Test device for measuring unsaturated permeability coefficient of saline soil

Abstract

The present invention discloses a test device for measuring the unsaturated permeability coefficient of saline soil. The test device includes a base, a sample assembly, a loading assembly, a water supply assembly, a drainage assembly, and a measuring assembly. The sample assembly is fixedly installed on the base, and the sample assembly has a first end and a second end arranged opposite to each other; the loading assembly is installed on the base, and the loading assembly is arranged toward the first end of the sample assembly; the water supply assembly includes a Martens flask and a water inlet component, and the Martens flask is connected to the first end of the sample assembly through the water inlet component to supply water to the saline soil sample; the drainage assembly includes a liquid accumulation bucket and a water outlet component, and the liquid accumulation bucket is connected to the second end of the sample assembly through the water outlet component to collect water seeping from the saline soil sample; the measuring assembly includes a weighing unit and multiple groups of sensing units, and the sensing units include a three-parameter sensor and a tensiometer. The sensing units are installed on the sample assembly to monitor the saline soil sample, and the weighing unit is used to monitor the weight of the Martens flask and the weight of the liquid accumulation bucket.

Description

Technical Field

[0001] The invention relates to the technical field of testing the permeability of porous materials, in particular to a test device for measuring the unsaturated permeability coefficient of saline soil. Background Art

[0002] Unsaturated soil is a three-phase medium consisting of soil, water, and air, with a saturation between 0 and 1. A certain amount of gas exists within the voids within the soil, making its properties significantly different from those of saturated soil. Unlike ordinary unsaturated soil, which contains no salt, unsaturated saline soil includes a salt phase in addition to the soil-water-air phase. The salt in the soil dissolves in the pore water under the influence of water flow, migrates with the flow, or crystallizes when the temperature drops. This makes the properties of unsaturated saline soil more complex, and its water-salt-mechanical coupling characteristics differ from those of ordinary unsaturated soil.

[0003] Current experimental equipment, such as conventional one-dimensional soil column seepage devices, calculates the hydraulic conductivity curves of unsaturated soils at varying matric suctions. These curves only consider the hydraulic properties of soils without salt content, but not conditions involving salt. Therefore, a test device for studying the unsaturated hydraulic conductivity of saline soils is urgently needed. Summary of the Invention

[0004] In order to solve at least one of the above technical problems, the present invention provides a test device for measuring the unsaturated permeability coefficient of saline soil, and the technical solution adopted is as follows:

[0005] The test device for measuring the unsaturated permeability coefficient of saline soil provided by the present invention includes a base, a sample assembly, a loading assembly, a water supply assembly, a drainage assembly, and a measuring assembly. The sample assembly is fixedly mounted on the base and is used to hold a saline soil sample to be tested. The sample assembly has a first end and a second end disposed opposite to each other. The loading assembly is mounted on the base and disposed toward the first end of the sample assembly. The loading assembly is used to apply a load to the saline soil sample. The water supply assembly includes a Martens flask and a water inlet. The Martens flask is connected to the first end of the sample assembly via the water inlet to supply water to the saline soil sample. The drainage assembly includes a liquid storage bucket and a water outlet. The liquid storage bucket is connected to the second end of the sample assembly via the water outlet to collect water seeping from the saline soil sample. The measuring assembly includes a weighing unit and multiple sets of sensing units. The sensing units include a three-parameter sensor and a tensiometer. The sensing units are mounted on the sample assembly to monitor the saline soil sample. The weighing unit is used to monitor the weight of the Martens flask and the weight of the liquid storage bucket.

[0006] In certain embodiments of the present invention, the loading assembly includes a driving member and a palm plate, wherein the driving member and the palm plate are connected via a ball screw pair, and the driving member drives the palm plate to apply a load to the saline soil sample to simulate the stress of soil layers at different depths.

[0007] In certain embodiments of the present invention, the loading device includes a displacement sensor, which is mounted on the palm plate and is used to record the axial deformation of the saline soil sample.

[0008] In certain embodiments of the present invention, the sample assembly includes an outer frame, eyebolts, and a cylindrical structure. Two cylindrical structures are provided, and the outer frame is fixed to the two cylindrical structures via the eyebolts.

[0009] In certain embodiments of the present invention, the sample assembly includes a flange, and the two cylindrical structures are sealed by the flange.

