Triaxial apparatus system suitable for frozen soil

Abstract

The triaxial apparatus system comprises a triaxial pressure chamber, a top cover and a base are arranged at the upper end and the lower end of a sample arranged in the triaxial pressure chamber respectively, and each of the top cover and the base comprises an anti-freezing solution inlet and an anti-freezing solution outlet; a spiral copper pipe is arranged in the triaxial pressure chamber and is connected with the hot bath system through a sealing connecting pipeline; the GDS pneumatic controller is connected into the triaxial pressure chamber, the load sensor applies axial force to a sample, the GDS backpressure controller is connected to the bottom of the triaxial pressure chamber, and the linear variable differential transformer LVDT is arranged outside the triaxial pressure chamber; and the axial Hall effect sensor and the radial Hall effect sensor are respectively arranged at the axial position and the radial position of the sample. The device is simple in structure, convenient to operate, high in measurement precision and good in repeatability and reliability, and the precision and efficiency of frozen soil mechanical property research are remarkably improved.

Description

Technical Field

[0001] The invention relates to the fields of civil engineering and geotechnical engineering, and in particular to a triaxial instrument system capable of accurately controlling the temperature of a frozen soil sample and measuring the small strain stiffness under multi-mode freezing / thawing cycle conditions. Background Art

[0002] Frozen soil is widely present in natural environments and engineering applications, and its mechanical properties have an important impact on the design and construction of infrastructure. With the intensification of global climate change, engineering construction in frozen areas faces more and more challenges. For example, the stability and safety of infrastructure such as roads, bridges, tunnels and dams are significantly affected by freeze-thaw cycles. Therefore, in-depth research on the changes in the mechanical properties of frozen soil during freezing and thawing is of great significance to ensure the durability and safety of engineering structures.

[0003] The existing triaxial test system has been widely used in the study of the mechanical properties of frozen soil. The traditional triaxial instrument is mainly used to measure the deformation and strength characteristics of soil samples under different stress states. However, the traditional triaxial test device has the following main problems when conducting freeze-thaw cycle tests:

[0004] 1. Inaccurate temperature control: When conducting freeze-thaw cycle tests, traditional triaxial instruments are usually unable to independently control the upper and lower boundaries and side wall temperatures of the specimen. This results in uneven temperature distribution inside the specimen, making it difficult to accurately simulate the actual temperature field of frozen soil in the natural environment.

[0005] 2. Uneven freezing process: Due to the lack of effective temperature control methods, it is difficult for traditional triaxial instruments to achieve multi-mode freezing processes, such as unidirectional freezing, bidirectional freezing or multi-directional freezing. This limits the comprehensive study of the mechanical behavior of frozen soil under different freezing modes.

[0006] 3. Inaccurate measurement of small strain stiffness: Under freezing conditions, the stiffness change of frozen soil has a significant impact on engineering structures. When measuring stiffness under small strain conditions, traditional triaxial instruments often lack sufficient accuracy and sensitivity and cannot accurately capture the subtle changes in stiffness of frozen soil during freezing and thawing.

[0007] 4. Low heat conduction efficiency: The materials and designs used for temperature control in traditional triaxial apparatus often lead to low heat conduction efficiency, slow and uneven freezing and melting processes, and affect the reliability and repeatability of test results.

[0008] 5. Limited data collection and analysis: Traditional triaxial instruments usually rely on limited sensors and measurement methods for data collection, making it difficult to simultaneously monitor shear wave velocities and deformation characteristics in multiple directions, limiting the comprehensive analysis of the mechanical behavior of frozen soil. Summary of the invention

[0009] The purpose of the present invention is to provide a triaxial instrument system suitable for frozen soil, aiming to solve the problems of inaccurate temperature control, uneven freezing process and inaccurate small strain stiffness measurement in the existing triaxial test device in frozen soil research. By improving the design of the top cover and the base, and setting the antifreeze inlet and outlet, the upper and lower boundary temperatures of the sample can be independently controlled. In addition, combined with an efficient shear wave velocity measurement system, the stress-strain characteristics of frozen soil can be accurately monitored under different freezing modes.

