Physical test method for finely screening fine-grained soil particles to nanoscale

Abstract

A physical test method for finely screening fine-grained soil particles to nanoscale comprises the following steps: step 1, obtaining loess fine particles with the particle size of less than 0.075 mm through a dry screen, and completing earlier-stage treatment work of a soil sample; secondly, a traditional vibration screening machine is transformed, and the transformed vibration screening machine is used for conducting wet screening on the loess fine particles with the particle size smaller than 0.075 mm; 3, after-treatment of the soil body after wet screening: separately drying the soil particle grading groups after wet screening separation through an oven or a drying oven, weighing after grinding, recording and storing; and 4, obtaining a particle score curve of the fine-grained soil: drawing the particle score curve of the soil particle content of each grade on the logarithmic coordinate system so as to represent the distribution condition of the fine-grained soil in different particle group intervals. On the basis of a traditional sieve shaker, the advantages of a wet screening method are combined, the steel sieve of the traditional sieve shaker is modified through the nylon filter cloth, the steel bars and the rubber rings, and the purpose of accurately and directly separating fine soil particles is achieved.

Description

Technical Field

[0001] The invention relates to the field of particle analysis in soil engineering properties, in particular to a physical test method for finely screening fine-grained soil particles to nanometer level. Background Art

[0002] The particle size distribution of soil is an important indicator of soil. Its particle composition and distribution can reveal the soil-forming environment. The particle composition determines the physical properties of the source soil. Particle analysis is a method to determine the percentage of various particle groups in the total mass of dry soil, so as to clarify the distribution of particle size and provide a theoretical basis for soil classification and rough judgment of soil engineering properties and material selection.

[0003] Traditional particle analysis methods include screening and sedimentation analysis. For soil particles with a particle size greater than 0.075 mm (coarse-grained soil), screening is used. Screening methods include dry screening and wet screening. Compared with dry screening, wet screening is more accurate in expressing particle size gradation, but both methods require the soil to pass through a steel sieve to obtain the mass percentage of particles in different particle size groups. For soil particles with a particle size less than 0.075 mm (fine-grained soil), two sedimentation analysis methods, densimeter method and pipette method, are used. Both methods are based on Stokes' law. The densimeter method uses a densimeter to measure the different sinking rates corresponding to soil particles of different particle sizes when the effective gravity and liquid resistance of soil particles in static water are balanced, and then the particle size is calculated; the pipette method is to dry the suspension extracted at a certain height when the soil particle turbidity drops freely, and calculate the particle size distribution from the change in sample concentration. The densitometer method and pipette method for fine-grained soil have the following shortcomings: it assumes that the soil particles are ideal rigid spheres with smooth surfaces, which is inconsistent with the actual shape of soil particles. The actual clay particles are mostly flake-shaped or needle-shaped; the pretreatment before the test and the concentration of the suspension may lead to large differences in the test results; in addition, the densitometer method and pipette method have many experimental steps and take a long time. With the development of science and technology, optical methods such as laser particle size analysis can also be used for fine-grained soil. However, the laser particle size analyzer is also an indirect measurement method. Using the principle of optics, soil particles will be blocked, resulting in errors. More importantly, soil particles of different particle groups cannot be separated.

[0004] The sieving method can physically separate soil particles, but due to the limitation of the size of the steel sieve aperture and the cohesive force of clay (soil particles smaller than 0.002mm) that can wrap and adhere to other particles to form aggregates, vibration sieving alone cannot separate them. Therefore, the current sieving method cannot complete the sieving of soil particles smaller than 0.075mm (fine-grained soil). Summary of the invention

[0005] In order to solve the problems of particle size limitation (to achieve the purpose of fine screening of fine-grained soil particles to the nanometer level) and the inability of vibrating to separate clay, the present invention adopts a method of combining wet screening and vibrating screening, that is, on the basis of a traditional vibrating screen machine, combined with the advantages of the wet screening method, the steel screen of the traditional vibrating screen machine is modified by using nylon filter cloth, steel bars and rubber rings to achieve the purpose of accurately and directly separating fine soil particles, wherein the nylon filter cloth with an aperture of less than 0.075 mm can achieve the separation of soil particles less than 0.075 mm and finely screen the fine soil particles to the nanometer level, thereby achieving the test goal of accurately determining the composition of fine-grained soil particles, and the vibration of the vibrating screen machine can reduce the time required for the test.

