Method for Preparing Frozen Soil Samples and Measuring Frozen Soil Deformation Using a Laterally Confined Metal Cylinder Apparatus

Abstract

This invention discloses a method for preparing frozen soil samples and measuring frozen soil volumetric deformation using a lateral confined metal cylinder device. The lateral confined metal cylinder device includes: a base, a support, a lateral confined metal cylinder, a pressure cap, a rubber membrane, permeable paper, permeable stones, fastening screws, and rubber bands. The base is located below the support, supporting and fixing the support. The top surface of the base supports the permeable stones, permeable paper, and frozen soil sample. The support is located above the base and below the lateral confined metal cylinder, supporting and fixing the lateral confined metal cylinder. The lateral confined metal cylinder is located above the support and below the pressure cap, and the lateral confined metal cylinder and the support are fixedly connected by screws 8. The lateral confined metal cylinder and the base form a cylindrical space on the sides and bottom for holding the frozen soil sample. A rubber membrane 5 is also provided between the metal cylinder and the frozen soil sample to isolate the frozen soil sample from the antifreeze silicone oil. The pressure cap is located at the top of the lateral confined metal cylinder and is used to transmit pressure to the frozen soil sample during the test.

Description

Technical Field

[0001] This invention relates to a lateral confined metal cylinder device, specifically a lateral confined metal cylinder device that adds lateral confined compression test function to a triaxial testing machine. Based on this device, it also relates to a method for preparing frozen soil samples and measuring frozen soil volume deformation using the lateral confined metal cylinder device, belonging to the field of frozen soil indoor testing technology. Background Technology

[0002] The constitutive relation or constitutive model of soil, which studies the stress-strain behavior of soil, is an important theoretical foundation of geotechnical engineering. Establishing a constitutive relation requires not only the relationship between shear stress q and effective mean principal stress p as a function of axial strain ε1, but also the relationship between volumetric strain ε1 and ε2. v Related information.

[0003] The most famous Modified Cambridge (MCC) model in soil mechanics was proposed by Roscoe and Burland et al., and its modeling approach is as follows: First, based on the void ratio e (or volumetric strain ε) in isotropic compression tests... v (The two are equivalent) to find a one-dimensional stress-strain relationship with respect to p; secondly, based on conventional triaxial consolidated drained shear (CD) tests and loading / unloading tests, the dilatation equation is summarized, which controls the volumetric strain ε. v and shear strain ε d The distribution ratio, therefore, the dilatation equation can extend the one-dimensional stress-strain relationship to a two-dimensional stress (p and q)-strain (volume strain ε) relationship. v and shear strain ε d Finally, the two-dimensional stress-strain relationship is transformed into a three-dimensional stress-strain relationship by transforming the stress or using the g(θ) method, and then applied to engineering simulation. It is evident that volumetric strain is indispensable in isotropic compression tests during the constitutive model establishment process.

[0004] Laterally confined compression tests, also known as uniaxial consolidation tests, restrict the lateral deformation of the soil, resulting in compression deformation only in the vertical direction. Since there is no strain in the lateral confinement, the axial strain in the vertical direction equals the volumetric strain. Laterally confined compression tests typically use a metal cylinder to restrict the lateral deformation of the soil sample, applying stress through axial displacement. The stress can be relatively large, and the equipment required is simple and the cost is low. In contrast, isotropic compression tests generally apply stress using hydraulic or pneumatic pressure. When the applied stress is large, the equipment requirements are more sophisticated, resulting in higher costs. The volumetric strain is typically calculated using the volume of water drained.

[0005] When establishing a constitutive model for frozen soil within the MCC model framework, the dilatation equations for different soils are of the same form, but their critical stress ratios M may differ. M is the ratio of q to p at shear failure (or critical state), therefore, CD tests must be conducted to obtain q and p. Afterward, the volumetric strain of the isotropic compression test needs to be measured. However, water in frozen soil exists in the form of ice, making it impossible to determine the volumetric strain ε from the drainage volume.v There are two solutions here. One is to measure the volumetric strain in the isotropic compression test of frozen soil by other methods, and then find the relationship between the volumetric strain (or e) and p. The other is to find a test equivalent to the isotropic compression test and find the relationship between the one-dimensional volumetric strain (or e) and p.

[0006] In existing technologies, local radial displacement sensors (Hall effect type) and local axial displacement sensors (Hall effect type) are added to the sample surface to measure the radial and axial displacement changes of the sample during isotropic compression or CD tests, and then the volumetric strain of the sample is calculated. This method can measure the volumetric strain of frozen soil under various stress paths and can be used for volumetric strain measurement in isotropic compression tests. However, the volumetric strain is not directly measured; a profile function of the generatrix of the cylindrical sample side is required. Different profile functions may yield different results, and the calculated volumetric strain needs to be verified with thawed soil drainage tests. In addition, due to the certain volume of the sensors, they are not suitable for testing instruments with a small distance between the temperature control cylinder and the sample. Finally, because frozen soil has a large modulus, a larger confining pressure is required to obtain a certain volumetric strain compared to thawed soil, placing higher demands on the pressure chamber and hydraulic servo system of the triaxial apparatus.

