A loess moisture migration testing device and method under simulated dry-wet cycles

Abstract

The application discloses a kind of loess moisture migration testing device and method under simulated dry-wet cycle, including test box, environmental simulation module, moisture migration characteristic parameter measurement module and loss soil particle collection module;Test box is three-layer combined structure, middle layer is independent sample tank;Environmental simulation module includes rainfall simulation unit and temperature simulation unit;Rainfall simulation unit includes main water inlet pipe, water tank and rainfall spray head;Temperature simulation unit includes heating belt, air blower, air inlet pipe, temperature sensor and air outlet;Temperature sensor is arranged at the upper layer side wall of test box;Air outlet is arranged at the top of test box;Moisture migration characteristic parameter measurement module includes soil moisture temperature sensor, soil moisture sensor, soil pressure gauge and pore water pressure gauge buried in the interior of soil sample in sample tank in multiple layers;Loss soil particle collection module includes step-by-step filtering device and laser particle size distribution instrument, solve how to reveal the deep mechanism of loess disaster problem.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of water conservancy projects, in particular to a device and method for testing water migration of loess under dry-wet cycles. BACKGROUND

[0002] Loess, as a kind of soil with special engineering geological properties, has unique physical and chemical properties. When loess is affected by external factors such as rainfall, evaporation, irrigation and human activities, it will show a clear dry-wet alternating state. This dry-wet alternating state not only affects the mechanical properties and structure of loess, but also causes water migration and redistribution, thereby accelerating the occurrence of disasters in loess areas. Dry-wet cycle refers to the periodic change of soil water content under natural conditions due to natural processes such as rainfall and evaporation. In this process, the pore structure, mechanical properties and water migration mechanism of loess will change, which directly relates to the stability and safety of loess. Water migration refers to the movement and redistribution of water in loess under external conditions (such as rainfall, evaporation, etc.). Water migration not only affects the mechanical properties of loess, but also is closely related to the occurrence of loess disasters.

[0003] Therefore, how to develop a comprehensive test device that can simultaneously simulate dry-wet cycles and water migration so that researchers can more comprehensively understand the mechanical properties and structural changes of loess, thereby revealing the deep mechanism of loess disasters becomes a problem to be solved. SUMMARY

[0004] The application provides a device and method for testing water migration of loess under dry-wet cycles, which solves the problem of how to develop a comprehensive test device that can simultaneously simulate dry-wet cycles and water migration so that researchers can more comprehensively understand the mechanical properties and structural changes of loess, thereby revealing the deep mechanism of loess disasters.

[0005] In a first aspect, the embodiments of the present application provide a device for testing water migration of loess under simulated dry-wet cycles, comprising a test box, an environment simulation module, a water migration characteristic parameter measurement module, and a lost soil particle collection module; the test box is a three-layer combined structure, divided into an upper layer, a middle layer, and a lower layer, and the upper layer, the middle layer, and the lower layer are connected in sequence, and the middle layer is an independent sample tank; the test box has an inner wall and an outer wall; the environment simulation module comprises a rainfall simulation unit and a temperature simulation unit; the rainfall simulation unit comprises a main water inlet pipe, a water tank, and a rainfall spray head; one end of the main water inlet pipe is connected to the water tank, the other end extends into the test box through a reserved hole in the upper layer of the test box and is connected to the rainfall spray head, a water inlet electromagnetic valve and a flow sensor are arranged on the main water inlet pipe, and a water pump is arranged in the water tank; the temperature simulation unit comprises a heating belt, an air blower, an air inlet pipe, a temperature sensor, and an air outlet; one end of the air inlet pipe is in communication with the upper layer of the test box, and the other end is in communication with the air blower; a temperature adjustment module and an air inlet valve are arranged on the air inlet pipe; the temperature sensor is arranged at the side wall of the upper layer of the test box; and the air outlet is arranged at the top of the test box; the water migration characteristic parameter measurement module comprises a monitoring assembly embedded in the soil sample in the sample tank in multiple layers; the monitoring assembly comprises a soil moisture temperature sensor, a soil moisture sensor, a soil pressure gauge, and a pore water pressure gauge; the lost soil particle collection module comprises a step-by-step filtering device and a laser particle size distribution instrument; the step-by-step filtering device comprises a plurality of screens with different pore sizes arranged at different heights below the sample tank, and the laser particle size distribution instrument is circumscribed around the step-by-step filtering device and used to obtain the loss result of soil particles.

[0006] In combination with the first aspect, in a possible implementation manner, the device further comprises thermal insulation material and steel columns; the thermal insulation material is filled between the inner wall and the outer wall of the test box; adjacent two sides of the test box are made of tempered glass, and a scale is arranged on the tempered glass to record the water level; four steel columns are connected to the combined screw reserved holes on the upper layer, the middle layer, and the lower layer of the test box through a plurality of combined screws and nuts; and a water seal ring is installed at the connection of the test box.

[0007] In combination with the first aspect, in a possible implementation manner, the device further comprises a gravity sensor; a water-permeable stone is laid on the top of the sample tank, a sieve plate is arranged at the bottom of the sample tank, and the gravity sensor is embedded at the bottom of the sieve plate; and a geotextile is arranged above the water-permeable stone.

