An indoor test device for testing the water migration characteristics of frozen soil

Abstract

The utility model relates to the field of highway subgrade soil body characteristic test, concretely relates to a kind of indoor test device for testing permafrost water migration characteristic.The utility model is along the height direction interval arrangement moisture temperature sensor on soil sample test cylinder, for detecting the moisture and temperature change condition of different position soil sample in soil sample test cylinder;Through water supplementing device simulation subgrade groundwater condition, make the water of bottom can be infiltrated into upper layer soil sample by capillary phenomenon, simulation subgrade soil body moisture migration process;Through setting cooling disc at the top of soil sample, and cooling disc is connected with temperature control device, the temperature of top of soil sample is controlled by temperature control device, provides freeze-thaw cycle condition, simulation subgrade ambient temperature, the displacement of cooling disc is detected by displacement sensor simultaneously, researches the influence change of soil sample volume by temperature and moisture, reveals the influence law of soil body freezing depth and moisture migration characteristic.

Description

Technical Field

[0001] This utility model relates to the field of highway subgrade soil property testing, and in particular to an indoor testing device for testing the water migration characteristics of frozen soil. Background Technology

[0002] In seasonally frozen soil regions, the cold winter causes frost heave in the roadbed soil. In the following spring, as the ice crystals in the surface of the roadbed begin to melt, the pore water in the soil cannot drain away immediately, weakening the foundation soil and essentially causing it to lose its bearing capacity. Under vehicle vibration loads, this easily leads to frost heave and mudslides, severely impacting urban and rural transportation. Especially in areas with deep frost and shallow groundwater levels, such as the Qinghai-Tibet Plateau, Northeast China, Northwest China, and Inner Mongolia, road frost damage severely affects economic development in these regions.

[0003] Moisture migration in permafrost refers to the migration of capillary and film water induced by temperature gradients during the freezing process, and is a major factor inducing road damage in seasonally frozen areas. Due to the complex and variable environment of highways in seasonally frozen areas and the numerous external influencing factors, it is difficult to accurately capture and understand the characteristics of moisture migration in permafrost using on-site monitoring instruments. Therefore, it is necessary to provide an indoor testing device to test and understand the characteristics of moisture migration in permafrost by simulating freeze-thaw cycles indoors, thus providing a theoretical basis for the prevention and control of highway frost damage. Utility Model Content

[0004] The purpose of this invention is to overcome the shortcomings of existing technologies that use on-site monitoring instruments to capture the water migration characteristics of roadbed permafrost in seasonally frozen areas, which are easily affected by the external environment and have low accuracy. This invention provides an indoor testing device for testing the water migration characteristics of permafrost, which can test the water migration characteristics of roadbed soil under freeze-thaw cycle conditions and reduce the influence of the external environment.

[0005] This utility model provides an indoor testing device for testing the water migration characteristics of frozen soil, comprising:

[0006] A soil sample test tube is used to hold soil samples. The side walls and top port of the soil sample test tube are covered with thermal insulation material.

[0007] A cooling plate is located inside the soil sample test tube. The cooling plate is used to contact the top surface of the soil sample and is sealed to the inner wall of the soil sample test tube. The cooling plate is provided with a liquid storage chamber, which is connected to an inlet and an outlet.

[0008] A temperature control device is connected to the liquid inlet and the liquid outlet respectively, and the temperature control device is used to provide refrigerant to the liquid storage chamber;

[0009] A displacement sensor is used to detect the vertical displacement of the cooling plate;

[0010] Moisture and temperature sensors are used to detect the temperature and moisture content of soil samples. The moisture and temperature sensors are arranged at intervals along the height direction of the soil sample test tube.

[0011] A water supply device is used to supply water to the soil sample test tube;

[0012] The computer is connected to the displacement sensor, temperature sensor, and moisture sensor, respectively.

