Device for artificially preparing structural soil sample

Abstract

The utility model discloses a device for artificially preparing a structural soil sample, which belongs to the field of geotechnical engineering and comprises a low-temperature forming module, a carbonization module and terminal equipment, the low-temperature forming module is composed of a liquid nitrogen refrigerating system and a sample preparation cabinet, the sample preparation cabinet comprises a sample preparation cabinet body, and an icebreaking disc, a screening system, a weighing disc, a stirring disc, a sample preparation mold and a hydraulic system are sequentially arranged in the sample preparation cabinet body from top to bottom; according to the method, mixed soil mixed with dry ice particles can be subjected to sample preparation under the condition that the temperature is always kept to be lower than the dry ice sublimation temperature, a carbonization module is composed of a CO2 gas cylinder, an N2 gas cylinder A, an N2 gas cylinder B, a humidity controller, a temperature controller, a circulating pump and a reaction cabin, an air bag and a constant-temperature base are arranged in the reaction cabin, nondestructive monitoring of the carbonization process in the sample preparation process is achieved, and the sample preparation efficiency is improved. And the water content of the prepared sample can be controlled. The device provided by the utility model can be used for predicting or simulating the engineering property of the soil body, and provides support for solving engineering problems.

Description

Technical Field

[0001] This utility model discloses a device for artificially preparing structural soil samples, belonging to the field of geotechnical engineering. Background Technology

[0002] Soil is heterogeneous, and fissures, wormholes, and impurities in naturally structured soils often significantly impact the study of soil structure. Furthermore, in structural studies, soil samples are relatively small, and structural differences frequently exist between samples, increasing uncontrollable factors and making the study more challenging. Moreover, the strength of natural soil structure is uncontrollable; obtaining soil samples with varying degrees of structure that meet experimental requirements is difficult, time-consuming, labor-intensive, and expensive. Therefore, artificially preparing soil samples with properties similar to natural structural soils and achieving controllable structural strength is a crucial prerequisite for soil structural research and a key technology for solving engineering problems caused by structural soils.

[0003] The key to preparing structural soil samples lies in the generation of cementing materials and how to simulate the large pores of natural structural soil. Currently, the cementing materials used in artificially prepared structural soil samples mainly include cement, iron oxide, calcium carbonate, and roadbed solidifying agents. Other methods simulate the large pores of natural structural soil by adding ice particles or salt particles to the sample. These methods have undoubtedly promoted the development of artificial structural soil preparation technology, but they still have shortcomings. Taking the sample preparation method using calcium carbonate as a cementing material as an example, lime is added to the remolded soil sample during the preparation process. After saturation, carbon dioxide gas is introduced. Due to the limited solubility of carbon dioxide in water, the contact with the generated calcium hydroxide is insufficient, resulting in a small amount of calcium carbonate produced. Furthermore, calcium carbonate has a certain degree of solubility in water, so the calcium carbonate cementation in the sample prepared by this method is limited, failing to effectively simulate the properties of natural loess, and the structure is uncontrollable. Adding ice and salt particles to reconstituted soil samples to simulate the large pores in natural soil has several drawbacks. Firstly, it fails to accurately reproduce the pore structure of natural soil, meaning it cannot truly replicate the content of pores of different sizes. Secondly, the subsequent removal of salt particles through methods such as seepage disrupts the pore structure of the soil sample, making it impossible to simulate the structure of natural loess. Furthermore, current technologies cannot achieve non-destructive testing for monitoring the formation process of cementing materials. Monitoring often relies on chemical reactions of parallel samples, which significantly increases the number of samples required. Moreover, due to differences between samples, the accuracy of the results is poor. Therefore, these technologies have limitations in monitoring experimental results. Utility Model Content

[0004] In view of the shortcomings of the above-mentioned background technology, the purpose of this utility model is to propose a device for artificially preparing structural soil samples, which can artificially prepare structural soil samples, realize non-destructive monitoring of carbonization process during sample preparation, and control the moisture content of the prepared artificial samples.

[0005] The technical solution adopted by this utility model to achieve the above objectives is as follows: This utility model proposes a device for artificially preparing structural soil samples. The device consists of a low-temperature molding module, a carbonization module, and terminal equipment. The low-temperature molding module consists of a liquid nitrogen refrigeration system and a sample preparation cabinet. The liquid nitrogen refrigeration system is used to supply liquid nitrogen to the sample preparation cabinet to keep the internal temperature of the sample preparation cabinet always below the sublimation temperature of dry ice. The sample preparation cabinet includes a sample preparation cabinet body, and inside the sample preparation cabinet body, from top to bottom, are arranged an ice-breaking plate, a sieving system, a weighing plate, a stirring plate, a sample preparation mold, and a hydraulic system. The ice-breaking plate is equipped with an ice-breaking device for crushing dry ice. The sieving system is used to sieve the crushed dry ice into dry ice particles of different particle sizes. The stirring plate is equipped with a stirring device. The hydraulic head of the hydraulic system is located inside the sample preparation mold. The carbonization module consists of a CO2 cylinder, an N2 cylinder A, an N2 cylinder B, a humidity controller, a temperature controller, a circulating pump, and a reaction chamber. The outlets of the CO2 cylinder and N2 cylinder A are connected to the humidity controller through an inlet manifold. The CO2 cylinder outlet is equipped with pressure switch one, and the N2 cylinder A outlet is equipped with pressure switch two. A vent valve one is located on the top of the humidity controller, which is connected to the temperature controller. A gas temperature and humidity sensor is located at the outlet of the temperature controller, which is connected to the reaction chamber via a pipeline. The bottom of the reaction chamber is connected to the circulation pump via an exhaust port. The circulation pump is connected to the main intake pipe to form a circuit. A pressure switch three is located at the outlet of N2 cylinder B, which is connected to the airbag in the reaction chamber via an airbag inflation / deflation channel. A vent valve two is located between the airbag inflation / deflation channel and pressure switch three. The reaction chamber consists of a visible sealed cover and a reaction chamber body. An airbag and a constant temperature base are located inside the reaction chamber body. The airbag is an annular airbag located in the middle of the inner wall of the reaction chamber body. The constant temperature base is located at the bottom of the reaction chamber body and contains a pressure sensor and a heating device. The terminal equipment is communicatively connected to pressure switch one, pressure switch two, pressure switch three, the gas temperature and humidity sensor, the pressure sensor inside the constant temperature base, and the heating device.