[0008] In combination with the first aspect, in a possible implementation manner, the plurality of screens are pull-out type; the plurality of screens are arranged at different heights below the sample tank in sequence from large to small in pore size; the distance between adjacent screens is equal; and the diameter of the rainfall hole of the rainfall spray head ranges from 0.5 mm to 1 mm.

[0009] With reference to the first aspect, in a possible implementation manner, the monitoring assembly is arranged in three layers, and each layer is provided with soil water temperature sensors, soil water sensors, soil pressure gauges and pore water pressure gauges; the same type of instruments are arranged in the same column, and the distance between the same type of instruments in adjacent layers is equal.

[0010] With reference to the first aspect, in a possible implementation manner, the device further comprises a plurality of sub-inlet pipes; one end of each sub-inlet pipe is connected to the water tank, and the other end of each sub-inlet pipe extends into the test box through a reserved hole in the lower side wall of the test box and is located above the plurality of screens; each sub-inlet pipe is provided with an inlet valve; the number of sub-inlet pipes is the same as the number of screens.

[0011] With reference to the first aspect, in a possible implementation manner, the device further comprises a wastewater tank and an outlet pipe; one end of the outlet pipe extends into the test box through a reserved hole in the bottom of the test box, and the other end of the outlet pipe is located at the upper end of the wastewater tank.

[0012] In the second aspect, the embodiments of the present application provide a use method of the device for testing water migration of loess under dry-wet cycles, which comprises the following steps: measuring the dry density, specific gravity and initial height of the soil sample to be tested; placing the soil sample into the sample tank and laying the water-permeable stones and the geotextile above the sample tank; tightly connecting the sample tank with the upper layer and the lower layer of the test box through the steel column, the plurality of combination screws and the plurality of nuts to form a complete test environment; equally dividing and burying the soil water temperature sensors, the soil water sensors, the soil pressure gauges and the pore water pressure gauges in the soil sample in multiple layers; wherein the soil water temperature sensors are used to measure the temperature change in the soil sample in real time, the soil water sensors are used to measure the water content in the soil sample, the soil pressure gauges are used to measure the pressure distribution in the soil sample, and the pore water pressure gauges are used to measure the pore water pressure in the pores of the soil sample; performing a dry-wet cycle step; the dry-wet cycle step comprises the following steps: opening the inlet water electromagnetic valve on the main inlet pipe, controlling the water inlet amount and flow rate through the flow sensor and the inlet water electromagnetic valve to simulate the rainfall process of the soil sample in the dry-wet cycle; observing and recording the change of the water accumulation height in the sample tank until the preset water accumulation height is reached, and then closing the inlet water electromagnetic valve; opening the inlet valve on the sub-inlet pipe to enable the water flow to wash the soil particles on the screen to simulate the scouring effect of rainfall on the soil surface; recording the water inlet time after the preset water accumulation height is reached and the time used when the water accumulation height in the sample tank decreases by a unit height; when the water accumulation height decreases to 0, closing the inlet valve on the sub-inlet pipe, taking out the screen, and after drying and weighing, combining the analysis result of the laser particle size distribution instrument to obtain the soil particle loss result; opening the air inlet valve on the air inlet pipe and starting the heating belt in the test box to simulate the drying process of the soil sample in the field environment; acquiring the change of the weight of the soil sample in real time through the gravity sensor, and when the predetermined soil sample weight is reached, closing the air inlet valve on the air inlet pipe and the heating belt, and re-putting the screen to complete the dry-wet cycle step; calculating the water migration coefficient in the soil sample and the water migration rate in the soil sample.

[0013] In conjunction with the second aspect, in one possible implementation, according to the formula Calculate the water migration coefficient in the soil sample; where k is the water migration coefficient of the soil sample, and L is the initial height of the soil sample. for The water level at any given moment; for The water level at any given time; calculated using the formula. Calculate the water migration rate in the soil sample; where, Let L be the water migration rate, and L be the initial height of the soil sample. This represents the dry density of the soil sample. The specific gravity of the soil sample. Let be the density of water, and t be the time required to complete the wet-dry cycle.

[0014] One or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:

[0015] The test device for simulating the moisture migration of loess under dry-wet cycles provided by the embodiment of the application can more accurately simulate the moisture migration process of loess under dry-wet cycles, because the three-layer combined structure of the test box, especially the independent sample tank design, makes the test conditions closer to the loess layer structure in the actual natural environment. This design not only improves the accuracy and reliability of the test, but also provides an effective tool for the study of the moisture migration characteristics of loess. The rainfall simulation unit and the temperature simulation unit in the environmental simulation module can accurately simulate the influence of rainfall and temperature changes on the moisture migration of loess. The rainfall simulation unit realizes accurate control of the rainfall intensity, rainfall time and rainfall mode through the cooperation of the main water inlet pipe, the water tank and the rainfall nozzle. The temperature simulation unit can simulate different temperature conditions and temperature change processes through the cooperative work of the heating belt, the air blower, the air inlet pipe, the temperature sensor and the air outlet, and then study the influence of temperature on the moisture migration of loess. The moisture migration characteristic parameter measurement module can obtain the moisture migration characteristic parameters of loess in the dry-wet cycle process in real time and accurately through the soil moisture temperature sensor, the soil moisture sensor, the soil pressure gauge and the pore water pressure gauge buried in the sample tank in multiple layers, and provides rich data support for analyzing the mechanism and rules of the moisture migration of loess. The loss soil particle collection module can effectively collect and analyze the loss soil particles of loess in the moisture migration process through the combination of the step-by-step filtering device and the laser particle size distribution instrument. The step-by-step filtering device separates the loss soil particles according to the particle size through the screens with different apertures, and the laser particle size distribution instrument can accurately measure the distribution of particles of each particle size, thereby providing an important basis for evaluating the erosion degree of loess and formulating effective water and soil conservation measures. The device can comprehensively and accurately simulate and study the moisture migration process and characteristics of loess under dry-wet cycles, and provides strong technical support for the ecological protection and sustainable development of loess areas. The device solves the problem of how to develop a comprehensive test device that can simultaneously simulate dry-wet cycles and moisture migration, so that researchers can more comprehensively understand the mechanical properties and structural changes of loess, thereby revealing the deep mechanism of loess disasters. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the description of the embodiments of the present application or the prior art. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0017] Figure 1 The schematic diagram of the test device for simulating the moisture migration of loess under dry-wet cycles provided by the embodiment of the application;

