Test method for manufacturing frozen soil sample by using lateral confinement metal cylinder device and measuring frozen soil deformation

Abstract

The invention discloses a test method for manufacturing a frozen soil sample and measuring frozen soil deformation by using a lateral confinement metal cylinder device, the lateral confinement metal cylinder device comprises a base, a support, a lateral confinement metal cylinder, a gland, a rubber membrane, permeable paper, permeable stone, a fastening screw and a rubber band; the base is located below the support and supports and fixes the support, and the top surface of the base is used for supporting the permeable stone, the permeable paper and the frozen soil sample; the support is located above the base and below the lateral confinement metal cylinder and used for supporting and fixing the lateral confinement metal cylinder. The lateral confinement metal cylinder is located above the support and below the gland, and the lateral confinement metal cylinder and the support are fixedly connected through a screw 8. The lateral confinement metal cylinder and the base form a cylindrical space on the side face and the bottom face and used for containing a frozen soil sample. A rubber membrane 5 is also arranged between the metal cylinder and the frozen soil sample and is used for isolating the frozen soil sample from the anti-freezing silicone oil; the gland is located at the top of the lateral confinement metal cylinder and used for transmitting pressure to the frozen soil sample during testing.

Description

Technical Field

[0001] The invention relates to a side confinement metal cylinder device, in particular to a side confinement metal cylinder device with a triaxial testing machine having a side confinement compression test function. The invention also relates to a method for making a frozen soil sample and measuring frozen soil volume deformation using the side confinement metal cylinder device, and belongs to the technical field of frozen soil indoor testing. Background Art

[0002] The constitutive relationship or constitutive model of soil takes the stress-strain law of soil as the research object and is an important theoretical basis of geotechnical engineering. To establish the constitutive relationship, not only the relationship between the shear stress q and the effective average principal stress p and the axial strain ε1 is required, but also the volume strain ε v Related information.

[0003] The most famous modified Cambridge (MCC) model in soil mechanics was proposed by Roscoe and Burland et al. The modeling idea is as follows: First, according to the porosity e (or volume strain ε) in the isotropic compression test v , the two are equivalent) with p to find the one-dimensional stress-strain relationship; secondly, the dilatancy equation is summarized based on the conventional triaxial consolidation drained shear (CD) test loading and unloading test. The dilatancy equation controls the volume strain ε v and shear strain ε d The shear dilatancy equation can be used to extend the one-dimensional stress-strain relationship to a two-dimensional stress (p and q) strain (volume strain ε v and shear strain ε d ) relationship. Finally, the two-dimensional stress-strain relationship is transformed into a three-dimensional stress-strain relationship by transforming stress or g(θ) method, and then applied to engineering simulation. It can be seen that the volume strain in the isotropic compression test is indispensable in the process of establishing the constitutive model.

[0004] The confined compression test is also commonly known as the unidirectional consolidation test. During the test, the soil is laterally restricted and only compressive deformation occurs in the vertical direction. Since there is no strain due to lateral restriction, the axial strain in the vertical direction is equal to the volume strain. The confined compression test usually uses a metal cylinder to restrict the lateral deformation of the soil sample, and applies stress through axial displacement. The stress can be large, and the equipment required for the test is simple and the cost is low. The isotropic compression test generally applies stress through hydraulic or pneumatic pressure. When the applied stress is large, the instrument requirements are high and the cost is high. The volume strain is generally calculated by the drainage volume.

[0005] When establishing the frozen soil constitutive model on the MCC model framework, the dilatancy equations of different soils are the same, but their critical state stress ratios M may be different. M is the ratio of q to p at shear failure (or critical state), so CD tests must be performed to obtain q and p. After that, the isotropic compression test volume strain needs to be measured, but the water in frozen soil exists in the form of ice, and the volume strain ε cannot be known by the displacement.v There are two solutions here. One is to measure the volume strain in the isotropic compression test of frozen soil by other methods, and then find the relationship between the volume 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 volume strain (or e) and p.

[0006] In the prior art, there is a method of adding a local radial displacement sensor (Hall effect type) and a local axial displacement sensor (Hall effect type) on the surface of the sample to measure the radial and axial displacement changes of the sample in an isotropic compression or CD test, and then calculating the volume change of the sample. This method can measure the volume strain of frozen soil under various stress paths and can be used for volume strain measurement in isotropic compression tests. However, the volume strain is not directly measured, and the contour function of the side generatrix of the cylindrical sample needs to be given. The results calculated by different contour functions may be different. The calculated volume change of the sample and the actual volume change need to be verified by a thawed soil drainage test. In addition, since the sensor has a certain volume, it is not suitable for test instruments with a small distance between the temperature control tube and the sample. Finally, since the modulus of frozen soil is large, a larger confining pressure is required to obtain a certain volume strain compared to thawed soil, which places higher requirements on the pressure chamber and hydraulic servo system of the triaxial instrument.

