High and low temperature control rock-soil nuclear magnetic resonance triaxial apparatus and use method thereof

Abstract

The invention discloses a high and low temperature control rock-soil nuclear magnetic resonance triaxial apparatus and a use method, the high and low temperature control rock-soil nuclear magnetic resonance triaxial apparatus comprises a high and low temperature control rock-soil nuclear magnetic resonance triaxial apparatus arranged in a low field nuclear magnetic resonance analyzer, the high and low temperature control rock-soil nuclear magnetic resonance triaxial apparatus comprises a temperature control system, a pressure chamber, an axial stress loading device and a data acquisition system, temperature control systems are arranged at the upper and lower ends of the pressure chamber; and an axial stress loading device and a data acquisition system are arranged below the pressure chamber. According to the invention, high and low temperature accurate and stable control can be realized, an in-situ occurrence temperature environment and a real stress state of a soil sample are really simulated, and the material and the size of the device are adaptive to the test requirements of a low-field nuclear magnetic resonance analyzer and the size of a pore cavity; the test research on the macroscopic strength characteristic, the micro-pore structure, the permeability characteristic and the like of the geotechnical material by the temperature can be carried out; while the strength and deformation mechanical property indexes of the sample are obtained, a high-resolution image of internal pore structure evolution and dynamic moisture migration can be captured.

Description

Technical Field

[0001] The invention relates to a rock and soil nuclear magnetic resonance triaxial apparatus and a use method thereof, and in particular to a high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus and a use method thereof. Background Art

[0002] In the field of geotechnical engineering, in-depth research on the physical and mechanical properties of geotechnical materials under different environmental conditions is crucial to the safety and stability of the project. Among them, the impact of high and low temperature changes on the performance of geotechnical materials is particularly critical.

[0003] As an effective non-destructive analytical method, low-field nuclear magnetic resonance technology can provide physical parameters such as the internal pore structure, water saturation, water phase distribution, and water migration of geotechnical materials. It can also perform tomography on the distribution of microcracks and water distribution inside geotechnical materials. These applications provide reliable microstructural data for the study of the mechanical properties of geotechnical materials. However, when used alone, the existing low-field nuclear magnetic resonance analyzer cannot directly simulate the complex stress state and high and low temperature cycle process that geotechnical materials are subjected to in actual engineering. Although the traditional triaxial instrument can apply axial and confining pressure to simulate stress conditions, it often lacks accuracy in temperature control and is difficult to meet the requirements for precise research on geotechnical materials in high and low temperature environments.

[0004] Under the alternating effects of low temperature in winter and high temperature in summer, the stability and mechanical properties of rock and soil will change significantly. If we cannot accurately simulate this high and low temperature cycle, and combine low-field nuclear magnetic resonance technology to deeply analyze the microstructural changes inside the rock and soil, and study the influence of different temperature changes on the strength and deformation characteristics of the rock and soil, it will be difficult to formulate effective protective measures to ensure the reliability and safety of engineering construction. However, the existing equipment cannot achieve high and low temperature control triaxial testing while combining it well with low-field nuclear magnetic resonance technology. In addition, some existing high and low temperature control devices have poor compatibility when used in geotechnical engineering with triaxial instruments and low-field nuclear magnetic resonance analyzers. For example, the temperature change rate is uneven, the temperature control range is limited, and the temperature fluctuation is large, which will affect the accuracy and reliability of the test results in geotechnical engineering research. At the same time, due to the wide variety and complex properties of geotechnical materials, an integrated device that can adapt to different types of geotechnical materials and can achieve precise control within a large temperature range is required. However, current technical means cannot meet this demand, which greatly limits the research on the performance of geotechnical materials under high and low temperature conditions.

