Device and method for testing loss rule and influence of phase change material of phase change soil

Abstract

The invention relates to a device and method for testing the loss rule and influence of a phase change material of phase change soil. The device comprises a test container, a loading assembly and a discharged liquid collecting assembly. The problem of research means of phase change material loss of the phase change soil is solved, and the phase change material loss rule of the phase change soil under different stress paths, stress states and seepage pressures and the influence of the phase change material loss rule on the mechanical and seepage properties of the phase change soil can be researched; the loss process and influence factors of the phase-change material in the phase-change soil can be researched, and the influence of the loss of the phase-change material on the permeation and mechanical properties of the phase-change soil can be tested; the loss process of the phase change material of the phase change soil under the conditions of different stress paths, axial pressure, lateral pressure, seepage pressure and the like can be considered, and the mechanical property of the phase change soil after loss is tested through loading.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy project construction, and particularly relates to a test device and method for testing the loss law and influence of phase change materials in phase change soil. Background Art

[0002] Plagued by the harsh environment of high-altitude, cold regions, soil is susceptible to freeze-thaw damage, leading to structural damage and cracking, a decrease in strength and impermeability, and the threat of loss of stability. To prevent soil from freezing, phase-change soil offers a new solution. By blending phase-change materials with the existing soil, they harness their latent heat absorption and release capabilities to impart active temperature-control properties. However, the incorporation of phase-change materials also introduces a new problem: loss of phase-change materials. Under the influence of seepage or stress, some of the phase-change materials, which are less strongly bonded to the soil, will be lost, potentially compromising the permeability and structural stability of the core wall.

[0003] Currently, there is a lack of experimental methods and means to study these issues. Many researchers have investigated the leakage and loss of PPCM using filter paper, weighing, or thermal methods, but these methods fail to reflect the mechanical and permeability boundary conditions experienced by the soil. While research methods on the migration and loss of light non-aqueous liquids (LNAPLs) such as gasoline and diesel in soils can provide valuable insights, the boundary conditions used in these studies differ from those for phase-change soils. Due to their differing focus and boundary conditions, they cannot be directly applied to testing for loss in phase-change soils. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the existing technology, provide a phase change soil phase change material loss law and influence test device and method, and provide important technical means for the research and application of phase change soil dam materials.

[0005] The present invention solves the technical problem by the following technical solutions:

[0006] A test device for the loss law and influence of phase change soil phase change material, comprising a test container, a loading component and a discharge liquid collection component;

[0007] The test container includes a pressure chamber, a sample base, a sample cap, a sample, an isolation membrane and a sealing rubber ring. The sample base is installed at the bottom of the pressure chamber, the sample is installed on the sample base, the sample cap is fixedly installed on the top of the sample, the side of the sample is wrapped by the isolation membrane, and the upper and lower edges of the isolation membrane are respectively connected to the sample base and the sample cap;

[0008] The loading assembly includes a loading device, an osmotic pressure and volume controller, and a phase change material isolation soft membrane. The osmotic pressure and volume controller is used to apply osmotic pressure. The top of the sample is connected to the phase change material isolation soft membrane and the osmotic pressure and volume controller in sequence. The lower end of the sample base is connected to the loading device. The phase change material isolation soft membrane is made of a flexible material that is incompatible with the sample and can prevent the backflow of the sample phase change material while transmitting pressure.

[0009] The discharge liquid collection component includes a collection container, a weighing instrument and a discharge liquid conduit. The outlet of the test container is connected to the collection container through the discharge liquid conduit. The collection container is used to collect water and discharged liquid of the phase change material discharged due to test force deformation and osmotic pressure; the lower end of the collection container is connected to the weighing instrument, which is used to obtain the total mass of the discharge liquid in real time.

[0010] Moreover, the pressure chamber is a conventional triaxial pressure chamber, a true triaxial pressure chamber or an infiltration instrument container; the sample base and the sample top cap are provided with seepage holes, and the seepage holes are used to apply osmotic pressure to the sample; the isolation membrane is made of polytetrafluoroethylene membrane, and the thickness does not exceed 0.5mm; the isolation membrane is sealed with a sealing rubber ring.

[0011] Moreover, the loading device is a conventional triaxial loading device (axial pressure and confining pressure), a true triaxial loading device (three-way axial pressure) or an osmotic pressure loading device (constant water head, variable water head).

