Segmented temperature-controllable soil column multi-field coupling freeze-thaw test device and test method

Abstract

The application particularly relates to a segmented temperature-controllable soil column multi-field coupling freeze-thaw test device and a test method. The device comprises a cylinder assembly, the cylinder assembly comprises a standard cylinder section and a piston cylinder section, a temperature control piston is arranged at the top of the piston cylinder section, a water permeable plate or a water filter layer is arranged at the bottom of the cylinder assembly, flow channels are arranged in the temperature control disc and the temperature control piston, in-line sensors are arranged on the standard cylinder section and the piston cylinder section, the temperature control piston is connected with a loading mechanism, a pressure sensor is arranged between the loading mechanism and the piston cylinder section, a displacement sensor is arranged on the temperature control piston, and a thermal insulation layer is arranged on the detachable cover of the cylinder assembly, the temperature control disc and the temperature control piston. The application establishes a controllable one-dimensional temperature boundary through the temperature control piston and the temperature control disc, realizes in-situ monitoring of multiple parameters along the path through the sensors, realizes switching of the mechanical constraint boundary and the open evaporation boundary, and forms closed, open water replenishment, drainage or salt solution supply boundaries.

Description

Technical Field

[0001] This invention belongs to the technical field of freeze-thaw testing of cold-region soil, soil hydrothermal salt migration testing, frost heave force and frost heave amount testing, and simulation of evaporation-freeze-thaw coupling process. Specifically, it relates to a segmented, temperature-controlled soil column multi-field coupled freeze-thaw test device and test method. Background Technology

[0002] Freeze-thaw cycles are widespread in seasonally frozen soil regions, perennially frozen soil regions, and in artificial freezing projects. During freezing and thawing, soil undergoes complex phenomena such as moisture migration, temperature field reconstruction, ice crystal formation and melting, salt migration and crystallization, structural deformation, and the development of frost heave forces. These phenomena are interconnected and directly affect the stability and service performance of roads, railways, canals, slopes, foundations, pipelines, and agricultural soils in cold regions.

[0003] Existing freeze-thaw testing devices typically focus on temperature control, frost heave testing, or single water migration testing, making it difficult to simultaneously obtain multi-field responses of water, heat, force, and salt within the same soil column. While some devices can set upper and lower temperature boundaries, they are usually monolithic cylinders, requiring soil samples to be removed as a whole or through destructive cutting after the test, making it difficult to accurately correspond the sampling layer to the in-situ monitoring height. Although some devices have detachable structures, their sections are mainly used for processing, cleaning, transportation, or sample replacement, and do not form a synergistic structure with freeze-thaw temperature boundaries, sidewall sealing of sensor holes, upper boundary switching, and water-salt boundary regulation to target freeze-thaw water-salt migration.

[0004] Therefore, there is a need for a comprehensive testing device that does not simply divide the cylinder into segments, but designs the segmented cylinder into functional soil column units that correspond to each other in terms of sample loading, in-situ monitoring, boundary control, and post-test layered sampling, in order to meet the needs of studying the multi-field coupling mechanism of water, heat, force, and salt during freeze-thaw processes, testing engineering parameters, and verifying in-situ monitoring results. Summary of the Invention

[0005] To address the technical challenges of existing devices in simultaneously achieving functional segmented sampling and stratified sampling, switching between controllable one-dimensional temperature boundaries, mechanically constrained boundaries and open evaporation boundaries, water-salt boundary regulation, and in-situ monitoring-boundary flux-post-test sampling verification within the same soil column, this invention provides a segmented controllable temperature soil column multi-field coupled freeze-thaw test device and test method.

[0006] The objective of this invention is achieved through the following technical solution. The segmented, temperature-controlled soil column multi-field coupled freeze-thaw test device proposed in this invention includes a cylindrical assembly. The cylindrical assembly comprises several detachable, vertically sealed standard cylindrical sections and a piston cylindrical section located at the top of the standard cylindrical sections. A temperature-controlled piston is detachably installed inside the top of the piston cylindrical section. A permeable plate or filter layer is provided at the bottom of the cylindrical assembly, through which water or salt solution is supplied to the interior of the cylindrical assembly. The cylindrical assembly is mounted on a temperature control plate. Both the temperature control plate and the temperature-controlled piston have flow channels for circulating cooling media. Friction sensors are installed on the standard cylindrical sections and the piston cylindrical section. The temperature-controlled piston is connected to a loading mechanism. A pressure sensor is installed between the loading mechanism and the piston cylindrical section. A displacement sensor is installed on the temperature-controlled piston. The pressure sensor, displacement sensor, and friction sensor are all connected to a data acquisition unit via corresponding signal harnesses. The data acquisition unit is connected to a computer via corresponding signal harnesses. A heat insulation layer is installed on a detachable cover on the cylindrical assembly, the temperature control plate, and the temperature-controlled piston.

[0007] Compared with the prior art, the advantages of the present invention are: This invention differs from ordinary segmented structures in other technical fields that are only designed for ease of assembly, cleaning, maintenance, or transportation. It does not simply make the cylinder assembly a detachable structure, but rather uses the cylinder assembly, temperature control piston, and temperature control plate as the core structure. The cylinder assembly provides a detachable soil column structure that can be sampled according to a height benchmark. The upper temperature control piston and the lower temperature control plate establish a controllable one-dimensional temperature boundary. Sensors enable in-situ monitoring of multiple parameters along the process, allowing switching between mechanically constrained boundaries and open evaporation boundaries, and forming closed, open water replenishment, drainage, or salt solution replenishment boundaries. Within the same soil column, it achieves detachable sampling and stratified sampling, a controllable one-dimensional temperature field, in-situ monitoring of multiple parameters along the process, switching between mechanically constrained and evaporation boundaries, and various boundary condition combinations such as closed, open water replenishment, drainage, and salt solution replenishment.

[0008] Furthermore, both the standard cylinder section and the piston cylinder section are equipped with height lines, cylinder section numbers, sampling layer marks, and sensor installation marks distributed on their side walls.

[0009] Compared with the prior art, the advantages of the present invention are: This invention designs the cylindrical assembly as a functional monitoring and sampling unit corresponding to the sensor height, boundary conditions, and post-test sampling layer. Unlike ordinary segmented structures that are only used for disassembly, cleaning, or transportation, the segmented structure of this invention, together with the sensor aperture, upper and lower temperature boundaries, upper boundary module, lower water-salt boundary, and post-test stratified sampling, constitutes a special technical combination for freeze-thaw water thermo-salt coupling tests. This combination enables the segmented cylindrical assembly to have comprehensive functions such as determining the monitoring layer, determining the sampling layer, switching boundary conditions, and verifying data closure.

[0010] The structure of this invention is arranged collaboratively according to a unified soil column height coordinate, thereby obtaining multi-field response data of water, heat, force and salt within the same soil column. The in-situ monitoring results are verified by correspondingly verifying the results of stratified sampling after the experiment. It can provide a highly integrated, multifunctional, verifiable and repeatable experimental platform for research on cold region engineering, saline soil management, farmland freeze-thaw water and salt migration and artificial freezing.

[0011] Furthermore, the sensors along the path include thermocouple temperature sensors, soil three-parameter sensors, and soil matrix potential sensors.