[0006] The present invention is achieved through the following technical methods:

[0007] A physical test method for finely screening fine-grained soil particles to nanometer level, comprising the following steps:

[0008] The first step is to obtain loess fine particles with a particle size of less than 0.075 mm through dry sieving to complete the preliminary processing of soil samples;

[0009] The second step is to modify the traditional vibrating screen machine and use the modified vibrating screen machine to wet screen the loess fine particles with a particle size of less than 0.075 mm;

[0010] The third step is the post-processing of the soil after wet screening: the soil particles separated by wet screening are dried separately through a furnace or oven, and then weighed, recorded and saved after grinding;

[0011] The fourth step is to obtain the particle distribution curve of fine-grained soil: the soil particle content of each level is plotted into a particle distribution curve on a logarithmic coordinate system to represent the distribution of fine-grained soil in different particle group intervals.

[0012] Furthermore, the first step specifically includes: pouring the air-dried soil sample into a conical flask, adding water, soaking for 10 hours to 12 hours, placing the conical flask on a boiling device, and boiling for 0.8 hours to 1 hour; after cooling, standing for 1-2 minutes, pouring the upper suspension into a measuring cylinder, carefully grinding the sediment at the bottom of the cup with a rubber-headed pestle, washing with water, passing through a 0.075mm sieve, pouring the sieved suspension into a measuring cylinder, obtaining loess fine particles with a particle size of less than 0.075mm, and then adding sodium hexametaphosphate dispersant to prevent soil particles from flocculating.

[0013] Furthermore, in the second step, the traditional vibrating screen machine is transformed, including:

[0014] The nylon filter cloth with a pore size less than 0.075mm is fixed on the steel screen of the traditional vibrating screen machine with steel bars and rubber rings, so that the pore size of the nylon filter cloth becomes the particle size range of the sieved soil sample, thereby completing the separation of fine-grained soil and finely screening it to the nanometer level;

[0015] Use rubber rings to seal the interfaces of traditional vibrating screens to prevent water overflow during wet screening;

[0016] Use a plastic bucket that is higher than the discharge port to collect soil samples smaller than the particle size at the discharge port to prevent mud from splashing out and reduce soil sample loss;

[0017] Remove the existing outlet of the steel frame of the soil screening layer, and then seal it with butyl tape and transparent tape.

[0018] Furthermore, in the second step, the modified vibrating screen machine is used to wet screen the loess fine particles with a particle size less than 0.075 mm, specifically including:

[0019] The soil sample with all particles smaller than 0.075 mm is poured into the feed port of the modified vibrating screen machine. The size of the separated soil particles is controlled by the mesh number of the nylon filter cloth. The separated soil particles flow from the discharge port into a plastic bucket whose height exceeds the discharge port.

[0020] Furthermore, the nylon filter cloth has multi-level pore sizes, with the smallest pore size being 800 nanometers.

[0021] The present invention has the following beneficial effects:

[0022] 1. The present invention can finely screen fine-grained soil particles to the nanometer level. The existing screening methods cannot finely screen fine-grained soil particles to the nanometer level due to the pore size limitation. The present invention uses a nylon filter cloth with multi-level pore size, in which the minimum pore size reaches 800 nanometers, which can achieve fine screening of fine-grained soil particles to the nanometer level. At the same time, on this basis, particles of different particle groups can be obtained, laying the foundation for further studying the relationship between the physical and mechanical properties of soil and the particle composition.

[0023] 2. The present invention is a direct measurement method. Compared with indirect measurement methods such as the density meter method, the pipette method, and the laser particle size analyzer method, the present invention reduces the errors existing in the intermediate links and makes the obtained particle size curve more accurate.

