Test device and method for swelling and shrinkage deformation of soil under simulated wet-dry cycles and rainfall infiltration dynamic water saturation

Abstract

The present invention discloses an experimental device and method for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of wet-dry cycles and rainfall infiltration. The device includes a specimen cylinder, and the specimen is arranged inside the specimen cylinder; the loading end of the axial compression loading assembly is arranged above the specimen cylinder to apply axial compression to the specimen; the wet-dry cycle assembly is arranged outside the specimen cylinder to conduct wet-dry cycle tests on the specimen; the wet-dry cycle assembly includes a heating cylinder, which is sleeved outside the specimen cylinder, and a water storage cavity is formed between the two; the air outlet of the hot air source is communicated with the inside of the bottom end of the specimen cylinder to conduct dynamic hot air drying on the specimen; the water outlet end of the water circulation and water conservation device is communicated with the inside of the bottom end of the specimen cylinder, and the water inlet end of the water circulation and water conservation device is communicated with the top end of the heating cylinder. Water flows in from the bottom of the specimen cylinder to conduct dynamic water saturation on the specimen, then flows out from the top of the specimen cylinder and enters the water storage cavity, and then flows back through the pipeline connecting the heating cylinder and the water circulation and water conservation device, realizing dynamic water absorption by water flow and dehumidification by ventilation.

Description

Technical Field

[0001] The present invention belongs to the technical field of simulating the seepage effect of expansive soil in a loaded saturated environment, and relates to an experimental device and method for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation action of wet-dry cycles and rainfall infiltration. Background Art

[0002] The deformation and instability of filled soil subgrades are common geological disasters in the construction of highways and railways in expansive soil areas, often causing serious engineering, economic losses and ecological environment damage. The swelling and shrinkage properties of expansive soil have a great impact on engineering. The swelling and shrinkage of soil not only reduce the strength of the soil, but also cause soil deformation, resulting in the damage of structures. For example, slopes composed of expansive soil often slide due to soil swelling, causing harm to engineering. Therefore, studying the swelling and shrinkage properties of expansive soil is of great significance in engineering practice. In engineering construction, structures built on expansive soil with constant water content will not suffer damage caused by swelling and shrinkage. However, when the water content of the soil changes, volume expansion in both vertical and horizontal directions will immediately occur, and a value of only 1% - 2% is sufficient to cause harmful expansion. Thoroughly understanding the swelling and shrinkage characteristics of expansive soil is the key to solving engineering problems caused by the swelling and shrinkage of expansive soil. The swelling and shrinkage properties of expansive soil are greatly affected by its degree of consolidation and the change of wet-dry cycles. Therefore, studying the swelling and shrinkage of expansive soil under different wet-dry cycle conditions is the key to understanding the swelling and shrinkage properties of expansive soil.

[0003] In the conventional wet-dry cycle, the loading method for the ring sample is to place a permeable stone on each of the upper and lower sides of the ring sample and then apply a load. However, expansive soil has the characteristics of hygroscopic micro-expansion and dehumidification shrinkage. When absorbing and dehumidifying, when the soil produces certain deformation under the action of the load, the load directly acts on the ring edge instead of the soil itself, and more force is borne by the ring edge. The invention patent with the publication number CN113514628A discloses a consolidated swelling and shrinkage and wet-dry cycle integrated test device for fine-grained soil and its test method. Although it also directly applies vertical load to the specimen, this loading method requires equipment such as a servo pressure device and various sensors, with high cost and reduced test efficiency.

[0004] In the past, during the simulation process of the wet-dry cycle environment, the processes of drying and saturation in the simulated wet-dry cycle environment were carried out separately. Drying was carried out in an oven, and saturation needed to be carried out separately in a saturation bucket. This would repeatedly disturb the specimen and damage the overall structure of the specimen, resulting in the loosening and shedding of the surface layer of the specimen. The simulation wet-dry cycle test device adopted by Yang Heping, Zhang Rui, and Zheng Jianlong. Law of swelling and shrinkage deformation and strength change of expansive soil under wet-dry cycle with load [J]. Chinese Journal of Geotechnical Engineering, 2006(11): 1936-1941 can carry out the entire wet-dry cycle process in one test device. This device dries and dehumidifies through a bathroom heater and soaks in still water for moisture absorption. However, the drying and dehumidifying methods of this device are somewhat different from the actual wet-dry cycle process of moisture absorption under the action of dynamic water and drying and dehumidifying in a ventilated environment, and the measured data may have a large gap from the actual situation.

