A mechanical properties testing system and method for lining structure under load freeze-thaw conditions

Abstract

The invention discloses a mechanical property testing system and method for a lining structure under load freeze-thaw conditions, which relate to the technical field of underground engineering, and include a fan-shaped box, an oil injection pump, an alcohol circulation refrigeration unit, a pressure pump, a plurality of temperature sensors and a plurality of force sensors; the interior of the fan-shaped box has four areas radially divided from the inside to the outside, namely a vacuum area, a concrete area, a clay area and an oil injection area, the concrete area is provided with concrete blocks, and the clay area is provided with clay blocks; a plurality of the temperature sensors and the force sensors are evenly placed inside the concrete blocks and the clay blocks; the testing system of the invention has a wide adjustable range, and by adjusting the temperature, it can simulate concrete under different temperatures and different load states, and at the same time has a good record of the corresponding force and temperature changes, and can more easily derive effective empirical laws, which is helpful for the implementation of engineering disaster reduction and has high scientific value.

Description

Technical Field

[0001] The invention relates to the technical field of underground engineering, and in particular to a mechanical property testing system and method for a lining structure under load freeze-thaw conditions. Background Art

[0002] In the process of coal mining, concrete plays a very important role, and its use in mine geological work is particularly common. Mine geological work is a vital component of coal mine production, construction and development. The degree of exploration, research and control of geological work directly affects the production and development of coal mines. Geological work runs through the entire process of coal mine development, utilization and scrapping. According to statistics, among all kinds of safety accidents in coal mines, about 60% to 70% are malignant accidents such as roof collapse, gas explosion, and water inrush, and all these accidents are closely related to mine geological work. Therefore, strengthening mine geological work can effectively prevent or avoid the occurrence of similar accidents, which is very important for promoting coal mine safety production, enhancing mine disaster prevention and disaster resistance capabilities, and improving economic and social benefits.

[0003] In actual engineering applications, the mine shaft wall is often constructed by artificial freezing. In this use scenario, the concrete is often in a low temperature and compressed state. Therefore, it is necessary to fully understand the working conditions and wear of concrete in such environments. However, in existing experiments, the concrete test blocks used are all cubic standard blocks, and the strength measurements are carried out in a relatively independent environment, which is obviously different from the actual engineering application environment. Therefore, the strength and related conclusions obtained by this method may not be directly applied to engineering practice. In engineering applications, especially in coal mining, it is very urgent to solve the safety hazards of mine geological engineering.

[0004] At present, the existing domestic patents on low-temperature concrete testing mainly include: (1) "Confining pressure equipment for low-temperature concrete impact test based on municipal construction" (authorization number: CN219830666U), which mainly conducts impact tests on concrete that has been cured at low temperatures to test the strength changes of concrete under low temperature conditions; (2) "A confining pressure equipment for low-temperature concrete impact test" (authorization number: CN220671102U), which improves the confining pressure device in the Hopkinson bar to facilitate the observation of the position changes of concrete during the impact test; (3) A ultra-low temperature concrete expansion coefficient test equipment (publication number: CN115951038A), which is mainly used for ultra-low temperature concrete expansion coefficient testing, emphasizing the characterization of concrete mechanical properties through macroscopic deformation. It can be seen that the existing patents on low-temperature concrete testing mainly focus on the changes in the mechanical properties of fully cured concrete under low temperature conditions. And because concrete is used in a variety of scenarios, and its strength and service life will change with environmental changes, it is impossible to evaluate concrete performance and damage through a single mechanical test.

[0005] The above problems need to be solved urgently. To this end, the present invention proposes a mechanical properties testing system and method for a lining structure under load freeze-thaw conditions. Summary of the invention

[0006] The purpose of the present invention is to provide a mechanical properties testing system and method for a lining structure under load freeze-thaw conditions, which can simulate the environment of shaft wall concrete in actual engineering and further evaluate the concrete performance and damage.

