Device and method for artificially preparing structural soil samples capable of controlling structural strength

Abstract

The present invention discloses an apparatus and method for artificially preparing structural soil samples capable of controlling the strength of their structural properties. The apparatus belongs to the field of geotechnical engineering and comprises a low-temperature forming module, a carbonization module, and a terminal device. The method, based on the apparatus, obtains the percentage of pores in each pore size interval of natural loess through a mercury intrusion test, air-dries and crushes the sample, adds CaO, and mixes uniformly. Distilled water is sprayed on the CaO-added soil material and stirred to generate Ca(OH)2, thereby preparing a mixed soil material. Dry ice pellets are prepared based on the percentage of pores in each pore size interval obtained through the mercury intrusion test, mixed uniformly with the mixed soil material, and pressed into a sample of the desired size. The sample is placed in a CO2 environment for curing, and CaCO3 cementation, similar to that of natural loess, is formed between the soil particles. The generated CaCO3 content controls the structural properties by varying the CaO incorporation ratio. Furthermore, the present invention enables non-destructive monitoring of the carbonization process during sample preparation and can control the moisture content of the prepared sample.

Description

Technical Field

[0001] The invention discloses a device and method for artificially preparing structural soil samples capable of controlling structural strength, and belongs to the field of geotechnical engineering. Background Art

[0002] Soil is heterogeneous, and cracks, wormholes, impurities, etc. in natural structural soils often have a significant impact on the study of soil structure. In addition, in structural research, the soil sample size is relatively small, and there are often structural differences between samples. The increase in uncontrollable factors increases the difficulty of structural research. In addition, the structural strength of natural soils is uncontrollable. It is difficult, time-consuming, labor-intensive, and expensive to obtain soils with different structural strengths that meet the test requirements. Therefore, artificially preparing soil samples with properties similar to natural structural soils and achieving controllable structural strength is one of the important prerequisites for conducting soil structural research, and it is also a key technology for solving engineering problems caused by structural soils.

[0003] The key to preparing structural soil samples is the generation of cementing materials and how to simulate the formation of large pores in natural structural soil. Among the current methods for artificially preparing structural soil samples, cementing materials mainly include cement, iron oxide, calcium carbonate, road fluid curing agent, etc. The large pores of natural structural soil are simulated by adding ice particles, salt particles, etc. to the sample. These methods have undoubtedly promoted the development of artificial preparation technology of structural soil, but there are still shortcomings. Taking the sample preparation method using calcium carbonate as a cementing material as an example, during the sample preparation process, lime is added to the reshaped soil sample, and carbon dioxide gas is introduced after saturation. Due to the limited solubility of carbon dioxide in water, it is not in sufficient contact with the generated calcium hydroxide, and the amount of calcium carbonate generated is less. Calcium carbonate has a certain solubility in water. Therefore, the calcium carbonate produced in the sample prepared by this method has limited cementation, cannot effectively simulate the properties of natural loess, and the structure is uncontrollable. Adding ice and salt particles to remolded soil samples to simulate the macropores found in natural soils, on the one hand, fails to reproduce the pore structure of natural soil samples, that is, it cannot truly restore the pore content of each pore size. On the other hand, the salt particles are later removed through methods such as seepage, and the flow of water destroys the pore structure of the soil sample, failing to simulate the structure of natural loess. Furthermore, existing technologies for monitoring the formation of cementitious substances cannot achieve non-destructive testing and are mostly monitored through chemical reactions on parallel samples. This significantly increases the number of samples prepared and, due to differences between different samples, the accuracy of the results is poor, resulting in drawbacks in monitoring test results. Summary of the Invention

[0004] In view of the shortcomings of the above-mentioned background technology, the purpose of the present invention is to propose a device and method for artificially preparing soil samples that can restore the natural loess structure and control the strength of the structure.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0006] On the one hand, a device for artificially preparing structural soil samples capable of controlling the strength of the structure is proposed, which consists of a low-temperature forming module, a carbonization module and a terminal device; the low-temperature forming module consists of a liquid nitrogen refrigeration system and a sample preparation cabinet, the liquid nitrogen refrigeration system is used to transport liquid nitrogen to the sample preparation cabinet so that the internal temperature of the sample preparation cabinet is always kept below the sublimation temperature of dry ice; the sample preparation cabinet includes a sample preparation cabinet body, and the sample preparation cabinet body is sequentially provided with an ice breaking disk, a screening system, a weighing disk, a stirring disk, a sample preparation mold and a hydraulic system from top to bottom; an ice breaking device for crushing dry ice is provided inside the ice breaking disk; the screening system is used to screen the crushed dry ice into dry ice particles of different particle size levels according to the particle size; a stirring device is provided inside the stirring disk; the hydraulic head of the hydraulic system is located inside the sample preparation mold; the carbonization module consists of a CO2 gas cylinder, an N2 gas cylinder A, an N2 gas cylinder B, a humidity controller, a temperature controller, a circulation pump and a reaction chamber, the outlets of the CO2 gas cylinder and the N2 gas cylinder A are connected to the humidity controller through the air inlet main pipe, and the CO2 The outlet of the gas cylinder is provided with a pressure switch 1, and the outlet of the N2 gas cylinder A is provided with a pressure switch 2; a relief valve 1 is provided on the top of the humidity controller, and the humidity controller is connected to the temperature controller; a gas temperature and humidity sensor is provided at the outlet of the temperature controller, and the outlet of the temperature controller is connected to the reaction chamber through a pipeline; the bottom of the reaction chamber is connected to the circulation pump through an exhaust hole; the circulation pump is connected to the air inlet main pipe to form a loop; a pressure switch 3 is provided at the outlet of the N2 gas cylinder B, and the outlet of the N2 gas cylinder B is connected to the airbag in the reaction chamber through an airbag filling and discharging channel, and a relief valve 2 is provided between the airbag filling and discharging channel and the pressure switch 3; the reaction chamber consists of a visible sealing cover and a reaction chamber body, and the reaction chamber body is provided with an airbag and a constant temperature base, the airbag is annular and is arranged in the middle of the inner wall of the reaction chamber; the constant temperature base is located at the bottom of the reaction chamber body, and is provided with a pressure sensor and a heating device; the terminal device is respectively connected to the pressure switch 1, pressure switch 2, pressure switch 3, the gas temperature and humidity sensor, the pressure sensor in the constant temperature base, and the heating device.

[0007] Furthermore, the liquid nitrogen refrigeration system consists of a liquid nitrogen tank, a temperature sensor and a valve, and the temperature sensor is located at the bottom of the sample preparation cabinet; the valve is arranged on the connecting pipe between the liquid nitrogen tank and the sample preparation cabinet, and the valve and the temperature sensor are both communicatively connected to the equipment terminal.

[0008] Furthermore, the ice-breaking device includes an ice-breaking blade and a driving motor for driving the ice-breaking blade to rotate around its own rotation axis.