[0005] In the actual rainfall environment, the erosion and leaching of rainwater need to be fully considered. Especially under extreme rainfall conditions, this effect will become particularly obvious. The moisture saturation of the soil body is a process of dynamic water infiltration. If the erosion and leaching effects of rainwater are not considered during the wet-dry cycle test, the test results will be very different from the actual situation. Most of the existing research methods are to simulate the saturated state of soil samples under rainfall conditions by using the static saturation method. In this static water environment, the ion exchange and the interaction between water and soil are relatively weak, and the influence of rainwater erosion and seepage on the soil structure during the rainfall infiltration process cannot be reproduced, which does not conform to the real process of rainfall infiltration. Summary of the Invention

[0006] The purpose of the embodiments of the present invention is to provide a test device and method for simulating the swelling and shrinkage deformation of soil under the action of wet-dry cycle and rainfall infiltration dynamic water saturation, so as to solve the problems of low test efficiency, high cost, differences in drying and dehumidifying methods from the actual wet-dry cycle process, and non-conformity between the simulated rainfall infiltration and the real process in the existing test devices for simulating the swelling and shrinkage deformation of soil under wet-dry cycle and rainfall infiltration.

[0007] The technical solution adopted by the embodiments of the present invention is: A test device for simulating the swelling and shrinkage deformation of soil under the action of wet-dry cycle and rainfall infiltration dynamic water saturation, including:

[0008] A specimen cylinder, with the specimen arranged inside the specimen cylinder;

[0009] An axial compression loading component, with the loading end of the axial compression loading component arranged above the specimen cylinder to apply axial compression to the specimen inside the specimen cylinder;

[0010] A wet-dry cycle component, arranged outside the specimen cylinder to conduct wet-dry cycle tests on the specimen;

[0011] Among them, the wet-dry cycle component includes:

[0012] A heating cylinder, which is sleeved around the periphery of the specimen cylinder, and there is a certain interval between the heating cylinder and the specimen cylinder to form a water storage cavity;

[0013] A hot air source, the air outlet of which is communicated with the inside of the bottom end of the specimen cylinder to dry the specimen with dynamic hot air flow;

[0014] A water circulation and water conservation device, the water outlet end of which is communicated with the inside of the bottom end of the specimen cylinder, and the water inlet end of which is communicated with the top end of the heating cylinder. The water flows into the specimen cylinder from the bottom, dynamically saturates the specimen with water, then flows out from the top of the specimen cylinder into the water storage cavity, and then returns through the pipeline connecting the heating cylinder and the water circulation and water conservation device.

[0015] Another technical solution adopted in the embodiment of the present invention is: an experimental method for simulating the swelling and shrinking deformation of soil under the action of dry-wet cycle and rainfall infiltration dynamic water saturation. The experimental device for simulating the swelling and shrinking deformation of soil under the action of dry-wet cycle and rainfall infiltration dynamic water saturation as described above is adopted, and the specific steps are as follows:

[0016] Step S1: After checking that each part of the experimental device for simulating the swelling and shrinking deformation of soil under the action of dry-wet cycle and rainfall infiltration dynamic water saturation is available, assemble it. Apply an acid corrosion prevention coating at the places where the specimen cylinder and the heating cylinder contact the aqueous solution, and operate the circular covers on each air outlet on the side of the heating cylinder to seal and close each air outlet;

[0017] Step S2: Arrange a lower permeable stone at the inner bottom of the specimen cylinder, place the prepared specimen on the lower permeable stone, and then arrange a porous bearing plate on the upper part of the specimen; make the loading vertical rod of the axial compression loading assembly contact the porous bearing plate, and apply a pressure of 2-3 kPa for preloading to make all parts in the specimen cylinder contact, and record the initial reading K of the dial gauge 0s ;

[0018] Step S3: Set the loading amount of the axial compression loading assembly to simulate the stress state at different depths of the soil layer;

[0019] Step S4: Control the solution flow rate through a peristaltic pump to make the solution flow into the specimen cylinder from the water inlet and return to the solution tank from the water outlet of the heating cylinder to form a dynamic water flow cycle to simulate different rainfall intensity conditions under rainfall environment;

[0020] Step S5: Adjust the position of the high-definition camera, and take pictures of the upper and side surfaces of the specimen at regular intervals; observe the data change of the dial gauge in real time, and record the data of the dial gauge at regular intervals; when the specimen expansion is stable, end the moisture absorption test, discharge the solution through a peristaltic pump, and record the data K of the dial gauge at the end of the moisture absorption test ts , K tsis the swelling amount of the specimen when it reaches swelling stability under the action of the set vertical load P, and the vertical swelling rate of the specimen is calculated according to the following formula :

[0021] ;

[0022] where h 0s is the initial height of the specimen in the vertical direction, and K ts is the reading of the dial indicator when the specimen reaches swelling stability under the action of the set vertical load P, and K ps is the compression deformation of the specimen by the porous bearing plate, the loading vertical rod, and the dial indicator under the action of the set vertical load P;

[0023] Step S6: Heat each circular cover on the side of the heating cylinder, open each air outlet, connect each air outlet to the corresponding second blower, and connect the water inlet to the first air outlet. Adjust the temperature and flow rate of the hot air flow output by the first blower and the second blower through the first air blower controller and the second air blower controller of the wet-dry cycle component, blow the hot air flow into the specimen cylinder and the heating cylinder, and perform dehumidification treatment on the specimen. During the heating process, continuously record the reading of the dial indicator at the original set reading frequency, and control the heating time according to the heating temperature designed in the test. When the moisture content of the specimen reaches the shrinkage limit moisture content, the heating ends, that is, one wet-dry cycle process is completed;

[0024] Step S7: Repeat steps S4 to S6 to complete the number of wet-dry cycle tests designed in the test in sequence, and complete the wet swelling deformation test under the wet-dry cycle environment.

