Soil penetration test device suitable for gradient variable-temperature freezing and thawing cycle test

Abstract

The invention provides a soil permeability test device suitable for gradient variable-temperature freeze-thaw cycle test, which comprises a temperature control cylinder formed by axially extending and combining a plurality of annular insulating cylinders with hollow structures, an insulating and heat-conducting soil sample cylinder is mounted in a central chamber formed by the temperature control cylinder, a water storage chamber is arranged on one side of the soil sample cylinder, and a water outlet is formed in the other side of the soil sample cylinder. A porous anode plate is arranged between the water storage chamber and the soil sample cylinder, a water collecting chamber is arranged on the other side of the soil sample cylinder, a porous cathode plate is arranged between the water collecting chamber and the soil sample cylinder, an orifice plate flowmeter is arranged between the water collecting chamber and the porous cathode plate, and the water storage chamber is connected with a water supply system; a pore pressure sensor and a temperature sensor are installed on the side wall of each annular insulating cylinder, and each annular insulating cylinder is connected with a refrigeration module and a heating module. The device can simulate a real environment to perform freezing and thawing and gradient temperature control on the sample, can effectively simulate a real geological environment in an alpine region, and provides a scientific basis for research on permeability of frozen soil under a gradient freezing and thawing cycle condition.

Description

Technical Field

[0001] The present invention relates to the technical field of soil permeability tests, and particularly to a soil permeability test device applicable to gradient variable temperature freeze-thaw cycle tests. Background Art

[0002] The soil permeameter test device is a relatively commonly used test equipment for studying soil permeability. However, the current existing soil permeameter tests only consider the testing of the characteristics of conventional normal-temperature soils. China has a vast territory, and there are many high-altitude and cold regions. The temperature is relatively low all year round in these regions, and frozen soil layers are widely distributed. Therefore, its disadvantage is that the permeability characteristics of frozen soil under the action of gradient variable temperature freeze-thaw cycles have not been taken into account. It cannot simulate such a temperature gradient and does not have the ability to study low-temperature frozen soil. Summary of the Invention

[0003] The purpose of the present invention is to provide a soil permeability test device applicable to gradient variable temperature freeze-thaw cycle tests, which can simulate frozen soil under the action of gradient variable temperature freeze-thaw cycles and conduct permeability characteristic tests. In order to achieve the above technical features, the purpose of the present invention is realized as follows: A soil permeability test device applicable to gradient variable temperature freeze-thaw cycle tests includes a temperature control cylinder formed by axially extending and combining a plurality of hollow-structured annular insulating cylinders. An insulating and heat-conducting soil sample cylinder is installed in the central chamber formed by the temperature control cylinder. A water storage chamber is provided on one side of the soil sample cylinder. A porous anode plate is provided between the water storage chamber and the soil sample cylinder. A water collection chamber is provided on the other side of the soil sample cylinder. A porous cathode plate is provided between the water collection chamber and the soil sample cylinder. An orifice plate flowmeter is provided between the water collection chamber and the porous cathode plate. The water storage chamber is connected to a water supply system; A pore pressure sensor and a temperature sensor are installed on the side wall of each annular insulating cylinder. The pore pressure sensor and the temperature sensor extend into the soil sample cylinder after passing through the side wall of the annular insulating cylinder. Each annular insulating cylinder is respectively connected to a refrigeration module and a heating module; The pore pressure sensor, the temperature sensor, the refrigeration module, and the heating module are respectively connected to a control and data acquisition system.

[0004] The heating module includes a resistance wire arranged in the inner cavity of the annular insulating cylinder. The resistance wire is connected to a heating power supply. The control and data acquisition system of the heating power supply is connected to the temperature sensor.

[0005] The refrigeration module includes a compressor, a condenser pipe, a dryer filter, a capillary tube, and an evaporator pipe. The compressor, the condenser pipe, the dryer filter, the capillary tube, and the evaporator pipe are connected in sequence. The output end of the evaporator pipe is connected to the refrigerant vapor inlet of the compressor. A flow control valve is provided on the evaporator pipe. The control and data acquisition system of the flow control valve is connected to the temperature sensor. The evaporator pipe is arranged on the inner wall of the annular insulating cylinder.

[0006] An insulating baffle with a ring structure is provided between every two of the annular insulating cylinders.

[0007] A carbon fiber porous separator is provided between the porous cathode plate and the soil sample cylinder.