[0007] Another method involves immersing frozen soil samples in silicone oil in a pressure chamber, allowing the volumetric strain to be directly measured by the confining pressure system through changes in the oil volume within the chamber. In 1997, the State Key Laboratory of Frozen Soil Engineering at the Lanzhou Regional Center for Large-Scale Instruments of Resources and Environment, Chinese Academy of Sciences, purchased an MTS-810 (10-ton) vibrating triaxial apparatus from the United States for 1.87 million yuan. This apparatus can conduct creep, fatigue, stress relaxation, and static / dynamic load tests on soil under conventional uniaxial, triaxial, and isotropic compressive stress paths at different temperatures. The triaxial apparatus has a maximum axial load of 100 kN with an accuracy of 0.5% (full scale); a maximum axial displacement of ±75 mm with an accuracy of 1%; a confining pressure range of 0–25 MPa with an accuracy of 0.5% (full scale); and a frequency range of 0–20 Hz, adjustable to a minimum of 0.1 Hz. Ma Wei et al. used the MTS-810 triaxial apparatus to conduct triaxial tests on frozen cohesive soil, obtaining the relationship between the volumetric strain of frozen cohesive soil and axial strain. This method allows for a direct understanding of the volume change of the submerged sample based on the oil level and bottom area of ​​the pressure chamber. It is applicable to various stress paths and can be used for volumetric strain measurement in isotropic compression tests. There is no issue with selecting the profile function; however, the surface tension of the oil varies under different compressive stresses, requiring the summarization of patterns and the installation of instruments capable of accurately measuring the oil level.

[0008] There are also custom-made lateral compression testers. The testing instrument consists of three parts: a temperature control system, a loading system, and a data acquisition system. The temperature control system refers to a low-temperature constant temperature chamber, which uses air cooling to provide a low-temperature environment for the sample. The temperature control range of the constant temperature chamber is -30℃ to 60℃, with a temperature control accuracy of ±0.1℃. Temperature control effectiveness testing showed that the sample reached the target temperature after 6 hours of temperature control, with a temperature fluctuation of less than ±0.1℃.

[0009] The loading system consists of a load frame system and a hydraulic loading device. Axial loading is applied to the top of the sample via a pressure shaft and indenter, with a maximum load of 100 kN and an error of ±1%. To limit lateral deformation of the soil sample, the instrument is equipped with a rigid sample container 15 cm high and 6.18 cm in inner diameter. The sidewalls are made of double-layered 304 stainless steel, with strain gauges placed between the two layers. Lateral pressure is calculated by measuring the minute deformations of the sidewalls using these strain gauges.

[0010] The data acquisition system includes a temperature sensor and a pressure-deformation sensor. The temperature sensor is a needle-shaped Pt100 temperature probe that extends into the soil sample through the bottom of the sample container, with the top of the probe approximately 5 cm from the bottom of the container. The temperature sensor is connected to the data collector to obtain the sample temperature in real time. The pressure and deformation data of the sample are acquired using an EDC fully digital servo controller from DOLI GmbH, Germany.

[0011] Custom-made temperature-controlled lateral compression apparatuses can perform lateral compression tests on frozen soil at different temperatures, providing a complete experimental pathway for establishing or validating constitutive models. They can also obtain large-scale strain under stress, making them suitable for establishing frozen soil constitutive models. However, this requires adding a temperature control system to the thawed soil lateral compression test apparatus, which increases the cost; purchasing the entire apparatus directly would be even more expensive. Summary of the Invention

[0012] The GT-061 dynamic triaxial testing machine, equipped at the National Key Laboratory of High-Speed ​​Railway Track Systems of the China Academy of Railway Sciences, features an oil temperature control system with a temperature control accuracy of ±0.1℃, a displacement sensor accuracy of 0.01mm, a load control accuracy of 5N, and a maximum loading force of 60kN. It can perform creep, fatigue, stress relaxation, and static and dynamic load tests on soil under conventional uniaxial, triaxial, and isotropic compressive stress paths at different temperatures. However, the GT-061 dynamic triaxial testing machine can only perform tests by draining the sample. The strain of frozen soil can be measured, but the water in frozen soil exists in the form of ice and will not be discharged, so it is impossible to measure the strain of frozen soil in the test. Moreover, because the distance between the temperature control sleeve and the rubber diaphragm of the sample is small in the GT-061 dynamic triaxial testing machine, and the soil sample bulges during compression, it is not suitable to install radial and axial displacement sensors. The lateral compression function of the triaxial testing machine can be increased by adding a lateral confining metal cylinder. Moreover, the cost of adding a lateral confining metal cylinder is low, so the GT-061 dynamic triaxial testing machine can be equipped with the function of frozen soil strain testing at a low cost.

[0013] Therefore, the technical problem to be solved is how to add a lateral confinement metal cylinder to the GT-061 dynamic triaxial testing machine to enhance its lateral confinement compression testing function, and thus conduct strain tests on frozen soil. To this end, the present invention provides a lateral confinement metal cylinder device for enhancing the lateral confinement compression testing function of a triaxial apparatus, the specific technical solution of which is as follows:

[0014] The lateral confinement metal cylinder device includes: a base, a support, a lateral confinement metal cylinder, a pressure cap, a rubber membrane, permeable paper, permeable stones, screws, and rubber bands. The base is used only during sample preparation, located below the support, and supports and fixes the support. The top surface of the base supports the permeable stones, permeable paper, and frozen soil sample. The support is located above the base and below the lateral confinement metal cylinder, and is used to support and fix the lateral confinement metal cylinder. The lateral confinement metal cylinder is located above the support and below the pressure cap, and the lateral confinement metal cylinder and the support are fixedly connected by screws. The lateral confinement metal cylinder and the base form a cylindrical space on the sides and bottom for holding the frozen soil sample. A rubber membrane 5 is also provided between the metal cylinder and the frozen soil sample to isolate the frozen soil sample from the antifreeze silicone oil. The pressure cap is located at the top of the lateral confinement metal cylinder and is used to transmit pressure to the frozen soil sample during the test.