[0005] Therefore, there is an urgent need for a triaxial testing device that can achieve precise and stable control of high and low temperatures and is compatible with a low-field nuclear magnetic resonance analyzer. The device can perform nuclear magnetic resonance scanning on soil samples in an in-situ temperature environment and under real stress conditions at different strain stages, revealing from a macro-micro dual perspective how the evolution of the microstructure determines the macroscopic strength characteristics, and providing a solid experimental basis for exploring the microscopic mechanisms behind the macroscopic mechanical properties of soil. Summary of the invention

[0006] Purpose of the invention: The purpose of the present invention is to propose a high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus and a method of use, so as to achieve precise and stable control of high and low temperatures, truly simulate the in-situ storage temperature environment and the actual stress state of the soil sample, obtain the macroscopic strength index of the rock and soil material while capturing its microscopic characteristic parameters.

[0007] Technical solution: The present invention includes a high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument placed inside a low-field nuclear magnetic resonance analyzer, wherein the high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument includes a temperature control system, a pressure chamber, an axial stress loading device and a data acquisition system, wherein the temperature control systems are provided at the upper and lower ends of the pressure chamber, and the axial stress loading device and the data acquisition system are provided below the pressure chamber.

[0008] The pressure chamber comprises an outer wall of the pressure chamber, a top cover and a sample base. A triaxial sample is placed in the pressure chamber. A top cap is arranged on the top of the triaxial sample. The top cap has a loading rod. A sample base is arranged on the bottom of the triaxial sample.

[0009] A temperature control system is provided at the bottom of the sample base and the bottom of the top cover, wherein a top plate temperature control component is provided at the bottom of the top cover, and a first bottom plate temperature control component and a second bottom plate temperature control component are provided at the bottom of the sample base, and the temperature control system is connected to a high and low temperature constant temperature circulation tank.

[0010] The lower part of the sample base is connected to the data acquisition system through a loading rod. The data acquisition system includes a force sensor and a displacement sensor. The lower part of the sample base is connected to the force sensor through the loading rod, and the force sensor is connected to the displacement sensor through a sensor fixture.

[0011] The lower part of the force sensor is connected to the axial stress loading device through a force sensor adapter, and the axial stress loading device is installed on the bottom plate.

[0012] A low-temperature nuclear magnetic resonance probe is arranged on the outer side of the outer wall of the pressure chamber.

[0013] An intermediate pressing plate is arranged at the bottom of the low-temperature nuclear magnetic resonance probe, and a supporting column is arranged between the intermediate pressing plate and the bottom plate.

[0014] A reaction column is connected between the top of the axial stress loading device and the second chassis temperature control component.

[0015] The bottom plate, the middle pressure plate and the supporting columns are all made of non-ferromagnetic materials.

[0016] A method for using a high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus comprises the following steps:

[0017] S1. Install the base plate, axial stress loading device, data acquisition system and intermediate pressure plate components of the above-mentioned high and low temperature control rock and soil nuclear magnetic resonance triaxial instrument;

[0018] S2. Install the triaxial specimen, put on and tighten the outer wall of the pressure chamber, then slowly pass the top cap through the top cover of the pressure chamber. After the loading rod of the top cap is completely exposed, tighten the top cover of the pressure chamber and fix the loading rod with the locking copper block and the locking nut. The main body of the pressure chamber device is assembled;

[0019] S3. Pass the low-temperature NMR probe directly through the pressure chamber from the top and place it outside the pressure chamber. Put the whole test device into the low-field NMR analyzer to realize the high and low temperature controlled NMR triaxial shear test with stress path or strain path control.

[0020] Beneficial effects: The present invention has the following advantages:

[0021] (1) The high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument of the present invention can realize accurate and stable control of high and low temperatures, truly simulate the in-situ storage temperature environment and the real stress state of the soil sample, and its material and size are adapted to the test requirements and pore size of the low-field nuclear magnetic resonance analyzer; it can conduct experimental research on the effects of temperature changes on the macroscopic strength characteristics, microscopic pore structure and permeability characteristics of rock and soil materials;

[0022] (2) During the high and low temperature control and triaxial shear process, nuclear magnetic resonance scanning is performed at different critical strain stages to obtain the strength and deformation mechanical properties of the specimen while capturing high-resolution images of the internal pore structure evolution and dynamic water migration;