[0008] A cation exchange membrane is provided between the porous cathode plate and the carbon fiber porous separator.

[0009] A plurality of annular electrodes are embedded in the side wall of the soil sample cylinder.

[0010] The pore pressure sensors are equally spaced.

[0011] The temperature sensors are equally spaced.

[0012] A method for using a soil permeability test device applicable to gradient variable-temperature freeze-thaw cycle tests includes the following steps: S1: When performing a permeability characteristic test, fill a saturated soil sample into the soil sample cylinder and assemble and connect all components. S2: Start the refrigeration module, perform the refrigeration process in different annular insulating cylinders, start absorbing the heat in the soil sample cylinder to cool down. The temperature sensor transmits the temperature signals of the saturated soil samples in the soil sample cylinder at different positions to the control and data acquisition system. The control and data acquisition system adjusts the refrigeration module according to the temperature signals, and the gradient refrigeration process of the saturated soil sample can be completed, causing frost heave of the saturated soil sample in the soil sample cylinder. Subsequently, control the refrigeration module to stop working. S3: Start the heating module to raise the temperature in the annular insulating cylinder. Heat exchange occurs between the annular insulating cylinder and the wall of the soil sample cylinder to heat the saturated soil sample in the soil sample cylinder. The control and data acquisition system regulates the corresponding heating module of the annular insulating cylinder according to the temperature signals transmitted by the temperature sensor, causing thaw settlement of the saturated soil sample in the soil sample cylinder. Subsequently, control the heating module to stop working. S4: Repeat the operations in steps S2 and S3 until the freeze-thaw cycle process is achieved. After the last refrigeration process is completed, adjust the temperature of the soil sample in the soil sample cylinder to the test set value through the control and data acquisition system. S5: Connect the porous anode plate and the porous cathode plate to direct current, replenish water into the water storage chamber, and the control and data acquisition system regularly collects the values of the pore pressure sensor, temperature sensor, and orifice plate flowmeter and transmits them to the computer for recording; S5: Use Darcy's law v = k * i, where: v is the seepage rate, k is the permeability coefficient, and i is the hydraulic gradient, to measure the permeability coefficient k of frozen soil. In this test system, the pore pressure gradient collected by the pore pressure sensor is equivalent to the hydraulic gradient i; According to another formula of Darcy's law v = Q / A, where: Q is the seepage flow, with the unit of mm³ / s; A is the cross-sectional area of the soil sample, and Q in the test is determined by the orifice plate flowmeter; plot the relationship curve between the seepage rate v and the hydraulic gradient i, and the slope of the linear segment is the permeability coefficient k of the frozen soil under this condition.

[0013] The present invention has the following beneficial effects: 1. Through the arrangement of multiple annular insulating cylinders 1a with a hollow structure and the soil sample cylinder 21, the production of samples within the sample device is realized, avoiding backfilling; at the same time, the design of equipped with a refrigeration module and a heating module realizes the precise and rapid regulation of gradient temperature control, facilitating the conduct of the test and saving a large amount of test time. The annular insulating cylinder, refrigeration module, and heating module constitute multiple temperature control units, which can simulate the real environment to conduct freeze-thaw and gradient temperature control on the sample. This design can effectively simulate the real geological environment in alpine regions, providing a scientific basis for the study of the permeability performance of frozen soil under gradient freeze-thaw cycle conditions, and ensuring the effective conduct of the permeability test of the sample in the in-situ gradient variable temperature freeze-thaw cycle state; 2. The radial electric field generated by the annular electrode array can cover most areas of the sample, reducing the edge effect of the traditional axial electric field and improving the measurement accuracy of the electroosmosis method. The cooperative work of multiple electrodes can disperse the current density, reduce the polarization effect of a single electrode, and extend the service life of the electrode. The annular electrode array can dynamically adjust the electric field strength according to the conductivity distribution of the sample, and is suitable for measuring the permeability coefficient of non-uniform frozen soil or unsaturated frozen soil; by adjusting the voltage and spacing of the annular electrodes, the electric field distribution under different working conditions can be simulated, providing more experimental data for the study of the permeability of frozen soil; 3. A cation exchange membrane is provided between the porous cathode plate and the carbon fiber porous separator, which is used to separate the anode area and the cathode area, allowing only cations to pass through, while repelling anions and gas molecules, realizing the directional migration of ions. Driven by the electric field, cations migrate through the membrane to balance the charge distribution in the water and maintain electrical neutrality; at the same time, the current efficiency is improved, ensuring safety and high efficiency; 4. Through the setting of the carbon fiber porous separator, a continuous conductive channel is formed through the carbon fiber network in the pores, enhancing the overall conductive performance. Description of the Drawings