[0015] Preferably, the base includes a first top surface, a first side surface, a second top surface, a second side surface, a third top surface, a third side surface, a fourth top surface, and a fourth side surface.

[0016] Preferably, the support includes: a first cylindrical side surface of the support, a first bottom surface of the support, a second cylindrical side surface of the support, a third cylindrical side surface of the support, a third cylindrical bottom surface of the support, a fourth cylindrical side surface of the support, a hollowed-out rectangular side surface of the support, a bottom surface of the support, a temperature sensor mounting groove, and screw holes.

[0017] To facilitate installation, the support is divided into two parts after the overall manufacturing is completed, forming a two-part support. The two screw holes are located in the middle of the two two-part supports respectively.

[0018] Preferably, the side-confining metal cylinder includes: a constricted opening, a vent hole, an outer surface of the side-confining metal cylinder, a fixing screw hole, a bottom surface of the side-confining metal cylinder, and an inner surface of the side-confining metal cylinder; the pressure cap includes: a central recessed surface of the pressure cap, a top surface of the pressure cap, a side surface of the pressure cap, and a bottom surface of the pressure cap; the base is located below the support, supporting and fixing the support, and the first top surface of the base is used to support the permeable stone, permeable paper, and frozen soil sample; the support is located above the base and below the side-confining metal cylinder, and is used to support and fix the side-confining metal cylinder; the side-confining metal cylinder is located above the support and below the pressure cap, and the side-confining metal cylinder and the support are fixedly connected by screws; the side-confining metal cylinder and the base form a cylindrical space on the side and bottom surfaces for holding the frozen soil sample; a rubber membrane is also provided between the metal cylinder and the frozen soil sample to isolate the frozen soil sample and the antifreeze silicone oil; the pressure cap is located at the top of the side-confining metal cylinder and is used to transmit pressure to the frozen soil sample during the test.

[0019] Preferably, a permeable stone is provided above the first top surface of the base, and permeable paper is placed on top of the permeable stone, with the permeable paper in direct contact with the frozen soil sample; the first side of the base is fitted with a rubber membrane and tightened by a rubber band; the first cylindrical side of the support is fitted with the outside of the side-limiting metal cylinder; the bottom surface of the side-limiting metal cylinder rests on the first bottom surface of the support, and the second cylindrical side of the support and the first side of the base form a rubber band space; the bottom surface of the support rests on the third top surface of the base; and the fourth cylindrical side of the support is fitted with the second side of the base.

[0020] Preferably, a rectangular hollowed-out section is cut out at the bottom of the support to avoid the protrusions of the liquid inlet and outlet set on the base of the dynamic triaxial testing machine. In addition, a groove is also provided on the side of the support for placing a temperature sensor.

[0021] A method for producing frozen soil using the lateral confined metal cylinder device described above includes:

[0022] Step 1: Prepare materials

[0023] A compaction test was conducted on the sand to obtain the maximum dry density; based on the density D... r Calculate the required mass of dry sand for sample preparation based on the maximum dry density, and calculate the required mass of water based on the required moisture content. Dry the sand, thoroughly mix the prepared dry sand and water, and soak for 24 hours before sample preparation.

[0024] Step 2: Assemble the sample preparation device

[0025] Place permeable stones on the base, and then place permeable paper on the stones. Install the rubber membrane on the first side of the base and tighten it with two rubber bands. Then, place the two-lobed supports on the base, and then place the side-limiting metal cylinder on the supports. Finally, connect and secure the side-limiting metal cylinder and the supports with screws. The rubber membrane above the metal cylinder should be turned outwards and downwards to cover the top of the side-limiting metal cylinder. If there is excess air between the rubber membrane and the side-limiting metal cylinder, it can be discharged through the air hole in the middle of the side-limiting metal cylinder.

[0026] Step 3: Sample preparation and freezing

[0027] The sample preparation method involves layered compaction, with five layers compacted to achieve the specified height using a certain mass of sand. After each layer is filled, the surface of the soil sample is roughened with a wire brush to prevent delamination before proceeding to the next layer. The sample preparation is complete after all five layers are filled. Permeable paper and permeable stones are placed on the soil sample, and a pressure cap is placed over it. The cap is then wrapped around the rubber membrane at the top of the side-confining metal cylinder, ensuring it covers the sides of the pressure cap, and secured with two rubber bands. The sample is then placed in a -18℃ freezer for 24 hours.

[0028] Step 4: Sample disassembly

[0029] Remove the frozen soil sample from the freezing chamber, unscrew the screws connecting the support and the side-confining metal cylinder, and remove the support. The rubber band at the bottom of the side-confining metal cylinder will then be exposed. Push this rubber band to the second side of the base, separating the rubber membrane from the base. Use a hammer to tap the base along the axial direction of the side-confining metal cylinder to separate the base from the frozen soil sample. Separate the pressure cap and the side-confining metal cylinder. Measure the distance between the two permeable stones and the side-confining metal cylinder to calculate the height of the frozen soil sample after frost heave. Calculate the volume based on the diameter of the side-confining metal cylinder.

