Fabricated one-way freezing and thawing test device and method for embankment and channel soil body

Abstract

The invention discloses an assembly type one-way freezing and thawing test device and method for embankment and channel soil bodies, and relates to the technical field of one-way freezing and thawing tests. Comprising a bearing base at the bottom, an assembly type sample box in the middle and a refrigeration top plate at the top, the bottom of the assembly type sample box is connected to the bearing base through a flange plate, and the refrigeration top plate is installed at the top of the assembly type sample box; the assembled sample box is filled with a test soil sample, a plurality of test design measuring points are arranged on the test soil sample, a water storage chamber is formed in a space between the bottom of the assembled sample box and the bearing base, a refrigeration bottom plate for controlling the temperature of supplied water is arranged in the bearing base at the lower part of the water storage chamber, and the water storage chamber is connected with a Markov bottle. The device can be used for researching and testing the process and characteristics of unidirectional freezing and thawing of embankment and channel soil samples under the condition that underground water is supplied to an open system, discussing the change rule of physical quantities such as the temperature, the water content, the frost heaving amount and the thaw collapse amount of the soil samples, and providing a test basis for researching a frost heaving and thaw collapse mechanism.

Description

Technical Field

[0001] The invention relates to the technical field of unidirectional freeze-thaw testing, and in particular to an assembled unidirectional freeze-thaw testing device and method for embankment and channel soil. Background Art

[0002] Frost heave and thaw settlement are the two most important diseases in cold region engineering construction, which bring great harm to cold region engineering construction and operation. Whether it is the roadbed soil in the seasonal frozen soil area or the soil layer reinforced by artificial freezing method, the soil is affected by freezing and thawing. The phase change and redistribution of water in the soil during freezing and thawing will change the structure of the soil, leading to changes in the permeability of the soil, which will cause damage and deterioration of the mechanical properties of the soil, and even cause engineering disasters. Therefore, it is of great significance to study the permeability of the soil after freezing and thawing, which can provide an important reference for design and construction. Indoors, an open system unidirectional freeze-thaw test is generally used to simulate the on-site freeze-thaw process.

[0003] In order to study the process and characteristics of unidirectional freeze-thaw of test embankment and channel soil samples in an open system with groundwater level recharge, and to explore the changing laws of physical quantities such as soil sample temperature, moisture content, frost heave, and thaw settlement, it is necessary to provide an assembled unidirectional freeze-thaw test device and method for embankment and channel soil, so as to provide an experimental basis for the study of frost heave mechanism. Summary of the invention

[0004] The main purpose of the present invention is to provide an assembled one-way freeze-thaw test device and method for embankment and channel soil, so as to overcome the problems existing in the prior art.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0006] An assembled unidirectional freeze-thaw test device for dike and channel soil, comprising a load-bearing base at the bottom, an assembled sample box at the middle, and a refrigeration top plate at the top, wherein the bottom of the assembled sample box is connected to the load-bearing base through a flange, and the refrigeration top plate is installed on the top of the inner cavity of the assembled sample box;

[0007] A refrigeration base plate is provided in the load-bearing base, a first circulation pipeline is provided in the refrigeration base plate, the first circulation pipeline is connected to a first thermostatic tank through a circulating liquid conduit, and the refrigeration base plate is used to control the set temperature of the supply water and keep the temperature constant;

[0008] The assembled sample box is filled with a test soil sample, and a plurality of test design measuring points are arranged on the test soil sample, each of which is buried with a temperature sensor and a moisture sensor, a water storage chamber is formed in the space between the bottom of the assembled sample box and the load-bearing base, and the water storage chamber is connected to a Marsh flask through a silicone tube for replenishing water to the test soil sample, a sand layer is laid on the bottom of the assembled sample box, a gauze is laid on the top of the sand layer, and the upper surface of the gauze contacts the test soil sample;

[0009] The refrigeration top plate is provided with a displacement sensor, the top of the refrigeration top plate is provided with a heat-insulating top plate, the bottom is provided with a permeable stone, and a second circulation pipeline is provided inside. The second circulation pipeline is connected to a second constant temperature tank through a circulating liquid conduit.

[0010] Furthermore, the load-bearing base includes two upper and lower load-bearing steel plates connected to each other, the refrigeration base plate is located in the hollow portion between the two load-bearing steel plates, and the load-bearing steel plate located at the lower portion is connected to a universal wheel.

[0011] Furthermore, the assembled sample box comprises a plurality of acrylic cylinders connected to each other, each acrylic cylinder is provided with flanges at the top and bottom, respectively, and the flanges on two adjacent acrylic cylinders are connected by a screw rod.