[0014] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0015] Figure 1 It is a schematic structural diagram of a soil permeability test device applicable to a gradient variable temperature freeze-thaw cycle test provided by an embodiment of the present invention; Figure 2 It is a structural diagram of a refrigeration module provided by an embodiment of the present invention; Figure 3 It is a schematic structural diagram of a porous cathode plate and a porous anode plate provided by an embodiment of the present invention; Figure 4 It is a cross-sectional view of the connection structure between an annular insulating cylinder and an annular electrode provided by an embodiment of the present invention; Figure 5 It is a schematic structural diagram of an annular electrode provided by an embodiment of the present invention; In the figure: temperature control cylinder 1, annular insulating cylinder 1a, inner cavity 1a1, central chamber 1b, water storage chamber 2, water injection port 2a, porous anode plate 3, water collection chamber 4, water collection chamber end cover 4a, porous cathode plate 5, orifice plate flowmeter 6, pore pressure sensor 7, temperature sensor 8, compressor 9, condenser tube 10, radiator 10a, drying filter 11, capillary tube 12, evaporation tube 13, flow control valve 14, carbon fiber porous partition 15, cation exchange membrane 16, annular electrode 17, peristaltic pump 18, water tank 19, heat insulation baffle 20, soil sample cylinder 21. Specific embodiments

[0016] The embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

[0017] In order to achieve the above technical features, the object of the present invention is achieved as follows: See Figures 1-5, A soil permeability test device applicable to gradient variable-temperature freeze-thaw cycle tests, comprising a temperature control cylinder 1 formed by axially extending and combining a plurality of annular insulating cylinders 1a with a hollow structure. An insulating and heat-conducting soil sample cylinder 21 is installed in the central chamber formed by the temperature control cylinder 1. The soil sample cylinder is used to fill saturated soil samples. A water storage chamber 2 is provided on one side of the soil sample cylinder 21. A porous anode plate 3 is provided between the water storage chamber 2 and the soil sample cylinder. A water collection chamber 4 is provided on the other side of the soil sample cylinder 21. A porous cathode plate 5 is provided between the water collection chamber 4 and the soil sample cylinder 21. The porous anode plate 3 and the porous cathode plate 5 are respectively connected to a DC power supply. An orifice plate flowmeter 6 is provided between the water collection chamber 4 and the porous cathode plate 5. The water storage chamber 2 is connected to a water supply system; a pore pressure sensor 7 and a temperature sensor 8 are installed on the side wall of each annular insulating cylinder 1a. The pore pressure sensor 7 and the temperature sensor 8 extend into the soil sample cylinder 21 after passing through the side wall of the annular insulating cylinder 1a. Each annular insulating cylinder 1a is respectively connected to a refrigeration module and a heating module. The pore pressure sensor 7, the temperature sensor 8, the refrigeration module and the heating module are respectively connected to a control and data acquisition system. Through the setting of a plurality of annular insulating cylinders 1a with a hollow structure and the soil sample cylinder 21, the production of freeze-thaw specimens in the soil sample cylinder 21 is realized, avoiding backfilling. At the same time, the design of equipping with a refrigeration module and a heating module realizes the precise and rapid regulation of gradient temperature control, facilitates the development of tests, and saves a lot of test time. The annular insulating cylinders 1a, the refrigeration module and the heating module constitute multiple temperature control units, which can simulate the real environment to carry out freeze-thaw and gradient temperature control on the specimens. This design can effectively simulate the real geological environment in alpine regions, provide a scientific basis for the study of the permeability performance of frozen soil under gradient freeze-thaw cycle conditions, and ensure the effective development of the permeability test of the specimens in the in-situ gradient variable-temperature freeze-thaw cycle state.

[0018] As an implementation manner, in this embodiment, the heating module includes a resistance wire disposed in the inner cavity 1a1 of the annular insulating cylinder 1a. The resistance wire is connected to a heating power supply. The control and data acquisition system of the heating power supply is connected to the temperature sensor 8 to realize the heating of the annular insulating cylinder.