[0009] Furthermore, the screening system has at least three oscillating screening plates arranged one above the other, and the sieve aperture of the upper oscillating screening plate of any two adjacent oscillating screening plates is larger than the sieve aperture of the lower oscillating screening plate. Except for the topmost oscillating screening plate, each oscillating screening plate has a discharge conduit for conveying dry ice pellets at its bottom, with a switch at its top and a connection to a weighing plate at its bottom. The weighing plate has a discharge port at its bottom, and the stirring plate has a discharge port and a baffle at its bottom. The screening system also has a waste tray, which is arranged below the bottommost oscillating screening plate.

[0010] In a second aspect, a method for preparing a structural soil sample based on the device for artificially preparing a structural soil sample capable of controlling the strength of the structure is proposed, the method comprising:

[0011] Step 1: Obtain natural loess and perform a mercury intrusion test on the obtained natural loess to obtain the percentage of pores in each pore size interval of the natural loess. Based on the percentage of pores in each pore size interval, calculate the mass of dry ice particles required for each pore size interval;

[0012] Step 2: Use the ring knife method to measure the natural density ρ and natural moisture content ω of natural loess, and calculate the dry density ρ of natural loess d , according to the dry density of natural loess ρ d Prepare artificial samples, that is, the target dry density of the artificial samples is equal to the dry density of natural loess ρ d ;

[0013] Step 3: Air-dry the natural loess, crush it, and sieve it to obtain air-dried soil. Test the moisture content of the air-dried soil. d ;

[0014] Step 4: Add CaO to the air-dried soil and mix well to obtain mixed soil material A. The amount of CaO added is determined by the target CaCO3 percentage content of the artificial sample. The CaO addition amount m CaO The determination process is as follows:

[0015]

[0016] Where, 0.56 is the conversion factor between CaCO3 and CaO, n is the target CaCO3 percentage of the artificial sample, m is d is the mass of air-dried soil, ω d is the moisture content of air-dried soil;

[0017] Step 5: Calculate and weigh the corresponding mass of mixed soil material A according to the target density and volume of the artificial sample, and calculate the dry weight m of mixed soil material A. As , the mass of mixed soil material A is m A and dry weight m As The calculation process is as follows;

[0018]

[0019] Where n is the target CaCO3 percentage of the artificial sample, ρ d is the dry density of natural loess, V is the target volume of the artificial sample, m d is the mass of air-dried soil, m CaO is the mass of CaO, ω d is the moisture content of air-dried soil;

[0020] Step 6: Towards a mass m A Spray distilled water on the mixed soil material A and stir it to ensure that CaO is fully in contact with water to generate Ca(OH)2, to obtain mixed soil material B, which is added to the stirring plate of the sample preparation cabinet;

[0021] Step 7: Turn on the liquid nitrogen refrigeration system, wait until the temperature in the sample preparation cabinet drops to -85°C, place the dry ice in the ice breaker tray and crush it;

[0022] Step 8: The ice-breaking disk stops working, and the crushed dry ice enters the screening system for screening, obtaining dry ice particles with particle sizes within each aperture range in step 1. The weighing disk then weighs the dry ice particles corresponding to each aperture range to ensure that they meet the dry ice particle mass required for each aperture range in step 1, and the weighed dry ice particles are transported to the stirring disk.

[0023] Step 9: Start the stirring plate, mix the mixed soil material B and the dry ice particles evenly to obtain the mixed soil material C, and transfer the mixed soil material C to the sample preparation mold;

[0024] Step 10: Start the hydraulic system at the bottom of the sample preparation mold to press the mixed soil material C into an artificial sample;

[0025] Step 11: Turn off the liquid nitrogen refrigeration system and take out the pressed artificial sample from the sample preparation cabinet. At this time, the dry ice in the artificial sample sublimates, forming large pores inside.

[0026] Step 12: Set the air pressure, gas humidity, and temperature in the reaction chamber to target values ​​in the terminal device, turn on pressure switch 1, start the circulation pump, and wait until the humidity and temperature reach the target values;

[0027] Step 13: Place the taken artificial sample on the constant temperature base in the reaction chamber; open the third pressure switch until the air bag and the artificial sample are in contact, close the third pressure switch, and close the visible sealing cover; wait until the system pressure reaches the target value;

[0028] Step 14: Close pressure switch 1 and open pressure switch 2, and N2 enters the system for circulation; at the same time, open bleed valve 1, and CO2 in the system is discharged through bleed valve 1. Close bleed valve 1 after 5 minutes; open bleed valve 2 to exhaust N2 in the air bag, so that the air bag and the artificial sample are separated; reduce the N2 humidity in the system through the humidity controller, and adjust the N2 to a predetermined temperature through the temperature controller to dry the artificial sample; measure the dry weight m1 of the artificial sample; at this time, m1 and m As The difference is the mass of CaCO3 generated. Combined with the mass of CaO added when preparing the artificial sample, the amount of carbonized calcium ions can be obtained. The percentage of carbonized calcium ions 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;

[0029]

[0030] Where P is the carbonization reaction progress index, m1 is the mass of the artificial sample after drying, and m As The dry weight of mixed soil material A required to prepare artificial samples, m CaO The mass of CaO in the mixed soil material A required to prepare the artificial sample;

[0031] Step 15: The target moisture content of the artificial sample and the target moisture content of the dry-wet cycle are controlled as follows: after the carbonization process is completed, the pressure switch 1 is closed and the pressure switch 2 is opened, and N2 enters the system for circulation; at the same time, the air release valve 1 is opened, and the CO2 in the system is discharged through the air release valve 1. After 5 minutes, the air release valve 1 is closed; the air release valve 2 is opened to exhaust the N2 in the air bag and separate the air bag from the artificial sample; the humidity of the N2 in the system is reduced by the humidity controller, and the N2 is adjusted to a predetermined temperature by the temperature controller to dry the artificial sample; the dry weight of the artificial sample is measured (m2); the humidity and temperature of the N2 are controlled to the target values ​​by the humidity controller and the temperature controller. During this process, the air release valve 2 is opened to exhaust the N2 in the air bag and separate the air bag from the artificial sample. The weight of the artificial sample is monitored in real time by the constant temperature base (m3). 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 is stopped;

[0032] Step 16: After the artificial sample reaches the target moisture content, turn off pressure switch 1, pressure switch 2, pressure switch 3 and the circulation pump, open the visible sealing cover of the reaction chamber, and take out the artificial sample.

[0033] According to a specific embodiment of the present invention, in step 4, the CaO addition ratio is 14%, wherein the air-dried soil moisture content ω d Calculated at 4%.

[0034] According to a specific embodiment of the present invention, in step 12, the target value of humidity is 80%, and the target value of temperature is 20°C.

[0035] According to a specific embodiment of the present invention, in step 13, the target value of the air pressure is 200 kPa.

[0036] According to a specific embodiment of the present invention, in step 14, the humidity is 2%, the temperature is 105° C., and the duration is 10 hours.

[0037] According to a specific embodiment of the present invention, in step 15, the N2 humidity in the system is adjusted to 2% and the temperature is 105°C through the humidity controller and the temperature controller. After continuous circulation for 10 hours, the dry weight m2 of the artificial sample is measured; the N2 humidity in the system is adjusted to 80% and the temperature is 20°C through the humidity controller and the temperature controller, and the mass m3 of the artificial sample is measured in real time. At this time, the moisture content of the artificial sample is (m3-m2) / m2.