[0007] There are also frozen soil samples immersed in silicone oil in the pressure chamber, and the volume change can also be directly measured by the confining pressure system through the change of the oil volume in the pressure chamber. The State Key Laboratory of Frozen Soil Engineering of the Lanzhou Regional Center for Large Instruments of Resources and Environmental Sciences of the Chinese Academy of Sciences purchased the American MTS-810 (10 tons) vibration triaxial instrument at a price of 1.87 million yuan in 1997. It can carry out creep, fatigue, stress relaxation and static and dynamic load tests of conventional uniaxial, triaxial and isotropic compression stress paths of soil at different temperatures. The maximum axial load of the triaxial instrument is 100kN, with an accuracy of 0.5% (full scale); the maximum axial displacement is ±75mm, with an accuracy of 1%; the confining pressure range is 0-25MPa, with an accuracy of 0.5% (full scale); the frequency range is 0-20Hz, and the minimum can be adjusted to 0.1Hz. Ma Wei et al. used the MTS-810 triaxial instrument to carry out triaxial tests on frozen clay soil and obtained the relationship between the volume change of frozen clay soil and the change of axial strain. This method can intuitively know the volume change of the sample immersed in the pressure chamber according to the oil level and bottom area. It is applicable to a variety of stress paths and can be used for volume strain measurement in isotropic compression tests. There is no problem of contour function selection, but the surface tension of oil is different under different compressive stresses. It is necessary to summarize the rules and install an instrument that can accurately measure the oil level.

[0008] There is also a custom-made side confinement compression tester. The test instrument consists of three parts: temperature control system, loading system and data acquisition system. The temperature control system refers to a low-temperature constant temperature box, which uses air cooling to provide a low-temperature environment for the sample. The temperature control range of the constant temperature box is -30℃~60℃, and the temperature control accuracy is ±0.1℃. After the temperature control effect test, it was found that the sample reached the target temperature after 6 hours of temperature control, and the sample temperature fluctuation value was less than ±0.1℃.

[0009] The loading system consists of a load frame system and a hydraulic loading device. The top of the sample is axially loaded through the pressure shaft and the pressure head. The maximum load that can be applied is 100kN with an error of ±1%. In order to limit the lateral deformation of the soil sample, the instrument is equipped with a rigid sample tank with a height of 15cm and an inner diameter of 6.18cm. The side wall is made of double-layer 304 stainless steel, and a strain gauge is installed between the double-layer side walls. The lateral pressure is calculated by measuring the slight deformation of the side wall through the strain gauge.

[0010] The data acquisition system includes a temperature acquisition sensor and a pressure-deformation acquisition sensor. The temperature sensor is a needle-shaped Pt100 temperature probe that extends into the soil sample through the bottom of the sample tank, and the top of the probe is about 5 cm from the bottom of the tank. 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 collected through the EDC fully digital servo measurement and control unit of the German DOLI company.

[0011] A specially customized temperature-controlled confined compression instrument can conduct frozen soil confined compression tests at different temperatures, completing the test path for establishing or verifying the constitutive model, and can obtain the body strain under large stress, which is suitable for establishing a frozen soil constitutive model. However, this requires adding a temperature control system to the thawing soil confined compression test instrument, which is also costly, and the cost of directly purchasing the entire machine is even higher. Summary of the invention

[0012] The GT-061 dynamic triaxial testing machine, which is equipped with the National Key Laboratory of High-speed Railway Track System of the China Academy of Railway Sciences, has an oil temperature control system with a temperature control accuracy of ±0.1°C, a displacement sensor accuracy of 0.01mm, a load control accuracy of 5N, and a maximum loading force of 60kN. It can carry out creep, fatigue, stress relaxation and static and dynamic load tests of conventional uniaxial, triaxial and isotropic compression stress paths of soil at different temperatures; however, the GT-061 dynamic triaxial testing machine can only drain the sample through The volume strain can be calculated by measuring the volume of frozen soil, but the water in the frozen soil exists in the form of ice and will not be discharged. Therefore, the volume strain of frozen soil in the test cannot be measured. Moreover, due to the small distance between the temperature control sleeve and the rubber membrane of the sample of the GT-061 dynamic triaxial testing machine, and the side bulging of the soil sample during the compression process, it is not suitable to install radial and axial displacement sensors. The side limit compression function of the triaxial testing machine can be increased by adding side limit metal cylinders, and the cost of adding side limit metal cylinders is low, so the GT-061 dynamic triaxial testing machine can be equipped with the function of frozen soil volume strain test at a low cost.