[0018] Figure 2A schematic diagram of the combined screw connection provided in the embodiments of the present application is shown in FIG. 1.

[0019] Figure 3 A top view of the test box provided in the embodiments of the present application is shown in FIG. 2.

[0020] Figure 4 A schematic diagram of the three-dimensional structure of the test box provided in the embodiments of the present application is shown in FIG. 3.

[0021] The reference signs: 1-test box; 11-sample tank; 111-water-permeable stone; 112-sieve plate; 2-environment simulation module; 21-rainfall simulation unit; 211-main water inlet pipe; 212-water tank; 213-rainfall nozzle; 214-water inlet electromagnetic valve; 215-flow sensor; 216-water pump; 22-temperature simulation unit; 221-heating belt; 222-blower; 223-air inlet pipe; 224-temperature sensor; 225-air outlet; 226-temperature adjustment module; 227-air inlet valve; 3-moisture migration characteristic parameter measurement module; 31-soil moisture temperature sensor; 32-soil moisture sensor; 33-soil pressure gauge; 34-pore water pressure gauge; 4-eroded soil particle collection module; 41-sieve; 5-thermal insulation material; 6-steel column; 7-combined screw reserved hole; 71-combined screw; 8-nut; 9-gravity sensor; 10-branch water inlet pipe; 101-water inlet valve; 12-wastewater tank; 13-water outlet pipe. DETAILED DESCRIPTION

[0022] In the description of the embodiments of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. The terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance. In addition, the terms "mounting", "connecting", "connecting" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium, or it can be the communication between two elements. For those skilled in the art, the specific meaning of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0023] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0024] Figure 1 A schematic diagram of a loess moisture migration testing device under simulated dry-wet cycles provided by the present application is shown in FIG. 1, which comprises a test box 1, an environment simulation module 2, a moisture migration characteristic parameter measurement module 3 and a loess particle collection module 4. Figure 1

[0025] Specifically, the test box 1 is a three-layer combined structure, which is divided into an upper layer, a middle layer and a lower layer. The upper layer, the middle layer and the lower layer are sequentially connected. The middle layer is an independent sample groove 11. The test box 1 has an inner wall and an outer wall. The loess moisture migration testing device under simulated dry-wet cycles provided by the present application further comprises a thermal insulation material 5 and a steel column 6. The thermal insulation material 5 is filled between the inner wall and the outer wall of the test box 1. The adjacent two sides of the test box 1 are tempered glass. The tempered glass is provided with a scale for recording the water height. The four steel columns 6 are connected with the combined screws reserved holes 7 on the upper layer, the middle layer and the lower layer of the test box 1 through a plurality of combined screws 71 and nuts 8. The connecting parts of the test box 1 are all provided with water sealing rings.

[0026] ​Further, the test box 1 is designed in a three-layer combined structure, namely, the upper layer, the middle layer and the lower layer. This design allows each part of the test box 1 to be operated independently while being closely connected together to form a complete test environment. This structure not only facilitates precise control of the test conditions, but also makes it more convenient to observe and study the soil samples at different layers. The middle layer is designed as an independent sample tank 11, which is used to accommodate the soil samples. The design of the sample tank 11 allows the loess samples to be placed separately, facilitating various tests and operations. At the same time, the independence of the sample tank 11 ensures that the soil samples are not disturbed by other parts during the test, thereby ensuring the accuracy of the test results. It should be noted that the soil samples in this application refer to loess samples. The inner wall and the outer wall of the test box 1 are filled with thermal insulation material 5, mainly to maintain the temperature stability inside the test box 1 and prevent external temperature fluctuations from affecting the test results. The addition of the thermal insulation material 5 improves the heat preservation performance of the test box 1, making it more close to the actual situation when simulating the moisture migration of loess under different environmental conditions. The adjacent two sides of the test box 1 are made of tempered glass. This design allows the state and changes of the loess samples to be clearly observed during the test. At the same time, the scale on the tempered glass is used to record the water level, which helps to accurately measure and analyze the moisture migration of loess during the dry-wet cycle.

[0027] Figure 2 The schematic diagram of the combined screw connection provided by the embodiment of the present application is shown in Figure 2 The four steel columns 6 are connected to the upper layer, the middle layer and the lower layer of the test box 1 through a plurality of combined screws 71 and nuts 8. This connection method not only ensures the stability of the test box 1, but also makes the connection between the parts more tight, preventing leakage and errors during the test. At the same time, this design also makes the assembly and disassembly of the test box 1 more convenient, improving the test efficiency. The connection of the test box 1 is equipped with a water seal ring to prevent water from leaking from the connection during the test, affecting the accuracy of the test results. The use of the water seal ring ensures the good sealing of the test box 1, making the simulated dry-wet cycle environment closer to the actual conditions.