[0023] (3) It is equipped with a displacement sensor and a force sensor. The displacement sensor can monitor and record the axial strain of the triaxial specimen in real time. The force sensor has a precise temperature compensation and internal pressure compensation system, which can effectively eliminate the zero offset change and monitor the axial stress applied to the triaxial specimen. The axial stress, confining pressure and back pressure are all controlled by closed-loop servo. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic diagram of the cross-sectional structure of the high and low temperature control rock and soil nuclear magnetic resonance triaxial instrument of the present invention;

[0025] Figure 2 This is a schematic diagram of the assembly structure of the high and low temperature control rock and soil nuclear magnetic resonance triaxial instrument of the present invention;

[0026] Figure 3It is a schematic diagram of the general assembly structure of the high and low temperature control rock and soil nuclear magnetic resonance triaxial instrument of the present invention;

[0027] Figure 4 The chassis temperature control component structure of the present invention is schematically shown in FIG. Figure 1 ;

[0028] Figure 5 The chassis temperature control component structure of the present invention is schematically shown in FIG. Figure 2 ;

[0029] Figure 6 The top plate temperature control component structure of the present invention is schematically shown in FIG. Figure 1 ;

[0030] Figure 7 The top plate temperature control component structure of the present invention is schematically shown in FIG. Figure 2 . DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings.

[0032] like Figure 1 to Figure 3 As shown, the high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument 22 of the present invention can be placed inside the low field nuclear magnetic resonance analyzer 23, and its material and size are adapted to the test requirements and cavity size of the low field nuclear magnetic resonance analyzer 23, such as Figure 3 shown.

[0033] like Figure 1 and Figure 2 As shown, the high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument 22 of the present invention includes a temperature control system, a pressure chamber, an axial stress loading device 2 and a data acquisition system, wherein the temperature control system is provided at the upper and lower ends of the pressure chamber, and the axial stress loading device 2 and the data acquisition system are provided below the pressure chamber, which can effectively simplify the pipeline and cable connections above the device, and the nuclear magnetic resonance coil probe can be directly placed from top to bottom on the outside of the outer wall of the triaxial pressure chamber, which is easy to load and unload, and can avoid the temperature escape of the temperature control components on both sides during loading and unloading. The adverse effects on the probe and the test structure can be avoided, and at the same time, it is convenient to calibrate the accuracy of the probe during the test to improve the test accuracy.

[0034] The pressure chamber includes an outer wall 10 of the pressure chamber, a top cover 15 and a sample base 9. A triaxial sample 11 is placed in the pressure chamber. A top cap 12 with a loading rod is provided on the top of the triaxial sample 11. A locking block 14 is connected between the upper part of the top cap 12 with the loading rod and the top cover 15. The top cap 12 with the loading rod passes through the locking block 14, and a locking nut 13 is installed on the upper part of the locking block 14. The top cap 12 with the loading rod is fixed by the locking nut 13. The top cap 12 has a loading rod and a pipeline is opened inside. The pipeline is directly connected to the pressure chamber from the top, and the back pressure is directly applied by a digital volume controller. A sample base 9 is provided at the bottom of the triaxial sample 11. The pressure chamber uses a pneumatic servo controller to apply radial stress (confining pressure) to the sample to simulate the squeezing effect of the surrounding soil on the geotechnical materials in actual engineering. A low-temperature nuclear magnetic resonance probe 17 is provided on the outside of the outer wall 10 of the pressure chamber.

[0035] The bottom of the sample base 9 and the bottom of the top cover 15 are provided with a temperature control system, wherein the bottom of the top cover 15 is provided with a top plate temperature control component 16, such as Figure 6 and Figure 7 As shown; the bottom of the sample base 9 is provided with a chassis temperature control component, such as Figure 4 and Figure 5 As shown, it includes a first chassis temperature control component 8 and a second chassis temperature control component 7. The first chassis temperature control component 8, the second chassis temperature control component 7 and the top plate temperature control component 16 constitute a temperature control system.