[0025] The beneficial effects of the embodiments of the present invention are:

[0026] 1. The porous bearing plate on the upper part of the core cutter specimen is directly loaded through the loading beam. The porous bearing plate is embedded in the core cutter and has the same width as the specimen. Therefore, the stress condition of the soil under different load depths under the condition of lateral confinement can be simulated, and the load will not be shared by the core cutter opening. The loading method uses the lever principle, and the hanging weights form a force arm for loading. The load can be adjusted by changing the mass of the weights. Such a loading method has the advantages of flexible loading, simple and convenient operation, low cost, enabling simultaneous loading of multiple groups of specimens, and improving the test efficiency, solving the problems of low test efficiency and high cost of the existing test devices for simulating the swelling and shrinkage deformation of soil under wet-dry cycles and rainfall infiltration;

[0027] 2. By adopting the combination of a sample cylinder and a heating cylinder, and the first blower and the second blower installed on the sample cylinder and the heating cylinder can blow-dry the sample from different directions. While the heating cylinder and the sample cylinder form a water storage cavity, the sample is also blow-heated from multiple directions, realizing moisture absorption in a dynamic water flow environment and multi-directional dehumidification in a ventilation environment. The wet-dry cycle process is closer to the actual situation, making the test results more real and accurate, and solving the problem that the drying and dehumidification methods of the existing test devices for simulating soil expansion and contraction deformation under wet-dry cycles and rainfall infiltration are different from the actual wet-dry cycle process;

[0028] 3. It can simulate the scouring and leaching effects on the soil during rainfall infiltration by the dynamic water flow in and out of the sample cylinder, and adopts the seepage method of water inlet from the bottom and water outlet from the upper part, which is beneficial to the more uniform infiltration of water flow into the sample and improves the efficiency of soil saturation, solving the problem that the ion exchange and the weak chemical interaction between water and soil in the static water saturation method lead to the inconsistency between the simulated rainfall infiltration and the real process, and is of great significance to the research on the deformation and instability of expansive soil fill subgrade under the action of rainfall infiltration;

[0029] 4. The whole wet-dry cycle process is completed in the sample cylinder and the heating cylinder, solving the problem of repeatedly disturbing the soil sample in the previous simulation of the wet-dry cycle environment; in addition, the deformation of the soil sample can be measured by the dial indicator on the loading device after each wet-dry cycle process, obtaining the consolidation expansion and contraction deformation of the sample in the real environment, and the use method is simple and convenient, and multiple groups of tests can be carried out at the same time, which is an improvement of the test method for the swelling rate under load and an optimization of subsequent tests such as direct shear test and triaxial test;

[0030] 5. During the wet-dry cycle process, the shrinkage deformation of the soil due to water loss will cause cracks on the surface of the sample. High-definition cameras are set above and on the side of the device to take pictures of the surface cracks of the sample, and the digital image processing technology is used to monitor and quantitatively analyze the evolution process of the surface cracks of the expansive soil in real time, supplementing the dynamic observation of the crack development during the drying and shrinking deformation process of the expansive soil, being able to measure both the expansion and contraction deformation and explore the morphological evolution law of the crack development of the expansive soil during the dehumidification process, thus realizing the measurement of the expansion deformation during the dynamic water absorption process and the observation of the shrinkage crack development during the water loss process. Description of the Drawings

[0031] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0032] Figure 1It is a schematic structural diagram of an experimental device for simulating the swelling and shrinkage deformation of soil under the action of simulated wet-dry cycles and rainfall infiltration dynamic water saturation in an embodiment of the present invention.

[0033] Figure 2 It is a schematic structural diagram of a sample cylinder assembly in an embodiment of the present invention.

[0034] Figure 3 It is a schematic structural diagram of a heating assembly in an embodiment of the present invention.

[0035] Figure 4 It is a combined schematic diagram of a heating assembly and a sample cylinder assembly in an embodiment of the present invention.