[0010] To achieve the above object, the present invention provides a triaxial instrument system suitable for frozen soil, comprising a triaxial pressure chamber, a GDS pneumatic controller, a load sensor, a linear variable differential transformer LVDT, a spiral copper tube, a radial Hall effect sensor, an axial Hall effect sensor, a GDS back pressure controller and a thermal bath system.

[0011] The upper end and the lower end of the sample arranged inside the triaxial pressure chamber are respectively provided with a top cover and a base, and the top cover and the base both include an antifreeze inlet and an antifreeze outlet, which are used to control the temperature of the top cover and the base through the antifreeze;

[0012] The triaxial pressure chamber is provided with a spiral copper tube, which is connected to the heat bath system through a sealed connecting pipe;

[0013] The GDS pneumatic controller is connected to the inside of the triaxial pressure chamber and is used to adjust the confining pressure of the sample. The load sensor applies an axial force to the sample. The GDS back pressure controller is connected to the bottom of the triaxial pressure chamber and is used to apply back pressure in the saturation stage. The linear variable differential transformer LVDT is set outside the triaxial pressure chamber and is used to measure the displacement of the sample during the shearing process.

[0014] The axial Hall effect sensor and the radial Hall effect sensor are respectively installed at the axial and radial positions of the sample and are used to measure the shear wave velocity and the small strain stiffness of the sample.

[0015] The connection ends of the top cover and the base with the sample are all provided with 2 mm thick copper plates to enhance the heat conduction efficiency between the soil sample and the antifreeze liquid.

[0016] A thermostat is installed inside the heat bath system, and the thermostat controls the temperature of the antifreeze liquid loaded inside the heat bath system. The antifreeze liquid in the heat bath system is transported to the spiral copper tube through a pump installed on the heat bath system.

[0017] The bottom of the triaxial pressure chamber is provided with a drainage system for removing the pore water pressure of the sample during the consolidation process.

[0018] The outer surface of the triaxial pressure chamber is covered with a rubber insulation material with low thermal conductivity to reduce energy loss and reduce fluctuations in sample temperature.

[0019] The top cover and the base are both made of acrylic material, and are provided with a hollow area for circulating antifreeze liquid.

[0020] The top cover and the middle of the base are each provided with a dedicated groove, which is filled with epoxy resin and embedded with a bending element. A pair of bending elements are installed in the middle of the sample. The bending elements are waterproofed by a polyurethane coating and are used to measure the shear wave velocity of the soil sample during the freezing / thawing process.

[0021] The spiral copper tube inputs the antifreeze liquid from the antifreeze liquid inlet and outputs it from the antifreeze liquid outlet, thereby realizing the circulation of the antifreeze liquid. By controlling the temperature of the antifreeze liquid, an all-round freezing mode of the device is realized.

[0022] The porous parts of the top cover and the base are made of porous copper material.

[0023] The beneficial effects of adopting the above embodiment are:

[0024] Independent control of the upper and lower boundary temperatures of frozen soil samples can be achieved, and a variety of freezing modes can be simulated to improve the authenticity and diversity of the test. Through the application of multiple sets of bending elements and Hall effect sensors, high-precision shear wave velocity measurement and multi-directional deformation monitoring are achieved, which improves the reliability of test data. The use of porous copper materials and 2 mm thick copper plates significantly improves the heat conduction efficiency, accelerates the freezing and melting process, and ensures the uniformity and stability of the temperature field. The system is simple in design, easy to operate, and has good repeatability and reliability. It provides a high-precision and reliable test tool for the study of the mechanical properties of frozen soil, and has broad application prospects and significant technical advantages. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0026] Figure 1 It is a schematic diagram of the overall structure of an embodiment of the present application;

[0027] Figure 2 is a schematic diagram of a self-made top cover of an embodiment of the present application;

[0028] Figure 3 It is a schematic diagram of a self-made base according to an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical scheme and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0030] It should be noted that the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0031] like Figures 1 to 3 As shown, the present invention provides a novel triaxial instrument system suitable for multi-mode freeze / thaw cycles and small strain stiffness measurement of frozen soil, including a triaxial pressure chamber 1, a top cover 17, a base 18, a spiral copper tube 5, a heat bath system 14, a bending element 19, an axial Hall effect sensor 8, a radial Hall effect sensor 7, a GDS pneumatic controller 2, a GDS back pressure controller 9, a load sensor 3, a linear variable differential transformer LVDT4, a copper plate 6 and an insulation material 20.