[0013] Therefore, the technical problem to be solved is how to add a side confinement metal cylinder to the GT-061 dynamic triaxial testing machine to increase its side confinement compression test function, and then conduct a frozen soil body strain test; for this purpose, the present invention provides a side confinement metal cylinder device for increasing the side confinement compression test function of the triaxial instrument, and the specific technical solution is as follows:

[0014] The side-limiting metal cylinder device includes: a base, a support, a side-limiting metal cylinder, a pressure cover, a rubber membrane, permeable paper, permeable stone, screws, and rubber bands; the base is only used during sample preparation, is located below the support, supports and fixes the support, and the top surface of the base is used to support the permeable stone, permeable paper and frozen soil samples; the support is located above the base and below the side-limiting metal cylinder, and is used to support and fix the side-limiting metal cylinder; the side-limiting metal cylinder is located above the support and below the pressure cover, and the side-limiting metal cylinder and the support are fixedly connected by screws; the side-limiting metal cylinder and the base form a cylindrical space on the side and bottom surfaces for holding frozen soil samples; a rubber membrane 5 is also provided between the metal cylinder and the frozen soil sample to isolate the frozen soil sample from antifreeze silicone oil; the pressure cover is located on the top of the side-limiting metal cylinder, and is used to transfer pressure to the frozen soil sample during the test.

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

[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 a screw hole.

[0017] To facilitate installation, the support is cut into two parts after the overall manufacturing is completed to form a two-petal support, and the two screw holes are respectively located in the middle of the two two-petal supports.

[0018] Preferably, the side-limiting metal cylinder includes: a closing surface, a vent hole, an outer surface of the side-limiting metal cylinder, a fixing screw hole, a bottom surface of the side-limiting metal cylinder, and an inner surface of the side-limiting metal cylinder; the pressure cover includes: a concave pit surface in the middle of the pressure cover, a top surface of the pressure cover; a side surface of the pressure cover, and a bottom surface of the pressure cover; the base is located below the support, supports and fixes the support, and the first top surface of the base is used to support permeable stone, permeable paper and frozen soil samples; the support is located above the base and below the side-limiting metal cylinder, and is used to support and fix the side-limiting metal cylinder; the side-limiting metal cylinder is located above the support and below the pressure cover, and the side-limiting metal cylinder and the support are fixedly connected by screws; the side-limiting metal cylinder and the base form a cylindrical space on the side and bottom for holding frozen soil samples; a rubber membrane is also provided between the metal cylinder and the frozen soil sample to isolate the frozen soil sample from antifreeze silicone oil; the pressure cover is located at the top of the side-limiting metal cylinder, and is used to transfer pressure to the frozen soil sample during the test.

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

[0020] Preferably, a hollow rectangle is cut out at the bottom of the support to avoid the protrusion of the liquid inlet and outlet arranged on the base of the dynamic triaxial testing machine. In addition, a groove is also opened on the side of the support for placing a temperature sensor.

[0021] The method for making frozen soil using the above-mentioned confining metal cylinder device comprises:

[0022] Step 1: Prepare the ingredients

[0023] Compact the sand to get the maximum dry density; according to the density D r Calculate the mass of dry sand required for sample preparation based on the maximum dry density, and calculate the mass of water required based on the required water content. Dry the sand, mix the prepared dry sand and water thoroughly, and soak them for a day and night for sample preparation.

[0024] Step 2: Assemble the sample preparation device

[0025] Place permeable stone on the base, and place permeable paper on the permeable stone; install the rubber membrane on the first side of the base and tighten it with two rubber bands; then place the two-petal support on the base, and then place the side limit metal tube on the support, and then use screws to connect and tighten the side limit metal tube and the support; the rubber membrane higher than the metal tube is turned outward and downward to wrap the top of the side limit metal tube; if there is excess air between the rubber membrane and the side limit metal tube, it can be discharged through the air hole in the middle of the side limit metal tube.

[0026] Step 3: Sample preparation and freezing

[0027] The sample is prepared by layered compaction, which is divided into 5 layers. A certain mass of sand and soil must be used to reach the specified height. After the current layer is loaded, the upper surface of the soil sample is roughened with an iron brush to avoid stratification, and then the next layer is loaded. After the 5 layers are loaded, the sample preparation is completed. Permeable paper and permeable stone are placed on the soil sample, covered with a gland, wrapped on the rubber film on the upper part of the side limit metal cylinder, so that it wraps the side of the gland, and tightened with two rubber bands. The sample is placed in a -18℃ freezer for 24 hours.

