Device and method for simulating freezing and thawing cycle process of collapsible loess in natural environment

Abstract

The invention discloses a device and method for simulating the freezing and thawing cycle process of collapsible loess in the natural environment, and belongs to the technical field of geotechnical engineering.The device comprises a test box provided with a sample groove, a rainfall simulation system is arranged on the upper portion in the test box, an underground water seepage simulation system is arranged on the lower portion in the test box, and the sample groove is connected with a loading system; a weighing system is arranged at the bottom in the test box, the weighing system is connected with an underground water seepage simulation system, a settlement and internal damage monitoring system is arranged between the weighing system and the rainfall simulation system, and a freezing and thawing circulation system is arranged on the inner side wall of the test box. According to the invention, the natural environment of the loess plateau area can be simulated, and the strength change of the strong salinized soil in the dry-wet process can be tested and researched under the combined action of various factors such as rainfall, load, underground water seepage and freeze-thaw cycle.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering, and in particular to a device and method for simulating the freeze-thaw cycle process of collapsible loess in a natural environment. Background Art

[0002] Collapsible loess in the Loess Plateau is characterized by high porosity and strong collapsibility, making it a typical collapsible soil. Under the combined effects of freeze-thaw cycles, precipitation, and groundwater seepage, the engineering properties of collapsible loess undergo significant changes. Freeze-thaw cycles lead to the reorganization and destruction of the soil's internal pore structure, while precipitation and groundwater seepage further alter the soil's moisture distribution and permeability. Changes in bearing capacity directly affect the soil's stability under engineering loading. Furthermore, internal damage gradually accumulates under the repeated effects of these environmental factors, profoundly affecting the soil's strength and deformation properties, thereby threatening the safety of the project. Therefore, in order to understand the changes in the engineering properties of collapsible loess caused by the above factors and the resulting geological disaster processes, a device for detecting the engineering properties of collapsible loess in a simulated natural environment is needed. Existing testing equipment and techniques suffer from numerous limitations: Traditional freeze-thaw chambers only consider temperature effects, ignoring natural coupling conditions such as seepage, humidity, and pressure; artificial simulations of loess collapsibility result in uneven distribution of water migration and temperature fields; there is a lack of precise control over the number of freeze-thaw cycles and simultaneous application of loads; and load-bearing tests ignore damage accumulation and progressive failure mechanisms. These deficiencies collectively limit in-depth research and accurate assessment of the mechanisms of collapsible loess disasters and changes in their engineering properties. Summary of the Invention

[0003] The purpose of the present invention is to provide a device and method for simulating the freeze-thaw cycle process of collapsible loess in a natural environment, so as to overcome the shortcomings of the prior art.

[0004] To achieve the above object, the present invention provides the following technical solutions: In the first aspect, the present invention provides a device for simulating the freeze-thaw cycle process of collapsible loess in a natural environment, comprising a test box provided with a sample trough, a precipitation simulation system provided above the interior of the test box, a groundwater seepage simulation system provided below the interior of the test box, the sample trough is connected to a loading system, a weighing system is provided at the bottom of the interior of the test box, the weighing system is connected to the groundwater seepage simulation system, and a settlement and internal damage monitoring system is provided between the weighing system and the precipitation simulation system, and a freeze-thaw cycle system is provided on the inner wall of the test box.

[0005] Furthermore, the test box includes an inner wall steel shell and an outer wall steel shell, an air outlet is provided on one side of the test box body, and an air inlet is provided on the top of the test box body. The precipitation simulation system includes mechanical telescopic rods, blowers and humidity sensors evenly arranged around the inner wall steel shell, each of the mechanical telescopic rods is provided with several ultrasonic atomizers and the water inlet of the ultrasonic atomizer is connected to the mechanical telescopic rod, and the mechanical telescopic rod is connected to the groundwater seepage simulation system; the outlet of the blower is connected to the air inlet through an air inlet pipe, an air inlet valve is provided on the air inlet pipe, and the humidity sensor is arranged on the inner wall steel shell.