[0010] In certain embodiments of the present invention, the side wall of the cylindrical structure is provided with a plurality of mounting holes, which are arranged at equal intervals along the axial direction of the cylindrical structure, and the sensing unit is embedded in the saline soil sample through the mounting holes.

[0011] In certain embodiments of the present invention, each group of mounting holes includes a first hole position for inserting the tensiometer and a second hole position for inserting the three-parameter sensor, the first hole position and the second hole position have the same height, and the first hole position and the second hole position are symmetrically distributed on the side wall of the cylindrical structure.

[0012] In certain embodiments of the present invention, the water replenishment assembly includes a throttle valve, which is arranged between the Malchnitz flask and the water inlet, and is used to adjust the amount of precipitation on the top of the saline soil sample.

[0013] In certain embodiments of the present invention, the drainage assembly includes a stop valve, which is disposed between the water outlet and the liquid accumulation barrel, and is used to control the discharge of moisture from the saline soil sample.

[0014] In certain embodiments of the present invention, the test device includes a control component electrically connected to the measurement component, and the control component is used to monitor and display data involved in the test process and analyze the data.

[0015] Embodiments of the present invention have at least the following beneficial effects: the test device applies loads to soil samples via a loading assembly to simulate soil stress conditions at different depths. Simultaneously, a water supply assembly and a drainage assembly simulate rainfall infiltration. A three-parameter sensor and a tensiometer measure the volumetric moisture content, matrix suction, temperature, and electrical conductivity at the soil sample cross section. The unsaturated permeability coefficient of saline soil is then calculated using the wetting front advance method. This application is widely applicable to the research field of unsaturated saline soil. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0017] Figure 1 This is a schematic diagram of the connection of the test device for measuring the unsaturated permeability coefficient of saline soil;

[0018] Figure 2 for Figure 1 A schematic diagram of the structure of the test device provided;

[0019] Figure 3 for Figure 1 Schematic diagram of the structure of the three-parameter sensor in the provided test device;

[0020] Figure 4 for Figure 1 Schematic diagram of the tensiometer structure in the provided test setup.

[0021] Figure numerals: 100, sample assembly; 110, cylindrical structure; 120, outer frame; 130, flange; 140, lifting eye bolt; 210, driving member; 220, palm plate; 221, displacement sensor; 310, Martens flask; 320, throttle valve; 330, rainwater distribution plate; 410, liquid storage barrel; 420, water outlet member; 430, stop valve; 511, first weighing member; 512, second weighing member; 520, tensiometer; 521, clay head; 522, tensiometer tube body; 523, water potential sensor; 530, three-parameter sensor; 531, four-pronged probe; 532, sensing part; 600, control assembly; 700, base. DETAILED DESCRIPTION

[0022] The following combination Figures 1 to 4 Embodiments of the present invention are described in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and are not to be construed as limiting the present invention.

[0023] In the description of the present invention, it should be understood that if the terms "center", "middle", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "axial", "radial", "circumferential" and the like appear, the orientation or position relationship indicated is based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the present invention. The features defined as "first" and "second" are used to distinguish the feature names, and do not have special meanings. In addition, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0024] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0025] Unsaturated soil is a three-phase medium consisting of soil, water, and air, with a saturation between 0 and 1. A certain amount of gas exists within the voids within the soil, making its properties significantly different from those of saturated soil. Unlike ordinary unsaturated soil, which contains no salt, unsaturated saline soil includes a salt phase in addition to the soil-water-air phase. The salt in the soil dissolves in the pore water under the influence of water flow, migrates with the flow, or crystallizes when the temperature drops. This makes the properties of unsaturated saline soil more complex, and its water-salt-mechanical coupling characteristics differ from those of ordinary unsaturated soil.

[0026] Current experimental equipment, such as conventional one-dimensional soil column seepage devices, calculates the hydraulic conductivity curves of unsaturated soils at varying matric suctions. These curves only consider the hydraulic properties of soils without salt content, but not conditions involving salt. Therefore, a test device for studying the unsaturated hydraulic conductivity of saline soils is urgently needed.