[0006] Furthermore, the liquid nitrogen refrigeration system consists of a liquid nitrogen tank, a temperature sensor, and a valve. The temperature sensor is located at the bottom of the sample preparation cabinet. The valve is installed on the connecting pipeline between the liquid nitrogen tank and the sample preparation cabinet, and both the valve and the temperature sensor are connected to the equipment terminal for communication.

[0007] Furthermore, the ice-breaking device includes an ice-breaking blade and a drive motor for driving the ice-breaking blade to rotate about its own rotation axis.

[0008] Furthermore, the screening system has at least three vibrating screening discs arranged vertically to each other, and the screen aperture of the upper vibrating screening disc in any two adjacent vibrating screening discs is larger than that of the lower vibrating screening disc. Except for the uppermost vibrating screening disc, each of the other vibrating screening discs is provided with a discharge conduit for conveying dry ice particles at its bottom, and the top of the discharge conduit is provided with a switch and the bottom leads to a weighing pan; the bottom of the weighing pan is provided with a discharge port; the bottom of the mixing disc is provided with a discharge port and a baffle.

[0009] Furthermore, the screening system also has a waste tray, which is located below the lowest vibrating screening tray.

[0010] Through the above design scheme, this utility model can bring the following beneficial effects: The device of this utility model can artificially prepare structural soil samples. This utility model can achieve non-destructive monitoring of the carbonation process during sample preparation and can control the moisture content of the artificial samples. It can prepare soil samples according to the actual conditions of a specific soil body, eliminate the influence of interfering factors, and predict or simulate the engineering properties of the soil, providing support for solving engineering problems. This device for artificially preparing structural soil samples can perform soil sample drying-wet and freeze-thaw cycle operations.

[0011] Further advantages: The reaction chamber of this invention contains an airbag and a constant-temperature base. After inflation, the airbag encloses the middle part of the artificial sample, fitting tightly against it and fixing it in place. This divides the reaction chamber into upper and lower sections, with gas flowing between them only through the artificial sample. CO2 enters the lower part of the reaction chamber only through the artificial sample, then enters the exhaust pipe through the exhaust port and is recycled. During this process, the CO2 gas has a single channel, ensuring full contact between the gas and the interior of the artificial sample, resulting in a uniform carbonization reaction. After degassing, the airbag separates from the artificial sample. The constant-temperature base is equipped with a pressure sensor to measure the mass of the artificial sample on it. A heating device is also included inside the constant-temperature base to prevent condensation on the outer wall of the base, which could affect the mass measurement results. Attached Figure Description

[0012] The accompanying drawings are provided to further illustrate the present invention and form part of this application. The illustrative embodiments and descriptions of the present invention are used to understand the present invention and do not constitute an undue limitation thereof. In the drawings:

[0013] Figure 1 A schematic diagram of the overall structure of the device for artificially preparing structural soil samples;

[0014] Figure 2 This is a diagram of the internal structure of the sample making cabinet;

[0015] Figure 3 This is a cross-sectional view of the reaction chamber;

[0016] Figure 4 This is a graph showing the percentage of porosity in sample No. 1.

[0017] Figure 5 The porosity percentage diagram for sample No. 2;

[0018] Figure 6 The porosity percentage diagram for sample No. 3;

[0019] Figure 7 SEM image of rod-shaped calcite in natural loess;

[0020] Figure 8 The image shows the energy dispersive spectroscopy (EDS) results of rod-shaped calcite in natural loess.

[0021] Figure 9 SEM image of cubic CaCO3 in an artificially prepared sample;

[0022] Figure 10 The energy dispersive spectroscopy (EDS) results of cubic CaCO3 in an artificially prepared sample are shown.

[0023] Figure 11 SEM image of spindle-shaped CaCO3 in an artificially prepared sample;

[0024] Figure 12 The energy dispersive spectroscopy (EDS) results of spindle-shaped CaCO3 in an artificially prepared sample are shown.

[0025] Figure 13 SEM images of thin-film CaCO3 in artificially prepared samples;

[0026] Figure 14 The image shows the energy dispersive spectroscopy (EDS) results of thin-film CaCO3 in artificially prepared samples.

[0027] Figure 15 SEM image of observation point 1 for artificially prepared loess sample;

[0028] Figure 16 Distribution map of C element observed at observation point 1 for artificially prepared loess samples;

[0029] Figure 17 Distribution map of Ca element observed at observation point 1 for artificially prepared loess samples;

[0030] Figure 18 SEM image of observation point 2 for artificially prepared loess sample;

[0031] Figure 19 Distribution map of C element observed at observation point 2 for artificially prepared loess samples;

[0032] Figure 20 Distribution map of Ca element observed at observation point 2 for artificially prepared loess samples;

[0033] Figure 21 The image shows the microstructure of natural loess at observation point 1, magnified 1000 times.