[0012] A test method for the loss law and influence of phase change soil phase change material is characterized by using the above test device and the steps of the method are as follows:

[0013] S1. The phase change soil material prepared in advance is pressed into the sample preparation mold in layers using the static pressure method to prepare a phase change soil sample;

[0014] S2. The phase change soil sample surrounded by the isolation membrane is placed into the test device for the loss law and influence of phase change materials;

[0015] S3. After applying mechanical boundary conditions according to the specified stress path, apply penetration boundary conditions at the upper and lower ends of the specimen;

[0016] S4. During the seepage loss test, the content of phase change material in the discharge liquid and the permeability coefficient of the current soil sample are measured at certain time intervals;

[0017] S5. After the seepage loss test is completed, the phase change soil sample is loaded through the phase change soil phase change material triaxial / true triaxial test device to test the mechanical properties of the phase change soil after seepage loss.

[0018] S6. After the test, take soil core samples to determine the content of phase change material and organize the test results.

[0019] Moreover, the S1 is specifically:

[0020] First, the phase change material and air-dried soil are evenly mixed together in a certain proportion; then, they are sealed in an inorganic container for more than 5 days to ensure that the phase change material is evenly distributed in the soil; finally, clean water is added to the aforementioned soil according to the specified moisture content to prepare a phase change soil with a specified phase change material dosage and moisture content, which can be used after being sealed for more than 1 day; the inorganic container used is preferably inorganic glass and sealed with a stopper; before using the soil, the total ratio of phase change material to water is verified by a heating and drying method, and its moisture content is adjusted in time. The drying conditions are: not less than 150°C and not less than 24 hours.

[0021] Moreover, the minimum size of the phase change soil sample is not less than 10 times the maximum soil particle size; for phase change gravel soil, the minimum size of the sample is not less than 5 times the maximum particle size.

[0022] Moreover, the order of applying the mechanical boundary conditions and the seepage boundary conditions of S3 is: normal stress load; deviatoric stress load; seepage pressure; the end mark of applying the mechanical boundary conditions is that the deformation of the soil sample tends to be stable; the seepage pressure difference should be determined according to the target hydraulic gradient.

[0023] Furthermore, the content of the S4 phase change material is determined by dye weighing method and infrared / ultraviolet spectroscopy; and the permeability coefficient is updated and calculated in real time according to the set osmotic pressure and the current flow rate.

[0024] The advantages and beneficial effects of the present invention are:

[0025] 1. The present invention solves the problem of research methods for phase change material loss in phase change soil, and can study the phase change material loss law of phase change soil under different stress paths, stress states and seepage pressures and its influence on the mechanical and permeability properties of phase change soil.

[0026] 2. The present invention can study the loss process and influencing factors of phase change materials in phase change soil, and test the influence of phase change material loss on the permeability and mechanical properties of phase change soil.

[0027] 3. The present invention can consider the loss process of phase change soil phase change material under different stress paths, axial pressure, lateral pressure, seepage pressure and other conditions, and test the mechanical properties of phase change soil after loss through loading. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a flow chart of the present invention;

[0029] Figure 2 This is a diagram of the triaxial phase change soil seepage loss test device of the present invention;

[0030] Figure 3This is a diagram of the true triaxial phase change soil seepage loss test device of the present invention;

[0031] Figure 4 This is a diagram of the test device for constant (variable) water head phase change soil seepage loss in the present invention;

[0032] Figure 5 This is a graph showing the change in mass loss and residual rate of phase change material under some working conditions of the present invention;

[0033] Figure 6 This is a comparison chart of the results of measuring the loss mass of phase change materials using the test method of the present invention and the infrared method. DETAILED DESCRIPTION

[0034] The present invention will be further described in detail below through specific examples. The following examples are only illustrative and not restrictive, and the scope of protection of the present invention cannot be limited thereto.

[0035] The embodiment of the present invention provides a test device for the loss law and influence of phase change soil phase change material, such as Figure 1 As shown in the figure, a triaxial phase change soil seepage loss test device was used to explore the loss law of phase change materials in phase change soil under different dry density, PPCM content, confining pressure, strain and hydraulic gradient.

[0036] The embodiment of the present invention provides a test method for the loss law and influence of phase change soil phase change material, such as Figure 2 As shown, the specific process is as follows:

[0037] S1. Prepare phase change materials with dosages of 4%, 12%, and dry density of 1.65 g / cm 3 , 1.75g / cm 3 Phase change soil samples.

