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

Abstract

The invention discloses an artificial structural soil sample preparation device and method capable of controlling structural strength, and belongs to the field of geotechnical engineering.The device is composed of a low-temperature forming module, a carbonization module and terminal equipment; the method comprises the following steps: based on the device, obtaining the percentage content of pores in each pore diameter interval of natural loess through a mercury injection test, air-drying and grinding, adding CaO and uniformly mixing, spraying distilled water on the soil material added with CaO and stirring to generate Ca (OH) 2, thereby preparing the mixed soil material. Dry ice particles are prepared according to the pore percentage content of each pore diameter interval obtained by a mercury injection test, are uniformly mixed with the mixed soil material, and are pressed into a sample with a required size. The sample is placed in a CO2 environment for maintenance, and CaCO3 cement which is the same as natural loess is formed among soil particles. And the content of the generated CaCO3 is changed by changing the doping ratio of CaO to control the constitutive property. In addition, nondestructive monitoring of the carbonization process in the sample preparation process is achieved, and the water content of the prepared sample can be controlled.

Description

Technical Field

[0001] The invention discloses a device and a 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 great impact on the study of soil structure. In addition, in structural research, the size of soil samples 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 those of 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. In the current methods of 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 of structural soil technology, 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 less calcium carbonate is generated. Calcium carbonate has a certain solubility in water. Therefore, the calcium carbonate produced in the sample prepared by this method has limited cementation, which cannot effectively simulate the properties of natural loess, and the structure is uncontrollable. By adding ice particles and salt particles to the reshaped soil sample to simulate the macropores in the natural soil, on the one hand, the pore structure of the natural soil sample cannot be restored, that is, the pore content of each pore size cannot be truly restored; on the other hand, the salt particles are removed by seepage and other methods in the later stage, and the flow of water destroys the pore structure of the soil sample, which cannot simulate the structure of natural loess. In addition, the existing technology cannot achieve non-destructive testing for the monitoring of the cementing material generation process, and is mostly monitored by chemical reactions of parallel samples, which greatly increases the number of sample preparations, and due to differences between different samples, the accuracy of the results is poor, so there are disadvantages in monitoring the 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] In the first aspect, a device for artificially preparing structural soil samples capable of controlling the strength of the structure is proposed, 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 to transport liquid nitrogen to the sample preparation cabinet so that the internal temperature of the sample preparation cabinet is always kept lower than 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 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 chamber, the outlets of the CO2 gas cylinder and the N2 gas cylinder A are connected to the humidity controller through an air intake manifold, 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 cabin through a pipeline; the bottom of the reaction cabin is connected to the circulating pump through an exhaust hole; the circulating 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 cabin 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 cabin is composed of a visible sealing cover and a reaction cabin body, and an airbag and a constant temperature base are provided in the reaction cabin body, the airbag is an annular airbag, and the airbag is arranged in the middle of the inner wall of the reaction cabin; the constant temperature base is located at the bottom of the reaction cabin body, and a pressure sensor and a heating device are provided therein; the terminal device is respectively connected to the pressure switch 1, the pressure switch 2, the 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 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 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 hole diameter of the upper oscillating screening plate of any two adjacent oscillating screening plates is larger than the sieve hole diameter of the lower oscillating screening plate. Except for the uppermost oscillating screening plate, the bottom of each of the other oscillating screening plates is provided with a discharge conduit for conveying dry ice particles, and the top of the discharge conduit is provided with a switch, and the bottom leads to a weighing plate; the bottom of the weighing plate is provided with a discharge port; the bottom of the stirring plate is provided with a discharge port and a baffle. The screening system also has a waste plate, which is arranged below the lowest 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, conduct a mercury injection test on the obtained natural loess, obtain the percentage of pores in each pore size interval of the natural loess, and calculate the mass of dry ice particles required for each pore size interval based on the percentage of pores in 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, and 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, and m is d is the air-dried soil mass, ω d is the moisture content of air-dried soil;