[0030] A method for conducting volumetric strain tests on frozen soil prepared using a laterally confined metal cylinder device as described above includes:

[0031] Step 1: Heat the frozen soil to the specified temperature and conduct a compression test: Place permeable stones and permeable paper sequentially on the base of the dynamic triaxial testing machine. Place the side-confining metal cylinder containing the soil sample on the base of the dynamic triaxial testing machine, ensuring the frozen soil sample is in contact with the permeable paper. Wrap the lower part of the rubber membrane of the side-confining metal cylinder around the uppermost cylindrical side of the base of the dynamic triaxial testing machine and tighten it with two rubber bands. Install the two-part support on the base and secure the two-part support to the side-confining metal cylinder with screws. Place permeable paper and permeable stones on top of the frozen soil sample, then place the pressure cap. Fold the rubber membrane up to cover the pressure cap and tighten it with two rubber bands. In this way, the rubber membrane isolates the soil sample from the outside environment.

[0032] Step 2: Install the temperature control sleeve: The inner diameter of the temperature control sleeve is larger than the outer diameter of the support. The temperature control sleeve is connected to the temperature control servo motor through two pipes, one inlet and one outlet. The temperature control sleeve rests on the base of the dynamic triaxial testing machine and is sealed with a sealing ring. Inject antifreeze silicone oil into the gap between the temperature control sleeve and the side limiting metal cylinder. The antifreeze silicone oil should cover the top of the frozen soil sample.

[0033] Step 3: Install the outer pressure chamber cover. The force transmission shaft above the outer pressure chamber cover mates with the recessed surface in the center of the pressure cover. Since lateral compression does not require liquid to apply confining pressure, the air pressure inside the pressure chamber is 0, and the air pressure on the antifreeze silicone oil outside the lateral confining metal cylinder is also 0. The frozen soil is only compressed under the lateral confining displacement conditions provided by the lateral confining metal cylinder. This pressure chamber cover does not perform pressure-bearing characteristics, but it does bear tensile characteristics. When the base rises, the upward force of the frozen soil sample is transmitted to the base of the dynamic triaxial testing machine through the force transmission shaft above the outer pressure chamber cover and the metal tie rods around the pressure chamber cover.

[0034] Step 4: Heating to the specified temperature: The soil sample temperature in the freezing chamber is approximately -18℃, while the test requires a specified temperature of -0.5 to -10℃. Therefore, the frozen soil needs to be heated. Antifreeze silicone oil at the specified temperature can flow out from the temperature control servo motor. Higher temperature antifreeze silicone oil can raise the temperature of the frozen soil sample inside the side-confined metal cylinder. Because the rubber membrane isolates the frozen soil sample from external water channels, the antifreeze silicone oil will not be contaminated by the frozen soil. After maintaining the specified temperature for 24 hours, the soil sample is considered to have reached the specified temperature both inside and out.

[0035] Step 5: Conduct the experiment: After heating to the specified temperature, perform staged compression, holding each stage for 6 hours to obtain the compressive stress and void changes.

[0036] Step 6: Data processing: The final goal is to obtain the relationship between the porosity e of frozen soil and the axial stress p.

[0037] (1) Moisture content of the sample w0

[0038] After the experiment, a portion of the sample was taken out for moisture content testing. Moisture content w0:

[0039]

[0040] In the formula, m d Represents dry soil mass; m w It represents water quality.

[0041] (2) Sample wet density ρ0:

[0042]

[0043] In the formula, m0 represents the mass of wet soil used for sample preparation; v 总 This represents the volume of the sample after freezing and swelling.

[0044] (3) Initial porosity e0 of the sample

[0045]

[0046] In the formula, G s The specific gravity of soil is represented by ρ, which is 2.67 for sandy soil.w This represents the density of water, which is 1000 kg / m³. 3 .

[0047] (4) Pore ratio e during compression i

[0048] e i =e0-ε v (1+e0) (4)

[0049] In the formula, ε v The volumetric strain occurs in the soil sample during compression. In a lateral confined compression test, the volumetric strain is equal to the axial strain, which is obtained by monitoring.

[0050] (5) Axial compressive stress

[0051] With the triaxial specimen base raised, the axial force F can be monitored. The specimen diameter d is 0.15 m, therefore the bottom area S of the soil sample and its axial stress p can be calculated.

[0052]

[0053] Step 7: Summarize the test results and obtain the results of the secondary compression test at different temperatures.

[0054] Beneficial effects

[0055] This invention fully utilizes the loading and monitoring functions of existing dynamic triaxial testing machines, eliminating the need to purchase new instruments for lateral compression testing and saving costs. Since the axial strain in a lateral compression test is the same as the volumetric strain, the axial strain can be monitored using the axial strain sensor of the original dynamic triaxial testing machine with high accuracy. Therefore, there is no need to add a new volumetric strain monitoring sensor, avoiding the problem of low accuracy when directly monitoring volumetric strain. Attached Figure Description

[0056] Figure 1 This is a schematic diagram of the side-confined metal cylinder device of the present invention;

[0057] Figure 2 This is a schematic diagram of the base of the side-limiting metal cylinder device of the present invention;

[0058] Figure 3 This is a schematic diagram of the support for the side-confined metal cylinder device of the present invention;

[0059] Figure 4 This is a schematic diagram of the side-confined metal cylinder of the side-confined metal cylinder device of the present invention;

[0060] Figure 5 This is a schematic diagram of the pressure cap of the side-limiting metal cylinder device of the present invention;

[0061] Figure 6 This is a schematic diagram of frozen soil sample preparation using the lateral confinement metal cylinder device of the present invention;

[0062] Figure 7 This is a schematic diagram of an experiment using the lateral confined metal cylinder device of the present invention to prepare frozen soil.