[0034] Figure 22 The image shows the microstructure of natural loess at observation point 1, magnified 2000 times.

[0035] Figure 23 This is a microscopic structure diagram of natural loess observation point 2, magnified 1000 times.

[0036] Figure 24 The image shows the microstructure of natural loess at observation point 2, magnified 2000 times.

[0037] Figure 25 Microscopic structure diagram of observation point 3 of loess sample prepared artificially at 1000x magnification;

[0038] Figure 26 Microscopic structure diagram of observation point 3 of loess sample prepared artificially at magnification of 2000x;

[0039] Figure 27 Microscopic structure diagram of observation point 4 of loess sample prepared artificially at 1000x magnification;

[0040] Figure 28 Microscopic structure diagram of observation point 4 of loess sample prepared artificially at magnification of 2000x;

[0041] Figure 29 Pore ​​content diagram of loess sample No. 4 prepared artificially;

[0042] Figure 30 Pore ​​content diagram of loess sample No. 5 prepared artificially;

[0043] Figure 31 The collapse coefficient of natural loess and artificially prepared loess is shown in the diagram.

[0044] The following labels are used in the diagram: 1-Liquid nitrogen tank, 2-Temperature sensor, 3-Valve, 4-Sample preparation cabinet, 5-Sample preparation cabinet body, 6-Ice breaking tray, 7-Weighing tray, 8-Stirring tray, 9-Sample preparation mold, 10-Hydraulic system, 11-Sieve No. 1, 12-Sieve No. 2, 13-Sieve No. 3, 14-Sieve No. 4, 15-Waste tray, 16-Discharge conduit, 17-CO2 cylinder, 18-N2 cylinder A, 19-N2 cylinder B. 20-Humidity controller, 21-Temperature controller, 22-Circulation pump, 23-Reaction chamber, 24-Pressure switch one, 25-Pressure switch two, 26-Relief valve one, 27-Gas temperature and humidity sensor, 28-Exhaust port, 29-Pressure switch three, 30-Airbag inflation / deflation channel, 31-Relief valve two, 32-Visual sealing cover, 33-Reaction chamber body, 34-Airbag, 35-Constant temperature base, 36-Terminal equipment. Detailed Implementation

[0045] To make the objectives, features, and advantages of this utility model more apparent and understandable, the technical solutions of this utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, this utility model is not limited to the following embodiments, and specific implementation methods can be determined according to the technical solutions of this utility model and actual conditions. To avoid obscuring the essence of this utility model, well-known methods, processes, flows, components, and circuits are not described in detail.

[0046] I. The device proposed in this utility model is described in detail below:

[0047] Combination Figure 1 , Figure 2 and Figure 3 The device for artificially preparing structural soil samples proposed in this utility model consists of a low-temperature molding module, a carbonization module, and a terminal device 36.

[0048] The cryogenic molding module consists of a liquid nitrogen cooling system and a sample preparation cabinet 4. The liquid nitrogen cooling system consists of a liquid nitrogen tank 1, a temperature sensor 2, and a valve 3. The temperature sensor 2 is located at the bottom of the sample preparation cabinet 4, and the valve 3 is located on the connecting pipe between the liquid nitrogen tank 1 and the sample preparation cabinet 4. The sample preparation cabinet 4 includes a cabinet body 5. Inside the cabinet body 5, from top to bottom, are arranged an ice-breaking tray 6, a sieving system, a weighing tray 7, a stirring tray 8, a sample preparation mold 9, and a hydraulic system 10. The sieving system includes a No. 1 sieve 11, a No. 2 sieve 12, a No. 3 sieve 13, a No. 4 sieve 14, a waste tray 15, and a discharge conduit 16.

[0049] The carbonization module consists of a CO2 cylinder 17, an N2 cylinder A18, an N2 cylinder B19, a humidity controller 20, a temperature controller 21, a circulating pump 22, and a reaction chamber 23. The outlet of the CO2 cylinder 17 is equipped with a pressure switch 24, which controls the CO2 pressure within the system to a target value. Increasing the CO2 concentration under pressure accelerates the formation of CaCO3. Furthermore, a certain pressure accelerates the rate at which CO2 passes through the artificial sample in the reaction chamber 23, ensuring sufficient CO2 contact with Ca(OH)2 for reaction. The outlet of the N2 cylinder A18 is equipped with a pressure switch 25, which heats the N2 to dry the artificial sample in the reaction chamber 23. During this process, the pressure switch 25 controls the internal gas pressure, accelerating the rate at which N2 passes through the artificial sample and speeding up the drying process. CO2 cylinder 17 and N2 cylinder A18 are connected to humidity controller 20 via an inlet manifold. Humidity controller 20 has a vent valve 26 at its top and is connected to temperature controller 21. Temperature controller 21 has a gas temperature and humidity sensor 27 at its outlet and is connected to reaction chamber 23. The bottom of reaction chamber 23 is connected to circulation pump 22 via an exhaust port 28. Circulation pump 22 is connected to the inlet manifold to form a circuit. N2 cylinder B19 has a pressure switch 29 at its outlet to control the pressure inside gas bladder 34, achieving inflation and deflation. N2 cylinder B19 is connected to reaction chamber 23 via gas bladder inflation / deflation channel 30. A vent valve 31 is located between gas bladder inflation / deflation channel 30 and pressure switch 29.