[0017] Step 5: According to the target density and volume of the 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 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 content 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 air-dried soil mass, 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-breaking tray and crush it;

[0022] Step 8: The ice-breaking disk stops working, and the crushed dry ice enters the screening system for screening, and the dry ice particles with particle sizes in each aperture interval in step 1 are obtained respectively. Then the weighing disk weighs the dry ice particles corresponding to each aperture interval respectively to make them meet the dry ice particle mass required for each aperture interval in step 1, and the weighed dry ice particles are transported to the stirring disk;

[0023] Step 9: Start the stirring plate, stir the mixed soil material B and the dry ice particles evenly to obtain the mixed soil material C, and transport 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 and large pores are formed inside;

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

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

[0028] Step 14: Close pressure switch 1, open pressure switch 2, and N2 enters the system for circulation; at the same time, open vent valve 1, and CO2 in the system is discharged through vent valve 1. Close vent valve 1 after 5 minutes; open vent valve 2 to exhaust N2 in the air bag to separate the air bag from the artificial sample; reduce the humidity of N2 in the system through the humidity controller, and adjust 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 calculation of the carbonization reaction progress index P is 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 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 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, close the pressure switch 1, open the pressure switch 2, and N2 enters the system for circulation; at the same time, open the air release valve 1, and the CO2 in the system is discharged through the air release valve 1, and close the air release valve 1 after 5 minutes; open the air release valve 2, exhaust the N2 in the air bag, and separate the air bag from the artificial sample; reduce the humidity of N2 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 of the artificial sample m2; control the humidity and temperature of N2 to the target value through the humidity controller and the temperature controller. In this process, open the air release valve 2, exhaust the N2 in the air bag, and separate the air bag from the artificial sample. The weight m3 of the artificial sample is monitored in real time through 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 stops circulating;

[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 humidity controller and the temperature controller are used to adjust the N2 humidity in the system to 2% and the temperature to 105°C. After continuous circulation for 10 hours, the dry weight m2 of the artificial sample is measured; the humidity controller and the temperature controller are used to adjust the N2 humidity in the system to 80% and the temperature to 20°C, 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 the artificial sample by changing the pore structure and pore content of the artificial sample, and can achieve the preparation of artificial samples with different structures while maintaining the same material composition, so as to facilitate the study of soil structure. 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 a specific soil actual situation, eliminate the influence of interference factors, and predict or simulate the engineering properties of the soil, 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 The overall structural diagram of the device for artificially preparing structural soil samples capable of controlling 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 diagram of sample No. 1;

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

[0045] Figure 6 This is the porosity percentage diagram 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 spectrum analysis of rod-shaped calcite in natural loess;

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

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

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

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

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

[0053] Fig.14 This is the result of the energy spectrum analysis of CaCO3 thin film in the artificially prepared sample;

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

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

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

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

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

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

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

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

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

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

[0064] Fig.25 The microstructure of the artificially prepared loess sample observation point 3 is magnified 1000 times;

[0065] Fig.26 The microstructure of observation point 3 of the artificially prepared loess sample is magnified 2000 times;

[0066] Fig. 27 The microstructure image of observation point 4 of the artificially prepared loess sample with a magnification of 1000 times;

[0067] Fig.28 The microstructure image of observation point 4 of the artificially prepared loess sample with a magnification of 2000 times;

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

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

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

[0071] The markings in the figure are as follows: 1-liquid nitrogen tank, 2-temperature sensor, 3-valve, 4-sample cabinet, 5-sample cabinet body, 6-ice breaking plate, 7-weighing plate, 8-stirring plate, 9-sample 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 one, 25-pressure switch two, 26-air relief valve one, 27-gas temperature and humidity sensor, 28-exhaust hole, 29-pressure switch three, 30-air bag filling and deflation channel, 31-air relief valve two, 32-visible sealing cover, 33-reaction chamber body, 34-air bag, 35-constant temperature base, 36-terminal equipment. DETAILED DESCRIPTION

[0072] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical scheme of the present invention is clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the present invention is not limited to the following embodiments, and the specific implementation method can be determined according to the technical scheme of the present invention and the actual situation. In order to avoid confusing the essence of the present invention, the known methods, processes, procedures, components and circuits are not described in detail.