[0036] The top and bottom plate temperature control components are designed with a double-layer structure. The outer layer protects the internal structure and insulates, reduces the interference of the external environment on the internal temperature control, and ensures the stability of temperature control. The inner layer is made of 6061-T6 high-strength aluminum alloy, which has excellent thermal conductivity and can quickly and evenly transfer heat to the sample or absorb heat from the sample to achieve efficient and accurate temperature regulation. The double-layer insulation design can effectively reduce the impact of the external environment temperature on the internal temperature of the temperature control plate, thereby avoiding damage to the triaxial specimen due to temperature fluctuations. During long-term testing, even if the ambient temperature of the laboratory changes significantly, the temperature inside the temperature control plate can still remain stable, ensuring that the strength and internal microstructure of the triaxial specimen will not deteriorate. In addition, the outer layer of the insulation structure not only plays a role in heat preservation, but also prevents the test operator from directly contacting the high or low temperature inner surface, reducing the risk of burns or frostbite, and improving the safety and reliability of the equipment. There is a heat exchange pipeline between the inner and outer layers. Through the high and low temperature constant temperature circulation tank and the silicone oil circulating in the heat exchange pipeline, it can accurately adjust between the lower freezing temperature (such as -20℃ or even lower) and the higher melting temperature (such as 20℃ or higher) to meet the temperature requirements of different geotechnical materials for the freeze-thaw process. The high-precision temperature control system can be accurate to ±0.1℃, ensuring that the temperature changes in the freeze-thaw cycle are accurate and stable, which is crucial for some geotechnical materials that are sensitive to temperature changes.

[0037] The surface of the temperature control disk is all covered with annularly distributed fins 24, which are tightly connected to the high and low temperature control disks and can quickly receive heat changes and transfer them. The design of multiple fins 24 greatly increases the surface area in contact with the air. The shape and arrangement of the fins 24 help guide the air flow, form a good convection effect, and achieve efficient temperature control. When the temperature control disk is in the heating stage, the fins 24 can increase the contact area with the surrounding environment, allowing heat to be transferred from the heating source to the temperature control disk and the sample in contact with it more quickly, thereby shortening the heating time. In the cooling stage, the fins 24 can also speed up the dissipation of heat from the temperature control disk to the cooling medium, increase the cooling rate, and enable the freeze-thaw cycle process to be completed faster. In some geotechnical sample processing that requires rapid cooling, the temperature control disk with annular fins can shorten the time for the sample to drop from room temperature to -20°C by about 30%-50%. In addition, the annularly distributed fins 24 can promote a more even distribution of heat on the surface of the temperature control disk. Since the fins 24 can guide heat transfer along their length, areas farther away from the heating or cooling source can reach the set temperature faster, reducing the temperature gradient on the surface of the temperature control disk, ensuring that the test sample is affected by the same temperature at all locations, and improving the accuracy of the test results.

[0038] The annularly distributed fins 24 can also play a certain reinforcement role, making the structure of the temperature control disk more stable. When the temperature control disk frequently experiences temperature changes resulting in thermal expansion and contraction, the fins 24 can share part of the stress and reduce the risk of deformation of the main structure of the temperature control disk.

