and the output end of the loading device to extend out of the third opening and enter the first opening to fit against the test piece.

5. The triaxial testing apparatus according to claim 1, characterized in that: The temperature control box includes a switch door and a box body. The side of the switch door is rotatably connected to the box body. An observation window is provided on the switch door, and the observation window is sealed with double-layer high-temperature resistant glass.

6. The triaxial testing apparatus according to claim 1, characterized in that: The loading device includes an electro-hydraulic servo cylinder and a magnetostrictive displacement sensor. The magnetostrictive displacement sensor is installed inside the electro-hydraulic servo cylinder and is used to monitor the displacement of the piston rod of the electro-hydraulic servo cylinder.

7. The triaxial testing apparatus according to claim 1, characterized in that: A rigid pad is provided between the constraint plate and the test piece.

8. The triaxial testing apparatus according to claim 2, characterized in that: The test rod is a zirconium oxide rod.

9. The triaxial testing apparatus according to claim 4, characterized in that: It also includes an upper connecting assembly, which includes an upper connecting seat, a first force transmission rod, and a pressure pad that are fixedly connected in sequence. The upper connecting seat is used to be fixedly connected to the output end of the loading device. The pressure pad is used to fit against the upper surface of the test piece. The support base includes a lower connecting seat, a second force transmission rod, and a placement platform that are fixedly connected in sequence. The lower connecting seat is used to be fixedly set on the base plate. The placement platform is used to fit against the lower surface of the test piece. Both the pressure pad and the placement platform are made of zirconium oxide and their ends are circumferentially filled with aluminum silicate insulation cotton.

10. A method for testing the mechanical properties of soil and rock, characterized in that: The triaxial testing apparatus as described in any one of claims 1-9 is used, and includes the following steps. S1: Place the test piece into the side constraint assembly inside the temperature control chamber, set the temperature control parameters, and start the heating system to heat up to the target temperature; S2: Install the first displacement sensor to monitor the displacement of the test bar; S3: Select an optical observation system to acquire surface images according to requirements; S4: Start the loading device to apply axial load according to the test target path; S5: Output the corresponding stress-strain curve.

Images