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

[0074] Combination Figure 1 , Figure 2 and Figure 3 The present invention proposes a method for artificially preparing structural soil samples that can control the strength of the structure. First, the obtained natural loess is subjected to a mercury injection test to obtain the percentage of pores in each pore size interval of the natural loess; then, the natural loess is air-dried and crushed, CaO is added and mixed evenly, distilled water is sprayed on the soil material with CaO added and stirred to ensure that CaO is fully in contact with water to generate Ca(OH)2, and a mixed soil material B is prepared. According to the percentage of pores in each pore size interval obtained by the mercury injection test, dry ice particles are prepared. That is, after the dry ice is crushed, according to the volume of pores in a certain pore size interval, for example, the pores in the pore size range of 15-45μm, the total volume is V1, then the dry ice particles with a particle size in the range of 15-45μm are taken, and the total volume is equal to V1. According to all large pore size intervals, the corresponding amount of dry ice particles are taken according to this method. The dry ice particles are mixed evenly with the mixed soil material B to obtain the mixed soil material C, which is pressed into an artificial sample of the required size. The above processes from preparing dry ice particles to pressing and molding artificial samples are all completed in a low temperature environment (below -78.5°C) to avoid dry ice sublimation. After the artificial sample is formed, the temperature is increased, and the dry ice in the artificial sample sublimates to form a large pore structure similar to natural loess. The artificial sample is further placed in a high humidity and high concentration CO2 environment for curing. The preferred humidity is 80%, the CO2 concentration is controlled by pressure, the temperature in the system is 20°C, and the pressure is 200kPa; CaCO3 cementation similar to natural loess is formed between 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] In addition, the present invention can realize non-destructive monitoring of the carbonization process during the sample preparation process, and can control the moisture content of the prepared artificial sample. The moisture content of the artificial sample can be achieved by adjusting the humidity and temperature of N2 in the system through the humidity controller 20 and the temperature controller 21. The humidity controller 20 and the temperature controller 21 of the present invention can realize the change of the humidity and temperature of the gas as needed, and input different values ​​of the humidity and temperature of the gas through the terminal device 36 to obtain the change curve of the humidity and temperature over time, which can simulate the dry-wet, freeze-thaw cycle of the soil sample under complex conditions, as well as the cycle under the coupling of dry-wet and freeze-thaw.

[0076] The device for artificially preparing structural soil samples capable of controlling the strength of the structure proposed by 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 is composed of a liquid nitrogen refrigeration system and a sample preparation cabinet 4. The liquid nitrogen refrigeration system is composed 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 arranged on the connecting pipeline between the liquid nitrogen tank 1 and the sample preparation cabinet 4. The sample preparation cabinet 4 includes a sample preparation cabinet body 5, and the sample preparation cabinet body 5 is sequentially provided with an ice breaking plate 6, a screening system, a weighing plate 7, a stirring plate 8, a sample preparation mold 9 and a hydraulic system 10 from top to bottom; the screening system includes a No. 1 screen 11, a No. 2 screen 12, a No. 3 screen 13, a No. 4 screen 14, a waste tray 15 and a discharge conduit 16.