[0038] Through the above-mentioned design scheme, the present invention can bring the following beneficial effects: the soil samples prepared by the device and method of the present invention, on the one hand, can simulate the pore structure of natural loess and restore the structure of natural loess to the maximum extent; on the other hand, can generate a large amount of cementing material, and further control the strength of the soil sample structure by controlling the amount of cementing material generated. In addition, the present invention can also control the strength of the structure of artificial samples by changing the pore structure and pore content of artificial samples, and can prepare artificial samples of different structures while maintaining the consistency of material composition, so as to facilitate soil structural research. The soil samples prepared by the method of the present invention can not only be used for the study of loess structure in the laboratory, but more importantly, in dealing with soil engineering problems in loess areas, such as loess landslides, tunnel collapses, etc., this method can prepare soil samples for the actual situation of a specific soil body, eliminate the influence of interference factors, and predict or simulate soil engineering properties, providing support for solving engineering problems. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The accompanying drawings herein are used to provide a further understanding of the present invention and constitute a part of the present application. The exemplary embodiments of the present invention and their descriptions are used to understand the present invention and do not constitute improper limitations of the present invention. In the accompanying drawings:

[0040] Figure 1 Schematic diagram of the overall structure of the device for artificially preparing structural soil samples that can control the strength of the structure;

[0041] Figure 2 This is the internal structure diagram of the sample preparation cabinet;

[0042] Figure 3 This is a cross-sectional view of the reaction chamber;

[0043] Figure 4 This is the porosity percentage graph of sample No. 1;

[0044] Figure 5This is the porosity percentage graph of sample No. 2;

[0045] Figure 6 This is the porosity percentage graph of sample No. 3;

[0046] Figure 7 This is the SEM image of rod-shaped calcite in natural loess;

[0047] Figure 8 This is the result of energy spectrum analysis of rod-shaped calcite in natural loess;

[0048] Figure 9 This is the SEM image of cubic CaCO3 in the artificially prepared sample;

[0049] Figure 10 This is the result of energy spectrum analysis of cubic CaCO3 in artificially prepared samples;

[0050] Figure 11 This is the SEM image of spindle-shaped CaCO3 in the artificially prepared sample;

[0051] Figure 12 This is the result of energy spectrum analysis of spindle-shaped CaCO3 in artificially prepared samples;

[0052] Figure 13 This is the SEM image of the thin film CaCO3 in the artificially prepared sample;

[0053] Figure 14 This is the result of energy spectrum analysis of thin film CaCO3 in artificially prepared samples;

[0054] Figure 15 This is the SEM image of observation point 1 of the artificially prepared loess sample;

[0055] Figure 16 The distribution of C element observed at observation point 1 for artificially prepared loess samples;

[0056] Figure 17 The distribution map of Ca element observed at observation point 1 for artificially prepared loess samples;

[0057] Figure 18 This is the SEM image of observation point 2 of the artificially prepared loess sample;

[0058] Figure 19 The distribution of C element observed at observation point 2 for artificially prepared loess samples;

[0059] Figure 20 The distribution map of Ca element observed at observation point 2 for artificially prepared loess samples;

[0060] Figure 21 This is the microstructure diagram of natural loess observation point 1 at a magnification of 1000 times;

[0061] Figure 22 This is the microstructure diagram of natural loess observation point 1 at a magnification of 2000 times;

[0062] Figure 23 This is the microstructure diagram of natural loess observation point 2 at a magnification of 1000 times;

[0063] Figure 24 This is the microstructure of natural loess observation point 2 at a magnification of 2000 times;

[0064] Figure 25 This is a microstructure image of observation point 3 of the artificially prepared loess sample with a magnification of 1000 times;

[0065] Figure 26 This is a microstructure image of observation point 3 of the artificially prepared loess sample with a magnification of 2000 times;

[0066] Figure 27 This is a microstructure image of observation point 4 of the artificially prepared loess sample at a magnification of 1000 times;

[0067] Figure 28 This is a microstructure image of observation point 4 of the artificially prepared loess sample at a magnification of 2000 times;

[0068] Figure 29 This is the pore content map of artificially prepared loess sample No. 4;

[0069] Figure 30 This is the pore content map of artificially prepared loess sample No. 5;

[0070] Figure 31 This is the collapse coefficient diagram of natural loess and artificially prepared loess.

[0071] The labels in the figure are as follows: 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-No. 1 sieve, 12-No. 2 sieve, 13-No. 3 sieve, 14-No. 4 sieve, 15-waste tray, 16-discharge pipe, 17-CO2 gas cylinder, 18-N2 gas cylinder A, 19-N2 gas cylinder B, 20-Humidity controller, 21-Temperature controller, 22-Circulating pump, 23-Reaction chamber, 24-Pressure switch 1, 25-Pressure switch 2, 26-Air relief valve 1, 27-Gas temperature and humidity sensor, 28-Exhaust hole, 29-Pressure switch 3, 30-Air bag charging and discharging channel, 31-Air relief valve 2, 32-Visual sealing cover, 33-Reaction chamber body, 34-Air bag, 35-Constant temperature base, 36-Terminal equipment. DETAILED DESCRIPTION

[0072] To make the objects, features, and advantages of the present invention more apparent and understandable, the technical solutions of the present invention are described clearly and completely below in conjunction with the accompanying drawings in accordance with the embodiments of the present invention. Obviously, the present invention is not limited to the following embodiments, and specific implementation methods can be determined based on the technical solutions of the present invention and actual conditions. To avoid obscuring the essence of the present invention, well-known methods, processes, procedures, components, and circuits are not described in detail.

[0073] 1. The specific contents of the device and method proposed in the present invention are as follows:

[0074] Combine Figure 1 、 Figure 2 and Figure 3 The present invention proposes a method for artificially preparing structured soil samples that can control the strength of the structure. First, a mercury intrusion test is performed on natural loess to determine the percentage of pores in each pore size range. Then, the natural loess is air-dried and crushed, CaO is added, and the mixture is evenly mixed. Distilled water is sprayed on the CaO-added soil and stirred to ensure sufficient contact between the CaO and the water to generate Ca(OH)2, thereby preparing mixed soil material B. Dry ice pellets are prepared based on the pore percentages in each pore size range obtained from the mercury intrusion test. Specifically, after the dry ice is crushed, based on the volume of pores in a specific pore size range (for example, the total volume of pores in the pore size range of 15-45 μm is V1), dry ice pellets with a total volume equal to V1 are collected from the pore size range of 15-45 μm. The corresponding amount of dry ice pellets is collected in this manner for all large pore size ranges. The dry ice pellets are evenly mixed with mixed soil material B to obtain mixed soil material C, which is then pressed into artificial samples of the desired size. The above-mentioned process, from preparing dry ice particles to pressing and molding artificial samples, is completed in a low-temperature environment (below -78.5°C) to prevent dry ice sublimation. After the artificial sample is formed, the temperature is increased, and the dry ice in the artificial sample sublimates, forming a large-pore structure similar to natural loess. The artificial sample is further placed in a high-humidity, high-concentration CO2 environment for curing. The preferred humidity is 80%, and the CO2 concentration is controlled by pressure. The temperature in the system is 20°C and the pressure is 200kPa. CaCO3 cementation, the same as natural loess, is formed between the soil particles. The generated CaCO3 content is controlled by changing the CaO incorporation ratio. The higher the CaCO3 content, the stronger the sample structure.