[0012] Furthermore, the sidewalls of the standard cylinder section and the piston cylinder section are vertically distributed with several thermocouple temperature sensor holes for installing thermocouple temperature sensors. Near the middle position of the sidewalls of the standard cylinder section and the piston cylinder section, there are soil three-parameter sensor holes for installing soil three-parameter sensors and soil matrix potential sensor holes for installing soil matrix potential sensors. The thermocouple temperature sensors, soil three-parameter sensors, and soil matrix potential sensors are all sealed and passed through the sidewalls of the standard cylinder section and the piston cylinder section.

[0013] Compared with the prior art, the advantages of the present invention are: This invention uses a sidewall-sealed sensor hole that matches the height reference of the cylinder section to arrange thermocouples, matrix potential sensors and three-parameter sensors inside the soil column, thereby realizing in-situ monitoring of multiple parameters along the process and avoiding the loss of time information caused by relying solely on post-test sampling.

[0014] Furthermore, the temperature control panel includes a temperature control panel base and a temperature control panel cover plate stacked together. The upper surface of the temperature control panel base is provided with several concentric circular and interconnected annular flow channels. The lower surface of the temperature control panel cover plate is provided with a cover plate annular flow channel corresponding to the annular flow channels of the base. The annular flow channels of the base are connected to the cooling medium inlet and the cooling medium outlet. The cooling medium inlet is connected to the lower circulation inlet of the outer wall of the temperature control panel base. The cooling medium outlet is connected to the lower circulation outlet of the outer wall of the temperature control panel base. The lower circulation inlet and the lower circulation outlet are connected to the first cooling medium tank through corresponding first cooling medium pipes. A peristaltic pump is provided on the first cooling medium pipe.

[0015] Furthermore, the upper surface of the temperature control plate cover is provided with fluid holes that communicate with the permeable plate or filter layer. The fluid holes are connected to the first fluid interface on the outer wall of the temperature control plate cover. A valve is provided on the first fluid interface to deliver water or salt solution into the cylinder assembly or to discharge water or salt solution.

[0016] Compared with the prior art, the advantages of the present invention are: This invention establishes a controllable one-dimensional temperature boundary through an upper temperature-controlled piston, a lower temperature-controlled disc, and a removable side insulation layer, reducing radial heat exchange and improving the accuracy of temperature field control during the freeze-thaw process. Closed and open water supply, drainage, and salt solution supply boundaries are achieved through lower water supply, drainage, and salt solution interfaces and a permeable plate or filter layer, simulating various water-salt boundary conditions. These boundaries, combined with the upper piston or open evaporation boundary, form an experimental matrix.

[0017] Furthermore, the temperature control piston is provided with a second fluid interface that communicates with the interior of the cylinder assembly and is used to discharge water or salt solution.

[0018] Furthermore, the piston module is replaced with an open evaporation module, which includes a vent cover, a weighing device, and a humidity control device. The vent cover is installed on the piston cylinder section and has an evaporation port that communicates with the interior of the cylinder assembly. The temperature control panel is installed on the weighing device, and the humidity control device is installed in the environment where the cylinder assembly is located. Alternatively, the vent cover is replaced with a breathable membrane that covers the top of the cylinder assembly.

[0019] Compared with the prior art, the advantages of the present invention are: This invention improves the versatility of the device and reduces the initial soil sample differences caused by changing the cylinder by using a replaceable upper boundary component.

[0020] The segmented, temperature-controlled, multi-field coupled freeze-thaw test method for soil columns includes the following steps: Soil samples were prepared according to the test plan, and the initial moisture content, dry density, salt content and sample loading height were determined. A unified height coordinate table was established between the cylinder section number, cylinder section interface height, sensor height and sampling layer. Install the permeable plate or filter layer at the bottom of the cylinder assembly, and seal the standard cylinder section and piston cylinder section in sequence. Fill the soil sample according to the uniform height benchmark. Sensors along the path are arranged in a sealed manner according to a predetermined height; An insulation layer is installed on the outer periphery of the cylinder assembly, and a temperature control panel, temperature control piston, data acquisition unit, and sensor are connected to it. Select either a temperature-controlled piston or an open evaporation module according to the experimental objective, apply temperature and water-salt boundaries, and begin data acquisition. During the experiment, the data acquisition unit continuously collected and recorded the temperature, matrix potential, moisture content, electrical conductivity, frost heave force, frost heave amount, and boundary flux along the path. After the test, the insulation layer and the friction sensor were removed, the cylinder components were disassembled in sequence, and samples were taken in layers according to the cylinder section number, sensor height or predetermined thickness. Analyze stratified samples to achieve mutual verification of in-situ monitoring data, boundary flux data, and post-experimental measured data.

[0021] Furthermore, during the lower open water replenishment mode test, the first fluid interface is connected to the constant head device or water tank, and water enters the soil column through the permeable plate or filter layer; during the lower closed mode test, the first fluid interface is closed or sealed; during the lower drainage mode test, the first fluid interface is opened and connected to the drainage container or negative pressure device; during the upper evaporation mode test, the open evaporation module replaces the temperature control piston or directly removes the temperature control piston, allowing the top surface of the soil column to connect with the outside air or the set humidity environment; during the salt solution replenishment mode test, the first fluid interface is connected to the solution tank with the set salt solution concentration. When conducting soil frost heave force tests, a temperature-controlled piston is installed to limit the axial deformation of the soil column. The change of frost heave force over time is recorded by a pressure sensor, while the water, heat, and salt responses inside the soil column are recorded by a friction sensor. When conducting soil frost heave tests, a temperature-controlled piston is installed and allowed to move as the soil sample expands. The change in frost heave over time is recorded by a displacement sensor, along with the evolution of the temperature field, moisture field, matrix potential field, and electrical conductivity field. When conducting soil evaporation and freeze-thaw coupling tests, the temperature control piston is removed or replaced with an open evaporation module to form an upper evaporation boundary at the top of the soil column. The lower boundary of the soil column is controlled by the lower closed, open water replenishment or salt solution replenishment modes to obtain the coupled response of evaporation, freezing, thawing, water migration and salt migration. When conducting the salt solution replenishment test, the first fluid interface is connected to the solution tank, and a salt solution of a set concentration is replenished to the bottom of the soil column through a permeable plate or filter layer. After the test, the soil column is sampled in layers according to the segment height or the predetermined sampling thickness to verify the consistency between the salt distribution and the in-situ monitoring results of electrical conductivity.

[0022] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the purpose, features and advantages of the present invention more obvious and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the segmented, temperature-controlled soil column multi-field coupled freeze-thaw test device of the present invention; Figure 2 for Figure 1 Schematic diagram of the end face of the annular flow channel on the base of the medium temperature control panel; Figure 3 for Figure 1 A schematic diagram of a standard cylindrical section; Figure 4 for Figure 1Cross-sectional view of the annular flow channel of the base of the medium temperature control panel; Figure 5 for Figure 1 Cross-sectional view of the fluid interface on the base of the medium temperature control panel.