[0006] Furthermore, the groundwater seepage simulation system includes a water storage chamber and a water tank. The water tank is connected to a water pump and a water inlet valve is provided at the connection. The water pump passes through the side wall of the test box to the water storage chamber through an inlet pipe and an outlet pipe. A multi-layer permeable board is provided above the water storage chamber, and a settlement and internal damage monitoring system is provided above the multi-layer permeable board; the water tank is connected to a water level regulator to control the water level height in the water tank, and the mechanical telescopic rod is connected to the water inlet pipe.

[0007] Furthermore, the weighing system includes several pressure sensing devices, the loading system is connected below the pressure sensing devices, a weighing platform is provided above the pressure sensing devices and the weighing platform is located below the water storage chamber.

[0008] Furthermore, the loading system includes a hydraulic actuator and a hydraulic pressure plate. The hydraulic pressure plate is arranged on the top of the test box and is provided with a strain acquisition device and a wind speed sensor. The hydraulic actuator is arranged below the weighing platform.

[0009] Furthermore, the settlement and internal damage monitoring system includes a semi-annular metal shell, which is located above the multi-layer permeable plate and is provided with a side-by-side high-definition camera and a micro CT probe, and is provided with relative laser transmitters and laser receivers.

[0010] Furthermore, the freeze-thaw cycle system includes a temperature sensor, a temperature control system, a condenser and a heating tube. The condenser and the heating tube are spaced apart on the inner wall steel shell, and the temperature control system and the temperature sensor are arranged on the inner wall steel shell.

[0011] Furthermore, the test box is provided with an acrylic door, and a heat-insulating material is provided between the inner wall steel shell and the outer wall steel shell.

[0012] In a second aspect, the present invention provides a method for simulating the freeze-thaw cycle of collapsible loess in a natural environment, comprising the following steps: S1, controlling the height of the sample tank through the loading system and adding the prepared collapsible loess sample into the sample tank, and then using the weighing system to weigh the collapsible loess sample; S2, set the precipitation amount and wind speed through the precipitation simulation system to simulate the natural rainfall environment, and turn off the precipitation simulation system when the set rainfall amount is reached; S3, after simulating the groundwater seepage in the natural environment through the groundwater seepage simulation system, the settlement and internal damage monitoring system is used to monitor the height of the collapsible loess sample and the collapse process of the collapsible loess sample in real time and generate the internal structure model of the collapsible loess sample; S4, turn on the freeze-thaw cycle system and set the number of freeze-thaw cycles. When each cycle is completed, the settlement and internal damage monitoring system automatically obtains the height and high-definition images of the collapsible loess sample and automatically calculates the soil porosity based on the CT data; S5, turn on the loading system, adjust the height of the sample tank, set the size, shape and loading rate of the collapsible loess sample, measure the stress-strain of the collapsible loess sample during the loading process, and automatically unload and record the peak load after the collapsible loess sample fails, and monitor the pore evolution and crack development of the collapsible loess sample in real time during the failure process; S6. After the test is completed, the collapsible loess sample is taken out by controlling the height of the sample tank through the loading system.

[0013] Compared with the prior art, the present invention has the following beneficial technical effects: The present invention provides a device for simulating the freeze-thaw cycle of collapsible loess in a natural environment. By integrating a test chamber equipped with a sample tank 36, a precipitation simulation system, a loading system, a groundwater seepage simulation system, a weighing system, a settlement and internal damage monitoring system, and a freeze-thaw cycle system, the device can simulate the natural environment of the Loess Plateau. This device can experimentally study the strength changes of highly saline soil during the drying and wetting process, using multiple factors, including precipitation, loading, groundwater seepage, and freeze-thaw cycles. Compared to single-factor simulation devices, this device is closer to the actual natural environment and can comprehensively study the changes in the physical and mechanical properties of collapsible loess in complex environments.

[0014] This method can accurately and in real time obtain data on the weight, settlement, and internal structural damage of collapsible loess samples during testing. Using high-definition cameras and micro-CT scanners, intuitive image data and detailed internal structural information can be obtained, providing rich data support for in-depth analysis of loess properties.

[0015] The present device integrates all systems within the test chamber, resulting in a compact structure and minimal space. The control system allows for automated or semi-automated operation of each system, resulting in a relatively simple operational process. This reduces operational difficulty and workload for test personnel, improves test efficiency, and facilitates large-scale experimental research on collapsible loess. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 The present invention is a schematic diagram of the structure of a device for simulating the freeze-thaw cycle process of collapsible loess in a natural environment.