[0028] Specifically, the environmental simulation module 2 includes a rainfall simulation unit 21 and a temperature simulation unit 22. The rainfall simulation unit 21 includes a main water inlet pipe 211, a water tank 212 and a rainfall spray head 213. The main water inlet pipe 211 is connected to the water tank 212 at one end and extends into the test box 1 through a reserved hole in the upper layer of the test box 1 and is connected to the rainfall spray head 213 at the other end. The main water inlet pipe 211 is provided with a water inlet electromagnetic valve 214 and a flow sensor 215, and the water tank 212 is provided with a water pump 216.

[0029] Further, the main function of the environmental simulation module 2 is to simulate the climatic conditions experienced by loess in the natural environment, particularly rainfall and temperature changes. The design of this module is crucial for accurately simulating the water migration process of loess. The rainfall simulation unit 21 is one of the core components of the environmental simulation module 2, designed to simulate the rainfall process of loess in the natural environment. The main water inlet pipe 211 is a key component that connects the water tank 212 and the rainfall sprinkler 213. One end of the main water inlet pipe 211 is connected to the water tank 212, and the other end is inserted into the test box 1 through the reserved hole on the upper layer of the test box 1, ensuring that the water flow can smoothly reach the rainfall sprinkler 213. The main water inlet pipe 211 is provided with a water inlet electromagnetic valve 214 and a flow sensor 215. The water inlet electromagnetic valve 214 is a valve that works on the principle of magnetic force. When the coil is powered, the magnetic material generates an attractive force to attract the iron core to drive the valve body to act, thereby controlling the on-off of the main water inlet pipe 211. In this device, the function of the water inlet electromagnetic valve 214 is to open or close the water flow according to the preset instructions, to realize the start and end of the simulated rainfall. In this way, the time, intensity and interval of the simulated rainfall can be accurately controlled, so as to more realistically simulate the rainfall process in the natural environment. The flow sensor 215 is used to monitor the water flow in the main water inlet pipe 211 in real time. By measuring the water flow, it can ensure that the water quantity in the rainfall simulation process matches the preset value, further improving the accuracy of the simulated rainfall. The flow data can also be used for subsequent data analysis and processing, helping researchers to better understand the water migration characteristics of loess in the rainfall process. The water tank 212 serves as a water source storage device, providing stable and sufficient water quantity for rainfall simulation. The water tank 212 is provided with a water pump 216, which functions to pump water out of the water tank 212 and deliver it to the rainfall sprinkler 213 through the main water inlet pipe 211. The operation of the water pump 216 can be adjusted as needed to meet the needs of rainfall simulation of different intensity and duration. The rainfall sprinkler 213 is a key component of the simulated rainfall, and its design and distribution are crucial for the uniformity and authenticity of the simulated rainfall. The rainfall sprinkler 213 simulates the rainfall process by spraying water mist or droplets, ensuring that the soil sample can uniformly receive water. The diameter of the rainfall holes of the rainfall sprinkler 213 is in the range of [0.5mm, 1mm].

[0030] Specifically, the temperature simulation unit 22 includes a heating belt 221, an air blower 222, an air inlet pipe 223, a temperature sensor 224, and an air outlet 225. The air inlet pipe 223 is in communication with the upper layer of the test box 1 at one end and in communication with the air blower 222 at the other end. The air inlet pipe 223 is provided with a temperature adjustment module 226 and an air inlet valve 227. The temperature sensor 224 is arranged at the side wall of the upper layer of the test box 1. The air outlet 225 is arranged at the top of the test box 1. The moisture migration characteristic parameter measurement module 3 includes a monitoring assembly buried in the soil sample inside the sample tank 11 in multiple layers. The monitoring assembly includes a soil moisture temperature sensor 31, a soil moisture sensor 32, a soil pressure gauge 33, and a pore water pressure gauge 34. The loss of soil particles collection module 4 includes a step-by-step filtering device and a laser particle size distribution instrument. The step-by-step filtering device includes multiple screens 41 with different pore sizes arranged at different heights below the sample tank 11. The laser particle size distribution instrument is circumscribed around the step-by-step filtering device to obtain the soil particle loss result.