[0027] The present invention relates to a test device for measuring the unsaturated permeability coefficient of saline soil. The test device includes a base 700, a sample assembly 100, a loading assembly, a water supply assembly, a drainage assembly, and a measuring assembly. The sample assembly 100 is fixedly mounted on the base 700. The sample assembly 100 is used to hold a saline soil sample to be tested. The sample assembly 100 has a first end and a second end that are relatively arranged. The loading assembly is mounted on the base 700 and is arranged toward the first end of the sample assembly 100. The loading assembly is used to apply a load to the saline soil sample. The water supply assembly includes a Marsh flask 310 and an inlet. The water supply assembly (Mahr flask 310) connects to the first end of the sample assembly 100 via the water inlet to replenish water to the saline soil sample. The drainage assembly includes a liquid storage bucket 410 and a water outlet 420. The liquid storage bucket 410 connects to the second end of the sample assembly 100 via the water outlet 420 to collect water seeping from the saline soil sample. The measurement assembly includes a weight measurement unit and multiple sensor units. The sensor units include a three-parameter sensor 530 and a tensiometer 520. The sensor units are installed in the sample assembly 100 to monitor the saline soil sample. The weight measurement unit is used to monitor the weight of the Mahr flask 310 and the liquid storage bucket 410. The test device applies loads to the soil sample through the loading assembly to simulate the stress conditions at different depths. Simultaneously, the water supply assembly and drainage assembly simulate rainfall infiltration. The three-parameter sensor 530 and tensiometer 520 measure the volumetric water content, matrix suction, temperature, and electrical conductivity at the soil sample cross section. The unsaturated permeability coefficient of the saline soil is then calculated using the wetting front advance method. This application is widely applicable to the research field of unsaturated saline soil.

[0028] Specifically, the weighing unit includes a first weighing piece 511 and a second weighing piece 512. The first weighing piece 511 is used to monitor the weight of the Martens flask 310 in real time, and the second weighing piece 512 is used to monitor the weight of the liquid storage bucket 410 in real time. The change in the amount of water in the sample assembly 100 is obtained by observing and reading the weight readings of the first weighing piece 511 and the second weighing piece 512.

[0029] Furthermore, the loading assembly includes a driver 210 and a palm plate 220. The driver 210 and the palm plate 220 are connected by a ball screw pair. The driver 210 drives the palm plate 220 to apply a load to the saline soil sample to simulate the forces acting on soil layers at different depths. Specifically, the palm plate 220 is also equipped with a pressure sensor to monitor the pressure applied by the loading assembly to the upper surface of the saline soil sample in real time, thereby improving test accuracy. It is understood that in other embodiments, the driver 210 and the palm plate 220 can also be connected by a threaded screw pair or a direct motor drive, so that the palm plate 220 presses down on the soil sample to simulate the forces acting on soil layers at different depths.

[0030] Furthermore, the loading assembly includes a displacement sensor 221 mounted on the palm plate 220. This displacement sensor 221 is used to record the axial deformation of the saline soil sample. It will be appreciated that the placement of the displacement sensor 221 on the palm plate 220 facilitates accurate and real-time reading of the axial deformation of the soil sample during wetting, enabling subsequent permeability coefficient calculation. In other embodiments, the axial deformation of the soil sample can also be read by, for example, providing a scale on the periphery of the sample assembly 100.

[0031] Furthermore, the sample assembly 100 includes an outer frame 120, eyebolts 140, and a cylindrical structure 110. Two cylindrical structures 110 are provided, and the outer frame 120 is fixedly installed with the two cylindrical structures 110 by the eyebolts 140. In conjunction with the accompanying drawings, the outer frame 120 and the cylindrical structure 110 are squeezed against each other by four eyebolts 140 to form a whole, which is placed inside the base 700. When removing the sample, it can be dragged out horizontally and then lifted or lifted away by the eyenuts. Specifically, an annular groove is provided on the top of the outer frame 120, and a rubber gasket is provided on the inner ring of the annular groove. The aperture of the annular groove is smaller than the outer diameter of the cylindrical structure 110, so that the outer frame 120 abuts against the cylindrical structure 110 and is further tightened by the eyebolts 140. In this embodiment, the outer frame 120 is made of stainless steel and the cylindrical structure 110 is made of organic glass. It can be understood that the sample assembly 100 includes a flange 130 , and the two cylindrical structures 110 are sealed by the flange 130 .

[0032] Furthermore, the sidewall of the cylindrical structure 110 is provided with multiple sets of mounting holes, arranged at equal intervals along the axial direction of the cylindrical structure 110. The sensing units are inserted into the saline soil sample through the mounting holes. Specifically, each set of mounting holes includes a first hole for inserting the tensiometer 520 and a second hole for inserting the three-parameter sensor 530. The first and second holes are at the same height and are symmetrically distributed along the sidewall of the cylindrical structure 110. It is understood that when the sensing units are not installed, the first and second holes should be sealed with corks to ensure the airtightness of the sample assembly 100.