[0075] Furthermore, the present invention enables non-destructive monitoring of the carbonization process during sample preparation and can control the moisture content of artificial samples. The moisture content of artificial samples can be controlled by regulating the humidity and temperature of nitrogen in the system via a humidity controller 20 and a temperature controller 21. The humidity controller 20 and the temperature controller 21 of the present invention can adjust the humidity and temperature of the gas on demand. By inputting different humidity and temperature values ​​through a terminal device 36, a humidity and temperature curve over time is generated, enabling simulation of soil sample drying and wetting, freeze-thaw cycles, and coupled drying and wetting and freeze-thaw cycles under complex conditions.

[0076] The device for artificially preparing structural soil samples capable of controlling the strength of the structure proposed in the present invention is composed of a low-temperature forming module, a carbonization module and a terminal device 36.

[0077] The low-temperature molding module consists of a liquid nitrogen refrigeration system and a sample preparation cabinet 4. The liquid nitrogen refrigeration system consists of a liquid nitrogen tank 1, a temperature sensor 2, and a valve 3. The temperature sensor 2 is located at the inner bottom of the sample preparation cabinet 4, and the valve 3 is installed in the connecting pipe between the liquid nitrogen tank 1 and the sample preparation cabinet 4. The sample preparation cabinet 4 includes a sample preparation cabinet body 5. Inside the sample preparation cabinet 5, there are, from top to bottom, an ice-breaking tray 6, a screening system, a weighing tray 7, a stirring tray 8, a sample preparation mold 9, and a hydraulic system 10. The screening 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 pipe 16.

[0078] 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 1 24. This pressure switch 1 24 controls the CO2 pressure in the system to a target value. This increases the CO2 concentration under pressure, accelerating the process of generating CaCO3. Furthermore, a certain pressure can accelerate the speed at which CO2 passes through the artificial sample in the reaction chamber 23, ensuring that there is enough CO2 to contact the Ca(OH)2 and participate in the reaction. The outlet of the N2 cylinder A18 is equipped with a pressure switch 2 25. By heating the N2, the artificial sample in the reaction chamber 23 is dried. During this process, the pressure in the system is controlled by the pressure switch 25, accelerating the speed at which N2 passes through the artificial sample and drying the artificial sample. The CO2 cylinder 17 and N2 cylinder A18 are connected to a humidity controller 20 via an intake manifold. A relief valve 1 26 is located at the top of the humidity controller 20. The humidity controller 20 is connected to a temperature controller 21, the outlet of which is equipped with a gas temperature and humidity sensor 27. The temperature controller 21 is also connected to the reaction chamber 23. The bottom of the reaction chamber 23 is connected to a circulation pump 22 via an exhaust port 28. The circulation pump 22 is connected to the intake manifold to form a circuit. The outlet of the N2 cylinder B19 is equipped with a pressure switch 3 29 to control the pressure within the airbag 34, achieving inflation and deflation. The N2 cylinder B19 is connected to the reaction chamber 23 via an airbag inflation and deflation channel 30. A relief valve 2 31 is located between the airbag inflation and deflation channel 30 and the pressure switch 3 29.

[0079] Liquid nitrogen refrigeration system: Open valve 3, liquid nitrogen enters the sample preparation cabinet 4, and the temperature sensor 2 monitors the temperature in real time. When the target temperature is reached, preferably -85°C, valve 3 is closed. When the ambient temperature is higher than the target temperature, valve 3 is opened.

[0080] Sample preparation cabinet 4 structure: An ice-breaking device for crushing dry ice is installed inside the ice-breaking tray 6. The ice-breaking device includes ice-breaking blades and a drive motor for driving the ice-breaking blades to rotate about their own rotation axis. The lower end of the ice-breaking tray 6 is a discharge port. After the dry ice is crushed, it enters the screening system through the discharge port of the ice-breaking tray 6. The screening system includes, from top to bottom, a No. 1 sieve 11, a No. 2 sieve 12, a No. 3 sieve 13, and a No. 4 sieve 14. The No. 1 sieve 11 preferably has a mesh size of 0.355mm and 45 mesh; the No. 2 sieve 12 preferably has a mesh size of 0.090mm and 170 mesh; the No. 3 sieve 13 preferably has a mesh size of 0.045mm and 325 mesh; and the No. 4 sieve 14 preferably has a mesh size of 0.015mm and 900 mesh. A discharge conduit 16 is located at the bottom of each of the No. 2, No. 3, and No. 4 sieves 12, 13, and 14 sieves. A switch is located at the top of each conduit, which 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 tray 15 is located at the bottom of the No. 4 sieve 14 and receives dry ice waste with a particle size less than 15 μm. The weighing pan 7 is connected to the stirring pan 8 below. A discharge port is located at the bottom of the weighing pan 7. Dry ice particles in the weighing pan 7 enter the stirring pan 8 through the discharge port. The stirring pan 8 is equipped with a stirring device, a discharge port, and a baffle at the bottom. When the baffle is opened, the mixed soil C in the stirring pan 8 enters the sample preparation mold 9 through the discharge port at the bottom of the stirring pan 8. The sample mold 9 is connected to the hydraulic system 10 at the bottom. The hydraulic head of the hydraulic system 10 is located inside the sample mold 9. The hydraulic head of the hydraulic system 10 cooperates with the inner cavity of the sample mold 9. The hydraulic head of the hydraulic system 10 rises to press the mixed soil material C into shape.

[0081] Humidity controller 20 humidifies incoming gas. Temperature controller 21 controls the temperature of the gas processed by humidity controller 20. The processed gas is measured by gas temperature and humidity sensor 27 and continues to circulate until it reaches the target value. It should be noted that in the present invention, humidity controller 20, temperature controller 21, and gas temperature and humidity sensor 27 are all commercially available products and are considered prior art, so they will not be described in detail.

[0082] The reaction chamber 23 consists of a visible sealing cover 32 and a reaction chamber body 33, which contains an airbag 34 and a constant-temperature base 35. After being inflated with N2 gas cylinder B19, the airbag 34 wraps around the middle of the artificial sample, fitting tightly against it, securing it and dividing the interior of the reaction chamber 23 into an upper and lower section. Gas between the two sections flows only through the artificial sample. CO2 enters the lower section of the reaction chamber 23 through the artificial sample, enters the exhaust duct through the exhaust port 28, and is recycled. During this process, the CO2 gas has a single path, ensuring full contact with the interior of the artificial sample and a uniform carbonization reaction. The airbag 34 is deflated through the air release valve 231, after which it separates from the artificial sample. The constant-temperature base 35 is equipped with a pressure sensor that can measure the mass of the artificial sample. The constant-temperature base 35 also includes a heating device to prevent condensation on the outer wall of the base, which could affect the mass measurement results.