[0024] Figure label: 1. Fixing nut; 2. Upper fixing plate; 3. Displacement sensor; 4. Upper circulation inlet; 5. Pressure sensor; 6. Upper circulation outlet; 7. Soil three-parameter sensor hole; 8. Connecting flange; 9. Fastening screw; 10. Thermocouple temperature sensor; 11. Soil three-parameter sensor; 12. Lower circulation outlet; 13. Temperature control panel base; 14. First fluid interface; 15. Lower circulation inlet; 16. Temperature control panel cover; 17. Soil matrix potential sensor 18. Soil matrix potential sensor hole; 19. Piston cylinder section; 20. Temperature control piston; 21. Second fluid interface; 22. Data acquisition unit; 23. Computer; 24. Signal harness; 25. First cooling medium pipe; 26. First cooling medium tank; 27. First standard cylinder section; 28. Second standard cylinder section; 29. ​​Second cooling medium tank; 30. Second cooling medium pipe; 31. Solution pipe; 32. Solution tank; 33. Insulation layer; 34. Lower fixing plate.

[0025] 13-1 Fastening hole; 13-2 Cooling medium inlet hole; 13-3 Cooling medium outlet hole; 13-4 Annular flow channel of base.

[0026] 16-1, Annular flow channel of cover plate; 16-2, Fluid hole.

[0027] 27-1. Thermocouple temperature sensor hole. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0029] An embodiment of the segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns of the present invention is as follows: Figure 1 The diagram shown is a schematic of the device structure of this embodiment. The device includes a segmented sealed cylinder assembly, a replaceable upper boundary assembly, a temperature control panel, a friction sensor, a water-salt boundary assembly, an insulation layer 33, a data acquisition unit 22, and a computer 23.

[0030] The segmented sealing cylinder assembly includes a piston cylinder section 19, a first standard cylinder section 27, and a second standard cylinder section 28 stacked from top to bottom. The first standard cylinder section 27 and the second standard cylinder section 28 are both 120mm high and 100mm in diameter; the piston cylinder section 19 is 170mm high and 100mm in diameter. Each cylinder section (including the first standard cylinder section 27, the second standard cylinder section 28, and the piston cylinder section 19) is a cylindrical shape made of transparent plexiglass, acrylic, polycarbonate, stainless steel, or other materials with sufficient strength and low-temperature resistance. Adjacent cylinder sections can be connected by connecting flanges 8, threaded posts, clamps, and sealing rings to form the segmented sealing cylinder assembly, hereinafter referred to as the cylinder assembly. The cylinder assembly is used to contain soil samples and form a detachable soil column structure. The connecting flange 8 has structural holes, and sealing rings are installed between adjacent connecting flanges 8. Fastening bolts 9 pass through the structural holes of the connecting flange 8 and are secured with nuts to fix adjacent connecting flanges 8. Clamps are then fitted onto the connecting flanges 8 for further sealing and fixation, ensuring the sidewall sealing of the soil column during freezing, thawing, water replenishment, drainage, and salt solution replenishment. This allows the cylinder assembly to remain sealed during the test and to be disassembled afterward for stratified sampling and verification of indicators such as salt and moisture along the height of the cylinder assembly. In other embodiments, two or more standard cylinder sections can be provided as needed.

[0031] The structure of the cylinder assembly allows for layered sampling of the soil column before testing, based on predetermined dry density, moisture content, and salinity. After testing, each cylinder section can be disassembled sequentially, and samples can be taken layer by layer according to section height, sensor location height, or even a smaller thickness. The samples can be used to determine moisture content, conductivity, ion concentration, salinity, ice content, or other physicochemical indicators, and compared with data measured by the sensors for verification.

[0032] To enhance the correlation between the structure of the cylindrical assembly and the freeze-thaw water-salt test, each section is marked with height lines, section numbers, sampling layer marks, and sensor installation marks distributed on its sidewalls. This determines the embedment height of each thermocouple temperature sensor 10, soil three-parameter sensor 11, and soil matrix potential sensor 17 on the cylindrical assembly, facilitating comparison and verification of data obtained during and after the test. The height lines of the sections correspond to the sampling layers after the test. A standard section is preferably used as a monitoring and sampling unit, establishing a correspondence between its height lines, sensor hole positions, and the sampling layers after the test. Unlike ordinary segmented cylindrical assemblies used only for disassembly or cleaning, the sections in this embodiment simultaneously serve the functions of sample placement, sensor placement, sealing, and post-test layered sampling placement. Each section of the cylindrical assembly can be disassembled sequentially after the test, and layered sampling can be performed according to the section height lines, sensor heights, or predetermined sampling thicknesses to verify the spatial distribution of moisture, salt, temperature, conductivity response, or other physicochemical indicators within the soil column.

[0033] The connection interface between adjacent cylindrical sections can be equipped with positioning stops, alignment marks, or flush positioning surfaces with the inner wall. Annular sealing rings, double sealing rings, or other sealing and tightening structures can be installed between the connection interfaces to ensure continuous sealing of the inner wall after the cylindrical sections are connected. This, in turn, ensures the continuity of the soil column's inner wall, preventing leakage and reducing the impact of the connection on soil moisture migration, salt migration, and sampling integrity. The sidewall sealing sensor holes used for sensor installation are staggered from the cylindrical section connection interface to avoid interference between sensor installation and the cylindrical section sealing structure.

[0034] A lower fixed plate 34 is provided at the top of the piston cylinder section 19. The lower fixed plate 34 has holes corresponding to the piston cylinder section 19. The temperature control piston 20 is slidably disposed within the lower fixed plate 34 and the piston cylinder section 19. The lower temperature control plate is disposed at the bottom of the second standard cylinder section 28. The temperature control plate includes a temperature control plate base 13 and a temperature control plate cover 16. Soil is filled into the cylinder section assembly to form a soil column. The lower end of the soil column contacts the temperature control plate, and the upper end contacts the temperature control piston 20, which is used to establish a controllable temperature boundary. Both the upper temperature control piston 20 and the lower temperature control plate are provided with circulating heat exchange channels. The temperature control plate is connected to the first cooling medium tank 26 through the first cooling medium pipe 25. A peristaltic pump is provided on the first cooling medium pipe 25 to circulate the cooling medium between the first cooling medium pipe 25, the first cooling medium tank 26, and the temperature control plate. The first cooling medium tank 26 is connected to the corresponding temperature control system, which is used to control the temperature of the cooling medium in the first cooling medium tank 26. The temperature control piston 20 is connected to the second cooling medium tank 29 via the second cooling medium pipe 30, and the second cooling medium tank 29 is connected to the corresponding temperature control system. The temperature control system can control the temperature of the cooling medium according to constant temperature, linear cooling, stepped cooling, periodic freeze-thaw, or user-defined functions. The cooling medium is delivered to the corresponding temperature control plate or temperature control piston 20, thereby controlling the temperature at the upper and lower ends of the cylinder assembly to form the target temperature boundary.

[0035] Temperature control panel, such as Figure 2 , Figure 4 , Figure 5As shown, the upper surface of the temperature control panel base 13 is provided with a base annular flow channel 13-4. Multiple base annular flow channels 13-4 are distributed in concentric circles, and adjacent base annular flow channels 13-4 are connected by slots. The innermost base annular flow channel 13-4 is connected to the cooling medium inlet 13-2, and the cooling medium inlet 13-2 is connected to the lower circulation inlet 15. The outermost base annular flow channel 13-4 is connected to the cooling medium outlet 13-3, and the cooling medium outlet 13-3 is connected to the lower circulation outlet 12. The lower circulation inlet 15 and the lower circulation outlet 12 are respectively connected to the first cooling medium tank 26 through the corresponding first cooling medium pipe 25. The lower surface of the temperature control panel cover 16 is provided with a cover annular flow channel 16-1 corresponding to the base annular flow channel 13-4. The temperature control panel cover 16 is fixed to the temperature control panel base 13, and the base annular flow channel 13-4 and the cover annular flow channel 16-1 form a complete annular flow channel. A cooling medium at a certain temperature flows through an annular channel to control the temperature of the temperature control panel. A sealing ring is provided near the edge between the temperature control panel cover 16 and the temperature control panel base 13 to seal the interior of the temperature control panel.