[0033] With reference to the accompanying drawings, the tensiometer 520 includes a clay head 521 and a water potential sensor 523, which are connected by a tensiometer tube 522. It should be noted that to ensure the accuracy of the results, the tensiometer 520 should not be inserted into the soil sample for a long time, and the angle of insertion of each tensiometer 520 into the soil sample should be consistent. In this embodiment, the tensiometer 520 filled with deionized water is inserted into the saline soil sample at an angle perpendicular to the circumferential wall of the cylindrical structure 110. Specifically, the model of the tensiometer 520 is TEROS-31, and its measured water potential range is -85 to +50 kPa and the temperature range is -30 to +60°C.

[0034] With reference to the accompanying drawings, the three-parameter sensor 530 includes a four-pronged probe 531 and a sensing portion 532, model number Hydraprobe II. It measures volumetric water content in the range of 0 to 100%, temperature in the range of -20 to +50°C, and conductivity in the range of 0 to 1.5 S / m.

[0035] Furthermore, the water replenishment component includes a throttle valve 320, which is arranged between the Malchow flask 310 and the water inlet. The throttle valve 320 is used to adjust the amount of precipitation on the top of the saline soil sample. It can be understood that by adjusting the throttle valve 320 to simulate the state of saline soil under different degrees of rainfall infiltration, the unsaturated permeability coefficient of the saline soil can be calculated. Specifically, the water inlet is configured as a rainwater distribution plate 330, which is evenly provided with a number of water holes to evenly introduce deionized water into the saline soil sample. In some embodiments, permeable stones are also arranged between the rainwater distribution plate 330 and the upper surface of the soil sample to further balance the water flow on the upper surface of the saline soil sample.

[0036] Furthermore, the drainage assembly includes a shut-off valve 430, which is disposed between the water outlet component 420 and the liquid storage barrel 410. The shut-off valve 430 is used to control the drainage of water from the saline soil sample. It is understood that the shut-off valve 430 is provided to direct the seepage water from the sample assembly 100 to flow into the liquid storage barrel 410 for weighing. At the same time, the water flow discharged from the shut-off valve 430 is also an important indicator for determining whether the test has ended. The test is considered to be completed when the water flow from the shut-off valve 430 is uniform and continuous, and the weight of the liquid storage barrel 410 measured by the second weighing component 512 increases at the same rate per unit time. In this embodiment, the water outlet component 420 is configured as a permeable stone. Water seeping from the bottom of the soil sample is collected through the permeable stone and flows into the liquid storage barrel 410 via a pipeline and the shut-off valve 430. It is understood that in other embodiments, the water outlet component 420 can also be replaced with filter paper to achieve the penetration of water from the bottom of the soil sample.

[0037] Furthermore, the test apparatus includes a control assembly 600, which is electrically connected to the measurement assembly and is used to monitor, display, and analyze data related to the test process. In some embodiments, the control assembly 600 is also electrically connected to the driver 210 of the loading assembly, as well as the displacement sensor 221 and pressure sensor, allowing test personnel to directly read relevant parameters and perform operations such as pressurization through the control assembly 600. It is understood that to further enhance the overall coordination of the test apparatus, the throttle valve 320 and the shut-off valve 430 can be configured as solenoid valves and electrically connected to the control assembly 600.

[0038] The present invention also relates to a test method implemented based on the test device provided by the present invention, the test method comprising:

[0039] Filling the sample assembly 100 with a saline soil sample to be tested and applying an axial load to the upper surface of the saline soil sample;

[0040] Deionized water was introduced into the upper surface of the sample assembly 100 to simulate rainfall infiltration;

[0041] The tensiometer 520 and the three-parameter sensor 530 are used to obtain the matrix suction parameter, volumetric moisture parameter, temperature parameter, and electrical conductivity parameter at the cross section of the saline soil sample;

[0042] According to the volumetric moisture content parameter, the wetting front advance speed of the saline soil sample in the sample assembly 100 is obtained using the wetting front advance method;

[0043] According to the conductivity parameters, the salt concentration parameters in the pore water at the corresponding cross section of the saline soil sample are obtained;

[0044] According to the temperature parameters and salt concentration parameters, the seepage suction parameters at the corresponding cross section of the saline soil sample are obtained;

[0045] The unsaturated permeability coefficient of saline soil samples was obtained based on matrix suction parameters, wetting front advance speed, volumetric water content parameters and infiltration suction parameters.