[0012] Furthermore, circular holes with a diameter of 25 mm are provided on both sides of the acrylic cylinder at the top and the acrylic cylinder at the bottom, and the flange at the upper part of the acrylic cylinder at the top and the flange at the lower part of the acrylic cylinder at the bottom are connected by a screw rod.

[0013] Furthermore, the refrigeration bottom plate and the refrigeration top plate are both made of stainless aluminum alloy metal, and the refrigeration bottom plate and the refrigeration top plate are both provided with cold liquid circulation ports.

[0014] Furthermore, it also includes a fixed bracket, which includes a bottom plate and side plates vertically connected to each other, the side plates are provided with two circular rings, the circular rings are provided with openings, the circular rings are sleeved on the outside of the assembled sample box, and the load-bearing base is located on the bottom plate.

[0015] Furthermore, an insulation box is provided on the outer side of the fixed support, and a particle image velocimetry system is provided between the fixed support and the insulation box for observing the dynamic changes of the soil during the freezing and thawing process.

[0016] A one-way freeze-thaw test method for embankment and channel soil, based on the above-mentioned test device, comprises the following steps:

[0017] (1) Determination of physical properties of test soil samples

[0018] The soil of the on-site embankments and channels is transported back to the laboratory for drying and subjected to physical and mechanical property tests at room temperature, including moisture content test, density test, liquid and plastic limit test, particle analysis test and compaction test;

[0019] (2) Device assembly and soil sample preparation

[0020] Install the load-bearing base at the bottom, place it on a flat ground, install the refrigeration base plate, connect the load-bearing base and the first acrylic cylinder through a flange, and make waterproof treatment at the connection; lay a 5cm thick sand layer at the bottom of the assembled sample box, and then lay a layer of gauze on the sand layer;

[0021] The prepared soil sample with a certain mass moisture content is filled into the first acrylic cylinder. At the same time, the temperature sensor and moisture sensor are buried at the test design measuring point. The soil should be filled and compacted in layers. The thickness of each layer should not exceed 5 cm to control the uniformity of the overall soil sample. When the height of the soil layer is close to the top of the first acrylic cylinder, the second acrylic cylinder is connected through the flange assembly, and waterproof treatment is done. Then the soil is filled to ensure the continuity of sample preparation and the success of sample preparation at one time. The required soil sample height is made in this way.

[0022] After the soil sample is loaded, place the cooling top plate on the soil sample and rotate it several times to ensure close contact between the cooling top plate and the soil sample to improve the temperature conduction efficiency. Apply silicone grease to the gap between the cooling top plate and the assembled sample box to seal it, ensure the freezing effect, and completely prevent the evaporation of water in the soil sample. Then install a fixed displacement sensor on the top of the cooling top plate.

[0023] Use a circulating liquid conduit to connect the refrigeration top plate and the second constant temperature tank, and use a silicone tube to connect the Martens flask and the water storage chamber; install a threading tube on the round hole with a diameter of 25 mm, connect the wires of the temperature sensor and the moisture sensor to the data collector through the threading tube, and then connect the USB cable of the data collector to the computer;

[0024] Push the assembled load-bearing base, assembled sample box and refrigeration top plate into the fixed bracket and connect and fix them firmly. Install a 5cm thick insulation board on the outside of the bracket to form an insulation box to insulate the ambient temperature of the entire test; adjust the ambient temperature to the design temperature and install a thermometer in the insulation box to measure the ambient temperature;

[0025] (3) Natural water redistribution and water replenishment

[0026] After the sample is loaded, adjust the ambient temperature, turn on the temperature sensor and moisture sensor to measure the temperature and moisture content of each layer, and the moisture in the prepared sample soil is naturally redistributed under the combined action of gravity and matrix suction. The change in moisture content is monitored until the natural redistribution of moisture is completed.

[0027] After the redistribution is completed, the groundwater is replenished in the soil using a Martens flask before refrigeration. The Martens flask is adjusted to a suitable position to replenish the soil sample with water at a constant pressure, and the water content is measured until the water content of each soil layer reaches a stable state.

[0028] (4) Keep the Martens flask in the position for water replenishment, start the data logger, set the temperature control scheme on the instrument panel of the first thermostatic bath and the second thermostatic bath, first start the first thermostatic bath connected to the refrigeration bottom plate, and start the second thermostatic bath connected to the refrigeration top plate after the temperature is constant, and start the test. At this time, freezing begins. The thermostatic bath will control the temperature of the top soil sample according to the set temperature, and the temperature and moisture sensor will record the temperature and moisture content data of the soil sample. The Martens flask will replenish water for the soil sample upwards, and the amount of water replenishment can be read in real time from the Martens flask scale;

[0029] During the test, the temperature, moisture content, and vertical displacement were recorded in real time. When the three monitoring values ​​were constant, the second thermostatic tank connected to the refrigeration top plate was closed. At this time, the top soil sample temperature was consistent with the ambient temperature and began to melt. The temperature, moisture content, and vertical displacement were continuously recorded until the three monitoring values ​​were constant. This was considered a freeze-thaw cycle completed.