[0017] Figure 2 Schematic top view of a device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to an embodiment of the present invention.

[0018] Figure 3 Schematic diagram of a precipitation simulation system in an embodiment of the present invention.

[0019] Figure 4 Detailed diagram of a precipitation simulation system in an embodiment of the present invention.

[0020] Figure 5 This is a front view of the settlement and internal damage monitoring system in an embodiment of the present invention.

[0021] Figure 6 2. It is a top view of the settlement and internal damage monitoring system in an embodiment of the present invention.

[0022] In the figure, there are laser emitter 1; air outlet 2; acrylic door 3; humidity sensor 4; temperature sensor 5; temperature control system 6; strain acquisition device 7; air inlet 8; wind speed sensor 9; high-definition camera 10; micro CT probe 11; porous water-permeable plate 12; water storage chamber 13; pressure sensing device 14; weighing platform 15; hydraulic actuator 16; water inlet pipe 17; water outlet pipe 18; semi-circular metal shell 19; water tank 20; ultrasonic atomizer 21; mechanical telescopic rod 22; insulation material 23; inner wall steel shell 24; condenser 25; heating tube 26; laser receiver 27; sealing ring 28; air inlet pipe 29; blower 30; water level regulator 31; water pump 32; hydraulic pressure plate 33; air inlet valve 34; water inlet valve 35; sample tank 36; outer wall steel shell 37. DETAILED DESCRIPTION

[0023] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0024] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0025] like Figure 1-6 As shown, the present invention provides a device for simulating the freeze-thaw cycle process of collapsible loess in a natural environment, including a test box provided with a sample tank 36, a precipitation simulation system, a loading system, a groundwater seepage simulation system, a weighing system, a settlement and internal damage monitoring system and a freeze-thaw cycle system. A precipitation simulation system is set above the inside of the test box to simulate the rainfall process in the natural environment, and a groundwater seepage simulation system is set below the inside of the test box. The sample slot 36 is connected to the loading system to apply loads of different sizes and types to the collapsible loess sample to simulate the various pressures that loess is subjected to in actual engineering. A weighing system is set at the bottom of the test box to measure the weight change of the collapsible loess sample in real time, which helps to understand the change of loess water content during precipitation, groundwater seepage and freeze-thaw cycles. The weighing system is connected to the groundwater seepage simulation system and a settlement and internal damage monitoring system is set between the weighing system and the precipitation simulation system to monitor the settlement deformation and internal structural damage of the collapsible loess sample under various effects. A freeze-thaw cycle system is set on the inner wall of the test box to adjust the temperature inside the test box to simulate the freeze-thaw cycle process experienced by collapsible loess in the natural environment.

[0026] In some preferred embodiments of the present invention, an openable and closable acrylic door 3 is provided on the front of the test box, the test box includes an inner wall steel shell 24 and an outer wall steel shell 37, and an insulation material 23 is provided between the inner wall steel shell 24 and the outer wall steel shell 37. The precipitation simulation system includes 4 mechanical telescopic rods 22, a blower 30 and a humidity sensor 4 evenly arranged around the inner wall steel shell 24. Each mechanical telescopic rod 22 is provided with a number of ultrasonic atomizers 21 and the water inlet of the ultrasonic atomizer 21 is connected to the mechanical telescopic rod 22, and the mechanical telescopic rod 22 is connected to the groundwater seepage simulation system; the mechanical telescopic rod 22 is connected to the groundwater seepage simulation system and can obtain moisture from the groundwater seepage simulation system. Water from the groundwater seepage simulation system is delivered through the internal channels of the mechanical telescopic rods 22 to the water inlet of the ultrasonic atomizers 21 on each rod, providing the water source required for operation. The ultrasonic atomizers 21 use the high-frequency oscillation of ultrasound to break up the input water into tiny mist particles. These mist particles diffuse within the test chamber, simulating natural precipitation processes and ensuring that the surface of the collapsible loess sample receives precipitation evenly. By means of a number of ultrasonic atomizers 21 arranged on the mechanical telescopic rod 22, the range and intensity of precipitation can be controlled to meet the requirements of different test conditions; the outlet of the blower 30 is connected to the air inlet 8 through the air inlet pipe 29, and a sealing ring 28 is provided at the connection between the air inlet pipe 29 and the air inlet 8, and an air inlet valve 34 is provided on the air inlet pipe 29; when it is necessary to adjust the air circulation and humidity distribution in the test chamber, the air inlet valve 34 can be opened, and the blower 30 will send external air or treated air into the test chamber through the air inlet pipe 29, thereby promoting the circulation of air in the test chamber, making the water mist particles more evenly distributed in the test chamber, avoiding the occurrence of local humidity unevenness, and also helping to simulate the influence of air flow in the natural environment on precipitation and test specimens; the humidity sensor 4 is arranged on the inner wall steel shell 24 to monitor the air humidity inside the test chamber in real time.