[0028] Step 4: Unpacking

[0029] Take the frozen soil sample out of the freezer, remove the screws connecting the support and the side-limiting metal cylinder, and remove the support. At this time, the rubber band at the bottom of the side-limiting metal cylinder is exposed, and the rubber band is withdrawn to the second side of the base, the rubber membrane is separated from the base, and the base is hit along the axial direction of the side-limiting metal cylinder with a hammer to separate the base from the frozen soil sample; separate the gland and the side-limiting metal cylinder; measure the distance between the two permeable stones and the side-limiting metal cylinder to calculate the height of the frozen soil sample after frost heave, and calculate the volume according to the diameter of the side-limiting metal cylinder.

[0030] The method for conducting a volume strain test on frozen soil prepared by the confined metal cylinder device as described above comprises:

[0031] Step 1: Warm up the frozen soil to the specified temperature and conduct a compression test: Place permeable stone and permeable paper on the base of the dynamic triaxial test machine in turn, place the side-limited metal cylinder with soil sample on the base of the dynamic triaxial test machine, and the frozen soil sample is in contact with the permeable paper; wrap the rubber membrane at the bottom of the side-limited metal cylinder around the uppermost cylindrical side of the base of the dynamic triaxial test machine and tighten it with two rubber bands; install the two-petal support on the base, fix the two-petal support and the side-limited metal cylinder with screws, and then place permeable paper and permeable stone on the top of the frozen soil sample in turn, and then place the gland, turn the rubber membrane up to cover the gland and tighten it with two rubber bands. In this way, the rubber membrane isolates the soil sample from the outside world.

[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 through two pipes, one inlet and one outlet. The temperature control sleeve falls on the base of the dynamic triaxial testing machine and is sealed with a sealing ring. Antifreeze silicone oil is injected into the gap between the temperature control sleeve and the side limit metal cylinder. The antifreeze silicone oil must cover the top of the frozen soil sample.

[0033] Step 3: Install the pressure chamber cover. The force transmission shaft above the pressure chamber cover cooperates with the concave surface in the middle of the pressure cap; since the lateral confinement compression does not require liquid to apply confining pressure, the air pressure in the pressure chamber is 0, and the air pressure on the antifreeze silicone oil outside the lateral confinement metal cylinder is also 0. The frozen soil is only compressed under the lateral confinement displacement conditions provided by the lateral confinement metal cylinder. In this case, the pressure cover does not play a pressure-bearing characteristic, but it bears a tensile characteristic. 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 pressure chamber cover and the metal pull rods around the pressure cover.

[0034] Step 4: Heating to the specified temperature: The temperature of the soil sample in the freezer is about -18℃, and 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 can flow out of the temperature control servo. The higher temperature antifreeze silicone oil can heat up the frozen soil sample in the side confining metal cylinder. Since the rubber membrane isolates the frozen soil sample from the external water channel, 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 inside and outside of the soil sample have reached the specified temperature.

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

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

[0037] (1) Sample moisture content w0

[0038] After the test is completed, some samples are taken out for moisture content test, moisture content w0:

[0039]

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

[0041] (2) Sample wet density ρ0:

[0042]

[0043] Where m0 represents the mass of wet soil used for sample preparation; v 总 Represents the volume of the sample after frost heave.

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

[0045]

[0046] In the formula, G s Represents the specific gravity of soil, sandy soil is 2.67; ρw Represents the density of water, which is 1000kg / m 3 .

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

[0048] e i =e0-ε v (1+e0) (4)

[0049] In the formula, ε v It is the volume strain of the soil sample during the compression process. In the lateral confinement compression test, the volume strain is equal to the axial strain, and the axial strain is obtained by monitoring.

[0050] (5) Axial compressive stress

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

[0052]

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

[0054] Beneficial Effects

[0055] The present invention can make full use of the loading and monitoring functions of the existing dynamic triaxial testing machine, and can perform the lateral confined compression test without purchasing new instruments, thereby saving costs. Since the axial strain in the lateral confined compression test is the body strain, the axial strain can be monitored by using the axial strain sensor of the original dynamic triaxial testing machine, and the monitoring accuracy is also high. Therefore, there is no need to add a body strain monitoring sensor, thereby avoiding the problem of low accuracy in directly monitoring the body strain. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0058] Figure 3 It is a schematic diagram of a support of the side limiting metal cylinder device of the present invention;

[0059] Figure 4 A schematic diagram of a side confinement metal cylinder of the side confinement metal cylinder device of the present invention;

[0060] Figure 5 It is a schematic diagram of the gland 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 a confining metal cylinder device according to the present invention;