[0050] Liquid nitrogen refrigeration system: Open valve 3 to allow liquid nitrogen to enter sample preparation chamber 4. Temperature sensor 2 monitors the temperature in real time. When the target temperature is reached (preferably -85℃), valve 3 closes. When the ambient temperature is higher than the target temperature, valve 3 opens.

[0051] The sample preparation cabinet 4 has the following structure: An ice-breaking device for crushing dry ice is installed inside the ice-breaking tray 6. This device includes ice-breaking blades and a drive motor to rotate the blades around their own axis of rotation. The lower end of the ice-breaking tray 6 is the discharge port; after the dry ice is crushed, it enters the screening system through the discharge port. The screening system includes, from top to bottom, sieves 11 (No. 1), 12 (No. 2), 13 (No. 3), and 14 (No. 4). Sieve 11 preferably has a mesh size of 0.355 mm (45 mesh); sieve 12 preferably has a mesh size of 0.090 mm (170 mesh); sieve 13 preferably has a mesh size of 0.045 mm (325 mesh); and sieve 14 preferably has a mesh size of 0.015 mm (900 mesh). Each of the No. 2 sieve 12, No. 3 sieve 13, and No. 4 sieve 14 has a discharge conduit 16 at its bottom. The top of each discharge conduit 16 has a switch, and the bottom leads to the weighing pan 7. Dry ice particles enter the weighing pan 7 through the discharge conduit 16. The amount of dry ice entering the weighing pan 7 can be controlled by the switch at the top of the discharge conduit 16. A waste pan 15 is located at the bottom of the No. 4 sieve 14 and receives dry ice waste with a particle size less than 15μm. A mixing pan 8 is connected below the weighing pan 7. The bottom of the weighing pan 7 has a discharge port, through which the dry ice particles in the weighing pan 7 enter the mixing pan 8. The mixing pan 8 is equipped with a stirring device and has a discharge port and baffle at its bottom. When the baffle is open, the mixed soil material C in the mixing pan 8 enters the sample preparation mold 9 through the discharge port at the bottom of the mixing pan 8. The sample preparation mold 9 is connected to the hydraulic system 10. The hydraulic head of the hydraulic system 10 is located inside the sample preparation mold 9. The hydraulic head of the hydraulic system 10 cooperates with the inner cavity of the sample preparation mold 9. When the hydraulic head of the hydraulic system 10 rises, it presses the mixed soil material C into shape.

[0052] Humidity controller 20 is used to humidify the incoming gas. Temperature controller 21 is used to control the temperature of the gas processed by humidity controller 20. After processing, the gas continues to circulate after being measured by gas temperature and humidity sensor 27 until the target value is reached. It should be noted that in this utility model, humidity controller 20, temperature controller 21 and gas temperature and humidity sensor 27 are all commercially available products and belong to the prior art, so they will not be described in detail.

[0053] The reaction chamber 23 consists of a visible sealing cover 32 and a reaction chamber body 33. The reaction chamber body 33 contains an airbag 34 and a constant-temperature base 35. The airbag 34, inflated by an N2 gas cylinder B19, wraps around the middle part of the artificial sample, fitting tightly against it and fixing it in place. This divides the interior of the reaction chamber 23 into upper and lower sections, with gas flowing between the two sections only through the artificial sample. CO2 enters the lower part of the reaction chamber 23 only through the artificial sample, enters the exhaust pipe through the exhaust port 28, and is recycled. During this process, the CO2 gas path is singular, ensuring full contact between the gas and the interior of the artificial sample, resulting in a uniform carbonization reaction. The airbag 34 is deflated through the second vent valve 31, after which it separates from the artificial sample. The constant-temperature base 35 is equipped with a pressure sensor to measure the mass of the artificial sample on it. The constant-temperature base 35 also contains a heating device to prevent condensation on the outer wall of the base, which could affect the mass measurement results.

[0054] Terminal device 36 is a computer or mobile phone.

[0055] II. Operating Procedures:

[0056] 1. The operational steps for preparing structural loess samples using the aforementioned apparatus for artificially preparing structural soil samples are as follows:

[0057] The start-up, shutdown, data analysis and processing, and parameter settings of the equipment are controlled by terminal device 36.

[0058] (1) Obtain natural loess and perform mercury intrusion porosimetry (MIP) tests on three undamaged samples to obtain pore distribution data. The average of the three MIP test data is used to determine the percentage content of macropores in each pore size range. Here, macropores with a diameter greater than 15 μm are preferred, and the macropore size ranges are divided into 15-45 μm, 45-90 μm, and 90-355 μm. Existing research generally considers pores with a diameter greater than 16 μm in loess to be macropores, and the percentage content of each range needs to be determined in conjunction with MIP tests. The boundary values ​​of the macropore size ranges measured by MIP tests are 45 μm, 90 μm, and 355 μm, respectively. Considering the sieve size, the initial macropore diameter is taken as 15 μm. Therefore, the macropore size ranges are divided as described above. Dividing macropores according to this range improves the accuracy of pore content calculation and effectively reduces the difference in macropore content between artificial samples and natural soil samples. Based on the percentage of pores in each pore size range, the required mass of dry ice particles for each pore size range is calculated. The mass of dry ice particles with a particle size in the range of 15-45 μm is m. 15-45 The masses of dry ice particles with diameters in the ranges of 45-90 μm and 90-355 μm are m and m, respectively. 45-90 and m 90-355 .