[0083] The terminal device 36 is a computer or a mobile phone.

[0084] 2. Operation steps:

[0085] 1. The steps for preparing structural loess samples using the above-mentioned device for artificially preparing structural soil samples that can control the strength of the structure are as follows:

[0086] The equipment start and stop, data analysis and processing, and parameter setting are controlled by the terminal device 36.

[0087] (1) Obtain natural loess, take three mercury injection samples with no damage on the surface, and conduct mercury injection tests to obtain pore distribution data. Take the average value of the test data of the three mercury injection samples to obtain the percentage of macropores in each pore size interval. Here, the macropore diameter is preferably greater than 15μm, and the macropore diameter interval is divided into 15-45μm, 45-90μm and 90-355μm. Existing studies generally believe that pores with a diameter greater than 16μm in loess are macropores, and this method needs to be combined with mercury injection tests to determine the pore percentage in each interval. The mercury injection test measured the boundary values ​​of the macropore diameter interval to be 45μm, 90μm and 355μm, respectively. At the same time, considering the sieve size, the starting pore diameter of the macropore is taken as 15μm, so the macropore diameter interval is determined as above. Dividing the macropores according to this interval can improve the accuracy of pore content measurement and effectively reduce the difference in macropore content between artificial samples and natural soil samples. According to the percentage of pores in each pore size range, the mass of dry ice particles required for the pore size range is calculated. The mass of dry ice particles in the range of 15-45μm is m 15-45 The mass of dry ice particles with particle sizes between 45-90μm and 90-355μm are respectively m 45-90 and m 90-355 .

[0088] (2) The natural density ρ and natural moisture content ω of natural loess are measured by the ring knife method, and the dry density ρ of natural loess is calculated. d ; Among them, the natural density ρ of natural loess is calculated as follows:

[0089]

[0090] Where V T is the volume of the natural loess sample cut by the ring knife, m is the mass of the natural loess sample cut by the ring knife in the natural state;

[0091] The natural moisture content of natural loess is ω, which is calculated as follows:

[0092]

[0093] Where m is the mass of the natural loess sample cut by ring knife in natural state, m s is the mass of natural loess with a mass of m after drying at 105℃ for 8 hours.

[0094] Dry density of natural loess ρ d Determined by natural density ρ and natural moisture content ω, the formula is as follows:

[0095]

[0096] (3) The natural loess was air-dried and crushed, and sieved with a 0.5 mm sieve to remove particles larger than 0.5 mm and impurities to ensure the uniformity of the artificial sample. At the same time, the moisture content of the air-dried soil was tested. d ; Air-dried soil moisture content ω d The calculation formula is as follows:

[0097]

[0098] Where m d is the mass of air-dried soil, m sd The mass is m d The mass of air-dried soil after drying at 105℃ for 8 hours;

[0099] (3) Add CaO to the air-dried soil and mix well. The amount of CaO added is determined by the target CaCO3 content of the artificial sample. The optimal CaO addition ratio (the ratio of the mass of the added material to the mass of the incorporated material) is: n is the target CaCO3 percentage of the artificial sample, which is 14%, and the moisture content of the air-dried soil is ω d Calculated at 4%.

[0100] CaO addition amount m CaO The determination process is as follows:

[0101]

[0102] Where, 0.56 is the conversion factor between CaCO3 and CaO, n is the target CaCO3 percentage of the artificial sample, m is d is the mass of air-dried soil, ω d is the moisture content of air-dried soil;

[0103] (5) According to the target density and volume of the artificial sample, calculate and weigh the corresponding mass of the mixed soil material A, and calculate the dry weight m of the mixed soil material A. As , the mass of mixed soil material A is m A and dry weight m As The calculation process is as follows;

[0104]

[0105] Where n is the target CaCO3 percentage of the artificial sample, ρ d is the dry density of natural loess, which is equal to the target dry density of the artificial sample, and V is the target volume of the artificial sample, m d is the mass of air-dried soil, m CaO is the mass of CaO, ω d is the moisture content of air-dried soil;

[0106] (6) Spray distilled water onto the mixed soil material A and stir to ensure that CaO is fully in contact with water to generate C a (OH)2, to obtain mixed soil material B, which is added into the stirring disk 8 of the sample preparation cabinet 4.

[0107] (7) Turn on the liquid nitrogen refrigeration system, wait until the temperature in the sample preparation cabinet 4 drops to -85°C, place dry ice in the ice breaking tray 6, close the door of the sample preparation cabinet 4, and start the ice breaking tray 6 to crush the dry ice.

[0108] (8) The ice-breaking disk 6 stops working, and the crushed dry ice enters the screening system. Start the oscillating screening disk, which oscillates the dry ice particles into five parts with particle sizes greater than 355μm, 90-355μm, 45-90μm, 15-45μm and less than 15μm, which are stored in the No. 1 sieve 11, the No. 2 sieve 12, the No. 3 sieve 13, the No. 4 sieve 14 and the waste tray 15 respectively. Turn on the discharge conduit 16 switch of the No. 2 sieve 12, and the dry ice particles with a particle size of 90-355μm fall into the weighing tray 7, with a mass of m 90-355 At this time, the top switch of the discharge conduit 16 of the No. 2 sieve 12 is closed. The No. 3 sieve 13 and the No. 4 sieve 14 are operated as above, and the dry ice particles m are taken out respectively. 45-90 、m 15-45 The discharge port at the bottom of the weighing plate 7 is opened, and the dry ice particles enter the stirring plate 8.

[0109] (9) Start the stirring disk 8, and mix the mixed soil material B and the dry ice particles in the stirring disk 8 to obtain the mixed soil material C. Open the bottom baffle of the stirring disk 8, and the mixed soil material C enters the sample preparation mold 9.

[0110] (10) Close the bottom baffle of the stirring plate 8 and start the hydraulic system 10 at the bottom of the sample preparation mold 9 to press the mixed soil material C into an artificial sample.

[0111] (11) Turn off the liquid nitrogen refrigeration system, open the door of the sample preparation cabinet 4, and take out the pressed artificial sample. At this time, the dry ice in the artificial sample sublimates, forming large pores inside.

[0112] (12) Set the CO2 pressure (i.e., the pressure in the reaction chamber 23), humidity, and temperature in the terminal device 36 to target values. Open the pressure switch 24 at the outlet of the CO2 cylinder 17 and start the circulation pump 22. Wait until the humidity and temperature reach the target values. Preferably, the humidity is 80% and the temperature is 20°C.

[0113] (13) Place the removed artificial sample on the constant temperature base 35 in the reaction chamber 23. Open the switch 29 at the outlet of the N2 gas cylinder B19 until the air bag 34 is in contact with the artificial sample. Close the switch 29 at the outlet of the N2 gas cylinder B19 and close the visible sealing cover 32. Wait until the system pressure reaches the target value, preferably 200 kPa.