[0024] 3. The present invention uses a modified vibrating screen machine, combined with wet screening and vibration screening. Compared with the sedimentation analysis method (densitometer method and pipette method), the grading curve obtained is more accurate and the particle size curve is more efficient. The particle size test of a 30g soil sample is completed in about 48 hours by the densitometer method and about 12 hours by the wet screening method. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a structural schematic diagram of a traditional vibrating screen machine;

[0026] Figure 2 It is loess particles after passing through a 0.075mm sieve;

[0027] Figure 3 This is a simplified working diagram of the modified vibrating screen machine for wet screening;

[0028] Figure 4 The following are pictures of filter cloths at various levels;

[0029] Figure 5 To dry the pictures;

[0030] Figure 6 are the loess particles of each particle size group after screening;

[0031] Figure 7 This is a set of Lanzhou loess particle size test curves. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example: Taking Lanzhou loess as an example, a modified traditional vibrating screen machine is used to complete the wet screening of soil particles with a particle size less than 0.075 mm. The Lanzhou loess is screened into 8 particle groups using nylon filter cloths with mesh sizes of 300, 800, 1500, 3000, 8000, 15000, and 18000 respectively. The maximum mesh nylon filter cloth aperture can finely screen fine soil particles to nanometer level. The corresponding relationship between the mesh size of the nylon filter cloth and the particle aperture is shown in Table 1:

[0034] Table 1 Correspondence between nylon filter cloth mesh number and particle pore size

[0035]

[0036] A physical test method for finely screening fine-grained soil particles to nanometer level, comprising the following steps:

[0037] The first step is to obtain loess fine particles with a particle size of less than 0.075 mm through dry sieving to complete the preliminary processing of Lanzhou loess soil samples

[0038] Soil was collected from the site in Lanzhou, Gansu, and sent to the wet sieving laboratory of the Changke Institute. After the soil samples were air-dried, 1000g of the air-dried soil samples were evenly divided into four conical flasks, each filled with 600ml of water and soaked for about 12 hours. The conical flasks were placed on a boiling device and boiled for about 1 hour. After the soil samples were cooled, the upper suspension was poured into a measuring cylinder. The sediment at the bottom of the cup was carefully ground with a pestle with a rubber head, rinsed with water, and passed through a 0.075mm sieve. The sieved suspension was poured into a measuring cylinder, and sodium hexametaphosphate dispersant was added to prevent flocculation. Figure 2 It is loess particles after passing through a 0.075mm sieve.

[0039] The function of the dispersant is to disperse the soil particles that are agglomerated together into individual fine particles. Although there are other types of dispersants such as alcohols (ethanol, isopropanol, etc.), considering the availability and safety of the dispersant and in order to better compare with the results of the density meter, the present invention uses sodium hexametaphosphate solution as a dispersant for testing.

[0040] The second step is to transform the traditional vibrating screen and then wet screen the Lanzhou loess fine-grained soil.

[0041] For traditional vibrating screen, Figure 1 For its structural diagram, some modifications and installations were carried out:

[0042] The nylon filter cloth with a pore size of less than 0.075mm is fixed on the steel screen of the traditional vibrating screen machine with steel bars and rubber rings, so that the pore size of the nylon filter cloth becomes the particle size range of the sieved soil sample, thereby completing the separation of fine-grained soil and finely screening it to the nanometer level;

[0043] Use rubber rings to seal the interfaces of traditional vibrating screens to prevent water overflow during wet screening;

[0044] Use a plastic bucket that is higher than the discharge port to collect soil samples smaller than the particle size at the discharge port to prevent mud from splashing out and reduce soil sample loss;

[0045] Remove the outlet of the steel frame of the soil screening layer, and use butyl tape and transparent tape to seal the outlet of the steel frame of the soil screening layer. Because the screening object is soil particles smaller than 0.075mm (fine-grained soil), it is difficult to flow out directly from the outlet, which easily causes soil sample overflow during the screening process. After the transformation, overflow can be prevented and the sound during the screening process can be reduced.