[0059] (2) The natural density ρ and natural moisture content ω of natural loess were measured using the ring cutter method, and the dry density ρ of natural loess was calculated.d The natural density ρ of natural loess is calculated as follows:

[0060]

[0061] In the formula, V T denoted as , where is the volume of the natural loess sample cut by the ring cutter, and m is the mass of the natural loess sample cut by the ring cutter in its natural state.

[0062] The natural water content of loess is ω, and its calculation process is as follows:

[0063]

[0064] In the formula, m is the mass of the natural loess sample taken by the ring cutter in its natural state, m s The mass of natural loess with mass m is the mass after drying at 105℃ for 8 hours.

[0065] Dry density ρ of natural loess d It is determined by the natural density ρ and the natural moisture content ω, using the following formula:

[0066]

[0067] (3) The natural loess was air-dried and crushed, then sieved using a 0.5mm sieve to remove particles larger than 0.5mm and impurities to ensure the uniformity of the artificial sample. Simultaneously, the moisture content ω of the air-dried soil was tested. d ; Moisture content of air-dried soil ω d The calculation formula is as follows:

[0068]

[0069] In the formula m d For the quality of air-dried soil, m sd For a mass of m d The mass of air-dried soil after drying at 105℃ for 8 hours;

[0070] (3) Add CaO to the air-dried soil and mix thoroughly. The amount of CaO incorporated is determined by the target CaCO3 content of the artificial sample. The optimal CaO incorporation ratio (the ratio of the mass of the admixture to the mass of the incorporated material) is selected. n represents the target CaCO3 percentage content of the artificial sample, which is 14%, where the moisture content of the air-dried soil is ω. d Calculated at 4%.

[0071] CaO doping amount m CaO The determination process is as follows:

[0072]

[0073] In the formula, 0.56 is the conversion factor between CaCO3 and CaO, n is the target percentage content of CaCO3 in the artificial sample, and m d For the quality of air-dried soil, ω d This refers to the moisture content of air-dried soil.

[0074] (5) Based on the target density and volume of the prepared artificial sample, calculate and weigh the corresponding mass of mixed soil material A, and calculate the dry weight m of mixed soil material A. As The mass m of mixed soil material A A and dry weight m As The calculation process is as follows;

[0075]

[0076]

[0077] In the formula, n is the target CaCO3 percentage content of the artificial sample, and ρ d The dry density of natural loess is equal to the target dry density of the artificial sample, and V is the target volume of the artificial sample (m). d For the quality of air-dried soil, m CaO For the mass of CaO, ω d This refers to the moisture content of air-dried soil.

[0078] (6) Spray distilled water onto the mixed soil A and stir to ensure that CaO and water are in full contact to generate Ca(OH)2, thus obtaining mixed soil B, which is then added to the mixing tray 8 of the sample preparation cabinet 4.

[0079] (7) Turn on the liquid nitrogen cooling system. When the temperature inside the sample preparation cabinet 4 drops to -85℃, place the dry ice in the ice breaking plate 6, close the cabinet door of the sample preparation cabinet 4, and start the ice breaking plate 6 to crush the dry ice.

[0080] (8) The ice-breaking disc 6 stops working, and the crushed dry ice enters the screening system. The vibrating screening disc is started, and the disc vibrates to separate the dry ice particles into five parts: larger than 355μm, 90-355μm, 45-90μm, 15-45μm, and smaller than 15μm. These are stored in sieves 11, 22, 33, 44, and waste tray 15, respectively. The discharge conduit 16 of sieve 2 is opened, and the dry ice particles in the 90-355μm range fall into the weighing tray 7, with a mass of m. 90-355 At that time, the top switch of the discharge conduit 16 of screen 2 (12) is closed. Screens 3 (13) and 4 (14) are operated as above, taking dry ice particles m respectively. 45-90 m 15-45 Open the bottom outlet of weighing pan 7, and dry ice particles enter the mixing pan 8.

[0081] (9) Start the mixing plate 8. Mix the soil material B and dry ice particles in the mixing plate 8 evenly to obtain the mixed soil material C. Open the bottom baffle of the mixing plate 8 and the mixed soil material C enters the sample preparation mold 9.

[0082] (10) Close the bottom baffle of the mixing plate 8, start the bottom hydraulic system 10 of the sample preparation mold 9, and press the mixed soil material C into an artificial sample.

[0083] (11) Turn off the liquid nitrogen cooling system, open the cabinet door of sample preparation cabinet 4, and take out the pressed artificial sample. At this time, the dry ice inside the artificial sample sublimates, forming large pores inside.

[0084] (12) Set the CO2 pressure (i.e., the pressure inside the reaction chamber 23) in the terminal equipment 36, and set the target values ​​for gas humidity and temperature. Turn on the pressure switch 24 at the outlet of the CO2 cylinder 17, start the circulation pump 22, and wait for the humidity and temperature to reach the target values. The preferred humidity is 80% and the temperature is 20℃.

[0085] (13) Place the extracted artificial sample on the constant temperature base 35 inside the reaction chamber 23. Open switch 29 at the outlet of N2 cylinder B19 until the air bag 34 is in contact with the artificial sample, then close switch 29 at the outlet of N2 cylinder B19 and close the visible sealing cover 32. Wait for the system pressure to reach the target value, preferably 200 kPa.