[0062] Figure 7 This is a schematic diagram of a test of frozen soil made using a confining metal cylinder device according to the present invention;

[0063] In the figure: 1. base; 2. support; 3. side limit metal cylinder; 4. gland; 5. rubber membrane; 6. permeable paper; 7. permeable stone; 8. screw; 9. rubber band; 10. frozen soil sample; 11. dynamic triaxial test machine base; 12. dynamic triaxial test machine lifting drive mechanism; 13. sealing ring; 14. dynamic triaxial test machine base; 15. antifreeze silicone oil 16. temperature control sleeve; 17. pressure chamber cover; 1-1. first top surface of base; 1-2. first side surface of base; 1-3. second top surface of base; 1-4. second side surface of base; 1-5. third top surface of base; 1-6. third side surface of base; 1-7. fourth top surface of base Surface; 1-8, fourth side surface of base; 2-1, first cylindrical side surface of support; 2-2, first bottom surface of support; 2-3, second cylindrical side surface of support; 2-4, third cylindrical side surface of support; 2-5, third cylindrical bottom surface of support; 2-6, fourth cylindrical side surface of support; 2-7, hollowed-out rectangular side surface of support; 2-8, bottom surface of support; 3-1, closing surface; 3-2, vent hole; 3-3, outside of side-limiting metal tube; 3-4, fixing screw hole; 3-5, bottom surface of side-limiting metal tube; 3-6, inner surface of side-limiting metal tube; 4-1, concave surface in the middle of pressure cover; 4-2, top surface of pressure cover; 4-3, side surface of pressure cover; 4-4, bottom surface of pressure cover. DETAILED DESCRIPTION

[0064] The following will be combined with the attached embodiment of the present invention Figure 1-7 The technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0065] The GT-061 dynamic triaxial testing machine, which is equipped with the National Key Laboratory of High-speed Railway Track System of the China Academy of Railway Sciences, has an oil temperature control system with a temperature control accuracy of ±0.1°C, a displacement sensor accuracy of 0.01mm, a load control accuracy of 5N, and a maximum loading force of 60kN. It can carry out creep, fatigue, stress relaxation and static and dynamic load tests of conventional uniaxial, triaxial and isotropic compression stress paths of soil at different temperatures; however, the GT-061 dynamic triaxial testing machine can only drain the sample through The volume strain can be calculated by measuring the volume of frozen soil, but the water in the frozen soil exists in the form of ice and will not be discharged. Therefore, the volume strain of frozen soil in the test cannot be measured. Moreover, due to the small distance between the temperature control sleeve and the rubber membrane of the sample of the GT-061 dynamic triaxial testing machine, and the side bulging of the soil sample during the compression process, it is not suitable to install radial and axial displacement sensors. The side limit compression function of the triaxial testing machine can be increased by adding side limit metal cylinders, and the cost of adding side limit metal cylinders is low, so the GT-061 dynamic triaxial testing machine can be equipped with the function of frozen soil volume strain test at a low cost.

[0066] See also Figure 1-7 The present invention provides a technical solution: a side-limiting metal cylinder device, comprising: a base 1, a support 2, a side-limiting metal cylinder 3, a pressure cover 4, a rubber membrane 5, permeable paper 6, permeable stone 7, screws 8, and rubber bands 9; the base is only used when preparing samples, is located below the support, supports and fixes the support, and the top surface of the base is used to support the permeable stone, the permeable paper and the frozen soil sample; the support is located above the base and below the side-limiting metal cylinder, and is used to support and fix the side-limiting metal cylinder; the side-limiting metal cylinder is located above the support and below the pressure cover, and the side-limiting metal cylinder and the support are fixedly connected by screws 8; the side-limiting metal cylinder and the base form a cylindrical space on the side and bottom surfaces 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 antifreeze silicone oil; the pressure cover is located at the top of the side-limiting metal cylinder, and is used to transfer pressure to the frozen soil sample during the test.

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

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

[0069] To facilitate installation, the support is cut into two parts after the overall manufacturing is completed to form a two-petal support, and the two screw holes are respectively located in the middle of the two two-petal supports.