[0046] like Figure 3As shown in the figure, after the modified traditional vibrating screen machine is started, the soil sample in the measuring cylinder in the previous treatment is poured into the feed port of the vibrating screen machine, and then the rubber ball and rubber belt are also put in from the feed port, so that the soil sample smaller than the aperture quickly passes through the nylon filter cloth and flows out from the discharge port. The size of the separated soil particles is controlled by the mesh number of the nylon filter cloth, and the separated soil particles flow from the discharge port into a plastic bucket whose height exceeds the discharge port. During the screening process, the soil particles can be prevented from being deposited on the surface of the filter cloth by vibration and the placement of rubber balls and rubber belts, which can effectively prevent the soil particles from agglomerating together and reduce the time required for the entire wet screening process. While improving the separation efficiency of soil particles, it also increases the accuracy of soil particle separation, ensuring that all small-size soil particles pass through the modified steel sieve to enter the next level of screening. The number of screening levels required varies according to the mesh number of the nylon filter cloth, and the minimum aperture of the nylon filter cloth reaches the nanometer level.

[0047] In this embodiment, Lanzhou loess with a particle size of less than 0.075 mm is passed through nylon filter cloths with mesh sizes of 300, 800, 1500, 3000, 8000, 15000, and 18000 (such as Figure 4 ), and divide it into 8 particle groups, and the smallest pore size of nylon filter cloth can finely screen fine-grained soil particles to nanometer level.

[0048] (1) 0.075mm~0.05mm

[0049] Fix the 300-mesh nylon filter cloth on the screen, place the screen and the modified steel frame, fix them with a tie ring, then install the top cover with the feed port, and seal the steel frame and the top cover with a rubber strip, and place plastic bucket A at the discharge port. Start the vibrating screen machine, pour the soil sample in the measuring cylinder in the previous treatment from the feed port, and then put in rubber balls and rubber belts. Soil samples smaller than 0.05 mm will flow into plastic bucket A through the discharge port. According to the test results, add clean water from the feed port. When it is observed that the water flowing out of the discharge port is clear, turn off the vibrating screen machine, remove the rubber strip, top cover, modified steel frame, screen, rubber ring and steel bar on the screen in turn, and rinse the remaining soil sample on it into tray No. 1. Tray No. 1 is used for subsequent drying (such as Figure 5 As shown), weighing and other operations are performed, and loess particles with a particle size of 0.075mm to 0.05mm can be obtained. In addition, the soil sample in plastic bucket A will be used for the next level of screening.

[0050] (2) 0.05mm~0.02mm

[0051] Fix the 800-mesh nylon filter cloth on the screen, place the screen and the modified steel frame, fix them with a tie ring, then install the top cover with the feed port, and seal the steel frame and the top cover with a rubber strip, and place the plastic bucket B at the discharge port. Start the vibrating screen machine, pour the soil sample in the plastic bucket A from the feed port, then put in the rubber ball and rubber belt, and the soil sample smaller than 0.02mm flows into the plastic bucket B through the discharge port. According to the test results, add clean water from the feed port. When the water flowing out of the discharge port is observed to be clear, turn off the vibrating screen machine, remove the rubber strip, top cover, tie ring, modified steel frame, screen, rubber ring and steel strip on the screen in turn, and rinse the remaining soil sample on it into the No. 2 tray. Clean the plastic bucket A, and the No. 2 tray is used for subsequent drying, weighing and other operations, and loess particles with a particle size of 0.05mm to 0.02mm can be obtained. In addition, the soil sample in the plastic bucket B will be used for the next level of screening.

[0052] (3) 0.02mm~0.01mm

[0053] Fix the 1500 mesh nylon filter cloth on the screen, place the screen and the modified steel frame, fix them with a tie ring, then install the top cover with the feed port, seal the steel frame and the top cover with a rubber strip, and place the plastic bucket A at the discharge port. Start the vibrating screen machine, pour the soil sample in the plastic bucket B from the feed port, then put in the rubber ball and rubber belt, and the soil sample smaller than 0.01mm flows into the plastic bucket A through the discharge port. According to the test results, add clean water from the feed port. When the water flowing out of the discharge port is observed to be clear, turn off the vibrating screen machine, remove the rubber strip, top cover, tie ring, modified steel frame, screen, rubber ring and steel strip on the screen in turn, and rinse the remaining soil sample on it into the No. 3 tray. Clean the plastic bucket B, and the No. 3 tray is used for subsequent drying, weighing and other operations, and loess particles with a particle size of 0.02mm to 0.01mm can be obtained. In addition, the soil sample in the plastic bucket A will be used for the next level of screening.