[0086] (14) During the reaction, evaluate the carbonization process: Close pressure switch 24 at the outlet of CO2 cylinder 17, and open pressure switch 25 at the outlet of N2 cylinder A18, allowing N2 to circulate within the system. Simultaneously open vent valve 26, allowing CO2 in the system to be discharged through vent valve 26. Close vent valve 26 after 5 minutes. Open vent valve 31 to discharge N2 from air bag 34, separating air bag 34 from the artificial sample. Reduce the humidity of N2 in the system to 2% using humidity controller 20, and adjust N2 to 105℃ using temperature controller 21 for 10 hours to dry the artificial sample. Measure the dry weight m1 of the artificial sample. At this time, m1 and m s The difference is the mass of CaCO3 produced. Combined with the amount of CaO added when preparing the artificial sample, the amount of carbonized calcium ions can be obtained, and thus the carbonization reaction process can be determined.

[0087] The percentage of carbonized calcium ions relative to the total amount of added calcium ions is used as the carbonization reaction progress index P. The carbonization reaction progress index P is calculated as follows.

[0088]

[0089] In the formula, P is the carbonization reaction progress index, m1 is the mass of the artificial sample after drying, and m As The dry weight of soil mixture A required for preparing the artificial sample, mCaO The required mass of CaO in soil mixture A for preparing artificial samples;

[0090] (15) The target moisture content of the artificial sample and the target moisture content control process of the wet-dry cycle are as follows: After the carbonization process is completed, the pressure switch 24 at the outlet of CO2 cylinder 17 is closed, and the pressure switch 25 at the outlet of N2 cylinder A18 is opened. N2 enters the system for circulation. At the same time, the vent valve 26 is opened, and CO2 in the system is discharged through the vent valve 26. After 5 minutes, the vent valve 26 is closed. The vent valve 31 is opened to discharge N2 in the air bag 34, so that N2 is separated from the artificial sample. The humidity of N2 in the system is reduced by the humidity controller 20, and the temperature controller 21 is used to adjust N2 to the predetermined temperature to dry the artificial sample. The dry weight m2 of the artificial sample is measured. The weight m3 of the artificial sample is monitored in real time by the constant temperature base. At this time, the moisture content of the artificial sample is (m3-m2) / m2. When the moisture content of the artificial sample reaches the target value, the gas circulation stops.

[0091] In this embodiment, in step (15), after the carbonization reaction process is completed, the humidity of N2 in the system is adjusted to 2% and the temperature is 105°C by the humidity controller 20 and the temperature controller 21. After 10 hours of continuous cycling, the dry weight m2 of the artificial sample is measured. The humidity of N2 in the system is adjusted to 80% and the temperature is 20°C by the humidity controller 20 and the temperature controller 21. The weight m3 of the artificial sample is measured in real time. The real-time moisture content (m3-m2) / m2 of the artificial sample can be obtained by measuring the difference between the weight m3 and the dry weight m2 of the artificial sample in real time until the real-time moisture content reaches the target moisture content.

[0092] (16) After the artificial sample reaches the target moisture content, turn off pressure switch 1 24, pressure switch 25, pressure switch 3 29 and circulation pump 22, open the visible sealing cover 32 of reaction chamber 23 and take out the artificial sample.

[0093] 2. The above-mentioned apparatus for artificially preparing structural soil samples is used to perform soil sample drying and wetting, freeze-thaw cycle operation steps. It should be noted that the soil sample here refers to any soil sample, and the apparatus can perform drying and wetting and freeze-thaw cycle tests on any soil sample, not limited to artificially prepared structural soil samples.

[0094] The device of this invention only requires a carbonization module and terminal equipment 36 to conduct soil sample wet-dry and freeze-thaw cycle tests. The wet-dry cycle operation steps are as follows:

[0095] (1) Place the soil sample on the constant temperature base 35 of the reaction chamber 23 and close the visible sealing cover 32 of the reaction chamber 23. Set the gas humidity to 2% and the temperature to 105℃ through the terminal device 36, open the pressure switch 25 at the outlet of N2 cylinder A18, and start the circulation pump 22. After 10 hours, turn off the pressure switch 25 and the circulation pump 22, and wait for the temperature inside the reaction chamber 23 to drop to room temperature. Measure the mass m4 of the soil sample at this time.

[0096] (2) Set the target humidity value for the soil sample. Depending on the experimental requirements, the target humidity can be a fixed value or a variation curve. For the process of the soil sample changing from dry to wet, set the gas humidity to 80% and the temperature to 20℃. For the process of changing from wet to dry, set the gas humidity to 2% and the temperature to 20℃. Turn on switch 25 at the outlet of N2 cylinder A18 and start the circulation pump 22. Measure the mass of the soil sample in real time using the constant temperature base 35, which is m5. The soil sample moisture content is then (m5-m4) / m4. Monitor the soil sample moisture content and control the experimental process accordingly.

[0097] The freeze-thaw cycle operation steps are as follows:

[0098] (1) Place the soil sample on the constant temperature base 35 of the reaction chamber 23 and close the visible sealing cover 32 of the reaction chamber 23. Set the gas humidity to 30% and the temperature to the target value through the terminal device 36. The target value can be a fixed value or a variation curve.

[0099] (2) Open pressure switch 25 at the outlet of N2 cylinder A18 and start circulation pump 22. Set the freezing or thawing time according to the test requirements.

[0100] When performing dry-wet and freeze-thaw coupled cycles, simply set both humidity and temperature to target values.