[0031] Further, the temperature simulation unit 22 is designed to simulate the temperature changes experienced by loess in natural environments. The temperature inside the test box 1 is controlled and adjusted to simulate temperature environments in different seasons or climate conditions. The heating belt 221 heats the inside of the test box 1 by generating heat through electricity. The power and temperature of the heating belt 221 can be adjusted as needed to achieve precise control of the temperature inside the test box 1. The air blower 222 introduces air into the test box 1 through the air inlet pipe 223, which is provided with a temperature adjustment module 226 and an air inlet valve 227. The temperature adjustment module 226 can heat or cool the air entering the test box 1 according to the preset temperature requirements to adjust the temperature inside the test box 1. The air inlet valve 227 is used to control the flow and speed of air intake to ensure uniform temperature distribution inside the test box 1. The temperature sensor 224 is arranged at the side wall of the upper layer of the test box 1 to monitor the temperature inside the test box 1 in real time. Figure 3 The top view of the test box 1 provided by the embodiment of the present application is shown in Figure 3As shown, the air outlet 225 is arranged at the top of the test box 1, which functions to circulate the air in the test box 1 to avoid uneven temperature distribution. The water migration characteristic parameter measurement module 3 is used to monitor and analyze the microstructure changes and water infiltration characteristics of loess during the water migration process in real time. The soil moisture and temperature sensor 31 is used to measure the temperature changes in the soil sample in real time. By monitoring the temperature changes, the heat conduction and heat convection of loess during the water migration process can be understood, and the thermodynamic properties of loess can be analyzed. The soil moisture sensor 32 is used to measure the moisture content in the soil sample. By monitoring the changes in moisture content in real time, the water infiltration and evaporation rules of loess during the dry-wet cycle process can be revealed, which provides an important basis for analyzing the water migration characteristics of loess. The soil pressure gauge 33 is used to measure the pressure distribution in the soil sample. By understanding the changes in pressure distribution, the deformation and damage that may occur in loess during the water migration process can be inferred, which helps to predict geological disasters in loess areas. The pore water pressure gauge 34 is used to measure the pore water pressure in the soil sample. The change of pore water pressure is closely related to the water migration of loess. By monitoring the changes, the water migration mechanism of loess can be understood in depth. The lost soil particle collection module 4 is mainly used to collect and analyze the soil particles lost from the loess sample during the dry-wet cycle process to reveal the erosion and degradation mechanism of loess. The step-by-step filtering device is the core part of the lost soil particle collection module 4, which includes multiple screens 41 with different pore sizes arranged at different heights below the sample tank 11. These screens 41 with different pore sizes can step-by-step filter the soil particles lost from the loess sample. By using screens 41 with different pore sizes, the lost soil particles can be separated according to particle size, which is convenient for subsequent analysis and processing. It should be noted that the soil moisture and temperature sensor 31, the soil moisture sensor 32, the soil pressure gauge 33 and the pore water pressure gauge 34 are arranged in three layers, and each type of instrument is arranged equidistantly in each layer. The distance between the same type of instruments in adjacent two layers is equal.

[0032] Figure 4 The schematic diagram of the three-dimensional structure of the test box 1 provided by the embodiment of the present application is shown in FIG. 1. Figure 4As shown, the plurality of screens 41 are all pull-out type, and the plurality of screens 41 are sequentially arranged at different heights below the sample tank 11 in descending order of aperture size. The distance between adjacent screens 41 is equal. It needs to be noted that the particle sizes of the screens 41 from top to bottom are 75 μm, 30 μm and 5 μm in sequence. These particle size limits are selected based on the particle size classification standard in soil science, which can effectively separate soil particles in different particle size ranges, and further analyze the particle loss characteristics of loess in the dry-wet cycle process. Specifically, the screen 41 with a particle size of 75 μm is used to separate silt and sand particles. In soil science, silt and sand particles are two larger types of soil particles, which play an important role in the structure and properties of soil. By using the screen 41 with a particle size of 75 μm, these two types of particles can be separated to provide basic data for subsequent analysis. The screen 41 with a particle size of 5 μm is used to separate silt and clay particles. Clay particles are the smallest particles in soil, which have strong adhesion and adsorption, and have a significant impact on the water retention and permeability of soil. By using the screen 41 with a particle size of 5 μm, clay particles can be separated from silt particles to further reveal the loss of clay particles in loess during the dry-wet cycle process. The screen 41 with a particle size of 30 μm is arranged in the middle, and the particle size is the peak value of the measured particle size distribution curve. This means that in the loess sample, the particles with a particle size of about 30 μm are the most numerous, which are the main components of loess. By arranging this screen 41, the loss of main particle size particles of loess during the dry-wet cycle process can be more accurately understood. In addition, according to the specific requirements of the experiment, the arrangement of the screen 41 can also be increased or reduced. For example, if it is necessary to analyze the particle loss in a certain particle size range in more detail, the screen 41 with the corresponding particle size can be added, and vice versa, if the particles in a certain particle size range have less impact on the experimental results, the corresponding screen 41 arrangement can be considered to be reduced. The laser particle size distribution instrument is connected to the step-by-step filtering device, and is used for particle size analysis of the soil particles collected from the screen 41. Through the laser particle size distribution instrument, key parameters such as particle size distribution and average particle size of the soil particles can be obtained, and the erosion and degradation degree of loess during the dry-wet cycle process can be analyzed.

[0033] The loess water migration testing device under simulated dry-wet cycle provided by the embodiment of the present application further comprises a gravity sensor 9, the top of the sample tank 11 is paved with a water-permeable stone 111, the bottom of the sample tank 11 is provided with a sieve plate 112, and the gravity sensor 9 is embedded in the bottom of the sieve plate 112. The water-permeable stone 111 is paved with a geotextile above.