[0019] As an implementation manner, in this embodiment, the refrigeration module includes a compressor 9, a condenser tube 10, a dryer filter 11, a capillary tube 12, and an evaporator tube 13. The compressor 9, the condenser tube 10, the dryer filter 11, the capillary tube 12, and the evaporator tube 13 are connected in sequence. The output end of the evaporator tube 13 is connected to the refrigerant vapor inlet of the compressor 9. A flow control valve 14 is provided on the evaporator tube 13. The control and data acquisition system of the flow control valve 14 is connected to the temperature sensor 8. The evaporator tube 13 is arranged on the inner wall 1a1 of the annular insulating cylinder and is distributed in a multi-bent and coiled manner. A heat sink 10a for auxiliary heat dissipation is provided on the condenser tube 10. During the refrigeration process, the compressor 9 sucks in the refrigerant vapor at low temperature and low pressure, compresses it into a high-temperature and high-pressure gas through the cylinder of the compressor 9, and then discharges it into the condenser tube 10; the high-temperature and high-pressure refrigerant gas cools down under the action of the condenser tube 10 and the heat sink 10a. The refrigerant gas is cooled into a saturated gas at normal temperature and high pressure, and is further cooled into a saturated high-pressure liquid, and the temperature remains unchanged for a short time after reaching the condensation temperature; the saturated high-pressure liquid after condensation flows into the capillary tube 12 after being filtered by the dryer filter 11 to remove moisture and impurities. After throttling and pressure reduction by the capillary tube 12, the refrigerant becomes a low-temperature and low-pressure liquid; the low-temperature and low-pressure refrigerant liquid enters the evaporator tube 13 and starts to absorb the heat in the annular insulating cylinder 1a, causing the temperature to drop. The refrigerant vaporizes from a low-temperature and low-pressure liquid into a low-temperature and low-pressure refrigerant vapor and flows back to the compressor 9. The temperature sensor 8 transmits the temperature signal in the annular insulating cylinder 1a to the control and data acquisition system, and the control and data acquisition system adjusts the opening of the flow control valve 14 according to the temperature signal, regulates the refrigerant flow rate of the evaporator tube 13, and adjusts the temperature, thus completing the gradient refrigeration process in the soil sample cylinder 21, so that the saturated soil sample in the soil sample cylinder 21 undergoes frost heaving phenomenon.

[0020] As an implementation manner, in this embodiment, an annular heat insulation baffle 20 is provided between every two of the annular insulating cylinders 1a.

[0021] As an implementation manner, in this embodiment, carbon fiber porous partitions 15 are provided between the porous cathode plate 5 and the soil sample cylinder 21, and between the porous anode plate 3 and the soil sample cylinder 21. The porous structure can achieve the separation of substances in different phases through the design of pore size. After being combined with a waterproof coating, it can be used stably for a long time in humid or low-temperature environments. The continuous carbon atom structure of carbon fiber forms a natural conduction path, and the conductivity can be enhanced by optimizing the fiber arrangement density (such as directional weaving). The porous structure can form a continuous conductive channel through the carbon fiber network in the pores, enhancing the overall conductive performance.

[0022] As an implementation manner, in this embodiment, a cation exchange membrane 16 is provided between the porous cathode plate 5 and the carbon fiber porous separator 15. The cation exchange membrane 21 is a polymer membrane with selective permeability. It is used to separate the anode region and the cathode region, allowing only cations to pass through while repelling anions and gas molecules, thus realizing the directional migration of ions. Driven by an electric field, cations migrate through the membrane to balance the charge distribution in water and maintain electrical neutrality. At the same time, the current efficiency is improved, ensuring safety and high efficiency.

[0023] As an implementation manner, in this embodiment, a plurality of annular electrodes 17 are embedded in the side wall of the soil sample cylinder. The radial electric field generated by the annular electrode array can cover most of the area of the specimen, reduce the edge effect of the traditional axial electric field, and improve the measurement accuracy of the electroosmosis method. The cooperative work of multiple electrodes can disperse the current density, reduce the polarization effect of a single electrode, and extend the service life of the electrode. The annular electrode array can dynamically adjust the electric field intensity according to the conductivity distribution of the specimen, and is applicable to the measurement of the permeability coefficient of non-uniform frozen soil or unsaturated frozen soil; by adjusting the voltage and spacing of the annular electrodes, the electric field distribution under different working conditions can be simulated, providing more experimental data for the study of the permeability of frozen soil.