[0063] In the diagram: 1. Base; 2. Support; 3. Side-limiting metal cylinder; 4. Pressure cap; 5. Rubber membrane; 6. Permeable paper; 7. Permeable stone; 8. Screw; 9. Rubber band; 10. Frozen soil sample; 11. Base of the dynamic triaxial testing machine; 12. Lifting drive mechanism of the dynamic triaxial testing machine; 13. Sealing ring; 14. Base of the dynamic triaxial testing machine; 15. Antifreeze silicone oil; 16. Temperature control sleeve; 17. External cover of the pressure chamber; 1-1. First top surface of the base; 1-2. First side surface of the base; 1-3. Second top surface of the base; 1-4. Second side surface of the base; 1-5. Third top surface of the base; 1-6. Third side surface of the base; 1-7. Fourth top surface of the base. Surface; 1-8, fourth side of the base; 2-1, side of the first cylinder of the support; 2-2, first bottom surface of the support; 2-3, side of the second cylinder of the support; 2-4, side of the third cylinder of the support; 2-5, bottom surface of the third cylinder of the support; 2-6, side of the fourth cylinder of the support; 2-7, side of the hollowed-out rectangle of the support; 2-8, bottom surface of the support; 3-1, closing surface; 3-2, vent hole; 3-3, outside of the side limiting metal cylinder; 3-4, fixing screw hole; 3-5, bottom surface of the side limiting metal cylinder; 3-6, inside surface of the side limiting metal cylinder; 4-1, recessed surface in the middle of the pressure cap; 4-2, top surface of the pressure cap; 4-3, side of the pressure cap; 4-4, bottom surface of the pressure cap. Detailed Implementation

[0064] The following will refer to the appendices in the embodiments of the present invention. Figure 1-7 The technical solutions in the embodiments of the present invention have been clearly and completely described. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] The GT-061 dynamic triaxial testing machine, equipped at the National Key Laboratory of High-Speed ​​Railway Track Systems of the China Academy of Railway Sciences, features an oil temperature control system with a temperature control accuracy of ±0.1℃, a displacement sensor accuracy of 0.01mm, a load control accuracy of 5N, and a maximum loading force of 60kN. It can perform creep, fatigue, stress relaxation, and static and dynamic load tests on soil under conventional uniaxial, triaxial, and isotropic compressive stress paths at different temperatures. However, the GT-061 dynamic triaxial testing machine can only perform tests by draining the sample. The strain of frozen soil can be measured, but the water in frozen soil exists in the form of ice and will not be discharged, so it is impossible to measure the strain of frozen soil in the test. Moreover, because the distance between the temperature control sleeve and the rubber diaphragm of the sample is small in the GT-061 dynamic triaxial testing machine, and the soil sample bulges during compression, it is not suitable to install radial and axial displacement sensors. The lateral compression function of the triaxial testing machine can be increased by adding a lateral confining metal cylinder. Moreover, the cost of adding a lateral confining metal cylinder is low, so the GT-061 dynamic triaxial testing machine can be equipped with the function of frozen soil strain testing at a low cost.

[0066] Please see Figure 1-7 This invention provides a technical solution: a side-confining metal cylinder device, comprising: a base 1, a support 2, a side-confining metal cylinder 3, a pressure cap 4, a rubber membrane 5, permeable paper 6, permeable stone 7, screws 8, and rubber bands 9; the base is used only during sample preparation, located below the support, supporting and fixing the support, and the top surface of the base is used to support the permeable stone, permeable paper, and frozen soil sample; the support is located above the base and below the side-confining metal cylinder, used to support and fix the side-confining metal cylinder; the side-confining metal cylinder is located above the support and below the pressure cap, and the side-confining metal cylinder and the support are fixedly connected by screws 8; the side-confining metal cylinder and the base form a cylindrical space on the side and bottom for holding the frozen soil sample; a rubber membrane 5 is also provided between the metal cylinder and the frozen soil sample to isolate the frozen soil sample from the antifreeze silicone oil; the pressure cap is located at the top of the side-confining metal cylinder and is used to transmit pressure to the frozen soil sample during the test.

[0067] The base includes a first top surface 1-1, a first side surface 1-2, a second top surface 1-3, a second side surface 1-4, a third top surface 1-5, a third side surface 1-6, a fourth top surface 1-7, and a fourth side surface 1-8.

[0068] The support includes: a first cylindrical side surface 2-1, a first bottom surface 2-2, a second cylindrical side surface 2-3, a third cylindrical side surface 2-4, a third cylindrical bottom surface 2-5, a fourth cylindrical side surface 2-6, a hollowed-out rectangular side surface 2-7, a bottom surface 2-8, a temperature sensor mounting slot 2-9, and screw holes 2-10.

[0069] To facilitate installation, the support is divided into two parts after the overall manufacturing is completed, forming a two-part support. The two screw holes are located in the middle of the two two-part supports respectively.