[0036] Both the temperature control panel base 13 and the temperature control panel cover 16 are provided with several corresponding fastening holes 13-1. The fastening holes 13-1 are distributed circumferentially around the temperature control panel base 13 and the temperature control panel cover 16, avoiding the annular flow channel. One end of the fastening screw 9 is fixed in the fastening hole 13-1 of the temperature control panel base 13. The fastening screw 9 passes through the temperature control panel cover 16, the connecting flange, the lower fixed plate 34, and the upper fixed plate 2 located above the lower fixed plate 34 in sequence. The fastening screw 9 is engaged with the fastening screw 9 by a nut to fix the temperature control panel base 13 and the temperature control panel cover 16, fix the adjacent cylinder section, fix the upper fixed plate 34 on the piston cylinder section 19, and fix the top of the fastening screw 9 on the upper fixed plate 2 by a nut.

[0037] The internal structure of the temperature control piston 20 is similar to that of the temperature control disc. The temperature control piston 20 has internal flow channels, with both ends connected to the upper circulation inlet 4 and the upper circulation outlet 6, respectively. The upper circulation inlet 4 and the upper circulation outlet 6 are connected to the second cooling medium tank 29 via corresponding second cooling medium pipes 30. Cooling medium at a certain temperature flows through the flow channels to control the temperature of the temperature control piston 20.

[0038] The temperature control disc and temperature control piston 20 are equipped with circulating heat exchange channels to apply constant temperature boundaries, unidirectional freezing boundaries, bidirectional temperature control boundaries, periodic freeze-thaw boundaries, or temperature boundaries that vary according to a specified function to the upper and lower ends of the soil column. Through this structure, the axial temperature gradient of the soil column can be precisely controlled.

[0039] To reduce radial heat exchange, a removable insulation layer 33 is installed on the outer cover of the cylindrical assembly. The insulation layer 33 can be a single sleeve structure, or a multi-semi-ring or segmented spliced ​​structure, and can be secured using Velcro, clips, cable ties, clamps, or the outer shell. Insulation materials can include polyurethane, rubber-plastic insulation cotton, vacuum insulation panels, foam materials, or combinations thereof. During testing, the insulation layer 33 covers the outer perimeter of the cylindrical assembly, causing heat transfer within the soil column primarily along the axial direction, creating an approximately one-dimensional temperature field, thus improving the controllability of temperature boundary conditions and the repeatability of test results.

[0040] This invention utilizes friction-sensor insertion into a soil column for multi-parameter in-situ monitoring. The friction-sensor includes a thermocouple temperature sensor 10, a soil matrix potential sensor 17, and a soil three-parameter sensor 11, such as... Figure 1 and Figure 3 As shown, taking the first standard cylindrical section 27 as an example, the sidewall of the first standard cylindrical section 27 is provided with multiple sidewall sealing sensor holes, hereinafter referred to as sensor holes. The positions of the sensor holes match the distribution of the friction sensors, including soil three-parameter sensor holes 7, soil matrix potential sensor holes 18, and thermocouple temperature sensor holes 27-1. Several thermocouple temperature sensor holes 27-1 are distributed on the upper and lower sides of the cylindrical section. Thermocouple temperature sensors 10 are installed in the thermocouple temperature sensor holes 27-1, so that the thermocouple temperature sensors 10 on the first standard cylindrical section 27 are installed at 30mm intervals along the height of the soil column to obtain temperature profiles, temperature gradient evolution, melting process, and freezing front advancement process. The soil matrix potential sensor hole 18 is located near the middle of the sidewall of the cylindrical section 27, and a soil matrix potential sensor 17 is installed inside it to obtain water potential changes. Each cylindrical section is provided with one soil matrix potential sensor. A soil three-parameter sensor 11 is installed inside the soil three-parameter sensor hole 7. One soil three-parameter sensor 11 is installed in each cylinder section to simultaneously acquire temperature, moisture content, and electrical conductivity, thereby characterizing the water migration and salt migration processes. The cylinder sections, side wall sealed sensor holes, and friction-line sensor system of the cylinder assembly are arranged collaboratively according to a unified height benchmark, so that each cylinder section forms a monitoring and sampling unit corresponding to sample loading, in-situ monitoring, and post-test stratified sampling. This allows for the acquisition of multi-field response data of water, heat, force, and salt within the same soil column and stratified verification. The number and type of sensors inserted in the cylinder section can be set according to the data to be measured as needed in the experiment.

[0041] Each sensor hole is equipped with a sealing ring, a clamping joint, a threaded cap, potting compound, a removable blind plug, an insertion depth limiter, or a combination thereof. After the probe of each sensor passes through the corresponding sensor hole from the outside of the cylindrical assembly sidewall and is inserted into the soil column, the sensor rod is pressed against the hole wall by the sealing ring or sealed with potting compound, thus preventing leakage of liquid water, salt solution, or gas along the pores. Alternatively, the sensor probe passes through a clamping joint, which can be made of a flexible cylindrical material. The clamping joint is forcibly installed inside the sensor hole, and the inner wall of the sensor hole presses against the clamping joint, causing the clamping joint to press against the sensor rod, achieving a seal. To ensure the sensor is positioned correctly, a depth limiter is installed inside the sensor hole. The depth limiter is a rigid cylindrical structure with its outer wall matching the sensor hole. The inner wall of the depth limiter has a stopping step or boss that cooperates with the sensor rod to stop it. The insertion depth limiter controls the depth and direction of the sensor probe entering the soil column. The inner end of the depth limiting component matches the inner wall of the cylindrical assembly, reducing disturbance to the lateral boundary of the soil. A sealing ring, crimp joint, or potting compound can be provided at the outer end of the sensor hole. In other embodiments, a threaded cap can be provided on the sensor rod, fitted onto the rod and axially limiting it. Its outer wall is threaded to the sensor hole, and sealing rings are provided between the threaded cap, the sensor hole, and the rod. Depending on the experimental requirements, for sensor holes that are temporarily not needed, a removable blind plug can be used to seal the unused holes, reducing disturbance to the lateral boundary of the soil sample. The removable blind plug is inserted and fixed inside the sensor hole and matches it. The inner wall of the removable blind plug's end is an arc surface that matches the inner wall of the cylindrical assembly. A limiting platform is provided at the outer end of the removable blind plug, stopping against the outer wall of the cylindrical assembly to limit the installation of the removable blind plug. A sealing ring is provided between the removable blind plug and the inner wall of the sensor hole. The sensor can be removed when sampling the soil inside the cylindrical assembly.