[0078] The carbonization module is composed of a CO2 cylinder 17, a N2 cylinder A18, a 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 provided with a pressure switch 24, through which the CO2 pressure in the system can be controlled to be a target value, and the CO2 concentration is increased under pressure, which can accelerate the process of generating CaCO3. On the other hand, a certain pressure can accelerate the speed of CO2 passing through the artificial sample in the reaction chamber 23, ensuring that there is enough CO2 to contact Ca(OH)2 to participate in the reaction. The outlet of the N2 cylinder A18 is provided with a pressure switch 25, which plays a role in drying the artificial sample in the reaction chamber 23 by heating N2. In this process, the air pressure in the system is controlled by the pressure switch 25, which can accelerate the speed of N2 passing through the artificial sample and accelerate the drying of the artificial sample. The CO2 gas cylinder 17 and the N2 gas cylinder A18 are connected to the humidity controller 20 through the air intake main pipe. The humidity controller 20 is provided with a gas relief valve 1 26 on the top. The humidity controller 20 is connected to the temperature controller 21. The outlet of the temperature controller 21 is provided with a gas temperature and humidity sensor 27. The temperature controller 21 is connected to the reaction chamber 23. The bottom of the reaction chamber 23 is connected to the circulation pump 22 through the exhaust hole 28. The circulation pump 22 is connected to the air intake main pipe to form a loop. The outlet of the N2 gas cylinder B19 is provided with a pressure switch 3 29 to control the air pressure in the air bag 34 to achieve the purpose of charging and discharging. The N2 gas cylinder B19 is connected to the reaction chamber 23 through the air bag charging and discharging channel 30. A gas relief valve 2 31 is provided between the air bag charging and discharging channel 30 and the pressure switch 3 29.

[0079] Liquid nitrogen refrigeration system: open valve 3, liquid nitrogen enters sample preparation cabinet 4, temperature sensor 2 monitors temperature in real time, and 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] The structure of the sample preparation cabinet 4: an ice-breaking device for crushing dry ice is arranged inside the ice-breaking tray 6; the ice-breaking device includes an ice-breaking knife and a driving motor for driving the ice-breaking knife to rotate around its own rotation axis; the lower end of the ice-breaking tray 6 is a discharge port, and 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 a No. 1 sieve 11, a No. 2 sieve 12, a No. 3 sieve 13 and a No. 4 sieve 14 arranged in sequence from top to bottom, and the No. 1 sieve 11 preferably has a sieve hole size of 0.355 mm and 45 mesh; the No. 2 sieve 12 preferably has a sieve hole size of 0.090 mm and 170 mesh; the No. 3 sieve 13 preferably has a sieve hole size of 0.045 mm and 325 mesh; the No. 4 sieve 14 preferably has a sieve hole size of 0.015 mm and 900 mesh. A discharge conduit 16 is provided at the bottom of each of the No. 2 sieve 12, the No. 3 sieve 13 and the No. 4 sieve 14. A switch is provided at the top of the discharge conduit 16. The bottom leads to the weighing pan 7. The 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. The waste pan 15 is located at the bottom of the No. 4 sieve 14 and receives the 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 provided at the bottom of the weighing pan 7. The dry ice particles in the weighing pan 7 enter the stirring pan 8 through the discharge port of the weighing pan 7. The stirring pan 8 is provided with a stirring device, and a discharge port and a baffle are provided 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 making mold 9 is connected to the hydraulic system 10 below, and the hydraulic head of the hydraulic system 10 is located inside the sample making mold 9. The hydraulic head of the hydraulic system 10 cooperates with the inner cavity of the sample making mold 9. The hydraulic head of the hydraulic system 10 rises to press the mixed soil material C into shape.

[0081] The humidity controller 20 is used to humidify the incoming gas. The temperature controller 21 is used to control the temperature of the gas processed by the humidity controller 20. The processed gas continues to circulate after being measured by the gas temperature and humidity sensor 27 until the target value is reached. It should be noted that in the present invention, the humidity controller 20, the temperature controller 21 and the gas temperature and humidity sensor 27 are all commercially available products, which belong to the prior art and will not be described in detail.