[0030] The test device remains constant and proceeds to the next freeze-thaw cycle test.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] The main features of the test device of the present invention are large size and assembly type. With the assembly type structure, the required diameter and height can be made according to the test requirements, and it has high flexibility; the large-sized assembled sample box can measure more data, the sensor arrangement is more diversified, and the large size is more in line with the macroscopic reality and has higher reliability; the assembly type can be more convenient to move and prepare samples, and the sample size can be flexibly controlled within a feasible range;

[0033] The temperature sensor and moisture content sensor are embedded in the soil sample. The probe can fully contact the soil sample and accurately monitor the temperature and moisture content data of the soil sample during the test.

[0034] It can be used to study the process and characteristics of one-way freezing and thawing of test embankment and channel soil samples in an open system with groundwater level recharge, explore the changing laws of physical quantities such as soil sample temperature, moisture content, frost heave, and thaw settlement, and provide an experimental basis for the study of frost heave and thaw settlement mechanism. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0036] Figure 2It is a partial structural schematic diagram of the present invention.

[0037] Figure 3 It is a schematic diagram of the load-bearing base of the present invention.

[0038] Figure 4 It is a front schematic diagram of the acrylic cylinder of the present invention.

[0039] Figure 5 It is a top view of the acrylic cylinder of the present invention.

[0040] Figure 6 It is a front schematic diagram of the refrigeration base plate of the present invention.

[0041] Figure 7 It is a top view of the refrigeration base plate of the present invention.

[0042] Figure 8 It is a front schematic diagram of the refrigeration top plate of the present invention.

[0043] Fig. 9 It is a top view of the refrigeration top plate of the present invention.

[0044] Fig.10 It is a schematic diagram of a fixing bracket of the present invention.

[0045] Fig.11 This is a front view of the arrangement of measuring points for the test design of the present invention.

[0046] Fig.12 This is a top view of the arrangement of measurement points for the test design of the present invention.

[0047] Among them, 1-displacement sensor, 2-refrigeration top plate, 3-flange, 4-permeable stone, 5-threading pipe, 6-assembled sample box, 7-sensor, 8-water storage chamber, 9-refrigeration bottom plate, 10-water supply port, 11-cold liquid circulation port, 12-insulation box, 13-load-bearing steel plate, 14-acrylic cylinder, 15-insulation top plate, 16-ring. DETAILED DESCRIPTION

[0048] The technical solution of the present invention is further described below through the accompanying drawings and embodiments.

[0049] Example 1

[0050] Combination Figures 1 to 10The present embodiment provides an assembled unidirectional freeze-thaw test device for embankment and channel soil, comprising a load-bearing base at the bottom, an assembled sample box 6 at the middle, and a refrigeration top plate 2 at the top, wherein the bottom of the assembled sample box 6 is connected to the load-bearing base through a flange 3, and the refrigeration top plate 2 is installed on the top of the inner cavity of the assembled sample box 6; the load-bearing base, the assembled sample box 6 and the refrigeration top plate 2 constitute the main body of the test device, and the main body of the test device is installed on a fixed bracket, and an insulation box 12 is provided on the outer side of the fixed bracket, and a particle image velocimetry system is arranged between the fixed bracket and the insulation box for observing the dynamic changes of the soil during the freeze-thaw process.

[0051] Preferably, a support column can be provided at the bottom of the thermal insulation box 12.

[0052] Preferably, the fixed bracket includes a bottom plate and side plates vertically connected to each other, the side plates are provided with two circular rings, the circular rings are provided with openings, the circular rings are sleeved on the outside of the assembled sample box 6, and the load-bearing base is located on the bottom plate.

[0053] Specifically, the fixing bracket is made of 50mm wide steel sheet, the bottom plate is a square of 800mm×800mm, the side plate is a rectangle of 2200mm high, and a circular ring 16 with a diameter of 600mm is connected at a height of 800mm and 1600mm. The circular ring 16 is open and can be adjusted in tightness by bolts to fix the main body of the entire test device.