[0027] In some preferred embodiments of the present invention, the groundwater seepage simulation system is further defined; it includes a water storage chamber 13 and a water tank 20, the water tank 20 is connected to a water pump 32 and a water inlet valve 35 is provided at the connection, the water pump 32 passes through the side wall of the test box to the water storage chamber 13 through the water inlet pipe 17 and the water outlet pipe 18, when the test requires groundwater seepage simulation, the water inlet valve 35 is opened, the water pump 32 is started, the water pump 32 will pump water from the water tank 20, and the water is transported to the water storage chamber 13 in the test box through the water inlet pipe 17, the water pumped by the water pump 32 enters the water storage chamber 13 through the water inlet pipe 17, a multi-layer permeable board 12 is provided above the water storage chamber 13, and the water entering the water storage chamber 13 Water penetrates upward through the multi-layer permeable board 12. The multi-layer permeable board 12 can make the water penetrate more evenly, simulating the seepage of groundwater in the soil layer under natural conditions. A settlement and internal damage monitoring system is set above the multi-layer permeable board 12; the penetrated water gradually enters the collapsible loess sample of the settlement and internal damage monitoring system above the multi-layer permeable board 12. The water tank 20 is connected to a water level regulator 31 to control the water level height in the water tank 20. The mechanical telescopic rod 22 is connected to the water inlet pipe 17. The water in the water inlet pipe 17 can flow into the mechanical telescopic rod 22, thereby providing a water source for the ultrasonic atomizer 21 set on the mechanical telescopic rod 22, thereby realizing the function of the precipitation simulation system.

[0028] In some preferred embodiments of the present invention, the weighing system is further defined as follows: the loading system is connected to the bottom of the pressure sensing device 14. When a load is applied to the collapsible loess sample, the loading system generates a corresponding force and transmits this force to the pressure sensing device 14. A weighing platform 15 is provided above the pressure sensing device 14 and is located below the water storage chamber 13. During the test, the weight of the water storage chamber 13 and the collapsible loess sample placed above the multi-layer permeable plate 12 is transmitted to the pressure sensing device 14 via the weighing platform 15. The pressure sensing device 14 is able to sense this pressure change.

[0029] In some preferred embodiments of the present invention, the loading system is further defined as comprising a hydraulic actuator 16 and a hydraulic pressure plate 33. The hydraulic pressure plate 33 is positioned at the top of the test chamber and is equipped with a strain acquisition device 7 and a wind speed sensor 9. The hydraulic actuator 16 is positioned below the weighing platform 15. When the force applied by the hydraulic actuator 16 is transmitted to the collapsible loess specimen via the weighing platform 15, the specimen undergoes corresponding deformation, which is then transmitted to the hydraulic pressure plate 33. The strain acquisition device 7 monitors the strain of the hydraulic pressure plate 33 in real time, indirectly reflecting the degree of deformation of the collapsible loess specimen. By analyzing this strain data, the stress-strain relationship of the collapsible loess specimen under different loading conditions can be understood, providing a basis for studying the mechanical properties of the collapsible loess specimen. The wind speed sensor 9 is used to monitor the wind speed within the test chamber. When simulating a natural environment, wind speed data can be measured in real time.