[0070] The side-limiting metal tube includes: a closing surface 3-1, a vent hole 3-2, an outer side of the side-limiting metal tube 3-3, a fixing screw hole 3-4, a bottom surface of the side-limiting metal tube 3-5, and an inner surface of the side-limiting metal tube 3-6. The pressure cover includes: a concave surface 4-1 in the middle of the pressure cover, a top surface 4-2 of the pressure cover; a side surface 4-3 of the pressure cover, and a bottom surface 4-4 of the pressure cover. The base is located below the support, supports and fixes the support, and the first top surface of the base is used to support permeable stone, permeable paper and frozen soil samples; the support is located above the base and below the side-limiting metal tube, and is used to support and fix the side-limiting metal tube; the side-limiting metal tube is located above the support and below the pressure cover, and the side-limiting metal tube and the support are fixedly connected by screws; the side-limiting metal tube and the base form a cylindrical space on the side and bottom for holding frozen soil samples; a rubber film 5 is also provided between the metal tube and the frozen soil sample to isolate the frozen soil sample from antifreeze silicone oil;

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

[0072] A permeable stone 7 is arranged above the first top surface 1-1 of the base, and a permeable paper 6 is arranged above the permeable stone, and the permeable paper is 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 outer side 3-3 of the side limiting metal tube; the bottom surface 3-5 of the side limiting metal tube falls 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 falls 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 hollow rectangle is cut out at the bottom of the support to avoid the protrusion of the liquid inlet and outlet arranged on the base of the dynamic triaxial testing machine. In addition, a groove 2-9 is opened on the side of the support for placing a temperature sensor.

[0074] The method for making frozen soil using the above-mentioned confining metal cylinder device comprises:

[0075] Step 1: Prepare the ingredients

[0076] Compact the sand to get the maximum dry density; according to the density D r Calculate the mass of dry sand required for sample preparation based on the maximum dry density, and calculate the mass of water required based on the required water content. Dry the sand, mix the prepared dry sand and water thoroughly, and soak them for a day and night for sample preparation.

[0077] Step 2: Assemble the sample preparation device

[0078] Place permeable stone on the base, and place permeable paper on the permeable stone; install the rubber membrane on the first side of the base and tighten it with two rubber bands; then place the two-petal support on the base, and then place the side limit metal tube on the support, and then use screws to connect and tighten the side limit metal tube and the support; the rubber membrane higher than the metal tube is turned outward and downward to wrap the top of the side limit metal tube; if there is excess air between the rubber membrane and the side limit metal tube, it can be discharged through the air hole in the middle of the side limit metal tube.

[0079] Step 3: Sample preparation and freezing

[0080] The sample is prepared by layered compaction, which is divided into 5 layers. A certain mass of sand and soil must be used to reach the specified height. After the current layer is loaded, the upper surface of the soil sample is roughened with an iron brush to avoid stratification, and then the next layer is loaded. After the 5 layers are loaded, the sample preparation is completed. Permeable paper and permeable stone are placed on the soil sample, covered with a gland, wrapped on the rubber film on the upper part of the side limit metal cylinder, so that it wraps the side of the gland, and tightened with two rubber bands. The sample is placed in a -18℃ freezer for 24 hours.

[0081] Step 4: Unpacking

[0082] Take the frozen soil sample out of the freezer, remove the screws connecting the support and the side-limiting metal cylinder, and remove the support. At this time, the rubber band at the bottom of the side-limiting metal cylinder is exposed, and the rubber band is withdrawn to the second side of the base, the rubber membrane is separated from the base, and the base is hit along the axial direction of the side-limiting metal cylinder with a hammer to separate the base from the frozen soil sample; separate the gland and the side-limiting metal cylinder; measure the distance between the two permeable stones and the side-limiting metal cylinder to calculate the height of the frozen soil sample after frost heave, and calculate the volume according to the diameter of the side-limiting metal cylinder.

[0083] The method of conducting a volume strain test on frozen soil prepared by the confined metal cylinder device as described above comprises:

[0084] Step 1: Warm up the frozen soil to the specified temperature and conduct a compression test: Place permeable stone and permeable paper on the base of the dynamic triaxial test machine in turn, place the side-limited metal cylinder with soil sample on the base of the dynamic triaxial test machine, and the frozen soil sample is in contact with the permeable paper; wrap the rubber membrane at the bottom of the side-limited metal cylinder around the uppermost cylindrical side of the base of the dynamic triaxial test machine and tighten it with two rubber bands; install the two-petal support on the base, fix the two-petal support and the side-limited metal cylinder with screws, and then place permeable paper and permeable stone on the top of the frozen soil sample in turn, and then place the gland, turn the rubber membrane up to cover the gland and tighten it with two rubber bands. In this way, the rubber membrane isolates the soil sample from the outside world.

[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 through two pipes, one inlet and one outlet. The temperature control sleeve falls on the base of the dynamic triaxial testing machine and is sealed with a sealing ring. Antifreeze silicone oil is injected into the gap between the temperature control sleeve and the side limit metal cylinder. The antifreeze silicone oil must cover the top of the frozen soil sample.