[0054] In this embodiment, a refrigeration base plate 9 is provided in the load-bearing base, and a first circulation pipeline is provided in the refrigeration base plate 9. The first circulation pipeline is connected to a first thermostatic tank through a circulating liquid conduit. The refrigeration base plate is used to control the set temperature of the supply water and keep the temperature constant; the assembled sample box 6 is filled with a test soil sample, and a plurality of test design measuring points are provided in the height direction or radial direction of the test soil sample. Each test design measuring point is buried with a sensor 7, and the sensor includes a temperature sensor and a moisture sensor. The space between the bottom of the assembled sample box 6 and the load-bearing base forms a water storage chamber 8, and the water storage chamber 8 is connected to a Marsh flask through a silicone tube for replenishing water to the test soil sample. A sand layer is laid on the bottom of the assembled sample box, and a gauze is laid on the top of the sand layer. The upper surface of the gauze contacts the test soil sample; a displacement sensor 1 is provided on the refrigeration top plate 2, and an insulating top plate 15 is provided on the top of the refrigeration top plate 2, and a permeable stone 4 is provided at the bottom, and a second circulation pipeline is provided inside, and the second circulation pipeline is connected to a second thermostatic tank through a circulating liquid conduit.

[0055] In a further embodiment, the load-bearing base includes two upper and lower load-bearing steel plates 13 connected to each other, the refrigeration bottom plate 9 is located in the hollow part between the two load-bearing steel plates 13, and the load-bearing steel plate 13 located at the lower part is connected with a universal wheel. The load-bearing steel plate 13 is a circular plate with a diameter of 650 mm and a thickness of 6 mm. The water supply port 10 passes through the refrigeration bottom plate 9 and the load-bearing steel plate 13 and is connected to the silicone tube.

[0056] In a further embodiment, the assembled sample box 6 includes a plurality of interconnected acrylic cylinders 14 , each of the acrylic cylinders 14 is provided with flanges 3 at the top and bottom, respectively, and the flanges 3 on two adjacent acrylic cylinders 14 are connected by a screw rod.

[0057] Preferably, both sides of the acrylic cylinder 14 at the top and the acrylic cylinder 14 at the bottom are provided with round holes with a diameter of 25 mm, and the flange 3 at the upper part of the acrylic cylinder 14 at the top and the flange 3 at the lower part of the acrylic cylinder 14 at the bottom are connected by a screw.

[0058] In this embodiment, the refrigeration bottom plate 9 and the refrigeration top plate 2 are both made of stainless aluminum alloy metal, and a cold liquid circulation port 11 is provided on the refrigeration bottom plate 9 and the refrigeration top plate 2.

[0059] Specifically, the refrigeration top plate 2 is made of 2.5mm thick stainless aluminum alloy, and its outer diameter is slightly smaller than the inner diameter of the acrylic cylinder 14, with dimensions of φ=59cm, H=2cm. The interior is a circulating pipeline that can be connected, and the refrigeration effect is achieved by circulating the refrigerant liquid through the connected second constant temperature tank; the refrigeration bottom plate 9 is made of stainless aluminum alloy, with dimensions of φ=61cm, H=2cm. The interior is a circulating pipeline that can be connected, and the refrigeration effect is achieved by circulating the refrigerant liquid through the connected first constant temperature tank; the insulation box 12 is composed of a 5cm thick polyurethane foam plastic board.

[0060] The test device of this embodiment includes a temperature control system, a monitoring system and a water replenishment system.

[0061] Among them, the temperature control system is mainly composed of a thermostatic bath and a freezing refrigeration plate. The models of the thermostatic baths are HX-4015 and DC-2010 respectively. A temperature control instrument with programming function is used, which can customize the temperature control mode and automatically control the temperature. The temperature control range is -40℃~100℃, the minimum division value is 0.01℃, the error is ±0.1℃, and propylene glycol is used as the circulating fluid; the freezing refrigeration top plate is made of stainless aluminum alloy metal plate to reduce the loss of cold due to the material. There are two interfaces outside, and the internal circulation pipeline is connected to circulate the antifreeze liquid for refrigeration and freezing, which is connected to the thermostatic bath HX-4015 (the second thermostatic bath); the refrigeration bottom plate is made of stainless aluminum alloy metal plate and connected to the thermostatic bath DC-2010 (the first thermostatic bath); the circulating fluid conduit is a high-temperature and low-temperature resistant silicone tube. A 5cm thick polyurethane foam plastic board is installed on the outside of the entire test device to insulate the entire test system.

[0062] The monitoring system includes a temperature monitoring system, a moisture content monitoring system and a displacement monitoring system. The temperature monitoring system consists of a temperature sensor and a temperature monitoring data acquisition instrument. By burying the temperature sensor at the soil layer height required by the test design and connecting the temperature monitoring data acquisition instrument, it has a fully automatic data acquisition function; the data acquisition supporting software is installed on the computer, which can display and automatically record the temperature and moisture content data in real time, and know the development of the one-way freezing temperature. The moisture content monitoring system and the displacement monitoring system are also composed of corresponding sensors and data acquisition instruments.