[0054] (4) 0.01mm~0.005mm

[0055] Fix the 3000 mesh nylon filter cloth on the screen, place the screen and the modified steel frame, fix them with a tie ring, then install the top cover with the feed port, seal the steel frame and the top cover with a rubber strip, and place the plastic bucket B at the discharge port. Start the vibrating screen machine, pour the soil sample in the plastic bucket A from the feed port, then put in the rubber ball and rubber belt, and the soil sample smaller than 0.005mm flows into the plastic bucket B through the discharge port. According to the test results, add clean water from the feed port. When the water flowing out of the discharge port is observed to be clear, turn off the vibrating screen machine, remove the rubber strip, top cover, tie ring, modified steel frame, screen, rubber ring and steel strip on the screen in turn, and rinse the remaining soil sample on it into the No. 4 tray. Clean the plastic bucket A, and the No. 4 tray is used for subsequent drying, weighing and other operations, and loess particles with a particle size of 0.01mm to 0.005mm can be obtained. In addition, the soil sample in the plastic bucket B will be used for the next level of screening.

[0056] (5) 0.005mm~0.002mm

[0057] Fix the 8000 mesh nylon filter cloth on the screen, place the screen and the modified steel frame, fix them with a tie ring, then install the top cover with the feed port, seal the steel frame and the top cover with a rubber strip, and place the plastic bucket A at the discharge port. Start the vibrating screen machine, pour the soil sample in the plastic bucket B from the feed port, then put in the rubber ball and rubber belt, and the soil sample smaller than 0.002mm flows into the plastic bucket A through the discharge port. According to the test results, add clean water from the feed port. When the water flowing out of the discharge port is observed to be clear, turn off the vibrating screen machine, remove the rubber strip, top cover, tie ring, modified steel frame, screen, rubber ring and steel strip on the screen in turn, and rinse the remaining soil sample on it into the No. 5 tray. Clean the plastic bucket B, and the No. 5 tray is used for subsequent drying, weighing and other operations, and loess particles with a particle size of 0.005mm to 0.002mm can be obtained. In addition, the soil sample in the plastic bucket A will be used for the next level of screening.

[0058] (6) 0.002mm~0.001mm

[0059] Fix the 15000 mesh nylon filter cloth on the screen, place the screen and the modified steel frame, fix them with a tie ring, then install the top cover with the feed port, seal the steel frame and the top cover with a rubber strip, and place the plastic bucket B at the discharge port. Start the vibrating screen machine, pour the soil sample in the plastic bucket A from the feed port, then put in the rubber ball and rubber belt, and the soil sample smaller than 0.001mm flows into the plastic bucket B through the discharge port. According to the test results, add clean water from the feed port. When the water flowing out of the discharge port is observed to be clear, turn off the vibrating screen machine, remove the rubber strip, top cover, tie ring, modified steel frame, screen, rubber ring and steel strip on the screen in turn, and rinse the remaining soil sample on it into the No. 6 tray. Clean the plastic bucket A, and the No. 6 tray is used for subsequent drying, weighing and other operations, and loess particles with a particle size of 0.002mm to 0.001mm can be obtained. In addition, the soil sample in the plastic bucket B will be used for the next level of screening.

[0060] (7) 0.001mm~0.0008mm

[0061] Fix the 18000 mesh nylon filter cloth on the screen, place the screen and the modified steel frame, fix them with a tie ring, then install the top cover with the feed port, seal the steel frame and the top cover with a rubber strip, and place the plastic bucket A at the discharge port. Start the vibrating screen machine, pour the soil sample in the plastic bucket B from the feed port, then put in the rubber ball and rubber belt, and the soil sample smaller than 0.0008mm flows into the plastic bucket A through the discharge port. According to the test results, add clean water from the feed port. When the water flowing out of the discharge port is observed to be clear, turn off the vibrating screen machine, remove the rubber strip, top cover, tie ring, modified steel frame, screen, rubber ring and steel strip on the screen in turn, and rinse the remaining soil sample on it into tray No. 7. Clean plastic bucket B, tray No. 7 is used for subsequent drying, weighing and other operations, and loess particles with a particle size of 0.001mm to 0.0008mm can be obtained. In addition, the soil sample in plastic bucket A is reserved for the next step.