[0013] This scheme uses displacement and temperature sensors spaced along the height of the soil sample test cylinder to detect changes in moisture and temperature at different locations within the cylinder. A water replenishment device simulates groundwater conditions in the roadbed, allowing water from the bottom to seep into the upper soil sample via capillary action, simulating the water migration process in the roadbed soil. A cooling plate with a liquid storage chamber is installed at the top of the soil sample, with the inlet and outlet connected to a temperature control device. The temperature control device supplies refrigerant to the storage chamber, and the refrigerant continuously circulates between the cooling plate and the temperature control device, achieving cooling through its state changes. This regulates the temperature at the top of the soil sample, providing freeze-thaw cycle conditions to simulate the roadbed environment temperature. Simultaneously, by detecting the displacement of the cooling plate using displacement sensors, the influence of temperature and moisture on the soil sample volume can be studied, revealing the relationship between soil freezing depth and water migration characteristics.

[0014] Preferably, the water replenishment device includes a water tank and a water level control system. The water tank is connected to the water level control system, which controls the water level in the water tank. The soil sample test cylinder is located inside the water tank, and its bottom is connected to the water tank. The water level control system adds a quantitative amount of water to the water tank to control the water level in the soil sample test cylinder.

[0015] Preferably, the water level control system includes a Marshall bottle, which is connected to the water tank via a connecting pipe, and the connecting pipe is equipped with a switch valve. The switch valve controls the amount of water flowing from the Marshall bottle to the water tank.

[0016] Preferably, the port of the water tank is provided with a waterproof plastic membrane for sealing, reducing water evaporation and heat loss.

[0017] Preferably, the bottom of the soil sample test tube is provided with a pad, and the pad is provided with filter paper to prevent the soil sample from directly contacting the water in the water tank. The water in the water tank can seep in through the filter paper.

[0018] Preferably, a rigid crossbeam is provided above the soil sample test tube, and support rods are provided at both ends of the rigid crossbeam. The displacement sensor is connected to the rigid crossbeam and is in contact with the cooling plate.

[0019] Preferably, the rigid crossbeam is slidably connected to the support rod, and nuts are provided on both the upper and lower sides of the rigid crossbeam, with the nuts threadedly connected to the support rod. This design allows for a detachable connection between the rigid crossbeam and the support rod, facilitating installation and disassembly. By adjusting the nuts, the height of the steel box crossbeam can be adjusted, allowing the displacement sensor to be positioned at a suitable height so that the displacement sensor probe can contact the cooling plate. This design offers flexible adjustment and good adaptability to various working conditions.

[0020] Preferably, the temperature control device employs a low-temperature thermostatic bath, which can provide the user with a controlled, uniform, and constant temperature environment suitable for various experiments and tests. Preferably, silicone sealant is provided between the cooling plate and the side wall of the soil sample test tube to achieve a seal.

[0021] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0022] The indoor testing device provided by this invention can be used to determine and study the influence of freeze-thaw history on the freezing depth, temperature gradient, total inflow and inflow of subgrade soil during the freezing process, to understand the characteristics of water migration, and to reduce the influence of the external environment during the test and improve the accuracy of the test results. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of an indoor test apparatus for testing the water migration characteristics of frozen soil, as described in the embodiment.

[0024] Figure 2 This is a longitudinal cross-sectional view of the cooling plate;

[0025] Figure 3 This is a schematic diagram of the planar structure of the cooling plate.

[0026] The markings in the diagram are: 1-Low-temperature constant temperature bath; 2-Rigid crossbeam; 3-Rubber tube; 4-Support rod; 5-Insulation material; 6-Moisture temperature sensor; 7-Plastic film; 8-Water tank; 9-Displacement sensor; 10-Cooling plate; 101-Liquid inlet; 102-Liquid outlet; 103-Handle; 104-Liquid storage chamber; 11-Soil sample test tube; 12-Soil sample; 13-Plate; 14-Marsh flask; 15-Moisture temperature acquisition card; 16-Computer; 17-Displacement acquisition card. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to specific embodiments. However, it should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0028] Unless otherwise specified, the use of terms such as "upper," "lower," "left," "right," "center," "inner," and "outer" to indicate orientation or positional relationships in the description of specific embodiments of this utility model is based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationship in which the utility model product / equipment / device is typically placed during use. These terms are merely for the purpose of facilitating the description of the utility model solution or simplifying the description in specific embodiments, enabling those skilled in the art to quickly understand the solution, and do not indicate or imply that a specific device / component / element must have a specific orientation, or be constructed and operated in a specific positional relationship. Therefore, they should not be construed as limitations on this utility model.