[0070] The side-confining metal cylinder includes: a constricting surface 3-1, a vent hole 3-2, an outer surface of the side-confining metal cylinder 3-3, a fixing screw hole 3-4, a bottom surface of the side-confining metal cylinder 3-5, and an inner surface of the side-confining metal cylinder 3-6. The pressure cap includes: a central recessed surface 4-1, a top surface 4-2, a side surface 4-3, and a bottom surface 4-4. The base is located below the support, supporting and fixing the support. The first top surface of the base is used to support the permeable stone, permeable paper, and frozen soil sample. The support is located above the base and below the side-confining metal cylinder, supporting and fixing the side-confining metal cylinder. The side-confining metal cylinder is located above the support and below the pressure cap, and the side-confining metal cylinder and the support are fixedly connected by screws. The side-confining metal cylinder and the base form a cylindrical space on the side and bottom for holding the frozen soil sample. A rubber membrane 5 is also provided between the metal cylinder and the frozen soil sample to isolate the frozen soil sample from the antifreeze silicone oil.

[0071] The pressure cap is located at the top of the side-confined metal cylinder and is used to transmit pressure to the frozen soil sample during the test.

[0072] A permeable stone 7 is provided above the first top surface 1-1 of the base, and a permeable paper 6 is placed on top of the permeable stone, with the permeable paper in direct contact with the frozen soil sample 10; the first side surface 1-2 of the base cooperates with the rubber membrane 5 and is tightened by the rubber band 9; the first cylindrical side surface 2-1 of the support cooperates with the outside of the side limiting metal cylinder 3-3; the bottom surface 3-5 of the side limiting metal cylinder rests on the first bottom surface 2-2 of the support, and the second cylindrical side surface 2-3 of the support and the first side surface 1-2 of the base form a rubber band space; the bottom surface 2-8 of the support rests on the third top surface 1-5 of the base; the fourth cylindrical side surface 2-6 of the support cooperates with the second side surface 1-4 of the base.

[0073] A rectangular hollowed-out section is cut out at the bottom of the support to avoid the protrusions of the liquid inlet and outlet on the base of the dynamic triaxial testing machine. In addition, grooves 2-9 are also cut on the side of the support for placing temperature sensors.

[0074] A method for producing frozen soil using the lateral confined metal cylinder device described above includes:

[0075] Step 1: Prepare materials

[0076] A compaction test was conducted on the sand to obtain the maximum dry density; based on the density D... r Calculate the required mass of dry sand for sample preparation based on the maximum dry density, and calculate the required mass of water based on the required moisture content. Dry the sand, thoroughly mix the prepared dry sand and water, and soak for 24 hours before sample preparation.

[0077] Step 2: Assemble the sample preparation device

[0078] Place permeable stones on the base, and then place permeable paper on the stones. Install the rubber membrane on the first side of the base and tighten it with two rubber bands. Then, place the two-lobed supports on the base, and then place the side-limiting metal cylinder on the supports. Finally, connect and secure the side-limiting metal cylinder and the supports with screws. The rubber membrane above the metal cylinder should be turned outwards and downwards to cover the top of the side-limiting metal cylinder. If there is excess air between the rubber membrane and the side-limiting metal cylinder, it can be discharged through the air hole in the middle of the side-limiting metal cylinder.

[0079] Step 3: Sample preparation and freezing

[0080] The sample preparation method involves layered compaction, with five layers compacted to achieve the specified height using a certain mass of sand. After each layer is filled, the surface of the soil sample is roughened with a wire brush to prevent delamination before proceeding to the next layer. The sample preparation is complete after all five layers are filled. Permeable paper and permeable stones are placed on the soil sample, and a pressure cap is placed over it. The cap is then wrapped around the rubber membrane at the top of the side-confining metal cylinder, ensuring it covers the sides of the pressure cap, and secured with two rubber bands. The sample is then placed in a -18℃ freezer for 24 hours.

[0081] Step 4: Sample disassembly

[0082] Remove the frozen soil sample from the freezing chamber, unscrew the screws connecting the support and the side-confining metal cylinder, and remove the support. The rubber band at the bottom of the side-confining metal cylinder will then be exposed. Push this rubber band to the second side of the base, separating the rubber membrane from the base. Use a hammer to tap the base along the axial direction of the side-confining metal cylinder to separate the base from the frozen soil sample. Separate the pressure cap and the side-confining metal cylinder. Measure the distance between the two permeable stones and the side-confining metal cylinder to calculate the height of the frozen soil sample after frost heave. Calculate the volume based on the diameter of the side-confining metal cylinder.

[0083] A method for conducting volumetric strain tests on frozen soil prepared using a laterally confined metal cylinder device as described above includes:

[0084] Step 1: Heat the frozen soil to the specified temperature and conduct a compression test: Place permeable stones and permeable paper sequentially on the base of the dynamic triaxial testing machine. Place the side-confining metal cylinder containing the soil sample on the base of the dynamic triaxial testing machine, ensuring the frozen soil sample is in contact with the permeable paper. Wrap the lower part of the rubber membrane of the side-confining metal cylinder around the uppermost cylindrical side of the base of the dynamic triaxial testing machine and tighten it with two rubber bands. Install the two-part support on the base and secure the two-part support to the side-confining metal cylinder with screws. Place permeable paper and permeable stones on top of the frozen soil sample, then place the pressure cap. Fold the rubber membrane up to cover the pressure cap and tighten it with two rubber bands. In this way, the rubber membrane isolates the soil sample from the outside environment.

[0085] Step 2: Install the temperature control sleeve: The inner diameter of the temperature control sleeve is larger than the outer diameter of the support. The temperature control sleeve is connected to the temperature control servo motor through two pipes, one inlet and one outlet. The temperature control sleeve rests on the base of the dynamic triaxial testing machine and is sealed with a sealing ring. Inject antifreeze silicone oil into the gap between the temperature control sleeve and the side limiting metal cylinder. The antifreeze silicone oil should cover the top of the frozen soil sample.