[0034] Specifically, the gravity sensor 9 is embedded in the bottom of the sieve plate 112 for real-time monitoring of the mass change of the loess sample in the sample tank 11 during the dry-wet cycle. When the loess absorbs or loses water, its mass will change accordingly, which can indirectly reflect the water migration of the loess. The high-precision measurement of the gravity sensor 9 can capture these subtle changes in mass. The water-permeable stone 111 is laid on the top of the sample tank 11, and its main function is to ensure that water can penetrate evenly into the loess sample. The water-permeable stone 111 has good water permeability, which can evenly distribute the simulated rainfall or irrigation water on the surface of the loess sample, thereby more realistically simulating the water infiltration process in the natural environment. The sieve plate 112 is arranged at the bottom of the sample tank 11, which serves to support the loess sample and prevent particle loss. The pore size of the sieve plate 112 is carefully selected to ensure that water and small particles can pass through, while larger soil particles are effectively intercepted, ensuring the accuracy of the test. The particle size of the sieve plate 112 can be set to 2mm, of course, other values can also be set, and the application is not limited to the above values. The geotextile is laid on top of the water-permeable stone 111, and its main purpose is to prevent the loess sample from leaking or eroding on the surface during the test. The geotextile has good filtering and protective properties, which can effectively maintain the integrity of the loess sample and improve the reliability of the test.

[0035] Specifically, the monitoring assembly is arranged in three layers, each layer is provided with a soil moisture and temperature sensor 31, a soil moisture sensor 32, a soil pressure gauge 33 and a pore water pressure gauge 34, the same type of instrument is arranged in the same column, and the distance between the same type of instruments in adjacent two layers is equal.

[0036] The loess water migration test device under simulated dry-wet cycle provided by the embodiment of the application further comprises a plurality of split water inlet pipes 10, one end of each split water inlet pipe 10 is connected to the water tank 212, the other end extends into the test box 1 through the reserved hole at the lower side wall of the test box 1, and each split water inlet pipe 10 is located above the plurality of screens 41, each split water inlet pipe 10 is provided with a water inlet valve 101, and the number of the split water inlet pipes 10 is the same as that of the screens 41.

[0037] Specifically, the split water inlet pipes 10 are arranged above the plurality of screens 41, which can ensure that water is evenly and accurately distributed to the loess sample area covered by each layer of screen. The water inlet valve 101 door is arranged on each split water inlet pipe 10 corresponding to each layer of screen, and these valves can independently control the water inlet of each layer of screen, thereby realizing accurate regulation and control of the water of different layers of loess sample. In addition, in order to avoid inaccurate particle size distribution results caused by soil particle accumulation, the design of each layer of screen and the split water inlet pipe 10 considers the passability and retention of soil particles, so as to ensure that soil particles can be effectively separated according to their particle size during simulation.

[0038] The loess moisture migration testing device under simulated dry-wet cycles provided by the embodiments of the present application further comprises a wastewater tank 12 and a water outlet pipe 13. One end of the water outlet pipe 13 extends into the test box 1 through a reserved hole in the bottom of the test box 1, and the other end is located at the upper end of the wastewater tank 12. The wastewater tank 12 is used to collect and store the wastewater discharged from the test box 1.

[0039] The embodiments of the present application provide a method for using the loess moisture migration testing device under simulated dry-wet cycles, comprising:

[0040] The dry density, specific gravity and initial height of the soil sample to be tested are measured,

[0041] Specifically, the dry density is the mass of the solid particles in the soil sample per unit volume, the specific gravity is the ratio of the density of the solid particles in the soil sample to the density of water, and the initial height is the original height of the soil sample before the test starts.

[0042] The soil sample is placed in the sample tank 11, and the water-permeable stone 111 and the geotextile are laid above it.

[0043] Specifically, the water-permeable stone 111 and the geotextile are arranged to help simulate the soil environment under natural conditions. The water-permeable stone 111 allows water to pass through while preventing soil particles from being lost. The geotextile further protects the soil sample and ensures its integrity. Such an arrangement can more realistically reflect the moisture migration of the soil sample under dry-wet cycles.

[0044] The sample tank 11 is tightly connected with the upper and lower layers of the test box 1 by the steel column 6, the plurality of combination screws 71 and the nuts 8, forming a complete test environment.

[0045] The soil moisture temperature sensor 31, the soil moisture sensor 32, the soil pressure gauge 33 and the pore water pressure gauge 34 are all buried in the soil sample in multiple layers. Among them, the soil moisture temperature sensor 31 is used to measure the temperature change in the soil sample in real time, the soil moisture sensor 32 is used to measure the moisture content in the soil sample, the soil pressure gauge 33 is used to measure the pressure distribution in the soil sample, and the pore water pressure gauge 34 is used to measure the pore water pressure in the soil sample.

[0046] A wet-dry cycle is performed. This cycle includes: opening the inlet solenoid valve 214 on the main inlet pipe 211; controlling the water flow rate and velocity via the flow sensor 215 and the solenoid valve 214 to simulate rainfall in the soil sample during the wet-dry cycle; observing and recording the change in water height in the sample tank 11 until a preset water height is reached, then closing the inlet solenoid valve 214; opening the inlet valve 101 on the branch inlet pipe 10 to allow water to flush the soil particles on the screen 41, simulating the scouring effect of rainfall on the soil surface; recording the water inlet time after reaching the preset water height and the time taken for the water height in the sample tank 11 to decrease by a unit height; and closing the inlet valve 101 on the branch inlet pipe 10 when the water height reaches 0, removing the screen 41, drying it, weighing it, and combining the analysis results from the laser particle size analyzer to obtain the soil particle loss results. Open the air intake valve 227 on the air intake pipe 223 and start the heating belt 221 in the test chamber 1 to simulate the drying process of the soil sample in the field environment. The change in soil sample weight is acquired in real time by the gravity sensor 9. When the predetermined soil sample weight is reached, close the air intake valve 227 and the heating belt 221 on the air intake pipe 223, put the sample back into the sieve 41, and complete the dry and wet cycle step.