[0029] Furthermore, the use of terms such as "horizontal," "vertical," "suspended," and "parallel" does not imply that the corresponding device / component / element must be absolutely horizontal, vertical, suspended, or parallel, but rather that it can be slightly tilted or have a deviation. For example, "horizontal" merely means that its direction is more horizontal relative to "vertical," not that the structure must be completely horizontal, but can be slightly tilted. Alternatively, it can be simplified to mean that the corresponding device / component / element, when set in a "horizontal," "vertical," "suspended," or "parallel" direction, can have an error / deviation of ±10% relative to the corresponding direction, more preferably within ±8%, more preferably within ±6%, more preferably within ±5%, and more preferably within ±4%. As long as the corresponding device / component / element is within the error / deviation range, it can still achieve its function in the present invention.

[0030] Furthermore, the use of terms such as "first," "second," and "third" in terminology is merely for distinguishing descriptions of identical or similar components and should not be interpreted as emphasizing or implying the relative importance of a particular component.

[0031] Furthermore, in the description of the embodiments of this utility model, "several", "multiple", and "several" represent at least two. The number can be any number, such as two, three, four, five, six, seven, eight, or nine, and can even exceed nine.

[0032] Furthermore, in the description of the technical solution of this utility model, unless otherwise explicitly specified / limited / restricted, the terms "set up," "install," "connect," "link," "equipped with," "laid out," and "arranged" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to common connection methods in the art, such as welding, riveting, bolting, and threaded connections. Such connections can be mechanical, electrical, or communication connections; they can be direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components.

[0033] Example

[0034] like Figure 1 As shown, an indoor testing device for testing the water migration characteristics of frozen soil includes a soil sample test cylinder 11, a cooling plate 10, a temperature control device, a data acquisition system, a water replenishment device, and a computer 16. The data acquisition system includes a displacement sensor 9, a moisture temperature sensor, a moisture temperature acquisition card 15, and a displacement acquisition card 17. The displacement sensor 9 is connected to the displacement acquisition card 17, and the displacement acquisition card 17 is connected to the computer 16. The moisture temperature sensor is connected to the moisture temperature acquisition card, and the moisture temperature acquisition card 15 is connected to the computer 16.

[0035] In this embodiment, the displacement sensor 9 can be a KTR-150mm self-resetting displacement sensor with a range of 150mm, an accuracy of ±0.1%, and a sensitivity of 1, featuring high accuracy, good sensitivity, and continuous durability. The displacement acquisition card uses a USB 2.0-4-20AD data acquisition unit, configured with an SQL 2000 PERSONAL data acquisition library on the computer, and connected to the displacement sensor. The displacement sensor collects the frost heave deformation displacement of the soil in real time during the freezing process. The collected data is transmitted to the data acquisition library for storage and is extracted once after the test is completed. It is set to collect data once every 5 minutes. The moisture and temperature sensor is used to collect soil temperature and moisture content. It is a model SM2802B with a temperature measurement range of -30℃ to +70℃, an accuracy of ±0.5℃, and a moisture measurement error of ±1%. An SR3201B-16 channel soil moisture recorder is used, connected to the moisture and temperature sensor with an RS485 conversion interface, to realize integrated online monitoring and recording of soil temperature and moisture. It is set to collect data once every 10 minutes.

[0036] In the indoor testing apparatus of this embodiment, the soil sample test cylinder 11 is used to hold the soil sample 12. The soil sample test cylinder 11 has several measuring holes and connecting holes spaced vertically along its upper edge. The measuring holes are located below the connecting holes and are used to insert moisture and temperature sensor probes to detect the moisture content and temperature of the soil sample 12 at different heights. The connecting holes are located on the upper side wall of the soil sample test cylinder 11. During the test, insulation material 5 is wrapped around the side wall and top port of the soil sample test cylinder 11 to reduce the influence of the external environment. The temperature sensor can detect the temperature distribution of the soil sample 12, generating a temperature curve. The moisture sensor can also measure the change in moisture content at various points on the soil sample 12 during the test, plotting relevant curves to explore the migration of moisture in the soil under different temperature gradients.