[0062] (8) <0.0008mm

[0063] Rinse the soil sample in plastic bucket A into tray No. 8, which is used for subsequent drying, weighing and other operations, and can obtain loess particles with a particle size of <0.0008mm.

[0064] Step 3: Post-processing of Lanzhou loess after wet sieving

[0065] The 8 particle groups of Lanzhou loess separated by wet screening were dried in a furnace and an oven respectively, and then weighed, recorded and stored after grinding.

[0066] Step 4: Obtain the particle size curve of Lanzhou loess

[0067] The soil particle content of each level is plotted on a logarithmic coordinate system to form a particle distribution curve to represent the distribution of fine-grained soil in different particle group intervals. The particle distribution curve of Lanzhou loess is drawn based on the test data, as shown in Figure 7 shown.

[0068] The above is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed by the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims.

Claims

1. A physical test method for finely screening fine-grained soil particles to nanometer level, characterized in that: The following steps are involved: The first step is to obtain loess fine particles with a particle size of less than 0.075 mm through dry sieving to complete the preliminary processing of soil samples; The second step is to modify the traditional vibrating screen machine and use the modified vibrating screen machine to wet screen the loess fine particles with a particle size of less than 0.075 mm; The third step is the post-processing of the soil after wet screening: the soil particles separated by wet screening are dried separately through a furnace or oven, and then weighed, recorded and saved after grinding; The fourth step is to obtain the particle distribution curve of fine-grained soil: the soil particle content of each level is plotted into a particle distribution curve on a logarithmic coordinate system to represent the distribution of fine-grained soil in different particle group intervals.

2. The physical test method for finely screening fine-grained soil particles to nanometer level as claimed in claim 1, characterized in that: The first step specifically includes: pouring the air-dried soil sample into a conical flask, adding water, soaking for 10 hours to 12 hours, placing the conical flask on a boiling device, and boiling for 0.8 hours to 1 hour; after cooling, let it stand for 1-2 minutes, pouring the upper suspension into a measuring cylinder, carefully grinding the sediment at the bottom of the cup with a rubber-headed pestle, washing with water, passing through a 0.075mm sieve, pouring the sieved suspension into a measuring cylinder, obtaining loess fine particles with a particle size of less than 0.075mm, and then adding sodium hexametaphosphate dispersant to prevent soil particles from flocculating.

3. The physical test method for finely screening fine-grained soil particles to nanometer level as claimed in claim 1 or 2, characterized in that: In the second step, the traditional vibrating screen machine is transformed, including: The nylon filter cloth with a pore size less than 0.075mm is fixed on the steel screen of the traditional vibrating screen machine with steel bars and rubber rings, so that the pore size of the nylon filter cloth becomes the particle size range of the sieved soil sample, thereby completing the separation of fine-grained soil and finely screening it to the nanometer level; Use rubber rings to seal the interfaces of traditional vibrating screens to prevent water overflow during wet screening; Use a plastic bucket that is higher than the discharge port to collect soil samples smaller than the particle size at the discharge port to prevent mud from splashing out and reduce soil sample loss; Remove the existing outlet of the steel frame of the soil screening layer, and then seal it with butyl tape and transparent tape.

4. The physical test method for finely screening fine-grained soil particles to nanometer level as claimed in claim 3, characterized in that: In the second step, the modified vibrating screen machine is used to wet screen the loess fine particles with a particle size of less than 0.075 mm, including: The soil sample with all particles smaller than 0.075 mm is poured into the feed port of the modified vibrating screen machine. The size of the separated soil particles is controlled by the mesh number of the nylon filter cloth. The separated soil particles flow from the discharge port into a plastic bucket whose height exceeds the discharge port.

5. The physical test method for finely screening fine-grained soil particles to nanometer level as claimed in claim 3, characterized in that: The nylon filter cloth has multiple apertures, with the smallest aperture being 800 nanometers.

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