[0039] The lower part of the sample base 9 is connected to the data acquisition system through the loading rod 6. The data acquisition system includes a force sensor 5 and a displacement sensor 21. The lower part of the sample base 9 is connected to the force sensor 5 through the loading rod 6. The force sensor 5 is connected to the displacement sensor 21 through the sensor fixture 20. The force sensor 5 and the displacement sensor 21 are respectively fixed in the circular through holes at both ends of the sensor fixture 20. The lower part of the force sensor 5 is connected to the axial stress loading device 2 through the force sensor adapter 4. The axial stress loading device 2 is installed on the bottom plate 1. The axial stress loading device 2 moves from bottom to top by applying hydraulic pressure through a digital pressure-volume controller. A low-friction hydraulic cylinder action mode of double-acting single rod from bottom to top is used to apply axial stress to the soil sample on the sample base of the pressure chamber. The cylinder piston rod is connected to the force sensor 5, and forms a closed-loop servo control with the control system and the force sensor. The axial stress can be directly applied to the sample to realize the stress path or strain path control experiment. An intermediate pressing plate 18 is provided at the bottom of the low-temperature nuclear magnetic resonance probe 17 , a supporting column 3 is provided between the intermediate pressing plate 18 and the bottom plate 1 , and a reaction column 19 is connected between the top of the axial stress loading device 2 and the second chassis temperature control component 7 .

[0040] The displacement sensor 21, axial stress loading device 2, force sensor 5 and the loading rods therebetween are all made of 6061-T6 aluminum, which has medium to high strength, good corrosion resistance and weldability, good oxidation effect and no ferromagnetic material, and will not affect the nuclear magnetic test results. Through the digital pressure volume controller, a specific upward pressure or a specific oil inlet amount is automatically applied to the hydraulic cylinder, and the axial stress or strain servo precision control can be achieved.

[0041] The bottom plate 1, the middle pressure plate 18, the supporting column 3, etc. in the above device are all made of high-strength aluminum alloy material which is non-ferromagnetic. Vertical positioning strips are provided on both sides of the middle pressure plate 18 for fixing the low-temperature nuclear magnetic resonance probe 17. The nuts for fixing all the above components are 316L nuts and have passed the non-magnetic detection, which will not have an adverse effect on the nuclear magnetic resonance test results.

[0042] The sample base 9 and the outer wall 10 of the pressure chamber are both made of non-metallic materials without hydrogen atoms to avoid interference with the nuclear magnetic resonance test results of the unsaturated soil sample. The sample base is made of PEEK polyetheretherketone material, and the outer wall of the pressure chamber is made of polytetrafluoroethylene material.

[0043] The sample base 9 is provided with a bubble flushing pipeline, which is connected to a water supply device that can be weighed by an electronic balance through two interfaces of the base. The two interfaces are connected at the bottom of the triaxial sample through a polymer permeable plate to form a loop. An external peristaltic pump is used to drive the water to circulate in the pipeline and replace the original air, thereby monitoring and recording the changes in moisture content, and obtaining the specific moisture migration value caused by the freeze-thaw cycle of the soil sample.

[0044] During the test, the axial stress, radial stress and back pressure were all pressurized using the existing pressurization system, which was placed at a safe distance that would not affect the operation of the NMR instrument and connected to the geotechnical NMR triaxial instrument through a pressure pipeline. The data acquisition instrument was also placed at a safe distance to collect test data.

[0045] All exposed outer surfaces of metal devices and the outer surfaces of the pressure chamber walls are wrapped with detachable thermal insulation cotton material for thermal insulation.

[0046] The size of the high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument of the present invention is compatible with the cavity space of the low-field nuclear magnetic resonance analyzer, the structure is compact, and the operation is convenient, which meets the basic requirements of conventional rock and soil triaxial instrument testing. At the same time, it does not affect the normal independent use of other functions of the low-field nuclear magnetic resonance analyzer, and there is no need to modify or upgrade the structure and other hardware and software of the low-field nuclear magnetic resonance analyzer.