[0082] The reaction chamber 23 is composed of a visible sealing cover 32 and a reaction chamber body 33, and the reaction chamber body 33 contains an airbag 34 and a constant temperature base 35. After the airbag 34 is inflated by the N2 gas cylinder B19, it wraps the middle part of the artificial sample, fits tightly with the artificial sample, fixes the artificial sample and divides the interior of the reaction chamber 23 into two parts, the upper and lower parts, and the gas between the two parts flows 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 hole 28, and is recycled. In this process, the CO2 gas channel is single, the gas is in full contact with the inside of the artificial sample, and the carbonization reaction is uniform. The airbag 34 is deflated through the deflation valve 231, and the airbag 34 is separated from the artificial sample after deflation. A pressure sensor is provided in the constant temperature base 35, which can measure the mass of the artificial sample thereon. A heating device is also provided in the constant temperature base 35 to prevent condensation water from forming on the outer wall of the base, which affects the quality measurement result.

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

[0084] 2. Operation steps:

[0085] 1. The operating 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 appearance, and conduct mercury injection tests to obtain pore distribution data. Take the average of the test data of the three mercury injection samples to obtain the percentage of macropores in each pore size interval. Here, it is preferred that the pore size of the macropores is greater than 15μm, and the macropore size intervals are divided into 15-45μm, 45-90μm and 90-355μm. Existing studies generally believe that pores with a pore size greater than 16μm in loess are macropores, and this method needs to be combined with mercury injection tests to determine the percentage of pores in each interval. The mercury injection test measures the boundary values ​​of the macropore size interval to be 45μm, 90μm and 355μm, respectively. At the same time, considering the sieve size, the starting pore size of the macropores is taken as 15μm, so the macropore size 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 in the range of 45-90μm and 90-355μm is 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 a ring knife, and m is the mass of the natural loess sample cut by a ring knife in the natural state;

[0091] The natural moisture content of natural loess is ω, and its calculation process is as follows:

[0092]

[0093] Where m is the mass of the natural loess sample cut by a ring knife in its natural state, m s It is the mass of natural loess with a mass of m after being dried 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 contentω d The calculation formula is as follows:

[0097]

[0098] Where m d is the air-dried soil mass, 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 preferred CaO addition ratio (ratio of the mass of the added substance to the mass of the substance to be added) is: n is the target CaCO3 content of the artificial sample, which is 14%, and the moisture content of the air-dried soil is ω d Calculated at 4%.

[0100] CaO doping 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, and m is d is the air-dried soil mass, 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 mixed soil material A, and calculate the dry weight of mixed soil material A m 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 content 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 air-dried soil mass, 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, obtain mixed soil material B, and add it into the stirring plate 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. The oscillating screening disk is started, and the oscillating screening disk vibrates to separate 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. The discharge conduit 16 switch of the No. 2 sieve 12 is turned on, 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 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 a mixed soil material C. Open the baffle at the bottom of the stirring disk 8, and the mixed soil material C enters the sample preparation mold 9.

[0110] (10) The baffle at the bottom of the stirring plate 8 is closed, and the hydraulic system 10 at the bottom of the sample preparation mold 9 is started 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), gas humidity and temperature in the terminal device 36 to target values, open the pressure switch 24 at the outlet of the CO2 cylinder 17, start the circulation pump 22, and 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 artificial sample taken out 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 fits 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 process, the progress of the carbonization reaction is evaluated: the pressure switch 24 at the outlet of the CO2 gas cylinder 17 is closed, and the pressure switch 25 at the outlet of the N2 gas cylinder A18 is opened, and N2 enters the system for circulation. At the same time, the vent valve 26 is opened, and the 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 exhaust the N2 in the air bag 34, so that the air bag 34 is separated from the artificial sample. The N2 humidity in the system is reduced to 2% by the humidity controller 20, and the N2 is 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 is 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 understood.