[0030] In some preferred embodiments of the present invention, the settlement and internal damage monitoring system is further defined as comprising a semi-circular metal shell 19 positioned above a multi-layer permeable plate 12; a laser emitter 1 and a laser receiver 27 are disposed relative to each other on the semi-circular metal shell 19; when the collapsible loess sample settles, the semi-circular metal shell 19, positioned above the multi-layer permeable plate, also shifts; this shift changes the relative positional relationship between the laser emitter 1 and the laser receiver 27, causing a change in the length of the laser propagation path. By accurately measuring the change in the laser propagation path length, the sample settlement can be calculated, thereby enabling real-time monitoring of the sample settlement.

[0031] A high-definition camera 10 and a micro-CT probe 11 are mounted side by side on the semi-circular metal shell 19. The HD camera 10 can capture real-time images of the surface of the collapsible loess sample. During the test, various factors, such as precipitation, loading, freeze-thaw cycles, and groundwater seepage, may cause surface damage such as cracks and spalling. The images captured by the HD camera 10 clearly show the development of these surface damages. By comparing and analyzing images taken at different times, the changes in the surface damage of the sample can be intuitively understood. The micro-CT probe 11 can perform tomographic scanning on the collapsible loess sample, acquiring internal structural images of the sample. Through 3D reconstruction and analysis of these tomographic images, internal damage information, such as changes in the sample's pore structure and crack propagation, can be clearly observed. Unlike the HD camera 10, which can only monitor the surface of the collapsible loess sample, the micro-CT probe 11 can penetrate deep into the sample, enabling non-destructive testing of internal damage.

[0032] In some preferred embodiments of the present invention, the freeze-thaw cycle system is further defined; the freeze-thaw cycle system includes a temperature sensor 5, a temperature control system 6, a condenser 25 and a heating tube 26; the temperature control system 6 and the temperature sensor 5 are arranged on the inner wall steel shell 24, and the temperature sensor 5 is arranged in the test chamber for real-time monitoring of the temperature conditions in the test chamber, collecting temperature data, and transmitting the data to the temperature control system 6; the temperature control system 6 receives the temperature data from the temperature sensor 5 and compares and analyzes it with the pre-set freeze-thaw cycle temperature parameters. Based on the comparison results, the temperature control system 6 will issue corresponding instructions to control the working state of the condenser 25 and the heating tube 26; the condenser 25 and the heating tube 26 are spaced apart on the inner wall steel shell 24.

[0033] The present invention also provides a method for simulating the freeze-thaw cycle of collapsible loess in a natural environment, which is specifically carried out in conjunction with the above-mentioned device and includes the following steps: S1, controlling the height of the sample tank through the loading system and adding the prepared collapsible loess sample into the sample tank, and then using the weighing system to weigh the collapsible loess sample; S2, set the precipitation amount and wind speed through the precipitation simulation system to simulate the natural rainfall environment, and turn off the precipitation simulation system when the set rainfall amount is reached; S3, after simulating the groundwater seepage in the natural environment through the groundwater seepage simulation system, the settlement and internal damage monitoring system is used to monitor the height of the collapsible loess sample and the collapse process of the collapsible loess sample in real time and generate the internal structure model of the collapsible loess sample; S4, turn on the freeze-thaw cycle system and set the number of freeze-thaw cycles. When each cycle is completed, the settlement and internal damage monitoring system automatically obtains the height and high-definition images of the collapsible loess sample and automatically calculates the soil porosity based on the CT data; S5, turn on the loading system, adjust the height of the sample tank, set the size, shape and loading rate of the collapsible loess sample, measure the stress-strain of the collapsible loess sample during the loading process, and automatically unload and record the peak load after the collapsible loess sample fails, and monitor the pore evolution and crack development of the collapsible loess sample in real time during the failure process; S6. After the test is completed, the collapsible loess sample is taken out by controlling the height of the sample tank through the loading system.