[0063] The temperature and moisture content sensors of traditional test equipment are mostly inserted into the soil sample from the wall of the soil sample container. This sensor layout method has two disadvantages: on the one hand, the sensor reading will be affected by the container wall and will be inaccurate, and on the other hand, this method cannot be used for tests with a large dry density. The temperature sensor and moisture content sensor of this embodiment are laid out in the soil sample by the embedding method. The probe can fully contact the soil sample, eliminating the above disadvantages and accurately monitoring the temperature and moisture content data of the soil sample during the test; using a data acquisition instrument and supporting computer software, the temperature and moisture content data in the soil sample can be monitored and automatically collected in real time.

[0064] The displacement monitoring uses LVDT displacement sensor, the displacement range is 50mm (20mm outer diameter, 345mm length), the repeatability is ≤1um, and it is installed on the top of the refrigeration top plate to collect the vertical displacement of the freeze-thaw process; the temperature detection uses PT100 temperature sensor, and its temperature measurement range is -40℃-1100℃. The temperature measurement accuracy is 0.1℃; the moisture content monitoring uses EC-5 small soil moisture sensor, the size is 8.9×1.8×0.7cm, the working temperature is -40~60℃, the range is 0-100%VWC, the accuracy is: mineral soil: ±3%VWC; ±2%VWC after separate calibration Resolution: mineral soil: 0.1%VWC; growth matrix: 0.25%VWC.

[0065] like Figure 11 to Figure 12 The temperature sensors are installed at the measuring point 1 and the measuring point 2 of the soil layer AG, with a total of 14 temperature sensors; the moisture sensor is installed at the measuring point 1 of the soil layer AG, with a total of 14 moisture sensors; the displacement sensor is installed at the measuring point 1 and the measuring point 2 on the top of the refrigeration top plate, with a total of 2 displacement sensors.

[0066] Example 2

[0067] This embodiment provides a one-way freeze-thaw test method for embankment and channel soil.

[0068] 1. Purpose of the test

[0069] In order to study the process and characteristics of unidirectional freeze-thaw of test embankment soil samples in an open system with groundwater level recharge, the changing laws of physical quantities such as soil temperature, moisture content, frost heave, and thaw settlement were explored to provide an experimental basis for the study of frost heave mechanism.

[0070] Experimental design variables: groundwater level, temperature gradient, number of freeze-thaw cycles. The groundwater level was adjusted by a Malvern flask; the temperature gradient was set by adjusting the temperature of the refrigeration top plate and the refrigeration bottom plate, and the thawing temperature was kept constant to conduct a one-way freeze-thaw test; the number of freeze-thaw cycles was determined by recording the temperature and moisture content to determine a freeze-thaw cycle, and then multiple freeze-thaw cycles were conducted.

[0071] All test soils are remolded soil samples. Compared with original soil, remolded soil can better control the physical and mechanical properties of soil, and artificial remolded soil is more operable in indoor environment. However, original soil is subject to structural damage and disturbance due to external forces, which will eventually affect the test results. Therefore, remolded soil samples are used in this test. The initial moisture content and initial dry density of the soil are the same as those at the embankment site.

[0072] The whole test process includes: determination of soil physical properties, soil sample preparation, sample loading, natural redistribution of water, groundwater recharge of soil before freezing, and freezing and thawing of soil under open conditions.

[0073] 2. Determination of initial and boundary conditions of the test

[0074] 2.1 Determination of temperature control mode

[0075] According to the characteristics of unidirectional freezing of the frozen soil layer in seasonal frozen soil areas, this test only applies a cold source to the top of the soil sample, and does not consider lateral freezing. One-dimensional unidirectional freezing from top to bottom is carried out under open conditions. During the test, the temperature of the bottom of the soil sample is kept at +1°C, and the surrounding temperature is kept at the ambient temperature. Under natural conditions, due to the random change of air temperature, complex ground temperature changes are caused, and it is difficult to simulate the real state indoors. Therefore, this test sets the top surface of the soil sample to a constant negative temperature control mode, and forms a temperature gradient with the temperature of the warm end surface, so that the soil sample freezes under this temperature gradient. Top temperature control process: Before freezing, in order to make the temperature of the soil sample reach a uniform distribution, it is necessary to keep a constant temperature at +1°C for 6 hours, and then the top of the soil sample is quickly reduced to the environmental freezing temperature required by the test. The frost heave displacement, soil body temperature and water content reach stability as the sign of the end of freezing, and then the top of the soil sample is quickly increased to the environmental melting temperature required by the test. The thaw displacement, soil body temperature and water content reach stability as the sign of the end of melting. The whole process of freezing and melting is a freeze-thaw process.