[0037] In this embodiment, the temperature control device uses a cryogenic constant temperature bath 1 to simulate the temperature of soil sample 12. The cryogenic constant temperature bath 1 has both circulating cooling and heating functions, providing a stable source of heat and cold for the experiment. Internal circulation ensures uniform and stable temperature within the bath, while external circulation can output a constant temperature liquid to establish an external constant temperature field or cool other equipment. The cryogenic constant temperature bath 1 typically has a wide temperature range to meet the needs of different experiments and can achieve high-precision temperature control with high safety. For example, some models can achieve a temperature resolution of 0.01℃ and a temperature fluctuation as low as ±0.05℃.

[0038] The cooling plate 10 is located inside the soil sample testing cylinder 11. The cooling plate 10 is used to contact the top surface of the soil sample 12 and to be sealed to the inner wall of the soil sample testing cylinder 11. Figure 2 , Figure 3 As shown, the cooling plate 10 has a handle 103 on top for easy hand operation. The cooling plate 10 contains a liquid storage chamber 104, which is connected to at least two interfaces, including an inlet 101 and an outlet 102. A rubber tube 3 is connected to each of the inlet and outlet 102. The two rubber tubes 3 extend out of the soil sample test cylinder 11 through two connecting holes on its side wall, and are circulated to the inlet and outlet of the low-temperature constant-temperature bath 1, forming a closed loop. This facilitates the circulation of refrigerant within the temperature control device, ensuring the stability and controllability of the cold end temperature. Refrigerant, such as alcohol, is circulated to the liquid storage chamber of the cooling plate 10 through the low-temperature constant-temperature bath 1. Utilizing the physical principle of alcohol evaporation and heat absorption, heat is absorbed from the surrounding environment to cool the external soil sample 12.

[0039] Furthermore, the water replenishment device in this embodiment includes a water tank 8 and a water level control system. The water tank 8 is connected to the water level control system, which controls the water level in the water tank 8. The soil sample test cylinder 11 is located inside the water tank 8, and the bottom of the soil sample test cylinder 11 is connected to the water tank 8. Water is added quantitatively to the water tank 8 through the water level control system to control the water level in the soil sample test cylinder 11, simulating the groundwater level of the soil sample 12. The water level control system includes a Marshall bottle 14, which is connected to the water tank 8 through a connecting pipe. A switch valve is provided on the connecting pipe, which controls the amount of water flowing from the Marshall bottle 14 to the water tank 8. During the test, the surface opening of the water tank 8 is sealed with a waterproof plastic film 7 to reduce water evaporation and heat loss. Insulation material 5 is wrapped around the side wall of the water tank 8 to reduce the influence of the external environment on the test device.

[0040] In this embodiment, the soil sample test tube 11 has a bottomless structure with openings at the top and bottom. During the test, the soil sample test tube 11 is placed in the water tank 8. An acrylic glass pad 13 is placed at the bottom of the soil sample test tube 11. The acrylic glass pad 13 fits the soil sample test tube 11 and seals the bottom, preventing the soil sample 12 inside from directly contacting the water in the water tank 8. Filter paper is further placed on the acrylic glass pad 13, and the edges of the filter paper are folded downwards to be immersed in the water tank 8, so that the water in the water tank 8 can be transferred to the soil sample 12 through the filter paper. By monitoring the water level changes in the water tank, the flow capacity of water inside the soil sample can be studied.

[0041] In this embodiment, a displacement sensor 9 is installed above the cooling plate 10 to detect its position. A rigid beam 2 is installed above the soil sample test cylinder 11, with support rods 4 at both ends. The bottom end of the support rods 4 can be connected to the bottom plate of the water tank 8 for easy movement of the entire test device. Two fixing holes are provided in the middle of the rigid beam 2, and the displacement sensor 9 is fixedly installed at these holes. The displacement sensor 9 is vertically positioned, with its bottom probe in contact with the cooling plate 10. Furthermore, the support rods 4 in this embodiment are threaded, and the rigid beam 2 is slidably connected to the support rods 4. Nuts are provided on the upper and lower sides of the rigid beam 2, and the nuts are threadedly connected to the support rods 4. The height of the rigid beam 2 can be adjusted by adjusting the nuts, thereby ensuring good contact between the displacement sensor 9 and the cooling plate 10. Under freeze-thaw cycle conditions, the soil sample 12 undergoes different frost heave displacements by adjusting its temperature and moisture content. The displacement sensor 9 collects the changes in the macroscopic frost heave deformation of the soil surface.