[0034] In the specific implementation, the specific process is: Step 1: Control the hydraulic actuator 16 via the loading system to raise the sample tank 36 to a suitable height, open the acrylic door 3, place the prepared collapsible loess sample into the sample tank 36, measure the weight of the collapsible loess sample using the pressure sensing device 14, and close the device. Finally, place a permeable stone on top of the collapsible loess sample. Step 2: Close the acrylic door 3, set the corresponding precipitation amount and wind speed through the precipitation simulation system, operate the mechanical telescopic rod 22 to extend and open the air outlet 2, air inlet 8 and air inlet valve 34, control the ultrasonic atomizer 21 to spray water mist and the blower 30 to supply air to the air inlet pipe 29 to simulate a natural rainfall environment, monitor the rainfall in real time through the humidity sensor 4, shut down the rainfall system when the set rainfall amount is reached, retract the mechanical telescopic rod 22, and close the air outlet 2, air inlet 8, ultrasonic atomizer 21, blower 30 and air inlet valve 34; Step 3: Open the water inlet valve 35 and the water pump 32, and use the water inlet pipe 17 and the water outlet pipe 18 to realize water filling and backflow in the water storage chamber 13. The water level in the water storage chamber 13 and the water tank 20 is controlled by the water level regulator 31. The water penetrates into the soil sample through the multi-layer permeable board 12, simulating the groundwater seepage in the natural environment; Step 4: Turn on the laser transmitter 1, the high-definition camera 10, the micro-CT probe 11, and the laser receiver 27. The laser transmitter 1, the high-definition camera 10, and the laser receiver 27 are used to monitor the soil sample height and process photos of the collapsible loess sample in real time. The micro-CT probe 11 is used to monitor the porosity evolution and water migration inside the collapsible loess sample in real time. A 3D reconstruction software is used to generate an internal structure model of the collapsible loess sample. Step 5: Turn on the freeze-thaw cycle system and set the number of freeze-thaw cycles. The temperature gradient inside the test box (-30°C-50°C) is changed by the condenser 25 and the heating tube 26. The temperature inside the box is monitored in real time by the temperature sensor 5 and fed back to the freeze-thaw cycle system to dynamically control the freeze-thaw cycle process. When each cycle is completed, the settlement and internal damage monitoring system automatically obtains the height and high-definition image of the collapsible loess sample, and automatically calculates the soil porosity based on the CT data; turn on the loading system, control the hydraulic actuator 16 to raise the collapsible loess sample to an appropriate height, set the soil sample size, shape and loading rate, and during the loading process, measure the stress-strain of the soil sample by the strain acquisition device 7. After the soil sample is destroyed, the loading system automatically unloads and records the peak load. The micro CT probe 11 monitors the pore evolution and crack development of the collapsible loess sample in real time during the destruction process. Step 6: After the test is completed, the loading system is used to control the hydraulic actuator 16 to descend to a suitable height to sample the collapsible loess sample, and the groundwater seepage system is operated to drain the water in the water storage chamber 13.

[0035] The test method of this embodiment, by applying the above-mentioned device for simulating the freeze-thaw cycle process of collapsible loess in a natural environment, makes the freeze-thaw cycle method consistent with the working conditions in actual engineering, thereby improving the accuracy of the test results.

[0036] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will be able to modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A device for simulating the freeze-thaw cycle of collapsible loess in a natural environment, characterized in that: The invention comprises a test box provided with a sample tank (36), a precipitation simulation system is provided on the upper part of the test box, a groundwater seepage simulation system is provided on the lower part of the test box, the sample tank (36) is connected to a loading system, a weighing system is provided on the bottom of the test box, the weighing system is connected to the groundwater seepage simulation system, and a settlement and internal damage monitoring system is provided between the weighing system and the precipitation simulation system, and a freeze-thaw cycle system is provided on the inner wall of the test box.

2. The device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to claim 1, characterized in that: The test box includes an inner wall steel shell (24) and an outer wall steel shell (37), an air outlet (2) is provided on one side of the test box body, and an air inlet (8) is provided on the top of the test box body. The precipitation simulation system includes four mechanical telescopic rods (22) evenly arranged around the inner wall steel shell (24), a blower (30) and a humidity sensor (4), each of the mechanical telescopic rods (22) is provided with a plurality of ultrasonic atomizers (21), and the water inlet of the ultrasonic atomizer (21) is connected to the mechanical telescopic rod (22), and the mechanical telescopic rod (22) is connected to the groundwater seepage simulation system; the outlet of the blower (30) is connected to the air inlet (8) through an air inlet pipe (29), and the air inlet pipe (29) is provided with an air inlet valve (34), and the humidity sensor (4) is provided on the inner wall steel shell (24).