[0032] The triaxial pressure chamber 1 is provided with a top cover 17 and a base 18, and the top cover 17 and the base 18 respectively include an antifreeze inlet 10 and an antifreeze outlet 11, which are used to control the temperature of the top cover and the base through the antifreeze, thereby realizing independent control of the temperature of the top and bottom of the sample and realizing a single freezing mode of the sample.

[0033] like Figure 2 and Figure 3 As shown, the top cover 17 and the base 18 are each provided with a special groove 21 in the middle, the groove is filled with epoxy resin 22, and a bending element 19 is embedded in the groove to measure the shear wave velocity of the soil sample during the freezing / thawing process. The ends of the top cover and the base are both provided with a 2 mm thick copper plate 6 to enhance the heat conduction efficiency between the soil sample and the antifreeze liquid, thereby accelerating the freezing and thawing process. The porous part uses porous copper material 23 to replace the traditional porous stone material to improve the drainage efficiency.

[0034] The spiral copper tube 5 is connected to the heat bath system 14 through a sealed connecting pipe. The thermostat 15 in the heat bath system is used to accurately control the temperature of the antifreeze liquid to ensure that the antifreeze liquid can circulate smoothly, and is used to achieve an all-round freezing mode, that is, to control the temperature of the side wall of the sample to freeze evenly. In this mode, the antifreeze liquid circulates on the side wall of the sample through the spiral copper tube to achieve lateral temperature control.

[0035] The axial Hall effect sensor 8 and the radial Hall effect sensor 7 are respectively installed at the axial and radial positions of the sample, and are used to measure the shear wave velocity of the sample and calculate the small strain stiffness of the sample according to a specific formula.

[0036] The GDS pneumatic controller is used to adjust the confining pressure of the sample, the load sensor applies an axial force to the sample, the back pressure controller is connected to the bottom of the triaxial pressure chamber and is used to apply back pressure in the saturation stage, the linear variable differential transformer LVDT is used to measure the displacement of the sample during shearing, and the drainage system 12 is used to remove the pore water pressure of the sample during consolidation.

[0037] The top cover 17 and the base 18 are both made of acrylic material, and are provided with a hollow area for circulating antifreeze 16 inside. The antifreeze is a 1:1 mixed solution of water and ethylene glycol, which is used to prevent the liquid from freezing at low temperatures.

[0038] The antifreeze inlet 10 and outlet 11 of the top cover 17 and the base 18 are used to circulate the antifreeze in the top cover and the base by controlling the temperature of the antifreeze to independently control the temperature of the top cover and the base, thereby realizing a single freezing mode of the sample.

[0039] A dedicated groove 21 is respectively provided in the middle of the top cover 17 and the base 18. The groove is filled with epoxy resin 22 and embedded with a bending element 19 for measuring the shear wave velocity of the soil sample during the freezing / thawing process.

[0040] The ends of the top cover 17 and the base 18 are provided with 2 mm thick copper plates 6 to enhance the heat conduction efficiency between the soil sample and the antifreeze liquid 16 and accelerate the freezing / thawing process.

[0041] The porous parts of the top cover 17 and the base 18 are made of porous copper material 23 to replace the traditional porous stone material, so as to achieve a more efficient drainage effect.

[0042] The outer surface of the triaxial pressure chamber 1 is covered with a rubber insulation material 20 with low thermal conductivity, so as to reduce energy loss and reduce fluctuation of sample temperature.

[0043] The bending element 19 is waterproofed by a polyurethane coating 24 and sealed by an epoxy resin 22 to ensure its stability and reliability during the freezing / thawing process.

[0044] The axial Hall effect sensor 8 and the radial Hall effect sensor 7 are installed at the axial and radial positions of the sample, respectively.