[0047] Specifically, the wet-dry cycle simulates the moisture changes of soil samples in the natural environment. By controlling the influent volume, flow rate, and drying conditions, the water migration and soil particle loss during the wet-dry cycle can be simulated, thus providing a deeper understanding of the soil's water migration characteristics. The water migration coefficient and water migration rate in the soil sample are calculated.

[0048] According to the formula Calculate the water migration coefficient in the soil sample. Where k is the water migration coefficient of the soil sample, and L is the initial height of the soil sample. for The water level at any given moment. for The water level at any given moment.

[0049] Specifically, the constant 2.3 in the water migration coefficient of the soil sample is derived empirically.

[0050] The following example illustrates the process of calculating the water migration coefficient in a soil sample. Of course, other examples are also possible, and this application is not limited to this example.

[0051] Assume the initial height L of the soil sample is 10 cm in the wet-dry cycle test. The following data were recorded after the test began: =Water level at 1 hour It is 8cm. =3 hours later, water level Reduced to 4cm. First, calculate the absolute value of the time difference: Hours later, calculate the logarithm of the relative change in water level: Substitute all known values ​​into the formula .

[0052] Furthermore, a larger k value indicates that the soil sample experienced greater water migration in a shorter period of time, meaning a faster water migration rate or stronger migration capacity. Conversely, a smaller k value indicates less water migration in the soil sample within the same timeframe, meaning a slower water migration rate or weaker migration capacity. Changes in the k value can reflect the water migration characteristics of the soil sample under different conditions, such as migration behavior under different soil types, different humidity conditions, or different environmental factors.

[0053] Calculate according to the formula Calculate the water migration rate in the soil sample. Among them, Let L be the water migration rate, and L be the initial height of the soil sample. This represents the dry density of the soil sample. The specific gravity of the soil sample. Let be the density of water, and t be the time required to complete the wet-dry cycle.

[0054] The following example illustrates the process of calculating the water migration rate in a soil sample. Of course, other examples are also possible, and this application is not limited to this example.

[0055] Assume the following data: the initial height L of the soil sample is 10 cm, and the dry density of the soil sample... 1.6 g / cm 3 The specific gravity of the soil sample The density of water is 2.7. 1g / cm 3 The time t for completing the wet-dry cycle is 24 hours.

[0056] Substitute all known values ​​into the formula In this embodiment, the calculated water migration rate in the soil sample is expressed in cm / h, which can be converted to millimeters per day (mm / d). Since 1 cm = 10 mm, 1 h = Therefore, 1cm / h = 10 × mm / d= mm / d.

[0057] The various embodiments in this specification are described in a progressive manner. For the same or similar parts between the various embodiments, please refer to each other. Each embodiment focuses on describing the differences from other embodiments.

[0058] The above examples are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that the technical solutions recorded in the foregoing examples can still be modified, or some or all of the technical features thereof can be replaced by equivalents; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the present application.

Claims

1. A device for testing moisture migration of loess under simulated dry-wet cycles, characterized in that, It includes a test chamber (1), an environmental simulation module (2), a moisture migration characteristic parameter measurement module (3), and a soil loss particle collection module (4); The test chamber (1) has a three-layer combined structure, which is divided into three parts: upper layer, middle layer and lower layer. The upper layer, middle layer and lower layer are connected in sequence, and the middle layer is an independent sample tank (11). The test chamber (1) has an inner wall and an outer wall; The environmental simulation module (2) includes a rainfall simulation unit (21) and a temperature simulation unit (22). The rainfall simulation unit (21) includes a main water inlet pipe (211), a water tank (212), and rainfall nozzles (213). One end of the main water inlet pipe (211) is connected to the water tank (212), and the other end extends into the test chamber (1) through the reserved hole on the upper layer of the test chamber (1) and is connected to the rain spray nozzle (213). The main water inlet pipe (211) is equipped with a water inlet solenoid valve (214) and a flow sensor (215). The water tank (212) is equipped with a water pump (216). The temperature simulation unit (22) includes a heating belt (221), a blower (222), an air inlet pipe (223), a temperature sensor (224), and an air outlet (225). One end of the air inlet pipe (223) is connected to the upper layer of the test chamber (1), and the other end is connected to the blower (222). A temperature regulation module (226) and an air inlet valve (227) are installed on the air inlet pipe (223). The temperature sensor (224) is located on the upper side wall of the test chamber (1); The air outlet (225) is located on the top of the test chamber (1); The moisture migration characteristic parameter measurement module (3) includes a monitoring component that is buried in multiple layers inside the soil sample in the sample cell (11); The monitoring components include a soil moisture temperature sensor (31), a soil moisture sensor (32), a soil pressure gauge (33), and a pore water pressure gauge (34). The soil particle collection module (4) includes a step-by-step filtration device and a laser particle size analyzer; The step-by-step filtration device includes multiple screens (41) with different apertures set at different heights below the sample cell (11). A laser particle size analyzer is connected to the step-by-step filtration device to obtain the results of soil particle loss.