[0114] (14) During the reaction, the progress of the carbonization reaction was evaluated: the pressure switch 24 at the outlet of the CO2 cylinder 17 was closed, and the pressure switch 25 at the outlet of the N2 cylinder A18 was opened, and N2 entered the system for circulation. At the same time, the bleed valve 26 was opened, and the CO2 in the system was discharged through the bleed valve 26. After 5 minutes, the bleed valve 26 was closed. The bleed valve 31 was opened to exhaust the N2 in the air bag 34, so that the air bag 34 was separated from the artificial sample. The humidity of N2 in the system was reduced to 2% by the humidity controller 20, and the N2 was adjusted to 105°C by the temperature controller 21 for 10 hours to dry the artificial sample. The dry weight m1 of the artificial sample was measured. At this time, m1 and m s The difference is the mass of CaCO3 generated. Combined with the amount of CaO added when preparing the artificial sample, the amount of carbonized calcium ions can be obtained, and then the progress of the carbonization reaction can be known.

[0115] The percentage of carbonized calcium ions to the total amount of added calcium ions is used as the carbonization reaction progress index P, which is calculated as follows:

[0116]

[0117] Where P is the carbonization reaction progress index, m i is the mass of the artificial sample after drying, m AsThe dry weight of mixed soil material A required to prepare artificial samples, m CaO The mass of CaO in the mixed soil material A required to prepare the artificial sample;

[0118] (15) The control process of the target moisture content of the artificial sample and the target moisture content of the dry-wet cycle is as follows: after the carbonization process is completed, the pressure switch 24 at the outlet of the CO2 gas cylinder 17 will be closed, and the pressure switch 25 at the outlet of the N2 gas cylinder A18 will be opened, and N2 will enter the system for circulation. At the same time, the relief valve 26 will be opened, and the CO2 in the system will be discharged through the relief valve 26. After 5 minutes, the relief valve 26 will be closed; the relief valve 231 will be opened to exhaust the N2 in the air bag 34 to separate the N2 from the artificial sample; the humidity of the N2 in the system will be reduced by the humidity controller 20, and the N2 will be adjusted to a predetermined temperature by the temperature controller 21 to dry the artificial sample; the dry weight m2 of the artificial sample will be measured; the weight m3 of the artificial sample will be 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 will stop;

[0119] In this embodiment, in step (15), after the carbonization reaction process is completed, the N2 humidity in the system is adjusted to 2% and the temperature is 105°C through the humidity controller 20 and the temperature controller 21. After continuous circulation for 10 hours, the dry weight m2 of the artificial sample is measured; the N2 humidity in the system is adjusted to 80% and the temperature is 20°C through the humidity controller 20 and the temperature controller 21, and the weight m3 of the artificial sample is measured in real time. The real-time moisture content of the artificial sample (m3-m2) / m2 can be obtained by measuring the difference between the real-time weight m3 of the artificial sample and the dry weight m2 of the artificial sample, until the real-time moisture content reaches the target moisture content.

[0120] (16) After the artificial sample reaches the target moisture content, turn off pressure switch 1 24, pressure switch 2 25, pressure switch 3 29 and circulation pump 22, open the visible sealing cover 32 of the reaction chamber 23, and take out the artificial sample.

[0121] 2. The above-mentioned device for artificially preparing structural soil samples that can control the strength of the structure is used to perform the soil sample drying, wetting, and freeze-thaw cycle operation steps. It should be noted that the soil sample here refers to any soil sample, and any soil sample can be subjected to drying, wetting, and freeze-thaw cycle tests, and is not limited to artificially prepared structural soil samples.

[0122] The carbonization module and the terminal device 36 are only needed to conduct the soil sample drying and wetting and freeze-thaw cycle test using the device of the present invention. The drying and wetting cycle operation steps are as follows:

[0123] (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°C through the terminal device 36, open the pressure switch 25 at the outlet of the N2 gas cylinder A18, and start the circulation pump 22. After 10 hours, turn off the pressure switch 25 and the circulation pump 22. Wait until the temperature in the reaction chamber 23 drops to room temperature and measure the mass m4 of the soil sample at this time.

[0124] (2) Set the target humidity value for the soil sample. Depending on the test requirements, the target humidity can be a fixed value or a variable curve. When the soil sample changes from dry to wet, set the gas humidity to 80% and the temperature to 20°C. When the soil sample changes from wet to dry, set the gas humidity to 2% and the temperature to 20°C. Turn on switch 3 25 at the outlet of N2 gas cylinder A18 and start the circulation pump 22. The mass of the soil sample at this time is measured in real time through the constant temperature base 35, which is m5. The moisture content of the soil sample is (m5-m4) / m4. Based on this, the moisture content of the soil sample is monitored and the test process is controlled.

[0125] The freeze-thaw cycle operation steps are as follows:

[0126] (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 variable curve.

[0127] (2) Open the pressure switch 25 at the outlet of N2 gas cylinder A18 and start the circulation pump 22. Set the freezing or melting time according to the test requirements.

[0128] When performing dry-wet and freeze-thaw coupled cycles, just set the humidity and temperature to the target values ​​at the same time.

[0129] 3. Examples

[0130] 1. Operation process

[0131] The method and apparatus of the present invention are used to prepare a sample. The sample is a cylinder with a diameter of 39.1 mm and a height of 80 mm. The specific steps are as follows:

[0132] a. Select natural loess for mercury intrusion test and obtain the pore contents of each pore size interval of three natural loess mercury intrusion samples (samples 1-3). Figure 4-Figure 6 As shown, the three natural loess mercury injection samples were taken from the same natural loess. Parallel testing of the three samples was performed to minimize the influence of cracks, wormholes, and plant roots in the natural loess, thereby ensuring that the test data represents the pore 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 dry ice pellet dosage was calculated as shown in Table 2. The calculation process is as follows.

[0133] Taking the pores with a diameter of 15-45 μm as an example, the content is:

[0134]

[0135] The mass of dry ice particles with a required particle size of 15-45 μm is:

[0136] m 15-45 =(39.1 / 2) 2 ×3.14×80×32.16%×17.11%÷1000×1.56=8.24, in g, density of dry ice = 1.56 g / cm 3 .

[0137] Similarly, the pore contents in the pore size ranges of 45-90 μm, 90-355 μm, and greater than 355 μm are 5.35%, 9.78%, and 0, respectively, and the mass of dry ice particles required in the corresponding particle size ranges are 2.58 g, 4.71 g, and 0, respectively.

[0138] Table 11-3 Macropore content of natural loess sample

[0139]

[0140]

[0141] Table 2 Mass of dry ice particles in various particle size ranges required for artificial preparation of soil samples

[0142] Dry ice particle size / μm 15-45 45-90 90-355 Dry ice particle mass / g 8.24 2.58 4.71

[0143] b. Take the natural loess, air-dry it, grind it, and sieve it with a 0.5mm sieve. At the same time, the natural moisture content of the natural loess is determined by the drying method, and the moisture content of the air-dried soil is tested. d . Add CaO to the air-dried soil and mix well. The CaO incorporation ratio is 14%.

[0144] c. The dry density of natural loess obtained from the experiment is 1.277 g / cm 3 After calculation, take 127.51g of mixed soil material A, spray it with distilled water and stir it, and add it to the stirring plate 8 of the sample preparation cabinet 4.

[0145] d. Follow the above steps (7)-(14) for the preparation of structural loess samples until the carbonization reaction is complete.