[0045] The GDS advanced controller 9 is connected to the base 18 through a sealed connecting pipe, ensuring that the antifreeze liquid can circulate smoothly in the system and can achieve precise control of back pressure and volume.

[0046] The pump 13 is used to circulate the antifreeze liquid, and transports the antifreeze liquid from the antifreeze liquid inlet 10 to the antifreeze liquid outlet 11 through the spiral copper tube 5 to realize the circulation of the antifreeze liquid. By controlling the temperature of the antifreeze liquid, an all-round freezing mode of the device is realized.

[0047] The drainage system 12 includes a porous copper material 23, which is used to allow the water inside the sample to be effectively discharged during freezing or melting, thereby preventing the accumulation of pore water pressure.

[0048] The bending element 19 includes a pair of elements arranged in the top cover 17 and the base 18 for measuring the velocity vsvh of the vertically transmitted shear wave; and a pair of bending element probes installed in the middle of the sample for measuring the velocities vshv and vshh of the horizontally transmitted shear wave.

[0049] The triaxial instrument system adopts an open system design, allowing an external water source to be supplied to the interior of the sample through the back pressure controller 9 during the freezing process, and allowing excess pore water pressure to dissipate through the back pressure controller 9 during the melting process.

[0050] The pump 13 is connected to the heat bath device 14, and the circulation speed and flow rate of the antifreeze liquid in the system can be precisely controlled by adjusting the flow rate of the pump.

[0051] The system can flexibly adjust the freezing mode of the sample to simulate different freezing / thawing conditions, ensure the uniform freezing process of the sample and effectively control the temperature field inside the sample.

[0052] The specific operations are as follows:

[0053] Step 1: Place the frozen soil sample in the triaxial pressure chamber 1, and install the top cover 17 and the base 18, ensuring that the upper and lower boundaries of the sample are in good contact with the top cover and the base.

[0054] Step 2: Adjust the confining pressure through the GDS pneumatic controller 2 and control the back pressure through the back pressure controller 9 to consolidate the sample and discharge the pore water pressure during the consolidation process through the drainage system 12.

[0055] Step 3: Inject antifreeze into the top cover 17 and the base 18 through the antifreeze inlet 10, connect the spiral copper tube 5 with the heat bath system 14, and start the pump 13 to circulate the antifreeze.

[0056] Step 4: Use the thermostat 15 to adjust the temperature of the antifreeze solution in the thermal bath system, independently control the temperature of the top cover and the base, set the desired freezing mode, and complete the freezing and thawing of the sample.

[0057] Step 5: Apply appropriate axial force through the load cell 3 and measure the displacement of the specimen during shearing through the linear variable differential transformer 4.

[0058] Step 6: Measure the shear wave velocity through the bending element 19 and monitor the shear wave of the sample using axial and radial Hall effect sensors 8, 7.

[0059] Step 7: Lower the temperature setting values ​​of the top cover and the base to gradually control the melting process of the sample and ensure a uniform and stable temperature field.

[0060] Step 8: Collect the shear wave velocity and deformation data of the sample during the freezing / thawing process, and analyze the stiffness change and mechanical properties of the sample. After measuring the shear wave velocity, the shear modulus (G) of the sample can be calculated according to the following formula to obtain the small strain stiffness characteristics of the soil sample. As shown in formula (1), the elastic shear modulus of the soil can be calculated by the shear wave velocity measured by the bending element:

[0061]

[0062] Where: i and j represent the directions of shear wave propagation. ij is the velocity of the shear wave in the ij plane. ρ is the density of the soil.

[0063] Through the above method, the system can efficiently control the freezing mode of the sample, accurately monitor the mechanical properties of frozen soil in the freeze / thaw cycle, and ensure the accuracy and reliability of the test data.

[0064] In summary, the new triaxial instrument system described in the present invention can independently adjust the upper and lower boundary temperatures of the sample through the temperature control of the antifreeze fluid, simulate a variety of freezing modes, and at the same time combine the bending element and the Hall effect sensor to achieve high-precision shear wave velocity measurement and sample deformation monitoring, which is suitable for in-depth research on the mechanical properties of frozen soil.