[0036] In the figure, 1. test bench, 2. loading bracket, 3. horizontal beam, 4. dial indicator, 5. weight, 6. loading vertical rod, 7. water inlet pipeline, 8. peristaltic pump, 9. water outlet pipeline, 10. solution tank, 11. permeable membrane, 12. porous bearing plate, 13. high-definition camera, 14. sample cylinder, 15. lower permeable stone, 16. water inlet, 17. circular hole, 18. air outlet pipe, 19. water outlet, 20. first air blower controller, 21. heating cylinder, 22. porous cover plate, 23. second air blower controller. Detailed implementation manners

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0038] Embodiment 1

[0039] This embodiment provides an experimental device for simulating the swelling and shrinkage deformation of soil under the action of simulated wet-dry cycles and rainfall infiltration dynamic water saturation, as Figure 1 shown, including:

[0040] A sample cylinder 14, with the sample set inside the sample cylinder 14;

[0041] An axial compression loading assembly, with the loading end of the axial compression loading assembly arranged above the sample cylinder 14 to apply axial compression to the sample;

[0042] A wet-dry cycle assembly, arranged outside the sample cylinder 14 to conduct wet-dry cycle tests on the sample;

[0043] Among them, the wet-dry cycle assembly includes:

[0044] A heating cylinder 21, with the heating cylinder 21 sleeved outside the sample cylinder 14, and a certain interval is set between the heating cylinder 21 and the sample cylinder 14 to form a water storage cavity;

[0045] A hot air source, the air outlet of the hot air source is connected to the inside of the bottom end of the specimen cylinder 14 to dry the specimen with dynamic hot air flow;

[0046] A water circulation and water preservation device, the water outlet end of the water circulation and water preservation device is connected to the inside of the bottom end of the specimen cylinder 14, and the water inlet end of the water circulation and water preservation device is connected to the top end of the heating cylinder 21. Water flows into the inside of the specimen cylinder 14 from the bottom, dynamically saturates the specimen, then flows out of the top of the specimen cylinder 14 and enters the water storage cavity, and then returns through the pipeline connecting the heating cylinder 21 and the water circulation and water preservation device.

[0047] In some embodiments, it further includes a test bench 1. A plurality of circular grooves are provided on the test bench 1, and a set of specimen cylinders 14 and heating cylinders 21 are arranged in each circular groove. A plurality of axial compression loading components are also provided on the tabletop of the test bench 1, and the plurality of axial compression loading components are arranged in one-to-one correspondence with the specimen cylinders 14 in the plurality of circular grooves.

[0048] In some embodiments, such as Figure 2 shown, the specimen cylinder 14 is of a cylindrical structure, with an unconfined design on its upper side. A clamping groove for fixing the cutting ring is provided on its inner side. A porous bearing plate 12 and a lower water-permeable stone 15 are arranged in the specimen cylinder 14. The porous bearing plate 12 is located at the upper part of the specimen and is stacked with the specimen in the cutting ring opening, and the width of the porous bearing plate 12 is the same as that of the specimen. The lower water-permeable stone 15 is placed at the bottom of the specimen and the specimen cylinder 14. A conical water inlet 16 is provided at the center of the bottom of the specimen cylinder 14. The water inlet 16 is designed to be conical, which can prevent local scouring of the bottom of the specimen cylinder 14 when the water flow is large.

[0049] In some embodiments, the hot air source includes a first blower. When simulating rainfall infiltration, the specimen cylinder 14 is connected to the water circulation and water preservation device through the water inlet 16; when drying the specimen, that is, after the moisture absorption process ends and the water in the pipeline is drained, the water inlet 16 is connected to the air outlet of the first blower. The first blower supplies hot air flow to the water inlet 16. The hot air flow output by the first blower enters from the water inlet 16 and discharges from the porous bearing plate 12 to dynamically blow-dry the specimen. A first air blowing controller 20 is provided on the first blower, and the first air blowing controller 20 is used to control the temperature and wind speed of the hot air flow conveyed by the first blower to the water inlet 16.

[0050] In some embodiments, the specimen cylinder 14, the heating cylinder 21 and the porous bearing plate 12 are all made of transparent materials to facilitate observing the test process and the state of the specimen.

[0051] In some embodiments, the hot air source includes a second blower, such as Figure 3As shown, at least two air blowing ports are provided at the middle position of the heating cylinder 21, which are evenly distributed on its side and communicate with the water storage cavity. A circular cover is provided on each air blowing port, and each air blowing port is opened / closed in a sealed manner by operating the circular cover; when simulating rainfall infiltration, each air blowing port is sealed and closed by operating the circular cover; when drying the specimen, each air blowing port is opened by operating the circular cover, and each air blowing port is connected to the air outlet of the corresponding second blower, so that the hot air flow output by the second blower enters from the air blowing port and discharges from the top of the heating cylinder 21 to dry the side of the specimen.

[0052] In some embodiments, the heating cylinder 21 is a cylindrical cylinder, and a porous cover plate 22 is provided at its top. A plurality of air outlet pipes 18 are evenly provided on the porous cover plate 22; the hot air flow output by the second blower enters from the air blowing port and discharges from the air outlet pipe 18 to dry the side of the specimen.