[0024] As an implementation manner, in this embodiment, the pore pressure sensors are evenly distributed.

[0025] As an implementation manner, in this embodiment, the temperature sensors are evenly distributed.

[0026] As an implementation manner, in this embodiment, an aerogel layer is provided between the heat insulation baffle 20 and the soil sample cylinder, and between the heat insulation baffle 20 and the annular insulating cylinder 1a. By introducing the aerogel layer, problems such as thermal interference, mechanical buffering, and insulation in the frozen soil experiment can be solved simultaneously without significantly increasing the complexity of the device.

[0027] A method for using a soil permeability test device applicable to gradient variable-temperature freeze-thaw cycle tests includes the following steps: S1: When performing permeability characteristic tests, fill the central chamber 1b of the soil sample cylinder 21 with a saturated soil sample and assemble and connect all components. S2: Start the refrigeration module and perform the refrigeration process in different annular insulating cylinders 1a, start absorbing the heat in the soil sample cylinder 21 and cool down. The temperature sensor 8 transmits the temperature signals of the saturated soil samples in different annular insulating cylinders 1a to the control and data acquisition system. The control and data acquisition system adjusts the refrigeration module according to the temperature signals, and the gradient refrigeration process of the saturated soil sample can be completed, causing the saturated soil sample in the soil sample cylinder 21 to undergo frost heaving. Subsequently, control the refrigeration module to stop working. S3: After turning on the heating power supply through the control and data acquisition system, the current flows through the resistance wire to release heat, thereby increasing the temperature inside the annular insulating cylinder 1a. Heat exchange occurs between the annular insulating cylinder and the wall of the soil sample cylinder to heat the saturated soil sample inside the soil sample cylinder. The control and data acquisition system regulates the heating power supply corresponding to the annular insulating cylinder 1a according to the temperature signal transmitted by the temperature sensor 8, causing the saturated soil sample inside the soil sample cylinder 21 to undergo thaw settlement. Subsequently, the control module stops working; S4: Repeat the operations in steps S2 and S3 until the freeze-thaw cycle process is achieved. After the last refrigeration process is completed, adjust the temperature of the soil sample inside the soil sample cylinder 21 to the test set value through the control and data acquisition system; S5: Connect the porous anode plate 3 and the porous cathode plate 5 to direct current, and replenish water into the water storage chamber 2. The control and data acquisition system periodically collects the values of the pore pressure sensor 7, the temperature sensor 8, and the orifice plate flowmeter 6 and transmits them to the computer for recording; S5: Use Darcy's law v = k * i, where: v is the seepage rate, k is the permeability coefficient, and i is the hydraulic gradient, to measure the permeability coefficient k of frozen soil. In this test system, the pore pressure gradient collected by the pore pressure sensor 7 is equivalent to the hydraulic gradient i; According to another formula of Darcy's law v = Q / A, where: Q is the seepage flow rate, with the unit of mm³ / s; A is the cross-sectional area of the soil sample. In the test, Q is determined by the orifice plate flowmeter 6. Plot the relationship curve between the seepage rate v and the hydraulic gradient i, and the slope of the linear segment is the permeability coefficient k of the frozen soil under this condition.

Claims

1. A soil permeability test device applicable to gradient variable temperature freeze-thaw cycle tests, characterized in that: It includes a temperature control cylinder formed by axially extending and combining a plurality of annular insulating cylinders with hollow structures. An insulating and heat-conducting soil sample cylinder is installed in the central chamber formed by the temperature control cylinder. A water storage chamber is provided on one side of the soil sample cylinder. A porous anode plate is provided between the water storage chamber and the soil sample cylinder. A water collection chamber is provided on the other side of the soil sample cylinder. A porous cathode plate is provided between the water collection chamber and the soil sample cylinder. An orifice plate flowmeter is provided between the water collection chamber and the porous cathode plate. The water storage chamber is connected to a water supply system; A pore pressure sensor and a temperature sensor are installed on the side wall of each annular insulating cylinder. The pore pressure sensor and the temperature sensor extend into the soil sample cylinder after passing through the side wall of the annular insulating cylinder. Each annular insulating cylinder is respectively connected to a refrigeration module and a heating module; The pore pressure sensor, the temperature sensor, the refrigeration module and the heating module are respectively connected to a control and data acquisition system.