[0007] The present invention solves the above technical problems through the following technical solutions. The present invention proposes a mechanical property testing system for a lining structure under load freeze-thaw conditions, including a fan-shaped box, an oil injection pump, an alcohol circulation refrigeration unit, a pressure pump, a plurality of temperature sensors and a plurality of force sensors; the interior of the fan-shaped box has four areas radially divided from the inside to the outside, namely a vacuum area, a concrete area, a clay area and an oil injection area, the concrete area is provided with concrete blocks, and the clay area is provided with clay blocks; a plurality of temperature sensors and force sensors are evenly placed inside the concrete blocks and the clay blocks, the oil injection pipe of the oil injection pump is connected to the side wall of the oil injection area, the oil injection pump realizes oil injection and oil discharge to the oil injection area, and realizes extrusion of the concrete area, the alcohol pipe of the alcohol circulation refrigeration unit is connected to the side wall of the oil injection area, the alcohol circulation refrigeration unit realizes cooling of the concrete area, and then uses the thermodynamic principle to cool the clay area and the concrete area, and the pressure pump is connected to the side wall of the oil injection area.

[0008] Furthermore, two oil filling pipe interfaces are installed on the outer arc surface of the sector-shaped box body near the end position, and the two oil filling pipe interfaces are connected to the oil filling pipe of the oil filling pump.

[0009] Furthermore, the test system also includes an air pump, the oil filling pipe is detachably connected to the oil filling pipe interface, and the air supply pipe of the air pump is connected to one of the oil filling pipe interfaces.

[0010] Furthermore, the fan-shaped box has a detachable first upper cover and a second upper cover, which are respectively arranged at the upper ends of the clay area and the concrete area. The lower sides of the first upper cover and the second upper cover are both provided with sealing rubber rings, and the test system is closed through the first upper cover and the second upper cover.

[0011] Furthermore, the angle of the fan-shaped box is 90°, and the concrete area, clay area and oil injection area are all fan-shaped structures.

[0012] Furthermore, two alcohol pipe interfaces are installed at the middle position of the outer arc surface of the fan-shaped box body, and the two alcohol pipe interfaces are connected to the alcohol circulation refrigeration unit.

[0013] Furthermore, the temperature sensor and the force sensor are both connected to an external monitoring system.

[0014] The present invention also proposes a method for testing the mechanical properties of a lining structure under load freeze-thaw conditions, and the test work is carried out using the above-mentioned test system, including the following steps:

[0015] Step 1: Prepare concrete blocks and clay blocks, and lay temperature sensors and force sensors inside the concrete blocks and clay blocks;

[0016] Step 2: Initially calibrate the NMR instrument. After the calibration is completed, place the prepared concrete block into the NMR instrument to measure its initial porosity and T2 spectrum;

[0017] Step 3: Place two iron power supply electrodes at both ends of the concrete block, connect the power supply with a wire, and connect a resistance meter in parallel between the two iron power supply electrodes. The resistance meter is connected to an external monitoring system to observe the resistance change of the concrete area in real time during the test;

[0018] Step 4: Start the alcohol circulation refrigeration unit to make the inside of the oil filling area reach the set temperature; and lay the clay blocks in the clay area and close the first upper cover;

[0019] Step 5: After reaching the set temperature, the oil filling area is filled with oil, and radial pressure is generated through the action of an external pressure pump, that is, confining pressure;

[0020] Step 6: Monitor the temperature change inside the clay block in real time through the temperature sensor inside the clay block. When the temperature inside the clay block reaches the set temperature, remove the first partition between the clay area and the concrete area, fill the concrete area with concrete blocks, and connect the iron power supply electrode, power supply, parallel resistance meter and external monitoring system in step 3. Remove the second partition between the concrete area and the vacuum area, and then close the second upper cover.