[0101] III. Examples

[0102] 1. Operation process

[0103] The device of this invention is used to prepare a sample, which is a cylinder with a diameter of 39.1 mm and a height of 80 mm. The specific steps are as follows:

[0104] a. Mercury intrusion porosimetry was performed on natural loess samples, and the porosity of three natural loess samples (samples 1-3) in each pore size range is as follows: Figures 4-6 As shown, the three natural loess mercury intrusion porosimetry samples were taken from the same type of natural loess. Parallel testing of these three samples was conducted to avoid the influence of fissures, wormholes, and plant roots in the natural loess, thus ensuring that the experimental data represent the porosity characteristics of the natural loess. The macropore content and porosity are shown in Table 1. Based on the volume of the artificially prepared soil sample and the target porosity (the average porosity in Table 1), the amount of dry ice particles used was calculated, as shown in Table 2. The calculation process is as follows.

[0105] Taking pores with a pore size in the range of 15-45 μm as an example, its content is:

[0106]

[0107] The required mass of dry ice particles with a diameter in the range of 15-45 μm is:

[0108] m 15-45 =(39.1 / 2) 2 ×3.14×80×32.16%×17.11%÷1000×1.56=8.24, the unit is g, and the density of dry ice is 1.56 g / cm³. 3 .

[0109] Similarly, the porosity in the pore size ranges of 45-90μm, 90-355μm, and greater than 355μm is 5.35%, 9.78%, and 0, respectively, and the required dry ice particle masses for the corresponding particle size ranges are 2.58g, 4.71g, and 0, respectively.

[0110] Table 11-3 Macroporosity of Natural Loess Samples

[0111]

[0112] Table 2. Mass of dry ice particles in each particle size range required for artificial soil sample preparation.

[0113] Dry ice particle size / pm 15-45 45-90 90-355 Dry ice particle mass / g 8.24 2.58 4.71

[0114] b. Take natural loess, air-dry it, and crush it. Sift it using a 0.5mm sieve. Simultaneously, determine the natural moisture content ω of the natural loess using the drying method, and test the moisture content ω of the air-dried soil. d Add CaO to the air-dried soil and mix thoroughly. The CaO incorporation ratio is 14%.

[0115] c. The dry density of natural loess was found to be 1.277 g / cm³. 3 After calculation, 127.51g of mixed soil material A was taken, sprayed with distilled water and stirred, and added to the mixing tray 8 of the sample preparation cabinet 4.

[0116] d. Follow the above-mentioned structural loess sample preparation steps (7)-(14) until the carbonization reaction is completed.

[0117] e. Following the above-mentioned procedures for preparing structural loess samples, the moisture content of the artificially prepared samples was ultimately controlled to be the same as that of natural loess, at 16.7%.

[0118] 2. Testing the properties of artificially prepared soil samples

[0119] Scanning electron microscopy, mercury porosimetry, and collapsibility tests were performed on natural loess and artificially prepared loess samples. The results are as follows.

[0120] (1) Scanning electron microscopy experiment

[0121] Compared with natural loess, energy dispersive spectroscopy (EDS) analysis revealed that calcite (a calcium carbonate mineral with the chemical formula CaCO3, the most common natural calcium carbonate mineral) formed between soil particles during sample preparation. Calcite exhibited three morphologies: cubic, spindle-shaped, and thin-film-shaped. In contrast, calcite in natural loess is mostly rod-shaped. Figure 7 , Figure 8 , Figure 9 , Figure 10 , Figure 11 , Figure 12 , Figure 13 , Figure 14 As shown in Tables 3, 4, 5, and 6, in artificially prepared loess samples, different forms of calcite work together to bind the soil particles together.

[0122] Table 3 Energy dispersive spectroscopy analysis of rod-shaped calcite in natural loess

[0123] Element number Element symbol Element name Atomic concentration Mass concentration 8 O Oxygen 62.52 45.82 20 Ca Calcium 11.28 20.71 14 Si Silicon 8.34 10.73 26 Fe Iron 5.66 14.48 13 Al Aluminium 2.24 2.77 6 C Carbon 9.97 5.49

[0124] Table 4 Energy dispersive spectroscopy analysis of cubic CaCO3 in artificially prepared samples

[0125]

[0126]

[0127] Table 5 Energy dispersive spectroscopy analysis of spindle-shaped CaCO3 in artificially prepared samples.

[0128] Element number Element symbol Element name Atomic concentration Mass concentration 8 O Oxygen 50.91 16.00 20 Ca Calcium 16.05 12.63 79 Au Gold 17.50 67.70 6 C Carbon 15.54 3.67

[0129] Table 6 Energy dispersive spectroscopy analysis of thin-film CaCO3 in artificially prepared samples.

[0130] Element number Element symbol Element name Atomic concentration Mass concentration 8 O Oxygen 59.42 36.56 20 Ca Calcium 19.13 29.49 6 C Carbon 18.06 8.34 79 Au Gold 3.38 25.61

[0131] To further clarify the distribution of CaCO3 in the samples, energy dispersive spectroscopy (EDS) was performed on different parts of the artificially prepared loess samples to obtain the distribution of different elements within the observation range. The results are shown in [Figure number missing]. Figures 15 to 20 Overall, the distribution of C and Ca elements in the samples was relatively consistent, mainly distributed in the contact areas between soil particles, or forming long aggregates that linked the soil particles together. In addition, they were also distributed on the surface of some aggregates and around clay particles attached to the surface of the framework particles. It is evident that the artificially structured loess prepared using the device of this invention can form effective CaCO3 cementation between soil particles.