[0053] The hot air flow in the specimen cylinder 14 is discharged to the heating cylinder 21 from the porous bearing plate 12, and the hot air flow in the heating cylinder 21 is discharged from the air outlet pipe 18 on the porous cover plate 22 to form a dynamic hot air flow in the device to dry the specimen. The specimen is dried by blowing air from multiple directions simultaneously, improving the drying efficiency. At the same time, since in the actual drying process, the dynamic hot air flow received by the soil sample is not in a fixed single direction, but in different directions, therefore, in this embodiment, the specimen is dynamically dried by blowing air from different directions, which can more realistically simulate the actual drying environment.

[0054] In some embodiments, a second air blowing controller 23 is provided on each second blower, and the second air blowing controller 23 is used to control the temperature and wind speed of the hot air delivered by the second blower to the corresponding air blowing port.

[0055] In some embodiments, a circular hole 17 for the loading end of the axial compression loading assembly to pass through is provided in the middle of the porous cover plate 22. An outlet 19 is provided on the upper part of the side of the heating cylinder 21. The outlet 19 is arranged lower than the top of the specimen cylinder 14, and the outlet 19 is connected to the circulating water conservation device.

[0056] In some embodiments, since the specimen will be partially dissolved during the loading process, a permeable membrane 11 is provided at the outlet 19 of the heating cylinder 21 to filter solid particles.

[0057] In some embodiments, as Figure 4 shown, there is a 2 cm gap between the heating cylinder 21 and the specimen cylinder 14, which will neither cause the water storage cavity formed between the heating cylinder 21 and the specimen cylinder 14 to be too large, resulting in an increase in the water circulation time, nor cause the water storage capacity of the water storage cavity to be too small due to the distance being too close, resulting in too fast a water circulation speed, and further causing the water level in the water storage cavity to overflow the outlet and affecting the dynamic water circulation, and avoiding excessive air pressure in the water storage cavity during air blowing drying.

[0058] In some embodiments, asFigure 1 As shown in the figure, the axial compression loading assembly includes a loading bracket 2, a horizontal beam 3, and a loading vertical rod 6. The loading bracket 2 is fixed on the test bench 1. One end of the horizontal beam 3 is hinged to the loading bracket 2 to form a lever structure. A suspension rope for hanging counterweight weights 5 is connected to the other end of the horizontal beam 3. A loading vertical rod 6 is provided in the middle of the horizontal beam 3. The loading vertical rod 6 vertically passes through the horizontal beam 3 and is fixedly connected to the horizontal beam 3. Specifically, for convenient connection, the loading vertical rod 6 can be provided with a threaded connection with the horizontal beam 3. The loading vertical rod 6 passes through the circular hole 17 at the top of the heating cylinder 21 and contacts the porous bearing plate 12 located inside the sample cylinder 14 and at the top of the sample.

[0059] In some embodiments, a data acquisition device is further provided. The data acquisition device includes a dial indicator 4 and a high-definition camera 13. The dial indicator 4 is fixedly connected to the loading bracket 2 and is vertically arranged above the loading vertical rod 6. The end of its pointer contacts the horizontal beam 3 above the loading vertical rod 6. The high-definition camera 13 is arranged above and on the side of the sample cylinder 14 and the heating cylinder 21. The high-definition camera 13 above the sample cylinder 14 and the heating cylinder 21 is slidably connected to the door frame type bracket on the test bench 1 through a multi-section adjustable bracket. The high-definition camera 13 on the side is installed on the test bench 1 through a vertical bracket. Specifically, the vertical bracket is installed in the chute on the test bench 1 and can move in this chute to conveniently adjust the high-definition camera 13 to the position where observation and shooting are required.

[0060] In some embodiments, as Figure 1 shown, the cyclic water saturation device includes a solution tank 10, a water inlet pipeline 7, and a water outlet pipeline 9. The bottom of the solution tank 10 is connected to the water inlet 16 at the bottom of the sample cylinder 14 through the water inlet pipeline 7. The top of the solution tank 10 is connected to the water outlet 19 of the heating cylinder 21 through the water outlet pipeline 9 to form a water flow cycle. A peristaltic pump 8 is provided on the water inlet pipeline 7, and the peristaltic pump 8 is used to control the water flow.

[0061] Embodiment 2

[0062] This embodiment provides a test method for simulating the swelling and shrinkage deformation of soil under the action of dry-wet cycle and rainfall infiltration dynamic water saturation. The test device for simulating the swelling and shrinkage deformation of soil under the action of dry-wet cycle and rainfall infiltration dynamic water saturation in Embodiment 1 is adopted. The specific steps are as follows:

[0063] Step S1: After checking that all parts of the test device for simulating the swelling and shrinkage deformation of soil under simulated dry-wet cycles and rainfall infiltration dynamic water saturation are available, assemble them. Apply an acid corrosion prevention coating at the places where the sample cylinder 14 and the heating cylinder 21 are in contact with the aqueous solution, and operate the circular covers on each air outlet on the side of the heating cylinder 21 to seal and close each air outlet; then cut the undisturbed soil sample according to the shape and size of the sample cylinder 14 as the test sample. In this embodiment, according to different test types, three types of sample cylinders 14 are configured: a conventional ring knife sample (Φ61.8mm*H20mm), a triaxial sample (Φ39.1mm*H80mm), and a nuclear magnetic resonance sample (Φ25 mm*H50 mm).