[0115] The percentage of the carbonized calcium ions to the total amount of added calcium ions is used as the carbonization reaction progress index P, and the carbonization reaction progress index P 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 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 is closed, and the pressure switch 25 at the outlet of the N2 gas cylinder A18 is opened, and N2 enters the system for circulation. At the same time, the vent valve 26 is opened, and the 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 exhaust the N2 in the air bag 34 to separate the N2 from the artificial sample; the humidity of the N2 in the system is reduced by the humidity controller 20, and the N2 is adjusted to a predetermined temperature by the temperature controller 21 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, and the moisture content of the artificial sample is (m3-m2) / m2 at this time. When the moisture content of the artificial sample reaches the target value, the gas circulation stops;

[0119] In this embodiment, in step (15), after the carbonization reaction process is completed, the humidity controller 20 and the temperature controller 21 are used to adjust the N2 humidity in the system to 2% and the temperature to 105°C. After continuous circulation for 10 hours, the dry weight m2 of the artificial sample is measured; the humidity controller 20 and the temperature controller 21 are used to adjust the N2 humidity in the system to 80% and the temperature to 20°C, 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 the pressure switch 1 24, the pressure switch 25, the pressure switch 3 29 and the 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 capable of controlling the strength of the structure is used to perform the soil sample drying and 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 and wetting and freeze-thaw cycle tests, and is not limited to artificially prepared structural soil samples.

[0122] The device of the present invention only needs a carbonization module and a terminal device 36 to perform a soil sample dry-wet and freeze-thaw cycle test. The dry-wet cycle operation steps are as follows:

[0123] (1) Place the soil sample on the thermostatic 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 value of soil sample humidity. According to the test requirements, the target humidity can be a fixed value or a changing 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. The moisture content of the soil sample is monitored and the test process is controlled accordingly.

[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 the 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 coupling 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 device of the present invention are used to prepare the sample, the sample is a cylinder with a diameter of 39.1 mm and a height of 80 mm, and 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) as follows Figure 4-Figure 6 As shown in Table 1, the three natural loess mercury injection samples were taken from the same natural loess. The three natural loess mercury injection samples were taken for parallel testing to avoid the influence of cracks, wormholes, plant roots, etc. in the natural loess, so as to ensure that the test data can represent the pore characteristics of the natural loess. Among them, the macropore content and porosity are shown in Table 1. According to the volume of the artificially prepared soil sample and the target porosity (the average porosity in Table 1), the amount of dry ice particles is calculated as shown in Table 2, and the calculation process is as follows.

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

[0134]

[0135] The mass of dry ice particles with a particle size between 15 and 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=1.56g / cm 3 .

[0137] Similarly, the pore contents in the pore sizes of 45-90 μm, 90-355 μm and greater than 355 μm are 5.35%, 9.78% and 0 respectively, and the masses of dry ice particles 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 sieve with a pore size of 0.5 mm. 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, with the CaO incorporation ratio being 14%.

[0144] c. The dry density of natural loess 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 into 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 samples, and finally control the moisture content of the artificially prepared samples to be the same as that of natural loess, which is 16.7%.

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

[0148] Scanning electron microscope test, mercury injection test and collapsibility test were carried out 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 during the sample preparation process, calcite (calcite is a calcium carbonate mineral with a chemical formula of CaCO3, and is the most common mineral in natural calcium carbonate) was generated between soil particles. 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 , Fig. 9 , Fig.10 , Fig.11 , Fig.12 , Fig.13 , Fig.14 , 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 Spectral 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 In general, the distribution of C and Ca in each sample is relatively consistent, mainly distributed in the contact parts between soil particles, or forming long aggregates between soil particles to connect them. In addition, they are distributed on the surface of some aggregates and around clay particles attached to the surface of skeleton particles. It can be seen that the sample preparation method of the present invention can form effective 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 skeleton structure, and the skeleton particles are mostly powder particles, with more clay particles attached to its surface and more open pores. In the photo with a magnification of 1000 times, the maximum diameter of the larger pores was measured using the measurement function of the scanning electron microscope. It can be seen that the larger pore diameters in natural loess are mostly in the range of 10μm to 20μm, and some large pores can reach 40μm in diameter. Compared with natural loess, artificially prepared loess can be seen with a skeleton structure and more open pores, and the larger pore diameters are mostly in the range of 15μm to 30μm, and some large pores can reach 60μm in diameter. Overall, the microstructures of the two are similar.