[0042] All sensors are connected to the data acquisition unit 22 via corresponding signal harnesses 24. The data acquisition unit 22 performs time-synchronized data acquisition from all sensors and is connected to the computer 23 via the corresponding signal harnesses 24 for processing and analyzing the acquired sensor data. Temperature data can be used to determine the location of the freezing front and the temperature gradient; matrix potential and moisture content data can be used to determine the direction and intensity of water migration; electrical conductivity data can reflect the salt concentration, migration, and redistribution process; and force and displacement data can reflect the mechanical response of the soil column during the freeze-thaw process.

[0043] In this embodiment, the mechanically constrained boundary and the open evaporation boundary can be switched using a replaceable upper boundary component.

[0044] like Figure 1As shown, the replaceable upper boundary components include a piston module and an open evaporation module. The piston module can be installed on the upper part of the piston cylinder section 19. The lower fixed plate 34 is provided with an installation interface for detachably connecting the piston module. The piston module includes a temperature-controlled piston 20 and a pressure sensor 5, a displacement sensor 3, and a loading mechanism connected to the temperature-controlled piston 20. The pressure sensor 5 and the displacement sensor 3 are both located on the top of the temperature-controlled piston 20. The loading structure includes a force-transmitting screw, a threaded hole structure detachably set on the lower fixed plate 34, and a handle. The force-transmitting screw is vertically rotatably mounted on the top of the temperature-controlled piston 20, and the bottom end of the force-transmitting screw is rotatably mounted on the temperature-controlled piston 20. The force-transmitting screw passes upward through the lower fixed plate 34 and is threadedly connected to the threaded hole structure set on the lower fixed plate 34. The outer end of the force-transmitting screw is detachably connected to the handle. Rotating the handle can move the force-transmitting screw downward and push the temperature-controlled piston 20. For ease of operation, the handle is replaced with a wrench. The wrench rotates the force-transmitting screw to displace and fix the temperature-controlled piston 20. In other embodiments, the loading mechanism can be a linear motor or hydraulic cylinder mounted on the lower fixed plate 34. The output shaft of the linear motor or hydraulic cylinder is vertically mounted and detachably connected to the temperature-controlled piston 20, enabling it to push the temperature-controlled piston 20 downward and maintain its position. The temperature-controlled piston 20 can form an axial mechanical constraint boundary on the soil column. The pressure sensor 5 is located between the top of the temperature-controlled piston 20 and the force transmission screw. When the temperature-controlled piston 20 is locked in a fixed position or a constant displacement constraint is applied, the pressure sensor 5 can be used to measure the frost heave force. When the temperature-controlled piston 20 moves axially with the deformation of the soil sample and the displacement is recorded by the displacement sensor 3, the loading mechanism is disassembled, allowing the temperature-controlled piston 20 to move freely up and down, which can be used to measure the frost heave amount. When the loading mechanism uses a linear motor or hydraulic cylinder, the pressure sensor is located between the output shaft and the temperature-controlled piston. The loading mechanism can be detachably mounted on the mounting interface via a flange, quick-release locking piece, or threaded connection.

[0045] An open evaporation module can replace the piston module. The open evaporation module includes a vent cover and its evaporation port, a weighing device, and a humidity control device. The vent cover is mounted above the piston cylinder section 19 via an installation interface. The vent cover has a through-hole serving as the evaporation port, which communicates with a through-hole on the lower fixed plate 34. The internal soil column communicates with the external environment through the evaporation port. In other embodiments, the vent cover can be replaced with a breathable membrane, which directly covers the upper fixed plate 34, allowing the upper end of the soil column to communicate with the external air or a set humidity environment, thus forming an upper evaporation boundary. A temperature control plate is mounted on the weighing device. The evaporation rate can be obtained through weighing or water vapor flux measurement. Combined with data from the flow sensors, the coupling relationship between evaporation and freezing, thawing, moisture migration, and salt migration can be analyzed. The humidity control device can be located in the external environment to control the actual environment of the simulated soil column.

[0046] Both the piston module and the open evaporation module can be detachably mounted on the cylinder assembly, allowing for configuration as needed. Test personnel can switch boundary conditions without replacing the entire cylinder assembly. This structure enables the same soil column device to be used for various test scenarios, including mechanically constrained boundaries, open evaporation boundaries, and combinations of both with different water-salt boundaries below. It also reduces errors introduced by changes in the initial state of the cylinder or soil sample between different tests.

[0047] In other embodiments, the piston module can be removed directly, and the soil column can be exposed to the air directly through the opening at the top of the cylindrical assembly for open evaporation, without the need for an additional open evaporation module.

[0048] This invention establishes a lower water-salt boundary using a water-salt boundary assembly. The water-salt boundary assembly includes a first fluid interface 15, a second fluid interface 21, a water tank or solution tank 32 or a drainage container or negative pressure device, and a transmission pipe 31.

[0049] Fluid interfaces are provided at the bottom or on the temperature control panel of the cylinder assembly, and at the top or on the temperature control piston 20 of the cylinder assembly. The bottom or temperature control panel of the cylinder assembly is used for replenishing water or salt solution, and the top or temperature control piston 20 of the cylinder assembly is used for draining water or draining solution. In this embodiment, as shown... Figure 1 , Figure 5As shown, the first fluid interface 14 is located on the side wall of the temperature control panel cover 16, and the second fluid interface 21 is located on the top of the temperature control piston 20. The first fluid interface 14 and the second fluid interface 21 can be connected to the solution tank 32 or the water tank as needed. The solution tank 32 or the water tank is connected to the first fluid interface 14 and the second fluid interface 21 respectively through corresponding transmission pipes 31. Both transmission pipes 31 are equipped with peristaltic pumps, which are used to deliver water or solution into the cylinder assembly through the first fluid interface 14 and to discharge water or solution outward through the second fluid interface 21. The discharged water or solution can be sent into the solution tank 32 or the water tank through the corresponding transmission pipes 31. In order to avoid contamination of the discharged water or solution with the water or solution to be transported, the solution tank 32 or the water tank is equipped with a partition to separate the discharged water or solution from the water or solution to be transported. The solution tank or water tank is replenished or discharged according to its volume. The top of the temperature control panel cover 16 is provided with a fluid hole 16-2, which is connected to the fluid inlet interface 14. A fluid hole is also provided at the bottom of the temperature control piston, which communicates with the second fluid interface 21. A permeable plate or filter layer is nested inside the bottom of the cylinder assembly. A gap exists between the permeable plate or filter layer and the top surface of the temperature control panel cover 16, with a fluid hole 16-2 at the bottom of the gap, allowing the fluid hole 16-2 to communicate with the permeable plate or filter layer. When the first fluid interface 14 is connected to a solution tank or water tank, water or solution is supplied to the cylinder assembly through the permeable plate or filter layer. When the first fluid interface 14 is connected to a drainage container or negative pressure device, drainage or solution can be discharged through the permeable plate or filter layer, the fluid hole 16-2, and the first fluid interface 14. The permeable plate or filter layer can be composed of porous ceramic plates, sintered metal plates, filter paper, sand layers, geotextile, or combinations thereof, used to ensure uniform distribution of fluid entering or exiting the soil column at the bottom of the cylinder assembly and to prevent soil particle loss. In other embodiments, the first fluid interface 14 can be connected to a constant head device for water replenishment, or connected to a solution replenishment device for solution replenishment, and excess water or solution can be directly discharged through the second fluid interface 21. Valves are provided on both the first fluid interface 14 and the second fluid interface 21, and the water volume, solution volume, and replenishment rate can be controlled by a peristaltic pump, and the solution concentration in the solution tank can be configured as needed.