[0086] Step 3: Install the outer pressure chamber cover. The force transmission shaft above the outer pressure chamber cover mates with the recessed surface in the center of the pressure cover. Since lateral compression does not require liquid to apply confining pressure, the air pressure inside the pressure chamber is 0, and the air pressure on the antifreeze silicone oil outside the lateral confining metal cylinder is also 0. The frozen soil is only compressed under the lateral confining displacement conditions provided by the lateral confining metal cylinder. This pressure chamber cover does not perform pressure-bearing characteristics, but it does bear tensile characteristics. When the base rises, the upward force of the frozen soil sample is transmitted to the base of the dynamic triaxial testing machine through the force transmission shaft above the outer pressure chamber cover and the metal tie rods around the pressure chamber cover.

[0087] Step 4: Heating to the specified temperature: The soil sample temperature in the freezing chamber is approximately -18℃, while the test requires a specified temperature of -0.5 to -10℃. Therefore, the frozen soil needs to be heated. Antifreeze silicone oil at the specified temperature can flow out from the temperature control servo motor. Higher temperature antifreeze silicone oil can raise the temperature of the frozen soil sample inside the side-confined metal cylinder. Because the rubber membrane isolates the frozen soil sample from external water channels, the antifreeze silicone oil will not be contaminated by the frozen soil. After maintaining the specified temperature for 24 hours, the soil sample is considered to have reached the specified temperature both inside and out.

[0088] Step 5: Conduct the experiment: After heating to the specified temperature, perform staged compression, holding each stage for 6 hours to obtain the compressive stress and void changes.

[0089] Step 6: Data processing: The final goal is to obtain the relationship between the porosity e of frozen soil and the axial stress p.

[0090] (1) Moisture content of the sample w0

[0091] After the experiment, a portion of the sample was taken out for moisture content testing. Moisture content w0:

[0092]

[0093] In the formula, m d Represents dry soil mass; m w It represents water quality.

[0094] (2) Sample wet density ρ0:

[0095]

[0096] In the formula, m0 represents the mass of wet soil used for sample preparation; v 总 This represents the volume of the sample after freezing and swelling.

[0097] (3) Initial porosity e0 of the sample

[0098]

[0099] In the formula, G s The specific gravity of soil is represented by ρ, which is 2.67 for sandy soil.w This represents the density of water, which is 1000 kg / m³. 3 .

[0100] (4) Pore ratio e during compression i

[0101] e i =e0-ε v (1+e0) (4)

[0102] In the formula, ε v The volumetric strain occurs in the soil sample during compression. In a lateral confined compression test, the volumetric strain is equal to the axial strain, which is obtained by monitoring.

[0103] (5) Axial compressive stress

[0104] With the triaxial specimen base raised, the axial force F can be monitored. The specimen diameter d is 0.15 m, therefore the bottom area S of the soil sample and its axial stress p can be calculated.

[0105]

[0106] Step 7: Summarize the test results, including the results of the constricted compression test at different temperatures.

[0107] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

[0108] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A side-confined metal cylinder device, comprising: The system comprises a base, a support, a side-confining metal cylinder, a pressure cap, a rubber membrane, permeable paper, permeable stones, fastening screws, and rubber bands. The base is located below the support, supporting and fixing the support; the top surface of the base supports the permeable stones, permeable paper, and frozen soil sample. The support is situated above the base and below the side-confining metal cylinder, supporting and fixing the side-confining metal cylinder. The support is divided into two parts after overall manufacturing, forming a bipartite support. The side-confining metal cylinder is located above the support and below the pressure cap, and the side-confining metal cylinder and the support are fixedly connected by screws. The side-confining metal cylinder and the base form a cylindrical space on the sides and bottom for holding the frozen soil sample. A rubber membrane is also provided between the metal cylinder and the frozen soil sample to isolate the frozen soil sample from the antifreeze silicone oil. The pressure cap is positioned... The base has a permeable stone on top of the side-confining metal cylinder for transmitting pressure to the frozen soil sample during testing. A permeable paper is placed on top of the first top surface of the base, and the permeable paper is in direct contact with the frozen soil sample. The first side of the base engages with a rubber membrane and is secured by a rubber band. The first cylindrical side of the support engages with the outside of the side-confining metal cylinder. The bottom surface of the side-confining metal cylinder rests on the first bottom surface of the support, and the second cylindrical side of the support and the first side of the base form a rubber band space. The bottom surface of the support rests on the third top surface of the base. The fourth cylindrical side of the support engages with the second side of the base. After the support is manufactured as a whole, it is divided into two parts to form a bipartite support, with two screw holes located in the middle of the two bipartite supports respectively.