[0021] Step 7: After the concrete block is stable, that is, after confirming that the concrete block is in a frozen state, remove the alcohol circulation refrigeration unit to gradually restore the clay block in the clay area to a normal temperature state, and continue to monitor the temperature change and stress condition inside the clay block;

[0022] Step 8: According to the test plan, adjust the corresponding test parameters to obtain the test curve, the temperature change of the concrete block and the resistance change of the concrete block during the whole test process;

[0023] Step 9: After the test, use an external pressure pump to remove the confining pressure and drain the oil in the oil injection area;

[0024] Step 10: Open the first upper cover of the clay area and the second upper cover of the concrete area, take the concrete blocks and clay blocks out of the fan-shaped box in turn, and clean the fan-shaped box;

[0025] Step 11: Place the taken out concrete block in a nuclear magnetic resonance instrument to measure the porosity and T2 spectrum of the concrete block after the test is completed.

[0026] Furthermore, in step eight, the test parameters include the magnitude of the applied confining pressure and the freezing temperature of the concrete; the test curves include the curve of the change of resistivity with the temperature of the concrete block, the curve of the change of the freezing rate of the concrete block with the confining pressure, the curve of the change of the stress condition of the concrete block with the confining pressure, and the curve of the change of the stress condition of the concrete block with the temperature of the concrete block.

[0027] Furthermore, in step nine, the specific operation is: remove the oil filling pipe interface and the oil filling pipe on the upper side, and connect the air pipe of the air pump to it, run the air pump to inject high-pressure air into the oil filling area, and the oil in the oil filling area will be squeezed downward and discharged through the oil filling pipe.

[0028] Compared with the prior art, the beneficial effects of the present invention are:

[0029] 1. This test system can simulate the environment of shaft wall concrete in actual engineering as much as possible, and the experimental conclusions can provide relatively accurate suggestions for engineering applications;

[0030] 2. This test system has a wide adjustable range. By adjusting the temperature, it can simulate the concrete load state in different areas during the artificial freezing method construction process. At the same time, it has a good record of the corresponding load changes and temperature changes, which can more easily draw effective empirical laws, help the project disaster reduction, and has a high scientific value;

[0031] 3. The raw materials used in many supporting equipment of this test system are recyclable, which is beneficial to environmental protection and can also reduce test costs.

[0032] 4. This test system adopts a test method that combines macro and micro, mechanics and electromagnetics, and comprehensively analyzes the changes in the mechanical properties of the lining structure under load freeze-thaw conditions from multiple angles, with strong foresight. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the principle block diagram of the mechanical properties test system of the lining structure under load freeze-thaw conditions;

[0034] Figure 2 for Figure 1 The structural diagram of the middle fan-shaped box;

[0035] Figure 3 It is a schematic diagram of the cross-sectional structure of the fan-shaped box from top view;

[0036] Figure 4 The figure is a flow chart of the mechanical properties testing method of lining structure under load freeze-thaw conditions.

[0037] The numbers in the figure represent:

[0038] 1-fan-shaped box; 2-pressure pump; 3-air pump; 4-oil injection pump; 5-alcohol circulation refrigeration unit; 6-oil injection pipe interface; 7-alcohol pipe interface; 8-temperature sensor; 9-force sensor; 10-first partition (distinguishing between clay area and concrete area); 11-oil injection area; 12-clay area; 13-concrete area; 14-vacuum area; 15-first upper cover; 16-second partition (distinguishing between concrete area and vacuum area); 17-second upper cover. DETAILED DESCRIPTION

[0039] The above and other technical features and advantages of the present invention are described in more detail below in conjunction with the accompanying drawings.