[0050] When the first fluid interface 14 is closed by the valve, the lower end of the soil column forms a closed lower section; when the first fluid interface 14 is connected to the water tank, a lower open water supply mode is formed; when the first fluid outlet 14 is connected to the drainage container or negative pressure device, a drainage mode is formed; when the first fluid interface 14 is connected to the solution tank 32, a salt solution supply mode is formed. In the salt solution supply mode, the solution concentration and flow rate can be set to simulate the freeze-thaw salt migration process under saline soil, salt solution infiltration, or groundwater supply conditions.

[0051] The aforementioned lower water-salt boundary can be used in combination with a piston module or an open evaporation module. For example, under conditions of open evaporation at the top and open water replenishment at the bottom, the upward movement of water and salt driven by evaporation can be simulated; under conditions of open evaporation at the top and salt solution replenishment at the bottom, the redistribution of salt under the combined effect of salt solution replenishment and evaporation freezing can be simulated; under conditions of upper piston constraint and lower closure, the frost heave force generated by freezing of closed water-bearing soil can be tested.

[0052] The data acquisition unit 22 is connected to the temperature sensor (in this embodiment, the temperature sensor is a thermocouple temperature sensor 10), matrix potential sensor 17, three-parameter sensor 11, pressure sensor 5, and displacement sensor 3 via signal harness 24. Flow meters are installed at the first fluid interface 14 and the second fluid interface 21, and the flow meters are connected to the data acquisition unit 22 via corresponding signal harnesses. The data acquisition unit 22 is electrically connected to the computer 23 to synchronously acquire and record the internal temperature, matrix potential, water content, electrical conductivity, frost heave force, frost heave amount, boundary temperature (measured by a temperature sensor near the temperature control plate and temperature control piston), and water replenishment or salt solution replenishment (measured by a flow meter) of the soil column. It also establishes the correspondence between sensor height, cylinder section number, sampling layer, and time series data to achieve synchronous acquisition and closure verification of multi-field response data within the same soil column.

[0053] In this embodiment, segmented monitoring and sampling closure verification can be performed. The cylindrical assembly is not merely for disassembly after the experiment, but rather for establishing the correspondence between "cylinder section—sensor—sampling layer". Before the experiment, the height of the upper and lower interfaces of each cylinder section, the burial depth of each sensor, and the replenishment conditions of the lower water-salt boundary are recorded. During the experiment, in-situ temperature, matrix potential, water content, conductivity, frost heave force, frost heave amount, and boundary flux are collected simultaneously. After the experiment, samples are taken layer by layer according to the cylinder section height or the layer adjacent to the sensor, and the water content, salt content, or ion concentration is measured. Through the above correspondence, the changes in in-situ conductivity, the salt distribution after the experiment, and the input amount of boundary salt solution can be cross-checked, thereby improving the reliability of the experimental results.

[0054] The types of experiments that can be performed by this invention are summarized as follows: Test type Implementation 1. Soil frost heave test Install the piston module and apply axial constraint to the piston. Use a pressure sensor to record the frost heave force of the soil sample during freezing, and use a friction sensor to record changes in temperature, moisture, matrix potential and electrical conductivity. 2. Soil frost heave test The piston is made axially movable, and the frost heave displacement of the soil sample is recorded by a displacement sensor to obtain the relationship between the frost heave amount and the changes in time and temperature boundary. 3. Testing of multi-field coupled water-thermal-mechanical-salt processes The synchronous response of temperature field, moisture field, matrix potential field, electrical conductivity field, frost heave force and frost heave amount is obtained through the upper temperature control piston, the lower temperature control plate, mechanical boundary, lower water-salt boundary and along-process sensor system. 4. Testing of the coupling process between soil evaporation and freeze-thaw cycles The piston module was replaced with an open evaporation module to form an evaporation boundary at the upper end. Combined with the lower closed or open water replenishment or salt solution replenishment boundary, the migration of freeze-thaw water salt driven by evaporation was studied. 5. Lower open water replenishment mode The lower first fluid interface is connected to a constant head device or water tank to simulate the process of replenishing the frozen soil column with groundwater or external water. 6. Lower closed mode The lower first fluid inlet is closed and sealed to simulate freezing, thawing, and frost heave behavior under conditions of no external water supply. 7. Top Evaporation Mode An open evaporation module is installed at the top, and the evaporation process is simulated and measured through ventilation, humidity control, or weighing. 8. Salt solution replenishment mode The lower first fluid interface is connected to a storage container for a salt solution of a set concentration, and provides the salt solution boundary to the soil column through a permeable plate or filter layer. 9. After the experiment, stratified sampling was performed to verify the salt distribution. After the test, the cylinder assembly was disassembled in sections, and samples were taken according to the sections or predetermined thickness to determine the salt content and water content, in order to verify the results of in-situ conductivity monitoring and water-salt migration analysis. 10. Segmented in-situ monitoring—post-test sampling and verification By establishing the correspondence between cylinder section number, sensor height, and sampling layer, the in-situ moisture content, conductivity, and temperature data are verified against the results of stratified sampling after the experiment. 11. Comparative Test of Fast Switching at Upper Boundary By replacing the piston module and the open evaporation module on the same piston cylinder section, the differences in hydrothermal salt response under mechanically constrained boundaries and open evaporation boundaries were compared. 12. Verification of water-salt mass balance The results of water and salt migration were closed-loop verification by combining the water replenishment volume, drainage volume, salt solution replenishment volume, changes in in-situ conductivity, and post-test salt distribution. In an embodiment of the segmented, temperature-controlled, multi-field coupled freeze-thaw test method for soil columns of the present invention, the test can be conducted using the device described above, as follows: Soil samples were prepared according to the test plan, and the initial moisture content, dry density, salt content and sample loading height were determined. A height coordinate table was also established for the cylinder section number, cylinder section interface height, sensor height and sampling layer. Install the permeable plate or filter layer at the bottom of the cylinder assembly, and seal the first standard cylinder section 27, the second standard cylinder section 28, and the piston cylinder section 19 in sequence. Fill the soil sample according to the uniform height benchmark. Thermocouple temperature sensor 10, soil matrix potential sensor 17 and soil three-parameter sensor 11 are arranged at a predetermined height and sealed and fixed through sensor holes. An insulation layer 33 is installed on the outer periphery of the cylinder assembly, and the temperature control panel is connected to the first cooling medium tank, the temperature control piston is connected to the second cooling medium tank, the data acquisition unit is connected to the sensor and computer, and the water-salt boundary assembly is connected to the temperature control panel and the temperature control piston. Select either the piston module or the open evaporation module according to the experimental objective, apply the temperature boundary and the water-salt boundary, and begin data acquisition. When conducting the lower open water replenishment mode test, the first fluid interface 14 is connected to the constant head device or water tank, and water can enter the soil column through the permeable plate or filter layer; when conducting the lower closed mode test, the first fluid interface 14 is closed or sealed; when conducting the lower drainage mode test, the first fluid interface 14 is opened and connected to the drainage container or negative pressure device; when conducting the upper evaporation mode test, the upper open evaporation module is installed to replace the piston module or the piston module is removed directly, so that the top surface of the soil column is connected to the outside air or the set humidity environment; when conducting the salt solution replenishment mode test, the first fluid interface 14 is connected to the solution tank with the set salt solution concentration. During the experiment, the data acquisition unit continuously recorded the temperature, matrix potential, water content, electrical conductivity, frost heave force, frost heave amount, and boundary flux (data corresponding to the temperature boundary and water-salt boundary) along the path. After the test, the insulation layer 33 and the sensor were removed, the cylinder components were disassembled in sequence, and samples were taken in layers according to the cylinder section number, sensor height or predetermined thickness. Layered samples can be used to determine moisture content and salt content, which can be used to verify conductivity monitoring results and salt distribution models. At the same time, by combining water replenishment, drainage and salt solution replenishment, moisture and salt mass balance can be checked, thereby realizing mutual verification between in-situ monitoring data, boundary flux data and post-experimental measured data.