[0086] Step 3: Install the pressure chamber cover. The force transmission shaft above the pressure chamber cover cooperates with the concave surface in the middle of the pressure cap; since the lateral confinement compression does not require liquid to apply confining pressure, the air pressure in the pressure chamber is 0, and the air pressure on the antifreeze silicone oil outside the lateral confinement metal cylinder is also 0. The frozen soil is only compressed under the lateral confinement displacement conditions provided by the lateral confinement metal cylinder. In this case, the pressure cover does not play a pressure-bearing characteristic, but it bears a tensile characteristic. 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 pressure chamber cover and the metal pull rods around the pressure cover.

[0087] Step 4: Heating to the specified temperature: The temperature of the soil sample in the freezer is about -18℃, and 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 can flow out of the temperature control servo. The higher temperature antifreeze silicone oil can heat up the frozen soil sample in the side confining metal cylinder. Since the rubber membrane isolates the frozen soil sample from the external water channel, 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 inside and outside of the soil sample have reached the specified temperature.

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

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

[0090] (1) Sample moisture content w0

[0091] After the test is completed, some samples are taken out for moisture content test, moisture content w0:

[0092]

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

[0094] (2) Sample wet density ρ0:

[0095]

[0096] Where m0 represents the mass of wet soil used for sample preparation; v 总 Represents the volume of the sample after frost heave.

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

[0098]

[0099] In the formula, G s Represents the specific gravity of soil, sandy soil is 2.67; ρw Represents the density of water, which is 1000kg / m 3 .

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

[0101] e i =e0-ε v (1+e0) (4)

[0102] In the formula, ε v It is the volume strain of the soil sample during the compression process. In the lateral confinement compression test, the volume strain is equal to the axial strain, and the axial strain is obtained by monitoring.

[0103] (5) Axial compressive stress

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

[0105]

[0106] Step 7: Summarize the test results and obtain the lower limit compression test results at different temperatures

[0107] The contents not described in detail in this specification belong to the prior art known to professionals in this field.

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

Claims

1. A side limiting metal cylinder device, comprising: Base, support, side limit metal cylinder, pressure cover, rubber membrane, permeable paper, permeable stone, fastening screws, rubber band; its characteristics are: the base is located below the support, supports and fixes the support, and the top surface of the base is used to support the permeable stone, permeable paper and frozen soil samples; the support is located above the base and below the side limit metal cylinder, used to support and fix the side limit metal cylinder, and the support is divided into two parts after the overall manufacturing is completed to form a two-petal support; the side limit metal cylinder is located above the support and below the pressure cover, and the side limit metal cylinder and the support are fixedly connected by screws; the side limit metal cylinder and the base form a cylindrical space on the side 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 antifreeze silicone oil; the pressure cover is located on the top of the side limit metal cylinder to transfer pressure to the frozen soil sample during the test.

2. A side limiting metal cylinder device according to claim 1, characterized in that: A permeable stone is arranged above the first top surface of the base, and a permeable paper is placed above the permeable stone, and the permeable paper is in direct contact with the frozen soil sample; the first side surface of the base cooperates with the rubber membrane and is tightened by a rubber band; the first cylindrical side surface of the support cooperates with the outside of the side-limiting metal tube; the bottom surface of the side-limiting metal tube falls on the first bottom surface of the support, and the second cylindrical side surface of the support and the first side surface of the base form a rubber band space; the bottom surface of the support falls on the third top surface of the base; the fourth cylindrical side surface of the support cooperates with the second side surface of the base; the support is cut into two parts after the overall manufacturing is completed to form a two-petal support, and the two screw holes are respectively located in the middle of the two two-petal supports.