[0076] 2.2 Freeze-thaw temperature selection

[0077] In order to simulate the influence of different ground temperatures on soil freezing and thawing during the freezing period, the cold end temperature condition of this experiment was selected based on the monthly average surface temperature during the freezing period in the study area.

[0078] Freezing temperature: Two temperatures were selected as variables; ① The average minimum temperature at the dike site over the years (the average minimum temperature in the Greater Khingan Range from 2000 to 2020 was -34.64°C) T1. ② The minimum temperature at the dike site over the years (the minimum temperature in the Greater Khingan Range from 2000 to 2020 was -37.14°C) T2. Melting temperature: Natural thawing at room temperature (around 20°C).

[0079] 3. Experimental plan

[0080] This one-way freeze-thaw test studies three factors: groundwater level, temperature gradient, and number of freeze-thaw cycles. Appropriate test parameters need to be selected based on actual needs. The test plan is shown in Table 3.3.

[0081] 3.1. Groundwater level: In order to study the process and characteristics of unidirectional freeze-thaw of test soil samples under different groundwater level recharge conditions, and to study the changing laws of physical quantities such as soil temperature, moisture content, frost heave, and thaw settlement, the experiment was designed at groundwater depths of H1 (representing deep groundwater) and H2 (representing shallow groundwater).

[0082] 3.2. Temperature gradient: Temperature conditions are one of the main factors affecting the strength of soil freeze-thaw characteristics. Its characteristic index is the speed at which the freezing front invades the soil per unit time, that is, the freezing rate. The difference in freezing rate will determine the ice formation characteristics and the strength of the freeze-thaw characteristics during the soil freezing process, as well as the changes in the structure and physical and mechanical properties of the frozen soil. The experimental freezing cold end temperature is designed with two temperatures T1 and T2, the warm end temperature is kept constant at 1°C, and the melting temperature is set to room temperature (about 20°C).

[0083] 3.3. Number of freeze-thaw cycles: In order to study the process and characteristics of unidirectional freeze-thaw of test soil samples under different numbers of freeze-thaw cycles, this test carried out multiple freeze-thaw cycles (N times) until the data of the two freeze-thaw cycles were relatively stable.

[0084] Table 3.3 Test plan

[0085]

[0086] 4. Test process

[0087] The specific steps of the test process are as follows:

[0088] (1) Determination of physical properties of test soil samples

[0089] The soil of the on-site embankments and channels is transported back to the laboratory for drying and subjected to physical and mechanical property tests at room temperature, including moisture content test, density test, liquid and plastic limit test, particle analysis test and compaction test;

[0090] (2) Device assembly and soil sample preparation

[0091] After the load-bearing base at the bottom is installed, it is placed on a flat ground, and the refrigeration base plate 9 is installed. The load-bearing base and the first acrylic cylinder 14 are connected through the flange 3, and the connection is waterproofed; a 5 cm thick sand layer is laid on the bottom of the assembled sample box 6, and then a layer of gauze is laid on the sand layer;

[0092] The prepared soil sample with a certain mass moisture content is filled into the first acrylic cylinder 14, and the temperature sensor and the moisture sensor are buried at the test design measuring point. The soil should be filled and compacted in layers, and the thickness of each layer should not exceed 5 cm to control the uniformity of the whole soil sample. When the height of the soil layer is close to the top of the first acrylic cylinder, the second acrylic cylinder is connected by the flange assembly, and waterproof treatment is done, and then the soil is filled to ensure the continuity of sample preparation and the success of sample preparation once, and the required soil sample height is made by analogy. The finished soil sample has a diameter of 60 cm, and the diameter and height can be made according to the test requirements. In this embodiment, the diameter is 60 cm and the height is 180 cm.

[0093] After the soil sample is loaded, the cooling top plate 2 is placed on the soil sample and rotated several times to ensure close contact between the cooling top plate 2 and the soil sample to improve the temperature conduction efficiency. The gap between the cooling top plate 2 and the assembled sample box 6 is filled with silicone grease to seal, ensure the freezing effect, and completely prevent the evaporation of water in the soil sample; then the fixed displacement sensor 1 is installed on the top of the cooling top plate 2;

[0094] Connect the refrigeration top plate 2 and the second constant temperature tank with a circulating liquid conduit, and connect the Martens flask and the water storage chamber 8 with a silicone tube; install a threading tube 5 on the circular hole with a diameter of 25 mm, connect the wires of the temperature sensor and the moisture sensor to the data collector through the threading tube 5, and then connect the USB cable of the data collector to the computer;

[0095] Push the assembled load-bearing base, assembled sample box 6 and refrigeration top plate 2 into the fixed bracket and connect and fix them to ensure firmness. Install a 5 cm thick insulation board outside the bracket to form an insulation box 12 to insulate the ambient temperature of the entire test; adjust the ambient temperature to the design temperature and install a thermometer in the insulation box 12 to measure the ambient temperature;

[0096] (3) Natural water redistribution and water replenishment

[0097] After the sample is loaded, adjust the ambient temperature, turn on the temperature sensor and moisture sensor to measure the temperature and moisture content of each layer, and the moisture in the prepared sample soil is naturally redistributed under the combined action of gravity and matrix suction. The change in moisture content is monitored until the natural redistribution of moisture is completed.