[0146] e. Follow the above-mentioned steps for preparing the structural loess sample, and ultimately control the moisture content of the artificially prepared sample to be the same as that of the natural loess, which is 16.7%.

[0147] 2. Test of properties of artificially prepared soil samples

[0148] Scanning electron microscopy, mercury intrusion and collapsibility tests were performed on natural loess and artificially prepared loess samples, and the test results are as follows.

[0149] (1) Scanning electron microscopy test

[0150] Compared with natural loess, combined with energy spectrum analysis, it was found that calcite (calcite is a calcium carbonate mineral with the chemical formula CaCO3, which is the most common mineral in natural calcium carbonate) was generated between soil particles during the sample preparation process. It has three forms, including cubic, spindle and film, while the calcite in natural loess is mostly rod-shaped, such as Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 、 Figure 12 、 Figure 13 、 Figure 14 , as shown in Table 3, Table 4, Table 5 and Table 6. In the artificially prepared loess samples, different forms of calcite work together to cement the soil particles together.

[0151] Table 3 Energy spectrum analysis of rod-shaped calcite in natural loess

[0152]

[0153]

[0154] Table 4 Energy spectrum analysis of cubic CaCO3 in artificially prepared samples

[0155] Element number Element symbols Element Name Atomic concentration Mass concentration 8 O oxygen 54.53 26.50 20 Ca calcium 18.06 21.99 6 C carbon 17.18 6.27 79 Au gold 5.18 30.99 41 Nb niobium 5.05 14.25

[0156] Table 5 Energy spectrum analysis of spindle-shaped CaCO3 in artificially prepared samples

[0157] Element number Element symbols 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

[0158] Table 6 Energy spectrum analysis of thin film CaCO3 in artificially prepared samples

[0159] Element number Element symbols 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

[0160] In order to further clarify the distribution of CaCO3 in the sample, the energy spectrum of different parts of the artificially prepared loess sample was scanned to obtain the distribution of different elements within the observation range. The results are shown in Figures 15 to 20 Overall, the distribution of C and Ca elements is relatively consistent across all samples, primarily located where soil particles come into contact with each other, or forming long aggregates between them to connect them. Furthermore, they are also found on the surfaces of some aggregates and around clay particles attached to the surface of the skeleton particles. This demonstrates that the sample preparation method of the present invention can effectively form CaCO3 cementation between soil particles.

[0161] The microstructure of natural loess and artificially prepared loess samples was observed, such as Figures 21 to 28 As shown. Natural loess has a skeletal structure, with skeletal particles mostly composed of silt, a large amount of clay particles adhering to its surface, and numerous open pores. In the photograph, magnified 1000x, the maximum diameter of the largest pores was measured using a scanning electron microscope. It can be seen that the largest pores in natural loess are mostly in the 10μm to 20μm range, with some reaching 40μm in diameter. Compared to natural loess, artificially prepared loess exhibits a skeletal structure and numerous open pores, with the largest pores mostly ranging from 15μm to 30μm in diameter, with some reaching 60μm in diameter. Overall, the microstructures of the two are similar.

[0162] (2) Mercury intrusion test

[0163] Two artificially prepared loess samples (numbered 4 and 5) were taken for mercury intrusion testing. The results are shown in Table 7. Figure 29 and Figure 30 Analysis shows that the artificial structural loess prepared by the method and device of the present invention is similar to natural loess in terms of pore distribution, especially in terms of macropore distribution, which is highly similar to natural loess.

[0164] Table 7 Macropore content of artificially prepared loess samples

[0165]

[0166] (3) Collapsibility test

[0167] The collapsibility test of natural loess and artificial loess samples was carried out, and the results are as follows: Figure 31 It can be seen that artificially prepared loess has collapsibility, but its collapsibility is slightly lower than that of natural loess, and its initial collapsibility pressure is higher than that of natural loess.

[0168] In summary, the method and device for preparing artificial structural loess of the present invention can prepare samples that have a high degree of similarity with natural loess in terms of cementing material, microstructure, pore distribution and collapsibility, and can be used for the study of loess structure.

Claims

1. A device for artificially preparing structural soil samples capable of controlling the strength of the structure, characterized in that: The device consists of a low-temperature forming module, a carbonization module and a terminal device; the low-temperature forming module consists of a liquid nitrogen refrigeration system and a sample preparation cabinet, the liquid nitrogen refrigeration system is used to transport liquid nitrogen to the sample preparation cabinet so that the internal temperature of the sample preparation cabinet is always kept below the sublimation temperature of dry ice; the sample preparation cabinet includes a sample preparation cabinet body, and the sample preparation cabinet body is sequentially provided with an ice breaking disk, a screening system, a weighing disk, a stirring disk, a sample preparation mold and a hydraulic system from top to bottom; an ice breaking device for crushing dry ice is provided inside the ice breaking disk; the screening system is used to screen the crushed dry ice into dry ice particles of different particle size levels according to the particle size; a stirring device is provided inside the stirring disk; the hydraulic head of the hydraulic system is located inside the sample preparation mold; the carbonization module consists 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 chamber, the outlets of the CO2 gas cylinder and the N2 gas cylinder A are connected to the humidity controller through the air inlet main pipe, the outlet of the CO2 gas cylinder is provided with a pressure switch 1, and the N2 gas cylinder A pressure switch 2 is provided at the outlet of A; a relief valve 1 is provided on the top of the humidity controller, and the humidity controller is connected to the temperature controller; a gas temperature and humidity sensor is provided at the outlet of the temperature controller, and the outlet of the temperature controller is connected to the reaction chamber through a pipeline; the bottom of the reaction chamber is connected to the circulation pump through an exhaust hole; the circulation pump is connected to the air intake main pipe to form a loop; a pressure switch 3 is provided at the outlet of the N2 gas cylinder B, and the outlet of the N2 gas cylinder B is connected to the airbag in the reaction chamber through the airbag filling and discharging channel, and a relief valve 2 is provided between the airbag filling and discharging channel and the pressure switch 3; the reaction chamber consists of a visible sealing cover and a reaction chamber body, and an airbag and a constant temperature base are provided in the reaction chamber body. The airbag is an annular airbag and is arranged in the middle of the inner wall of the reaction chamber; the constant temperature base is located at the bottom of the reaction chamber body, and is provided with a pressure sensor and a heating device; the terminal device is respectively communicated with pressure switch 1, pressure switch 2, pressure switch 3, the gas temperature and humidity sensor, the pressure sensor in the constant temperature base, and the heating device.

2. The device for artificially preparing structural soil samples capable of controlling structural strength according to claim 1, characterized in that: 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 arranged on the connecting pipe between the liquid nitrogen tank and the sample preparation cabinet, and the valve and the temperature sensor are both communicatively connected to the equipment terminal.

3. The device for artificially preparing structural soil samples capable of controlling structural strength according to claim 1, characterized in that: The ice-breaking device comprises an ice-breaking blade and a driving motor for driving the ice-breaking blade to rotate around its own rotation axis.