[0038] First, a certain mass of air-dried soil was weighed, and the required amount of water and the mass of the phase change material were calculated based on the natural moisture content of the air-dried soil. A trace amount of Sudan Red Ш was then titrated to dye the phase change material at 0.1% of the phase change material dosage. The phase change material and the air-dried soil were then evenly mixed in a stainless steel basin, sealed in a glass container, and allowed to stand for 5 days. Afterwards, the stored mixed soil was removed, a certain amount of water was evenly sprayed into the mixed soil, and the mixture was sealed in a glass container and allowed to stand for 1 day.

[0039] Finally, take an appropriate amount of phase change soil material into the compaction mold with a size of Φ38mm×76mm, load it layer by layer, and use static loading to slowly press it layer by layer to ensure that the pore pressure in the soil sample is basically dissipated before proceeding to the next step, thus forming phase change soil samples with a dosage of 4% and 12% at a specified density.

[0040] S2. Place the prepared phase change soil sample 14 into a triaxial phase change soil seepage loss test device.

[0041] The triaxial phase change soil seepage loss test device consists of a test container 1, a loading component 2, and a discharge liquid collection component 3.

[0042] The test container 1 includes: a pressure chamber 11, which provides an environment for applying confining pressure; a base 12 and a top cap 13, which work together to fix the sample 14; an isolation membrane 15, which wraps the sample and is made of polytetrafluoroethylene; and a sealing rubber ring 16, which tightly fits the isolation membrane 15 to the base 12 and the top cap 13 to ensure the sealing of the sample.

[0043] The loading assembly 2 includes: a loading device 21 and an osmotic pressure volume controller 22 , which together provide a sample pressure environment; and a phase change material isolation soft membrane 23 , which isolates the sample 14 from contaminants.

[0044] The drainage liquid collection assembly 3 includes: a collection container 31, which is a conical flask with a stopper; a high-precision weighing instrument 32, which weighs the mass of the collected drainage liquid; and a drainage liquid conduit 33, which guides the drainage liquid to the collection container 31 and is made of polytetrafluoroethylene.

[0045] Furthermore, in specific implementation, a true triaxial pressure chamber or permeameter can be selected as the test container according to the test requirements, and a true triaxial loading device or a constant (variable) head pressure tube can be selected as the loading component, such as Figure 3 、 Figure 4 shown.

[0046] Before placing the sample into the permeation loss sample device, apply a small amount of water on the surface of the sample. After the pore pressure of the soil sample dissipates, wrap it with a polytetrafluoroethylene membrane 15 (thickness 0.2mm) that is almost insoluble in all solvents; then, use a sealing ring 16 and iron wire to fasten it to the base 12 and the upper cap 13, and use a hot air gun to evenly heat the outer surface so that the polytetrafluoroethylene membrane heats up and shrinks to fit tightly against the sample to ensure sealing; finally, place porous ceramic pieces at the top and bottom as permeable stones, and then it can be placed in the pressure chamber 11 of the test device.

[0047] S3. Apply mechanical and permeability boundary conditions. Apply mechanical boundary conditions according to the test plan in Table 1. First, start the axial load press and confining pressure volume controller to apply axial and confining pressure to isobaric consolidation of the phase change soil sample 14. After consolidation is complete, begin applying strain to simulate the actual stress state of the soil sample. After the stress state is applied, calculate the required permeability pressure based on the hydraulic gradient, and apply permeability boundary conditions at the upper and lower ends.

[0048] Table 1 Experimental plan for exploring PPCM loss patterns

[0049]

[0050] S4. During the seepage loss test, the content of phase change material in the discharge liquid and the permeability coefficient of the current soil sample are measured at certain time intervals.