[0098] After the redistribution is completed, the groundwater is replenished in the soil using a Martens flask before refrigeration. The Martens flask is adjusted to a suitable position to replenish the soil sample with water at a constant pressure, and the water content is measured until the water content of each soil layer reaches a stable state.

[0099] (4) Keep the Martens flask in the position for water replenishment, start the data acquisition device, set the temperature control scheme on the instrument panel of the first thermostatic bath and the second thermostatic bath, first start the first thermostatic bath connected to the refrigeration bottom plate 9, and start the second thermostatic bath connected to the refrigeration top plate 2 after the temperature is constant, and start the test. At this time, freezing begins. The thermostatic bath will control the temperature of the top soil sample according to the set temperature, and the temperature and moisture sensor will record the temperature and moisture content data of the soil sample. The Martens flask will replenish water for the soil sample upwards, and the amount of water replenishment can be read in real time by the Martens flask scale;

[0100] During the test, the temperature, moisture content, and vertical displacement are recorded in real time. When the three monitoring values ​​are constant, the second thermostatic tank connected to the refrigeration top plate 2 is closed. At this time, the top soil sample temperature is consistent with the ambient temperature and begins to melt. The temperature, moisture content, and vertical displacement are continuously recorded until the three monitoring values ​​are constant. This is considered a freeze-thaw cycle completed.

[0101] The test device remains constant and proceeds to the next freeze-thaw cycle test.

[0102] The above description is only a preferred embodiment of the present invention and does not limit the technical scope of the present invention. Therefore, any slight modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. An assembled one-way freeze-thaw test device for embankments and channel soils, characterized in that: It includes a load-bearing base at the bottom, an assembled sample box at the middle, and a refrigeration top plate at the top, wherein the bottom of the assembled sample box is connected to the load-bearing base through a flange, and the refrigeration top plate is installed on the top of the inner cavity of the assembled sample box; A refrigeration base plate is provided in the load-bearing base, a first circulation pipeline is provided in the refrigeration base plate, the first circulation pipeline is connected to a first thermostatic tank through a circulating liquid conduit, and the refrigeration base plate is used to control the set temperature of the supply water and keep the temperature constant; The assembled sample box is filled with a test soil sample, and a plurality of test design measuring points are arranged on the test soil sample, each of which is buried with a temperature sensor and a moisture sensor, a water storage chamber is formed in the space between the bottom of the assembled sample box and the load-bearing base, and the water storage chamber is connected to a Marsh flask through a silicone tube for replenishing water to the test soil sample, a sand layer is laid on the bottom of the assembled sample box, a gauze is laid on the top of the sand layer, and the upper surface of the gauze contacts the test soil sample; The refrigeration top plate is provided with a displacement sensor, the top of the refrigeration top plate is provided with a heat-insulating top plate, the bottom is provided with a permeable stone, and a second circulation pipeline is provided inside. The second circulation pipeline is connected to a second constant temperature tank through a circulating liquid conduit.

2. The assembled one-way freeze-thaw test device for embankment and channel soil as claimed in claim 1, characterized in that: The load-bearing base includes two upper and lower load-bearing steel plates connected to each other, the refrigeration base plate is located in the hollow portion between the two load-bearing steel plates, and the load-bearing steel plate located at the lower portion is connected to a universal wheel.

3. The assembled one-way freeze-thaw test device for embankment and channel soil as claimed in claim 1, characterized in that: The assembled sample box comprises a plurality of acrylic cylinders connected to each other, the upper part and the lower part of each acrylic cylinder are respectively provided with flanges, and the flanges on two adjacent acrylic cylinders are connected by a screw rod.

4. The assembled one-way freeze-thaw test device for embankment and channel soil as claimed in claim 3, characterized in that: Round holes with a diameter of 25 mm are provided on both sides of the acrylic cylinder at the top and the acrylic cylinder at the bottom, and the flange at the upper part of the acrylic cylinder at the top and the flange at the lower part of the acrylic cylinder at the bottom are connected by a screw rod.

5. The assembled one-way freeze-thaw test device for embankment and channel soil as claimed in claim 1, characterized in that: The refrigeration bottom plate and the refrigeration top plate are both made of stainless aluminum alloy metal, and are provided with cold liquid circulation ports.