4. The device for artificially preparing structural soil samples capable of controlling structural strength according to claim 1, characterized in that: The screening system has at least three vibrating screening plates arranged one above the other, and the sieve hole diameter of the upper vibrating screening plate of any two adjacent vibrating screening plates is larger than the sieve hole diameter of the lower vibrating screening plate. Except for the vibrating screening plate located at the top, a discharge conduit for conveying dry ice particles is provided at the bottom of each of the other vibrating screening plates, and a switch is provided at the top of the discharge conduit, and the bottom leads to the weighing plate; a discharge port is provided at the bottom of the weighing plate; a discharge port and a baffle are provided at the bottom of the stirring plate; the screening system also has a waste plate, which is arranged below the lowest vibrating screening plate.

5. A method for preparing structural soil samples based on the device for artificially preparing structural soil samples capable of controlling structural strength according to any one of claims 1 to 4, characterized in that: The method includes: Step 1: Obtain natural loess and perform a mercury intrusion test on the obtained natural loess to obtain the percentage of pores in each pore size interval of the natural loess. Based on the percentage of pores in each pore size interval, calculate the mass of dry ice particles required for each pore size interval; Step 2: Use the ring knife method to measure the natural density ρ and natural moisture content ω of natural loess, and calculate the dry density ρ of natural loess d , according to the dry density of natural loess ρ d Prepare artificial samples, that is, the target dry density of the artificial samples is equal to the dry density of natural loess ρ d ; Step 3: Air-dry the natural loess, crush it, and sieve it to obtain air-dried soil. Test the moisture content of the air-dried soil. d ; Step 4: Add CaO to the air-dried soil and mix well to obtain mixed soil material A. The amount of CaO added is determined by the target CaCO3 percentage content of the artificial sample. The CaO addition amount m CaO The determination process is as follows: Where, 0.56 is the conversion factor between CaCO3 and CaO, n is the target CaCO3 percentage of the artificial sample, m is d is the mass of air-dried soil, ω d is the moisture content of air-dried soil; Step 5: Calculate and weigh the corresponding mass of mixed soil material A according to the target density and volume of the artificial sample, and calculate the dry weight m of mixed soil material A. As , the mass of mixed soil material A is m A and dry weight m As The calculation process is as follows; Where n is the target CaCO3 percentage of the artificial sample, ρ d is the dry density of natural loess, V is the target volume of the artificial sample, m d is the mass of air-dried soil, m CaO is the mass of CaO, ω d is the moisture content of air-dried soil; Step 6: Towards a mass m A Spray distilled water on the mixed soil material A and stir it to ensure that CaO is fully in contact with water to generate Ca(OH)2, to obtain mixed soil material B, which is added to the stirring plate of the sample preparation cabinet; Step 7: Turn on the liquid nitrogen refrigeration system, wait until the temperature in the sample preparation cabinet drops to -85°C, place the dry ice in the ice breaker tray and crush it; Step 8: The ice-breaking disk stops working, and the crushed dry ice enters the screening system for screening, obtaining dry ice particles with particle sizes within each aperture range in step 1. The weighing disk then weighs the dry ice particles corresponding to each aperture range to ensure that they meet the dry ice particle mass required for each aperture range in step 1, and the weighed dry ice particles are transported to the stirring disk. Step 9: Start the stirring plate, mix the mixed soil material B and the dry ice particles evenly to obtain the mixed soil material C, and transfer the mixed soil material C to the sample preparation mold; Step 10: Start the hydraulic system at the bottom of the sample preparation mold to press the mixed soil material C into an artificial sample; Step 11: Turn off the liquid nitrogen refrigeration system and take out the pressed artificial sample from the sample preparation cabinet. At this time, the dry ice in the artificial sample sublimates, forming large pores inside. Step 12: Set the air pressure, gas humidity, and temperature in the reaction chamber to target values ​​in the terminal device, turn on pressure switch 1, start the circulation pump, and wait until the humidity and temperature reach the target values; Step 13: Place the taken artificial sample on the constant temperature base in the reaction chamber; open the third pressure switch until the air bag and the artificial sample are in contact, close the third pressure switch, and close the visible sealing cover; wait until the system pressure reaches the target value; Step 14: Close pressure switch 1 and open pressure switch 2, and N2 enters the system for circulation; at the same time, open bleed valve 1, and CO2 in the system is discharged through bleed valve 1. Close bleed valve 1 after 5 minutes; open bleed valve 2 to exhaust N2 in the air bag, so that the air bag and the artificial sample are separated; reduce the N2 humidity in the system through the humidity controller, and adjust the N2 to a predetermined temperature through the temperature controller to dry the artificial sample; measure the dry weight m1 of the artificial sample; at this time, m1 and m As The difference is the mass of CaCO3 generated. Combined with the mass of CaO added when preparing the artificial sample, the amount of carbonized calcium ions can be obtained. The percentage of carbonized calcium ions 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; Where P is the carbonization reaction progress index, m1 is the mass of the artificial sample after drying, and m As The dry weight of mixed soil material A required to prepare artificial samples, m CaO The mass of CaO in the mixed soil material A required to prepare the artificial sample; Step 15: The target moisture content of the artificial sample and the target moisture content of the dry-wet cycle are controlled as follows: after the carbonization process is completed, the pressure switch 1 is closed and the pressure switch 2 is opened, and N2 enters the system for circulation; at the same time, the air release valve 1 is opened, and the CO2 in the system is discharged through the air release valve 1. After 5 minutes, the air release valve 1 is closed; the air release valve 2 is opened to exhaust the N2 in the air bag and separate the air bag from the artificial sample; the humidity of the N2 in the system is reduced by the humidity controller, and the N2 is adjusted to a predetermined temperature by the temperature controller to dry the artificial sample; the dry weight of the artificial sample is measured in m2; the humidity and temperature of the N2 are controlled to the target values ​​by the humidity controller and the temperature controller. During this process, the air release valve 2 is opened to exhaust the N2 in the air bag and separate the air bag from the artificial sample. The weight of the artificial sample is monitored in real time in m3 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 is stopped; Step 16: After the artificial sample reaches the target moisture content, turn off pressure switch 1, pressure switch 2, pressure switch 3 and the circulation pump, open the visible sealing cover of the reaction chamber, and take out the artificial sample.

6. The method according to claim 5, characterized in that In step 4, the CaO addition ratio is 14%, where the air-dried soil moisture content ω d Calculated at 4%.

7. The method according to claim 5, characterized in that In step 12, the target value of humidity is 80%, and the target value of temperature is 20°C.

8. The method according to claim 5, characterized in that In step 13, the target value of the air pressure is 200 kPa.

9. The method according to claim 5, characterized in that In step 14, the humidity is 2%, the temperature is 105° C., and the duration is 10 hours.

10. The method according to claim 5, characterized in that In step 15, the N2 humidity in the system is adjusted to 2% and the temperature is 105°C through the humidity controller and the temperature controller. After continuous circulation for 10 hours, the dry weight m2 of the artificial sample is measured; the N2 humidity in the system is adjusted to 80% and the temperature is 20°C through the humidity controller and the temperature controller, and the weight m3 of the artificial sample is measured in real time. At this time, the moisture content of the artificial sample is (m3-m2) / m2.

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