[0040] Embodiment 1

[0041] This embodiment provides a technical solution: a mechanical performance testing system for lining structures under load freeze-thaw conditions, which can simulate the actual use scenario of concrete and the changes in the temperature and load environment around the concrete. Based on this, the load condition of concrete in the dynamic process of freeze-thaw can be tested. The corresponding testing system can also intuitively evaluate the performance and damage of concrete. Figure 1-Figure 3 The test system includes a fan-shaped box 1, that is, the main test box. The structure of the fan-shaped box 1 includes an outer frame mainly formed by overlapping channel steel and angle steel. The outer frame is welded to the foundation bottom plate. The fan-shaped box 1 has a detachable first upper cover 15. A sealing rubber ring is arranged on the lower side of the first upper cover 15 to cooperate with the fan-shaped box 1. The fan-shaped box 1 is in the shape of a quarter cylinder, that is, the angle of the fan-shaped box 1 is 90°. The interior of the fan-shaped box 1 is radially divided into four areas from the inside to the outside, namely, a vacuum area 14, a concrete area 13, a clay area 12, and an oil injection area 11. The vacuum area 14 is a fan-shaped structure, and the concrete area 13, the clay area 12 and the oil injection area 11 are all fan-shaped ring structures. Concrete blocks are arranged in the concrete area 13, and clay blocks are arranged in the clay area 12. A plurality of temperature sensors 8 and a plurality of force sensors 9 are evenly placed inside the concrete blocks and the clay blocks. The temperature sensors 8 and the force sensors 9 are connected to an external monitoring system, and the monitored parameters are sent to the monitoring system in real time to record the temperature and load parameters. The vacuum area 14 can simulate the open area inside the mine, and on the other hand, it can also reduce heat dissipation, and ensure that the fan-shaped box 1 is an independent individual as much as possible, thereby reducing the natural heat exchange between the inside and outside of the box.

[0042] In addition to the main test box, the test system also includes an external oil injection pump 4, an alcohol circulation refrigeration unit 5, a pressure pump 2, an air pump 3 and other supporting facilities. The oil injection pipe of the oil injection pump 4 is connected to the side wall of the oil injection area 11 (i.e., the outer arc surface of the fan-shaped box body 1). The oil injection pump 4 exists to inject and release oil into the oil injection area 11 outside the clay block, apply confining pressure to the clay block, and squeeze the concrete area 13, so that the concrete inside the clay is in a loaded state. Two oil injection pipe interfaces 6 are installed near the end position of the outer arc surface of the fan-shaped box body 1, so as to completely discharge the oil in the oil injection area 11 or inject the oil liquid, and the two oil injection pipe interfaces 6 are detachably connected to the oil injection pipe of the oil injection pump 4. The oil can be injected into the oil injection area 11 through the left oil injection pipe and the oil injection pipe interface 6, and the oil can be discharged from the oil injection area 11 through the right oil injection pipe and the oil injection pipe interface 6.

[0043] It should be noted that the alcohol circulation refrigeration unit 5 is not in direct contact with the clay area 12 and the concrete area 13, which can reduce the disturbance of the raw materials during the test and improve the accuracy and credibility of the test results.

[0044] Two alcohol pipe interfaces 7 are installed in the middle of the outer arc surface of the sector box 1, and both alcohol pipe interfaces 7 are connected to the alcohol circulation refrigeration unit 5. The alcohol circulation refrigeration unit 5 can cool down the inside of the test main box to achieve the purpose of controlling the temperature of the concrete block. The presence of the oil injection pump 4 and the alcohol circulation refrigeration unit 5 ensures that the clay block and the concrete block are in a low temperature load state;

[0045] The pressure pump 2 is connected to the side wall of the oil injection area 11. After injecting a proper amount of oil into the oil injection area 11, the pressure pump 2 can continuously apply pressure to the oil injection area 11 through control, thereby achieving the effect of applying confining pressure and ensuring the normal progress of the test.

[0046] The function of the air pump 3 is to remove the oil filling pipe interface 6 and the oil filling pipe on the left side after the test is completed, and connect the air supply pipe of the air pump 3 to the oil filling pipe interface 6 on the left side, run the air pump 3 to inject high-pressure gas into the oil filling area 11, and squeeze the oil in the oil filling area 11 out from the oil filling pipe interface 6 and the oil filling pipe on the right side, so as to achieve the purpose of recycling the oil, which is beneficial to environmental protection and can also reduce the test cost.