[0047] The method for using the high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus of the present invention comprises the following steps:

[0048] S1. First, fix the axial stress loading device on the bottom plate, connect it to the force sensor through the force sensor adapter, and use the sensor fixture to connect the displacement sensor. The above components are directly connected to the chassis temperature control structure through the reaction column through the middle pressure plate, wherein the upper part of the chassis temperature control structure is directly embedded with the sample base, and the bottom plate and the middle pressure plate use four supporting columns to form a loading reaction force frame to enhance the structural stability;

[0049] S2. Place the sample, polytetrafluoroethylene permeable plate, and loading rod cap on the sample base in sequence. Put the rubber membrane inside the membrane tube and outside the sample, take out the membrane tube, use rubber ring to tie the rubber membrane to the sample base and the loading rod cap respectively, put it on and tighten the outer wall of the pressure chamber, then straighten the loading rod cap and slowly pass it through the pressure chamber top cover. During the process, the loading rod cap should be slightly lifted to prevent collision and squeezing of the sample. After the loading rod cap is completely exposed, tighten the pressure chamber top cover and fix the loading rod with the locking copper block and locking nut. The main body of the pressure chamber device is assembled;

[0050] S3. Finally, the low-temperature NMR probe is passed directly through the pressure chamber from the top and placed outside the pressure chamber. The whole set of test equipment is placed between the C-shaped holes of the low-field NMR analyzer to realize the high and low temperature controlled NMR triaxial shear test with stress path or strain path control.

Claims

1. A high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument, characterized in that: It includes a high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument placed inside a low-field nuclear magnetic resonance analyzer. The high and low temperature controlled rock and soil nuclear magnetic resonance triaxial instrument includes a temperature control system, a pressure chamber, an axial stress loading device and a data acquisition system. The temperature control system is provided at the upper and lower ends of the pressure chamber, and the axial stress loading device and the data acquisition system are provided below the pressure chamber.

2. A high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to claim 1, characterized in that: The pressure chamber comprises an outer wall of the pressure chamber, a top cover and a sample base. A triaxial sample is placed in the pressure chamber. A top cap is arranged on the top of the triaxial sample. The top cap has a loading rod. A sample base is arranged on the bottom of the triaxial sample.

3. A high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to claim 2, characterized in that: A temperature control system is provided at the bottom of the sample base and the bottom of the top cover, wherein a top plate temperature control component is provided at the bottom of the top cover, and a first bottom plate temperature control component and a second bottom plate temperature control component are provided at the bottom of the sample base, and the temperature control system is connected to a high and low temperature constant temperature circulation tank.

4. The high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to claim 2, characterized in that: The lower part of the sample base is connected to the data acquisition system through a loading rod. The data acquisition system includes a force sensor and a displacement sensor. The lower part of the sample base is connected to the force sensor through the loading rod, and the force sensor is connected to the displacement sensor through a sensor fixture.

5. A high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to claim 4, characterized in that: The lower part of the force sensor is connected to the axial stress loading device through a force sensor adapter, and the axial stress loading device is installed on the bottom plate.

6. The high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to claim 5, characterized in that: A low-temperature nuclear magnetic resonance probe is arranged on the outer side of the outer wall of the pressure chamber.

7. The high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to claim 6, characterized in that: An intermediate pressing plate is arranged at the bottom of the low-temperature nuclear magnetic resonance probe, and a supporting column is arranged between the intermediate pressing plate and the bottom plate.

8. The high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to claim 3, characterized in that: A reaction column is connected between the top of the axial stress loading device and the second chassis temperature control component.

9. The high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to claim 7, characterized in that: The bottom plate, the middle pressure plate and the supporting columns are all made of non-ferromagnetic materials.

10. A method for using the high and low temperature controlled rock and soil nuclear magnetic resonance triaxial apparatus according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1. Install the base plate, axial stress loading device, data acquisition system and intermediate pressure plate components of the above-mentioned high and low temperature control rock and soil nuclear magnetic resonance triaxial instrument; S2. Install the triaxial specimen, put on and tighten the outer wall of the pressure chamber, then slowly pass the top cap through the top cover of the pressure chamber. After the top cap loading rod is completely exposed, tighten the top cover of the pressure chamber and fix the loading rod. The main body of the pressure chamber device is assembled; S3. Pass the low-temperature NMR probe directly through the pressure chamber from the top and place it outside the pressure chamber. Put the whole test device into the low-field NMR analyzer to realize the high and low temperature controlled NMR triaxial shear test with stress path or strain path control.

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