[0162] (2) Mercury intrusion test

[0163] Two artificially prepared loess samples (No. 4 and No. 5) were taken for mercury intrusion testing. The results are shown in Table 7. Fig.29 and Fig.30 It can be seen from the analysis 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 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: Fig.31 As shown in Figure 2, 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, the prepared samples 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 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 to transport liquid nitrogen to the sample preparation cabinet so that the internal temperature of the sample preparation cabinet is always kept lower than 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 arranged 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 arranged inside the stirring disk; 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 to the humidity controller through an air intake main pipe, the outlet of the CO2 gas cylinder is provided with a pressure switch 1, and the outlet of 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 circulating pump through an exhaust hole; the circulating 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 is composed 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 the airbag 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 a pressure sensor and a heating device are provided therein; the terminal device is respectively connected to the pressure switch 1, the pressure switch 2, the 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 pipeline 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 oscillating screening plates arranged one above the other, and the sieve hole diameter of the oscillating screening plate located on the upper side of any two adjacent oscillating screening plates is larger than the sieve hole diameter of the oscillating screening plate located on the lower side. Except for the oscillating screening plate located on the uppermost side, a discharge conduit for conveying dry ice particles is provided at the bottom of each of the other oscillating screening plates, and a switch is provided at the top of the discharge conduit, and the bottom leads to a 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 oscillating screening plate.

5. A method for preparing structural soil samples based on the device for artificially preparing structural soil samples capable of controlling the strength of the structure according to any one of claims 1 to 4, characterized in that: The method includes: Step 1: Obtain natural loess, conduct a mercury injection test on the obtained natural loess, obtain the percentage of pores in each pore size interval of the natural loess, and calculate the mass of dry ice particles required for each pore size interval based on the percentage of pores in 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, and 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, and m is d is the air-dried soil mass, ω d is the moisture content of air-dried soil; Step 5: According to the target density and volume of the 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 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 content 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 air-dried soil mass, 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-breaking tray and crush it; Step 8: The ice-breaking disk stops working, and the crushed dry ice enters the screening system for screening, and the dry ice particles with particle sizes in each aperture interval in step 1 are obtained respectively. Then the weighing disk weighs the dry ice particles corresponding to each aperture interval respectively to make them meet the dry ice particle mass required for each aperture interval in step 1, and the weighed dry ice particles are transported to the stirring disk; Step 9: Start the stirring plate, stir the mixed soil material B and the dry ice particles evenly to obtain the mixed soil material C, and transport 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 and large pores are formed inside; Step 12: Set the air pressure, gas humidity and temperature in the reaction chamber to the target values ​​in the terminal device, turn on the pressure switch 1, start the circulation pump, and wait until the humidity and temperature reach the target values; Step 13: Place the artificial sample taken out on the constant temperature base in the reaction chamber; open the pressure switch three until the air bag fits the artificial sample, close the pressure switch three, and close the visible sealing cover; wait until the system air pressure reaches the target value; Step 14: Close pressure switch 1, open pressure switch 2, and N2 enters the system for circulation; at the same time, open vent valve 1, and CO2 in the system is discharged through vent valve 1. Close vent valve 1 after 5 minutes; open vent valve 2 to exhaust N2 in the air bag to separate the air bag from the artificial sample; reduce the humidity of N2 in the system through the humidity controller, and adjust 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 calculation of the carbonization reaction progress index P is 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 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, close the pressure switch 1, open the pressure switch 2, and N2 enters the system for circulation; at the same time, open the air release valve 1, and the CO2 in the system is discharged through the air release valve 1, and close the air release valve 1 after 5 minutes; open the air release valve 2, exhaust the N2 in the air bag, and separate the air bag from the artificial sample; reduce the humidity of N2 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 of the artificial sample m2; control the humidity and temperature of N2 to the target value through the humidity controller and the temperature controller. In this process, open the air release valve 2, exhaust the N2 in the air bag, and separate the air bag from the artificial sample. The weight m3 of the artificial sample is monitored in real time through 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 stops circulating; 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%, and the moisture content of the air-dried soil is 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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