[0046] Specifically, the salt concentration parameters in the pore water at the corresponding cross section of the saline soil sample are obtained based on the conductivity parameters. According to the Van Loon empirical formula, when the volumetric water content and conductivity of the cross section at a certain moment are known, the salt concentration in the pore water solution at this moment can be converted. The specific formula is:

[0047]

[0048] Among them, C l is the concentration of salt in pore water, σ a is the conductivity measured by the three-parameter sensor 530, θ u is the volumetric moisture content measured by the three-parameter sensor 530, Q is the relative dielectric constant of salt, which can be obtained by looking up the table when the type of salt is known, and A and B are two empirical parameters related to the soil type, which can be obtained by calibration before the formal test.

[0049] Furthermore, taking a certain section B in a saline soil sample as an example, the calculation formula for the unsaturated permeability coefficient is:

[0050]

[0051] Among them, k ave is the average permeability coefficient at section B during the time period t1 to t2, θ(h B ,t1) and θ(h B,t2) are the volumetric water contents at time t1 and time t2 at section B, θ i is the initial volumetric moisture content of the sample, γ w is the density of water, v is the speed of the wetting front, ψ(h B ,t1) and ψ(h B ,t2) are the total suction forces at section B at time t1 and time t2 respectively.

[0052] Furthermore, the total suction force is the sum of the osmotic suction force and the matrix suction force. The matrix suction force is read in real time by the tensiometer 520. The osmotic suction force is:

[0053] π=ξRTcφ

[0054] Where π is the osmotic suction, ξ is the number of ions that the solute can decompose, R is the generalized gas constant, T is the absolute temperature, c is the mass molar concentration of the solute, and φ is the osmotic suction coefficient.

[0055] Specifically, in the calculation formula of the penetration suction, ξ and R are known, T can be directly read by the three-parameter sensor 530, and c can be obtained from the aforementioned C l Obtained, φ is related to multiple factors such as the type, concentration, temperature, etc. of the solution. The present invention proposes an empirical formula based on the Debye-Hückel theory:

[0056]

[0057] Among them, u M and u X is the number of cations M and anions X in the chemical formula, z M and z X is the corresponding chemical valence, and m is the mass molar concentration. MX and C MX is an empirical parameter, where C MX It can be directly obtained by looking up the table, B MX and f are further calculated by Eq.

[0058] Specifically, B MX The calculation formula is:

[0059]

[0060] Among them, β MX (0) and β MX (1) It can be obtained by looking up the table, a = 2, I is the ionic strength, equal to ∑(m i z i 2 ) / 2.

[0061] The calculation formula for f is:

[0062]

[0063] Where A is the Debye-Hückel coefficient. When the absolute temperature T is 298K, the Debye-Hückel coefficient of the aqueous solution is 0.392; b is an empirical parameter, generally 1.2.

[0064] Furthermore, a first volumetric moisture content is preset. When the volumetric moisture content parameter of the three-parameter sensor 530 reaches the first volumetric moisture content, it is considered that the wetting front has reached the cross-section where the three-parameter sensor 530 is located. Identifying the wetting front by the volumetric moisture content at the cross-section measured by the three-parameter sensor 530 eliminates the human error caused by visual inspection in traditional test methods and breaks through the limitation that the wetting front cannot be observed due to the unclear dry-wet boundary of the soil sample. Specifically, the monitoring of the volumetric moisture content can be observed and recorded regularly by the test personnel, or it can be automatically identified and recorded by the preset program of the control component 600. It can be understood that the first volumetric moisture content should be selected to be greater than the initial moisture content of the soil sample and less than the saturated moisture content of the soil sample.

[0065] Specifically, obtaining the wetting front advance speed based on the volumetric moisture content parameter includes fitting a curve of the relationship between the wetting front advance distance and time based on the time when the three-parameter sensor 530 reaches the first volumetric moisture content and the coordinates of the cross section along the height direction of the soil sample, and deriving the wetting front advance speed. The specific formula is:

[0066]

[0067] Wherein, h is the distance that the wetting front advances from the top of the sample to the cross section where the three-parameter sensor 530 is located, and t is the time taken by the wetting front to advance this distance.