[0132] The microstructure of natural loess and artificially prepared loess samples was observed, such as... Figures 21 to 28 As shown, natural loess exhibits a skeletal structure, with skeletal particles primarily consisting of silt and numerous clay particles adhering to its surface, resulting in a large number of porous structures. In the 1000x magnification image, the maximum diameter of larger pores was measured using a scanning electron microscope. It can be seen that the diameter of larger pores in natural loess is mostly in the range of 10μm to 20μm, with some large pores reaching 40μm. In contrast, artificially prepared loess shows a skeletal structure and more porous structures, with larger pores mostly in the range of 15μm to 30μm, and some large pores reaching 60μm. Overall, the microstructures of the two are similar.

[0133] (2) Mercury porosimetry

[0134] Two artificially prepared loess samples (numbered 4 and 5) were subjected to mercury intrusion porosimetry. The results are shown in Table 7. Figure 29 and Figure 30 As shown in the figure. Analysis shows that the artificial structured loess prepared using the device of this invention is quite similar to natural loess in terms of pore distribution, especially in terms of macropore distribution, where it shows a high degree of similarity to natural loess.

[0135] Table 7 Macropore content of artificially prepared loess samples

[0136]

[0137] (3) Collapsibility test

[0138] Collapsibility tests were conducted on natural loess and artificially prepared loess samples, and the results are as follows: Figure 31 As shown, artificially prepared loess exhibits collapsibility, but its collapsibility is slightly lower than that of natural loess, while its initial collapsibility pressure is higher than that of natural loess.

[0139] In summary, the apparatus for preparing artificially structured loess of this invention produces samples that are highly similar to natural loess in terms of cementing materials, microstructure, pore distribution, and collapsibility, and can be used for the study of loess structure.

Claims

1. An apparatus for artificially preparing a structural soil sample, characterized by comprising: The device is composed of a low-temperature forming module, a carbonization module and a terminal device; the low-temperature forming module is composed of a liquid nitrogen refrigeration system and a sample preparation cabinet, the liquid nitrogen refrigeration system is used for delivering liquid nitrogen to the sample preparation cabinet to keep the temperature inside the sample preparation cabinet below the dry ice sublimation temperature at all times; the sample preparation cabinet includes a sample preparation cabinet body, the inside of the sample preparation cabinet body is sequentially provided from top to bottom with an ice breaking disc, a screening system, a weighing disc, a stirring disc, a sample preparation mold and a hydraulic system; the ice breaking disc is internally provided with an ice breaking device for crushing dry ice; the screening system is used for screening dry ice particles of different particle size levels according to the particle size of the crushed dry ice; the stirring disc is internally provided with a stirring device; the hydraulic head of the hydraulic system is located inside the sample preparation mold; the carbonization module is composed of a CO2 gas cylinder, an N2 gas cylinder A, an N2 gas cylinder B, a humidity controller, a temperature controller, a circulating pump and a reaction cabin, the outlets of the CO2 gas cylinder and the N2 gas cylinder A are connected with the humidity controller through a gas inlet main pipe, the outlet of the CO2 gas cylinder is provided with a pressure switch one, and the outlet of the N2 gas cylinder A is provided with a pressure switch two; the top of the humidity controller is provided with a gas release valve one, and the humidity controller is connected with the temperature controller; the outlet of the temperature controller is provided with a gas temperature and humidity sensor, and the outlet of the temperature controller is connected with the reaction cabin through a pipeline; the bottom of the reaction cabin is connected with the circulating pump through an exhaust hole; the circulating pump is connected with the gas inlet main pipe to form a loop; the outlet of the N2 gas cylinder B is provided with a pressure switch three, the outlet of the N2 gas cylinder B is communicated with a gas bag in the reaction cabin through a gas bag charging and discharging channel, and the gas bag charging and discharging channel is provided with a gas release valve two between the pressure switch three; the reaction cabin is composed of a visible sealing cover and a reaction cabin body, the reaction cabin body is internally provided with a gas bag and a constant temperature base, the gas bag is an annular gas bag, and the gas bag is arranged at the middle part of the inner wall of the reaction cabin body; the constant temperature base is located at the bottom of the reaction cabin body, and is internally provided with a pressure sensor and a heating device; the terminal device is in communication connection with the pressure switch one, the pressure switch two, the pressure switch three, the gas temperature and humidity sensor, the pressure sensor in the constant temperature base and the heating device respectively; The liquid nitrogen refrigeration system is composed of a liquid nitrogen tank, a temperature sensor and a valve, the temperature sensor is located at the bottom of the sample preparation cabinet; the valve is arranged on the connecting pipeline between the liquid nitrogen tank and the sample preparation cabinet, and the valve and the temperature sensor are both in communication connection with the equipment terminal; The ice breaking device includes an ice breaking knife and a driving motor for driving the ice breaking knife to rotate around the rotation axis thereof; The screening system has at least three oscillating screening discs arranged one above another, and the mesh hole diameter of the oscillating screening disc located at the upper side of any adjacent two oscillating screening discs is greater than the mesh hole diameter of the oscillating screening disc located at the lower side; except the oscillating screening disc located at the uppermost side, the bottom of each of the other oscillating screening discs is provided with a discharge conduit for conveying dry ice particles, and the top of the discharge conduit is provided with an on-off valve and the bottom is communicated with the weighing disc; the bottom of the weighing disc is provided with a discharge port; the bottom of the stirring disc is provided with a discharge port and a baffle.

2. The apparatus for artificially preparing a structural soil sample according to claim 1, wherein The screening system further has a waste disc, which is arranged below the lowermost oscillating screening disc.

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