6. The assembled one-way freeze-thaw test device for embankment and channel soil as claimed in claim 1, characterized in that: It also includes a fixed bracket, which includes a bottom plate and side plates vertically connected to each other, two rings are arranged on the side plates, openings are arranged on the rings, the rings are sleeved on the outside of the assembled sample box, and the load-bearing base is located on the bottom plate.

7. The assembled one-way freeze-thaw test device for embankment and channel soil as claimed in claim 6, characterized in that: An insulation box is provided on the outer side of the fixed support, and a particle image velocimetry system is arranged between the fixed support and the insulation box for observing the dynamic changes of the soil during the freezing and thawing process.

8. A one-way freeze-thaw test method for embankment and channel soil, based on the test device according to any one of claims 1 to 7, characterized in that: The following steps are involved: (1) Determination of physical properties of test soil samples The soil of the on-site embankments and channels is transported back to the laboratory for drying and subjected to physical and mechanical property tests at room temperature, including moisture content test, density test, liquid and plastic limit test, particle analysis test and compaction test; (2) Device assembly and soil sample preparation Install the load-bearing base at the bottom, place it on a flat ground, install the refrigeration base plate, connect the load-bearing base and the first acrylic cylinder through a flange, and make waterproof treatment at the connection; lay a 5cm thick sand layer at the bottom of the assembled sample box, and then lay a layer of gauze on the sand layer; The prepared soil sample with a certain mass moisture content is filled into the first acrylic cylinder. At the same time, the temperature sensor and moisture sensor are buried at the test design measuring point. The soil should be filled and compacted in layers. The thickness of each layer should not exceed 5 cm to control the uniformity of the overall soil sample. When the height of the soil layer is close to the top of the first acrylic cylinder, the second acrylic cylinder is connected through the flange assembly, and waterproof treatment is done. Then the soil is filled to ensure the continuity of sample preparation and the success of sample preparation at one time. The required soil sample height is made in this way. After the soil sample is loaded, place the cooling top plate on the soil sample and rotate it several times to ensure close contact between the cooling top plate and the soil sample to improve the temperature conduction efficiency. Apply silicone grease to the gap between the cooling top plate and the assembled sample box to seal it, ensure the freezing effect, and completely prevent the evaporation of water in the soil sample. Then install a fixed displacement sensor on the top of the cooling top plate. Use a circulating liquid conduit to connect the refrigeration top plate and the second constant temperature tank, and use a silicone tube to connect the Martens flask and the water storage chamber; install a threading tube on the round hole with a diameter of 25 mm, connect the wires of the temperature sensor and the moisture sensor to the data collector through the threading tube, and then connect the USB cable of the data collector to the computer; Push the assembled load-bearing base, assembled sample box and refrigeration top plate into the fixed bracket and connect and fix them firmly. Install a 5cm thick insulation board on the outside of the bracket to form an insulation box to insulate the ambient temperature of the entire test; adjust the ambient temperature to the design temperature and install a thermometer in the insulation box to measure the ambient temperature; (3) Natural water redistribution and water replenishment After the sample is loaded, adjust the ambient temperature, turn on the temperature sensor and moisture sensor to measure the temperature and moisture content of each layer, and the moisture in the prepared sample soil is naturally redistributed under the combined action of gravity and matrix suction. The change in moisture content is monitored until the natural redistribution of moisture is completed. After the redistribution is completed, the groundwater is replenished in the soil using a Martens flask before refrigeration. The Martens flask is adjusted to a suitable position to replenish the soil sample with water at a constant pressure, and the water content is measured until the water content of each soil layer reaches a stable state. (4) Keep the Martens flask in the position for water replenishment, start the data logger, set the temperature control scheme on the instrument panel of the first thermostatic bath and the second thermostatic bath, first start the first thermostatic bath connected to the refrigeration bottom plate, and start the second thermostatic bath connected to the refrigeration top plate after the temperature is constant, and start the test. At this time, freezing begins. The thermostatic bath will control the temperature of the top soil sample according to the set temperature, and the temperature and moisture sensor will record the temperature and moisture content data of the soil sample. The Martens flask will replenish water for the soil sample upwards, and the amount of water replenishment can be read in real time from the Martens flask scale; During the test, the temperature, moisture content, and vertical displacement were recorded in real time. When the three monitoring values ​​were constant, the second thermostatic tank connected to the refrigeration top plate was closed. At this time, the top soil sample temperature was consistent with the ambient temperature and began to melt. The temperature, moisture content, and vertical displacement were continuously recorded until the three monitoring values ​​were constant. This was considered a freeze-thaw cycle completed. The test device remains constant and continues to the next freeze-thaw cycle test.

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