2. A method for preparing frozen soil samples using a lateral confined metal cylinder device, the method being based on the lateral confined metal cylinder device of claim 1, characterized in that it comprises: Step 1: Prepare materials The maximum dry density was obtained by conducting a compaction test on the sand. Calculate the mass of dry sand required for sample preparation based on the density Dr and the maximum dry density, and calculate the mass of water required based on the required moisture content; dry the sand, mix the prepared dry sand and water thoroughly, and soak for 24 hours for sample preparation. Step 2: Assemble the sample preparation device Place permeable stones on the base, and permeable paper on the permeable stones; install the rubber membrane on the first side of the base and tighten it with rubber bands; then place the two-lobed supports on the base, place the side-limiting metal cylinder on the supports, and then connect and tighten the side-limiting metal cylinder and the supports with screws; the rubber membrane above the metal cylinder folds outward and downward to cover the top of the side-limiting metal cylinder; if there is excess air between the rubber membrane and the side-limiting metal cylinder, it will be discharged through the air hole in the middle of the side-limiting metal cylinder. Step 3: Sample preparation and freezing The sample preparation method is layered compaction, consisting of 5 layers. A certain mass of sand is used to reach the specified height. After each layer is filled, the surface of the soil sample is roughened with an iron brush to prevent stratification before adding the next layer. After all 5 layers are filled, the sample preparation is complete. Permeable paper and permeable stones are placed on the soil sample, and a pressure cap is placed on top. The cap is then wrapped around the rubber membrane on the upper part of the side-limiting metal cylinder and pulled to cover the sides of the pressure cap. It is then tightened with two rubber bands. The sample is then placed in a -18℃ freezer for 24 hours. Step 4: Sample disassembly Remove the frozen soil sample from the freezing chamber, unscrew the screws connecting the support and the side confinement metal cylinder, and remove the support; at this point, the rubber band at the bottom of the side confinement metal cylinder will be exposed. Move this rubber band to the second side of the base, separate the rubber membrane from the base, and use a hammer to tap the base along the axial direction of the side confinement metal cylinder to separate the base from the frozen soil sample; separate the pressure cap and the side confinement metal cylinder; measure the distance between the two permeable stones and the side confinement metal cylinder to calculate the height of the frozen soil sample after frost heave, and calculate the volume based on the diameter of the side confinement metal cylinder.

3. A method for measuring the volumetric strain of frozen soil using a laterally confined metal cylinder device, the method being based on the laterally confined metal cylinder device as described in claim 1, characterized in that... include: Step 1: Heat the frozen soil to the specified temperature and conduct a compression test: Place permeable stones and permeable paper in sequence on the base of the dynamic triaxial testing machine. Place the side-confining metal cylinder containing the soil sample on the base of the dynamic triaxial testing machine, with the frozen soil sample in contact with the permeable paper. Wrap the lower rubber membrane of the side-confining metal cylinder around the uppermost cylindrical side of the base of the dynamic triaxial testing machine and tighten it with two rubber bands. Install the two-part support on the base and fix the two-part support to the side-confining metal cylinder with screws. Place permeable paper and permeable stones on the top of the frozen soil sample in sequence, then place the pressure cap. Fold the rubber membrane up to wrap around the pressure cap and tighten it with two rubber bands. Step 2, Install the temperature control sleeve: The inner diameter of the temperature control sleeve is larger than the outer diameter of the support. The temperature control sleeve is connected to the temperature control servo motor through two pipes, one inlet and one outlet. The temperature control sleeve rests on the base of the dynamic triaxial testing machine and is sealed with a sealing ring. Inject antifreeze silicone oil into the gap between the temperature control sleeve and the side limiting metal cylinder. The antifreeze silicone oil should cover the top of the frozen soil sample. Step 3, Install the outer cover of the pressure chamber: The force transmission shaft above the outer cover of the pressure chamber mates with the recessed surface in the middle of the pressure cover; Since lateral compression does not require liquid to apply confining pressure, the air pressure inside the pressure chamber is 0, and the air pressure on the antifreeze silicone oil outside the lateral confining metal cylinder is also 0. The frozen soil is only compressed under the lateral confining displacement provided by the lateral confining metal cylinder; When the base rises, the upward force of the frozen soil sample is transmitted to the base of the dynamic triaxial testing machine through the force transmission shaft above the outer cover of the pressure chamber and the metal tie rods around the pressure chamber; Step 4: Heating to the specified temperature: The soil sample temperature in the freezing chamber is around -18℃, while the test requires a specified temperature of -0.5~-10℃, so the frozen soil needs to be heated; antifreeze silicone oil of the specified temperature flows out from the temperature control servo motor, and the higher temperature antifreeze silicone oil heats the frozen soil sample in the side-confined metal cylinder; since the rubber membrane isolates the frozen soil sample from the external water circuit, the antifreeze silicone oil will not be contaminated by the frozen soil; after maintaining the specified temperature for 24 hours, it is considered that the soil sample has reached the specified temperature both inside and outside. Step 5: Conduct the experiment: After heating to the specified temperature, perform staged compression, holding each stage for 6 hours to obtain the compressive stress and void changes; Step 6: Data Processing: The final goal is to obtain the relationship between the porosity e of frozen soil and the axial stress p. (1) Moisture content of the sample : After the experiment, some samples were taken out for moisture content testing. : （1）； In the formula, Represents dry soil quality; Represents water quality; The quality of the wet soil used for sample preparation; (2) Wet density of the sample : （2）； In the formula, This represents the volume of the sample after freezing and swelling. (3) Initial porosity of the sample : （3）； In the formula, The specific gravity of soil is represented by 2.67 for sandy soil. This represents the density of water, which is 1000 kg / m³. 3 ; (4) Pore ratio during compression : （4）； In the formula, The volumetric strain of the soil sample during compression is equal to the axial strain in the lateral confined compression test. The axial strain is obtained by monitoring. (5) Axial compressive stress The triaxial specimen base was raised, and the axial force F was monitored. The specimen diameter d was 0.15m. The bottom area S of the soil sample was calculated, and its axial stress p was: （5）； Step 7: Summarize the test results, including the results of the secondary compression test at different temperatures.

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