[0042] This indoor testing apparatus can be used to determine and study the influence of freeze-thaw history on the freezing depth, temperature gradient, total inflow, and inflow rate of subgrade soil during the freezing process. It helps to understand the characteristics of water migration, minimize the influence of the external environment during the experiment, and improve the accuracy of test results. It has a simple structure and is easy to use.

[0043] Total inflow refers to the total amount of water entering the roadbed through its surface or boundary per unit time. Total inflow determines the intensity of the water source; for example, a large total inflow during heavy rainfall may lead to surface saturation, forming a transient saturation zone. Inflow flux refers to the water flux passing through a unit area of ​​the roadbed interface (such as the surface or a cross-section) per unit time. Inflow flux reflects the ability of water to move within the soil. For example, in highly permeable sandy soil, a large inflow flux leads to rapid water infiltration; in low-permeability clay soil, a small inflow flux easily leads to water accumulation or lateral flow.

[0044] Total inflow is the "source" of water input, while inflow rate is the "rate" of water movement; together, they determine the spatial and temporal distribution of water in the roadbed. Understanding the relationship between the two can optimize drainage design, prevent road damage, and improve the long-term stability of the roadbed.

[0045] The specific implementation process of the above-mentioned indoor testing device is as follows:

[0046] (1) Preparation of soil sample 12

[0047] ① The soil sample 12 transported from the construction site was air-dried outdoors. After air-drying, the clumps of soil particles were broken up and then placed into a vibrating sieve for sieving. The soil sample 12 remaining on the standard sieve was placed into sealed plastic bags for later use, and the names of each particle group were marked on the plastic bags.

[0048] ② Prepare soil sample 12 according to the particle analysis results, mix thoroughly, take two sets of a certain amount of soil sample 12 to determine the air-dried moisture content, then put them into a sealed plastic bag and put them into a humidifier for later use.

[0049] ③ Prepare soil sample 12 with the required moisture content for the test. Spread the prepared air-dried soil sample 12 evenly in an enamel dish, spray water evenly on the soil sample 12, mix thoroughly, put it into a sealed plastic bag, and then put it into a humidifier to keep it moist for 24 hours.

[0050] (2) Experimental procedure:

[0051] ① Apply a thin layer of petroleum jelly evenly to the inner wall of the soil sample test tube 11, place an plexiglass pad 13 inside the tube, and place a filter paper on the pad 13.

[0052] ② Compact soil sample 12. Fill soil sample 12 into layers according to the required dry density. Based on the volume of soil sample test cylinder 11, the required dry density, and the moisture content, the required mass of wet soil for each layer of soil sample 12 can be calculated. Pour the required mass of wet soil for each layer into soil sample test cylinder 11, compact it to the layering point, then roughen the surface, fill the next layer, and repeat this process until soil sample 12 is compacted to the predetermined point. Compaction is then complete.

[0053] ③ Insert the moisture and temperature sensor 6 into the measuring hole on the side wall of the soil sample test tube 11, then wrap the soil sample test tube 11 with the insulation material 5 and put it into the water tank 8;

[0054] ④ Place the cooling plate 10 on the top surface of the soil column, making it in close contact with the surface of the soil sample 12; extend the rubber tube 3 connected to the liquid circulation inlet and outlet interface on the cooling plate 10 through a small hole in the wall of the soil sample test cylinder 11, and connect it to the circulation inlet and outlet of the low temperature constant temperature bath 1; fill the gap between the cooling plate 10 and the wall of the soil sample test cylinder 11 with silicone to prevent the water generated by the liquefaction of air from entering the soil and to prevent heat loss;