[0064] Step S2: Arrange the lower permeable stone 15 at the inner bottom of the sample cylinder 14, place the prepared sample on the lower permeable stone 15, and then arrange the porous bearing plate 12 on the upper part of the sample; make the loading vertical rod 6 of the axial compression loading assembly contact the porous bearing plate 12, and apply a pressure of 2 - 3 kPa for preloading to make all parts in the sample cylinder 14 contact, and record the initial reading K of the dial gauge 4 0s ; Apply a pressure of 2 - 3 kPa for preloading, and all parts in the sample cylinder 14 contact. This is mainly to eliminate the test error caused by the gap between all parts in the sample cylinder 14 and the sample. Recording the initial reading at this time is to obtain the initial deformation data of the test, that is, the initial reading, which is used to compare with the data recorded during the subsequent test process. The difference obtained is the deformation value of the sample;

[0065] Step S3: Set the loading amount of the axial compression loading assembly to simulate the stress state at different depths of the soil layer;

[0066] Step S4: Control the solution flow rate through the peristaltic pump 8, so that the solution flows into the sample cylinder 14 from the water inlet 16, flows out from the water outlet 19 of the heating cylinder 21, and then returns to the solution tank 10 to form a dynamic water flow cycle to simulate different rainfall intensity conditions under rainfall environment;

[0067] Step S5: Adjust the position of the high-definition camera 13, and take pictures of the upper and side surfaces of the sample at regular intervals; Observe the data change of the dial gauge 4 in real time, record the data of the dial gauge 4 at regular intervals, and end the moisture absorption test when the sample expands stably. Drain the solution through the peristaltic pump 8; Record the data K of the dial gauge 4 at the end of the moisture absorption test ts , K ts is the swelling amount of the sample when it reaches swelling stability under the set vertical load P. Subsequently, calculate the vertical swelling ratio with load of the sample according to the following formula :

[0068] ;

[0069] where, h0s is the initial height of the specimen in the vertical direction, K ts is the reading of the dial indicator 4 at the time of expansion stability under the action of the set vertical load P on the specimen, K ps is the compression deformation of the specimen by the porous bearing plate 12, the loading vertical rod 6, and the dial indicator 4 under the action of the set vertical load P;

[0070] Step S6: Heat each circular cover on the side of the heating cylinder 21, open each air outlet, connect each air outlet to the corresponding second blower, and connect the water inlet 16 to the first air outlet. Adjust the temperature and flow rate of the hot air flow output by the first blower and the second blower through the first air blower controller 20 and the second air blower controller 23 of the wet-dry cycling component, blow the hot air flow into the specimen cylinder 14 and the heating cylinder 21, and perform dehumidification treatment on the specimen. During the heating process, continuously record the reading of the dial indicator 4 at the original set reading frequency, and control the heating time according to the heating temperature designed in the test. When the moisture content of the specimen reaches the shrinkage limit moisture content, the heating ends, that is, one wet-dry cycle process is completed;

[0071] Step S7: Repeat Steps S4 to S6, complete the number of wet-dry cycle tests designed in the test in sequence, complete the wet expansion deformation test under the wet-dry cycle environment, and perform digital image processing on the surface images of the specimen taken by the high-definition camera 13 to analyze the evolution process of the surface cracks of the expansive soil during the dehumidification process;

[0072] Step S8: Take out the tested specimen and the core cutter together and demold them. After replacing the new specimen, repeat Steps S2 to S7, and re-adjust the magnitude of the vertical load P, the flow rate of the water flow, and the pH value of the solution according to the test plan to obtain the wet expansion deformation law of the specimen under different test conditions.

[0073] The above are only the preferred embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention are all included in the protection scope of the present invention.