2. The device for testing moisture migration of loess under simulated dry-wet cycles according to claim 1, characterized in that, It also includes thermal insulation materials (5) and steel columns (6); Insulation material (5) is filled between the inner and outer walls of the test chamber (1); The two adjacent sides of the test chamber (1) are made of tempered glass, and the tempered glass is provided with scales for recording the water height; The four steel columns (6) are connected to the pre-drilled holes (7) of the upper, middle and lower layers of the test chamber (1) by multiple combination screws (71) and nuts (8); Water seal rings are installed at all the connection points of the test chamber (1).

3. The device for testing moisture migration of loess under simulated dry-wet cycles according to claim 1, characterized in that, It also includes a gravity sensor (9); The top of the sample tank (11) is covered with permeable stone (111), and the bottom of the sample tank (11) is provided with a sieve plate (112). The gravity sensor (9) is embedded in the bottom of the sieve plate (112); Geotextile was laid on top of the permeable stone (111).

4. The device for testing moisture migration of loess under simulated dry-wet cycles according to claim 1, characterized in that, All screens (41) are pull-out type; Multiple sieves (41) are arranged in descending order of aperture size at different heights below the sample cell (11); The distance between adjacent screens (41) is equal; The diameter range of the rain holes of the rain nozzle (213) is [0.5mm, 1mm].

5. The device for testing moisture migration of loess under simulated dry-wet cycles according to claim 1, characterized in that, The monitoring components are arranged in three layers, each layer is equipped with a soil moisture temperature sensor (31), a soil moisture sensor (32), a soil pressure gauge (33), and a pore water pressure gauge (34). Similar instruments are arranged in the same column, and similar instruments in adjacent layers are equidistant.

6. The device for testing moisture migration of loess under simulated dry-wet cycles according to claim 1, characterized in that, It also includes multiple branch water inlet pipes (10); One end of the water inlet pipe (10) is connected to the water tank (212), and the other end extends into the test chamber (1) through the reserved hole on the lower side wall of the test chamber (1), and is located above multiple screens (41); Each of the branch water inlet pipes (10) is equipped with a water inlet valve (101). The number of the water inlet pipes (10) is the same as the number of the screens (41).

7. The device for testing moisture migration of loess under simulated dry-wet cycles according to claim 1, characterized in that, It also includes a wastewater tank (12) and an outlet pipe (13); One end of the outlet pipe (13) extends into the test chamber (1) through the reserved hole at the bottom of the test chamber (1), and the other end is located at the top of the wastewater tank (12).

8. A method for using a device for testing water migration of loess under simulated dry-wet cycles, characterized in that, The apparatus for simulating loess moisture migration under wet-dry cycles as described in any one of claims 1 to 7 includes: The dry density, specific gravity, and initial height of the soil sample to be tested were determined. Soil samples are placed in sample troughs (11) and permeable stones (111) and geotextiles are laid on top of them; The sample slot (11) is tightly connected to the upper and lower layers of the test chamber (1) by steel columns (6), multiple combination screws (71) and nuts (8) to form a complete test environment; The soil moisture temperature sensor (31), soil moisture sensor (32), soil pressure gauge (33), and pore water pressure gauge (34) are buried in multiple layers inside the soil sample. The soil moisture temperature sensor (31) is used to measure the temperature change in the soil sample in real time, the soil moisture sensor (32) is used to measure the water content in the soil sample, the soil pressure gauge (33) is used to measure the pressure distribution in the soil sample, and the pore water pressure gauge (34) is used to measure the pore water pressure in the pores of the soil sample. Perform a wet-dry cycle; The dry-wet cycle steps include: Open the water inlet solenoid valve (214) on the main water inlet pipe (211), and control the water inlet volume and flow rate through the flow sensor (215) and the water inlet solenoid valve (214) to simulate the rainfall process of the soil sample in the wet-dry cycle; Observe and record the change in the water height in the sample tank (11) until the preset water height is reached, then close the water inlet solenoid valve (214). Open the water inlet valve (101) on the water inlet pipe (10) so that the water flow can wash the soil particles on the screen (41) to simulate the scouring effect of rainfall on the soil surface; Record the water inlet time after the preset water accumulation height is reached and the time taken for the water height in the sample tank (11) to drop by a unit height; When the water level drops to 0, close the inlet valve (101) on the branch inlet pipe (10), take out the screen (41), dry and weigh it, and then combine the analysis results of the laser particle size analyzer to obtain the result of soil particle loss. Open the air inlet valve (227) on the air inlet pipe (223) and start the heating belt (221) in the test chamber (1) to simulate the drying process of the soil sample in the field environment; The soil sample weight change is obtained in real time by gravity sensor (9). When the predetermined soil sample weight is reached, the air inlet valve (227) and heating belt (221) on the air inlet pipe (223) are closed, and the sample is put back into the sieve (41) to complete the dry and wet cycle step. Calculate the water migration coefficient and water migration rate in the soil sample.

9. The method of using the loess moisture migration testing device under simulated wet-dry cycles according to claim 8, characterized in that, include: According to the formula Calculate the water migration coefficient in the soil sample; where k is the water migration coefficient of the soil sample, and L is the initial height of the soil sample. for The water level at any given moment; for The water level at any given moment; Calculate according to the formula Calculate the water migration rate in the soil sample; where, Let L be the water migration rate, and L be the initial height of the soil sample. This represents the dry density of the soil sample. The specific gravity of the soil sample. Let be the density of water, and t be the time required to complete the wet-dry cycle.

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