[0051] Specifically, the method for measuring the content of the phase change material in the discharge liquid by using the discharge liquid collecting device 3 at equal time intervals is as follows:

[0052] a. During the boundary condition loading process, the outlet valve of the permeation loss test device is closed at intervals, and the air is allowed to flow into the discharge liquid collection device (denoted as conical flask No. 1) to collect the discharged phase change material-water mixture. The total mass of the discharge liquid from time point j-1 to time point j is recorded as

[0053] b. Pour the mixed solution collected in No. 1 conical flask into the separatory funnel and record the total mass of the mixed solution poured into the separatory funnel as Take an empty conical flask (referred to as conical flask No. 2) and place it under the separatory funnel. Using the incompatibility and density difference between the phase change material and water, wait for the mixed liquid in the separatory funnel to naturally separate. Then open the valve of the separatory funnel to allow pure water to slowly flow into the conical flask No. 2. After all the pure water flows out of the separatory funnel, close the valve and weigh to calculate the total mass of pure water flowing into the conical flask No. 2, which is recorded as The outflow mass of the phase change material from time point j-1 to time point j can be calculated

[0054]

[0055] c. Calculate the outflow of phase change material:

[0056] ①The proportion of phase change material in the discharge liquid from time point j-1 to time point j is

[0057] ② Cumulative phase change material outflow mass up to the jth time point

[0058] ③ Residual rate of phase change material as of the jth time point It can be estimated according to the formula: Among them, m d To test dry soil quality, is the initial dosage of phase change material.

[0059] Specifically, the calculation formula for the permeability coefficient of the current soil sample is as follows:

[0060]

[0061] Among them, k j is the permeability coefficient of the soil sample measured at the jth time point; Qj is the cumulative mass of discharged liquid up to the jth time point; A is the cross-sectional area of ​​the sample; Δt j is the duration of the trial up to the jth time point;

[0062] S5. After the seepage loss test, the phase change soil sample is loaded through a triaxial device to test the mechanical properties of the phase change soil after seepage loss.

[0063] S6. After the test, core samples were taken from different parts of the soil sample, and the residual content of the phase change material in the soil sample was determined by ultrasonic extraction and infrared method, and the residual content was verified with the loss during the test. The test results were sorted to obtain the phase change material loss curve and the phase change material residual rate curve as shown below: Figure 5 As shown, the results of the infrared method and the present method were further compared ( Figure 6 ), it was found that the residual PCM content measured by the infrared method was slightly smaller than that by the weighing method, and the average deviation between the two was only 0.35%, indicating that this method is feasible and effective for determining the outflow mass of PPCM during the test, and is more convenient than the infrared method and does not damage the sample.

[0064] Specifically, the method for determining the residual amount of phase change material in soil samples using ultrasonic extraction and infrared method is as follows:

[0065] a. Weigh 10-20g of the soil sample to be tested, add an appropriate amount of anhydrous sodium sulfate, grind until it becomes a quicksand, and transfer it to a stoppered conical flask. At the same time, weigh approximately 10-20g of the sample and determine its dry matter content using the oven-drying weighing method.

[0066] b. Add an appropriate amount of tetrachloroethylene to a stoppered conical flask, seal, and extract in an oscillator at 200 vibrations / min for 30 minutes. Let stand for 10 minutes, then filter the extract into a 50ml colorimetric tube. Repeat this extraction process 3-5 times, washing the apparatus and soil sample with an appropriate amount of tetrachloroethylene. Combine the extracts and prepare for testing.

[0067] c. Transfer the above extract to a quartz cuvette and add tetrachloroethylene as a dopant at a wave number of 2930 cm -1 、2960cm -1 3030cm -1 Measure the absorbance A2930, A2960, and A3030, and calculate the mass concentration of phase change material ρ(P) in the extract according to the following formula:

[0068] ρ(P)=XA 2930 +YA 2960 +Z(A 3030 +A 2930 / F)

[0069] Among them, X, Y, Z, and F are related correction coefficients

[0070] d. Phase change material content in soil sample ω P , can be calculated as follows:

[0071]