Claims

1. An experimental device for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated wet-dry cycles and rainfall infiltration, characterized in that, Comprising: A specimen cylinder (14) for placing specimens; a conical water inlet (16) is provided at the center of the bottom of the specimen cylinder (14). During simulated rainfall infiltration, the specimen cylinder (14) is connected to the water recycling and water conservation device through the water inlet (16); when drying the specimen, the water inlet (16) is connected to the air outlet of the first blower; the specimen cylinder (14) is of a cylindrical structure, with an unconfined design on its upper side, and a clamping groove for fixing the cutting ring is provided on its inner side. The porous bearing plate (12) is located above the specimen and is stacked with the specimen in the cutting ring opening, and the width of the porous bearing plate (12) is the same as that of the specimen. The lower permeable stone (15) is placed at the bottom of the specimen and the specimen cylinder (14); when drying the specimen, the hot air flow output by the first blower enters from the water inlet (16) and discharges from the porous bearing plate (12) to perform dynamic air-blowing drying on the specimen; An axial compression loading assembly for applying axial compression to the specimen, and the loading end of the axial compression loading assembly is arranged above the specimen cylinder (14); A dry-wet cycling assembly for performing dry-wet cycling tests on the specimen, and the dry-wet cycling assembly is arranged outside the specimen cylinder (14); Wherein, the dry-wet cycling assembly includes: A heating cylinder (21), the heating cylinder (21) is sleeved outside the specimen cylinder (14), and a certain interval is provided between the heating cylinder (21) and the specimen cylinder (14) to form a water storage cavity; at least two air blowing ports evenly distributed on its side and communicating with the water storage cavity are provided at the middle position of the heating cylinder (21), and a circular cover is provided on each air blowing port, and each air blowing port is opened or sealed by operating the circular cover; during simulated rainfall infiltration, each air blowing port is sealed by operating the circular cover; A hot air source, the air outlet of the hot air source is communicated with the inside of the bottom end of the specimen cylinder (14) to perform dynamic hot air flow drying on the specimen; A water recycling and water conservation device, the water outlet end of the water recycling and water conservation device is communicated with the inside of the bottom end of the specimen cylinder (14), and the water inlet end of the water recycling and water conservation device is communicated with the top end of the heating cylinder (21). Water flows into the specimen from the bottom of the specimen cylinder (14) to perform dynamic saturation on the specimen, then flows out from the top of the specimen cylinder (14) into the water storage cavity, and then returns through the pipeline connecting the heating cylinder (21) and the water recycling and water conservation device.

2. The test device for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated dry-wet cycles and rainfall infiltration is characterized in that, A first air blowing controller (20) is provided on the first blower, and the first air blowing controller (20) is used to control the temperature and wind speed of the hot air flow conveyed by the first blower to the water inlet (16).

3. The test device for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated dry-wet cycles and rainfall infiltration is characterized in that, When drying the specimen, each air blowing port is opened by operating the circular cover, and each air blowing port is connected to the air outlet of the corresponding second blower. The hot air flow output by the second blower enters from the air blowing port and discharges from the top of the heating cylinder (21) to dry the side of the specimen.

4. The test device for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated dry-wet cycles and rainfall infiltration is characterized in that, The heating cylinder (21) is a cylindrical cylinder, and a porous cover plate (22) is provided at its top. A plurality of air outlet pipes (18) are evenly provided on the porous cover plate (22). When drying the specimen, the hot air flow output by the second blower enters from the air blowing port and discharges from the air outlet pipes (18) to dry the side of the specimen; A circular hole (17) through which the loading end of the axial compression loading assembly passes is provided in the middle of the porous cover plate (22). An outlet (19) is provided in the upper part of the side surface of the heating cylinder (21). The outlet (19) is arranged lower than the top of the specimen cylinder (14), and the outlet (19) is connected to the circulating water conservation device.

5. The test device for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated dry-wet cycles and rainfall infiltration is characterized in that, A permeable membrane (11) is provided at the outlet (19) of the heating cylinder (21) to filter solid particles; Each second blower is provided with a second air blowing controller (23), and the second air blowing controller (23) is used to control the temperature and wind speed of the hot air conveyed by the second blower to the corresponding air blowing port.

6. The test device for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated dry-wet cycles and rainfall infiltration is characterized in that, The axial compression loading assembly includes a loading bracket (2), a horizontal beam (3) and a loading vertical rod (6). The loading bracket (2) is fixed on the test bench (1). One end of the horizontal beam (3) is hinged to the loading bracket (2) to form a lever structure. A suspension rope for hanging counterweight weights (5) is connected to the other end of the horizontal beam (3). A loading vertical rod (6) is provided in the middle of the horizontal beam (3). The loading vertical rod (6) vertically passes through the horizontal beam (3) and is fixedly connected to the horizontal beam (3). The loading vertical rod (6) passes through the circular hole (17) at the top of the heating cylinder (21) and contacts the porous bearing plate (12) located inside the specimen cylinder (14) and at the top of the specimen.

7. The test device for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated dry-wet cycles and rainfall infiltration is characterized in that, A data acquisition device is also provided, and the data acquisition device includes: A dial indicator (4), the dial indicator (4) is fixedly connected to the loading bracket (2), and the dial indicator (4) is vertically arranged above the loading vertical rod (6), and the end of its pointer contacts the horizontal beam (3) above the loading vertical rod (6); A high-definition camera (13), the high-definition camera (13) is arranged above and on the side of the specimen cylinder (14) and the heating cylinder (21); The high-definition camera (13) above the specimen cylinder (14) and the heating cylinder (21) is slidably connected to the door frame type bracket on the test bench (1) through a multi-section adjustable bracket, and the high-definition camera (13) on the side of the specimen cylinder (14) and the heating cylinder (21) is installed on the test bench (1) through a vertical bracket, and the vertical bracket is slidably connected to the test bench (1).