[0047] The first partition 10 and the second partition 16 are used to separate the clay area 12, the concrete area 13 and the vacuum area 14. After the clay area 12 and the concrete area 13 are completely laid, the first partition 10 and the second partition 16 are removed to allow the clay blocks to fully and quickly contact with the concrete, so as to simulate the effect between the confining pressure and the well wall during the well wall construction process.

[0048] In order to ensure that the fan-shaped box body 1 can better withstand pressure, the strength and quality of the entire fan-shaped box body 1 are very large. At the same time, in order to ensure the overall sealing, the first upper cover 15 and the second upper cover 17 are required to close the entire system during the experiment.

[0049] In actual engineering applications, the outside of the well wall is often wrapped in clay. The main factor that causes concrete to be squeezed at low temperatures is that the surrounding rock frost heaves and exerts pressure on the inner concrete. The concrete blocks and clay blocks are set up to truly simulate the use scenarios of concrete. The temperature sensor 8 and force sensor 9 placed inside are connected to an external computer to monitor and record the changes in temperature and force during the experiment in real time for further adjustment. Setting up multiple sets of non-overlapping temperature sensors 8 and force sensors 9 is on the one hand to provide temperature and pressure at different positions, and on the other hand to ensure that when the sensors in one or some parts are damaged, it will not affect the overall experiment. After injecting oil into the oil injection area 11, the radial pressure on the clay block, that is, the lateral direction of the fan-shaped box 1, simulates the force changes of concrete in real scenes, so the experimental conclusions obtained can provide relatively accurate suggestions for engineering applications.

[0050] Embodiment 2

[0051] This embodiment provides a technical solution: a model test method for a lining structure under low temperature load conditions, using the test system of embodiment 1 to perform concrete testing, referring to Figure 4 , including the following steps:

[0052] Step 1: determine the physical parameters and related properties of the clay area 12, as well as the physical parameters of the concrete area (determined according to the structure of the well wall in the actual project), prepare concrete blocks and clay blocks, and lay the temperature sensor 8 and the force sensor 9 inside the concrete blocks and the clay blocks;

[0053] Step 2: Initially calibrate the NMR instrument. After the calibration is completed, place the prepared concrete block into the NMR instrument to measure its initial porosity and T2 spectrum;

[0054] Step 3: two iron power supply electrodes are placed at both ends of the concrete block, a dry battery is connected between the two iron power supply electrodes with a wire (the dry battery is regarded as a power source), and a resistance meter is connected in parallel between the two iron power supply electrodes, and the resistance meter is connected to an external monitoring system to observe the resistance change of the concrete area 13 in real time during the test;

[0055] Step 4: Start the alcohol circulation refrigeration unit 5 to make the inside of the oil filling area 11 reach the set temperature; and evenly lay the clay blocks in the clay area 12, and close the first upper cover 15;

[0056] Step 5: After reaching the set temperature, the oil filling area 11 is filled with oil (hydraulic oil), and radial pressure, i.e., confining pressure, is generated through the action of the external pressure pump 2;

[0057] Step 6: Monitor the temperature change inside the clay block in real time through the temperature sensor 8 inside the clay block. When the temperature inside the clay block reaches the set temperature, remove the first partition 10 between the clay area 12 and the concrete area 13, fill the concrete area 13 with concrete blocks and lay the circuit components mentioned in step 3, remove the second partition 16 between the concrete area 13 and the vacuum area 14, and then close the second upper cover 17;

[0058] Step 7: After the concrete block is stable, that is, after the concrete block is in a frozen state, remove the alcohol circulation refrigeration unit 5, so that the clay in the clay area 12 gradually returns to a normal temperature state, and continue to monitor the temperature change and stress condition inside the clay block;

[0059] Step 8: According to the test plan, adjust the corresponding test parameters (including but not limited to the size of the confining pressure applied, the freezing temperature of the concrete, etc.), and obtain the test curve, the temperature change of the concrete block, and the resistance change of the concrete block during the whole test process;

[0060] Step 9: After the test is completed, the confining pressure is removed by using the external pressure pump 2, and the oil in the oil injection area 11 is discharged;

[0061] Step 10: Open the first upper cover 15 of the clay area 12 and the second upper cover 17 of the concrete area 13, and take the concrete blocks and clay blocks out of the fan-shaped box in turn, and clean the fan-shaped box;

[0062] Step 11: Place the taken out concrete block in a nuclear magnetic resonance instrument to measure the porosity and T2 spectrum of the concrete block after the test is completed.