3. A method for making a frozen soil sample using a confined metal cylinder device, the method is based on the confined metal cylinder device according to any one of claims 1 to 2, and is characterized by comprising: Step 1: Prepare the ingredients Compaction test was carried out on sandy soil to obtain the maximum dry density; 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 water content; dry the sand, mix the prepared dry sand and water thoroughly, and soak them for a day and night for sample preparation; Step 2: Assemble the sample preparation device Place a permeable stone on the base, and place permeable paper on the permeable stone; install the rubber membrane on the first side of the base and tighten it with a rubber band; then place the two-petal support on the base, place the side limit metal cylinder on the support, and then use screws to connect and tighten the side limit metal cylinder and the support; the rubber membrane that is higher than the metal cylinder is turned outward and downward to wrap the top of the side limit metal cylinder; if there is excess air between the rubber membrane and the side limit metal cylinder, it will be discharged through the air hole in the middle of the side limit metal cylinder; Step 3: Sample preparation and freezing The sample is prepared by layered compaction, which is divided into 5 layers. A certain mass of sand and soil is used to reach the specified height. After the current layer is loaded, the upper surface of the soil sample is roughened with an iron brush to avoid stratification, and then the next layer is loaded. After the 5 layers are loaded, the sample preparation is completed; permeable paper and permeable stone are placed on the soil sample, covered with a gland, wrapped on the rubber film on the upper part of the side limit metal cylinder, so that it wraps the side of the gland, and tightened with two rubber bands; the sample is placed in a -18℃ freezer for 24 hours; Step 4: Unpacking Take the frozen soil sample out of the freezer, remove the screws connecting the support and the side-limiting metal cylinder, and remove the support; at this time, the rubber band at the bottom of the side-limiting metal cylinder is exposed, and the rubber band is withdrawn to the second side of the base, the rubber membrane is separated from the base, and the base is knocked on the base along the axial direction of the side-limiting metal cylinder with a hammer to separate the base from the frozen soil sample; separate the pressure cover and the side-limiting metal cylinder; measure the distance between the two permeable stones and the side-limiting metal cylinder to calculate the height of the frozen soil sample after frost heave, and calculate the volume according to the diameter of the side-limiting metal cylinder.

4. A method for measuring frozen soil volume deformation using a confined metal cylinder device, the method is based on the confined metal cylinder device according to any one of claims 1-2, and is characterized by: include: Step 1, warming the frozen soil to a specified temperature and conducting a compression test: placing permeable stones and permeable paper on the base of the dynamic triaxial testing machine in sequence, placing a side-limited metal cylinder containing a soil sample on the base of the dynamic triaxial testing machine, and the frozen soil sample is in contact with the permeable paper; wrapping the rubber membrane at the bottom of the side-limited metal cylinder around the uppermost cylindrical side of the base of the dynamic triaxial testing machine, and tightening it with two rubber bands; installing the two-petal support on the base, fixing the two-petal support and the side-limited metal cylinder with screws, placing permeable paper and permeable stones on the upper part of the frozen soil sample in sequence, and then placing a gland, turning the rubber membrane up to wrap the gland and tightening 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 through two pipes, one inlet and one outlet. The temperature control sleeve falls on the base of the dynamic triaxial testing machine and is sealed with a sealing ring. Antifreeze silicone oil is injected into the gap between the temperature control sleeve and the side limit metal cylinder. The antifreeze silicone oil should cover the top of the frozen soil sample; Step 3, install the pressure chamber outer cover: the force transmission shaft above the pressure chamber outer cover cooperates with the concave surface in the middle of the pressure cover; since the lateral limit compression does not require liquid to apply confining pressure, the air pressure in the pressure chamber is 0, and the air pressure on the antifreeze silicone oil outside the lateral limit metal cylinder is also 0, and the frozen soil is only compressed under the lateral limit displacement conditions provided by the lateral limit 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 pressure chamber outer cover and the metal pull rods around the pressure cover; Step 4: Heating to the specified temperature: The temperature of the soil sample in the freezer is about -18℃, and the test requires a specified temperature of -0.5~-10℃, so the frozen soil needs to be heated up; antifreeze silicone oil of the specified temperature flows out of the temperature control servo, and the higher temperature antifreeze silicone oil heats up the frozen soil sample in the side confinement metal cylinder; because the rubber membrane isolates the frozen soil sample from the external water channel, 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 inside and outside of the soil sample have reached the specified temperature; Step 5: Conduct the test: after heating to the specified temperature, perform graded compression, each stage is maintained for 6 hours, and the compressive stress and void changes are obtained; Step 6: Data processing: Finally, we need to obtain the relationship between the porosity e of frozen soil and the axial stress p: (1) Sample moisture content w0 After the test is completed, some samples are taken out for moisture content test, moisture content w0: In the formula, m d Represents dry soil mass; m w represents the mass of water; m0 represents the mass of wet soil used for sample preparation; (2) Sample wet density ρ0: In the formula, v 总 Represents the volume of the specimen after frost heave; (3) Initial porosity of the sample e0 In the formula, G s Represents the specific gravity of soil, sandy soil is 2.67; ρ w Represents the density of water, which is 1000kg / m 3 ; (4) Porosity ratio e during compression i by i =e0-ε v (1+e0) (4) In the formula, ε v It is the volume strain of soil sample during compression. In the confined compression test, the volume strain is equal to the axial strain, which is obtained by monitoring. (5) Axial compressive stress The base of the triaxial specimen rises, and the axial force F is monitored. The diameter of the specimen d is 0.15m, and the bottom area S of the soil specimen is calculated, and its axial stress p is: Step 7: Summarize the test results and obtain the lower limit compression test results at different temperatures.

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