[0068] Furthermore, during the soil filling process, the three-parameter sensor 530 is inserted into the sample assembly 100 and pressed along with the soil sample, ensuring full contact between the probes of the three-parameter sensor 530 and the soil sample. It will be appreciated that during the insertion process of the three-parameter sensor 530, the four-pronged probe 531 of each three-parameter sensor 530 should be kept in the same orientation to eliminate errors in identifying the wetting front based on volumetric moisture content and improve test accuracy.

[0069] Furthermore, during the soil filling process, a steel needle is pre-embedded at the insertion position of the tensiometer 520. When the wetting front is about to reach the cross section where the tensiometer 520 is located, the pre-embedded steel needle is removed and the tensiometer 520 filled with deionized water is inserted. It is understood that the tensiometer 520 should not be inserted into the soil sample for a long time. Therefore, the steel needle is pre-embedded before the tensiometer 520 is inserted into the soil sample to ensure the airtightness of the sample assembly 100. At the same time, the insertion position of the tensiometer 520 is reserved, so that the tensiometer 520 can be quickly inserted into the saline soil sample at a specified angle for measurement before the wetting front arrives.

[0070] Furthermore, when filling the sample assembly 100 with saline soil samples, the sample assembly 100 is filled in layers, and the filling height and compaction degree of the soil sample are determined according to the test requirements. It is understood that the test method provided by the present invention is also applicable to measuring the permeability coefficient of unsaturated soil without salt. That is, the soil sample can be a normal soil sample or a saline soil sample, and the size of the soil sample matches the cylindrical structure 110 of the sample assembly 100.

[0071] Furthermore, after the soil sample is filled, permeable stones are placed on the upper surface of the soil sample, and the permeable stones are covered with rainwater distribution plates 330. It can be understood that the rainwater distribution plates 330 and permeable stones are immediately installed so that the loading assembly can evenly apply load to the surface of the saline soil sample.

[0072] Next, the loading assembly is activated, and the driver 210 drives the palm plate 220 down until it contacts the rainwater distribution plate 330. A load is then applied to the saline soil sample according to the test requirements. Deionized water is introduced after the axial displacement of the sample stabilizes. Specifically, the axial displacement of the soil sample is monitored by reading the displacement sensor 221 in the sample assembly 100. It will be appreciated that in some embodiments, the displacement sensor 221 is electrically connected to the control assembly 600 to monitor and record the axial displacement of the soil sample, facilitating subsequent curve generation and result calculation.

[0073] Furthermore, before using the tensiometer 520 , the clay head 521 of the tensiometer 520 is subjected to a degassing process to remove the gas dissolved in water in the clay head 521 , so as to improve the accuracy of the result of measuring the matrix suction by the tensiometer 520 .

[0074] The content of the present invention is described in detail below with reference to a specific embodiment. It should be noted that the following description is only for illustrative purposes and is not a specific limitation to the invention.

[0075] Before the test began, a saline soil sample was layered and compacted within the two overlapping plexiglass cylinders 110. The filling height and compaction level were adjusted according to the test plan. During the sample filling process, a three-parameter sensor 530 was inserted into the second hole, and a steel needle was pre-embedded in the first hole. After the sample was prepared, a permeable stone was placed on the upper surface of the soil sample, covered with a rainwater distribution plate 330. The driver 210 was activated, forcing the palm plate 220 toward the soil sample until the displacement sensor 221 and pressure sensor at the bottom of the palm plate 220 contacted the rainwater distribution plate 330. Axial pressure was then applied to the top of the soil column according to the test requirements. Once the axial displacement stabilized, the throttle valve 320 was opened, allowing the deionized water in the Malchow flask 310 to flow through the pipeline, the rainwater distribution plate 330, and the permeable stone to the top of the soil column, and the test began. The throttle valve 320 was adjusted to precisely control the amount of precipitation.

[0076] During the test, the wetting front advances downward along the height of the soil column over time. When it approaches the section where the first tensiometer 520 is located, the pre-embedded steel needle in the soil sample is removed and replaced with a tensiometer 520 filled with deionized water for measurement. The pre-embedded steel needle is then replaced with a tensiometer 520 at each section where the three-parameter sensor 530 is located, until the wetting front has passed through the entire soil column. The test ends when a continuous and uniform flow of water is observed from the stop valve 430 at the bottom of the soil sample and the reading of the second weight measuring element 512 increases consistently over a period of time.