[0063] In step eight, the test curves include but are not limited to: a curve showing a change in resistivity with concrete temperature, a curve showing a change in concrete freezing rate with confining pressure, a curve showing a change in concrete stress with confining pressure, a curve showing a change in concrete stress with concrete temperature, and the like.

[0064] In this embodiment, (1) by obtaining the temperature change and stress conditions inside the clay block, the influence of the change of the concrete area on the clay area during the test can be understood, thereby simulating the interaction between the well wall and the surrounding rock in actual working conditions, and then deriving the interaction mechanism between the well wall and the surrounding rock; (2) by measuring the resistance change of the concrete block, it can be intuitively reflected that the physical properties of the concrete block have changed during the entire freezing-thawing process; (3) by scanning and detecting the pore structure of the concrete block before and after the test, it can be concluded that the dynamic process of freezing-thawing has an influence on the structural change of the concrete, and the problem can be analyzed from a microscopic perspective. At the same time, it can also be compared with the conclusions obtained from macroscopic physical experiments and electrical tests, and more comprehensively reveal the influence of the dynamic process of freezing-thawing on the physical properties of the concrete block.

[0065] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A mechanical properties testing system for lining structures under load freeze-thaw conditions, characterized by: It includes a fan-shaped box, an oil injection pump, an alcohol circulation refrigeration unit, a pressure pump, a plurality of temperature sensors and a plurality of force sensors; the interior of the fan-shaped box is divided into four areas radially from the inside to the outside, namely, a vacuum area, a concrete area, a clay area, and an oil injection area, the concrete area is provided with concrete blocks, and the clay area is provided with clay blocks; a plurality of temperature sensors and force sensors are evenly placed inside the concrete blocks and clay blocks, the oil injection pipe of the oil injection pump is connected to the side wall of the oil injection area, the oil injection pump can fill and drain the oil into the oil injection area, and realize the extrusion of the concrete area, the alcohol pipe of the alcohol circulation refrigeration unit is connected to the side wall of the oil injection area, the alcohol circulation refrigeration unit can realize the cooling of the concrete area, and then use the thermodynamic principle to cool the clay area and the concrete area, and the pressure pump is connected to the side wall of the oil injection area; The test system also includes a first partition and a second partition for distinguishing the clay area, the concrete area and the vacuum area. After the clay area and the concrete area are completely paved, the first partition and the second partition are removed to allow the clay block to fully contact the concrete, simulating the interaction between the confining pressure and the well wall during the well wall construction process.

2. A mechanical properties testing system for lining structures under load freeze-thaw conditions according to claim 1, characterized in that: Two oil injection pipe interfaces are installed near the end of the outer arc surface of the sector-shaped box body, and the two oil injection pipe interfaces are connected to the oil injection pipe of the oil injection pump.

3. A mechanical properties testing system for lining structures under load freeze-thaw conditions according to claim 2, characterized in that: The test system also includes an air pump, the oil filling pipe is detachably connected to the oil filling pipe interface, and the air delivery pipe of the air pump is connected to one of the oil filling pipe interfaces.

4. The mechanical properties testing system for lining structures under load freeze-thaw conditions according to claim 1 is characterized in that: The fan-shaped box has a detachable first upper cover and a second upper cover, which are respectively arranged at the upper ends of the clay area and the concrete area. The lower sides of the first upper cover and the second upper cover are both provided with sealing rubber rings, and the test system is closed through the first upper cover and the second upper cover.