[0055] During the sample loading, sensor installation, and post-test sampling process, a unified height coordinate table is established. The height coordinate table includes the cylinder section number, the position of the upper and lower interfaces of the cylinder section, the sensor burial height, the sampling layer number, and the sampling layer depth range.

[0056] When conducting soil frost heave force tests, a piston module is installed to limit the axial deformation of the soil column. The change of frost heave force over time is recorded by a pressure sensor, while the water, heat, and salt responses inside the soil column are recorded by a friction sensor system.

[0057] When conducting soil frost heave tests, a piston module is installed and the piston is allowed to move as the soil sample expands. The change in frost heave over time is recorded by a displacement sensor, along with the evolution of the temperature field, moisture field, matrix potential field, and electrical conductivity field.

[0058] When conducting soil evaporation and freeze-thaw coupling tests, the piston module is replaced with an open evaporation module to form an upper evaporation boundary at the top of the soil column. The lower boundary of the soil column is controlled by the lower closed, open water replenishment, or salt solution replenishment modes to obtain the coupled response of evaporation, freezing, thawing, water migration, and salt migration.

[0059] When conducting the salt solution replenishment test, the first fluid interface is connected to the solution tank, and a salt solution of a set concentration is replenished to the bottom of the soil column through a permeable plate or filter layer. After the test, the soil column is sampled in layers according to the segment height or the predetermined sampling thickness to verify the consistency between the salt distribution and the in-situ monitoring results of electrical conductivity.

[0060] Based on the changes in water replenishment, drainage, salt solution replenishment, in-situ conductivity, and post-test stratified sampling results before and after the experiment, a mass balance check for water and salt is established to determine the consistency between boundary conditions, in-situ monitoring results, and post-test sampling results.

[0061] In summary, this invention differs from ordinary segmented structures in other technical fields that are merely designed for ease of assembly, cleaning, maintenance, or transportation. It does not simply involve making the cylinder detachable; instead, it uses a segmented sealed cylinder assembly, an upper temperature-controlled piston, a lower temperature-controlled disc, a replaceable upper boundary assembly, and a lower water-salt boundary assembly as its core structure. The cylinder assembly provides a detachable soil column structure that can be sampled according to a height benchmark. The upper temperature-controlled piston and lower temperature-controlled disc establish a controllable one-dimensional temperature boundary. Sensors enable in-situ monitoring of multiple parameters along the process. The replaceable upper boundary assembly allows switching between mechanically constrained boundaries and open evaporation boundaries. The lower water-salt boundary assembly forms closed, open water replenishment, drainage, or salt solution replenishment boundaries. Within the same soil column, it achieves detachable sampling and stratified sampling, a controllable one-dimensional temperature field, in-situ monitoring of multiple parameters along the process, switching between mechanically constrained and evaporation boundaries, and various boundary condition combinations such as closed, open water replenishment, drainage, and salt solution replenishment. In particular, this invention designs the cylindrical assembly as a functional monitoring and sampling unit corresponding to the sensor height, boundary conditions, and post-test sampling layer. Unlike ordinary segmented structures used only for disassembly, cleaning, or transportation, the segmented structure of this invention, together with the sensor aperture, upper and lower temperature boundaries, upper boundary module, lower water-salt boundary, and post-test stratified sampling, constitutes a specialized technical combination for freeze-thaw water-thermal-salt coupling experiments. This combination enables the segmented cylindrical assembly to have comprehensive functions including monitoring layer determination, sampling layer determination, switchable boundary conditions, and data closure verification. The structure of this invention is arranged collaboratively according to a unified soil column height coordinate, thereby obtaining multi-field response data of water, heat, force, and salt within the same soil column. The in-situ monitoring results are then correlated and verified with the post-test stratified sampling results. This provides a highly integrated, multifunctional, verifiable, and repeatable experimental platform for research in cold region engineering, saline soil remediation, farmland freeze-thaw water-salt migration, and artificial freezing. The beneficial effects of this invention are summarized as follows: (1) The present invention forms a detachable soil column structure by segmented sealed cylinder assembly, and uses each standard cylinder section as a monitoring and sampling unit corresponding to sample loading, in-situ monitoring and post-test sampling; the structure is not simply easy to disassemble and assemble, but makes the monitoring height correspond to the sampling layer, which is convenient for verifying the spatial distribution of salt, moisture and other indicators.

[0062] (2) The present invention establishes a controllable one-dimensional temperature boundary by means of the upper temperature control piston, the lower temperature control plate and the side detachable insulation layer, thereby reducing radial heat exchange and improving the temperature field control accuracy of the freeze-thaw process.

[0063] (3) The present invention uses a sidewall-sealed sensor hole that matches the height reference of the cylinder section to arrange thermocouples, matrix potential sensors and three-parameter sensors inside the soil column, thereby realizing in-situ monitoring of multiple parameters along the process and avoiding the loss of time information caused by relying solely on post-test sampling.

[0064] (4) The present invention enables the same piston cylinder section to switch between piston mechanical constraint boundary and open evaporation boundary by replacing the upper boundary component, thereby improving the versatility of the device and reducing the difference in initial soil samples caused by replacing the cylinder.

[0065] (5) The present invention achieves closed and open water supply, drainage and salt solution supply boundaries through the lower water supply, drainage and salt solution interface and water permeable plate or filter layer, which can simulate a variety of water and salt boundary conditions and form an experimental matrix with the upper piston or open evaporation boundary.

[0066] (6) The present invention can simultaneously obtain multi-field response data of water, heat, force and salt in the same soil column, and realize data closure verification by the correspondence between the results of segmented sampling, boundary flux recording and in-situ conductivity monitoring.

[0067] (7) The present invention combines the cylindrical section assembly, side wall sealing monitoring, upper temperature boundary and lower temperature boundary, upper boundary rapid switching and lower water-salt boundary regulation into a special structure suitable for the freeze-thaw water-thermal-salt coupling process. Compared with ordinary integral test devices or other fields that only have detachable cylindrical structures, it can produce a synergistic technical effect of multi-field synchronous monitoring and post-test layer verification.