8. The test device for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated dry-wet cycle and rainfall infiltration is characterized in that, The circulating water saturation device includes a solution tank (10), a water inlet pipeline (7) and a water outlet pipeline (9). The bottom of the solution tank (10) is connected to the water inlet (16) at the bottom of the specimen cylinder (14) through the water inlet pipeline (7), and the top of the solution tank (10) is connected to the outlet (19) of the heating cylinder (21) through the water outlet pipeline (9). A peristaltic pump (8) is provided on the water inlet pipeline (7).

9. A test method for simulating the swelling and shrinkage deformation of soil under the dynamic water saturation of simulated wet-dry cycles and rainfall infiltration, characterized in that, Using the test device for simulating the swelling and shrinkage deformation of soil under the action of simulated dry-wet cycle and rainfall infiltration dynamic water saturation as described in claim 8, the specific steps are as follows: Step S1: After checking that each part of the test device for simulating the swelling and shrinkage deformation of soil under the action of simulated dry-wet cycle and rainfall infiltration dynamic water saturation is available, assemble it. Apply an acid-proof corrosion coating at the places where the specimen cylinder (14) and the heating cylinder (21) contact the aqueous solution, and operate the circular covers on each air blowing port on the side of the heating cylinder (21) to seal and close each air blowing port; Step S2: Arrange the lower permeable stone (15) at the inner bottom of the sample cylinder (14), place the prepared sample on the lower permeable stone (15), and then arrange the porous bearing plate (12) on the upper part of the sample; make the loading vertical rod (6) of the axial compression loading assembly contact the porous bearing plate (12), and apply a pressure of 2 - 3 kPa for preloading to make all parts in the sample cylinder (14) in contact, and record the initial reading K of the dial indicator (4). 0s ; Step S3: Set the loading amount of the axial compression loading assembly to simulate the stress states at different depths of the soil layer; Step S4: Control the solution flow rate through the peristaltic pump (8) so that the solution flows into the specimen cylinder (14) from the water inlet (16) and returns to the solution tank (10) from the water outlet (19) of the heating cylinder (21), forming a dynamic water flow cycle to simulate different rainfall intensity conditions in a rainfall environment; Step S5: Adjust the position of the high-definition camera (13) and take pictures of the upper and side surfaces of the specimen at regular intervals; Real-time observe the data change of the dial micrometer (4), and record the data of the dial micrometer (4) at regular intervals; when the specimen expansion is stable, end the moisture absorption test, discharge the solution through the peristaltic pump (8), and record the data of the dial micrometer (4) at the moment when the moisture absorption test ends. is the expansion amount when the specimen reaches expansion stability under the action of the set vertical load P, and calculate the vertical loaded expansion rate of the specimen according to the following formula : ； where h 0s is the initial height of the specimen in the vertical direction, and K ts is the reading of the dial indicator (4) when the specimen expands and stabilizes under the action of the set vertical load P, and K ps is the compression deformation of the specimen by the porous bearing plate (12), the loading vertical rod (6), and the dial indicator (4) under the action of the set vertical load P; Step S6: Actuate each circular cover on the side of the heating cylinder (21), open each air outlet, connect each air outlet to the corresponding second blower, and connect the water inlet (16) to the first air outlet. Adjust the temperature and flow rate of the hot air flow output by the first blower and the second blower through the first air blower controller (20) and the second air blower controller (23) of the wet-dry cycling component, and blow hot air flow into the specimen cylinder (14) and the heating cylinder (21) to perform dehumidification treatment on the specimen. During the heating process, continuously record the readings of the dial indicator (4) at the original set reading frequency, and control the heating time according to the heating temperature designed in the experiment. End the heating when the water content of the specimen reaches the shrinkage limit water content, that is, complete one wet-dry cycling process; Step S7: Repeat Steps S4 to S6 to sequentially complete the number of wet-dry cycling tests designed in the experiment and complete the wetting and swelling deformation test under the wet-dry cycling environment.

10. The test method for swelling and shrinkage deformation of soil under the action of simulated dry-wet cycle and rainfall infiltration dynamic water saturation according to claim 9, characterized in that, After Step S7 completes the wetting and swelling deformation test under the wet-dry cycling environment, perform digital image processing on the specimen surface pictures taken by the high-definition camera (13) to analyze the evolution process of surface cracks during the dehumidification process of the expansive soil; After Step S7 completes the wetting and swelling deformation test under the wet-dry cycling environment, take out the tested specimen and the core cutter together and demold them. After replacing the new specimen, repeat Steps S2 to S7, and re-adjust the magnitude of the vertical load P, the flow rate of the water flow, and the solution pH value according to the test plan to obtain the wetting and swelling deformation law of the specimen under different test conditions.

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