[0055] ⑤ Seal the top of the soil sample test tube 11 with insulation material 5 and let it stand overnight. The next day, connect the water tank 8 and the Marshall bottle 14 with rubber tubing 3, add water to the water tank 8 to 3cm above the bottom of the soil column, open the Marshall bottle 14, and adjust the water level in the glass tube according to the water level in the glass tube of the Marshall bottle 14 so that it is at the same level as the lower tube opening, or so that there are a few air bubbles at the lower end of the glass tube. At this time, the water level in the water tank 8 remains unchanged. Then seal the port of the water tank 8 with waterproof plastic film 7 and wrap the side wall of the water tank 8 with insulation material 5.

[0056] ⑥ Connect the moisture and temperature sensor 6 to the moisture and temperature acquisition card 15, connect the moisture and temperature acquisition card 15 to the computer, turn on the computer, open the automatic moisture and temperature acquisition software on the computer 16, and set it to automatically collect the moisture and temperature of each measuring point every ten minutes.

[0057] ⑦ Turn on the low-temperature constant temperature bath 1 and start cooling according to the set cooling method;

[0058] ⑧ After the test, take out soil sample 12 and take two groups of soil samples 12 at different heights. Use the drying method to measure the moisture content of the soil mass after the test.

[0059] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. An indoor testing apparatus for testing the water migration characteristics of frozen soil, characterized in that, include: A soil sample test tube (11) is used to hold a soil sample (12). The side walls and top port of the soil sample test tube (11) are covered with thermal insulation material (5). The cooling plate (10) is located inside the soil sample test tube (11). The cooling plate (10) is used to contact the top surface of the soil sample (12) and is sealed to the inner wall of the soil sample test tube (11). The cooling plate (10) is provided with a liquid storage chamber (104). The liquid storage chamber (104) is connected to an inlet and an outlet. A temperature control device is connected to the liquid inlet (101) and the liquid outlet (102) respectively, and the temperature control device is used to provide refrigerant to the liquid storage chamber; Displacement sensor (9) is used to detect the vertical displacement of the cooling plate (10); A moisture temperature sensor is used to detect the temperature and moisture content of the soil sample (12). The moisture temperature sensor is arranged at intervals along the height direction of the soil sample test tube (11). A water supply device is used to supply water to the soil sample test tube (11); The computer (16) is connected to the displacement sensor (9) and the moisture temperature sensor respectively.

2. The indoor testing apparatus according to claim 1, characterized in that, The water replenishment device includes a water tank (8) and a water level control system. The water tank (8) is connected to the water level control system. The water level control system is used to control the water level in the water tank (8). The soil sample test tube (11) is located inside the water tank (8) and the bottom of the soil sample test tube (11) is connected to the water tank (8).

3. The indoor testing apparatus according to claim 2, characterized in that, The water level control system includes a Marshall bottle (14), which is connected to the water tank (8) via a connecting pipe, and the connecting pipe is equipped with a switch valve.

4. The indoor testing apparatus according to claim 2, characterized in that, The port of the water tank (8) is provided with a waterproof plastic membrane (7) for sealing.

5. The indoor testing apparatus according to claim 1, characterized in that, The bottom of the soil sample test tube (11) is provided with a pad (13), and filter paper is provided on the pad (13).

6. The indoor testing apparatus according to any one of claims 1-5, characterized in that, A rigid crossbeam (2) is provided above the soil sample test tube (11). Support rods (4) are provided at both ends of the rigid crossbeam (2). The displacement sensor (9) is connected to the rigid crossbeam (2) and is in contact with the cooling plate (10).

7. The indoor testing apparatus according to claim 6, characterized in that, The rigid beam (2) is slidably connected to the support rod (4), and nuts are provided on the upper and lower sides of the rigid beam (2), and the nuts are threadedly connected to the support rod (4).

8. The indoor testing apparatus according to any one of claims 1-5, characterized in that, The temperature control device uses a low-temperature constant temperature bath (1).

9. The indoor testing apparatus according to any one of claims 1-5, characterized in that, Silica gel is provided between the cooling plate (10) and the side wall of the soil sample test tube (11).

Images