[0068] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns, comprising a cylindrical assembly, characterized in that: The cylindrical assembly includes several detachable, vertically sealed standard cylindrical sections and a piston section (19) located at the top of the standard cylindrical sections. A temperature control piston (20) is detachably installed inside the top of the piston section (19). A water permeable plate or filter layer is provided at the bottom of the cylindrical assembly, through which water or salt solution is supplied to the interior of the cylindrical assembly. The cylindrical assembly is mounted on a temperature control plate. Both the temperature control plate and the temperature control piston (20) are provided with flow channels for circulating cooling medium. A friction sensor is installed on both the standard cylindrical sections and the piston section (19). The temperature control piston (20) is connected to the loading mechanism. A pressure sensor (5) is installed between the loading mechanism and the piston cylinder section (19). A displacement sensor (3) is installed on the temperature control piston. The pressure sensor, displacement sensor, and friction sensor are all connected to the data acquisition unit (22) through the corresponding signal harness (24). The data acquisition unit (22) is connected to the computer (23) through the corresponding signal harness (24). A heat insulation layer (33) is installed on the removable cover of the cylinder assembly, temperature control plate, and temperature control piston (20).

2. The segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns according to claim 1, characterized in that: The standard cylinder section and piston cylinder section (19) are equipped with height lines, cylinder section numbers, sampling layer marks and sensor installation marks distributed on their side walls.

3. The segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns according to claim 1, characterized in that: The sensors along the path include a thermocouple temperature sensor (10), a soil three-parameter sensor (11), and a soil matrix potential sensor (17).

4. The segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns according to claim 3, characterized in that: The sidewalls of the standard cylinder section and piston cylinder section (19) are vertically distributed with several thermocouple temperature sensor holes (27-1) for installing thermocouple temperature sensors (10). Near the middle position of the sidewalls of the standard cylinder section and piston cylinder section (19) are provided soil three-parameter sensor holes (7) for installing soil three-parameter sensors (11) and soil matrix potential sensor holes (18) for installing soil matrix potential sensors (17). The thermocouple temperature sensor (10), soil three-parameter sensor (11) and soil matrix potential sensor (17) are all sealed and passed through the sidewalls of the standard cylinder section and piston cylinder section (19).

5. The segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns according to claim 1, characterized in that: The temperature control panel includes a temperature control panel base (13) and a temperature control panel cover (16) stacked together. The upper surface of the temperature control panel base (13) is provided with several concentric circular and interconnected base annular channels (13-4). The lower surface of the temperature control panel cover (16) is provided with a cover annular channel (16-1) corresponding to the base annular channel (13-4). The base annular channel (13-4) is connected to the cooling medium inlet (13-2) and the cooling medium outlet (13-3). The cooling medium inlet (13-2) is connected to the lower circulation inlet (15) of the outer wall of the temperature control panel base (13). The cooling medium outlet (13-3) is connected to the lower circulation outlet (12) of the outer wall of the temperature control panel base (13). The lower circulation inlet (15) and the lower circulation outlet (12) are connected to the first cooling medium tank (26) through the corresponding first cooling medium pipe (25). A peristaltic pump is provided on the first cooling medium pipe (25).

6. The segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns according to claim 5, characterized in that: The upper surface of the temperature control plate cover (16) is provided with a fluid hole (16-2) that communicates with the water permeable plate or filter layer. The fluid hole (16-2) is connected to the first fluid interface (14) on the outer wall of the temperature control plate cover (16). A valve is provided on the first fluid interface (14) to deliver water or salt solution into the cylinder assembly or to discharge water or salt solution.

7. The segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns according to claim 1, characterized in that: The temperature control piston (20) is provided with a second fluid interface (21) that communicates with the inside of the cylinder assembly and is used to discharge water or salt solution.

8. The segmented, temperature-controlled, multi-field coupled freeze-thaw test device for soil columns according to claim 1, characterized in that: The piston module is replaced with an open evaporation module, which includes a vent cover, a weighing device, and a humidity control device. The vent cover is set on the piston cylinder section (19), and the vent cover is provided with an evaporation port. The evaporation port is connected to the inside of the cylinder assembly. The temperature control plate is set on the weighing device, and the humidity control device is set in the environment where the cylinder assembly is located. Alternatively, the vent cover is replaced with a breathable membrane, which covers the top of the cylinder assembly.

9. A segmented, temperature-controlled soil column multi-field coupled freeze-thaw test method, characterized in that: Includes the following steps: Soil samples were prepared according to the test plan, and the initial moisture content, dry density, salt content and sample loading height were determined. A unified height coordinate table was established between the cylinder section number, cylinder section interface height, sensor height and sampling layer. Install the permeable plate or filter layer at the bottom of the cylinder assembly, and seal the standard cylinder section and piston cylinder section (19) in sequence, and fill the soil sample according to the uniform height benchmark; Sensors along the path are arranged in a sealed manner according to a predetermined height; An insulation layer (33) is installed on the outer periphery of the cylinder assembly, and a temperature control panel, a temperature control piston, a data acquisition unit, and a sensor are connected to it. Select either a temperature-controlled piston or an open evaporation module according to the experimental objective, apply temperature and water-salt boundaries, and begin data acquisition. During the experiment, the data acquisition unit continuously collected and recorded the temperature, matrix potential, moisture content, electrical conductivity, frost heave force, frost heave amount, and boundary flux along the path. After the test, the insulation layer (33) and the friction sensor were removed, the cylinder assembly was disassembled in sequence, and samples were taken in layers according to the cylinder section number, sensor height or predetermined thickness. Analyze stratified samples to achieve mutual verification of in-situ monitoring data, boundary flux data, and post-experimental measured data.

10. The segmented, temperature-controlled soil column multi-field coupled freeze-thaw test method according to claim 9, characterized in that: When conducting the lower open water replenishment mode test, the first fluid interface (14) is connected to the constant head device or water tank, and water enters the soil column through the permeable plate or filter layer; when conducting the lower closed mode test, the first fluid interface (14) is closed or sealed; when conducting the lower drainage mode test, the first fluid interface (14) is opened and connected to the drainage container or negative pressure device; when conducting the upper evaporation mode test, the open evaporation module replaces the temperature control piston or directly removes the temperature control piston, so that the top surface of the soil column is connected to the outside air or the set humidity environment; when conducting the salt solution replenishment mode test, the first fluid interface (14) is connected to the solution tank (32) with the set salt solution concentration; When conducting soil frost heave force tests, a temperature-controlled piston is installed to limit the axial deformation of the soil column. The change of frost heave force over time is recorded by a pressure sensor, while the water, heat, and salt responses inside the soil column are recorded by a friction sensor. When conducting soil frost heave tests, a temperature-controlled piston is installed and allowed to move as the soil sample expands. The change in frost heave over time is recorded by a displacement sensor, along with the evolution of the temperature field, moisture field, matrix potential field, and electrical conductivity field. When conducting soil evaporation and freeze-thaw coupling tests, the temperature control piston is removed or replaced with an open evaporation module to form an upper evaporation boundary at the top of the soil column. The lower boundary of the soil column is controlled by the lower closed, open water replenishment or salt solution replenishment modes to obtain the coupled response of evaporation, freezing, thawing, water migration and salt migration. When conducting the salt solution replenishment test, the first fluid interface is connected to the solution tank, and a salt solution of a set concentration is replenished to the bottom of the soil column through a permeable plate or filter layer. After the test, the soil column is sampled in layers according to the segment height or the predetermined sampling thickness to verify the consistency between the salt distribution and the in-situ monitoring results of electrical conductivity.

Images