[0077] The present invention calculates the salt concentration of pore water in the soil at the cross section based on the Van Loon empirical formula, and then converts the salt concentration into the seepage suction of the soil at the cross section through the van der Waals formula and the Debye-Hückel theory. Combined with the matrix suction, temperature, volume moisture content measured by the measurement component and the calculated wetting front advance speed and other parameters, a relationship curve between the unsaturated permeability coefficient and the total suction is obtained. At the same time, the changes in electrical conductivity at each cross section are analyzed to study the water and salt migration law of saline soil under rainfall conditions.

[0078] Throughout this specification, references to "one embodiment," "some examples," "some embodiments," "illustrative embodiments," "examples," "specific examples," or "some examples" refer to specific features, structures, materials, or characteristics described in conjunction with the embodiment or example in at least one embodiment or example of the present invention. In this specification, the illustrative use of these terms does not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0079] The embodiments of the present invention are described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. A test device for measuring the unsaturated permeability coefficient of saline soil, characterized in that: include: Base (700); A sample assembly (100), the sample assembly (100) is fixedly mounted on the base (700), the sample assembly (100) is used to contain a saline soil sample to be tested, and the sample assembly (100) has a first end and a second end that are arranged opposite to each other; a loading assembly, the loading assembly being mounted on the base (700), the loading assembly being disposed toward the first end of the sample assembly (100), and being used to apply a load to the saline soil sample; A water replenishment component, the water replenishment component comprising a Malvern flask (310) and a water inlet, the Malvern flask (310) being connected to the first end of the sample assembly (100) via the water inlet to replenish water to the saline soil sample; A drainage assembly, the drainage assembly comprising a liquid collection barrel (410) and a water outlet (420), the liquid collection barrel (410) being connected to the second end of the sample assembly (100) via the water outlet (420) to collect water seeping out of the saline soil sample; A measuring assembly, the measuring assembly comprising a weighing unit and a plurality of sensor units, the sensor units comprising a three-parameter sensor (530) and a tensiometer (520), the sensor units being installed on the sample assembly (100) to monitor saline soil samples, and the weighing unit being used to monitor the weight of the Malchnitz flask (310) and the weight of the liquid storage bucket (410); The loading assembly comprises a driving member (210) and a palm plate (220), wherein the driving member (210) and the palm plate (220) are connected via a ball screw pair, and the driving member (210) drives the palm plate (220) to apply a load to a saline soil sample to simulate the stress of soil layers at different depths; The sample assembly (100) comprises an outer frame (120), a lifting eye bolt (140), and a cylindrical structure (110). Two cylindrical structures (110) are provided. The outer frame (120) is fixedly mounted to the two cylindrical structures (110) via the lifting eye bolt (140). The side wall of the cylindrical structure (110) is provided with multiple groups of mounting holes. The multiple groups of mounting holes are arranged at equal intervals along the axial direction of the cylindrical structure (110). The sensing unit is embedded in the saline soil sample through the mounting holes. Each group of mounting holes comprises a first hole position for inserting the tensiometer (520) and a second hole position for inserting the three-parameter sensor (530). The first hole position and the second hole position have the same height. The first hole position and the second hole position are symmetrically distributed on the side wall of the cylindrical structure (110).

2. The test device for measuring the unsaturated permeability coefficient of saline soil according to claim 1, characterized in that: The loading assembly comprises a displacement sensor (221), the displacement sensor (221) being mounted on the palm plate (220), and the displacement sensor (221) being used to record the axial deformation of the saline soil sample.

3. The test device for measuring the unsaturated permeability coefficient of saline soil according to claim 1, characterized in that: The sample assembly (100) includes a flange (130), and the two cylindrical structures (110) are sealed by the flange (130).

4. The test device for measuring the unsaturated permeability coefficient of saline soil according to claim 1, characterized in that: The water replenishment component comprises a throttle valve (320), which is arranged between the Malchnitz flask (310) and the water inlet component, and is used to adjust the amount of precipitation on the top of the saline soil sample.

5. The test device for measuring the unsaturated permeability coefficient of saline soil according to claim 4, characterized in that: The drainage assembly comprises a stop valve (430), which is arranged between the water outlet member (420) and the liquid accumulation barrel (410), and is used to control the discharge of water inside the saline soil sample.

6. The test device for measuring the unsaturated permeability coefficient of saline soil according to any one of claims 1 to 5, characterized in that: The test device comprises a control component (600), wherein the control component (600) is electrically connected to the measurement component, and the control component (600) is used to monitor and display data involved in the test process and to analyze the data.

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