5. The mechanical properties testing system for lining structures under load freeze-thaw conditions according to claim 1 is characterized in that: The angle of the fan-shaped box is 90°, and the concrete area, clay area and oil injection area are all fan-shaped structures.

6. The mechanical properties testing system for lining structures under load freeze-thaw conditions according to claim 1 is characterized in that: Two alcohol pipe interfaces are installed at the middle of the arc-shaped surface outside the fan-shaped box body, and the two alcohol pipe interfaces are both connected to the alcohol circulation refrigeration unit.

7. The mechanical properties testing system for lining structures under load freeze-thaw conditions according to claim 1 is characterized in that: The temperature sensor and the force sensor are both connected to an external monitoring system.

8. A method for testing the mechanical properties of a lining structure under load freeze-thaw conditions, using the test system according to any one of claims 1 to 7 for testing, characterized in that: The following steps are involved: Step 1: Prepare concrete blocks and clay blocks, and lay temperature sensors and force sensors inside the concrete blocks and clay blocks; Step 2: Initially calibrate the NMR instrument. After the calibration is completed, place the prepared concrete block into the NMR instrument to measure its initial porosity and T2 spectrum; Step 3: Place two iron power supply electrodes at both ends of the concrete block, connect the power supply with a wire, and connect a resistance meter in parallel between the two iron power supply electrodes. The resistance meter is connected to an external monitoring system to observe the resistance change of the concrete area in real time during the test; Step 4: Start the alcohol circulation refrigeration unit to make the inside of the oil filling area reach the set temperature; and lay the clay blocks in the clay area and close the first upper cover; Step 5: After reaching the set temperature, the oil filling area is filled with oil, and radial pressure is generated through the action of an external pressure pump, that is, confining pressure; Step 6: Monitor the temperature change inside the clay block in real time through the temperature sensor inside the clay block. When the temperature inside the clay block reaches the set temperature, remove the first partition between the clay area and the concrete area, fill the concrete area with concrete blocks, and connect the iron power supply electrode, power supply, parallel resistance meter and external monitoring system in step 3. Remove the second partition between the concrete area and the vacuum area, and then close the second upper cover. Step 7: After the concrete block is stable, that is, after confirming that the concrete block is in a frozen state, remove the alcohol circulation refrigeration unit to gradually restore the clay block in the clay area to a normal temperature state, and continue to monitor the temperature change and stress condition inside the clay block; Step 8: According to the test plan, adjust the corresponding test parameters to obtain the test curve, the temperature change of the concrete block and the resistance change of the concrete block during the whole test process; Step 9: After the test, use an external pressure pump to remove the confining pressure and drain the oil in the oil injection area; Step 10: Open the first upper cover of the clay area and the second upper cover of the concrete area, take the concrete blocks and clay blocks out of the fan-shaped box in turn, and clean the fan-shaped box; Step 11: Place the taken out concrete block in a nuclear magnetic resonance instrument to measure the porosity and T2 spectrum of the concrete block after the test is completed.

9. The method for testing the mechanical properties of a lining structure under load freeze-thaw conditions according to claim 8, characterized in that: In step eight, the test parameters include the magnitude of the applied confining pressure and the freezing temperature of the concrete; the test curves include the curve of the change of resistivity with the temperature of the concrete block, the curve of the change of the freezing rate of the concrete block with the confining pressure, the curve of the change of the stress condition of the concrete block with the confining pressure, and the curve of the change of the stress condition of the concrete block with the temperature of the concrete block.

10. The method for testing mechanical properties of lining structures under load freeze-thaw conditions according to claim 8, characterized in that: In step nine, the specific operation is: remove the upper oil filling pipe interface and the oil filling pipe, and connect the air pipe of the air pump to it, run the air pump to inject high-pressure air into the oil filling area, and the oil in the oil filling area will be squeezed downward and discharged through the oil filling pipe.

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