[0065] Those skilled in the art may implement the present invention in a variety of variations without departing from the scope and essence of the present invention, such as using a feature of one embodiment to obtain another embodiment. Any modification, equivalent substitution and improvement made within the technical concept of the present invention shall be within the scope of the present invention.

Claims

1. A triaxial instrument system suitable for frozen soil, characterized in that: The invention comprises a triaxial pressure chamber (1), a GDS pneumatic controller (2), a load sensor (3), a linear variable differential transformer LVDT (4), a spiral copper tube (5), a radial Hall effect sensor (7), an axial Hall effect sensor (8), a GDS back pressure controller (9) and a thermal bath system (14). A top cover (17) and a base (18) are respectively provided at the upper and lower ends of the sample arranged inside the triaxial pressure chamber (1), and the top cover (17) and the base (18) both include an antifreeze inlet (10) and an antifreeze outlet (11) for controlling the temperature of the top cover and the base through the antifreeze; A spiral copper tube (5) is arranged in the triaxial pressure chamber (1), and the spiral copper tube (5) is connected to the heat bath system (14) through a sealed connecting pipe; The GDS pneumatic controller (2) is connected to the inside of the triaxial pressure chamber (1) and is used to adjust the confining pressure of the sample. The load sensor (3) applies an axial force to the sample. The GDS back pressure controller (9) is connected to the bottom of the triaxial pressure chamber (1) and is used to apply back pressure in the saturation stage. The linear variable differential transformer LVDT (4) is arranged outside the triaxial pressure chamber (1) and is used to measure the displacement of the sample during the shearing process. The axial Hall effect sensor (8) and the radial Hall effect sensor (7) are respectively installed at the axial and radial positions of the sample and are used to measure the shear wave velocity and the small strain stiffness of the sample.

2. A triaxial instrument system suitable for frozen soil according to claim 1, characterized in that: The connection ends of the top cover (17) and the base (18) with the sample are both provided with a 2 mm thick copper plate (6) for enhancing the heat conduction efficiency between the soil sample and the antifreeze liquid.

3. A triaxial instrument system suitable for frozen soil according to claim 1, characterized in that: A thermostat (15) is installed inside the heat bath system (14), and the thermostat (15) controls the temperature of the antifreeze liquid (16) loaded inside the heat bath system (14). The antifreeze liquid (16) in the heat bath system (14) is transported to the spiral copper tube (5) through a pump (13) installed on the heat bath system (14).

4. The triaxial instrument system suitable for frozen soil according to claim 1, characterized in that: The bottom of the triaxial pressure chamber (1) is provided with a drainage system (12) for draining away the pore water pressure of the sample during the consolidation process.

5. The triaxial instrument system suitable for frozen soil according to claim 1, characterized in that: The outer surface of the triaxial pressure chamber (1) is covered with a rubber heat-insulating material (20) with low thermal conductivity, so as to reduce energy loss and lower fluctuations in sample temperature.

6. A triaxial instrument system suitable for frozen soil according to claim 1, characterized in that: The top cover (17) and the base (18) are both made of acrylic material, and are provided with a hollow area for circulating antifreeze liquid (16) therein.

7. The triaxial instrument system suitable for frozen soil according to claim 1, characterized in that: The top cover (17) and the base (18) are each provided with a dedicated groove (21) in the middle, the groove (21) is filled with epoxy resin (22) and embedded with a bending element (19), a pair of bending elements (19) are installed in the middle of the sample, and the bending elements (19) are waterproofed by a polyurethane coating (24) and are used to measure the shear wave velocity of the soil sample during the freezing / thawing process.

8. The triaxial instrument system suitable for frozen soil according to claim 1, characterized in that: The spiral copper tube (5) inputs the antifreeze liquid from the antifreeze liquid inlet (10) and discharges it from the antifreeze liquid outlet (11), thereby realizing the circulation of the antifreeze liquid. By controlling the temperature of the antifreeze liquid, an all-round freezing mode of the device is realized.

9. The triaxial instrument system suitable for frozen soil according to claim 1, characterized in that: The porous parts of the top cover (17) and the base (18) are made of porous copper material (23).

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