3. The device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to claim 2, characterized in that: The groundwater seepage simulation system includes a water storage chamber (13) and a water tank (20), wherein the water tank (20) is connected to a water pump (32) and a water inlet valve (35) is provided at the connection point, wherein the water pump (32) passes through the side wall of the test chamber to the water storage chamber (13) via a water inlet pipe (17) and a water outlet pipe (18), wherein a multi-layer permeable plate (12) is provided above the water storage chamber (13), and a settlement and internal damage monitoring system is provided above the multi-layer permeable plate (12); the water tank (20) is connected to a water level regulator (31) to control the water level in the water tank (20), and the mechanical telescopic rod (22) is connected to the water inlet pipe (17).

4. The device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to claim 3, characterized in that: The weighing system comprises a plurality of pressure sensing devices (14), the loading system is connected below the pressure sensing devices (14), a weighing platform (15) is arranged above the pressure sensing devices (14), and the weighing platform (15) is located below the water storage chamber (13).

5. The device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to claim 4, characterized in that: The loading system includes a hydraulic actuator (16) and a hydraulic pressure plate (33), wherein the hydraulic pressure plate (33) is arranged on the top of the test box and a strain acquisition device (7) and a wind speed sensor (9) are arranged on the hydraulic pressure plate (33), and the hydraulic actuator (16) is arranged below the weighing platform (15).

6. The device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to claim 3, characterized in that: The settlement and internal damage monitoring system comprises a semi-annular metal shell (19), which is located above a multi-layer permeable plate (12) and is provided with a high-definition camera (10) and a micro CT probe (11) arranged side by side on the semi-annular metal shell (19), and a laser transmitter (1) and a laser receiver (27) arranged opposite to each other on the semi-annular metal shell (19).

7. The device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to claim 2, characterized in that: The freeze-thaw cycle system comprises a temperature sensor (5), a temperature control system (6), a condenser (25) and a heating tube (26), wherein the condenser (25) and the heating tube (26) are spaced apart on the inner wall steel shell (24), and the temperature control system (6) and the temperature sensor (5) are arranged on the inner wall steel shell (24).

8. The device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to claim 2, characterized in that: The test box is provided with an acrylic door (3), and a heat-insulating material (21) is provided between the inner wall steel shell (24) and the outer wall steel shell (37).

9. The device for simulating the freeze-thaw cycle of collapsible loess in a natural environment according to claim 2, characterized in that: A sealing ring (28) is provided at the connection between the air inlet pipe (29) and the air inlet (8).

10. A method for simulating the freeze-thaw cycle of collapsible loess in a natural environment, characterized in that: The following steps are involved: S1, controlling the height of the sample tank through the loading system and adding the prepared collapsible loess sample into the sample tank, and then using the weighing system to weigh the collapsible loess sample; S2, set the precipitation amount and wind speed through the precipitation simulation system to simulate the natural rainfall environment, and turn off the precipitation simulation system when the set rainfall amount is reached; S3, after simulating the groundwater seepage in the natural environment through the groundwater seepage simulation system, the settlement and internal damage monitoring system is used to monitor the height of the collapsible loess sample and the collapse process of the collapsible loess sample in real time and generate the internal structure model of the collapsible loess sample; S4, turn on the freeze-thaw cycle system and set the number of freeze-thaw cycles. When each cycle is completed, the settlement and internal damage monitoring system automatically obtains the height and high-definition images of the collapsible loess sample and automatically calculates the soil porosity based on the CT data; S5, turn on the loading system, adjust the height of the sample tank, set the size, shape and loading rate of the collapsible loess sample, measure the stress-strain of the collapsible loess sample during the loading process, and automatically unload and record the peak load after the collapsible loess sample fails, and monitor the pore evolution and crack development of the collapsible loess sample in real time during the failure process; S6. After the test is completed, the collapsible loess sample is taken out by controlling the height of the sample tank through the loading system.

Images