2. The soil permeability test device applicable to the gradient variable temperature freeze-thaw cycle test according to claim 1, wherein: The heating module includes a resistance wire arranged in the inner cavity of the annular insulating cylinder. The resistance wire is connected to a heating power supply. The control and data acquisition system of the heating power supply is connected to the temperature sensor.

3. The soil permeability test device applicable to gradient variable temperature freeze-thaw cycle tests according to claim 1, characterized in that: The refrigeration module includes a compressor, a condenser pipe, a dryer filter, a capillary tube and an evaporator pipe. The compressor, the condenser pipe, the dryer filter, the capillary tube and the evaporator pipe are connected in sequence. The output end of the evaporator pipe is connected to the refrigerant vapor inlet of the compressor. A flow control valve is arranged on the evaporator pipe. The control and data acquisition system of the flow control valve is connected to the temperature sensor. The evaporator pipe is arranged on the inner wall of the annular insulating cylinder.

4. The soil permeability test device applicable to the gradient variable temperature freeze-thaw cycle test according to claim 1, characterized in that: An annular heat insulation baffle is provided between every two annular insulating cylinders.

5. The soil permeability test device applicable to gradient variable temperature freeze-thaw cycle tests according to claim 1, characterized in that: A carbon fiber porous partition board is provided between the porous cathode plate and the soil sample cylinder.

6. The soil permeability test device applicable to the gradient variable temperature freeze-thaw cycle test according to claim 5, characterized in that: A cation exchange membrane is provided between the porous cathode plate and the carbon fiber porous partition board.

7. The soil permeability test device applicable to the gradient variable temperature freeze-thaw cycle test according to claim 6, characterized in that: A plurality of annular electrodes are embedded in the side wall of the soil sample cylinder.

8. The soil permeability test device applicable to the gradient variable temperature freeze-thaw cycle test according to claim 1, wherein: The pore pressure sensors are evenly distributed.

9. The soil permeability test device applicable to gradient variable temperature freeze-thaw cycle tests according to claim 1, characterized in that: The temperature sensors are evenly distributed.

10. The method of using the soil permeability test device applicable to the gradient variable temperature freeze-thaw cycle test according to any one of claims 1-9, characterized in that, It includes the following steps: S1: When performing the permeability characteristic test, fill the saturated soil sample into the soil sample cylinder and assemble and connect each component; S2: Start the refrigeration module, perform the refrigeration process in different annular insulating cylinders, start to absorb the heat in the soil sample cylinder, and cool down. The temperature sensor transmits the temperature signals of the saturated soil sample in the soil sample cylinder at different positions to the control and data acquisition system. The control and data acquisition system adjusts the refrigeration module according to the temperature signals, and the gradient refrigeration process of the saturated soil sample can be completed, so that the saturated soil sample in the soil sample cylinder undergoes frost heaving. Subsequently, control the refrigeration module to stop working; S3: Start the heating module to increase the temperature in the annular insulating cylinder. Heat exchange occurs between the annular insulating cylinder and the wall of the soil sample cylinder to heat the saturated soil sample in the soil sample cylinder. The control and data acquisition system controls the corresponding heating module of the annular insulating cylinder according to the temperature signals transmitted by the temperature sensor, so that the saturated soil sample in the soil sample cylinder undergoes thaw settlement. Subsequently, control the heating module to stop working; S4: Repeat the operations in steps S2 and S3 until the freeze-thaw cycle process is achieved. After the last refrigeration process is completed, adjust the temperature of the soil sample in the soil sample cylinder to the test set value through the control and data acquisition system; S5: Connect the porous anode plate and the porous cathode plate to direct current, and replenish water into the water storage chamber. The control and data acquisition system periodically collects the values of the pore pressure sensor, temperature sensor, and orifice plate flowmeter and transmits them to the computer for recording; S5: Use Darcy's law v = k * i, where: v is the seepage velocity, k is the permeability coefficient, and i is the hydraulic gradient, to measure the permeability coefficient k of frozen soil. In this test system, the pore pressure gradient collected by the pore pressure sensor is equivalent to the hydraulic gradient i; According to another formula of Darcy's law v = Q / A, where: Q is the seepage flow rate, with the unit of mm³ / s; A is the cross-sectional area of the soil sample, and Q in the test is determined by the orifice plate flowmeter; plot the relationship curve between the seepage velocity v and the hydraulic gradient i, and the slope of the linear segment is the permeability coefficient k of the frozen soil under this condition.

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