[0072] Although the embodiments and drawings of the present invention are disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A test device for the loss law and influence of phase change soil phase change material, characterized by: It comprises a test container (1), a loading component (2) and a discharge liquid collecting component (3); The test container (1) comprises a pressure chamber (11), a sample base (12), a sample top cap (13), a sample (14), an isolation membrane (15) and a sealing rubber ring (16); the sample base (12) is installed at the bottom of the pressure chamber (11); the sample (14) is installed on the sample base (12); the sample top cap (13) is fixedly installed on the top of the sample (14); the side of the sample (14) wraps the isolation membrane (15); the upper and lower edges of the isolation membrane (15) are respectively connected to the sample base (12) and the sample top cap (13); The loading assembly (2) includes a loading device (21), an osmotic pressure volume controller (22) and a phase change material isolation soft membrane (23), wherein the osmotic pressure volume controller (22) is used to apply osmotic pressure; the top of the sample (14) is connected to the phase change material isolation soft membrane (23) and the osmotic pressure volume controller (22) in sequence; the lower end of the sample base (12) is connected to the loading device (21); the phase change material isolation soft membrane (23) is made of a flexible material that is not soluble in the sample (14) and can prevent the backflow of the phase change material of the sample (14) while transmitting pressure; The discharge liquid collection assembly (3) comprises a collection container (31), a weighing instrument (32) and a discharge liquid conduit (33); the outlet of the test container (1) is connected to the collection container (31) via the discharge liquid conduit (33); the collection container (31) is used to collect water and discharge liquid of the phase change material discharged due to test force deformation and osmotic pressure; the lower end of the collection container (31) is connected to the weighing instrument (32); the weighing instrument (32) is used to obtain the total mass of the discharge liquid in real time.

2. The test device for the loss law and influence of phase change soil phase change material according to claim 1 is characterized by: The pressure chamber (11) is a conventional triaxial pressure chamber, a true triaxial pressure chamber or a permeameter container; the sample base (12) and the sample top cap (13) are provided with seepage holes, and the seepage holes are used to apply permeation pressure to the sample (14); the isolation membrane (15) is a polytetrafluoroethylene membrane with a thickness not exceeding 0.5 mm; the isolation membrane (15) is sealed with a sealing rubber ring (16).

3. The test device for the loss law and influence of phase change soil phase change material according to claim 1 is characterized by: The loading device (21) is a conventional triaxial loading device (axial pressure and confining pressure), a true triaxial loading device (three-way axial pressure) or an osmotic pressure loading device (constant water head, variable water head).

4. A test method for the loss pattern and impact of phase change soil phase change material, characterized by: Using the test device according to any one of claims 1 to 3, the steps of the method are: S1. The phase change soil material prepared in advance is pressed into the sample preparation mold in layers using the static pressure method to prepare a phase change soil sample; S2. The phase change soil sample surrounded by the isolation membrane is placed into the test device for the loss law and influence of phase change materials; S3. After applying mechanical boundary conditions according to the specified stress path, apply penetration boundary conditions at the upper and lower ends of the specimen; S4. During the seepage loss test, the content of phase change material in the discharge liquid and the permeability coefficient of the current soil sample are measured at certain time intervals; S5. After the seepage loss test is completed, the phase change soil sample is loaded through the phase change soil phase change material triaxial / true triaxial test device to test the mechanical properties of the phase change soil after seepage loss. S6. After the test, take soil core samples to determine the content of phase change material and organize the test results.

5. The test method for the loss law and influence of phase change soil phase change material according to claim 4, characterized in that: The S1 is specifically: First, the phase change material and air-dried soil are evenly mixed together in a certain proportion; then, they are sealed in an inorganic container for more than 5 days to ensure that the phase change material is evenly distributed in the soil; finally, clean water is added to the aforementioned soil according to the specified moisture content to prepare a phase change soil with a specified phase change material dosage and moisture content, which can be used after being sealed for more than 1 day; the inorganic container used is preferably inorganic glass and sealed with a stopper; before using the soil, the total ratio of phase change material to water is verified by a heating and drying method, and its moisture content is adjusted in time. The drying conditions are: not less than 150°C and not less than 24 hours.

6. The test method for the loss law and influence of phase change soil phase change material according to claim 4, characterized in that: The minimum size of the phase change soil sample is not less than 10 times the maximum soil particle size; for phase change gravel soil, the minimum size of the sample is not less than 5 times the maximum particle size.

7. The test method for the loss pattern and impact of phase change soil phase change material according to claim 4, characterized in that: The order of applying the mechanical boundary conditions and the seepage boundary conditions of S3 is: (1) normal stress load; (2) deviatoric stress load; (3) seepage pressure; the end of the application of the mechanical boundary conditions is when the deformation of the soil sample tends to be stable; the seepage pressure difference should be determined according to the target hydraulic gradient.

8. The test method for the loss law and influence of phase change soil phase change material according to claim 4, characterized in that: The content of the S4 phase change material is determined by dye weighing method and infrared / ultraviolet spectroscopy; the permeability coefficient is updated and calculated in real time according to the set osmotic pressure and current flow rate.

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